Colloidal silica and method for producing colloidal silica

Abstract

The present invention provides: colloidal silica which has both a smooth surface and a reduced content of alkali metal impurities, and preferably has little surface change with time; and a method for producing the colloidal silica.　The present invention specifically provides colloidal silica which is characterized by satisfying the following requirements (1) and (2) at the same time. (1) The degree of unevenness represented by formula (i) is 1.0740 or less.　Formula (i): (Degree of unevenness) = (Equivalent circle diameter converted from length of periphery calculated from projection image that is obtained by image analysis with electronic microscope (equivalent circle diameter in terms of length of periphery)) / (Equivalent circle diameter converted from projection area that is obtained by image analysis with electronic microscope (equivalent circle diameter in terms of area)) (2) The content of the metal impurities is 1 ppm or less.

Description

Colloidal silica and method for producing colloidal silica

[0001] The present invention relates to colloidal silica and a method for producing colloidal silica, and more particularly to colloidal silica having smooth particle surfaces and a method for producing the same.

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

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

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

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

[0006] Furthermore, in order to achieve a higher polishing rate than the colloidal silica produced by the method of Patent Document 1, a polishing composition has also been proposed in which the protrusions on the particle surface have been optimized (Patent Document 2).

[0007] Furthermore, in contrast to the colloidal silica produced by the method of Patent Document 1, colloidal silica has been proposed that is superior in maintaining the surface irregularities even under basic conditions (Patent Document 3).

[0008] As described above, various studies have been conducted on colloidal silica having irregularities or protrusions on the surface.

[0009] Meanwhile, in the field of semiconductor wafer abrasives, for example, there has been a need in recent years to meet various demands. For example, colloidal silica is used in polishing at various liquid solubility levels, including acidic, neutral, and alkaline, with slurries using neutral to alkaline colloidal silica being particularly preferred. This is because, particularly in silicon wafer polishing, colloidal silica acts chemically on the silicon wafer surface to promote etching and increase the polishing rate, removes impurities such as abrasive grains and chelating agents adsorbed on the silicon wafer surface, improves wafer flatness and defect performance, and further reduces the coefficient of friction with the polishing pad, thereby suppressing heat generation and wear during polishing and stabilizing polishing quality. Therefore, colloidal silica that exhibits little change over time, especially in neutral to alkaline solutions, is desired. Furthermore, as in the aforementioned Patent Documents 1 to 3, colloidal silica with an uneven surface has a high physical polishing rate for the polished object, but there are concerns that it may also cause problems such as scratches on the polished object.

[0010] In contrast, colloidal silica with a smooth surface has a relatively low physical polishing rate for the object to be polished. However, since the polishing rate can be achieved with chemical polishing, colloidal silica with a smooth surface is advantageous for objects to be polished that are not prone to scratches, making it a useful colloidal silica abrasive that uses smooth surface particles. In addition, particles with a small surface roughness usually have the advantage of being less susceptible to changes over time due to unevenness.

[0011] Here, when colloidal silica is produced using a catalyst derived from an alkali metal such as NaOH or KOH, the alkali metal-derived catalyst is generally highly alkaline, so the solubility of the silica source is high, the growth rate is low, and particles tend to grow uniformly, and therefore the surface roughness of the obtained silica particles tends to be small. However, when such an alkali metal-derived catalyst is used, the alkali metal becomes an impurity, making it unsuitable for application to semiconductor manufacturing.

[0012] For this reason, when attempting to obtain colloidal silica to be used in semiconductor manufacturing, catalysts derived from alkali metals tend to be avoided, and production methods using organic hydrolysis catalysts have been proposed, such as those described in the aforementioned Patent Document 1. However, among organic hydrolysis catalysts, there is concern that low-boiling point ammonia and organic amines tend to volatilize during reactions in aqueous solvents at high temperatures, preventing stable reactions.

[0013] For these reasons, from the viewpoint of producing stable colloidal silica with few alkali metal impurities, an organic amine catalyst with a relatively high boiling point is desirable. However, in conventional reaction methods using high-boiling organic amine catalysts, the organic amine catalysts have weak alkalinity, so the solubility of the silica source is low, the growth rate is high, and the particles tend to have little room to form a stable configuration, resulting in colloidal silica with a relatively large surface roughness. In other words, colloidal silica with a smooth surface and few alkali metal impurities has not been found until now.

[0014] JP 2007-153732 A JP 2012-104800 A WO2020 / 179558

[0015] Therefore, the inventors of the present application conducted extensive research to develop colloidal silica that combines the properties of a smooth surface and low alkali metal impurities, and discovered that this can be achieved by devising the reaction conditions when adding the silica source in a method of reacting a silica source with a hydrolysis catalyst selected from organic amines, thereby completing the present invention. In doing so, they also conducted extensive research into the properties related to changes in the colloidal silica surface over time, and succeeded in finding a preferred embodiment that further specifies that changes over time are minimal, in addition to the above.

[0016] Therefore, an object of the present invention is to provide colloidal silica that has both a smooth surface and low alkali metal impurity content, and preferably exhibits little change over time on the surface, and a method for producing the same. Another object of the present invention is to define the characteristics of the change over time on the surface of such colloidal silica, and to provide a method for evaluating the definition.

[0017] That is, the gist of the present invention is as follows. [1] A colloidal silica characterized by simultaneously satisfying the following (1) and (2): (1) The degree of irregularity represented by the following formula (i) is 1.0740 or less: degree of irregularity = equivalent circle diameter converted from the perimeter determined from a projection image obtained by image analysis using an electron microscope (perimeter-equivalent circle diameter) / equivalent circle diameter converted from the projected area obtained by image analysis using an electron microscope (area-equivalent circle diameter) ... (i) (2) The content of metal impurities is 1 ppm or less. [2] The colloidal silica according to [1], characterized in that after being kept at a temperature of 60°C for 7 days, the rate of change in silanol group density is minus 5% or more. [3] After being kept at a temperature of 60°C for 7 days, the rate of change in nuclide concentration measured by time-domain nuclear magnetic resonance spectroscopy is １ [4] The colloidal silica according to [1], characterized in that the rate of change in the transverse relaxation time of H is 24% or less. ２ [5] The colloidal silica according to [1], characterized in that it is: １The colloidal silica according to [1], characterized in that the transverse relaxation time of H is 650 ms or more and less than 1,300 ms. [6] The colloidal silica according to [1], characterized in that the electron microscope is one or more of a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), and a transmission electron microscope (TEM). [7] An abrasive containing the colloidal silica according to any of [1] to [6]. [8] A method for producing colloidal silica by supplying and reacting an easily hydrolyzable organosilicate to a reaction solution containing a hydrolysis catalyst consisting of one or a mixture of two or more selected from organic amines, wherein the production condition constant represented by the following formula (ii) is 0.024 or less: Production condition constant = silica concentration after reaction (mass%) / supply time (hr) of easily hydrolyzable organosilicate / reaction temperature (°C) ... (ii)

[0018] According to the present invention, it is possible to provide colloidal silica that has both a smooth surface and low alkali metal impurity content. Furthermore, in addition to the above, it is possible to obtain colloidal silica in a preferred embodiment that exhibits minimal change in its surface properties over time. It is also possible to provide a method for producing such colloidal silica.

[0019] FIG. 1 shows an SEM image (200,000 magnification) of the colloidal silica obtained in Example 1. FIG. 2 shows an STEM image (200,000 magnification) of the colloidal silica obtained in Example 1. FIG. 3 shows an SEM image (200,000 magnification) of the colloidal silica obtained in Example 3. FIG. 4 shows an SEM image (200,000 magnification) of the colloidal silica obtained in Example 3. FIG. 5 shows an SEM image (200,000 magnification) of the colloidal silica obtained in Comparative Example 1. FIG. 6 shows an SEM image (200,000 magnification) of the colloidal silica obtained in Comparative Example 1. FIG. 7 shows an SEM image (200,000 magnification) of the colloidal silica obtained in Comparative Example 3. FIG. 8 shows an STEM image (200,000 magnification) of the colloidal silica obtained in Comparative Example 3. FIG. 9 shows STEM analysis images of the colloidal silica of Examples 1 to 6 and Comparative Examples 1 to 4.

[0020] <Colloidal Silica> As described above, the colloidal silica of the present invention is characterized by simultaneously satisfying the following (1) and (2): (1) The degree of irregularity represented by the following formula (i) is 1.0740 or less: degree of irregularity = equivalent circle diameter converted from the perimeter determined from a projection image obtained by image analysis using an electron microscope (perimeter-equivalent circle diameter) / equivalent circle diameter converted from the projected area obtained by image analysis using an electron microscope (area-equivalent circle diameter) (i) (2) Metal impurities are 1 ppm or less.

[0021] The following will begin with the above (1). The colloidal silica of the present invention has a roughness of 1.0740 or less. By satisfying the roughness defined in this way, the colloidal silica particle surfaces can be specified as being relatively smooth with little roughness. The reason for this is as follows.

[0022] That is, because colloidal silica particles do not necessarily have perfectly spherical shapes due to factors such as the manufacturing method, and the surface shapes vary widely, it is difficult to immediately determine whether a particle has a smooth surface. Therefore, in the present invention, as described above, the inventors have conceived the idea that the degree of surface roughness of colloidal silica particles can be determined by calculating the ratio of the area-equivalent circle diameter, which is the circle-equivalent diameter converted from the projected area obtained by image analysis under an electron microscope, to the perimeter-equivalent circle diameter, which is the circle-equivalent diameter converted from the perimeter determined from the projected image obtained by image analysis under an electron microscope. That is, as the degree of surface roughness of a particle increases, the perimeter of the particle as viewed in a projected image under an electron microscope is thought to increase, and therefore the diameter of a circle having the same circumference as that perimeter also increases. Here, in the present invention, the perimeter is defined as the perimeter determined from the projected image obtained by image analysis under an electron microscope. Therefore, unlike the degree of roughness of the particle surface, by comparing with the area-converted circle equivalent diameter, which is thought not to particularly reflect the degree of roughness, it becomes possible to relatively grasp the magnitude of the degree of roughness of the particle surface, and it has been found that this is a preferable method and criterion for grasping whether the surface is smooth. In this regard, in the case of spherical monodisperse particles, if the degree of roughness is roughly the same, the particle diameter tends to become smaller as the BET specific surface area increases, and therefore it is an unexpected technical matter discovered in the present invention that the BET specific surface area and the above-mentioned roughness defined this time do not necessarily tend to be in the same direction.

[0023] First, the circumferential length-equivalent diameter is also called the projected circumferential length-equivalent diameter, and is the diameter of a circle having the same peripheral length as the circumferential length. This circumferential length-equivalent diameter is determined taking into consideration the surface shape of the particle, and is one of the parameters that affect the shape and contour of the particle.

[0024] The area-converted equivalent circle diameter is usually also called the Heywood diameter, and may be in accordance with JIS Z 8827-1:2018, Particle size analysis - image analysis method. When measuring particles of various shapes, such as colloidal silica particles with irregularities on the particle surface or particles with constrictions due to aggregation, manual measurement is prone to errors and requires a long time, so it is preferable to use such a standardized equivalent circle diameter, since it allows the outer diameter of the particles to be objectively evaluated.

[0025] The irregularity is preferably 1.0735 or less, more preferably 1.0730 or less, and even more preferably 1.0725 or less. On the other hand, there is no lower limit to the irregularity. The theoretical lower limit of the irregularity is more than 1.0000, preferably 1.0300 or more, more preferably 1.0400 or more, and even more preferably 1.0500 or more.

[0026] The electron microscope used is not limited as long as it can acquire images applicable to the measurement and analysis of the equivalent diameter. Known electron microscopes, such as scanning electron microscopes (SEM), transmission electron microscopes (TEM), and scanning transmission electron microscopes (STEM), can be used without limitation. Preferably, a combination of SEM or TEM and STEM is used, more preferably a combination of SEM and STEM, and even more preferably STEM. In particle analysis, particles are identified by binarization, which separates the black parts of the particles from the white parts other than the particles. However, when particles with irregularities are observed with an SEM, the irregularities on the particles appear black and white, making it difficult to determine the particle boundaries. Therefore, observation with a TEM or STEM, which does not produce black and white irregularities, is required. However, it is difficult to determine from TEM observation alone whether the particles are a single particle formed by association with each other or simply overlapping each other and appearing as a single particle. Therefore, capturing an STEM image and analyzing the image allows for a more accurate capture of the particle shape, allowing for more accurate determination of the perimeter-equivalent circle diameter and area-equivalent circle diameter.

[0027] Specifically, the STEM image is imported into any image analysis software such as that used in the Examples, the particle area is measured, the results are imported into calculation software, overlapping particle data is removed, and the perimeter-equivalent circle diameter and area-equivalent circle diameter are measured from the remaining particle images. After the equivalent diameters of all particles are tallied, the roughness can be calculated from the ratio of the two in accordance with the above-mentioned formula (i).

[0028] Furthermore, as described above, the colloidal silica of the present invention has a metal impurity content of 1 ppm or less. Preferably, it is 0.01 ppm or less, more preferably 0.001 ppm or less, and even more preferably 0.0001 ppm or less. To obtain colloidal silica with such low metal impurities, methods using sodium silicate as a raw material or methods using NaOH or KOH as a hydrolysis catalyst leave alkali metals such as sodium derived from the raw materials, making it difficult to produce colloidal silica with a metal impurity content of 1 ppm or less. Therefore, in order to achieve the metal impurity content of 1 ppm or less in the colloidal silica of the present invention, although there are no particular limitations, a preferred embodiment is to use high-purity raw materials, such as the silica source, hydrolysis catalyst, and water, used in the production, that have a metal impurity content of 1 ppm or less, preferably 0.01 ppm or less.

[0029] Here, for the colloidal silica of the present invention having the above-described characteristics of roughness and metal impurities, it is preferable that the particle surface undergo little change over time. This small change over time on the particle surface tends to be useful in actual use, and is preferable because, for example, it reduces the variation in polishing rate. While several factors are thought to cause this change over time, one is due to silanol groups (Si—OH) on the particle surface. The presence of many silanol groups reduces the distance between silanol groups, making adjacent silanol groups more likely to condense with each other. This makes it easier for protons to be removed from silanol groups, particularly in neutral and alkaline conditions, which makes the silanol groups more likely to condense, resulting in change over time. Furthermore, a relatively small number of silanol groups also leads to the above-described small roughness, which is preferable because it allows the particle to have the above-described roughness and results in little change over time.

[0030] In the present invention, the small change over time is determined by the silanol group density (unit: particles / nm) of the colloidal silica. ２ ) over time. That is, one example is to measure the change in silanol group density after holding for a certain period under heated conditions. Here, the pH conditions are not limited, and the pH conditions used in production can be used. Specifically, as will be described in the Examples below, a temperature of at least 60°C or higher is used as a severe condition that does not involve a phase change such as water evaporation, and the change in silanol group density after holding for 7 days under these conditions is confirmed. If the rate of change is minus 5% or more, it can be determined that there is no change in silanol group density. The solid content concentration during this measurement is not limited, and it is preferable to measure the silanol group density at a solid content concentration that is suited to the application and actual use.

[0031] The reason why the method of holding at 60°C or higher for 7 days is preferably applied is that it has been found that holding at 60°C for 7 days results in a change over time test roughly equivalent to holding at room temperature for 1 year, thereby confirming that there is no change in silanol group density over time in at least a 1-year change over time test at room temperature. The change rate is preferably minus 4% or more, and more preferably minus 3% or more. On the other hand, there is no upper limit to the change rate. This is because, although the change in silanol group density is expected to decrease due to condensation reactions of silanol groups, it is generally believed that no new silanol groups will increase under these measurement conditions. Therefore, taking into account the variation (coefficient of variation) of the change rate based on the measured value, the upper limit to the change rate is typically preferably plus 10% or less, more preferably plus 7% or less, and even more preferably plus 5% or less.

[0032] Furthermore, the colloidal silica of the present invention has a silanol group density of 3 / nm on the particle surface. ２ It is preferable that the density of silanol groups is 2.7 or less. This is because, as mentioned above, when the silanol group density is high, the silanol groups tend to condense with each other in a solution under neutral to alkaline conditions, resulting in a decrease in the number of silanol groups over time. It is more preferable that the density is 2.7 or less. ２ On the other hand, there is no lower limit, but it is 1 particle / nm ２ It is preferable that the number of particles is 1.5 / nm or more. ２ If the number of silanol groups is too small, the affinity for water decreases, and the colloidal silica particles are more likely to settle.

[0033] The colloidal silica of the present invention has a silanol group number per unit mass of the colloidal silica of 2.70 × 10 ２０ It is preferable that the number of silanol groups is 2.50×10 or less. If the number of silanol groups is large, as described above, the silanol groups tend to condense with each other in a solution under neutral to alkaline conditions, resulting in a decrease in the number of silanol groups over time. More preferably, it is 2.50×10 ２０On the other hand, there is no lower limit, but it is 1.00 × 10 ２０ It is preferable that the number of particles is 1.20 × 10 ２０ If the number of silanol groups is too small, the affinity for water decreases, and the colloidal silica particles are more likely to settle.

[0034] Furthermore, the rate of change of the number of silanol groups per unit mass when maintained for 7 days under the same conditions as above, preferably at a temperature of 60° C., is preferably −7% or more, and more preferably −5% or more. On the other hand, as for the upper limit of the rate of change, as described above, since it is believed that essentially no new silanol groups will be added, taking into consideration the fluctuation (coefficient of variation) of the rate of change based on the measured value, the upper limit of the rate of change is usually preferably +10% or less, more preferably +5% or less, and even more preferably +3% or less.

[0035] In the present invention, the small change over time can also be measured by a method other than the change in silanol group density or number of silanol groups. One method is the measurement of nuclide concentration by time domain nuclear magnetic resonance (TD-NMR). １ Changes over time can be confirmed by measuring the rate of change in the transverse relaxation time of H [unit: milliseconds (ms)]. The reason for performing this measurement using TD-NMR is as follows. That is, information on relaxation time can be obtained from measurements using TD-NMR, and the smaller the change in relaxation time, the smaller the change in particle surface over time. Here, relaxation refers to the process in which energy once absorbed decays, and nuclear spins excited by radio waves are relaxed by the surrounding environment and energy exchange with the nuclear spins. The time required for this process is the relaxation time, and this time is called T １ (longitudinal relaxation time, spin-lattice relaxation time), T ２For example, in the case of particles dispersed in water, it is known that the response to a change in magnetic field differs between water in contact with or adsorbed to the particle surface (bound water) and free water not in contact with the particle surface (bulk water), resulting in different relaxation times.

[0036] The change over time of the particle surface of the colloidal silica of the present invention can be evaluated by the change in wettability due to the silanol groups present on the particle surface, i.e., the change in the relaxation time. １ It is suitable to observe H, and the observed nuclide is １ It is thought that the silanol groups present on the surface of colloidal silica particles interact with the bound water molecules on the particle surface through hydrogen bonds, etc., but on the other hand, there is also the bulk water that has little or no direct interaction with the silanol groups, and the bound water is prone to energy exchange. １ The relaxation time of H is short, and the relaxation time of H is １A long relaxation time for H can be obtained. In other words, good wettability indicates a state in which many hydrogen bonds are present and a large amount of bound water is present, resulting in a short relaxation time. Regarding the relaxation time, it is preferable to use the transverse relaxation time because it is easily affected by molecular mobility and interactions and is suitable for evaluating the physical properties of a sample. Furthermore, for theoretical reasons, the Carr-Purcell-Meiboom-Gill (CPMG) method is preferably used to measure the transverse relaxation time. While other conditions for measuring the transverse relaxation time are not limited, a temperature of 40°C is preferred. 40°C is preferred because it is the temperature at which the molecular motion of many organic compounds and polymer compounds becomes active, is lower than the boiling point of water, is suitable for measuring samples containing moisture, and is easy to control. In this regard, if the temperature is too low, molecular motion may be suppressed, resulting in an excessively long relaxation time. Furthermore, if the temperature is too high, moisture may evaporate easily, potentially changing the composition and physical properties of the sample and reducing measurement accuracy. Other measurement conditions may be determined as appropriate.

[0037] The colloidal silica of the present invention is preferably kept at a temperature of 60° C. for 7 days under the same conditions as those for the change over time of the silanol group density, etc., and then the nuclide content measured by time-domain nuclear magnetic resonance (TD-NMR) is １ It is preferable that the rate of change in the transverse relaxation time of H is 24% or less. The colloidal silica according to the present invention having such properties has good wettability, which means that the particle dispersibility and silanol group change little over time. １ The rate of change of the transverse relaxation time of H is more preferably 23% or less, and even more preferably 22% or less. On the other hand, the lower limit of the rate of change of the transverse relaxation time is more preferably 0% or more, since it is preferable that the rate of change be as small as possible.

[0038] Here, the nuclide measured by TD-NMR １The transverse relaxation time of H is preferably less than 1300 ms. More preferably, it is 1100 ms or less, even more preferably 1050 ms or less, and even more preferably 1010 ms or less. On the other hand, the lower limit is preferably 650 ms or more, and more preferably 700 ms or more. If the transverse relaxation time is too long, the particles tend to have low wettability with respect to a dispersion medium such as water, which is not preferable. On the other hand, if the transverse relaxation time is too short, the particles tend to have high wettability with respect to a dispersion medium such as water and a large number of silanol groups, which is not preferable, as it tends to cause large changes over time.

[0039] The silica concentration of the colloidal silica of the present invention can be appropriately set depending on the application and actual use, but in a preferred embodiment, the silica concentration after concentration is 1% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 35% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less. The pH value is also not limited, but since both acidic and basic pH values ​​are used in actual use, such as polishing, depending on the application, a neutral pH value of 6.0 to 9.0 is preferred, which allows the colloidal silica itself to be adjusted to both pH ranges. Furthermore, due to the above-mentioned properties, excellent dispersion stability is exhibited, usually for several weeks or even several years, and the occurrence of two-layer separation is extremely rare.

[0040] The colloidal silica of the present invention can accommodate a wide range of particle sizes, and therefore the BET specific surface area is 1 to 3,000 m ２ / g, and 2 to 2000m ２ / g, and more preferably 5 to 2700m ２ / g, because if the BET specific surface area is too small, the colloidal silica will be prone to settling, whereas if the BET specific surface area is too large, it will be difficult to determine the smoothness of the particle surface.

[0041] The colloidal silica of the present invention is not limited in particle size, but preferably has a size within a range that allows image analysis using an electron microscope. For example, the BET particle size (nm) determined from the BET specific surface area is preferably 1 nm to 500 nm, more preferably 5 nm to 300 nm, and even more preferably 10 nm to 200 nm.

[0042] The particle shape of the colloidal silica of the present invention can be controlled by adjusting the feed composition, etc., to form monodisperse spheres (spherical products) or morphologies in which particles are aggregated and associated (associated products). For example, by adding a large amount of catalyst and a relatively slow rate of introducing an organosilicate as the silica raw material into the reaction field, the organosilicate hydrolyzes rapidly and uniformly and grows mildly, resulting in seed particles gradually growing while maintaining their spherical shape, forming spherical products. Alternatively, by adding a small amount of catalyst and a relatively fast rate of introducing an organosilicate as the silica raw material into the reaction field, the organosilicate hydrolyzes non-uniformly, acting as an adhesive between particles, resulting in an associated product (cocoon-shaped, chain-like, branched) that appears to be formed by two- or three-dimensional aggregation of multiple particles under electron microscope observation. The above-described manufacturing methods can also be employed within the scope of the manufacturing methods described below.

[0043] The colloidal silica of the present invention may be subjected to known treatments, provided that the object of the present invention is not impaired. Examples of such treatments include the dispersion stabilization treatment described below, surface treatments (e.g., modification treatments, silane coupling agents, polymers, metal oxides, etc.), pH adjustment, and ionic strength adjustment.

[0044] The colloidal silica of the present invention has the above-mentioned properties and is therefore suitable for applications such as an abrasive (for silicon wafers, hard disks, etc.), a coating agent (for eyeglasses, displays, building materials, paper, etc.), and a binder (for ceramics, catalysts, etc.).

[0045] <Method for Producing Colloidal Silica> There are no particular limitations on the method for producing the colloidal silica of the present invention, but in order to provide the above-mentioned properties, it is preferable to employ a method in which a silica source is reacted with a hydrolysis catalyst selected from organic amines. That is, it is preferable to employ a method in which an easily hydrolyzable organosilicate is supplied to and reacted with a reaction liquid containing a hydrolysis catalyst consisting of one or a mixture of two or more organic amines.

[0046] In the present invention, in the above-mentioned preferred production method, the conditions for supplying and reacting the easily hydrolyzable organosilicate are adjusted so that the production condition constant represented by the following formula (ii) is 0.024 or less: Production condition constant = silica concentration after reaction (mass %) / supply time of easily hydrolyzable organosilicate (hr) / reaction temperature (°C) (ii)

[0047] By adjusting the manufacturing condition constants to satisfy these, it is possible to manufacture colloidal silica particles with a relatively low degree of unevenness and a smooth surface, as described above. Furthermore, it is preferable to obtain colloidal silica particles with little change over time on the particle surface, as described above. Furthermore, the silanol group density on the surface of the colloidal silica particles, the number of silanol groups per unit mass of the colloidal silica, and the nuclide concentration measured by TD-NMR can be controlled. １ The transverse relaxation time of H and the rate of change thereof can be preferably satisfied. The production condition constant is preferably 0.022 or less, more preferably 0.020 or less. There is no restriction on the lower limit, and it is most preferable that the numerical value is as small as possible. However, based on the respective preferred ranges of the silica concentration after the reaction, the supply time of the easily hydrolyzable organosilicate, and the reaction temperature described below, it is preferable that it is 0.0001 or more. The lower limit is more preferably 0.001 or more, even more preferably 0.002 or more, and even more preferably 0.005 or more.

[0048] Here, the silica concentration after the reaction is preferably 1 to 40% by mass or less based on the intended use and actual use. The silica concentration after the reaction can be adjusted by the concentration of the easily hydrolyzable organosilicate used. A relatively low silica concentration is preferable because the hydrolysis reaction proceeds smoothly, but if it is too low, the yield tends to decrease. Conversely, if the silica concentration is too high, the hydrolysis reaction tends to proceed more slowly, resulting in a large amount of alkoxy groups remaining in the easily hydrolyzable organosilicate. Therefore, the preferred lower limit of the silica concentration after the reaction is 2% by mass or more, more preferably 4% by mass or more, even more preferably 6% by mass or more, and even more preferably 8% by mass or more. On the other hand, the preferred upper limit of the silica concentration after the reaction is 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0049] The supply time (hr) of the easily hydrolyzable organosilicate refers to the time required to supply the easily hydrolyzable organosilicate to a reaction solution containing a hydrolysis catalyst consisting of one or a mixture of two or more organic amines. In this context, the supply time refers to the actual time required for the colloidal silica growth reaction. For example, in a method in which an easily hydrolyzable organosilicate is further supplied to a reaction solution containing colloidal silica seed particles having particle growth properties to grow particles, as in some of the methods described in the Examples below, the supply time required for the reaction to obtain the seed particles is not included in the supply time when calculating the production condition constants. That is, in this method, the actual time required for supplying the easily hydrolyzable organosilicate to the reaction solution containing the seed particles is used as the supply time when calculating the production condition constants. The reason for not including the supply time required for the reaction to obtain the seed particles is that, at least within the above-described roughness range characterized by this invention, the surface roughness of the seed particles is completely covered during the subsequent growth reaction, and therefore does not affect the surface roughness of the colloidal silica obtained in the end. Similarly, even when seed particles (grown seed particles) obtained by growing seed particles are used to carry out a reaction to further grow the grown seed particles, the time required for the reaction to obtain the grown seed particles is not included in the supply time when calculating the manufacturing condition constants. The supply time used to calculate the manufacturing condition constants is preferably 1 to 100 hours. A relatively long supply time is preferable because it improves the hydrolysis reaction, but if it is too long, the yield tends to decrease. Conversely, if the supply time is too short, the hydrolysis reaction tends to proceed more slowly, leaving many alkoxy groups in the easily hydrolyzable organosilicate. Therefore, the upper limit of the supply time is preferably 50 hours or less, and even more preferably 20 hours or less.

[0050] The reaction temperature (°C) is preferably 40°C or higher and 100°C or lower, more preferably 55°C or higher and 80°C or lower. A low temperature tends to result in a smaller particle size and greater irregularities, but a temperature that is too low is undesirable because the hydrolysis reaction proceeds relatively slowly, resulting in the formation of aggregates. A high reaction temperature also tends to result in a larger particle size and less irregularities, but a temperature that is too high causes the reaction solution to boil, facilitating the formation of side reactions and the formation of small particles. As with the supply time described above, the reaction temperature used to calculate the production condition constants is not the reaction temperature used in the reaction to obtain seed particles, but rather the reaction temperature in the growth reaction of colloidal silica, particularly the maximum reaction temperature.

[0051] The readily hydrolyzable organosilicate preferably used in the present invention is one in which 10 g of organosilicate and 100 g of pure water containing 0.1 ppb or less are hydrolyzed with stirring at 25°C, with the hydrolysis reaction completing within 1 hour. Specific examples of such readily hydrolyzable organosilicate include trimethyl silicate (hydrolysis reaction time until completion: approximately 3 minutes), tetramethyl silicate (hydrolysis reaction time: approximately 5 minutes), triethyl silicate (hydrolysis reaction time: approximately 5 minutes), and methyl trimethyl silicate (hydrolysis reaction time: approximately 7 minutes). Tetraethyl silicate and organosilicates with a higher carbon number than tetraethyl silicate have a slow hydrolysis rate and tend to gel (hydrolysis reaction time: 24 hours or more for both), so the aforementioned readily decomposable organosilicates are preferably used.

[0052] In addition, the organic amines suitable for use as hydrolysis catalysts in the present invention are not limited, and can be one or a mixture of two or more selected from quaternary ammoniums, tertiary amines, secondary amines, primary amines, and their carbonates, bicarbonates, and silicates. Examples of quaternary ammoniums include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), trimethylethylammonium hydroxide, trimethylethanolammonium hydroxide (choline), triethylethanolammonium hydroxide, tetrapropylammonium hydroxide, and butylammonium hydroxide, as well as their carbonates, bicarbonates, and silicates. Since a relatively high pH is desirable for the hydrolysis reaction, tetramethylammonium hydroxide (TMAH), choline, or tetraethylammonium hydroxide (TEAH) is preferred.

[0053] Furthermore, the organic amines used as hydrolysis catalysts, such as primary amines, secondary amines, and tertiary amines, are not limited to, and examples thereof include aminoalcohols, morpholines, piperazines, aliphatic amines, aliphatic ether amines, etc. Here, various aminoalcohols including ethanolamine derivatives can be used, with ethanolamine derivatives being preferred, such as monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-di-n-butylethanolamine, N-(β-aminoethyl)ethanolamine, N-methylethanolamine, N-methyldiethanolamine, N-ethylethanolamine, Nn-butylethanolamine, Nn-butyldiethanolamine, N-tert-butylethanolamine, and N-tert-butyldiethanolamine.

[0054] Furthermore, various morpholine derivatives can be used as the morpholine organic amines used as hydrolysis catalysts, with preferred examples including morpholine, N-methylmorpholine, and N-ethylmorpholine. Furthermore, various piperazine derivatives can be used as the piperazine organic amines used as hydrolysis catalysts, with preferred examples including piperazine and hydroxyethylpiperazine. Regarding the aliphatic amines and aliphatic etheramines used as the hydrolysis catalysts, preferred examples of the aliphatic amines include alkylamines having 1 to 8 carbon atoms, such as triethylamine, dipropylamine, pentylamine, hexylamine, heptylamine, and octylamine. Preferred examples of the aliphatic 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.

[0055] The organic amines used as the hydrolysis catalyst may be used alone or, if necessary, as a mixture of two or more kinds.

[0056] The reaction liquid contains the easily hydrolyzable organosilicate and hydrolysis catalyst as described above, but may also contain water, alcohols, aldehydes, ketones, surfactants, etc. Preferably, the reaction liquid contains the easily hydrolyzable organosilicate, hydrolysis catalyst, and water in a total amount of 90% by mass or more, and more preferably 95% by mass or more.

[0057] In the mixture obtained after the reaction of the easily hydrolyzable organosilicate with the hydrolysis catalyst (hereinafter sometimes referred to as the "reaction mixture"), or in the reaction mixture that has subsequently been subjected to treatments such as alcohol removal and acid dispersion stabilization, as described below (hereinafter sometimes referred to as the "reaction concentrate"), the ratio of the hydrolysis catalyst (A) to the easily hydrolyzable organosilicate (B) {catalyst residual molar ratio (A / B)} is preferably 0.012 or less, more preferably 0.00035 to 0.012, and even more preferably 0.0035 to 0.011, and the hydrolysis reaction is carried out by adding the hydrolysis catalyst to the reaction system. This is preferable because it allows the pH of the reaction mixture or reaction concentrate to be optimized and also prevents thickening and gelation.

[0058] The method for achieving such a catalyst remaining molar ratio is not particularly limited, and examples thereof include a method in which an easily hydrolyzable organosilicate calculated so that the final catalyst remaining molar ratio (A / B) falls within the above-mentioned range is continuously or intermittently introduced into a reaction vessel charged with water and the hydrolysis catalyst (A). Furthermore, examples of methods in which the hydrolysis catalyst and the easily hydrolyzable organosilicate are charged from separate supply routes include a method in which the hydrolysis catalyst and the easily hydrolyzable organosilicate calculated so that the final catalyst remaining molar ratio falls within the above-mentioned range are continuously or intermittently introduced into a reaction vessel charged with only water, and a method in which the hydrolysis catalyst and the easily hydrolyzable organosilicate calculated so that the final catalyst remaining molar ratio falls within the above-mentioned range are continuously or intermittently introduced into a reaction vessel charged with water and a small amount of the hydrolysis catalyst (A).

[0059] 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 remaining catalyst molar ratio (A / B) falls within the above-mentioned range. This is preferred because it allows the production of colloidal silica having uniform particles.

[0060] As described above, the easily hydrolyzable organosilicate, hydrolysis catalyst, and water used as raw materials for the hydrolysis reaction should have a low content of metal impurities.

[0061] Here, in the present invention, after the reaction between the easily hydrolyzable organosilicate and the hydrolysis catalyst, it is preferable to remove the alcohol generated from the hydrolyzable organosilicate. The method for such alcohol removal treatment is not particularly limited, but an example is a method in which the alcohol is distilled by heating using an apparatus equipped with a distillation tube with a condenser. By performing such alcohol removal treatment, it is not necessary to consider the alcohol resistance of materials used in subsequent steps, and the elimination of highly volatile alcohol is advantageous in terms of stabilizing the concentration of colloidal silica, etc.

[0062] Next, it is preferable to stabilize the dispersion of the reaction mixture after the alcohol removal treatment described above with an acid. Such a dispersion stabilization treatment can be carried out by a carbon dioxide gas injection method in which carbon dioxide gas is injected or an acid solution addition method in which an acid solution is added under stirring. Either the carbon dioxide gas injection method or the acid solution addition method can be used, or these methods can be used in combination. In either case, during the dispersion stabilization treatment, it is necessary to maintain the reaction mixture in an agitated state by operations such as bubbling with carbon dioxide gas or stirring.

[0063] When the dispersion stabilization treatment is carried out by the carbon dioxide gas injection method, the carbon dioxide gas injected into the reaction mixture may be 100% by volume carbon dioxide gas, or may be inert gas-diluted carbon dioxide gas diluted to about 0.1% by volume with an inert gas such as nitrogen gas, or may even be air, but is preferably 100% by volume carbon dioxide gas or inert gas-diluted carbon dioxide gas of 1% by volume or more.

[0064] As for the treatment conditions for this carbon dioxide gas injection method, since the injection of carbon dioxide gas itself has a stirring effect, it is preferable to introduce carbon dioxide gas into the reaction mixture under stirring usually at a rate of 0 rpm to 3000 rpm, preferably 0 rpm to 1000 rpm, at a temperature higher than 0°C but lower than 100°C, preferably 5°C to 80°C, at a rate preferably exceeding 0 mL / min and not exceeding 100,000 mL / min, more preferably 1 mL / min to 10,000 mL / min.

[0065] Furthermore, when the dispersion stabilization treatment is carried out by the acid solution addition method, the acid solution used is preferably an aqueous acid solution having a concentration of 20% by weight or less, and is one or a mixture of two or more selected from an aqueous carbonic acid solution, a dilute mineral acid solution having a concentration of 20% by weight or less, and a dilute organic acid solution having a concentration of 20% by weight or less, and is preferably one or a mixture of two or more selected from a dilute mineral acid solution having a concentration of 10% by weight or less and a dilute organic acid solution having a concentration of 10% by weight or less. Specific examples of the acid include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, lactic acid, diglycolic acid, 2-furancarboxylic acid, 2,5-furandicarboxylic acid, 3-furancarboxylic acid, 2-tetrahydrofurancarboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, phenoxyacetic acid, methanesulfonic acid, ethanesulfonic acid, and isethionic acid, and the like, and the like, and the like, and the like.

[0066] The treatment conditions for this acid aqueous solution addition method are as follows: stirring is usually at 1 rpm or more and 3000 rpm or less, preferably 10 rpm or more and 1000 rpm or less, at a temperature usually at 0°C or more and 100°C or less, preferably 5°C or more and 80°C or less; and the acid solution is added in an amount of usually 0.0001 mol or more and 10 mol or less, preferably 0.001 mol or more and 1 mol or less, relative to 1 mol of catalyst in the reaction mixture to be treated.

[0067] In the production method of the present invention, it is also preferable to prevent the easily hydrolyzable organosilicate from scattering when being supplied, thereby preventing it from scattering onto the surrounding walls of the reaction vessel and the like and causing side reactions. If the easily hydrolyzable organosilicate scatters onto the surrounding walls of the reaction vessel, it may come into contact with water droplets adhering to the surrounding walls and cause side reactions, resulting in unwanted colloidal silica being mixed into the reaction liquid.

[0068] Therefore, in the production method of the present invention, it is preferable to supply the silica source to the reaction solution through a supply port immersed in the reaction solution surface. By immersing the supply port in the reaction solution surface and supplying (discharging) the silica source within the reaction solution, scattering of the silica source at the supply port or the reaction solution surface can be minimized compared to aerial injection, in which the supply is performed from outside the reaction solution (in the air above the reaction solution surface). In this case, the supply port is preferably immersed for a sufficient length so that the easily hydrolyzable organosilicate supplied (discharged) from the supply port does not splash out above the reaction solution surface. More preferably, the length of the immersed supply port is at least three times the outer diameter of the supply port (the outer diameter of the outer tube when a double-tube nozzle described below is used). The upper limit of the length of the immersed supply port can be determined taking into account contact with other equipment (e.g., a stirrer, the wall or bottom of the reaction vessel, etc.), and is preferably a length that does not contact the bottom surface inside the reaction vessel. The supply port may be any known shape and size without limitation as long as it does not impair the object of the present invention, and may be a commonly used nozzle or pipe having a circular or rectangular discharge portion. The outer diameter of the supply port is not limited, but may usually be about 1 mm to 100 mm. Similarly, the reaction vessel in which the reaction is carried out may be any known shape and size without limitation.

[0069] Furthermore, when the easily hydrolyzable organosilicate is supplied (discharged) while the supply port is immersed in the reaction liquid, it is preferable to use a means for promoting or assisting the supply (discharge). Examples of such a means include using an inert gas or a neutral gas that does not react with the easily hydrolyzable organosilicate, water, or catalyst. More preferably, a supply port for supplying an inert gas is provided adjacent to or separately from the supply port for the easily hydrolyzable organosilicate, thereby promoting or assisting the supply (discharge) of the easily hydrolyzable organosilicate into the reaction liquid. Inert gases such as nitrogen, argon, and helium can be used appropriately depending on the purpose. The use of such a means is preferable because it allows the hydrolysis reaction to proceed sufficiently without problems such as retention of the supplied easily hydrolyzable organosilicate near the supply port or clogging due to side reactions.

[0070] In order to more reliably supply the easily hydrolyzable organosilicate to the reaction solution, a preferred embodiment is to use a nozzle having an inner / outer double-pipe structure equipped with an outer pipe and an inner pipe inserted into the outer pipe as a means for supplying the easily hydrolyzable organosilicate, and to supply the silica source or inert gas from each pipe. In this case, in order to prevent the easily hydrolyzable organosilicate from scattering from the supply port, it is preferable to flow the easily hydrolyzable organosilicate through the inner pipe and the inert gas through the outer pipe. Any nozzle having a known double-pipe structure can be used for such a double-pipe structure without any restrictions. In this case, the pipes may be multiple, as long as they are equipped with at least a double pipe for supplying the easily hydrolyzable organosilicate and the inert gas.

[0071] Regarding the diameters of the tubes through which the respective substances are flowed using such a nozzle having a double-tube structure, it is preferable that the ratio O / I of the outer diameter (I) of the inner tube through which the silica source is supplied to the inner diameter (O) of the outer tube through which the inert gas is supplied is set to be 1 to 10. By setting such an O / I ratio, the effect and efficiency of supplying the inert gas from the outer tube can be improved, and retention and clogging near the supply port of the silica source can be suppressed, which tends to realize a more reliable supply of the silica source.

[0072] The inner diameters of the respective tubes can be appropriately set depending on the scale of production, the supply amount, the flow rate, etc., but the outer diameter (I) of the inner tube for supplying the silica source is usually 5 to 96 mm, more preferably 4 to 99 mm. The inner diameter (O) of the outer tube for supplying the inert gas is usually 4 to 99 mm, more preferably 6 to 98 mm.

[0073] Furthermore, in such an embodiment, it is preferable to make the length of the outer tube through which the inert gas flows longer than the length of the inner tube through which the easily hydrolyzable organosilicate flows, since this improves the effectiveness and efficiency of supplying the inert gas from the outer tube, making it possible to prevent stagnation or clogging near the supply port of the easily hydrolyzable organosilicate and tends to achieve reliable supply.

[0074] Preferred embodiments of the present invention will be specifically described below based on examples and comparative examples.

[0075] Example 1: A 1000-liter (L) stainless steel reactor equipped with a stirrer, temperature sensor, heated steam pipe, cooling water pipe, exhaust gas pipe, and double-walled organosilicate inlet pipe was charged with 542.58 kg of pure water containing 0.1 ppb or less of metal impurities and 0.84 kg of triethanolamine. After charging, it was confirmed that the double-walled organosilicate inlet pipe was immersed 20 cm below the liquid surface while stirring. The outer tube of the double-walled pipe had an outer diameter of 25.4 mm, an inner diameter of 22 mm, and an internal length of 723 mm. The inner tube had an outer diameter of 6.35 mm, an inner diameter of 3.5 mm, and an internal length of 553 mm. After confirmation, while maintaining the liquid temperature in the reaction vessel at 70 ° C. using steam and cooling water, 198.19 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was flowed into the inside of the double pipe, and nitrogen was continuously supplied over 10 hours with stirring at 0.5 L / min while flowing into the outer pipe. Thereafter, the temperature in the reaction vessel was lowered to 40 ° C., and a 12% by mass reaction product was obtained. This reaction product was transferred to a 500 L stainless steel distillation vessel equipped with a stirrer, temperature sensor, pressure sensor, liquid level control sensor, heating steam piping, cooling water piping, and an 800 L stainless steel distillate receiver-equipped condenser connected to the exhaust gas piping, and a 500 L stainless steel intermediate vessel. Then, the heated and evaporated gas was cooled in the condenser and distilled into the distillate receiver. Each time the liquid in the distillation vessel decreased, the reaction crude product was supplied from the intermediate tank. After the reaction crude product was exhausted from the intermediate tank, 125.2 kg of pure water was supplied, and the solvent was replaced with water to obtain a concentrated 20% by mass colloidal silica. Carbon dioxide gas was blown into this concentrate at 1.2 L / min for 10 minutes to perform a dispersion stabilization treatment, and then observation under an electron microscope confirmed that the particles were spherical with a uniform particle size and smooth surface. Image analysis was performed using the procedure described below to measure the projected area [A] and perimeter [L] of the particles, and the roughness was calculated using the formula described below. An SEM photograph is shown in Figure 1, STEM photographs are shown in Figures 2 and 9, and other analytical results are shown in Tables 1 to 3.

[0076] [Example 2] In an apparatus similar to that of Example 1, 179.78 kg of the reaction product of Example 1 as seed particles, 392.47 kg of pure water with a metal impurity content of 0.1 ppb or less, and 1.24 kg of triethanolamine were charged. After charging, while maintaining the liquid temperature in the reaction vessel at 80°C, 42.04 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was flowed into the inside of the double-walled tube, and nitrogen was continuously supplied to the outer tube at 0.5 L / min over 10 hours with stirring. A 12% by mass reaction product was obtained, after which a distillation process similar to that of Example 1 was performed. After a dispersion stabilization process of the concentrate was performed, observation with an electron microscope confirmed that the particles were spherical particles with a uniform particle size and smooth surfaces. The following analysis was performed in the same manner as in Example 1. An STEM photograph is shown in FIG. 9, and other analytical results are shown in Tables 1 to 3.

[0077] [Example 3] In an apparatus similar to that of Example 1, 73.39 kg of the reaction product of Example 1 as seed particles, 386.45 kg of pure water with a metal impurity content of 0.1 ppb or less, and 1.21 kg of triethanolamine were charged. After charging, while maintaining the liquid temperature in the reaction vessel at 80 °C, 167.72 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was flowed into the inside of the double-walled tube, and while flowing nitrogen at 0.5 L / min into the outer tube, it was continuously supplied over 10 hours with stirring. A 12% by mass reaction product was obtained, after which a distillation process similar to that of Example 1 was performed. After a dispersion stabilization process of the concentrate was performed, observation with an electron microscope confirmed that the particles were spherical particles with a uniform particle size and smooth surfaces. The following analysis was performed in the same manner as in Example 1. SEM photographs are shown in FIG. 3, STEM photographs are shown in FIGS. 4 and 9, and other analysis results are shown in Tables 1 to 3.

[0078] [Example 4] In an apparatus similar to that of Example 1, 66.71 kg of the reaction product of Example 1 as seed particles, 507.04 kg of pure water with a metal impurity content of 0.1 ppb or less, and 1.30 kg of triethanolamine were charged. After charging, while maintaining the liquid temperature in the reaction vessel at 80 °C, 166.57 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was flowed into the inside of the double-walled tube, and nitrogen was continuously supplied to the outer tube at 0.5 L / min over 6 hours with stirring. After obtaining a 10% by mass reaction product, the same distillation process as in Example 1 was performed. After performing a dispersion stabilization process on the concentrate, electron microscopy confirmed that the product was spherical particles with a uniform particle size and smooth surfaces. The following analysis was performed in the same manner as in Example 1. STEM photographs are shown in FIG. 9, and other analysis results are shown in Tables 1 to 3.

[0079] Example 5: In an apparatus similar to that of Example 1, 53.36 kg of the reaction product from Example 1 as seed particles, 553.64 kg of pure water with a metal impurity content of 0.1 ppb or less, and 1.31 kg of triethanolamine were charged. After charging, while maintaining the liquid temperature in the reaction vessel at 80°C, 133.25 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was flowed into the inside of the double-walled tube, and nitrogen was continuously supplied to the outer tube at 0.5 L / min over 10 hours with stirring. After obtaining an 8% by mass reaction product, the same distillation process as in Example 1 was performed. After the concentrate was subjected to a dispersion stabilization treatment, electron microscopy confirmed that the product was spherical particles with a uniform particle size and smooth surfaces. The following analysis was performed in the same manner as in Example 1. STEM photographs are shown in FIG. 9, and other analytical results are shown in Tables 1 to 3.

[0080] Example 6: 437.51 kg of pure water with a metal impurity content of 0.1 ppb or less and 0.32 kg of 3-ethoxypropylamine were charged into an apparatus similar to that used in Example 1. After charging, while maintaining the liquid temperature in the reaction vessel at 70°C, 190.92 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was flowed into the inside of the double-walled pipe, and nitrogen was continuously supplied to the outer pipe at 0.5 L / min over 6 hours with stirring. The temperature in the reaction vessel was then lowered to 40°C, and a 12% by mass reaction product was obtained. 96.54 kg of this reaction product as seed particles, 486.87 kg of pure water with a metal impurity content of 0.1 ppb or less, and 0.88 kg of 3-ethoxypropylamine were charged into an apparatus similar to that used in Example 1. After charging, while maintaining the liquid temperature in the reaction vessel at 85 ° C., 157.34 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was flowed into the inside of the double-walled tube, and nitrogen was continuously supplied to the outer tube at 0.5 L / min while stirring for 6 hours, obtaining a 10 mass % reaction product, which was then subjected to a distillation treatment similar to that in Example 1, and the concentrate was subjected to a dispersion stabilization treatment. After that, it was confirmed by observation with an electron microscope that the particles were spherical particles with a uniform particle size and smooth surfaces. The following analysis was performed in the same manner as in Example 1, and an STEM photograph is shown in Figure 9, and other analysis results are shown in Tables 1 to 3.

[0081] Comparative Example 1: 521.23 kg of pure water with a metal impurity content of 0.1 ppb or less and 0.56 kg of triethanolamine were charged into the same apparatus as in Example 1. Then, while maintaining the liquid temperature in the reaction vessel at 70 ° C, 227.45 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was flowed into the inside of the double-walled tube, and nitrogen was continuously supplied to the outer tube at 0.5 L / min over 6 hours with stirring. A 12% by mass reaction product was obtained, and then the same distillation process as in Example 1 was carried out. After the concentrate was subjected to a dispersion stabilization process, observation under an electron microscope confirmed that the particles were spherical particles with uniform particle size and protrusions. The following analysis was carried out in the same manner as in Example 1. SEM photographs are shown in FIG. 5, STEM photographs are shown in FIGS. 6 and 9, and other analysis results are shown in Tables 1 to 3.

[0082] Comparative Example 2: 181.73 kg of the reaction solution from Comparative Example 1 was charged as seed particles, along with 396.73 kg of pure water containing 0.1 ppb or less of metal impurities and 1.23 kg of triethanolamine, into an apparatus similar to that used in Example 1. Then, while maintaining the liquid temperature in the reaction vessel at 70°C, 170.00 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was poured into the inside of the double-walled tube, and nitrogen was continuously supplied to the outer tube at 0.5 L / min over 6 hours with stirring. A 12% by mass reaction product was obtained, followed by a distillation treatment similar to that used in Example 1. The concentrate was then subjected to a dispersion stabilization treatment, and observation under an electron microscope confirmed that the product was spherical particles with uniform particle size and protrusions. The product was then analyzed in the same manner as in Example 1. The STEM photograph is shown in FIG. 9, and other analytical results are shown in Tables 1 to 3.

[0083] Comparative Example 3: 87.50 kg of the reaction solution from Comparative Example 1 was charged as seed particles, along with 458.07 kg of pure water containing 0.1 ppb or less of metal impurities and 1.44 kg of triethanolamine, into an apparatus similar to that used in Example 1. After charging, while maintaining the liquid temperature in the reaction vessel at 80°C using steam and cooling water, 199.88 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was passed through the inside of the double-walled tube, and nitrogen was continuously supplied to the outer tube at 0.5 L / min over 6 hours with stirring. A 12% by mass reaction product was obtained, which was then subjected to a distillation treatment similar to that used in Example 1. The concentrate was then subjected to a dispersion stabilization treatment. Observation under an electron microscope confirmed that the product was spherical particles with uniform particle size and protrusions. The product was analyzed in the same manner as in Example 1, with SEM photographs shown in FIG. 7, STEM photographs shown in FIGS. 8 and 9, and other analytical results shown in Tables 1 to 3.

[0084] Comparative Example 4: 526.45 kg of seed particles of the reaction product obtained under the same conditions as in Example 6, 2218.66 kg of pure water with a metal impurity content of 0.1 ppb or less, and 2.36 kg of 3-ethoxypropylamine were charged into the same apparatus as in Example 1. After charging, while maintaining the liquid temperature in the reaction vessel at 80°C, 180.04 kg of tetramethyl silicate (silica source; manufactured by Tama Chemicals Co., Ltd.) with a metal impurity content of 10 ppb or less was flowed into the inside of the double-walled pipe, and nitrogen was continuously supplied over 3 hours with stirring at 0.5 L / min while flowing into the outer pipe. 12% by mass of the reaction product was obtained, and then subjected to a distillation process similar to that in Example 1. After performing a dispersion stabilization process on the concentrate, observation with an electron microscope confirmed that the product was spherical particles with a uniform particle size and protrusions. The following analysis was performed in the same manner as in Example 1. STEM photographs are shown in FIG. 9, and other analytical results are shown in Tables 1 to 3.

[0085]

[0086]

[0087]

[0088] The physical properties of the resulting colloidal silica were evaluated by the following methods: (1) Silica concentration: The residue after evaporation of the contained water was taken as the silica concentration.

[0089] (2) pH: Measured at 25°C.

[0090] (3) Average particle size (nm): The median value of the particle size distribution measured using a disk centrifugal particle size distribution measuring device manufactured by CPS Instruments, USA, was taken as the average particle size (nm).

[0091] (4) Electron microscope (SEM, STEM) observation: Colloidal silica was diluted with water, placed on a TEM indicator film, and then dried. Using a Hitachi High-Technologies Corporation ultra-high resolution field emission scanning electron microscope SU9000, observation was performed at a magnification of 200,000 to 500,000 times, so that 20 or more particles were included in one field of view. The obtained STEM image was imported into Hakuto's Image-Pro software, and the particle projected area [A] and perimeter [L] were measured. The results were then imported into calculation software, and compared with the SEM image taken at the same time, and data on overlapping particles and particles cut off from surrounding particles was removed. The diameter [r1 = 2(A / π)] was calculated from the projected area A of the remaining particles, assuming an ideal circle. ０．５ ] was taken as the area-equivalent circle diameter (r1). In addition, the diameter calculated from the perimeter L assuming an ideal circle [r2 = L / π] was taken as the perimeter-equivalent circle diameter (r2), and the average value of r2 / r1 of 300 randomly selected particles from the remaining particles was taken as the irregularity. Figure 9 shows photographs of particles extracted one by one and adjusted to the same size.

[0092] (5) BET specific surface area: The BET specific surface area of ​​the spherical colloidal silica particles constituting the colloidal silica particles was measured by the nitrogen adsorption method (BET method).

[0093] (6) BET particle size: BET specific surface area Sm ２ / g, D ２ Particle diameter D calculated by the formula ２ .

[0094] (7) Silanol group (SiOH) density: A sample equivalent to 1.5 g of silica is placed in a beaker. While maintaining the temperature at 25°C using a thermostatic bath, pure water is added to bring the volume to 90 mL. 0.1 mol / L hydrochloric acid is added to adjust the pH to 3.6-3.7. 30 g of sodium chloride is added, and the solution is diluted to 150 mL with pure water and stirred for 10 minutes. A pH electrode is attached, and while stirring, 0.1 mol / L sodium hydroxide solution is added dropwise to adjust the pH to 4.0. The sample adjusted to pH 4.0 is titrated with 0.1 mol / L sodium hydroxide solution, and the titration volume and pH value are recorded at four or more points in the pH range of 8.7-9.3. A calibration curve is created, with the titration volume of 0.1 mol / L sodium hydroxide solution represented as X and the pH value at that time represented as Y. The titration volume V (mL) for the range from pH 4.0 to 9.0 is calculated using the following formula: V = (A x f x 100 x 1.5) / (W x C) where A is SiO ２ is the amount (mL) of 0.1 mol / L sodium hydroxide solution titrated per 1.5 g to bring the pH from 4.0 to 9.0, f is the titer of 0.1 mol / L sodium hydroxide solution, and C is the SiO ２ The sodium hydroxide consumption (mmol / g) per 1 g of silica is calculated using the following formula: Titration volume of sodium hydroxide solution from pH 4.0 to 9.0 V (mL) / 1.5 (g) x 0.1 (mol / L) The amount of silanol substance per unit surface area (mmol / m ２ ) is calculated by the sodium hydroxide consumption per 1 g of silica (mmol / g) / BET specific surface area (m ２ / g) From the following formula, the silanol group density per unit surface area (number / nm ２ ) is calculated. The amount of silanol substance per unit surface area (mmol / m ２ ) x 10 －３ x10 －１８ x 6.02 x 10 ２３ (number / mol) Furthermore, the number of silanol groups per 1 g (×10 ２０ The sodium hydroxide consumption per 1 g of silica (mmol / g) is calculated by multiplying the amount by 10 －３ x 6.02 x 10 ２３ (pieces / mol)

[0095] (8) TD-NMR: Transverse relaxation time T2 of a colloidal silica solution measured using a TD-NMR apparatus minispec mq20 manufactured by Bruker. The measurement conditions were: magnetic field: 0.47 T, measurement frequency: 20 MHz, measurement nucleus: １ H NMR, measurement method: CPMG pulse sequence method, measurement temperature: 40°C.

[0096] (9) Metal impurity content: Metal impurities (total of Na, Fe, Cu, Al, K, Cr, Ni, Pb, Mn, Mg, Zn, and Ca) were measured using an atomic absorption spectrophotometer on a 10 g sample.

[0097] (10) Method for measuring changes over time: Each of the solutions of Examples 1 to 6 and Comparative Examples 1 to 4 was dispensed into three 250 mL polypropylene containers: one for STEM observation, silica concentration and pH measurement, one for TD-NMR measurement, and one for BET specific surface area, average particle size and silanol group density measurement. The containers were then placed in a constant temperature dryer at 60°C and allowed to cool to room temperature after 7 days, after which the respective analyses were carried out.

[0098] 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. A colloidal silica characterized by simultaneously satisfying the following (1) and (2): (1) The degree of irregularity represented by the following formula (i) is 1.0740 or less: degree of irregularity = equivalent circle diameter converted from the perimeter determined from a projected image obtained by image analysis using an electron microscope (equivalent circle diameter converted from perimeter) / equivalent circle diameter converted from the projected area obtained by image analysis using an electron microscope (equivalent circle diameter converted from area) ... (i) (2) Metal impurities are 1 ppm or less.

2. The colloidal silica according to claim 1, wherein the rate of change in silanol group density after being kept at 60° C. for 7 days is minus 5% or more.

3. Nuclides measured by time-domain nuclear magnetic resonance after being kept at 60°C for 7 days １ 2. The colloidal silica according to claim 1, wherein the rate of change in transverse relaxation time of H is 24% or less.

4. Silanol group density is 3 / nm ２ 2. The colloidal silica according to claim 1, wherein the colloidal silica is:

5. Nuclides measured by time-domain nuclear magnetic resonance １ 2. The colloidal silica according to claim 1, characterized in that the transverse relaxation time of H is 650 ms or more and less than 1,300 ms.

6. The colloidal silica according to claim 1, characterized in that the electron microscope is one or more of a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), and a transmission electron microscope (TEM).

7. A polishing agent comprising the colloidal silica according to any one of claims 1 to 6.

8. A method for producing colloidal silica by supplying an easily hydrolyzable organosilicate to a reaction liquid containing a hydrolysis catalyst consisting of one or a mixture of two or more organic amines, and reacting the organosilicate with the reaction liquid, wherein the production condition constant represented by the following formula (ii) is 0.024 or less. Production condition constant=silica concentration after reaction (mass%) / supply time of easily hydrolyzable organosilicate (hr) / reaction temperature (° C.) (ii)

Images