WO2025028454A1 - Monovalent alkali metal ion-containing hollow silica sol and method for producing same - Google Patents

Abstract

[Problem] To provide an aqueous sol containing hollow silica particles having high stability, an organic solvent sol containing said silica particles, additionally, a method for improving the stability of the sol with reduced storage stability, and a method for producing the same. [Solution] The present invention provides a hollow silica sol that contains hollow silica particles having a space inside an outer shell and monovalent alkali metal ions and contains the monovalent alkali metal ions, in terms of the molar number obtained by conversion to M₂O (where M represents a monovalent alkali metal atom), in a ratio of 7.12×10^-6 to 285×10^-6 relative to the molar number of SiO₂ of the hollow silica particles, wherein the average particle diameter as measured by a dynamic light scattering method after storing the sol at 50°C for 48 hours is within a range of 2.0 times or less as compared with the average particle diameter as measured by the dynamic light scattering method before storage. The average particle diameter is 20-150 nm as measured by the dynamic light scattering method. Also provided is a stabilization method comprising adding, to a hollow silica sol having a dynamic-light-scattering-method particle diameter value increased as compared with the dynamic-light-scattering-method particle diameters during the production thereof, monovalent alkali metal ions at the above ratio relative to SiO₂ of hollow silica particles in said hollow silica sol to reduce the increased dynamic-light-scattering-method particle diameter value.

Description

Monovalent alkali metal ion-containing hollow silica sol and method for producing same

The present invention relates to a sol in which hollow silica particles containing monovalent alkali metal ions such as sodium ions are dispersed in water or an organic solvent, a method for producing the sol, and a coating-forming composition.

Hollow silica particles have a silica outer shell and a space inside the shell, and due to these characteristics, they have properties such as a low refractive index, low thermal conductivity (thermal insulation), and electrical insulation.
Hollow silica particles consist of a core, which corresponds to the hollow portion, and a shell that forms the outside of the core. An aqueous dispersion of hollow silica particles can be obtained by forming a silica layer on the outside of the core in an aqueous medium and then removing the core.
Disclosed is a silica-based fine particle having a cavity inside an outer shell, characterized in that the average particle size is in the range of 5 to 500 nm, the refractive index is in the range of 1.15 to 1.38, the molar ratio M _{O X /} SiO ₂ is in the range of 0.0001 to 0.2 when silica is represented by SiO ₂ and inorganic oxides other than silica are represented by M O X, and the content of alkali metal oxide as A ₂ O (A: alkali metal element) is 5 ppm or less (see Patent Document 1).

Disclosed is a silica-based microparticle having a porous substance and/or cavities inside an outer shell layer, characterized in that the ratio (SB/SC) of the specific surface area (SB) of the microparticle measured by the BET method to the specific surface area (SC) represented by the following formula is in the range of 1.1 to 5, the refractive index is in the range of 1.15 to 1.38, the content of alkali metal oxide is 5 ppm or less as _M2O (M: alkali metal element) per silica-based microparticle, and the content of ammonia and/or ammonium ion is 1500 ppm or less as _NH3 per silica-based microparticle (see Patent Document 2).
SC (m ² /g) = 6000/Dp (nm)・ρ
(where Dp is the average particle diameter (nm) of the silica-based fine particles, and ρ is the density (g/ml).)

Patent Publication 2011-046606 Patent Publication No. 2013-121911

The present invention relates to an aqueous sol and an organic solvent sol containing highly stable hollow silica particles, and further to a method for improving the stability of the above sol whose storage stability has decreased, and a method for producing the same.

In a first aspect, the present invention provides a hollow silica sol comprising hollow silica particles having a space inside an outer shell and monovalent alkali metal ions, the number of moles of the monovalent alkali metal ions converted to M ₂ O (wherein M represents a monovalent alkali metal atom) being 7.12×10 ^-6 to 285×10 ^-6 relative to the number of moles of SiO ₂ of the hollow silica particles, the average particle size measured by dynamic light scattering method after storing the sol at 50° C. for 48 hours being within a range of 2.0 times the average particle size measured by dynamic light scattering method before said storage;
or a sol comprising hollow silica particles having a space inside an outer shell and a monovalent alkali metal ion in a molar ratio of 7.12×10 ⁻⁶ to 285×10 ⁻⁶ relative to the SiO ₂ of the hollow silica particles, calculated as M ₂ O (wherein M is a monovalent alkali metal), and the particle diameter value measured by a dynamic light scattering method after storing the sol at 50° C. for 48 hours is within a range of 2.0 times that before storage;
As a second aspect, the hollow silica sol according to the first aspect, wherein the monovalent alkali metal ion is a sodium ion.
As a third aspect, the hollow silica sol according to the first aspect or the second aspect, which has an average particle size of 20 to 150 nm as measured by a dynamic light scattering method.
As a fourth aspect, the hollow silica sol according to any one of the first to third aspects, further comprising an amine, the amine being present in an amount of 0.001 to 10 mass% relative to the SiO ₂ of the hollow silica particles.
As a fifth aspect, the hollow silica sol according to the fourth aspect, in which the amine is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines having 1 to 10 carbon atoms.
As a sixth aspect, the hollow silica sol according to the fourth or fifth aspect, wherein the amine is a water-soluble amine having a water solubility of 80 g/L or more.
As a seventh aspect, the hollow silica sol according to any one of the first to sixth aspects, further comprising: the hollow silica particles containing aluminum atoms forming aluminosilicate sites, the aluminum atoms being bonded to the surfaces of the hollow silica particles; the mass of the aluminum atoms being in a range of a ratio (A ₎ of 100 to 20,000 ppm in terms of Al ₂ O ₃ relative to the mass of SiO 2 of the hollow silica particles; and the mass of the aluminum atoms being a value measured by a leaching method.
or the hollow silica _sol according to any one of the first to sixth aspects, further comprising hollow silica particles which contain aluminum atoms forming aluminosilicate sites, and the aluminum atoms are bonded to the surface of the hollow silica particles at a ratio (A ₎ of 100 to 20,000 ppm/ _SiO2 in terms of _Al2O3 relative to 1 g of SiO2 of the hollow silica particles, as measured by a leaching method.
As an eighth aspect, the hollow silica sol according to the seventh aspect, in which aluminum atoms are leached from a compound containing aluminum atoms bonded to the surface of the hollow silica particles, and the leaching method measurement uses an aqueous solution of at least one mineral acid selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid.
or the hollow silica sol according to the seventh aspect, wherein the leaching method measurement is performed by leaching hollow silica particles with an aqueous solution of at least one mineral acid selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid, and measuring the ratio (A) of a compound containing aluminum atoms bonded to the surface of the hollow silica particles, calculated as Al ₂ O ₃ , per 1 g of SiO ₂ of the hollow silica particles.
As a ninth aspect, the hollow silica sol according to the seventh or eighth aspect, wherein a mass of aluminum atoms present in the entire hollow silica particles is expressed as a ratio (B) of 120 to 50,000 ppm in terms of Al ₂ O ₃ relative to a mass of SiO ₂ of the hollow silica particles, the mass of the aluminum atoms is a value measured by dissolving the hollow silica particles in an aqueous hydrofluoric acid solution, and the ratio (A)/the ratio (B) is 0.002 to 1.0.
or the hollow silica sol according to the _seventh or _eighth aspect, in which aluminum atoms present throughout the hollow silica particles as measured by dissolving the hollow silica particles in an aqueous hydrofluoric acid solution are bonded at a ratio (B) of 120 to 50,000 ppm/ _SiO2 in terms of Al2O3 relative to 1 g of _SiO2 of the hollow silica particles, and the ratio (A)/(B) is 0.001 to 1.0.
As a tenth aspect, the hollow silica sol according to any one of the first to ninth aspects, comprising the hollow silica particles, in which a ratio of [specific surface area (C) of the silica particles measured by a BET method (nitrogen gas adsorption method)]/[specific surface area (D) of the silica particles measured by a transmission electron microscope] is 1.40 to 5.00.

（式（１）中、
Ｒ^１は、ケイ素原子に結合する基であって、互いに独立して、
アルキル基、ハロゲン化アルキル基、アルケニル基、アリール基を表すか、又はエポキシ基、（メタ）アクリロイル基、メルカプト基、アミノ基、ウレイド基、ポリエーテル基、カルボキシ基、保護されたカルボキシ基、カルボキシ基発生基、イミド基、もしくはシアノ基を有する有機基であり且つＳｉ－Ｃ結合によりケイ素原子と結合している基を表すか、あるいはこれらの基の組み合わせを表し、
Ｒ^２は、ケイ素原子に結合する基又は原子であって、互いに独立して、炭素原子数１以上のアルコキシ基、アシルオキシ基、ヒドロキシ基、又はハロゲン原子を表すか、あるいはこれらの基の組み合わせを表し、
ａは１～３の整数を表し、
式（２）中、
Ｒ^３は、ケイ素原子に結合する基であって、互いに独立してアルキル基、ハロゲン化アルキル基、アルケニル基、アリール基を表すか、又はエポキシ基、（メタ）アクリロイル基、メルカプト基、アミノ基、ウレイド基、ポリエーテル基、カルボキシ基、保護されたカルボキシ基、カルボキシ基発生基、イミド基、もしくはシアノ基を有する有機基であり且つＳｉ－Ｃ結合によりケイ素原子と結合している基を表すか、あるいはこれらの基の組み合わせを表し、
Ｒ^４は、ケイ素原子に結合する基又は原子であって、互いに独立して炭素原子数１以上のアルコキシ基、アシルオキシ基、ヒドロキシ基、又はハロゲン原子を表すか、あるいはこれらの基の組み合わせを表し、
Ｙは、ケイ素原子に結合する基又は原子であって、アルキレン基、ＮＨ基、又は酸素原子を表し、
ｂは１～３の整数を表し、ｃは０又は１の整数を表す。）
で表される化合物からなる群より選ばれる少なくとも１種のシラン化合物で被覆されている中空シリカ粒子を含む、請求項１乃至請求項１１のいずれか１項に記載の中空シリカゾル、
第１３観点として、分散媒が水、炭素原子数１～１０のアルコール、ケトン、エーテル、アミド、ウレア、又はエステルである、第１観点乃至第１２観点のいずれか一つに記載の中空シリカゾル、
第１４観点として、第１観点乃至第１３観点の何れか一つに記載の中空シリカゾルに由来する中空シリカ粒子と、有機樹脂又はポリシロキサンを含む、被膜形成組成物、
第１５観点として、第１４観点に記載の被膜形成組成物から得られた可視光線透過率が８０％以上である膜、
第１６観点として、下記（Ｉ）工程～（ＩＩ）工程：
（Ｉ）工程：分散媒を含む中空シリカゾルを準備する工程、
（ＩＩ）工程：（Ｉ）工程の中空シリカゾルに、中空シリカ粒子のＳｉＯ_２に対して１価アルカリ金属イオンをＭ_２Ｏ（ただし、Ｍは１価アルカリ金属原子を表す）に換算したモル比で７．１２×１０^－６～２８５×１０^－６の割合になるように１価アルカリ金属イオンを添加して調整する工程
を含む第１観点乃至第１３観点の何れか一つに記載の中空シリカゾルの製造方法、
第１７観点として、（ＩＩ）工程で１価アルカリ金属イオンがナトリウムイオンである、第１６観点に記載の中空シリカゾルの製造方法、
第１８観点として、上記（ＩＩ）工程でナトリウムイオン含有量の調整が、（Ｉ）工程で得られた中空シリカゾルを陽イオン交換樹脂に接触すること、又はナトリウム源を添加することである第１７観点に記載の中空シリカゾルの製造方法、
第１９観点として、上記（ＩＩ）工程でナトリウム源の添加が水酸化ナトリウムの添加である、第１７観点に記載の中空シリカゾルの製造方法、
第２０観点として、上記（Ｉ）工程及び（ＩＩ）工程の分散媒が、水、炭素原子数１～１０のアルコール、ケトン、エーテル、アミド、ウレア、又はエステルである、第１６観点乃至第１９観点のいずれか一つに記載の中空シリカゾルの製造方法、
第２１観点として、上記（Ｉ）工程、（ＩＩ）工程、又は両工程で下記（ｉ）乃至（ｉｖ）から選ばれる少なくとも一つの工程を付加する、第１６観点乃至第２０観点のいずれか一つに記載の中空シリカゾルの製造方法、
（ｉ）：中空シリカゾルにアミンを添加する事、
（ｉｉ）：アルミニウム源としてアルミン酸ナトリウムを添加し加熱して中空シリカ粒子にアルミノシリケートサイトを形成する事、
（ｉｉｉ）：分散媒を他の分散媒に置換する事、
（ｉｖ）：中空シリカ粒子を更に式（１）及び式（２）からなる群より選ばれる少なくとも１種のシラン化合物で被覆する事、
第２２観点として、外殻の内部に空間を有する中空シリカ粒子を含む中空シリカゾルの安定化方法であって、
製造時に比べて動的光散乱法による平均粒子径の値が増大した中空シリカゾルに、
上記１価アルカリ金属イオンをＭ_２Ｏ（ただし、Ｍは１価アルカリ金属原子を表す）に換算したモル数が該中空シリカゾル中の中空シリカ粒子のＳｉＯ_２のモル数に対して７．１２×１０^－６～２８５×１０^－６のモル比となるように該１価アルカリ金属イオンを添加し、
増大した動的光散乱法による平均粒子径を低下させる事を特徴とする、第１観点に記載の中空シリカゾルの安定化方法、
　又は、外殻の内部に空間を有する中空シリカ粒子を含む中空シリカゾルの安定化方法であって、製造時の動的光散乱法粒子径に比べて増大した動的光散乱法粒子径の値を有する中空シリカゾルに、該中空シリカゾル中の中空シリカ粒子のＳｉＯ_２に対して１価アルカリ金属イオンをＭ_２Ｏ（ただし、Ｍは１価アルカリ金属である。）に換算したモル比で
７．１２×１０^－６～２８５×１０^－６の割合で添加し、増大した動的光散乱法粒子径値を低下させる事を特徴とする、第１観点に記載の中空シリカゾルの安定化方法、及び
第２３観点として、上記１価アルカリ金属イオンがナトリウムイオンである、第２２観点に記載の中空シリカゾルの安定化方法である。 According to an eleventh aspect, the hollow silica sol according to any one of the first to tenth aspects includes hollow silica particles having a surface charge amount of 5 to 250 μeq/g per 1 g in terms of _SiO2 .
Or the hollow silica sol according to any one of the first to tenth aspects, comprising hollow silica particles having a surface charge amount calculated per 1 g of SiO ₂ of the hollow silica particles of 5 to 250 μeq/g.
As a twelfth aspect, the hollow silica particles may further be represented by the following formula (1) and formula (2):

(In formula (1),
^R1 is a group bonded to a silicon atom, and each R1 is independently
represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or represents an organic group having an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a polyether group, a carboxy group, a protected carboxy group, a carboxy group-generating group, an imido group, or a cyano group, and which is bonded to a silicon atom via a Si—C bond, or represents a combination of these groups;
^R2 is a group or atom bonded to a silicon atom, and each independently represents an alkoxy group having one or more carbon atoms, an acyloxy group, a hydroxy group, or a halogen atom, or represents a combination of these groups;
a represents an integer of 1 to 3;
In formula (2),
^R3 is a group bonded to a silicon atom, and each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, or an aryl group, or an organic group having an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a polyether group, a carboxy group, a protected carboxy group, a carboxy group-generating group, an imido group, or a cyano group and bonded to a silicon atom via a Si-C bond, or a combination of these groups;
^R4 is a group or atom bonded to a silicon atom, and each independently represents an alkoxy group having one or more carbon atoms, an acyloxy group, a hydroxy group, or a halogen atom, or represents a combination of these groups;
Y is a group or atom bonded to a silicon atom and represents an alkylene group, an NH group, or an oxygen atom;
b represents an integer of 1 to 3, and c represents an integer of 0 or 1.
The hollow silica sol according to any one of claims 1 to 11, comprising hollow silica particles coated with at least one silane compound selected from the group consisting of compounds represented by the following formula:
As a thirteenth aspect, the hollow silica sol according to any one of the first to twelfth aspects, in which the dispersion medium is water, an alcohol having 1 to 10 carbon atoms, a ketone, an ether, an amide, a urea, or an ester.
As a fourteenth aspect, there is provided a film-forming composition comprising hollow silica particles derived from the hollow silica sol according to any one of the first to thirteenth aspects, and an organic resin or a polysiloxane.
As a fifteenth aspect, a film obtained from the film-forming composition according to the fourteenth aspect, the film having a visible light transmittance of 80% or more.
As a sixteenth aspect, the present invention relates to a method for producing a method for producing a semiconductor device comprising the following steps (I) to (II):
Step (I): preparing a hollow silica sol containing a dispersion medium;
A process for producing a hollow silica sol according to any _one of the first to thirteenth aspects, comprising a process for adjusting by adding monovalent alkali metal ions to the hollow silica sol in the process (I) so that the molar ratio of the monovalent alkali metal ions converted into M ₂ O (wherein M represents a monovalent alkali metal atom) relative to the SiO 2 of the hollow silica particles is 7.12×10 ⁻⁶ to 285×10 ⁻⁶ ;
As a seventeenth aspect, the method for producing a hollow silica sol according to the sixteenth aspect, in which the monovalent alkali metal ion in the step (II) is a sodium ion;
As an eighteenth aspect, the method for producing a hollow silica sol according to the seventeenth aspect, in which the adjustment of the sodium ion content in the step (II) is performed by contacting the hollow silica sol obtained in the step (I) with a cation exchange resin or by adding a sodium source.
As a 19th aspect, the method for producing a hollow silica sol according to the 17th aspect, wherein the addition of the sodium source in the step (II) is addition of sodium hydroxide.
As a twentieth aspect, the method for producing a hollow silica sol according to any one of the sixteenth to nineteenth aspects, in which the dispersion medium in the steps (I) and (II) is water, an alcohol having 1 to 10 carbon atoms, a ketone, an ether, an amide, a urea, or an ester.
As a 21st aspect, the method for producing a hollow silica sol according to any one of the 16th to 20th aspects, further comprising adding at least one step selected from the following (i) to (iv) to the step (I), the step (II), or both of the steps:
(i): Adding an amine to a hollow silica sol;
(ii): adding sodium aluminate as an aluminum source and heating to form aluminosilicate sites in hollow silica particles;
(iii): replacing the dispersion medium with another dispersion medium;
(iv): further coating the hollow silica particles with at least one silane compound selected from the group consisting of formula (1) and formula (2);
As a twenty-second aspect, there is provided a method for stabilizing a hollow silica sol containing hollow silica particles having a space inside an outer shell, the method comprising the steps of:
The hollow silica sol has an increased average particle size measured by dynamic light scattering compared to when it was manufactured.
the monovalent alkali metal ion is added so that the molar ratio of the monovalent alkali metal ion converted into M ₂ O (wherein M represents a monovalent alkali metal atom) to the molar number of SiO ₂ of the hollow silica particles in the hollow silica sol is 7.12×10 ⁻⁶ to 285×10 ⁻⁶ ;
The method for stabilizing a hollow silica sol according to the first aspect, characterized in that the average particle size determined by an increased dynamic light scattering method is reduced.
Alternatively, there is provided a method for stabilizing a hollow silica sol containing hollow silica particles having a space inside an outer shell, the method being characterized in _that a monovalent alkali metal ion is added to a hollow silica sol having a dynamic light scattering particle diameter value that is increased compared to the dynamic light scattering particle diameter value at the time of production, in a molar ratio converted to M ₂ O (wherein M is a monovalent alkali metal) of 7.12×10 ^-6 to 285×10 ^-6 relative to the SiO 2 of the hollow silica particles in the hollow silica sol, thereby reducing the increased dynamic light scattering particle diameter value. As a twenty-third aspect, there is provided a method for stabilizing a hollow silica sol according to the twenty-second aspect, in which the monovalent alkali metal ion is a sodium ion.

A dispersion containing hollow silica particles (hollow silica sol) has stability, so that the hollow silica particles do not aggregate, and a hollow silica sol with little change in hollow silica particle diameter can be obtained. When a highly stable hollow silica sol is used as a coating film, the particle diameter changes little, so that the unevenness of the coating film surface can be reduced and the transparency can be improved.
The alkali metal ion (for example, sodium ion) in hollow silica sol is preferably within a certain range, and if it is too much, it may cause problems such as alkali metal ion elution from coating film or electric insulation of coating film.Also, if it is too little, the inside of the shell of hollow silica particles is hollow, and the specific gravity of hollow silica particles itself is lower than that of solid silica particles, so that when the repulsive force of particles is low, particles tend to gather and aggregate, and in this case, a certain amount of alkali metal ion (for example, sodium ion) is required to increase the repulsive force of particles.

In the present invention, the stability is improved by combining amine molecules and sodium ions as the alkaline component. It is believed that the repulsive force between silica particles is improved by the mutual presence of bulky amine molecules and sodium ions on the particle surface.
Furthermore, in the present invention, aluminosilicate sites can be formed by doping the silica particle surface with aluminum atoms, and the presence of an alkali metal that serves as a counter ion for the negatively charged aluminum atoms improves the stabilization of the aluminosilicate sites.

The present invention relates to a hollow silica sol which contains hollow silica particles having a space inside their shells and monovalent alkali metal ions, the molar ratio of the monovalent alkali metal ions being 7.12× ^10-6 to 285× ^10-6 relative to the _SiO2 of the hollow silica particles, calculated as _M2O (wherein M represents a monovalent alkali metal atom), and in which the particle size value (average particle size) measured by dynamic light scattering after storing the sol at 50°C for 48 hours is within a range of 2.0 times the particle size value measured by dynamic light scattering before storage.
Hollow silica particles have a silica shell and a space inside the shell. Hollow silica particles are obtained by forming a shell mainly composed of silica on the surface of a part corresponding to a core, called a template, in a dispersion medium, and then removing the part corresponding to the core.

Hollow silica particles are required to be stably dispersed in a dispersion medium, and the presence of silanol groups, organic functional groups, and aluminum-doped aluminosilicate sites on the surface of hollow silica particles are stabilized by adding monovalent alkali metal ions to the surface of hollow silica particles. The silanol groups, organic functional groups, and aluminosilicate sites have polymerizable functional groups such as hydroxyl groups, and the interaction between these polymerizable functional groups leads to particle destabilization and an increase in particle size due to weak condensation (entanglement) between particles and interparticle crosslinking due to hydrogen bonds, but the addition of monovalent alkali metal ions to these polymerizable functional groups changes the form of the hydroxyl groups, which is thought to suppress the cause of destabilization. These polymerizable functional groups may be destabilized by heating, and the stability of hollow silica sol can be evaluated by checking at 50°C for 48 hours.
Examples of monovalent alkali metal ions include lithium ion, sodium ion, potassium ion, rubidium ion and cesium ion, with lithium ion, sodium ion and potassium ion being preferred, and sodium ion being particularly preferred.

The content of the monovalent alkali metal ion can be 7.12×10 -6 to 285×10 -6, or 7.12×10 _-6 to 237× ₁₀ -6, or 7.12×10 ^-6 to 190×10 ^{-6, or 20×10 -6 to 285×10 -6} , or 50×10 ^-6 to 285×10 ^-6 _, in terms of a molar ratio of monovalent alkali _metal ion ^converted to ^M 2 O (wherein M represents a monovalent alkali metal atom) per mass of ^{SiO 2} of the ^hollow silica particles in the ^dispersion (sol).
The content of the monovalent alkali metal ion can be set to an amount equivalent to 15 ppm to 600 ppm, 15 ppm to 500 ppm, or 15 ppm to 400 ppm in terms of the molar ratio of monovalent alkali metal ion per mass of SiO2 _of the hollow silica particles in the dispersion (sol) converted to _M2O (wherein M represents a monovalent alkali metal atom).

The hollow silica sol of the present invention can be set to have an average particle size in the range of 20 to 150 nm as measured by dynamic light scattering. The value of the particle size as measured by dynamic light scattering after storing the hollow silica sol at 50° C. for 48 hours is within 2.0 times, 1.5 times, or 1.1 times that before storage. It is also included in the present invention that the particle size as measured by dynamic light scattering after storing the hollow silica sol at 50° C. for 48 hours is smaller than that before storage. Therefore, the lower limit can be set to 0.8 times or more, 0.9 times or more, or 1.0 times or more.
In the present invention, the stability of the hollow silica sol can be ensured by including sodium ions in the above range, and this is because sodium ions can be included in the above range before the sol containing hollow silica particles becomes unstable. Also, by adding the sodium ions to the sol containing the unstable hollow silica particles, the aggregated state of the hollow silica particles is released, and the particle size range of the hollow silica particles before aggregation can be restored.

In the present invention, the aluminum atoms can be expressed in terms of Al ₂ O 3 by measuring the aluminum present on the silica particle surface by leaching silica particles with an aqueous solution of at least one mineral acid selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid. That is, the mass of aluminum atoms measured by the leaching method is bonded to _the silica particles on the surface of the hollow silica particles at a ratio _(A) of ₁₀₀ to 20,000 ppm/SiO ₂ , or 100 to 15,000 ppm/SiO ₂ , 100 to 10,000 ppm/SiO ₂ , or 200 to 5,000 ppm/SiO ₂ , or 500 to 5,000 ppm/SiO ₂ , or 800 to 3,000 ppm/SiO ₂ relative to the mass of _{SiO 2} of the hollow silica particles, calculated as Al 2 O 3. The presence of aluminosilicate sites on the surface of silica particles is important for dispersion in solvents and resins.
The aluminum atoms present on the surface of the silica particles as aluminosilicates are leached (eluted) from the silica particles in an aqueous solution of at least one mineral acid selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid, with the aluminum atoms being in a structure similar to aluminum salt, aluminum oxide, or aluminum hydroxide, and the aluminum atoms can be measured from the solution using an ICP emission spectrometer and expressed in terms of Al ₂ O _3. In particular, a method of leaching (elution) using an aqueous nitric acid solution is used. The aqueous nitric acid solution used for leaching can be used in a pH range of 0.5 to 4.0, 0.5 to 3.0, 0.5 to 2.0, or 1.0 to 1.5, and typically, an aqueous nitric acid solution with a pH of 1.0 can be used. For example, 100 mL of the above-mentioned aqueous nitric acid solution is added to 1 g of silica, and the solution is kept at a temperature of 20 to 70° C. or 40 to 60° C. for 10 to 24 hours to elute the aluminum compounds from the surface of the silica particles, which can be used as an analytical sample.

In the present invention, the silica particle surface can be defined as the area where the aluminum compound can be eluted by the above-mentioned leaching. The silica gel obtained by evaporating the solvent from the silica sol and drying it at 250°C is ground to obtain silica powder, and 20 mL of a nitric acid aqueous solution of pH 1.0 is added to _0.2 g of the silica powder, shaken thoroughly, and then kept in a thermostatic chamber at 50°C for 17 hours. The aluminum content in the filtrate obtained by centrifugal filtration is measured with an ICP emission spectrometer, and the aluminum content converted to _Al2O3 is divided by the mass of the silica powder to obtain the amount of aluminum bound to the silica particle surface ( _Al2O3 / _SiO2 ) ₍ ppm).
Also, even when aluminosilicate is formed on the surface of silica particles, aluminosilicate may be selectively formed not only on the surface but also inside the silica particles depending on the production method. The mass of aluminum atoms present in the entire hollow silica particles including the surface and inside is bonded to the silica particles at a ratio (B ₎ of ₁₂₀ to 50,000 ppm/SiO ₂ , or 500 to 20,000 ppm/SiO ₂ , or 500 to 10,000 ppm/SiO ₂ , or 1,000 to 5,000 ppm/SiO ₂ , or 1,000 to 4,000 ppm/SiO ₂ in terms of Al 2 O 3 relative to the mass of SiO ₂ of the hollow silica particles.

The ratio (A)/(B), which is the ratio of aluminum present on the silica particle surface to the entire silica particle, can be set in the range of 0.001 to 1.0, or 0.01 to 1.0, or 0.1 to 1.0, or 0.3 to 1.0, or 0.4 to 1.0.
Silica particles are dissolved in a hydrofluoric acid solution to measure the aluminum atoms present in the entire silica particles, and the aluminum atoms present in the entire silica particles can be expressed in terms of Al ₂ O _3. That is, the aluminum atoms present as aluminosilicate in the entire silica particles can be measured from the solution by dissolving them in a hydrofluoric acid solution, and the aluminum atoms present in the entire silica particles can be expressed in terms of Al ₂ O _3. The hydrofluoric acid solution may have a concentration that can dissolve the silica particles, and for example, a 48 mass% hydrofluoric acid solution can be used. In addition, in order to completely dissolve the silica particles, the amount of hydrofluoric acid solution used must be at least equivalent to the silica particles, and a molar ratio of 1.1 to 1000 equivalents is preferable.

By forming aluminosilicate sites on the silica particle surface in this manner, the negative charge amount (surface charge amount) of the hollow silica particles present on the silica particle surface is measured in _a range of 5 to 250 μeq/g, 5 to 150 μeq/g, 5 to 100 μeq/g, 25 to 150 μeq/g, or 25 to 100 μeq/g per gram in terms of SiO2.
The hollow silica particles can be obtained as a hollow silica sol in which the hollow silica particles are dispersed in a dispersion medium. The hollow silica sol can be obtained as a sol in which the hollow silica particles are dispersed in a dispersion medium, and has an average particle size of 20 to 150 nm as measured by a dynamic light scattering method.
Hollow silica can be obtained by forming an outer shell, mainly composed of silica, on the surface of a part that corresponds to a core, called a template, in a dispersion medium, and then removing the part that corresponds to the core. In this state, it is a hollow silica aqueous sol.
The hollow silica aqueous sol thus obtained can be subjected to solvent substitution with an alcohol solvent as an organic solvent. The alcohol solvent is preferably an alcohol having 1 to 5 carbon atoms which may have an ether bond, such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, etc. Thereafter, if desired, the resulting mixture can be covered with a silane compound, and then the solvent can be further substituted with another organic solvent.

In the present invention, organic solvents include alcohols, ketones, ethers, amides, ureas, and esters having 1 to 10 carbon atoms.
The alcohol having 1 to 10 carbon atoms is an aliphatic alcohol, and examples of such alcohol include primary alcohols, secondary alcohols, and tertiary alcohols. Furthermore, it is also possible to use polyhydric alcohols, such as dihydric alcohols and trihydric alcohols.

Examples of the monohydric primary alcohol include methanol, ethanol, 1-propanol, 1-butanol, and 1-hexanol.
Examples of the monohydric secondary alcohol include 2-propanol, 2-butanol, cyclohexanol, propylene glycol monomethyl ether, and propylene glycol monoethyl ether.
An example of the monohydric tertiary alcohol is tert-butyl alcohol.
Examples of the dihydric alcohol include methanediol, ethylene glycol, and propylene glycol.
An example of the trihydric alcohol is glycerin.

As the ketone having 1 to 10 carbon atoms, an aliphatic ketone can be preferably used, such as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone, and methyl cyclopentanone.
As the ether having 1 to 10 carbon atoms, an aliphatic ether can be preferably used, such as dimethyl ether, ethyl methyl ether, diethyl ether, tetrahydrofuran, 1,4-dioxane, etc.

Examples of the amide having 5 to 20 carbon atoms include N-methylpyrrolidone, dimethylacetamide, and diethylacetamide.
Examples of ureas having 5 to 20 carbon atoms include tetramethylurea and 1,3-dimethyl-2-imidazolidinone.
As the ester having 1 to 10 carbon atoms, an aliphatic ester can be preferably used, for example, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl acrylate, ethyl acrylate, propyl acrylate, dimethyl maleate, diethyl maleate, dipropyl maleate, dimethyl adipate, diethyl adipate, dipropyl adipate, etc.

In the hollow silica aqueous sol and hollow silica organic solvent sol, which are the above raw materials, the average particle size of the hollow silica particles, as measured by a dynamic light scattering method (DLS method), can be in the range of 20 to 150 nm, or 30 to 150 nm, or 40 to 150 nm, or 50 to 150 nm, or 50 to 120 nm, or 50 to 100 nm.
The average primary particle size as determined by observation with a transmission electron microscope can be in the range of 20 to 150 nm, or 30 to 150 nm, or 40 to 150 nm, or 50 to 150 nm, or 50 to 120 nm, or 50 to 100 nm.

The specific surface area (C) measured by the BET method (nitrogen gas adsorption method) can be set to 18 to 200 m ² /g, or 50 to 160 m ² /g, or 60 to 160 m ² /g, or 70 to 160 m ² /g, or 80 to 150 m ² /g.
In addition, the specific surface area (D) calculated from a transmission electron microscope can be set to 18 to 136 m ² /g, or 18 to 90 m ² /g, or 18 to 68 m ² /g, or 18 to 54 m ² /g, or 18 to 27 m ² /g, or 18 to 23 m ² /g.

The ratio of [specific surface area (C) measured by the BET method (nitrogen gas adsorption method)]/[specific surface area (D) calculated from a transmission electron microscope] can be set in the range of 1.40 to 5.00, or 1.40 to 3.50, or 1.50 to 3.00, or 1.50 to 2.80. When the value of (C)/(D) is close to 1.0, the silica particles are solid silica particles with no space present inside the outer shell, and when the value of (C)/(D) exceeds 1.0, the silica particles are hollow silica particles with space present inside the outer shell.
The thickness of the shell of the hollow silica particles as determined by observation with a transmission electron microscope is in the range of 3.0 to 15.0 nm, or 4.0 to 12.0 nm, or 5.0 to 10.0 nm.
The refractive index of the hollow silica particles can be in the range of 1.20 to 1.45, or 1.20 to 1.40, or 1.25 to 1.40.

The hollow silica sol has a SiO ₂ particle concentration of 1 to 50% by mass, or 5 to 40% by mass, and can be typically used at 10 to 30% by mass.
The pH of the above sol can be adjusted from acidic to alkaline. Adjustment to acidic is performed by adding an inorganic acid or an organic acid. Adjustment to alkaline is performed by adding an inorganic base or an organic base, and amines can be added as organic bases for the purpose of adjusting the pH and the amount of surface charge. The pH can be set to 1 to less than 7 on the acidic side, and to 7 or more and 13 or less on the alkaline side.

The aqueous sol of hollow silica can be set, for example, to a pH range of 2.0 to 6.0 or 2.0 to 4.5 before the addition of the amine, and can be adjusted, for example, to a pH range of 3.0 to 10.0 or 3.0 to 9.0 by adding the amine.
In the case of an organic solvent sol, the above pH is the pH when the organic solvent sol and the same mass of pure water are mixed in a 1:1 ratio. The pH can be measured when an organic solvent that can be mixed with water is used, but when the solvent is subsequently replaced with a hydrophobic organic solvent, it is preferable to measure the pH in advance at the stage of the methanol solvent sol.
For example, when the dispersion medium is a hydrophilic organic solvent, such as methanol sol and propylene glycol monomethyl ether sol, the measurement can be performed using a solution prepared by mixing pure water and the sol in a mass ratio of 1:1. When the dispersion medium is a hydrophobic organic solvent, such as methyl ethyl ketone sol, the measurement can be performed using a solution prepared by mixing pure water, methanol, and methyl ethyl ketone sol in a mass ratio of 1:1:1.

The hollow silica organic solvent sol undergoes solvent replacement of the aqueous medium with an alcohol solvent having 1 to 5 carbon atoms, and then with an organic solvent, but moisture may remain during this process. At the stage of the hollow silica alcohol sol, the sol may contain, for example, 0.1 to 3.0% by mass, or 0.1 to 1.0% by mass of residual moisture. And at the stage of the hollow silica organic solvent sol (wherein the dispersion medium is an organic solvent other than alcohol), the sol may contain 0.01 to 0.5% by mass.
In addition, the viscosity of the hollow silica organic solvent sol can be set in the range of 1.0 to 10.0 mPa·s.

An amine can be added to the hollow silica sol of the present invention.
The amine used in the present invention may be a water-soluble amine having a water solubility of 80 g/L or more, or 100 g/L or more.
The raw material hollow silica aqueous sol and the hollow silica organic solvent sol obtained by solvent replacement may contain amine, or amine and ammonia. The amine may be added and contained in the range of 0.001 to 10 mass%, or 0.01 to 10 mass%, or 0.1 to 10 mass% relative to the SiO ₂ of the hollow silica particles. The amine, or the amine and ammonia, may be expressed as the total nitrogen amount of these basic components in the hollow silica particle organic solvent sol, and may be contained in the range of, for example, 10 to 100,000 ppm, or 100 to 10,000 ppm, or 100 to 3,000 ppm, or 100 to 2,000 ppm, typically 200 to 2,000 ppm.

The above amines include aliphatic amines and aromatic amines, with aliphatic amines being preferred. At least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines having 1 to 10 carbon atoms can be used. The amines are water-soluble and at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines having 1 to 10 carbon atoms.
For example, primary amines include monomethylamine, monoethylamine, monopropylamine, monoisopropylamine, monobutylamine, monoisobutylamine, monosec-butylamine, mono-tert-butylamine, monomethanolamine, monoethanolamine, monopropanolamine, monoisopropanolamine, monobutanolamine, monoisobutanolamine, monosec-butanolamine, and mono-tert-butanolamine.

Examples of secondary amines include dimethylamine, diethylamine, dipropylamine, diisopropylamine, N-methylethylamine, N-ethylisobutylamine, dimethanolamine, diethanolamine, dipropanolamine, diisopropanolamine, N-methanolethylamine, N-methylethanolamine, N-ethanolisobutylamine, and N-ethylisobutanolamine.
Examples of tertiary amines include trimethylamine, triethylamine, tripropylamine, triisopropylamine, tributylamine, triisobutylamine, trisecbutylamine, tritertbutylamine, trimethanolamine, triethanolamine, tripropanolamine, triisopropanolamine, tributanolamine, triisobutanolamine, trisecbutanolamine, tritertbutanolamine, tripentylamine, 3-(dimethylamino)ethyl acrylate, 2-(dimethylamino)ethyl acrylate, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl acrylate, and 2-(diethylamino)ethyl methacrylate.

The amines preferably have a water solubility of 80 g/L or more, or 100 g/L or more. Primary and secondary amines are preferred as these amines, and secondary amines are preferred because of their low volatility and high solubility, such as diisopropylamine and diethanolamine.
In the present invention, by containing the above-mentioned amine, the surface charge amount of the hollow silica particles can be set to 5 μeq/g or more, or 25 μeq/g or more per gram of _SiO2 . Typically, it can be set in the range of 5 to 250 μeq/g, or 25 to 250 μeq/g, or 25 to 100 μeq/g, or 25 to 80 μeq/g.
In the present invention, the surface charge amount of the hollow silica particles can be adjusted to any desired value by adjusting the type and amount of the amine added.

In the present invention, the surfaces of the hollow silica particles can be coated with a silane compound.
The silane compound may be a hydrolysate of at least one silane compound selected from the group consisting of the formula (1) and the formula (2).
In formula (1), R ¹ is an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or an organic group having a polyether group, an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, or a cyano group, and is bonded to a silicon atom by a Si-C bond; R ² is an alkoxy group, an acyloxy group, or a halogen group; a is an integer of 1 to 3;
In formula (2), ^R3 is an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 30 carbon atoms and is bonded to a silicon atom via a Si-C bond; ^R4 is an alkoxy group, an acyloxy group, or a halogen group; Y is an alkylene group, an NH group, or an oxygen atom; b is an integer of 1 to 3; c is an integer of 0 or 1; and d is an integer of 1 to 3.

The alkyl group is an alkyl group having 1 to 18 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, a cyclopropyl group, an n-butyl group, an i-butyl group, an s-butyl group, a t-butyl group, a cyclobutyl group, a 1-methyl-cyclopropyl group, a 2-methyl-cyclopropyl group, an n-pentyl group, a 1-methyl-n-butyl group, a 2-methyl-n-butyl group, a 3-methyl-n-butyl group, a 1,1-dimethyl-n-propyl group, a 1,2-dimethyl-n-propyl group, a 2,2-dimethyl-n-propyl group, a 1-ethyl-n-propyl group, a cyclopentyl group, a 1-methyl-cyclobutyl group, a 2-methyl-cyclobutyl group, a 3-methyl-cyclo ... cyclobutyl group, 1,2-dimethyl-cyclopropyl group, 2,3-dimethyl-cyclopropyl group, 1-ethyl-cyclopropyl group, 2-ethyl-cyclopropyl group, n-hexyl group, 1-methyl-n-pentyl group, 2-methyl-n-pentyl group, 3-methyl-n-pentyl group, 4-methyl-n-pentyl group, 1,1-dimethyl-n-butyl group, 1,2-dimethyl-n-butyl group, 1,3-dimethyl-n-butyl group, 2,2-dimethyl-n-butyl group, 2,3-dimethyl-n-butyl group, 3,3-dimethyl-n-butyl group, 1-ethyl-n-butyl group, 2-ethyl-n-butyl group, 1,1,2-trimethyl-n-propyl group, 1,2,2-trimethyl-n-propyl group, ethyl-n-propyl group, 1-ethyl-1-methyl-n-propyl group, 1-ethyl-2-methyl-n-propyl group, cyclohexyl group, 1-methyl-cyclopentyl group, 2-methyl-cyclopentyl group, 3-methyl-cyclopentyl group, 1-ethyl-cyclobutyl group, 2-ethyl-cyclobutyl group, 3-ethyl-cyclobutyl group, 1,2-dimethyl-cyclobutyl group, 1,3-dimethyl-cyclobutyl group, 2,2-dimethyl-cyclobutyl group, 2,3-dimethyl-cyclobutyl group, 2,4-dimethyl-cyclobutyl group, 3,3-dimethyl-cyclobutyl group, 1-n-propyl-cyclopropyl group, 2-n-propyl-cyclopropyl group, 1-i Examples of the cyclopropyl cyclopropyl group include, but are not limited to, 1-propyl-cyclopropyl group, 2-i-propyl-cyclopropyl group, 1,2,2-trimethyl-cyclopropyl group, 1,2,3-trimethyl-cyclopropyl group, 2,2,3-trimethyl-cyclopropyl group, 1-ethyl-2-methyl-cyclopropyl group, 2-ethyl-1-methyl-cyclopropyl group, 2-ethyl-2-methyl-cyclopropyl group and 2-ethyl-3-methyl-cyclopropyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group and the like.
Furthermore, examples of the alkylene group include alkylene groups derived from the above-mentioned alkyl groups.

The aryl group is an aryl group having 6 to 30 carbon atoms, and examples thereof include a phenyl group, a naphthyl group, an anthracene group, and a pyrene group.
The alkenyl group is an alkenyl group having 2 to 10 carbon atoms, and examples of the alkenyl group include ethenyl group, 1-propenyl group, 2-propenyl group, 1-methyl-1-ethenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 2-methyl-1-propenyl group, 2-methyl-2-propenyl group, 1-ethylethenyl group, 1-methyl-1-propenyl group, 1-methyl-2-propenyl group, 1-pentenyl group, 2-pentenyl group, 3-pentenyl group, 4-pentenyl group, 1-n-propylethenyl group, 1-methyl-1-butenyl group, 1-methyl-2-butenyl group, 1-methyl-3-butenyl group, 2-ethyl-2-propenyl group, 2-methyl-1-butenyl group, 2-methyl-2-butenyl group, 2-methyl-3-butenyl group, 3 Examples of aryl groups include, but are not limited to, 1-methyl-1-butenyl group, 3-methyl-2-butenyl group, 3-methyl-3-butenyl group, 1,1-dimethyl-2-propenyl group, 1-i-propylethenyl group, 1,2-dimethyl-1-propenyl group, 1,2-dimethyl-2-propenyl group, 1-cyclopentenyl group, 2-cyclopentenyl group, 3-cyclopentenyl group, 1-hexenyl group, 2-hexenyl group, 3-hexenyl group, 4-hexenyl group, 5-hexenyl group, 1-methyl-1-pentenyl group, 1-methyl-2-pentenyl group, 1-methyl-3-pentenyl group, 1-methyl-4-pentenyl group, 1-n-butylethenyl group, 2-methyl-1-pentenyl group, and 2-methyl-2-pentenyl group.

The alkoxy group includes alkoxy groups having 1 to 10 carbon atoms, such as, for example, a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, an n-butoxy group, an i-butoxy group, an s-butoxy group, a t-butoxy group, an n-pentyloxy group, a 1-methyl-n-butoxy group, a 2-methyl-n-butoxy group, a 3-methyl-n-butoxy group, a 1,1-dimethyl-n-propoxy group, a 1,2-dimethyl-n-propoxy group, a 2,2-dimethyl-n-propoxy group, a 1-ethyl-n-propoxy group, and an n-hexyloxy group, but are not limited to these.
The acyloxy group has 2 to 10 carbon atoms, and examples of the acyloxy group include a methylcarbonyloxy group, an ethylcarbonyloxy group, an n-propylcarbonyloxy group, an i-propylcarbonyloxy group, an n-butylcarbonyloxy group, an i-butylcarbonyloxy group, an s-butylcarbonyloxy group, a t-butylcarbonyloxy group, an n-pentylcarbonyloxy group, a 1-methyl-n-butylcarbonyloxy group, a 2-methyl-n-butylcarbonyloxy group, a 3-methyl-n-butylcarbonyloxy group, a 1,1-dimethyl-n-propylcarbonyloxy group, a 1,2-dimethyl-n-propylcarbonyloxy group, a 2,2-dimethyl-n-propylcarbonyloxy group, a 1-ethyl-n-propylcarbonyloxy group, an n-hexylcarbonyloxy group, a 1-methyl-n-pentylcarbonyloxy group, and a 2-methyl-n-pentylcarbonyloxy group, but are not limited thereto.
The halogen group includes fluorine, chlorine, bromine, iodine, and the like.
An example of an organic group having a polyether group is a polyetherpropyl group having an alkoxy group, such as (CH ₃ O) ₃ SiC ₃ H ₆ (OC ₂ H ₄ ) n OCH _3. n can be in the range of 1 to 100 or 1 to 10.

Examples of the organic group having an epoxy group include a 2-(3,4-epoxycyclohexyl)ethyl group and a 3-glycidoxypropyl group.
The above-mentioned (meth)acryloyl group refers to both acryloyl and methacryloyl groups. Examples of organic groups having a (meth)acryloyl group include a 3-methacryloxypropyl group and a 3-acryloxypropyl group.

An example of the organic group having a mercapto group is a 3-mercaptopropyl group.
Examples of organic groups having an amino group include a 2-aminoethyl group, a 3-aminopropyl group, an N-2-(aminoethyl)-3-aminopropyl group, an N-(1,3-dimethyl-butylidene)aminopropyl group, an N-phenyl-3-aminopropyl group, and an N-(vinylbenzyl)-2-aminoethyl-3-aminopropyl group.
An example of the organic group having a ureido group is a 3-ureidopropyl group.
An example of the organic group having a cyano group is a 3-cyanopropyl group.
The compound of the above formula (2) capable of forming a trimethylsilyl group on the surface of silica particles is preferred.

　上記式中、Ｒ^１２はアルコキシ基であり、例えばメトキシ基、エトキシ基が挙げられる。上記シラン化合物は信越化学工業（株）製のシラン化合物を使用する事ができる。
シリカ粒子の表面にヒドロキシル基、例えばシリカ粒子であればシラノール基と上記シラン化合物が反応してシロキサン結合によりシリカ粒子の表面に上記シラン化合物を被覆する工程である。反応温度は２０℃からその分散媒の沸点の範囲までの温度で行うことができるが、例えば２０℃～１００℃の範囲で行うことができる。反応時間は０．１～６時間程度で行うことができる。 Examples of such compounds include the following.

In the above formula, R ¹² is an alkoxy group, for example, a methoxy group or an ethoxy group. As the silane compound, a silane compound manufactured by Shin-Etsu Chemical Co., Ltd. can be used.
This is a process in which the silane compound reacts with hydroxyl groups on the surface of silica particles, for example, silanol groups in the case of silica particles, to coat the surface of the silica particles with the silane compound through siloxane bonds. The reaction temperature can be from 20°C to the boiling point of the dispersion medium, for example, in the range of 20°C to 100°C. The reaction time can be about 0.1 to 6 hours.

The above silane compound can be added to the silica sol in an amount equivalent to a coating amount of 0.1 to 6.0 silicon atoms/nm ² on the silica particle surface, so that the silane compound can be added to the silica sol in an amount equivalent to a coating amount of 0.1 to 6.0 silicon atoms/nm ² on the silica particle surface.
Water is necessary for the hydrolysis of the silane compound, and if the sol is an aqueous solvent, the aqueous solvent is used. When the aqueous medium is replaced with an organic solvent, the water remaining in the solvent can be used. For example, water present at 0.01 to 1% by mass can be used. The hydrolysis can be performed with or without a catalyst.

When the hydrolysis is performed without a catalyst, the silica particle surface is on the acidic side, and when a catalyst is used, the hydrolysis catalyst may include a metal chelate compound, an organic acid, an inorganic acid, an organic base, or an inorganic base. Examples of the metal chelate compound as the hydrolysis catalyst include triethoxy mono(acetylacetonato)titanium and triethoxy mono(acetylacetonato)zirconium. Examples of the organic acid as the hydrolysis catalyst include acetic acid and oxalic acid. Examples of the inorganic acid as the hydrolysis catalyst include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid. Examples of the organic base as the hydrolysis catalyst include pyridine, pyrrole, piperazine, and quaternary ammonium salts. Examples of the inorganic base as the hydrolysis catalyst include ammonia, sodium hydroxide, and potassium hydroxide.
The organic acid is at least one organic acid selected from the group consisting of divalent aliphatic carboxylic acids, aliphatic oxycarboxylic acids, amino acids, and chelating agents, the divalent aliphatic carboxylic acids being oxalic acid, malonic acid, and succinic acid, the aliphatic oxycarboxylic acids being glycolic acid, lactic acid, malic acid, tartaric acid, and citric acid, the amino acids being glycine, alanine, valine, leucine, serine, and threonine, and the chelating agents being ethylenediaminetetraacetic acid, L-aspartic acid-N,N-diacetic acid, and diethylenetriaminepentaacetic acid. The organic acid salts include alkali metal salts, ammonium salts, and amine salts of the above organic acids. The alkali metals include sodium and potassium.

In the present invention, a film-forming composition is obtained which contains the above-mentioned hollow silica organic solvent sol and an organic resin or polysiloxane.
A film-forming composition can be obtained by selecting and mixing a thermosetting or photosetting resin as the organic resin or polysiloxane, and then forming a cured product by adding a curing agent such as an amine-based curing agent, an acid anhydride-based curing agent, a radical generator-based curing agent (thermal radical generator, photoradical generator), or an acid generator-based curing agent (thermal acid generator, photoacid generator).
This composition can form a cured product by applying or filling a film-forming composition containing an organic resin or polysiloxane and a curing agent to a substrate and heating, irradiating with light, or a combination thereof. The organic resin and polysiloxane (curable resin) can be a resin having a functional group such as an epoxy group or a (meth)acryloyl group, or an isocyanate-based resin. For example, a photocurable polyfunctional acrylate can be preferably used.

Examples of the polyfunctional acrylate include polyfunctional acrylates having difunctional, trifunctional, tetrafunctional or higher functional groups in the molecule, such as neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.
These polyfunctional acrylates may also be described below.

The film-forming composition of the present invention may contain a surfactant (leveling agent).
The surfactant (leveling agent) may be an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, or a silicone surfactant. The surfactant (leveling agent) may be added in an amount of 0.01 to 5 phr or 0.01 to 1 phr relative to the organic resin or polysiloxane.
Examples of the anionic surfactants that can be used in the present invention include sodium and potassium salts of fatty acids, alkylbenzenesulfonates, higher alcohol sulfates, polyoxyethylene alkyl ether sulfates, α-sulfofatty acid esters, α-olefinsulfonates, monoalkyl phosphates, and alkanesulfonates.
For example, alkylbenzene sulfonates include sodium salts, potassium salts and lithium salts, such as sodium C10-C16 alkylbenzene sulfonate, C10-C16 alkylbenzene sulfonic acid, and sodium alkylnaphthalene sulfonate.

Examples of higher alcohol sulfates include sodium dodecyl sulfate (sodium lauryl sulfate) having 12 carbon atoms, triethanolamine lauryl sulfate, and triethanolammonium lauryl sulfate.
Examples of polyoxyethylene alkyl ether sulfates include sodium polyoxyethylene styrenated phenyl ether sulfate, ammonium polyoxyethylene styrenated phenyl ether sulfate, sodium polyoxyethylene decyl ether sulfate, ammonium polyoxyethylene decyl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, ammonium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene tridecyl ether sulfate, and sodium polyoxyethylene oleyl cetyl ether sulfate.
The α-olefin sulfonate salts include sodium α-olefin sulfonate.

Examples of the alkane sulfonate include sodium 2-ethylhexyl sulfate.
Examples of the cationic surfactant that can be used in the present invention include alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkyldimethylbenzylammonium salts, and amine salt-based agents.
Alkyltrimethylammonium salts are quaternary ammonium salts that have a chloride ion or a bromide ion as a counter ion, such as dodecyltrimethylammonium chloride, cetyltrimethylammonium chloride, coconut alkyltrimethylammonium chloride, and alkyl(C16-18)trimethylammonium chloride.
Dialkyldimethylammonium salts have two lipophilic main chains and two methyl groups. Examples include bis(hydrogenated tallow)dimethylammonium chloride. Examples include didecyldimethylammonium chloride, dicoconucleic acid alkyldimethylammonium chloride, dihydrogenated tallow alkyldimethylammonium chloride, and dialkyl(C14-18)dimethylammonium chloride.

Alkyl dimethyl benzyl ammonium salts are quaternary ammonium salts having one lipophilic main chain, two methyl groups, and a benzyl group, and examples thereof include benzauconium chloride, such as alkyl (C8-18) dimethyl benzyl ammonium chloride.
Amine salt agents are those in which the hydrogen atom of ammonia has been substituted with one or more hydrocarbon groups, and examples thereof include N-methylbishydroxyethylamine fatty acid ester hydrochloride.
The amphoteric surfactants used in the present invention include N-alkyl-β-alanine type alkylamino fatty acid salts, alkylcarboxybetaine type alkylbetaines, and N,N-dimethyldodecylamine oxide type alkylamine oxides, examples of which include lauryl betaine, stearyl betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, and lauryl dimethylamine oxide.

The nonionic surfactant used in the present invention is selected from polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, alkyl glucosides, polyoxyethylene fatty acid esters, sucrose fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and fatty acid alkanolamides. For example, examples of polyoxyethylene alkyl ethers include polyoxyethylene dodecyl ether (polyoxyethylene lauryl ether), polyoxyalkylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyalkylene tridecyl ether, polyoxyethylene myristyl ether, polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene behenyl ether, polyoxyethylene-2-ethylhexyl ether, and polyoxyethylene isodecyl ether.
Examples of polyoxyethylene alkylphenol ethers include polyoxyethylene styrenated phenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene distyrenated phenyl ether, and polyoxyethylene tribenzyl phenyl ether.

The alkyl glucoside includes decyl glucoside and lauryl glucoside.
Examples of polyoxyethylene fatty acid esters include polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, polyethylene glycol distearate, polyethylene glycol dioleate, and polypropylene glycol dioleate.
Examples of sorbitan fatty acid esters include sorbitan monocaprylate, sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, sorbitan monosesquioleate, and ethylene oxide adducts thereof.

Examples of polyoxyethylene sorbitan fatty acid esters include polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, and polyoxyethylene sorbitan triisostearate.
Examples of fatty acid alkanolamides include coconut oil fatty acid diethanolamide, beef tallow fatty acid diethanolamide, lauric acid diethanolamide, and oleic acid diethanolamide.

Further examples include polyoxyalkyl ethers or polyoxyalkyl glycols such as polyoxyethylene polyoxypropylene glycol, polyoxyethylene fatty acid esters, polyoxyethylene hydrogenated castor oil ether, sorbitan fatty acid ester alkyl ethers, alkyl polyglucosides, sorbitan monooleate, and sucrose fatty acid esters.
Silicone surfactants can be used. Silicone surfactants are compounds having a repeating unit containing a siloxane bond in the main chain. Silicone surfactants can be used with a weight average molecular weight in the range of 500 to 50,000. These may be modified silicon surfactants, and examples of such surfactants include those having an organic group introduced into the side chain and/or end of a polysiloxane. Examples of the organic group include an amino group, an epoxy group, an alicyclic epoxy group, a carbinol group, a mercapto group, a carboxyl group, an aliphatic ester group, an aliphatic amide group, and a polyether group. Examples of silicone surfactants include trade names such as Toray Silicone DC3PA, Toray Silicone SH7PA, Toray Silicone DC11PA, Toray Silicone SH21PA, Toray Silicone SH28PA, Toray Silicone SH29PA, Toray Silicone SH30PA, and Toray Silicone SH8400 (all manufactured by Dow Corning Toray Co., Ltd.), Silwet 1-77, L-7280, L-7001, L-7002, L-7200, L-7210, L-7220, L-7230, L7500, L-7600, L-7602, L-7604, L-7605, L-7622, L-765 7, L-8500, and L-8610. (all manufactured by Momentive Performance Materials), KP-341, KF-6001, KF-6002 (all manufactured by Shin-Etsu Silicones Co., Ltd.), BYK307, BYK323, BYK330 (all manufactured by BYK-Chemie), etc. For example, a product name L-7001 (manufactured by Dowsil Corporation) can be suitably used as a polyether-modified silicone.

In the present invention, a film-forming composition containing the above organic solvent sol and an organic resin or polysiloxane is obtained. The film-forming composition can be obtained by removing the organic solvent from the organic solvent sol to form a film-forming composition containing hollow silica particles and an organic resin.
In the case of the thermosetting coating-forming composition, the heat curing agent can be added in the range of 0.01 to 50 phr or 0.01 to 10 phr to the resin containing a functional group such as an epoxy group or a (meth)acryloyl group, and for example, the heat curing agent can be contained in a ratio of 0.5 to 1.5 equivalents, preferably 0.8 to 1.2 equivalents, to the functional group such as an epoxy group or a (meth)acryloyl group. The equivalent of the heat curing agent to the curable resin is represented by the equivalent ratio of the heat curing agent to the functional group.

Examples of the heat curing agent include phenol resins, amine-based curing agents, polyamide resins, imidazoles, polymercaptans, acid anhydrides, heat radical generators, heat acid generators, etc. In particular, radical generator-based curing agents, acid anhydride-based curing agents, and amine-based curing agents are preferred.
Even if these thermosetting agents are solid, they can be used by dissolving them in a solvent. However, evaporation of the solvent reduces the density of the cured product and creates pores, resulting in reduced strength and reduced water resistance. Therefore, it is preferable for the curing agent itself to be liquid at room temperature and normal pressure.
Examples of the phenol resin include phenol novolac resin and cresol novolac resin.

Examples of the amine curing agent include piperidine, N,N-dimethylpiperazine, triethylenediamine, 2,4,6-tris(dimethylaminomethyl)phenol, benzyldimethylamine, 2-(dimethylaminomethyl)phenol, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylaminopropylamine, N-aminoethylpiperazine, di(1-methyl-2-aminocyclohexyl)methane, menthanediamine, isophoronediamine, diaminodicyclohexylmethane, 1,3-diaminomethylcyclohexane, xylylenediamine, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, 3,3'-diethyl-4,4'-diaminodiphenylmethane, and diethyltoluenediamine. Of these, liquid diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylaminopropylamine, N-aminoethylpiperazine, di(1-methyl-2-aminocyclohexyl)methane, menthenediamine, isophoronediamine, diaminodicyclohexylmethane, 3,3'-diethyl-4,4'-diaminodiphenylmethane, diethyltoluenediamine, etc. can be preferably used.
The polyamide resin is produced by condensation of dimer acid and polyamine, and is a polyamide amine having a primary amine and a secondary amine in the molecule.

Examples of the imidazoles include 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, and epoxy imidazole adduct.
The polymercaptan is, for example, one having a mercaptan group at the end of a polypropylene glycol chain or one having a mercaptan group at the end of a polyethylene glycol chain, and is preferably in a liquid form.

　Ｒは炭素数１～１２のアルキル基、炭素数６～２０アリール基が挙げられ、特に炭素数１～１２のアルキル基が好ましい。 As the acid anhydride curing agent, the anhydride of the compound having a plurality of carboxyl groups in one molecule is preferable.As these acid anhydride curing agents, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bis trimellitate, glycerol tris trimellitate, maleic anhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalic anhydride, endomethylene tetrahydrophthalic anhydride, methyl endomethylene tetrahydrophthalic anhydride, methyl butenyl tetrahydrophthalic anhydride, dodecenyl succinic anhydride, hexahydrophthalic anhydride, methyl hexahydrophthalic anhydride, succinic anhydride, methylcyclohexene dicarboxylic anhydride, chlorendic anhydride, etc. can be mentioned.
Examples of the thermal acid generator include sulfonium salts and phosphonium salts, with sulfonium salts being preferred. For example, the following compounds can be mentioned.

R may be an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 20 carbon atoms, and is particularly preferably an alkyl group having 1 to 12 carbon atoms.

Among these, methyltetrahydrophthalic anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride (methylnadic anhydride, methylhimic anhydride), hydrogenated methylnadic anhydride, methylbutenyltetrahydrophthalic anhydride, dodecenylsuccinic anhydride, methylhexahydrophthalic anhydride, and a mixture of methylhexahydrophthalic anhydride and hexahydrophthalic anhydride, which are liquid at room temperature and normal pressure, are preferred. These liquid acid anhydrides have a viscosity of about 10 mPa·s to 1000 mPa·s when measured at 25° C.
Examples of the thermal radical generator include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methylpropionate)dimethyl, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, tert-butyl hydroperoxide, cumene hydroperoxide, di-tert-butyl peroxide, dicumyl peroxide, benzoyl peroxide, etc. These can be obtained from Tokyo Chemical Industry Co., Ltd.

In addition, when obtaining the above-mentioned cured product, a curing assistant may be used in combination as appropriate. Examples of the curing assistant include organic phosphorus compounds such as triphenylphosphine and tributylphosphine, quaternary phosphonium salts such as ethyltriphenylphosphonium bromide and methyltriphenylphosphonium diethyl phosphate, and quaternary ammonium salts such as 1,8-diazabicyclo(5,4,0)undecane-7-ene, salts of 1,8-diazabicyclo(5,4,0)undecane-7-ene and octylic acid, zinc octylate, and tetrabutylammonium bromide. These curing assistants can be contained in a ratio of 0.001 to 0.1 parts by mass per part by mass of the curing agent.
The composition is a thermosetting varnish obtained by mixing a resin, a curing agent, and optionally a curing aid, which can be mixed in a reaction vessel using a stirring blade or a kneader.

The mixing is carried out by a hot mixing method at a temperature of 60° C. to 100° C. for 0.5 to 1 hour.
The obtained curable film-forming composition is a thermosetting coating composition, and has a suitable viscosity for use, for example, as a liquid sealant. The liquid thermosetting film-forming composition can be prepared to any viscosity, and can be partially sealed at any desired location for use as a transparent sealant for LEDs, etc., by casting, potting, dispenser, printing, etc. The liquid thermosetting composition is directly mounted on an LED, etc., in the liquid state, by the above-mentioned method, and then dried and cured to obtain a cured epoxy resin body.
The thermosetting film-forming composition (thermosetting coating composition) is applied to a substrate and heated at a temperature of 80 to 200° C. to obtain a cured product.
In the case of a photocurable resin composition in the above-mentioned film-forming composition, a photocuring agent (photoradical generator, photoacid generator) can be added in the range of 0.01 to 50 phr or 0.01 to 10 phr to a resin containing a functional group such as an epoxy group or a (meth)acryloyl group, and for example, the photocuring agent (photoradical generator, photoacid generator) can be contained in a ratio of 0.5 to 1.5 equivalents, preferably 0.8 to 1.2 equivalents, to a functional group such as an epoxy group or a (meth)acryloyl group. The equivalent of the photocuring agent to the curable resin is represented by the equivalent ratio of the photocuring agent to the functional group.
The photoradical generator is not particularly limited as long as it generates radicals directly or indirectly upon irradiation with light.

The photoradical generator may be, for example, an imidazole compound, a diazo compound, a bisimidazole compound, an N-arylglycine compound, an organic azide compound, a titanocene compound, an aluminate compound, an organic peroxide, an N-alkoxypyridinium salt compound, or a thioxanthone compound. Examples of the azide compound include p-azidobenzaldehyde, p-azidoacetophenone, p-azidobenzoic acid, p-azidobenzalacetophenone, 4,4'-diazidochalcone, 4,4'-diazidodiphenyl sulfide, and 2,6-bis(4'-azidobenzal)-4-methylcyclohexanone. Examples of the diazo compound include 1-diazo-4-N,N-dimethylaminobenzene chloride, and 1-diazo-4-N,N-diethylaminobenzeneborofluoride. Examples of the bisimidazole compound include 2,2'-bis(o-chlorophenyl)-4,5,4',5'-tetrakis(3,4,5-trimethoxyphenyl)-1,2'-bisimidazole, and 2,2'-bis(o-chlorophenyl)-4,5,4',5'-tetraphenyl-1,2'-bisimidazole. Examples of the titanocene compound include dicyclopentadienyl-titanium-dichloride, dicyclopentadienyl-titanium-bisphenyl, dicyclopentadienyl-titanium-bis(2,3,4,5,6-pentafluorophenyl), dicyclopentadienyl-titanium-bis(2,3,5,6-tetrafluorophenyl), dicyclopentadienyl-titanium-bis(2,4,6-trifluorophenyl), dicyclopentadienyl-titanium-bis(2,6-difluorophenyl), dicyclopentadienyl -titanium-bis(2,4-difluorophenyl), bis(methylcyclopentadienyl)-titanium-bis(2,3,4,5,6-pentafluorophenyl), bis(methylcyclopentadienyl)-titanium-bis(2,3,5,6-tetrafluorophenyl), bis(methylcyclopentadienyl)-titanium-bis(2,6-difluorophenyl), and dicyclopentadienyl-titanium-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl).

Examples of photoradical generators include 1,3-di(tert-butyldioxycarbonyl)benzophenone, 3,3',4,4'-tetrakis(tert-butyldioxycarbonyl)benzophenone, 3-phenyl-5-isoxazolone, 2-mercaptobenzimidazole, 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone.
These photoradical polymerization agents are available, for example, under the trade name Irgacure TPO (the component is 2,4,6-trimethylbenzoyldiphenylphosphine oxide) (formula (c1-1-1)) manufactured by BASF, under the trade name Omnirad 819 (the component is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide) (formula (c1-1-2)) manufactured by IGM RESINS, and under the trade name Irgacure 184 (the component is 1-hydroxycyclohexyl phenyl ketone) (formula (c1-1-3)) manufactured by IGM RESINS.

The photoacid generator is not particularly limited as long as it generates an acid directly or indirectly upon irradiation with light.
Specific examples of the photoacid generator that can be used include triazine-based compounds, acetophenone derivative compounds, disulfone-based compounds, diazomethane-based compounds, sulfonic acid derivative compounds, onium salts such as iodonium salts, sulfonium salts, phosphonium salts, and selenium salts, metallocene complexes, and iron arene complexes.

The onium salts used as the photoacid generators include iodonium salts such as diphenyliodonium chloride, diphenyliodonium trifluoromethanesulfonate, diphenyliodonium mesylate, diphenyliodonium tosylate, diphenyliodonium bromide, diphenyliodonium tetrafluoroborate, diphenyliodonium hexafluoroantimonate, diphenyliodonium hexafluoroarsenate, bis(p-tert-butylphenyl)iodonium hexafluorophosphate, bis(p-tert-butylphenyl)iodonium mesylate, bis(p-tert-butylphenyl)iodonium tosylate, bis(p-tert-butylphenyl)iodonium trifluoromethanesulfonate, and bis(p-tert-butylphenyl)iodonium. Examples of the iodonium salts include bis(alkylphenyl)iodonium salts such as iodonium tetrafluoroborate, bis(p-tert-butylphenyl)iodonium chloride, bis(p-chlorophenyl)iodonium chloride, bis(p-chlorophenyl)iodonium tetrafluoroborate, and bis(4-t-butylphenyl)iodonium hexafluorophosphate, alkoxycarbonylalkoxy-trialkylaryliodonium salts (e.g., 4-[(1-ethoxycarbonyl-ethoxy)phenyl]-(2,4,6-trimethylphenyl)-iodonium hexafluorophosphate, etc.), and bis(alkoxyaryl)iodonium salts (e.g., bis(alkoxyphenyl)iodonium salts such as (4-methoxyphenyl)phenyliodonium hexafluoroantimonate).

Sulfonium salts include triphenylsulfonium chloride, triphenylsulfonium bromide, tri(p-methoxyphenyl)sulfonium tetrafluoroborate, tri(p-methoxyphenyl)sulfonium hexafluorophosphonate, tri(p-ethoxyphenyl)sulfonium tetrafluoroborate, triphenylsulfonium triflate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, and other triphenylsulfonium salts, as well as (4-phenylthiophenyl)diphenylsulfonium hexafluoroantimonate, (4-phenylthiophenyl)diphenylsulfonium hexafluorophosphate, bis[4-(diphenylsulfonio)phenyl]sulfide-bis-hexafluoroantimonate, bis[4-(diphenylsulfonio)phenyl]sulfide-bis-hexafluorophosphate, (4-methoxyphenyl)diphenylsulfonium hexafluoroantimonate, and other sulfonium salts.

Examples of the phosphonium salt include triphenylphosphonium chloride, triphenylphosphonium bromide, tri(p-methoxyphenyl)phosphonium tetrafluoroborate, tri(p-methoxyphenyl)phosphonium hexafluorophosphonate, tri(p-ethoxyphenyl)phosphonium tetrafluoroborate, 4-chlorobenzenediazonium hexafluorophosphate, and benzyltriphenylphosphonium hexafluoroantimonate.
Examples include selenium salts such as triphenylselenium hexafluorophosphate, and metallocene complexes such as (η5 or η6-isopropylbenzene)(η5-cyclopentadienyl)iron(II) hexafluorophosphate.

In addition, the following compounds can also be used as the photoacid generator.

As the photoacid generator, sulfonium salt compounds and iodonium salt compounds are preferred. _Examples of the anion species thereof include _CF3SO3- ^, _C4F9SO3- , _C8F17SO3- ^, _{camphorsulfonate} anion ^, tosylate anion, _BF4- ^, _PF6- ^, _AsF6- ^, and _SbF6- ^. In particular, anion species such as phosphorus hexafluoride and _{antimony hexafluoride} , which show strong acidity _, are preferred.
The film-forming composition of the present invention may contain conventional additives as necessary. Examples of such additives include pigments, colorants, thickeners, sensitizers, defoamers, coating improvers, lubricants, stabilizers (antioxidants, heat stabilizers, light resistance stabilizers, etc.), plasticizers, dissolution promoters, fillers, antistatic agents, etc. These additives may be used alone or in combination of two or more.
Examples of methods for applying the coating composition of the present invention include flow coating, spin coating, spray coating, screen printing, casting, bar coating, curtain coating, roll coating, gravure coating, dipping, and slit coating.

In the present invention, the photo-coating composition (film-forming composition) can be applied onto a substrate and cured by irradiation with light. It can also be heated before or after irradiation with light.
The thickness of the coating film can be selected from the range of about 0.01 μm to 10 mm depending on the application of the cured product. For example, when used as a photoresist, it can be about 0.05 to 10 μm (particularly 0.1 to 5 μm), when used as a printed wiring board, it can be about 5 μm to 5 mm (particularly 100 μm to 1 mm), and when used as an optical thin film, it can be about 0.1 to 100 μm (particularly 0.3 to 50 μm).
When a transparent coating is obtained, the visible light transmittance of the coating can be 80% or more, or 90% or more, typically 90 to 96%.

The light to be irradiated or exposed when a photoacid generator is used may be, for example, gamma rays, X-rays, ultraviolet rays, visible light, etc., and is usually visible light or ultraviolet rays, particularly ultraviolet rays. The wavelength of the light is, for example, about 150 to 800 nm, preferably about 150 to 600 nm, and more preferably about 150 to 400 nm. The amount of light to be irradiated varies depending on the thickness of the coating film, but can be, for example, about 2 to 20,000 mJ/cm ² , preferably about 5 to 5,000 mJ/cm ^2. The light source can be selected according to the type of light to be exposed. For example, in the case of ultraviolet rays, a low-pressure mercury lamp, a high-pressure mercury lamp, an extra-high-pressure mercury lamp, a deuterium lamp, a halogen lamp, or a laser beam (helium-cadmium laser, excimer laser, etc.) can be used. Such light irradiation causes the curing reaction of the composition to proceed.
When a thermal acid generator is used or when a photoacid generator is used, the coating film is heated as necessary after light irradiation, for example at 60 to 350° C., preferably at about 100 to 300° C. The heating time can be selected from the range of 3 seconds or more (for example, about 3 seconds to 5 hours), for example, 5 seconds to 2 hours, preferably about 20 seconds to 30 minutes, and usually about 1 minute to 3 hours (for example, about 5 minutes to 2.5 hours).

Furthermore, when forming a pattern or an image (for example, when manufacturing a printed wiring board, etc.), the coating film formed on the substrate may be pattern-exposed, and this pattern exposure may be performed by scanning with laser light or by irradiating light through a photomask. A pattern or an image can be formed by developing (or dissolving) the non-irradiated area (unexposed part) generated by such pattern exposure with a developer.
The developer may be an aqueous alkaline solution or an organic solvent.
Examples of the alkaline aqueous solution include aqueous solutions of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, potassium carbonate, and sodium carbonate; aqueous solutions of quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, and choline; and aqueous solutions of amines such as ethanolamine, propylamine, and ethylenediamine.

The alkaline developer is generally an aqueous solution of 10% by mass or less, and preferably an aqueous solution of 0.1 to 3.0% by mass, etc. Furthermore, alcohols and surfactants may be added to the developer, and each of these is preferably 0.05 to 10 parts by mass relative to 100 parts by mass of the developer.
Of these, an aqueous solution of 0.1 to 2.38% by weight of tetramethylammonium hydroxide can be used.
The organic solvent used as the developer may be a general organic solvent, such as acetone, acetonitrile, toluene, dimethylformamide, methanol, ethanol, isopropanol, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol propyl ether, propylene glycol butyl ether, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, propylene glycol butyl ether acetate, ethyl lactate, cyclohexanone, etc., and may be used alone or in combination of two or more of these. In particular, propylene glycol methyl ether, propylene glycol methyl ether acetate, ethyl lactate, etc. are preferably used.

In the present invention, an adhesion promoter can be added for the purpose of improving adhesion to the substrate after development. These adhesion promoters include chlorosilanes such as trimethylchlorosilane, dimethylvinylchlorosilane, methyldiphenylchlorosilane, and chloromethyldimethylchlorosilane; alkoxysilanes such as trimethylmethoxysilane, dimethyldiethoxysilane, methyldimethoxysilane, dimethylvinylethoxysilane, diphenyldimethoxysilane, and phenyltriethoxysilane; silazanes such as hexamethyldisilazane, N,N'-bis(trimethylsilyl)urea, dimethyltrimethylsilylamine, and trimethylsilylimidazole; vinyltrichlorosilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, and 3-chloropropyltrimethoxysilane; Examples of the adhesion promoter include silanes such as aminopropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-(N-piperidinyl)propyltrimethoxysilane; heterocyclic compounds such as benzotriazole, benzimidazole, indazole, imidazole, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, urazole, thiouracil, mercaptoimidazole, and mercaptopyrimidine; and ureas such as 1,1-dimethylurea and 1,3-dimethylurea, or thiourea compounds. One or more of the adhesion promoters may be used in combination. The amount of these adhesion promoters added is usually 18% by mass or less, preferably 0.0008 to 9% by mass, and more preferably 0.04 to 9% by mass, based on the solid content.

In the present invention, a sensitizer may be included. Examples of sensitizers that can be used include anthracene, phenothiazene, perylene, thioxanthone, and benzophenone thioxanthone. Examples of sensitizing dyes include thiopyrylium salt dyes, merocyanine dyes, quinoline dyes, styrylquinoline dyes, ketocoumarin dyes, thioxanthene dyes, xanthene dyes, oxonol dyes, cyanine dyes, rhodamine dyes, and pyrylium salt dyes. Anthracene sensitizers are particularly preferred, and when used in combination with a cationic curing catalyst (radiation-sensitive cationic polymerization initiator), the sensitivity is dramatically improved and the radical polymerization initiator function is also present. In the hybrid type in which the cationic curing system of the present invention and the radical curing system are used in combination, the catalyst species can be simplified. Specific examples of anthracene compounds that are effective include dibutoxyanthracene and dipropoxyanthraquinone. The amount of the sensitizer added is from 0.01 to 20% by weight, preferably from 0.01 to 10% by weight, based on the solid content.
The composition of the present invention can be photocured or thermally cured using a photoradical generator, a thermal radical generator, a photoacid generator, or a thermal acid generator. When a photoacid generator or a thermal acid generator is used, for example, a commonly used epoxy curing agent (e.g., amine or acid anhydride) is not used, or even if it is used, the content of such an agent is extremely small, so that the storage stability of the composition is improved.

The above composition has been found to be applicable to photocationic polymerization. It has a higher curing speed than conventional liquid epoxy compounds (e.g., alicyclic epoxy compounds having an epoxycyclohexyl ring). Because of the fast curing speed, it is possible to reduce the amount of acid generator added and to use weak acid generators. Reducing the amount of acid generator is important for preventing metal corrosion because acid active species may remain even after UV irradiation. Because of the fast curing speed, thick film curing is possible.
Curing by UV irradiation can be applied to materials (equipment) that are sensitive to heat.
The thermosetting and photocuring materials using the film-forming composition of the present invention have characteristics such as low dielectric constant, low dielectric loss tangent, fast curing, high transparency, and small cure shrinkage, and can be used for coating and bonding electronic parts, optical parts (anti-reflection coating), and precision mechanical parts. For example, they can be used for bonding mobile phone and camera lenses, optical elements such as light-emitting diodes (LEDs) and semiconductor lasers (LDs), liquid crystal panels, biochips, camera lenses and prisms, magnetic parts of hard disks of personal computers, pickups of CD and DVD players (parts that capture optical information reflected from the disk), speaker cones and coils, motor magnets, circuit boards, electronic parts, and parts inside the engine of automobiles.

As a hard coating material for surface protection of automobile bodies, lamps, electrical appliances, building materials, plastics, etc., it can be applied to, for example, automobile and motorcycle bodies, headlight lenses and mirrors, plastic lenses of glasses, mobile phones, game consoles, optical films, ID cards, etc.
Examples of ink materials for printing on metals such as aluminum and plastics include credit cards, membership cards and other cards, switches for electrical appliances and office equipment, printing ink for keyboards, and inkjet printer ink for CDs, DVDs, etc.
Examples of applications include a technology that can be used in combination with 3D CAD to harden resin to create complex three-dimensional objects, photolithography for producing models of industrial products, and optical fiber coating, bonding, optical waveguides, thick-film resists, etc.

The film-forming composition of the present invention can also be suitably used as an insulating resin for electronic materials, such as anti-reflection films, semiconductor encapsulation materials, adhesives for electronic materials, printed wiring board materials, interlayer insulating film materials, buffer coating agents for semiconductors, enamel insulating materials, and encapsulants for power modules, as well as an insulating resin for use in high-voltage equipment, such as generator coils, transformer coils, and gas-insulated switchgear.
The hollow silica sol of the present invention can be produced by the following steps (I) and (II).
Step (I): preparing a hollow silica sol;
Step (II): A hollow silica sol can be obtained by adjusting the molar ratio of monovalent alkali metal ions converted to _M2O (wherein M represents a monovalent alkali metal atom) relative to the _SiO2 of the hollow silica particles in the hollow silica sol of step (I) to 7.12× ^10-6 to 285× ^10-6 .
In the above step (II), it is preferable to use a sodium ion as the monovalent alkali metal ion.
In the above step (II), the sodium ion content can be adjusted by contacting the hollow silica sol obtained in the above step (I) with a cation exchange resin or by adding a sodium source. The sodium source added in the above step (II) is preferably sodium hydroxide, and is preferably added as an aqueous sodium hydroxide solution.
The dispersion medium in step (I) and step (II) may be water, an alcohol having 1 to 10 carbon atoms, a ketone, an ether, an amide, a urea, or an ester. Examples of the dispersion medium include the above-mentioned solvents.

In the present invention, at least one step selected from the following (i) to (iv) can be added to the above step (I), step (II), or both steps:
(i): Adding an amine to a hollow silica sol;
(ii): adding sodium aluminate as an aluminum source and heating to form aluminosilicate sites in hollow silica particles;
(iii): replacing the dispersion medium with another dispersion medium;
(iv) The hollow silica particles are further coated with at least one silane compound selected from the group consisting of the formula (1) and the formula (2).
The present invention can provide a method for stabilizing a hollow silica sol containing hollow silica particles having a space inside their shells, by adding monovalent alkali metal ions to a hollow silica _sol having an increased particle size value by dynamic light scattering compared to the particle size value by dynamic light scattering at the time of production in a molar ratio of 7.12× ^10-6 to 285× ^10-6 converted into _M2O (wherein M represents a monovalent alkali metal atom) relative to the SiO2 of the hollow silica particles in the hollow silica sol, thereby reducing the increased particle size value by dynamic light scattering. In the above stabilization method, sodium ions can be used as the monovalent alkali metal ions.

The hollow silica sol in step (ii) is prepared by adding 0.0001 to 0.5 g of an aluminum compound per 1 g of hollow silica particles to an aqueous sol, and then heating at 40 to 260°C for 0.1 to 24 hours. The amount of aluminum compound added in step (ii) per 1 g of hollow silica particles can be in the range of 0.0001 to 0.5 g, 0.001 to 0.1 g, or 0.001 to 0.05 g. The heating temperature in step (ii) is 40 to 260°C, 50 to 260°C, or 60 to 240°C, but in the case of non-hydrothermal treatment, a temperature of 40 to less than 100°C, 50 to less than 100°C, or 60 to less than 100°C is used, and in the case of hydrothermal treatment, a temperature of 100 to 260°C, or 150 to 240°C can be used. The heating time in step (ii) can be in the range of 0.1 to 48 hours, or 0.1 to 24 hours, or 0.1 to 10 hours, or 1 to 10 hours.

The hollow silica particles used in step (I) have a silica shell and a space inside the shell. Hollow silica is obtained by forming a shell mainly composed of silica on the surface of a part corresponding to a core, which is called a template, in an aqueous dispersion medium, and removing the part corresponding to the core. The template can be an organic material (e.g., hydrophilic organic resin particles such as polyethylene glycol, polystyrene, polyester, etc.) or an inorganic material (e.g., hydrophilic inorganic compound particles such as calcium carbonate, sodium aluminate, etc.).
The hollow silica aqueous sol used as the raw material in the step (I) can be a non-hydrothermally treated hollow silica aqueous sol which has been subjected to heating in an aqueous medium at a temperature of less than 100° C., for example, from 20 to less than 100° C., or from 40 to less than 100° C., or from 50 to less than 100° C.
The hollow silica aqueous sol used in step (I) may be a hydrothermally treated hollow silica aqueous sol which has been heated in an aqueous medium at a temperature of 100°C to 240°C or 110°C to 240°C.

The raw material hollow silica sol used in the present invention can be a non-hydrothermally treated hollow silica aqueous sol, a hydrothermally treated hollow silica aqueous sol, or a mixture thereof. This forms aluminosilicate sites on the outer shells of hollow silica particles, but since the aluminosilicate sites may hold alkali metals, the raw material hollow silica sol can be selected so that aluminum atoms measured by the leaching _method are bonded to the hollow silica particle surface at 100 to 20,000 ppm/ _SiO2 in terms of _Al2O3 relative to the mass of _SiO2 of the hollow silica particles.
In the step (ii), an aluminum compound is added to the hollow silica aqueous sol. The aluminum compound can be added to the hollow silica aqueous sol in the form of a solid or an aqueous solution.
The aluminum compound used in step (ii) is at least one aluminum compound selected from the group consisting of aluminates, aluminum alkoxides, and hydrolysates thereof, and can be used as an aqueous solution containing them. Examples of aluminates include sodium aluminate, potassium aluminate, calcium aluminate, magnesium aluminate, ammonium aluminate, and amine aluminate. Examples of aluminum alkoxides include aluminum isopropoxide and aluminum butoxide. In particular, aluminates are preferably used.

These aluminum compounds are added in the form of an aqueous solution to the hollow silica aqueous sol obtained in step (I), and the concentration of the aqueous solution of the aluminum compound is in the range of 0.01 to 20 mass%, or 0.1 to 10 mass%, or 0.5 to 5 mass%. The addition can be performed while stirring the hollow silica aqueous sol obtained in step (I). The addition can be completed before heating, or can be performed throughout the entire heating time.
Whether the aluminum compound is impregnated into the hollow silica particles in a desired amount depends on the treatment temperature in step (ii), and the heat treatment must be carried out within the above temperature range.
The step (i) may further include a step of adding an amine. The amine may be any of the above-mentioned amines, and may be contained in the hollow silica sol in the above-mentioned range.

The above step (ii) may include a step of contacting the aluminum compound or the aluminum compound with at least one additive consisting of an amine and a neutral salt, followed by heat treatment, and then contacting the aluminum compound with a cation exchange resin, adding an acid, or a combination thereof. The cation exchange resin is a strongly acidic H-type cation exchange resin, and may then be contacted with an anion exchange resin. The acid may be an inorganic acid such as sulfuric acid, nitric acid, hydrochloric acid, or phosphoric acid, or an organic acid such as citric acid, acetic acid, malic acid, lactic acid, succinic acid, tartaric acid, butyric acid, fumaric acid, propionic acid, or formic acid.
In the present invention, the above-mentioned step (ii) can be carried out by adding the above-mentioned aluminum compound (e.g., sodium aluminate), carrying out a heat treatment at 100 to 240° C. for 0.1 to 48 hours, adding an acid (e.g., sulfuric acid, nitric acid, hydrochloric acid), and contacting with a cation exchange resin. The addition of the acid is a leaching operation in which aluminum-containing components that were not doped into the particles by the heat treatment and metal impurities contained in the particles are eluted into the liquid, and these metal-containing components are removed with a cation exchange resin. Further, a step of heat aging at 40 to 100° C. for 0.1 to 48 hours and then contacting with a cation exchange resin again can be carried out.

(iii) A step of replacing the aqueous medium of the aqueous sol of hollow silica with an alcohol, ketone, ether, or ester having 1 to 10 carbon atoms;
The method may further comprise a step (iv) of adding at least one silane compound selected from the group consisting of the above formula (1) and formula (2) and heating.
The above steps (iii) and (iv) can be steps in which, after completion of the above step (ii), in step (iii), the solvent is replaced with an alcohol having 1 to 10 carbon atoms, and then in step (iv), at least one silane compound selected from the group consisting of the above formulas (1) and (2), is added and heated, and then the solvent is further replaced with a ketone, ether, amide, urea, or ester having 1 to 10 carbon atoms.
By using the above-mentioned method for producing a hollow silica sol, it is possible to adjust the surface charge of the hollow silica particles contained in the sol.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.
The hollow silica sols used in the examples and comparative examples are as follows.

[Hollow silica sol]
Water-dispersed hollow silica sol (manufactured by Ningbo Dilato, product name: HKT-A20-40D, hollow silica aqueous sol heated in an aqueous medium at 100°C to 240°C, pH 9.3, dynamic light scattering particle size 55 nm, average primary particle size by TEM observation: 43 nm, TEM converted specific surface area (D) 63 m ² /g, specific surface area ratio (C/D ratio) 2.4, silica concentration 20 mass%, Na content: 14 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained is 6.64 x 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ )

[Basic Compounds]
Sodium hydroxide solution (Kanto Chemical Co., Ltd., product name: 4 mol/L sodium hydroxide solution)
Diethanolamine (Tokyo Chemical Industry Co., Ltd., product name: Diethanolamine)
According to the following methods, the physical properties of the water-dispersed hollow silica sol, the dispersions of silica particles prepared in the Examples and Comparative Examples, and the hollow silica sol and dispersions during the dispersion production process were measured and evaluated.

[Measurement of Silica (SiO ₂ ) Concentration]
The silica concentrations of the water-dispersed hollow silica sol, the methanol-dispersed hollow silica sol, the hollow silica sol during the production process of the methanol-dispersed hollow silica sol, and the dispersion of surface-modified silica particles were calculated by placing the hollow silica sol or the dispersion in a crucible, heating to remove the solvent, calcining at 1000° C., and weighing the calcination residue.

[pH Measurement]
The measurement was performed at 25° C. using a pH meter (manufactured by DKK Toa Corporation, trade name: MM-43X).
For organic solvents that can be arbitrarily mixed with water, such as methanol sol and propylene glycol monomethyl ether sol, the measurement was performed using a solution in which pure water and the sol were mixed in a mass ratio of 1:1. For organic solvent sols with low solubility in water, such as methyl ethyl ketone sol, the measurement was performed using a solution in which pure water, methanol, and the organic solvent sol were mixed in a mass ratio of 1:1:1.

[Moisture measurement]
The water content of the organic solvent dispersion sol was measured by Karl Fischer titration.

[Method for analyzing the amount of Na content]
0.2 g of the powder obtained by drying the hollow silica sol was treated with 20 mL of 48 mass % hydrofluoric acid solution to remove the silica component, and the residue was dissolved in 20 mL of 0.1 mol/L (N/10) aqueous nitric acid solution. The Na content in the resulting aqueous solution was measured using an ICP-OES analyzer (trade name: CIROS120 E0P, manufactured by Rigaku Corporation), and the Na content in the entire silica particles was calculated by dividing the measured value by the Si content.

[Dynamic Light Scattering (DLS) Particle Size Measurement]
The dynamic light scattering particle size was measured using a dynamic light scattering particle size measuring device (manufactured by Spectris, product name: Zetasizer Nano). The Z-average particle size was used as the dynamic light scattering particle size.

[Measurement of specific surface area (C) (S _N2 ) by nitrogen adsorption method (BET method)]
The nitrogen adsorption specific surface area (S _N2 ) of the silica particles in the water-dispersed hollow silica sol was measured by removing the water-soluble cations in the water-dispersed hollow silica sol with a cation exchange resin (manufactured by The Dow Chemical Company, product name: Amberlite IR-120B), drying the hollow silica sol at 290°C to prepare a measurement sample, and using a nitrogen adsorption specific surface area measuring device, Monosorb (manufactured by Quantachrome Instruments Japan, LLC).

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

[TEM conversion specific surface area (D)]
Assuming that the particles are truly spherical with a true density of 2.2 g/ ^cm3 , the average primary particle diameter was calculated as (TEM-converted specific surface area (D) = 2720/average primary particle diameter) using the average primary particle diameter obtained by [Measurement of average primary particle diameter by TEM (transmission electron microscope)].

[Measurement of the amount of aluminum (A) bound to the surface of hollow silica particles/Leaching method]
The cationic components in the hollow silica sol were removed with an H-type cation exchange resin, and the dried product from which the solvent was removed by heating was pulverized in a mortar and further treated at 250°C for 2 hours. 0.2 g of the obtained powder was put into a polypropylene container (PP sampler bottle 50 mL) containing 20 mL of 0.1 mol/L (N/10) nitric acid aqueous solution, and vigorously shaken and mixed by hand. Next, ultrasonic treatment was performed for 10 minutes in an ultrasonic cleaner (ASU CLEANER ASU-10M, manufactured by AS ONE) to thoroughly blend the powder with the nitric acid aqueous solution. It was then put into a 50°C thermostatic bath and held for 17 hours. The internal solution was then cooled to room temperature and loaded into a centrifugal ultrafiltration filter (Amicon Ultra-15, molecular weight cutoff: 10,000). The amount of aluminum in the filtrate obtained by centrifugation was measured using an ICP emission spectrometer, and the ratio of the amount of aluminum bound to the surface of the hollow silica particles in terms of Al ₂ O ₃ to the mass of SiO ₂ of the hollow silica (Al ₂ O ₃ (ppm)/SiO ₂ ) was calculated.

[Measurement of the amount of aluminum (B) present in the entire hollow silica particle/dissolution method]
The weighted hollow silica sol was dried to obtain a powder (0.2 g), which was treated with 20 mL of 48% by mass hydrofluoric acid solution to remove the silica component, and the residue was dissolved in 20 mL of 0.1 mol/L (N/ ₁₀ ) aqueous nitric acid solution. The amount of aluminum in the resulting aqueous solution was measured with an ICP emission spectrometer, and the ratio of the amount of aluminum present in the entire hollow silica particles to the mass of _SiO2 of the hollow silica in terms of _Al2O3 ( _Al2O3 ( _ppm )/ _SiO2 ) was calculated.

[Measurement of surface charge amount of hollow silica particles]
The hollow silica sol was added to 10 mL of methanol and diluted to a silica concentration of 0.5 mass % to prepare a measurement sample. Using a particle charge meter (manufactured by Voith Turbo K.K., product name PCD-06), a titration value was measured until the flow potential of the measurement sample reached zero using a 0.001 mol/L (N/1000) diallyldimethylammonium chloride solution (manufactured by Voith Turbo K.K.) as a standard cation titrant. The obtained titration value was divided by the mass of silica contained in the measurement sample to convert it to a value per 1 g of hollow silica particles, which was taken as the surface charge amount (μeq/g-SiO ₂ ).

Example 1
Step (a): 150 g of water-dispersed hollow silica sol (manufactured by Ningbo Dilato, product name: HKT-A20-40D) was placed in a 500 cc eggplant-shaped flask, and while stirring with a magnetic stirrer, an aqueous sodium hydroxide solution was added dropwise so that the sodium content in the water-dispersed hollow silica sol became 384 ppm/SiO ₂ (i.e., the amount of Na ₂ O contained was 182.16×10 ⁻⁶ mol/SiO ₂ in terms of the molar ratio of Na ₂ O to SiO ₂ ). The obtained silica sol had a pH of 10.1, a particle size measured by dynamic light scattering of 55 nm, an average primary particle size measured by TEM observation of 43 nm, a silica concentration of 20 mass%, a specific surface area measured by BET method of 150 m ² /g, a specific surface area converted into TEM of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the water-dispersed hollow silica sol was 384 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
(b) step: Then, 56g of methanol is added to 150g of the obtained water-dispersed hollow silica sol, and water is distilled off while feeding methanol using a rotary evaporator under heating and reduced pressure (bath temperature: 120°C, reduced pressure: 580 Torr), to obtain a methanol dispersion of hollow silica (methanol-dispersed hollow silica sol). When the water content of the methanol-dispersed hollow silica sol becomes 2.0 mass% or less, the methanol replacement is terminated, and 150g of methanol-dispersed hollow silica sol is obtained.
The obtained methanol-dispersed hollow silica sol had a silica concentration of 21 mass%, a water content of 1.3 mass%, a particle size by dynamic light scattering of 66 nm, a pH of 9.0, a specific surface area (C) by BET method of 150 m ² /g, a specific surface area (D) converted into TEM of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) converted into Al ₂ O ₃ of 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) converted into Al ₂ O ₃ of 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) of 0.20, and an amount of sodium contained in the methanol-dispersed hollow silica sol of 384 ppm/SiO ₂ , i.e., an amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as a molar ratio of Na ₂ O to SiO ₂ .
The obtained methanol-dispersed hollow silica sol was sealed in a 30 cc glass bottle and further stored in an explosion-proof thermostatic chamber (manufactured by Espec Corp., product name: thermostatic chamber with safety door) kept at 50°C for 48 hours, and the stability of the methanol-dispersed hollow silica sol was confirmed by comparing the dynamic light scattering particle diameter before and after storage at 50°C. When the dynamic light scattering particle diameter before introduction at 50°C was within a range of 2.0 times that before storage, the sol was evaluated as "stable", and when it exceeded 2.0 times, the sol was evaluated as "unstable". The stability of the methanol-dispersed hollow silica sol obtained in Example 1 is shown in Table 1.

Example 2
Step (a): 150 g of water-dispersed hollow silica sol (manufactured by Ningbo Dilato, product name: HKT-A20-40D) was placed in a 500 cc eggplant-shaped flask, and while stirring with a magnetic stirrer, an aqueous sodium hydroxide solution was added dropwise so that the sodium content in the water-dispersed hollow silica sol was 384 ppm/SiO ₂ (i.e., the amount of Na ₂ O contained was 182.16×10 ⁻⁶ mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ ). Furthermore, 0.16 g of diethanolamine was added dropwise while stirring with a magnetic stirrer. The obtained silica sol had a pH of 10.2, a particle size measured by dynamic light scattering of 55 nm, an average primary particle size measured by TEM observation of 43 nm, a silica concentration of 20 mass%, a specific surface area measured by BET method of 150 m ² /g, a specific surface area converted into TEM of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the water-dispersed hollow silica sol was 384 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
(b) step: Then, 56g of methanol is added to 150g of the obtained water-dispersed hollow silica sol, and water is distilled off while feeding methanol using a rotary evaporator under heating and reduced pressure (bath temperature: 120°C, reduced pressure: 580 Torr), to obtain a methanol dispersion of hollow silica (methanol-dispersed hollow silica sol). When the water content of the methanol-dispersed hollow silica sol becomes 2.0 mass% or less, the methanol replacement is terminated, and 150g of methanol-dispersed hollow silica sol is obtained.
The obtained methanol-dispersed hollow silica sol had a silica concentration of 21 mass%, a water content of 0.4 mass%, a particle diameter by dynamic light scattering of 66 nm, a specific surface area (C) by BET method of 150 m ² /g, a TEM-converted specific surface area (D) of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the methanol-dispersed hollow silica sol was 384 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
The same stability test as in Example 1 was carried out and the results are shown in Table 1.

Example 3
Step (a): 150 g of water-dispersed hollow silica sol (manufactured by Ningbo Dilato, product name: HKT-A20-40D) was placed in a 500 cc eggplant-shaped flask, and while stirring with a magnetic stirrer, an aqueous sodium hydroxide solution was added dropwise so that the sodium content in the water-dispersed hollow silica sol was 384 ppm/SiO ₂ (i.e., the amount of Na ₂ O contained was 182.16×10 ⁻⁶ mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ ). Furthermore, 0.16 g of diethanolamine was added dropwise while stirring with a magnetic stirrer. The obtained silica sol had a pH of 10.2, a particle size measured by dynamic light scattering of 55 nm, an average primary particle size measured by TEM observation of 43 nm, a silica concentration of 20 mass%, a specific surface area measured by BET method of 150 m ² /g, a specific surface area converted into TEM of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the water-dispersed hollow silica sol was 384 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
(b) step: Then, 56g of methanol is added to 150g of the obtained water-dispersed hollow silica sol, and water is distilled off while feeding methanol using a rotary evaporator under heating and reduced pressure (bath temperature: 120°C, reduced pressure: 580 Torr), to obtain a methanol dispersion of hollow silica (methanol-dispersed hollow silica sol). When the water content of the methanol-dispersed hollow silica sol becomes 2.0 mass% or less, the methanol replacement is terminated, and 150g of methanol-dispersed hollow silica sol is obtained.
30 g of the methanol-dispersed hollow silica sol was placed in a 50 cc eggplant-shaped flask, and 0.33 g of pure water was added thereto while stirring with a magnetic stirrer. The obtained methanol-dispersed hollow silica sol had a silica concentration of 21 mass%, a water content of 1.5 mass%, a particle diameter by dynamic light scattering of 66 nm, a specific surface area (C) by BET method of 150 m ² /g, a TEM-converted specific surface area (D) of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the methanol-dispersed hollow silica sol was 384 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
The same stability test as in Example 1 was carried out and the results are shown in Table 1.

Example 4
Step (a): 150 g of water-dispersed hollow silica sol (manufactured by Ningbo Dilato, product name: HKT-A20-40D) was placed in a 500 cc eggplant-shaped flask, and while stirring with a magnetic stirrer, an aqueous sodium hydroxide solution was added dropwise so that the sodium content in the water-dispersed hollow silica sol was 192 ppm/SiO ₂ (i.e., the amount of Na ₂ O contained was 91.08×10 ⁻⁶ mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ ). Furthermore, 0.16 g of diethanolamine was added dropwise while stirring with a magnetic stirrer. The obtained silica sol had a pH of 9.8, a particle size measured by dynamic light scattering of 55 nm, an average primary particle size measured by TEM observation of 43 nm, a silica concentration of 20 mass%, a specific surface area measured by BET method of 150 m ² /g, a specific surface area converted into TEM of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the water-dispersed hollow silica sol was 192 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 91 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
(b) step: Then, 56g of methanol is added to 150g of the obtained water-dispersed hollow silica sol, and water is distilled off while feeding methanol using a rotary evaporator under heating and reduced pressure (bath temperature: 120°C, reduced pressure: 580 Torr), to obtain a methanol dispersion of hollow silica (methanol-dispersed hollow silica sol). When the water content of the methanol-dispersed hollow silica sol becomes 2.0 mass% or less, the methanol replacement is terminated, and 150g of methanol-dispersed hollow silica sol is obtained.
The obtained methanol-dispersed hollow silica sol had a silica concentration of 21 mass%, a water content of 0.6 mass%, a particle diameter by dynamic light scattering of 66 nm, a specific surface area (C) by BET method of 150 m ² /g, a TEM-converted specific surface area (D) of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the methanol-dispersed hollow silica sol was 192 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
The same stability test as in Example 1 was carried out and the results are shown in Table 1.

Example 5
Step (a): 150 g of water-dispersed hollow silica sol (manufactured by Ningbo Dilato, product name: HKT-A20-40D) was placed in a 500 cc eggplant-shaped flask, and while stirring with a magnetic stirrer, an aqueous sodium hydroxide solution was added dropwise so that the sodium content in the water-dispersed hollow silica sol was 192 ppm/SiO ₂ (i.e., the amount of Na ₂ O contained was 91.08×10 ⁻⁶ mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ ). Furthermore, 0.16 g of diethanolamine was added dropwise while stirring with a magnetic stirrer. The obtained silica sol had a pH of 9.8, a particle size measured by dynamic light scattering of 55 nm, an average primary particle size measured by TEM observation of 43 nm, a silica concentration of 20 mass%, a specific surface area measured by BET method of 150 m ² /g, a specific surface area converted into TEM of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the water-dispersed hollow silica sol was 192 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 91 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
(b) step: Then, 56g of methanol was added to 150g of the obtained water-dispersed hollow silica sol, and water was distilled off while feeding methanol under heating and reduced pressure (bath temperature: 120°C, reduced pressure: 580 Torr) using a rotary evaporator, to obtain a methanol dispersion of hollow silica (methanol-dispersed hollow silica sol). When the water content of the methanol-dispersed hollow silica sol became 2.0 mass% or less, the methanol replacement was terminated, and 150g of methanol-dispersed hollow silica sol was obtained.
30 g of the resulting methanol-dispersed hollow silica sol was placed in a 50 cc eggplant-shaped flask, and 0.27 g of pure water was added thereto while stirring with a magnetic stirrer. The obtained methanol-dispersed hollow silica sol had a silica concentration of 21 mass%, a water content of 1.5 mass%, a particle diameter by dynamic light scattering of 66 nm, a specific surface area (C) by BET method of 150 m ² /g, a specific surface area (D) converted into TEM of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) converted into Al ₂ O ₃ of 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) converted into Al ₂ O ₃ of 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) of 0.20, and an amount of sodium contained in the methanol-dispersed hollow silica sol of 192 ppm/SiO ₂ , i.e., an amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as a molar ratio of Na ₂ O to SiO ₂ .
The same stability test as in Example 1 was carried out and the results are shown in Table 1.

Example 6
Step (a): 150 g of water-dispersed hollow silica sol (manufactured by Ningbo Dilato Co., Ltd., product name: HKT-A20-40D) was placed in a 500 cc eggplant-shaped flask, and 0.16 g of diethanolamine was added dropwise thereto while stirring with a magnetic stirrer. The obtained silica sol had a pH of 9.5, a particle diameter of 55 nm measured by dynamic light scattering, an average primary particle diameter of 43 nm measured by TEM observation, a silica concentration of 20 mass%, a specific surface area (C) measured by BET method of 150 m ² /g, a specific surface area (D) converted into TEM of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the water-dispersed hollow silica sol was 14 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 6.64 × 10 ^-6 mol/SiO ₂ as the molar ratio of Na ₂ O to SiO ₂ .
(b) step: Then, 56g of methanol is added to 150g of the obtained water-dispersed hollow silica sol, and water is distilled off while feeding methanol using a rotary evaporator under heating and reduced pressure (bath temperature: 120°C, reduced pressure: 580 Torr), to obtain a methanol dispersion of hollow silica (methanol-dispersed hollow silica sol). When the water content of the methanol-dispersed hollow silica sol becomes 2.0 mass% or less, the methanol replacement is terminated, and 150g of methanol-dispersed hollow silica sol is obtained.
Step (c): Then, to 100 g of the obtained methanol-dispersed hollow silica sol, while stirring with a magnetic stirrer, an aqueous sodium hydroxide solution diluted with methanol was added dropwise so that the sodium content in the water-dispersed hollow silica sol was 384 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 182.16×10 ⁻⁶ mol/SiO ₂ in terms of the molar ratio of Na ₂ O to SiO ₂ .
The obtained methanol-dispersed hollow silica sol had a silica concentration of 20 mass%, a water content of 1.8 mass%, a particle diameter by dynamic light scattering of 78 nm, a specific surface area (C) by BET method of 150 m ² /g, a TEM-converted specific surface area (D) of 63 m ² /g, a specific surface area ratio (C/D ratio) of 2.4, an amount of aluminum bonded to the particle surface (A) calculated as Al ₂ O ₃ was 0.1 ppm relative to the mass of SiO ₂ of the hollow silica particles, an amount of aluminum present in the entire particle (B) calculated as Al ₂ O ₃ was 0.5 ppm relative to the mass of SiO ₂ of the hollow silica particles, (A/B ratio) was 0.20, and the amount of sodium contained in the methanol-dispersed hollow silica sol was 384 ppm/SiO ₂ , i.e., the amount of Na ₂ O contained was 182 × 10 ^-6 mol/SiO ₂ as a molar ratio of Na ₂ O to SiO ₂ .
The same stability test as in Example 1 was carried out and the results are shown in Table 1.

Comparative Example 1
Step (a): 150 g of water-dispersed hollow silica sol (manufactured by Ningbo Dilato Co., Ltd., product name: HKT-A20-40D) was placed in a 500 cc eggplant-shaped flask, and 0.16 g of diethanolamine was added dropwise thereto while stirring with a magnetic stirrer.
(b) step: Then, 56g of methanol is added to 150g of the obtained water-dispersed hollow silica sol, and water is distilled off while feeding methanol using a rotary evaporator under heating and reduced pressure (bath temperature: 120°C, reduced pressure: 580 Torr), to obtain a methanol dispersion of hollow silica (methanol-dispersed hollow silica sol). When the water content of the methanol-dispersed hollow silica sol becomes 2.0 mass% or less, the methanol replacement is terminated, and 150g of methanol-dispersed hollow silica sol is obtained.
The obtained methanol-dispersed hollow silica sol had a silica concentration of 20% by mass, a water content of 0.8% by mass, and a particle size of 123 nm as measured by dynamic light scattering. The amount of Na ₂ O contained was 6.64×10 ⁻⁶ moles/SiO ₂ (the molar ratio of Na ₂ O to SiO ₂ ).
The same stability test as in Example 1 was carried out and the results are shown in Table 1.
[Table 1]
Table 1
――――――――――――――――――――――――――――――――――
DLS particle size (nm) DLS particle size (nm) DLS particle size (nm) Result (Initial) (Before stability test) (After stability test)
Example 1 66 66 67 Stable Example 2 66 66 66 Stable Example 3 66 66 67 Stable Example 4 66 66 67 Stable Example 5 66 66 67 Stable Example 6 78 78 73 Stable Comparative Example 1 105 105 235 Unstable

In Examples 1 to 6, which are sols having an average particle size of 20 to 150 nm as measured by dynamic light scattering and containing monovalent alkali metal ions in a molar ratio of 7.12 x ^10-6 to 285 x ^10-6 relative to the _SiO2 of the hollow silica particles, converted to _M2O (wherein M represents a monovalent alkali metal atom), the particle size values as measured by dynamic light scattering after storage for 48 hours at 50°C were within a range of 2.0 times that before storage, confirming high stability.
On the other hand, in Comparative Example 1, which is a sol containing monovalent alkali metal ions in a molar ratio converted to M ₂ O (wherein M represents a monovalent alkali metal atom) relative to the SiO ₂ of the hollow silica particles of less than 7.12 × 10 ^-6 , even though the average particle size measured by dynamic light scattering was 20 to 150 nm, the particle size measured by dynamic light scattering after storage at 50°C for 48 hours was more than 2.0 times that before storage, confirming that the stability was low.

Furthermore, as shown in Table 1, even in the case of a sol having an average particle size of 20 to 150 nm as measured by a dynamic light scattering method and containing monovalent alkali metal ions in a molar ratio of less than 7.12 x ^10-6 relative to the _SiO2 of the hollow silica particles, calculated as _M2O (wherein M represents a monovalent alkali metal atom), the particle size value of Example ₆ , which is a sol obtained by adding monovalent alkali metal ions after methanol replacement and containing monovalent alkali metal ions in a molar ratio of 7.12 x ^10-6 to 285 x ^10-6 relative to the SiO2 of the hollow silica particles, calculated as _M2O (wherein M represents a monovalent alkali metal atom), after storage at 50°C for 48 hours, was within a range of 2.0 times that before storage, confirming high stability.

The present invention relates to an aqueous sol and an organic solvent sol containing highly stable hollow silica particles, and further to a method for improving the stability of the sol having a reduced storage stability, and a method for producing the same.

Claims (23)

The silica particles contain hollow silica particles having spaces inside their shells, and monovalent alkali metal ions.
the sol contains the monovalent alkali metal ions in a ratio of 7.12×10 ⁻⁶ to 285×10 ⁻⁶ in moles calculated as M ₂ O (wherein M represents a monovalent alkali metal atom) relative to the moles of SiO ₂ of the hollow silica particles,
The average particle size, as measured by dynamic light scattering after storing the sol at 50° C. for 48 hours, is within a range of 2.0 times the average particle size, as measured by dynamic light scattering, before the storage. The hollow silica sol according to claim 1, wherein the monovalent alkali metal ion is a sodium ion. The hollow silica sol according to claim 1 or 2, having an average particle size of 20 to 150 nm as measured by dynamic light scattering. The hollow silica sol according to any one of claims 1 to 3, further comprising an amine, the amine being 0.001 to 10 mass% relative to the SiO ₂ of the hollow silica particles. The hollow silica sol according to claim 4, wherein the amine is at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines having 1 to 10 carbon atoms. The hollow silica sol according to claim 4 or 5, wherein the amine is a water-soluble amine having a water solubility of 80 g/L or more. Further, the hollow silica particles contain aluminum atoms forming aluminosilicate sites,
The aluminum atoms are bonded to the surface of the hollow silica particles,
The mass of the aluminum atoms is in the range of 100 to 20,000 ppm (A) calculated as Al ₂ O ₃ relative to the mass of SiO ₂ of the hollow silica particles,
The mass of the aluminum atom is a value measured by a leaching method.
The hollow silica sol according to any one of claims 1 to 6. The hollow silica sol according to claim 7, wherein the leaching method measurement, which leaches aluminum atoms from a compound containing aluminum atoms bonded to the surface of hollow silica particles, uses an aqueous solution of at least one mineral acid selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid. the mass of aluminum atoms present in the entire hollow silica particles is expressed as a ratio (B) of 120 to 50,000 ppm in terms of Al ₂ O ₃ relative to the mass of SiO ₂ of the hollow silica particles,
The mass of the aluminum atoms is a value measured by dissolving the hollow silica particles in an aqueous hydrofluoric acid solution,
The hollow silica sol according to claim 7 or 8, wherein the ratio (A)/the ratio (B) is 0.002 to 1.0. The hollow silica sol according to any one of claims 1 to 9, which contains hollow silica particles having a ratio of [specific surface area (C) of silica particles measured by the BET method (nitrogen gas adsorption method)]/[specific surface area (D) of silica particles calculated from a transmission electron microscope] of 1.40 to 5.00. The hollow silica sol according to any one of claims 1 to 10, comprising hollow silica particles having a surface charge amount of 5 to 250 μeq/g per 1 g in terms of _SiO2 . The hollow silica particles may further comprise the following formula (1) and formula (2):

(In formula (1),
^R1 is a group bonded to a silicon atom, and each R1 is independently
represents an alkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, or represents an organic group having an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a polyether group, a carboxy group, a protected carboxy group, a carboxy group-generating group, an imido group, or a cyano group, and which is bonded to a silicon atom via a Si—C bond, or represents a combination of these groups;
^R2 is a group or atom bonded to a silicon atom, and each independently represents an alkoxy group having one or more carbon atoms, an acyloxy group, a hydroxy group, or a halogen atom, or represents a combination of these groups;
a represents an integer of 1 to 3;
In formula (2),
^R3 is a group bonded to a silicon atom, and each independently represents an alkyl group, a halogenated alkyl group, an alkenyl group, or an aryl group, or an organic group having an epoxy group, a (meth)acryloyl group, a mercapto group, an amino group, a ureido group, a polyether group, a carboxy group, a protected carboxy group, a carboxy group-generating group, an imido group, or a cyano group and bonded to a silicon atom via a Si-C bond, or a combination of these groups;
^R4 is a group or atom bonded to a silicon atom, and each independently represents an alkoxy group having one or more carbon atoms, an acyloxy group, a hydroxy group, or a halogen atom, or represents a combination of these groups;
Y is a group or atom bonded to a silicon atom and represents an alkylene group, an NH group, or an oxygen atom;
b represents an integer of 1 to 3, and c represents an integer of 0 or 1.
The hollow silica sol according to any one of claims 1 to 11, comprising hollow silica particles coated with at least one silane compound selected from the group consisting of compounds represented by the following formula: The hollow silica sol according to any one of claims 1 to 12, wherein the dispersion medium is water, an alcohol having 1 to 10 carbon atoms, a ketone, an ether, an amide, a urea, or an ester. A film-forming composition comprising hollow silica particles derived from the hollow silica sol according to any one of claims 1 to 13, and an organic resin or a polysiloxane. A film obtained from the film-forming composition according to claim 14, having a visible light transmittance of 80% or more. The following steps (I) to (II):
Step (I): preparing a hollow silica sol containing a dispersion medium;
Step (II): adding and adjusting a monovalent alkali metal ion to the hollow silica sol of step ( _I ) so that the molar ratio of the monovalent alkali metal ion converted to M ₂ O (wherein M represents a monovalent alkali metal atom) relative to the SiO 2 of the hollow silica particles is 7.12×10 ⁻⁶ to 285×10 ⁻⁶ ;
The method for producing the hollow silica sol according to any one of claims 1 to 13, comprising: The method for producing hollow silica sol according to claim 16, wherein the monovalent alkali metal ion in step (II) is a sodium ion. The method for producing hollow silica sol according to claim 17, wherein the sodium ion content in step (II) is adjusted by contacting the hollow silica sol obtained in step (I) with a cation exchange resin or by adding a sodium source. The method for producing hollow silica sol according to claim 17, wherein the sodium source added in step (II) is sodium hydroxide. The method for producing hollow silica sol according to any one of claims 16 to 19, wherein the dispersion medium in steps (I) and (II) is water, an alcohol having 1 to 10 carbon atoms, a ketone, an ether, an amide, a urea, or an ester. The method for producing a hollow silica sol according to any one of claims 16 to 20, wherein at least one step selected from the following (i) to (iv) is added to the above step (I), step (II), or both steps:
(i): Adding an amine to a hollow silica sol;
(ii): adding sodium aluminate as an aluminum source and heating to form aluminosilicate sites in hollow silica particles;
(iii): replacing the dispersion medium with another dispersion medium;
(iv): The hollow silica particles are further coated with at least one silane compound selected from the group consisting of formula (1) and formula (2). A method for stabilizing a hollow silica sol containing hollow silica particles having a space inside an outer shell, comprising the steps of:
The hollow silica sol has an increased average particle size measured by dynamic light scattering compared to when it was manufactured.
the monovalent alkali metal ion is added so that the molar ratio of the monovalent alkali metal ion converted into M ₂ O (wherein M represents a monovalent alkali metal atom) to the molar number of SiO ₂ of the hollow silica particles in the hollow silica sol is 7.12×10 ⁻⁶ to 285×10 ⁻⁶ ;
2. The method for stabilizing hollow silica sol according to claim 1, characterized in that the average particle size determined by an increased dynamic light scattering method is reduced. The method for stabilizing a hollow silica sol according to claim 22, wherein the monovalent alkali metal ion is a sodium ion.