Colloidal silica and method for producing the same

Abstract

To provide colloidal silica containing silica particles with excellent denseness and excellent maintenability of an uneven surface shape under basic conditions, and a method for producing the colloidal silica.SOLUTION: Colloidal silica that contains silica particles having an uneven surface shape, is characterized in that (1) the silica particles have an alkoxy group content of 1000 ppm or more, and (2) the silica particles have a specific surface area reduction rate of 15.0% or less when heat-treated under basic conditions.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to colloidal silica and a method for producing the same, and more particularly to colloidal silica containing silica particles having a surface uneven shape and a method for producing the same.

Background Art

[0002] Colloidal silica is obtained by dispersing silica fine particles in a medium such as water, and is used as a physical property improver in fields such as paper, fibers, and steel, and is also used as a polishing agent for electronic materials such as semiconductor wafers. The silica particles dispersed in the colloidal silica used for such applications are required to have high purity and density.

[0003] As a method for producing colloidal silica that can meet the above requirements, for example, a method for producing an aqueous silica sol in which an alkyl silicate is added to a reaction medium having an alkali concentration within a specific range is disclosed (see, for example, Patent Document 1).

[0004] However, according to the production method described in Patent Document 1, spherical particles are produced, and the shape of the silica particles has not been studied.

[0005] A method for producing colloidal silica containing silica particles having small protrusions on the particle surface using a quaternary ammonium salt or the like as a hydrolysis catalyst is disclosed (see, for example, Patent Document 2). Colloidal silica can exhibit higher polishing performance as an abrasive when the silica particles are deformed such as having protrusions on the surface.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

[0007] The present inventors have found that the colloidal silica produced by the production method described in Patent Document 2 has a problem that the surface uneven shape cannot be maintained under basic conditions.

[0008] As a result of intensive studies, the present inventors have succeeded in producing colloidal silica containing silica particles excellent in maintaining the surface uneven shape even under basic conditions. And, the inventors have conceived that such colloidal silica can be suitably used as an abrasive and can solve the above problems perfectly, and thus have reached the present invention.

[0009] An object of the present invention is to provide a colloidal silica containing silica particles excellent in airtightness and in maintaining the surface uneven shape even under basic conditions, and a production method capable of producing the colloidal silica. [Means for Solving the Problems]

[0010] As a result of intensive studies to achieve the above object, the present inventors have found that a colloidal silica containing silica particles having a surface uneven shape, in which the content of alkoxy groups in the silica particles is in a specific range and the silica particles exhibit a specific range of reduction rate of specific surface area when heat-treated under basic conditions, can achieve the above object, and have completed the present invention.

[0011] That is, the present invention relates to the following colloidal silica and a method for producing the same. 1. A colloidal silica containing silica particles having a surface uneven shape, (1) the silica particles have an alkoxy group content of 1000 ppm or more, (2) the reduction rate of the specific surface area of the silica particles when heat-treated under basic conditions is 15.0% or less, characterized in that it is a colloidal silica. 2. The colloidal silica according to item 1, wherein the true specific gravity of the silica particles is 1.95 or more. 3. The colloidal silica according to item 1 or 2, wherein the silica particles contain at least 1 kind of amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (however, hydroxy groups are excluded as substituents) in an amount of 5 μmol or more per 1 g of the silica particles. 4. A method for producing colloidal silica containing silica particles having a surface uneven shape, comprising: (1) Step 1 of preparing a mother liquor containing an alkali catalyst and water; (2) Step 2 of adding an alkoxysilane to the mother liquor to prepare a seed particle dispersion; and (3) Step 3 of adding water, an alkali catalyst, and an alkoxysilane to the seed particle dispersion in this order, wherein the alkali catalyst is at least 1 kind of amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (however, hydroxy groups are excluded as substituents), and the molar ratio (s3 / c3) of the addition amount s3 (mol) of the alkoxysilane to the addition amount c3 (mol) of the alkali catalyst in Step 3 is more than 185 and 400 or less. A method for producing colloidal silica, characterized by the above.

Effect of the Invention

[0012] The colloidal silica of the present invention contains silica particles having excellent denseness and excellent maintainability of the surface uneven shape under basic conditions. Further, the method for producing the colloidal silica of the present invention can produce the colloidal silica.

Brief Description of the Drawings

[0013]

Figure 1

Modes for Carrying Out the Invention

[0014] Hereinafter, the colloidal silica of the present invention and its manufacturing method will be described in detail.

[0015] Since the colloidal silica of the present invention contains silica particles having a surface uneven shape, it can exhibit high abrasiveness. Further, since the content of the alkoxy group in the silica particles of the present invention is 1000 ppm or more, the amount of the alkoxy group per unit weight of the silica particles is high, and defects on the surface of a substrate or the like as an object to be polished can be suppressed. Furthermore, since the colloidal silica of the present invention has a reduction rate of specific surface area of 15.0% or less when heat-treated under basic conditions, it is excellent in maintaining the surface uneven shape under basic conditions and can maintain high abrasiveness even under basic conditions. In addition, the method for producing the colloidal silica of the present invention uses at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (however, hydroxy groups are excluded as substituents) as an alkali catalyst, and in step 3, the molar ratio (s3 / c3) of the addition amount s3 (mol) of alkoxysilane to the addition amount c3 (mol) of the alkali catalyst is set within a specific range to perform a sol-gel reaction, whereby colloidal silica having few metal impurities and excellent in maintaining the surface uneven shape under basic conditions and capable of maintaining high abrasiveness even under basic conditions can be produced.

[0016] 1. Colloidal silica The colloidal silica of the present invention is a colloidal silica containing silica particles having a surface uneven shape silica, characterized in that (1) the silica particles have an alkoxy group content of 1000 ppm or more, and (2) the reduction rate of the specific surface area of the silica particles when heat-treated under basic conditions is 15.0% or less.

[0017] In this specification, the surface uneven shape of the silica particles refers to a shape having minute protrusions on the surface of the silica particles, meaning a state where the silica particles have a shape similar to confectionery sugar. Such a surface uneven shape can be defined by the range of the surface roughness (B1 / S1) calculated by dividing the BET specific surface area (B1) by the specific surface area (S1) calculated from the SEM minor axis. Note that the specific surface area (S1) can be obtained by converting the value of 2727 / SEM minor axis (nm) assuming the true specific gravity of silica is 2.2. The surface roughness (B1 / S1) is preferably 1.1 or more, more preferably 1.4 or more. Also, the surface roughness (B1 / S1) is preferably 2.0 or less, more preferably 1.8 or less.

[0018] The above silica particles have an alkoxy group content of 1000 ppm or more. If the alkoxy group content is less than 1000 ppm, the polishing property of the colloidal silica of the present invention deteriorates, and defects on the surface of the object to be polished cannot be suppressed. The alkoxy group content is preferably 4000 ppm or more, more preferably 5000 ppm or more. Also, the alkoxy group content is preferably 45000 ppm or less, more preferably 40000 ppm or less. By the upper limit of the alkoxy group content being within the above range, the polishing property of the colloidal silica of the present invention is further improved.

[0019] Note that the alkoxy group content can be measured by the following method.

[0020] (Alkoxy group content (ppm)) After centrifuging the colloidal silica at 215000G for 90 minutes, the supernatant is discarded, and the solid content is vacuum dried at 60°C for 90 minutes. Weigh 0.50 g of the obtained silica dry solid, put it into 50 ml of 1M sodium hydroxide aqueous solution, and dissolve the silica by heating at 50°C for 24 hours while stirring. The silica solution is analyzed by gas chromatography to determine the alcohol content, and the alkoxy amount per 1 g of silica is calculated. The detector of the gas chromatograph uses a flame ionization detector (FID). The gas chromatograph analysis is performed according to JIS K0114.

[0021] (BET specific surface area (m 2 / g)) The colloidal silica is pre-dried on a hot plate and then heat-treated at 800 °C for 1 hour to prepare a sample for measurement. The prepared sample for measurement is measured by the nitrogen gas adsorption method (BET method).

[0022] (Average primary particle size (nm)) Assuming the true specific gravity of silica is 2.2, convert the value of 2727 / BET specific surface area (m 2 / g) from the measured value of the above BET specific surface area to obtain the average primary particle size (nm) of the silica particles in the colloidal silica.

[0023] When the above silica particles are heat-treated under basic conditions, the reduction rate of the specific surface area is 15.0% or less. If the reduction rate of the specific surface area exceeds 15.0%, the alkali resistance of the protrusions will be low, the maintainability of the surface uneven shape of the silica particles under basic conditions will decrease, and the abrasiveness under basic conditions cannot be maintained. The reduction rate of the specific surface area is preferably 14.5% or less, more preferably 14.3% or less. Also, the lower limit of the reduction rate of the specific surface area is not particularly limited, and it may be about 0.1%.

[0024] Note that the reduction rate of the above specific surface area is measured by the following measurement method. (Reduction rate of specific surface area) Add 3-ethoxypropylamine to 800 g of colloidal silica and adjust the pH to 9.9 - 10.3. Put the above colloidal silica into a flask equipped with a reflux tube and heat it to maintain a reflux state for 3 hours to perform a base treatment. Adjust the pH of the base-treated colloidal silica to 7.6 - 7.8, and measure the BET specific surface area according to the measurement method of the above BET specific surface area. Based on the following formula, calculate the reduction rate of the specific surface area from the BET specific surface areas before and after the base treatment by the following formula. Reduction rate of specific surface area (%) = (BET specific surface area before base treatment - BET specific surface area after base treatment) / BET specific surface area before base treatment × 100

[0025] The silica particles preferably have a true specific gravity of 1.95 or more. When the true specific gravity is 1.95 or more, the hardness of the silica particles is further improved, and the abrasiveness of the colloidal silica is further improved. The true specific gravity of the silica particles is more preferably 2.00 or more, and even more preferably 2.10 or more. Further, the true specific gravity is preferably 2.20 or less, and more preferably 2.16 or less.

[0026] The true specific gravity of the silica particles can be measured by a measuring method in which colloidal silica is dried on a hot plate at 150 ° C, held in a furnace at 300 ° C for 1 hour, and then measured by a liquid phase replacement method using ethanol.

[0027] The silica particles preferably contain at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines. The amine is not particularly limited and is represented by the following general formula (X). 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. However, when all of R a , R b , R c are hydrogen, that is, ammonia is excluded.) R a , R b , R c may be the same or different. R a , R b , R c may be linear, branched, or cyclic.

[0028] The number of carbon atoms of the linear or branched alkyl group may be 1 to 12, preferably 1 to 8, more preferably 1 to 6. Examples of the linear alkyl group include a methyl group, an e Examples include a methyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, etc. Examples of branched alkyl groups include an isopropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1,1-dimethylpropyl group, a 1,2-dimethylpropyl group, a 2,2-dimethylpropyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, a 1-methyl-1-ethylpropyl group, a 2-methyl-2-ethylpropyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-ethylhexyl group, a 2-ethylhexyl group, a 3-ethylhexyl group, a 4-ethylhexyl group, a 5-ethylhexyl group, etc. Preferred linear or branched alkyl groups are an n-propyl group, an n-hexyl group, a 2-ethylhexyl group, an n-octyl group, etc.

[0029] The number of carbon atoms of the cyclic alkyl group may be, for example, 3 to 12, etc., 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, a cyclooctyl group, etc. A preferred cyclic alkyl group is a cyclohexyl group.

[0030] R in the general formula (X) a , R b , R c The alkyl group may be substituted. The number of substituents may be, for example, 0, 1, 2, 3, 4, etc., and preferably 0, 1 or 2, more preferably 0 or 1. When the number of substituents is 0 The alkyl group is an unsubstituted alkyl group. Examples of the substituent include an alkoxy group having 1 to 3 carbon atoms (e.g., methoxy group, ethoxy group, propoxy group, isopropoxy group), an amino group, a primary amino group substituted with a linear alkyl group having 1 to 4 carbon atoms, an amino group disubstituted with a linear alkyl group having 1 to 4 carbon atoms (e.g., dimethylamino group, di-n-butylamino group, etc.), an unsubstituted amino group, etc. However, a hydroxyl group is excluded as the substituent. In the alkyl group having a plurality of substituents, the substituents may be the same or different.

[0031] R in the general formula (X) above a 、R b 、R c is a linear or branched alkyl group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms) which may be substituted. Also, R a 、R b 、R c is 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.

[0032] Also, R a 、R b 、R c may not be substituted. 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 having 1 to 12 carbon atoms substituted with an alkoxy group.

[0033] Examples of the above amines include at least one amine selected from the group consisting of aliphatic ether amines such as 3-ethoxypropylamine, 2-methoxyethylamine, 2-(2-ethoxyethyl)amine, 3-methoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, 3-butoxypropylamine, 3-isobutoxypropylamine, 3-(2-ethylhexyloxy)propylamine, 3-(2-methoxyethoxy)propylamine, and aliphatic amines such as pentylamine, hexylamine, dipropylamine, and triethylamine. Among these, aliphatic ether amines are preferred, and 3-ethoxypropylamine is more preferred, in that the content of silica particles excellent in maintaining the surface uneven shape under more basic conditions can be increased.

[0034] The above amines may be used alone or in combination of two or more.

[0035] The content of at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (excluding hydroxy groups as substituents) in the silica particles is preferably 5 μmol or more per 1 g of silica particles, and more preferably 10 μmol or more per 1 g of silica particles. When the lower limit of the above amine content is within the above range, the content of silica particles excellent in maintaining the surface uneven shape under basic conditions in the colloidal silica further increases, and the colloidal silica exhibits more sufficient abrasiveness. Also, the above amine content is preferably 100 μmol or less per 1 g of silica particles, and more preferably 90 μmol or less per 1 g of silica particles. When the upper limit of the above amine content is within the above range, silica particles having a surface uneven shape are more likely to be formed.

[0036] Incidentally, the amine content can be measured by the following method. That is, after centrifuging colloidal silica at 215000G for 90 minutes, the supernatant is discarded, and the solid content is vacuum-dried at 60°C for 90 minutes. Weigh 0.50 g of the obtained silica dry solid, put it into 50 ml of 1M sodium hydroxide aqueous solution, and dissolve the silica by heating at 50°C for 24 hours while stirring. Analyze the silica solution by ion chromatography to determine the amine content. The ion chromatography analysis is performed according to JIS K0127.

[0037] The boiling point of the above amine is preferably 85°C or higher, more preferably 90°C or higher. When the lower limit of the boiling point is within the above range, vaporization during the reaction is further suppressed, and it can be preferably used as a catalyst. Also, the above boiling point is preferably 500°C or lower, more preferably 300°C or lower.

[0038] The colloidal silica of the present invention preferably contains 20% or more, more preferably 30% or more, of silica particles having a surface uneven shape among the number of particles in an arbitrary visual field at 200,000 times magnification observed by a scanning electron microscope. When the lower limit of the content of the above silica particles is within the above range, the polishing property of the colloidal silica is further improved. The upper limit of the content is not particularly limited and may be 100% or 70%.

[0039] In this specification, the content of the silica particles having the above surface uneven shape can be measured by the following measurement method. That is, count the particles having a surface uneven shape from among the number of particles in an arbitrary visual field at 200,000 times magnification observed by a scanning electron microscope (SEM), and set the ratio of those particles as the content (%).

[0040] The short SEM diameter of the silica particles in the colloidal silica is preferably 8 nm or more, more preferably 15 nm or more. When the lower limit of the short SEM diameter of the silica particles is within the above range, the polishing property of the colloidal silica of the present invention is further improved. Further, the short SEM diameter of the silica particles is preferably 100 nm or less, more preferably 80 nm or less. When the upper limit of the short SEM diameter of the silica particles is within the above range, the occurrence of scratches on the object to be polished is further reduced.

[0041] The above short SEM diameter can be measured by the following method. An image of the silica particles taken with a scanning electron microscope is approximated to 1000 particles with ellipses using image analysis software ("WinRoof2015" manufactured by Mitani Trading Co., Ltd.) ) and the minor axis of the ellipse is measured. The number frequency distribution of the minor axis of the ellipse is taken, and the minor axis of the ellipse with a number frequency of 50% is defined as the short SEM diameter (nm).

[0042] The average secondary particle diameter of the silica particles in the colloidal silica is preferably 8 nm or more, more preferably 15 nm or more. When the lower limit of the average secondary particle diameter of the silica particles is within the above range, the polishing property of the colloidal silica of the present invention is further improved. Further, the average secondary particle diameter of the silica particles is preferably 400 nm or less, more preferably 300 nm or less. When the upper limit of the average secondary particle diameter of the silica particles is within the above range, the occurrence of scratches on the object to be polished is further reduced.

[0043] In this specification, the average secondary particle diameter of the silica particles in the above colloidal silica can be measured by the following measurement method. That is, as a sample for measuring the dynamic light scattering method, a sample prepared by adding colloidal silica to an aqueous solution of 0.3% by weight of citric acid and homogenizing it is prepared. Using the sample for measurement, the secondary particle diameter is measured by the dynamic light scattering method ("ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd.).

[0044] The aspect ratio of the silica particles in the colloidal silica is preferably 1.0 or more, more preferably 1.1 or more. When the lower limit of the aspect ratio is within the above range, the abrasiveness is further improved. Also, the aspect ratio of the silica particles is preferably 4.0 or less, more preferably 3.0 or less. When the upper limit of the aspect ratio is within the above range, the generation of scratches on the object to be polished is further suppressed.

[0045] In this specification, the aspect ratio of the silica particles in the above colloidal silica can be measured by the following measurement method. That is, an image of the silica particles taken with a scanning electron microscope is approximated to an ellipse for 1000 particles using image analysis software ("WinRoof2015" manufactured by Mitani Corporation). The major axis and minor axis of the ellipse are measured for each particle. The aspect ratio is calculated as the ratio of the major axis to the minor axis of the ellipse (major axis of the ellipse / minor axis of the ellipse) for each particle, and the average value is taken as the aspect ratio.

[0046] The colloidal silica of the present invention preferably has a content of metal impurities such as sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt of 1 ppm or less. When the content of the metal impurities is 1 ppm or less, it can be suitably used for polishing electronic materials and the like.

[0047] In this specification, the content of the above metal impurities is a value measured using an atomic absorption spectrometer.

[0048] The aggregation ratio of the silica particles in the colloidal silica is preferably 1.5 or more, more preferably 1.7 or more. When the lower limit of the aggregation ratio of the silica particles is within the above range, the abrasiveness of the colloidal silica of the present invention is further improved. Also, the aggregation ratio of the silica particles is preferably 5.5 or less, more preferably 5.0 or less. When the upper limit of the aggregation ratio of the silica particles is within the above range, the generation of scratches on the object to be polished is further reduced.

[0049] In this specification, the aggregation ratio of silica particles in the colloidal silica is a value obtained by calculating the average secondary particle diameter / average primary particle diameter of silica particles in the colloidal silica.

[0050] The silanol group density of silica particles in the colloidal silica is preferably 1.5 pieces / nm 2 or more, more preferably 1.6 pieces / nm 2 or more. When the lower limit of the silanol group density is within the above range, the generation of scratches on the object to be polished is further reduced. In addition, the silanol density of silica particles is preferably 5.0 pieces / nm 2 or less, more preferably 4.0 pieces / nm 2 or less. When the upper limit of the silanol group density is within the above range, the polishing performance of the colloidal silica of the present invention is further improved.

[0051] Note that the silanol group density of silica particles in the colloidal silica can be determined by the Sears method. The Sears method was carried out with reference to the description in G.W. Sears, Jr., “Determination of Specific Surface Area of Colloidal Silica by Titration with Sodium Hydroxide”, Analytical Chemistry, 28(12), 1981(1956). For the measurement, a 1 wt% silica dispersion was used, titrated with a 0.1 mol / L aqueous sodium hydroxide solution, and the silanol group density was calculated based on the following formula. ρ=(a×f×6022)÷(c×S) In the above formula, ρ: silanol group density (pieces / nm 2 ), a: the dropping amount (mL) of 0.1 mol / L aqueous sodium hydroxide solution at pH 4 - 9, f: the factor of 0.1 mol / L aqueous sodium hydroxide solution, c: the mass (g) of silica particles, S: BET specific surface area (m 2 / g) respectively represent.

[0052] 2. Method for producing colloidal silica The method for producing the colloidal silica of the present invention is a method for producing colloidal silica containing silica particles having a surface uneven shape, (1) Step 1 of preparing a mother liquor containing an alkali catalyst and water, (2) Step 2 of adding an alkoxysilane to the mother liquor to prepare a seed particle dispersion, and (3) Step 3 of adding water, an alkali catalyst, and an alkoxysilane to the seed particle dispersion in this order, The alkali catalyst is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (however, hydroxy groups are excluded as substituents), In the step 3, the molar ratio (s3 / c3) of the addition amount s3 (mol) of the alkoxysilane to the addition amount c3 (mol) of the alkali catalyst is more than 185 and 400 or less.

[0053] (Step 1) Step 1 is a step of preparing a mother liquor containing an alkali catalyst and water.

[0054] The alkali catalyst is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (however, hydroxy groups are excluded as substituents). As the amine, the same amine as described for the colloidal silica above may be used.

[0055] The content of the amine in the mother liquor is preferably 0.30 mmol / kg or more, more preferably 0.50 mmol / kg or more. When the lower limit of the content of the amine is within the above range, it becomes easier to control the particle size. Also, the content of the amine in the mother liquor is preferably 20.0 mmol / kg or less, more preferably 15.0 mmol / kg or less. When the content of the amine is within the above range, it is difficult to gel during the reaction.

[0056] The method for preparing the mother liquor is not particularly limited, and the alkali catalyst may be added to water by a conventionally known method and stirred.

[0057] The pH of the mother liquor is not particularly limited, 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 even further. Also, the pH of the mother liquor is preferably 12.0 or lower, more preferably 11.5 or lower. When the upper limit of the pH of the mother liquor is within the above range, it becomes even easier to control the average secondary particle size of the silica particles having a surface uneven shape, and the aggregation of the seed particles in the seed particle dispersion liquid obtained in Step 2 described later is suppressed, and the storage stability of the colloidal silica is further improved.

[0058] (Step 2) Step 2 is a step of adding an alkoxysilane to the above mother liquor to prepare a seed particle dispersion liquid.

[0059] The alkoxysilane is not particularly limited, and is represented by the following general formula (2) Si(OR 1 )4(2) (In the formula, R 1 represents an alkyl group.) Examples of the alkoxysilane represented by the formula include those.

[0060] In the above general formula (2), R 1 represents an alkyl group. R 1 is not particularly limited as long as it is an alkyl group, preferably a lower alkyl group having 1 to 8 carbon atoms, more preferably a lower alkyl group having 1 to 4 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a hexyl group, and the like. Examples of the alkoxysilane represented by the above general formula (2) include tetramethoxysilane (tetramethyl orthosilicate) in which R 1 is a methyl group, tetraethoxysilane (tetraethyl orthosilicate) in which R 1 is an ethyl group, and tetraisopropoxysilane in which R 1 is an isopropyl group. Tetramethoxysilane in which R 1 is a methyl group and tetraethoxysilane in which R 1 is an ethyl group are more preferable, and tetramethoxysilane is even more preferable.

[0061] The alkoxysilane represented by the general formula (2) above may be a derivative. Examples of the derivative of the alkoxysilane include low condensates obtained by partially hydrolyzing the alkoxysilane represented by the general formula (2) above.

[0062] The alkoxysilane represented by the general formula (2) above may be used alone or in combination of two or more.

[0063] The addition amount of the alkoxysilane represented by the general formula (2) above in the seed particle dispersion is not particularly limited. The molar ratio (s2 / c1) of the addition amount s2 (mol) of the alkoxysilane in Step 2 to the amount c1 (mol) of the alkali catalyst in the mother liquor is preferably 10 or more, more preferably 100 or more, and even more preferably 150 or more. When the lower limit of s2 / c1 is within the above range, the content of silica particles in the colloidal silica can be further increased. Also, s2 / c1 is preferably 8500 or less, more preferably 8000 or less. When the upper limit of s2 / c1 is within the above range, it is difficult to gel during the reaction.

[0064] The addition time of the alkoxysilane in Step 2 is preferably 5 minutes or more, more preferably 10 minutes or more. When the lower limit of the addition time is within the above range, it is difficult to gel during the reaction. Also, the addition time of the alkoxysilane is preferably 1000 minutes or less, more preferably 600 minutes or less. When the upper limit of the addition time is within the above range, the productivity is further improved and the manufacturing cost can be further suppressed.

[0065] The pH of the seed particle dispersion is preferably 8.5 or less, more preferably 8.0 or less. When the upper limit of the pH of the seed particle dispersion is within the above range, it becomes easier to form silica particles having a surface uneven shape. Also, the pH of the seed particle dispersion is preferably 4.5 or more, more preferably 4.9 or more. When the lower limit of the pH of the seed particle dispersion is within the above range, gelation is further suppressed.

[0066] The temperature of the seed particle dispersion liquid in Step 2 is preferably 70 °C or higher, more preferably 75 °C or higher. When the lower limit of the temperature of the seed particle dispersion liquid is within the above range, gelation during the reaction is further suppressed. Also, the temperature of the seed particle dispersion liquid is preferably 95 °C or lower, more preferably 90 °C or lower. When the upper limit of the temperature of the seed particle dispersion liquid is within the above range, vaporization of the alkoxysilane is further suppressed.

[0067] (Step 3) Step 3 is a step of adding water, an alkali catalyst, and an alkoxysilane to the seed particle dispersion liquid.

[0068] The alkali catalyst is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (however, hydroxy groups are excluded as substituents). As the amine, the same amines as those described for the colloidal silica above may be used. Also, the alkali catalyst used in Step 3 may be the same as or different from the alkali catalyst used in Step 1.

[0069] In Step 3, silica particles having a surface concavo-convex shape are formed in the colloidal silica. Although the mechanism of this action is not clear, it is presumed as follows. That is, in Step 3, the addition of alkoxysilane reduces the pH of the seed particle dispersion. In the reaction for forming silica particles in Step 3, under conditions of a relatively high pH which is basic, no new seed particles are generated, and it is considered that the alkoxylane is consumed so that the silica particles simply grow, and silica particles having a surface concavo-convex shape cannot be generated. On the other hand, when the pH gradually decreases and the seed particle dispersion becomes weakly basic, the condensation rate of the hydrolyzate of alkoxysilane increases, and the dissolution of embryos which are precursors of the seed particles does not occur, so it is predicted that new seed particles will be generated. Furthermore, when the pH decreases to near neutrality, it is considered that the seed particles generated in the weakly basic state combine with the original seed particles generated in Step 2, and concavities and convexities are formed on the particle surface. Therefore, it is considered that colloidal silica containing a surface concavo-convex shape can be produced by the production method of the present invention.

[0070] From the above-predicted mechanism of action, in Step 3, it is preferable that the pH of the seed particle dispersion decreases while being controlled to an appropriate pH from strongly basic to near neutral. For this reason, as the alkali catalyst used in Step 3, an alkali catalyst that maintains a high pH or an alkali catalyst whose pH rapidly decreases is not suitable, and an alkali catalyst having a buffering ability that gradually decreases while being controlled within an appropriate pH range is preferably used. From the above mechanism of action, since the pKa value representing the physical properties of an acid or a base is the central value of the buffering region, in Step 3, it serves as a criterion for whether a substance has a buffering ability that gradually decreases while being controlled within an appropriate pH range. That is, the amine represented by the above general formula (X) having a pKa value of 8.5 or more and less than 11 is preferable as the alkali catalyst used in Step 3, and the amine represented by the above general formula (X) having a pKa value of 9 or more and less than 10 is more preferable.

[0071] From the above mechanism of action, since the pKa value representing the physical properties of an acid or a base is the central value of the buffering region, in Step 3, it serves as a criterion for whether a substance has a buffering ability that gradually decreases while being controlled within an appropriate pH range. That is, the amine represented by the above general formula (X) having a pKa value of 8.5 or more and less than 11 is preferable as the alkali catalyst used in Step 3, and the amine represented by the above general formula (X) having a pKa value of 9 or more and less than 10 is more preferable.

[0072] In addition, examples of the amine represented by the general formula (X) and its pKa value include, for aliphatic ether amines, 3-ethoxypropylamine (9.79), 2-methoxyethylamine (9.89), 3-methoxypropylamine (9.73), 3-propoxypropylamine (9.78), 3-isopropoxypropylamine (9.82), and 3-butoxypropylamine (9.77). For aliphatic amines, examples include pentylamine (10.63), hexylamine (10.56), dipropylamine (10.91), and triethylamine (10.75).

[0073] The alkoxysilane used in Step 3 is not particularly limited, and the same alkoxysilanes as those described in Step 2 above can be used. The alkoxysilane used in Step 3 may be the same as or different from the alkoxysilane used in Step 2, but it is preferable to use the same alkoxysilane as that used in Step 2.

[0074] In Step 3, the molar ratio (s3 / c3) of the addition amount s3 (mol) of the alkoxysilane to the addition amount c3 (mol) of the alkali catalyst exceeds 185. When the lower limit of s3 / c3 exceeds 185, the concavo-convex shape on the surface is more likely to be formed. s3 / c3 is preferably 200 or more, more preferably 220 or more. Also, the above s3 / c3 is 400 or less. When s3 / c3 is 400 or less, the gelation of colloidal silica is further suppressed. s3 / c3 is preferably 380 or less, more preferably 350 or less.

[0075] In Step 3, alcohol may be added to the seed particle dispersion liquid in addition to the above-mentioned water, alkali catalyst, and alkoxysilane.

[0076] The alcohol is not particularly limited as long as it is soluble in water, and the same alcohol as the alcohol that is a by-product when the alkoxysilane used is hydrolyzed is preferred. For example, when the alkoxysilane is tetramethyl orthosilicate, it is preferable to use methanol, and when the alkoxysilane is tetraethyl orthosilicate, it is preferable to use ethanol.

[0077] In Step 3, the content of alcohol in the mixed solution obtained by mixing the seed particle dispersion, water, an alkali catalyst, and alcohol, based on 100% by mass of the mixed solution, is preferably 25% by mass or less, more preferably 20% by mass or less. When the upper limit of the alcohol content is within the above range, it becomes easier to further increase the temperature of the mixed solution in Step 3. Also, the lower limit of the alcohol content is not particularly limited and may be 0% by mass or may be 2% by mass.

[0078] The addition amount of the alkoxysilane in Step 3 is not particularly limited, and the molar ratio (s3 / sp3) of the addition amount s3 (mol) of the alkoxysilane in Step 3 to the amount sp3 (mol) of seed particles in the mixed solution obtained by mixing the seed particle dispersion, water, an alkali catalyst, and alcohol is preferably 0 or more and 30 or less. When the upper limit of s3 / sp3 is within the above range, it is difficult for new nuclei particles to be generated during the reaction, and the growth of the main particles is further promoted. The above molar ratio is a value defined assuming the molecular weight of the seed particles is 60.08 g / mol.

[0079] The temperature of the mixed solution in Step 3 is preferably 70°C or higher, more preferably 75°C or higher. When the lower limit of the temperature of the mixed solution is within the above range, gelation during the reaction is further suppressed. Also, the temperature of the mixed solution is preferably 95°C or lower, more preferably 90°C or lower. When the upper limit of the temperature of the seed particle dispersion is within the above range, vaporization of the alkoxysilane is further suppressed.

[0080] In Step 3, the addition time of alkoxysilane is preferably 5 minutes or more, more preferably 10 minutes or more. When the lower limit of the addition time is within the above range, gelation is less likely to occur during the reaction. Also, the addition time of alkoxysilane is preferably 1000 minutes or less, more preferably 600 minutes or less. When the upper limit of the addition time is within the above range, productivity can be further improved and manufacturing costs can be further reduced.

[0081] The colloidal silica of the present invention can be produced by the production method described above.

[0082] The pH of the colloidal silica is preferably 11.0 or less, more preferably 10.0 or less. When the upper limit of the pH of the colloidal silica is within the above range, dissolution of silica particles is further suppressed. Also, the pH of the colloidal silica is preferably 5.8 or more, more preferably 6.0 or more. When the lower limit of the pH of the colloidal silica is within the above range, gelation is further suppressed.

[0083] The method for producing colloidal silica of the present invention may further include a step of concentrating the colloidal silica after Step 3. The concentration method is not particularly limited, and concentration can be performed by a conventionally known method. Examples of such a concentration method include a method of heating and concentrating at a temperature of about 65 to 100°C.

[0084] The concentration of silica particles in the colloidal silica after concentration is not particularly limited, and is preferably about 1 to 50% by mass with the colloidal silica being 100% by mass.

[0085] The method for producing colloidal silica of the present invention may further include a step of distilling off methanol by-produced during the reaction outside the system after Step 3. The method for distilling off methanol outside the system is not particularly limited. For example, a method of dropping pure water while heating the colloidal silica and keeping the volume constant to replace the dispersion medium with pure water can be mentioned. Also, as another method, a method of redispersing in water after separating the colloidal silica from the solvent by precipitation / separation, centrifugation, etc. can be exemplified.

[0086] The colloidal silica of the present invention and the colloidal silica produced by the production method of the present invention can be used in various applications such as abrasive agents and paper coating agents. The abrasive agent containing the above colloidal silica is also one of the present inventions. Since the colloidal silica of the present invention can have a high purity with a content of metal impurities such as sodium of 1 ppm or less, it can be suitably used particularly as an abrasive agent for chemical mechanical polishing of semiconductor wafers.

Examples

[0087] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples.

[0088] Example 1 (Step 1) 6767 g of pure water as a solvent and 6.98 g of 3-ethoxypropylamine (3-EOPA) as an alkali catalyst were placed in a flask to prepare a mother liquor. The pH of the mother liquor was 11.0. (Step 2) After heating the mother liquor to an internal temperature of 80°C, 2472 g of tetraethyl orthosilicate was added dropwise at a constant rate over 210 minutes while controlling the temperature so that the internal temperature did not fluctuate, to prepare a seed particle dispersion. (Step 3) 5704 g of pure water as a solvent, 6.50 g of 3-ethoxypropylamine (3-EOPA) as an alkali catalyst, and 1075 g of the seed particle dispersion prepared in Step 2 were placed in a flask. Then, after heating to an internal temperature of 80°C, 2397 g of tetraethyl orthosilicate was added dropwise at a constant rate over 180 minutes while controlling the temperature so that the internal temperature did not fluctuate. Stirring was maintained for 15 minutes after the completion of the dropwise addition to prepare a colloidal silica dispersion. Then, the colloidal silica dispersion was made to have a base amount of 800 mL under normal pressure and heated and concentrated until the silica concentration reached 20 wt%. Next, in order to distill off the methanol by-produced during the reaction outside the system, while keeping the volume constant, the dispersion medium was replaced with 500 mL of pure water to prepare colloidal silica.

[0089] In Example 1, the molar ratio (s3 / c3) of the addition amount s3 (mol) of alkoxysilane (tetramethyl orthosilicate) to the addition amount c3 (mol) of the alkali catalyst (3-ethoxypropylamine) in Step 3 was 250.

[0090] Example 2 (Step 1) 6767 g of pure water as a solvent and 10.47 g of 3-ethoxypropylamine (3-EOPA) as an alkali catalyst were placed in a flask to prepare a mother liquor. The pH of the mother liquor was 11.3. (Step 2) After heating the mother liquor to an internal temperature of 85°C, 2472 g of tetramethyl orthosilicate was added dropwise at a constant rate over 210 minutes while controlling the temperature so that the internal temperature did not fluctuate, to prepare a seed particle dispersion. (Step 3) 5704 g of pure water as a solvent, 6.50 g of 3-ethoxypropylamine (3-EOPA) as an alkali catalyst, 242 g of methanol, and 667 g of the seed particle dispersion prepared in Step 2 were placed in a flask. Then, after heating to an internal temperature of 80°C, 2397 g of tetramethyl orthosilicate was added dropwise at a constant rate over 180 minutes while controlling the temperature so that the internal temperature did not fluctuate. Stirring was maintained for 15 minutes after the completion of the dropwise addition to prepare a colloidal silica dispersion. Next, the colloidal silica dispersion was concentrated by heating under normal pressure to a base amount of 9000 mL until the silica concentration reached 20 wt%. Then, in order to distill off the methanol by-produced during the reaction outside the system, while keeping the volume constant, the dispersion medium was replaced with 5680 mL of pure water to prepare colloidal silica.

[0091] In Example 2, the molar ratio (s3 / c3) of the addition amount s3 (mol) of alkoxysilane (tetramethyl orthosilicate) to the addition amount c3 (mol) of the alkali catalyst (3-ethoxypropylamine) in Step 3 was 250.

[0092] Comparative Example 1 (Step 1) 7500 g of pure water as a solvent and 1.35 g of 3-ethoxypropylamine (3-EOPA) as an alkali catalyst were placed in a flask to prepare a mother liquor. The pH of the mother liquor was 10.3. (Step 2) After heating the mother liquor to an internal temperature of 85°C, 2740 g of tetraethyl orthosilicate was added dropwise at a constant rate over 60 minutes while controlling the temperature so that the internal temperature did not fluctuate, and then stirred for 15 minutes to prepare a seed particle dispersion. (Step 3) 50 g of 3-ethoxypropylamine (3-EOPA) as an alkali catalyst was added to the seed particle dispersion to prepare a mixed solution. Separately, 5379 g of pure water as a solvent was placed in a flask, and 2382 g of the mixed solution of the above-mentioned 3-ethoxypropylamine and the seed particle dispersion was added. (Step 4) After heating to an internal temperature of 80°C, 1712.5 g of tetraethyl orthosilicate was added dropwise at a constant rate over 180 minutes while controlling the temperature so that the internal temperature did not fluctuate. After the dropping was completed, stirring was maintained for 15 minutes to prepare a colloidal silica dispersion. Then, the colloidal silica dispersion was concentrated by heating under normal pressure to a base amount of 800 mL until the silica concentration reached 20 wt%. Next, in order to distill off the by-produced methanol during the reaction outside the system, the dispersion medium was replaced with 500 mL of pure water while keeping the volume constant to prepare colloidal silica. No surface uneven shape was formed on the obtained particles. (Step 5) In Comparative Example 1, the molar ratio (s3 / c3) of the addition amount s3 (mol) of alkoxysilane (tetraethyl orthosilicate) to the addition amount c3 (mol) of alkali catalyst (3-ethoxypropylamine) in Step 3 was 100. (Step 6) (Step 1) 9492 g of pure water as a solvent and 3.28 g of triethanolamine (TEA) as an alkali catalyst were placed in a flask to prepare a mother liquor. The pH of the mother liquor was 9.4.

[0093]

[0094] Comparative Example 2 (Step 1) 9492 g of pure water as a solvent and 3.28 g of triethanolamine (TEA) as an alkali catalyst were placed in a flask to prepare a mother liquor. The pH of the mother liquor was 9.4. (Step 2) After heating the mother liquor to an internal temperature of 80°C, 1704 g of tetramethoxysilicate was added dropwise at a constant rate over 180 minutes while controlling the temperature so that the internal temperature did not fluctuate. After the supply of tetramethylsilicate into the reaction vessel was completed, the reaction solution in the reaction vessel was heated, and methanol was distilled out from the distillation tube equipped with a condenser. While distilling out methanol, the reaction solution prepared under the same conditions was fed into the reaction vessel for concentration to prepare a seed particle dispersion with a silica concentration of 12.2 wt%. (Step 3) 5582 g of pure water as a solvent, 9.43 g of triethanolamine (TEA) as an alkali catalyst, and 857 g of the seed particle dispersion prepared in Step 2 were placed in a flask. Then, after heating to an internal temperature of 80°C, 3878 g of tetramethoxysilicate was added dropwise at a constant rate over 180 minutes while controlling the temperature so that the internal temperature did not fluctuate. After the dropping was completed, stirring was maintained for 15 minutes to prepare a colloidal silica dispersion. Then, the colloidal silica dispersion was heated and concentrated under normal pressure to a base amount of 4500 mL until the silica concentration reached 20 wt%. Next, in order to distill off the methanol by-produced during the reaction outside the system, while keeping the volume constant, the dispersion medium was replaced with 5680 mL of pure water to prepare colloidal silica. Stirring was maintained to prepare a colloidal silica dispersion. Then, the colloidal silica dispersion was heated and concentrated under normal pressure to a base amount of 4500 mL until the silica concentration reached 20 wt%. Next, in order to distill off the methanol by-produced during the reaction outside the system, while keeping the volume constant, the dispersion medium was replaced with 5680 mL of pure water to prepare colloidal silica.

[0095] In Comparative Example 2, the molar ratio (s3 / c3) of the addition amount s3 (mol) of alkoxysilane (tetramethoxysilicate) to the addition amount c3 (mol) of alkali catalyst (triethanolamine) in Step 3 was 403.

[0096] The properties of the colloidal silica of the examples and comparative examples obtained as described above were evaluated by the following method.

[0097] (Content of alkoxy groups (ppm)) After centrifuging colloidal silica at 215,000 G for 90 minutes, the supernatant was discarded, and the solid content was vacuum dried at 60 °C for 90 minutes. 0.50 g of the obtained silica dry solid was weighed and placed in 50 ml of 1 M sodium hydroxide aqueous solution, and the silica was dissolved by heating at 50 °C for 24 hours while stirring. The silica solution was analyzed by gas chromatography to determine the alcohol content, which was taken as the alkoxy amount. A flame ionization detector (FID) was used as the detector for the gas chromatograph. The gas chromatograph analysis was performed according to JIS K0114.

[0098] (BET specific surface area (m 2 / g)) After pre-drying colloidal silica on a hot plate, it was heat-treated at 800 °C for 1 hour to prepare a measurement sample. Using the prepared measurement sample, the BET specific surface area was measured by the following nitrogen gas adsorption method (BET method). Nitrogen gas adsorption method Pretreatment device: BELPREP-vacII (manufactured by Microtrac BEL Co., Ltd.) Pretreatment method: Vacuum degassing was performed at 120 °C for 8 hours. Measurement device: BELSORP-miniII (manufactured by Microtrac BEL Co., Ltd.) Measurement method: Using the constant volume method, the adsorption isotherm by nitrogen was measured. Measurement conditions: Adsorption temperature 77 K; Adsorbate nitrogen; Saturated vapor pressure measured; Adsorbate cross-sectional area 0.162 nm 2 ; Equilibrium waiting time (waiting time after reaching the adsorption equilibrium state (the state where the pressure change during adsorption and desorption is below a predetermined value)) 500 sec From the measurement results, the specific surface area was calculated by the BET method.

[0099] (Average primary particle diameter (nm)) Assuming the true specific gravity of silica is 2.2, the value of 2727 / BET specific surface area (m 2 / g) was converted from the measured value of the BET specific surface area to obtain the average primary particle diameter (nm) of the silica particles in the colloidal silica.

[0100] (Average secondary particle diameter) As a sample for measurement by dynamic light scattering method, a sample was prepared by adding colloidal silica to an aqueous solution of 0.3 wt% citric acid and homogenizing it. Using the said measurement sample, the average secondary particle diameter was measured by the dynamic light scattering method (manufactured by Otsuka Electronics Co., Ltd., "ELSZ-2000S").

[0101] (Reduction rate of specific surface area) 3-Ethoxypropylamine was added to 800 g of colloidal silica to adjust the pH to 9.9 - 10.3. The above colloidal silica was placed in a flask equipped with a reflux tube and heated, and the reflux state was maintained for 3 hours to perform base treatment. The pH of the base-treated colloidal silica was adjusted to 7.6 - 7.8, and the BET specific surface area was measured according to the above-mentioned measurement method of BET specific surface area. Based on the BET specific surface areas before and after the base treatment, the reduction rate of the specific surface area was calculated by the following formula. Reduction rate of specific surface area (%) = (BET specific surface area before base treatment - BET specific surface area after base treatment) / BET specific surface area before base treatment × 100

[0102] (SEM minor axis) Images of silica particles taken with a scanning electron microscope were each approximated by an ellipse for 1000 particles using image analysis software (manufactured by Mitani Shoko Co., Ltd., "WinRoof2015"), and the minor axis of the ellipse was measured. The number frequency distribution of the minor axis of the ellipse was obtained, and the minor axis of the ellipse with a number frequency of 50% was taken as the SEM minor axis (nm).

[0103] (Aspect ratio) Images of silica particles taken with a scanning electron microscope were each approximated by an ellipse for 1000 particles using image analysis software (manufactured by Mitani Shoko Co., Ltd., "WinRoof2015"), and the major axis and minor axis of the ellipse were measured for each particle. The ratio of the major axis to the minor axis of the ellipse (major axis of the ellipse / minor axis of the ellipse) of each particle was calculated, and the average value was taken as the aspect ratio.

[0104] (Surface roughness) The surface roughness was calculated by dividing the BET specific surface area (B1) by the specific surface area (S1) calculated from the short diameter of the SEM. The specific surface area (S1) was determined by converting the value of 2727 / SEM short diameter (nm) assuming the true specific gravity of silica is 2.2.

[0105] (True specific gravity) The true specific gravity was measured by a measurement method in which colloidal silica was dried on a hot plate at 150 °C and then held in a furnace at 300 °C for 1 hour, followed by measurement by the liquid phase replacement method using ethanol.

[0106] (Amine content) Colloidal silica was centrifuged at 215000G for 90 minutes, the supernatant was discarded, and the solid content was vacuum dried at 60 °C for 90 minutes. 0.50 g of the obtained silica dry solid was weighed, put into 50 ml of 1M aqueous sodium hydroxide solution, and heated at 50 °C for 24 hours with stirring to dissolve the silica. The silica solution was analyzed by ion chromatography to determine the amine content. The ion chromatography analysis was performed according to JIS K0127.

[0107] (Silanol group density) The silanol group density of silica particles was determined by the Sears method. The Sears method was carried out with reference to the description in G.W. Sears, Jr., “Determination of Specific Surface Area of Colloidal Silica by Titration with Sodium Hydroxide”, Analytical Chemistry, 28(12), 1981(1956). A 1wt% silica dispersion was used for the measurement, titration was performed with 0.1mol / L aqueous sodium hydroxide solution, and the silanol group density was calculated based on the following formula. ρ=(a×f×6022)÷(c×S) In the above formula, ρ: silanol group density (number / nm 2 ), a: the amount of 0.1mol / L aqueous sodium hydroxide solution dropped at pH 4 - 9 (mL), f: 0.1mol / L aqueous sodium hydroxide The factors of the solution, c: mass of silica particles (g), S: BET specific surface area (m 2 / g) are represented respectively.

[0108] (Content of metal impurities) The content of metal impurities was measured using an atomic absorption spectrometer. The sum of the contents of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in colloidal silica was taken as the content of metal impurities.

[0109]

Table 1

[0110] ※1: In Comparative Example 2, no amine selected from the group consisting of primary amines, secondary amines, and tertiary amines (however, excluding hydroxy groups as substituents) was used, so the amine content was not detected.

Claims

1. A colloidal silica containing silica particles, (1) The silica particles have a BET specific surface area reduction rate of 15.0% or less when heat-treated under basic conditions; (2) The silica particles have a surface roughness (B1 / S1) of 1.1 or more and 1.8 or less, the surface roughness being calculated by dividing a BET specific surface area (B1) measured by the following BET specific surface area measurement method by a specific surface area (S1) calculated from a SEM minor axis; (3) The colloidal silica has a metal impurity content of 1 ppm or less as measured using an atomic absorption spectrometer; The reduction rate of the BET specific surface area, the BET specific surface area (B1), and the specific surface area calculated from the SEM minor axis (S1) are measured by the following measurement method. Colloidal silica characterized by: [Method for measuring the reduction rate of BET specific surface area] 3-Ethoxypropylamine is added to 800 g of colloidal silica to adjust the pH to 9.9 to 10.

3. The colloidal silica is placed in a flask equipped with a reflux condenser and heated, and the reflux state is maintained for 3 hours to perform base treatment. The pH of the base-treated colloidal silica is adjusted to 7.6 to 7.8, and the BET specific surface area is measured according to the method for measuring BET specific surface area described below. The reduction rate of the BET specific surface area is calculated based on the BET specific surface area before and after the base treatment according to the following formula. Reduction rate of BET specific surface area (%) = (BET specific surface area before base treatment - BET specific surface area after base treatment) / BET specific surface area before base treatment x 100 [Method for measuring BET specific surface area] A measurement sample is prepared by pre-drying the colloidal silica on a hot plate and then heat-treating it for 1 hour at 800° C. The BET specific surface area of ​​the measurement sample thus prepared is measured by the nitrogen gas adsorption method (BET method). [Method for measuring specific surface area (S1) calculated from SEM minor axis] An image of the silica particles taken with a scanning electron microscope is used to approximate 1,000 particles into an ellipse and measure the minor axis of the ellipse using image analysis software ("WinRoof2015" manufactured by Mitani Shoji Co., Ltd.). The number frequency distribution of the minor axis of the ellipse is taken, and the minor axis of the ellipse with a number frequency of 50% is defined as the SEM minor axis (nm). The true specific gravity of silica is set to 2.2, and the value of 2727 / SEM minor axis (nm) is converted to calculate the specific surface area (S1) calculated from the SEM minor axis.

Images