Method for producing colloidal silica

Abstract

strange sex To provide a method for producing colloidal silica that improves the modification rate of the treatment. The present invention provides a method for producing colloidal silica having an anion-modified surface, comprising the steps of: The reaction mixture containing the hydrolysis catalyst consisting of an organic amine is easily Add water a raw material preparation step of supplying and reacting a decomposable organosilicate to prepare raw material colloidal silica; a concentration adjusting step of adjusting the solid content concentration of the raw material colloidal silica to 13% by mass or less and adjusting the concentration of alcohols generated in the raw material preparing step to 1 to 25% by mass; a modification treatment step of modifying the raw colloidal silica whose concentration has been adjusted; and a concentration step of concentrating the modified colloidal silica so that the residual organic solvent in the modified colloidal silica is 1% by mass or less, A method for producing colloidal silica, wherein the modification rate in the modification treatment step is 90% or more.

Description

[Technical Field]

[0001] The present invention relates to a method for producing colloidal silica. [Background technology]

[0002] As methods for industrially producing high-purity colloidal silica, methods such as ion-exchanging an aqueous sodium silicate solution, thermal decomposition of silicon tetrachloride, and hydrolyzing an organosilicate in a water-alcohol mixed solvent in the presence of an acid catalyst or an alkali catalyst have been proposed and put into practice. However, methods of hydrolyzing organosilicates allow the use of highly pure organosilicates, catalysts, solvents, etc., for the reaction, and therefore the amount of impurities derived from these raw materials is extremely small, making them suitable as a method for producing high-purity colloidal silica with a particularly low content of metal impurities. To date, several methods for hydrolyzing organosilicates have been proposed.

[0003] Regarding colloidal silica used in various applications, particularly colloidal silica used in the field of abrasives for semiconductor wafers, with the increasing integration density of today's LSIs, various types of metal wiring, oxide films, etc. are present on a single wafer, and polishing performance suited to each type of semiconductor wafer is required, resulting in a demand for colloidal silica with a variety of slightly different compositions and properties.

[0004] Furthermore, for colloidal silica used in applications where even slight alkali metal impurities should not be present, such as binders for hard coating agents and ceramics, chromic acid-based metal surface treatment agents, and soil improvement grouting agents, acidic colloidal silica is required, and several proposals for methods of producing such acidic colloidal silica have been proposed.

[0005] For example, the applicant of the present application has investigated a method for easily producing colloidal silica having predetermined properties, such as spherical colloidal silica, which does not require special post-treatments such as acid treatment, ion exchange treatment, or modification treatment, has an extremely low content of metal impurities, including alkali metals, and has an average particle size in the range of 5 to 500 nm, a standard deviation of 20 or less, and a polydispersity index of 0.15 or less, as determined by particle size distribution analysis using an electron microscope.As a result, the applicant has proposed that neutral colloidal silica with a pH of 5 to 8 can be easily produced without special post-treatments such as acid treatment, ion exchange treatment, or modification treatment by using an easily hydrolyzable organosilicate with a high hydrolysis rate and a specific hydrolysis catalyst, and adding and reacting this hydrolysis catalyst so that the ratio of hydrolysis catalyst (A) to silica (B) in the reaction mixture at least at the end of the reaction {catalyst remaining molar ratio (A / B)} is a predetermined value or less (Patent Document 1).

[0006] Meanwhile, in the field of abrasives for semiconductor wafers and substrates, for example, there has been a need to meet various requirements in recent years, but with conventional colloidal silica of several tens of nanometers (nm), it is difficult to fine-tune the polishing process, resulting in problems such as not being able to form a clean surface, the particles remaining on the surface of the object to be polished, and the particles themselves becoming unstable under acidic conditions because their zeta potential approaches the isoelectric point. Therefore, it has become necessary to adjust the electrical affinity of silica particles with the surface of the object to be polished and to modify them to have excellent dispersibility even under acidic conditions.

[0007] One way to solve this problem is to modify the surface of colloidal silica. Patent Document 2, for example, relates to modified colloidal silica that contains a small number of microparticles and can improve the stability of the polishing rate over time when used as an abrasive. According to Patent Document 2, in order to set the number distribution ratio of microparticles to a predetermined value or less, before the modification treatment, an organic solvent distillation step is carried out to remove the organic solvent coexisting with the colloidal silica, so that the organic solvent concentration in the raw material colloidal silica produced by a hydrolysis-condensation reaction (sol-gel method) is less than 1% by mass. However, after extensive investigations, the present inventors have unexpectedly found that when a step of distilling off the organic solvent before the modification treatment is carried out in this manner, the modification rate in the modification treatment described below is reduced.

[0008] Furthermore, for example, Patent Document 3 provides colloidal silica and a method for producing the same, in which the average secondary particle diameter of silica particles is small and the dispersion stability of the silica particles can be maintained for a long period of time even under strongly acidic conditions of pH 3 or less. According to Patent Document 3, the above object can be achieved by using colloidal silica that has an average secondary particle diameter of 20 nm or less as measured by dynamic light scattering, a zeta potential of −20 mV or less as measured under pH 3 conditions, and is surface-modified with sulfonic acid groups. However, the present inventors have conducted extensive research and found that the method described in Patent Document 3 does not necessarily provide a high degree of surface modification (modification degree in the present application, which will be described later). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-153732 [Patent Document 2] International Publication No. 2016 / 117560 [Patent Document 3] International Publication No. 2025 / 018234 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, the inventors of the present invention have developed a surface-modified colloidal silica, sex As a result of extensive research into how to improve the modification rate of the treatment, the present inventors discovered that this could be achieved by devising the raw material preparation process, concentration adjustment process, etc., and by subjecting colloidal silica to modification treatment at a predetermined timing, thereby completing the present invention.

[0011] Therefore, the object of the present invention is to sex The present invention provides a method for producing colloidal silica that can improve the modification rate of the treatment. [Means for solving the problem]

[0012] That is, the gist of the present invention is as follows. (1) A method for producing colloidal silica having an anion-modified surface, comprising the steps of: The reaction mixture containing the hydrolysis catalyst consisting of an organic amine is easily Addition of water a raw material preparation step of supplying and reacting a decomposable organosilicate to prepare raw material colloidal silica; a concentration adjusting step of adjusting the solid content concentration of the raw material colloidal silica to 13% by mass or less and adjusting the concentration of alcohols generated in the raw material preparing step to 1 to 25% by mass; a modification treatment step of modifying the raw colloidal silica whose concentration has been adjusted; and a concentration step of concentrating the modified colloidal silica so that the residual organic solvent in the modified colloidal silica is 1% by mass or less, A method for producing colloidal silica, wherein the modification rate in the modification treatment step is 90% or more. (2) The method for producing colloidal silica according to (1), wherein the modification rate in the modification treatment step is 95% or more. (3) The above-mentioned change sexThe method for producing colloidal silica according to (1) or (2), wherein the pH during the modification treatment in the treatment step is 8.0 or less. (4) The method for producing colloidal silica according to (1) or (2), wherein in the raw material preparing step, the reaction is carried out under conditions where the feed rate of the easily hydrolyzable organosilicate is less than 1.5 mass% / min of the total amount of the easily hydrolyzable organosilicate introduced, the reaction time is 6 hours or less, and the reaction temperature is 80°C or lower. (5) The method for producing colloidal silica according to (1) or (2), characterized in that in the concentrating step, the colloidal silica after the modifying treatment step is concentrated so that the solid content concentration in the colloidal silica is 15 mass % or more. (6) The method for producing colloidal silica according to (1) or (2), characterized in that in the raw material preparation step, raw material colloidal silica having a cumulant mean diameter of more than 20 nm as measured by dynamic light scattering is prepared. (7) The method for producing colloidal silica according to (1) or (2), characterized in that the modification treatment step comprises a step of reacting a modifier having a functional group that can be converted into an anionic group with the colloidal silica that has been subjected to the concentration adjustment step, and a step of converting the functional group in the modifier that has been subjected to the reaction into an anionic group. (8) The method for producing colloidal silica according to (7), wherein the modifying agent has mercapto groups and / or sulfide groups, and the mercapto groups and / or sulfide groups are converted to sulfo groups by treating the modifying agent with an oxidizing agent, thereby obtaining colloidal silica having sulfo groups on the surface. [Effects of the Invention]

[0013] According to the present invention, in order to obtain surface-modified colloidal silica, sex The modification rate of the treatment can be improved. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Method for producing colloidal silica> The method for producing colloidal silica of the present invention essentially includes the following steps: (a) A reaction solution containing a hydrolysis catalyst made of an organic amine is easily Addition of water A raw material preparation step in which a decomposable organosilicate is supplied and reacted to prepare raw material colloidal silica. (b) A concentration adjusting step of adjusting the solid content concentration of the raw material colloidal silica to 13% by mass or less and adjusting the concentration of alcohols generated in the raw material preparation step to 1 to 25% by mass. (c) A modification treatment step in which the raw material colloidal silica whose concentration has been adjusted in the step (b) is modified. (d) A concentration step of concentrating the colloidal silica modified in the step (c) so that the residual organic solvent in the colloidal silica is 1% by mass or less. Here, the modification rate in the modification treatment in the (c) modification treatment step is 90% or more. These steps are described below.

[0015] [Process (a)] First, in step (a), a reaction solution containing a hydrolysis catalyst made of an organic amine is easily added. Addition of water A decomposable organosilicate is supplied and reacted to prepare raw colloidal silica. In the present invention, the colloidal silica prepared in step (a) is referred to as raw colloidal silica.

[0016] Although there are no limitations on the particle size of the raw colloidal silica obtained in this step (a), it is important to select a particle size that is easy to obtain from the viewpoint of avoiding aggregation, etc. Addition of water From the viewpoint of stable production of raw colloidal silica by supplying and reacting the decomposable organosilicate, the BET diameter, which is the particle diameter converted to BET specific surface area, is preferably 5 nm or more and 80 nm or less. A more preferred lower limit is 6 nm or more, an even more preferred lower limit is 10 nm or more, and an even more preferred lower limit is 14 nm or more. On the other hand, a more preferred upper limit is 70 nm or less, an even more preferred upper limit is 60 nm or less, and an even more preferred upper limit is 50 nm or less. Here, in the present invention, the BET diameter is preferably defined because, as will be explained later, not only monodisperse spherical particles but also colloidal silica produced by two-dimensionally or three-dimensionally coalescing a plurality of particles may be used, and the production method of the present invention may result in colloidal silica with an uneven surface and a relatively large specific surface area. In light of these circumstances, it is preferable to adopt the BET diameter assuming a spherical shape while also taking the specific surface area into consideration in determining the performance relative to the particle shape.

[0017] In the present invention, the BET diameter refers to the BET specific surface area S (unit: m) of colloidal silica measured by the BET method. 2 / g) and true density ρ (unit: g / cm 3 Specifically, it can be calculated from the following formula (1): BET diameter (nm)=6000 / (S×ρ) ···(1) where ρ is the typical true density of SiO2, 2.2 g / cm 3 is.

[0018] Furthermore, with regard to particle diameter, from the same viewpoint as above and because relatively small particle diameters may result in some portions being difficult to grasp using an electron microscope, the cumulant mean diameter (hereinafter sometimes simply referred to as "cumulant mean diameter" or "DLS diameter") measured by dynamic light scattering, which has a wide measurement range, is preferably 6 nm or more, more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably more than 20 nm. On the other hand, the upper limit of the cumulant mean diameter is not limited, but is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.

[0019] Although commercially available products can be used as the raw material colloidal silica, the hydrolysis method is used because it can reduce metal impurities, can obtain colloidal silica with a relatively large surface area, and can produce highly uniform particles. The hydrolysis method involves supplying a silica source to a reaction solution containing a hydrolysis catalyst and causing a hydrolysis reaction. Because it is easy to control the particle size, it is preferred to use an organic amine as the silica source in a reaction solution containing a hydrolysis catalyst. Addition of water A method is used in which a decomposable organosilicate is supplied and subjected to a hydrolysis reaction.

[0020] Here, the silica source preferably used in step (a) is an easily hydrolyzable organosilicate with a fast hydrolysis rate. An easily hydrolyzable organosilicate is preferably one that is prepared by stirring 10 g of organosilicate with 100 g of pure water containing 0.1 ppb or less of impurities at 25°C, and completing the hydrolysis reaction within 1 hour. Specific examples of such easily hydrolyzable organosilicates include trimethyl silicate (hydrolysis reaction time until completion: approximately 3 minutes), tetramethyl silicate (hydrolysis reaction time: approximately 5 minutes), triethyl silicate (hydrolysis reaction time: approximately 5 minutes), and methyl trimethyl silicate (hydrolysis reaction time: approximately 7 minutes). Tetraethyl silicate and organosilicates with a higher carbon number than tetraethyl silicate have a slow hydrolysis rate and tend to gel easily (hydrolysis reaction time: 24 hours or more for both). Therefore, the aforementioned easily hydrolyzable organosilicates are not suitable. Addition of water Decomposable organosilicates are preferably used.

[0021] The organic amines used as the hydrolysis catalyst in step (a) are not limited, but may be one or a mixture of two or more selected from quaternary ammoniums, tertiary amines, secondary amines, primary amines, and their carbonates, bicarbonates, and silicates. Examples of quaternary ammoniums include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), trimethylethylammonium hydroxide, trimethylethanolammonium hydroxide (choline), triethylethanolammonium hydroxide, tetrapropylammonium hydroxide, and butylammonium hydroxide, as well as their carbonates, bicarbonates, and silicates. Because a relatively high pH is desirable for the hydrolysis reaction, tetramethylammonium hydroxide (TMAH), choline, or tetraethylammonium hydroxide (TEAH) is preferred.

[0022] Furthermore, the organic amines used as hydrolysis catalysts, such as primary amines, secondary amines, and tertiary amines, are not limited to, and examples thereof include aminoalcohols, morpholines, piperazines, aliphatic amines, aliphatic ether amines, etc. Here, various aminoalcohols including ethanolamine derivatives can be used, with ethanolamine derivatives being preferred, such as monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-di-n-butylethanolamine, N-(β-aminoethyl)ethanolamine, N-methylethanolamine, N-methyldiethanolamine, N-ethylethanolamine, Nn-butylethanolamine, Nn-butyldiethanolamine, N-tert-butylethanolamine, and N-tert-butyldiethanolamine.

[0023] Furthermore, various morpholine derivatives can be used as the organic amine morpholines used as hydrolysis catalysts, with preferred examples including morpholine, N-methylmorpholine, and N-ethylmorpholine. Furthermore, various piperazine derivatives can be used as the organic amine piperazines used as hydrolysis catalysts, with preferred examples including piperazine and hydroxyethylpiperazine. Regarding the organic amine aliphatic amines and aliphatic ether amines used as hydrolysis catalysts, preferred examples of the aliphatic amines include alkylamines having 1 to 8 carbon atoms, such as triethylamine, dipropylamine, pentylamine, hexylamine, heptylamine, and octylamine. Preferred examples of the aliphatic ether amines include aliphatic ether amines having 1 to 8 carbon atoms, such as 2-methoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, and 3-butoxypropylamine.

[0024] Among these hydrolysis catalysts, for example, from the viewpoint of setting the pH during the modification treatment in the modification treatment step (c) described below within a preferred range, it is preferable to use triethanolamine, monoethanolamine, diethanolamine, n-butylamine, n-nonylamine, dodecylamine, benzylamine, diethylamine, piperazine, pyridine, piperidine, 3-diethylaminopropylamine, dibenzylamine, or 3-ethoxypropylamine as the hydrolysis catalyst, more preferably triethanolamine, monoethanolamine, diethanolamine, benzylamine, piperazine, pyridine, 3-diethylaminopropylamine, dibenzylamine, or 3-ethoxypropylamine, and even more preferably triethanolamine, diethanolamine, piperazine, or dibenzylamine. The use of such a hydrolysis catalyst is a preferred embodiment not only for the reasons described in step (c) described below, but also in this step (a) in that it can prevent the hydrolysis from proceeding too quickly, thereby preventing self-aggregation and the like.

[0025] The organic amines used as the hydrolysis catalyst may be used singly or, if necessary, as a mixture of two or more kinds.

[0026] As for the reaction solution, as mentioned above, the silica source was Addition of water The composition essentially contains a decomposable organosilicate and a hydrolysis catalyst, but other components such as water, alcohols, aldehydes, ketones, and surfactants can also be used. Preferably, the composition contains a total of 90% by mass or more of the silica source, hydrolysis catalyst, and water. More preferably, the total of these components is 95% by mass or more.

[0027] In the mixture obtained after the reaction of the silica source with the hydrolysis catalyst (hereinafter sometimes referred to as the "reaction mixture"), or in the reaction mixture after subsequent treatment, for example, by adjusting the solids concentration or alcohol concentration or by adding an acid for dispersion stabilization, as described below (hereinafter sometimes referred to as the "reaction concentrate"), the ratio of the hydrolysis catalyst (A) to the silica (B) {catalyst remaining molar ratio (A / B)} is preferably 0.012 or less, more preferably 0.00035 to 0.012, and even more preferably 0.0035 to 0.011, and the hydrolysis reaction is carried out by adding the hydrolysis catalyst to the reaction system. This is preferable because it allows the pH of the reaction mixture or reaction concentrate to be optimized and also prevents thickening and gelation.

[0028] The method for achieving such a catalyst remaining molar ratio is not particularly limited, and examples thereof include a method of continuously or intermittently introducing a silica source calculated so that the final catalyst remaining molar ratio (A / B) falls within the above-mentioned range into a reaction vessel charged with water and the hydrolysis catalyst (A); a method of continuously or intermittently introducing a hydrolysis catalyst and a silica source calculated so that the final catalyst remaining molar ratio falls within the above-mentioned range into a reaction vessel charged with only water; and a method of continuously or intermittently introducing a hydrolysis catalyst and a silica source calculated so that the final catalyst remaining molar ratio falls within the above-mentioned range into a reaction vessel charged with water and a small amount of the hydrolysis catalyst (A).

[0029] Alternatively, prior to the hydrolysis reaction of the silica source, colloidal silica seeds having particle growth properties may be charged into the reaction system for the hydrolysis reaction, and the silica source and hydrolysis catalyst may be gradually added to the reaction system so that the remaining catalyst molar ratio (A / B) falls within the above-mentioned range. This is preferred because it allows the production of colloidal silica having uniform particles.

[0030] The silica source, hydrolysis catalyst, and water used as raw materials for the hydrolysis reaction preferably have a metal impurity content of 1 ppm or less, more preferably 0.01 ppm or less, and are of high purity. This ensures that the resulting raw colloidal silica and modified colloidal silica after modification also satisfy the aforementioned ranges for the metal impurity content.

[0031] In step (a), the method for adjusting the BET diameter of the starting colloidal silica and the cumulant average diameter to fall within the above-mentioned ranges is not limited, but it is preferable to adjust the rate at which the silica source is dropped into the reaction liquid (feed rate), the reaction temperature, and the reaction time.

[0032] It is an easy source of silica Addition of water When using decomposable organosilicate, the feed rate is Addition of waterThe feed rate is preferably less than 1.5% by mass / min of the total amount of decomposable organosilicate added, more preferably 1.3% by mass or less, and even more preferably 1.2% by mass or less. If the feed rate is 1.5% by mass or more, the particles tend to be dispersed unevenly or not nearly spherical. The reason why the total amount is used as the standard is because the amount added varies depending on the production scale, etc., and it is preferable to consider completing the feed within the reaction time described below. In other words, it is preferable to keep the feed rate as slow as possible, which makes it easier to form the desired small particle size. There is no lower limit to the feed rate, but if the feed rate is too slow, the target particle size may not be achieved, so it is preferably 1.0% by mass / min or more of the total amount added.

[0033] The reaction temperature is preferably 80°C or lower, more preferably 75°C or lower, and even more preferably 70°C or lower. If the reaction temperature exceeds 80°C, the reaction solution will volatilize more, making the liquid composition more likely to change, which may make it difficult to control the particle size. On the other hand, the lower limit of the reaction temperature can be set appropriately, but if the temperature is too low, the hydrolysis reaction tends to be slow and particle growth may be promoted, so it is preferable to set the temperature at 20°C or higher.

[0034] The reaction time is preferably 6 hours or less, more preferably 3 hours or less, and even more preferably 2 hours or less. If the reaction time exceeds 6 hours, the target particle size may not be achieved. On the other hand, the lower limit of the reaction time can be set appropriately, but if the reaction time is too short, the hydrolysis reaction may not be completed, and particle formation and particle growth may not be sufficiently achieved. Therefore, the reaction time is preferably 20 minutes or more.

[0035] In step (a), the solid content concentration during the reaction is preferably generally 3 to 13% by mass. If the solid content concentration is less than 3% by mass, particle formation and particle growth may not occur sufficiently. On the other hand, if the solid content concentration is too high, particle aggregation is likely to occur. In step (a), the solid content concentration of the colloidal silica after the reaction is preferably within the range of 3 to 13% by mass.

[0036] [Step (b)] In step (b), the solid content of the raw colloidal silica obtained in step (a) is adjusted to 13% by mass or less. By adjusting the solid content to 13% by mass or less, even when the BET diameter or cumulant mean diameter is relatively small, the occurrence of aggregation can be reduced, and the subsequent step (c) (modification treatment step) can be performed without causing aggregation gelation. In other words, by adjusting the solid content within this range, the subsequent step (c) (modification treatment step) can be performed at a concentration that exhibits relatively high dispersibility. This also makes it easier to achieve a high modification rate in the modification treatment in step (c). Preferably, the solid content is adjusted to 12% by mass or less, more preferably 10% by mass or less. Here, although it is difficult to clearly define or categorize the term "aggregation gelation," it generally refers to a state in which the aggregation of colloidal silica has progressed to the point where it has become a jelly-like mass that can be visually observed.

[0037] Here, if the solids concentration of the raw material colloidal silica obtained in step (a) is already 13% by mass or less, there is no need to actively adjust the solids concentration in step (b), and in that case, step (b) may be treated as a step for confirming the solids concentration, or a step for maintaining the solids concentration as is. Ensuring that the solids concentration is 13% by mass or less in step (b) before the modification treatment in the next step (c) is a characteristic step in obtaining the final modified colloidal silica of the present invention that is substantially non-agglomerated, has a high degree of modification, and has a relatively high solids concentration.

[0038] The method for adjusting the solid content concentration in step (b) is not limited, but is preferably carried out by adding the same solvent as that contained in the raw colloidal silica. The solvent to be added is preferably water and / or alcohols, more preferably water, methanol and / or ethanol, and even more preferably water and / or methanol. As described above, the solvent to be added may include water, alcohols, aldehydes, ketones, surfactants, etc.

[0039] In this step (b), the concentration of the alcohols produced in the step (a) is adjusted to 1 to 25 mass %. Addition of water Depending on the decomposition organosilicate, alcohols are generated. Addition of water When the decomposable organosilicate has a methoxy group, such as trimethyl silicate or tetramethyl silicate, methanol is produced as an alcohol. Addition of water When the decomposable organosilicate has an ethoxy group, such as triethyl silicate, ethanol is produced as the alcohol.

[0040] Here, in step (b), the concentration of the alcohols generated from the hydrolysis reaction in step (a) must be adjusted to 1 to 25 mass%. Although the detailed mechanism is unclear, it is believed that maintaining or adjusting the concentration of the alcohols within this range can slow the reaction rate of the hydrolysis of the modifier, such as a silane coupling agent, used in the next step (c) (modification treatment step) and the subsequent condensation, thereby suppressing unintended self-condensation reactions between modifiers, such as silane coupling agents, and thus increasing the modification rate of the modification treatment in step (c). Furthermore, although the detailed mechanism is unclear, maintaining or adjusting the concentration of the alcohols within this range can reduce the occurrence of aggregation, even when the BET diameter or the cumulant mean diameter is relatively small due to the polarity of the solvent, and it is believed that the next step (c) can be performed without causing aggregation and gelation. The concentration of the generated alcohols is determined by the amount of the facile solvent used in step (a). Addition of water The content can be appropriately adjusted by the amount of decomposable organosilicate used, the substitution of alcohols with pure water by distillation, etc., but the lower limit is preferably 5% by mass or more, more preferably 12% by mass or more, and the upper limit is preferably 20% by mass or less.

[0041] As with the adjustment of the solids concentration (13% by mass or less) in step (b), if the alcohol concentration of the raw colloidal silica obtained in step (a) is already 1 to 25% by mass, active adjustment of the alcohol concentration is not necessary. In this case, step (b) may be treated as a step for confirming the alcohol concentration, or as a step for maintaining the alcohol concentration produced in step (a). Ensuring that the alcohol concentration is 1 to 25% by mass in step (b) before the modification treatment in the next step (c) is a characteristic step in obtaining the final modified colloidal silica of the present invention that is substantially non-agglomerated, has a high degree of modification, and has a relatively high solids concentration, as in the adjustment of the solids concentration (13% by mass or less). The alcohol may serve as part of the solvent in the modification treatment in the next step (c).

[0042] The method for adjusting the alcohol concentration in step (b) is not limited. However, when adjusting to increase the alcohol concentration, it is preferable to add an organic solvent containing the same organic solvent as the produced alcohol as the main component (e.g., 95% by mass or more). As described above, the organic solvent added here may include water, alcohols, aldehydes, ketones, surfactants, etc. On the other hand, the method for adjusting to decrease the alcohol concentration is not limited, but an example is a method in which the alcohol is evaporated by heating and distilled from a distillation tube equipped with a condenser. In this case, pure water may be added.

[0043] [Process (c)] In step (c), the raw colloidal silica, whose solids concentration and the concentration of the produced alcohols have been adjusted through step (b), is modified. In the present invention, an anionic modification is performed. Although the reason why an anionic modification is preferred as the modification is not entirely clear, it is presumed that an anionic modification changes the surface potential of the colloidal silica, which is expected to have effects such as attraction to the object to be polished, thereby improving the selectivity for the object to be polished. In particular, compared to unmodified colloidal silica, the anionic modification tends to improve dispersion stability not only in alkaline conditions but also in acidic conditions, where the colloidal silica is metastable and relatively prone to aggregation.

[0044] For details about the anion modification treatment, reference can be made to, for example, JP-A-2010-269985 and JP-A-2013-041992.

[0045] Here, the specific method of anion modification treatment is not limited, but a suitable method of anion modification is, for example, a method in which a modifier having an anionic group is chemically bonded to the surface of colloidal silica. Another method is a method in which a modifier having a functional group that can be converted into an anionic group is chemically bonded to the surface of colloidal silica by a chemical method or the like, and then a treatment is performed to convert the functional group into an anionic group. For reasons such as the efficiency of the modification treatment, the ability to stably introduce anionic groups into colloidal silica, and the difficulty of directly obtaining a modifier having an anionic group, a method using a modifier having a functional group that can be converted into an anionic group is preferred.

[0046] Compounds (modifiers) having functional groups that can be converted into anionic groups include, but are not limited to, silane coupling agents having functional groups that can be converted into anionic groups. Examples of anionic groups include, but are not limited to, sulfo groups, carboxy groups, and phosphate groups. Anionic groups may also be ionically bonded with cations to form salts. Even with such anionic groups, the cations are released in aqueous solutions, allowing them to function as anionic groups. Examples of cations that ionically bond with anionic groups include alkali metal ions such as sodium ions and potassium ions, and alkaline earth metal ions such as calcium ions. From the viewpoint of improving selectivity for the polishing target, among the anionic groups, sulfo groups and carboxy groups are preferred, and sulfo groups are more preferred.

[0047] A sulfo group will be used as an example of an anionic group as a preferred embodiment. Examples of modifying agents having a functional group that can be converted to a sulfo group include silane coupling agents having a sulfonate ester group that can be converted to a sulfo group by hydrolysis, and silane coupling agents having a mercapto group and / or a sulfide group that can be converted to a sulfo group by oxidation. Among these, a method using a silane coupling agent having a mercapto group and / or a sulfide group is more preferred because it is easy to modify colloidal silica. In the present invention, only one type of modifying agent may be used, or two or more types may be used in combination.

[0048] Examples of silane coupling agents having a mercapto group include 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, etc. Examples of silane coupling agents having a sulfide group include bis(3-triethoxysilylpropyl)disulfide.

[0049] Among the anionic modifications, the sulfo group, which is exemplified as a preferred embodiment, will be taken as an example for explanation.

[0050] (Example of anion modification treatment using sulfo groups) As described above, sulfo groups can be formed on the surface of colloidal silica by known methods. Preferably, a method is used in which a modifying agent having a functional group that can be converted into a sulfo group by a chemical method or the like is chemically bonded to the surface of colloidal silica, and then a treatment is carried out to convert the functional group into a sulfo group, and a modifying agent having a functional group that can be converted into a sulfo group by oxidation is preferred. As described above, a preferred modifying agent among these is a silane coupling agent having a mercapto group and / or a sulfide group, and a representative example is described below.

[0051] This method preferably includes a step (c1) of reacting raw colloidal silica, the solid content of which and the concentration of the produced alcohols of which have been adjusted through steps (a) and (b) as described above, in the presence of the silane coupling agent, and a step (c2) of oxidizing the reaction product of step (c1) to convert mercapto groups and / or sulfide groups to sulfo groups. Steps c1 and c2 can also be carried out with reference to the aforementioned Japanese Patent Application Laid-Open Nos. 2010-269985 and 2013-041992. Other steps may also be included as appropriate, provided they do not impair the objectives of the present invention. Examples of such other steps include adjusting the viscosity of the reaction solution and adjusting the pH.

[0052] (Step c1) In step c1, the raw colloidal silica, the solid content of which and the concentration of the produced alcohols of which have been adjusted through steps (a) and (b), is reacted in the presence of a silane coupling agent having a mercapto group and / or a sulfide group, whereby the silane coupling agent is chemically bonded to the surface of the raw colloidal silica.

[0053] The reaction in step c1 can be carried out within a temperature range appropriate for the use of the denaturant, and is not limited thereto, for example, at a temperature range of 40°C or higher and up to the boiling point of the reaction liquid (solvent). To improve reactivity, the reaction is preferably carried out at a temperature of 50°C or higher, more preferably 60°C or higher, and up to the boiling point of the reaction liquid (solvent), preferably 100°C or lower. The reaction time is also not limited, but is preferably carried out for 10 minutes to 10 hours, and more preferably 1 to 8 hours.

[0054] In the reaction of step c1, a solvent for improving the solubility of the modifier or silane coupling agent can be added within a range that does not impair the object of the present invention. Such a solvent can be a hydrophilic solvent, for example, an alcohol such as methanol, ethanol, isopropanol, etc., but is not limited thereto. It is more preferable to use the same alcohol as the alcohol produced by the hydrolysis reaction to obtain the raw colloidal silica.

[0055] As described above, the amount of the modifier (silane coupling agent) used is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 6 parts by mass, and even more preferably 0.3 to 4 parts by mass, per 100 parts by mass of the solid content of the raw colloidal silica. That is, the modifier is preferably present in an amount of 0.1 to 10% by mass, more preferably 0.2 to 6% by mass, and even more preferably 0.3 to 4% by mass, based on the solid content of the modified colloidal silica. An amount used within this range ensures sufficient anionization of the colloidal silica particle surfaces. Furthermore, such an amount allows for the production of stable, anion-modified colloidal silica without aggregation and with a high degree of modification. A solvent (e.g., water, a hydrophilic organic solvent) for dissolving the modifier may be used during the modification treatment.

[0056] In addition, when denaturing, sexThe pH during the treatment is preferably weakly alkaline or lower, more preferably 8.0 or lower, even more preferably 7.8 or lower, and even more preferably 7.5 or lower. In other words, a preferred embodiment is to adjust the pH of the raw colloidal silica after the concentration adjustment step in step (b) for use in step (c) to be within the above-mentioned range. By adjusting the pH during the modification treatment to this range, decomposition of the modifier used, such as the silane coupling agent, can be suppressed. While the lower limit of the pH during the modification treatment is not limited, a pH of 6.5 or higher is preferred, more preferably 6.8 or higher, and even more preferably 7.0 or higher.

[0057] The method for adjusting the pH during the modification treatment to the preferred range is not limited. For example, by appropriately selecting the hydrolysis catalyst used in the above-mentioned step (a), the raw colloidal silica in step (a) and the raw colloidal silica after concentration adjustment in the subsequent step (b) can be adjusted to the preferred pH range. As mentioned above, by appropriately selecting the hydrolysis catalyst, it is possible to prevent the hydrolysis from becoming excessively rapid in step (a), which can cause self-aggregation, and at the same time, it is possible to adjust the pH during the modification treatment in step c1. Therefore, selecting the above-mentioned preferred catalyst as the hydrolysis catalyst in step (a) is a more preferred embodiment. In addition, in step c1, the pH during the modification treatment can be adjusted by adding a known pH adjuster or by using a method of contacting with a cation exchange resin (see, for example, JP 2022-152370 A).

[0058] The reaction in step c1 can be understood, for example, by analyzing the functional groups introduced into the colloidal silica, for example, by pulse NMR (TD-NMR), ion chromatography, 29 Qualitative and / or quantitative analysis of functional groups can be performed using Si-NMR, organic elemental analysis, FT-IR (infrared spectroscopy), and the like.

[0059] (Step c2) In step c2, the functional groups introduced onto the surface of the raw colloidal silica in step c1 are converted into anionic groups by a chemical method. Here, a method for converting the functional groups introduced by a silane coupling agent having a mercapto group and / or a sulfide group into sulfo groups by oxidation treatment is described.

[0060] Methods for converting mercapto groups and / or sulfide groups to sulfo groups by oxidation treatment include, but are not limited to, the use of an oxidizing agent. Examples of oxidizing agents include nitric acid, hydrogen peroxide, oxygen, ozone, organic peracids (percarboxylic acids), bromine, hypochlorite, potassium permanganate, and chromic acid. Among these, hydrogen peroxide and organic peracids (peracetic acid, perbenzoic acids) are preferred in terms of handling and reactivity (oxidation yield). Hydrogen peroxide is most preferred because it generates fewer by-products in the reaction. The amount of oxidizing agent added may be in excess of the amount of modifier (silane coupling agent), but it is preferable to minimize the amount of residual oxidizing agent. To ensure a sufficient oxidation reaction, it is more preferable to use 3 to 5 moles of oxidizing agent per mole of silane coupling agent. The oxidation reaction is not limited, but can be carried out under reaction conditions suitable for the oxidizing agent used, as long as it does not impair the objectives of the present invention. For example, it is preferable to carry out the reaction at a temperature above room temperature and below the boiling point of the solvent used in the reaction solution (for example, 100° C. or below) for 3 to 5 hours.

[0061] By this step c2, colloidal silica having anionic groups (sulfo groups) on the surface can be obtained. Note that step c2 may include other steps after the oxidation treatment. For example, it may include a step for removing the oxidizing agent or a step for adjusting the pH of the solution after the reaction, and these steps may be appropriately selected and performed within the scope that does not impair the object of the present invention.

[0062] The modification treatment in step (c) is characterized by a high modification rate, and a particularly high modification rate can be achieved by performing step (b) or adjusting the pH during the modification treatment in step (c) to a preferred range. The modification rate in the present invention is 90% or higher, preferably 95% or higher, more preferably 98% or higher, even more preferably 99% or higher, still more preferably close to 100%, and most preferably 100%. The modification rate in the present invention can be calculated from the amount of modifier used for the modification treatment and the amount of modifier (anionic groups after conversion) introduced onto the surface of the modified colloidal silica, as will be described in the Examples below. For example, as shown in the examples, an analytical method such as ion chromatography is used to quantify the amount of functional groups of the modifying agent that are not introduced onto the colloidal silica surface as unreacted (unmodified) and the amount of anionic groups after conversion in the modified colloidal silica solution, and this amount is subtracted from the amount of modifying agent added for the modification treatment to determine the amount introduced (modified) onto the colloidal silica surface (amount of agent; amount modified by anionic groups), which can be expressed as a ratio to the amount of modifying agent added. 29 The modification rate can also be measured using one or more analytical means such as Si-NMR, organic elemental analysis, or FT-IR.

[0063] [Step (d)] After step (c) is performed, step (d) involves concentrating the colloidal silica obtained after step (c) so that the residual organic solvent in the resulting colloidal silica is 1% by mass or less. Preferably, the residual organic solvent is 0.1% by mass or less, more preferably 0.05% by mass or less. By reducing the residual organic solvent to this range, the solids concentration can be adjusted or increased to a predetermined range, and in the case of highly volatile residual organic solvents, this is preferable because it prevents fluctuations in the colloidal silica concentration associated with the evaporation of the organic solvent. Another advantage of using the colloidal silica of the present invention is that it is no longer necessary to consider the resistance of the material to residual organic solvents used in the intended application.

[0064] The method for removing and concentrating the residual organic solvent is not particularly limited, and any known method can be used, such as a method in which the residual organic solvent is distilled off by heating using an apparatus equipped with a distillation tube with a condenser.

[0065] In step (d), the residual organic solvent and water are removed by concentration, allowing the solids concentration to be adjusted to a suitable concentration, taking into consideration the intended use and purpose. In the present invention, modified colloidal silica is obtained through steps (a) to (c) described above. Even if the solids concentration is relatively high in step (d), substantially non-aggregated colloidal silica can be obtained. The modified colloidal silica obtained by the modification treatment typically has a solids concentration of about 6% by mass due to factors such as the manufacturing process. However, considering the intended use and purpose of the colloidal silica, the solids concentration of the colloidal silica obtained by step (c) in step (d) is preferably 15% by mass or higher, more preferably 17% by mass or higher, and even more preferably 19% by mass or higher. The upper limit of the solids concentration is the same as described above, and is preferably 50% by mass or lower, more preferably 40% by mass or lower, and even more preferably 30% by mass or lower.

[0066] The colloidal silica of the present invention can be produced by carrying out the above steps (a) to (d). However, other steps may be appropriately included after step (d) as long as they do not impair the object of the present invention. For example, it is preferable to subject the colloidal silica after step (d) to dispersion stabilization. Known processes can be used for the dispersion stabilization treatment.

[0067] Colloidal silica that has been subjected to dispersion stabilization treatment by the method of the present invention exhibits excellent dispersion stability for a period of at least one week, and even for several years, and does not undergo two-layer separation.

[0068] In the present invention, colloidal silica whose surface is anion-modified can be obtained at a high modification rate as described above. However, as in conventional methods, a method in which the obtained colloidal silica is used as seed particles, and a silica source is supplied to a reaction liquid containing the seed particles and the hydrolysis catalyst, and reacted with the seed particles to grow the particle size, is also not excluded.

[0069] <Modified colloidal silica> As described above, the anion-modified colloidal silica produced through the above steps (a) to (d) (hereinafter referred to as "modified colloidal silica") preferably has a solids concentration of 15% by mass or more, more preferably 17% by mass or more, and even more preferably 19% by mass or more. There is no upper limit to the solids concentration, but it is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

[0070] As described above, the modified colloidal silica obtained by the method of the present invention has a modification rate of 90% or more. The modification rate is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, still more preferably close to 100%, and most preferably 100%. The modification rate can be measured and defined by the method described above.

[0071] The particle size of the modified colloidal silica, as a BET particle size, is preferably 5 nm or more and 80 nm or less, similar to the raw colloidal silica. The lower limit is more preferably 6 nm or more, even more preferably 10 nm or more, and even more preferably 14 nm or more. On the other hand, the upper limit is more preferably 70 nm or less, even more preferably 60 nm or less, and even more preferably 50 nm or less.

[0072] The particle size of the modified colloidal silica, as a DLS diameter, is preferably 6 nm or more, more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably more than 20 nm. On the other hand, although there is no upper limit for the cumulant mean diameter, it is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.

[0073] In addition, modified colloidal silica 、 The term "substantially free of aggregation" is used here for the following reason. Generally, methods for confirming whether colloidal silica is aggregated include methods using an electron microscope, measuring viscosity increase, and measuring the cumulant mean diameter using dynamic light scattering (DLS). However, it is difficult to completely determine whether each and every particle is monodispersed. The above-mentioned methods are only capable of determining or understanding the particle dispersion state with a certain degree of certainty. Therefore, as long as there is substantially no aggregation to the extent that it does not cause practical problems, the colloidal silica will function properly and will not cause problems in terms of application.

[0074] To more specifically grasp the "substantially non-aggregated" state, the above-mentioned techniques can be used for measurement, but some areas may be difficult to grasp using an electron microscope. Therefore, it is preferable to use dynamic light scattering (DLS) to determine the change in cumulant mean diameter measured thereby. More specifically, the change (or lack of change) in the cumulant mean diameter can be confirmed by DLS measurement over time. For example, in the production method of the present invention, the occurrence of aggregation can be confirmed by checking the DLS measurement results before and after concentration in step (d) (concentration step). That is, by determining the presence or absence of aggregation with an increase in solid content concentration, it is possible to determine whether the colloidal silica has properties that make it prone to aggregation. This is because, in reality, aggregation is less likely when the solid content concentration is relatively low, but becomes more likely as the solid content concentration increases. This tendency usually becomes more pronounced when the solid content concentration is 10% by mass or higher, more specifically, 12% by mass or higher.

[0075] Among DLS measurement methods, a more practically preferred method for determining aggregation involves measuring the change in particle size by DLS measurement after holding the sample under heated conditions for a certain period of time (period). This method makes it possible to determine whether the colloidal silica has the properties of easily agglomerating without actively changing the solid content concentration. Specifically, as will be described in the Examples below, the change in cumulant mean diameter after holding the sample for 7 days at a temperature of at least 60°C, which is a temperature at which particles are easily agglomerated, is observed, and if the rate of change is within 20%, it can be determined that no aggregation has occurred. Here, the reason why the method of holding the sample at 60°C or above for 7 days is preferred is that it has been found that a 7-day period at 60°C is roughly equivalent to a 1-year aging test at room temperature, thereby making it possible to determine whether aggregation has occurred in a 1-year aging test at room temperature. Preferably, the rate of change in cumulant mean diameter by DLS measurement is within 10%, more preferably within 8%, and even more preferably within 5%. Here, for the reasons described above, when performing such DLS measurement, it is advisable to maintain or measure the solid content concentration at 12% by mass or more, more specifically 18% by mass or more, even more specifically 19% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. The solid content concentration at this time is not limited, and it is preferable to perform the DLS measurement at a solid content concentration suited to the application and practical use.

[0076] The modified colloidal silica may have any shape and other properties depending on the application and purpose. In particular, colloidal silica obtained by the method of the present invention preferably has a relatively high particle surface area, and preferably has numerous irregular small protrusions, giving the particles as a whole a shape resembling that of a confetti candy. Such a shape has a large BET specific surface area relative to its large SEM average particle diameter, measured as the arithmetic mean of particle images observed by SEM, and a high particle density (true specific gravity) measured by the liquid phase displacement method, in other words, high hardness, and is suitable for use as a polishing agent for CMP, due to its excellent polishing rate. Therefore, the BET specific surface area is 50 m 2 / g or more, and 100m 2 Although there is no upper limit to the BET specific surface area, it is preferable that the upper limit is 500 m / g or more from the viewpoint of stability. 2 / g or less, and 2 It is more preferable that the saturation coefficient is 1 / g or less.

[0077] The particle shape of the modified colloidal silica can be controlled by adjusting the feed composition, etc., to form monodisperse spheres (spherical products) or spheres in which particles coalesce and associate (associated products). For example, by adding a large amount of catalyst and a relatively slow rate of introducing an organosilicate as a silica raw material into the reaction field, the organosilicate hydrolyzes quickly and uniformly and grows mildly, resulting in gradual growth of seed particles while maintaining their spherical shape, resulting in a spherical product. Alternatively, by adding a small amount of catalyst and a relatively fast rate of introducing an organosilicate as a silica raw material into the reaction field, the organosilicate hydrolyzes unevenly, acting as an adhesive between particles, resulting in an associated product in which the particles associate.

[0078] The viscosity of the modified colloidal silica is preferably 1 to 100 mPa·s, more preferably 1 to 50 mPa·s, and even more preferably 1 to 20 mPa·s.

[0079] Furthermore, as described above, the modified colloidal silica may be a monodisperse spherical product, or may be an associated product (such as a cocoon-shaped, chain-like, or branched product) that appears to be formed by two-dimensional or three-dimensional coalescence of multiple particles when observed under an electron microscope.

[0080] The pH of the modified colloidal silica may be adjusted to a value that does not impair dispersion stability, depending on the modification treatment. For example, in the case of the anion-modified colloidal silica, the pH is preferably 1 to 5, and more preferably 1.5 to 4.5. Adjusting the pH to this range is preferable in terms of dispersion stability of the colloidal silica.

[0081] Furthermore, the modified colloidal silica preferably has a metal impurity content of 1 ppm or less, more preferably 0.01 ppm or less, and even more preferably 0.0001 ppm or less. Although not limited thereto, such high-purity colloidal silica can be achieved, for example, in the production method described below, by using silica source, hydrolysis catalyst, and water that satisfy the above-mentioned metal impurity contents as raw materials for the hydrolysis reaction to obtain the raw colloidal silica. [Example]

[0082] Preferred embodiments of the present invention will be specifically described below based on examples and comparative examples.

[0083] [Example 1] A 5-L glass vessel equipped with a stirrer, thermometer, condenser-equipped distillation tube, and organosilicate inlet tube was charged with 3184 g of pure water containing 0.1 ppb or less of metal impurities and 3.41 g of triethanolamine containing 10 ppb or less of metal impurities. While maintaining the liquid temperature in the vessel at 70°C using a mantle heater, 1413 g of tetramethyl silicate (manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was continuously added with stirring over 6 hours. 625 g of the resulting colloidal silica with a silica concentration of 12.6% by mass, 2767 g of pure water containing 0.1 ppb or less of metal impurities, and 7.91 g of triethanolamine containing 10 ppb or less of metal impurities were added. While maintaining the liquid temperature in the vessel at 80°C using a mantle heater, 1200 g of tetramethyl silicate (manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was continuously added with stirring over 6 hours. The obtained raw colloidal silica was subjected to various analyses, and the results are shown in Table 1. <1> shown in.

[0084] Next, 3900 g of the resulting reaction product (colloidal silica, solids concentration 12.5 wt%, methanol concentration 14 wt%) was added to a 5 L glass container without changing the solids concentration or methanol concentration. Next, while maintaining the temperature at 80°C, 15.6 g of 3-mercaptopropyltrimethoxysilane mixed with 140.4 g of methanol was continuously added over 6 hours. After the addition, 27.0 g of 30 wt% aqueous hydrogen peroxide was continuously added over 4 hours while maintaining the temperature at 80°C, thereby modifying the raw colloidal silica.

[0085] After the hydrogen peroxide solution was added, the temperature inside the reaction vessel was temporarily lowered to 40°C, and the pressure inside the system was reduced using a vacuum pump. Heating was then resumed, and the reaction mixture inside the reaction vessel was further heated to 52-68°C. The resulting methanol was distilled from the condenser-equipped distillation tube at a distillation temperature of 32-67°C. 250 g of pure water was then added while distilling off the water and methanol, yielding colloidal silica with a solids concentration of approximately 20% by mass. The residual organic solvent content of the resulting colloidal silica was 0.1% by mass. The colloidal silica obtained was subjected to various analyses, and the results are shown in Table 1. <2> The modification rate (anion group modification reaction rate) was calculated from the formula described below, with the modification amount being the amount of sulfate ions determined by anion chromatography subtracted from the amount of 3-mercaptopropyltrimethoxysilane added to the colloidal silica. The resulting colloidal silica was then stored at 60°C for 7 days, and various analyses were carried out on the resulting colloidal silica, confirming that essentially no aggregation had occurred, particularly from the results of DLS measurements. The results are shown in Table 1. <3> shown in.

[0086] [Example 2] A 5L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube was charged with 3184g of pure water with a metal impurity content of 0.1 ppb or less and 3.41g of triethanolamine with a metal impurity content of 10 ppb or less, and while maintaining the liquid temperature in the reaction vessel at 70°C using a mantle heater, 1413g of tetramethyl silicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over 6 hours. Various analyses were performed on the resulting raw colloidal silica, and the results are shown in Table 1. <4> shown in.

[0087] Next, 3900 g of the resulting reaction product (colloidal silica, solids concentration 12.5 wt%, methanol concentration 15 wt%) was added to a 5 L glass container without changing the solids concentration or methanol concentration. Next, while maintaining the temperature at 80°C, 13.1 g of 3-mercaptopropyltrimethoxysilane mixed with 117.8 g of methanol was continuously added over 6 hours. After the addition, 22.7 g of 30 wt% aqueous hydrogen peroxide was continuously added over 4 hours while maintaining the temperature at 80°C, thereby modifying the raw colloidal silica.

[0088] After the hydrogen peroxide solution was added, the temperature inside the reaction vessel was temporarily lowered to 40°C, and the pressure inside the system was reduced using a vacuum pump. Heating was then resumed, and the reaction mixture inside the reaction vessel was further heated to 52-68°C. The resulting methanol was distilled from the condenser-equipped distillation tube at a distillation temperature of 32-67°C. 250 g of pure water was then added while distilling off the water and methanol, yielding colloidal silica with a solids concentration of approximately 20% by mass. The residual organic solvent content of the resulting colloidal silica was 0.1% by mass. The colloidal silica obtained was subjected to various analyses, and the results are shown in Table 1. <5> The modification rate (anion group modification reaction rate) was calculated from the formula described below, with the modification amount being the amount of sulfate ions determined by anion chromatography subtracted from the amount of 3-mercaptopropyltrimethoxysilane added to the colloidal silica. The resulting colloidal silica was then stored at 60°C for 7 days, and various analyses were carried out on the resulting colloidal silica, confirming that essentially no aggregation had occurred, particularly from the results of DLS measurements. The results are shown in Table 1. <6> shown in.

[0089] [Example 3] A 5L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube was charged with 3890g of pure water with a metal impurity content of 0.1 ppb or less and 3.42g of triethanolamine with a metal impurity content of 10 ppb or less. While maintaining the liquid temperature in the reactor at 60°C using a mantle heater, 707g of tetramethyl silicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over 90 minutes. Various analyses of the resulting raw colloidal silica were carried out, and the results are shown in Table 1. <7> shown in.

[0090] Next, 3900 g of the resulting reaction product (colloidal silica, solids concentration 6.4 wt%, methanol concentration 14 wt%) was added to a 5 L glass container without changing the solids concentration or methanol concentration. Next, while maintaining the temperature at 80°C, 13.1 g of 3-mercaptopropyltrimethoxysilane mixed with 117.8 g of methanol was continuously added over 6 hours. After the addition, 22.7 g of 30 wt% aqueous hydrogen peroxide was continuously added over 4 hours while maintaining the temperature at 80°C, thereby modifying the raw colloidal silica.

[0091] After the hydrogen peroxide solution was added, the temperature inside the reaction vessel was temporarily lowered to 40°C, and the pressure inside the system was reduced using a vacuum pump. Heating was then resumed, and the reaction mixture inside the reaction vessel was further heated to 52-68°C. The resulting methanol was distilled from the condenser-equipped distillation tube at a distillation temperature of 32-67°C. 250 g of pure water was then added while distilling off the water and methanol, yielding colloidal silica with a solids concentration of approximately 20% by mass. The residual organic solvent content of the resulting colloidal silica was 0.1% by mass. The colloidal silica obtained was subjected to various analyses, and the results are shown in Table 1. <8> The modification rate (anion group modification reaction rate) was calculated from the formula described below, with the modification amount being the amount of sulfate ions determined by anion chromatography subtracted from the amount of 3-mercaptopropyltrimethoxysilane added to the colloidal silica. The resulting colloidal silica was then stored at 60°C for 7 days, and various analyses were carried out on the resulting colloidal silica, confirming that essentially no aggregation had occurred, particularly from the results of DLS measurements. The results are shown in Table 1. <9> shown in.

[0092] [Comparative Example 1] A 5L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube was charged with 510g of pure water containing less than 0.1 ppb of metal impurities, 3412g of methanol, and 140g of 29% aqueous ammonia. While maintaining the liquid temperature in the vessel at 20°C using a thermostatic water bath, 425g of tetramethyl silicate (manufactured by Tama Chemicals Co., Ltd.) containing less than 10 ppb of metal impurities mixed with 113g of methanol was continuously added over 25 minutes with stirring, and then thermally concentrated water substitution was carried out under conditions of pH 7 or higher. Various analyses of the resulting raw colloidal silica were carried out, and the results are shown in Table 2. <10> shown in.

[0093] Next, 1000 g of the resulting reaction product (colloidal silica, solids concentration 19.5% by mass, methanol concentration less than 1% by mass) was placed in a 5 L glass container, and 1.7 g of 29% by mass ammonia water was added to reduce the viscosity. Next, 2.5 g of 3-mercaptopropyltrimethoxysilane mixed with 22.5 g of methanol was added dropwise over 5 minutes, followed by heating and boiling, followed by water substitution for 6 hours. The reaction solution was then cooled to 25°C, after which 4.3 g of 30% by mass hydrogen peroxide solution was added and boiled again. After boiling, water substitution was continued for 4 hours, and the mixture was then cooled to room temperature, whereupon the raw colloidal silica was modified. The colloidal silica obtained was subjected to various analyses, and the results are shown in Table 2. <11> The modification rate (anion group modification reaction rate) was calculated from the formula described below, with the modification amount being the amount of sulfate ions determined by anion chromatography subtracted from the amount of 3-mercaptopropyltrimethoxysilane added to the colloidal silica. The resulting colloidal silica was then stored at 60°C for 7 days, and various analyses were carried out on the resulting colloidal silica, confirming that essentially no aggregation had occurred, particularly from the results of DLS measurements. The results are shown in Table 2. <12> shown in.

[0094] Comparative Example 2 A 10 L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube was charged with 8836 g of pure water containing less than 0.1 ppb of metal impurities and 13.968 g of 3-ethoxypropylamine, and while maintaining the liquid temperature in the reaction vessel at 85°C using a mantle heater, 1534 g of tetramethyl silicate (manufactured by Tama Chemicals Co., Ltd.) containing less than 10 ppb of metal impurities was continuously fed into the vessel over 15 minutes with stirring. Various analyses were performed on the resulting raw colloidal silica, and the results are shown in Table 2. <13> shown in.

[0095] Next, 900 g of the resulting reaction product (colloidal silica, solids concentration 6.4% by mass, methanol concentration 15% by mass) was added to a 2 L glass container without changing the solids concentration or methanol concentration. Next, while maintaining the temperature at 80°C, 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of 30% by mass hydrogen peroxide solution were added to modify the raw colloidal silica.

[0096] Next, the methanol was replaced with water by adding pure water to obtain colloidal silica with a solid content of about 6% by mass, and the residual organic solvent in the obtained colloidal silica was 0.1% by mass.

[0097] The colloidal silica obtained was subjected to various analyses, and the results are shown in Table 2. <14> The modification rate (anion group modification reaction rate) was calculated from the formula described below, with the modification amount being the amount of sulfate ions determined by anion chromatography subtracted from the amount of 3-mercaptopropyltrimethoxysilane added to the colloidal silica. The resulting colloidal silica was then stored at 60°C for 7 days, and various analyses were carried out on the resulting colloidal silica, confirming that essentially no aggregation had occurred, particularly from the results of DLS measurements. The results are shown in Table 2. <15> shown in.

[0098] [Table 1]

[0099] [Table 2]

[0100] The physical properties of the resulting colloidal silica were evaluated by the following methods. (1) BET specific surface area, BET equivalent particle size: Measurements were made using a NOVA4200e (manufactured by Anton Paar). The BET specific surface area S (m 2 / g) and the true density of SiO2 is 2.2 g / cm 3 ) and the particle diameter obtained from the above formula (1) using the formula 2727 / S is the BET diameter. (2) Cumulant mean diameter by dynamic scattering (DLS diameter): Measurement was performed using an SZ-100 (manufactured by Horiba, Ltd.) The silica content in the measurement sample was adjusted to 1.13 g with pure water and ammonium nitrate, and the adjusted solution was measured. (3) Silica solid concentration: Using an SMS-70 (manufactured by A&D Co., Ltd.) as the equipment, the residue after evaporating the contained water was taken as the silica concentration. (4) pH: Measured at 25°C using a D-51 (manufactured by Horiba Ltd.). (5) Viscosity: Measured at 25°C using a VM-10A (manufactured by Sekonic Corporation). (6) Methanol concentration: Measured using a GC-2025 (Shimadzu Corporation). (7) Modification rate (anion group modification reaction rate): Using a Dionex Integrion HPIC system (Thermo Fisher Scientific Co., Ltd.), each colloidal silica sample obtained in each Example and Comparative Example was diluted 100 times with pure water to give a solution (approximately 0.2 mass% solution), which was then subjected to ultrafiltration, and 1 mL of the sample was sampled and measured by anion chromatography under the following measurement conditions:

[0101] (Measurement conditions) Eluent: Na2CO3 (1.8mM) + NaHCO3 (1.7mM), flow rate: 1.5mL / min, temperature: 35.0℃, injection volume: 1mL.

[0102] (Calculation of denaturation rate) The modification rate was calculated from the following formula, where the modification amount (mol) was calculated by subtracting the amount of sulfate ions (A, mol) determined by anion chromatography from the amount of 3-mercaptopropyltrimethoxysilane (B, mol) added to modify the colloidal silica. Denaturation rate (%) = 100 × (BA) / B [Industrial Applicability]

[0103] The colloidal silica of the present invention is suitable for applications such as abrasives (silicon wafers, hard disks, etc.), coating agents (eyeglasses, displays, building materials, paper, etc.), and binders (ceramics, catalysts, etc.).

Claims

1. 1. A method for producing colloidal silica having an anion-modified surface, comprising the steps of: a raw material preparation step of supplying an easily hydrolyzable organosilicate to a reaction solution containing a hydrolysis catalyst comprising an organic amine and reacting the organosilicate to prepare raw material colloidal silica; a concentration adjusting step of adjusting the solid content concentration of the raw material colloidal silica to 13% by mass or less and adjusting the concentration of alcohols generated in the raw material preparing step to 1 to 25% by mass; a modification treatment step of modifying the raw colloidal silica whose concentration has been adjusted; and a concentration step of concentrating the modified colloidal silica so that the residual organic solvent in the modified colloidal silica is 1% by mass or less, The method for producing colloidal silica, wherein the modification rate in the modification treatment step is 90% or more.

2. 2. The method for producing colloidal silica according to claim 1, wherein the modification rate in the modification treatment step is 95% or more.

3. 3. The method for producing colloidal silica according to claim 1, wherein the pH during the modification treatment in the modification treatment step is 8.0 or less.

4. 3. The method for producing colloidal silica according to claim 1, wherein in the raw material preparing step, the reaction is carried out under conditions where the feed rate of the easily hydrolyzable organosilicate is less than 1.5 mass% / min of the total amount of the easily hydrolyzable organosilicate introduced, the reaction time is 6 hours or less, and the reaction temperature is 80°C or lower.

5. 3. The method for producing colloidal silica according to claim 1, wherein the concentration step is performed so that the solid content concentration in the colloidal silica after the modification treatment step is 15% by mass or more.

6. 3. The method for producing colloidal silica according to claim 1, wherein in the raw material preparing step, raw material colloidal silica having a cumulant mean diameter measured by dynamic light scattering exceeding 20 nm is prepared.

7. 3. The method for producing colloidal silica according to claim 1, wherein the modification treatment step comprises: a step of reacting the colloidal silica after the concentration adjustment step with a modifier having a functional group that can be converted into an anionic group; and a step of converting the functional group in the modifier after the reaction into an anionic group.

8. 8. The method for producing colloidal silica according to claim 7, wherein the modifying agent has mercapto groups and / or sulfide groups, and the mercapto groups and / or sulfide groups are converted to sulfo groups by treating the modifying agent with an oxidizing agent, thereby obtaining colloidal silica having sulfo groups on its surface.

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