JP2014055083A - Method for producing hollow silica particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing hollow silica particles, which is capable of stably producing hollow silica particles even in the case when the silica concentration converted from a silica source in a reaction liquid is high.SOLUTION: The method for producing hollow silica particles comprises: a step of forming an aqueous dispersion of emulsified oil droplets containing a hydrophobic organic compound by applying supersonic vibration to a mixed liquid containing the hydrophobic organic compound, a polyvinyl alcohol, and an aqueous solvent; a step of forming an outer shell part constituted of a component containing silica and having a mesoporous structure, on the surface of each emulsified oil droplet, in a reaction liquid obtained by mixing the aqueous dispersion of the emulsified oil droplets and a silica source in the presence of a cationic surfactant; and a step of removing the emulsified oil drops from composite silica particles each including the outer shell part and the emulsified oil droplet existing on the inner side of the outer shell part.

Description

  The present invention relates to a method for producing hollow silica particles.

  In recent years, silica-containing outer shell portions and silica particles having cavities inside the outer shell portions (hereinafter also referred to as “hollow portions”) (hereinafter also referred to as “hollow silica particles”) have attracted attention as inorganic particles. Has been. In particular, hollow silica particles whose outer shell portion has a mesoporous structure having pores with a pore diameter of several nm (hereinafter also referred to as “hollow mesoporous silica particles”) have a large porosity and specific surface area. Therefore, various applications such as a low dielectric constant material, a low refractive index material, a separating material, an adsorbing material, a catalyst carrier, an enzyme carrier, a sustained release material, and a drug delivery (DDS) carrier can be expected.

  Non-Patent Document 1 discloses a method for producing hollow mesoporous silica particles using ultrasonic irradiation. Patent Document 2 discloses a method for producing hollow mesoporous silica particles having a mesoporous structure using emulsion oil droplets obtained by stirring a hydrophobic organic substance such as rapeseed oil or squalene in an aqueous medium. Patent Document 3 discloses a method for producing hollow mesoporous silica particles using emulsified oil droplets obtained by adding an aqueous solvent to a solution containing a hydrophobic organic substance such as rapeseed oil, hexane, or dodecane.

Rohit K. Rana et al., Advanced Materials, Vol. 14, p1414 (2002) JP 2008-150229 A JP 2011-126761 A

However, in any production method, the silica (SiO ₂ ) concentration converted from the silica source used for the preparation of the reaction liquid containing the emulsified oil droplets and the silica source is about 0.2 wt% (33 mmol / L). Therefore, the productivity of hollow mesoporous silica particles is low. Increasing the silica concentration in the reaction solution to improve productivity deteriorates the stability of the emulsified oil droplets over time, and the emulsified oil droplets coalesce to form an oil layer separation, stably producing hollow mesoporous silica particles. Difficult to do. This is a problem common to the production of hollow silica particles whose outer shell portion does not have a mesoporous structure.

  This invention provides the manufacturing method of the hollow silica particle which can manufacture a hollow silica particle stably, even if the silica concentration converted from the silica source in a reaction liquid is high.

The method for producing the hollow silica particles of the present invention comprises:
Providing an ultrasonic vibration to a mixed liquid containing a hydrophobic organic compound, polyvinyl alcohol and an aqueous solvent to form an emulsified oil droplet aqueous dispersion containing emulsified oil droplets containing the hydrophobic organic compound;
In the reaction liquid obtained by mixing the emulsified oil droplet water dispersion and the silica source in the presence of a cationic surfactant, the emulsified oil droplet surface has a mesoporous structure composed of components containing silica. Forming the outer shell,
Removing the emulsified oil droplets from the composite silica particles including the outer shell portion and the emulsified oil droplets present inside the outer shell portion.

  According to the method for producing hollow silica particles of the present invention, the hollow silica particles can be produced stably even if the silica concentration calculated from the silica source in the reaction solution is high. Therefore, according to the method for producing hollow silica particles of the present invention, the productivity of hollow silica particles can be increased.

1 is a TEM image of hollow mesoporous silica particles of Example 1. FIG. FIG. 2 is a TEM image of the silica particles of Comparative Example 1.

  Although the details of the reason why the effects of the present invention are manifested are not clear, the applicant presumes as follows.

  Since the mixture is emulsified by applying ultrasonic vibration to the mixture containing the hydrophobic organic compound and the aqueous solvent, the average primary particle diameter is high even if the concentration of the hydrophobic organic compound in the mixture is high. A hydrophobic organic compound having a small droplet size and a narrow particle size distribution can be easily obtained, and the polyvinyl alcohol (hereinafter abbreviated as PVA) contained in the mixed liquid is droplet-shaped hydrophobic. Adsorbed on the surface of the organic compound to form emulsified oil droplets. PVA is strongly adsorbed to the droplet-like hydrophobic organic compound in a state in which PVA molecules are bonded to each other by hydrogen bonds through the OH group. As a result, it is surmised that the surface of the droplet-like hydrophobic organic compound was stabilized, and a high-concentration and stable emulsified oil droplet water dispersion was obtained. In addition, by making the cationic surfactant coexist with the silica source during the reaction of the silica source, the surface of the stable emulsified oil droplet containing PVA and the cationic surfactant has a positive charge. Silicate anions, which are silica precursors, are selectively accumulated to form an outer shell portion composed of silica-containing components and having a mesoporous structure. Therefore, even if the silica concentration converted from the silica source in the reaction liquid containing the emulsified oil droplets and the silica source is high, the hollow silica particles can be stably produced. However, the present invention is not limited to these estimations.

  In the present application, the “hollow silica particle” is a particle including an outer shell portion and a hollow portion existing inside the outer shell portion, and a gas such as air exists in the hollow portion. The “hollow silica particles” include both hollow silica particles whose outer shell portion has a mesoporous structure, that is, hollow mesoporous silica particles, and hollow silica particles whose outer shell portion does not have a mesoporous structure. .

  In the present application, the “composite silica particles” refers to silica particles composed of an outer shell portion composed of a component containing silica and other substances encapsulated by the outer shell portion. “Other substances contained in the outer shell” include “hydrophobic organic compounds”, “PVA” and the like described later.

  In the present specification, the “outer shell part composed of a component containing silica” means that the main component forming the skeleton of the outer shell part is silica, and preferably the component forming the skeleton of the outer shell part. Means 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, still more preferably 95% or more silicon dioxide.

  In the present specification, the “outer shell portion” refers to a portion including the outermost layer when the particles are multi-layered into two or more with the center portion of the particles as the center.

  In this specification, the “mesopore structure” refers to a structure formed when, for example, a silica source and a cationic surfactant are mixed and self-organized by hydrothermal synthesis. And a structure having uniform and regular pores (pore diameter 1 to 10 nm). The pore penetrates the outer shell portion so that the outside of the particle communicates with the hollow portion.

  In the present application, “hollow mesoporous silica particles” includes an outer shell portion having a mesoporous structure and a hollow portion existing inside the outer shell portion, and a gas such as air exists in the hollow portion and pores. Particles.

  In the present application, the “composite mesoporous silica particle” refers to a silica particle composed of an outer shell part having a mesoporous structure composed of a component containing silica and other substances encapsulated by the outer shell part. . “Other substances contained in the outer shell” include “hydrophobic organic compounds”, “PVA” and the like described later.

(Hydrophobic organic compounds)
The hydrophobic organic compound means a compound having low solubility in water and forming a phase separation with water.

  When water is used as the aqueous solvent, the hydrophobic organic compound is preferably in a liquid state at 20 to 90 ° C. and in a liquid state at 0 to 100 ° C. from the viewpoint of improving productivity and forming stable emulsified oil droplets. It is more preferable.

From the viewpoint of forming stable emulsified oil droplets, the hydrophobic organic compound preferably has LogP _OW of 1 or more, more preferably 2 to 25. Here, LogP _OW is a 1-octanol / water partition coefficient of a chemical substance and refers to a value obtained by calculation by the log K _OW method. Specifically, the chemical structure of a compound is decomposed into its constituents, and the hydrophobic fragment constants of each fragment are integrated (Meylan, WM and PH Howard. 1995. Atom / fragment contribution method for a reference octanol -water partition coefficients. See J. Pharm. Sci. 84: 83-92).

  As a hydrophobic organic compound, oil agents, such as a hydrocarbon compound, an ester compound, a C6-C22 fatty acid, and silicone oil, are mentioned, for example.

  Examples of hydrocarbon compounds include alkanes having 5 to 18 carbon atoms, alkenes having 5 to 18 carbon atoms, cycloalkanes having 5 to 18 carbon atoms, liquid paraffin, liquid petroleum jelly, squalane, squalene, perhydrosqualene, trimethylbenzene, and xylene. , Benzene and the like.

  Examples of the ester compound include fats and oils such as glycerin esters of fatty acids having 6 to 22 carbon atoms, specifically, mink oil, titol oil, soybean oil, sweet almond oil, beauty leaf oil, palm oil, grape seed. And oil, sesame seed oil, corn oil, parrham oil, arara oil, rapeseed oil, sunflower oil, cottonseed oil, apricot oil, castor oil, avocado oil, jojoba oil, olive oil, or grain germ oil.

  Examples of ester compounds include condensates of fatty acids having 4 to 22 carbon atoms and monohydric or polyhydric alcohols other than glycerin, such as isopropyl myristate and isopropyl palmitate. Butyl stearate, hexyl laurate, isononyl isononanoate, 2-ethylhexyl palmitate, 2-hexyldecyl laurate, 2-octyldecyl palmitate, 2-octyldecyl myristate, and the like. Examples of the ester compound include esters of an alcohol having 1 to 22 carbon atoms, preferably 8 to 22 carbon atoms, more preferably 12 to 18 carbon atoms, and (meth) acrylic acid. Examples include (meth) acrylic acid esters having 1 to 22 carbon atoms such as stearyl methacrylate, palmityl (meth) acrylate, myristyl (meth) acrylate, and lauryl (meth) acrylate. Examples of other ester compounds include esters of polyvalent carboxylic acid compounds and alcohols, specifically, diisopropyl adipate, lactic acid 2-octyldodecyl ester, 2-diethylhexyl oxalate, diisostearyl malate, etc. Is mentioned.

  Examples of the fatty acid having 6 to 22 carbon atoms include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, and isostearic acid.

  Examples of the silicone oil include polydimethylsiloxane (PDMS), fatty acid, aliphatic alcohol, polysiloxane modified with polyoxyalkylene, fluorosilicone, perfluorosilicone oil, and the like.

  These hydrophobic organic compounds may be used alone or in admixture of two or more at any ratio.

  Among the hydrophobic organic compounds, from the viewpoint of forming stable emulsified oil droplets, alkanes having 5 to 18 carbon atoms, alkenes having 5 to 18 carbon atoms, cycloalkanes having 5 to 18 carbon atoms, and 1 to 22 carbon atoms ( (Meth) acrylic acid esters and squalane are preferred, alkanes having 10 to 18 carbon atoms, alkenes having 10 to 18 carbon atoms, cycloalkanes having 10 to 18 carbon atoms, (meth) acrylic acid esters having 1 to 22 carbon atoms, and Squalane is more preferable, alkane having 12 to 16 carbon atoms, alkene having 12 to 16 carbon atoms, cycloalkane having 12 to 16 carbon atoms, (meth) acrylic acid ester having 12 to 18 carbon atoms, and squalane, and dodecane is more preferable. 1-dodecene, hexadecane, isostearyl methacrylate and squalane are even more preferred.

  The hydrophobic organic compound is preferably an alkane having 12 to 16 carbon atoms and more preferably dodecane from the viewpoint of obtaining hollow silica particles having a thick outer shell and a small pore diameter. In addition, from the viewpoint of obtaining hollow silica particles having a smaller average primary particle size, (meth) acrylic acid esters having 12 to 18 carbon atoms are preferable, and stearyl methacrylate is more preferable.

(Polyvinyl alcohol)
PVA stabilizes emulsified oil droplets, and water-soluble PVA is preferable from the viewpoint of producing hollow silica particles having a highly uniform particle structure such as primary particle diameter, hollow part diameter, outer shell part thickness, and particle shape. .

  The degree of saponification of PVA is preferably 30 mol% or more, more preferably 50 mol% or more, and even more preferably 70 mol% or more from the viewpoint of stabilizing the emulsified oil droplets and producing hollow silica particles having a highly uniform particle structure. . Moreover, from the same viewpoint, 99 mol% or less is preferable, 95 mol% or less is more preferable, and 90 mol% or less is still more preferable.

  From the viewpoint of obtaining hollow silica particles having a small average primary particle size, PVA is preferably cation-modified PVA into which a cationic group has been introduced. The amount of cation modification is preferably 0.01 mol% or more, and more preferably 0.05 mol% or more, from the viewpoint of producing hollow silica particles having a highly uniform particle structure. From the same viewpoint, it is preferably 10 mol% or less, more preferably 2 mol% or less.

  The cationic group is preferably a quaternary ammonium type from the viewpoint of availability, and the monomer used for introducing the cationic group is at least selected from the group consisting of methylacrylamide-n-propyltrimethylammonium chloride and diallyldimethylammonium chloride. One is preferred, and methylacrylamide-n-propyltrimethylammonium chloride is more preferred.

  Examples of the cation-modified PVA include PVA CM-318 (manufactured by Kuraray Co., Ltd.), PVA C-506 (manufactured by Kuraray Co., Ltd.), PVA K-210 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), and the like. Examples of the non-PVA include PVA-505 (manufactured by Kuraray Co., Ltd.).

  The PVA contained in the mixed solution may be composed of one type of PVA, but may be composed of two or more types of PVA. From the viewpoint of stabilizing the emulsified oil droplets and producing hollow silica particles having a highly uniform particle structure, it is preferable to use one type of PVA alone.

  The weight average molecular weight of PVA is preferably 5000 or more, more preferably 10,000 or more, still more preferably 20000 or more, and the same from the viewpoint of producing hollow silica particles having a highly uniform particle structure by stabilizing emulsified oil droplets. In view of the above, 300,000 or less is preferable, 200,000 or less is more preferable, and 90000 or less is more preferable. Moreover, from the same viewpoint, 5000-300000 are preferable, 10000-200000 are more preferable, 20000-90000 are still more preferable.

(Aqueous solvent)
Examples of the aqueous solvent used in the production method of the present invention include water or a mixed solvent composed of water and a water-soluble organic solvent. From the viewpoint of improving the stability of the emulsified oil droplets, the aqueous solvent is Preferably it consists only of water. Examples of water include distilled water, ion exchange water, and ultrapure water. Examples of the water-soluble organic solvent include methanol, ethanol, acetone, propanol, and isopropanol. When the aqueous solvent contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the aqueous solvent is preferably 0.1 to 50% by mass, more preferably 1 to 50% from the viewpoint of the stability of the emulsified oil droplets. It is 40 mass%, More preferably, it is 1-30 mass%.

(Cationic surfactant)
As the cationic surfactant used in the present invention, a quaternary ammonium salt represented by the following general formula (1) from the viewpoint of stably producing hollow silica particles even when the silica equivalent concentration of the silica source is high and One or more surfactants selected from quaternary ammonium salts represented by the general formula (2) are preferred. In the formula, R ¹ and R ² each independently represent a linear or branched alkyl group having 4 to 22 carbon atoms, and X ⁻ represents a monovalent anion.
[R ¹ (CH ₃ ) ₃ N] ⁺ X ⁻ (1)
[R ¹ R ² (CH ₃ ) ₂ N] ⁺ X ⁻ (2)

R ¹ and R ² in the above general formula (1) and general formula (2) are each independently and preferably carbon from the viewpoint of stably producing hollow silica particles even when the silica equivalent concentration of the silica source is high. A linear or branched alkyl group having 6 to 18, more preferably 8 to 16 carbon atoms. Examples of the alkyl group having 4 to 22 carbon atoms include various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, various tetradecyl groups, and various hexadecyl groups. , Various octadecyl groups, various eicosyl groups, and the like.

X ⁻ in general formula (1) and general formula (2) is preferably a monovalent anion such as halide ion, hydroxide ion, or nitrate ion from the viewpoint of forming highly ordered mesopores. It is. X ⁻ is more preferably a halide ion, still more preferably a chloride ion or bromide ion, and still more preferably a chloride ion.

  Examples of the alkyltrimethylammonium salt represented by the general formula (1) include butyltrimethylammonium chloride, hexyltrimethylammonium chloride, octyltrimethylammonium chloride, decyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethyl Ammonium chloride, stearyltrimethylammonium chloride, butyltrimethylammonium bromide, hexyltrimethylammonium bromide, octyltrimethylammonium bromide, decyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide Bromide, stearyl trimethyl ammonium bromide, and the like.

  Examples of the dialkyldimethylammonium salt represented by the general formula (2) include dibutyldimethylammonium chloride, dihexyldimethylammonium chloride, dioctyldimethylammonium chloride, dihexyldimethylammonium bromide, dioctyldimethylammonium bromide, didodecyldimethylammonium bromide, ditetradecyl. Examples thereof include dimethylammonium bromide.

  Among these quaternary ammonium salts, from the viewpoint of forming regular mesopores, the alkyltrimethylammonium salt represented by the general formula (1) is particularly preferable, and alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is more preferable. Preferably, dodecyltrimethylammonium chloride is more preferable.

  These cationic surfactants may be used alone or in admixture of two or more at any ratio.

  The outer shell portion having a mesopore structure is formed by the hydrolysis and dehydration condensation of the following silica source in the presence of the above cationic surfactant.

[Silica source]
As a silica source, what produces | generates a silanol compound by a hydrolysis is preferable, and the compound shown by following General formula (3)-(7) is mentioned specifically ,.
SiY ₄ (3)
R ³ SiY ₃ (4)
R ³ ₂ SiY ₂ (5)
R ³ ₃ SiY (6)
Y ₃ Si—R ⁴ —SiY ₃ (7)

In the formula, each R ³ independently represents an organic group in which a carbon atom is directly bonded to a silicon atom, R ⁴ represents a hydrocarbon group or phenylene group having 1 to 4 carbon atoms, and Y represents a hydrolyzed group. A monovalent hydrolyzable group that becomes a hydroxy group by decomposition is shown.

In general formulas (3) to (7), more preferably, each R ³ independently represents a hydrocarbon group having 1 to 22 carbon atoms in which a part of hydrogen atoms may be substituted with fluorine atoms. Specifically, it is an alkyl group having 1 to 22 carbon atoms, preferably 4 to 18 carbon atoms, more preferably 6 to 18 carbon atoms, and still more preferably 8 to 16 carbon atoms, a phenyl group, or a benzyl group. ⁴ is an alkanediyl group having 1 to 4 carbon atoms (methylene group, ethylene group, trimethylene group, propane-1,2-diyl group, tetramethylene group, etc.) or phenylene group, and Y is 1 to 22 carbon atoms. More preferably, it is a C1-C8 alkoxy group, More preferably, a C1-C4 alkoxy group or a halogen group except a fluorine.

Preferable examples of the silica source include the following compounds.
-In General formula (3), Y is a C1-C3 alkoxy group or a halogen group except a fluorine, Preferably, it is a C1-C2 alkoxy group.
In general formula (4) or (5), R ³ is a phenyl group, a benzyl group, or a hydrogen atom in which part of the hydrogen atom is substituted with a fluorine atom, preferably 1 to 10 carbon atoms, preferably a hydrocarbon group having 1 to 5 carbon atoms, more preferably, R ³ is a phenyl group, a benzyl group, a methyl group or an ethyl group.
In general formula (7), Y is a methoxy group and R ⁴ is a methylene group, an ethylene group or a phenylene group.

  Among these, tetramethoxysilane, tetraethoxysilane, and phenyltriethoxysilane are preferable, and tetramethoxysilane is more preferable. These silica sources may be used alone or in admixture of two or more at any ratio.

  Next, a method for producing the hollow silica particles of the present invention (hereinafter sometimes abbreviated as “the production method of the present invention”) will be described. The production method of the present invention includes the following steps (I) to (III).

Step (I): Ultrasonic vibration is applied to a mixed solution containing a hydrophobic organic compound, polyvinyl alcohol, and an aqueous solvent to form an emulsified oil droplet water dispersion containing emulsified oil droplets containing the hydrophobic organic compound. Process.
Step (II): In the reaction liquid obtained by mixing the emulsified oil droplet aqueous dispersion and the silica source in the presence of a cationic surfactant, the emulsion oil droplet surface is composed of a component containing silica. Forming an outer shell having a mesoporous structure;
Step (III): a step of removing the emulsified oil droplets from the composite silica particles including the outer shell portion and the emulsified oil droplets present inside the outer shell portion.

  In the step (II), “mixing the emulsified oil droplet water dispersion and the silica source in the presence of a cationic surfactant” means, for example, adding the emulsified oil droplet water dispersion to the cationic surfactant. This can be done by mixing a silica source in the presence of an agent or together with a cationic surfactant. “In the presence of a cationic surfactant or together with a cationic surfactant” means that the cationic surfactant is mixed with the emulsified oil droplet water dispersion before mixing the silica source into the emulsified oil droplet water dispersion. It may mean that it may be mixed in the emulsified oil droplet water dispersion together with the silica source.

That is, the step (II) includes the following two aspects.
(Aspect 1)
Step (II-a): A step of mixing the emulsified oil droplet water dispersion and the cationic surfactant.
Step (II-b): In a reaction liquid obtained by mixing a mixed liquid containing the emulsified oil droplet water dispersion and the cationic surfactant and the silica source, silica is added to the surface of the emulsified oil droplets. A step of forming an outer shell portion having a mesopore structure composed of the components to be included.
In the aspect 1, the emulsified oil droplet water dispersion and the cationic surfactant are mixed, and then these are mixed with the silica source.

(Aspect 2)
Step (II-c): a reaction liquid obtained by mixing the emulsified oil droplet water dispersion, the cationic surfactant, and the silica source, and is composed of a component containing silica on the surface of the emulsified oil droplets. Forming an outer shell having a mesoporous structure;
In aspect 2, a cationic surfactant and a silica source are mixed simultaneously with an emulsified oil droplets aqueous dispersion.

  Aspect 1 is preferable from the viewpoint of obtaining hollow silica having a highly uniform particle structure such as primary particle diameter, hollow diameter, outer shell thickness, and particle shape.

[Step (I)]
In step (I), first, a mixed solution containing a hydrophobic organic compound, polyvinyl alcohol, and an aqueous medium is prepared, and then an ultrasonic vibration is applied to the prepared mixed solution to emulsify the hydrophobic organic compound. An emulsion containing oil droplets (emulsified oil droplet water dispersion) is formed.

  In the preparation of the mixed liquid, the order of mixing the hydrophobic organic compound, polyvinyl alcohol, and the aqueous medium is not limited, but for example, the hydrophobic organic compound and polyvinyl alcohol can be added to the aqueous medium. The hydrophobic organic compound and polyvinyl alcohol may be added to the aqueous medium in this order, or may be added simultaneously. The aqueous medium may be stirred during the addition of the hydrophobic organic compound and / or polyvinyl alcohol, or may be stirred after the addition.

  The stirring time varies depending on the type of stirrer used and the like, but in a state where the whole is uniformly mixed, it is preferably 1 minute or more, more preferably 2 minutes or more, still more preferably 5 minutes or more, From the viewpoint of improving productivity, it is preferably 24 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less.

  There is no restriction | limiting in particular about the kind of stirrer used for the said stirring. Examples of the stirrer include a magnetic stirrer, a pencil mixer, a homomixer, a homogenizer, and an ultrasonic disperser. As a commercially available stirrer, for example, Disper (manufactured by PRIMIX), Clearmix (manufactured by M-Technique), Cavitron (manufactured by Taiheiyo Kiko) and the like can be used.

  The temperature of the mixed liquid during stirring is preferably 90 ° C. or lower, more preferably 50 ° C. or lower, from the viewpoint of preventing evaporation of the aqueous medium and suppressing fluctuations in the concentration of the hydrophobic organic compound and polyvinyl alcohol in the mixed liquid. Preferably, it is 35 ° C. or lower, preferably 0 ° C. or higher, and more preferably 10 ° C. or higher from the viewpoint of improving productivity.

  The content of the hydrophobic organic compound in the liquid mixture to which ultrasonic vibration is applied is preferably set to 0. 0 from the viewpoint of increasing the silica equivalent concentration of the silica source used for forming the outer shell and improving the productivity. It is preferably 1% by mass or more, more preferably 1% by mass or more, and further preferably 2% by mass or more. Further, from the viewpoint of forming stable emulsified oil droplets, it is preferably 30% by mass or less, more preferably 10% by mass or less, and further preferably 4% by mass or less.

  The content of PVA in the mixed liquid to which ultrasonic vibration is applied is 0.005% by mass or more from the viewpoint of stabilizing the emulsified oil droplets and producing hollow silica particles having a highly uniform particle structure. And more preferably 0.01% by mass or more, and further preferably 0.02% by mass or more. Further, from the viewpoint of stable emulsified oil droplet formation and cost, it is preferably 3% by mass or less, more preferably 1% by mass or less, and further preferably 0.35% by mass or less.

  The mass ratio of the PVA and the hydrophobic organic compound (mass of PVA / mass of the hydrophobic organic compound) in the reaction liquid containing the mixed liquid or the emulsified oil droplets and the silica source is 0 from the viewpoint of forming stable emulsified oil droplets. 0.001 or more is preferable, 0.005 or more is more preferable, 0.008 or more is still more preferable, and 0.01 or more is still more preferable. Moreover, 1 or less is preferable from a viewpoint of formation of the stable emulsified oil droplet, and an economical viewpoint, 0.5 or less is more preferable, 0.2 or less is further more preferable, and 0.1 or less is still more preferable.

<Applying ultrasonic vibration>
The temperature of the mixed liquid at the time of applying ultrasonic vibration is preferably 0 ° C. or higher, preferably 100 ° C. or lower, more preferably 50 ° C. or lower, from the viewpoint of improving the structural uniformity and stability of the resulting emulsified oil droplets. It is preferably 25 ° C. or lower, more preferably 10 ° C. or lower. That is, under ice cooling (0 to 10 ° C.) is preferable.

  The time for applying the ultrasonic vibration to the mixed liquid is preferably 1 minute or more, more preferably 5 minutes or more, and further preferably 8 minutes or more, from the viewpoint of improving the structural uniformity and stability of the resulting emulsified oil droplets. From the viewpoint of improving the productivity of the hollow silica particles, 60 minutes or less is preferable, 30 minutes or less is more preferable, and 15 minutes or less is even more preferable.

  Application of ultrasonic vibration to the mixed liquid can be performed using a commercially available ultrasonic generator. As a commercially available ultrasonic generator, for example, an ultrasonic homogenizer US-300T, US-600T, US-1000T manufactured by Nippon Seiki Co., Ltd. or an ultrasonic homogenizer USH-1000Z20S manufactured by Ultrasonic Industrial Co., Ltd. can be used.

  The frequency of the ultrasonic waves is preferably 1 to 400 kHz, more preferably 10 to 100 kHz, and further preferably 15 to 50 kHz, from the viewpoint of improving the structural uniformity and stability of the resulting emulsified oil droplets and the versatility of the emulsifying device. preferable.

  The rated output of the ultrasonic generator is preferably 10 to 5000 W, more preferably 50 to 2000 W, more preferably 100 to 2000 W from the viewpoint of improving the structural uniformity and stability of the resulting emulsified oil droplets and the versatility of the emulsifier. 1000W is still more preferable, and 200-500W is still more preferable.

  In addition, the ultrasonic output current is preferably 10 to 1000 μA, more preferably 100 to 800 μA, and more preferably 300 to 500 μA, from the viewpoint of improving the structural uniformity and stability of the resulting emulsified oil droplets and the versatility of the emulsifying device. Is more preferable.

  The tip diameter of the ultrasonic generator of the ultrasonic generator is preferably 5 to 50 mm, and preferably 10 to 40 mm from the viewpoint of improving the structural uniformity and stability of the resulting emulsified oil droplets and the versatility of the emulsifier. More preferably, 15-30 mm is still more preferable.

In the step (I), the volume-based average particle diameter (D ₅₀ ) of the emulsified oil droplets is preferably 10 nm or more, preferably 100 nm or more, from the viewpoint of forming hollow silica particles having a large porosity and a uniform particle structure. Is more preferable, 350 nm or more is more preferable, 5000 nm or less is preferable, 1000 nm or less is more preferable, and 750 nm or less is still more preferable. The volume-based average particle diameter (D ₅₀ ) means a particle diameter at which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle diameter.

[Process (II)]
In step (II), an emulsified oil droplet aqueous dispersion and a silica source are mixed in the presence of a cationic surfactant, and the outer shell portion having a mesoporous structure composed of components containing silica on the emulsified oil droplet surface. To form composite silica particles including an outer shell part and emulsified oil droplets present inside the outer shell part, and a composite silica particle dispersion liquid in which the composite silica particles are dispersed in a dispersion medium is obtained.

  The formation of the outer shell part and the formation of the composite silica particles are carried out by, for example, emulsifying oil droplet water dispersion in the presence of the cationic surfactant, a silica source that generates a silanol compound by hydrolysis, and an alkali agent as necessary. After stirring, it can be performed by standing still. In the reaction solution containing the emulsified oil droplets and the silica source, the silica is precipitated on the emulsified oil droplets by hydrolysis and dehydration condensation reaction of the silica source, and the mesopores are composed of components containing silica on the emulsified oil droplets. An outer shell having a structure is formed.

  Examples of the alkaline agent include sodium hydroxide, ammonia, and tetraalkylammonium hydroxide such as tetramethylammonium hydroxide. These alkali agents are preferably mixed in the emulsified oil droplet water dispersion before mixing the silica source and the emulsified oil droplet water dispersion from the viewpoint of obtaining hollow silica particles having a highly uniform particle structure.

  In aspect 1, from the viewpoint of obtaining hollow silica particles having a highly uniform particle structure, the cationic surfactant is preferably added to the emulsified oil droplet aqueous dispersion together with the alkali agent. The emulsified oil droplet water dispersion to which the cationic surfactant and the alkali agent are added is preferably sufficiently stirred before the silica source is added, and the stirring time is preferably 1 minute to 10 hours, More preferably, it is 10 minutes-5 hours, More preferably, it is 30 minutes-3 hours.

  From the viewpoint of efficiently hydrolyzing and dehydrating and condensing the silica source, the pH of the emulsified oil droplet aqueous dispersion before the addition of the cationic surfactant and the alkali agent and the silica source is 8.5 to 12.0, More preferably, it is 9.0-11.5.

From the viewpoint of forming hollow silica particles having a large porosity and a uniform particle structure, the volume-based average particle size (D ₅₀ ) of the emulsified oil droplets in the presence of a cationic surfactant and an alkali agent is 10 nm or more is preferable, 100 nm or more is more preferable, 350 nm or more is further preferable, 5000 nm or less is preferable, 1000 nm or less is more preferable, and 750 nm or less is more preferable.

  In aspect 2, from the viewpoint of obtaining hollow silica particles having a highly uniform particle structure, an alkali agent is added to the emulsified oil droplet water dispersion before mixing the silica source and the cationic surfactant with the emulsified oil droplet water dispersion. It is preferred if The emulsified oil droplet water dispersion to which the alkali agent is added is preferably sufficiently stirred before the silica source and the cationic surfactant are added, and the stirring time is preferably 1 minute to 10 hours. More preferably, it is 10 minutes-5 hours, More preferably, it is 30 minutes-3 hours.

  The pH of the emulsified oil droplet aqueous dispersion before the addition of the alkaline agent and the cationic surfactant and the silica source is preferably 8.5 from the viewpoint of efficiently hydrolyzing and dehydrating and condensing the silica source. It is 12.0, More preferably, it is 9.0-11.5.

  The silica source may be added as it is to the emulsified oil droplet water dispersion, or a silica source-containing liquid obtained by adding the silica source to a predetermined solvent may be added to the emulsified oil droplet water dispersion. Examples of the solvent include water-soluble organic solvents such as methanol, ethanol, acetone, propanol, isopropanol, and preferably methanol. These water-soluble organic solvents are preferably dehydrated.

  The addition of the silica source may be carried out all at once, but may be continuous or intermittent. In order to prevent aggregation of the generated hollow silica particles, it is preferable to continue stirring the reaction liquid containing the emulsified oil droplets and the silica source until the reaction of the silica source is completed, and preferably 10 to 10 after the addition of the silica source is completed. It is preferable to keep stirring at 80 ° C., more preferably 10 to 50 ° C., preferably 0.01 to 5 hours, more preferably 1 to 3 hours.

  The addition rate of the silica source is desirably adjusted as appropriate in consideration of the capacity of the reaction system, the type of the silica source, the rate of increase in the concentration of the silica source added to the emulsified oil droplet water dispersion, and the like.

  During the addition of the silica source, the temperature of the reaction solution is preferably 10 ° C. or more, more preferably from the viewpoint of improving the stability of the emulsified oil droplets and suppressing the variation in the concentration of the cationic surfactant in the reaction solution. It is 15 ° C. or higher, preferably 90 ° C. or lower, more preferably 80 ° C. or lower, still more preferably 50 ° C. or lower, and still more preferably 35 ° C. or lower.

  The pH of the reaction solution during the addition of the silica source and after the reaction of the silica source, that is, the pH of the aqueous dispersion of the composite mesoporous silica particles is determined from the viewpoint of efficiently hydrolyzing and dehydrating and condensing the silica source. It is preferable to adjust to 8.5 to 12.0, more preferably 9.0 to 11.5 using an alkali agent.

  The content of the silica source is preferably 10 mmol / L or more, more preferably 100 mmol / L or more, more preferably 150 mmol in terms of silica, from the viewpoint of improving productivity in the reaction solution containing the emulsified oil droplets and the silica source. / L or more is more preferable, 200 mmol / L or more is more preferable, and 250 mmol / L or more is still more preferable. Further, from the viewpoint of obtaining hollow silica particles having a highly uniform particle structure, it is preferably 2000 mmol / L or less, more preferably 1000 mmol / L or less, still more preferably 800 mmol / L or less, and more preferably 600 mmol / L or less. More preferably, it is more preferably 400 mmol / L or less, and even more preferably 350 mmol / L or less. In addition, the said content is a value about the total amount of the silica source used for mixing with an emulsified oil droplet water dispersion, and is the value which disregarded the consumption of the silica source accompanying reaction.

  The content of the silica source is preferably 0.06% by mass or more, more preferably 0.6% by mass or more, and 0.9% by mass in terms of silica, from the viewpoint of improving productivity in the reaction solution. The above is more preferable, 1.2% by mass or more is more preferable, and 1.5% by mass or more is more preferable. Further, from the viewpoint of obtaining hollow silica particles having a highly uniform particle structure, the content of the silica source in the reaction solution is preferably 12% by mass or less, more preferably 6% by mass or less, and 4.8% by mass or less. Is more preferable, 3.6 mass% or less is still more preferable, and 3.0 mass% or less is still more preferable.

  When the content of the silica source in the reaction solution is a value within the above preferred range, the content of the hydrophobic organic compound in the reaction solution is the silica equivalent concentration of the silica source used for forming the outer shell. From the viewpoint of increasing the productivity and improving the productivity, 0.1% by mass or more is preferable, 0.5% by mass or more is more preferable, 1% by mass or more is further preferable, and 2% by mass or more is even more preferable. The content of the hydrophobic organic compound suppresses the collision of the emulsified oil droplets containing the hydrophobic organic compound and the phase separation of the hydrophobic organic compound accompanying the coalescence, so that the hollow silica particles having a highly uniform particle structure can be obtained. From the viewpoint of production, it is preferably 30% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, still more preferably 7% by mass or less, and still more preferably 5% by mass or less.

  The content of PVA in the reaction solution is preferably 0.005% by mass or more, and 0.01% by mass or more from the viewpoint of forming stable emulsified oil droplets and producing hollow silica particles having a highly uniform particle structure. More preferred is 0.02% by mass or more. In addition, the PVA content is preferably 3% by mass or less, more preferably 1% by mass or less, and still more preferably 0.35% by mass or less from the viewpoint of stable emulsion oil droplet formation and cost.

  The content of the cationic surfactant in the reaction solution may be appropriately adjusted according to the surface area of the emulsified oil droplets, but from the viewpoint of improving the yield and dispersibility of the hollow silica particles, it is 1 mmol / L or more. Is preferably 10 mmol / L or more, and more preferably 30 mmol / L or more. From the same viewpoint, the content of the cationic surfactant in the reaction solution is preferably 500 mmol / L or less, more preferably 100 mmol / L or less, and further preferably 70 mmol / L or less.

  In the reaction solution, the ratio of the molar concentration of the cationic surfactant to the molar molar concentration of the cationic surfactant in the reaction solution (the molar concentration of the cationic surfactant / the molar molar concentration of the silica source in terms of silica) is the yield of the hollow silica particles and From the viewpoint of improving dispersibility, it is preferably 0.01 or more, more preferably 0.05 or more, and still more preferably 0.1 or more. Further, from the same viewpoint, it is preferably 10 or less, more preferably 1 or less, and further preferably 0.5 or less.

[Step (III)]
Step (III) is a step of removing the emulsified oil droplets from the composite silica particles (composite mesoporous silica particles) obtained in step (II). In step (III), for example, after separating the composite silica particles from the dispersion medium, the composite silica particles are dried and then baked using an electric furnace or the like, and the cation in the inner and outer shells of the composite silica particles is obtained. Active surfactants, PVA, hydrophobic organic compounds and the like are removed. The composite silica particles may be separated from the dispersion medium by drying the dispersion medium. In an example of the production method of the present invention, if necessary, the composite silica particles may be subjected to at least one treatment selected from the group consisting of contacting with an acidic solution, washing with water, and drying before firing. . When the composite silica particles are brought into contact with the acidic liquid, cationic surfactants such as quaternary ammonium salts in the mesopores of the composite silica particles can be efficiently reduced or removed.

  In the method for producing hollow silica particles whose outer shell part has a mesoporous structure (hollow mesoporous silica particles), the calcination temperature is selected from the viewpoints of reliably removing the cationic surfactant, the hydrophobic organic compound, and the PVA. From the viewpoint of improving the strength of the pore structure, it is preferably 350 ° C. or higher, and more preferably 450 ° C. or higher. Further, from the viewpoint of obtaining hollow silica particles having an outer shell portion having a mesoporous structure, the firing temperature is preferably 800 ° C. or lower, more preferably 700 ° C. or lower. The firing time is preferably 1 hour or more from the viewpoint of reliably removing the cationic surfactant, the hydrophobic organic compound, and PVA, and the strength of the mesopore structure. From the viewpoint of improving productivity, Preferably it is 10 hours or less, More preferably, it is 5 hours or less.

  In the method for producing hollow silica particles in which the outer shell portion does not have a mesopore structure, the firing temperature is such that the mesopore structure disappears and the outer shell portion not having the mesopore structure and the hollow portion inside the mesopore structure are removed. From the viewpoint of obtaining hollow silica particles, it is preferably 900 ° C. or higher, more preferably 950 ° C. or higher, and from the viewpoint of maintaining the hollow particle structure, it is preferably 1200 ° C. or lower, more preferably 1100 ° C. or lower. is there. The firing time is preferably 1 hour or more, more preferably 24 hours or more, from the viewpoint of surely removing the cationic surfactant, hydrophobic organic compound, PVA and the like and the disappearance of the mesopore structure. From the viewpoint of improving productivity, it is preferably 72 hours or shorter, more preferably 48 hours or shorter.

  Examples of the separation method include a filtration method, a centrifugal separation method, and a removal removal of the dispersion medium. In the drying process performed after separating the composite silica particles from the dispersion medium by these methods and before firing, the temperature in the dryer is a viewpoint of sufficiently drying and a viewpoint of suppressing carbonization of organic substances attached to the composite silica particles. Therefore, the drying time is preferably from 50 to 150 ° C., more preferably from 80 to 120 ° C., and the drying time is preferably 0 from the viewpoint of sufficiently drying and the suppression of carbonization of organic substances attached to the composite silica particles. .1 to 48 hours, more preferably 5 to 30 hours.

  Examples of the acidic liquid include inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid; organic acids such as acetic acid and citric acid; liquids obtained by adding a cation exchange resin or the like to water or ethanol. The pH of the acidic liquid is preferably 1.5 to 5.0.

[Hollow mesoporous silica particles]
Next, among the hollow silica particles obtained by the production method of the present invention, hollow silica particles whose outer shell part has a mesoporous structure (hollow mesoporous silica particles) will be described.

[Hollow silica particles whose outer shell has a mesoporous structure]
According to the production method of the present invention, hollow mesoporous silica particles having an average pore diameter of the mesopore structure of the outer shell part of preferably 1 to 10 nm, more preferably 1 to 5 nm, and further preferably 1 to 3 nm are produced. it can.

  The average pore diameter of the mesopore structure can be determined by nitrogen adsorption measurement and from the nitrogen adsorption isotherm by the BJH method.

  According to the production method of the present invention, hollow mesoporous silica particles having a uniform mesopore diameter can be produced, more preferably 70% or more of the mesopores, still more preferably 75% or more, and still more preferably 80% or more. However, it is possible to produce hollow mesoporous silica particles having a pore diameter in the range of average pore diameter ± 30%. The pore size distribution of the mesopores can be determined from the differential pore volume within a predetermined range with reference to the peak top of the pore size determined by the BJH method.

  The structure of the outer shell having a mesopore structure can be observed using a transmission electron microscope (TEM), and the pore diameter, the regularity of the arrangement of the pores, and from the outside of the outer shell to the inner side of the outer shell It is possible to observe how the pores are connected to each other.

  The regularity of the arrangement of mesopores in the outer shell can also be evaluated from a spectrum obtained by powder X-ray diffraction (XRD). Specifically, in the powder X-ray diffraction spectrum of hollow mesoporous silica particles obtained by irradiating with CuKα1 rays (λ = 0.154050 nm), the crystal lattice spacing (d) corresponds to a range of 2 to 10 nm. If one or more peaks (XRD peaks) having a vertex in the region of the diffraction angle (2θ) are present, it can be evaluated that the regularity of the arrangement of the mesopores in the outer shell portion is high.

According to the production method of the present invention, the BET specific surface area is preferably 300 m ² / g or more, more preferably 400 m ² / g or more, still more preferably 500 m ² / g or more, and still more preferably 600 m ² / g or more. Yes, it is possible to produce hollow mesoporous silica particles that are preferably 1500 m ² / g or less, more preferably 1400 m ² / g or less, still more preferably 1300 m ² / g or less, and even more preferably 1000 m ² / g or less.

  According to the production method of the present invention, the average primary particle diameter is preferably 50 nm or more, more preferably 100 nm or more, still more preferably 300 nm or more, still more preferably 500 nm or more, preferably 5000 nm or less, more preferably 3000 nm. Hereinafter, hollow mesoporous silica particles having a diameter of 2000 nm or less and more preferably 1200 nm or less can be produced.

  The average primary particle size of the hollow mesoporous silica particles can be adjusted by the selection of the cationic surfactant or the hydrophobic organic compound, the stirring power during mixing, the concentration of each component, the temperature of the reaction solution, and the like.

  According to the production method of the present invention, the average diameter of the hollow portion is preferably 10 nm or more, more preferably 100 nm or more, still more preferably 300 nm or more, still more preferably 400 nm or more, preferably 2000 nm or less, more preferably Hollow mesoporous silica particles having a thickness of 1500 nm or less, more preferably 1000 nm or less, and still more preferably 900 nm or less can be produced.

  According to the production method of the present invention, the average primary particle diameter of the entire hollow mesoporous silica particles obtained by the production method of the present invention is preferably 80% or more, more preferably 82% or more, still more preferably 85% or more. Hollow mesoporous silica particles having a primary particle size in the range of ± 30% and composed of particles having a very uniform primary particle size can be produced.

  According to the production method of the present invention, the average thickness of the outer shell is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 30 nm or more, and preferably 700 nm or less, more preferably 500 nm or less, Hollow mesoporous silica particles having a diameter of preferably 200 nm or less, more preferably 150 nm or less can be produced.

[Hollow silica particles whose outer shell has no mesoporous structure]
According to the production method of the present invention, BET specific surface area is preferably 1 m ² / g or more, more preferably 2m ² / g or more, more preferably at 3m ² / g or more, preferably not more than 300 meters ² / g, More preferably, hollow silica particles of 100 m ² / g or less, more preferably 50 m ² / g or less, and still more preferably 20 m ² / g or less can be produced.

  According to the production method of the present invention, the average primary particle size is preferably 50 nm or more, more preferably 100 nm or more, still more preferably 300 nm or more, preferably 5000 nm or less, more preferably 3000 nm or less, still more preferably 1000 nm or less. The hollow silica particle which is can be manufactured.

  The average primary particle diameter of the hollow silica particles can be adjusted by the selection of the cationic surfactant or the hydrophobic organic compound, the stirring force at the time of mixing, the concentration of each component, the temperature of the reaction solution, and the like.

  According to the production method of the present invention, the average diameter of the hollow portion is preferably 10 nm or more, more preferably 100 nm or more, still more preferably 200 nm or more, still more preferably 300 nm or more, preferably 1000 nm or less, more preferably Hollow silica particles that are 900 nm or less, more preferably 800 nm or less, and still more preferably 700 nm or less can be produced.

  According to the production method of the present invention, 80% or more of the entire hollow silica particles obtained by the production method of the present invention, more preferably 82% or more, and still more preferably 85% or more have an average primary particle size of ± 30%. Hollow silica particles having a primary particle diameter in the range and composed of a group of particles having a very uniform particle diameter can be produced.

  According to the production method of the present invention, the average thickness of the outer shell is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 30 nm or more, preferably 700 nm or less, more preferably 500 nm or less, still more preferably. Hollow silica particles that are 200 nm or less, more preferably 100 nm or less can be produced.

  In the present application, the average primary particle size and particle size distribution of the hollow silica particles, the average diameter of the hollow portion (average hollow portion diameter), and the average thickness of the outer shell portion (average outer shell portion thickness) are as follows. (TEM) Value measured by observation. Specifically, under a transmission electron microscope, the diameter (primary particle diameter) of all particles in the field of view containing 20 to 30 hollow silica particles, the diameter of the hollow portion, and the outer shell thickness are shown on the photograph. Measure. This operation is performed by changing the field of view five times. From the obtained data, the number average primary particle size and the degree of particle size distribution, the number average diameter of the hollow portion, and the number average outer shell thickness are determined. The standard of magnification of the transmission electron microscope is 10,000 to 100,000 times, but the magnification of the transmission electron microscope is appropriately adjusted depending on the size of the hollow silica particles. In the measurement, data is taken on at least 100 hollow silica particles.

  The present application further discloses the following [1] to [25].

[1] Forming an emulsified oil droplet aqueous dispersion including emulsified oil droplets containing the hydrophobic organic compound by applying ultrasonic vibration to a mixed solution containing the hydrophobic organic compound, polyvinyl alcohol, and an aqueous solvent; ,
In the reaction liquid obtained by mixing the emulsified oil droplet water dispersion and the silica source in the presence of a cationic surfactant, the emulsified oil droplet surface has a mesoporous structure composed of components containing silica. Forming the outer shell,
Removing the emulsified oil droplets from the composite silica particles including the outer shell portion and the emulsified oil droplets present inside the outer shell portion.
[2] The method for producing hollow silica particles according to [1], wherein the step of forming the outer shell includes the following steps (II-a) and (II-b).
Step (II-a): A step of mixing the emulsified oil droplet water dispersion and the cationic surfactant.
Step (II-b): In a reaction liquid obtained by mixing a mixed liquid containing the emulsified oil droplet water dispersion and the cationic surfactant and the silica source, silica is added to the surface of the emulsified oil droplets. A step of forming an outer shell portion having a mesopore structure composed of the components to be included.
[3] The content of the silica source in the reaction solution is 10 mmol / L or more, preferably 100 mmol / L or more, more preferably 150 mmol / L or more, still more preferably 200 mmol / L in terms of silica. Or more, more preferably 250 mmol / L or more, and 2000 mmol / L or less, preferably 1000 mmol / L or less, more preferably 800 mmol / L or less, still more preferably 600 mmol / L or less, and still more. The method for producing hollow silica particles according to [1] or [2], which is preferably 400 mmol / L or less, and more preferably 350 mmol / L or less.
[4] The content of the hydrophobic organic compound in the mixed solution is 0.1% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more, and 30% by mass or less, preferably 10%. The method for producing hollow silica particles according to any one of [1] to [3], wherein the content is at most mass%, more preferably at most 4 mass%.
[5] The hydrophobic organic compound includes an alkane having 5 to 18 carbon atoms, an alkene having 5 to 18 carbon atoms, a cycloalkane having 5 to 18 carbon atoms, a (meth) acrylic acid ester having 1 to 22 carbon atoms, and squalane. At least one selected from the group consisting of: preferably an alkane having 10 to 18 carbon atoms, an alkene having 10 to 18 carbon atoms, a cycloalkane having 10 to 18 carbon atoms, and (meth) acrylic acid having 1 to 22 carbon atoms An alkane having 12 to 16 carbon atoms, an alkene having 12 to 16 carbon atoms, a cycloalkane having 12 to 16 carbon atoms, and 12 to 18 carbon atoms. At least one selected from the group consisting of (meth) acrylic acid esters and squalane; more preferably dodecane, 1-dodecene, The method for producing hollow silica particles according to any one of [1] to [4], which is at least one selected from the group consisting of xadecane, isostearyl methacrylate, and squalane.
[6] The method for producing hollow silica particles according to any one of [1] to [4], wherein the hydrophobic organic compound is an alkane having 12 to 16 carbon atoms, preferably dodecane.
[7] The hollow according to any one of [1] to [4], wherein the hydrophobic organic compound is a (meth) acrylic acid ester having 12 to 18 carbon atoms, preferably stearyl methacrylate. A method for producing silica particles.
[8] The mass ratio of polyvinyl alcohol to the hydrophobic organic compound (the mass of polyvinyl alcohol / the mass of the hydrophobic organic compound) in the mixed solution is 0.001 or more, preferably 0.005 or more, more preferably 0. 0.008 or more, more preferably 0.010 or more, and 1 or less, preferably 0.5 or less, more preferably 0.2 or less, and even more preferably 0.1 or less. The method for producing hollow silica particles according to any one of [7].
[9] The method for producing hollow silica particles according to any one of [1] to [8], wherein the polyvinyl alcohol is cation-modified polyvinyl alcohol.
[10] The hollow portion according to [9], wherein the amount of cation modification of the polyvinyl alcohol is 0.01 mol% or more, preferably 0.05 mol% or more, and 10 mol% or less, preferably 2 mol% or less. A method for producing silica particles.
[11] The method for producing hollow silica particles according to [9] or [10], wherein the cationic group introduced into the polyvinyl alcohol is a quaternary ammonium type.
[12] The monomer used for introduction of the cationic group is at least one selected from the group consisting of methylacrylamide-n-propyltrimethylammonium chloride and diallyldimethylammonium chloride; preferably methylacrylamide-n-propyltrimethylammonium chloride. The method for producing hollow silica particles according to [11].
[13] The saponification degree of the polyvinyl alcohol is 30 mol% or more, preferably 50 mol% or more, more preferably 70 mol% or more, and 99 mol% or less, preferably 95 mol% or less, more preferably 90 mol% or less. The method for producing hollow silica particles according to any one of [9] to [12].
[14] The weight average molecular weight of the polyvinyl alcohol is 5000 or more, preferably 10,000 or more, more preferably 20000 or more, and 300,000 or less, preferably 200000 or less, more preferably 90000 or less, and 5000 to 5000 The method for producing hollow silica particles according to any one of [1] to [13], which is 300,000, preferably 10,000 to 200,000, more preferably 20,000 to 90,000.
[15] The content of the polyvinyl alcohol in the mixed solution is 0.005% by mass or more, preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and 3% by mass or less. The method for producing hollow silica particles according to any one of [1] to [14], preferably 1% by mass or less, more preferably 0.35% by mass or less.
[16] The volume-based average particle diameter (D ₅₀ ) of the emulsified oil droplet in the step of forming the emulsified oil droplet aqueous dispersion is 10 nm or more, preferably 100 nm or more, more preferably 350 nm or more, and 5000 nm. Hereinafter, the method for producing hollow silica particles according to any one of [1] to [15], which is preferably 1000 nm or less, more preferably 750 nm or less.
[17] The volume-based average particle diameter (D ₅₀ ) of the emulsified oil droplets in the presence of the cationic surfactant and the alkali agent is 10 nm or more, preferably 100 nm or more, more preferably 350 nm. In addition, the method for producing hollow silica particles according to any one of [1] to [14], which is 5000 nm or less, preferably 1000 nm or less, and more preferably 750 nm or less.
[18] The content of the cationic surfactant in the reaction solution is 1 mmol / L or more, preferably 10 mmol / L or more, more preferably 30 mmol / L or more, and 500 mmol / L or less. The method for producing hollow silica particles according to any one of [1] to [17], preferably 100 mmol / L or less, more preferably 70 mmol / L or less.
[19] The ratio of the molar concentration of the cationic surfactant to the molar molar concentration of the cationic surfactant in the reaction solution (the molar concentration of the cationic surfactant / the molar molar concentration of the silica source in terms of silica) is 0.01. Any of [1] to [18] above, preferably 0.05 or more, more preferably 0.1 or more, and 10 or less, preferably 1 or less, more preferably 0.5 or less. A process for producing hollow silica particles according to claim 1.
[20] The hollow silica particles, which are hollow mesoporous silica particles including an outer shell portion having a mesoporous structure composed of a component containing silica and a hollow portion existing inside the outer shell portion. 1] to the method for producing hollow silica particles according to any one of [19].
[21] The average pore diameter of the hollow mesoporous silica particles is 1 to 10 nm, preferably 1 to 5 nm, more preferably 1 to 3 nm, and the average primary particle diameter is 50 nm or more, preferably 100 nm or more, more preferably. The method for producing hollow silica particles according to the above [20], which is 300 nm or more, more preferably 500 nm or more, 5000 nm or less, preferably 3000 nm or less, more preferably 2000 nm or less, and further preferably 1200 nm or less.
[22] BET specific surface area of the hollow mesoporous silica particles, 300 meters ² / g or more, preferably 400 meters ² / g or more, more preferably 500 meters ² / g or more, more preferably 600 meters ² / g or more, 1500 m ² / g or less, preferably 1400 m ² / g or less, more preferably 1300 m ² / g or less, still more preferably 1000 m ² / g or less, the production method of the hollow silica particles according to [20] or the [21] .
[23] In the step of removing the emulsified oil droplets from the composite silica particles, the composite silica particles are baked at 350 ° C or higher, preferably 450 ° C or higher, and 800 ° C or lower, preferably 700 ° C or lower, The method for producing hollow silica particles according to any one of [20] to [22], wherein the emulsified oil droplets are removed from the composite silica particles.
[24] The cationic surfactant is one or more surfactants selected from a quaternary ammonium salt represented by the following general formula (1) and a quaternary ammonium salt represented by the general formula (2). Preferably an alkyltrimethylammonium salt represented by the general formula (1); more preferably at least one selected from the group consisting of alkyltrimethylammonium bromide and alkyltrimethylammonium chloride; more preferably dodecyltrimethyl The method for producing hollow silica particles according to any one of [1] to [23], which is ammonium chloride.
[R ¹ (CH ₃ ) ₃ N] ⁺ X ⁻ (1)
[R ¹ R ² (CH ₃ ) ₂ N] ⁺ X ⁻ (2)
However, in the formula, R ¹ and R ² each independently represent a linear or branched alkyl group having 4 to 22 carbon atoms, and X ⁻ represents a monovalent anion.
[25] The silica source is a silica source that generates a silanol compound by hydrolysis; preferably one or more selected from compounds represented by the following general formulas (3) to (7); more preferably general In the formula (3), Y is an alkoxy group having 1 to 3 carbon atoms or a halogen group excluding fluorine, preferably an alkoxy group having 1 to 2 carbon atoms. In the general formula (4) or (5), , R ³ is a phenyl group, a benzyl group, or a hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, in which a part of hydrogen atoms are substituted with fluorine atoms More preferably, R ³ is a trialkoxysilane or dialkoxysilane, wherein R ³ is a phenyl group, a benzyl group, a methyl group or an ethyl group. In the general formula (7), Y is a methoxy group, and R ⁴ Is a methylene group, ethylene group or phenylene group; more preferably at least one selected from the group consisting of tetramethoxysilane, tetraethoxysilane, and phenyltriethoxysilane; and still more preferably tetramethoxysilane. The method for producing hollow silica particles according to any one of [1] to [24].
SiY ₄ (3)
R ³ SiY ₃ (4)
R ³ ₂ SiY ₂ (5)
R ³ ₃ SiY (6)
Y ₃ Si—R ⁴ —SiY ₃ (7)
In the formula, each R ³ independently represents an organic group in which a carbon atom is directly bonded to a silicon atom, R ⁴ represents a hydrocarbon group or a phenylene group having 1 to 4 carbon atoms, and Y represents A monovalent hydrolyzable group that becomes a hydroxy group by hydrolysis is shown.

  Hereinafter, the present invention will be described by way of examples. In Examples and Comparative Examples described later, various measurements and evaluations of hollow mesoporous silica particles were performed by the following methods.

(1) Measurement of powder X-ray diffraction (XRD) pattern Powder X-ray diffraction measurement was performed using a powder X-ray diffractometer (manufactured by Rigaku Corporation, trade name: RINT2500VPC). A continuous scanning method with a scanning range of diffraction angle (2θ) of 1 to 20 ° and a scanning speed of 4.0 ° / min was used.
X-ray source: Cu-kα
Tube voltage: 40 mA
Tube current: 40 kV
Sampling width: 0.02 °
Divergent slit: 1/2 °
Divergence slit length: 1.2mm
Scattering slit: 1/2 °
Receiving slit: 0.15mm

(2) Measurement of particle shape, average primary particle diameter, average hollow part diameter (average inner diameter of outer shell part) and average outer shell part thickness Transmission electron microscope (TEM) (manufactured by JEOL Ltd., trade name: JEM- 2100) was used to observe silica particles at an acceleration voltage of 160 kV. The diameter (primary particle diameter), hollow part diameter and outer shell part thickness of all particles in 5 fields containing 20 to 30 hollow silica particles are measured on the photograph, and the number average primary particle diameter and number average hollow are measured. The part diameter and the number average outer shell part thickness were determined. In addition, the observation of the silica particles was performed using a sample obtained by attaching a sample to a Cu mesh with a high-resolution carbon support film (200-A mesh, manufactured by Oken Shoji Co., Ltd.) and removing the excess sample by blowing.

(3) Measurement of BET specific surface area and average pore diameter Using a specific surface area / pore distribution measuring device (manufactured by Shimadzu Corporation, trade name: ASAP2020), parameter C is a multipoint method using liquid nitrogen. The BET specific surface area of the silica particles was measured in a range that becomes positive. The BJH method was employed to derive the pore size distribution, and the peak top was defined as the average pore size. The sample was pretreated by heating at 200 ° C. for 2 hours.

(5) Measurement of particle size of emulsified oil droplets Using a light scattering particle size distribution meter (LA-920, manufactured by Horiba, Ltd.), in water dispersion medium, ultrasonic intensity 7, ultrasonic irradiation 1 minute, relative refractive index 1 under the conditions of .06 was measured volume basis average particle size (D _50, median diameter) as the particle size of the emulsified oil droplets.

(6) Weight average molecular weight of polyvinyl alcohol The weight average molecular weight of polyvinyl alcohol was measured by the viscosity method (JIS-K6726).

(7) Amount of cation modification of polyvinyl alcohol It was determined from the composition of the monomer raw material and shown in Table 1.

(8) Saponification degree of polyvinyl alcohol The saponification degree of the polymer was measured according to JIS-K6726 and shown in Table 1.

  The details of the polyvinyl alcohol used in Examples and Comparative Examples are shown in Table 1.

<Example 1>
At 25 ° C., 1 g of dodecane (manufactured by Wako Pure Chemical Industries, Ltd.), 2 g of 5% by weight aqueous solution of polyvinyl alcohol 1 (trade name: PVA CM-318, manufactured by Kuraray Co., Ltd.) (polymer / dodecane = 0.1 mass ratio) , And 32 g of water (2.9% by mass of dodecane, 0.29% by mass of PVA) were stirred at 25 ° C. for 1 hour using a magnetic stirrer. An ultrasonic device (Ultrasonic homogenizer US-300T manufactured by Nippon Seiki Kogyo Co., Ltd., rated output 300 W, oscillation frequency 19 kHz, Tip select: 20φ (20 mm), output: 400 μA) was used for this mixed solution at 5 ° C. Then, ultrasonic vibration was applied for 10 minutes to emulsify the mixed solution (step (I)). The volume-based average particle diameter (D ₅₀ ) of the emulsified oil droplets was 440 nm.

  The obtained emulsion containing dodecane emulsified oil droplets (dodecane emulsified oil droplet dispersion) is an emulsion in which phase separation (release of dodecane) has not occurred and the emulsified oil droplets are uniformly dispersed. Was confirmed visually. In addition, the dodecane emulsified oil droplet dispersion was excellent in storage stability even after standing at room temperature for 1 day or longer.

At 25 ° C., 0.15 g of a cationic surfactant dodecyltrimethylammonium chloride (hereinafter abbreviated as C12TAC) (manufactured by Tokyo Chemical Industry Co., Ltd.), 10 g of water, which is an alkaline agent, 0.18 g of tetramethylammonium oxide (hereinafter abbreviated as TMAOH) (manufactured by Wako Pure Chemical Industries, Ltd., 25% aqueous solution) was added and stirred for 2 hours (step (II-a)). The volume-based average particle size (D ₅₀ ) of the emulsified oil droplets in the aqueous dispersion of dodecane emulsified oil droplets containing the cationic surfactant and the alkali agent was 660 nm.

  Next, at 25 ° C., 0.46 g of tetramethoxysilane (hereinafter abbreviated as TMOS) (manufactured by Tokyo Chemical Industry Co., Ltd.) as a silica source is added to the dodecane emulsified oil droplets aqueous dispersion containing the surfactant. Further, stirring was continued at 25 ° C. for 2 hours to obtain an aqueous dispersion of composite mesoporous silica particles (step (II-b)).

  After drying the composite silica aqueous dispersion (100 ° C., 1 day), using a baking furnace (manufactured by Motoyama Co., Ltd., Superburn), airflow (flow rate 3 L / min) to 600 ° C. over 6 hours After the temperature rise, firing was performed at 600 ° C. for 2 hours to obtain hollow mesoporous silica particles (step (III)).

  Table 3 shows the average primary particle diameter, average outer shell part thickness, average hollow part diameter, XRD peak spacing (d), average pore diameter, and BET specific surface area of the hollow mesoporous silica particles of Example 1. 1 is a TEM image of the hollow mesoporous silica particles of Example 1. FIG.

In addition, in Table 2, the density | concentration of each component used for manufacture of the silica particle of Examples 1-7 and Comparative Examples 1-4 was shown. Hydrophobic organic compounds and polymers are in the concentration in the mixed solution in step (I), and dodecyltrimethylammonium chloride and tetramethoxysilane are in the reaction solution in step (II).

<Example 2>
In Example 1, except that the 5 mass% aqueous solution of polyvinyl alcohol 1 (trade name: PVA CM-318, manufactured by Kuraray Co., Ltd.) was changed to 1 g (polymer / dodecane = 0.05 mass ratio) and 34 g of water. In the same manner as in Example 1, hollow mesoporous silica particles were produced.

  Table 3 shows the average primary particle diameter, average outer shell thickness, average hollow diameter, XRD peak spacing (d), average pore diameter, and BET specific surface area of the hollow mesoporous silica particles of Example 2.

<Example 3>
In Example 1, 0.2 g (polymer / dodecane = 0.01 mass ratio) of a 5% by mass aqueous solution of polyvinyl alcohol 1 (trade name: PVA CM-318, manufactured by Kuraray Co., Ltd.) used for adjusting the mixed solution, Hollow mesoporous silica particles were produced in the same manner as in Example 1 except that the water was changed to 34.8 g.

  Table 3 shows the average primary particle diameter, average outer shell thickness, average hollow diameter, XRD peak spacing (d), average pore diameter, and BET specific surface area of the hollow mesoporous silica particles of Example 3.

<Example 4>
In Example 1, hollow mesoporous silica particles were produced in the same manner as in Example 1 except that polyvinyl alcohol 2 (trade name: PVA C-506, manufactured by Kuraray Co., Ltd.) was used instead of polyvinyl alcohol 1.

  Table 3 shows the average primary particle diameter, average outer shell thickness, average hollow diameter, XRD peak spacing (d), average pore diameter, and BET specific surface area of the hollow mesoporous silica particles of Example 4.

<Example 5>
Hollow mesoporous silica particles were produced in the same manner as in Example 1, except that stearyl methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) was used instead of dodecane.

  Table 3 shows the average primary particle diameter, average outer shell thickness, average hollow diameter, XRD peak spacing (d), average pore diameter, and BET specific surface area of the hollow mesoporous silica particles of Example 5.

<Example 6>
In Example 2, hollow mesoporous silica particles were produced in the same manner as in Example 2 except that stearyl methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) was used instead of dodecane.

  Table 3 shows the average primary particle diameter, average outer shell thickness, average hollow diameter, XRD peak face interval (d), average pore diameter, and BET specific surface area of the hollow mesoporous silica particles of Example 6.

<Example 7>
In Example 3, hollow mesoporous silica particles were produced in the same manner as in Example 3 except that stearyl methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) was used instead of dodecane.

  Table 3 shows the average primary particle diameter, average outer shell part thickness, average hollow part diameter, XRD peak spacing (d), average pore diameter, and BET specific surface area of the hollow mesoporous silica particles of Example 7.

<Comparative Example 1>
In Example 1, silica particles were produced in the same manner as in Example 1, except that the cationic surfactant dodecyltrimethylammonium chloride was not added.

As a result of performing XRD measurement on the silica particles of Comparative Example 1, no XRD peak derived from the mesopore structure was observed. From TEM observation, no hollow particles were observed, and the particles were amorphous silica particles. The BET specific surface area was 400 m ² / g. FIG. 2 is a TEM image of the silica particles of Comparative Example 1.

<Comparative example 2>
In Example 1, a dodecane emulsified droplet aqueous dispersion was prepared in the same manner as in Example 1 except that polyvinyl alcohol 1 was not added. In the dodecane emulsified oil droplets aqueous dispersion, phase separation was partially observed, and the emulsified oil droplets were unstable. Steps (II-a) to (III) were performed in the same manner as in Example 3 using the above-described dodecane emulsified oil droplet water dispersion in which partial phase separation was observed to produce silica particles.

As a result of XRD measurement of the silica particles of Comparative Example 2, an XRD peak (plane spacing d = 3.1 nm) derived from the mesopore structure was confirmed. From TEM observation, no hollow particles were observed, and the particles were amorphous silica particles. The BET specific surface area was 1100 m ² / g, and the average pore diameter was 1.8 nm.

<Comparative Example 3>
In Example 1, a dodecane emulsified droplet aqueous dispersion was prepared in the same manner as in Example 1 except that instead of applying ultrasonic vibration to the mixed liquid, magnetic stirring (rotation speed: 500 rpm, 60 minutes) was performed. In the dodecane emulsified oil droplets aqueous dispersion, phase separation was partially observed, and the emulsified oil droplets were unstable. Steps (II-a) to (III) were performed in the same manner as in Example 3 using the above-described dodecane emulsified oil droplet water dispersion in which partial phase separation was observed to produce silica particles.

As a result of XRD measurement on the silica particles of Comparative Example 3, an XRD peak (plane spacing d = 3.1 nm) derived from the mesopore structure was confirmed. From TEM observation, no hollow particles were observed, and the particles were amorphous silica particles. The BET specific surface area was 1200 m ² / g, and the average pore diameter was 1.8 nm.

<Comparative Example 4>
In a 500 mL flask, 100 g of methanol (manufactured by Wako Pure Chemical Industries, Ltd.), 6.2 g of dodecyltrimethylammonium chloride (hereinafter abbreviated as C12TAC) (manufactured by Tokyo Chemical Industry Co., Ltd.), 13 g of hexane (manufactured by Wako Pure Chemical Industries, Ltd.) The mixture was stirred and liquid A was prepared. In a 500 mL flask, 300 g of water and 10.7 g of tetramethylammonium hydroxide (hereinafter abbreviated as TMAOH) (manufactured by Wako Pure Chemical Industries, Ltd., 25% aqueous solution) were added and stirred to prepare solution B. Liquid B was added while stirring liquid A at 25 ° C., and then 22.1 g of tetramethoxysilane (hereinafter abbreviated as TMOS) (manufactured by Tokyo Chemical Industry Co., Ltd.) was added. An aqueous methanol mixed dispersion of silica particles was obtained. The concentrations of the dispersion are hexane = 2.9 mass%, C12TAC = 52 mmol / L, and TMOS = 322 mmol / L.

  Silica particles were produced by drying and firing the aqueous dispersion of composite silica particles in the same manner as in Example 1.

As a result of XRD measurement of the silica particles of Comparative Example 4, an XRD peak (plane spacing d = 3.0 nm) derived from the mesopore structure was confirmed. From TEM observation, no hollow particles were observed, and the particles were amorphous silica particles. The BET specific surface area was 1000 m ² / g, and the average pore diameter was 1.7 nm.

  From the above, when ultrasonic vibration is applied to a liquid mixture containing a hydrophobic organic compound and an aqueous solvent in the presence of polyvinyl alcohol, the silica equivalent concentration of the silica source in the reaction liquid containing the emulsified oil droplets and the silica source It was found that the hollow silica particles can be produced stably even when the particle size is high.

  As described above, according to the production method of the present invention, the hollow silica particles can be stably produced even if the silica-concentrated concentration of the silica source in the reaction solution is high, so that the productivity of the hollow silica particles can be increased.

Claims (10)

Providing an ultrasonic vibration to a mixed liquid containing a hydrophobic organic compound, polyvinyl alcohol and an aqueous solvent to form an emulsified oil droplet aqueous dispersion containing emulsified oil droplets containing the hydrophobic organic compound;
In the reaction liquid obtained by mixing the emulsified oil droplet water dispersion and the silica source in the presence of a cationic surfactant, the emulsified oil droplet surface has a mesoporous structure composed of components containing silica. Forming the outer shell,
Removing the emulsified oil droplets from the composite silica particles including the outer shell portion and the emulsified oil droplets present inside the outer shell portion. The method for producing hollow silica particles according to claim 1, wherein the step of forming the outer shell includes the following steps (II-a) and (II-b).
Step (II-a): A step of mixing the emulsified oil droplet water dispersion and the cationic surfactant.
Step (II-b): In a reaction liquid obtained by mixing a mixed liquid containing the emulsified oil droplet water dispersion and the cationic surfactant and the silica source, silica is added to the surface of the emulsified oil droplets. A step of forming an outer shell portion having a mesopore structure composed of the components to be included.   The method for producing hollow silica particles according to claim 1 or 2, wherein the content of the silica source in the reaction solution is 100 to 1000 mmol / L in terms of silica.   Content of the said hydrophobic organic compound in the said liquid mixture is 0.1-30 mass%, The manufacturing method of the hollow silica particle of any one of Claims 1-3.   The mass ratio of the polyvinyl alcohol and the hydrophobic organic compound (the mass of the polyvinyl alcohol / the mass of the hydrophobic organic compound) in the mixed liquid is 0.001 to 1, according to any one of claims 1 to 4. Of producing hollow silica particles.   The method for producing hollow silica particles according to any one of claims 1 to 5, wherein the polyvinyl alcohol is cation-modified polyvinyl alcohol.   The hollow silica particles are hollow mesoporous silica particles comprising an outer shell portion composed of a component containing silica and having a mesoporous structure, and a hollow portion existing inside the outer shell portion. The method for producing hollow silica particles according to any one of the above.   The method for producing hollow silica particles according to claim 7, wherein the hollow mesoporous silica particles have an average pore diameter of 1 to 10 nm and an average primary particle diameter of 50 nm to 5000 nm. The cationic surfactant is at least one surfactant selected from a quaternary ammonium salt represented by the following general formula (1) and a quaternary ammonium salt represented by the general formula (2). The manufacturing method of the hollow silica particle of any one of Claims 1-8.
[R ¹ (CH ₃ ) ₃ N] ⁺ X ⁻ (1)
[R ¹ R ² (CH ₃ ) ₂ N] ⁺ X ⁻ (2)
However, in the formula, R ¹ and R ² each independently represent a linear or branched alkyl group having 4 to 22 carbon atoms, and X ⁻ represents a monovalent anion.   The method for producing hollow silica particles according to any one of claims 1 to 9, wherein the silica source is a silica source that produces a silanol compound by hydrolysis.