Colloidal silica and methods for producing colloidal silica

Abstract

To provide colloidal silica with reduced true density and a method for producing the same. [Solution] True density is 2.068 g / cm³ 3 This colloidal silica is characterized by being less than [amount]. Furthermore, in a method for producing colloidal silica, in which a readily hydrolyzable organosilicate is supplied to and reacted with a reaction solution containing a hydrolysis catalyst consisting of one or more organic amines selected from organic amines to obtain a reaction product, alcohols generated from the reaction are removed, and then the solution is concentrated to a residual organic solvent content of 1% by mass or less to produce colloidal silica, The method for producing colloidal silica is characterized by containing, as the easily hydrolyzable organosilicate, an alkyltrimethylsilicate having an alkyl group with 1 to 3 carbon atoms in an amount of 5% to 40% by mass.

Description

[Technical Field]

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

[0002] Several methods have been proposed and implemented for the industrial production of high-purity colloidal silica, including ion exchange of an aqueous sodium silicate solution, thermal decomposition of silicon tetrachloride, and hydrolysis of organosilicate in a water-alcohol mixed solvent in the presence of an acid or alkali catalyst. However, the hydrolysis of organosilicate is particularly suitable for producing high-purity colloidal silica with low metal impurity content because it allows the use of highly pure organosilicate, catalyst, and solvent in the reaction, resulting in very few impurities derived from these raw materials. Several methods for hydrolyzing organosilicate have been proposed to date.

[0003] Here, regarding colloidal silica used in various applications, particularly in the field of semiconductor wafer polishing, with the increasing integration of LSIs today, various types of metal wiring and oxide films exist on a single wafer, and each semiconductor wafer requires polishing performance suited to its specific needs. Therefore, colloidal silica with subtly different compositions and properties is required.

[0004] Furthermore, for applications where even slight alkali metal impurities are undesirable, such as binders for hard coatings and ceramics, chromic acid-based metal surface treatment agents, and ground improvement injection agents, acidic colloidal silica is required, and several methods for producing such acidic colloidal silica are known.

[0005] For example, the applicant of this 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 modification treatment, has an extremely low content of metal impurities, including alkali metals, and whose average particle size, as determined by particle size distribution analysis using an electron microscope, is in the range of 5 to 500 nm, with a standard deviation of 20 or less and a polydispersity index of 0.15 or less. 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-treatment such as acid treatment or ion exchange treatment by using an easily hydrolyzable organosilicate with a fast hydrolysis rate and using a specific hydrolysis catalyst as the hydrolysis catalyst, and by adding 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 below a predetermined value and carrying out the reaction (Patent Document 1).

[0006] Incidentally, in the field of polishing agents for semiconductor wafers and substrates, for example, there is a need to meet various demands in recent years, and polishing performance suitable for the workpiece is required. In other words, there is a demand for polishing agents containing colloidal silica that can control how pressure is applied to the workpiece by the physical properties of colloidal silica, and that have various physical properties such as particle size, particle shape, and viscoelastic properties of the particles, and improving the processing quality is a challenge. However, the reality is that sufficient studies have not been conducted on such colloidal silica and polishing agents containing it. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-153732 [Patent Document 2] Japanese Patent Publication No. 2024-044024 [Patent Document 3] Special Publication No. 2011-521866 [Patent Document 4] Special Publication No. 2024-092301 [Patent Document 5] Patent No. 7129548 [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, the inventors of this application conducted thorough research based on these facts regarding colloidal silica, and concluded that the general true density of amorphous SiO2 (quartz glass) is 2.2 g / cm³. 3 Given this situation, we arrived at the idea that colloidal silica with reduced true density exhibits excellent viscoelasticity and can contribute to improving processing quality. We then found a solution that primarily focused on the compounding composition of easily hydrolyzable organosilicates, and thus completed the present invention.

[0009] Therefore, the object of the present invention is to provide colloidal silica with reduced true density and a method for producing the same.

[0010] Regarding colloidal silica, there are reports of a technique to change the composition of easily hydrolyzable organosilicates to replace some of the tetramethyl silicate with methyltrimethyl silicate (for example, Patent Document 2). However, Patent Document 2 deals with silica particles having a high refractive index, and methyltrimethyl silicate only provides a relatively low range, not a true density. Furthermore, as discussed in the Examples section below, the method corresponding to Patent Document 2 was prone to aggregation and gelation even at practical solid content concentrations (for example, around 20% by mass). In addition, Patent Document 3 only reports that methyltrimethyl silicate is used for surface modification of silica sols. Furthermore, there are reports of colloidal silica having a relatively low range of true density and true specific gravity (for example, Patent Documents 4 and 5). Patent Document 4 aims to provide an abrasive composition that can be polished at a high polishing speed, and provides inorganic particles with organic acids immobilized on the surface, primarily aiming for a relatively high range of true density for the sake of high polishing speed. Furthermore, Patent Document 4 only specifically describes a method for immobilizing organic acids on colloidal silica, but does not describe a specific method for producing colloidal silica, nor does it describe colloidal silica itself having a relatively low true density. Moreover, Patent Document 5 describes colloidal silica containing silica particles with alkoxy groups, in which the increase in the average secondary particle diameter after storage is suppressed, and the main objective is a relatively high true specific gravity for abrasive purposes, and specifically describes a high value. In addition, Patent Document 5 does not describe a method for reducing the true specific gravity derived from the components of easily hydrolyzable organosilicates. [Means for solving the problem]

[0011] In other words, the gist of this invention is as follows: (1) True density is 2.068 g / cm³ 3 Colloidal silica characterized by being less than [amount missing]. (2) True density is 2.035 g / cm³ 3The colloidal silica according to (1), characterized by being less than (3) The colloidal silica according to (1) or (2), characterized by containing a structural unit of Si-R (where R represents an alkyl group having 1 to 3 carbon atoms) in the structure. (4) The colloidal silica according to (3), characterized in that R is a methyl group and the structure contains a structural unit of Si-CH3. (5) The colloidal silica according to (1) or (2), characterized in that the metal impurity content is 100 ppb or less. (6) An abrasive characterized by containing the colloidal silica according to (1) or (2). (7) A method for producing the colloidal silica according to (1) or (2), In a method for producing colloidal silica, after supplying and reacting an easily hydrolyzable organosilicate to a reaction solution containing a hydrolysis catalyst composed of one or more mixtures selected from organic amines to obtain a reaction product, removing the alcohols generated from the reaction, and then concentrating so that the residual organic solvent is 1% by mass or less, The method for producing colloidal silica, characterized in that the easily hydrolyzable organosilicate contains 5% by mass or more and 40% by mass or less of an alkyltrimethylsilicate having an alkyl group with 1 to 3 carbon atoms. (8) The method for producing colloidal silica according to (7), characterized in that the alkyltrimethylsilicate is methyltrimethylsilicate. (9) In a method for producing grown colloidal silica with grown particle size, after adding the hydrolysis catalyst again to the obtained reaction product and supplying and reacting an easily hydrolyzable organosilicate to the reaction solution, removing the alcohols generated from the reaction, and then concentrating so that the residual organic solvent is 1% by mass or less, The method for producing colloidal silica according to (7), characterized in that the easily hydrolyzable organosilicate contains 5% by mass or more and 40% by mass or less of the alkyltrimethylsilicate. (10) In the above reaction, the reaction is carried out under the conditions that the supply rate of the hydrolyzable organosilicate is less than 1.5% by mass per minute of the total input amount of the hydrolyzable organosilicate, the reaction time is within 12 hours, and the reaction temperature is 60°C or higher and 90°C or lower. This is the method for producing colloidal silica according to (7).

Advantages of the Invention

[0012] According to the present invention, it is possible to provide colloidal silica with a reduced true density and a method for producing the same.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a photograph showing the state in which colloidal silica is aggregated and gelled in Comparative Example 1, and shows the state in which the aggregated and gelled colloidal silica is contained in a spherical glass container.

Modes for Carrying Out the Invention

[0014] <Colloidal Silica> The colloidal silica of the present invention is characterized in that the true density is less than 2.068 g / cm 3 Preferably, the true density is less than 2.066 g / cm 3 More preferably, it is less than 2.050 g / cm 3 Still more preferably, it is less than 2.035 g / cm 3 Even more preferably, it is less than 2.000 g / cm<所定の数字>Particularly preferably, it is less than 1.950 g / cm 3 Most preferably, it is less than 1.900 g / cm 3 or less. As described above, the general true density of amorphous SiO2 (quartz glass) is about 2.2 g / cm 3 However, since the true density of the colloidal silica of the present invention is less than the above upper limit value, the viscoelasticity of the colloidal silica particles can be increased, and for example, the processing quality can be improved by making it easier to control the way pressure is applied to a workpiece such as a semiconductor wafer.

[0015] On the other hand, the lower limit of the true density of the colloidal silica of the present invention is not limited, but is preferably 1,700 g / cm³. 3 More preferably 1,750 g / cm³ 3 More preferably, 1,800 g / cm³ 3 More preferably, 1.825 g / cm³ 3 In particular, 1.850 g / cm³ is preferred. 3 That concludes the explanation. By ensuring that the true density is above the aforementioned lower limit, it is possible to prevent the viscoelasticity of colloidal silica from becoming excessively high, thereby preventing an excessive decrease in polishability and processability.

[0016] Herein, the method for measuring the true density of colloidal silica in the present invention is not limited, and examples include the gas displacement method, the liquid displacement method, and the gas adsorption method. However, it is preferable to use the gas adsorption method using a dry densimeter as described in the examples, because it can remove the catalyst remaining in the solution.

[0017] To obtain the colloidal silica of the present invention having a true density within the aforementioned range, it is preferable that a sparse portion (structure) is introduced into the chemical structure consisting only of Si, O, and H obtained by a conventional manufacturing method. Although the chemical structure of the colloidal silica of the present invention is not limited, it is preferable that the structure contains a Si-R structural unit. Here, R represents an alkyl group having 1 to 3 carbon atoms, and is a methyl group (-CH3), an ethyl group (-C2-CH3), an n-propyl group (-CH2-CH2-CH3), or an isopropyl group [-CH(CH3)2]. Furthermore, the colloidal silica of the present invention may be a mixture of colloidal silicas with different R groups. By including Si-R in the chemical structure, a structure that does not form a siloxane bond (Si-O-Si bond) is included, and a sparse substructure that cannot bond with the Si element can be introduced. This makes it possible to reduce the true density of the resulting colloidal silica. In addition, by using an alkyl group having 1 to 3 carbon atoms as R, the effect of reducing the true density can be effectively obtained without excessively changing the physical properties of the resulting colloidal silica.

[0018] As the R group can be adapted to introduce the aforementioned sparse substructure, a greater number of carbon atoms is expected to reduce the true density. The R group can be appropriately selected within a range that does not impair the objective of the present invention, taking into consideration the effect of reducing the true density and the hydrolysis rate of the easily hydrolyzable organosilicate raw material from which the R group is derived. In other words, by selecting and using a lower alkyl group with 1 to 3 carbon atoms as the R group, the effect of reducing the true density can be effectively obtained without excessively changing the basic structure, properties, and physical characteristics of the resulting colloidal silica. The R group is more preferably a methyl group and / or an ethyl group, and even more preferably a methyl group. That is, the Si-R structural unit more preferably includes a Si-CH3 structural unit and / or a Si-CH2-CH3 structural unit, and even more preferably includes a Si-CH3 structural unit.

[0019] While there are no restrictions on the method of introducing such Si-R structural units, as will be described later, it can be adjusted by the blending composition of the easily hydrolyzable organosilicate used as a raw material. For example, if the R group is a methyl group as the easily hydrolyzable organosilicate, one method is to adjust the content of methyltrimethylsilicate. In other words, the Si-R structural unit refers to a structural unit (structural part) derived from the easily hydrolyzable organosilicate raw material having an R group in the colloidal silica of the present invention. Thus, using an easily hydrolyzable organosilicate having Si-R structural units based on an R group such as a methyl group is preferable because it allows for easy adjustment of the type and content of Si-R structural units introduced into the resulting colloidal silica, as well as the resulting true density. On the other hand, using an easily hydrolyzable organosilicate having Si-R structural units allows for not only a reduction in true density as a relatively easy method, but also the adjustment of the rate and time of the hydrolysis reaction.

[0020] The content of such Si-R structural units can be appropriately adjusted, taking into consideration the effect of reducing the true density or other properties that the colloidal silica of the present invention preferably possesses. By not reducing the content excessively, the true density of the resulting colloidal silica can be effectively reduced.

[0021] On the other hand, by ensuring that the content of the Si-R structural units is not excessively high, it is possible to prevent the true density from becoming excessively low. Furthermore, it is possible to prevent a decrease in the storage stability of colloidal silica caused by aggregates that did not form particles.

[0022] The colloidal silica of the present invention is not limited as long as it has the true density described above, and its basic structure is not limited as long as it has silanol groups on its surface, similar to ordinary colloidal silica. However, 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 (for example, the easily hydrolyzable organosilicate or its derivatives described later) as a raw material is preferred. Colloidal silica can be used by mixing one or more types.

[0023] The colloidal silica of the present invention preferably has a solid content 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 solid content 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.

[0024] The colloidal silica of the present invention preferably has a BET diameter (BET equivalent particle diameter) of 5 nm or more and 80 nm or less. A more preferable lower limit is 6 nm or more, an even more preferable lower limit is 10 nm or more, and an even more preferable lower limit is 14 nm or more. On the other hand, a more preferable upper limit is 70 nm or less, an even more preferable upper limit is 60 nm or less, and an even more preferable upper limit is 50 nm or less.

[0025] Here, in this invention, the BET diameter is defined as the BET specific surface area S (unit: m²) of colloidal silica measured by the BET method. 2 The true density ρ of silica particles (unit: g / cm³) measured by gas adsorption method (unit: g / cm³) 3 This is the particle size calculated from ). Specifically, it can be determined from the following equation (1). BET diameter (nm)=6000 / (S×ρ) ···(1)

[0026] Furthermore, regarding particle size, from the same viewpoint as above, and because there is a possibility that some parts may be difficult to grasp with an electron microscope, it is also preferable to define it by the cumulant average diameter (hereinafter sometimes simply referred to as "cumulant average diameter" or "DLS diameter") measured by dynamic light scattering, which has a wide measurement range. The cumulant average diameter of the colloidal silica of the present invention is preferably 6 nm or more, more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more. On the other hand, there is no upper limit to the cumulant average diameter, but it is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.

[0027] Furthermore, the colloidal silica of the present invention may have any shape and other properties depending on the application and purpose. In particular, it is preferable that the particle surface area is relatively high, and that the particle as a whole has a shape like a konpeito (Japanese sugar candy) with many irregular small protrusions. With such a shape, the BET specific surface area is large despite the large SEM average particle diameter, which is the arithmetic mean of the particle images observed by SEM, and the particle density (true specific gravity) measured by the liquid phase displacement method is high, in other words, it has high hardness, and has an excellent polishing speed, making it suitable as an abrasive for CMP (Chemical Polishing). For this reason, the BET specific surface area is 50 m². 2 It is preferable that it be 100m or more per gram. 2 It is more preferable that the value be 500m or more. Although there is no upper limit on the BET specific surface area, from the standpoint of stability, etc.2 It is preferable that it be less than / g, and 400m 2 It is more preferable that the value be less than or equal to / g.

[0028] Furthermore, the shape of the colloidal silica particles of the present invention can be controlled by the initial composition, etc., to be monodisperse spherical (spherical product) or to a shape in which particles are aggregated and associated (associated product). For example, by using a larger amount of catalyst and introducing the organosilicate as the silica raw material into the reaction site relatively slowly, the organosilicate hydrolyzes rapidly and uniformly and grows mildly, so that the seed particles gradually grow while maintaining their spherical shape, resulting in a spherical product. Alternatively, by using a smaller amount of catalyst and introducing the organosilicate as the silica raw material into the reaction site relatively quickly, the organosilicate hydrolyzes unevenly, so that it behaves like an adhesive between particles, and as a result, it is possible to produce an associated product in which particles are aggregated.

[0029] Furthermore, 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.

[0030] Furthermore, as described above, the colloidal silica of the present invention may be a monodisperse spherical product, or it may be an aggregate product (such as a cocoon-shaped, chain-like, or branched shape) that appears to be formed by the two-dimensional or three-dimensional aggregation of multiple particles when observed with an electron microscope.

[0031] Furthermore, the colloidal silica of the present invention may be adjusted to a pH that does not impair its dispersion stability. For example, a pH of 6 to 9 is preferred, and more preferably 7 to 8.5. Adjusting the pH to this range is advantageous in terms of the dispersion stability of the colloidal silica.

[0032] Furthermore, the colloidal silica of the present invention preferably has a metal impurity content of 100 ppb or less, more preferably 10 ppb or less, and even more preferably 1 ppb or less. Such high-purity colloidal silica can be achieved, for example, by using a silica source, hydrolysis catalyst, and water that satisfy the above-mentioned metal impurity content as raw materials for the hydrolysis reaction when obtaining the colloidal silica raw material in the manufacturing method described later.

[0033] (Uses of colloidal silica) Because the colloidal silica of the present invention has the properties described above, it is suitable for applications such as abrasives (silicon wafers, hard disks, etc.), coatings (eyeglasses, displays, building materials, paper, etc.), and binders (ceramics, catalysts, etc.).

[0034] <Method for producing colloidal silica> The method for producing colloidal silica according to the present invention is not limited, but it is preferable to use a method in which a silica source is reacted with a hydrolysis catalyst selected from organic amines. That is, it is preferable to supply and react an easily hydrolyzable organosilicate with a reaction solution containing a hydrolysis catalyst consisting of one or more organic amines selected from organic amines.

[0035] Furthermore, in the method for producing colloidal silica of the present invention, in order to achieve the aforementioned true density, the readily hydrolyzable organosilicate contains 5% to 40% by mass of alkyltrimethylsilicate having an alkyl group with 1 to 3 carbon atoms. That is, the content of the alkyltrimethylsilicate is 5% to 40% by mass of 100% by mass of the total readily hydrolyzable organosilicate used. The preferred lower limit for the content of the alkyltrimethylsilicate in 100% by mass of the total readily hydrolyzable organosilicate used is 10% by mass or more, a more preferred lower limit is 15% by mass or more, an even more preferred lower limit is 18% by mass or more, and a particularly preferred lower limit is 20% by mass or more. By having a content above the above lower limit, the true density of the resulting colloidal silica can be effectively reduced.

[0036] On the other hand, a more preferable upper limit for the alkyltrimethyl silicate content is 35% by mass or less, an even more preferable upper limit is 30% by mass or less, and an even more preferable upper limit is 25% by mass or less. By keeping the content below these upper limits, it is possible to prevent the true density from becoming excessively low. Furthermore, it is possible to prevent a decrease in the storage stability of colloidal silica caused by aggregates that did not form particles.

[0037] Here, examples of alkyltrimethyl silicates having an alkyl group with 1 to 3 carbon atoms include methyltrimethyl silicate, ethyltrimethyl silicate, n-propyltrimethyl silicate, and isopropyltrimethyl silicate. Among these, methyltrimethyl silicate and / or ethyltrimethyl silicate are preferred from the viewpoint of reducing true density and hydrolysis rate, and methyltrimethyl silicate is more preferred. In other words, it can be said that a particularly preferred embodiment is to use such preferred methyltrimethyl silicate and / or ethyltrimethyl silicate, or more preferred methyltrimethyl silicate, within the above-mentioned content range.

[0038] In the present invention, the silica source preferably used in the method for producing colloidal silica is an easily hydrolyzable organosilicate with a fast hydrolysis rate. The easily hydrolyzable organosilicate is preferably one in which 10 g of organosilicate and 100 g of pure water with impurities of 0.1 ppb or less are subjected to a hydrolysis reaction at 25°C under stirring, and the hydrolysis reaction is completed 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 methyltrimethyl silicate (hydrolysis reaction time: approximately 7 minutes). Tetraethyl silicate and organosilicates with a higher number of carbon atoms tend to have a relatively slow hydrolysis rate and are more prone to gelation (both with a hydrolysis reaction time of 24 hours or more). Therefore, it is preferable to appropriately select and adjust raw materials with different hydrolysis rates. However, in order to achieve the reduction of true density which is a particular objective of the present invention, as described above, it is preferable to use an easily hydrolyzable organosilicate containing methyl trimethyl silicate and / or ethyl trimethyl silicate, more preferably methyl trimethyl silicate, within the predetermined range described above.

[0039] Furthermore, while there are no restrictions on the organic amines used as hydrolysis catalysts, one selected from quaternary ammonium compounds, tertiary amines, secondary amines, and primary amines, as well as their carbonates, bicarbonates, and silicates, or mixtures of two or more thereof, can be widely used. For example, quaternary ammonium compounds 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. Since a relatively high pH is desirable for the hydrolysis reaction, tetramethylammonium hydroxide (TMAH), choline, or tetraethylammonium hydroxide (TEAH) are preferred.

[0040] Furthermore, the organic amines used as hydrolysis catalysts are not limited to primary, secondary, or tertiary amines, but examples include amino alcohols, morpholines, piperazines, aliphatic amines, and aliphatic etheramines. Here, various amino alcohols can be used, including ethanolamine derivatives, but ethanolamine derivatives are preferred, such as monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N-butyldiethanolamine, N-(β-aminoethyl)ethanolamine, N-methylethanolamine, N-methyldiethanolamine, N-ethylethanolamine, Nn-butylethanolamine, Nn-butyldiethanolamine, N-tert-butylethanolamine, and N-tert-butyldiethanolamine.

[0041] Furthermore, various morpholine derivatives can be used as morpholines among the organic amines used as hydrolysis catalysts, but morpholine, N-methylmorpholine, N-ethylmorpholine, etc. are preferred. Furthermore, various piperazine derivatives can be used as piperazines among the organic amines used as hydrolysis catalysts, but piperazine, hydroxyethylpiperazine, etc. are preferred. In addition, as aliphatic amines and aliphatic etheramines among the organic amines used as hydrolysis catalysts, suitable aliphatic amines include alkylamines having 1 to 8 carbon atoms such as triethylamine, dipropylamine, pentylamine, hexylamine, heptylamine, and octylamine. Suitable aliphatic etheramines include aliphatic etheramines having 1 to 8 carbon atoms such as 2-methoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, and 3-butoxypropylamine.

[0042] These organic amines used as hydrolysis catalysts can be used individually or, if necessary, as a mixture of two or more.

[0043] The reaction solution, as described above, contains an easily hydrolyzable organosilicate as a silica source and a hydrolysis catalyst, but other components such as water, alcohols, aldehydes, ketones, and surfactants can also be used. Preferably, the reaction solution contains a total of 90% by mass or more of the silica source, hydrolysis catalyst, and water. More preferably, the reaction solution contains 95% by mass or more of these components.

[0044] In the reaction product after the reaction between the silica source and the hydrolysis catalyst, or in the reaction product after subsequent treatments such as adjusting the solid content concentration or alcohol concentration as described later, or performing dispersion stabilization with acid (hereinafter, this may be specifically referred to as the "reaction concentrate"), it is preferable to add the hydrolysis catalyst to the reaction system and carry out the hydrolysis reaction so that the ratio of the hydrolysis catalyst (A) to the silica source (B) {catalyst residual 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. This is preferable because it allows for the optimization of the pH of the reaction product or reaction concentrate, and also suppresses thickening and gelation.

[0045] There are no particular limitations on the method for achieving such a catalyst remaining molar ratio. Examples include continuously or intermittently introducing a silica source into a reaction vessel containing water and hydrolysis catalyst (A) such that the final catalyst remaining molar ratio (A / B) falls within the aforementioned range; continuously or intermittently introducing a hydrolysis catalyst and silica source into a reaction vessel containing only water such that the final catalyst remaining molar ratio falls within the aforementioned range; or continuously or intermittently introducing a hydrolysis catalyst and silica source into a reaction vessel containing water and a small amount of hydrolysis catalyst (A) such that the final catalyst remaining molar ratio falls within the aforementioned range.

[0046] Furthermore, it is preferable to introduce colloidal silica seeds with particle growth properties into the reaction system of the hydrolysis reaction prior to the hydrolysis reaction of the silica source, and then gradually add the silica source and hydrolysis catalyst to this reaction system so that the catalyst residual molar ratio (A / B) is within the above range. This allows for the production of colloidal silica particles of uniformity.

[0047] For example, by adding the hydrolysis catalyst to the reaction solution obtained above, and then supplying and reacting the easily hydrolyzable organosilicate again, grown colloidal silica with increased particle size can be produced. Furthermore, this method can produce colloidal silica with uniform particles. In this method as well, as with the easily hydrolyzable organosilicate to be supplied and reacted again, it is preferable in order to achieve the aforementioned true density if the easily hydrolyzable organosilicate used here contains 5% to 40% by mass of alkyltrimethylsilicate having an alkyl group with 1 to 3 carbon atoms, as described above, in 100% by mass of the total easily hydrolyzable organosilicate used here.

[0048] Furthermore, the silica source, hydrolysis catalyst, and water used as raw materials for the hydrolysis reaction preferably have a metal impurity content of 100 ppb or less, more preferably 10 ppb or less, and even more preferably 1 ppb or less. This ensures that the resulting colloidal silica also satisfies the aforementioned range of metal impurity content.

[0049] The method for setting the BET diameter and cumulant average diameter of the colloidal silica of the present invention within the above range is not limited, but it is preferable to adjust the rate at which the silica source is added to the reaction solution (supply rate), the reaction temperature, and the reaction time.

[0050] When using readily hydrolyzable organosilicate as a silica source, the supply rate is preferably less than 1.5% by mass / min of the total amount of readily hydrolyzable organosilicate added, more preferably 1.3% by mass / min or less, and even more preferably 1.2% by mass / min or less. If the supply rate is 1.5% by mass / min or more, the particles tend not to disperse evenly and do not become nearly spherical. The reason why the total amount added is used as a criterion is that the amount added changes depending on the manufacturing scale, etc., and it is preferable to consider completing the supply within the reaction time described later. In other words, it is preferable to make the supply rate as slow as possible, as this 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, the target particle size may not be achieved, so it is preferably 1.0% by mass / min or more of the total amount added.

[0051] Furthermore, the reaction temperature is preferably 90°C or lower, more preferably 85°C or lower, and even more preferably 80°C or lower. If the reaction temperature exceeds 90°C, the volatilization of the reaction solution increases, making it easier for the liquid composition 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 as appropriate, but if the temperature is too low, the hydrolysis reaction tends to slow down, which may promote particle growth, so it is preferable to set it to 60°C or higher.

[0052] Furthermore, the reaction time is preferably 12 hours or less, more preferably 10 hours or less, and even more preferably 6 hours or less. If the reaction time exceeds 12 hours, the target particle size may not be achieved. On the other hand, the lower limit of the reaction time can be set as appropriate, but if the reaction time is too short, the hydrolysis reaction may not be completed, and particle formation or growth may not occur sufficiently, so it is preferably 20 minutes or more.

[0053] In the above reaction, it is preferable that the solid content concentration during the reaction be 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 other words, it is preferable that the solid content concentration of the colloidal silica after the reaction is also within the range of 3 to 13% by mass.

[0054] Furthermore, while there are no restrictions on the conditions such as the supply rate of the easily hydrolyzable organosilicate, the reaction temperature, the reaction time, and the solid content concentration during and after the reaction, the method can be applied not only to the initial stage reaction without seed particles, but also to a method in which the hydrolysis catalyst is further added to the reactants from the initial stage reaction, and then the easily hydrolyzable organosilicate is supplied and reacted again in that reaction solution. In other words, the above conditions can be applied to each stage of the reaction.

[0055] Furthermore, after the reaction in the above-mentioned step, or after a reaction is carried out again using a hydrolysis catalyst and an easily hydrolyzable organosilicate, it is preferable to remove the alcohols produced from the reaction, and then concentrate the solution so that the residual organic solvent is 1% by mass or less.

[0056] The method for removing alcohols is not particularly limited, but one example is to distill off the alcohols by heating using equipment equipped with a condenser-equipped distillation tube. Removing alcohols in this way is preferable because it eliminates the need to consider the alcohol resistance of materials used in subsequent processes, and because the highly volatile alcohols are removed, which helps stabilize the concentration of colloidal silica.

[0057] Furthermore, reducing the residual organic solvent to this range allows for adjustment or increase of the solid content concentration to a predetermined range, and is preferable because it prevents fluctuations in the colloidal silica concentration due to the volatilization of the organic solvent, especially when the residual organic solvent is highly volatile. Additionally, when using the colloidal silica of the present invention, there is no longer a need to consider the resistance of the residual organic solvent in the materials used at the application site, which is another advantage. Preferably, the residual organic solvent is 0.1% by mass or less, more preferably 0.05% by mass or less.

[0058] The method for removing and concentrating the residual organic solvent is not particularly limited, and known methods can be used. For example, one method is to distill off the residual organic solvent by heating using an apparatus equipped with a condenser-equipped distillation tube.

[0059] Furthermore, by concentrating the colloidal silica during the process of removing alcohols, residual organic solvents, and water, it is possible to achieve the desired solid content concentration, taking into account its intended use and purpose. In this invention, considering the intended use and purpose of the colloidal silica, as mentioned above, it is preferable to have a solid content 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 solid content concentration, but it is preferable to have a solid content concentration of 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

[0060] The colloidal silica of the present invention can be produced by following these steps, but other steps or treatments may be appropriately included in each of the above steps (stages) as long as they do not impair the objective of the present invention. For example, it is preferable to employ a dispersion stabilization treatment or a modification treatment in each of the above steps (stages). As for the dispersion stabilization treatment, any known dispersion stabilization treatment can be used without limitation, for example, dispersion stabilization by acid by a carbon dioxide blowing method or an acid solution addition method by adding an acid solution under stirring. As for the modification treatment, for example, it is possible to select from known modification treatments that combine a modifying agent or a silane coupling agent with a treatment that further converts substituents, for example, known nonionic modification, anionic modification, and cation modification treatments can be mentioned.

[0061] The colloidal silica obtained by the method of the present invention exhibits excellent dispersion stability for several weeks or even several years, and does not undergo bilayer separation.

[0062] In the present invention, colloidal silica with reduced true density 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 again to a reaction solution containing these seed particles and the hydrolysis catalyst and reacted to increase the particle size is not excluded. [Examples]

[0063] Preferred embodiments of the present invention will be specifically described below based on examples and comparative examples.

[0064] [Example 1] In a 5-liter (L) glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 1725 g of pure water with a metal impurity content of 0.1 ppb or less, 192 g of methanol, and 4.73 g of triethanolamine (boiling point (bp): 361°C) with a metal impurity content of 10 ppb or less were charged. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 678 g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyltrimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 80:20 (by weight) was continuously supplied over 360 minutes under stirring.

[0065] Next, 527 g of the reaction product, 2536 g of pure water, 282 g of methanol, and 8.01 g of triethanolamine (bp: 361°C) were charged into a 5 L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 1248 g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyltrimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 80:20 (by weight) was continuously supplied over 360 minutes under stirring.

[0066] The temperature of the reaction vessel containing the obtained reactants was lowered to 40°C, the system was depressurized using a vacuum pump, and then heating was resumed. The reaction mixture in the vessel was further heated to 52-68°C, and the generated methanol was distilled off from a condenser-equipped distillation tube at a distillation temperature of 32-67°C. Further, water and methanol were removed by distillation while adding 900g of pure water to obtain colloidal silica with a solid content of approximately 20% by mass. The residual organic solvent in the obtained colloidal silica was 0.1% by mass. Various analyses were performed on the obtained colloidal silica, and the results are shown in Table 1. <1> As shown. Note that the "alkyltrimethylsilicate concentration" in Table 1 represents the alkyltrimethylsilicate content in 100% by mass of the total easily hydrolyzable organosilicate used.

[0067] [Example 2] In a 5L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 1725g of pure water with a metal impurity content of 0.1 ppb or less, 192g of methanol, and 4.73g of triethanolamine (bp:361℃) with a metal impurity content of 10 ppb or less were charged. While maintaining the liquid temperature inside the reaction vessel at 80℃ using a mantle heater, 678g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyltrimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 85:15 (by weight) was continuously supplied over 360 minutes under stirring.

[0068] Next, 527 g of the obtained reaction product, 2536 g of pure water, 282 g of methanol, and 8.01 g of triethanolamine (bp: 361°C) were charged into a 5 L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 1248 g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyltrimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 85:15 (by weight) was continuously supplied over 360 minutes under stirring.

[0069] The temperature of the reaction vessel containing the obtained reactants was lowered to 40°C, the system was depressurized using a vacuum pump, and then heating was resumed. The reaction mixture in the vessel was further heated to 52-68°C, and the generated methanol was distilled off from a condenser-equipped distillation tube at a distillation temperature of 32-67°C. Further, 714 g of pure water was added while distilling off the water and methanol to obtain colloidal silica with a solid content of approximately 20% by mass. The residual organic solvent in the obtained colloidal silica was 0.1% by mass. Various analyses were performed on the obtained colloidal silica, and the results are shown in Table 1. <2> As shown.

[0070] [Example 3] In a 5L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 1725g of pure water with a metal impurity content of 0.1 ppb or less, 192g of methanol, and 4.73g of triethanolamine (bp:361℃) with a metal impurity content of 10 ppb or less were charged. While maintaining the liquid temperature inside the reaction vessel at 80℃ using a mantle heater, 678g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyltrimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 90:10 (by weight) was continuously supplied over 360 minutes under stirring.

[0071] Next, 527 g of the obtained reaction product, 2536 g of pure water, 282 g of methanol, and 8.01 g of triethanolamine (bp: 361°C) were charged into a 5 L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 1248 g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyltrimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 90:10 (by weight) was continuously supplied over 360 minutes under stirring.

[0072] The temperature of the reaction vessel containing the obtained reactants was lowered to 40°C, the system was depressurized using a vacuum pump, and then heating was resumed. The reaction mixture in the vessel was further heated to 52-68°C, and the generated methanol was distilled off from a condenser-equipped distillation tube at a distillation temperature of 32-67°C. Further, 1010 g of pure water was added while distilling off the water and methanol to obtain colloidal silica with a solid content of approximately 20% by mass. The residual organic solvent in the obtained colloidal silica was 0.1% by mass. Various analyses were performed on the obtained colloidal silica, and the results are shown in Table 1. <3> As shown.

[0073] [Example 4] In a 5L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 1725g of pure water with a metal impurity content of 0.1 ppb or less, 192g of methanol, and 4.73g of triethanolamine (bp:361℃) with a metal impurity content of 10 ppb or less were charged. While maintaining the liquid temperature inside the reaction vessel at 80℃ using a mantle heater, 678g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyltrimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 95:5 (by weight) was continuously supplied over 360 minutes under stirring.

[0074] Next, 527 g of the reaction product, 2536 g of pure water, 282 g of methanol, and 8.01 g of triethanolamine (bp: 361°C) were charged into a 5 L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 1248 g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyltrimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 95:5 (by weight) was continuously supplied over 360 minutes under stirring.

[0075] The temperature of the reaction vessel containing the obtained reactants was lowered to 40°C, the system was depressurized using a vacuum pump, and then heating was resumed. The reaction mixture in the vessel was further heated to 52-68°C, and the generated methanol was distilled off from a condenser-equipped distillation tube at a distillation temperature of 32-67°C. Further, 719g of pure water was added while distilling off the water and methanol to obtain colloidal silica with a solid content of approximately 20% by mass. The residual organic solvent content of the obtained colloidal silica was 0.1% by mass. Various analyses were performed on the obtained colloidal silica, and the results are shown in Table 1. <4> As shown.

[0076] [Comparative Example 1] The method described in Examples 1 to 3 of Patent Document 2 (Japanese Patent Publication No. 2024-044024) was used as a reference, and the amount of methyltrimethylsilicate used was changed. Tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyl trimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less were mixed in a ratio of 80:20 (weight ratio). Solution (B) was prepared by mixing this solution with methanol in a ratio of 85:15 (weight ratio), and solution (C) was prepared by mixing a 2.4 mass% aqueous ammonia solution. Solution (A), which had been pre-mixed with methanol, pure water, and ammonia, was charged into a glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate introduction tube. The concentration of water in solution (A) was set to 15 mass%, and the concentration of ammonia in solution (A) was set to 0.85 mass%. While maintaining the temperature of the reaction solution at 26°C, 100 volume% of solution (B) and 36 volume% of solution (C) were added dropwise at a constant rate to 160 volume% of solution (A), respectively, to obtain a dispersion of silica particles. Solution (B) was added dropwise at a constant rate, with a rate of 0.243 kg / hour / L relative to the volume of solution (A).

[0077] The resulting silica particle dispersion was heated to remove methanol and ammonia while adjusting the volume by adding pure water until the silica particle content reached approximately 20% by mass. When the silica particle content reached approximately 20.54% by mass, the dispersion lost its fluidity and formed an aggregated gel. The results are shown in Table 1. <5> The process of aggregation and gelation is shown in Figure 1.

[0078] [Comparative Example 2] The method described in Example 1 of Patent Document 2 (Japanese Patent Publication No. 2024-044024) was used as a reference. Tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) containing 10 ppb or less of metal impurities and methyl trimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) containing 10 ppb or less of metal impurities were mixed in a 99:1 (weight ratio). Solution (B) was prepared by mixing this solution with methanol in an 85:15 (weight ratio), and solution (C) was prepared using a 2.4% by mass aqueous solution of ammonia. Solution (A), which had been pre-mixed with methanol, pure water, and ammonia, was charged into a glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube. The concentration of water in solution (A) was set to 15% by mass, and the concentration of ammonia in solution (A) was set to 0.85% by mass. While maintaining the reaction mixture temperature at 26°C, 100% by volume of solution (B) and 36% by volume of solution (C) were added dropwise to 160% by volume of solution (A) at a constant rate to obtain a dispersion of silica particles. The addition rate of solution (B) per unit time relative to the volume of solution (A) was set to 0.243 kg / hour / L, and the solution (B) was added dropwise at a constant rate.

[0079] The resulting silica particle dispersion was heated to remove methanol and ammonia by adjusting the volume of the solution by adding pure water until the silica particle content was approximately 20% by mass, thereby obtaining a silica particle dispersion with a silica particle content of approximately 20% by mass. Various analyses were performed on the obtained colloidal silica, and the results are shown in Table 1. <6> As shown.

[0080] [Reference example 1] The method described in Examples 1 to 3 of Patent Document 2 (Japanese Patent Publication No. 2024-044024) was used as a reference, and the amount of methyltrimethylsilicate used was changed. Tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and methyl trimethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less were mixed in a 95:5 (weight ratio). Solution (B) was prepared by mixing this solution with methanol in an 85:15 (weight ratio), and solution (C) was prepared by mixing a 2.4 mass% aqueous ammonia solution. Solution (A), which had been pre-mixed with methanol, pure water, and ammonia, was charged into a glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate introduction tube. The concentration of water in solution (A) was set to 15 mass%, and the concentration of ammonia in solution (A) was set to 0.85 mass%. While maintaining the temperature of the reaction solution at 26°C, 100 volume% of solution (B) and 36 volume% of solution (C) were added dropwise at a constant rate to 160 volume% of solution (A), respectively, to obtain a dispersion of silica particles. Solution (B) was added dropwise at a constant rate, with a rate of 0.243 kg / hour / L relative to the volume of solution (A).

[0081] The resulting silica particle dispersion was heated to remove methanol and ammonia by adjusting the volume of the solution by adding pure water until the silica particle content was approximately 20% by mass, thereby obtaining a silica particle dispersion with a silica particle content of approximately 20% by mass. Various analyses were performed on the obtained colloidal silica, and the results are shown in Table 1. <7> As shown.

[0082] [Example 5] In a 1L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 610g of pure water with a metal impurity content of 0.1 ppb or less, 68g of methanol, and 1.67g of triethanolamine (boiling point (bp): 361°C) with a metal impurity content of 10 ppb or less were charged. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 240g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and ethyl trimethyl silicate (manufactured by Tokyo Chemical Industry Co., Ltd.) in a ratio of 90:10 (by weight) was continuously supplied over 360 minutes under stirring.

[0083] Next, 105 g of the obtained reaction product, 507 g of pure water, 56 g of methanol, and 1.60 g of triethanolamine (bp: 361°C) were charged into a 1 L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 250 g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and ethyl trimethyl silicate (manufactured by Tokyo Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 90:10 (by weight) was continuously supplied over 360 minutes under stirring.

[0084] The temperature of the reaction vessel containing the obtained reactants was lowered to 40°C, the system was depressurized using a vacuum pump, and then heating was resumed. The reaction mixture in the vessel was further heated to 52-68°C, and the generated methanol was distilled off from a condenser-equipped distillation tube at a distillation temperature of 32-67°C. Further, 153g of pure water was added while distilling off the water and methanol to obtain colloidal silica with a solid content of approximately 20% by mass. The residual organic solvent in the obtained colloidal silica was 0.1% by mass. Various analyses were performed on the obtained colloidal silica, and the results are shown in Table 1. <8> As shown.

[0085] [Example 6] In a 1L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube, 610g of pure water with a metal impurity content of 0.1 ppb or less, 68g of methanol, and 1.67g of triethanolamine (boiling point (bp): 361°C) with a metal impurity content of 10 ppb or less were charged. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 240g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and propyltrimethyl silicate (manufactured by Tokyo Chemical Industry Co., Ltd.) in a ratio of 90:10 (by weight) was continuously supplied over 360 minutes under stirring.

[0086] Next, 105 g of the obtained reaction product, 507 g of pure water, 56 g of methanol, and 1.60 g of triethanolamine (bp: 361°C) were charged into a 1 L glass container equipped with a stirrer, thermometer, distillation tube with condenser, and organosilicate inlet tube. While maintaining the liquid temperature inside the reaction vessel at 80°C using a mantle heater, 250 g of a solution prepared by mixing tetramethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less and propyltrimethyl silicate (manufactured by Tokyo Chemical Industry Co., Ltd.) with a metal impurity content of 10 ppb or less in a ratio of 90:10 (by weight) was continuously supplied over 360 minutes under stirring.

[0087] The temperature of the reaction vessel containing the obtained reactants was lowered to 40°C, the system was depressurized using a vacuum pump, and then heating was resumed. The reaction mixture in the vessel was further heated to 52-68°C, and the generated methanol was distilled off from a condenser-equipped distillation tube at a distillation temperature of 32-67°C. Further, 151 g of pure water was added while distilling off the water and methanol to obtain colloidal silica with a solid content of approximately 20% by mass. The residual organic solvent in the obtained colloidal silica was 0.1% by mass. Various analyses were performed on the obtained colloidal silica, and the results are shown in Table 1. <9> As shown.

[0088] [Table 1]

[0089] The physical properties of the obtained colloidal silica were evaluated using the following method. (1) BET specific surface area, BET equivalent particle size: Measured using NOVA4200e (manufactured by Anton Paar). BET specific surface area S(m²) measured by nitrogen adsorption method (BET method) 2 The true density ρ (g / cm³) measured by the gas adsorption method 3 The particle size derived from the above equation (1) is defined as the BET-equivalent particle size. (2) Cumulant mean diameter (DLS diameter) by dynamic scattering method: Measured using the SZ-100 instrument (manufactured by Horiba, Ltd.). During measurement, the silica content in the sample was adjusted to 1.13 g using pure water and ammonium nitrate, and the adjusted solution was measured. (3) Silica solid content concentration: Using the SMS-70 instrument (manufactured by A&D Company, Limited), the silica concentration was determined from the residue after evaporating the contained water. (4) pH: Measured at 25°C using a D-51 instrument (manufactured by Horiba, Ltd.). (5) Viscosity: Measured at 25°C using a VM-10A instrument (manufactured by Sekonic Corporation). (6) Methanol concentration: Measured using GC-2025 (manufactured by Shimadzu Corporation). (7) True density: Measured at 25°C using an Accupic II 1340 (Micromerities). [Industrial applicability]

[0090] The colloidal silica of the present invention is suitable for applications such as abrasives (silicon wafers, hard disks, etc.), coatings (eyeglasses, displays, building materials, paper, etc.), and binders (ceramics, catalysts, etc.).

Claims

1. True density is 2.068 g / cm³ ３ Colloidal silica characterized by being less than [amount missing] and containing a structural unit of Si-R (where R represents an alkyl group having 1 to 3 carbon atoms) in its structure.

2. True density is 2.035 g / cm³ ３ The colloidal silica according to claim 1, characterized in that it is less than [amount missing].

3. The aforementioned R is a methyl group, and the structure contains Si-CH ３ The colloidal silica according to claim 1, characterized by containing structural units.

4. The colloidal silica according to claim 1 or 2, characterized in that the metal impurity content is 100 ppb or less.

5. An abrasive characterized by containing colloidal silica as described in claim 1 or 2.

6. A method for producing colloidal silica having a true density of less than 2.068 g / cm³, In a method for producing colloidal silica, a reaction solution containing a hydrolysis catalyst consisting of one or more organic amines selected from organic amines is supplied with and reacted with an easily hydrolyzable organosilicate to obtain a reaction product, alcohols generated from the reaction are removed, and then the solution is concentrated to a residual organic solvent content of 1% by mass or less, A method for producing colloidal silica, characterized in that the readily hydrolyzable organosilicate contains 5% by mass or more and 40% by mass or less of alkyltrimethylsilicate having an alkyl group having 1 to 3 carbon atoms.

7. The method for producing colloidal silica according to claim 6, characterized in that the alkyltrimethylsilicate is methyltrimethylsilicate.

8. In a method for producing grown colloidal silica with increased particle size, the hydrolysis catalyst is further added to the reaction solution obtained above, an easily hydrolyzable organosilicate is supplied again and reacted, alcohols generated from the reaction are removed, and then the solution is concentrated so that the residual organic solvent is 1% by mass or less, The method for producing colloidal silica according to claim 6, characterized in that the readily hydrolyzable organosilicate contains 5% by mass or more and 40% by mass or less of the alkyltrimethylsilicate.

9. The method for producing colloidal silica according to claim 6, characterized in that the reaction is carried out under the conditions that the supply rate of the easily hydrolyzable organosilicate is less than 1.5% by mass of the total amount of the easily hydrolyzable organosilicate added per minute, the reaction time is within 12 hours, and the reaction temperature is 60°C or higher and 90°C or lower.

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