JP2014055082A - Method for producing hollow silica particle - Google Patents

Abstract

The present invention provides a method for producing hollow silica particles, which can produce hollow silica particles stably even when the silica concentration calculated from the silica source in the reaction solution is high.
A step of pressurizing a mixed solution containing a hydrophobic organic compound, polyvinyl alcohol, and an aqueous solvent by a high-pressure emulsification method to form an emulsified oil droplet water dispersion containing emulsified oil droplets containing the hydrophobic organic compound. And a mesopore structure comprising a component containing silica on the surface of the emulsified oil droplets in a reaction liquid obtained by mixing the emulsified oil droplet water dispersion and the silica source in the presence of a cationic surfactant. And 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. A method for producing silica particles.
[Selection] Figure 1

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.

  Patent Document 1 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 2 discloses a method for producing hollow mesoporous silica particles using emulsified oil droplets obtained by adding an aqueous solvent to a solution containing hydrophobic organic substances such as rapeseed oil, hexane, and dodecane. Patent Document 3 discloses a method for producing hollow mesoporous silica particles using emulsified oil droplets obtained by a high-pressure emulsification method.

JP 2008-150229 A JP 2011-126761 A JP 2011-126747 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:
Pressurizing a mixed liquid containing a hydrophobic organic compound, polyvinyl alcohol and an aqueous solvent by a high-pressure emulsification method to form an emulsified oil droplet water dispersion containing emulsified oil droplets containing the hydrophobic organic compound;
The emulsified oil droplet aqueous dispersion and the silica source are mixed in the presence of a cationic surfactant to form an outer shell portion having a mesoporous structure composed of components containing silica on the surface of the emulsified oil droplet. Process,
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 hollow silica particles of Example 2. FIG. 3 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 inventors presume as follows.

  Since the mixed liquid containing the hydrophobic organic compound and the aqueous solvent is emulsified by adopting the high pressure emulsification method, the average primary particle diameter is small and the particle diameter even if the concentration of the hydrophobic organic compound in the mixed liquid is high. A hydrophobic organic compound having a narrow distribution can be easily obtained, and polyvinyl alcohol (hereinafter abbreviated as PVA) contained in the mixed solution is adsorbed on the surface of the droplet-like hydrophobic organic compound. Thus, emulsified oil droplets are formed. 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 in the reaction solution is high, 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 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 these 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 squalane are preferable. More preferable are alkanes having 10 to 18 carbon atoms, alkenes having 10 to 18 carbon atoms, cycloalkanes having 10 to 18 carbon atoms, and squalane, alkanes having 12 to 16 carbon atoms, alkenes having 12 to 16 carbon atoms, and 12 to 16 carbon atoms. Cycloalkanes and squalanes are more preferred, and dodecane, 1-dodecene, hexadecane, and squalane are even more preferred.

(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 the stability of the emulsified oil droplets, the aqueous solvent is water. Preferably it consists only of. 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 the general formula (1) and the general formula (2) is preferably a monovalent anion such as halide ion, hydroxide ion, or nitrate ion from the viewpoint of forming highly regular mesopores. Ion. 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 preferable, and alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is more preferable. More preferred is dodecyltrimethylammonium chloride.

  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): A mixed liquid containing a hydrophobic organic compound, polyvinyl alcohol, and an aqueous solvent is pressurized by a high-pressure emulsification method 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), “the emulsified oil droplet water dispersion and the silica source are mixed in the presence of a cationic surfactant” means, for example, the emulsified oil droplet water dispersion in the cationic interface. This can be done by mixing a silica source in the presence of an activator or 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, 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 the prepared mixed solution is pressurized by a high-pressure emulsification method to emulsify containing the hydrophobic organic compound. An emulsion containing oil droplets (emulsified oil droplet water dispersion) is formed.

  In the preparation of the mixed solution, 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, preferably 1 minute or more, more preferably 2 minutes or more, from the viewpoint of improving productivity, Preferably it is 60 minutes or less, More preferably, it is 10 minutes 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 maintained at 0 to 90 ° C. 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. .

  The content of the hydrophobic organic compound in the mixed solution is preferably 0.1% by mass or more from the viewpoint of increasing the silica equivalent concentration of the silica source used for forming the outer shell portion and improving the productivity. It is 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 solution is preferably 0.005% by mass or more and 0.01% by mass or more from the viewpoint of stabilizing the emulsified oil droplets and producing hollow silica particles having a highly uniform particle structure. More preferably, it is more preferably 0.02% by mass or more. Moreover, from a viewpoint of stable emulsified oil droplet formation and economical efficiency, it is preferable in it being 3 mass% or less, more preferable in it being 1 mass% or less, and still more preferable in it being 0.35 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 further preferable, and 0.010 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.

  The high-pressure emulsification of the mixed liquid is performed, for example, in a high-pressure dispersion unit of a high-pressure emulsification disperser. The high-pressure dispersion unit includes a thin channel. When the mixed liquid is pushed into the high-pressure dispersion section at a predetermined pressure and passes through the flow path, a shearing force or the like is applied to the mixed liquid, whereby the mixed liquid becomes an emulsion containing emulsified oil droplets.

  The cross-sectional shape of the flow path is not particularly limited as long as the mixed liquid can be pressurized at a predetermined pressure. For example, in the case of a circular shape, the diameter is preferably 20 to 200 μm, and more preferably 50 to 50 μm. 100 μm.

  Although there is no restriction | limiting in particular about the high-pressure emulsification disperser which can be used, From a viewpoint of the simplicity of handling operation, a microfluidizer (M-110EHi made by Mizuho Kogyo Co., Ltd.), Starburst (made by Sugino Machine Co., Ltd.), Nanomizer (Yoshida Machine Industry Co., Ltd.) And the like are preferred.

  The form of the high-pressure dispersion unit may be any of a collision type, a penetration type, a ball collision type, and the like. The counter-collision type has, for example, a structure in which a flow path is branched into a plurality of parts in the middle, and fluid flowing through each branch path can be collided at a portion where the flow paths merge again. The through type has, for example, a structure in which a plurality of through holes having a uniform diameter are integrated. The ball collision type has a structure in which the material can be atomized by causing the material injected at an ultra-high pressure to collide with a ceramic ball.

  From the viewpoint of forming a stable emulsified oil droplet with a narrow particle size distribution, the pressure applied to the mixture when high-pressure emulsification of the mixture is preferably 20 to 250 MPa, more preferably 30 to 220 MPa, and further 40 to 200 MPa. preferable. By adjusting the pressure applied to the mixed liquid, it is possible to form emulsified oil droplets having a desired average primary particle size and a narrow particle size distribution. The said pressure can be confirmed with the pressure display part with which a high-pressure emulsification disperser is equipped.

  The number of high-pressure emulsification treatments may be appropriately selected according to the pressure and the desired average primary particle size of the emulsified oil droplets, etc. From the viewpoint, it is preferably 1 to 10 times, more preferably 1 to 5 times.

  The set temperature of the apparatus when performing the high-pressure emulsification treatment, that is, the cooling temperature, is preferably 0 ° C. or higher, more preferably 5 ° C. or higher, and 90 ° C. or lower from the viewpoint of productivity improvement and stable emulsified oil droplet formation. Preferably, it is 50 ° C. or less, more preferably 30 ° C. or less, and even more preferably 20 ° C. or less.

In 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, 300 nm or more is more preferable, 5000 nm or less is preferable, 1000 nm or less is more preferable, and 600 nm or less is still more preferable.

[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 the aspect 1, from the viewpoint of obtaining hollow silica particles having a highly uniform particle structure, it is preferable that the cationic surfactant is added to the emulsified oil droplet water dispersion together with the alkaline agent, and the cationic surfactant and the alkaline agent are added. The emulsified oil droplet aqueous dispersion is preferably sufficiently stirred before the silica source is added, and the stirring time is preferably 1 minute to 10 hours, more preferably 10 minutes to 5 hours. More preferably, it is 30 minutes to 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 cationic surfactant and alkali agent are added and the silica source is added is 8.5 to 12.0. Is preferable, and 9.0-11.5 is more preferable.

The volume-based average particle diameter (D ₅₀ ) of the emulsified oil droplets in the coexistence with the cationic surfactant and the alkali agent is a viewpoint of forming hollow silica particles having a large porosity and a uniform particle structure. Therefore, 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 850 nm or less is still 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 0.1 to 2 hours.

  From the viewpoint of efficiently hydrolyzing and dehydrating and condensing the silica source, the pH of the emulsified oil droplet water dispersion before the addition of the alkaline agent and the cationic surfactant and the silica source is 8.5 to 12. 0 is preferable, and 9.0 to 11.5 is more preferable.

  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 agglomeration of each hollow silica particle to be generated, 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 even after the addition of the silica source is completed. It is preferable to keep stirring at -80 ° C, more preferably 10-50 ° C, preferably 0.01-5 hours, more preferably 1-3 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 15 from the viewpoint of suppressing the fluctuation of the stability of the emulsified oil droplets and the concentration of the cationic surfactant in the reaction solution. It is 90 degreeC or more, Preferably it is 90 degrees C or less, More preferably, it is 80 degrees C or less, More preferably, it is 50 degrees C or less, More preferably, it is 35 degrees C or less.

  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. From the viewpoint of obtaining hollow silica particles having a highly uniform particle structure, it is preferably 12% by mass or less, more preferably 6% by mass or less, still more preferably 4.8% by mass or less, and more preferably 3.6% by mass or less. More preferably, 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 0.5% by mass or less from the viewpoints of stable emulsion oil droplet formation and economy.

  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. Moreover, from the same viewpoint, 500 mmol / L or less is preferable, 100 mmol / L or less is more preferable, and 70 mmol / L or less is still more preferable.

  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, 0.01 or more is preferable, 0.05 or more is more preferable, and 0.10 or more is still more preferable. From the same viewpoint, it is preferably 10 or less, more preferably 1 or less, still more preferably 0.5 or less, and even more preferably 0.25 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. 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. When one or more peaks having apexes in the region of the diffraction angle (2θ) exist, 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, BET specific surface area is preferably 500 meters ² / g or more, more preferably 700 meters ² / g or more, further preferably 900 meters ² / g or more, preferably not more than 1500 m ² / g, More preferably, hollow mesoporous silica particles having a size of 1400 m ² / g or less, more preferably 1300 m ² / g or less can be produced.

  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 hydrocarbon 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 500 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 800 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, preferably 700 nm or less, more preferably 500 nm or less, still more preferably. Hollow mesoporous silica particles of 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, the average primary particle size of the entire hollow silica particles obtained by the production method of the present invention is preferably 80% or more, more preferably 82% or more, and still more preferably 85% or more. Hollow silica particles having a primary particle size in the range of 30% and composed of a group of particles having a very uniform 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, 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.

  According to the production method of the present invention, the porosity is preferably 5% or more, more preferably 10% or more, still more preferably 15% or more, preferably 60% or less, more preferably 55% or less, More preferably, hollow silica particles of 50% 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 [27].

[1] A step of pressurizing a mixed liquid containing a hydrophobic organic compound, polyvinyl alcohol and an aqueous solvent by a high-pressure emulsification method to form an emulsified oil droplet water 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.
[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, 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 Is 10 mass% or less, More preferably, it is 4 mass% or less, The manufacturing method of the hollow silica particle in any one of said [1]-[3].
[5] The hydrophobic organic compound is at least one selected from the group consisting of alkanes having 5 to 18 carbon atoms, alkenes having 5 to 18 carbon atoms, cycloalkanes having 5 to 18 carbon atoms, and squalane; At least one selected from the group consisting of alkanes having 10 to 18 carbon atoms, alkenes having 10 to 18 carbon atoms, cycloalkanes having 10 to 18 carbon atoms and squalane; more preferably alkanes having 12 to 16 carbon atoms and 12 to 16 carbon atoms [1] to [1], which is at least one selected from the group consisting of alkenes, cycloalkanes having 12 to 16 carbon atoms and squalane; more preferably at least one selected from the group consisting of dodecane, 1-dodecene, hexadecane and squalane. The method for producing hollow silica particles according to any one of [4].
[6] 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 [5].
[7] The method for producing hollow silica particles according to any one of [1] to [6], wherein the polyvinyl alcohol is cation-modified polyvinyl alcohol.
[8] The hollow portion according to [7], wherein the polyvinyl alcohol has a cation modification amount of 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.
[9] The method for producing hollow silica particles according to [7] or [8], wherein the cationic group introduced into the polyvinyl alcohol is a quaternary ammonium type.
[10] 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 [9] above.
[11] 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 [7] to [10].
[12] The weight average molecular weight of the polyvinyl alcohol is 5000 or more, preferably 10,000 or more, more preferably 20000 or more, 300000 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 [11], which is 300,000, preferably 10,000 to 200,000, more preferably 20000 to 90,000.
[13] The content of 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 [12], which is preferably 1% by mass or less, more preferably 0.35% by mass or less.
[14] The volume-based average particle diameter (D ₅₀ ) of the emulsified oil droplets in the step of forming the emulsified oil droplet aqueous dispersion is 10 nm or more, preferably 100 nm or more, more preferably 300 nm or more, and 5000 nm. Hereinafter, the method for producing hollow silica particles according to any one of [1] to [13], which is preferably 1000 nm or less, more preferably 600 nm or less.
[15] 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. The method for producing hollow silica particles according to any one of [1] to [14] above, which is 5000 nm or less, preferably 1000 nm or less, and more preferably 850 nm or less.
[16] 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 [15], preferably 100 mmol / L or less, more preferably 70 mmol / L or less.
[17] 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. The above [1] to [16], 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. The method for producing hollow silica particles according to any one of the above.
[18] The hollow silica particles 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] The method for producing hollow silica particles according to any one of [17].
[19] 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 300 nm or more. More preferably, it is 500 nm or more, 5000 nm or less, preferably 3000 nm or less, more preferably 2000 nm or less, still more preferably 1200 nm or less, the method for producing hollow silica particles according to the above [18].
[20] BET specific surface area of the hollow mesoporous silica particles, 500 meters ² / g or more, preferably 700 meters ² / g or more, more preferably 900 meters ² / g or more, 1500 m ² / g or less, preferably 1400 m ² / The method for producing hollow silica particles according to [18] or [19] above, which is not more than g, more preferably not more than 1300 m ² / g.
[21] In the step of removing the emulsified oil droplets from the composite silica particles, the composite silica particles are calcined 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 [18] to [20], wherein the emulsified oil droplets are removed from the composite silica particles.
[22] The production of the hollow silica particles according to any one of [1] to [17], wherein the hollow silica particles are hollow silica particles in which the outer shell portion does not have a mesopore structure. Method.
[23] The BET specific surface area of the hollow silica particles is 1 m ² / g or more, preferably 2 m ² / g or more, more preferably 3 m ² / g or more, 300 m ² / g or less, preferably 100 m ² / g. Hereinafter, the method for producing hollow silica particles according to [22], which is more preferably 50 m ² / g or less.
[24] The average primary particle diameter of the hollow silica particles is 50 nm or more, preferably 100 nm or more, more preferably 300 nm or more, 5000 nm or less, preferably 3000 nm or less, more preferably 1000 nm or less [22] or The method for producing hollow silica particles according to [23].
[25] In the step of removing the emulsified oil droplets from the composite silica particles, the composite silica particles are baked at 900 ° C or higher, preferably 950 ° C or higher, 1200 ° C or lower, preferably 1100 ° C or lower, The method for producing hollow silica particles according to any one of [22] to [24], wherein the emulsified oil droplets are removed from the composite silica particles.
[26] 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 [25] above, 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.
[27] The silica source is a silica source that produces 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 phenyl group, a benzyl group, a methyl group or an ethyl group, and in the general formula (7), Y is a methoxy group, and R ⁴ is a methylene group, an ethylene group or a phenylene group. ; More preferably, it is at least one selected from the group consisting of tetramethoxysilane, tetraethoxysilane, and phenyltriethoxysilane; and more preferably tetramethoxysilane, any one of [1] to [26] The manufacturing method of the hollow silica particle of description.
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.

(4) Measurement of porosity of hollow silica particles whose outer shell portion does not have a mesoporous structure Deaeration treatment for 1 minute using a true density measuring device (trade name: Ultra Pycnometer 1000, manufactured by Kantachrome Co., Ltd.) Then, the average value of 10 measurements was taken as the true density. The porosity was calculated from the true density of hollow silica and the true density of silica (2.2 g / cm ³ ).

(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 Measured under the condition of 0.06. The volume-based average particle diameter (D ₅₀ , median diameter) was used as the particle diameter of the emulsified oil droplets.

(6) Weight average molecular weight of polymer The weight average molecular weight of the polymer was measured by a viscosity method (JIS-K6726) and shown in Table 1.

(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 polyvinyl alcohol was measured according to JIS-K6726 and shown in Table 1.

  Details of the polymers used in Examples and Comparative Examples are shown in Table 1.

<Example 1>
At 25 ° C., 40 g (polymer / dodecane = 0.1 mass ratio) of 20 g of dodecane (manufactured by Wako Pure Chemical Industries, Ltd.) and 5% by mass aqueous solution of polyvinyl alcohol 1 (trade name: PVA CM-318, manufactured by Kuraray Co., Ltd.) ), And a mixed solution composed of 640 g of water was stirred at 25 ° C. for 2 minutes using a pencil mixer. A high-pressure emulsification apparatus (trade name: Starburst HJP-25005, cooling temperature: 15 ° C., manufactured by Sugino Machine Co., Ltd.) equipped with a ball collision type chamber (manufactured by Sugino Machine Co., Ltd.) having a flow path diameter of 100 μm. ) And an emulsification treatment was performed on the mixed solution by applying a pressure of 70 MPa to the mixed solution (step (I)). The volume-based average particle diameter (D ₅₀ ) of the emulsified oil droplets was 440 nm.

  The resulting emulsion containing dodecane emulsified oil droplets (dodecane emulsified oil droplet water dispersion) is an emulsion in which phase separation (free release of dodecane) has not occurred and the emulsified oil droplets are uniformly dispersed. Was confirmed visually. Moreover, there was no phase separation even after standing at room temperature for 1 day or more, and the dodecane emulsified oil droplets aqueous dispersion was excellent in storage stability.

At 25 ° C., 5.3 g of dodecyltrimethylammonium chloride (hereinafter abbreviated as C12TAC) (manufactured by Tokyo Chemical Industry Co., Ltd.), which is a cationic surfactant, 7.5 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 diameter (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 530 nm.

  Next, 10.25 g of tetramethoxysilane (hereinafter referred to as TMOS) (manufactured by Tokyo Chemical Industry Co., Ltd.) as a silica source is added to the dodecane emulsified oil droplet water dispersion containing the surfactant at 25 ° C. 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.

<Example 2>
The hollow mesoporous silica particles of Example 1 were heated up to 1000 ° C. over 10 hours using a baking furnace (Superburn, manufactured by Motoyama Co., Ltd.) and air flow (flow rate 3 L / min), and then 38 ° C. at 1000 ° C. By performing time firing, hollow silica particles having no mesopores were obtained.

  Table 3 shows the average primary particle diameter, average outer shell thickness, average hollow diameter, XRD peak spacing (d), average pore diameter, BET specific surface area, and porosity of the hollow silica particles of Example 2. 2 is a TEM image of silica particles having no mesopore structure of Example 2. FIG. In Example 1, after raising the temperature to 600 ° C. over 6 hours and firing at 600 ° C. for 2 hours, raising the temperature to 1000 ° C. over 10 hours and then firing at 1000 ° C. for 38 hours In addition, hollow silica particles having no mesopore structure were obtained.

<Examples 3 and 4>
In Examples 1 and 2, hollow mesoporous silica particles and hollow silica particles having no mesopore structure were produced in the same manner as in Example 1 except that the high-pressure emulsification pressure was changed to 100 MPa.

<Examples 5 and 6>
In Examples 3 and 4, hollow mesoporous silica particles and hollow silica particles having no mesoporous structure were produced in the same manner as in Examples 3 and 4 except that the polymer / dodecane mass ratio was changed to 0.05. .

<Examples 7 and 8>
In Examples 3 and 4, hollow mesoporous silica particles and hollow silica particles having no mesoporous structure were produced in the same manner as in Examples 3 and 4 except that the polymer / dodecane mass ratio was changed to 0.01. .

<Examples 9 and 10>
In Examples 3 and 4, hollow mesoporous silica was obtained in the same manner as in Examples 3 and 4 except that polyvinyl alcohol 1 was changed to polyvinyl alcohol 2 (trade name: PVA K-210, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.). Particles, hollow silica particles having no mesopore structure were produced.

<Examples 11 and 12>
In Examples 3 and 4, hollow mesoporous silica particles and meso were obtained in the same manner as in Examples 3 and 4 except that polyvinyl alcohol 1 was changed to polyvinyl alcohol 3 (trade name: PVA C-506, manufactured by Kuraray Co., Ltd.). Hollow silica particles having no pore structure were produced.

<Examples 13 and 14>
In Examples 3 and 4, hollow mesoporous silica particles and mesofine were obtained in the same manner as in Examples 3 and 4 except that polyvinyl alcohol 1 was changed to polyvinyl alcohol 4 (trade name: PVA-505, manufactured by Kuraray Co., Ltd.). Hollow silica particles having no pore structure were produced.

<Examples 15 and 16>
In Examples 3 and 4, hollow mesoporous silica particles and mesofine particles were obtained in the same manner as in Examples 3 and 4 except that 1-dodecene (trade name: Linearlen 12, manufactured by Idemitsu Kosan Co., Ltd.) was used instead of dodecane. Hollow silica particles having no pore structure were produced.

<Examples 17 and 18>
In Examples 3 and 4, hollow mesoporous silica particles and hollow having no mesopore structure were obtained in the same manner as in Examples 3 and 4 except that hexadecane (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of dodecane. Silica particles were produced.

<Examples 19 and 20>
In Examples 3 and 4, hollow mesoporous silica particles and hollow having no mesopore structure were obtained in the same manner as in Examples 3 and 4 except that squalane (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of dodecane. Silica particles were produced.

<Comparative Example 1>
In Example 3, silica particles were produced in the same manner as in Example 3 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. 3 is a TEM image of the silica particles of Comparative Example 1.

<Comparative example 2>
In Example 3, a dodecane emulsified oil droplet water dispersion was prepared in the same manner as in Example 3 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 1210 m ² / g, and the average pore diameter was 1.8 nm.

<Comparative Example 3>
In Example 3, a dodecane emulsified oil droplet / water dispersion was prepared in the same manner as in Example 3 except that the mixture was subjected to high-pressure emulsification treatment instead of magnetic stirring (rotation speed: 500 rpm, 60 minutes). In the dodecane emulsified oil droplets aqueous dispersion, phase separation was partially observed, and the emulsified oil droplets were unstable. Using the emulsion in which the partial phase separation was observed, steps (II-a) to (III) were performed in the same manner as in Example 3 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 Example 3, instead of polyvinyl alcohol 1, polyvinyl pyrrolidone (trade name: PVP-K25, manufactured by Wako Pure Chemical Industries, Ltd.) was used. Prepared. 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) are carried out in the same manner as in Example 3 using the emulsion in which the partial phase separation is observed. Silica particles were produced.

As a result of XRD measurement of the silica particles of Comparative Example 4, an XRD peak (plane spacing d = 3.2 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 5>
In a 500 mL flask, methanol (Wako Pure Chemical Industries, Ltd.) 100 g, dodecyltrimethylammonium chloride (hereinafter abbreviated as C12TAC) (Tokyo Chemical Industry Co., Ltd.) 6.2 g, hexane (Wako Pure Chemical Industries, Ltd.) 13 g The solution A was prepared by stirring. 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. B liquid was added to A liquid while stirring A liquid at 25 ° C, then 22.1 g of tetramethoxysilane (hereinafter abbreviated as TMOS) (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and further stirred at 25 ° C for 5 hours Then, an aqueous methanol mixed dispersion of composite 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 5, 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.

In addition, in Table 2, the density | concentration of each component used for manufacture of the silica particle of Examples 1-20 and Comparative Examples 1-5 was shown. The concentration of the hydrophobic organic compound and the polymer is the concentration in the mixed solution in step (I), and the concentration of dodecyltrimethylammonium chloride and tetramethoxysilane is the concentration in the reaction solution in step (I).

  From the above, when a mixed liquid containing a hydrophobic organic compound and an aqueous solvent is pressurized by the high-pressure emulsification method in the presence of polyvinyl alcohol, the silica conversion 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 stably produced even when the concentration 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 (11)

Pressurizing a mixed liquid containing a hydrophobic organic compound, polyvinyl alcohol and an aqueous solvent by a high-pressure emulsification method to form an emulsified oil droplet water 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 to 5000 nm.   The method for producing hollow silica particles according to claim 1, wherein the hollow silica particles are hollow silica particles having no mesopore structure. 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 method for producing hollow silica particles according to any one of claims 1 to 9.
[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 10, wherein the silica source is a silica source that produces a silanol compound by hydrolysis.