Colloidal silica and method of producing colloidal silica

Abstract

To provide colloidal silica in a single nano-size or a small particle size close to the single nano-size, in which its agglomeration does not substantially occur, and a method of producing the same.SOLUTION: The colloidal silica is characterized by being surface modified, having a BET diameter of not larger than 12 nm, and being not substantially agglomerated. The method of producing the colloidal silica is characterized by including a raw material preparation step of supplying easily decomposable organo-silicate to a reaction liquid including a hydrolysis catalyst consisting of an organic amine to make the organo-silicate react with the reaction liquid, to prepare raw material colloidal silica having a BET diameter of not larger than 12 mn, a concentration adjustment step of adjusting the solid content concentration of the raw material colloidal silica to not greater than 13 mass% and adjusting the concentration of the alcohol formed in the raw material preparation step to 1 to 25 mass%, a modification step of modifying the raw material colloidal silica of which concentration has been adjusted, and a concentration step of concentrating the content of residual organic solvent in the colloidal silica which has been modified, to be not greater than 1 mass%.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

[0003] Regarding colloidal silica used for various applications, particularly colloidal silica used in the field of polishing agents for semiconductor wafers, various types of metal wiring, oxide films, and the like are present on a single wafer with the increasing integration density of today's LSIs, and each semiconductor wafer requires its own appropriate polishing performance, resulting in a demand for colloidal silica with various slightly different compositions and properties.

[0004] Furthermore, for colloidal silica used in applications where even slight alkali metal impurities should not be contained, such as binders for hard coating agents and ceramics, chromate-based metal surface treatment agents, and ground improvement grout, acidic colloidal silica is required, and several proposals for methods for producing such acidic colloidal silica are known.

[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-treatment such as acid treatment, ion exchange treatment, or further 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, and has proposed that neutral colloidal silica with a pH of 5 to 8 can be easily produced without special post-treatment such as acid treatment, ion exchange treatment, or the like, by using an easily hydrolyzable organosilicate having a high hydrolysis rate and a specific hydrolysis catalyst as a hydrolysis catalyst, and adding and reacting this hydrolysis catalyst so that at least the ratio of hydrolysis catalyst (A) to silica (B) in the reaction mixture at the end of the reaction {catalyst remaining molar ratio (A / B)} is a predetermined value or less (Patent Document 1).

[0006] Incidentally, in the field of polishing agents for semiconductor wafers, for example, it has become necessary to meet various demands in recent years, and with conventionally manufactured colloidal silica of several tens of nanometers (nm), fine adjustment during polishing is difficult, and problems arise such as the surface being over-etched or a clean surface not being formed. In addition, there is also the situation of semiconductors becoming increasingly miniaturized.

[0007] Therefore, there is a demand for colloidal silica with a particle size smaller than that of conventional colloidal silica, that is, a so-called single nano size of several nm or a particle size close to that. However, when the particle size is such, the tendency of the particles to aggregate due to the solid content of the colloidal silica increases, and even if the particle size is close to the single nano size, there is a concern that the characteristics (e.g., polishability, improvement of the number of defects in the polished object, etc.) cannot be fully utilized. In this regard, according to the study by the inventors of the present application, it has been found that aggregation becomes more prominent, especially as the solid content concentration of the colloidal silica increases. That is, colloidal silica that has a particle size of single nano size or close to single nano size and has a stable dispersed state without causing aggregation even when the solid content concentration is relatively high has not been found so far. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2007-153732 A [Patent Document 2] International Publication No. 2016 / 117560 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the inventors of the present application conducted extensive research to develop colloidal silica having a small particle size of single nano size or a similar range, which does not substantially aggregate even when the solid concentration is relatively high. As a result, they discovered that this can be achieved by devising a raw material preparation process, a concentration adjustment process, etc., and by subjecting colloidal silica to a modification treatment at a predetermined timing, thereby completing the present invention.

[0010] Therefore, an object of the present invention is to provide colloidal silica having a small particle size of single nano size or close to that size and substantially no aggregation, and a method for producing the same.

[0011] Although some techniques for modifying colloidal silica have been reported (for example, Patent Document 2), Patent Document 2 relates to modified colloidal silica that can improve the stability of the polishing rate over time when used as an abrasive grain with few microparticles, and does not specifically teach colloidal silica of single nano size or a small particle size close to that, and does not disclose particle size in the examples. In addition, in the manufacturing method described in Patent Document 2, it is essential to provide a process of concentrating the colloidal silica so that the residual organic solvent concentration is 1 mass% or less (organic solvent distillation process) before the modification process for modifying the colloidal silica. Therefore, in such a manufacturing process, when trying to obtain colloidal silica of single nano size or a small particle size close to that, there is a risk of aggregation before the modification process is performed. [Means for solving the problem]

[0012] That is, the gist of the present invention is as follows. (1) A colloidal silica characterized by having a surface modified, a BET diameter of 12 nm or less, and being substantially free of aggregation. (2) BET specific surface area is 227m 2 / g or more. (3) The colloidal silica according to (1), wherein the modification is anion-modified or cation-modified. (4) The colloidal silica according to (3), wherein the anion-modification is performed with a sulfo group. (5) The colloidal silica according to (3), wherein the cation modification is by a primary amino group. (6) The colloidal silica according to (1), having a solid content of 12% by mass or more. (7) The colloidal silica according to (1), characterized in that it has a solid content of 12% by mass or more, and in that, with respect to the cumulant average diameter measured by a dynamic light scattering method, a rate of change in the cumulant average diameter after being kept at a temperature of 60°C for one week is within 20% compared to before the keeping. (8) A method for producing the colloidal silica according to any one of (1) to (7), comprising the steps of: a raw material preparation step of supplying and reacting a readily decomposable organosilicate to a reaction solution containing a hydrolysis catalyst made of an organic amine to prepare raw material colloidal silica having a BET diameter of 12 nm or less; 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; a modification treatment step of modifying the raw colloidal silica having the adjusted concentration; a concentrating 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, comprising: (9) The method for producing colloidal silica according to (8), wherein in the raw material preparing step, the reaction is carried out under conditions in which the feed rate of the easily hydrolyzable organosilicate is less than 1.5 mass% / min of a total amount of the easily hydrolyzable organosilicate introduced, the reaction time is 6 hours or less, and the reaction temperature is 70° C. or lower. (10) The method for producing colloidal silica according to (8), wherein in the concentrating step, the colloidal silica after the modification treatment step is concentrated so that the solid content in the colloidal silica is 12 mass % or more. (11) The method for producing colloidal silica according to (8), 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 after the concentration adjustment step, and a step of converting the functional group in the modifier after the reaction into an anionic group. (12) The method for producing colloidal silica according to (11), wherein the modifying agent has a mercapto group and / or a sulfide group, and the mercapto group and / or the sulfide group are converted to a sulfo group by treating with an oxidizing agent to obtain colloidal silica having sulfo groups on the surface. (13) The method for producing colloidal silica according to (8), wherein the modification treatment step comprises a step of reacting a modifier having a cationic group with the colloidal silica after the concentration adjustment step. Effect of the Invention

[0013] According to the present invention, it is possible to obtain colloidal silica that has a small particle size of single nano size or close to that size and does not substantially undergo aggregation even when the solid content concentration is relatively high. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 shows an SEM image (magnification: 500,000) of the colloidal silica obtained in Example 1. [Diagram 2] FIG. 2 shows an SEM image (magnification: 500,000) of the colloidal silica obtained in Example 2. [Diagram 3] 3 is a photograph showing the state of aggregated gelation in Comparative Example 2. (a) is a photograph showing the state in which the gel was placed in a spherical glass container, (b) is a photograph showing the state in which a part of the gel was taken out and placed on a petri dish, and (c) is a photograph showing the state in which the gel was crushed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] <Colloidal Silica> The colloidal silica of the present invention has a modified surface, a BET diameter of 12 nm or less, and is substantially free of aggregation.

[0016] The colloidal silica used as the raw material is not limited as long as it has silanol groups on the surface, but considering that it does not contain metal impurities or corrosive ions such as chlorine, colloidal silica obtained by hydrolysis and condensation using a hydrolyzable silicon compound as the raw material (for example, an easily hydrolyzable organosilicate or its derivative described below) is preferred. The colloidal silica used as the raw material can be used alone or in combination of two or more types.

[0017] First, the BET diameter will be described. As described above, the colloidal silica of the present invention has a small particle size of single nano size or close to single nano size, and has a BET diameter of 12 nm or less. As described below in terms of industrial applicability, small-particle colloidal silica having a BET diameter of 12 nm or less is useful in that it is easy to prepare as an abrasive for semiconductor wafers and is less likely to be scratched during polishing.

[0018] The BET diameter is preferably 12 nm or less, more preferably 10 nm or less, in terms of polishing efficiency, etc. The lower limit of the BET diameter is not limited, but can be appropriately set in consideration of the application, characteristics, etc. For example, in order to ensure dispersion stability, it is preferably 1 nm or more, more preferably 5 nm or more.

[0019] Here, in the present invention, the significance of using the BET diameter to express a small particle diameter is that, for example, as will be explained later, not only monodispersed spherical products but also colloidal silica produced by two- or three-dimensional coalescence of 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 high specific surface area. In light of these circumstances, it is preferable to adopt the BET diameter assuming a spherical shape while also taking into account the specific surface area in determining the performance relative to the particle shape.

[0020] That is, in the present invention, the BET diameter is the BET specific surface area S (unit: m 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 It is.

[0021] The colloidal silica of the present invention has a BET specific surface area of ​​227 m 2 / g or more. This BET specific surface area is favorable in terms of polishing efficiency. The preferred BET specific surface area is 230 m 2 / g or more, and more preferably 300m 2 Although there is no upper limit for the BET specific surface area, it is recommended to limit it to 500 m 2 / g or less, and more preferably 400m 2 / g or less.

[0022] Next, the modification will be described. The colloidal silica of the present invention is obtained by subjecting raw colloidal silica to a modification treatment. Here, the modification treatment in the present invention is not limited as long as it contributes to the improvement or modification of the properties such as the improvement of dispersion stability, the suppression of aggregation, and the affinity with the object to be polished, which are the objects of the present invention, and can be appropriately selected from the modification treatments of colloidal silica known in the art. For example, nonionic modification, anionic modification, cationic modification, etc. can be mentioned. Specifically, it is preferable to subject colloidal silica to anionic or cationic modification, and more preferably anionic modification. As such a modification treatment, anionic or cationic modification is preferable, and although the reason why anionic modification is more preferable is not necessarily clear, it is presumed that the surface potential of colloidal silica is changed by modification, and the action of attracting with the object to be polished is expected, and the selectivity of the object to be polished is improved. In particular, compared with colloidal silica that has not been modified, the dispersion stability tends to be improved not only in alkaline conditions but also in acidic conditions where it is metastable and relatively prone to aggregation, so it is more preferable to perform anionic modification.

[0023] As described above, the modification treatment can be appropriately selected from known methods, but as a preferred embodiment of the modification treatment, an anion modification treatment and a cation modification treatment are typically described below. For an anion modification treatment, for example, JP-A-2010-269985 and JP-A-2013-041992 can be referenced. For a cation modification treatment, for example, JP-A-2005-162533 and JP-A-2020-73445 can be referenced.

[0024] The specific method of anion modification is not limited, but for example, a method of chemically bonding a modifier having an anion group to the surface of colloidal silica can be mentioned.In addition, as another method, a method of chemically bonding a modifier having a functional group that can be converted to an anion group by a chemical method or the like to the surface of colloidal silica, and then performing a process of converting the functional group to an anion group to form an anion group on the surface of colloidal silica can be mentioned.Because of the efficiency of modification, the fact that an anion group can be stably introduced into colloidal silica, and the fact that it is difficult to directly obtain a modifier having an anion group, a method of using a modifier having a functional group that can be converted to an anion group is preferred.

[0025] The compound (modifier) ​​having a functional group that can be converted into an anion group is not limited, but for example, a silane coupling agent having a functional group that can be converted into an anion group can be suitably mentioned. Here, the anion group is not limited, but for example, a sulfo group, a carboxy group, a phosphate group, etc. can be mentioned. It may be ionic bonded with a cation to form a salt. Even with such an anion group, the cation is released in an aqueous solution and functions as an anion group. Examples of the cation that ionic bonds with the anion group 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 the selectivity of the polishing object, among the anion groups, a sulfo group and a carboxy group are preferable, and a sulfo group is more preferable.

[0026] A sulfo group will be taken as an example of a preferred embodiment of the anion group. Modifiers having a functional group that can be converted to a sulfo group include silane coupling agents having a sulfonic acid 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, the modifier may be one type only, or two or more types may be used in combination.

[0027] 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.

[0028] A more specific method of the anion modification treatment will be described in detail in the explanation of the manufacturing method described later, but the amount of the above-mentioned modifier used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 0.8 to 6 parts by mass, relative to 100 parts by mass of the solid content of the raw colloidal silica. That is, the modifier is preferably 0.1 to 10% by mass, more preferably 0.5 to 7% by mass, and even more preferably 0.8 to 6% by mass in the solid content of the colloidal silica after modification. If the amount used is within this range, the particle surface of the colloidal silica can be sufficiently anionized. In addition, if the amount used is such, it is possible to produce a colloidal silica that has been stably anion-modified without aggregation. In addition, a solvent (water, a hydrophilic organic solvent, etc.) for dissolving the modifier may be used during the modification treatment.

[0029] In addition, as for the cationic modification, for example, a method of chemically bonding a modifying agent having a cationic group to the surface of colloidal silica, a method of chemically bonding a modifying agent having a functional group that can be converted to a cationic group by a chemical method or the like to the surface of colloidal silica, and then performing a treatment to convert the functional group to a cationic group to form a cationic group on the surface of colloidal silica, etc. are exemplified. Preferably, a method of chemically bonding a silane coupling agent having a cationic group to the surface of colloidal silica is exemplified.

[0030] The cationic group is not limited, but may be, for example, a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, or an iminium group. A primary amino group, a secondary amino group, a tertiary amino group, or a quaternary ammonium group is preferable. A primary amino group is more preferable. The cationic group may be ionically bonded with an anion to form a salt. Even in the case of such a cationic group, the anion is released in the mixed liquid and the cationic group functions as a cationic group. Examples of an anion ionically bonded with the cationic group include fluoride ions, chloride ions, bromide ions, iodide ions, hydrochloride ions, acetate ions, sulfate ions, hydrofluoric acid ions, and carbonate ions.

[0031] Examples of silane coupling agents having a cationic group include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane.

[0032] A more specific method of the cation modification treatment will be described in detail in the explanation of the manufacturing method described later, but as described above, it is preferable to use a method using a modifying agent having a cationic group. The amount of the modifying agent having a cationic group is preferably 0.1 to 1.5 parts by mass, more preferably 0.5 to 1.2 parts by mass, and even more preferably 0.6 to 1 part by mass, relative to 100 parts by mass of the solid content of the raw colloidal silica. That is, the amount of the modifying agent having a cationic group in the solid content of the colloidal silica after the cation modification is preferably 0.1 to 1.5% by mass, more preferably 0.5 to 1.2% by mass, and even more preferably 0.6 to 1% by mass. If the amount is within this range, the particle surface of the colloidal silica can be sufficiently cationized. Furthermore, if the amount is such, it is possible to produce a cation-modified colloidal silica stably without aggregation. In addition, a solvent (water, a hydrophilic organic solvent, etc.) for dissolving the modifying agent may be used during the modification treatment.

[0033] The modified colloidal silica of the present invention obtained by the above-mentioned modification treatment (hereinafter, sometimes referred to as "modified colloidal silica") has excellent dispersion stability and does not substantially aggregate even when the solid content concentration is relatively low, and is suitable for various applications. The solid content concentration is usually about 6% by mass due to the manufacturing process, etc., but is preferably 12% by mass or more, more preferably 15% by mass or more, even more preferably 18% by mass or more, and particularly preferably 19% by mass or more, because it can improve polishing performance and reduce transportation costs. The solid content concentration can be appropriately set depending on the application, etc. On the other hand, the upper limit of the solid content concentration is not limited, but is preferably 50% by mass or less, because there is a tendency for the handleability to decrease due to an increase in viscosity, etc., and for the dispersion stability to decrease.

[0034] It is known that, in general, as the solid content increases, the distance between particles decreases, and therefore, colloidal silica becomes more susceptible to aggregation. However, the modified colloidal silica of the present invention has a relatively small particle size as described above, and does not substantially aggregate even at a relatively high solids concentration as described above, and a practical colloidal silica of this kind has not yet been clearly identified.

[0035] As described above, the colloidal silica of the present invention is substantially not aggregated. Here, the wording "substantially" is used for the following reason. That is, in general, methods for confirming whether colloidal silica is aggregated include a method of confirming with an electron microscope, measuring the increase in viscosity, and measuring the cumulant mean diameter by dynamic light scattering (DLS), but it is difficult to completely grasp whether each and every particle of the colloidal silica of the present invention, which is a very small particle having a BET diameter of 12 nm or less, is monodispersed. Since it is considered that the above-mentioned methods can only grasp or understand the dispersion state of the particles with a certain degree of certainty, as long as there is substantially no aggregation to the extent that there is no practical problem, the colloidal silica will not exhibit its functions or cause problems in use.

[0036] In order to grasp the above-mentioned "substantially not aggregated" more specifically, the above-mentioned method can be used for measurement, but since the particles are small, some parts may be difficult to grasp with an electron microscope. Therefore, it is preferable to use dynamic light scattering (DLS) and judge from the change in the cumulant mean diameter measured by the method. More specifically, it is preferable to confirm the change (or the absence of change) in the cumulant mean diameter by DLS measurement over time. For example, in the production method of the present invention, in the concentration step described below, the presence or absence of aggregation can be confirmed by confirming the DLS measurement results before and after concentration. That is, by grasping the presence or absence of aggregation with an increase in solid content concentration, it becomes possible to confirm whether the colloidal silica has a property that aggregation is likely to occur. This is because, as described above, when the solid content concentration is relatively low, aggregation does not occur much, and as the solid content concentration increases, aggregation becomes more likely. Such a tendency usually tends to be prominent when the solid content concentration is 10% by mass or more, more specifically, 12% by mass or more.

[0037] Among the methods using DLS measurement, a more practical method for grasping aggregation is to measure the change in particle diameter by DLS measurement after holding for a certain time (period) under heated conditions. With this method, it is possible to confirm whether the colloidal silica has a property that aggregation is likely to occur without causing an active change in solid content concentration. Specifically, as also performed in the examples described later, the change in the cumulant mean diameter after holding for 7 days at at least 60°C as a temperature at which particles are likely to aggregate is confirmed, and it can be determined that there is no aggregation if the change rate is within 20%. Here, the reason why the method of holding at 60°C or higher for 7 days is preferably applied is that it is known that the condition at 60°C for 7 days is approximately equivalent to a time-dependent change test in a state held at room temperature for 1 year, and thus the occurrence or absence of aggregation can be confirmed in a time-dependent change test at least at room temperature for 1 year. And, preferably, the change rate of the cumulant mean diameter by DLS measurement is within 10%, more preferably within 5%. Here, for the reasons described above, in such DLS measurement, it is preferable to maintain or measure the solid content concentration at 12 mass% or more, more specifically 18 mass% or more, even more specifically 19 mass% or more, and preferably 50 mass% or less, more preferably 40 mass% or less, and even more preferably 30 mass% or less. The solid content concentration at this time is not limited, and it is preferable to carry out the DLS measurement at a solid content concentration suited to the application or practical use.

[0038] In addition, the colloidal silica of the present invention may have any shape and other properties depending on the application and purpose, so long as it has the above-mentioned properties of BET diameter, modification, and substantial absence of aggregation. In particular, the colloidal silica obtained by the present invention preferably has the above-mentioned BET specific surface area, a relatively high particle surface area, and a large number of irregular small protrusions, so to speak, a confetti-like shape as a whole particle. Such a shape has a large BET specific surface area compared to a large SEM average particle diameter measured by measuring the arithmetic mean of particle images observed by SEM, and also has a high particle density (true specific gravity) measured by a liquid phase displacement method, in other words, a high hardness, and is suitable for a CMP abrasive with an excellent polishing rate.

[0039] The shape of the colloidal silica particles of the present invention can be controlled by the charged composition, etc., to be monodisperse spherical (spherical product), or to be an associated shape of particles that are bonded together (associated product). For example, by adding a large amount of catalyst and relatively slowly introducing organosilicate as a silica raw material into the reaction field, the organosilicate is hydrolyzed quickly and uniformly and grows mildly, so that the seed particles grow gradually while maintaining their spherical shape, and a spherical product can be obtained. In addition, by adding a small amount of catalyst and relatively quickly introducing organosilicate as a silica raw material into the reaction field, the organosilicate is hydrolyzed non-uniformly, so that it acts like an adhesive between particles, and as a result, an associated product in which the particles are associated can be obtained.

[0040] The colloidal silica of the present invention preferably has a viscosity of 1 to 100 mPa·s, more preferably 1 to 50 mPa·s, and even more preferably 1 to 20 mPa·s.

[0041] As described above, the colloidal silica of the present invention may be a monodisperse spherical product, or may be an associated product (cocoon-shaped, chain-like, branched, etc.) having a shape that appears to be formed by a plurality of particles coalescing two-dimensionally or three-dimensionally when observed under an electron microscope.

[0042] The colloidal silica of the present invention may be adjusted to a pH level that does not impair the dispersion stability, depending on the above-mentioned modification treatment. For example, in the case of the anion-modified colloidal silica, the pH is preferably 1 to 5, more preferably 2 to 3. For example, in the case of the cation-modified colloidal silica, the pH is preferably 8 to 11, more preferably 8.5 to 10. Adjusting the pH to such a range is favorable in terms of the dispersion stability of the colloidal silica.

[0043] Furthermore, the colloidal silica of the present invention 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 metal impurity content as raw materials for hydrolysis reaction in obtaining the raw colloidal silica.

[0044] <Method of manufacturing colloidal silica> The method for producing colloidal silica of the present invention essentially includes the following steps. (a) A raw material preparation step of supplying a readily decomposable organosilicate to a reaction liquid containing a hydrolysis catalyst made of an organic amine and reacting the organosilicate to prepare raw material colloidal silica having a BET diameter of 12 nm or less. (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 of modifying the raw material colloidal silica whose concentration has been adjusted in the step (b). (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 mass % or less. These steps are described below.

[0045] [Process (a)] First, in step (a), a colloidal silica having a BET diameter of 12 nm or less is prepared by supplying and reacting a readily decomposable organosilicate to a reaction solution containing a hydrolysis catalyst made of an organic amine. In the present invention, the colloidal silica prepared in step (a) is called raw colloidal silica. Although a commercially available product can be used as the raw colloidal silica, a hydrolysis method is used because it reduces metal impurities, can obtain colloidal silica with a relatively large surface area, and can produce highly uniform particles. As the hydrolysis method, a method is used in which a silica source is supplied to a reaction solution containing a hydrolysis catalyst and hydrolyzed, and a method is used in which a readily decomposable organosilicate is supplied as a silica source to a reaction solution containing a hydrolysis catalyst made of an organic amine and hydrolyzed, because it is easy to control the particle diameter.

[0046] Here, the silica source preferably used in step (a) is an easily hydrolyzable organosilicate with a fast hydrolysis rate. The easily hydrolyzable organosilicate is preferably one which is hydrolyzed within 1 hour by stirring 10 g of organosilicate and 100 g of pure water with impurities of 0.1 ppb or less at 25°C. Specific examples of such easily hydrolyzable organosilicate include trimethyl silicate (hydrolysis reaction time until hydrolysis reaction is completed: about 3 minutes), tetramethyl silicate (hydrolysis reaction time: about 5 minutes), triethyl silicate (hydrolysis reaction time: about 5 minutes), and methyl trimethyl silicate (hydrolysis reaction time: about 7 minutes). Tetraethyl silicate and organosilicates with a larger carbon number than tetraethyl silicate have a slow hydrolysis rate and tend to gel easily (hydrolysis reaction time: 24 hours or more for both), so the above-mentioned easily decomposable organosilicate is preferably used.

[0047] In addition, the organic amines used as hydrolysis catalysts 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, and primary amines, as well as their carbonates, bicarbonates, and silicates. For example, the quaternary ammoniums include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), trimethylethylammonium hydroxide, trimethylethanolammonium hydroxide (choline), triethylethanolammonium hydroxide, tetrapropylammonium hydroxide, butylammonium hydroxide, and other quaternary ammoniums, as well as their carbonates, bicarbonates, and silicates. Since a relatively high pH is desirable for the hydrolysis reaction, tetramethylammonium hydroxide (TMAH), choline, or tetraethylammonium hydroxide (TEAH) is preferred.

[0048] In addition, the primary amines, secondary amines, and tertiary amines of the organic amines used as the hydrolysis catalyst are not limited, and examples thereof include aminoalcohols, morpholines, piperazines, aliphatic amines, aliphatic ether amines, etc. Here, as for the aminoalcohols, various aminoalcohols including ethanolamine derivatives can be used, and preferably ethanolamine derivatives, 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, etc. can be mentioned.

[0049] Furthermore, various morpholine derivatives can be used for the morpholines of the organic amines used as the hydrolysis catalyst, and preferably, morpholine, N-methylmorpholine, N-ethylmorpholine, etc. can be mentioned. Furthermore, various piperazine derivatives can be used for the piperazines of the organic amines used as the hydrolysis catalyst, and preferably, piperazine, hydroxyethylpiperazine, etc. can be mentioned. Furthermore, as for the aliphatic amines and aliphatic etheramines of the organic amines used as the hydrolysis catalyst, the aliphatic amines can be preferably alkylamines having 1 to 8 carbon atoms, such as triethylamine, dipropylamine, pentylamine, hexylamine, heptylamine, and octylamine. Furthermore, the aliphatic etheramines can be preferably aliphatic etheramines having 1 to 8 carbon atoms, such as 2-methoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, and 3-butoxypropylamine.

[0050] The organic amines used as the hydrolysis catalyst may be used alone or, if necessary, in the form of a mixture of two or more kinds.

[0051] The reaction liquid essentially contains an easily decomposable organosilicate as a silica source and a hydrolysis catalyst as described above, but other than that, water, alcohols, aldehydes, ketones, surfactants, etc. can be used. It is preferable that the total content of the silica source, hydrolysis catalyst, and water is 90% by mass or more. More preferably, the total content of these is 95% by mass or more.

[0052] In the mixture after the reaction of the silica source with the hydrolysis catalyst (hereinafter, this may be referred to as the "reaction mixture"), or in the reaction mixture after the reaction, for example, by adjusting the solid content concentration or the alcohol concentration or by treating the dispersion stabilization with an acid as described later (hereinafter, this may be particularly referred to as the "reaction concentrate"), it is preferable to add the hydrolysis catalyst to the reaction system so that the ratio of the hydrolysis catalyst (A) to the silica (B) {catalyst remaining molar ratio (A / B)} is 0.012 or less, more preferably in the range of 0.00035 to 0.012, and even more preferably in the range of 0.0035 to 0.011, to carry out the hydrolysis reaction. This is preferable because the pH of the reaction mixture or reaction concentrate can be optimized and thickening and gelation can be suppressed.

[0053] 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).

[0054] 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 the hydrolysis catalyst may be gradually added to the reaction system so that the catalyst remaining molar ratio (A / B) falls within the above-mentioned range. This is preferable because it enables the production of colloidal silica having uniform particles.

[0055] 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 a high purity of 0.01 ppm or less, so that the raw colloidal silica obtained and the modified colloidal silica after modification also satisfy the above-mentioned range of metal impurity content.

[0056] In the step (a), the method for making the BET diameter of the raw material colloidal silica 12 nm or less 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.

[0057] When a readily decomposable organosilicate is used as the silica source, the supply rate is preferably less than 1.5 mass% / min of the total amount of readily decomposable organosilicate added, more preferably 1.3 mass% or less / min, and even more preferably 1.2 mass% or less / min. If the supply rate is 1.5 mass% or more / min, the particles tend not to be uniformly dispersed or to be close to a perfect sphere. Here, the reason why the total amount is used as the standard is that the amount added varies depending on the production scale, etc., and it is preferable to consider completing the supply within the reaction time described below. That is, it is preferable to make the supply rate as slow as possible, which makes it easier to form the desired small particle size. There is no lower limit to the supply rate, but if the supply rate is too slow, there is a risk that the target particle size will not be achieved, so it is preferably 1.0 mass% / min or more of the total amount added.

[0058] The reaction temperature is preferably 70° C. or less, more preferably 65° C. or less, and even more preferably 60° C. or less. If the reaction temperature exceeds 70° C., the reaction solution will volatilize more and the liquid composition will be 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 preferably set to 20° C. or more.

[0059] The reaction time is preferably within 6 hours, more preferably within 3 hours, and even more preferably within 2 hours. 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 or particle growth may not be sufficiently performed, so the reaction time is preferably 20 minutes or more.

[0060] In step (a), the solid content during the reaction is preferably 3 to 13% by mass. If the solid content is less than 3% by mass, particle formation and growth may not be sufficient. On the other hand, if the solid content is too high, particles tend to aggregate. In step (a), the solid content of the colloidal silica after the reaction is preferably within the range of 3 to 10% by mass.

[0061] [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 if the BET diameter is 12 nm or less, the occurrence of aggregation can be reduced, and the next step (c) (modification treatment step) can be performed without causing aggregation gelation. Preferably, the solid content is 10% by mass or less, more preferably 8% by mass or less. Here, although it is difficult to clearly define or classify the term "aggregation gelation," it generally refers to a state in which the aggregation of colloidal silica has progressed further and has become a jelly-like mass when viewed with the naked eye (for example, see FIG. 3 in Comparative Example 2 described later).

[0062] Here, if the solid content 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 solid content in step (b), and in that case, it may be treated as a step of confirming the solid content, or a step of maintaining the solid content as it is, etc. Ensuring that the solid content is certainly 13% by mass or less in this 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-aggregated and has a relatively high solid content.

[0063] The method of adjusting the solid content concentration in step (b) is not limited, but it is preferable to add 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.

[0064] In addition, in this step (b), the concentration of the alcohols generated from the step (a) is adjusted to 1 to 25 mass%. In the step (a), the alcohols are generated by the hydrolysis reaction according to the easily decomposable organosilicate used as the silica source. For example, when the easily decomposable organosilicate used has a methoxy group such as trimethyl silicate or tetramethyl silicate, methanol is generated as the alcohol. When the easily decomposable organosilicate used has an ethoxy group such as triethyl silicate, ethanol is generated as the alcohol. The same applies to other cases.

[0065] Here, the detailed mechanism of the need to adjust the concentration of the alcohols generated from the hydrolysis reaction in step (a) to 1 to 25% by mass is not clear, but it is presumed that by maintaining the concentration of the organic solvent in this range, the occurrence of aggregation can be reduced even if the BET diameter is 12 nm or less due to the polarity of the solvent, and the next step (c) (modification treatment step) can be performed without causing aggregation and gelation. The concentration of the generated alcohols can be appropriately adjusted by the amount of the easily decomposable organosilicate used in step (a) or by replacing the alcohols with pure water by distillation, but the preferred lower limit is 5% by mass or more, and the more preferred lower limit is 12% by mass or more. On the other hand, the preferred upper limit is 20% by mass or less.

[0066] In addition, similar to the case of the adjustment of the solid content concentration (13% by mass or less) in this step (b), if the alcohol concentration of the raw colloidal silica obtained in step (a) is already 1 to 25% by mass, it is not necessary to actively adjust the alcohol concentration. In that case, it may be treated as a step of confirming the alcohol concentration, or as a step of maintaining the alcohol concentration generated in step (a) as it is. In this step (b), before the modification treatment in the next step (c), ensuring that the alcohol concentration is 1 to 25% by mass is a characteristic step in obtaining the finally modified colloidal silica of the present invention that is substantially not aggregated and has a relatively high solid content concentration, similar to the case of the adjustment of the solid content concentration (13% by mass or less). In addition, this alcohol may be a part of the solvent in the modification treatment in the next step (c).

[0067] The method of adjusting the concentration of the alcohols in this step (b) is not limited, but when adjusting to increase the concentration of the alcohols, it is preferable to add an organic solvent containing the same organic solvent as the produced alcohols as the main component (for example, 95 mass% or more). The organic solvent added here may contain water, alcohols, aldehydes, ketones, surfactants, etc., as described above. On the other hand, as a method of adjusting to decrease the concentration of the alcohols, for example, a method of distilling the alcohols from a distillation tube equipped with a condenser while volatilizing them by heating, as performed in Comparative Example 1 described later, can be mentioned. In this case, pure water may be added.

[0068] [Process (c)] In step (c), the raw colloidal silica, the solid content concentration of which and the concentration of the generated alcohols have been adjusted through step (b), is modified. As described above, the modification is not limited and can be selected from known modification treatments, but anion modification or cation modification is preferred, and anion modification is more preferred. Here, anion modification or cation modification is as exemplified above, and anion modification is preferred, and a suitable method for anion modification is a method of chemically bonding a modifying agent having a functional group that can be converted to an anion group by a chemical method or the like to the surface of colloidal silica. Among anion modifications, the sulfo group exemplified as a preferred embodiment will be taken as an example. Also, among cation modifications, the primary amino group exemplified as a preferred embodiment will be taken as an example.

[0069] (Embodiment of anion modification treatment using sulfo group as an example) To form sulfo group on the surface of colloidal silica, it can be carried out by a known method as described above.Preferably, a method can be mentioned in which a modifying agent having a functional group that can be converted to a sulfo group by a chemical method or the like is chemically bonded to the surface of colloidal silica, and then the functional group is converted to a sulfo group, and a modifying agent having a functional group that can be converted to a sulfo group by oxidation is preferable.Among these, a preferred modifying agent is a silane coupling agent having a mercapto group and / or a sulfide group as described above, and a representative one will be described below.

[0070] In this method, it is preferable to include a step (step c1) of reacting the raw colloidal silica, the solid content concentration of which has been adjusted through the steps (a) and (b) in the presence of the silane coupling agent, and a step (step c2) of oxidizing the reaction product of the step c1 to convert the mercapto group and / or sulfide group to a sulfo group. The steps c1 and c2 can also be performed with reference to the above-mentioned JP-A-2010-269985 and JP-A-2013-041992. It should be noted that other steps may be appropriately included as long as they do not impair the object of the present invention. Examples of other steps include adjusting the viscosity of the reaction solution and adjusting the pH.

[0071] (Step c1) In step c1, the raw colloidal silica, the solid content of which has 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, so that the silane coupling agent is chemically bonded to the surface of the raw colloidal silica.

[0072] The reaction in step c1 can be carried out within a temperature range suitable for use of the denaturant, and is not limited thereto, for example, at 40° C. or higher and below the boiling point of the reaction liquid (solvent). In order to improve reactivity, the reaction is preferably carried out at a temperature of 50° C. or higher, more preferably 60° C. or higher, and preferably below the boiling point of the reaction liquid (solvent), at 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.

[0073] In the reaction of step c1, a solvent can be added to improve the solubility of the modifier or silane coupling agent within the scope that does not impair the object of the present invention.As such a solvent, a hydrophilic solvent can be included, for example, alcohols such as methanol, ethanol, isopropanol, etc., but not limited thereto.It is more preferable to use the same alcohols as those produced by the hydrolysis reaction to obtain raw material colloidal silica.

[0074] As described above, the amount of the above-mentioned modifying agent (silane coupling agent) used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 0.8 to 5 parts by mass, relative to 100 parts by mass of the solid content in the raw material colloidal silica.

[0075] The reaction in step c1 can also be understood, for example, by analyzing the functional groups introduced into the colloidal silica. For example, the functional groups can be qualitatively and / or quantitatively analyzed using pulsed NMR (TD-NMR).

[0076] (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.

[0077] The method of converting the mercapto group and / or sulfide group to a sulfo group by oxidation treatment is not limited, but may be the use of an oxidizing agent. Examples of the oxidizing agent include nitric acid, hydrogen peroxide, oxygen, ozone, organic peracid (percarboxylic acid), bromine, hypochlorite, potassium permanganate, and chromic acid. Among these, hydrogen peroxide and organic peracid (peracetic acid, perbenzoic acid) are preferred in terms of handling and reactivity (oxidation yield). It is most preferred to use hydrogen peroxide because it produces few by-products in the reaction. The amount of the oxidizing agent added may be in excess of the amount of the modifying agent (silane coupling agent), but it is preferred to minimize the amount of the remaining oxidizing agent, and it is more preferred to use 3 to 5 moles of the oxidizing agent per mole of the silane coupling agent in order to ensure sufficient oxidation reaction. The oxidation reaction is not limited, but may be carried out under suitable reaction conditions for the oxidizing agent used within a range that does not impair the object of the present invention. For example, the reaction is preferably carried out at a temperature not lower than room temperature and not higher than the boiling point of the solvent used in the reaction solution (for example, not higher than 100° C.) for a period of 3 to 5 hours.

[0078] By this step c2, colloidal silica having an anion group (sulfo group) on the surface can be obtained. In addition, in step c2, other steps may be included after the oxidation treatment. For example, a step for removing the oxidizing agent, a step for adjusting the pH of the solution after the reaction, etc. may be included, and these steps may be appropriately selected and performed within a range that does not impair the object of the present invention.

[0079] (Embodiment of cationic modification treatment using amino groups as an example) To form amino groups on the surface of colloidal silica, known methods can be used as described above. A preferred method is to carry out a treatment in which a modifying agent having an amino group is chemically bonded to the surface of colloidal silica. As described above, a preferred modifying agent among these is a silane coupling agent having an amino group, which will be described below as a representative example.

[0080] In this method, it is preferable to include a step of reacting the raw colloidal silica, the solid content concentration of which has been adjusted through step (a) and step (b) as described above, in the presence of the silane coupling agent. Such a step can also be performed with reference to the above-mentioned JP-A-2005-162533 and JP-A-2020-73445. In addition, other steps may be appropriately included as long as they do not impair the object of the present invention. Examples of other steps include adjusting the viscosity of the reaction solution and adjusting the pH, but for dispersion stability, it is preferable to adjust the pH before performing the cation modification treatment. The pH adjusted at this time is preferably 8 to 11, more preferably 8.5 to 10. The pH can be adjusted by a method using a known compound (pH adjuster), but for example, a preferred method is to use the same compound as the hydrolysis catalyst used in step (a) as the pH adjuster.

[0081] That is, the raw colloidal silica, the solid content of which has been adjusted through steps (a) and (b), is reacted in the presence of a silane coupling agent having an amino group, whereby the silane coupling agent is chemically bonded to the surface of the raw colloidal silica.

[0082] This reaction can be carried out within a temperature range suitable for use of the modifying agent, and is not limited, but can be carried out, for example, at a temperature range of 40° C. or higher and below the boiling point of the reaction liquid (solvent). In order to improve reactivity, the reaction is preferably carried out at a temperature of 50° C. or higher, more preferably 60° C. or higher, and preferably below the boiling point of the reaction liquid (solvent), 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.

[0083] In this reaction, a solvent can be added to improve the solubility of the modifier or silane coupling agent within the scope that does not impair the purpose of the present invention. Such a solvent can include hydrophilic solvents, for example, alcohols such as methanol, ethanol, isopropanol, etc., but are not limited thereto. It is more preferable to use the same alcohols as those produced by the hydrolysis reaction to obtain the raw colloidal silica.

[0084] As described above, the amount of the above-mentioned modifying agent (silane coupling agent) used is preferably 0.1 to 1.5 parts by mass, more preferably 0.5 to 1.2 parts by mass, and even more preferably 0.6 to 1 part by mass, relative to 100 parts by mass of the solid content in the raw material colloidal silica.

[0085] This reaction can also be understood, for example, by analyzing the functional groups introduced into the colloidal silica. For example, pulsed NMR (TD-NMR) can be used to perform qualitative and / or quantitative analysis of the functional groups.

[0086] Further, for the sake of dispersion stability, it is preferable to adjust the pH even after the cationic modification treatment is performed. The pH adjusted in this case is preferably 8 to 11, more preferably 8.5 to 10. As described above, the pH can be adjusted by a method using a known compound (pH adjuster), but a preferred method is, for example, to use the same compound as the hydrolysis catalyst used in step (a) as the pH adjuster.

[0087] [Step (d)] After carrying out the step (c), in step (d), the residual organic solvent in the colloidal silica obtained after step (c) is concentrated to 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 solid content concentration can be adjusted or increased to a predetermined range, and in the case of a highly volatile residual organic solvent, it is preferable to prevent the concentration of colloidal silica from fluctuating due to the evaporation of the organic solvent. In addition, when using the colloidal silica of the present invention, there is an advantage that it is not necessary to consider the resistance of the residual organic solvent in the material used at the destination of the application.

[0088] The method for removing and concentrating the residual organic solvent is not particularly limited, and any known method can be used, for example, a method in which the residual organic solvent is distilled by heating using an apparatus equipped with a distillation tube with a condenser can be used.

[0089] In this step (d), the solid content concentration can be adjusted to a level suitable for use, taking into consideration the intended use and purpose, etc., by concentrating the process of removing the residual organic solvent and water. In the present invention, the modified colloidal silica is obtained through the above-mentioned steps (a) to (c), and even if the solid content concentration is relatively high in this step (d), a colloidal silica that does not substantially aggregate can be obtained. In consideration of such features of the present invention and the intended use and purpose of the colloidal silica, as described above, the solid content concentration in the colloidal silica after the modification step (c) is preferably 12 mass% or more, more preferably 15 mass% or more, even more preferably 18 mass% or more, and particularly preferably 19 mass% or more. The upper limit of the solid content concentration is the same as described above, and is preferably 50 mass% or less, more preferably 40 mass% or less, and even more preferably 30 mass% or less.

[0090] The colloidal silica of the present invention can be produced by carrying out the above steps (a) to (d), but 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 perform dispersion stabilization on the colloidal silica after step (d). The dispersion stabilization treatment may be a known treatment.

[0091] Colloidal silica that has been subjected to dispersion stabilization treatment by the method of the present invention exhibits excellent dispersion stability for usually more than one week, and even for several years, and is free from the phenomenon of two-layer separation.

[0092] In the present invention, colloidal silica having a small particle size, such as a BET diameter of 12 nm or less, can be obtained 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. EXAMPLES

[0093] Hereinafter, preferred embodiments of the present invention will be described in detail based on examples and comparative examples.

[0094] [Example 1] Into a 5 liter (L) glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3200 g of pure water with a metal impurity content of 0.1 ppb or less and 3.42 g of triethanolamine (boiling point (bp): 361°C) with a metal impurity content of 10 ppb or less were charged, and while maintaining the liquid temperature inside the reaction vessel at 60°C using a mantle heater, 706 g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over a period of 90 minutes. Various analyses were carried out on the obtained raw colloidal silica, and the results are shown in Table 1. <1> As shown in.

[0095] Next, 3900 g of the obtained reaction product (colloidal silica, solid content concentration 6.45 mass%, methanol concentration 15 mass%) was added to a 5 L glass container, and no operation was performed to change the solid content concentration or methanol concentration. Next, while maintaining the temperature at 80°C, 13.1 g of 3-mercaptopropyltrimethoxysilane dissolved in 117.9 g of methanol was continuously fed over 6 hours. After the feeding, 22.7 g of 30 mass% hydrogen peroxide solution was further continuously fed over 4 hours while maintaining the temperature at 80°C, and the raw colloidal silica was modified.

[0096] After the hydrogen peroxide solution was fed, the temperature in the reaction vessel was temporarily lowered to 40°C, the pressure in the system was reduced using a vacuum pump, and then heating was resumed, the reaction mixture in the reaction vessel was further heated to 52-68°C, and the generated methanol was distilled from a distillation tube equipped with a condenser at a distillation temperature of 32-67°C, and 250 g of pure water was added while distilling off the water and methanol, yielding colloidal silica with a solid concentration of approximately 20% by mass. The residual organic solvent in 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 results are shown in Table 1. The colloidal silica obtained was then stored at 60°C for 7 days and various analyses were carried out on the colloidal silica obtained. In particular, the DLS measurement results confirmed that no aggregation had occurred. <3> As shown in.

[0097] [Example 2] In a 5L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 3374g of pure water with a metal impurity content of 0.1 ppb or less and 3.608g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were charged, and while maintaining the liquid temperature in the reaction vessel at 70°C using a mantle heater, 1122g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over a period of 270 minutes. Various analyses of the obtained raw colloidal silica were carried out, and the results are shown in Table 1. <4> As shown in.

[0098] Next, 2000 g of the resulting reaction product (colloidal silica, solid content concentration 10.38 mass%, methanol concentration 20 mass%) was added to a 2 L glass container, and no operation was performed to change the solid content concentration or methanol concentration. Next, while maintaining the temperature at 80°C, 6.71 g of 3-mercaptopropyltrimethoxysilane dissolved in 60.35 g of methanol was continuously fed over 6 hours. After feeding, 11.63 g of 30 mass% hydrogen peroxide solution was further continuously fed over 4 hours while maintaining the temperature at 80°C, and the raw colloidal silica was modified.

[0099] After the hydrogen peroxide solution was supplied, 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, and the generated methanol was distilled from the distillation tube equipped with a condenser at a distillation temperature of 32-67°C. Further, 320 g of pure water was added while distilling off the water and methanol, yielding colloidal silica with a solid concentration of approximately 20% by mass. Various analyses of the obtained colloidal silica were carried out, and the results are shown in Table 1. <5> The results are shown in Table 1. Furthermore, the colloidal silica obtained was stored at 60°C for 7 days, and various analyses were carried out on the obtained colloidal silica. In particular, the DLS measurement results confirmed that substantially no aggregation had occurred. <6> As shown in.

[0100] [Example 3] In a 5L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 3463g of pure water with a metal impurity content of 0.1 ppb or less and 0.336g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were charged, and while maintaining the liquid temperature in the reaction vessel at 70°C using a mantle heater, 911.6g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over a period of 90 minutes. Various analyses of the obtained raw colloidal silica were carried out, and the results are shown in Table 1. <7> As shown in.

[0101] Next, 4200 g of the resulting reaction product (colloidal silica, solid content concentration 8.82 mass%, methanol concentration 17 mass%) was added to a 5 L glass container, and no operation was performed to change the solid content concentration or methanol concentration. Next, while maintaining the temperature at 80°C, 11.98 g of 3-mercaptopropyltrimethoxysilane dissolved in 107.8 g of methanol was continuously fed over 6 hours. After feeding, 20.77 g of 30 mass% hydrogen peroxide solution was further continuously fed over 4 hours while maintaining the temperature at 80°C, and the raw colloidal silica was modified.

[0102] After the hydrogen peroxide solution was supplied, 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, and the generated methanol was distilled from the distillation tube equipped with a condenser at a distillation temperature of 32-67°C. 700 g of pure water was further added while distilling off the water and methanol, yielding colloidal silica with a solid concentration of approximately 20% by mass. Various analyses of the obtained colloidal silica were carried out, and the results are shown in Table 1. <8> The results are shown in Table 1. Furthermore, the colloidal silica obtained was stored at 60°C for 7 days, and various analyses were carried out on the obtained colloidal silica, and it was confirmed that no aggregation had occurred, particularly from the results of DLS measurements. <9> As shown in.

[0103] [Comparative Example 1] In a 5L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 3200g of pure water with a metal impurity content of 0.1ppb or less and 3.42g of triethanolamine (bp: 361°C) with a metal impurity content of 10ppb or less were charged, and while maintaining the liquid temperature inside the reaction vessel at 60°C using a mantle heater, 706g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10ppb or less was continuously fed with stirring over a period of 90 minutes. Various analyses of the obtained raw colloidal silica were carried out, and the results are shown in Table 1. <10> As shown in.

[0104] Next, 3900 g of the obtained reaction product (colloidal silica) was added to a 5 L glass container, and unlike the above Examples 1 to 3, this was heated to 52°C to 72°C at this point, and the generated methanol was distilled from a distillation tube equipped with a condenser at a distillation temperature of 32 to 67°C. Further, 1800 g of pure water was added while distilling off the water and methanol.

[0105] 3900 g of the reaction product (colloidal silica, solid content concentration 6.45 mass%, methanol concentration 0.1 mass%) from which water and methanol had been distilled off was added to a 5 L glass container, and no operation was performed to change the solid content concentration. Next, while maintaining the temperature at 100°C, 13.7 g of 3-mercaptopropyltrimethoxysilane dissolved in 123.6 g of methanol was continuously fed over 6 hours. After the feeding, 23.8 g of 30 mass% hydrogen peroxide solution was further continuously fed over 4 hours while maintaining the temperature at 100°C, and the raw colloidal silica was modified.

[0106] After the hydrogen peroxide solution was supplied, the temperature in the reaction vessel was temporarily lowered to 40°C, and the pressure in the system was reduced using a vacuum pump. After that, heating was resumed, and the reaction mixture in the reaction vessel was further heated to 52-68°C, yielding colloidal silica with a solid content of approximately 20% by mass. Various analyses of the obtained colloidal silica were carried out, and the results are shown in Table 1. <11> The results of the analysis, particularly the DLS measurement, showed that the change in the cumulant mean diameter by DLS measurement exceeded 20%, confirming the presence of aggregation. The colloidal silica obtained was then stored at 60°C for 7 days, and various analyses of the resulting colloidal silica were carried out. The results are shown in Table 1. <12> The results are shown in <11> This result is due to the fact that colloidal silica is aggregated at this point. <12> Even in this case, the DLS results are <11> The results are comparable to <10> was higher than

[0107] [Comparative Example 2] In a 5L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 3200g of pure water with a metal impurity content of 0.1ppb or less and 3.42g of triethanolamine (bp: 361°C) with a metal impurity content of 10ppb or less were charged, and while maintaining the liquid temperature inside the reaction vessel at 60°C using a mantle heater, 706g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10ppb or less was continuously fed with stirring over a period of 90 minutes. Various analyses of the obtained colloidal silica were carried out, and the results are shown in Table 1. <13> As shown in.

[0108] Next, 4500 g of the obtained reaction product (colloidal silica, solid content concentration 6.01 mass%, methanol concentration 15 mass%) was added to a 3 L glass container, and no operation was performed to change the solid content concentration or methanol concentration. Then, without performing a modification treatment step, it was heated at 52°C to 72°C, and the generated methanol was distilled from a distillation tube with a condenser at a distillation temperature of 32 to 67°C. Further, while adding pure water, water and methanol were distilled off, and when the solid content concentration reached 16 mass%, coagulation and gelation occurred. The state of coagulation and gelation is shown in Figure 3.

[0109] [Comparative Example 3] In a 5L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3463g of pure water with a metal impurity content of 0.1 ppb or less and 0.336g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were charged, and while maintaining the liquid temperature in the reaction vessel at 80°C using a mantle heater, 1136g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over a period of 480 minutes. Various analyses of the obtained colloidal silica were carried out, and the results are shown in Table 1. <14> In this Comparative Example 3, the BET diameter exceeded 12 nm due to the temperature at the time of adding the silica source.

[0110] [Table 1]

[0111] [Table 2]

[0112] [Example 4] In a 5 L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 3889 g of pure water with a metal impurity content of 0.1 ppb or less and 3.42 g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were charged, and while maintaining the liquid temperature in the reaction vessel at 60°C using a mantle heater, 707 g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over a period of 90 minutes. Various analyses were carried out on the obtained raw colloidal silica, and the results are shown in Table 3. <15> As shown in.

[0113] Next, 3800 g of the obtained reaction product (colloidal silica, solid content concentration 6.39 mass%, methanol concentration 13 mass%) and 20 g of triethanolamine (bp: 361 ° C) with a metal impurity content of 10 ppb or less were added to a 5 L glass container, and no operation was performed to change the solid content concentration and methanol concentration. The pH of the colloidal silica at this time was 8.9. Next, while maintaining the temperature at 80 ° C, a modifying agent obtained by dissolving 1.71 g of 3-aminopropyltrimethoxysilane in 50 g of methanol was continuously supplied over 6 hours to modify the raw colloidal silica.

[0114] After the modifier was supplied, the temperature in the reaction vessel was temporarily lowered to 40°C, 20 g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less was added, the pressure in the system was reduced using a vacuum pump, and then heating was resumed. The reaction mixture in the reaction vessel was further heated to 52 to 68°C, and the generated methanol was distilled from the distillation tube equipped with a condenser at a distillation temperature of 32 to 67°C. Further, 670 g of pure water was added while distilling off the water and methanol, thereby obtaining colloidal silica with a solid concentration of approximately 20 mass%. The obtained colloidal silica was subjected to various analyses, and the results are shown in Table 3. <16> The results are shown in Table 3. The colloidal silica obtained was then stored at 60°C for 7 days and various analyses were carried out on the colloidal silica obtained. It was confirmed, particularly from the results of DLS measurements, that substantially no aggregation had occurred. <17> As shown in.

[0115] [Example 5] In a 5 L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 3890 g of pure water with a metal impurity content of 0.1 ppb or less and 3.42 g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were charged, and while maintaining the liquid temperature in the reaction vessel at 60°C using a mantle heater, 707 g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over a period of 90 minutes. Various analyses were carried out on the obtained raw colloidal silica, and the results are shown in Table 3. <18> As shown in.

[0116] Next, 4001 g of the resulting reaction product (colloidal silica, solid content concentration 6.41 mass%, methanol concentration 13 mass%) and 20 g of triethanolamine (bp: 361 ° C) with a metal impurity content of 10 ppb or less were added to a 5 L glass container, and no operation was performed to change the solid content concentration and methanol concentration. The pH of the colloidal silica at this time was 9.0. Next, while maintaining the temperature at 80 ° C, a modifying agent obtained by dissolving 1.83 g of 3-aminopropyltrimethoxysilane in 54 g of methanol was continuously supplied over 6 hours to modify the raw colloidal silica.

[0117] After the modifier was fed, the temperature in the reaction vessel was lowered to 40°C for 1975 g of the reaction mixture, 10 g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less was added, the pressure in the system was reduced using a vacuum pump, heating was then resumed, and the reaction mixture in the reaction vessel was further heated to 52 to 68°C, and the generated methanol was distilled from the distillation tube equipped with a condenser at a distillation temperature of 32 to 67°C, and 340 g of pure water was added while distilling off the water and methanol, thereby obtaining colloidal silica with a solid concentration of approximately 20 mass%. The obtained colloidal silica was subjected to various analyses, and the results are shown in Table 3. <19> The results are shown in Table 3. The colloidal silica obtained was then stored at 60°C for 7 days and various analyses were carried out on the colloidal silica obtained. It was confirmed, particularly from the results of DLS measurements, that substantially no aggregation had occurred. <20> As shown in.

[0118] [Example 6] In a 5 L glass vessel equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 3890 g of pure water with a metal impurity content of 0.1 ppb or less and 3.43 g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were charged, and while maintaining the liquid temperature in the reaction vessel at 60°C using a mantle heater, 707 g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was continuously fed with stirring over a period of 90 minutes. Various analyses were carried out on the obtained raw colloidal silica, and the results are shown in Table 3. <21> As shown in.

[0119] Next, 2350 g of the obtained reaction product (colloidal silica, solid content concentration 6.47 mass%, methanol concentration 13 mass%) and 12 g of triethanolamine (bp: 361 ° C) with a metal impurity content of 10 ppb or less were added to a 5 L glass container, and no operation was performed to change the solid content concentration and methanol concentration. The pH of the colloidal silica at this time was 8.9. Next, while maintaining the temperature at 80 ° C, a modifying agent obtained by dissolving 1.08 g of 3-aminopropyltrimethoxysilane in 30 g of methanol was continuously supplied over 6 hours to modify the raw colloidal silica.

[0120] After the modifier was supplied, the temperature in the reaction vessel was temporarily lowered to 40°C, 12 g of triethanolamine (bp: 361°C) having a metal impurity content of 10 ppb or less was added, the pressure in the system was reduced using a vacuum pump, and then heating was resumed. The reaction mixture in the reaction vessel was further heated to 52 to 68°C, and the generated methanol was distilled from the distillation tube equipped with a condenser at a distillation temperature of 32 to 67°C. Furthermore, 351 g of pure water was added while distilling off the water and methanol, thereby obtaining colloidal silica with a solid concentration of approximately 20 mass%. The obtained colloidal silica was subjected to various analyses, and the results are shown in Table 3. <22> The results are shown in Table 3. The colloidal silica obtained was then stored at 60°C for 7 days and various analyses were carried out on the colloidal silica obtained. It was confirmed, particularly from the results of DLS measurements, that substantially no aggregation had occurred. <23> As shown in.

[0121] [Table 3]

[0122] The physical properties of the resulting colloidal silica were evaluated by the following methods. (1) BET specific surface area, BET diameter: Measured using a NOVA4200e (manufactured by Anton Paar). The BET specific surface area S (m 2 / g) and the true density of SiO2 is 2.2g / cm 3 ) and the particle diameter calculated from the above formula (1) using the formula 2727 / S is regarded as the BET diameter. (2) Cumulant mean diameter by dynamic scattering method: 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 liquid was measured. (3) Silica solids concentration: The device used was an SMS-70 (manufactured by A&D Co., Ltd.), and the residue after evaporating the water content 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). [Industrial Applicability]

[0123] 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 colloidal silica having a surface that has been modified, a BET diameter of 12 nm or less, and being substantially free of aggregation.

2. BET specific surface area is 227m ２ 2. The colloidal silica according to claim 1, wherein the molecular weight of the colloidal silica is 1 / g or more.

3. 2. The colloidal silica according to claim 1, wherein the modification is anion-modified or cation-modified.

4. 4. The colloidal silica according to claim 3, wherein the anion-modified silica is a sulfo group.

5. 4. The colloidal silica according to claim 3, wherein the cation modification is by a primary amino group.

6. 2. The colloidal silica according to claim 1, having a solid content concentration of 12 mass % or more.

7. 2. The colloidal silica according to claim 1, wherein the colloidal silica has a solid content concentration of 12% by mass or more, and a rate of change in the cumulant average diameter measured by a dynamic light scattering method after being kept at a temperature of 60° C. for 7 days is within 20% compared to the rate before the keeping.

8. A method for producing the colloidal silica according to any one of claims 1 to 7, comprising the steps of: a raw material preparation step of supplying and reacting a readily decomposable organosilicate to a reaction solution containing a hydrolysis catalyst made of an organic amine to prepare raw material colloidal silica having a BET diameter of 12 nm or less; 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; a modification treatment step of modifying the raw colloidal silica having the adjusted concentration; a concentrating step of concentrating the modified colloidal silica so that a residual organic solvent in the modified colloidal silica is 1 mass % or less; A method for producing colloidal silica, comprising:

9. 9. The method for producing colloidal silica according to claim 8, wherein in the raw material preparing step, the reaction is carried out under conditions in which 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 70° C. or lower.

10. 9. The method for producing colloidal silica according to claim 8, wherein in the concentrating step, the colloidal silica after the modification treatment step is concentrated so that the solid content concentration in the colloidal silica after the modification treatment step is 12 mass % or more.

11. 9. The method for producing colloidal silica according to claim 8, 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 after the concentration adjustment step; and a step of converting the functional group in the modifier after the reaction into an anionic group.

12. 12. The method for producing colloidal silica according to claim 11, characterized in that the modifying agent has a mercapto group and / or a sulfide group, and the mercapto group and / or the sulfide group are converted to a sulfo group by treating with an oxidizing agent, thereby obtaining colloidal silica having sulfo groups on the surface thereof.

13. 9. The method for producing colloidal silica according to claim 8, wherein the modification treatment step comprises a step of reacting a modifying agent having a cationic group with the colloidal silica after the concentration adjustment step.

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