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

Abstract

This 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 composed of an average of 4-300 spherical primary particles, as observed with a field emission-type scanning electron microscope, linked in a chain shape to have an average length of 35-1,800 nm, and the surfaces of the colloidal silica particles are coated with a silane coupling agent or the like having a functional group such as a vinyl group. The average particle diameter of the spherical primary particles is 6-20 nm, and the average aspect ratio of the spherical primary particles is in the range of 1.0-1.3. Each of the colloidal silica particles contains at most 3,500 ppm by mass of impurities such as K, Na, or NH3 and less than 1 ppm by mass of impurities such as alkaline earth metals or aluminum.

Description

Technical Field

[0001] The present invention relates to a sol in which surface-treated silica particles in which spherical primary particles are connected in a chain are dispersed and a method for producing the same. More specifically, the present invention relates to a surface-treated silica particle dispersion sol that can form a film with a low refractive index when applied on a substrate and has good storage stability, and a method for producing the same. The present invention also relates to a film obtained using the surface-treated silica particle dispersion sol. This application claims priority based on Japanese Patent Application No. 2021-170419 filed in Japan on October 18, 2021, and incorporates the content herein by reference.

Background Art

[0002] Conventionally, as this type of silica sol, the ratio D1 / D2 of the measured particle diameter (D1 μm) by the dynamic light scattering method to the measured particle diameter (D2 μm) by the nitrogen gas adsorption method is 5 or more, D1 is 40 to 500 millimicrons, and an amorphous colloidal silica particle having a uniform thickness within the range of 5 to 40 millimicrons and having an elongation only in one plane in the form of an elongated shape is dispersed in a liquid medium to form a stable silica sol having an SiO2 concentration of 0.5 to 30% by weight (see Patent Document 1 (Claims 1 to 3, page 4, upper right column, lines 5 to 9)).

[0003] Claim 2 of Patent Document 1 discloses a method for producing an alkaline silica sol comprising the following steps (a), (b), and (c). (a) A colloidal aqueous solution of active silicic acid containing 1 to 6% by weight as SiO2 and having a pH of 2 to 4 is mixed with an aqueous solution containing a water-soluble calcium salt, a magnesium salt, or a mixture thereof in an amount such that the weight ratio of CaO, MgO, or both to SiO2 of the active silicic acid is 1500 to 8500 ppm. (b) Adding an alkali metal hydroxide, a water-soluble organic base, or a water-soluble silicate thereof to the aqueous solution obtained in step (a) so that the SiO2 / M2O (where SiO2 represents the content of silica derived from the above active silica, and M represents the above alkali metal atom or the molecule of the organic base) molar ratio is 20 to 200, and mixing them. (c) Heating the mixture obtained in step (b) at 60 to 150 °C for 0.5 to 40 hours.

[0004] Claim 3 of Patent Document 1 further states that the colloidal aqueous solution of active silica used in step (a) is obtained by contacting an aqueous solution of sodium water glass having an SiO2 / Na2O molar ratio of 1 to 4.5 and an SiO2 concentration of 1 to 6% by weight with a hydrogen-type cation exchange resin, having an SiO2 concentration of 1 to 6% by weight and a pH of 2 to 4, and not containing colloidal silica having a particle size of 3 millimicrons or more. The method for producing a stable alkaline aqueous silica sol according to claim 2 is shown.

[0005] Patent Document 1 describes that this invention provides a stable silica sol showing improved performance by modifying the shape of colloidal silica particles, and further provides a method for efficiently producing the silica sol related to this improvement.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the method for producing an elongated silica sol disclosed in Patent Document 1, an aqueous solution of active silica is obtained by passing water glass, which is a raw material, through a column filled with an ion exchange resin. In this metal ion removal step, there is a problem of low efficiency because a lot of labor and time are required.

[0008] In addition, in order to add an aqueous solution containing a water-soluble calcium salt, a magnesium salt, or a mixture thereof to a colloidal aqueous solution of activated silicic acid, metal atoms as impurities were contained in the solution, and over time, metal particles of these impurities eluted from the surface of the silica particles and acicular impurities precipitated, lacking storage stability. For this reason, the silica sol obtained by the method of Patent Document 1 had a problem that it was not suitable for use in fields such as semiconductors where the influence of impurities was a concern.

[0009] On the other hand, for high-purity spherical colloidal silica particles used in chemical mechanical polishing (CMP), abrasives with uniform particle diameters are required. However, when a film is formed from spherical colloidal silica particles, the particles in the film tend to be in close packing, and there has been a problem that it is difficult to obtain a film with a low refractive index.

[0010] An object of the present invention is to provide a surface-treated silica particle dispersion sol that can form a film with a low refractive index when coated on a substrate and has good storage stability. Another object of the present invention is to provide a method for easily producing this surface-treated silica particle dispersion sol and a film with a low refractive index.

Means for Solving the Problems

[0011] The inventor of the present invention prepared pure water in a predetermined ratio with respect to Si in alkyl silicate, dissolved alkyl silicate in a mixed solvent of this pure water and an organic solvent at a predetermined ratio to prepare an alkyl silicate solution, and then added and mixed an alkali catalyst to this solution at a predetermined ratio. By heating the raw material liquid at a predetermined temperature and time, it was found that the colloidal silica particles were connected in a chain, and the present invention was achieved.

[0012] A first aspect of the present invention is that spherical primary particles grasped by field emission scanning electron microscope observation are connected in a chain with 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, a methyl group, an epoxy group, a styryl group, or a methacryl group, orIsopropyltriisostearoyl titanate, which is a titanate coupling agent, or aluminum diisopropylate alkyl acetate, which is an aluminate coupling agent A surface-treated silica particle dispersion sol formed by dispersing a group of colloidal silica particles coated with Isopropyltriisostearoyl titanate, which is a titanate coupling agent, or aluminum diisopropylate alkyl acetate, which is an aluminate coupling agent in a hydrophobic solvent, wherein the average particle diameter of the spherical primary particles is 6 nm to 20 nm, 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 having 1 to 4 carbon atoms or a water-soluble glycol compound having 2 to 4 carbon atoms, and the content ratio of each of the impurities of K, Na or NH3 per colloidal silica particle is 3500 mass ppm or less, and the content ratio of each of the impurities of alkaline earth metal or aluminum is less than 1 mass ppm.

[0013] A second aspect of the present invention is: (a) a step of mixing an alkyl silicate having an alkyl group having 1 to 2 carbon atoms in a mixed solvent of pure water and an organic solvent which is an alcohol having 1 to 4 carbon atoms or a water-soluble glycol compound having 2 to 4 carbon atoms to obtain an alkyl silicate solution; (b) a step of adding and mixing an alkali catalyst which is an alkali metal hydroxide, ammonia or an alkylamine to the alkyl silicate solution to obtain a raw material solution; (c) a step of heating the raw material solution at 40°C to 100°C for 24 hours to 100 hours to obtain a first precursor sol in which colloidal silica particles are dispersed; (d) a step of adding and mixing an alcohol having 1 to 4 carbon atoms to the first precursor sol to obtain an alcohol-diluted sol; (e) adding a surface treatment agent which is a silane coupling agent having a functional group of a vinyl group, a methyl group, an epoxy group, a styryl group or a methacryl group to the alcohol-diluted sol or Isopropyltriisostearoyl titanate, which is a titanate coupling agent, or aluminum diisopropylate alkyl acetate, which is an aluminate coupling agentWhen the surface treatment agent is 100% by mass of the silica particles in the alcohol-diluted sol, it is added and mixed at a ratio of 10% by mass to 100% by mass, and heated at 40°C to 100°C for 3 hours to 24 hours to obtain a second precursor sol in which the surface-treated silica particles are dispersed. (f) A step of adding and mixing a hydrophobic solvent to the second precursor sol so that the silica concentration in the second precursor sol becomes 1% by mass to 25% by mass, and heating at 40°C to 80°C for 3 hours to 12 hours for solvent replacement, wherein the pure water is contained in the mixed solvent at a ratio of 8 molar concentration to 23 molar concentration with respect to Si in the alkyl silicate. In the step (a), when the alkyl silicate solution is 100% by mass, the alkyl silicate is mixed at a ratio of 18% by mass to 44% by mass. In the step (b), when the alkyl silicate is converted to silica, the alkali catalyst is mixed at a ratio of 0.02% by mass to 0.40% by mass with respect to the silica. It is a method for producing a surface-treated silica particle-dispersed sol according to the first aspect, characterized in that.

[0014] A third aspect of the present invention is an invention based on the second aspect, in which spherical primary particles having an average aspect ratio of 1.0 to 1.1 and an average particle diameter of less than 5 nm are formed at the initial stage of heating in the step (c), and at the end of heating, the spherical primary particles in the initial stage of heating have an average particle diameter of 6 nm to 20 nm and are connected in a chain at an average number of 4 to 300 to grow into a group of colloidal silica particles having an average length of 35 nm to 1800 nm. It is a method for producing a surface-treated silica particle-dispersed sol.

[0015] A fourth aspect of the present invention is a film obtained by using the surface-treated silica particle-dispersed sol according to the first aspect, and the film is characterized in that the refractive index is 1.10 to 1.25. That is, the film according to the fourth aspect of the present invention may be obtained by applying the surface-treated silica particle-dispersed sol according to the first aspect on a substrate and then drying it.

Effect of the Invention

[0016] The surface-treated silica particle dispersion sol according to the first aspect of the present invention is formed by dispersing a group of colloidal silica particles having an average length of 35 nm to 1800 nm, in which 4 to 300 spherical primary particles grasped by field emission scanning electron microscope observation are connected in a chain, in a mixed solvent. Therefore, when a film is formed, pores are likely to be formed in the film, and the film has a low refractive index. Further, since the average particle diameter of the spherical primary particles is 6 nm to 20 nm and the particle surface is surface-treated with a surface treatment agent, aggregation of the particles is suppressed, and the storage stability of the silica particle dispersion sol is good. Since the average aspect ratio of the spherical primary particles is in the range of 1.0 to 1.3, the surface-treated silica particle dispersion sol has a low viscosity, and the refractive index of the formed film has little variation. Further, since the content ratio of each of the impurities of K, Na, or NH3 per colloidal silica particle is 3500 mass ppm or less, the spherical primary particles become chain-like. Furthermore, since the content ratio of each of the impurities of alkaline earth metal or aluminum in the surface-treated silica particle dispersion sol is less than 1 mass ppm, the particles do not coarsen even after the passage of the storage time, and a surface-treated silica particle dispersion sol having high storage stability is obtained.

[0017] In the method for producing a surface-treated silica particle dispersion sol according to the second aspect of the present invention, first, an alkyl silicate is dissolved in a mixed solvent to obtain an alkyl silicate solution, and then a predetermined ratio of an alkali catalyst is added to the alkyl silicate solution having a predetermined concentration, and the mixture is heated at a predetermined temperature for a predetermined time. Since the alkyl silicate has a predetermined concentration, the spherical primary particles become chain-like by heating, and the alkyl silicate solution does not gel. By adding an alkali catalyst at a predetermined ratio, spherical primary particles are generated, and by heating the raw material solution at a predetermined temperature for a predetermined time, the spherical primary particles increase to an average particle diameter of 6 nm to 20 nm and grow into a group of colloidal silica particles having an average length of 35 nm to 1800 nm, which are connected in a chain with an average number of 4 to 300, to obtain a first precursor sol.

[0018] Next, a surface treatment agent is added and mixed at a predetermined ratio to the alcohol-diluted sol obtained by adding and mixing alcohol to this first precursor sol, and heated at a predetermined temperature and for a predetermined time to obtain a second precursor sol in which surface-treated silica particles are dispersed. Finally, a hydrophobic solvent is added and mixed to this second precursor sol, and heated at a predetermined temperature and for a predetermined time to perform solvent substitution, thereby producing a surface-treated silica particle-dispersed sol in which surface-treated silica particles are dispersed in the hydrophobic solvent. In this surface-treated silica particle-dispersed sol, aggregation between particles is prevented by coating the particle surface with the surface treatment agent, and gelation is suppressed. As a result, even if the concentration of silica in the sol is increased, gelation can be prevented.

[0019] In the method for producing the surface-treated silica particle-dispersed sol according to the third aspect of the present invention, at the end of the heating in step (c), spherical primary particles grow and form a group of colloidal silica particles that are connected in a chain with an average number of 4 to 300 and have an average length of 35 nm to 1800 nm.

[0020] Since the film according to the fourth aspect of the present invention is obtained using the surface-treated silica particle-dispersed sol according to the first aspect, the particles in the film are less likely to be in the closest packing, and the film has a low refractive index of 1.10 to 1.25.

Brief Description of the Drawings

[0021]

Figure 1

Embodiments for Carrying Out the Invention

[0022] Next, embodiments for carrying out the present invention will be described with reference to the drawings.

[0023] 〔Method for Producing Surface-Treated Silica Particle-Dispersed Sol〕 The surface-treated silica particle-dispersed sol of this embodiment is roughly manufactured by the following method. As shown in Fig. 1, an alkyl silicate 12 having an alkyl group with 1 to 2 carbon atoms is added to and mixed with a mixed solvent 11 of pure water and an organic solvent to obtain an alkyl silicate solution 13. Next, an alkali catalyst 14 is added to and mixed with this alkyl silicate solution 13 to obtain a raw material solution 15. Then, this raw material solution 15 is heated at a predetermined temperature for a predetermined time to obtain a first precursor sol 16 in which colloidal silica particles are dispersed.

[0024] Next, alcohol 17 is added to and mixed with this first precursor sol 16, and a surface treatment agent 19 is added to and mixed with the resulting alcohol-diluted sol 18, followed by heating at a predetermined temperature and time to obtain a second precursor sol 20 in which surface-treated silica particles are dispersed. After that, a hydrophobic solvent 21 is added to and mixed with this second precursor sol 20 at a predetermined ratio, and heating is performed at a predetermined temperature and time to produce a surface-treated silica particle-dispersed sol 22 by solvent substitution.

[0025] 〔Preparation of Mixed Solvent of Pure Water and Organic Solvent〕 The organic solvent is an alcohol having 1 to 4 carbon atoms or a water-soluble glycol compound having 2 to 4 carbon atoms. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, 2-propanol, n-propanol, and butanol. Examples of the aqueous glycol compound having 2 to 4 carbon atoms include ethylene glycol (2 carbon atoms), propylene glycol (3 carbon atoms), propylene glycol monomethyl ether (PGM) (4 carbon atoms), 1,3-butylene glycol (4 carbon atoms), and the like.

[0026] The mixed solvent 11 of pure water and an organic solvent is a mixed solvent of pure water and an alcohol having 1 to 4 carbon atoms, or a mixed solvent of pure water and a water-soluble glycol compound having 2 to 4 carbon atoms. Such mixed solvents are preferably used because they easily dissolve alkyl silicate. Also, pure water in the mixed solvent is used for hydrolysis of alkyl silicate, and the organic solvent is used to enhance the compatibility between pure water and alkyl silicate. The content ratio of the organic solvent in the alkyl silicate solution is preferably 10% by mass to 35% by mass. If the content ratio of the organic solvent is less than the lower limit value, it is difficult for spherical primary particles to grow and it is also difficult for chain-like particles to grow sufficiently. If it exceeds the upper limit value, the spherical primary particles tend to coarsen. The amount of pure water is adjusted to be 8 molar concentration to 23 molar concentration with respect to Si (silicon) in the alkyl silicate. If it is less than the lower limit value, the spherical primary particles coarsen in the heating step. If it exceeds the upper limit value, it is difficult for the spherical primary particles to increase and they do not grow sufficiently in a chain shape. The amount of pure water is preferably 8 molar concentration to 16 molar concentration with respect to Si in the alkyl silicate, and more preferably 9 molar concentration to 15 molar concentration.

[0027] 〔Preparation of alkyl silicate solution〕 An alkyl silicate 12 is added to and mixed with a mixed solvent 11 to prepare an alkyl silicate solution 13. The alkyl silicate 12 is a silicate having an alkyl group with 1 to 2 carbon atoms that is easily hydrolyzed. For example, tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), a mixture thereof, or an oligomer of an alkyl silicate can be mentioned. For example, trimers to pentamers of tetramethoxysilane (TMOS) (manufactured by Mitsubishi Chemical Corporation, trade name: MKC Silicate MS51, hereinafter sometimes simply referred to as 'MS51') are preferably used. When the alkyl silicate solution 13 is 100% by mass, the alkyl silicate 12 is mixed at a ratio of 18% to 44% by mass. If it is less than the lower limit value, spherical primary particles are difficult to grow in the heating process. If it exceeds the upper limit value, the number of connected primary particles tends to increase, and accordingly, the chain tends to become longer. Also, the alkyl silicate solution gels. When the alkyl silicate solution 13 is 100% by mass, the alkyl silicate 12 is preferably mixed at a ratio of 21% to 43% by mass, and more preferably mixed at a ratio of 26% to 38% by mass. Preferably, the alkyl silicate solution is prepared by stirring at a temperature of 0°C to 30°C for 1 minute to 30 minutes. The content ratio of the alkyl silicate in the alkyl silicate solution is determined by measurement using nuclear magnetic resonance (NMR) (manufactured by BRUKER, product number: AVANCE III 400).

[0028] 〔Preparation of raw material liquid〕 When converting the alkyl silicate to silica in the alkyl silicate solution 13, an alkali catalyst 14 is added and mixed at a ratio of 0.02% to 0.40% by mass with respect to this silica to prepare a raw material liquid 15. The alkali catalyst 14 is an alkali metal hydroxide, ammonia, or an alkylamine. In the case of other alkaline earth metal hydroxides or alkali catalysts containing aluminum, spherical primary particles increase, the particles become coarser, and the length of the chain of the primary particles is difficult to increase in the heating process.

[0029] For using such an alkali catalyst 14, the content ratio of alkaline earth metal or aluminum impurities per final colloidal silica particle is less than 1 mass ppm. Examples of the alkali metal hydroxide include potassium hydroxide (KOH) or sodium hydroxide (NaOH), and examples of the alkylamine include methylamine (CH3NH2), dimethylamine ((CH3)2NH), trimethylamine ((CH3)3N), etc. The alkali catalyst promotes the hydrolysis of the alkyl silicate in the alkyl silicate solution 13 in the presence of pure water and an organic solvent. If the addition ratio of this alkali catalyst is less than 0.02 mass%, the reactivity is poor, spherical primary particles are not sufficiently generated, and the particles are unlikely to become chain-like. If it exceeds the upper limit value of 0.40 mass%, in the heating step, the hydrolysis is excessively promoted, the reactivity becomes too high, and spherical particles are generated instead of chain-like particles. Preferably, the raw material liquid is prepared by stirring at a temperature of 0°C to 30°C for 1 minute to 30 minutes. The addition ratio of the alkali catalyst is preferably 0.02 mass% to 0.30 mass%, and more preferably 0.05 mass% to 0.25 mass%.

[0030] 〔Heating of the raw material liquid and production of the first precursor sol〕 The raw material liquid 15 is heated at 40°C to 100°C for 24 hours to 100 hours. As a result, the spherical primary particles grow to an average particle diameter of 6 nm to 20 nm, and grow into a group of colloidal silica particles having an average length of 35 nm to 1800 nm, connected in a chain with an average number of 4 to 300. The first precursor sol in which this group of colloidal silica particles is dispersed in the above mixed solvent is obtained. The length of the chain varies depending on the addition ratio of the alkali catalyst, the addition ratio of the alkyl silicate, and the heating temperature. The average particle diameter of the spherical primary particles is the average value of the particle diameters grasped by FE-SEM observation (number of grasped particles: 50). The average number of the connected numbers is the average value of the connected numbers grasped by FE-SEM observation (number of grasped particles: 50). Further, the average length of the chain-like particles is the average value of the lengths grasped by FE-SEM observation (number of grasped particles: 50). The heating temperature of the raw material liquid 15 is preferably 50°C to 85°C. The heating time of the raw material liquid 15 is preferably 24 hours to 72 hours.

[0031] [Production of Second Precursor Sol with Surface-Treated Silica Particles] As a pretreatment for easily modifying the surface of the silica particles dispersed in the first precursor sol, the first precursor sol is diluted with an alcohol having 1 to 4 carbon atoms that is easily evaporated during the subsequent solvent substitution to prepare an alcohol-diluted sol. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, 2-propanol, n-propanol, and butanol. The dilution ratio is, for example, 1.5 to 5 times (150 mass% to 500 mass% with respect to the silica particles in the first precursor sol).

[0032] A surface treatment agent is added to this alcohol-diluted sol, stirred and mixed, and held at 40°C to 100°C for 3 to 24 hours. As a result, the hydroxy groups on the particle surface are bonded to a coupling agent described later, and the silica particles are surface-treated, and a second precursor sol in which the surface-treated silica particles are dispersed is prepared. This surface treatment agent is a silane coupling agent having a functional group such as a vinyl group, a methyl group, an epoxy group, a styryl group, or a methacryl group, or a titanate-based coupling agent or an aluminate-based coupling agent. When the silica particles in the alcohol-diluted sol are 100 mass%, the surface treatment agent is added and mixed at a ratio of 10 mass% to 100 mass%. The addition ratio of the surface treatment agent is preferably 10 mass% to 80 mass%, and more preferably 15 mass% to 70 mass%. The heating temperature of the mixed solution of the alcohol-diluted sol and the surface treatment agent is preferably 50°C to 90°C, and more preferably 60°C to 90°C. The heating time of the mixed solution of the alcohol-diluted sol and the surface treatment agent is preferably 3 to 18 hours, and more preferably 3 to 12 hours.

[0033] Examples of silane coupling agents having a vinyl group as a functional group include vinyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBM-1003), vinylethoxysilane (manufactured by the same company, product name: KBE-1003). Examples of silane coupling agents having a methyl group as a functional group include methoxysilane (manufactured by the same company, product name: KBM-13), methyltriethoxysilane (manufactured by the same company, product name: KBE-13). Examples of silane coupling agents having an epoxy group as a functional group include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (manufactured by the same company, product name: KBM-303). Examples of silane coupling agents having a styryl group as a functional group include p-styryltrimethoxysilane (manufactured by the same company, product name: KBM-1403). Examples of silane coupling agents having a methacryl group as a functional group include 3-methacryloxypropylmethyldimethoxysilane (manufactured by the same company, product name: KBM-502), etc. In addition, product names such as KBM-22, KBM-403, KBM-503, SZ31 (all manufactured by Shin-Etsu Chemical Co., Ltd.) can be mentioned.

[0034] Examples of titanate coupling agents include isopropyltriisostearoyl titanate (manufactured by Ajinomoto Fine-Techno Co., Inc., product name: Ken-act TTS). In addition, product names such as Ken-act 55, Ken-act 46B, Ken-act 338X, Ken-act 238S, Ken-act 38S, Ken-act 138S, Ken-act 41B, Ken-act 9SA (all manufactured by Ajinomoto Fine-Techno Co., Inc.) can be mentioned. Further, examples of aluminate coupling agents include, for example, alkyl acetoacetate aluminum diisopropylate (for example, manufactured by Ajinomoto Fine-Techno Co., Inc., product name: Ken-act AL-M).

[0035] 〔Solvent substitution with a hydrophobic solvent and production of a surface-treated silica particle dispersion sol〕 A hydrophobic solvent is added to the obtained second precursor sol, and the mixture is stirred and maintained at 40°C to 80°C for 3 hours to 12 hours, thereby evaporating the mixed solvent of pure water and organic solvent used in the initial stage of production and the alcohol diluting the first precursor sol to perform solvent substitution. As a result, a surface-treated silica particle-dispersed sol in which surface-treated silica particles are dispersed in a hydrophobic solvent is obtained. Here, the hydrophobic solvent is mixed so that the silica concentration in the second precursor sol is 1% by mass to 25% by mass. The heating temperature of the mixed solution of the second precursor sol and the hydrophobic solvent is preferably 50°C to 80°C, more preferably 50°C to 70°C. The hydrophobic solvent is preferably mixed so that the silica concentration in the second precursor sol is 1% by mass to 20% by mass, more preferably 1% by mass to 10% by mass. Examples of the hydrophobic solvent include toluene, butyl acetate, cyclohexane, methyl isobutyl ketone, 2-methoxy-1-methylethyl acetate, 1-methoxy-2-propanol, and the like.

[0036] The silica (SiO2) concentration of the surface-treated silica particle-dispersed sol of the present embodiment is preferably 10% by mass to 35% by mass. If it is less than the lower limit value, the film formed may not be a film with a low refractive index. If it exceeds the upper limit value, SiO2 is likely to aggregate in the surface-treated silica particle-dispersed sol. A more preferable SiO2 concentration is 5% by mass to 10% by mass.

[0037] 〔Properties of surface-treated silica particle-dispersed sol〕 The surface-treated silica particle dispersion sol of this embodiment is manufactured by the above manufacturing method, and a group of colloidal silica particles in which 4 to 300 spherical primary particles grasped by FE-SEM observation are continuously linked in a chain shape and have an average length of 35 nm to 1800 nm are dispersed in a hydrophobic solvent. The average particle diameter of the spherical primary particles is 6 nm to 20 nm, the average aspect ratio of the spherical primary particles is in the range of 1.0 to 1.3, the content ratio of each of the impurities of K, Na, or NH3 per colloidal silica particle is 3500 mass ppm or less, and the content ratio of each of the impurities of alkaline earth metals or aluminum is less than 1 mass ppm. The average aspect ratio of the spherical primary particles is the average value of the numerical values obtained by dividing the major axis of the constituent particles by the minor axis. The aspect ratio is determined individually for 100 or more arbitrary particles and calculated as the average value thereof. The concentration of impurities other than NH3 is determined by measurement with an ICP (high-frequency inductively coupled plasma) emission spectroscopic mass analyzer (manufactured by PerkinElmer, product number: Avio 500). The concentration of NH3 impurities is determined by measurement with an ammonia meter (manufactured by Toei Chemical Research Institute Co., Ltd., model number: TiN-9001).

[0038] When the average number of connected colloidal silica particles is less than 4, the refractive index of the film becomes high when the film is formed. When it exceeds 300, the storage stability of the surface-treated silica particle dispersion sol decreases. The preferable average number of connections is 50 to 200. When the average chain length of the colloidal silica particles is less than 35 nm, the refractive index of the film does not decrease when the film is formed. When it exceeds 1800 nm, the storage stability of the surface-treated silica particle dispersion sol decreases and gelation occurs. The preferable average chain length is 50 nm to 1000 nm.

[0039] When the average particle diameter of the spherical primary particles is less than 6 nm, it is difficult for the particles to form a chain. When it exceeds 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 preferable average particle diameter of the spherical primary particles is 7 nm to 15 nm. 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 variation in the refractive index of the film when the film is formed. When the average aspect ratio of the spherical primary particles exceeds 1.3, the thickness of the chains of the colloidal silica particles becomes non-uniform. The refractive index of the coating film is determined by measurement with a spectroscopic ellipsometer (manufactured by J.A. Woollam Japan Co., Ltd., product number: M-2000).

[0040] When the content ratio of each of the impurities of K, Na, or NH3 per colloidal silica particle exceeds 3500 mass ppm, the reaction is promoted excessively, the hydrolysis rate increases too much, and the spherical primary particles do not become chain-like. When the content ratio of each of the impurities of alkaline earth metal or aluminum per colloidal silica particle becomes 1 mass ppm or more, as the storage time elapses, the particles of the surface-treated silica particle dispersion sol become coarser and the storage stability decreases. The content ratio of each of the impurities of K, Na, or NH3 per colloidal silica particle is preferably 3000 mass ppm or less, and more preferably 2500 mass ppm or less.

[0041] [Method for forming the surface-treated silica particle dispersion sol on the substrate surface] The method for forming the surface-treated silica particle dispersion sol of the present embodiment on the substrate surface is not particularly limited. For example, there is a method in which after applying the surface-treated silica particle dispersion sol on the substrate, it is dried at room temperature in the air to form a film. The substrate is not particularly limited, and examples thereof include a glass substrate, a silicon wafer, a resin substrate, and a metal foil substrate. Examples of the coating method of the surface-treated silica particle dispersion sol include a spin coating method, a screen printing method, a bar coating method, a die coating method, a doctor blade method, and a brush coating method. The refractive index of the obtained film is 1.10 to 1.25. By using the chain-like colloidal silica particle dispersion sol of the present embodiment, it becomes difficult for the particles in the film to be in the closest packing, and a film with a low refractive index can be obtained.

Examples

[0042] Next, the examples of the present invention will be described in detail together with comparative examples.

[0043] <Example 1> 63.5 g of ethanol and 63.5 g of pure water were mixed in a flask to prepare a mixed solvent. The mass ratio of pure water to ethanol was 1:1. 73.0 g of tetraethoxysilane (TEOS) was added to this mixed solvent to prepare a tetraethoxysilane solution. The concentration of tetraethoxysilane in the tetraethoxysilane solution was 34.8% by mass. Also, the pure water was contained at a molar concentration ratio of 11.6 with respect to Si in the tetraethoxysilane. While stirring this solution, 10 g of an aqueous potassium hydroxide (KOH) solution was added dropwise as an alkali catalyst to prepare a raw material solution. Potassium hydroxide was added dropwise at a ratio of 0.12% by mass with respect to this silica when converting tetraethoxysilane to silica. After adding the aqueous potassium hydroxide solution dropwise, the raw material solution was heated at 60 °C for 96 hours to age the raw material solution. After heating, the raw material solution was gradually cooled to room temperature to obtain a first precursor sol in which colloidal silica particles were dispersed. In addition, the solvent evaporated or volatilized by heating was transferred to a cooling system to be liquefied and returned to the raw material solution.

[0044] Next, methanol was added to the first precursor sol and mixed at a ratio of 400% by mass with respect to the silica particles in the first precursor sol to obtain a methanol-diluted sol. Then, as a surface treatment agent, methyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBE-13) was added at a ratio of 50% by mass with respect to the silica particles in the methanol-diluted sol, and the mixture was stirred and held at 60 °C for 5 hours to obtain a second precursor sol.

[0045] Finally, 2-methoxy-1-methylethyl acetate, which is a hydrophobic solvent, was added to the second precursor sol so that the silica concentration in the second precursor sol became 10% by mass, and the mixture was stirred and held at 60 °C for 3 hours to evaporate the solvent in the second precursor sol so far and replace it with a hydrophobic solvent. Thereby, a surface-treated silica particle-dispersed sol of Example 1 was obtained.

[0046] Table 1 and Table 2 below show the preparation conditions of alkyl silicate solutions and the like, and the preparation conditions of the raw material solutions for Example 1 and Examples 2 to 21 and Comparative Examples 1 to 12 described below. In Comparative Example 11, as will be described later, an aqueous sodium silicate (sodium silicate) solution was used instead of the alkyl silicate solution.

[0047]

Table 1

[0048]

Table 2

[0049] <Examples 2 to 21 and Comparative Examples 1 to 10, 12> As shown in Table 1, in the preparation of the alkyl silicate solutions of Examples 2 to 21 and Comparative Examples 1 to 10, 12, in Example 11, as the alkyl silicate, trimers to pentamers of tetramethoxysilane (TMOS) (manufactured by Mitsubishi Chemical Corporation, trade name: MKC Silicate MS51) and tetramethoxysilane (TMOS) were used. The mixing ratio of MS51 and TEOS was 1:1 by mass. In Example 13, MS51 was used as the alkyl silicate. In the other Examples and Comparative Examples 1 to 10, 12, the same tetraethoxysilane (TEOS) as in Example 1 was used.

[0050] In Examples 2 to 21 and Comparative Examples 1 to 10 and 12, the mixing ratio of alkyl silicate in the alkyl silicate solution was the same as or changed from that in Example 1, as shown in Table 1. The molar concentration ratio of pure water to Si in the alkyl silicate in Examples 2 to 21 and Comparative Examples 1 to 10 and 12 was the same as or changed from that in Example 1, as shown in Table 1. The organic solvents in Examples 2 to 21 and Comparative Examples 1 to 10 and 12 were the same as or changed from that in Example 1, as shown in Table 1. As the organic solvent, propylene glycol monomethyl ether was used in Examples 4 and Comparative Example 6, methanol was used in Examples 14 and 21, 2-propanol 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 to 5, 7 to 10, and 12, the same ethanol as in Example 1 was used.

[0051] As shown in Table 2, when preparing the raw material liquid in Examples 2 to 21 and Comparative Examples 1 to 10 and 12, the type of alkali catalyst was the same as or changed from that in Example 1. All were alkaline aqueous solutions. As the alkali catalyst, magnesium hydroxide (Mg(OH)2) was used in Comparative Example 1, and a liquid obtained by mixing aluminum chloride (AlCl3) hexahydrate and ammonia (NH3) water so that Al and N in the solution were 1:1 was used in Comparative Example 2. Also, the addition ratio of the alkali catalyst to silica when converting alkyl silicate to silica was the same as or changed from that in Example 1. Further, as shown in Table 2, when heating the raw material liquid in Examples 2 to 21 and Comparative Examples 1 to 10 and 12, the temperature and time were the same as or changed from those in Example 1. Under these production conditions, first precursor sols in which colloidal silica particles were dispersed in Examples 2 to 21 and Comparative Examples 1 to 10 and 12 were obtained respectively.

[0052] <Comparative Example 11> In Comparative Example 11, a first precursor sol in which colloidal silica particles were dispersed was obtained by a method according to Example 1 of Patent Document 1. Specifically, an aqueous colloidal solution of active silica was obtained by passing an aqueous sodium silicate solution with a SiO2 concentration of 3.6% by mass through a column filled with a cation exchange resin. 2000 g of this aqueous colloidal solution of active silica was put into a glass container, and then, while stirring the aqueous solution, 8.0 g of a 10% by mass aqueous calcium chloride solution was dropped into this aqueous solution and mixed. While stirring this mixed solution, after 30 minutes, 12.0 g of a 10% by mass aqueous sodium hydroxide solution was further dropped to prepare a raw material solution. This raw material solution was put into a stainless steel autoclave and heated at 130°C for 6 hours, and then the content was taken out to obtain a first precursor sol.

[0053] The surface treatment conditions and solvent replacement conditions of the silica particles in eight types of first precursor sols are shown as Conditions 1 to 8 in Table 3 below. Methanol or ethanol was used as a diluting solvent at a ratio of 400% by mass with respect to the silica particles in the first precursor sol. In the surface treatment conditions, the heating temperature and heating time of each of the eight Conditions 1 to 8 were the same as or changed from those in Example 1. In Condition 8, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBM-602) having a functional group of an amino group, which is not described in the first aspect of the present invention, was used.

[0054]

Table 3

[0055] For the replacement of the solvent in the second precursor 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 with a hydrophobic solvent, as shown in Table 3, in all of Conditions 1 to 8, it was carried out by heating at 60°C for 3 hours. Also, the hydrophobic solvent was added so that the silica concentration in the second precursor sol became 10% by mass.

[0056] <Evaluation> (1) State of colloidal silica particles after heating of the raw material solution Using the FE-SEM described above, the states of the colloidal silica particles were observed at 1 hour after heating (initial heating) and at the end of heating (final) of the raw material liquids of Examples 1 to 21 and Comparative Examples 1 to 12. The results are shown in Table 4 below. After heating for 1 hour, the average particle diameter of the primary particles of the colloidal silica particles in Example 1 was 4 nm, and its average aspect ratio was 1.0. It had not yet formed into a chain shape. After heating for 96 hours at the end of heating, the primary particles of the colloidal silica particles in Example 1 were spherical with an average particle diameter of 10 nm, an average aspect ratio of 1.1, and an average of 70 primary particles were connected in a chain with an average length of 700 nm. As shown in Table 4, after heating for 6 hours at the end of heating in Comparative Example 11, the primary particles of the colloidal silica particles were not spherical, with an average particle diameter of 12 nm, an average aspect ratio of 1.4, and an average of 4 primary particles were connected in a chain with an average length of 50 nm. This is presumably because the dissolved calcium ions elute the surface of the silica particles.

[0057]

Table 4

[0058] (2) Content ratio of impurities in colloidal silica particles Using the ICP emission spectrometry-mass spectrometer and ammonia meter described above, the content ratios of impurities in the colloidal silica particles of the first precursor sols of Examples 1 to 21 and Comparative Examples 1 to 12 were measured. The results are shown in Table 5 below. Since KOH was used as the alkali catalyst for the colloidal silica particles in Example 1, the K concentration per colloidal silica particle was 850 ppm by mass. Na, NH3, Ca, Mg, and Al were all less than 1 ppm by mass, which was below the detection limit. In Table 5, '<1' indicates that the content ratio of the impurity is less than 1 ppm by mass.

[0059]

Table 5

[0060] (3) Storage stability of the surface-treated silica particle dispersion sol The storage stability of the surface-treated silica particle dispersion sols of Examples 1 to 21 and Comparative Examples 1 to 12 was visually confirmed by placing this dispersion sol in a transparent glass container and allowing it to stand for 1 month in an environment of 25°C and a relative humidity of 60%. When no aggregates appeared in the dispersion sol and the dispersion sol did not gel, it was judged as 'good', and when aggregates appeared in the dispersion sol or the dispersion sol gelled, it was judged as 'bad'. The results are shown in Table 5 above.

[0061] (4) Refractive index of the coating film The surface-treated silica particle dispersion sols of Examples 1 to 21 and Comparative Examples 1 to 12 were applied by spin coating method onto a glass substrate so that the thickness after drying would be 0.15 μm, and dried at a temperature of 120°C for 30 minutes. The refractive index of the coating film formed on the glass substrate was measured using the spectroscopic ellipsometer described above. The results are shown in Table 5 above. The variation in the refractive index of the film was measured at three different locations on the film and calculated by the following formula (1). [(Maximum value - Minimum value) / Average value] × 100% (1) When it was 'less than ±5%', it was judged that the variation in the refractive index of the film was good, and when it was '±5% or more', it was judged that the variation in the refractive index of the film was bad. In Table 5, '-' indicates that the measurement was impossible.

[0062] <Evaluation results> As is clear from Table 4, in Comparative Example 1, magnesium hydroxide (Mg(OH)2) was used as the alkali catalyst. As a result, dissolved magnesium ions eluted from the surface of the silica particles, promoting the formation of coarse particles, causing the particles to coarsen and the average particle diameter of the primary particles to become as large as 30 nm. The average length of the chain-like colloidal silica particles was 250 nm, and the average number of linked particles was 9. Therefore, the coarse particles aggregated and did not disperse, and a coating film could not be formed on the glass substrate, so the refractive index of the film could not be measured. Also, the content ratio of impurities of Mg (magnesium) in the colloidal silica particles was 420 mass ppm. The storage stability of the dispersion sol was 'poor'. Since the coarse particles aggregated and did not disperse, surface treatment and solvent replacement could not be performed.

[0063] In Comparative Example 2, a mixture of aluminum chloride hexahydrate and aqueous ammonia was used as the alkali catalyst. As a result, aluminum ions, which became impurities, eluted from the surface of the silica particles, promoting the formation of coarse particles, causing the colloidal silica particles to coarsen and the average particle diameter of the primary particles to become 30 nm. The average length of the chain-like colloidal silica particles was 400 nm, and the average number of linked particles was 14. Therefore, the coarse particles aggregated and did not disperse, and a coating film could not be formed on the glass substrate, so the refractive index of the film could not be measured. Also, the content ratio of NH3 impurities in the colloidal silica particles was 990 mass ppm, and the content ratio of Al (aluminum) impurities was 1000 mass ppm. The storage stability of the dispersion sol was 'poor'. Since the coarse particles aggregated and did not disperse, surface treatment and solvent replacement could not be performed.

[0064] In Comparative Example 3, since the concentration of NaOH, which was the alkali catalyst, was too low at 0.01 mass%, the reactivity was poor, spherical primary particles were not sufficiently formed, the average length of the chains of the colloidal silica particles was too short at 20 nm, and the average number of linked primary particles was too small at 2. Therefore, a coating film could be formed, but the refractive index of the film was as high as 1.30. Also, the content ratio of Na (sodium) impurities in the colloidal silica particles was 12 mass ppm. The storage stability of the dispersion sol was 'good'.

[0065] In Comparative Example 4, the mixing ratio of tetraethoxysilane was too high at 60.8% by mass with respect to the tetraethoxysilane solution. As a result, the ratio of pure water to Si in tetraethoxysilane was 4.2 mol / L, causing the tetraethoxysilane solution to gel. Therefore, although the average number of connected primary particles was 250, the average length of the chains of colloidal silica particles became too long at 2500 nm, preventing the formation of a coating film on the glass substrate and making it impossible to measure the refractive index of the film. Also, the content ratio of Na (sodium) impurities in the colloidal silica particles was 700 ppm by mass. The storage stability of the dispersion sol was "poor". Surface treatment and solvent replacement could not be performed because the average length of the chains of colloidal silica particles became too long and the colloidal silica particles did not disperse.

[0066] In Comparative Example 5, the mixing ratio of tetraethoxysilane was too low at 8.7% by mass with respect to the tetraethoxysilane solution. As a result, the ratio of pure water to Si in tetraethoxysilane was 64.0 mol / L, so that in the heating process, the spherical primary particles did not increase sufficiently and the average particle diameter of the primary particles was too small at 4 nm. The average number of connected primary particles was 20, and the average length of the chains of colloidal silica particles was 80 nm, allowing the formation of a coating film. However, since the spherical particles were aggregated, the refractive index of the film was as high as 1.30. Also, the content ratio of Na (sodium) impurities in the colloidal silica particles was 700 ppm by mass. The storage stability of the dispersion sol was "good" because, although the spherical particles were aggregated, the average length of the chains was short.

[0067] In Comparative Example 6, the mixing ratio of tetraethoxysilane was appropriate at 34.8% by mass with respect to the tetraethoxysilane solution, but the ratio of pure water to Si in tetraethoxysilane was too low at 1.6 molar concentration. For this reason, the primary particles coarsened, and the average particle diameter of the primary particles became too large at 35 nm. The average number of connected primary particles was 15, and the average length of the chain of colloidal silica particles was 250 nm, and a coating film could be formed, but since they were coarse spherical particles, the refractive index of the film was as high as 1.37. Also, the content ratio of impurities of Na (sodium) in the colloidal silica particles was 700 ppm by mass. The storage stability of the dispersion sol was "good".

[0068] In Comparative Example 7, the mixing ratio of tetraethoxysilane was appropriate at 34.8% by mass with respect to the tetraethoxysilane solution, but the ratio of pure water to Si in tetraethoxysilane was too low at 1.6 molar concentration. For this reason, the primary particles coarsened, the average particle diameter of the primary particles became too large at 40 nm, and the average aspect ratio of the primary particles became too large at 1.4. The average number of connected primary particles was 5, and the average length of the chain of colloidal silica particles was 200 nm, and a coating film could be formed, but since the spherical particles were aggregated, the refractive index of the film was as high as 1.38. Also, the content ratio of impurities of Na (sodium) in the colloidal silica particles was 700 ppm by mass. The storage stability of the dispersion sol was "good".

[0069] In Comparative Example 8, since the concentration of NH3 (ammonia), which is an alkaline catalyst, was too high at 0.60% by mass, the reaction rate of hydrolysis of tetraethoxysilane increased significantly, the spherical primary particles coarsened, and the average particle diameter of the primary particles became too large at 30 nm. The average aspect ratio of the primary particles was 1.2. The average length of the chain of colloidal silica particles was 90 nm, and the average number of connected primary particles was only 3 aggregated particles. For this reason, a coating film could be formed, but the refractive index of the film was as high as 1.30. Also, the content ratio of impurities of NH3 in the colloidal silica particles was 490 ppm by mass. The storage stability of the dispersion sol was "good".

[0070] In Comparative Example 9, the mixing ratio of tetraethoxysilane was too high at 69.5% by mass with respect to the tetraethoxysilane solution. As a result, the ratio of pure water to Si in tetraethoxysilane was 2.9 mol / L, causing the tetraethoxysilane solution to gel. The average number of connected primary particles was extremely high at 400, and the average length of the chains of colloidal silica particles became too long at 3200 nm. Therefore, a coating film could not be formed on the glass substrate, and the refractive index of the film could not be measured. Also, the content ratio of the impurity Na (sodium) in the colloidal silica particles was 700 ppm by mass. The storage stability of the dispersion sol was "poor". Surface treatment and solvent replacement could not be performed because the average length of the chains of the colloidal silica particles became too long and the colloidal silica particles did not disperse.

[0071] In Comparative Example 10, the concentration of the alkali catalyst NaOH was too high at 0.70% by mass. As a result, the reaction rate of the hydrolysis of tetraethoxysilane increased significantly, causing the primary particles to coarsen and the average primary particle diameter to become too large at 500 nm. The average length of the chains of the colloidal silica particles was 4000 nm, and aggregated particles with an average number of connected primary particles of 10 were obtained. The average aspect ratio of the primary particles became too large at 2.0. Coarse spherical particles aggregated, so a coating film could not be formed on the glass substrate, and the refractive index of the film could not be measured. Also, the content ratio of the impurity Na (sodium) in 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 because the coarse spherical particles aggregated.

[0072] In Comparative Example 11, an aqueous sodium silicate (sodium silicate) solution was used instead of the alkyl silicate, and an aqueous calcium chloride solution was added to this aqueous sodium silicate solution. Therefore, at the time of particle synthesis, the concentration of impurity Na (sodium) was 9691 mass ppm and the concentration of Ca (calcium) was 4052 mass ppm. Further, due to concentration, the concentration of impurity Na increased to 5886 mass ppm and the concentration of Ca increased to 3843 mass ppm. However, as time passed, these impurity sodium ions and calcium ions eluted from the surface of the silica particles and acicular impurities precipitated, so particles with a very large average aspect ratio of 1.4 were observed. Also, the storage stability of the sol was "poor". Since there was no gelation or increase in viscosity in the dispersion sol, a coating film could be formed, and the refractive index of the film was 1.20. However, since the chain thickness was not uniform and there was also variation in the number of connected particles, the variation in the refractive index of the film was as large as 5%.

[0073] In Comparative Example 12, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBM-602) having a functional group of an amino group, which is not described in the first aspect of the present invention, was used as a surface treatment agent. Therefore, since the pH in the liquid changed due to the amino group, the silica particles in the dispersion sol aggregated. For this reason, a coating film could not be formed on the glass substrate, and the refractive index of the film could not be measured.

[0074] On the other hand, in Examples 1 to 21, since a surface-treated silica particle dispersion sol was produced under conditions satisfying the production conditions of the second aspect of the present invention described above, a surface-treated silica particle dispersion sol having the characteristics of the first aspect of the present invention could be obtained.

Industrial Applicability

[0075] The surface-treated silica particle dispersion sol of the present invention is used in the field of forming an antireflection film used to prevent reflection of incident light in display panels such as cathode ray tubes, liquid crystals, and organic ELs, solar cells, showcase glass, etc., or in the field of forming an intermediate film using a refractive index difference used in sensors, camera modules, etc.

Description of Symbols

[0076] 11 Mixed solvent of pure water and organic solvent 12 Alkyl silicate 13 Alkyl silicate solution 14 Alkali catalyst 15 Feed solution 16 First precursor sol 17 Alcohol 18 Alcohol-diluted sol 19 Surface treatment agent 20 Second precursor sol 21 Hydrophobic solvent 22 Surface-treated silica particle-dispersed sol

Claims

1. A surface-treated silica particle dispersion sol formed by dispersing a group of colloidal silica particles in a hydrophobic solvent, wherein spherical primary particles grasped by field emission scanning electron microscope observation are connected in a chain with 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 of a vinyl group, a methyl group, an epoxy group, a styryl group or a methacryl group, or isopropyltriisostearoyl titanate which is a titanate coupling agent or alkyl acetate aluminum diisopropylate which is an aluminate coupling agent, wherein 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 content ratio of each of K, Na or NH per colloidal silica particle ３ is 3500 mass ppm or less, and the content ratio of each of alkaline earth metal or aluminum impurities is less than 1 mass ppm, and the surface-treated silica particle dispersion sol is characterized by this.

2. (a) A step of mixing an alkyl silicate having an alkyl group having 1 to 2 carbon atoms with a mixed solvent of pure water and an organic solvent which is an alcohol having 1 to 4 carbon atoms or a water-soluble glycol compound having 2 to 4 carbon atoms to obtain an alkyl silicate solution; (b) A step of adding and mixing an alkali catalyst which is an alkali metal hydroxide, ammonia or an alkylamine to the alkyl silicate solution to obtain a raw material liquid; (c) A step of heating the raw material liquid at 40°C to 100°C for 24 hours to 100 hours to obtain a first precursor sol in which colloidal silica particles are dispersed; (d) A step of adding and mixing an alcohol having 1 to 4 carbon atoms to the first precursor sol to obtain an alcohol-diluted sol; (e) A surface treatment agent which is a silane coupling agent having a functional group of a vinyl group, a methyl group, an epoxy group, a styryl group or a methacryl group or isopropyltriisostearoyl titanate which is a titanate coupling agent or alkyl acetate aluminum diisopropylate which is an aluminate coupling agent is added and mixed with the alcohol-diluted sol at a ratio of 10% by mass to 100% by mass when the silica particles in the alcohol-diluted sol are 100% by mass, and heated at 40°C to 100°C for 3 hours to 24 hours to obtain a second precursor sol in which surface-treated silica particles are dispersed; (f) A step of adding and mixing a hydrophobic solvent to the second precursor sol so that the silica concentration in the second precursor sol becomes 1% by mass to 25% by mass, and heating at 40°C to 80°C for 3 hours to 12 hours to perform solvent substitution, the pure water is contained in a proportion of 8 molar concentration to 23 molar concentration with respect to Si in the alkyl silicate, in the step (a), when the alkyl silicate solution is 100% by mass, the alkyl silicate is mixed in a proportion of 18% by mass to 44% by mass, in the step (b), when converting the alkyl silicate to silica, the alkali catalyst is mixed in a proportion of 0.02% by mass to 0.40% by mass with respect to the silica A method for producing the surface-treated silica particle dispersion sol according to claim 1, characterized by the above.

3. In the initial stage of heating in the step (c), spherical primary particles having an average aspect ratio of 1.0 to 1.1 and an average particle diameter of less than 5 nm are formed, and at the end of heating, the spherical primary particles in the initial stage of heating have an average particle diameter of 6 nm to 20 nm and grow into a group of colloidal silica particles having an average length of 35 nm to 1800 nm and connected in a chain with an average number of 4 to 300. The method for producing a surface-treated silica particle dispersion sol according to claim 2.

4. A film obtained by using the surface-treated silica particle dispersion sol according to claim 1, A film characterized in that the refractive index is 1.10 to 1.25.

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