Surface-treated silica particle dispersion sol and method for producing the same

Abstract

A surface-treated silica particle dispersion sol (22) is formed by dispersing a group of colloidal silica particles in a hydrophobic solvent (21), wherein the colloidal silica particles are spherical primary particles observed by field emission type scanning electron microscope, are chain-like connected in an average number of 4 to 300, and have an average length of 35 nm to 1800 nm, and the particle surface is coated with a silane coupling agent having a functional group such as a vinyl group. The average particle diameter of the spherical primary particles is 6 nm to 20 nm, and the average aspect ratio of the spherical primary particles is in the range of 1.0 to 1.3. The proportion of K, Na, or NH3 impurities in each colloidal silica particle is 3500 mass ppm or less, and the proportion of alkaline earth metal or aluminum impurities is less than 1 mass ppm.

Description

Technical Field

[0001] This invention relates to a sol containing surface-treated silica particles arranged in a chain of spherical primary particles, and a method for manufacturing the same. More specifically, it relates to a surface-treated silica particle dispersion sol that forms a film with a low refractive index and good stability when coated onto a substrate, and a method for manufacturing the same. Furthermore, it relates to a film obtained using this surface-treated silica particle dispersion sol.

[0002] This application claims priority based on Japanese Patent Application No. 2021-170419, filed on October 18, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Conventionally, as such silica sols, stable silica sols have been disclosed that consist of elongated amorphous colloidal silica particles dispersed in a liquid medium and have a SiO2 concentration of 0.5 to 30% by weight. In these sols, the ratio of the particle size (D1 μm) of the amorphous colloidal silica particles, measured by dynamic light scattering, to the particle size (D2 μm) measured by nitrogen adsorption, is D1 / D2, which is 5 or more. D1 is 40 to 500 nanometers. Furthermore, the amorphous colloidal silica particles elongate in a single plane with the same thickness within a range of 5 to 40 nanometers as observed by an electron microscope (see Patent Document 1 (claims 1 to 3, page 4, upper right column, lines 5 to 9)).

[0004] Claim 2 of Patent Document 1 shows a method for manufacturing an alkaline silica sol comprising the following steps (a), (b) and (c).

[0005] (a) Step: In a colloidal aqueous solution containing 1 to 6% by weight of SiO2 and pH 2 to 4 of active silicic acid, an aqueous solution containing water-soluble calcium salt, magnesium salt or a mixture thereof is added and mixed in a weight ratio of CaO, MgO or the amount of the two relative to the SiO2 of the active silicic acid of the above-mentioned active silicic acid of 1500 to 8500 ppm.

[0006] (b) In the aqueous solution obtained by step (a), the above-mentioned alkali metal hydroxide, water-soluble organic base or their water-soluble silicate are added and mixed in such a way that the molar ratio of SiO2 / M2O (wherein SiO2 represents the content of silicon dioxide component derived from the above-mentioned active silicic acid and M represents the molecule of alkali metal atom or organic base) is 20 to 200.

[0007] (c) The mixture obtained from step (b) is heated at 60–150°C for 0.5–40 hours.

[0008] In claim 3 of patent document 1, a method for manufacturing a stable alkaline aqueous silica sol according to claim 2 is also shown, characterized in that, in step (a), the colloidal aqueous solution of active silica is obtained by contacting an aqueous solution of sodium silicate with a SiO2 / Na2O molar ratio of 1 to 4.5 and a SiO2 concentration of 1 to 6% by weight with a hydrogen-form cation exchange resin, having a SiO2 concentration of 1 to 6% by weight and a pH of 2 to 4, and not containing colloidal silica with a particle size of 3 nanometers or larger.

[0009] Patent document 1 describes an invention that provides a stable silica sol exhibiting improved properties by changing the shape of colloidal silica particles, and further provides a method for efficiently manufacturing the improved silica sol.

[0010] Patent Document 1: Japanese Patent Application Publication No. 1-317115

[0011] In the method for manufacturing an elongated silica sol disclosed in Patent Document 1, water glass, as a raw material, is passed through a column filled with ion exchange resin to obtain an aqueous solution of active silicic acid. This metal ion removal process requires a significant amount of time and effort, resulting in poor efficiency.

[0012] Furthermore, since an aqueous solution containing water-soluble calcium salts, magnesium salts, or mixtures thereof is added to the colloidal aqueous solution of active silicic acid, metal atoms as impurities are present in the solution. Over time, these impurity metal particles dissolve from the surface of the silica particles and precipitate as needle-shaped impurities, resulting in poor storage stability. Therefore, the silica sol obtained by the method of Patent Document 1 presents a problem of being unsuitable for use in fields such as semiconductors where the influence of impurities is a concern.

[0013] On the other hand, high-purity spherical colloidal silica particles are required to have uniform particle size when used as abrasives in chemical mechanical polishing (CMP). However, when forming films from spherical colloidal silica particles, there is a problem that the particles in the film tend to be densely packed, making it difficult to obtain films with low refractive index. Summary of the Invention

[0014] The object of this invention is to provide a surface-treated silica particle dispersion sol that can form a film with a low refractive index when coated onto a substrate and maintains good stability. Another object of this invention is to provide a simple method for manufacturing the surface-treated silica particle dispersion sol and a film with a low refractive index.

[0015] The inventors prepared an alkylsilicate solution by dissolving the alkylsilicate in a mixture of pure water and an organic solvent in a specified ratio using pure water in a specified ratio. Then, they heated the raw material liquid, which was prepared by adding and mixing an alkaline catalyst in a specified ratio to the solution, at a specified temperature and time, and found that the colloidal silica particles were linked in a chain-like manner.

[0016] The first aspect of this invention is a surface-treated silica particle dispersion sol, characterized in that the surface-treated silica particle dispersion sol is formed by dispersing colloidal silica particles in a hydrophobic solvent, wherein the colloidal silica particles are spherical primary particles observed by field emission scanning electron microscopy, linked in chains with an average number of 4 to 300 particles and having an average length of 35 nm to 1800 nm, and the particle surface is coated with silicon having vinyl, methyl, epoxy, styrene, or methacrylamide functional groups. The spherical primary particles are coated with alkane coupling agents, or with titanate-based or aluminate-based coupling agents. The average particle size of the spherical primary particles is 6 nm to 20 nm, and the average aspect ratio of the spherical primary particles is in the range of 1.0 to 1.3. The organic solvent is an alcohol with 1 to 4 carbon atoms or a water-soluble diol compound with 2 to 4 carbon atoms. The content of K, Na, or NH3 impurities in each colloidal silica particle is less than 3500 ppm by mass, and the content of alkaline earth metals or aluminum impurities is less than 1 ppm by mass.

[0017] The second aspect of this invention is a method for manufacturing a surface-treated silica particle dispersion sol, characterized in that the manufacturing method is the same as the method for manufacturing the surface-treated silica particle dispersion sol of the first aspect, comprising: (a) a step of mixing an alkyl silicate having 1 to 2 carbon atoms in a mixed solvent of pure water and an organic solvent to obtain an alkyl silicate solution, wherein the organic solvent is an alcohol having 1 to 4 carbon atoms or a water-soluble diol compound having 2 to 4 carbon atoms; and (b) a step of adding and mixing an alkaline catalyst into the alkyl silicate solution. (c) A step of obtaining a raw material solution by means of an alkaline catalyst, wherein the alkaline catalyst is an alkali metal hydroxide, ammonia, or an alkylamine; (d) a step of heating the raw material solution at 40°C to 100°C for 24 to 100 hours to obtain a first precursor sol dispersed with colloidal silica particles; (e) a step of adding and mixing an alcohol having 1 to 4 carbon atoms into the first precursor sol to obtain an alcohol-diluted sol; and (f) a step of adding an alcohol of 10% to 100% by mass to the alcohol-diluted sol when the silica particles in the alcohol-diluted sol are set to 100% by mass. (f) In a step of adding and mixing a surface treatment agent as a silane coupling agent having vinyl, methyl, epoxy, styrene, or methacryloyl functional groups, or a surface treatment agent as a titanate-based or aluminate-based coupling agent, and heating at 40°C to 100°C for 3 to 24 hours, a second precursor sol dispersed with surface-treated silica particles is obtained; (f) In a step of adding and mixing a hydrophobic solvent into the second precursor sol at a silica concentration of 1% to 25% by mass, and heating at 40°C to 80°C... Solvent replacement is performed by heating at ℃ for 3 to 12 hours. The mixed solvent contains pure water at a ratio of 8 to 23 moles of Si relative to the alkyl silicate. In step (a), when the alkyl silicate solution is set to 100% by mass, the alkyl silicate is mixed at a ratio of 18% to 44% by mass. In step (b), when the alkyl silicate is converted to silicon dioxide, the base catalyst is mixed at a ratio of 0.02% to 0.40% by mass relative to the silicon dioxide.

[0018] The third aspect of the present invention is based on the second aspect and is a method for manufacturing a surface-treated silica particle dispersion sol, wherein, in the initial heating stage of step (c), spherical primary particles with an average aspect ratio of 1.0 to 1.1 and an average particle size of less than 5 nm are formed; at the end of heating, the spherical primary particles in the initial heating stage become an average particle size of 6 nm to 20 nm, and grow into a group of colloidal silica particles that are linked in a chain with an average number of 4 to 300 and have an average length of 35 nm to 1800 nm.

[0019] The fourth aspect of the present invention is a film, characterized in that the film is obtained using a surface-treated silica particle dispersion sol from the first aspect, and the refractive index of the film is 1.10 to 1.25. That is, the film of the fourth aspect of the present invention can be obtained by coating a surface-treated silica particle dispersion sol from the first aspect onto a substrate and then drying it.

[0020] The first aspect of this invention relates to a surface-treated silica particle dispersion sol, which is formed by dispersing colloidal silica particles—observed using a field emission scanning electron microscope—in a mixed solvent. These particles are chained together in an average of 4 to 300 spherical primary particles, with an average length of 35 nm to 1800 nm. Therefore, during film formation, pores are easily formed, resulting in a film with a low refractive index. Furthermore, since the average particle size of the spherical primary particles is 6 nm to 20 nm, and the particle surfaces are treated with a surface-treatment agent, particle aggregation is suppressed, leading to excellent storage stability of the silica particle dispersion sol. Because the average aspect ratio of the spherical primary particles is in the range of 1.0 to 1.3, the viscosity of the surface-treated silica particle dispersion sol is low, resulting in a smaller deviation in the refractive index of the formed film. Additionally, since the content of K, Na, or NH3 impurities in each colloidal silica particle is 3500 ppm by mass or less, the spherical primary particles form a chain. Furthermore, since the proportion of alkaline earth metals or aluminum impurities in the surface-treated silica particle dispersion sol is less than 1 ppm by mass, the particles will not coarsen even after storage time, making it a surface-treated silica particle dispersion sol with high storage stability.

[0021] In the method for manufacturing a surface-treated silica particle dispersion sol according to the second aspect of the present invention, firstly, after dissolving an alkyl silicate in a mixed solvent to obtain an alkyl silicate solution, a predetermined proportion of an alkaline catalyst is added to the alkyl silicate solution at a predetermined concentration, and the solution is heated at a predetermined temperature for a predetermined time. Because the alkyl silicate concentration is predetermined, the spherical primary particles become chain-like upon heating, and the alkyl silicate solution does not gel. By adding an alkaline catalyst in a predetermined proportion, spherical primary particles are generated, and by heating the raw material solution for a predetermined time and at a predetermined temperature, the spherical primary particles are increased to an average particle size of 6 nm to 20 nm, growing into a first precursor sol consisting of a group of colloidal silica particles linked in chains with an average number of 4 to 300 particles and an average length of 35 nm to 1800 nm.

[0022] Next, a surface treatment agent is added and mixed in a predetermined proportion to an alcohol-diluted sol obtained by adding and mixing alcohol into the first precursor sol, and the mixture is heated at a predetermined temperature and time to obtain a second precursor sol in which surface-treated silica particles are dispersed. Finally, a hydrophobic solvent is added and mixed into the second precursor sol, and solvent displacement is performed by heating at a predetermined temperature and time, thereby producing a surface-treated silica particle dispersion sol in which surface-treated silica particles are dispersed in a hydrophobic solvent. Regarding this surface-treated silica particle dispersion sol, gelation is suppressed by preventing particle aggregation by coating the particle surface with the surface treatment agent. Therefore, even if the silica concentration in the sol is increased, gelation can be prevented.

[0023] In the method for manufacturing a surface-treated silica particle dispersion sol according to the third aspect of the present invention, at the end of the heating in step (c), the spherical primary particles grow into a group of colloidal silica particles that are linked in a chain with an average number of 4 to 300 and have an average length of 35 nm to 1800 nm.

[0024] The fourth aspect of the present invention uses a surface-treated silica particle dispersion sol from the first aspect to obtain a film. Therefore, the particles in the film are difficult to fill at the densest point, resulting in a low refractive index film with a refractive index of 1.10 to 1.25. Attached Figure Description

[0025] Figure 1 A flowchart for manufacturing the surface-treated silica particle dispersion sol of this embodiment. Detailed Implementation

[0026] Next, the methods for carrying out the present invention will be described with reference to the accompanying drawings.

[0027] [Method for manufacturing surface-treated silica particle dispersion sol]

[0028] The surface-treated silica particle dispersion sol of this embodiment is generally manufactured by the following method.

[0029] like Figure 1 As shown, an alkylsilicate 12 having 1 to 2 carbon atoms is added and mixed into a mixed solvent 11 of pure water and an organic solvent to obtain an alkylsilicate solution 13. Next, an alkaline catalyst 14 is added and mixed into the alkylsilicate solution 13 to obtain a feed liquid 15. Then, the feed liquid 15 is heated at a specified temperature for a specified time to obtain a first precursor sol 16 containing dispersed colloidal silica particles.

[0030] Next, a surface treatment agent 19 is added and mixed into an alcohol-diluted sol 18 obtained by adding and mixing alcohol 17 into the first precursor sol 16, and heated at a specified temperature and time to obtain a second precursor sol 20 in which surface-treated silica particles are dispersed. Then, a hydrophobic solvent 21 is added and mixed into the second precursor sol 20 in a specified proportion, and solvent replacement is performed by heating at a specified temperature and time to produce a surface-treated silica particle dispersion sol 22.

[0031] [Preparation of a mixed solvent of pure water and organic solvent]

[0032] Organic solvents are alcohols with 1 to 4 carbon atoms or water-soluble diols with 2 to 4 carbon atoms. Examples of alcohols with 1 to 4 carbon atoms include methanol, ethanol, isopropanol, n-propanol, and butanol. Examples of water-soluble diols with 2 to 4 carbon atoms include ethylene glycol (2 carbon atoms), propylene glycol (3 carbon atoms), propylene glycol monomethyl ether (PGM) (4 carbon atoms), and 1,3-butanediol (4 carbon atoms).

[0033] The mixed solvent 11, consisting of pure water and an organic solvent, is either a mixture of pure water and an alcohol having 1 to 4 carbon atoms, or a mixture of pure water and a water-soluble diol compound having 2 to 4 carbon atoms. Such a mixed solvent is suitable for easily dissolving alkyl silicates. Furthermore, the pure water in the mixed solvent is used for the hydrolysis of alkyl silicates, and the organic solvent is used to improve the miscibility between pure water and alkyl silicates. The content of the organic solvent in the alkyl silicate solution is preferably 10% to 35% by mass. If the content of the organic solvent is less than the lower limit, it is difficult for spherical primary particles to grow and for them to grow sufficiently into chain-like particles. Conversely, if it is greater than the upper limit, the spherical primary particles tend to become coarse.

[0034] The amount of pure water is adjusted to a concentration of 8 to 23 mol relative to the amount of Si (silicon) in the alkylsilicate. If the concentration is less than the lower limit, the spherical primary particles will become coarser during the heating process. If the concentration is greater than the upper limit, the spherical primary particles will be difficult to increase in size and cannot grow sufficiently into a chain-like structure. The amount of pure water relative to Si in the alkylsilicate is preferably 8 to 16 mol, more preferably 9 to 15 mol.

[0035] [Preparation of alkylsilicate solutions]

[0036] Alkyl silicate 12 is added to and mixed in mixed solvent 11 to prepare alkyl silicate solution 13. Alkyl silicate 12 is a silicate that is easily hydrolyzable and has an alkyl group having 1 to 2 carbon atoms. Examples include tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), or mixtures thereof, or oligomers of alkyl silicates. For example, a trimer to pentamer of tetramethoxysilane (TMOS) (manufactured by Mitsubishi Chemical Corporation, trade name: MKC Silicate MS51, sometimes abbreviated as "MS51") is suitable. When the alkyl silicate solution 13 is set to 100% by mass, alkyl silicate 12 is mixed in a ratio of 18% to 44% by mass. If the ratio is less than the lower limit, the spherical primary particles are difficult to increase in size during the heating process. Conversely, if the ratio is greater than the upper limit, the number of primary particle connections tends to increase, and the chains tend to grow. Additionally, the alkyl silicate solution may gel. When the alkyl silicate solution 13 is set to 100% by mass, it is preferable to mix the alkyl silicate 12 in a ratio of 21% to 43% by mass, and more preferably in a ratio of 26% to 38% by mass.

[0037] The alkylsilicate solution is preferably prepared by stirring at a temperature of 0°C to 30°C for 1 to 30 minutes. The proportion of alkylsilicate in the alkylsilicate solution is determined by nuclear magnetic resonance (NMR) (manufactured by BRUKER, product number: AVANCE III 400).

[0038] [Preparation of the feed solution]

[0039] In the alkylsilicate solution 13, when the alkylsilicate is converted to silicon dioxide, an alkaline catalyst 14 is added and mixed in a ratio of 0.02% to 0.40% by mass relative to the silicon dioxide to prepare the feed solution 15. The alkaline catalyst 14 is an alkali metal hydroxide, ammonia, or an alkylamine. In the case of other alkaline catalysts containing alkaline earth metal hydroxides or aluminum, the spherical primary particles increase in size and become coarser during the heating process, making it difficult to increase the chain length of the primary particles.

[0040] Because of the use of such an alkaline catalyst 14, the content of alkaline earth metal or aluminum impurities in each final colloidal silica particle is less than 1 ppm by mass. Examples of alkali metal hydroxides include potassium hydroxide (KOH) or sodium hydroxide (NaOH), and examples of alkylamines include methylamine (CH3NH2), dimethylamine ((CH3)2NH), trimethylamine ((CH3)3N), etc. The alkaline catalyst promotes the hydrolysis of alkyl silicates in the alkyl silicate solution 13 in the presence of pure water and an organic solvent. When the addition ratio of this alkaline catalyst is less than the lower limit of 0.02% by mass, there is a lack of reactivity, and spherical primary particles cannot be sufficiently generated; the particles are difficult to form chains. If it exceeds the upper limit of 0.40% by mass, hydrolysis is excessively promoted during the heating process, the reactivity becomes too high, and spherical particles are generated instead of chain-like particles. It is preferable to prepare the feed solution by stirring at a temperature of 0°C to 30°C for 1 to 30 minutes. The preferred addition ratio of the alkaline catalyst is 0.02% to 0.30% by mass, more preferably 0.05% to 0.25% by mass.

[0041] [Heating of the feed solution and preparation of the first precursor sol]

[0042] The feed solution 15 is heated at 40°C to 100°C for 24 to 100 hours. As a result, the spherical primary particles increase in size to an average particle size of 6 nm to 20 nm, growing into a group of colloidal silica particles linked in chains of an average number of 4 to 300 particles each, with an average length of 35 nm to 1800 nm. This group of colloidal silica particles is then dispersed in the aforementioned mixed solvent to obtain a first precursor sol. The chain length varies depending on the proportion of the alkaline catalyst added, the proportion of alkyl silicate added, and the heating temperature. Furthermore, the average particle size of the spherical primary particles is the average particle size obtained through FE-SEM observation (number of known particles: 50). Additionally, the average number of links is the average number of links obtained through FE-SEM observation (number of known particles: 50). Further, the average length of the chain particles is the average length obtained through FE-SEM observation (number of known particles: 50). The heating temperature of the feed solution 15 is preferably 50°C to 85°C. The heating time for raw material liquid 15 is preferably 24 hours to 72 hours.

[0043] [Preparation of a second precursor sol obtained by surface treatment of silica particles]

[0044] As a pretreatment to facilitate surface modification of the silica particles dispersed in the first precursor sol, an alcohol-diluted sol is prepared by diluting the first precursor sol with an alcohol having 1 to 4 carbon atoms that is easily evaporated during solvent replacement (described later). Examples of alcohols having 1 to 4 carbon atoms include methanol, ethanol, isopropanol, n-propanol, and butanol. The dilution ratio is, for example, 1.5 to 5 times (150% to 500% by mass relative to the silica particles in the first precursor sol).

[0045] By adding a surface treatment agent to the alcohol-diluted sol and stirring, and maintaining the mixture at 40°C to 100°C for 3 to 24 hours, the hydroxyl groups on the particle surface are combined with the coupling agent described later, thereby surface-treating the silica particles and preparing a second precursor sol containing the surface-treated silica particles. The surface treatment agent is a silane coupling agent having vinyl, methyl, epoxy, styrene, or methacrylamide functional groups, or a titanate-based or aluminate-based coupling agent. When the silica particles in the alcohol-diluted sol are set to 100% by mass, the surface treatment agent is added and mixed at a ratio of 10% to 100% by mass. The preferred addition ratio of the surface treatment agent is 10% to 80% by mass, more preferably 15% to 70% by mass. The heating temperature of the mixture of the alcohol-diluted sol and the surface treatment agent is preferably 50°C to 90°C, more preferably 60°C to 90°C. The heating time for the mixed solution of alcohol-diluted sol and surface treatment agent is preferably 3 to 18 hours, more preferably 3 to 12 hours.

[0046] Examples of vinyl coupling agents include vinyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.). Manufactured by Ltd., product name: KBM-1003); vinylethoxysilane (manufactured by the same company, product name: KBE-1003); as methyl-functionalized silane coupling agents, examples include methoxysilane (manufactured by the same company, product name: KBM-13) and methyltriethoxysilane (manufactured by the same company, product name: KBE-13); as epoxy-functionalized silane coupling agents, examples include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (manufactured by the same company, product name: KBM-303); as styryl-functionalized silane coupling agents, examples include p-styryltrimethoxysilane (manufactured by the same company, product name: KBM-1403); as methacryloyl-functionalized silane coupling agents, examples include 3-methacryloyloxypropylmethyldimethoxysilane (manufactured by the same company, product name: KBM-502), etc. In addition, products with the names KBM-22, KBM-403, KBM-503, and SZ31 (all manufactured by Shin-Etsu Chemical Co., Ltd.) can be listed.

[0047] In addition, as a titanate coupling agent, isopropyl triisostearoyl titanate (manufactured by Ajinomoto Precision Technology Co., Ltd., product name: Plenact TTS) can be listed. Other examples include products with product names such as Plenact 55, Plenact 46B, Plenact 338X, Plenact 238S, Plenact 38S, Plenact 138S, Plenact 41B, and Plenact 9SA (all manufactured by Ajinomoto Precision Technology Co., Ltd.). Furthermore, as an aluminate coupling agent, alkyl acetoacetate aluminum diisopropylate (e.g., manufactured by Ajinomoto Precision Technology Co., Ltd., product name: Plenact AL-M) can be listed.

[0048] [Preparation of silica particle dispersion sol via solvent displacement and surface treatment with hydrophobic solvent]

[0049] A hydrophobic solvent is added to the obtained second precursor sol and stirred to mix. The mixture is then maintained at 40°C to 80°C for 3 to 12 hours, allowing the mixed solvent of pure water and organic solvent used in the initial manufacturing stage, as well as the alcohol used to dilute the first precursor sol, to evaporate, thus performing solvent replacement. As a result, a surface-treated silica particle dispersion sol is obtained, in which surface-treated silica particles are dispersed in the hydrophobic solvent. Here, the hydrophobic solvent is mixed in such a way that the silica concentration in the second precursor sol is 1% to 25% by mass. The heating temperature of the mixture of the second precursor sol and the hydrophobic solvent is preferably 50°C to 80°C, more preferably 50°C to 70°C. It is preferable that the hydrophobic solvent is mixed in such a way that the silica concentration in the second precursor sol is 1% to 20% by mass, more preferably 1% to 10% by mass.

[0050] Examples of hydrophobic solvents include toluene, butyl acetate, cyclohexane, methyl isobutyl ketone, 2-methoxy-1-methylethyl acetate, and 1-methoxy-2-propanol.

[0051] The silica (SiO2) concentration in the surface-treated silica particle dispersion sol of this embodiment is preferably 10% to 35% by mass. If it is less than the lower limit, a low refractive index film may not be formed during film formation. Furthermore, if it is greater than the upper limit, SiO2 aggregation is likely to occur in the surface-treated silica particle dispersion sol. A more preferred SiO2 concentration is 5% to 10% by mass.

[0052] [Characteristics of surface-treated silica particle dispersion sol]

[0053] The surface-treated silica particle dispersion sol of this embodiment is manufactured by the above-described manufacturing method. It is formed by dispersing colloidal silica particles, which are observed by FE-SEM and are chained together in an average number of 4 to 300 particles, with an average length of 35 nm to 1800 nm, in a hydrophobic solvent. The average particle size of the spherical primary particles is 6 nm to 20 nm, and the average aspect ratio of the spherical primary particles is in the range of 1.0 to 1.3. The content of K, Na, or NH3 impurities in each colloidal silica particle is less than 3500 ppm by mass, and the content of alkaline earth metals or aluminum impurities is less than 1 ppm by mass. The average aspect ratio of the spherical primary particles is the average value obtained by dividing the major axis of the constituent particles by the minor axis. The aspect ratio is calculated for any number of 100 or more particles, and the average value is calculated. In addition, the concentrations of impurities other than NH3 were determined using an ICP (Inductively Coupled Plasma) luminescence spectrophotometer (manufactured by PerkinElmer, Inc., product number: Avio 500). The concentration of NH3 impurities was determined using an ammonia analyzer (manufactured by Toko Chemical Research Institute Co., Ltd., model: TiN-9001).

[0054] If the average number of links between colloidal silica particles is less than 4, the refractive index of the film increases during film formation; if it is greater than 300, the storage stability of the surface-treated silica particle dispersion sol decreases. The preferred average number of links is 50 to 200. Furthermore, if the average length of the colloidal silica particle chains is less than 35 nm, the refractive index of the film will not decrease during film formation. However, if it is greater than 1800 nm, the storage stability of the surface-treated silica particle dispersion sol decreases, and gelation occurs. The preferred average chain length is 50 nm to 1000 nm.

[0055] If the average particle size of the spherical primary particles is less than 6 nm, the particles are difficult to form a chain; if it is greater than 20 nm, a film cannot be formed, or even if a film is formed, the refractive index of the film tends to be high. The preferred average particle size of the spherical primary particles is 7 nm to 15 nm.

[0056] The closer the average aspect ratio of the spherical primary particles is to 1, the lower the viscosity of the surface-treated silica particle dispersion sol, and the smaller the deviation in the refractive index of the film during film formation. If the average aspect ratio of the spherical primary particles is greater than 1.3, the thickness of the colloidal silica particle chains becomes uneven. The refractive index of the coating film was determined by measuring it using a spectroellipsometer (JAWoollam, Japan, product number: M-2000).

[0057] If the proportion of K, Na, or NH3 impurities in each colloidal silica particle exceeds 3500 ppm by mass, the reaction is excessively accelerated, the hydrolysis rate is too high, and the spherical primary particles cannot form chains. If the proportion of alkaline earth metals or aluminum impurities in each colloidal silica particle exceeds 1 ppm by mass, the surface-treated silica particle dispersion sol will coarsen over time, resulting in decreased storage stability. Preferably, the proportion of K, Na, or NH3 impurities in each colloidal silica particle is 3000 ppm by mass or less, more preferably 2500 ppm by mass or less.

[0058] [Method for forming a surface-treated silica particle dispersion sol on a substrate surface]

[0059] The method for forming the surface-treated silica particle dispersion sol of this embodiment on the substrate surface is not particularly limited. For example, methods include coating the surface-treated silica particle dispersion sol onto the substrate and then drying it in the atmosphere at room temperature to form a film. The substrate is not particularly limited and can include glass substrates, silicon wafers, resin substrates, metal foil substrates, etc. The coating method for the above-mentioned surface-treated silica particle dispersion sol can include spin coating, screen printing, rod coating, mold coating, doctor blade coating, brush coating, etc. The refractive index of the obtained film is 1.10 to 1.25. By using the chain-like colloidal silica particle dispersion sol of this embodiment, the particles in the film are difficult to be densely packed, and a film with a low refractive index can be obtained.

[0060] Example

[0061] Next, embodiments and comparative examples of the present invention will be described in detail.

[0062] <Example 1>

[0063] A mixed solvent was prepared by mixing 63.5 g of ethanol and 63.5 g of pure water in a flask. The mass ratio of pure water to ethanol was 1:1. A tetraethoxysilane solution was prepared by adding 73.0 g of tetraethoxysilane (TEOS) to this mixed solvent. The concentration of tetraethoxysilane in the tetraethoxysilane solution was 34.8% by mass. Pure water was also included at a ratio of 11.6 mol% of Si in the tetraethoxysilane. The solution was stirred, and 10 g of an aqueous solution of potassium hydroxide (KOH) as a base catalyst was added dropwise to prepare a feedstock solution. Potassium hydroxide was added dropwise at a ratio of 0.12% by mass relative to the silica when converting the tetraethoxysilane to silica. After adding the potassium hydroxide aqueous solution, the feedstock solution was heated at 60°C for 96 hours to mature it. After heating, the feedstock solution was slowly cooled to room temperature to obtain a first precursor sol containing dispersed colloidal silica particles. In addition, the solvent that has evaporated or volatilized by heating is transferred to a cooling system for liquefaction and then returned to the feed liquid.

[0064] Next, methanol was added and mixed into the first precursor sol at a ratio of 400% by mass relative to the silica particles in the first precursor sol to obtain a methanol-diluted sol. Then, methyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBE-13) as a surface treatment agent was added and mixed at a ratio of 50% by mass relative to the silica particles in the methanol-diluted sol, and the mixture was kept at 60°C for 5 hours to obtain a second precursor sol.

[0065] Finally, 2-methoxy-1-methylethyl acetate, a hydrophobic solvent, was added to the second precursor sol at a concentration of 10% by mass relative to the silica concentration in the second precursor sol, and the mixture was stirred and kept at 60°C for 3 hours to allow the solvent in the second precursor sol up to this point to evaporate and be replaced by a hydrophobic solvent. Thus, the surface-treated silica particle dispersion sol of Example 1 was obtained.

[0066] Tables 1 and 2 below show the preparation conditions of the alkyl silicate solutions, etc., and the preparation conditions of the raw material solutions for Example 1, Examples 2 to 21 described below, and Comparative Examples 1 to 12, respectively. Furthermore, in Comparative Example 11, as described later, an aqueous solution of sodium silicate (Na silicate) was used instead of the alkyl silicate solution.

[0067] [Table 1]

[0068]

[0069] [Table 2]

[0070]

[0071] <Examples 2-21 and Comparative Examples 1-10, 12>

[0072] As shown in Table 1, in preparing the alkyl silicate solutions of Examples 2-21 and Comparative Examples 1-10, 12, in Example 11, a trimer-pentamer of tetramethoxysilane (TMOS) (manufactured by Mitsubishi Chemical Corporation, trade name: MKC silicate MS51) and tetramethoxysilane (TMOS) were used as the alkyl silicate. The mixing ratio of MS51 to TEOS was 1:1 by mass. In Example 13, MS51 was used as the alkyl silicate. In the other examples and Comparative Examples 1-10, 12, tetraethoxysilane (TEOS) was used in the same manner as in Example 1.

[0073] As shown in Table 1, the mixing ratio of alkyl silicates in the alkyl silicate solutions of Examples 2-21 and Comparative Examples 1-10, 12 was the same as in Example 1 or was modified. As shown in Table 1, the molar concentration ratio of pure water to Si in the alkyl silicates of Examples 2-21 and Comparative Examples 1-10, 12 was the same as in Example 1 or was modified. As shown in Table 1, the organic solvents of Examples 2-21 and Comparative Examples 1-10, 12 were the same as in Example 1 or were modified. As organic solvents, propylene glycol monomethyl ether was used in Examples 4 and 6, methanol was used in Examples 14 and 21, isopropanol was used in Example 15, n-propanol was used in Example 16, ethylene glycol was used in Example 17, and butanol was used in Example 18. In the other examples and Comparative Examples 1-5, 7-10, 12, ethanol was used in the same manner as in Example 1.

[0074] As shown in Table 2, the types of alkaline catalysts used in the preparation of the feed solutions of Examples 2-21 and Comparative Examples 1-10 and 12 were either the same as in Example 1 or modified. All were alkaline aqueous solutions. Magnesium hydroxide (Mg(OH)2) was used as the alkaline catalyst in Comparative Example 1, and a liquid prepared by mixing aluminum chloride (AlCl3) hexahydrate and ammonia (NH3) water in a 1:1 ratio of Al to N in the solution was used in Comparative Example 2. Furthermore, the ratio of alkaline catalyst to silicon dioxide was either the same as in Example 1 or modified when converting alkyl silicates to silicon dioxide. Further, as shown in Table 2, the temperature and time for heating the feed solutions of Examples 2-21 and Comparative Examples 1-10 and 12 were either the same as in Example 1 or modified. Under these manufacturing conditions, first precursor sols containing dispersed colloidal silicon dioxide particles were obtained for Examples 2-21 and Comparative Examples 1-10 and 12, respectively.

[0075] <Comparative Example 11>

[0076] In Comparative Example 11, a first precursor sol containing dispersed colloidal silica particles was obtained using the method of Example 1 in Patent Document 1. Specifically, a 3.6% by mass sodium silicate aqueous solution was passed through a column filled with cation exchange resin to obtain a colloidal aqueous solution of active silicic acid. 2000g of this colloidal aqueous solution of active silicic acid was added to a glass container, and while stirring the aqueous solution, 8.0g of a 10% by mass calcium chloride aqueous solution was added dropwise for mixing. The mixture was stirred, and after 30 minutes, 12.0g of a 10% by mass sodium hydroxide aqueous solution was further added dropwise to prepare a raw material solution. This raw material solution was placed in a stainless steel autoclave and heated at 130°C for 6 hours, after which the contents were removed to obtain the first precursor sol.

[0077] Table 3 below shows the surface treatment conditions and solvent replacement conditions for silica particles in eight types of first precursor sols, as conditions 1 to 8. Methanol or ethanol was used as the diluent in a ratio of 400% by mass relative to the silica particles in the first precursor sol. In the surface treatment conditions, the heating temperature and heating time for each of the eight types of conditions 1 to 8 were the same as in Example 1 or were modified. In condition 8, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBM-602), which has an amino functional group and is not described in the first aspect of the present invention, was used.

[0078] [Table 3]

[0079]

[0080] Regarding the replacement of the solvent in the second precursor sol with a hydrophobic solvent, as shown in Table 3, in all conditions 1 to 8, the process was performed by heating at 60°C for 3 hours. The second precursor sol was a sol obtained by surface-treating the silica particles in the first precursor sols obtained in Examples 1 to 21 and Comparative Examples 1 to 12. Furthermore, a hydrophobic solvent was added in such a way that the silica concentration in the second precursor sol was 10% by mass.

[0081] <Evaluation>

[0082] (1) The state of colloidal silica particles after heating the raw material liquid

[0083] Using the aforementioned FE-SEM, the state of colloidal silica particles in Examples 1-21 and Comparative Examples 1-12 was observed after heating for 1 hour (initial heating) and at the end of heating (final heating). The results are shown in Table 4 below. After one hour of heating, the average particle size of the primary particles of the colloidal silica particles in Example 1 was 4 nm, and the average aspect ratio was 1.0. They had not yet formed chains. At the end of heating, i.e., after 96 hours of heating, the primary particles of the colloidal silica particles in Example 1 were spherical with an average particle size of 10 nm, an average aspect ratio of 1.1, and an average of 70 primary particles were linked in chains with an average length of 700 nm. As shown in Table 4, the primary particles of the colloidal silica particles in Comparative Example 11 at the end of heating, i.e., after 6 hours of heating, were not spherical, with an average particle size of 12 nm, an average aspect ratio of 1.4, and an average of 4 primary particles were linked in chains with an average length of 50 nm. This is presumably because dissolved calcium ions dissolve on the surface of the silica particles.

[0084] [Table 4]

[0085]

[0086] (2) The proportion of impurities in colloidal silica particles

[0087] The impurity content in the colloidal silica particles of the first precursor sols of Examples 1-21 and Comparative Examples 1-12 was determined using the aforementioned ICP-based spectrophotometer and ammonia analyzer. The results are shown in Table 5 below. In Example 1, because KOH was used as the alkaline catalyst, the K concentration per colloidal silica particle was 850 ppm by mass. Na, NH3, Ca, Mg, and Al were all below the detection limit, i.e., less than 1 ppm by mass. In Table 5, "<1" indicates that the impurity content is less than 1 ppm by mass.

[0088] [Table 5]

[0089]

[0090] (3) Storage stability of surface-treated silica particle dispersion sol

[0091] Regarding the storage stability of the surface-treated silica particle dispersions in Examples 1-21 and Comparative Examples 1-12, visual confirmation was performed by placing the dispersions in a transparent glass container and allowing them to stand for one month at 25°C and 60% relative humidity. A dispersion without agglomerates and without gelation was classified as "good," while a dispersion with agglomerates or gelation was classified as "poor." The results are shown in Table 5 above.

[0092] (4) Refractive index of the coating

[0093] The surface-treated silica particle dispersion sol of Examples 1-21 and Comparative Examples 1-12 was dried to a thickness of 0. . The coating was applied to a glass substrate at a thickness of 15 μm using spin coating and dried at 120 °C for 30 minutes. The refractive index of the coating formed on the glass substrate was measured using the aforementioned spectroscopic ellipsometry. The results are shown in Table 5 above. Regarding the deviation of the film's refractive index, the refractive index of three different locations on the film was measured and calculated using the following formula (1).

[0094] [(Maximum value - Minimum value) / Average value] × 100% (1)

[0095] Cases with a deviation of "less than ±5%" are considered to have a good refractive index deviation, while cases with a deviation of "more than ±5%" are considered to have a poor refractive index deviation. In Table 5, "-" indicates that the measurement could not be performed.

[0096] <Evaluation Results>

[0097] As shown in Table 4, in Comparative Example 1, because magnesium hydroxide (Mg(OH)2) was used as an alkaline catalyst, dissolved magnesium ions were released from the surface of the silica particles, promoting the formation of coarse particles and thus making the particles coarse. The average particle size of the primary particles was too large, at 30 nm. The average chain length of the colloidal silica particles was 250 nm, and the average number of links was 9. Therefore, the coarse particles aggregated and did not disperse, failing to form a coating on the glass substrate, and thus the refractive index of the film could not be measured. In addition, the Mg (magnesium) impurity content of the colloidal silica particles was 420 ppm by mass. The storage stability of the dispersion sol was "poor". Due to the coarse particles agglomerating and not dispersing, surface treatment and solvent replacement could not be performed.

[0098] In Comparative Example 2, because a mixture of aluminum chloride hexahydrate and ammonia was used as the alkaline catalyst, aluminum ions, as impurities, dissolved from the surface of the silica particles, promoting the formation of coarse particles. This resulted in coarsened colloidal silica particles, with an average primary particle size of 30 nm, an average chain length of 400 nm, and an average number of 14 links. Consequently, the coarse particles aggregated and failed to disperse, failing to form a coating on the glass substrate, thus preventing the determination of the film's refractive index. Furthermore, the colloidal silica particles contained 990 ppm by mass of NH3 impurities and 1000 ppm by mass of Al (aluminum) impurities. The storage stability of the dispersion sol was "poor." Due to the coarse particles agglomerating and failing to disperse, surface treatment and solvent replacement could not be performed.

[0099] In Comparative Example 3, the concentration of NaOH, acting as an alkaline catalyst, was too low, at 0. . The concentration of sodium (Na) in the colloidal silica particles was 0.01 ppm, resulting in poor reactivity. Spherical primary particles were not sufficiently generated, the average chain length of the colloidal silica particles was too short (20 nm), and the average number of primary particle connections was too low (2). Therefore, although a coating could form, the film had a high refractive index of 1.30. Furthermore, the Na impurity content in the colloidal silica particles was 12 ppm. The storage stability of the dispersion sol was rated as "good".

[0100] In Comparative Example 4, the mixing ratio of tetraethoxysilane was excessive relative to the tetraethoxysilane solution, at 60.8% by mass. Consequently, the ratio of pure water to Si in the tetraethoxysilane solution was 4.2 mol%, leading to gelation of the tetraethoxysilane solution. Therefore, although the average number of primary particle connections was 250, the average chain length of the colloidal silica particles was too long, at 2500 nm, preventing the formation of a coating on the glass substrate and thus hindering the determination of the film's refractive index. Furthermore, the colloidal silica particles contained 700 ppm by mass of Na (sodium) impurities. The storage stability of the dispersion sol was "poor." Due to the excessively long average chain length of the colloidal silica particles, they were not dispersed, thus preventing surface treatment and solvent replacement.

[0101] In Comparative Example 5, the mixing ratio of tetraethoxysilane was too low relative to the tetraethoxysilane solution, at 8.7% by mass. Consequently, the ratio of pure water to Si in the tetraethoxysilane was 64.0 mol / L. Therefore, during the heating process, the spherical primary particles did not sufficiently increase in size, resulting in an average particle size of 4 nm. The average number of primary particle connections was 20, and the average chain length of the colloidal silica particles was 80 nm. Although a coating could be formed, the film's refractive index was high (1.30) due to the aggregation of spherical particles. Furthermore, the colloidal silica particles contained 700 ppm by mass of Na (sodium) impurities. Although the spherical particles aggregated, the average chain length was short, therefore the storage stability of the dispersion sol was rated as "good".

[0102] In Comparative Example 6, although the mixing ratio of tetraethoxysilane was appropriate relative to the tetraethoxysilane solution at 34.8% by mass, the proportion of pure water relative to the Si in the tetraethoxysilane was too low, at 1.6 mol concentration. Therefore, the primary particles were coarse, with an excessively large average particle size of 35 nm. The average number of primary particle links was 15, and the average chain length of the colloidal silica particles was 250 nm. Although a coating could be formed, the film had a high refractive index of 1.37 due to the coarse spherical particles. Furthermore, the colloidal silica particles contained 700 ppm by mass of Na (sodium) impurities. The storage stability of the dispersion sol was rated as "good".

[0103] In Comparative Example 7, although the mixing ratio of tetraethoxysilane was appropriate relative to the tetraethoxysilane solution at 34.8% by mass, the proportion of pure water relative to the Si in the tetraethoxysilane was too low, at 1.6 mol concentration. Therefore, the primary particles were coarse, with an excessively large average particle size of 40 nm and an excessively large average aspect ratio of 1.4. The average number of primary particle connections was 5, and the average chain length of the colloidal silica particles was 200 nm. Although a coating could be formed, the film's refractive index was high at 1.38 due to the aggregation of spherical particles. Furthermore, the colloidal silica particles contained 700 ppm by mass of Na (sodium) impurities. The storage stability of the dispersion sol was rated as "good".

[0104] In Comparative Example 8, due to the excessively high concentration of NH3 (ammonia) as the alkaline catalyst (0.60% by mass), the hydrolysis rate of tetraethoxysilane increased significantly, resulting in coarser spherical primary particles with an excessively large average particle size of 30 nm. The average aspect ratio of the primary particles was 1.2. The average chain length of the colloidal silica particles was 90 nm, and the average number of aggregated primary particles was only 3. Therefore, although a coating could be formed, the film had a high refractive index of 1.30. Furthermore, the NH3 impurity content of the colloidal silica particles was 490 ppm by mass. The storage stability of the dispersion sol was rated as "good".

[0105] In Comparative Example 9, the mixing ratio of tetraethoxysilane was excessive relative to the tetraethoxysilane solution, at 69.5% by mass. Consequently, the ratio of pure water to Si in the tetraethoxysilane was 2.9 mol%, leading to gelation of the tetraethoxysilane solution. The average number of primary particle connections increased drastically to 400, and the average chain length of the colloidal silica particles was excessively long, at 3200 nm. Therefore, a coating could not be formed on the glass substrate, and the refractive index of the film could not be measured. Furthermore, the Na (sodium) impurity content of the colloidal silica particles was 700 ppm by mass. The storage stability of the dispersion sol was "poor." Due to the excessively long average chain length of the colloidal silica particles, they were not dispersed, thus preventing surface treatment and solvent replacement.

[0106] In Comparative Example 10, the concentration of NaOH as the alkaline catalyst was too high (0.70% by mass), resulting in a significant increase in the hydrolysis rate of tetraethoxysilane. This led to coarsening of the primary particles, with an average particle size of 500 nm. Agglomerated particles were obtained with an average chain length of 4000 nm and an average number of primary particle connections of 10. The average aspect ratio of the primary particles was too high (2.0). Due to the aggregation of coarse spherical particles, a coating could not be formed on the glass substrate, and the refractive index of the film could not be measured. Furthermore, the Na (sodium) impurity content of the colloidal silica particles was 4020 ppm by mass. The storage stability of the dispersion sol was "poor." Surface treatment and solvent replacement could not be performed due to the aggregation of coarse spherical particles.

[0107] In Comparative Example 11, because an aqueous solution of sodium silicate (Na silicate) was used instead of alkyl silicates, and an aqueous solution of calcium chloride was added to this sodium silicate solution, the concentration of Na (sodium) as an impurity was 9691 ppm by mass and the concentration of Ca (calcium) was 4052 ppm by mass during particle synthesis. Furthermore, through concentration, the concentration of Na as an impurity increased to 5886 ppm by mass and the concentration of Ca increased to 3843 ppm by mass. However, over time, needle-like impurities precipitated from the surface of the silica particles due to the dissolution of sodium and calcium ions, resulting in very large particles with an average aspect ratio of 1.4. Additionally, the storage stability of the sol was "poor." Since the dispersed sol did not gel or increase in viscosity, a coating film could be formed with a refractive index of 1.20. However, due to the uneven chain thickness and deviations in the number of connected particles, the refractive index deviation of the film was very large, at 5%.

[0108] In Comparative Example 12, because N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBM-602), which has an amino functional group and is not described in the first aspect of the present invention, was used as a surface treatment agent, the pH of the liquid was changed by the amino group, causing the silica particles in the dispersed sol to aggregate. Therefore, a coating film could not be formed on the glass substrate, and the refractive index of the film could not be measured.

[0109] In contrast, in Examples 1 to 21, since the surface-treated silica particle dispersion sol is manufactured under the manufacturing conditions that satisfy the second aspect of the present invention described above, it is possible to obtain a surface-treated silica particle dispersion sol having the characteristics of the first aspect of the present invention.

[0110] Industrial availability

[0111] The surface-treated silica particle dispersion sol of the present invention is used in the fields of forming anti-reflective films or intermediate films, etc. The anti-reflective film is used in display panels such as cathode ray tubes, liquid crystals, organic ELs, solar cells, and glass for display cases to prevent the reflection of incident light, and the intermediate film is used in sensors or camera modules and is formed by utilizing the difference in refractive index.

[0112] Explanation of reference numerals in the attached figures

[0113] 11. Mixed solvent of pure water and organic solvent

[0114] 12-alkylsilicate

[0115] 13-alkylsilicate solution

[0116] 14 Alkali Catalyst

[0117] 15 Raw Material Liquid

[0118] 16 First precursor sol

[0119] 17 alcohol

[0120] 18-Alcohol Diluted Sol

[0121] 19 Surface Treatment Agent

[0122] 20 Second precursor sol

[0123] 21 Hydrophobic solvents

[0124] 22 Surface-treated silica particle dispersion sol

Claims

1. A surface-treated silica particle dispersion sol, characterized in that, The surface-treated silica particle dispersion sol is formed by dispersing colloidal silica particles in a hydrophobic solvent. These colloidal silica particles, as observed by field emission scanning electron microscopy, are spherical primary particles linked in chains of an average of 4 to 300 particles, with an average length of 35 nm to 1800 nm. The particle surface is coated with a silane coupling agent having vinyl, methyl, epoxy, styrene, or methacrylamide functional groups, or with a titanate-based or aluminate-based coupling agent. The titanate-based coupling agent is triisostearoyl titanate isopropyl, and the aluminate-based coupling agent is diisopropyl alkyl acetoacetate aluminum. The average particle size of the spherical primary particles is 6 nm to 20 nm, and the average aspect ratio of the spherical primary particles is in the range of 1.0 to 1.

3. The proportion of K, Na, or NH3 impurities in each of the colloidal silica particles is less than 3500 ppm by mass, and the proportion of alkaline earth metals or aluminum impurities is less than 1 ppm by mass.

2. A method for manufacturing a surface-treated silica particle dispersion sol, characterized in that, The manufacturing method is a method for manufacturing the surface-treated silica particle dispersion sol as described in claim 1, comprising: (a) Step: An alkyl silicate solution is obtained by mixing an alkyl silicate having 1 to 2 carbon atoms in a mixed solvent of pure water and an organic solvent, wherein the organic solvent is an alcohol having 1 to 4 carbon atoms or a water-soluble diol compound having 2 to 4 carbon atoms. (b) Step, in which an alkaline catalyst is added to and mixed in the alkyl silicate solution to obtain a feed solution, wherein the alkaline catalyst is an alkali metal hydroxide, ammonia or an alkylamine; (c) Step: The raw material liquid is heated at 40°C to 100°C for 24 hours to 100 hours to obtain a first precursor sol with dispersed colloidal silica particles. (d) Step: Add and mix an alcohol with 1 to 4 carbon atoms into the first precursor sol to obtain an alcohol-diluted sol; (e) In the alcohol-diluted sol, a surface treatment agent having vinyl, methyl, epoxy, styrene, or methacryloyl functional groups, or a titanate-based or aluminate-based coupling agent, is added and mixed in a proportion of 10% to 100% when the silica particles in the alcohol-diluted sol are set to 100% by mass. The sol is then heated at 40°C to 100°C for 3 to 24 hours to obtain a second precursor sol with surface-treated silica particles dispersed therein. The titanate-based coupling agent is triisostearoyl titanate isopropyl, and the aluminate-based coupling agent is aluminum diisopropyl alkyl acetoacetate. (f) In the second precursor sol, a hydrophobic solvent is added and mixed in such a way that the silica concentration in the second precursor sol is 1% to 25% by mass, and the solvent is replaced by heating at 40°C to 80°C for 3 to 12 hours. The pure water is contained in a ratio of 8 to 23 moles of Si relative to the concentration of Si in the alkyl silicate. In step (a), when the alkyl silicate solution is set to 100% by mass, the alkyl silicate is mixed in a ratio of 18% to 44% by mass. In step (b), when converting the alkyl silicate to silicon dioxide, the base catalyst is mixed in a ratio of 0.02% to 0.40% by mass relative to the silicon dioxide.

3. The method for manufacturing surface-treated silica particle dispersion sol according to claim 2, characterized in that, In the initial heating stage of process (c), spherical primary particles with an average aspect ratio of 1.0 to 1.1 and an average particle size of less than 5 nm are formed. At the end of heating, the spherical primary particles in the initial heating stage become a group of colloidal silica particles with an average particle size of 6 nm to 20 nm and grow into a chain of 4 to 300 particles with an average length of 35 nm to 1800 nm.

4. A membrane, characterized in that, The membrane is obtained using the surface-treated silica particle dispersion sol as described in claim 1. The refractive index of the film is 1.10 to 1.25.

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