Aluminum atom-containing hollow silica sol and process for producing the same

Abstract

To provide a hollow silica particle which has high dispersion stability in a medium and has no risk of outflow of an alkali metal or the like.SOLUTION: An aluminum atom-containing hollow silica sol, wherein in 27Al NMR measurement of the hollow silica sol, a ratio [(α 0) / {(α 0) + (β 0)}] of a total integrated value (α 0) of peaks indicating tetracoordinated aluminum atoms to a sum of the total integrated value (α 0) of peaks indicating tetracoordinated aluminum atoms and a total integrated value (β 0) of peaks indicating aluminum atoms other than tetracoordinated aluminum atoms is 0.50 to 1.0, and a method for producing the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sol in which hollow silica particles containing aluminum atoms are dispersed (aluminum atom-containing hollow silica sol), a method for producing the same, and a coating-forming composition. [Background technology]

[0002] Silica sol is used in various fields as an abrasive, functional inorganic filler, etc. Although silica sol is stable and does not gel in the alkaline range, when alkaline silica sol is blended into a composition containing an organosilicon compound or resin as a binder, the alkaline condition tends to cause cloudiness and thickening. Furthermore, when preparing organosilica sol by solvent substitution, problems remain, such as gelation upon mixing with alcohol, etc. On the other hand, in the acidic range, the zeta potential of silica particles is small, resulting in small electrical repulsion, making silica sol unstable and prone to gelation. However, silica sol is often required in the acidic range, such as in acidic abrasives, raw materials for ceramic fibers, and chromium-based surface treatment agents.

[0003] One method for improving the stability of silica sol in acidic regions is to modify the surface of silica particles with an aluminum compound. In this method, aluminosilicate sites are formed on the silica particle surface by reaction between aluminate ions derived from the aluminum compound and silanol groups on the silica particle surface. The aluminosilicate sites impart a negative charge to the silica particles, i.e., increase the negative zeta potential of the silica particles, thereby improving the dispersion stability of the silica particles in the dispersion medium. This method also improves the compatibility of silica particles with highly polar organic solvents and charged resins. For example, a method for producing an acidic silica sol has been disclosed (see Patent Document 1), in which an aqueous alkali aluminate solution is added to a dispersion of solid silica particles so that the Al2O3 / SiO2 molar ratio is greater than 0.0006 but less than 0.004, and the resulting silica sol is heated at 80 to 250°C and then subjected to cation exchange.

[0004] Furthermore, hollow silica particles have a silica outer shell and a space inside the shell, and because of these characteristics, they have properties such as a low refractive index, low thermal conductivity (thermal insulation), and electrical insulation. Hollow silica particles consist of a core corresponding to the hollow portion and an outer shell that forms the outside of the core. An aqueous dispersion of hollow silica particles can be obtained by forming a silica layer on the outside of a template particle in an aqueous medium and then removing the template particle. For example, a method has been disclosed in which a core-shell particle having an aluminosilicate shell is produced by reacting a silane compound and an aluminum precursor with a Si / Al molar ratio of 7 to 15 on a template core made of an organic polymer in the form of a micelle or reverse micelle, and then reacting this with a basic or acidic aqueous solution to simultaneously form pores in the shell (outer shell) and remove the core, followed by a hydrothermal reaction at 160 to 200°C to produce a hollow silica sol with a high density shell (see Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-199515 [Patent Document 2] Korean Patent No. 10-1659709 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to stabilize silica sol containing hollow silica particles with cavities inside the shell, the particles are modified from the outside with an aluminum compound (impregnated with the aluminum compound, so to speak), and the aluminum compound penetrates into the shell and remains outside the shell (impregnated). The aluminum compounds that penetrate the outer shell (i.e., penetrate into the shell) and the aluminum compounds that penetrate into the shell (i.e., penetrate into the shell) form aluminosilicate sites, respectively. The alkali metals present in the silica particles and derived from the alkali metal silicate, which is the raw material of the silica sol, are captured by the respective aluminosilicate sites. However, depending on the manufacturing, use, and storage conditions of the silica particles, the alkali metal encapsulated within the silica particles may be released over time, resulting in an increase in the pH of the system and the aforementioned instability. In the case of hollow silica particles, the alkali metal present in the aluminosilicate sites outside the shell can be removed during manufacturing by cation exchange or other methods, but it is difficult to remove the alkali metal present in the aluminosilicate sites inside the shell. Furthermore, since aluminosilicate may be generated even inside the silica particles, which is not originally involved in the dispersion stabilization of the silica particles, the amount of aluminum present in the aluminosilicate per silica particle increases, resulting in an increase in the amount of alkali metal present in the aluminosilicate sites. Moreover, the alkali metal may leak into the dispersion medium through the pores of the shell over time, which may cause an increase in the pH of the system and may impair the dimensional stability of the hollow silica particles and the storage stability of the silica sol. [Means for solving the problem]

[0007] In view of the above circumstances, the present inventors conducted extensive research and found that by specifying the amount of sulfuric acid added to the system to adjust the pH, hollow silica particles can be obtained that have high dispersion stability in a medium and are free from concerns about alkali metal leakage, etc.

[0008] That is, in a first aspect, the present invention relates to an aluminum atom-containing hollow silica sol containing aluminum atom-containing hollow silica particles and sulfuric acid, wherein the amount of sulfuric acid contained in the hollow silica sol is 1 ppm to 150 ppm. As a second aspect, the present invention relates to the hollow silica sol according to the first aspect, wherein the amount of sulfuric acid contained in the hollow silica sol is 1 ppm to 5000 ppm / SiO2 relative to the mass of the hollow silica particles contained in the hollow silica sol. As a third aspect, the hollow silica sol is 27 The hollow silica sol according to the first aspect relates to a hollow silica sol, wherein in Al-NMR measurement, the ratio [(α0) / {(α0)+(β0)}] of the total integral value (α0) of peaks representing tetracoordinated aluminum atoms to the sum of the total integral value (α0) of peaks representing tetracoordinated aluminum atoms and the total integral value (β0) of peaks representing aluminum atoms other than tetracoordinated aluminum atoms is 0.4 to 1.0. As a fourth aspect, the present invention relates to the hollow silica sol according to the first aspect, wherein the amount of aluminum atoms present in all of the hollow silica particles in the hollow silica sol is 120 to 50,000 ppm / SiO2 in terms of Al2O3 relative to the mass of the hollow silica particles. As a fifth aspect, the present invention relates to the hollow silica sol according to the first aspect, wherein the amount of surface charge calculated per 1 g of hollow silica particles in the hollow silica sol is 5 to 250 μeq / g. As a sixth aspect, the hollow silica particles in the hollow silica sol are at least partially coated with a silane compound, and the silane compound is a compound represented by the formula (1) and the formula (2): [ka] (In formula (1), R 1 are groups bonded to silicon atoms, and each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, or an aryl group, or an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a polyether group, a carboxy group, a protected carboxyl group, represents an organic group having a carboxy group, a carboxy group-generating group, an imide group, or a cyano group and bonded to a silicon atom by a Si-C bond, or represents a combination of these groups; R 2are groups or atoms bonded to the silicon atom, which independently represent an alkoxy group, an acyloxy group, a hydroxy group, or a halogen atom, or a combination of these groups or atoms; a represents an integer of 1 to 3; In formula (2), R 3 are groups bonded to a silicon atom, and each independently represent an alkyl group, a halogenated alkyl group, an alkenyl group, or an aryl group, or an organic group having an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a polyether group, a carboxy group, a protected carboxy group, a carboxy group-generating group, an imide group, or a cyano group, and which are bonded to a silicon atom via a Si-C bond, or a combination of these groups; R 4 are groups or atoms bonded to the silicon atom, which independently represent an alkoxy group, an acyloxy group, a hydroxy group, or a halogen atom, or a combination of these groups or atoms; b represents an integer of 1 to 3, and c represents an integer of 0 or 1. Y is a group or atom bonded to the silicon atom and represents an alkylene group, an NH group, or an oxygen atom. The hollow silica sol according to the first aspect of the present invention is at least one silane compound selected from the group consisting of compounds represented by the following formula: According to a seventh aspect, the present invention relates to the hollow silica sol according to the first aspect, wherein the hollow silica particles in the hollow silica sol have an average particle size of 20 to 150 nm as measured by a dynamic light scattering method. As an eighth aspect, the present invention relates to the hollow silica sol according to the first aspect, wherein the hollow silica sol contains an organic solvent selected from the group consisting of alcohols having 1 to 10 carbon atoms, ketones having 1 to 10 carbon atoms, ethers having 1 to 10 carbon atoms, esters having 1 to 10 carbon atoms, and amides. According to a ninth aspect, there is provided a film-forming composition comprising the aluminum atom-containing hollow silica sol according to any one of the first to eighth aspects and an organic resin. According to a tenth aspect, there is provided a method for producing an aluminum atom-containing hollow silica sol according to any one of the first to eighth aspects, comprising the steps of: The following steps (I) and (II): Step (I): preparing a hollow silica aqueous sol having a sulfuric acid content of 1 ppm to 5000 ppm / SiO2 relative to the mass of aluminum atom-containing hollow silica particles; Step (II): adjusting the amount of sulfuric acid contained in the hollow silica aqueous sol prepared in step (I) to 1 ppm to 150 ppm; The present invention relates to a method for producing an aluminum atom-containing hollow silica sol, comprising the steps of: According to an eleventh aspect, there is provided a method for producing an aluminum atom-containing hollow silica sol according to any one of the first to eighth aspects, comprising: The following steps (III), (IV), (V), and (VI): Step (III): preparing a hollow silica aqueous sol containing hollow silica particles; Step (IV): adding an aluminum compound to the hollow silica aqueous sol prepared in Step (III) in an amount of 0.0001 to 0.5 g, calculated as Al2O3, per 1 g of hollow silica particles, and maintaining the mixture at 40 to 260°C for 0.1 to 48 hours to obtain an aluminum atom-containing hollow silica aqueous sol; Step (V): adding sulfuric acid to the aluminum atom-containing hollow silica aqueous sol obtained in Step (IV) in a ratio of 1 ppm to 5000 ppm / SiO2 relative to the mass of the hollow silica particles in the sol, and maintaining the mixture at 5 to 100°C for 0.1 to 48 hours; Step (VI): The aluminum atom-containing hollow silica aqueous sol obtained in the step (V) is subjected to cationization. contacting with an ion exchange resin; The present invention relates to a method for producing an aluminum atom-containing hollow silica sol, comprising the steps of: As a twelfth aspect, the method further comprises the following step (VII): Step (VII): A step of replacing the dispersion medium in the aluminum atom-containing hollow silica aqueous sol obtained in the step (VI) from water to an organic solvent by heating replacement under reduced pressure, heating replacement under normal pressure, or ultrafiltration, The present invention relates to a method for producing an aluminum atom-containing hollow silica sol according to an eleventh aspect. As a thirteenth viewpoint, The present invention relates to a method for producing an aluminum atom-containing hollow silica sol according to a tenth aspect, which comprises a step of replacing the dispersing medium in the aluminum atom-containing hollow silica aqueous sol obtained in the step (II) from water to an organic solvent by heating replacement under reduced pressure, heating replacement under normal pressure, or ultrafiltration. The present invention also provides an aluminum atom-containing hollow silica sol containing aluminum atom-containing hollow silica particles, The hollow silica sol is 27 In Al-NMR measurement, the ratio [(α0) / {(α0)+(β0)}] of the total integral value (α0) of the peaks representing tetracoordinated aluminum atoms to the sum of the total integral value (α0) of the peaks representing tetracoordinated aluminum atoms and the total integral value (β0) of the peaks representing aluminum atoms other than tetracoordinated aluminum atoms is 0.50 to 1.0. A hollow silica sol inventive aspect is also disclosed. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an aluminum atom-containing hollow silica sol having good storage stability, in which the rate of change in DLS average particle size is 5% or less even before and after storage at 50° C. for 1 week. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of the 27Al-NMR spectrum showing the peak positions of tetrahedral aluminum atoms and non-tetrahedral aluminum atoms. [Figure 2] FIG. 2 shows the results of an 27Al-NMR measurement spectrum of the heat-treated water-dispersed sol (before adding sulfuric acid) prepared in Synthesis Example 1 (FIG. 2(A)), and the results of an 27Al-NMR measurement spectrum of the water-dispersed sol (A1) of aluminum atom-containing hollow silica particles (FIG. 2(B)). DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention is directed to an aluminum atom-containing hollow silica sol, characterized in that the amount of sulfuric acid contained in the hollow silica sol is controlled to 1 ppm to 150 ppm.

[0012] The aluminum atom-containing hollow silica sol (hereinafter also simply referred to as "hollow silica sol" or "silica sol") according to the present invention is a dispersion system containing aluminum atom-containing hollow silica particles (hereinafter also simply referred to as "hollow silica particles," "hollow silica," or "silica particles") and a solvent, in which the hollow silica particles are dispersed as dispersoids in the solvent. The hollow silica particles have a silica (SiO2)-containing outer shell and have a space inside the shell.

[0013] In the aluminum atom-containing hollow silica sol of the present invention, the hollow silica particles are considered to have the form of aluminum atom-containing hollow particles by aluminum atoms forming aluminosilicate sites at least on their surfaces. The aluminosilicate sites formed on the surfaces of the hollow silica particles are partially converted to aluminum sulfate by contact with sulfuric acid, which is added to adjust the pH of the silica sol to remove impurities. Aluminum sulfate is a compound with such high coagulation power that it is used as a coagulant. When aluminum sulfate reacts with an alkali metal in water to produce positively charged aluminum hydroxide, the aluminum sulfate is deposited on the surface of the silica particles. The aluminum sulfate conversion described above means that aluminum is stripped from the aluminosilicate sites on the surface of the silica particles, which may promote the outflow of alkali metals contained within the aluminosilicate sites, resulting in an increase in the pH value of the silica sol and a tendency toward alkalinity. In the present invention, it has been discovered that by controlling the amount of sulfuric acid in the hollow silica sol, it is possible to suppress the conversion of aluminosilicate sites formed on the particle surfaces to aluminum sulfate, thereby obtaining a sol with excellent storage stability in which the particle diameter of the hollow silica particles changes little before and after long-term storage and aggregation of the particles is suppressed. The amount of sulfuric acid includes both sulfuric acid itself present in the system and sulfuric acid in the form of aluminum sulfate. Furthermore, control of the amount of sulfuric acid can be suitably carried out in an aqueous hollow silica sol (aqueous dispersion sol), and storage stability can also be ensured in an organic solvent sol obtained by solvent substitution of this sol.

[0014] Furthermore, in the aluminum atom-containing hollow silica sol according to the present invention, the amount of sulfuric acid contained in the hollow silica sol can be, for example, 1 ppm to 150 ppm, 1 ppm to 140 ppm, 10 ppm to 150 ppm, 30 ppm to 150 ppm, or 50 ppm to 140 ppm. By setting the amount of sulfuric acid contained in the hollow silica sol to 1 ppm or more, the thickness of the electric double layer of the hollow silica particles contained in the hollow silica sol is reduced, thereby reducing the viscosity of the hollow silica sol and stabilizing the pH in the system, thereby improving the storage stability of the silica sol. By setting the amount of sulfuric acid contained in the hollow silica sol to 150 ppm or less, aluminum sulfate reacts with alkali metal in water to produce positively charged aluminum hydroxide, which neutralizes the negative charge on the surface of the silica particles and prevents aggregation.

[0015] Furthermore, in the aluminum atom-containing hollow silica sol according to the present invention, the amount of sulfuric acid relative to the mass (g) of the hollow silica particles contained in the sol can be, for example, 1 ppm to 5000 ppm / SiO2, 1 ppm to 3000 ppm / SiO2, 1 ppm to 1500 ppm / SiO2, 1 ppm to 1100 ppm / SiO2, 1 ppm to 1000 ppm / SiO2, 10 ppm to 1000 ppm / SiO2, 100 ppm to 1000 ppm / SiO2, 100 ppm to 3000 ppm / SiO2, 200 ppm to 1000 ppm / SiO2, or 400 ppm to 1000 ppm / SiO2. By setting the amount of sulfuric acid relative to the mass (g) of the hollow silica particles contained in the hollow silica sol to 1 ppm / SiO2 or more, the thickness of the electric double layer of the hollow silica particles contained in the hollow silica sol becomes thin, the viscosity of the hollow silica sol can be reduced, the pH in the system can be stabilized, and the storage stability of the silica sol can be improved.By setting the amount of sulfuric acid relative to the mass (g) of the hollow silica particles contained in the hollow silica sol to 5000 ppm / SiO2 or less, aluminum sulfate reacts with alkali metal in water to produce positively charged aluminum hydroxide, which neutralizes the negative charge on the surface of the silica particles and suppresses aggregation. In this specification, the unit of the amount of sulfuric acid in the silica sol may be distinguished as "ppm" or "ppm / sol" when indicating the amount of sulfuric acid relative to the silica sol, and as "ppm / SiO2 (silica particles)" when indicating the amount of sulfuric acid relative to the mass of hollow silica particles in the silica sol.

[0016] The hollow silica sol according to the present invention is 27 From the peak position of the spectrum obtained by Al-NMR measurement, it can be determined whether the aluminum in the system is in the form of aluminosilicate sites (four-coordinate aluminum atoms) formed on the particle surface, or whether it has dissolved into the system and become cationized (aluminum atoms other than four-coordinate (e.g., three-coordinate or six-coordinate)). 27The peaks representing tetrahedral aluminum atoms obtained by Al-NMR measurements are observed around 54 ppm (50 to 65 ppm), and the peaks representing non-tetrahedral aluminum atoms are observed around 0 ppm (-5 to 10 ppm) (see Figure 1). By comparing the fractional values, the proportion of tetrahedral aluminum atoms and non-tetrahedral aluminum atoms can be evaluated. In the present invention, the amount of sulfuric acid in the silica sol system is controlled to suppress the conversion of aluminosilicate sites to aluminum sulfate, and the sol has a low amount of aluminum in the aluminum sulfated (cationized) system, which leads to good stability of the silica sol after long-term storage.

[0017] For example, in the hollow silica sol according to the present invention, 27 In Al-NMR measurements, the ratio [(α0) / {(α0)+(β0)}] of the total integral value (α) of the peaks representing tetracoordinated aluminum atoms to the sum of the total integral value (α) of the peaks representing tetracoordinated aluminum atoms and the total integral value (β0) of the peaks representing non-tetracoordinated aluminum atoms can be 0.4 to 1.0, for example, 0.45 to 1.0, or 0.50 to 1.0. By making the ratio [(α0) / {(α0)+(β0)}] of the total integral value (α) of the peaks representing tetracoordinated aluminum atoms of the hollow silica sol 0.4 or more, aluminum sulfate reacts with the alkali metal in water to produce positively charged aluminum hydroxide, which neutralizes the negative charge on the silica particle surface and prevents aggregation.

[0018] Furthermore, the hollow silica sol is 27 From the results of Al-NMR measurement, the tetrahedral Al ratio calculated from the following formula (1) can be determined to be 0.4 to 1.0, for example, 0.45 to 1.0, or alternatively, 0.50 to 1.0. 4-coordination Al ratio=(α) / {(α)+(β)} ························································································· mean, 4-coordinate Al ratio = (α) / {(α) + (β)} ········································Formula (1) (α): 27The total integral of the peaks observed in the range of 50 to 65 ppm in Al-NMR measurements (β): 27 The total integral value of the peaks observed in the range of -5 to 10 ppm during Al-NMR measurement the above 27 The peaks observed in the Al-NMR measurement range from 50 to 65 ppm are attributable to tetracoordinated aluminum atoms, and the peaks observed in the range from −5 to 10 ppm are attributable to aluminum atoms other than tetracoordinated aluminum atoms. the above 27 Al-NMR measurements can be performed on both aqueous hollow silica sol (water-dispersed sol) and organic solvent sols obtained by solvent substitution of the aqueous hollow silica sol. For example, data obtained from the water-dispersed sol can be selected as the peak data to be used in calculating the tetrahedral Al ratio.

[0019] In the hollow silica particles of the present invention, aluminum atoms may be present as aluminosilicate, and aluminosilicate may be formed at least on the surface of the particle, and aluminosilicate may be formed not only on the particle surface but also inside the hollow silica particles. The aluminum atom-containing hollow silica sol according to the present invention can be dissolved using an aqueous hydrofluoric acid solution (also referred to as an aqueous hydrofluoric acid solution) to determine the amount of aluminum atoms present in the entire hollow silica particles (i.e., the entire particles including the particle surface and interior) in the silica sol (i.e., the aluminum atom content in the hollow silica particles) in terms of Al2O3. Specifically, the hollow silica particles are dissolved in an aqueous hydrofluoric acid solution, and the resulting solution is measured and analyzed using an ICP emission spectrometer, whereby the amount of aluminum atoms present in the entire hollow silica particles can be determined in terms of Al2O3. More specifically, the silica sol is first dried to remove the dispersion medium, resulting in hollow silica particles. 250 mg of the particles are then dissolved in a hydrofluoric acid solution (e.g., a mixture of 2.5 ml of nitric acid and 2.5 ml of 38% hydrofluoric acid) to obtain an aqueous solution. The amount of aluminum atoms in the aqueous solution is measured using an ICP emission spectrometer to obtain the aluminum atom content (ppm) converted to Al2O3. This is then divided by the mass of the silica particles to obtain the hollow silica particles. The total amount of aluminum atoms present (Al2O3 (ppm) / SiO2) can be determined. For example, the aluminum atom-containing hollow silica sol according to the present invention preferably has an amount of aluminum atoms present throughout the entire hollow silica particles in the sol, calculated as Al2O3 relative to the mass of the hollow silica particles, of 120 to 50,000 ppm / SiO2 (silica particles), as measured by a dissolution method using an aqueous hydrofluoric acid solution, and can be, for example, 300 to 20,000 ppm / SiO2, or 500 to 20,000 ppm / SiO2, or 500 to 10,000 ppm / SiO2, or 500 to 5,000 ppm / SiO2, or 500 to 1,000 ppm / SiO2. By adjusting the amount of aluminum atoms present throughout the hollow silica particles to 120 to 50,000 ppm / SiO2 in terms of Al2O3 relative to the mass of the hollow silica particles, the negative charge on the surface of the silica particles increases, causing charge repulsion to the extent that the silica particles do not come into contact with each other, allowing the dispersion state to be maintained, thereby improving the storage stability of the hollow silica sol. In this specification, the amount of aluminum atoms present in the entire hollow silica particle is expressed as "ppm / SiO2" as a unit showing the amount relative to the mass (g) of the hollow silica particle.

[0020] The hollow silica particles in the hollow silica sol according to the present invention preferably have a surface charge (negative charge) calculated per 1 g of hollow silica particles of, for example, 5 to 250 μeq / g, or alternatively, can be in the range of 5 to 150 μeq / g, or 10 to 150 μeq / g, or 20 to 150 μeq / g, or 10 to 100 μeq / g, or 15 to 100 μeq / g, or 20 to 50 μeq / g, or 20 to 40 μeq / g. By making the surface charge amount (negative charge amount) converted per 1 g of the hollow silica particles 5 μeq / g or more, the charge repulsion force between the silica particles increases, thereby improving the dispersion stability of the silica particles in the dispersion medium. Furthermore, by setting the surface charge (negative charge) per gram of the hollow silica particles to 250 μeq / g or less, the amount of aluminum eluted from the hollow silica particles can be reduced, the amount of aluminum sulfate produced can be reduced, and particle aggregation can be suppressed.Furthermore, by setting the surface charge (negative charge) to 250 μeq / g or less, the leakage of alkali metals present in the aluminosilicate into the dispersion medium through the pores of the silica particle outer shell over time can be reduced, and an increase in pH in the system can be suppressed, thereby improving the dimensional stability of the hollow silica particles and the storage stability of the silica sol.

[0021] In addition, the high absolute value of the zeta potential of hollow silica particles in the acidic region causes electrical repulsion, which is desirable from the perspective of dispersibility.The amount of surface charge on hollow silica particles varies, in part, depending on the amount of aluminum atoms (aluminosilicate) present in the hollow silica particles. For example, if the amount of aluminum atoms present in the entire silica particle (as calculated as Al2O3, relative to SiO2) is less than 120 ppm / SiO2, the stability of the hollow silica particles tends to decrease. On the other hand, when the amount of aluminum atoms (Al2O3 equivalent, relative to SiO2) present in the entire silica particle is 50,000 ppm / SiO2 or more, the particle size after doping tends to increase compared to the particle size measured by dynamic light scattering (DLS particle size) before doping with aluminum atoms at the aqueous sol stage.

[0022] In the hollow silica sol according to the present invention, the hollow silica particles preferably have an average particle size (DLS average particle size: Z-average particle size, harmonic mean particle size) measured by dynamic light scattering (DLS) of 20 to 150 nm, and can be, for example, in the range of 30 to 150 nm, or 40 to 150 nm, or 50 to 150 nm, or 50 to 120 nm, or 50 to 100 nm. The DLS average particle size represents the average value of the secondary particle size (dispersed particle size). It can be determined that the larger the particle diameter, the more agglomerated the silica particles are in the medium.

[0023] In the hollow silica sol according to the present invention, the average primary particle diameter of the hollow silica particles as determined by observation with a transmission electron microscope (TEM) can be, for example, in the range of 20 to 150 nm, or 30 to 150 nm, or 40 to 150 nm, or 50 to 150 nm, or 50 to 120 nm, or 50 to 100 nm.

[0024] In addition, the hollow silica particles according to the present invention have a specific surface area measured by the BET method (nitrogen gas adsorption method) of, for example, 18 to 200 m 2 / g, or 50-160m 2 / g, or 60-160m 2 / g, or 70 to 160 m 2 / g, or 80 to 150 m 2 / g.

[0025] Furthermore, the outer shell of the hollow silica particles can be observed using a transmission electron microscope (TEM). In the hollow silica particles according to the present invention, the thickness of the outer shell as determined by observation with a transmission electron microscope can be, for example, in the range of 3.0 to 15.0 nm, or 4.0 to 12.0 nm, or 5.0 to 10.0 nm.

[0026] The hollow silica particles have a number density of silanol groups on the surface of the silica particles of, for example, 0.2 to 6.0 / nm 2 , or 0.5 to 5.0 particles / nm 2 , 0.5~3.0 pieces / nm 2, 0.5~2.0 pieces / nm 2 , 0.7~2.0 pieces / nm 2 , 1.1~2.0 pieces / nm 2 It can be said that: The number density of silanol groups on the surface of the silica particles is 0.2 / nm 2 By setting the number density of silanol groups on the surface of the silica particles to 6.0 / nm or more, the negative charge of the silica particles becomes large, and the dispersion stability of the silica particles in the dispersion medium can be improved. 2 By setting the content below, aggregation due to dehydration condensation between silanol groups among silica particles can be suppressed, and dispersion stability can be improved. The number density of silanol groups on the surface of silica particles can be determined by, for example, The specific surface area of ​​colloidal silica can be measured by the Sears method described in "Specific Surface Area of ​​Colloidal Silica by Titration with Sodium Hydroxide" (GW Sears, Jr., Analytical Chemistry, 28(12), 1981 (1956)).

[0027] The refractive index of the hollow silica particles according to the present invention can be set in the range of, for example, 1.20 to 1.45, or 1.20 to 1.40, or 1.20 to 1.30. Furthermore, the hollow silica particles according to the present invention can have a carbon content measured by elemental analysis in the range of, for example, 0.1% to 10.0% by mass. For elemental analysis, a poor solvent and a good solvent are first selected for a hollow silica sol in which the hollow silica particles to be measured are dispersed, and the hollow silica particles are separated from the organic components not bonded to the hollow silica particles using a centrifuge or the like. The resulting mixture is then dried to remove even the adsorbed water, thereby preparing a measurement sample. The obtained silica particle measurement sample is then measured using an elemental analyzer to determine the carbon content (%) in the sample.

[0028] In the present invention, the hollow silica particles in the aluminum atom-containing hollow silica sol may be at least partially coated with a silane compound. In the present invention, "coated with a silane compound" refers to an embodiment in which the surface of a silica particle is coated with a silane compound, and also includes an embodiment in which a silane compound is bonded to the surface of a silica particle. The term "an embodiment in which the surface of a silica particle is coated with a silane compound" refers to an embodiment in which the silane compound coats at least a portion of the surface of a silica particle, i.e., an embodiment in which the silane compound covers a portion of the surface of a silica particle, or an embodiment in which the silane compound covers the entire surface of a silica particle. In this embodiment, it does not matter whether or not the silane compound is bonded to the surface of the silica particles. Furthermore, "an embodiment in which a silane compound is bonded to the surface of a silica particle" means an embodiment in which a silane compound is bonded to at least a portion of the surface of a silica particle, i.e., an embodiment in which the silane compound is bonded to a portion of the surface of a silica particle, an embodiment in which the silane compound is bonded to a portion of the surface of a silica particle and covers at least a portion of the surface, and even an embodiment in which the silane compound is bonded to the entire surface of a silica particle and covers the entire surface.

[0029] The silane compound may be at least one silane compound selected from the group consisting of compounds represented by the following formulas (1) and (2). [ka]

[0030] In the above formula (1), R 1are groups bonded to a silicon atom, and each independently represent an alkyl group, a halogenated alkyl group, an alkenyl group, or an aryl group, or an organic group having an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a polyether group, a carboxy group, a protected carboxy group, a carboxy group-generating group, an imide group, or a cyano group, and which are bonded to a silicon atom via a Si-C bond, or a combination of these groups; R 2 are groups or atoms bonded to the silicon atom, which independently represent an alkoxy group, an acyloxy group, a hydroxy group, or a halogen atom, or a combination of these groups or atoms; a represents an integer of 1 to 3. In the definition of the groups of the silane compound in this specification, the term "independently of each other" means that multiple groups can each independently represent a group defined as an alternative. For example, in formula (1), R 1 If there are two or more (a is 2 to 3), multiple R 1 may be the same group (for example, all methyl groups), or may be a combination of different groups (for example, when a is 2, a methyl group and a phenyl group, or a methyl group and a (meth)acryloylpropyl group, etc.).

[0031] In the above formula (2), R 3 are groups bonded to a silicon atom, and each independently represent an alkyl group, a halogenated alkyl group, an alkenyl group, or an aryl group, or an organic group having an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a polyether group, a carboxy group, a protected carboxy group, a carboxy group-generating group, an imide group, or a cyano group, and which are bonded to a silicon atom via a Si-C bond, or a combination of these groups; R 4 are groups or atoms bonded to the silicon atom, which independently represent an alkoxy group, an acyloxy group, a hydroxy group, or a halogen atom, or a combination of these groups or atoms; Y is a group or atom bonded to the silicon atom and represents an alkylene group, an NH group, or an oxygen atom; b represents an integer of 1 to 3, and c represents an integer of 0 or 1.

[0032] In the above formula, examples of the alkyl group include linear or branched alkyl groups having 1 to 18 carbon atoms and cyclic alkyl groups having 3 to 10 carbon atoms. Examples of such groups include, but are not limited to, straight-chain, branched, or cyclic propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups.

[0033] The halogenated alkyl group is an alkyl group substituted with one or more halogen atoms, and specific examples of such alkyl groups are the same as those mentioned above, i.e., linear or branched alkyl groups having 1 to 18 carbon atoms and cyclic alkyl groups having 3 to 10 carbon atoms. Examples of the halogen atom include a fluorine atom (such as a trifluoropropyl group), a chlorine atom, a bromine atom, and an iodine atom.

[0034] The alkenyl group may be, for example, an alkenyl group having 2 to 10 carbon atoms, which may be linear, branched, or cyclic, and the position of the double bond contained in the alkenyl group is not particularly limited. Examples include, but are not limited to, ethenyl (vinyl), linear, branched, or cyclic propenyl, butenyl, pentenyl, and hexenyl groups.

[0035] The aryl group may be, for example, an aryl group having 6 to 30 carbon atoms, such as a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a 1-anthryl group, a 2-anthryl group, a 9-anthryl group, a 1-pyrenyl group, or a 2-pyrenyl group.

[0036] Examples of the organic group having an epoxy group include a glycidoxymethyl group, a glycidoxyethyl group, a glycidoxypropyl group, a glycidoxybutyl group, and a 2-(3,4-epoxycyclohexyl)ethyl group. The (meth)acryloyl group refers to both an acryloyl group and a methacryloyl group. Examples of organic groups having a (meth)acryloyl group include a methacryloyloxymethyl group, an acryloyloxymethyl group, a methacryloyloxyethyl group, an acryloyloxyethyl group, a 3-methacryloyloxypropyl group, and a 3-acryloyloxypropyl group. The methacryloyloxy group and the acryloyloxy group are also referred to as a methacryloxy group and an acryloxy group. Examples of the organic group having a mercapto group include an ethyl mercapto group, a 3-mercaptopropyl group, a butyl mercapto group, a hexyl mercapto group, an octyl mercapto group, and a mercaptophenyl group. Examples of the organic group having an amino group include an aminomethyl group, a 2-aminoethyl group, a 3-aminopropyl group, an N-2-(aminoethyl)-3-aminopropyl group, an N-(1,3-dimethyl-butylidene)aminopropyl group, an N-phenyl-3-aminopropyl group, an N-(vinylbenzyl)-2-aminoethyl-3-aminopropyl group, a dimethylaminoethyl group, and a dimethylaminopropyl group. Examples of the organic group having a carboxy group include a carboxymethyl group, a carboxyethyl group, a carboxypropyl group, and a carboxybutyl group. The term "protected carboxy group" refers to a carboxy group protected by a protecting group used in conventional organic synthesis reactions. The term "carboxy group generating group" refers to a group in which a carboxy group is esterified or amidated with alcohols, amines, or the like. A specific example of a silane compound containing a protected carboxy group and an organic group having a carboxy group generating group is a silane coupling agent having a carboxylic acid ester structure. In the silane coupling agent, the carboxylic acid ester moiety and the alkoxysilyl group may be linked by an alkylene group or an alkylene group containing a heteroatom (nitrogen atom, oxygen atom). The carboxylic acid ester moiety of the silane coupling agent is hydrolyzed to a carboxylic acid, and if it contains a nitrogen atom (heteroatom), the silane coupling agent is hydrolyzed to an amino acid due to the presence of a carboxy group and an amino group, so the silane coupling agent can be used as an amino acid generator. These compounds are, for example, represented by the formula (1-1): For example, a product manufactured by Shin-Etsu Chemical Co., Ltd. under the trade name X-88-475 shown in the following formula can be used. [ka]

[0037] The alkoxy group includes an alkoxy group having 1 to 10 carbon atoms, such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, etc., but is not limited to these.

[0038] The acyloxy group is a group derived by removing a hydrogen atom from the carboxy group (—COOH) of a carboxylic acid compound, and specific examples thereof include acyloxy groups having 2 to 10 carbon atoms.

[0039] Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0040] Examples of the alkylene group include alkylene groups derived from the alkyl groups described above, and specific examples thereof include, but are not limited to, linear, branched, or cyclic alkylene groups having 1 to 10 carbon atoms, such as methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, nonamethylene, and decamethylene.

[0041] Preferred examples of the silane compounds represented by the above formulas (1) and (2) include compounds that can form trimethylsilyl groups on the surfaces of silica particles. Examples of such compounds include compounds represented by the following formulas (1-2), (2-1) and (2-2). [ka] In the above formula (1-2), R 12 is an alkoxy group, such as a methoxy group or an ethoxy group. Silane compounds represented by the above formulas (1-2), (2-1) and (2-2) can be silane compounds manufactured by Shin-Etsu Chemical Co., Ltd.

[0042] The hollow silica particles at least partially coated with a silane compound can be obtained, for example, by adding a silane compound to a hollow silica sol and then heat-treating the mixture for about 0.1 to 20 hours at 10 to 100° C. In this case, the amount of silane compound added relative to the hollow silica particles in the hollow silica sol (aqueous sol or organic solvent dispersion sol) can be set to, for example, a mass ratio of silane compound / hollow silica particles of 0.1 to 10.0. The amount of the silane compound coated on the surface of the hollow silica particles (amount of surface treatment) is 1 nm of the surface 2 The amount can be set so that the number of silicon atoms in the silane compound is, for example, about 0.1 to 12, or about 0.1 to 6, per unit area.

[0043] The reaction between silica particles and silane compounds proceeds through the reaction between silanol groups generated by hydrolysis of the silane compounds and hydroxyl groups (silanol groups) on the surface of the silica particles. The hydrolysis requires the presence of water, but in the case of an aqueous silica sol, the aqueous solvent can fulfill this role. In the case of an organic solvent sol in which the aqueous medium has been replaced with an organic solvent, the water remaining in the organic solvent can fulfill this role. For example, water present in the organic solvent at 0.01 to 1% by mass can be used for the hydrolysis.

[0044] The hydrolysis can be carried out with or without a catalyst. If the silica particle surface is on the acidic side (pH less than 7), hydrolysis can be carried out without a catalyst. When a catalyst is used, examples of the catalyst include metal chelate compounds, organic acids (acetic acid, oxalic acid, lactic acid, etc.), inorganic acids (hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, etc.), organic bases (heterocyclic amines, quaternary ammonium salts, sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, etc.), and inorganic bases (ammonia, sodium hydroxide, potassium hydroxide, etc.).

[0045] The hollow silica sol according to the present invention can contain, as its dispersion medium, an organic solvent selected from the group consisting of alcohols having 1 to 10 carbon atoms, ketones having 1 to 10 carbon atoms, ethers having 1 to 10 carbon atoms, esters having 1 to 10 carbon atoms, and amides. The number of carbon atoms refers to the total number of carbon atoms contained in the compounds such as the alcohols. The hollow silica sol according to the present invention also includes an aqueous sol (water-dispersed sol). The aqueous sol can be solvent-substituted with an organic solvent selected from the group consisting of the above-mentioned alcohols, ketones, ethers, esters, and amides. After the hollow silica particles are coated with the above-mentioned silane compound using the aqueous sol, the solvent can be solvent-substituted with an organic solvent such as the above-mentioned alcohol.

[0046] The alcohol having 1 to 10 carbon atoms includes an aliphatic alcohol, which may be a primary alcohol, a secondary alcohol, or a tertiary alcohol. Furthermore, it is also possible to use polyhydric alcohols such as dihydric alcohols and trihydric alcohols as these alcohols. Examples of the monohydric primary alcohol include methanol, ethanol, 1-propanol, 1-butanol, and 1-hexanol. Examples of the monohydric secondary alcohol include 2-propanol, 2-butanol, cyclohexanol, propylene glycol monomethyl ether, and propylene glycol monoethyl ether. The monohydric tertiary alcohol includes, for example, tert-butyl alcohol. Examples of the dihydric alcohol (glycol) include methanediol, ethylene glycol, and propylene glycol. The trihydric alcohol includes glycerin.

[0047] The ketone having 1 to 10 carbon atoms is preferably an aliphatic ketone, such as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone, cyclopentanone, or methylcyclopentanone.

[0048] As the ether having 1 to 10 carbon atoms, an aliphatic ether is preferably used. Examples include dimethyl ether, ethyl methyl ether, diethyl ether, tetrahydrofuran, and 1,4-dioxane.

[0049] As the ester having 1 to 10 carbon atoms, an aliphatic ester can be preferably used, such as methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl lactate, methyl propionate, ethyl propionate, propyl propionate, methyl acrylate, ethyl acrylate, propyl acrylate, dimethyl maleate, diethyl maleate, dipropyl maleate, dimethyl adipate, diethyl adipate, dipropyl adipate, methyl 2-hydroxyisobutyrate, and propylene glycol monomethyl ether acetate.

[0050] Examples of the amide include N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and tetramethylurea.

[0051] In the hollow silica sol according to the present invention, the concentration of hollow silica particles can be, for example, 1 to 50% by mass, or 3 to 40% by mass, or 5 to 40% by mass, and typically 10 to 30% by mass. In this specification, the hollow silica particle concentration in silica sol is a value determined by a calcination method, specifically, by calcining the target silica sol at, for example, 1000°C for 30 minutes or more, and dividing the mass of the resulting calcination residue by the mass of the target silica sol. The mass of the calcination residue is also sometimes referred to as the "silica solid content."

[0052] The pH of the hollow silica sol according to the present invention can be adjusted from acidic to alkaline. Adjustment to acidic is achieved by adding an inorganic or organic acid. Adjustment to alkaline is achieved by adding an inorganic or organic base. An amine can be added as the organic base for the purpose of adjusting the pH and the surface charge amount, as described below. The pH can be set to a value between 1 and less than 7 on the acidic side, or between 7 and 13 on the alkaline side.

[0053] When the hollow silica sol is an aqueous sol, before the addition of the amine, the pH can be set to, for example, a pH range of 2.0 to 6.0 or 2.0 to 4.5 on the acidic side, and by adding the amine, the pH can be adjusted to, for example, a pH range of 3.0 to 10.0 or 3.0 to 9.0. On the alkaline side, the pH of the aqueous sol can be set to 7 to 10.

[0054] When the hollow silica sol is an organic solvent sol, the pH can be the pH when the organic solvent sol and an equal mass of pure water are mixed at a ratio of 1: 1. The pH is measured in the form of a sol of an organic solvent that can be mixed with water, and when the solvent is subsequently replaced with a hydrophobic organic solvent, the pH is measured in advance at the stage of a hydrophilic organic solvent sol such as methanol, or the pH is measured after adding a hydrophilic organic solvent to the hydrophobic solvent sol. For example, when the dispersion medium is a hydrophilic organic solvent, such as methanol sol or propylene glycol monomethyl ether sol, the pH can be measured using a solution prepared by mixing pure water and the sol in a mass ratio of 1:1. When the dispersion medium is a hydrophobic organic solvent, such as methyl ethyl ketone sol, cyclopentanone sol, or cyclohexanone sol, the pH can be measured using a solution prepared by mixing pure water, methanol, and the sol in a mass ratio of 1:1:1.

[0055] The conversion from an aqueous sol to a hydrophobic organic solvent sol can be achieved by solvent-substituting the aqueous medium with a hydrophilic organic solvent (such as an alcohol), followed by further solvent-substituting with a hydrophobic organic solvent, and moisture may remain during this process. For example, the residual moisture content of the hollow silica particles in the alcohol sol can be about 0.1 to 3.0% by mass, or about 0.1 to 1.0% by mass. The residual moisture content of the sol (dispersion medium is an organic solvent other than alcohol) can be set to about 0.01 to 0.5% by mass.

[0056] Furthermore, the viscosity (25°C) of the hollow silica organic solvent sol can be set in the range of 0.5 to 10.0 mPa·s, or alternatively, in the range of 1.0 to 10.0 mPa·s.

[0057] The hollow silica sol (aqueous sol, organic solvent sol, etc.) according to the present invention may contain an amine, or an amine and ammonia. The amine may be added and contained in an amount of 0.001 to 10 mass%, 0.01 to 10 mass%, or 0.1 to 10 mass% relative to the mass of the hollow silica particles. The amine, or the amine and ammonia, can be contained in such an amount that the total nitrogen amount in the sol containing the hollow silica particles is expressed as the total nitrogen amount of these basic components, and is, for example, in the range of 0.001 to 10 mass%, or 0.01 to 1 mass%, or 0.01 to 0.3 mass%, or 0.01 to 0.2 mass%, typically 0.02 to 0.2 mass%.

[0058] Examples of the amine include aliphatic amines and aromatic amines, with aliphatic amines being preferred. At least one amine selected from the group consisting of primary, secondary, and tertiary amines having 1 to 10 carbon atoms can be used. The amine is water-soluble and is at least one amine selected from the group consisting of primary, secondary, and tertiary amines having 1 to 10 carbon atoms.

[0059] Examples of primary amines include monomethylamine, monoethylamine, monopropylamine, monoisopropylamine, monobutylamine, monoisobutylamine, monosecbutylamine, monotertbutylamine, monomethanolamine, monoethanolamine, monopropanolamine, monoisopropanolamine, monobutanolamine, monoisobutanolamine, monosecbutanolamine, and monotertbutanolamine. Examples of secondary amines include dimethylamine, diethylamine, dipropylamine, diisopropylamine, N-methylethylamine, N-ethylisobutylamine, dimethanolamine, diethanolamine, dipropanolamine, diisopropanolamine, N-methanolethylamine, N-methylethanolamine, N-ethanolisobutylamine, and N-ethylisobutanolamine. Examples of tertiary amines include trimethylamine, triethylamine, tripropylamine, triisopropylamine, diisopropylethylamine, tributylamine, triisobutylamine, tri-sec-butylamine, tri-tert-butylamine, trimethanolamine, triethanolamine, tripropanolamine, triisopropanolamine, tributanolamine, triisobutanolamine, tri-sec-butanolamine, tri-tert-butanolamine, tripentylamine, 3-(dimethylamino)ethyl acrylate, 2-(dimethylamino)ethyl acrylate, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl acrylate, and 2-(diethylamino)ethyl methacrylate. The water solubility of the amine is preferably 80 g / L or more, or 100 g / L or more. Among these, primary amines and secondary amines are preferred, with secondary amines being more preferred due to their low volatility and high solubility, such as diisopropylamine and diethanolamine. Diisopropylethylamine, a tertiary amine, is also preferably used.

[0060] <Method for producing aluminum atom-containing hollow silica sol> The aluminum atom-containing hollow silica sol of the present invention comprises the following steps (I) and (II): It can be produced by the production method. Step (I): preparing a hollow silica aqueous sol having a sulfuric acid content of 1 ppm to 5000 ppm / SiO2 relative to the mass of aluminum atom-containing hollow silica particles; Step (II): A step of adjusting the amount of sulfuric acid contained in the hollow silica aqueous sol prepared in step (I) to 1 ppm to 150 ppm.

[0061] More specifically, the aluminum atom-containing hollow silica sol of the present invention can be produced by a production method including the following steps (III), (IV), (V), and (VI): In this specification, steps (III) to (VI) and steps (I) to (II) exist independently, and step (III) is not numbered with the intention of being carried out after step (II). Step (III): preparing a hollow silica aqueous sol; Step (IV): adding an aluminum compound to the hollow silica aqueous sol prepared in step (III) in a proportion of 0.0001 to 0.5 g, calculated as Al2O3, per 1 g of hollow silica particles, and maintaining the mixture at 40 to 260°C for 0.1 to 24 hours to obtain an aluminum atom-containing hollow silica aqueous sol; Step (V): adding sulfuric acid to the aluminum atom-containing hollow silica aqueous sol obtained in step (IV) in a ratio of 1 ppm to 5000 ppm / SiO2 relative to the mass of hollow silica particles in the sol, and maintaining the mixture at 5 to 100°C for 0.1 to 48 hours. Step (VI): A step of contacting the aluminum atom-containing hollow silica aqueous sol obtained in the step (V) with a cation exchange resin. By the above-mentioned method for producing hollow silica sol, the amount of sulfuric acid contained in the sol can be adjusted to a predetermined amount.

[0062] [(III) Process] The hollow silica particles constituting the hollow silica sol prepared in step (III) have an outer shell containing silica and have a space inside the outer shell. Note that the "hollow silica sol" and "hollow silica particles" prepared in step (III) are distinguished from the abbreviations for the aluminum atom-containing hollow silica sol and aluminum atom-containing hollow silica particles described above, and are, so to speak, the raw materials for the silica sol and silica particles according to the present invention. That is, the "hollow silica particles" in this step are hollow silica particles that do not contain aluminum atoms (however, the inclusion of aluminum atoms as impurities is permitted). The raw material hollow silica particles are obtained by forming a silica-based shell on the surface of a core portion, called a template, in an aqueous dispersion medium, and then removing the core portion (template). The template can be made of an organic material (e.g., hydrophilic organic resin particles such as polyethylene glycol, polystyrene, or polyester) or an inorganic material (e.g., hydrophilic inorganic compound particles such as calcium carbonate or sodium aluminate).

[0063] The raw material hollow silica aqueous sol prepared in step (III) can be any of a non-hydrothermally treated hollow silica aqueous sol, a hydrothermally treated hollow silica aqueous sol, or a mixture thereof. The non-hydrothermally treated hollow aqueous silica sol is an aqueous sol of silica particles treated in an aqueous medium via heating at a temperature below 100°C, for example, from 20°C to less than 100°C, or from 40°C to less than 100°C, or from 50°C to less than 100°C. The hydrothermally treated silica aqueous sol is an aqueous sol of silica particles treated in an aqueous medium via heating at a temperature of from 100°C to 240°C, or from 110°C to 240°C.

[0064] The raw material hollow silica aqueous sol (non-hydrothermally treated hollow silica aqueous sol, hydrothermally treated hollow silica aqueous sol, or a mixture thereof) is subjected to the step (IV) described below. The hollow silica particles may contain aluminum atoms, specifically, aluminosilicate sites may be formed on the outer shells of the hollow silica particles. Since the aluminosilicate sites may retain alkali metals, the raw material hollow silica sol can be selected so that aluminum atoms are present on the surface of the hollow silica particles at a ratio of 100 to 20,000 ppm / SiO2 (based on the mass of the hollow silica particles) calculated as Al2O3, as measured by a so-called leaching method using a mineral acid.

[0065] [(IV) Process] In step (IV), an aluminum compound is added to the raw material hollow silica aqueous sol prepared in step (III) and the mixture is heated to obtain an aluminum atom-containing hollow silica aqueous sol. This step allows the aluminum compound to act on (impregnate) the raw material hollow silica particles from the outside, causing aluminum atoms to be present on the surfaces of the hollow silica particles, i.e., aluminosilicate sites are formed at least on the surfaces of the particles.

[0066] When an aluminum compound is applied (impregnated) from the outside after the formation of the (raw material) hollow silica particles, there are two methods: one is to subject the hollow silica particles before impregnation to a hydrothermal treatment in advance, thereby increasing the density of the outer shell, and then impregnate the hollow silica particles with the aluminum compound by heat treatment; and the other is to impregnate hollow silica particles that have not been subjected to a hydrothermal treatment in advance with the aluminum compound by heat treatment. In either the former method or the latter method, it is preferable to impregnate the hollow silica particles with the aluminum compound so that the amount of aluminum atoms (in terms of Al2O3) present throughout the hollow silica particles is in the specific ratio described above, as measured by the dissolution method using the hydrofluoric acid aqueous solution described above.

[0067] The aluminum compound used in step (IV) can be added in an amount of 0.0001 to 0.5 g, 0.001 to 0.1 g, or 0.001 to 0.05 g calculated as Al2O3 per 1 g of hollow silica particles in the hollow silica aqueous sol. The heating temperature in step (IV) is 40 to 260°C, or 50 to 260°C, or 60 to 240°C. In the case of non-hydrothermal treatment, the heating temperature can be 40 to less than 100°C, or 50 to less than 100°C, or 60 to less than 100°C, and in the case of hydrothermal treatment, the heating temperature can be 100 to 260°C, or 150 to 240°C. The heating time in step (IV) can be in the range of 0.1 to 48 hours, or 0.1 to 24 hours, or 0.1 to 10 hours, or 1 to 10 hours. The impregnation of the hollow silica particles with the aluminum compound to form an aluminosilicate and the resulting presence of the desired amount of aluminum atoms depends in part on the treatment temperature in step (IV), and it is therefore important to carry out the heat treatment within the above temperature range.

[0068] Specific examples of the aluminum compound include at least one aluminum compound selected from the group consisting of aluminates, aluminum alkoxides, and hydrolysates thereof. Examples of the aluminates include sodium aluminate, potassium aluminate, calcium aluminate, magnesium aluminate, ammonium aluminate, and amine aluminate. Examples of the aluminum alkoxides include aluminum isopropoxide and aluminum butoxide. Among these, aluminates such as sodium aluminate are preferably used.

[0069] The aluminum compound can be added to the hollow silica aqueous sol in the form of a solid or an aqueous solution, and is preferably added in the form of an aqueous solution. When the aluminum compound is added to the hollow silica aqueous sol in the form of an aqueous solution, the concentration of the aluminum compound in the aqueous solution can be in the range of 0.01 to 20% by mass, 0.1 to 10% by mass, or 0.5 to 5% by mass. The aluminum compound can be added while stirring the hollow silica aqueous sol. This addition may be completed before the heating, may be started before the heating and completed during the heating, or may be continued throughout the entire heating period.

[0070] The step (IV) may further include a step (IV-i) of adding an amine. The amine may be any of the above-mentioned amines, and may be contained in the hollow silica sol in the above-mentioned range. Step (IV) may also include step (IV-ii), in which a neutral salt consisting of a combination of at least one cation selected from sodium ions, potassium ions, and ammonium ions and an inorganic or organic anion is added in an amount of 0.1 to 10 mass% relative to the mass of the hollow silica particles. Examples of the inorganic anion used in step (IV-ii) include sulfate ions, chloride ions, and phosphate ions, and examples of the organic anion include carboxylate ions, oxycarboxylate ions, and amino acids. Examples of preferred neutral salts include sodium sulfate, potassium sulfate, and ammonium sulfate.

[0071] [(V) Process] Step (V) is a step of adding sulfuric acid to the aluminum atom-containing hollow silica aqueous sol obtained in step (IV) above at a ratio of 1 ppm to 5000 ppm / SiO2 relative to the hollow silica particles in the sol, and maintaining the mixture at a predetermined temperature. This step is a so-called leaching step in which aluminum atom-containing components that were not doped on the surface or inside of the hollow silica particles in step (IV) above, metal impurities contained in the particles, and impurity basic components such as counter ion components that are eluted by the added sulfuric acid are eluted into the liquid. In this step, after adding sulfuric acid, the mixture is maintained at 5 to 100° C. for 0.1 to 48 hours. By passing through this step, the above-mentioned step (I): a step of preparing a hollow silica aqueous sol in which the amount of sulfuric acid relative to the mass of aluminum atom-containing hollow silica particles is 1 ppm to 5000 ppm / SiO2 is achieved.

[0072] [(VI) Process] Step (VI) is a step in which the aluminum atom-containing hollow silica aqueous sol obtained in step (V) is contacted with a cation exchange resin. This step makes it possible to remove metal-containing components, such as aluminum sulfate, or impurity base components that have been eluted into the solution by adding sulfuric acid. In other words, this step achieves the aforementioned step (II): a step in which the amount of sulfuric acid contained in the hollow silica aqueous sol prepared in step (I) is adjusted to 1 ppm to 150 ppm. Furthermore, since this step makes it possible to remove impurity base components that affect the stability of the sol, it is expected that the storage stability of the sol will be improved. The operation in step (VI) may be carried out before maintaining the temperature at a predetermined level in step (V), i.e., before or after maintaining the temperature at a predetermined level in step (V), and the operation may be carried out multiple times, for example, 2 to 10 times, 2 to 8 times, 2 to 5 times, or 3 to 5 times, as necessary.

[0073] After step (VI), an ultrafiltration (UF) step may be optionally included. This step involves ultrafiltration (UF) of the silica sol obtained in step (VI), and aims to adjust the amount of sulfuric acid in the system to a desired value.

[0074] [(VII) Process] Furthermore, after completion of the above step (II) or the above step (VI) or any subsequent UF step, a step (VII) can be included in which the dispersion medium (water) in the aluminum atom-containing hollow silica aqueous sol obtained in the above steps is replaced with an organic solvent by vacuum replacement (heat replacement under reduced pressure), heat replacement under normal pressure, or ultrafiltration (UF). Examples of the organic solvent to be substituted include alcohols having 1 to 10 carbon atoms, ketones having 1 to 10 carbon atoms, ethers having 1 to 10 carbon atoms, and esters having 1 to 10 carbon atoms. Specific examples of these compounds include the organic solvents mentioned as the dispersion medium for the hollow silica sol according to the present invention. The pressure reduction conditions can be about 10 to 600 Torr, and heating at about 30 to 200° C. may be performed in combination with the pressure reduction.

[0075] Furthermore, after the above step (VI), a step (surface modification step) of coating the surface of the silica particles with the aforementioned silane compound [at least one silane compound selected from the group consisting of compounds represented by formula (1) and formula (2)] may be included. This step can be carried out after the step (VI) by adding the silane compound described above and then heat treating at 10 to 100° C. for about 0.1 to 20 hours. As described above, the surface modification step is a reaction that proceeds through hydrolysis of the silane compound. Therefore, it is preferable to carry out the surface modification step in the presence of water, for example, in the form of an aqueous sol, that is, before the solvent substitution step (VII) (if carried out) (or without carrying out the solvent substitution step). Alternatively, the solvent substitution step (VII) may be carried out after the step (VI), and then the surface modification step may be carried out, followed by the solvent substitution step (VII).

[0076] <Film-forming composition> The present invention also covers a film-forming composition containing the aluminum atom-containing hollow silica sol and an organic resin. Furthermore, the film-forming composition according to the present invention can be prepared by removing the dispersion medium (water, organic solvent) from the aluminum atom-containing hollow silica sol to form aluminum atom-containing hollow silica particles, and then combining the aluminum atom-containing hollow silica particles with the organic resin. In the film-forming composition, the aluminum atom-containing hollow silica particles can account for, for example, 1% to 90% by mass of the total solid content (100% by mass in total), and the organic resin can account for, for example, 10% to 99% by mass. The solid content in the film-forming composition refers to all components other than the solvent, and can be the value calculated from the residue obtained by heating the film-forming composition at a temperature of about 200 to 300°C to remove the solvent.

[0077] The organic resin may be, for example, a thermosetting or photocurable resin (curable resin), such as a styrene-based resin, an epoxy-based resin, a thioepoxy resin, a novolac-based resin, a cyanate-based resin, a phenol-based resin, an acrylic-based resin, a maleimide-based resin, a polyester-based resin, a urethane-based resin, a polyurea resin, a polyimide-based resin, a polyamide-based resin, a polyamic acid resin, a polyhydroxyimide resin, a polybenzoxazole resin, a polybenzimidazole resin, a polybenzothiazole resin, a polyhydroxyamide resin, a polyhydroxyazomethine resin, a polyether-based resin, a polybenzoxazine resin, a polytetrafluoroethylene-based resin, a cycloolefin polymer-based resin, an unsaturated polyester-based resin, a vinyltriazine-based resin, a polyphenylene sulfide-based resin, a crosslinkable polyphenylene oxide-based resin, a curable polyphenylene ether-based resin, and a condensation-based resin, but is not limited thereto.

[0078] Furthermore, the film-forming composition of the present invention may contain various curing agents as needed, such as amine-based curing agents, acid anhydride-based curing agents, radical generator-based curing agents (thermal radical generators, photoradical generators), acid generator-based curing agents (thermal acid generators or photoacid generators), and base generators (thermal base generators, photobase generators), as well as curing aids (organic phosphorus compounds, quaternary phosphonium salts, quaternary ammonium salts). Furthermore, the film-forming composition of the present invention may contain conventional additives as needed. Examples of such additives include surfactants (leveling agents), pigments, colorants, thickeners, adhesion promoters, sensitizers, antifoaming agents, coating property improvers, lubricants, stabilizers (antioxidants, heat stabilizers, light resistance stabilizers, etc.), plasticizers, dissolution promoters, fillers, antistatic agents, development inhibitors (diazonaphthoquinone, etc.), etc. These additives may be used alone or in combination of two or more. It may be possible.

[0079] The film-forming composition can be applied to or filled on a substrate and then heated, irradiated with light, or a combination thereof to form a cured product. For example, a photocurable film-forming composition can be applied to a substrate to form a coating film, which can then be cured by irradiating the coating film with light to obtain a coating (cured product). Heating can also be performed before or after light irradiation. Examples of methods for applying the film-forming composition include flow coating, spin coating, spray coating, screen printing, casting, bar coating, curtain coating, roll coating, gravure coating, dipping, and slitting. The thickness of the coating film can be selected from a range of about 0.01 μm to 10 mm depending on the application of the cured product; for example, when used as a photoresist, it can be about 0.05 to 10 μm (particularly 0.1 to 5 μm), when used as a printed wiring board, it can be about 5 μm to 5 mm (particularly 100 to 1 mm), and when used as an optical thin film, it can be about 0.1 to 100 μm (particularly 0.3 to 50 μm). When a transparent coating is to be obtained, it is desirable that the visible light transmittance of the coating is 80% or more, or 90% or more, typically 90% to 96%. When the film-forming composition of the present invention is a thermosetting film-forming composition, it can be obtained in the form of a thermosetting varnish by mixing the thermosetting resin (curable resin), the curing agent (such as a thermal acid generator), and, if desired, the curing aid. Mixing can be carried out in a reaction vessel using a stirring blade or a kneader.

[0080] Thermosetting materials and photocurable materials using the coating-forming composition of the present invention have characteristics such as fast curing, transparency, and little cure shrinkage, and can be used for coating or bonding electronic components, optical components (anti-reflective coatings), and precision mechanical components. For example, it can be used to bond mobile phone and camera lenses, optical elements such as light-emitting diodes (LEDs) and semiconductor lasers (LDs), liquid crystal panels, biochips, camera lenses and prisms, magnetic components in hard disks for computers, CD and DVD player pickups (the part that captures the optical information reflected from the disc), speaker cones and coils, motor magnets, circuit boards, electronic components, and internal engine parts for automobiles. It can also be used as a hard coating material (coating material) for surface protection of automobile bodies, lamps, electrical appliances, building materials, plastics, etc., and can be applied to, for example, automobile and motorcycle bodies, headlight lenses and mirrors, plastic lenses for eyeglasses, mobile phones, game consoles, optical films, ID cards, etc. Other applications include the creation of complex three-dimensional hardened objects in combination with 3D CAD, photolithography for producing models of industrial products, coating of optical fibers, adhesion, optical waveguides, thick-film resists, etc.

[0081] The film-forming composition of the present invention can also be suitably used as an insulating resin for electronic materials such as anti-reflection films, semiconductor encapsulation materials, adhesives for electronic materials, printed wiring board materials, interlayer insulating film materials, and encapsulants for power modules, as well as an insulating resin for use in high-voltage equipment such as generator coils, transformer coils, and gas-insulated switchgears. [Example]

[0082] The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples.

[0083] The hollow silica sol, silane compound, pH adjuster, and solvent used were as follows: (Raw material: hollow silica aqueous sol) Product name HKT-A20-40D: Water-dispersed silica sol of hollow silica particles (Ningbo Manufactured by Dilato), average particle size by DLS: 47 nm, average primary particle size by TEM: 40 nm, specific surface area by BET: 125 m 2 / g, shell thickness 5nm, refractive index 1.3, silanol group density 1.6 / nm 2 , pH 10.4, viscosity 9.6 mPa·s, silica particle concentration 20.2 mass% (Silane compound, manufactured by Shin-Etsu Chemical Co., Ltd.) AcPS: 3-acryloxypropyltrimethoxysilane MPS: 3-methacryloxypropyltrimethoxysilane PTMS: Phenyltrimethoxysilane MPMDMS: 3-methacryloxypropylmethyldimethoxysilane DMDMS: Dimethyldimethoxysilane HMDS: Hexamethyldisiloxane TMPSA: 3-trimethoxysilylpropylsuccinic anhydride AAPS: 2-(allyloxymethyl)acrylate (trimethoxysilyl)propyl MTMS: Methyltrimethoxysilane DMEVS: Dimethylethoxyvinylsilane DMPS: Dimethoxymethylphenylsilane (pH adjuster: base) DiPA: Diisopropylamine DiPEA: Diisopropylethylamine (organic solvent) MeOH: Methanol MEK: Methyl ethyl ketone PGME: Propylene glycol monomethyl ether CPN: Cyclopentanone PGMEA: Propylene glycol monomethyl ether acetate MIBK: Methyl isobutyl ketone EL: Ethyl lactate HBM: 2-hydroxyisobutyric acid methyl ester

[0084] The methods and procedures for measuring the physical properties of each hollow silica sol are as follows. (Measurement of silica particle concentration in silica sol) 1 g of each hollow silica sol was placed in a crucible and heated on a hot plate at a temperature 10°C higher than the boiling point of the dispersion medium (water or methanol (MeOH)) to dry and remove the solvent, and then calcined at 1,000°C for 30 minutes. The calcination residue was weighed and the silica particle concentration (% by mass) was calculated. As will be described later, the sol prepared in each synthesis example contains sulfuric acid, amines for pH adjustment, and the like, but after the above calcination, the organic components such as amines are almost completely eliminated by volatilization / thermal decomposition, and the amounts of these components, including sulfuric acid, added are very small, so the concentration calculated by the above method can be treated as the hollow silica particle concentration in the silica sol.

[0085] (pH measurement of silica sol) The pH of the water-dispersed hollow silica sol was measured at 23°C using a pH meter (manufactured by DKK-TOA Corporation, product name: MM-43X). The pH of the organic solvent-dispersed hollow silica sol was measured at 20°C using a pH meter (MM-43X, manufactured by DKK-TOA Corporation) using a solution prepared by mixing pure water and the sol at a mass ratio of 1:1 for organic solvent sols that can be mixed with water arbitrarily, such as MeOH dispersion sol and PGME dispersion sol, and a solution prepared by mixing pure water, methanol, and the organic solvent sol at a mass ratio of 1:1:1 for organic solvent sols with low solubility in water, such as MEK dispersion sol and CPN dispersion sol.

[0086] (Viscosity measurement) Measurement was carried out at 25°C using an Ostwald viscometer (manufactured by Shibata Scientific Co., Ltd.).

[0087] (Measurement of moisture content) The water content of the organic solvent dispersion sol was measured by Karl Fischer titration.

[0088] (Measurement of MeOH amount) The amount of methanol (MeOH) contained in the target sol was measured using a gas chromatograph (manufactured by Shimadzu Corporation, product name: GC-2014s) under the conditions described below. Column: 3mm x 1m glass column Filler: Polar Pack Q Column temperature: 130-230°C (heating rate: 8°C / min) Carrier: N240mL / min Detector: FID Injection volume: 1μL Internal standard: acetonitrile.

[0089] (Specific surface area by nitrogen adsorption method (S N2 ) Measurement The specific surface area (S) of hollow silica particles in water-dispersed hollow silica sol was measured by nitrogen adsorption. N2 ) was measured by removing water-soluble cations in the water-dispersed hollow silica sol with an H-type cation exchange resin (Dow Chemical Company, trade name: Amberlite IR-120B), drying the silica sol at 290°C, pulverizing the dried material in a mortar, and further heating it at 250°C for 2 hours to prepare a measurement sample. This was then measured by the BET single-point method using a nitrogen adsorption specific surface area measuring device, Monosorb (Quantachrome Instruments Japan LLC), with a mixed gas of 30% N2 (nitrogen) and 70% He (helium) as the carrier gas. The specific surface area (S) of hollow silica particles in organic solvent-dispersed hollow silica sol was measured by nitrogen adsorption. N2) was measured using the BET single-point method. 4 ml of the organic solvent-dispersed hollow silica sol was added to a 42 ml pear-shaped settling tube (Thermo Fisher Scientifics, product name: Nalgene Oak Ridge), and 4 ml of MEK and 20 ml of hexane were added. The mixture was left to stand for 5 minutes to induce cloudiness, separation, or precipitation due to aggregation. The mixture was then centrifuged (temperature: 5°C, rotation speed: 20,000 rpm, time: 30 minutes) using a centrifuge (Tomy Seiko Co., Ltd., product name: High-Speed ​​Refrigerated Centrifuge Suprema 21), and the supernatant was removed. 4 ml of acetone was then added, and the precipitate was redissolved using a test tube mixer (As One Corporation, product name: MVM-10). 20 ml of hexane was then added. The mixture was then centrifuged again, and the supernatant was removed. 4 ml of acetone was then added, and the precipitate was redissolved using a test tube mixer. 20 ml of hexane was then added. The mixture was then centrifuged and the supernatant was removed. The resulting precipitate (mixture) was vacuum dried (temperature: 60°C, pressure: -0.1 MPa), and the resulting powder was ground in a mortar for 10 minutes to obtain silica particles (powder). The resulting silica particles were heated at 150°C to remove adsorbed water, and the resulting particles were used as a measurement sample.

[0090] (Particle size measured by dynamic light scattering (average particle size (nm) measured by DLS method) The average particle size (Z-average particle size) by the DLS method was measured using a dynamic light scattering particle size analyzer (manufactured by Malvern Panalytical, product name: Zetasizer Nano). The dilution solvent used when measuring the average particle size by the DLS method was the same as the dispersion medium of each sol. Specifically, 0.1 g of the target silica sol was dispensed into a glass cell with an optical path length of 10 mm, and the same solvent as the dispersion medium of the silica sol was further added to obtain a silica sol with a silica particle concentration adjusted so that the count rate at an attenuator of 7 was 200 to 400 kcps. The prepared silica sol was then placed in the cell. The height of the liquid surface from the bottom of the cell was adjusted to about 1 cm, and the dynamic light scattering particle diameter of the silica sol was measured using an attenuator 7.

[0091] (Measurement of average primary particle size using a TEM (transmission electron microscope)) The particles in the hollow silica sol were photographed using a transmission electron microscope (manufactured by JEOL Ltd., product name JEM-F200), and 300 arbitrarily selected particles were binarized using an automatic image processing analyzer (manufactured by Nireco Corporation, product name LUZEX' AP), and the diameter of the projected area converted into a circle was measured as the average primary particle diameter (HEYWOOD diameter).

[0092] (Shell thickness measurement) The particles in the hollow silica sol were photographed using a transmission electron microscope (manufactured by JEOL Ltd., trade name JEM-F200), and 300 randomly selected particles were binarized using an automatic image processing analyzer (manufactured by Nireco Corporation, trade name LUZEX' AP). The inner diameters calculated by converting the projected areas into circles were averaged, and the difference from the primary particle diameter measured by TEM was measured, and the obtained results were then averaged.

[0093] ( 27 Measurement of tetrahedral Al ratio by Al-NMR) 1.5 mL of water-dispersed hollow silica sol was mixed with 1.5 mL of heavy water and added to a 10 mm diameter Teflon (registered trademark) test tube. Then, measurements were performed using a nuclear magnetic resonance (NMR) spectrometer (trade name: ECA500, manufactured by JEOL Ltd.) under the following conditions. The area of ​​the signal obtained from the measurement at 50 to 65 ppm was defined as (α0), and the area of ​​the signal obtained from -5 to 10 ppm was defined as (β0). When multiple signals were observed, the area of ​​all the signals was calculated as the sum. From the above (α0) and (β0), the tetrahedral Al ratio (maximum value: 1) was calculated using the following formula. 4-coordination Al ratio=(α0) / {(α0)+(β0)}] Probe: 10mm silicone backing-free probe Nuclide: 27 Al (1H decoupling, NOE off) Observation frequency: 500.15992MHz ·Measurement temperature: 23℃) 90 degree pulse width: 15μs Pulse repetition time: 2.5s Waiting time: 2 seconds Accumulation count: 10,000 Points: 32768 Rotation: off Analysis software: Delta (V5.0.6) (manufactured by JEOL Ltd.) Window function: sexp BF:5.0Hz

[0094] (Measurement of the amount of sulfuric acid in the water-dispersed sol (hereinafter referred to as the amount of sulfuric acid in the system (ppm / sol))) The obtained water-dispersed hollow silica sol was diluted 10 times with pure water, and then the amount of sulfuric acid in the system (ppm / sol) was measured by ion chromatography using an anion analyzer (trade name Dionex ICS-2100, manufactured by Thermo Scientific).

[0095] (Measurement of the amount of sulfuric acid in hollow silica particles (hereinafter referred to as the amount of sulfuric acid in the system (ppm / SiO2))) The amount of sulfuric acid (ppm) in the system was divided by the silica particle concentration (mass %) to calculate a value, and the resulting value was taken as a constant (ppm / SiO2).

[0096] (Measurement of the amount of aluminum present in the entire hollow silica particle / Dissolution method using hydrofluoric acid solution) The precisely weighed hollow silica sol was dried, and 250 mg of the obtained particles was dissolved in 2.5 ml of nitric acid (manufactured by Kanto Chemical Co., Ltd., trade name: nitric acid 1.38, purity 60.0%) and 38% hydrofluoric acid (Tama Chemical The amount of aluminum in the resulting aqueous solution was measured using an ICP-OES analyzer (Rigaku Corporation, product name: CIROS120 EOP), and the amount of aluminum present in the entire hollow silica particles was calculated in terms of Al2O3 (per mass of hollow silica particles) (Al2O3 (ppm) / SiO2).

[0097] (Measurement of surface charge of hollow silica particles) The hollow silica sol was diluted with 10 mL of methanol to a silica particle concentration of 0.5% by mass to prepare a measurement sample. Using a particle charge meter (Voyt Turbo, product name PCD-06) and a 0.001 mol / L (N / 1000) DADMAC solution (Voyt Turbo) as a standard cation titrant, the titration value until the streaming potential of the measurement sample reached zero was measured. The titration value obtained was divided by the amount of silica particles contained in the measurement sample to obtain the surface charge (μeq / g) per 1 g of hollow silica particles. DADMAC stands for diallyldimethylammonium chloride.

[0098] (Synthesis Example 1) Preparation of Water-Dispersed Sol (A1) of Aluminum Atom-Containing Hollow Silica Particles 1856 g of water-dispersed hollow silica sol HKT-A20-40D (Ningbo Dilato Co., Ltd., product name) was placed in a 3 L plastic container. 32.2 g of sodium aluminate solution diluted to 1.0 mass% Al2O3 was added dropwise over 1 minute while stirring at 650 rpm using a mechanical stirrer equipped with a glass impeller. The mixture was then stirred at the same speed for 30 minutes. 643.6 g of purified water was then added and stirred for an additional 20 minutes to obtain a mixture. Next, 2502 g of this mixture was placed in a 3 L stainless steel autoclave and heated at 150°C for 5 hours while stirring at 80 rpm. The mixture was then cooled to below 50°C. The above series of operations was carried out twice, and the results were combined to obtain 4605 g of a heat-treated water-dispersed sol. 5.6 g of an 8.2% aqueous sulfuric acid solution was then added dropwise to 3070 g of the heat-treated water-dispersed sol, followed by stirring at 25°C for 1 hour to obtain a sulfuric acid-added heat-treated water-dispersed sol. Next, the obtained sulfuric acid-added heat-treated water-dispersed sol was passed through a 400 mL column-packed cation exchange resin (H-type Amberlite (trade name) IR-120B, harmonic mean diameter 0.6 to 0.8 mm, Organo Corporation) at a space velocity (SV) of 5 / hour to obtain a water-dispersed sol of aluminum atom-containing hollow silica particles. The resulting water-dispersed sol was then heated at 80°C for 10 hours, cooled to 30°C or below, and then passed through a column of cation exchange resin (H-type Amberlite (trade name) IR-120B) at a space velocity (SV) of 5 / hour to obtain a water-dispersed sol (A1) of aluminum atom-containing hollow silica particles. The pH of the obtained water-dispersed sol (A1) was 2.5, and the amount of sulfuric acid in the system was 136 ppm / sol. 2 / g, silica particle concentration 14.8 mass%, viscosity 1.4 mPa·s, average particle size by DLS method 50 nm, tetrahedral Al ratio 0.59, amount of aluminum atoms present in the whole hollow silica particle converted to Al2O3 688 ppm / SiO2, amount of surface charge converted to 1 g of hollow silica particle 29 μeq / g, thickness of outer shell 5 nm. Figure 2 shows the heat-treated water-dispersed sol (before adding sulfuric acid). 27 The Al-NMR spectrum (Fig. 2(A)) of the water-dispersed sol (A1) of aluminum-atom-containing hollow silica particles (after adding sulfuric acid) is shown. 27 The Al-NMR measurement spectrum results (FIG. 2(B)) are shown respectively.

[0099] (Synthesis Example 2) Preparation of Water-Dispersed Sol (A2) of Aluminum-Atom-Containing Hollow Silica Particles A water-dispersed sol (A2) of aluminum atom-containing hollow silica particles was obtained in the same manner as in Synthesis Example 1, except that the amount of 8.2% aqueous sulfuric acid solution added was 1.4 g per 1535 g of the heat-treated water-dispersed sol. The pH of the obtained water-dispersed sol (A2) was 2.7, and the amount of sulfuric acid in the system was 67 ppm / sol. In addition, the specific surface area of ​​the BET method is 125m 2 / g, silica particle concentration 14.8 mass%, viscosity 1.6 mPa·s, average particle size by DLS method 51 nm, tetrahedral Al ratio 0.72, the amount of aluminum atoms present in the entire hollow silica particle converted to Al2O3 was 701 ppm / SiO2, the surface charge converted to 1 g of hollow silica particle was 26 μeq / g, and the thickness of the outer shell was 5 nm.

[0100] (Synthesis Example 3) Preparation of Water-Dispersed Sol (A3) of Aluminum Atom-Containing Hollow Silica Particles 1,400 g of the water-dispersed sol (A1) of aluminum-atom-containing hollow silica particles obtained in Synthesis Example 1 and 186 g of pure water were placed in a stirring-type ultraholder UHP-150K (manufactured by Advantec Co., Ltd.) equipped with a 150 mm diameter, 200,000 cut-off ultrafilter (manufactured by Advantec Co., Ltd.), and then filtered while applying a nitrogen pressure of 0.2 MPa. 365 g of pure water was then added to 905 g of the filtered water-dispersed sol, yielding 1,270 g of water-dispersed sol (A3) of aluminum-atom-containing hollow silica particles. The pH of the obtained water-dispersed sol (A3) was 2.7, and the amount of sulfuric acid in the system was 90 ppm / sol. 2 / g, silica particle concentration 14.8 mass%, viscosity 1.5 mPa·s, average particle size by DLS method 50 nm, tetrahedral Al ratio 0.65, the amount of aluminum atoms present in the entire hollow silica particle converted to Al2O3 was 688 ppm / SiO2, the surface charge converted to 1 g of hollow silica particle was 29 μeq / g, and the thickness of the outer shell was 5 nm.

[0101] (Synthesis Example 4) Preparation of Water-Dispersed Sol (A4) of Aluminum Atom-Containing Hollow Silica Particles 2500 g of water-dispersed hollow silica sol HKT-A20-40D (Ningbo Dilato Co., Ltd., product name) was placed in a 3 L plastic container, and 42.5 g of sodium aluminate solution diluted to 1.0 mass% Al2O3 was added dropwise over 1 minute while stirring at 600 rpm with a mechanical stirrer equipped with a glass impeller. The mixture was then stirred at the same speed for 30 minutes. 2442 g of this mixture was then placed in a 3 L stainless steel autoclave and heated at 150°C for 5 hours while stirring at 80 rpm, after which it was cooled to below 50°C. Then, 5.31 g of an 8% aqueous sulfuric acid solution was added dropwise to 2178 g of the obtained silica sol, and the mixture was stirred at 25°C for 2 hours to obtain a sulfuric acid-added heat-treated water-dispersed sol. Thereafter, the same procedure as in Synthesis Example 1 was carried out to obtain a water-dispersed sol (A4) of aluminum atom-containing hollow silica particles. The pH of the obtained water-dispersed sol (A4) was 2.2, the amount of sulfuric acid in the system was 201 ppm / sol, the silica particle concentration was 17.7 mass%, the average particle diameter by DLS method was 60 nm, and the specific surface area by BET method was 125 m 2 / g, tetrahedral Al ratio 0.42, the amount of aluminum atoms present in the entire hollow silica particle was 620 ppm / SiO2 in terms of Al2O3, the surface charge amount converted to 1 g of hollow silica particle was 24 μeq / g, the particle refractive index was 1.3, and the shell thickness was 5 nm.

[0102] (Synthesis Example 5) Preparation of Water-Dispersed Sol (A5) of Aluminum Atom-Containing Hollow Silica Particles 1856 g of water-dispersed hollow silica sol HKT-A20-40D (Ningbo Dilato Co., Ltd., product name) was placed in a 3-L plastic container. 32.2 g of sodium aluminate solution diluted to 1.0% by mass (Al2O3 equivalent) was added dropwise over 1 minute while stirring at 650 rpm with a mechanical stirrer equipped with a glass impeller. The mixture was then stirred at the same speed for 30 minutes. Next, 1888 g of this mixture was placed in a 3-L stainless steel autoclave and heated at 150°C for 5 hours while stirring at 80 rpm. The mixture was then cooled to below 50°C. 4.4 g of 8.2% sulfuric acid solution was then added dropwise to the resulting 1888 g of heat-treated water-dispersed sol. The mixture was then stirred at 25°C for 1 hour to obtain a sulfuric acid-added heat-treated water-dispersed sol. The obtained sulfuric acid-added heat-treated water-dispersed sol was then passed through a 200 mL column of cation exchange resin (H-type Amberlite (trade name) IR-120B, harmonic mean diameter 0.6 to 0.8 mm, Organo Corporation) at a space velocity (SV) of 5 / hour to obtain a water-dispersed sol of aluminum atom-containing hollow silica particles. The resulting water-dispersed sol was then heat-treated at 100°C for 5 hours, and then cooled to 30°C or below. After that, the liquid was passed through a column-packed cation exchange resin (H-type Amberlite (trade name) IR-120B) at a space velocity (SV) of 5 / hour to obtain a water-dispersed sol of aluminum atom-containing hollow silica particles. The resulting water-dispersed sol had a pH of 2.4, a silica particle concentration of 13.1% by mass, and an average particle size measured by DLS of 55 nm. The obtained water-dispersed sol was then placed in a stirring type ultra holder UHP-150K (manufactured by Advantec Co., Ltd.) equipped with a 150 mm diameter, 200,000 fractionation ultra filter (manufactured by Advantec Co., Ltd.), and then filtered while applying a nitrogen pressure of 0.2 MPa until the silica particle concentration reached 20 mass %, thereby obtaining a water-dispersed sol of hollow silica particles (A5). The pH of the obtained water-dispersed sol (A5) was 2.4, the amount of sulfuric acid in the system was 115 ppm / sol, the silica particle concentration was 20.4 mass%, the average particle diameter by DLS method was 55 nm, and the specific surface area by BET method was 125 m 2 / g, the amount of aluminum atoms present in the entire hollow silica particle was 611 ppm / SiO2 in terms of Al2O3, the surface charge amount converted to 1 g of hollow silica particle was 24 μeq / g, the particle refractive index was 1.3, and the shell thickness was 5 nm.

[0103] (Synthesis Example 6) Preparation of Water-Dispersed Sol (LA1) of Aluminum-Containing Hollow Silica Particles by Long-Term Storage of Water-Dispersed Sol (A1) of Aluminum-Containing Hollow Silica Particles The water-dispersed sol (A1) of aluminum-atom-containing hollow silica particles obtained in Synthesis Example 1 was stored at 23°C for 2 months to obtain a water-dispersed sol (LA1) of aluminum-atom-containing hollow silica particles stored for a long period of time. The tetrahedral Al ratio was 0.46.

[0104] (Synthesis Example 7) Preparation of Water-Dispersed Sol of Aluminum-Containing Hollow Silica Particles (LA2) by Long-Term Storage of Water-Dispersed Sol of Aluminum-Containing Hollow Silica Particles (A2) The water-dispersed sol (A2) of aluminum-atom-containing hollow silica particles obtained in Synthesis Example 2 was stored at 23°C for 2 months to obtain a water-dispersed sol (LA2) of aluminum-atom-containing hollow silica particles stored for a long period of time. The tetrahedral Al ratio was 0.67.

[0105] (Synthesis Example 8) Preparation of Water-Dispersed Sol of Aluminum-Containing Hollow Silica Particles (LA3) by Long-Term Storage of Water-Dispersed Sol of Aluminum-Containing Hollow Silica Particles (A3) The water-dispersed sol (A3) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 3 was stored at 23°C for 2 months to obtain a water-dispersed sol (LA3) of aluminum atom-containing hollow silica particles stored for a long period of time. The tetrahedral Al ratio was 0.62.

[0106] (Synthesis Example 9) Preparation of Water-Dispersed Sol of Aluminum-Containing Hollow Silica Particles (LA4) by Long-Term Storage of Water-Dispersed Sol of Aluminum-Containing Hollow Silica Particles (A4) The water-dispersed sol (A4) of aluminum-atom-containing hollow silica particles obtained in Synthesis Example 4 was stored at 23°C for 3 months to obtain a water-dispersed sol (LA4) of aluminum-atom-containing hollow silica particles stored for a long period of time. The tetrahedral Al ratio was 0.47.

[0107] (Synthesis Example 10) Preparation of Water-Dispersed Sol of Aluminum-Containing Hollow Silica Particles (LA5) by Long-Term Storage of Water-Dispersed Sol of Aluminum-Containing Hollow Silica Particles (A5) The water-dispersed sol (A5) of aluminum-atom-containing hollow silica particles obtained in Synthesis Example 5 was stored at 23°C for 5 months to obtain a water-dispersed sol (LA5) of aluminum-atom-containing hollow silica particles stored for a long period of time. The tetrahedral Al ratio was 0.56.

[0108] (Synthesis Example 11) Preparation of MeOH Dispersion Sol (Me1) of Aluminum Atom-Containing Hollow Silica Particles In a 200 mL recovery flask, aluminum atom-containing hollow silica particles obtained in Synthesis Example 1 were 80 g of the water-dispersed sol (A1) was placed in the container. The pressure was reduced to 580 Torr using a rotary evaporator, and the solvent was replaced with methanol (MeOH) while the container was heated to 120°C. Methanol was then added to adjust the concentration, yielding a 20 mass% MeOH-dispersed sol (Me1) of aluminum atom-containing hollow silica particles. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.1, average particle diameter by DLS method 72 nm, and moisture content 1.2 mass %.

[0109] (Synthesis Example 12) Preparation of MeOH Dispersion Sol (Me2) of Aluminum Atom-Containing Hollow Silica Particles A 20 mass% MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles was obtained by the same method as in Synthesis Example 11, except that the water dispersion sol (A2) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 2 was used as the target for solvent substitution. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.3, average particle diameter by DLS method 74 nm, and moisture content 1.3 mass %.

[0110] (Synthesis Example 13) Preparation of MeOH Dispersion Sol (Me3) of Aluminum Atom-Containing Hollow Silica Particles A 20 mass% MeOH dispersion sol (Me3) of aluminum atom-containing hollow silica particles was obtained by the same method as in Synthesis Example 11, except that the water dispersion sol (A3) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 3 was used as the target for solvent substitution. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.2, average particle diameter by DLS method 71 nm, and moisture content 1.0 mass %.

[0111] (Synthesis Example 14) Preparation of MeOH Dispersion Sol (Me4) of Aluminum Atom-Containing Hollow Silica Particles A 200 mL recovery flask was charged with 118.3 g of the aqueous dispersion sol (A4) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 4, and 15.0 g of methanol was added. The pressure was reduced to 580 Torr using a rotary evaporator, and the solvent was replaced with methanol while heating to 120°C. Methanol was then added to adjust the concentration, yielding a 20.2 mass % MeOH dispersion sol (Me4) of aluminum atom-containing hollow silica particles. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.6, average particle diameter by DLS method 70 nm, and moisture content 1.0 mass %.

[0112] (Synthesis Example 15) Preparation of MeOH Dispersion Sol (LMe1) of Aluminum Atom-Containing Hollow Silica Particles A 20 mass% MeOH dispersion sol (LMe1) of aluminum atom-containing hollow silica particles was obtained by the same method as in Synthesis Example 11, except that the water dispersion sol (LA1) of aluminum atom-containing hollow silica particles that had been stored for a long period of time obtained in Synthesis Example 6 was used as the target for solvent replacement. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.4, average particle diameter by DLS method 71 nm, and moisture content 1.1 mass %.

[0113] (Synthesis Example 16) Preparation of MeOH Dispersion Sol (LMe2) of Aluminum Atom-Containing Hollow Silica Particles The same method as in Synthesis Example 11 was carried out, except that the water-dispersed sol (LA2) of aluminum atom-containing hollow silica particles that had been stored for a long period of time, obtained in Synthesis Example 7, was used as the target for solvent replacement. A 20% by mass MeOH dispersion sol (LMe2) of hollow silica particles containing nium atoms was obtained. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.7, average particle diameter by DLS method 76 nm, and moisture content 1.2 mass %.

[0114] (Synthesis Example 17) Preparation of MeOH Dispersion Sol (LMe3) of Aluminum Atom-Containing Hollow Silica Particles A 20 mass% MeOH dispersion sol of aluminum atom-containing hollow silica particles (LMe3) was obtained by the same method as in Synthesis Example 11, except that the water dispersion sol (LA3) of aluminum atom-containing hollow silica particles that had been stored for a long period of time obtained in Synthesis Example 8 was used as the target for solvent replacement. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.4, average particle diameter by DLS method 74 nm, and moisture content 1.0 mass %.

[0115] (Synthesis Example 18) Preparation of MeOH Dispersion Sol (LMe4) of Aluminum Atom-Containing Hollow Silica Particles A 20 mass% MeOH dispersion sol of aluminum atom-containing hollow silica particles (LMe4) was obtained by the same method as in Synthesis Example 14, except that the water dispersion sol (LA4) of aluminum atom-containing hollow silica particles that had been stored for a long period of time obtained in Synthesis Example 9 was used as the target for solvent replacement. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.7, average particle diameter by DLS method 64 nm, and moisture content 1.0 mass %.

[0116] (Synthesis Example 19) Preparation of MeOH Dispersion Sol (LMe5) of Aluminum Atom-Containing Hollow Silica Particles A 20 mass% MeOH dispersion sol (LMe5) of aluminum atom-containing hollow silica particles was obtained by the same method as in Synthesis Example 11, except that the water dispersion sol (LA5) of aluminum atom-containing hollow silica particles that had been stored for a long period of time obtained in Synthesis Example 10 was used as the target for solvent replacement. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 3.4, average particle diameter by DLS method 74 nm, and moisture content 0.5 mass %.

[0117] (Synthesis Example 20) Preparation of PGME Dispersion Sol (P1) of Aluminum Atom-Containing Hollow Silica Particles 50 g of the aqueous dispersion sol (A2) of hollow silica particles obtained in Synthesis Example 2 was placed in a 100 mL eggplant-shaped flask and set in a rotary evaporator. Distillation was carried out while supplying PGME at a bath temperature of 85°C under reduced pressure of 350 to 100 Torr, and the dispersion medium was replaced with PGME to obtain a PGME-dispersed sol (P1) of aluminum atom-containing hollow silica particles. The physical properties of the obtained sol were an average particle size of 57 nm measured by DLS, pH 3.8, viscosity 3.0 mPa s, silica particle concentration 19.7 mass%, and water content 0.4 mass%. The obtained sol had no sediment and showed good dispersibility (dispersed in the dispersion medium without cloudiness or aggregation; the same applies hereinafter).

[0118] (Synthesis Example 21) Preparation of PGME dispersion sol of hollow silica particles (O1) by coating PGME dispersion sol of aluminum atom-containing hollow silica particles (P1) with a silane compound 50 g of the PGME-dispersed sol (P1) of hollow silica particles obtained in Synthesis Example 20 was placed in a 100 mL eggplant-shaped flask, and while stirring with a magnetic stirrer, 0.7 g of pure water and 15.0 g of PGME were added to adjust the concentration to 15.0 mass %. 0.47 g of MPS was then added, and the mixture was heated to 70°C and maintained for 5 hours to obtain a PGME-dispersed sol (O1) of aluminum-atom-containing hollow silica particles whose surfaces were coated with a silane compound (MPS). The physical properties of the obtained sol were as follows: average primary particle diameter by TEM: 40 nm; average by DLS method: The particle size was 58 nm, pH 4.4, viscosity 3.0 mPa·s, silica particle concentration 14.9 mass%, and water content 1.2 mass%. The obtained sol was free of sediment and showed good dispersibility.

[0119] (Synthesis Example 22) Preparation of MeOH dispersion sol (O2) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 50 g of the MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 12 was placed in a 100 mL eggplant-shaped flask, and while stirring with a magnetic stirrer, MeOH was added to adjust the concentration to 15.5 mass %. Then, 0.46 g of AcPS was added, and the mixture was heated to 60 °C and maintained for 5 hours to obtain a MeOH dispersion sol (O2) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (AcPS). The physical properties of the obtained sol were: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 78 nm, pH: 4.0, viscosity: 0.9 mPa·s, silica particle concentration: 15.8 mass%, water content: 1.0 mass%, silanol group density: 1.2 / nm 2 The obtained sol was free of sediment and showed good dispersibility.

[0120] (Synthesis Example 23) Preparation of MeOH dispersion sol (O3) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 30 g of the MeOH dispersion sol (O2) of hollow silica particles coated with a silane compound obtained in Synthesis Example 22 was placed in a 100 mL eggplant-shaped flask and set in a rotary evaporator. The pressure was then reduced to 550-350 Torr, and the solvent methanol (MeOH) was distilled off while the flask was heated to 70°C, resulting in a silica particle concentration of 30 mass %. This yielded a MeOH dispersion sol (O3) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (AcPS). The physical properties of the obtained sol were: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 74 nm, pH: 3.3, viscosity: 2.4 mPa·s, silica particle concentration: 31.3 mass%, water content: 1.8 mass%, silanol group density: 1.2 / nm 2 The obtained sol was free of sediment and showed good dispersibility.

[0121] (Synthesis Example 24) Preparation of MeOH dispersion sol (O4) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 50 g of the MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 12 was added to a 500 mL eggplant-shaped flask. While stirring with a magnetic stirrer, 1.0 g of pure water, 7.5 g of MEK, and 3.7 g of DMDMS were added, and the mixture was heated to 60°C and maintained for 3 hours. Next, 3.8 g of HMDS was added, and the mixture was heated to 60°C and maintained for 3 hours. DiPA was then added to adjust the pH to 8.0-10.0, and the mixture was heated to 60°C and maintained for 1 hour to obtain a MeOH dispersion sol (O4) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (DMDMS + HMDS). The physical properties of the obtained sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 73 nm, pH: 8.9, viscosity: 1.0 mPa s, silica particle concentration: 16.9 mass%, water content: 2.7 mass%. The obtained sol showed good dispersibility with no sediment.

[0122] (Synthesis Example 25) Preparation of CPN dispersion sol (O5) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 89.4 g of the MeOH sol (O4) of hollow silica particles coated with a silane compound obtained in Synthesis Example 24 was placed in a 200 mL eggplant-shaped flask and set in a rotary evaporator. Distillation was carried out while supplying CPN at a bath temperature of 80°C and a reduced pressure of 30 to 100 Torr, and the dispersion medium was replaced with CPN to obtain a CPN dispersion sol (O5) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (DMDMS + HMDS). The physical properties of the obtained sol were: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 56 nm, pH: 5.1, silica particle concentration: 30.6 mass%, water content: 1.2 mass%, M The amount of eOH was less than 0.1% by mass. The obtained sol was free of sediment and showed good dispersibility.

[0123] (Synthesis Example 26) Preparation of MEK dispersion sol (O6) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound Step A: 50 g of the MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 12 was placed in a 1-L recovery flask. The solvent, methanol (MeOH), was then removed using a rotary evaporator under reduced pressure of 580 Torr and heated to 120°C, resulting in a silica particle concentration of 30% by mass. The physical properties of the resulting sol were: average particle size (measured by DLS) of 72 nm, pH 3.1, viscosity of 1.8 mPa·s, water content of 1.7% by mass, and silica particle concentration of 30.3% by mass. The resulting sol exhibited good dispersibility with no sediment. Step B: 30 g of the MeOH sol containing 30% by weight of silica particles obtained in Step A was added to a 100 mL eggplant-shaped flask. While stirring with a magnetic stirrer, 0.47 g of purified water, 4.5 g of MEK, and 0.43 g of MPMDMS were added, and the mixture was heated to 60°C and maintained for 3 hours. Next, 0.5 g of HMDS was added, and the mixture was heated to 60°C and maintained for 3 hours. DiPA was then added to adjust the pH to 8.0-10.0, and the mixture was heated to 60°C and maintained for 1 hour to obtain an MeOH sol of aluminum-containing hollow silica particles coated with a silane compound (MPMDMS + HMDS). The mixture was then placed in a rotary evaporator, and distilled under a bath temperature of 80°C and a reduced pressure of 550-400 Torr while feeding MEK. The dispersion medium was replaced with MEK, yielding an MEK-dispersed sol (O6) of aluminum-containing hollow silica particles coated with a silane compound (MPMDMS + HMDS). The physical properties of the obtained sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 64 nm, pH 6.7, viscosity 2.9 mPa s, silica particle concentration 31.2 mass%, water content 0.2 mass%, MeOH content 0.2 mass%. The obtained sol showed good dispersibility with no sediment.

[0124] (Synthesis Example 27) Preparation of MEK dispersion sol (O7) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 30 g of the 30 mass % MeOH sol of aluminum atom-containing hollow silica particles obtained in Step A of Synthesis Example 26 was added to a 100 mL recovery flask, and while stirring with a magnetic stirrer, 0.50 g of pure water and 0.48 g of PTMS were added, heated to 60°C, and maintained for 2 hours. DiPEA was then added so that the pH was 7.5 to 8.5, and the mixture was heated to 60°C and maintained for 2 hours. 0.25 g of PTMS was then added, heated to 60°C, and maintained for 2 hours. The eggplant-shaped flask containing the obtained sol was placed in a rotary evaporator, and distillation was carried out while supplying MEK at a bath temperature of 80°C and a reduced pressure of 550 to 350 Torr. By replacing the dispersion medium with MEK, an MEK-dispersed sol (O7) of aluminum-atom-containing hollow silica particles whose surfaces were coated with a silane compound (PTMS) was obtained. The physical properties of the obtained sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 70 nm, pH 5.4, viscosity 1.8 mPa s, silica particle concentration 30.9 mass%, water content less than 0.1 mass%, MeOH content less than 0.1 mass%. The obtained sol had no sediment and showed good dispersibility.

[0125] (Synthesis Example 28) Preparation of MeOH dispersion sol (O8) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 30 g of the 30 mass % MeOH sol of aluminum atom-containing hollow silica particles obtained in Step A of Synthesis Example 26 was added to a 100 mL recovery flask, and 0.37 g of TMPSA was added while stirring with a magnetic stirrer. The mixture was heated to 60°C and maintained for 3 hours. Thereafter, the pressure was reduced to 580 Torr in a rotary evaporator, and the mixture was heated to 120°C. The solvent methanol (MeOH) was distilled off and the silica particle concentration was concentrated to 30 mass %, to obtain an MeOH dispersion sol (O8) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (TMPSA). The physical properties of the obtained sol were: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 77 nm, pH: 3.2, viscosity: 3.4 mPa·s, silica particle concentration: 31.6 mass%, water content: 3.2 mass%, silanol group density: 2.0 / nm 2 The obtained sol was free of sediment and showed good dispersibility.

[0126] (Synthesis Example 29) Preparation of MEK dispersion sol (O9) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 30g (460g) of the 30% by mass MeOH sol of aluminum-atom-containing hollow silica particles obtained in Step A of Synthesis Example 26 was added to a 1-L recovery flask, and while stirring with a magnetic stirrer, 0.5g of pure water, 4.5g of MEK, and 0.99g of HMDS were added, and the mixture was heated to 60°C and maintained for 3 hours. The recovery flask containing the resulting sol was placed in a rotary evaporator, and distillation was carried out while supplying MEK at a bath temperature of 80°C and a reduced pressure of 550 to 350 Torr. The dispersion medium was replaced with MEK, yielding an MEK-dispersed sol (O9) of aluminum-atom-containing hollow silica particles whose surfaces were coated with a silane compound (HMDS). The physical properties of the obtained sol were as follows: average particle size by DLS: 71 nm, pH: 3.5, viscosity: 1.7 mPa·s, silica particle concentration: 31.7 mass%, silanol group density: 1.3 particles / nm 2 The water content was 0.1% by mass, and the MeOH content was 0.2% by mass. The obtained sol had no sediment and showed good dispersibility.

[0127] (Synthesis Example 30) Preparation of MeOH dispersion sol (O10) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 30 g of the 30 mass % MeOH sol of aluminum atom-containing hollow silica particles obtained in Step A of Synthesis Example 26 was added to a 100 mL eggplant-shaped flask, and while stirring with a magnetic stirrer, 0.37 g of AAPS was added, and the mixture was heated to 60 ° C and maintained for 3 hours. Thereafter, the pressure was reduced to 580 Torr in a rotary evaporator, and the solvent methanol (MeOH) was distilled off while heating to 120 ° C., and the silica particle concentration was concentrated to 30 mass %, yielding a MeOH dispersion sol (O10) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (AAPS). The physical properties of the obtained sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 76 nm, pH: 3.4, viscosity: 2.5 mPa·s, silica particle concentration: 31.2 mass%, water content: 1.3 mass%. The obtained sol showed good dispersibility with no sediment.

[0128] (Synthesis Example 31) Preparation of MeOH dispersion sol (O11) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 30 g of the 30 mass % MeOH sol of aluminum atom-containing hollow silica particles obtained in Step A of Synthesis Example 26 was added to a 500 mL eggplant-shaped flask, and while stirring with a magnetic stirrer, 0.17 g of MTMS was added, and the mixture was heated to 60°C and maintained for 3 hours. The mixture was then reduced in pressure to 580 Torr in a rotary evaporator, heated to 120°C, and the MeOH solvent was distilled off, concentrating the mixture to a silica particle concentration of 30 mass %, yielding an MeOH dispersion sol (O11) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (MTMS). The physical properties of the obtained sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 74 nm, pH: 3.4, viscosity: 2.1 mPa s, silica particle concentration: 31.4 mass%, water content: 1.3 mass%. The obtained sol showed good dispersibility with no sediment.

[0129] (Synthesis Example 32) Preparation of PGME dispersion sol of hollow silica particles (O12) by coating PGME dispersion sol of aluminum atom-containing hollow silica particles (P1) with a silane compound 30 g of the PGME-dispersed sol of hollow silica particles (P1) obtained in Synthesis Example 20 was placed in a 100 mL eggplant-shaped flask, and while stirring with a magnetic stirrer, 0.4 g of pure water and 9 g of PGME were added to adjust the concentration to 15.0 mass %. 0.27 g of AcPS was then added, and the mixture was heated to 70°C and maintained for 5 hours to obtain a PGME-dispersed sol (O12) of aluminum-atom-containing hollow silica particles whose surfaces were coated with a silane compound (AcPS). The physical properties of the obtained sol were an average primary particle diameter of 40 nm by TEM, an average particle diameter of 59 nm by DLS, a pH of 3.6, a silica particle concentration of 15.0% by mass, and a water content of 1.1% by mass. The obtained sol was free of sediment and showed good dispersibility.

[0130] (Synthesis Example 33) Preparation of Water-Dispersed Sol (A6) of Aluminum Atom-Containing Hollow Silica Particles 1745 g of water-dispersed hollow silica sol HKT-A20-40D (Ningbo Dilato Co., Ltd., product name) was placed in a 3-L plastic container. 30 g of sodium aluminate solution diluted to 1.0% by mass (Al2O3 equivalent) was added dropwise over 1 minute while stirring at 650 rpm using a mechanical stirrer equipped with a glass impeller. The mixture was then stirred at the same speed for 30 minutes. 725 g of purified water was then added and stirred for an additional 20 minutes to obtain a mixture. Next, 2320 g of this mixture was placed in a 3-L stainless steel autoclave and heated at 150°C for 5 hours while stirring at 80 rpm. The mixture was then cooled to below 50°C. 0.03 g of 8.2% sulfuric acid solution was added dropwise to 500 g of the heated water-dispersed sol, and the mixture was stirred at 25°C for 1 hour to obtain a water-dispersed sol of aluminum-atom-containing hollow silica particles (A6). The pH of the obtained water-dispersed sol (A6) was 9.9, and the amount of sulfuric acid in the system was 2 ppm / sol. 2 / g, silica particle concentration 13.8 mass%, viscosity 1.7 mPa·s, average particle size by DLS method 50 nm, tetrahedral Al ratio 1.0, amount of aluminum atoms present in the whole hollow silica particle converted to Al2O3 688 ppm / SiO2, amount of surface charge converted to 1 g of hollow silica particle 142 μeq / g, and thickness of outer shell 5 nm.

[0131] (Synthesis Example 34) Preparation of Water-Dispersed Sol (A7) of Aluminum Atom-Containing Hollow Silica Particles A water-dispersed sol (A7) of aluminum atom-containing hollow silica particles was obtained in the same manner as in Synthesis Example 33, except that 0.2 g of 8.2% sulfuric acid aqueous solution was added to 33 g of the heat-treated water-dispersed sol, and then 117 g of pure water was added. The pH of the obtained water-dispersed sol (A7) was 9.4, and the amount of sulfuric acid in the system was 138 ppm / sol. 2 / g, silica particle concentration 3.1 mass%, viscosity 1.0 mPa·s, average particle size by DLS method 50 nm, tetrahedral Al ratio 1.0, the amount of aluminum atoms present in the entire hollow silica particle converted to Al2O3 was 688 ppm / SiO2, the surface charge converted to 1 g of hollow silica particle was 126 μeq / g, and the shell thickness was 5 nm.

[0132] (Synthesis Example 35) Preparation of MeOH Dispersion Sol (Me6) of Aluminum Atom-Containing Hollow Silica Particles 350 g of the aqueous dispersion sol (A6) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 33 was placed in a 200 mL recovery flask. The pressure was reduced to 580 Torr using a rotary evaporator, and the solvent was replaced with methanol (MeOH) while the mixture was heated to 120°C. Methanol was then added to adjust the concentration, yielding a 15 mass % MeOH dispersion sol (Me6) of aluminum atom-containing hollow silica particles. The physical properties of the obtained sol were a specific surface area of ​​125 m2 by BET method. 2 / g, particle refractive index 1.3, shell thickness 5 nm, pH 7.1, average particle diameter by DLS method 77 nm, and moisture content 0.9 mass %.

[0133] (Synthesis Example 36) Preparation of MeOH dispersion sol (O13) of hollow silica particles by coating MeOH dispersion sol (Me6) of aluminum atom-containing hollow silica particles with a silane compound 120 g of the MeOH dispersion sol (Me6) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 35 was added to a 500 mL eggplant-shaped flask. While stirring with a magnetic stirrer, 1.5 g of pure water and 1.0 g of DMMPS were added, and the mixture was heated to 60°C and maintained for 3 hours. Next, 1.2 g of DMEVS was added, and the mixture was heated to 60°C and maintained for 3 hours. DiEPA was then added to adjust the pH to 8.0-10.0, and the mixture was heated to 60°C and maintained for 1 hour to obtain a MeOH dispersion sol (O13) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (DMMPS + DMEVS). The physical properties of the obtained sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 72 nm, pH: 10.0, viscosity: 1.0 mPa s, silica particle concentration: 14.3 mass%, water content: 2.1 mass%. The obtained sol showed good dispersibility with no sediment.

[0134] (Synthesis Example 37) Preparation of PGMEA dispersion sol (O14) of hollow silica particles obtained by coating aluminum atom-containing hollow silica particles (Me6) in MeOH with a silane compound 20 g of the MeOH sol (O13) of hollow silica particles coated with a silane compound obtained in Synthesis Example 36 was placed in a 200 mL eggplant-shaped flask and set in a rotary evaporator. Distillation was carried out while supplying PGMEA at a bath temperature of 80°C and a reduced pressure of 100 Torr, and the dispersion medium was replaced with PGMEA, thereby obtaining a PGMEA-dispersed sol (O14) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (DMMPS+DMEVS). The physical properties of the obtained sol were an average primary particle diameter of 40 nm by TEM, an average particle diameter of 107 nm by DLS, pH 7.9, silica particle concentration of 17.8 mass%, water content of 1.0 mass%, and MeOH content of 3.3 mass%. The obtained sol was free of sediment and showed good dispersibility.

[0135] (Synthesis Example 38) Preparation of an MIBK dispersion sol (O15) of hollow silica particles obtained by coating an MeOH dispersion sol (Me6) of aluminum atom-containing hollow silica particles with a silane compound 20 g of the MeOH sol (O13) of hollow silica particles coated with a silane compound obtained in Synthesis Example 36 was placed in a 200 mL eggplant-shaped flask and set in a rotary evaporator. Distillation was performed while supplying MIBK at a bath temperature of 80°C and a reduced pressure of 100 Torr, and the dispersion medium was replaced with MIBK to obtain an MIBK dispersion sol (O15) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (DMMPS+DMEVS). The physical properties of the obtained sol were an average primary particle diameter of 40 nm by TEM, an average particle diameter of 73 nm by DLS, pH 8.4, silica particle concentration of 16 mass%, water content 1.0 mass%, and MeOH content less than 0.1 mass%. The obtained sol was free of sediment and showed good dispersibility.

[0136] (Synthesis Example 39) Preparation of MeOH Dispersion Sol (O16) of Aluminum Atom-Containing Hollow Silica Particles 80 g of the aqueous dispersion sol (A7) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 34 was placed in a 200 mL recovery flask. The pressure was reduced to 580 Torr using a rotary evaporator, and the solvent was replaced with methanol (MeOH) while the mixture was heated to 120°C. Methanol was then added to adjust the concentration, yielding a 20 mass % MeOH dispersion sol (O16) of aluminum atom-containing hollow silica particles. The physical properties of the obtained sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 70 nm, pH: 3.7, viscosity: 0.6 mPa s, silica particle concentration: 2.9 mass%, water content: 1.0 mass%. The obtained sol showed good dispersibility with no sediment.

[0137] (Synthesis Example 40) Preparation of EL dispersion sol (O17) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound 200 g of the MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles obtained in Synthesis Example 12 was added to a 500 mL eggplant-shaped flask, and 0.78 g of MPS was added while stirring with a magnetic stirrer. The mixture was heated to 60°C and maintained at this temperature for 5 hours. Then, a 100 mL eggplant-shaped flask containing 60 g of the obtained MeOH dispersion sol of hollow silica particles coated with the silane compound was placed in a rotary evaporator, and distillation was performed while supplying EL at a bath temperature of 90°C and a reduced pressure of 500 to 80 Torr. By replacing the dispersion medium with EL, an EL dispersion sol (O17) of aluminum atom-containing hollow silica particles whose surfaces were coated with the silane compound (MPS) was obtained. The physical properties of the obtained EL dispersion sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 60 nm, pH: 2.7, viscosity: 5.3 mPa·s, silica particle concentration: 14.8 mass%, water content: 0.1 mass%, and MeOH content: less than 0.1 mass%.

[0138] (Synthesis Example 41) Preparation of EL dispersion sol (O18) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound An EL dispersion sol (O18) of aluminum atom-containing hollow silica particles surface-coated with a silane compound (TMPSA) was obtained in the same manner as in Synthesis Example 40, except that 1.39 g of TMPSA was added instead of 0.78 g of MPS in Synthesis Example 40. The physical properties of the obtained EL dispersion sol were as follows: average primary particle diameter by TEM: 40 nm, average particle diameter by DLS method: 60 nm, pH: 2.7, viscosity: 5.5 mPa·s, silica particle concentration: 15.6 mass%, water content: 0.1 mass%, and MeOH content: less than 0.1 mass%.

[0139] (Synthesis Example 42) Preparation of HBM dispersion sol (O19) of hollow silica particles by coating MeOH dispersion sol (Me2) of aluminum atom-containing hollow silica particles with a silane compound A 100 mL eggplant-shaped flask containing 30 g of the MEK dispersion sol (O6) obtained in Synthesis Example 26 was placed in a rotary evaporator, and distillation was performed while supplying HBM at a bath temperature of 90°C and a reduced pressure of 400 to 100 Torr. By replacing the dispersion medium with HBM, an HBM dispersion sol (O19) of aluminum atom-containing hollow silica particles whose surfaces were coated with a silane compound (MPMDMS+HMDS) was obtained. The physical properties of the obtained HBM dispersion sol were an average primary particle diameter of 40 nm by TEM, an average particle diameter of 73 nm by DLS, pH 6.7, silica particle concentration of 36.8 mass%, water content less than 0.1 mass%, and MeOH content less than 0.1 mass%.

[0140] Examples 1 to 7 and Comparative Examples 1 and 2: Storage stability results of MeOH dispersion sol The MeOH dispersion sols prepared in Synthesis Examples 11 to 19 were stored at 50°C for 1 week and 4 weeks, and the change in average particle size (%, absolute value) was calculated using the following formula from the results of measuring the average particle size by DLS before and after storage. The results are also shown in Table 1. DLS change rate (%, absolute value) = 100 × [(DLS average particle size after storage at 50°C - DLS average particle size before storage at 50°C) / DLS average particle size before storage at 50°C] The storage stability was evaluated based on the obtained DLS change rate using the following criteria: A indicates the best storage stability, B indicates somewhat good, and C indicates poor storage stability. The results are also shown in Table 1. <Storage stability evaluation> A: DLS change rate: Absolute value: 0% or more and less than 6% B: DLS change rate: Absolute value: 6% or more and less than 30% C: DLS change rate: 30% or more as absolute value

[0141] [Table 1]

[0142] As shown in Table 1, the water-dispersed sols with an in-system sulfuric acid content (amount of sulfuric acid in the sol) of 150 ppm / sol or less and a tetrahedral Al ratio of 0.45 or more showed DLS changes of 5% or less before and after storage at 50°C for 1 week and 4 weeks in the organic solvent-dispersed sols (MeOH-dispersed sols), indicating good storage stability. On the other hand, for water-dispersed sols with an in-system sulfuric acid content (amount of sulfuric acid in the sol) of 200 ppm / sol or more, even though the tetrahedral Al ratio was a low value of around 0.45, the DLS change rate in the organic solvent-dispersed sol exceeded 100% after storage at 50°C for one week, resulting in a lack of storage stability.

[0143] Examples 8 to 25: Storage stability results of organic solvent dispersion sol The organic solvent dispersion sols prepared in Synthesis Examples 21 to 32 and Synthesis Examples 37 to 42 The samples were stored at 50°C for one week. From the results of measuring the average particle size by DLS before and after storage, the rate of change in average particle size (%, absolute value) was calculated using the formula for determining the [DLS rate of change] shown in the above [Storage stability results of MeOH dispersion sol]. In addition, the storage stability was evaluated from the obtained DLS rate of change according to the above <Storage stability evaluation>. The obtained results are shown in Table 2 (Table 2-1, Table 2-2). As shown in Table 2 (Table 2-1, Table 2-2), all of the organic solvent-dispersed sols obtained in Synthesis Examples 21 to 32 and Synthesis Examples 37 to 42 had DLS change rates of 0% or more and less than 6% as absolute values, demonstrating good dispersion stability.

[0144] [Table 2-1]

[0145] [Table 2-2]

Claims

[Claim 1] An aluminum atom-containing hollow silica sol containing aluminum atom-containing hollow silica particles, The hollow silica sol is ２７ In the Al-NMR measurement, the total integral value of the peaks showing tetracoordinated aluminum atoms (α ０ ) and the total integral value of the peaks representing aluminum atoms other than tetrahedral ones (β ０ ) the total integral value (α ０ ) ratio [(α ０ ) / {(α ０ ) + (β ０ )}] is 0.50 to 1.0, Hollow silica sol.

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