Quaternary ammonium-modified silica dispersion and method for producing quaternary ammonium-modified silica dispersion

Abstract

To provide a neutral quaternary ammonium-modified silica dispersion and a production method therefor.SOLUTION: A quaternary ammonium-modified silica dispersion is neutral with a pH of 6.5 to 8.5 and has an average secondary particle diameter increase ratio of 10% or less due to surface modification compared with unmodified silica. A method for producing the quaternary ammonium-modified silica dispersion includes the following steps: (1) adding a basic compound b to silica a dispersed in water and / or an organic solvent to prepare a mixed solution; (2) adding a silane coupling agent c containing a quaternary ammonium group to the mixed solution prepared in step (1) to obtain a basic quaternary ammonium-modified silica dispersion; and (3) replacing an organic solvent and / or the basic compound b in the basic quaternary ammonium-modified silica dispersion obtained in step (2) with water to obtain a neutral quaternary ammonium-modified silica dispersion.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a quaternary ammonium modified silica dispersion and a method for producing the quaternary ammonium modified silica dispersion. [Background technology]

[0002] With the recent advances in semiconductor device performance, there is a need for technologies to build multilayer wiring on wafer surfaces and manufacture highly integrated VLSIs (Large Scale Integration). CMP (Chemical Mechanical Polishing) is one such technology, and is used to selectively polish and flatten thin films for multilayer wiring, such as oxide films, metal films, and ceramic films, formed on wafer surfaces.

[0003] During CMP, polishing compositions containing various additives such as polishing accelerators and pH adjusters are commonly used in addition to the main component, the abrasive. Silica is widely used as the abrasive, and surface modification treatments are carried out on silica to impart properties suited to various applications. One such surface modification treatment is silane coupling agent treatment. In silane coupling agent treatment, hydrolyzable silanes or their hydrolysis condensates having various functional groups undergo a condensation reaction with silanol groups on the silica surface to form covalent bonds (siloxane bonds).

[0004] For example, Patent Document 1 describes a technique for producing a quaternary ammonium-modified silica dispersion by performing a surface modification treatment using a quaternary ammonium group-containing silane coupling agent or the like. However, the surface modification conditions were not carefully examined, and there was a problem that silica aggregated significantly during the modification process. There is a concern that this aggregated silica will deteriorate the polishing performance.

[0005] Patent Document 2 also describes a technique for producing a quaternary ammonium-modified silica dispersion by performing a surface modification treatment with an epoxy group-containing silane coupling agent and simultaneously ring-opening the epoxy group with a tertiary amine. This method can suppress silica aggregation and halogen inclusion, but has the problem that the reaction is not completed unless an acid is added after surface modification. Adding such an acid only produces an acidic quaternary ammonium-modified silica dispersion, and furthermore, a neutralization salt with the tertiary amine is formed, reducing the degree of freedom in formulation as a polishing composition. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5843613 [Patent Document 2] Patent No. 7284573 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a neutral quaternary ammonium-modified silica dispersion that suppresses silica aggregation during the surface modification process with a silane coupling agent, and a method for producing the same. [Means for solving the problem]

[0008] [Concept 1] The quaternary ammonium modified silica dispersion according to the present invention comprises: The quaternary ammonium-modified silica dispersion may have a surface modification with an increase in average secondary particle size of 10% or less, and may have a neutral pH of 6.5 to 8.5.

[0009] [Concept 2] In the quaternary ammonium modified silica dispersion according to concept 1, The silica surface may have quaternary ammonium groups covalently immobilized thereon.

[0010] [Concept 3] The method for producing a quaternary ammonium modified silica dispersion according to the present invention comprises the steps of: The following steps (1) to (3) may be included. Step (1): A step of adding a basic compound b to silica a dispersed in water and / or an organic solvent to prepare a mixed liquid. Step (2): A step of adding a quaternary ammonium group-containing silane coupling agent c to the mixture prepared in step (1) to obtain a basic quaternary ammonium-modified silica dispersion. Step (3): A step of replacing the organic solvent and / or basic compound b in the basic quaternary ammonium-modified silica dispersion obtained in step (2) with water to obtain a neutral quaternary ammonium-modified silica dispersion.

[0011] [Concept 4] In step (1) of the method for producing a quaternary ammonium-modified silica dispersion according to Concept 3, the average secondary particle size of silica a may be 300 nm or less.

[0012] [Concept 5] In step (2) of the method for producing a quaternary ammonium-modified silica dispersion according to Concept 3 or 4, the amount of the quaternary ammonium group-containing silane coupling agent c added may be 0.1 to 100 mass % relative to the silica a.

[0013] [Concept 6] In step (2) of the method for producing a quaternary ammonium-modified silica dispersion according to any one of concepts 3 to 5, the pH of the basic quaternary ammonium-modified silica dispersion may be greater than 8.5.

[0014] [Concept 7] 10. A method for producing a quaternary ammonium-modified silica dispersion according to any one of Concepts 3 to 6, comprising: The following step (1') may be included before step (1) or step (2). Step (1'): A step of preparing a quaternary ammonium group-containing silane coupling agent c.

[0015] [Concept 8] In step (3) of the method for producing a quaternary ammonium-modified silica dispersion according to any one of concepts 3 to 7, the pH of the neutral quaternary ammonium-modified silica dispersion may be 6.5 to 8.5.

[0016] [Concept 9] 10. A method for producing a quaternary ammonium-modified silica dispersion according to any one of Concepts 3 to 8, comprising: The silica concentration in the quaternary ammonium-modified silica dispersion may be 50% by mass or less. [Effects of the Invention]

[0017] According to the present invention, a neutral quaternary ammonium-modified silica dispersion is provided with little silica aggregated during the surface modification process, and therefore the dispersion has a high degree of formulation freedom as a polishing composition and can be widely used. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described. The quaternary ammonium-modified silica dispersion of this embodiment has an average secondary particle size that increases by 10% or less due to surface modification compared to unmodified silica, and has a neutral pH of 6.5 to 8.5.

[0019] The method for producing a quaternary ammonium-modified silica dispersion according to this embodiment includes the following steps (1) to (3). Step (1): A step of adding a basic compound b to silica a dispersed in water and / or an organic solvent to prepare a mixed liquid. Step (2): A step of adding a quaternary ammonium group-containing silane coupling agent c to the mixture prepared in step (1) to obtain a basic quaternary ammonium-modified silica dispersion. Step (3): A step of replacing the organic solvent and / or basic compound b in the basic quaternary ammonium-modified silica dispersion obtained in step (2) with water to obtain a neutral quaternary ammonium-modified silica dispersion.

[0020] The silica used in the dispersion of silica a (hereinafter also referred to as "dispersion of silica a") is not particularly limited, and may be synthesized by hydrolysis of alkoxysilane (sol-gel silica), ion exchange of sodium silicate (ion-exchange silica), flame hydrolysis of silicon tetrachloride (fumed silica), etc. However, from the viewpoint of metal impurities, it is preferable to use sol-gel silica, which can obtain high-purity silica.

[0021] Surface modification treatments include treatment with a silane coupling agent (covalent bonding) and treatment with a polymer (ionic bonding, hydrogen bonding, etc.). In this embodiment, the surface modification treatment refers to treatment with a silane coupling agent. Such treatments result in stable surface-modified silica, with almost no elimination of functional groups due to strong covalent bonds even under strongly acidic or strongly basic conditions.

[0022] In consideration of the solubility of the silane coupling agent, the silica a dispersion may contain an organic solvent other than water. Examples of the organic solvent include alcohol, and the same as the by-product alcohol in the hydrolysis of the silane coupling agent is preferable, with methanol and ethanol being more preferable, and methanol being even more preferable.

[0023] The water concentration in the silica a dispersion is not particularly limited, but is preferably 5 to 99% by mass, and more preferably 10 to 95% by mass. When the water concentration is within the range of 5 to 99% by mass, the hydrolysis of the silane coupling agent proceeds rapidly, and when the water concentration is within the range of 10 to 95% by mass, the hydrolysis of the silane coupling agent proceeds even more rapidly, which is preferable.

[0024] The silica concentration of the silica a dispersion is not particularly limited, but is preferably 1 to 60% by mass, more preferably 5 to 50% by mass. A silica concentration in the range of 1 to 60% by mass can increase productivity, and a silica concentration in the range of 5 to 50% by mass can further increase productivity, which is preferable.

[0025] The average secondary particle size of silica a is not particularly limited, but from the viewpoint of the polishing rate, it is preferably 1 to 500 nm, more preferably 2 to 400 nm, and even more preferably 5 to 300 nm.

[0026] The basic compound b is not particularly limited, but from the viewpoint of removal by water substitution in the above step (3), it is preferable to use an amine having a boiling point of 100°C or less. This includes ammonia and primary amines, secondary amines, and tertiary amines having 1 to 7 carbon atoms. Examples include ammonia, isoamylamine, diisopropylamine, trimethylamine, triethylamine, and N-butyldimethylamine. Among these, diisopropylamine and triethylamine, which are easy to handle and inexpensive, are more preferred.

[0027] The amount of basic compound b added is difficult to define uniquely, since the range of the amount added varies depending on the balance between the specific surface area of ​​silica a, the amount of silanol, the silica concentration in the silica a dispersion, the basicity of basic compound b, etc. Since the reaction is significantly affected by pH, from the viewpoint of quickly modifying the silica at the start of the reaction and suppressing silica aggregation, the silica dispersion after the addition of basic compound b in step (1) above preferably has a pH of more than 8.5, more preferably a pH of 9.0 or higher, and even more preferably a pH of 9.5 or higher.

[0028] The quaternary ammonium group-containing silane coupling agent c may be used as a stock solution, or may be diluted with water or an organic solvent in consideration of solubility. Examples of organic solvents include alcohol, and the same as the by-product alcohol in the hydrolysis of the silane coupling agent are preferred, with methanol and ethanol being more preferred, and methanol being even more preferred.

[0029] The concentration of the quaternary ammonium group-containing silane coupling agent c is not particularly limited, but from the viewpoint of solubility, the concentration of the silane coupling agent is preferably 5 to 100 mass %, more preferably 5 to 60 mass %.

[0030] The number of quaternary ammonium groups in the quaternary ammonium group-containing silane coupling agent c is not particularly limited, but empirically, the effect of the functional group is enhanced, and therefore, it is preferably 1 to 4. The position of the quaternary ammonium group is also not particularly limited, but empirically, it is preferably located at the terminal where steric hindrance is small.

[0031] The quaternary ammonium group-containing silane coupling agent c may be a commercially available product or may be prepared in advance. The quaternary ammonium group-containing silane coupling agent c may be used as a hydrolyzable silane or its hydrolysis condensate.

[0032] A commercially available quaternary ammonium group-containing silane coupling agent c is represented by the general formula (i). R 2 3-n Si(OR 1 ) n L-NR 3 3 + X - (i) R 1 is an alkyl group having 1 to 6 carbon atoms, a hydrogen atom, or a silicon atom. n is 1, 2 or 3. R 2 is an alkyl group having 1 to 6 carbon atoms or a hydrogen atom. L is a spacer. R 3 is an alkyl group having 1 to 18 carbon atoms. X - is an anion.

[0033] More specifically, R in general formula (i) 1 When R is an alkyl group, it preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and even more preferably 1 to 2 carbon atoms. Examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and a phenyl group. A methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group are more preferred, and a methyl group and an ethyl group are even more preferred. 1When is a hydrogen atom or a silicon atom, it represents a hydrolysis condensation product. In general formula (i), n is preferably 2 or 3, and more preferably 3. R in general formula (i) 2 When the alkyl group is an alkyl group, it preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and even more preferably 1 or 2 carbon atoms. In general formula (i), L is a spacer, which is a group that connects the silicon atom and the quaternary ammonium group. For example, it is an alkylene group, and the main chain preferably has 1 to 18 carbon atoms, more preferably 1 to 8 carbon atoms. Examples include methylene, ethylene, propylene, butylene, octylene, and octadecylene groups, and more preferably methylene, ethylene, propylene, butylene, and octylene groups. Furthermore, when a side chain is present, the side chain preferably has 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms. The alkylene group may have a substituent. For example, it may have a hydroxyl group, an amino group, a quaternary ammonium group, an alkyl group having 1 to 4 carbon atoms, etc. The substituent may be one type or a combination of two or more types. The number of substituents in the main chain and the side chain is preferably 0 to 5, and more preferably 0 to 4. The alkylene group may have a heteroatom inside or at a terminal. For example, an oxygen atom, a nitrogen atom, a sulfur atom, etc. One type of heteroatom may be used alone or in combination with multiple types. The number of heteroatoms in the main chain and the side chain is preferably 0 to 4, and more preferably 0 to 3. R in general formula (i) 3 represents an alkyl group, preferably having 1 to 18 carbon atoms, more preferably having 1 to 4 carbon atoms, and even more preferably having 1 or 2 carbon atoms. X in general formula (i) - is an anion, and examples thereof include chloride ion, bromide ion, iodide ion, hydroxide ion, carbonate ion, hydrogen carbonate ion, acetate ion, and nitrate ion.

[0034] For example, commercially available hydrolyzable silanes include trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, trimethyl[3-(triethoxysilyl)propyl]ammonium chloride, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and POLON-V8 manufactured by Shin-Etsu Chemical Co., Ltd. Commercially available hydrolyzed condensates include POLON-V8 manufactured by Shin-Etsu Chemical Co., Ltd. VOC-free water-based silane coupling agents such as X-12-1126, X-12-1139, and X-12-1354-1 manufactured by Gakushu Kogyo Co., Ltd. are readily available.

[0035] On the other hand, there are many methods for preparing quaternary ammonium group-containing silane coupling agents (c), such as alkylation of amino group-containing silane coupling agents, reaction of leaving group- or epoxy group-containing compounds with tertiary amines (either one or both are silane coupling agents), and bonding of quaternary ammonium group-containing compounds to silane coupling agents. Furthermore, the prepared hydrolyzable silane may be hydrolyzed, and the organic solvent may be removed. These preparation methods can lead to desired structures not found in commercially available products, and can also suppress the inclusion of metals and halogens.

[0036] The amount of the quaternary ammonium group-containing silane coupling agent c added is difficult to define uniquely because the range of the amount added varies depending on the specific surface area of ​​the silica a, the amount of silanol, the molecular weight of the silane coupling agent c, etc. From the viewpoint of sufficiently modifying the silica a and obtaining a stable quaternary ammonium-modified silica dispersion, the amount of the quaternary ammonium group-containing silane coupling agent c added is preferably 0.1 to 100 mass % relative to the silica a, more preferably 0.5 to 75 mass %, and even more preferably 1 to 50 mass %.

[0037] The temperature when adding the quaternary ammonium group-containing silane coupling agent c is not particularly limited, but is preferably from 5°C to the boiling point of the silica a dispersion, more preferably from 10°C to 70°C, and even more preferably from 10°C to 50°C. The addition time is also not particularly limited, but from the viewpoint of suppressing silica aggregation, the addition time is preferably from 1 minute to 24 hours, and more preferably from 1 minute to 10 hours.

[0038] After the addition of the quaternary ammonium group-containing silane coupling agent c, it is preferable to carry out heat aging to complete the reaction. The aging temperature is not particularly limited, but is preferably from 5°C to the boiling point of the silica a dispersion, and more preferably from 10°C to 70°C. In order to avoid silica aggregation due to a sudden temperature change, it is more preferable to start aging at the same temperature as the addition temperature. The aging time is also not particularly limited. However, from the viewpoint of completing the reaction and obtaining a stable quaternary ammonium-modified silica dispersion, the aging time is preferably 24 hours or less, and more preferably 10 hours or less.

[0039] From the viewpoint of ensuring that the modification of silica a progresses sufficiently and that a stable quaternary ammonium-modified silica dispersion is obtained, the quaternary ammonium-modified silica dispersion after aging in step (2) above preferably has a pH of more than 8.5, more preferably a pH of 8.6 or higher.

[0040] The water substitution method in the above step (3) can be exemplified by a method in which the quaternary ammonium-modified silica dispersion is heated under normal pressure or reduced pressure and water is added in an amount equal to the fraction, a method in which the dispersion is concentrated using an ultrafiltration membrane and water is added in an amount equal to the waste liquid, etc. Among these, water substitution under normal pressure or reduced pressure is preferred from the viewpoint of rapid removal of the organic solvent and / or basic compound b.

[0041] The quaternary ammonium-modified silica dispersion may be diluted or concentrated as necessary during or after water replacement. The silica concentration of the quaternary ammonium-modified silica dispersion is not particularly limited. However, from the viewpoint of suppressing silica aggregation, the silica concentration of the quaternary ammonium-modified silica dispersion is preferably 1 to 60% by mass, more preferably 1 to 50% by mass.

[0042] Since the content of the organic solvent and / or basic compound b is minimized at a neutral pH, the quaternary ammonium-modified silica dispersion after water substitution in step (3) above has a pH of preferably 6.0 to 8.5, more preferably 6.5 to 8.5, from the viewpoint of increasing the degree of freedom in formulation as a polishing composition.

[0043] From the viewpoint of suppressing scratch defects during polishing, the increase rate of the average secondary particle diameter compared to the silica before modification is preferably 10% or less, more preferably 6% or less, and even more preferably 4% or less.

[0044] The quaternary ammonium group-containing silane coupling agent c or the quaternary ammonium-modified silica dispersion may be subjected to ion exchange using an anion exchange resin. The ion exchange may be performed once or, if necessary, twice or more times. [Example]

[0045] [Silica concentration] The silica dispersion was precisely weighed into a ceramic crucible, dried at 105°C for 10 hours, and the residue was precisely weighed to calculate the silica concentration. [Average secondary particle size] The silica dispersion was diluted with water to a silica concentration of 0.2% by mass, and a tetramethylammonium tartrate aqueous solution was added to homogenize the dispersion to prepare a measurement sample. The average secondary particle diameter (nm) of the measurement sample was measured by dynamic light scattering (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.). [Average secondary particle size increase rate] The increase rate of the average secondary particle size before and after surface modification was calculated using the following formula. ((average secondary particle size after surface modification / average secondary particle size before surface modification)-1)*100 [pH] The pH was measured using a pH meter (Twin pH Meter II, manufactured by Horiba Ltd.). [Zeta potential] The silica dispersion was diluted with water to a silica concentration of 1.0% by mass to prepare a measurement sample. The zeta potential (mV) of the measurement sample was measured by electrophoretic light scattering (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.). [pH at isoelectric point] The pH at the isoelectric point (zeta potential 0 mV) was estimated from the pH at which the zeta potential was approximately ±10 mV.

[0046] In the examples and comparative examples, the following were used. [Silica a dispersion] 25nm silica dispersion water (silica concentration 10-20% by mass, average secondary particle diameter 49.1nm) 95nm silica dispersion water (silica concentration 20% by mass, average secondary particle diameter 181.5nm) Ludox CL-X silica dispersion (silica concentration 45% by mass, average secondary particle size 35.0 nm) [Basic compound b] Basic compounds b are represented by abbreviations. DIPA: Diisopropylamine TEA: Triethylamine TMA: Trimethylamine (25-27% by mass solution in methanol) [Silane coupling agent c] Silane coupling agent c is expressed by a molecular formula. C9H 24 ClNO3Si: Trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride (48-53% by mass solution in methanol) C6H 15 ClO3Si: 3-trimethoxysilylpropyl chloride C9H 20 O5Si: 3-glycidyloxypropyltrimethoxysilane

[0047] [Example 1] Process (1): 200 g of 25 nm silica dispersion water (silica concentration 20 mass %, average secondary particle diameter 49.1 nm) was placed in a flask, and 1.2 g of diisopropylamine was added and mixed in. The pH of the resulting mixture was 11.2.

[0048] Process (2): To the mixture obtained in step (1), 8.0 g of trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride (48 to 53 mass % methanol solution) was added over 8 minutes at 25°C. After the entire amount was added, stirring was maintained at 25°C for 30 minutes. Subsequently, the mixture was heated to 60°C and then stirred for an additional 180 minutes to obtain a quaternary ammonium-modified silica dispersion with a pH of 9.9.

[0049] Process (3): The quaternary ammonium-modified silica dispersion obtained in step (2) was heated to distill off methanol and diisopropylamine, while adding water dropwise to maintain the weight of the silica dispersion constant, to obtain a quaternary ammonium-modified silica dispersion with a pH of 7.2.

[0050] [Example 2] Process (1'): 3.9 g of 3-trimethoxysilylpropyl chloride and 9.2 g of trimethylamine (25 to 27 mass % methanol solution) were placed in a plastic bottle and sealed. The bottle was heated at 60°C for 46 hours to prepare 13.1 g of a quaternary ammonium group-containing silane coupling agent.

[0051] Process (1): 200 g of 25 nm silica dispersion water (silica concentration 10 mass %, average secondary particle diameter 49.1 nm) was placed in a flask, and 0.8 g of triethylamine was added and mixed in. The pH of the resulting mixture was 11.1.

[0052] Process (2): To the mixture obtained in step (1), 13.1 g of the quaternary ammonium group-containing silane coupling agent prepared in step (1') was added over 20 minutes at 25°C. After the entire amount was added, stirring was maintained at 25°C for 30 minutes. Subsequently, the mixture was heated to 60°C and then stirred for an additional 180 minutes to obtain a quaternary ammonium-modified silica dispersion with a pH of 9.2.

[0053] Process (3): The quaternary ammonium-modified silica dispersion obtained in step (2) was heated to distill off methanol, trimethylamine, and triethylamine, while adding water dropwise to maintain the weight of the silica dispersion constant, to obtain a quaternary ammonium-modified silica dispersion with a pH of 6.8.

[0054] [Example 3] Process (1): 200 g of 95 nm silica dispersion water (silica concentration 20 mass %, average secondary particle diameter 181.5 nm) was placed in a flask, and 0.6 g of diisopropylamine was added and mixed in. The pH of the resulting mixture was 11.6.

[0055] Process (2): To the mixture obtained in step (1), 3.0 g of trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride (48-53 mass% methanol solution) was added over 3 minutes at 25°C. After the entire amount was added, stirring was maintained at 25°C for 30 minutes. Subsequently, the mixture was heated to 60°C and then stirred for an additional 180 minutes to obtain a quaternary ammonium-modified silica dispersion with a pH of 10.3.

[0056] Process (3): The quaternary ammonium-modified silica dispersion obtained in step (2) was heated to distill off methanol and diisopropylamine, while adding water dropwise to maintain the weight of the silica dispersion constant, to obtain a quaternary ammonium-modified silica dispersion with a pH of 7.0.

[0057] [Comparative Example 1] A flask was charged with 89.0 g of Ludox CL-X silica dispersion (silica concentration 45% by mass, average secondary particle size 35.0 nm), 28.4 g of water, and 71.0 g of methanol. The pH of the resulting mixture was 9.9. 12.4 g of trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride (48-53% by mass methanol solution) was added to the mixture, and the mixture was heated at 68°C for 24 hours. The resulting quaternary ammonium-modified silica dispersion had a pH of 8.3, but a large amount of gel was generated.

[0058] Comparative Example 2 A flask was charged with 900 g of a 25 nm silica dispersion (silica concentration 20% by mass, average secondary particle diameter 49.1 nm), and 16.0 g of triethylamine was added. The pH of the resulting dispersion was 11.6. This dispersion was heated to an internal temperature of 55°C, and then a mixture of 12.5 g of 3-glycidyloxypropyltrimethoxysilane and 49.9 g of methanol was added over 60 minutes while adjusting the temperature to prevent fluctuations in the internal temperature. After the entire amount was added, the mixture was maintained at 55°C for 30 minutes. 345 g of the resulting dispersion with a pH of 11.5 was placed in another flask, and 3.1 g of acetic acid was added at 20°C. The pH of the resulting mixture was 6.0. To distill off the methanol from this mixture, the mixture was heated under normal pressure, and water was added dropwise while maintaining a constant volume, replacing the methanol with water, yielding a quaternary ammonium-modified silica dispersion with a pH of 5.7.

[0059] [Table 1] * 1 It is expressed as the theoretical amount of the quaternary ammonium group-containing silane coupling agent produced by the reaction of trimethylamine with 3-trimethoxysilylpropyl chloride. * 2 It is expressed as the theoretical amount of the quaternary ammonium group-containing silane coupling agent produced by the reaction of triethylamine with 3-glycidyloxypropyltrimethoxysilane.

[0060] In the silane coupling agent c / silica a ratio in Table 1 above, the value shown is the weight of the active ingredient of silane coupling agent c divided by the weight of silica a in the silica a dispersion (note that trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride is calculated as 50 mass %). For example, in Example 1, silane coupling agent c / silica a 8.0g×0.5÷(200g*0.2)*100=10 This becomes:

[0061] In Example 2 and Comparative Example 2, silane coupling agent c was prepared, but because an excess amount of trimethylamine or triethylamine was added, the theoretical amount of silane coupling agent c produced was calculated based on 3-trimethoxysilylpropyl chloride or 3-glycidyloxypropyltrimethoxysilane. In Example 2 calculated using the theoretical amount, the substance amount of 3-trimethoxysilylpropyl chloride was 3.9 g ÷ 198.72 g / mol = 0.0196 mol, and the theoretical amount of the silane coupling agent c produced was 0.0196 mol * 257.83 g / mol = 5.05 g. Silane coupling agent c / silica a 5.05g ÷ (200g * 0.1) * 100 = 25 This becomes: In Comparative Example 2, which was also calculated using the theoretical amount, the substance amount of 3-glycidyloxypropyltrimethoxysilane was 12.5 g ÷ 236.34 g / mol = 0.0529 mol, and the theoretical amount of the produced silane coupling agent c was 0.0529 mol * 337.53 g / mol = 17.86 g. Silane coupling agent c / silica a 17.86g ÷ (900g * 0.2) * 100 = 10 This becomes:

[0062] In the examples, the addition of basic compound b suppressed silica aggregation during the surface modification process, and a neutral quaternary ammonium-modified silica dispersion was obtained by water replacement in step (3). Surprisingly, the isoelectric point was passed during the reaction and water replacement without pH adjustment. Furthermore, the high pH of the isoelectric point and the large zeta potential resulted in a very stable quaternary ammonium-modified silica dispersion.

[0063] On the other hand, in the production method of Comparative Example 1, since basic compound b was not added, a neutral quaternary ammonium-modified silica dispersion with a pH of 8.3 was obtained in step (2), resulting in the formation of a large amount of gel.

[0064] In the manufacturing method of Comparative Example 2, the addition of basic compound b largely suppressed the aggregation of silica, but only an acidic quaternary ammonium-modified silica dispersion with a pH of 5.7 was obtained. Moreover, the pH of the isoelectric point was lower than in the Examples, and the zeta potential was also small, probably because the reaction was not completed, resulting in a less stable quaternary ammonium-modified silica dispersion.

Claims

1. A quaternary ammonium-modified silica dispersion, characterized in that the increase rate of the average secondary particle diameter due to surface modification is 10% or less, and the quaternary ammonium-modified silica dispersion is neutral with a pH of 6.5 to 8.

5.

2. The quaternary ammonium-modified silica dispersion according to claim 1 , wherein the silica surface has quaternary ammonium groups immobilized thereon by covalent bonds.

3. A method for producing a quaternary ammonium-modified silica dispersion, comprising the following steps (1) to (3): Step (1): A step of adding a basic compound b to silica a dispersed in water and / or an organic solvent to prepare a mixed liquid. Step (2): A step of adding a quaternary ammonium group-containing silane coupling agent c to the mixed liquid prepared in step (1) to obtain a basic quaternary ammonium-modified silica dispersion. Step (3): A step of substituting water for the organic solvent and / or the basic compound b in the basic quaternary ammonium-modified silica dispersion obtained in step (2) to obtain a neutral quaternary ammonium-modified silica dispersion.

4. The method according to claim 3, wherein in step (1), the average secondary particle diameter of silica a is 300 nm or less.

5. 5. The method according to claim 3, wherein in step (2), the amount of the quaternary ammonium group-containing silane coupling agent c added is 0.1 to 100 mass % relative to the silica a.

6. 5. The method according to claim 3, wherein in step (2), the pH of the basic quaternary ammonium-modified silica dispersion is greater than 8.

5.

7. The method according to claim 3 or 4, comprising the following step (1') before step (1) or step (2): Step (1'): A step of preparing a quaternary ammonium group-containing silane coupling agent c.

8. 5. The method according to claim 3, wherein in step (3), the neutral quaternary ammonium-modified silica dispersion has a pH of 6.5 to 8.

5.

9. The method according to claim 3 or 4, wherein the silica concentration in the quaternary ammonium-modified silica dispersion is 50% by mass or less.

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