Chain-like colloidal silica particle dispersion sol and its manufacturing method

Abstract

A chain-like colloidal silica particle dispersion sol (16) is formed by dispersing a group of colloidal silica particles, observed using a field emission scanning electron microscope, consisting of 4 to 300 spherical primary particles linked in a chain and having an average length of 35 nm to 1800 nm, in a mixed solvent (11) of pure water and an organic 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 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.

Description

TECHNICAL FIELD

[0001] The present application relates to a sol of colloidal silica particles in which spherical primary particles are connected in a chain shape, and a production method thereof. More specifically, it relates to a sol of colloidal silica particles in a chain shape which is capable of forming a film having a low refractive index and which has good storage stability when applied to a substrate, and a production method thereof. In addition, it relates to a film obtained using the sol of colloidal silica particles in a chain shape.

[0002] This application claims priority based on Patent Application No. 2021-166421 filed in Japan on October 8, 2021, and the contents thereof are hereby incorporated by reference. BACKGROUND

[0003] In the past, as such a silica sol, a stable silica sol in which amorphous colloidal silica particles in an elongated shape are dispersed in a liquid medium and the SiO2 concentration is 0.5 to 30% by weight, and in which the ratio D1 / D2 of the particle diameter (D1 μm) measured by a dynamic light scattering method to the particle diameter (D2 μm) measured by a nitrogen adsorption method of the amorphous colloidal silica particles is 5 or more, the D1 is 40 to 500 nm, and the amorphous colloidal silica particles are elongated in only one plane with the same thickness in a range of 5 to 40 nm observed by an electron microscope (see Patent Document 1 (Claims 1 to 3, p. 4, right column, lines 5 to 9)).

[0004] In Claim 2 of Patent Document 1, a production method of an alkaline silica sol composed of the following (a), (b), and (c) processes is shown.

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

[0006] (b) Process, in the aqueous solution obtained by the (a) process, an alkali metal hydroxide, a water-soluble organic base, or a water-soluble silicate thereof is added in a molar ratio of SiO2 / M2O (wherein SiO2 represents the content of the silica component derived from the above-mentioned active silicic acid, and M represents the above-mentioned alkali metal atom or the molecule of the organic base) of 20 to 200 and mixed;

[0007] (c) Process, the mixture obtained by the (b) process is heated at 60 to 150°C for 0.5 to 40 hours.

[0008] In claim 3 of patent document 1, a method for manufacturing alkaline aqueous silica sol according to claim 2 is further shown, characterized in that, in step (a), the colloidal aqueous solution of active silica is obtained by contacting an aqueous solution of sodium silicate having a SiO2 / Na2O molar ratio of 1 to 4.5 and a SiO2 concentration of 1 to 6 wt% with a hydrogen-form cation exchange resin, having a SiO2 concentration of 1 to 6 wt% 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 water-soluble calcium salts, magnesium salts, or mixtures thereof are 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, precipitating as needle-shaped impurities, resulting in a lack of storage stability. Therefore, the silica sol obtained by the method of Patent Document 1 presents a problem that makes it 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 present invention aims to provide a chain-like colloidal silica particle dispersion sol that can form a film with low refractive index and good stability when coated onto a substrate. Another objective of the present invention is to provide a simple method for manufacturing this chain-like colloidal silica particle dispersion sol and a film with 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 chain-like colloidal silica particle dispersion sol, characterized in that the colloidal silica particle dispersion sol is formed by dispersing a group of colloidal silica particles, observed using a field emission scanning electron microscope, consisting of 4 to 300 spherical primary particles linked in a chain and having an average length of 35 nm to 1800 nm, in a mixed solvent of pure water and an organic 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 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 the present invention is a method for manufacturing a chain-like colloidal silica particle dispersion sol, characterized in that the manufacturing method is a method for manufacturing the chain-like colloidal 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; (b) a step of adding and mixing an alkaline catalyst into the alkyl silicate solution to obtain a raw material liquid; and (c) a step of heating the raw material liquid at 40°C to 100°C for 24 hours to 100 hours, wherein the pure water is heated relative to the alkyl silicate... The Si in the salt is contained in the mixed solvent at a concentration of 8 to 23 moles. The organic solvent is an alcohol with 1 to 4 carbon atoms or a water-soluble diol compound with 2 to 4 carbon atoms. In step (a), when the alkyl silicate solution is set to 100% by mass, the alkyl silicate is mixed at a concentration of 18% to 44% by mass. In step (b), when the alkyl silicate is converted to silicon dioxide, the alkaline catalyst is mixed at a concentration of 0.02% to 0.40% by mass relative to the silicon dioxide. The alkaline catalyst is an alkali metal hydroxide, ammonia, or an alkylamine.

[0018] The third aspect of the present invention is based on the second aspect and is a method for manufacturing a chain-like colloidal silica particle dispersion sol. 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 by dispersing a sol of chain-like colloidal silica particles as described in the first aspect, and has a refractive index of 1.10 to 1.25. That is, the film of the fourth aspect of the present invention can be obtained by coating a sol of chain-like colloidal silica particles as described in the first aspect onto a substrate and then drying it.

[0020] The first aspect of this invention, a chain-like colloidal silica particle dispersion sol, 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 particles and have an average length of 35 nm to 1800 nm. Therefore, during film formation, the film is prone to pore formation, 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, the colloidal silica particle dispersion sol exhibits excellent storage stability. Because the average aspect ratio of the spherical primary particles is in the range of 1.0 to 1.3, the chain-like colloidal silica particle dispersion sol has a low viscosity, 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 are in a chain-like formation. Furthermore, since the proportion of alkaline earth metals or aluminum impurities in the chain-like colloidal silica particle dispersion sol is less than 1 ppm by mass, the particles will not coarsen even after storage time, thus becoming a chain-like colloidal silica particle dispersion sol with high storage stability.

[0021] In the method for manufacturing a chain-like colloidal 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 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 with an average number of 4 to 300 particles and an average length of 35 nm to 1800 nm.

[0022] In the method for manufacturing chain-like colloidal silica particle dispersion sol according to the third aspect of the present invention, at the end of heating in step (c), 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.

[0023] The fourth aspect of the present invention uses a sol dispersed in chain-like colloidal silica particles as described in the first aspect. 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

[0024] Figure 1 This is a flowchart of the process for manufacturing the chain-like colloidal silica particle dispersion sol of this embodiment.

[0025] Figure 2A This is a field emission scanning electron microscope (FE-SEM) image of the chain-like colloidal silica particle clusters after heating for 1 hour in Example 1. (Manufactured by Hitachi High-Tech Corporation, product number: Regulus230, hereinafter referred to as FE-SEM).

[0026] Figure 2B This is an FE-SEM image of the chain-like colloidal silica particle clusters after heating for 6 hours in Example 1.

[0027] Figure 2C This is an FE-SEM image of the chain-like colloidal silica particle clusters after heating for 24 hours in Example 1.

[0028] Figure 2D This is an FE-SEM image of the chain-like colloidal silica particle clusters after heating for 48 hours in Example 1.

[0029] Figure 2EThis is an FE-SEM image of the chain-like colloidal silica particle clusters after heating for 72 hours in Example 1.

[0030] Figure 2F This is an FE-SEM image of the chain-like colloidal silica particle clusters after heating for 96 hours in Example 1.

[0031] Figure 3 This is an FE-SEM image of the chain-like colloidal silica particle group from Example 2.

[0032] Figure 4 This is an FE-SEM image of the chain-like colloidal silica particle group of Comparative Example 11. Detailed Implementation

[0033] Next, the method for carrying out the present invention will be described with reference to the accompanying drawings.

[0034] [Method for manufacturing chain-like colloidal silica particle dispersion sol]

[0035] The chain-like colloidal silica particle dispersion sol of this embodiment is generally manufactured by the following method.

[0036] 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 solution 15. Then, the feed solution 15 is heated at a temperature of 40°C to 100°C for 24 to 100 hours to produce a chain-like colloidal silica particle dispersion sol 16.

[0037] [Preparation of a mixed solvent of pure water and organic solvent]

[0038] 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).

[0039] 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 mixed solvents are 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 compatibility between pure water and alkyl silicates.

[0040] The organic solvent content in the alkylsilicate solution is preferably 10% to 35% by mass. If the organic solvent content 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.

[0041] 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.

[0042] [Preparation of alkylsilicate solutions]

[0043] 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 readily 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 for use.

[0044] When the alkyl silicate solution 13 is set to 100% by mass, the 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. Furthermore, 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.

[0045] 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 III400).

[0046] [Preparation of raw material solution]

[0047] 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 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.

[0048] 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, reactivity is lacking, 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, 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.

[0049] [Heating of raw material solution and preparation of chain-like colloidal silica particle dispersion sol]

[0050] The raw material 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 dispersed in the aforementioned mixed solvent to produce a chain-like colloidal silica particle dispersion sol. The chain length varies depending on the proportion of 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 as determined by FE-SEM observation (number of determinations: 50). The average number of links is also the average number of links as determined by FE-SEM observation (number of determinations: 50). Furthermore, the average length of the chain-like particles is the average length as determined by FE-SEM observation (number of determinations: 50). The heating temperature of the raw material solution 15 is preferably 50°C to 85°C. The heating time for raw material liquid 15 is preferably 24 hours to 72 hours.

[0051] In this embodiment, the SiO2 concentration of the chain-like colloidal silica particle dispersion sol is preferably 10% to 35% by mass. If it is below the lower limit, a film with a low refractive index may not be formed during film formation. Furthermore, if it exceeds the upper limit, SiO2 tends to aggregate in the chain-like colloidal silica particle dispersion sol. A more preferred SiO2 concentration is 5% to 10% by mass.

[0052] [Properties of chain-like colloidal silica particle dispersions in sol]

[0053] The chain-like colloidal silica particle dispersion sol of this embodiment is manufactured by the above-described manufacturing method. It is formed by dispersing a group of colloidal silica particles (observed by FE-SEM) consisting of 4 to 300 spherical primary particles linked in a chain, with an average length of 35 nm to 1800 nm, in a mixed solvent of pure water and an organic solvent. The average particle size of the spherical primary particles is 6 nm to 20 nm, and the average aspect ratio 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 by the minor axis of the constituent particles. 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 Perkin Elmer, Inc., product number: Avio500). 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 the number of links is greater than 300, the storage stability of the chain-like colloidal 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 the length is greater than 1800 nm, the storage stability of the chain-like colloidal 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 can be 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 chain-like colloidal 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 (manufactured by JA Woollam, 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 is 1 ppm by mass or more, the chain-like colloidal silica particle dispersion will coarsen over time, thus reducing its storage stability. The proportion of K, Na, or NH3 impurities in each colloidal silica particle is preferably 3000 ppm by mass or less, more preferably 2500 ppm by mass or less.

[0058] [A method for forming a chain-like colloidal silica particle dispersion sol on a substrate surface]

[0059] The method for forming the chain-like colloidal silica particle dispersion sol of this embodiment on the substrate surface is not particularly limited. For example, methods include coating the chain-like colloidal 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 chain-like colloidal 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 not densely packed, and a film with a low refractive index can be obtained.

[0060] Example

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

[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. 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. 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 raw material 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 the addition of the potassium hydroxide aqueous solution, the raw material solution was heated at 60°C for 96 hours to mature it. After heating, the raw material solution was slowly cooled to room temperature to obtain a chain-like colloidal silica particle dispersion sol. In addition, the solvent that has evaporated or volatilized through heating is transferred to a cooling system for liquefaction and then returned to the feed liquid.

[0064] 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 11, respectively. In Comparative Example 11, as described later, an aqueous solution of sodium silicate (Na silicate) was used instead of the alkyl silicate solution.

[0065] [Table 1]

[0066]

[0067] [Table 2]

[0068]

[0069] <Examples 2-21 and Comparative Examples 1-10>

[0070] As shown in Table 1, in preparing the alkyl silicate solutions of Examples 2-21 and Comparative Examples 1-10, 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, the same tetraethoxysilane (TEOS) as in Example 1 was used.

[0071] 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 was the same as in Example 1 or varied. 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 was the same as in Example 1 or varied. As shown in Table 1, the organic solvents of Examples 2-21 and Comparative Examples 1-10 were the same as in Example 1 or varied. 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 and 7-10, the same ethanol as in Example 1 was used.

[0072] As shown in Table 2, the type of alkaline catalyst used in the preparation of the raw material solutions of Examples 2-21 and Comparative Examples 1-10 was the same as that 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, when converting alkyl silicates to silica, the addition ratio of the alkaline catalyst relative to silica was the same as in Example 1 or modified. Further, as shown in Table 2, the temperature and time for heating the raw material solutions of Examples 2-21 and Comparative Examples 1-10 were the same as in Example 1 or modified. Under these manufacturing conditions, chain-like colloidal silica particle dispersions of Examples 2-21 and Comparative Examples 1-10 were obtained, respectively.

[0073] <Comparative Example 11>

[0074] In Comparative Example 11, a chain-like colloidal silica particle dispersion sol was obtained using the method of Example 1 in Patent Document 1. Specifically, a colloidal aqueous solution of active silicic acid was obtained in a column filled with cation exchange resin using a sodium silicate aqueous solution with a SiO2 concentration of 3.6% by mass. 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. The contents were then removed to obtain a chain-like colloidal silica particle dispersion sol.

[0075] Figures 2A-2FThese are FE-SEM images showing the particle growth from 1 hour of heating in Example 1 to 96 hours of heating. Figures 2A-2F The diagram shows the heating process of the raw material liquid from Example 1 for 1 hour. Figure 2A Heating for 6 hours ( Figure 2B Heating for 24 hours ( Figure 2C Heating for 48 hours ( Figure 2D Heating for 72 hours ( Figure 2E ) and after heating for 96 hours ( Figure 2F FE-SEM images of the dispersion state of each particle.

[0076] Figure 3 The image shown is an FE-SEM image of the feed solution from Example 2 after heating for 24 hours. Further, Figure 4 The image shown is a FE-SEM image of the particle dispersion state after the feed liquid of Comparative Example 11 was heated for 6 hours.

[0077] <Evaluation>

[0078] (1) The state of colloidal silica particles after heating the raw material liquid

[0079] Using the aforementioned FE-SEM, the state of colloidal silica particles was observed after heating the raw material solutions of Examples 1-21 and Comparative Examples 1-11 for 1 hour (initial heating) and at the end of heating (final heating). The results are shown in Table 3 below. Figure 2A The image shows the state of the colloidal silica particles in Example 1 after the initial heating period, i.e., one hour of heating. The primary particle size of the colloidal silica particles in Example 1 is 4 nm, and the average aspect ratio is 1.0. They have not yet formed into chains. Figure 2F The diagram shows the state of the colloidal silica particles 96 hours after heating. The primary particles of the colloidal silica particles in Example 1 are spherical with an average particle size of 10 nm and an average aspect ratio of 1.1. An average of 70 primary particles are linked together in a chain with an average length of 700 nm. Figure 3 The state of the colloidal silica particles is shown 24 hours after the heating ends in Example 2. Figure 4 The table shows the state of the colloidal silica particles after 6 hours of heating following the end of heating in Comparative Example 11. As shown in Table 3, the primary particles of the colloidal silica particles after 6 hours of heating following the end of heating in Comparative Example 11 were not spherical, with an average particle size of 12 nm, an average aspect ratio of 1.4, and an average of four primary particles linked together in a chain with an average length of 50 nm. It is speculated that this is because dissolved calcium ions dissolve on the surface of the silica particles.

[0080] [Table 3]

[0081]

[0082] (2) The proportion of impurities in colloidal silica particles

[0083] Using the aforementioned ICP-based spectrophotometer and ammonia analyzer, the impurity content of the colloidal silica particles in Examples 1-21 and Comparative Examples 1-11 was determined. The results are shown in Table 4 below. In Example 1, the K concentration of each colloidal silica particle was 850 ppm by mass because KOH was used in the alkaline catalyst. Na, NH3, Ca, Mg, and Al were all less than 1 ppm by mass, which is below the detection limit. In Table 4, "<1" indicates that the impurity content is less than 1 ppm by mass.

[0084] [Table 4]

[0085]

[0086] (3) Storage stability of chain-like colloidal silica particle dispersion sol

[0087] Regarding the storage stability of the chain-like colloidal silica particle dispersions of Examples 1-21 and Comparative Examples 1-11, the stability was visually assessed 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 4 above.

[0088] (4) Refractive index of the coating

[0089] The chain-like colloidal silica particle dispersion sols of Examples 1-21 and Comparative Examples 1-11 were spin-coated onto a glass substrate to a thickness of 0.15 μm after drying, and then 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 4 above. Regarding the deviation of the film's refractive index, the refractive index of three different parts of the film was measured and calculated using the following formula (1).

[0090] [(maximum value - minimum value) / average value] × 100% (1)

[0091] A deviation of "less than ±5%" is considered a good deviation in the film's refractive index, while a deviation of "more than ±5%" is considered a poor deviation. In Table 4, "-" indicates that it cannot be measured.

[0092] <Evaluation Results>

[0093] 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 excessively large, at 30 nm. The average chain length of the colloidal silica particles was 250 nm, with an average of 9 links. Therefore, the coarse particles aggregated but 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".

[0094] In Comparative Example 2, because a mixture of aluminum chloride hexahydrate and ammonia was used as the alkaline catalyst, aluminum ions, which became impurities, dissolved on the surface of the silica particles, promoting the formation of coarse particles. This resulted in coarsening of the 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 rather than dispersed, failing to form a coating on the glass substrate, thus making it impossible to measure 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 rated as "poor".

[0095] In Comparative Example 3, the concentration of NaOH as the alkaline catalyst was too low, at 0.01% by mass, 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 be formed, the film had a high refractive index of 1.30. Furthermore, the Na (sodium) impurity content of the colloidal silica particles was 12 ppm by mass. The storage stability of the dispersion sol was rated as "good".

[0096] 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 (2500 nm), preventing the formation of a coating on the glass substrate and thus making it impossible to measure 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 rated as "poor."

[0097] 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%. Therefore, during the heating process, the spherical primary particles did not sufficiently increase in size, resulting in an excessively small 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 storage stability of the dispersion sol was due to the aggregation of spherical particles, it was rated as "good" because of the short average chain length.

[0098] 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".

[0099] 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".

[0100] 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".

[0101] 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 solution was 2.9 mol / L, 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".

[0102] In Comparative Example 10, due to the excessively high concentration of NaOH as the alkaline catalyst (0.70% by mass), the hydrolysis rate of tetraethoxysilane increased significantly, resulting in coarsening of the primary particles and an excessively large average particle size of 500 nm. The average chain length of the colloidal silica particles was 4000 nm, resulting in aggregated particles with an average of 10 primary particle connections. The average aspect ratio of the primary particles was excessively 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".

[0103] In Comparative Example 11, an aqueous solution of sodium silicate (Na silicate) was used instead of alkyl silicates. Due to the addition of an aqueous solution of calcium chloride 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%.

[0104] In contrast, in Examples 1 to 21, chain-like colloidal silica particle dispersion sols were manufactured under manufacturing conditions that satisfy the second aspect of the present invention described above, thus enabling the production of chain-like colloidal silica particle dispersion sols with the characteristics of the first aspect of the present invention.

[0105] Industrial availability

[0106] The chain-like colloidal silica particle dispersion sol of the present invention is used in the fields of forming antireflective films or intermediate films, etc., wherein the antireflective film is used in display panels such as cathode ray tubes, liquid crystals, organic ELs, solar cells, display case glass, etc. to prevent the reflection of incident light, and the intermediate film, etc., is formed by utilizing the refractive index difference used in sensors or camera modules, etc.

[0107] Explanation of reference numerals in the attached figures

[0108] 11. Mixed solvent of pure water and organic solvent

[0109] 12-alkylsilicate

[0110] 13-alkylsilicate solution

[0111] 14 Alkali Catalyst

[0112] 15 raw material liquid

[0113] 16-chain colloidal silica particle dispersion sol

Claims

1. A chain-like colloidal silica particle dispersion sol, characterized in that, the colloidal silica particle dispersion sol is formed by dispersing a population of colloidal silica particles having an average length of 35 nm to 1800 nm and being chain-like connected at an average number of 50 to 300 by primary particles of a spherical shape observed by a field emission type scanning electron microscope in a mixed solvent of pure water and an organic solvent, the average particle diameter of the primary particles of a spherical shape is 6 nm to 20 nm, and the average aspect ratio of the primary particles of a spherical shape is in a range of 1.0 to 1.3, the organic solvent is an alcohol having a carbon number of 1 to 4 or a water-soluble dihydric alcohol compound having a carbon number of 2 to 4, each of the K, Na, or NH3 impurities of each of the colloidal silica particles has a contained ratio of 3500 mass ppm or less, and each of the alkaline earth metal or aluminum impurities has a contained ratio of less than 1 mass ppm.

2. A manufacturing method of a chain-like colloidal silica particle dispersion sol, characterized in that, the manufacturing method is a method of manufacturing the chain-like colloidal silica particle dispersion sol according to claim 1, and includes: (a) a step of mixing an alkyl silicate having an alkyl group having a carbon number of 1 to 2 in a mixed solvent of pure water and an organic solvent to obtain an alkyl silicate solution; (b) a step of adding and mixing an alkali catalyst in the alkyl silicate solution to obtain a raw material liquid; and (c) a step of heating the raw material liquid at 40°C to 100°C for 24 hours to 100 hours, 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, the organic solvent is an alcohol having a carbon number of 1 to 4 or a water-soluble dihydric alcohol compound having a carbon number of 2 to 4, in the (a) step, the alkyl silicate solution is mixed at a ratio of 18 mass% to 44 mass% when the alkyl silicate solution is set to 100 mass%, in the (b) step, the alkali catalyst is mixed at a ratio of 0.02 mass% to 0.40 mass% with respect to the silica when the alkyl silicate is converted into the silica, the alkali catalyst is an alkali metal hydroxide, ammonia, or an alkyl amine.

3. The manufacturing method of the chain-like colloidal silica particle dispersion sol according to claim 2, wherein, at an initial stage of heating in the (c) step, primary particles of a spherical shape 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 primary particles of a spherical shape at the initial stage of heating become primary particles of a spherical shape having an average particle diameter of 6 nm to 20 nm and grow into a population of colloidal silica particles chain-like connected at an average number of 50 to 300 and having an average length of 35 nm to 1800 nm. the film is obtained using the chain-like colloidal silica particle dispersion sol according to claim 1, and has a refractive index of 1.10 to 1.

25. ​ 4. A film characterized by, ​

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