Citric acid-containing colloidal silica and method for producing the same

Abstract

The present invention provides citric acid-containing colloidal silica in which generation of coarse particles having a size of 0.20 μm or more is suppressed when a shear force is applied.SOLUTION: The present invention provides citric acid-containing colloidal silica containing silica particles and citric acids, wherein (1) a silanol group concentration per unit surface area of the silica particles is 1.6 * 1019 to 14.5 * 1019 / m2, and (2) a content of the citric acids per unit surface area of the silica particles is 1.0 to 10.0 μ g / m2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to citric acid-containing colloidal silica and a method for producing the same. [Background technology]

[0002] Colloidal silica is silica particles dispersed in a medium such as water, and is used as a property improver in fields such as paper, textiles, and steel, as well as an abrasive used in polishing semiconductor devices such as semiconductor wafers (CMP).

[0003] In chemical mechanical polishing (CMP) performed during the manufacturing process of semiconductor devices, a polishing composition containing few coarse particles is required to reduce polishing scratches on the surface of the substrate to be polished. Colloidal silica having an average particle size of about 10 to 200 nm is used as a raw material for preparing such a polishing composition. However, due to the need to reduce polishing scratches, the colloidal silica is required to contain a small amount of coarse particles having a size of 0.20 μm or more.

[0004] When preparing a polishing composition using colloidal silica as an abrasive grain raw material, a process of stirring a mixture of colloidal silica and other chemical components is usually carried out. For example, Patent Document 1 describes a method for preparing a polishing composition in which the silanol group density of silica particles is 1.0 to 3.0 / nm 2 It is disclosed that the content of the polycarboxylic acid is 0.001 to 3.0% by mass. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-16344 Summary of the Invention [Problem to be solved by the invention]

[0006] As a result of extensive research, the present inventors have found that conventional colloidal silica has the following problem. Specifically, the colloidal silica contained in the chemical mechanical polishing aqueous dispersion has a high content of polycarboxylic acid per unit surface area of ​​silica particles, resulting in an increase in the content of coarse particles having a size of 0.20 μm or more when shear force is applied. Such colloidal silica is unable to reduce polishing scratches on the surface of a substrate to be polished during chemical mechanical polishing or other processes performed in the manufacturing process of semiconductor devices.

[0007] In view of the above circumstances, an object of the present invention is to provide a polycarboxylic acid-containing colloidal silica in which the generation of coarse particles having a size of 0.20 μm or more is suppressed when a shear force is applied. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned object, the present inventors have found that the above-mentioned object can be achieved by using citric acid-containing colloidal silica containing silica particles and colloidal silica containing citric acid, in which the silanol group density per unit surface area of ​​the silica particles and the citric acid content per unit surface area of ​​the silica particles are within specific ranges, and have thus completed the present invention.

[0009] That is, the present invention relates to the following citric acid-containing colloidal silica and a method for producing the same. 1. Citric acid-containing colloidal silica containing silica particles and citric acid, (1) The silanol group density per unit surface area of ​​the silica particles is 1.6 × 10 19 ~14.5×10 19 pieces / m 2 and (2) The content of the citric acid per unit surface area of ​​the silica particles is 1.0 to 10.0 μg / m 2 That is, Citric acid-containing colloidal silica characterized by: 2. The citric acid-containing colloidal silica according to Item 1, wherein the silica particles have an average secondary particle size of 10 to 200 nm. 3. The BET specific surface area of ​​the silica particles is 20 to 300 m 2 Item 3. The citric acid-containing colloidal silica according to Item 1 or 2, wherein the citric acid content is 1 / g. 4. The amount of silanol groups per unit weight of the silica particles is 1.5 × 10 21 ~5.0×10 21 Item 4. The citric acid-containing colloidal silica according to any one of Items 1 to 3, wherein the citric acid-containing colloidal silica is present in an amount of 1 / g. 5. The citric acid-containing colloidal silica according to any one of items 1 to 4, wherein the content of the silica particles is 10% by mass or more. 6. A method for producing citric acid-containing colloidal silica according to any one of items 1 to 5, comprising: (1) Step 1: preparing a mother liquor containing an alkali catalyst, an alcohol, and water; (2) Step 2 of adding a raw material solution containing an alkoxysilane and an alcohol to the mother liquor to prepare a reaction liquid; and (3) adding citric acid to the reaction solution; A manufacturing method comprising the steps of: 7. The production method according to Item 6, wherein the step 2 is a step of adding the raw material solution to the mother liquor at a constant rate. 8. The production method according to Item 6 or 7, further comprising, after Step 3, Step 4 of concentrating the silica particle concentration of the citric acid-containing colloidal silica and substituting the solvent with water. Item 9. The method according to Item 8, wherein step 4 is a step of heating the citric acid-containing colloidal silica for a heating time of 15 hours or less. 10. The production method according to any one of items 6 to 9, wherein in step 2, the water concentration in the reaction solution is 14.5% by mass or less. 11. The production method according to any one of items 6 to 10, wherein in step 2, the temperature of the reaction solution is 15 to 25°C. 12. The method according to any one of items 6 to 11, wherein the amount of citric acid added per 1 g of silica particles is 50 to 600 μg / g. [Effects of the Invention]

[0010] The citric acid-containing colloidal silica of the present invention is inhibited from generating coarse particles having a size of 0.20 μm or more when a shear force is applied. Furthermore, the production method of the present invention can produce the citric acid-containing colloidal silica of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below. Note that the following description of the components may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

[0012] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. Furthermore, in this specification, a numerical value connected with "~" means a numerical range that includes the numbers before and after "~" as the upper and lower limits.

[0013] In this specification, the expressions "contain" and "comprise" include the concepts of "contain," "include," "consist essentially of," and "consist only of."

[0014] The citric acid-containing colloidal silica of the present invention (hereinafter also simply referred to as "colloidal silica") is a citric acid-containing colloidal silica containing silica particles and citric acid, and (1) the silanol group density per unit surface area of ​​the silica particles is 1.6 × 10 19 ~14.5×10 19 pieces / m 2 (2) the content of the citric acid per unit surface area of ​​the silica particles is 1.0 to 10.0 μg / m 2The colloidal silica of the present invention contains silica particles and citric acid, but because it has the above-mentioned configurations (1) and (2), particle aggregation is unlikely to proceed even when shear force is applied under conditions of high silica particle concentration, and an increase in the content of coarse particles having a size of 0.20 μm or more is suppressed. This colloidal silica can be extremely suitably used as abrasive grains for polishing.

[0015] The production method of the present invention is a method for producing the citric acid-containing colloidal silica of the present invention, and includes: (1) step 1 of preparing a mother liquor containing an alkali catalyst, an alcohol, and water; (2) step 2 of adding a raw material solution containing an alkoxysilane and an alcohol to the mother liquor to prepare a reaction liquid; and (3) step 3 of adding citric acid to the reaction liquid. According to this production method of the present invention, the citric acid-containing colloidal silica of the present invention can be produced.

[0016] The colloidal silica of the present invention and its production method will be described in detail below.

[0017] 1. Citric acid-containing colloidal silica The citric acid-containing colloidal silica of the present invention is a citric acid-containing colloidal silica containing silica particles and citric acid, wherein (1) the silanol group density per unit surface area of ​​the silica particles is 1.6×10 19 ~14.5×10 19 pieces / m 2 (2) the content of the citric acid per unit surface area of ​​the silica particles is 1.0 to 10.0 μg / m 2 is.

[0018] The silica particles contained in the colloidal silica of the present invention have a silanol group density per unit surface area of ​​1.6 × 10 19 ~14.5×10 19 pieces / m 2 The silanol group density is 1.6×10 19If the silanol group density is less than 14.5 × 10, the dispersion stability of the silica particles will decrease, and the silica particles will aggregate, generating coarse particles when shear force is applied. 19 pieces / m 2 If the silanol group density exceeds 1.8×10, the dispersion stability of the silica particles decreases, the silica particles aggregate, and coarse particles are generated when a shear force is applied. 19 ~14.2×10 19 pieces / m 2 is preferred, and 1.9 × 10 19 ~14.0×10 19 pieces / m 2 is more preferred.

[0019] In this specification, the silanol group density per unit surface area of ​​silica particles contained in colloidal silica is measured by the following measurement method.

[0020] (Method for measuring silanol group density per unit surface area of ​​silica particles) [Step 1] The colloidal silica is centrifuged at 77,400 G, 5°C, and 90 minutes, and the resulting precipitate is dried under reduced pressure at 60°C and a gauge pressure of -0.1 MPa or less for 90 minutes to obtain a dry silica powder.

[0021] [Step 2] The dried silica powder obtained in step 1 was solidified. 29 Analyzed by Si-DD / MAS-NMR, 29 A Si-NMR spectrum is obtained. The NMR analysis uses the DD-MAS method. An NMR device such as the ECZ500R manufactured by JEOL Ltd. can be used. An 8 mm HXMAS probe manufactured by JEOL Ltd. can be used as a probe for detecting NMR signals.

[0022] [Step 3] Obtained in step 2 29The Si-NMR spectrum data is analyzed, and the peak with a chemical shift of approximately -84 ppm (when the signal of the silicon atom of tetramethylsilane is set to 0 ppm) is designated as Q1, the peak with a chemical shift of approximately -92 ppm as Q2, the peak with a chemical shift of approximately -101 ppm as Q3, and the peak with a chemical shift of approximately -111 ppm as Q4. The signal areas a1, a2, a3, and a4 of Q1, Q2, Q3, and Q4, respectively, are calculated.

[0023] In analyzing the spectral data, optimization calculations are performed for each peak in the spectrum after Fourier transformation using the nonlinear least squares method, with the center position, height, and half-width of the peak shape created by mixing Lorentzian and Gaussian waveforms as variable parameters.

[0024] Q1 is thought to be derived from the silicon atom with a coordination number of 1 adjacent to the oxygen atom, and the composition formula is SiO 1 / 2 It can be expressed as (OH)3, with a formula weight of 87.11 g / mol. Q2 is thought to be derived from a silicon atom with a coordination number of 2 adjacent to an oxygen atom, and can be expressed as SiO(OH)2 with a formula weight of 78.10 g / mol. Q3 is thought to be derived from a silicon atom with a coordination number of 3 adjacent to an oxygen atom, and can be expressed as SiO 3 / 2 It can be expressed as (OH) and has a formula weight of 69.09 g / mol. Q4 is thought to be derived from the silicon atom with a coordination number of 4 adjacent to the oxygen atom, and can be expressed as SiO2 and has a formula weight of 60.08 g / mol.

[0025] [Step 4]. From the signal areas a1, a2, a3, and a4 and the formula weights of the Q1, Q2, Q3, and Q4 components obtained in step 3, the amount of silanol groups per unit weight of silica particles is calculated using the following formula. The amount of silanol groups per unit weight of silica particles (×10 21 pieces / g) ={[(a1×3)+(a2×2)+(a3×1)]×N A x10 -21} ÷{(a1×87.11)+(a2×78.10)+(a3×69.09)+(a4×60.08)} where N A is Avogadro's number: 6.022 x 10 23 Represents.

[0026] [Step 5] The silanol group density per unit surface area of ​​the silica particles is calculated using the following formula from the amount of silanol groups per unit weight of the silica particles calculated in step 4 and the BET specific surface area of ​​the silica particles obtained by the measurement method described below. The silanol group density per unit surface area of ​​silica particles (×10 19 pieces / m 2 ) = [silanol group amount per unit weight of silica particles (× 10 21 pieces / g)×10 2 ] ÷BET specific surface area (m 2 / g)

[0027] The BET specific surface area of ​​the silica particles contained in the colloidal silica of the present invention is 20 to 300 m 2 / g is preferred, and 25 to 200m 2 / g is more preferable, and 30 to 150m 2 / g is even more preferable. When the lower limit of the BET specific surface area is within the above range, the flatness of the surface of a substrate to be polished is further improved when the colloidal silica of the present invention is used as abrasive grains for polishing. Furthermore, when the upper limit of the BET specific surface area is within the above range, the dispersion stability of the silica particles is further improved.

[0028] In this specification, the BET specific surface area of ​​the silica particles contained in the colloidal silica is measured by the following measurement method.

[0029] (BET specific surface area) The colloidal silica is pre-dried on a hot plate and then heat-treated at 800°C for 1 hour to prepare a measurement sample. The BET specific surface area (m) of the prepared measurement sample is measured by the nitrogen gas adsorption method (BET method). 2 / g) is measured.

[0030] The average primary particle diameter of the silica particles contained in the colloidal silica of the present invention is preferably 135 nm or less, more preferably 110 nm or less, and even more preferably 90 nm or less. When the upper limit of the average primary particle diameter is within the above range, the flatness when polished using the colloidal silica of the present invention is further improved. Furthermore, the average primary particle diameter of the silica particles is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. When the lower limit of the average primary particle diameter of the silica particles is within the above range, the storage stability of the colloidal silica is further improved. The average primary particle diameter of the silica particles is measured by the following measurement method.

[0031] (Method for measuring average primary particle size) The colloidal silica is pre-dried on a hot plate and then heat-treated at 800°C for 1 hour to prepare a measurement sample. The BET specific surface area is measured using the prepared measurement sample. The true specific gravity of silica is 2.2, and the BET specific surface area (m 2 / g) is converted to the average primary particle diameter (nm) of silica particles in the colloidal silica.

[0032] The average secondary particle diameter of the silica particles contained in the colloidal silica of the present invention is 10 to 200 nm. If the average secondary particle diameter is less than 10 nm, the dispersion stability of the silica particles decreases, and coarse particles are likely to be generated when shear force is applied. If the average secondary particle diameter exceeds 200 nm, polishing scratches are likely to be caused on the surface of the substrate to be polished when used as abrasive grains. The average secondary particle diameter is preferably 20 to 170 nm, more preferably 30 to 150 nm. The average secondary particle diameter of the silica particles is measured by the following measurement method.

[0033] (Method for measuring average secondary particle size) To prepare a sample for measuring the average secondary particle size, colloidal silica was added to a 0.3% by mass aqueous citric acid solution and homogenized to a silica concentration of 0.8% by mass. Using this sample for measurement, the average secondary particle size (nm) was measured by dynamic light scattering ("ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd.).

[0034] The association ratio of the silica particles contained in the colloidal silica of the present invention is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. When the upper limit of the association ratio is within the above range, the silica particles can be more stably dispersed, and the occurrence of aggregation that causes defects during polishing is further suppressed. Furthermore, the association ratio of the silica particles is preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.4 or more. When the lower limit of the association ratio of the silica particles is within the above range, the polishing performance when the colloidal silica of the present invention is used as an abrasive is further improved.

[0035] (Calculation method of association ratio) The association ratio of silica particles is calculated using the following formula from the average primary particle size and average secondary particle size of silica particles obtained by the above-mentioned measurement method. Association ratio = average secondary particle size of silica particles (nm) ÷ average primary particle size of silica particles (nm)

[0036] The silica particles contained in the colloidal silica of the present invention have a silanol group content of 1.5×10 21 ~5.0×10 21 pieces / g is preferable, 1.8 × 10 21 ~4.7×10 21 pcs / g is more preferable, 2.0 x 10 21 ~4.5×10 21 When the amount of silanol groups per unit weight is within the above range, the silica particles are appropriately stabilized by the interaction between the silica particles and citric acid, allowing the silica particles to be more stably dispersed, and the occurrence of aggregation that causes defects during polishing is further suppressed.

[0037] The content of silica particles in the colloidal silica of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on 100% by mass of the colloidal silica. Furthermore, the content of silica in the colloidal silica is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, based on 100% by mass of the colloidal silica. By setting the lower limit of the content of silica particles in the colloidal silica within the above range, the polishing performance when the colloidal silica is used as an abrasive is further improved. Furthermore, by setting the upper limit of the content of silica particles in the colloidal silica within the above range, the dispersion stability of the silica particles is further improved.

[0038] The colloidal silica of the present invention has a citric acid content per unit surface area of ​​silica particles of 1.0 to 10.0 μg / m 2 The citric acid content is 1.0 μg / m 2 If the citric acid content is less than 10.0 μg / m, the dispersion stability of the silica particles will decrease, and the silica particles will aggregate, generating coarse particles when shear force is applied. 2 If the content of citric acid exceeds 1.5 μg / m, the dispersion stability of the silica particles decreases, and the silica particles aggregate, generating coarse particles when shear force is applied. 2 More than 2.0 μg / m is preferable. 2 More preferably, the content of citric acid is 9.5 μg / m or more. 2 Less than 9.0 μg / m 2 The following is more preferred:

[0039] In this specification, the content of citric acid per unit surface area of ​​silica particles is measured by the following measurement method.

[0040] (Citric acid content per unit surface area of ​​silica particles) [Step 1] 5 g of colloidal silica is placed in a crucible, 9 mL of 38% hydrofluoric acid is added, and the mixture is heated on a hot plate heated to 100°C for 6 hours to decompose and evaporate the silica.

[0041] [Step 2] Add 6 mL of 0.1 mol / L diammonium hydrogen phosphate aqueous solution to dissolve the residue in the crucible, and recover the entire amount of the aqueous solution. After recovery, add additional 0.1 mol / L diammonium hydrogen phosphate aqueous solution to the aqueous solution to dilute it to a total amount of 10 g, and use it as the diluted solution for measurement.

[0042] [Step 3] The diluted solution for measurement obtained in step 2 is analyzed by liquid chromatography, and the citric acid concentration is measured using the absolute calibration curve method. The liquid chromatography apparatus used can be Shimadzu LC-2010CHT, and the chromatography column can be GL Sciences Inertsil ODS-3 or the like.

[0043] [Step 4] The citric acid concentration of the diluted measurement solution obtained in step 3 is defined as C (μg / g), and the citric acid content per unit surface area of ​​the silica particles is calculated using the following formula from the content of silica particles and the BET specific surface area of ​​the silica particles obtained by the above-mentioned measurement method. Citric acid content per unit surface area of ​​silica particles (μg / m 2 ) = {C (μg / g) × 10 ÷ (5 × silica particle content (mass%) ÷ 100)} ÷BET specific surface area of ​​silica particles (m 2 / g)

[0044] The pH of the colloidal silica of the present invention may be appropriately set depending on the application of the colloidal silica, and is not particularly limited, but is preferably 2.0 or higher, more preferably 3.0 or higher. The pH is preferably 11.0 or lower, more preferably 10.0 or lower. By setting the lower limit of the pH within the above range, the long-term dispersion stability of the silica particles in the colloidal silica is further improved. By setting the upper limit of the pH within the above range, the long-term dispersion stability of the colloidal silica is further improved.

[0045] The colloidal silica of the present invention preferably contains 1 ppm or less of metal impurities, such as sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt. If the metal impurity content exceeds 1 ppm, the citric acid contained in the colloidal silica coordinates with the metal ions, resulting in a decrease in the amount of citric acid adsorbed to the silica particle surface and a decrease in the dispersion stability of the silica particles. By keeping the metal impurity content at 1 ppm or less, a sufficient amount of citric acid is adsorbed to the silica particle surface, improving the dispersion stability of the silica particles. Furthermore, since the metal impurity content is 1 ppm or less, the risk of metal contamination is reduced, making the colloidal silica suitable for polishing electronic materials and the like.

[0046] (Method for measuring metal impurity content) The content of metal impurities can be measured using an atomic absorption spectrometer.

[0047] The colloidal silica of the present invention can be used as an abrasive (CMP) for semiconductor devices such as semiconductor wafers. It can also be used as a property improver in the fields of paper, textiles, steel, etc., and can also be used as a filler additive, a toner external additive, etc. by drying it into a powder.

[0048] 2. Colloidal Silica Manufacturing Method The method for producing colloidal silica of the present invention is characterized by comprising: (1) Step 1 of preparing a mother liquor containing an alkali catalyst, an alcohol, and water; (2) Step 2 of adding a raw material solution containing an alkoxysilane and an alcohol to the mother liquor to prepare a reaction liquid; and (3) Step 3 of adding citric acid to the reaction liquid. The production method of the present invention has the above-mentioned configuration, and thus can suitably produce the above-mentioned citric acid-containing colloidal silica of the present invention.

[0049] Each step of the production method of the present invention will be described in detail below.

[0050] (Process 1) Step 1 is a step of preparing a mother liquor containing an alkali catalyst, an alcohol, and water.

[0051] The alkali catalyst is not particularly limited, and is preferably at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines. As such an amine, an amine represented by the following general formula (X) can be suitably used. NR a R b R c (X) (In the formula, R a , R b , R c represents an optionally substituted alkyl group having 1 to 12 carbon atoms, or hydrogen.

[0052] The amines include R a , R b , R c When all of the above are hydrogen, that is, ammonia can be suitably used.

[0053] R a , R b , R c may be the same or different. a , R b , R c may be linear, branched or cyclic.

[0054] The number of carbon atoms in the linear or branched alkyl group may be 1 to 12, preferably 1 to 8, and more preferably 1 to 6. Examples of linear alkyl groups include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group. Examples of branched alkyl groups include isopropyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 1-methyl-1-ethylpropyl, 2-methyl-2-ethylpropyl, 1-ethylbutyl, 2-ethylbutyl, 1-ethylhexyl, 2-ethylhexyl, 3-ethylhexyl, 4-ethylhexyl, and 5-ethylhexyl. Preferred linear or branched alkyl groups include n-propyl, n-hexyl, 2-ethylhexyl, and n-octyl.

[0055] The number of carbon atoms in the cyclic alkyl group may be, for example, 3 to 12, and preferably 3 to 6. Examples of the cyclic alkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group. A preferred cyclic alkyl group is a cyclohexyl group.

[0056] R in the above general formula (X) a , R b , R cIn the above, the alkyl group may be substituted. The number of substituents may be, for example, 0, 1, 2, 3, or 4, preferably 0, 1, or 2, and more preferably 0 or 1. An alkyl group having zero substituents is an unsubstituted alkyl group. Examples of the substituent include an alkoxy group having 1 to 3 carbon atoms (e.g., a methoxy group, an ethoxy group, a propoxy group, or an isopropoxy group), an amino group, a primary amino group substituted with a linear alkyl group having 1 to 4 carbon atoms, an amino group di-substituted with a linear alkyl group having 1 to 4 carbon atoms (e.g., a dimethylamino group or a di-n-butylamino group), and an unsubstituted amino group. However, a hydroxyl group is excluded as a substituent. In an alkyl group having multiple substituents, the substituents may be the same or different.

[0057] R in the above general formula (X) a , R b , R c is preferably a linear or branched alkyl group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms) which may be substituted. a , R b , R c may be a linear or branched alkyl group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms) which may be substituted with an alkoxy group having 1 to 3 carbon atoms.

[0058] Also, R a , R b , R c may be unsubstituted. Preferably, R a , R b , R c is an unsubstituted linear or branched alkyl group having 1 to 12 carbon atoms, or a linear or branched alkyl group substituted with an alkoxy group having 1 to 12 carbon atoms. In one embodiment, the amine may be at least one amine selected from the group consisting of 3-ethoxypropylamine, pentylamine, hexylamine, dipropylamine, and triethylamine.

[0059] The above amines may be used alone or in combination of two or more.

[0060] The content of the alkali catalyst in the mother liquor is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.5% by mass or more, based on 100% by mass of the mother liquor. The lower limit of the alkali catalyst content within the above range makes it easier to control the particle size of the silica particles. The upper limit of the alkali catalyst content in the mother liquor is not particularly limited, and may be 3.0% by mass or less, 2.5% by mass or less, or 2.0% by mass or less.

[0061] The alcohol is not particularly limited, and examples thereof include methanol, ethanol, isopropanol, n-butanol, and isobutanol.

[0062] The alcohol content in the mother liquor is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more, based on 100% by mass of the mother liquor. The lower limit of the alcohol content within the above range makes it easier to control the particle size of the silica particles. The upper limit of the alcohol content in the mother liquor is not particularly limited, and may be 95% by mass or less, 90% by mass or less, or 87% by mass or less.

[0063] The water content in the mother liquor is preferably 10.0 to 14.5% by mass, more preferably 11.0 to 14.0% by mass, and even more preferably 12.0 to 13.5% by mass. If the water content in the mother liquor is below the lower limit of the above range, silica particle aggregates are likely to form. If the water content in the mother liquor exceeds the upper limit of the above range, the silanol group density per unit surface area of ​​the silica particles decreases, resulting in reduced dispersion stability of the silica particles.

[0064] The method for preparing the mother liquor is not particularly limited, and an alkali catalyst and an alcohol may be added to water by a conventionally known method, followed by stirring.

[0065] The pH of the mother liquor is not particularly limited, but is preferably 9.5 or higher, more preferably 10.0 or higher. When the lower limit of the pH of the mother liquor is within the above range, it becomes easier to control the particle size. The upper limit of the pH of the mother liquor is not particularly limited, but is about 11.5 or lower, or about 11.0 or lower.

[0066] By the above-described step 1, a mother liquor containing an alkali catalyst, an alcohol, and water is prepared.

[0067] (Process 2) Step 2 is a step of preparing a reaction liquid by adding a raw material solution containing an alkoxysilane and an alcohol to the mother liquid.

[0068] The alcohol used in step 2 can be the same as the alcohol described in step 1 above.

[0069] The alcohol content in the raw material solution is not particularly limited as long as colloidal silica can be formed, and can be adjusted appropriately. The alcohol content is preferably 10% by mass or more, more preferably 15% by mass or more, based on 100% by mass of the raw material solution. The alcohol content is preferably 40% by mass or less, more preferably 30% by mass or less, based on 100% by mass of the raw material solution.

[0070] The alkoxysilane is not particularly limited, and an alkoxysilane represented by the following general formula (1) can be used. In addition, a derivative of the alkoxysilane can also be used.

[0071] Si(OR)4(1) [In the formula, R is an alkyl group, preferably a lower alkyl group having 1 to 8 carbon atoms, and more preferably a lower alkyl group having 1 to 4 carbon atoms.]

[0072] Examples of R include methyl, ethyl, propyl, isopropyl, butyl, pentyl, and hexyl groups, with tetramethoxysilane, where R is a methyl group, tetraethoxysilane, where R is an ethyl group, and tetraisopropoxysilane, where R is an isopropyl group, being preferred. Furthermore, examples of alkoxysilane derivatives include low-condensation products obtained by partially hydrolyzing alkoxysilane. In the present invention, it is preferable to use tetramethoxysilane because the hydrolysis rate is easily controlled and there is little residual unreacted material.

[0073] The content of alkoxysilane in the raw material solution is not particularly limited as long as colloidal silica can be formed, and can be adjusted appropriately. The content of alkoxysilane is preferably 50% by mass or more, more preferably 70% by mass or more, based on 100% by mass of the raw material solution. Furthermore, the content of alkoxysilane is preferably 95% by mass or less, more preferably 90% by mass or less, based on 100% by mass of the raw material solution.

[0074] The method for preparing the raw material solution is not particularly limited, and it is sufficient to mix an alkoxysilane and an alcohol and stir them by a conventionally known method.

[0075] In step 2, the raw material solution is added to the mother liquor to prepare a reaction liquid.

[0076] The rate at which the raw material solution is added to the mother liquor is not particularly limited, but is preferably a constant rate, preferably 1.0 to 20 g / min / kg of mother liquor, more preferably 2.0 to 15 g / min / kg of mother liquor, and even more preferably 3.0 to 10 g / min / kg of mother liquor.

[0077] In step 2, the temperature of the reaction solution is preferably 15 to 25°C. If the temperature of the reaction solution is below the lower limit of the above range, the silanol group density per unit surface area of ​​the silica particles becomes excessively high, resulting in a decrease in the dispersion stability of the silica particles. If the temperature of the reaction solution is above the upper limit of the above range, the silanol group density per unit surface area of ​​the silica particles becomes low, resulting in a decrease in the dispersion stability of the silica particles.

[0078] In step 2, the water concentration in the reaction solution is preferably 14.5% by mass or less, more preferably 14.0% by mass or less. When the upper limit of the water concentration in the reaction solution is within the above range, the silanol group density per unit surface area of ​​the silica particles increases, and the dispersion stability of the silica particles increases. The lower limit of the water concentration in the reaction solution is not particularly limited, and may be, for example, 5% by mass.

[0079] In step 2 described above, the raw material solution containing alkoxysilane and alcohol is added to the mother liquor to prepare the reaction liquid.

[0080] (Step 3) Step 3 is a step of adding citric acid to the reaction solution.

[0081] The method for adding citric acid to the reaction solution is not particularly limited, and citric acid may be added dropwise to the reaction solution by a conventionally known method and stirred.

[0082] In step 3, when citric acid is added to the reaction solution, the amount of citric acid added per 1 g of silica particles is preferably 50 to 600 μg / g, more preferably 100 to 595 μg / g. When the lower limit of the amount of citric acid added is within the above range, the dispersion stability of the silica particles is further improved, aggregation of the silica particles is suppressed, and the generation of coarse particles when a shear force is applied can be further suppressed. When the upper limit of the amount of citric acid added is within the above range, the dispersion state is further improved, and the generation of coarse particles when a shear force is applied can be further suppressed.

[0083] Citric acid is added to the reaction liquid in the above-described step 3. The colloidal silica of the present invention can be produced by the above-described step 3.

[0084] (Step 4) The production method of the present invention may further include step 4, in which the silica particle concentration of the citric acid-containing colloidal silica is concentrated and the solvent is replaced with water, after step 3. By including step 4 in the production method of the present invention, the solvent containing impurities and the like in the colloidal silica prepared in step 3 is replaced with new water, thereby further improving the dispersion stability of the silica particles in the colloidal silica, further suppressing the aggregation of the silica particles, and further suppressing the generation of coarse particles when a shear force is applied.

[0085] The method for concentrating the silica particle concentration of colloidal silica is not particularly limited, and examples thereof include a method in which colloidal silica is heated by a conventionally known method to evaporate the solvent.

[0086] The heating temperature when concentrating the silica particle concentration of the colloidal silica is not particularly limited as long as it can evaporate the solvent of the colloidal silica, and is preferably 50 to 100°C.

[0087] The heating time for concentrating the silica particle concentration of the colloidal silica is preferably 0 to 15 hours. If the heating time exceeds the upper limit of the above range, the silanol group density per unit surface area of ​​the silica particles will decrease, and the dispersion stability of the silica particles will deteriorate.

[0088] The method for replacing the solvent in colloidal silica with water is not particularly limited, and examples thereof include a method in which water is added to concentrated colloidal silica and heated by a conventionally known method to replace the solvent with water.

[0089] The heating temperature when the solvent of the colloidal silica is replaced with water is preferably 60 to 100°C. If the heating temperature is below the lower limit of the above range, the alcohol contained in the colloidal silica cannot be sufficiently distilled off. If the heating temperature is above the upper limit of the above range, the silanol group density per unit surface area of ​​the silica particles decreases, and the dispersion stability of the silica particles decreases.

[0090] The heating time when the solvent of the colloidal silica is replaced with water is preferably 0 to 15 hours. If the heating time exceeds the upper limit of the above range, the silanol group density per unit surface area of ​​the silica particles will decrease, and the dispersion stability of the silica particles will decrease.

[0091] In step 4, the sum of the heating time during the concentration and the heating time during substitution with water, i.e., the heating time of the colloidal silica in step 4, is preferably 15 hours or less, more preferably 13 hours or less. If the heating time in step 4 exceeds the upper limit of the above range, the silanol group density per unit surface area of ​​the silica particles decreases, and the dispersion stability of the silica particles decreases.

[0092] By the above-described step 4, the concentration of silica particles in the colloidal silica is increased, and the solvent is replaced with water.

[0093] The citric acid-containing colloidal silica of the present invention can be produced by the production method having the steps described above. [Example]

[0094] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

[0095] Example 1 (Production of citric acid-containing colloidal silica) A mother liquor containing 11,693 parts by mass of a mixture of 1,186 parts by mass of pure water, 452 parts by mass of 26% by mass aqueous ammonia, and 10,055 parts by mass of methanol was prepared. Next, 1,552 parts by mass of a raw material solution containing 1,236 parts by mass of tetramethoxysilane and 316 parts by mass of methanol was added to the mother liquor at a constant rate over 25 minutes while maintaining the liquid temperature in the reaction system at 23°C, to prepare a silica sol reaction liquid containing water and methanol as a dispersion medium. 7.673 parts by mass of a 2% by mass aqueous citric acid solution was added to the silica sol reaction liquid and stirred for 30 minutes. After stirring and mixing, 4,317 parts by mass of the silica sol was concentrated by heating and distillation under atmospheric pressure. The heating time in the concentration step was 10.0 hours. This concentrated liquid was heated and distilled under atmospheric pressure while adding pure water to maintain a constant volume. The methanol and ammonia in the concentrated liquid were replaced with water, and when the pH reached 8 or less, the dropwise addition of pure water and heating were stopped to produce citric acid-containing colloidal silica. The heating time in the water replacement step was 3.0 hours.

[0096] Example 2 Citric acid-containing colloidal silica was produced under the same production conditions as in Example 1, except that the heating time in the concentration step was 7.0 hours and the heating time in the water substitution step was 2.0 hours.

[0097] Example 3 Citric acid-containing colloidal silica was produced under the same production conditions as in Example 2, except that the heating time in the concentration step was changed to 5.0 hours.

[0098] Example 4 Citric acid-containing colloidal silica was produced under the same production conditions as in Example 2, except that the amount of 2 mass % citric acid aqueous solution added to the silica sol reaction liquid was 3.215 parts by mass.

[0099] Example 5 Citric acid-containing colloidal silica was produced under the same production conditions as in Example 2, except that the amount of 2 mass % citric acid aqueous solution added to the silica sol reaction liquid was 11.936 parts by mass.

[0100] Example 6 Citric acid-containing colloidal silica was produced under the same production conditions as in Example 2, except that the liquid temperature in the reaction system was maintained at 25°C when the raw material solution was poured into the mother liquor, and the amount of 2 mass% citric acid aqueous solution added to the silica sol reaction liquid was 14.470 parts by mass.

[0101] Example 7 Citric acid-containing colloidal silica was produced under the same production conditions as in Example 2, except that the liquid temperature in the reaction system was maintained at 18°C ​​when the raw material solution was poured into the mother liquor, and the amount of 2 mass% citric acid aqueous solution added to the silica sol reaction liquid was 4.409 parts by mass.

[0102] Comparative Example 1 A mother liquor containing 11,693 parts by mass of a mixture of 1,712 parts by mass of pure water, 452 parts by mass of 26% by mass aqueous ammonia, and 9,529 parts by mass of methanol was prepared. Next, 1,552 parts by mass of a raw material solution containing 1,236 parts by mass of tetramethoxysilane and 316 parts by mass of methanol was added to the mother liquor at a constant rate over 25 minutes while maintaining the liquid temperature in the reaction system at 23°C, to prepare a silica sol reaction liquid containing water and methanol as a dispersion medium. 7.673 parts by mass of a 2% by mass aqueous citric acid solution was added to the silica sol reaction liquid and stirred for 30 minutes. After stirring and mixing, 4,317 parts by mass of the silica sol was concentrated by heating and distillation under atmospheric pressure. The heating time in the concentration step was 7.0 hours. This concentrated liquid was heated and distilled under atmospheric pressure while adding pure water to maintain a constant volume. The methanol and ammonia in the concentrated liquid were replaced with water, and when the pH reached 8 or less, the dropwise addition of pure water and heating were stopped to produce citric acid-containing colloidal silica. The heating time in the water replacement step was 2.0 hours.

[0103] Comparative Example 2 A mother liquor containing 11,693 parts by mass of a mixture of 952 parts by mass of pure water, 452 parts by mass of 26% aqueous ammonia, and 10,289 parts by mass of methanol was prepared. Next, 1,552 parts by mass of a raw material solution containing 1,236 parts by mass of tetramethoxysilane and 316 parts by mass of methanol was added to the mother liquor at a constant rate over 25 minutes while maintaining the liquid temperature in the reaction system at 14°C, to prepare a silica sol reaction liquid containing water and methanol as a dispersion medium. 7.673 parts by mass of a 2% by mass aqueous citric acid solution was added to the silica sol reaction liquid and stirred for 30 minutes. After stirring and mixing, 4,317 parts by mass of the silica sol was concentrated by heating and distillation under atmospheric pressure. The heating time in the concentration step was 7.0 hours. This concentrated liquid was heated and distilled under atmospheric pressure while adding pure water to maintain a constant volume. The methanol and ammonia in the concentrated liquid were replaced with water, and when the pH reached 8 or less, the dropwise addition of pure water and heating were stopped to produce citric acid-containing colloidal silica. The heating time in the water replacement step was 2.0 hours.

[0104] Comparative Example 3 Citric acid-containing colloidal silica was produced under the same production conditions as in Example 2, except that the amount of 2 mass % citric acid aqueous solution added to the silica sol reaction liquid was 0.706 parts by mass.

[0105] Comparative Example 4 Citric acid-containing colloidal silica was produced under the same production conditions as in Example 2, except that the amount of 2 mass % citric acid aqueous solution added to the silica sol reaction liquid was 15.347 parts by mass.

[0106] Regarding the production conditions for colloidal silica described in Examples 1 to 7 and Comparative Examples 1 to 4, the injection amount of the raw material solution, the tetramethoxysilane (TMOS) concentration of the raw material solution, the amount of mother liquor, the water concentration of the mother liquor, the ammonia concentration of the mother liquor, the injection rate of the raw material solution into the mother liquor, the reaction temperature, the maximum water concentration during the reaction, the amount of citric acid added to the reaction solution, the heating time in the concentration step, the heating time in the water replacement step, and the total heating time in the concentration step and the water replacement step are shown in Table 1.

[0107] Evaluation method The colloidal silica of the Examples and Comparative Examples obtained as described above was evaluated by the following methods.

[0108] (Silanol group density per unit surface area of ​​silica particles, silanol group amount per unit weight of silica particles) The silanol group density per unit surface area of ​​silica particles was evaluated by the following procedure.

[0109] [Step 1] The colloidal silica was centrifuged at 77,400 G, 5°C, and 90 minutes, and the resulting precipitate was dried under reduced pressure at 60°C and a gauge pressure of -0.1 MPa or less for 90 minutes to obtain a dry silica powder.

[0110] [Step 2] The dried silica powder obtained in step 1 was solidified. 29 Analyzed by Si-DD / MAS-NMR, 29 Si-NMR spectra were obtained. The NMR analysis was performed using the DD-MAS method. The NMR device used was the ECZ500R manufactured by JEOL Ltd. The probe used to detect the NMR signal was an 8 mm HXMAS probe manufactured by JEOL Ltd.

[0111] [Step 3] Obtained in step 2 29 The Si-NMR spectrum data was analyzed, and the peak at a chemical shift of approximately -84 ppm, when the signal of the silicon atom of tetramethylsilane was set to 0 ppm, was designated Q1, the peak at approximately -92 ppm was designated Q2, the peak at approximately -101 ppm was designated Q3, and the peak at approximately -111 ppm was designated Q4. The signal areas a1, a2, a3, and a4 of Q1, Q2, Q3, and Q4, respectively, were calculated.

[0112] In analyzing the spectral data, optimization calculations were performed for each peak in the spectrum after Fourier transformation using the nonlinear least squares method, with the center position, height, and half-width of the peak shape created by mixing Lorentzian and Gaussian waveforms as variable parameters.

[0113] [Step 4] The amount of silanol groups per unit weight of silica particles was calculated using the following formula from the signal areas a1, a2, a3, and a4 and the formula weights of the Q1, Q2, Q3, and Q4 components obtained in step 3. The amount of silanol groups per unit weight of silica particles (×10 21 pieces / g) ={[(a1×3)+(a2×2)+(a3×1)]×N A x10 -21} ÷{(a1×87.11)+(a2×78.10)+(a3×69.09)+(a4×60.08)} where N A is Avogadro's number: 6.022 x 10 23 Represents.

[0114] [Step 5] The silanol group density per unit surface area of ​​the silica particles was calculated using the following formula from the amount of silanol groups per unit weight of the silica particles calculated in step 4 and the BET specific surface area of ​​the silica particles obtained by the measurement method described below. The silanol group density per unit surface area of ​​silica particles (×10 19 pieces / m 2 ) = [silanol group amount per unit weight of silica particles (× 10 21 pieces / g)×10 2 ] ÷BET specific surface area (m 2 / g)

[0115] (Citric acid content per unit surface area of ​​silica particles) The citric acid content per unit surface area of ​​the silica particles was evaluated by the following procedure.

[0116] [Step 1] 5 g of colloidal silica was placed in a crucible, 9 mL of 38% hydrofluoric acid was added, and the mixture was heated on a hot plate heated to 100° C. for 6 hours to decompose and evaporate the silica.

[0117] [Step 2] The residue in the crucible was dissolved by adding 6 mL of a 0.1 mol / L aqueous solution of diammonium hydrogen phosphate, and the entire solution was collected. After collection, the solution was diluted to a total volume of 10 g by adding an additional 0.1 mol / L aqueous solution of diammonium hydrogen phosphate, and this was used as the diluted solution for measurement.

[0118] [Step 3] The diluted solution for measurement obtained in step 2 was analyzed by liquid chromatography, and the citric acid concentration was measured using the absolute calibration curve method. The liquid chromatography apparatus used was a Shimadzu LC-2010CHT, and the chromatography column was an Inertsil ODS-3 manufactured by GL Sciences.

[0119] [Step 4] The citric acid concentration of the diluted solution for measurement obtained in step 3 was defined as C (μg / g), and the citric acid content per unit surface area of ​​the silica particles was calculated using the following formula from the content of silica particles and the BET specific surface area of ​​the silica particles obtained by the measurement method described below. Citric acid content per unit surface area of ​​silica particles (μg / m 2 ) = {C (μg / g) × 10 ÷ (5 × silica particle content (mass%) ÷ 100)} ÷BET specific surface area of ​​silica particles (m 2 / g)

[0120] (BET specific surface area) The colloidal silica was pre-dried on a hot plate and then heat-treated at 800°C for 1 hour to prepare a measurement sample. The BET specific surface area (m 2 / g) was measured.

[0121] (Average primary particle size) Colloidal silica was pre-dried on a hot plate and then heat-treated at 800°C for 1 hour to prepare a measurement sample. The BET specific surface area was measured using the prepared measurement sample. The true specific gravity of silica was 2.2, and the BET specific surface area (m 2 / g) was converted to the average primary particle diameter (nm) of silica particles in the colloidal silica.

[0122] (Average secondary particle size) Colloidal silica was added to a 0.3% by mass aqueous citric acid solution and homogenized to a silica concentration of 0.8% by mass. The average secondary particle diameter (nm) of the measurement sample was measured using a dynamic light scattering method ("ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd.).

[0123] (association ratio) The association ratio of the silica particles was calculated using the following formula from the average primary particle size and average secondary particle size of the silica particles obtained by the above-mentioned measurement method. Association ratio = average secondary particle size of silica particles (nm) ÷ average primary particle size of silica particles (nm)

[0124] (Silica particle content) The content of silica particles in the colloidal silica was calculated using the following formula, where 10.0 g of colloidal silica was dried on a hot plate at 150°C, then heated at 800°C for 1 hour to remove moisture, and the amount of the resulting solid content was defined as Wg. Silica particle content in colloidal silica [%] = (W ÷ 10.0) × 100

[0125] (Metal impurity content) The content of metal impurities was measured using an atomic absorption spectrometer. The total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in the colloidal silica was defined as the content of metal impurities.

[0126] (LPC increase rate when shear force is applied by stirring) The colloidal silica of each Example and Comparative Example was subjected to stirring treatment by the method described below in order to apply shear force. The number of large particles (LPC) of 0.2 μm or more was measured before and after the stirring treatment by the method described below, and the LPC increase rate when shear force was applied by stirring treatment was calculated using the following formula. LPC increase rate (%) when shear force is applied by stirring = {[LPC after stirring (# / mL) - LPC before stirring (# / mL)] × 100} ÷LPC before stirring (# / mL)

[0127] (Colloidal silica stirring treatment) The colloidal silica of each of the Examples and Comparative Examples was subjected to stirring treatment in the following manner in order to apply shear force.

[0128] [Step 1] A 500 mL round-bottom flask was charged with 400 mL of colloidal silica.

[0129] [Step 2] Two paddle blades with a blade diameter of 8.6 mm were installed in the round-bottom flask prepared in step 1, and the colloidal silica was stirred at room temperature at a rotation speed of 350 rpm for 24 hours.

[0130] (LPC measurement) Colloidal silica was diluted with ultrapure water to a silica concentration of 1.0% by mass. The diluted solution was used as a measurement sample, and the number of coarse particles of 0.2 μm or more was measured using an Accusizer FX-nano manufactured by Particle Sizing System Inc. The measurement conditions were as follows:

[0131] <System Setup> ·Stirred Vessel Volume:13.22mL Sample Loop Volume: 0.52mL ·Autodilution delay time:3sec. ·Normal Speed ​​Flow Rate:15 mL / min <Sensor Setup Menu> ·FX-Nano HG Minimum Size:0.15μm ·FX-Nano HG Maximum Size:0.27μm ·FX-Nano HG Collection Time:60sec. ·HG Starting Concentration:8000# / mL

[0132] The results are shown in Table 1.

[0133] [Table 1]

Claims

[Claim 1] A citric acid-containing colloidal silica containing silica particles and citric acid, (1) The amount of silanol groups per unit weight of the silica particles is 1.5 × 10 ２１ ~5.0 x 10 ２１ pieces / g, (2) The content of the citric acid per unit surface area of ​​the silica particles is 1.0 to 10.0 μg / m ２ That is, Citric acid-containing colloidal silica characterized by:

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