Method for producing aqueous-dispersible colloidal silica

Abstract

To provide a simple method for producing water-dispersible colloidal silica with a very low content of fine particles. [Solution] A method for producing water-dispersible colloidal silica comprising the following steps (A1), (B1), (C), and (D). Step (A1): A step to obtain colloidal silica (A1) by hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), its partially hydrolyzed condensate, or a mixture thereof in a solution containing a hydrophilic organic solvent and water in the presence of a basic substance. Si(OR 1 )4(I)(wherein, R 1 (Each represents a monovalent hydrocarbon group with 1 to 6 carbon atoms.) Step (B1): A step in which hydrophilic organic solvents in the dispersion medium are replaced with water. Process (C): A process to reduce the proportion of particles with a particle size of less than 20 nm in colloidal silica to 10% or less by centrifugal separation with a centrifugal force of 10,000 G or more. Step (D): The process of filtering colloidal silica using a filter.

Description

[Technical Field]

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

[0002] With the recent advancements in semiconductor devices, there is a growing demand for high-purity colloidal silica used in processes such as silicon wafer polishing and chemical mechanical polishing (CMP) of semiconductor devices, in order to prevent contamination of silicon wafers and other materials.

[0003] In particular, the presence of fine particles in colloidal silica causes various problems during the polishing process, such as the fine particles remaining on the polished surface, making cleaning difficult, worsening the polishing rate, and even reducing the yield in semiconductor manufacturing. From this perspective, various proposals have been made for colloidal silica with fewer fine particles.

[0004] Patent Document 1 discloses a method for obtaining colloidal silica with fewer fine particles by adjusting the electrical conductivity during the hydrolysis and condensation reactions of alkoxysilanes or their condensates. Furthermore, Patent Documents 2 and 3 state that colloidal silica with fewer fine particles can be obtained by adjusting the water concentration in the reaction system during the hydrolysis and condensation reaction of tetraalkoxysilane.

[0005] Patent Document 4 discloses a method of reducing fine particles by heating and distilling to reduce the organic solvent concentration to less than 1% by mass, Patent Document 5 discloses a method of reducing intermediate products by adding a neutral oxidizing agent (hydrogen peroxide), and Patent Document 6 discloses a method of removing intermediate products using an ultrafiltration membrane with a molecular weight cutoff of 5,000 to 80,000. Patent Document 7 discloses a method of reducing fine particles by reacting at atmospheric pressure for 11 to 35 hours at the boiling point of water and at a pH of 9.0 to 10.5.

[0006] However, there has been a demand for a method capable of achieving a reduction in the level of fine particles required in the CMP process at a lower cost and in a shorter time.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, an object of the present invention is to provide a simple method for producing a water - dispersible colloidal silica having a very low content of fine particles.

Means for Solving the Problems

[0009] As a result of intensive research to achieve the above object, the present inventors have found that a water - dispersible colloidal silica having a very low content of fine particles can be obtained by a production method including specific steps, and have completed the present invention. That is, the present invention provides a method for producing the following colloidal silica.

[0010] <1> A method for producing water - dispersible colloidal silica having the following steps (A1), (B1), (C) and (D). Step (A1): Obtaining colloidal silica (A1) by hydrolytically condensing a tetrafunctional silane compound represented by the following formula (I), a partial hydrolyzate thereof, or a mixture thereof in a solution containing a hydrophilic organic solvent and water in the presence of a basic substance. Si(OR 1 )4(I) (In the formula, R 1 independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.) Step (B1): Replacing the hydrophilic organic solvent in the dispersion medium with water. Step (C): Centrifuging at a centrifugal force of 10,000 G or more to make the ratio of the number of particles having a particle size of less than 20 nm among all the particles in the colloidal silica 10% or less. Step (D): Filtering the colloidal silica through a filter. <2> A method for producing a water-dispersed colloidal silica according to <1>, having the following step (A2) after step (A1). Step (A2): Adding a trifunctional silane compound represented by the following formula (II), a partial hydrolyzate thereof, or a mixture thereof to the colloidal silica (A1) obtained in step (A1), and introducing an R 2 SiO 3 / 2 unit onto the surface of the colloidal silica to obtain surface-treated colloidal silica (A2). R 2 Si(OR 3 )3(II) (In the formula, R 2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and R 3 independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.) <3> A method for producing a water-dispersed colloidal silica according to <2>, having the following step (A3) after step (A2). Step (A3): Adding one or more dispersants selected from aspartic acid, glutamic acid, and citric acid to the surface-treated colloidal silica (A1) obtained in step (A1) to obtain dispersant-containing colloidal silica (A3). <4> The process (A1) is followed by the following process (A3'). <1> A method for producing water-dispersible colloidal silica as described above. Step (A3'): A step to obtain dispersant-containing colloidal silica (A3') by adding one or more dispersants selected from aspartic acid, glutamic acid, and citric acid to the surface-treated colloidal silica (A1) obtained in step (A1). <5> The process (B2) follows process (B1). <1> ~ <4> A method for producing aqueous-dispersible colloidal silica as described in any one of the items. Process (B2): Process of pressurizing and heating colloidal silica. <6> In the centrifugal separation of process (C), a disk-type centrifugal separator is used. <1> ~ <5> A method for producing aqueous-dispersible colloidal silica as described in any one of the items. <7> The Z-mean particle size of silica particles in water-dispersed colloidal silica, as determined by dynamic light scattering, is 20-100 nm. <1> ~ <6> A method for producing aqueous-dispersible colloidal silica as described in any one of the items. <8> In the particle size distribution of silica particles in aqueous-dispersed colloidal silica using the differential electrical mobility method, no particles smaller than 20 nm in diameter were observed. <1> ~ <7> A method for producing aqueous-dispersible colloidal silica as described in any one of the items. <9> In the particle size distribution of silica particles in aqueous-dispersed colloidal silica, measured by disk centrifugal particle size measurement, no particles with a diameter of less than 20 nm were observed. <1> ~ <8> A method for producing aqueous-dispersible colloidal silica as described in any one of the items. <10> In a field emission scanning electron microscope image of silica particles in aqueous-dispersed colloidal silica, the proportion of particles with a particle size of less than 20 nm relative to the total number of silica particles is 10% or less. <1> ~ <9> A method for producing aqueous-dispersible colloidal silica as described in any one of the items. <11> The production method of the aqueous-dispersed colloidal silica according to any one of <1> to <10>, wherein the number of coarse particles of 0.5 μm or more measured by a particle counter of the aqueous-dispersed colloidal silica is 300,000 particles / mL or less.

Advantages of the Invention

[0011] The colloidal silica obtained by the production method of the present invention is useful as an abrasive grain for polishing a silicon wafer, a CMP process of a semiconductor device, etc., because reduction of fine particles and a silica precursor can be achieved at a lower cost and in a shorter time.

Brief Description of the Drawings

[0012] [Figure 1] It is a FE-SEM image of the aqueous-dispersed colloidal silica (i) obtained in Example 1. [Figure 2] It is a FE-SEM image of the aqueous-dispersed colloidal silica (ix) obtained in Comparative Example 1.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail.

[0014] The production method of the aqueous-dispersed colloidal silica of the present invention has the following steps (A1), (B1), (C) and (D). Step (A1): A step of obtaining colloidal silica (A1) by hydrolytic condensation of a tetrafunctional silane compound represented by the following formula (I), a partial hydrolytic condensate thereof or a mixture thereof in a solution containing a hydrophilic organic solvent and water in the presence of a basic substance (step of obtaining colloidal silica) Si(OR 1 )4 (I) (In the formula, R 1 independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.) Step (B1): A step of replacing the hydrophilic organic solvent in the dispersion medium with water (step of replacing the dispersion medium) Process (C): A process (centrifugation process) in which the proportion of particles with a particle size of less than 20 nm among all particles in colloidal silica is reduced to 10% or less by centrifugal separation with a centrifugal force of 10,000 G or more. Process (D): Process of filtering colloidal silica through a filter (filter filtration process)

[0015] A preferred method for producing colloidal silica according to the present invention is a method comprising the above steps (A1), (B1), (C), and (D), and further comprising the following step (A2) after step (A1). Step (A2): Add a trifunctional silane compound represented by the following formula (II), its partially hydrolyzed condensate, or a mixture thereof to the colloidal silica (A1) obtained in step (A1), and apply R to the surface of the colloidal silica. 2 SiO 3 / 2 A process to introduce units and obtain surface-treated colloidal silica (A2) (surface treatment process using a trifunctional silane compound). R 2 Si(OR 3 )3(II) (In the formula, R 2 R represents a substituted or unsubstituted monovalent hydrocarbon group with 1 to 20 carbon atoms, 3 (Each represents a monovalent hydrocarbon group with 1 to 6 carbon atoms.)

[0016] A preferred method for producing colloidal silica according to the present invention is a method comprising the above steps (A1), (A2), (B1), (C), and (D), and further comprising the following step (A3) after step (A2). Step (A3): A step to obtain dispersant-containing colloidal silica (A3) by adding one or more dispersants selected from aspartic acid, glutamic acid, and citric acid to the surface-treated colloidal silica (A1) obtained in step (A1) (dispersant addition step).

[0017] A more preferable method for producing colloidal silica according to the present invention is a method comprising the above steps (A1), (B1), (C), and (D), and further comprising the following step (A3') after step (A1). Step (A3'): A step to obtain dispersant-containing colloidal silica (A3') by adding one or more dispersants selected from aspartic acid, glutamic acid, and citric acid to the surface-treated colloidal silica (A1) obtained in step (A1) (dispersant addition step).

[0018] A more preferable method for producing colloidal silica according to the present invention is a method comprising the above steps (A1), (B1), (C), and (D), and further comprising the following step (B2) after step (B1). Process (B2): Process of pressurized and heated colloidal silica (Pressurized heating process)

[0019] A more preferred method for producing colloidal silica according to the present invention is a method comprising the above steps (A1), (B1), (C), and (D), and after step (D), the following step (E). Process (E): Addition of disinfectant (Addition of disinfectant)

[0020] A more preferred method for producing colloidal silica according to the present invention is a method comprising the above steps (A1), (A2), (A3), (B1), (B2), (C), (D), and (E).

[0021] Particularly preferred as a method for producing colloidal silica according to the present invention is a method comprising the above steps (A1), (A3'), (B1), (B2), (C), (D), and (E).

[0022] The following describes each of the above steps.

[0023] Process (A1): Process for obtaining colloidal silica This process involves hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), its partially hydrolyzed condensate, or a mixture thereof in a solution containing a hydrophilic organic solvent and water in the presence of a basic substance to obtain colloidal silica (A1). Si(OR 1 )4(I) (In the formula, R 1(Each represents a monovalent hydrocarbon group with 1 to 6 carbon atoms.)

[0024] In the above equation (I), R 1 R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably having 1 to 4 carbon atoms, and particularly preferably having 1 to 2 carbon atoms. 1 Examples of monovalent hydrocarbon groups represented by include methyl, ethyl, propyl, butyl, and phenyl groups, with methyl, ethyl, propyl, and butyl groups being preferred, and methyl and ethyl groups being particularly preferred.

[0025] Examples of the tetrafunctional silane compound represented by formula (I) above include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and tetraphenoxysilane, with tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane being preferred, and tetramethoxysilane and tetraethoxysilane being particularly preferred. Examples of the partial hydrolysis condensates of the tetrafunctional silane compound represented by formula (I) above include methyl silicate and ethyl silicate.

[0026] Examples of basic substances include ammonia, dimethylamine, and diethylamine, with ammonia and diethylamine being preferred, and ammonia being particularly preferred. These basic substances can be used after being dissolved in water in the required amounts.

[0027] The hydrophilic organic solvent is not particularly limited as long as it dissolves the compound represented by formula (I) above and / or its partially hydrolyzed condensates and water. Examples include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and t-butanol; ethers such as tetrahydrofuran and dioxane; and glycols such as diethylene glycol and dipropylene glycol, with alcohols being preferred. As the number of carbon atoms in the alcohol increases, the particle size of the resulting silica particles increases, so the type of alcohol can be selected depending on the desired particle size of the silica particles. Among these, methanol and ethanol are particularly preferred. Note that the hydrophilic organic solvent may be used alone or in combination of two or more types.

[0028] In this process, a preferred method is to dropwise add (b) a tetrafunctional silane compound represented by the above formula (I), its partially hydrolyzed condensate, or a mixture thereof to a solution (a) containing water, a basic substance, and a hydrophilic organic solvent.

[0029] (a) The concentration of water in (a) is preferably 3% to 20% by mass, and more preferably 5% to 15% by mass, out of 100% by mass of (a), from the viewpoint of balancing hydrolysis and condensation reactions and controlling particle shape.

[0030] The concentration of the basic substance in (a) is preferably 0.5% to 2.0% by mass, and more preferably 0.6% to 1.5% by mass, of 100% by mass of (a), from the viewpoint of controlling the reaction and the dispersibility of the silica fine particles produced.

[0031] (b) may be used dissolved in a solution containing a hydrophilic organic solvent, and the concentration of the hydrophilic organic solvent in the solution containing component (b) is preferably 3% to 30% by mass, more preferably 5% to 20% by mass, of 100% by mass of the solution. Within this range, it is possible to suppress gel adhesion to the area around the discharge port and the inner wall of the reaction vessel when dispensing the solution containing component (b) dropwise.

[0032] Furthermore, it is preferable to add (c) an aqueous solution containing a basic substance and water at the same time as adding (b). The total amount of water contained in (a) and (c) is preferably 0.5 to 5 moles, more preferably 0.6 to 2 moles, and particularly preferably 0.7 to 1 mole, per mole of total hydrocarbyloxy groups of the tetrafunctional silane compound represented by formula (I) and / or its partially hydrolyzed condensate. (c) The concentration of the basic substance in (c) is preferably 1% to 10% by mass out of 100% by mass of (c), from the viewpoint of controlling the reaction and the dispersibility of the silica fine particles produced.

[0033] The reaction conditions for hydrolysis condensation in this process are preferably a reaction temperature of 20 to 120°C and a reaction time of 1 to 10 hours, and more preferably a reaction temperature of 20 to 100°C and a reaction time of 1 to 8 hours.

[0034] The concentration of silica particles in the colloidal silica (A1) obtained in step (A1) is preferably 2 to 20% by mass, and particularly preferably 3 to 10% by mass.

[0035] Process (A2): Surface treatment process with trifunctional silane compound This step is an optional step in which a trifunctional silane compound represented by the following formula (II), its partially hydrolyzed condensate, or a mixture thereof is added to the colloidal silica (A1) obtained in step (A1), and R is applied to the surface of the colloidal silica. 2 SiO 3 / 2 This process involves introducing units to obtain surface-treated colloidal silica (A2). R 2 Si(OR 3 )3(II) (In the formula, R 2 R represents a substituted or unsubstituted monovalent hydrocarbon group with 1 to 20 carbon atoms, 3 (Each represents a monovalent hydrocarbon group with 1 to 6 carbon atoms.)

[0036] In the above equation (II), R 2 R is a monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and particularly preferably 1 to 3 carbon atoms. 2Examples of monovalent hydrocarbon groups represented by include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl, and decyl groups, with methyl, ethyl, and propyl groups being particularly preferred. Furthermore, some or all of the hydrogen atoms of these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine, chlorine, or bromine atoms, preferably fluorine atoms.

[0037] In the above equation (II), R 3 R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, but those having 1 to 4 carbon atoms are preferred, and those having 1 to 2 carbon atoms are particularly preferred. 3 Examples of monovalent hydrocarbon groups represented by include methyl, ethyl, propyl, butyl, and phenyl groups, with methyl, ethyl, propyl, and butyl groups being preferred, and methyl and ethyl groups being particularly preferred.

[0038] Specific examples of the trifunctional silane compound represented by formula (II) above include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane.

[0039] The amount of the trifunctional silane compound represented by formula (II) used is preferably 0.001 to 1 mole, more preferably 0.01 to 0.1 moles, and particularly preferably 0.01 to 0.05 moles, per mole of SiO2 units (Si atoms derived from formula (I)) in the colloidal silica (A1) obtained in step (A1).

[0040] In step (A2), a trifunctional silane compound represented by formula (II) above is added to the colloidal silica (A1) obtained in step (A1), and a surface treatment reaction of silica with the trifunctional silane compound is carried out under the following reaction conditions. The reaction conditions in step (A2) are preferably a reaction temperature of 40 to 60°C and a reaction time of 1 to 10 hours, and more preferably a reaction temperature of 50 to 60°C and a reaction time of 1 to 8 hours.

[0041] Steps (A3') and (A3): Dispersant addition step This step involves adding a dispersant to the colloidal silica (A1) obtained in step (A1) or the surface-treated colloidal silica (A2) obtained in step (A2). Examples of dispersants include amino acids such as aspartic acid and glutamic acid; and organic acids such as oxalic acid, malic acid, and citric acid, with one or more selected from aspartic acid, glutamic acid, and citric acid being preferred.

[0042] Aspartic acid and glutamic acid may be used in D, L, or DL ​​form, or in combination.

[0043] The amount of dispersant added is preferably 10 to 3000 ppm by mass relative to the silica particles, and more preferably 500 to 2000 ppm by mass.

[0044] Process (B1): Dispersion medium replacement process This process involves replacing the hydrophilic organic solvent in the dispersion medium of the colloidal silica (A1) obtained in process (A1), the colloidal silica (A2) obtained in the surface treatment process (A2) with a trifunctional silane compound in process (A2), the dispersant-containing colloidal silica (A3') obtained in process (A3'), and the dispersant-containing surface-treated colloidal silica (A3) obtained in process (A3) with water. The hydrophilic organic solvent includes the hydrophilic organic solvent used in processes (A1) and (A2) and alcohols produced by the hydrolysis of the alkoxysilane compound.

[0045] Substitution methods include an atmospheric pressure heating concentration method in which the colloidal silica (A1) obtained in step (A1), the colloidal silica (A2) obtained in the surface treatment step (A2) with a trifunctional silane compound, the dispersant-containing colloidal silica (A3') obtained in step (A3'), and the dispersant-containing surface-treated colloidal silica (A3) obtained in step (A3) are heated and concentrated while adding water under atmospheric pressure, and a reduced pressure heating concentration method in which the operation of heating and concentrating under reduced pressure after adding water is repeated. In the case of concentration by heating at atmospheric pressure, it is preferable to concentrate the solution by adding water to replace the hydrophilic organic solvent, until the internal temperature approaches the boiling point of water. In the case of concentration by heating under reduced pressure, it is preferable to repeatedly perform the concentration operation under a pressure of 0.003 to 0.020 MPa after adding water.

[0046] Examples of water added in this process include distilled water, ion-exchanged water, and ultrapure water, with ultrapure water being preferred due to its low content of ions and fine particles.

[0047] The amount of water added is preferably 1.0 to 4.0 times, and more preferably 1.5 to 3.0 times, the total mass of the hydrophilic organic solvent containing the alcohol produced by the hydrolysis of the alkoxysilane compound. Within this range, silica aggregation can be suppressed.

[0048] The amount of hydrophilic organic solvent remaining in the colloidal silica dispersion medium after this process is preferably 0% to 0.002% by mass, and more preferably 0% to 0.001% by mass, of the total mass of the dispersion medium.

[0049] The concentration of silica particles in the aqueous-dispersed colloidal silica (B1) obtained in step (B1) is preferably 10 to 40% by mass, and more preferably 20 to 35% by mass.

[0050] Process (B2): Pressure heating process This process involves applying pressure and heat treatment to the water-dispersed colloidal silica (B1) obtained in process (B1) as needed to further promote the condensation reaction and reduce fine particles.

[0051] While there are no particular restrictions on the pressurized heating conditions, the temperature is preferably 100°C to 200°C, and more preferably 140°C to 180°C. The pressure is preferably 0.65 MPa to 2.0 MPa, and more preferably 0.7 MPa to 1.5 MPa. The pressurized heating time is preferably 1 to 6 hours.

[0052] Step (C): Centrifugation step This process involves removing or reducing fine particles (partial hydrolysis condensates of the silane compound containing silica) in the aqueous-dispersed colloidal silica (B1) obtained in process (B1) or the aqueous-dispersed colloidal silica (B2) obtained in process (B2) by centrifugation, so that the proportion of particles with a particle size of less than 20 nm among all particles in the colloidal silica is 10% or less.

[0053] In this process, centrifugal force of 10,000G or more, preferably 10,000G to 15,000G, is applied to perform centrifugation. Within this range, fine particles with a particle size of less than 20 nm can be efficiently reduced.

[0054] Examples of devices used for centrifugal separation include basket-type centrifuges, disk-type centrifuges, and decanter-type centrifuges, but disk-type centrifuges, which can apply a large centrifugal force in practical use, are preferred. A disc-type centrifuge is a type of centrifuge that stacks many cone-shaped separation discs in a bowl and rotates them at high speed to apply centrifugal force to the material being processed. By stacking many separation discs with small gaps between them, this disc-type centrifuge can secure an extremely large separation and sedimentation area relative to the installation area, making it possible to separate large quantities of slurry in a short time. Furthermore, a disc-type centrifuge is preferable from the viewpoint of being able to separate slurries with a relatively high specific gravity of 1.1 to 1.2, such as colloidal silica solutions.

[0055] When performing centrifugation using a disk-type centrifuge, the supply rate of water-dispersed colloidal silica is preferably between 50 L / h and 400 L / h, and more preferably between 70 L / h and 250 L / h. A supply rate of 50 L / h or more allows for efficient separation, while a supply rate of 400 L / h or less can suppress a decrease in separation efficiency.

[0056] The presence of minute particles smaller than 20 nm in aqueous-dispersed colloidal silica can be confirmed by differential mobility analysis (DMA), disk centrifugal particle size measurement, or field emission scanning electron microscopy (FE-SEM) image analysis.

[0057] The differential electrical mobility (DMA) method involves introducing a diluted colloidal silica sample into a measuring instrument, removing the solvent while heating, adjusting the surface charge of the silica particles, and then classifying and measuring the nanoparticles using a particle classifier. This method allows for the simultaneous determination of the particle size distribution of colloidal silica and the presence or absence of particles smaller than 20 nm in diameter. Suitable measuring instruments include the LiquiScan-ES from TSI and the APM-II Model 3602 from KANOMAX. In the particle size distribution of silica particles in water-dispersed colloidal silica using the differential electrical mobility method, it is preferable that no particles with a particle size of less than 20 nm are observed.

[0058] The disk centrifugal particle size measurement method is an analytical method that determines particle size by centrifuging particles in a density gradient liquid within a rapidly rotating disk and measuring the sedimentation velocity. Based on Stokes' law, it utilizes the fact that the velocity at which particles move due to centrifugal force depends on the particle size, and can measure particle size distribution with high resolution. Suitable measuring instruments include the Disc Centrifuge DC2400UHR from CPS Corporation and the Partica CENTRIFUGE from Horiba, Ltd. In the particle size distribution of silica particles in water-dispersed colloidal silica, measured by disk centrifugal particle size measurement, it is preferable that no particles with a particle size of less than 20 nm are observed.

[0059] Furthermore, the presence of minute particles smaller than 20 nm can be confirmed from field emission scanning electron microscope (FE-SEM) images, and minute particles that cannot be measured by the DMA method or centrifugal method, which are below the detection limit, can also be detected by FE-SEM. Examples of FE-SEM instruments include those manufactured by Hitachi High-Tech Corporation and JEOL Ltd.

[0060] A sample prepared by diluting water-dispersed colloidal silica with an alcohol-based solvent to a silica particle concentration of 0.1 to 0.05 mass% is coated onto a substrate such as a silicon wafer and dried. Fifty images are then taken at a magnification of 1,000,000x in different locations, and the ratio of silica particles smaller than 20 nm to the total number of silica particles in the calculated images is preferably 10% or less, and more preferably 5% or less.

[0061] [Z average particle diameter] When colloidal silica dispersed in water is diluted with deionized water to a silica particle concentration of 0.1% by mass, the particle size distribution can be measured by dynamic light scattering using a Zetasizer Ultra (Malvern Panalytical). The Z-mean particle size of silica particles in water-dispersed colloidal silica, as measured by dynamic light scattering, is preferably 20 to 100 nm, more preferably 25 to 95 nm, and particularly preferably 30 to 90 nm.

[0062] Process (D): Filter filtration process This step involves removing coarse particles by filtering the water-dispersed colloidal silica. This step may be performed before or after step (C) described above, but it is preferable to perform it after step (C).

[0063] Various commercially available filters can be used, but depth filters are preferred. Depth filters have a structure in which fibrous porous filter material is folded three-dimensionally, and by capturing the material to be filtered not only on the surface of the filter but also inside, they can hold a large amount of particles and have a relatively long filter life, making them suitable for the present invention.

[0064] Furthermore, by using depth filters with different pore sizes in combination, impurity particles of a desired size can be removed. From the standpoint of the overall filter lifespan and cost, it is preferable to pass the water-dispersed colloidal silica through depth filters with coarser pore sizes, gradually through filters with smaller pore sizes, thereby efficiently purifying it. In the present invention, filtration is preferably performed in the following order: a filter with a coarse pore size (70-30 μm), a filter with a medium pore size (0.7-0.4 μm), and a filter with a fine pore size (0.05-0.2 μm).

[0065] Coarse particles in water-dispersed colloidal silica can be identified, for example, using a particle size distribution analyzer with a counting method, such as the Accusizer® A7000APS (manufactured by Nippon Integris LLC). In the aqueous dispersion colloidal silica obtained by the manufacturing method of the present invention, the number of coarse particles 0.5 μm or larger is preferably 300,000 / mL or less, more preferably 150,000 / mL or less, and even more preferably 100,000 / mL or less.

[0066] Process (E): Addition of disinfectant The manufacturing method of the present invention may include a step of adding a disinfectant in order to improve the storage stability of the water-dispersed colloidal silica.

[0067] Examples of disinfectants include hydrogen peroxide, isothiazolinone compounds, quaternary ammonium salts, methyl p-hydroxybenzoate, and sodium chlorite, with hydrogen peroxide being preferred. These fungicides may be used individually or in combination of two or more.

[0068] The amount of the above-mentioned disinfectant added is preferably 0.0001% to 10.0% by mass, and more preferably 0.001% to 1.0% by mass, based on 100% by mass of water-dispersed colloidal silica.

[0069] The pH of the aqueous-dispersible colloidal silica obtained by the manufacturing method of the present invention is preferably 6.0 to 8.5, and more preferably 6.5 to 8.0. A pH of 6.0 or higher provides excellent dispersion stability of silica particles, while a pH of 8.5 or lower suppresses the dissolution of silica particles. A pH adjuster may be used to adjust the pH of the aqueous-dispersed colloidal silica. [Examples]

[0070] The present invention will be specifically described below using examples and comparative examples. The following examples do not limit the present invention in any way. The water-dispersed colloidal silica obtained in each example and comparative example was evaluated as follows, and the results are shown in Tables 1 and 2.

[0071] [Solid content concentration] 1.5 g of water-dispersed colloidal silica was accurately weighed and placed in an aluminum petri dish, dried at 105°C for 3 hours, and the residual (X) g was accurately weighed. The silica solid content concentration was then calculated using the following formula. Silica solid content concentration (mass%) = (X / 1.5) × 100

[0072] [Z average particle diameter] The particle size distribution of water-dispersed colloidal silica, diluted with deionized water to a silica particle concentration of 0.1% by mass, was measured using a Zetasizer Ultra (Malvern Panalytical) to determine the Z-mean particle size by dynamic light scattering.

[0073] [Presence or absence of particles smaller than 20 nm by differential electrical mobility (DMA) method] Water-dispersed colloidal silica was diluted with a 20 mM ammonium acetate aqueous solution to a silica particle concentration of 0.1% by mass. The particle size distribution in the range of 1 to 1,000 nm was measured using the differential electrical mobility method (DMA) with a liquid nanoparticle measurement system LiquiScan-ES (TSI Corporation) to confirm the presence or absence of particles smaller than 20 nm.

[0074] [Presence or absence of particles smaller than 20 nm by disk centrifugal particle size measurement] Water-dispersed colloidal silica was diluted with deionized water to a silica particle concentration of 3% by mass. The particle size distribution in the range of 10 to 1,000 nm was measured using a disc centrifugal particle size analyzer (Disc Centrifuge DC2400UHR, manufactured by CPS Corporation) to confirm the presence or absence of particles smaller than 20 nm.

[0075] [Percentage of particles smaller than 20 nm in field emission scanning electron microscope (FE-SEM) images] A sample was prepared by hydrophilizing a polished silicon wafer using ozone treatment, then adding three drops of a solution of water-dispersed colloidal silica diluted with methanol to achieve a silica particle concentration of 0.1% by mass, spreading it out, drying it at 25°C, and subsequently performing Pd deposition. Using a field emission scanning electron microscope (Hitachi S-4700), 50 images were taken at a magnification of 1,000,000x in different locations, and the ratio of silica particles smaller than 20 nm to the total number of silica particles in the images was calculated. Percentage of silica particles smaller than 20 nm (%) = (Number of silica particles smaller than 20 nm / Total number of silica particles) × 100

[0076] [Number of coarse particles] For water-dispersed colloidal silica, the number of coarse particles (particles / mL) larger than 0.5 μm was measured using the Accusizer® A7000APS particle size distribution analyzer (manufactured by Nippon Integris LLC).

[0077] [Example 1] ·Process (A1) In a 50-liter glass reactor equipped with a stirrer, dropping funnel, and thermometer, 15,860 g of methanol, 642 g of deionized water, and 812 g of 28% by mass aqueous ammonia were added and mixed. This solution was adjusted to 27°C, and while stirring, 12,930 g of tetramethoxysilane and 3,218 g of 5.9% by mass aqueous ammonia were simultaneously added dropwise, with the former added over 6 hours and the latter over 4 hours. After the addition of tetramethoxysilane was complete, stirring was continued for another 0.5 hours to carry out hydrolysis condensation and obtain colloidal silica (A1).

[0078] ·Process (A2) To the colloidal silica (A1) obtained in the above step (A1), 117 g of methyltrimethoxysilane (equivalent to 0.01 moles per mole of SiO2 units in the colloidal silica) was added at 25°C, and then the mixture was stirred at 55°C for 1 hour to obtain surface-treated colloidal silica (A2).

[0079] ·Process (A3) To the surface-treated colloidal silica (A2) obtained in the above step (A2), 33 g of DL-aspartic acid was added while stirring at 25°C to obtain surface-treated colloidal silica (A3) containing a dispersant.

[0080] ·Process (B1) To the dispersant-containing surface-treated colloidal silica (A3) obtained in the above step (A3), 20,000 g of ultrapure water was added at 25°C. Then, while dropping another 20,000 g of ultrapure water to maintain a constant liquid level, methanol was removed by distillation until the internal temperature was 99°C or higher and the pH was 7.5 or lower, yielding 16,700 g of water-dispersed colloidal silica (B1).

[0081] ·Process (B2) The aqueous-dispersed colloidal silica (B1) obtained in the above step (B1) was placed in an autoclave and reacted at an internal pressure of 0.7 MPa under nitrogen pressure and 140°C for 1 hour to obtain aqueous-dispersed colloidal silica (B2).

[0082] ·Process (C) The aqueous colloidal silica (B2) obtained in the above step (B2) was subjected to centrifugal separation for 25 minutes at a centrifugal force of 10,000 G and a flow rate of 70 L / h using a Mitsubishi Chemical Machinery Co., Ltd. disk-type centrifuge SJ10F (rotating body sludge space approximately 1.6 L), yielding 16,650 g of aqueous colloidal silica (C).

[0083] ·Process (D) The aqueous-dispersed colloidal silica (C) obtained in step (C) above was purified by filtration by passing it through a 50 μm depth filter, a 0.5 μm depth filter, and a 0.1 μm depth filter in that order to obtain 15,000 g of aqueous-dispersed colloidal silica (D).

[0084] ·Process (E) To the aqueous-dispersed colloidal silica (D) obtained in step (D) above, 1.0 g of 30% by mass hydrogen peroxide solution was added as a disinfectant and mixed to obtain aqueous-dispersed colloidal silica (i) with a pH of 7.1. Figure 1 shows an FE-SEM image of the obtained aqueous-dispersed colloidal silica (i).

[0085] [Example 2] ·Process (A1) In a 50-liter glass reactor equipped with a stirrer, dropping funnel, and thermometer, 12,518 g of methanol, 1,652 g of deionized water, and 697 g of 28% by mass aqueous ammonia were added and mixed. This solution was adjusted to 36°C, and while stirring, 11,100 g of tetramethoxysilane and 2,760 g of 5.8% by mass aqueous ammonia were simultaneously added dropwise, with the former added over 6 hours and the latter over 4 hours. After the addition of tetramethoxysilane was complete, stirring was continued for another 0.5 hours to carry out hydrolysis condensation and obtain colloidal silica (A1).

[0086] ·Process (A3') To the surface-treated colloidal silica (A1) obtained in step (A1), 29 g of DL-aspartic acid was added while stirring at 25°C to obtain dispersant-containing colloidal silica (A3').

[0087] ·Process (B1) To the dispersant-containing surface-treated colloidal silica (A3') obtained in the above step (A3'), 20,000 g of ultrapure water was added at 25°C, and methanol was removed by distillation at a pressure of 0.02 to 0.003 MPa and a temperature of 40 to 60°C. This operation was repeated three times to obtain 15,110 g of aqueous-dispersed colloidal silica (B1) with a pH of 7.5.

[0088] ·Process (C) The aqueous-dispersed colloidal silica (B1) obtained in the above step (B1) was subjected to centrifugal separation for 20 minutes at a centrifugal force of 10,000 G and a flow rate of 70 L / h using a Mitsubishi Chemical Industries, Ltd. disk-type centrifuge SJ10F (rotating body sludge space approximately 1.6 L), yielding 14,602 g of aqueous-dispersed colloidal silica (C).

[0089] ·Process (D) The obtained aqueous-dispersed colloidal silica was purified by filtration by passing it through a 50 μm depth filter, a 0.5 μm depth filter, and a 0.1 μm filter. The aqueous-dispersed colloidal silica (C) obtained in step (C) was purified by filtration by passing it through a 50 μm depth filter, a 0.5 μm depth filter, and a 0.1 μm depth filter in that order to obtain 13,500 g of aqueous-dispersed colloidal silica (D).

[0090] ·Process (E) To the aqueous-dispersed colloidal silica (D) obtained in step (D) above, 0.9 g of 30% by mass hydrogen peroxide solution was added as a disinfectant and mixed to obtain aqueous-dispersed colloidal silica (ii) with a pH of 7.3.

[0091] [Example 3] ·Process (A1) In a 50-liter glass reactor equipped with a stirrer, dropping funnel, and thermometer, 12,475 g of methanol, 1,532 g of deionized water, and 426 g of 28% by mass aqueous ammonia were added and mixed. This solution was adjusted to 26°C, and while stirring, a solution of 10,351 g of tetramethoxysilane and 779 g of methanol, and 2,570 g of 4.9% by mass aqueous ammonia were simultaneously added dropwise. The former was added dropwise over 6 hours, and the latter over 4 hours. After the addition of tetramethoxysilane was completed, stirring was continued for another 0.5 hours to carry out hydrolysis condensation and obtain colloidal silica (A1).

[0092] ·Process (A2) To the colloidal silica (A1) obtained in step (A1) above, 94 g of methyltrimethoxysilane (equivalent to 0.01 moles per mole of SiO2 units in the colloidal silica) was added at 25°C, and then the mixture was stirred at 55°C for 1 hour to obtain surface-treated colloidal silica (A2).

[0093] ·Process (A3): To the surface-treated colloidal silica (A2) obtained in the above step (A2), 27 g of DL-aspartic acid was added while stirring at 25°C to obtain surface-treated colloidal silica (A3) containing a dispersant.

[0094] ·Process (B1) To the dispersant-containing surface-treated colloidal silica (A3) obtained in the above step (A3), 20,000 g of ultrapure water was added at 25°C, and methanol was removed by distillation at a pressure of 0.02 to 0.003 MPa and a temperature of 40 to 60°C. This operation was repeated three times to obtain 14,100 g of aqueous-dispersed colloidal silica (B1) with a pH of 7.5.

[0095] ·Process (B2) The aqueous-dispersed colloidal silica (B1) obtained in the above step (B1) was placed in an autoclave and reacted at an internal pressure of 0.7 MPa under nitrogen pressure and 140°C for 1 hour to obtain aqueous-dispersed colloidal silica (B2).

[0096] ·Process (C) The aqueous-dispersed colloidal silica (B2) obtained in the above step (B2) was subjected to centrifugal separation for 20 minutes at a centrifugal force of 10,000 G and a flow rate of 70 L / h using a Mitsubishi Chemical Machinery Co., Ltd. disk-type centrifuge SJ10F model (rotating body sludge space approximately 1.6 L), yielding 13,500 g of aqueous-dispersed colloidal silica (C).

[0097] ·Process (D) The aqueous-dispersed colloidal silica (C) obtained in step (C) above was purified by filtration by passing it through a 50 μm depth filter, a 0.5 μm depth filter, and a 0.1 μm depth filter in that order to obtain 13,400 g of aqueous-dispersed colloidal silica (D).

[0098] ·Process (E) To the aqueous-dispersed colloidal silica (D) obtained in step (D) above, 0.9 g of 30% by mass hydrogen peroxide solution was added as a disinfectant and mixed to obtain aqueous-dispersed colloidal silica (iii) with a pH of 7.0.

[0099] [Example 4] ·Process (A1) In a 50-liter glass reactor equipped with a stirrer, dropping funnel, and thermometer, 15,860 g of methanol, 642 g of deionized water, and 812 g of 28% by mass aqueous ammonia were added and mixed. This solution was adjusted to 30°C, and while stirring, 12,930 g of tetramethoxysilane and 3,218 g of 5.5% by mass aqueous ammonia were simultaneously added dropwise, with the former added over 6 hours and the latter over 4 hours. After the addition of tetramethoxysilane was complete, stirring was continued for another 0.5 hours to carry out hydrolysis condensation and obtain colloidal silica (A1).

[0100] ·Process (B1) To the dispersant-containing surface-treated colloidal silica (A1) obtained in step (A1), 20,000 g of ultrapure water was added at 25°C. Then, while dropping another 20,000 g of ultrapure water to maintain a constant liquid level, methanol was removed by distillation until the internal temperature reached 99°C or higher and the pH was 7.5 or lower, yielding 16,800 g of water-dispersed colloidal silica (B1).

[0101] ·Process (C) The aqueous colloidal silica (B1) obtained in the above step (B1) was subjected to centrifugal separation for 25 minutes at a centrifugal force of 10,000 G and a flow rate of 70 L / h using a Mitsubishi Chemical Industries, Ltd. disk-type centrifuge SJ10F (rotating body sludge space of approximately 1.6 L), yielding 16,690 g of aqueous colloidal silica (C).

[0102] ·Process (D) The aqueous-dispersed colloidal silica (C) obtained in step (C) above was purified by filtration by passing it through a 50 μm depth filter, a 0.5 μm depth filter, and a 0.1 μm depth filter in that order to obtain 15,500 g of aqueous-dispersed colloidal silica (D).

[0103] ·Process (E) To the aqueous-dispersed colloidal silica (D) obtained in step (D) above, 1.1 g of 30% by mass hydrogen peroxide solution was added as a disinfectant and mixed to obtain aqueous-dispersed colloidal silica (iv) with a pH of 7.3.

[0104] [Example 5] ·Process (A1) In a 50-liter glass reactor equipped with a stirrer, dropping funnel, and thermometer, 12,475 g of methanol, 1,532 g of deionized water, and 426 g of 28% by mass aqueous ammonia were added and mixed. This solution was adjusted to 26°C, and while stirring, a solution of 10,351 g of tetramethoxysilane and 779 g of methanol, and 2,570 g of 4.9% by mass aqueous ammonia were simultaneously added dropwise. The former was added dropwise over 6 hours, and the latter over 4 hours. After the addition of tetramethoxysilane was completed, stirring was continued for another 0.5 hours to carry out hydrolysis condensation and obtain colloidal silica (A1).

[0105] ·Process (A3) To the surface-treated colloidal silica (A1) obtained in the above step (A1), 16 g of citric acid was added while stirring at 25°C to obtain surface-treated colloidal silica (A3) containing a dispersant.

[0106] ·Process (B1) To the dispersant-containing surface-treated colloidal silica (A3) obtained in the above step (A3), 20,000 g of ultrapure water was added at 25°C, and methanol was removed by distillation at a pressure of 0.003 to 0.02 MPa and a temperature of 40 to 60°C. This operation was repeated three times to obtain 14,150 g of aqueous-dispersed colloidal silica (B1) with a pH of 7.5.

[0107] ·Process (C) The water-dispersed colloidal silica (B2) obtained in the above step (B1) was subjected to centrifugal separation for 20 minutes using a Mitsubishi Chemical Machinery Co., Ltd. disk-type centrifuge SJ10F model (rotating body sludge space approximately 1.6 L) at a centrifugal force of 15,000 G and a flow rate of 70 L / h to remove fine particles, thereby obtaining 13,900 g of water-dispersed colloidal silica (C).

[0108] ·Process (D) The aqueous-dispersed colloidal silica (C) obtained in step (C) above was purified by filtration by passing it through a 50 μm depth filter, a 0.5 μm depth filter, and a 0.1 μm depth filter in that order to obtain 13,300 g of aqueous-dispersed colloidal silica (D).

[0109] ·Process (E) To the aqueous-dispersed colloidal silica (D) obtained in step (D) above, 1.0 g of 30% by mass hydrogen peroxide solution was added as a disinfectant and mixed to obtain aqueous-dispersed colloidal silica (v) with a pH of 7.2.

[0110] [Example 6] Except for changing the reaction temperature to 31°C in step (A1) of Example 3 and changing the amount of 30% by mass hydrogen peroxide solution added to 2.6 g in step (E), the same procedure as in Example 3 was carried out to obtain 15,300 g of aqueous-dispersed colloidal silica (vi) with a pH of 7.0.

[0111] [Example 7] In Example 6, the same procedure as in Example 6 was followed, except that steps (A2) and (B2) were omitted, to obtain 15,400 g of aqueous-dispersed colloidal silica (vii) at pH 7.0.

[0112] [Example 8] The same procedure as in Example 5 was followed, except that the reaction temperature in step (A1) of Example 5 was changed to 36°C, to obtain 15,400 g of aqueous-dispersed colloidal silica (viii) with a pH of 7.1.

[0113] [Comparative Example 1] In Example 1, the same procedure as in Example 1 was followed except that step (C) was omitted, and 15,300 g of aqueous-dispersed colloidal silica (ix) with a pH of 7.5 was obtained. Figure 2 shows an SEM image of the obtained aqueous-dispersed colloidal silica (ix).

[0114] [Comparative Example 2] In Example 2, the same procedure as in Example 2 was followed, except that step (C) was omitted, to obtain 13,600 g of aqueous-dispersed colloidal silica (x) with a pH of 7.4.

[0115] [Comparative Example 3] In Example 8, the same procedure as in Example 8 was followed, except that step (C) was omitted, to obtain 15,500 g of aqueous-dispersed colloidal silica (xi) with a pH of 7.6.

[0116] [Comparative Example 4] In step (C) of Example 1, the same procedure as in Example 1 was performed except that the centrifugal force was set to 5,000 G, to obtain 15,400 g of aqueous-dispersed colloidal silica (xii) with a pH of 7.8.

[0117] [Comparative Example 5] In step (C) of Example 1, the same procedure as in Example 1 was performed except that a decanter-type centrifuge (PTM type, manufactured by Tomoe Engineering Co., Ltd.) was used to set the centrifugal force to 3,000 G, thereby obtaining 15,000 g of aqueous-dispersed colloidal silica (xiii) with a pH of 7.6.

[0118] [Table 1]

[0119] [Table 2]

Claims

1. A method for producing aqueous-dispersible colloidal silica, comprising the following steps (A1), (B1), (C), and (D). Step (A1): A step to obtain colloidal silica (A1) by hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), a partially hydrolyzed condensate thereof, or a mixture thereof in a solution containing a hydrophilic organic solvent and water in the presence of a basic substance. Si(OR １ ) ４ (I) (In the formula, R １ (Each represents a monovalent hydrocarbon group with 1 to 6 carbon atoms.) Step (B1): A step of replacing hydrophilic organic solvents in the dispersion medium with water. Step (C): A step in which the proportion of particles with a particle size of less than 20 nm among all particles in colloidal silica is reduced to 10% or less by centrifugal separation with a centrifugal force of 10,000 G or more. Step (D): A step in filtering colloidal silica using a filter.

2. A method for producing aqueous-dispersible colloidal silica according to claim 1, comprising the following step (A2) after step (A1). Step (A2): Add a trifunctional silane compound represented by the following formula (II), its partially hydrolyzed condensate, or a mixture thereof to the colloidal silica (A1) obtained in step (A1), and apply R to the surface of the colloidal silica. ２ SiO ３／２ A process to introduce units and obtain surface-treated colloidal silica (A2). R ２ Si(OR ３ ) ３ (II) (In the formula, R ２ represents a monovalent hydrocarbon group having 1 to 20 carbon atoms which may be substituted or unsubstituted, and R ３ independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)

3. A method for producing aqueous-dispersible colloidal silica according to claim 2, comprising the following step (A3) after step (A2). Step (A3): A step to obtain dispersant-containing colloidal silica (A3) by adding one or more dispersants selected from aspartic acid, glutamic acid, and citric acid to the surface-treated colloidal silica (A1) obtained in step (A1).

4. A method for producing aqueous-dispersible colloidal silica according to claim 1, comprising the following step (A3') after step (A1). Step (A3'): A step to obtain dispersant-containing colloidal silica (A3') by adding one or more dispersants selected from aspartic acid, glutamic acid, and citric acid to the surface-treated colloidal silica (A1) obtained in step (A1).

5. A method for producing aqueous-dispersible colloidal silica according to claim 1, comprising the following step (B2) after step (B1). Process (B2): Process of pressurizing and heating colloidal silica.

6. A method for producing aqueous-dispersible colloidal silica according to claim 1, wherein a disk-type centrifuge is used in the centrifugal separation of step (C).

7. A method for producing aqueous-dispersible colloidal silica according to claim 1, wherein the Z-average particle size of silica particles in aqueous-dispersible colloidal silica, as measured by dynamic light scattering, is 20 to 100 nm.

8. A method for producing water-dispersed colloidal silica according to claim 1, wherein no particles with a particle size of less than 20 nm are observed in the particle size distribution of silica particles in water-dispersed colloidal silica by differential electrical mobility method.

9. A method for producing aqueous-dispersible colloidal silica according to claim 1, wherein no particles with a particle size of less than 20 nm are observed in the particle size distribution of silica particles in aqueous-dispersible colloidal silica by disk centrifugal particle size measurement.

10. A method for producing aqueous-dispersible colloidal silica according to claim 1, wherein in a field emission scanning electron microscope image of silica particles in aqueous-dispersible colloidal silica, the ratio of particles with a particle size of less than 20 nm to the total number of silica particles is 10% or less.

11. A method for producing aqueous-dispersible colloidal silica according to claim 1, wherein the number of coarse particles of 0.5 μm or larger measured by a particle counter in the aqueous-dispersible colloidal silica is 300,000 particles / mL or less.

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