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

Abstract

To provide a quaternary ammonium-modified silica dispersion suppressed in coagulation of silica in a surface modification process with a silane coupling agent, and having a high pH at an isoelectric point, and a production method of the same.SOLUTION: A quaternary ammonium-modified silica dispersion has a pH at an isoelectric point of 11.0 or higher. A production method of a quaternary ammonium-modified silica dispersion having a pH at an isoelectric point of 11.0 or higher includes the following processes (1)-(3). Process (1): a process of adding a basic compound b to silica a dispersed in water and / or an organic solvent to prepare a mixture. Process (2): a process of adding a quaternary ammonium group-containing silane coupling agent c to the mixture prepared in the process (1), and heating to obtain a quaternary ammonium-modified silica dispersion. Process (3): a process of substituting water for the organic solvent and / or the basic compound b in the quaternary ammonium-modified silica dispersion obtained in the process (2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a quaternary ammonium modified silica dispersion and a method for producing a 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, 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 groups with a tertiary amine. This method can suppress silica aggregation and halogen inclusion, but has the problem that the epoxy group ring-opening does not proceed easily, resulting in an insufficient amount of quaternary ammonium groups. This results in a quaternary ammonium-modified silica dispersion with a low isoelectric point pH. [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 quaternary ammonium-modified silica dispersion that suppresses silica aggregation during the surface modification process with a silane coupling agent and has a high pH isoelectric point, 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 pH of the isoelectric point may be 11.0 or higher.

[0009] [Concept 2] In the quaternary ammonium modified silica dispersion according to concept 1, The increase in average secondary particle size due to surface modification may be 10% or less.

[0010] [Concept 3] In the quaternary ammonium modified silica dispersion according to concept 1 or 2, Quaternary ammonium groups may be covalently immobilized on the surface of the silica.

[0011] [Concept 4] The manufacturing method according to the present invention comprises the steps of: The method may include the following steps (1) to (3), and may be a method for producing a quaternary ammonium-modified silica dispersion having an isoelectric point pH of 11.0 or higher. 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 solution prepared in step (1) and heating to obtain a quaternary ammonium-modified silica dispersion. Step (3): A step of substituting the organic solvent and / or basic compound b in the quaternary ammonium-modified silica dispersion obtained in step (2) with water.

[0012] [Concept 5] In the manufacturing method according to Concept 4, In step (1), the average secondary particle size of silica a may be 300 nm or less.

[0013] [Concept 6] In the manufacturing method according to Concept 4 or 5, In step (2), the quaternary ammonium group-containing silane coupling agent c may be an aqueous silane coupling agent having an organic solvent concentration of 3% by mass or less.

[0014] [Concept 7] 7. The method of manufacturing according to any one of Concepts 4 to 6, In the step (2), the amount of the quaternary ammonium group-containing silane coupling agent c added may be 0.1 to 100% by mass relative to the silica a.

[0015] [Concept 8] 8. A method of manufacturing according to any one of Concepts 4 to 7, comprising: In step (2), the pH of the resulting quaternary ammonium-modified silica dispersion may be 10.0 or higher.

[0016] [Concept 9] 9. A method of manufacturing according to any one of Concepts 4 to 8, comprising: Furthermore, 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.

[0017] [Concept 10] 10. The process according to any one of Concepts 4 to 9, The silica concentration in the quaternary ammonium-modified silica dispersion may be 50% by mass or less. [Effects of the Invention]

[0018] According to the present invention, a quaternary ammonium-modified silica dispersion is provided which has little silica agglomeration during the surface modification process and a high pH isoelectric point, and therefore has a large positive zeta potential and high stability over a wide basic range, making it widely usable as a polishing composition. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described.

[0020] The inventors of the present application have discovered that by treating a silica dispersion prepared with a basic compound with a quaternary ammonium group-containing VOC (volatile organic compound)-free aqueous silane coupling agent, silica aggregation can be suppressed and a quaternary ammonium-modified silica dispersion with a high isoelectric point pH can be obtained.

[0021] In the quaternary ammonium-modified silica dispersion of this embodiment, the pH of the isoelectric point is preferably 11.0 or higher, from the viewpoint of having a large positive zeta potential and high stability over a wide basic range. In previous embodiments, it was difficult to achieve a pH of 11.0 or higher at the isoelectric point. However, this embodiment makes it possible to achieve a pH of 11.0 or higher at the isoelectric point, which is extremely advantageous in that the pH of the isoelectric point can be increased to approximately 13. Furthermore, from the viewpoint of stability, it is even more advantageous to set the lower limit of the pH of the isoelectric point to 12.0. The upper limit of the pH of the isoelectric point is not particularly limited, but may be 13.0.

[0022] In this embodiment, there is provided a method for producing a quaternary ammonium-modified silica dispersion, which 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 mixed solution prepared in step (1) and heating to obtain a quaternary ammonium-modified silica dispersion. Step (3): A step of substituting the organic solvent and / or basic compound b in the quaternary ammonium-modified silica dispersion obtained in step (2) with water.

[0023] The silica in the silica a dispersion liquid used in the present embodiment is not particularly limited, and can 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. Among these, sol-gel silica is preferred because it can produce high-purity silica in terms of suppressing metal impurities.

[0024] Surface modification treatments include treatment with a silane coupling agent (covalent bond) and treatment with a polymer (ionic bond, hydrogen bond, etc.). When a quaternary ammonium group is immobilized on the silica surface by a covalent bond, the strong covalent bond is advantageous in that the functional group is hardly detached even under strongly acidic or strongly basic conditions, and stable surface-modified silica can be obtained.

[0025] The silica a dispersion may contain an organic solvent other than water. Examples of the organic solvent include alcohol, with methanol and ethanol being more preferred, and methanol being even more preferred.

[0026] The water concentration of the silica a dispersion is not particularly limited, but from the viewpoint of rapid hydrolysis of the silane coupling agent, it is preferably 5 to 99 mass %, more preferably 10 to 95 mass %.

[0027] The silica concentration of the silica a dispersion is not particularly limited, but is preferably 1 to 60 mass %, more preferably 5 to 50 mass %. When the lower limit of the silica concentration is within the above range, it is advantageous in that productivity can be increased.

[0028] The average secondary particle size of silica a is not particularly limited, but from the viewpoint of enabling a high polishing rate, it is preferably from 1 to 500 nm, more preferably from 2 to 400 nm, and even more preferably from 5 to 300 nm.

[0029] The basic compound b is not particularly limited, but is preferably an amine having a boiling point of 100°C or less from the viewpoint of removal by water substitution in step (3). This includes ammonia and primary, secondary, 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.

[0030] The amount of basic compound b added is difficult to define uniquely because the range of the amount added varies depending on the balance between the specific surface area and silanol content of silica a, the silica concentration in the silica a dispersion, the basicity of basic compound b, etc. Since the reaction is significantly affected by pH, the silica dispersion after the addition of basic compound b in step (1) preferably has a pH of 10.0 or higher, more preferably 10.5 or higher, and even more preferably 11.0 or higher, from the viewpoints of rapid modification and suppressing silica aggregation.

[0031] The quaternary ammonium group-containing silane coupling agent c may be used in its undiluted form, or may be diluted with water as desired in consideration of solubility.

[0032] The concentration of the quaternary ammonium group-containing silane coupling agent c is not particularly limited, but is preferably 1 to 50 mass %, more preferably 5 to 40 mass %. From the viewpoint of excellent solubility, it is beneficial to set the upper limit at this value.

[0033] The organic solvent concentration of the quaternary ammonium group-containing silane coupling agent c is not particularly limited, but from the viewpoint of reducing the environmental load, it is preferably 3% by mass or less, and more preferably 1% by mass or less.

[0034] The number of quaternary ammonium groups in the quaternary ammonium group-containing silane coupling agent c is not particularly limited, but from the empirical rule that the effect of the functional group is enhanced, it is preferably 1 to 4. The position of the quaternary ammonium group is also not particularly limited, but it is preferably present at a terminal where steric hindrance is small.

[0035] The quaternary ammonium group-containing silane coupling agent c may be a commercially available product, or may be prepared in advance.

[0036] The quaternary ammonium group-containing silane coupling agent c may be used as a hydrolyzable silane or as a hydrolysis condensate thereof.

[0037] 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 represents an alkyl group having 1 to 6 carbon atoms, a hydrogen atom, or a silicon atom n is 1, 2 or 3 R2 represents an alkyl group having 1 to 6 carbon atoms or a hydrogen atom L is the spacer R 3 is an alkyl group having 1 to 18 carbon atoms X - is an anion

[0038] 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. 1 When 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.

[0039] L in general formula (i) 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 a methylene group, an ethylene group, a propylene group, a butylene group, an octylene group, and an octadecylene group, and more preferably a methylene group, an ethylene group, a propylene group, a butylene group, and an octylene group. Furthermore, when there is a side chain, the side chain preferably has 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms. The alkylene group may have a substituent. Examples of the substituent include a hydroxyl group, an amino group, a quaternary ammonium group, and an alkyl group having 1 to 4 carbon atoms. 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.

[0040] 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.

[0041] 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.

[0042] For example, commercially available hydrolysis condensates include VOC-free water-based silane coupling agents X-12-1126, X-12-1139, and X-12-1354-1 manufactured by Shin-Etsu Chemical Co., Ltd., which are readily available.

[0043] On the other hand, commercially available hydrolyzable silanes include, for example, trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, trimethyl[3-(triethoxysilyl)propyl]ammonium chloride, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, POLON-V8 manufactured by Shin-Etsu Chemical Co., Ltd., and the like. Alternatively, hydrolyzable silanes prepared by alkylating an amino group-containing silane coupling agent, reacting a leaving group- or epoxy group-containing compound with a tertiary amine (either one or both are silane coupling agents), or bonding a quaternary ammonium group-containing compound to a silane coupling agent, etc., may be hydrolyzed and the organic solvent removed to prepare the silane. These preparation methods can lead to desired structures not found in commercially available products, and can also suppress the inclusion of metals and halogens.

[0044] 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 and silanol content of silica a, the molecular weight of silane coupling agent c, etc. However, from the viewpoint of sufficiently modifying silica a and obtaining a stable quaternary ammonium-modified silica dispersion, the amount is preferably 0.1 to 100 mass % relative to silica a, more preferably 0.5 to 75 mass %, and even more preferably 1 to 50 mass %.

[0045] The temperature when adding the quaternary ammonium group-containing silane coupling agent c is not particularly limited, and 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, and is preferably from 1 minute to 24 hours, and more preferably from 1 minute to 10 hours. When the addition temperature and addition time are within the above ranges, aggregation of the silica can be suppressed.

[0046] 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, and is preferably from 5°C to the boiling point of the silica a dispersion, and more preferably from 10°C to 70°C. However, 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, but from the viewpoint of completing the reaction and obtaining a stable quaternary ammonium-modified silica dispersion, the upper limit of the aging time is preferably 24 hours or less, and in some cases may be 10 hours or less.

[0047] 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 pH of the quaternary ammonium-modified silica dispersion after aging in step (2) is preferably 10.0 or higher, more preferably 10.5 or higher.

[0048] The water substitution method in 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.

[0049] 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, but is preferably 1 to 60% by mass, more preferably 1 to 50% by mass. The upper limit of the silica concentration within the above range is advantageous in that silica aggregation can be suppressed.

[0050] The pH of the quaternary ammonium-modified silica dispersion after water replacement in step (3) is preferably 6.0 to 8.5, more preferably 6.5 to 8.5. If the pH after water replacement is within the above range, the dispersion is neutral and the content of the organic solvent and / or basic compound b is minimized, thereby increasing the degree of freedom in formulation as a polishing composition.

[0051] 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.

[0052] 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]

[0053] [Silica concentration] The silica dispersion was precisely weighed into a ceramic crucible and dried at 105°C for 10 hours, and the residue was precisely weighed to calculate the silica concentration.

[0054] [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.).

[0055] [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

[0056] [pH] The pH was measured using a pH meter (Twin pH Meter II, manufactured by Horiba Ltd.).

[0057] [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.).

[0058] [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.

[0059] [Silica a dispersion] The following silica a dispersion was used. 25nm silica dispersion water (silica concentration 10-20% by mass, average secondary particle diameter 49.1nm) 95nm silica dispersion water (silica concentration 10% 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)

[0060] [Basic compound b] The basic compounds b used are represented by abbreviations. DIPA: Diisopropylamine TEA: Triethylamine

[0061] [Silane coupling agent c] Silane coupling agent c is expressed by product name or molecular formula. X-12-1126 (VOC-free water-based silane coupling agent, approximately 10% by weight aqueous solution, manufactured by Shin-Etsu Chemical Co., Ltd.) C9H 24 ClNO3Si: Trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride (48-53% by mass solution in methanol) C9H 20 O5Si: 3-glycidyloxypropyltrimethoxysilane

[0062] [Example 1] 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 5.0 g of diisopropylamine was added and mixed in. The pH of the resulting mixture was 12.0.

[0063] Process (2): To the mixture obtained in step (1), 80.0 g of X-12-1126 (approximately 10% by mass aqueous solution) was added over 80 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 11.2.

[0064] Process (3): The quaternary ammonium-modified silica dispersion obtained in step (2) was heated to distill off 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 8.2.

[0065] [Example 2] Process (1): 200 g of 95 nm silica dispersion water (silica concentration 10 mass %, average secondary particle diameter 181.5 nm) was placed in a flask, and 2.0 g of diisopropylamine was added and mixed in. The pH of the resulting mixture was 12.2.

[0066] Process (2): To the mixture obtained in step (1), 40.0 g of X-12-1126 (approximately 10% by mass aqueous solution) was added over 40 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 11.2.

[0067] Process (3): The quaternary ammonium-modified silica dispersion obtained in step (2) was heated to distill off 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 7.9.

[0068] [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 pH of the resulting quaternary ammonium-modified silica dispersion was 8.3, but a large amount of gel was generated.

[0069] 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 maintaining the temperature constant. 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. Water was added dropwise while maintaining the volume constant, replacing the methanol with water, yielding a quaternary ammonium-modified silica dispersion with a pH of 5.7.

[0070] The results of the examples and comparative examples are shown in Table 1 below. [Table 1]

[0071] 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 X-12-1126 is calculated as 10 mass %). For example, in Example 1, silane coupling agent c / silica a The result is 80.0g*0.1 / (200g*0.1)*100=40.

[0072] Similarly, in Comparative Example 1, calculations are made assuming that trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride is 50% by mass.

[0073] In addition, in Comparative Example 2, silane coupling agent c was prepared, but because an excess amount of triethylamine was added, the theoretical amount of silane coupling agent c produced was calculated based on 3-glycidyloxypropyltrimethoxysilane. For example, the amount of substance of 3-glycidyloxypropyltrimethoxysilane is 12.5g / 236.34g / mol=0.0529mol, and the theoretical amount of the resulting silane coupling agent c is 0.0529mol*337.53g / mol=17.86g. Therefore, the ratio of silane coupling agent c / silica a is 17.86g / (900g*0.2)*100=10.

[0074] In the examples, the addition of basic compound b suppressed silica aggregation during the surface modification process, and the use of VOC-free aqueous silane coupling agent X-12-1126 in step (2) resulted in a quaternary ammonium-modified silica dispersion with a high isoelectric pH. Surprisingly, the isoelectric point was passed during the reaction without pH adjustment. Furthermore, the zeta potential became positive over a wide basic range, resulting in a very stable quaternary ammonium-modified silica dispersion.

[0075] 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.

[0076] In the manufacturing method of Comparative Example 2, the aggregation of silica is largely suppressed by adding basic compound b. However, the pH of the isoelectric point is lower than in the Examples, and the zeta potential is also small, possibly because the reaction is not complete, resulting in a quaternary ammonium-modified silica dispersion with low stability.

Claims

1. A quaternary ammonium-modified silica dispersion, characterized in that the pH of the isoelectric point is 11.0 or higher.

2. 2. The quaternary ammonium-modified silica dispersion according to claim 1, wherein the increase rate of the average secondary particle size due to the surface modification is 10% or less.

3. 3. The quaternary ammonium-modified silica dispersion according to claim 1, wherein the quaternary ammonium groups are immobilized on the surface of the silica by covalent bonds.

4. A method for producing a quaternary ammonium-modified silica dispersion having an isoelectric point pH of 11.0 or higher, 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 solution prepared in step (1) and heating to obtain a quaternary ammonium-modified silica dispersion. Step (3): A step of substituting the organic solvent and / or basic compound b in the quaternary ammonium-modified silica dispersion obtained in step (2) with water.

5. 5. The method for producing a quaternary ammonium-modified silica dispersion according to claim 4, wherein in step (1), the average secondary particle diameter of silica a is 300 nm or less.

6. 6. The method for producing a quaternary ammonium-modified silica dispersion according to claim 4 or 5, wherein in step (2), the quaternary ammonium group-containing silane coupling agent c is an aqueous silane coupling agent having an organic solvent concentration of 3 mass% or less.

7. The method for producing a quaternary ammonium-modified silica dispersion according to claim 4 or 5, 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.

8. 6. The method for producing a quaternary ammonium-modified silica dispersion according to claim 4 or 5, wherein in step (2), the pH of the resulting quaternary ammonium-modified silica dispersion is 10.0 or higher.

9. The method for producing a quaternary ammonium-modified silica dispersion according to claim 4 or 5, further 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.

10. The method according to claim 4 or 5, wherein the silica concentration in the quaternary ammonium-modified silica dispersion is 50% by mass or less.

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