Method for producing hollow silica particle having organic group on surface
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- KAO CORP
- Filing Date
- 2023-07-19
- Publication Date
- 2026-07-03
AI Technical Summary
Conventional hollow silica particles with hydrophilic silanol groups on the surface lead to increased melting viscosity when mixed with resin monomers, making it difficult to handle and manufacture resin compositions effectively.
A method to produce hollow silica particles with organic groups on the surface by creating hydrophobic emulsions using cation surfactants, forming a hollow silica particle precursor, and treating it with a silane coupling agent to reduce particle size and improve distribution in resin compositions.
The method results in hollow silica particles with reduced dielectric constant and viscosity, facilitating easier handling and production of resin compositions with improved properties.
Abstract
Description
[Technical field]
[0001] The present invention relates to a method for producing hollow silica particles having organic groups on their surfaces, hollow silica particles having organic groups on their surfaces, and a resin composition containing the hollow silica particles. [Background technology]
[0002] The use of high frequencies of several tens of GHz is being considered for high-speed communication technologies such as 5G and radars used in autonomous driving. In high-frequency circuits that handle such high-frequency radio waves, insulating materials with low dielectric constants and low dielectric dissipation factors are required to reduce transmission losses and transmission delays, and low dielectric constants and low dielectric dissipation factors are also required for silica particles that are currently blended into insulating materials to improve thermal properties. In addition, miniaturization of high-frequency circuits is desired, and the particle size of silica particles blended into insulating materials is also required to be reduced. Currently, the use of hollow silica particles to reduce the dielectric constant of silica particles is being investigated.
[0003] For example, various methods have been developed as a method for producing hollow silica. For example, Patent Document 1 describes a method for producing hollow silica particles that can easily produce hollow silica particles with a reduced alkali metal content, the method including: (1) a step of spray-drying a silica solution obtained by dissolving silica in an organic alkali aqueous solution to obtain a hollow silica precursor; and (2) a step of calcining the hollow silica precursor to obtain hollow silica particles. Patent Document 2 describes a method for producing silica-based particles, which comprises the steps of: (a) spray-drying an aqueous alkali silicate solution into a hot air current to prepare precursor particles of silica-based particles; (b) immersing the precursor particles of silica-based particles in an aqueous acid solution to remove the alkali; and (c) drying and heat-treating the particles. [Prior art documents] [Patent documents]
[0004] [Patent Document 1] JP 2017-193462 A [Patent Document 2] JP 2011-256098 A Summary of the Invention [Problem to be solved by the invention]
[0005] In order to utilize the characteristics of hollow silica particles such as low dielectric constant and low dielectric loss tangent, hollow silica particles are sometimes used by being blended as a filler in low dielectric resin. As a method of blending a filler into a resin, a resin monomer and a filler are mixed to prepare a resin composition precursor, and then the resin composition precursor is cured to obtain a resin composition. However, when conventional hollow silica particles as disclosed in Patent Documents 1 and 2 are mixed with a resin monomer, the hollow silica surface has a hydrophilic silanol group, so that the hollow silica particles are not sufficiently dispersed in the resin monomer, and the melt viscosity of the resin composition precursor containing the hollow silica particles is high, which causes a problem that the handleability of the resin composition precursor is poor and it is difficult to manufacture the resin composition. The present invention provides a method for producing hollow silica particles having organic groups on the surface thereof, which have a low dielectric constant and dielectric tangent, and which, when mixed with a resin monomer to form a resin composition precursor, suppress an increase in the viscosity of the resin composition precursor, thereby facilitating the production of a resin composition. [Means for solving the problem]
[0006] The present invention relates to the following [1] to [3]. [1] A method for producing hollow silica particles having organic groups on their surfaces, comprising the steps of: Step A: A step of preparing an aqueous emulsion of a hydrophobic liquid using a cationic surfactant A. Step B: A step of adding a silanol precursor, an alkaline substance, and a cationic surfactant B to the aqueous emulsion obtained in step A to produce hollow silica particle precursors. Step C: A step of heat treating the hollow silica particle precursor obtained in step B at a temperature of more than 1000° C. and not more than 1200° C. for 1 hour or more. Step D: A step of treating the surfaces of the hollow silica particles obtained in step C with a silane coupling agent. [2] Hollow silica particles having a total content of alkali metals and alkaline earth metals of 50 ppm by mass or less relative to the silica content in the particles, a relative dielectric constant of 2.5 or less and a dielectric dissipation factor of 0.0050 or less at a measurement frequency of 10 GHz, and having organic groups on the surface. [3] A resin composition containing the hollow silica particles described in [2] above. Effect of the Invention
[0007] According to the present invention, it is possible to provide a method for producing hollow silica particles having organic groups on the surface thereof, which reduces an increase in viscosity when mixed with a resin monomer to form a resin composition precursor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0008] [Method of manufacturing hollow silica particles] The method for producing hollow silica particles of the present invention includes the following steps. Step A: A step of preparing an aqueous emulsion of a hydrophobic liquid using a cationic surfactant A. Step B: A step of adding a silanol precursor, an alkaline substance, and a cationic surfactant B to the aqueous emulsion obtained in step A to produce hollow silica particle precursors. Step C: A step of heat treating the hollow silica particle precursor obtained in step B at a temperature of more than 1000° C. and not more than 1200° C. for 1 hour or more. Step D: A step of treating the surfaces of the hollow silica particles obtained in step C with a silane coupling agent.
[0009] Although the details of the mechanism by which the effects of the present invention are manifested are not clear, it is presumed to be as follows. The reason why the hollow silica particles obtained by the production method of the present invention have a low relative dielectric constant and dielectric loss tangent and are less likely to thicken the resin composition precursor is not clear, but is thought to be as follows. In the production of hollow silica particles having an organic group on the surface of the present invention, first, a silanol precursor and a cationic surfactant B are added to an aqueous emulsion of a hydrophobic liquid, thereby coating the surface of the droplets of the hydrophobic liquid with a silanol precursor. Then, the silanol obtained by hydrolyzing the silanol precursor with an alkaline substance is condensed to obtain a hollow silica particle precursor. When preparing an aqueous emulsion of a hydrophobic liquid, the particle size of the droplets of the hydrophobic liquid can be sufficiently small, so that the particle size of the hollow silica particle precursor can be made to be a desired particle size. In addition, when preparing an aqueous emulsion of a hydrophobic liquid, a cationic surfactant A is used, and a silanol precursor, an alkaline substance, and a cationic surfactant B are further added, so that the silanol condensed with the cationic surfactant micelle forms a complex, which is considered to be incorporated into the outer shell of the hollow silica particle precursor. The hydrophobic liquid incorporated inside the hollow silica precursor volatilizes through the gaps between the cationic surfactant incorporated in the shell and the silica during drying or the initial stage of calcination, so that large pores are not generated in the shell of the hollow silica precursor due to the volatilization of the hydrophobic liquid during drying or calcination. Next, the hollow silica particle precursor is heat-treated at a temperature of more than 1000°C and not more than 1200°C. At that time, the cationic surfactant incorporated in the outer shell of the hollow silica particle precursor in the initial stage is decomposed and volatilized, forming uniform pores of a few nm in size in the outer shell. Since the pore size is very small at a few nm, even if it does not contain alkali metal or alkaline earth metal as a flux, the pores disappear easily in the high temperature state in the later stage of firing, and the outer shell of the hollow silica particles becomes uniform and dense, and the dielectric loss tangent is thought to be low. In addition, since the outer shell of the hollow silica particle precursor is dense without large holes, it is possible to reduce shrinkage during heat treatment, and as a result of the high porosity of the hollow silica particles, the relative dielectric constant is thought to be low. By treating the surface of the hollow silica particles thus obtained with a silane coupling agent, the affinity between the hollow silica particles having organic groups on the surface and the resin is increased, the aggregation of the hollow silica particles in the resin composition precursor can be suppressed, and the hollow silica particles can be dispersed in the resin composition precursor, and the increase in the viscosity of the resin composition precursor can be suppressed more than that of conventional silica particles.Therefore, the resin composition precursor that contains the hollow silica particles having organic groups on the surface has excellent handling properties, and is considered to facilitate the production of the resin composition. However, the present invention need not be interpreted as being limited to this mechanism.
[0010] [Process A] In step A, cationic surfactant A and a hydrophobic liquid are mixed and stirred with liquid A containing water to prepare an aqueous emulsion of the hydrophobic liquid in which droplets of the hydrophobic liquid are dispersed. The preparation of the aqueous emulsion of the hydrophobic liquid can be carried out by a general method.
[0011] Examples of the water contained in Liquid A include distilled water, ion-exchanged water, and ultrapure water. Liquid A may also contain an organic solvent compatible with water, from the viewpoint of more uniform and stable emulsion of the hydrophobic liquid. Examples of the organic solvent compatible with water include lower alcohols such as methanol, ethanol, and isopropyl alcohol, and acetone. From the viewpoint of instantly reducing the solubility of the hydrophobic liquid in liquid A, the water content in liquid A is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 98% by mass or more, and even more preferably 100% by mass.
[0012] (Cationic Surfactant A) From the viewpoint of facilitating the formation of a complex with the condensed silanol in step B described below, and from the viewpoint of decomposition and volatilization in step C described below, the cationic surfactant A is preferably a quaternary ammonium salt, more preferably at least one selected from alkyltrimethylammonium salts and dialkyldimethylammonium salts, and even more preferably at least one selected from the group consisting of quaternary ammonium salts represented by the following general formula (1) or general formula (2). [R 1 R 3 3N] + X ― (1) [R 1 R 2 R 3 2N] + X ― (2)
[0013] In the general formula (1) and the general formula (2), R 1 and R 2 each independently represents a linear or branched alkyl group having 4 to 22 carbon atoms; R 3 represents an alkyl group having 1 to 3 carbon atoms, and multiple R 3 may each be a different group, and X ― indicates a monovalent anion. Examples of the alkyl group having 4 to 22 carbon atoms include various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, various tetradecyl groups, various hexadecyl groups, various octadecyl groups, and various eicosyl groups. Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. 3 is preferably a methyl group.
[0014] X in general formulas (1) and (2) ― From the viewpoint of being easily decomposed and volatilized during firing, X is preferably at least one type selected from monovalent anions such as halogen ions, hydroxide ions, and nitrate ions. ―More preferably, the cation is a halide ion, and even more preferably, a chloride ion.
[0015] Examples of the alkyl trimethyl ammonium salt represented by the general formula (1) include butyl trimethyl ammonium chloride, hexyl trimethyl ammonium chloride, octyl trimethyl ammonium chloride, decyl trimethyl ammonium chloride, lauryl trimethyl ammonium chloride (dodecyl trimethyl ammonium chloride), tetradecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, butyl trimethyl ammonium bromide, hexyl trimethyl ammonium bromide, octyl trimethyl ammonium bromide, decyl trimethyl ammonium bromide, lauryl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, stearyl trimethyl ammonium bromide, and behenyl trimethyl ammonium bromide.
[0016] Examples of the dialkyldimethylammonium salt represented by the general formula (2) include dibutyldimethylammonium chloride, dihexyldimethylammonium chloride, dioctyldimethylammonium chloride, dihexyldimethylammonium bromide, dioctyldimethylammonium bromide, dilauryldimethylammonium bromide, and ditetradecyldimethylammonium bromide.
[0017] From the viewpoint of facilitating the formation of a complex with the condensed silanol in step B and facilitating decomposition and volatilization in step C, the quaternary ammonium salt is preferably lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, or behenyltrimethylammonium chloride, and more preferably stearyltrimethylammonium chloride or behenyltrimethylammonium chloride.
[0018] (hydrophobic liquid) The hydrophobic liquid is preferably capable of forming emulsified droplets (emulsified oil droplets) in water. In addition, in terms of using liquid A containing water as a dispersion medium and improving the utilization efficiency of the hydrophobic liquid, the temperature range in which the liquid is in a liquid state is preferably 0 to 100°C, and more preferably 20 to 90°C. Specific examples of hydrophobic liquids include those described in paragraphs
[0015] to
[0023] of JP2016-121060A. Among these, hydrocarbons having 6 to 18 carbon atoms are preferred, hydrocarbons having 8 to 14 carbon atoms are more preferred, and dodecane is more preferred.
[0019] In step A, the mass ratio of the hydrophobic liquid to water [hydrophobic liquid / water] is preferably 0.3 or more, more preferably 0.35 or more, even more preferably 0.4 or more, from the viewpoint of keeping the particle size of the resulting hydrophobic liquid droplets in an appropriate range, and is preferably 0.8 or less, more preferably 0.75 or less, even more preferably 0.7 or less.
[0020] In step A, the mass ratio of cationic surfactant A to the hydrophobic liquid [cationic surfactant A / hydrophobic liquid], from the viewpoint of dispersing the hydrophobic liquid in liquid A, is preferably 0.0005 or more, more preferably 0.001 or more, even more preferably 0.0015 or more, and is preferably 0.05 or less, more preferably 0.04 or less, even more preferably 0.035 or less.
[0021] In step A, the particle size of the resulting droplets containing the hydrophobic liquid can be adjusted to an appropriate range by appropriately adjusting the stirring speed, temperature, etc. Step A is preferably carried out at a temperature of 15°C to 80°C. The volume average particle diameter of the droplets containing the hydrophobic liquid obtained in step A is preferably 0.1 μm or more, more preferably 0.3 μm or more, even more preferably 0.4 μm or more, and is preferably 2.5 μm or less, more preferably 2.0 μm or less, even more preferably 1.5 μm or less, from the viewpoint of obtaining a suitable average particle diameter of 0.5 μm to 3.0 μm for the hollow silica particles having organic groups on the surface obtained by the present invention. The volume average particle size of droplets containing a hydrophobic liquid can be determined by the method described in the Examples.
[0022] [Process B] In step B, a silanol precursor, an alkaline substance, and a cationic surfactant B are added to the aqueous emulsion obtained in step A to generate a hollow silica particle precursor. In detail, the silanol precursor present on the surface of the hydrophobic liquid droplets is first hydrolyzed in the presence of an alkaline substance to obtain silanol. The obtained silanol is then condensed in the presence of the alkaline substance to form a hollow silica particle precursor having an outer shell containing silica and cationic surfactant B on the surface of the hydrophobic liquid droplets and containing the hydrophobic liquid inside. The addition of the silanol precursor, the alkaline substance, and the cationic surfactant B to the aqueous emulsion may be performed by adding the silanol precursor and the cationic surfactant B simultaneously or separately to the aqueous emulsion and then adding the alkaline substance, or by adding the aqueous emulsion to either the silanol precursor or the cationic surfactant B, then adding the remaining one, and then adding the alkaline substance. When the alkaline substance and the cationic surfactant B are added to the aqueous emulsion containing the silanol precursor, the alkaline substance and the cationic surfactant B may be mixed and then the mixture may be added. In this case, the aqueous emulsion containing the silanol precursor may contain the cationic surfactant B.
[0023] Step B may include, after the formation of the hollow silica particle precursor and before step C, a step of isolating the hollow silica particle precursor and a step of drying the hollow silica particle precursor. The hollow silica particles can be isolated, for example, by filtration. In addition, the hollow silica particle precursor can be dried, for example, by heating to a temperature of 100°C or higher and lower than the boiling point of the hydrophobic liquid, if the boiling point of the hydrophobic liquid contained in the hollow silica particle precursor is higher than 100°C. If the boiling point of the hydrophobic liquid contained in the hollow silica particle precursor is 100°C or lower, the hollow silica particle precursor can be dried, for example, by freeze-drying or the like.
[0024] (Silanol precursor) The silanol precursor is a compound that generates a silanol compound by hydrolysis of alkoxysilane, etc., and is preferably selected from orthosilicate alkyl esters and pyrosilicate alkyl esters. Specific examples include compounds represented by the following general formulas (3) to (7), or combinations thereof. SiY4(3) R 3 SiY3(4) R 3 2SiY2(5) R 3 3SiY (6) Y3Si-O-SiY3(7)
[0025] In general formulas (3) to (7), R 3 each independently represents an organic group in which a carbon atom is directly bonded to a silicon atom, and Y represents a monovalent hydrolyzable group that becomes a hydroxyl group upon hydrolysis.
[0026] In general formulas (4) to (6), R 3 are each independently preferably a hydrocarbon group having 1 to 22 carbon atoms in which some of the hydrogen atoms may be substituted with fluorine atoms, and from the viewpoint of improving the utilization efficiency of the hydrophobic organic substance, are preferably an alkyl group, a phenyl group, or a benzyl group having 1 to 22 carbon atoms, more preferably 4 to 18 carbon atoms, and even more preferably 8 to 16 carbon atoms. In the general formulas (3) to (7), Y is preferably an alkoxy group having 1 to 8 carbon atoms or a halogen group other than fluorine, and more preferably an alkoxy group having 2 to 4 carbon atoms. When Y is an alkoxy group having 1 carbon atom or a halogen group other than fluorine, the hydrolysis reaction rate is too fast, so that the outer shell of the hollow silica precursor is difficult to become dense, and shrinkage during firing increases, so that the relative dielectric constant and dielectric loss tangent of the hollow silica particles having an organic group on the surface tend to be high. Conversely, an alkoxy group having 5 or more carbon atoms slows down the hydrolysis rate.
[0027] The silanol precursor is preferably selected from compounds represented by general formula (3) and general formula (7). From the viewpoint of suppressing the generation of metal-corrosive acid and from the viewpoint of hydrolysis reactivity, the silanol precursor is preferably selected from compounds represented by general formula (3) and general formula (7) in which Y is an alkoxy group having 2 to 4 carbon atoms, and more preferably selected from compounds represented by general formula (3) and general formula (7) in which Y is an ethoxy group. The silanol precursor may be used alone or in combination of two or more kinds.
[0028] The mass ratio of the silanol precursor to the hydrophobic liquid [silanol precursor / hydrophobic liquid] is preferably 10 or more, more preferably 20 or more, even more preferably 25 or more, from the viewpoint of keeping the porosity of the hollow silica particles having organic groups on the surface in an appropriate range, and is preferably 90 or less, more preferably 80 or less, even more preferably 75 or less.
[0029] (Cationic Surfactant B) As the cationic surfactant B, the same cationic surfactant B as the cationic surfactant A shown in step A can be used. As the cationic surfactant B, from the viewpoint of facilitating the formation of a complex with the condensed silanol and facilitating decomposition and volatilization in step C, a quaternary ammonium salt is preferable, more preferably lauryl trimethyl ammonium chloride (dodecyl trimethyl ammonium chloride), stearyl trimethyl ammonium chloride, and behenyl trimethyl ammonium chloride, and further preferably lauryl trimethyl ammonium chloride. The cationic surfactant B used in this step may be the same as or different from the cationic surfactant A used in step A. In addition, the cationic surfactant B may be used alone or in combination of two or more kinds.
[0030] The mass ratio of the silanol precursor to the cationic surfactant B [silanol precursor / cationic surfactant B] is, from the viewpoint of dispersibility of the hollow silica particle precursor, preferably 3 or more, more preferably 5 or more, even more preferably 6 or more, and is preferably 25 or less, more preferably 20 or less, even more preferably 18 or less.
[0031] (Alkaline substances) The silanol precursor is hydrolyzed by an alkaline substance to form silanol, which is then dehydrated and condensed to form silica. Specific examples of the alkaline substance include those described in paragraph
[0014] of JP 2016-121060 A. Among these, hydroxide salts of quaternary ammonium are preferred. Specific examples of hydroxide salts of quaternary ammonium include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tributylmethylammonium hydroxide, trimethylhydroxyethylammonium hydroxide (choline), tetraethanolammonium hydroxide, methyltriethanolammonium hydroxide, and dimethylbis(2-hydroxyethyl)ammonium hydroxide. From the viewpoint of making the outer shell of the hollow silica particle precursor dense, preferred are tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylhydroxyethylammonium hydroxide, and methyltriethanolammonium hydroxide, and dimethylbis(2-hydroxyethyl)ammonium hydroxide, and more preferred are tetramethylammonium hydroxide and dimethylbis(2-hydroxyethyl)ammonium hydroxide.
[0032] The mass ratio of the silanol precursor to the alkaline substance [silanol precursor / alkaline substance] is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more, from the viewpoint of densely forming the outer shell of the hollow silica particle precursor, and is preferably 100 or less, more preferably 80 or less, and even more preferably 70 or less, from the viewpoint of efficiently carrying out the condensation reaction of the silanol precursor.
[0033] The alkaline substance may contain, for example, an alkali metal salt, an alkaline earth metal salt, etc., in addition to the hydroxide salt of the quaternary ammonium, but in order to reduce the content of the alkali metal and alkaline earth metal in the obtained hollow silica particles, the total content of the alkali metal and alkaline earth metal relative to the silanol precursor is 50 mass ppm or less in terms of silica (SiO2).Moreover, the content is preferably 30 mass ppm or less, more preferably 10 mass ppm or less.
[0034] By mixing the alkaline substance with the cationic surfactant B and contacting it with the silanol precursor, hollow silica particles having a small maximum particle size and a moderate coefficient of variation can be obtained. The contact between the mixture of the alkaline substance and the cationic surfactant B and the silanol precursor may be performed by adding the mixture of the alkaline substance and the cationic surfactant B to a reaction system containing the silanol precursor, or by adding the silanol precursor to a reaction system containing the mixture of the alkaline substance and the cationic surfactant B. However, from the viewpoint of increasing the porosity and increasing the synthesis concentration to increase productivity, it is preferable to add the mixture of the alkaline substance and the cationic surfactant B to a reaction system containing the silanol precursor.
[0035] The temperature at which step B is carried out can be appropriately adjusted depending on the type and amount of the silanol precursor and alkaline substance used, and is preferably 0° C. or higher and 100° C. or lower from the viewpoint of making the outer shell of the hollow silica particle precursor dense. For example, when orthosilicate ethyl ester or pyrosilicate ethyl ester is used as the silanol precursor, the temperature is preferably 20° C. or higher and 45° C. or lower, and when orthosilicate methyl ester or pyrosilicate methyl ester is used, the temperature is preferably 0° C. or higher and 20° C. or lower. Among these, step B is preferably carried out using orthosilicate ethyl ester or pyrosilicate ethyl ester at 20° C. or higher and 45° C. or lower from the viewpoint of reaction control.
[0036] The time for carrying out step B is preferably 30 minutes or more, more preferably 1 hour or more, and even more preferably 2 hours or more, from the viewpoint of densifying the outer shell of the hollow silica particle precursor, and is preferably 24 hours or less, more preferably 20 hours or less, and even more preferably 16 hours or less, from the viewpoint of production efficiency.
[0037] (Hollow silica particle precursor) The hollow silica particle precursor is a composite silica particle having a shell containing silica and a hydrophobic liquid inside the shell, in which pores are formed radially toward the center of the particle using a cationic surfactant as a template.
[0038] [Process C] In step C, the hollow silica particle precursor obtained in step B is heat-treated at a temperature of more than 1000°C and not exceeding 1200°C for one hour or more to decompose and volatilize the cationic surfactant present in the outer shell of the hollow silica particle precursor and volatilize the hydrophobic liquid inside, and then the pores present in the outer shell are closed by firing to obtain hollow silica particles having a uniform outer shell.
[0039] The heat treatment temperature in step C is preferably 1010° C. or higher, more preferably 1030° C. or higher, and even more preferably 1050° C. or higher, from the viewpoint of reducing silanol groups on the surface of the hollow silica particles, and is 1200° C. or lower, preferably 1190° C. or lower, more preferably 1180° C. or lower, and even more preferably 1160° C. or lower, from the viewpoint of avoiding aggregation of the hollow silica particles.
[0040] The heat treatment time in step C is preferably 15 minutes or more, more preferably 30 minutes or more, and even more preferably 45 minutes or more, from the viewpoint of reducing silanol groups on the surface of the hollow silica particles, and is preferably 3 hours or less, more preferably 2 hours or less, and even more preferably 1.5 hours or less, from the viewpoint of avoiding aggregation of the hollow silica particles.
[0041] [Process D] In step D, the surfaces of the hollow silica particles obtained in step C are surface-treated with a silane coupling agent to obtain hollow silica particles having organic groups on the surface. In step D, the silanol groups present on the surfaces of the hollow silica particles react with the silane coupling agent, making the surfaces of the hollow silica particles hydrophobic, thereby obtaining hollow silica particles having organic groups on the surface that are easily dispersed in a resin monomer. When the resin is an epoxy resin, the dispersion effect of the hollow silica particles having organic groups on the surface in the resin composition precursor becomes more remarkable.
[0042] (Silane coupling agent) Examples of the silane coupling agent used in the surface treatment include aminosilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, organosilazane compounds, and organohalogenated silanes. Specific examples include aminosilane coupling agents such as aminopropyltrimethoxysilane, aminopropyltriethoxysilane, ureidopropyltriethoxysilane, N-phenylaminopropyltrimethoxysilane, and N-2(aminoethyl)aminopropyltrimethoxysilane; epoxysilane coupling agents such as glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane, glycidoxypropyldiethoxysilane, glycidylbutyltrimethoxysilane, and (3,4-epoxycyclohexyl)ethyltrimethoxysilane; mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, and mercaptopropyltriethoxysilane; silane and other mercaptosilane coupling agents; methyltrimethoxysilane, vinyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, metachloroxypropyltrimethoxysilane, imidazole silanes such as triethoxy-3-(2-imidazolin-1-yl)propylsilane; triazinethiol silane coupling agents such as 6-triethoxysilylpropylamino-1,3,5-triazine-2,4-dithiol monosodium salt; organosilazane compounds such as hexamethyldisilazane; and organohalogenated silanes such as methyltrichlorosilane and phenyltrichlorosilane. Among these, 3-glycidoxypropyltrimethoxysilane and N-phenylaminopropyltrimethoxysilane are preferred from the viewpoint of improving the handleability of the resin composition precursor containing hollow silica particles having an organic group on the surface. These silane coupling agents may be used alone or in combination of two or more.
[0043] The conditions for the surface treatment are not particularly limited, and examples thereof include a wet method in which hollow silica particles are dispersed in a solvent and then a silane coupling agent is added to cause a reaction, and a dry method in which a silane coupling agent is sprayed onto hollow silica particles. In the wet treatment method, the hollow silica particles after the surface treatment are filtered using filter paper or the like and dried to obtain uniform surface-treated hollow silica particles. The amount of the silane coupling agent to be used is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, based on 100 parts by mass of the hollow silica particles. When the wet treatment method is used as the surface treatment condition, an alkaline substance may be used to improve the reactivity between the silane coupling agent and the hollow silica. Preferred examples of the alkaline substance include the alkaline substances listed in step B and aqueous ammonia.
[0044] [Hollow silica particles with organic groups on the surface] The hollow silica particles of the present invention are hollow silica particles having a total content of alkali metal and alkaline earth metal of 50 ppm by mass or less relative to the content of silica in the particles, a relative dielectric constant of 2.5 or less and a dielectric dissipation factor of 0.0050 or less at a measurement frequency of 10 GHz, and having organic groups on the surfaces.
[0045] The average particle size of the hollow silica particles having an organic group on the surface is preferably 0.5 μm or more, more preferably 0.7 μm or more, and even more preferably 0.9 μm or more, from the viewpoint of suppressing an increase in viscosity when mixed with a resin monomer and maintaining processability, and is preferably 3.0 μm or less, more preferably 2.5 μm or less, and even more preferably 2.0 μm or less, from the viewpoint of improving the appearance of the resin composition. In addition, from the viewpoint of blending a large number of hollow silica particles having organic groups on their surfaces into a resin composition and reducing the relative dielectric constant and dielectric tangent of the resin composition, the coefficient of variation of the average particle size of the hollow silica particles having organic groups on their surfaces is preferably 15% or more, more preferably 20% or more, even more preferably 25% or more, and is preferably 300% or less, more preferably 200% or less, even more preferably 100% or less, even more preferably 75% or less, even more preferably 50% or less. From the viewpoint of improving the appearance of the resin composition, the maximum particle size of the hollow silica particles having an organic group on the surface is preferably 1.5 μm or more, more preferably 1.8 μm or more, even more preferably 2.0 μm or more, and is preferably 5.0 μm or less, more preferably 4.7 μm or less, even more preferably 4.5 μm or less. The average particle size and maximum particle size of the hollow silica particles having an organic group on the surface can be determined by the method described in the Examples. In the present invention, the average particle size and maximum particle size of the hollow silica particles having an organic group on the surface are based on volume.
[0046] The total content of alkali metals and alkaline earth metals relative to the content of silica in the hollow silica particles having organic groups on their surfaces is 50 ppm by mass or less, preferably 30 ppm by mass or less, more preferably 20 ppm by mass or less, and even more preferably 15 ppm by mass or less, from the viewpoint of suitable use in insulating materials, and is preferably 1 ppb by mass or more, more preferably 5 ppb by mass or more, from the viewpoint of productivity of the hollow silica particles having organic groups on their surfaces. The alkali metal content and alkaline earth metal content in the hollow silica particles having an organic group on the surface can be measured by the method described in US EPA METHOD 3051 A. The lithium, rubidium, and cesium contents in the hollow silica particles having an organic group on the surface can also be measured by the method described in US EPA METHOD 3051 A.
[0047] The dielectric constant of the hollow silica particles having an organic group on the surface is 2.5 or less at a measurement frequency of 10 GHz, so that the dielectric constant of the resin composition containing the hollow silica particles having an organic group on the surface can be sufficiently low. The dielectric constant at a measurement frequency of 10 GHz is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more from the viewpoint of the strength of the hollow silica having an organic group on the surface, and is preferably 2.2 or less, more preferably 2.0 or less, and even more preferably 1.8 or less from the viewpoint of sufficiently lowing the dielectric constant of the resin composition. The relative dielectric constant of the hollow silica particles having an organic group on the surface thereof can be determined by the method described in the Examples.
[0048] The dielectric loss tangent of the hollow silica particles having an organic group on the surface is 0.0050 or less at a measurement frequency of 10 GHz, so that the dielectric loss tangent of the resin composition containing the hollow silica particles having an organic group on the surface can be sufficiently low. From the viewpoint of the strength of the hollow silica having an organic group on the surface, the dielectric loss tangent at a measurement frequency of 10 GHz is preferably 0.0001 or more, more preferably 0.0005 or more, and even more preferably 0.0010 or more, and from the viewpoint of sufficiently lowing the dielectric loss tangent of the resin composition, it is preferably 0.0048 or less, more preferably 0.0046 or less, and even more preferably 0.0044 or less. The dielectric loss tangent of the hollow silica particles having an organic group on the surface thereof can be determined by the method described in the Examples.
[0049] The porosity of the hollow silica particles having organic groups on their surfaces is preferably 50 vol% or more, more preferably 55 vol% or more, and even more preferably 60 vol% or more from the viewpoint of reducing the relative dielectric constant of the hollow silica particles having organic groups on their surfaces, and is preferably 80 vol% or less, more preferably 77 vol% or less, and even more preferably 74 vol% or less from the viewpoint of providing the hollow silica particles having organic groups on their surfaces with sufficient strength. The porosity of the hollow silica particles having an organic group on the surface thereof can be determined by the method described in the Examples.
[0050] The BET specific surface area of the hollow silica particles having an organic group on the surface is preferably 5 m from the viewpoint of increasing the porosity of the hollow silica and decreasing the relative dielectric constant. 2 / g or more, 7m 2 / g or more, 8.5m 2 / g or more, and from the viewpoint of lowering the dielectric tangent of the hollow silica particles having an organic group on the surface, and from the viewpoint of reducing the amount of a surface treatment agent used when blended with a resin and lowering the dielectric tangent of the resin composition, it is preferably 30 m 2 / g or less, more preferably 25m 2 / g or less, more preferably 20m 2 / g or less. The BET specific surface area of the hollow silica particles having an organic group on the surface thereof can be determined by the method described in the Examples.
[0051] [Resin composition] The hollow silica particles having an organic group on the surface thereof according to the present invention can be mixed with a resin monomer to form a resin composition precursor, and the resin composition precursor can be cured to form a resin composition. The resin contained in the resin composition is not particularly limited, but in order to provide the resin composition with low dielectric properties, it is preferable to use resins having low relative dielectric constants and dielectric loss tangents, such as polyparaphenylene resins, liquid crystal polymer resins, epoxy resins using a curing agent selected from ester- or ether-based curing agents, acid anhydride-based curing agents, and imidazole-based curing agents, bismaleimide resins, cycloolefin resins, and fluorine-based resins, or derivatives of these resins.
[0052] The resin monomer may be a low molecular weight compound that becomes the above-mentioned resin through a polymerization reaction, a condensation reaction, etc. When the hollow silica and the resin monomer are mixed to produce a resin composition precursor, one or more types of low molecular weight compounds may be used as the resin monomer.
[0053] The amount of hollow silica particles having an organic group on the surface in the resin composition is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, from the viewpoint of reducing the relative dielectric constant and dielectric tangent of the resin composition, and is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, from the viewpoint of suppressing an increase in viscosity of the resin composition precursor and improving processability.
[0054] From the viewpoint of being suitably used as an insulating material for high-frequency circuit boards, the resin composition of the present invention has a relative dielectric constant at a measurement frequency of 10 GHz of preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and preferably 2.8 or less, more preferably 2.5 or less. The relative dielectric constant of the resin composition can be determined by inserting a resin composition precursor into a Teflon tube, curing the resin composition, and then using a method similar to the method for measuring the relative dielectric constant of hollow silica particles having organic groups on the surface described in the examples. From the viewpoint of being suitably used as an insulating material for high-frequency circuit boards, the resin composition of the present invention has a dielectric loss tangent at a measurement frequency of 10 GHz of preferably 0.0001 or more, more preferably 0.0005 or more, even more preferably 0.0010 or more, and preferably 0.029 or less, more preferably 0.028 or less, even more preferably 0.027 or less. The dielectric loss tangent of the resin composition can be determined by inserting a resin composition precursor into a Teflon tube, curing the resin composition, and then measuring the dielectric loss tangent in the same manner as in the measurement method for the dielectric loss tangent of hollow silica particles having organic groups on the surface described in the examples.
[0055] [Insulating material] By including the resin composition of the present invention in an insulating material, it is possible to provide an insulating material capable of reducing transmission loss and transmission delay. The insulating material can be used, for example, in build-up insulating films, insulating layers of copper-clad laminates, prepregs, sealing materials, insulating members of connectors, and coating materials for electric wires. EXAMPLES
[0056] In the examples and comparative examples described later, various measurements of the hollow silica particles having an organic group on the surface, the resin composition precursor, and the resin composition were carried out by the following methods.
[0057] [Measurement method] (Measurement of the average particle size of hollow silica particles having organic groups on the surface) The average particle size of the hollow silica particles having organic groups on the surface was measured by the Coulter counter method using a Multisizer 3 (manufactured by Beckman Coulter, Inc., using a 20 μm aperture tube). The average particle size and standard deviation of the particle size were determined on a volume basis, and the coefficient of variation was calculated using the following formula. (Coefficient of variation) (%) = (Standard deviation of particle size) / (Average particle size) x 100 The maximum particle size was defined as the particle size at 99% of the cumulative frequency distribution on a volume basis.
[0058] (Measurement of the content of alkali metals and alkaline earth metals in hollow silica particles having organic groups on the surface) 100 mg of hollow silica particles having organic groups on their surface were placed in a platinum crucible, to which 3 mL of concentrated nitric acid, 1 mL of concentrated hydrofluoric acid, and 1 mL of concentrated hydrochloric acid were added, and the mixture was heated to evaporate to dryness. The residue in the crucible was then diluted with hydrochloric acid and measured using an inductively coupled plasma mass spectrometer (Agilent Technologies, Inc., product name: Agilent 8900).
[0059] (Measurement of the dielectric constant and dielectric loss tangent of hollow silica particles having organic groups on the surface) The dielectric constant and dielectric loss tangent of the hollow silica particles having organic groups on their surfaces were measured at a temperature of 25°C and a measurement frequency of 10 GHz using a network analyzer (Agilent Technologies, product name: N5221A) connected to a perturbation method cavity resonator (CP-580) manufactured by Kanto Electronics Application Development Co., Ltd., using the cavity resonator perturbation method (CP-MA dielectric constant measurement software, manufactured by Kanto Electronics Application Development Co., Ltd.). A measurement sample was prepared by filling a Teflon tube (manufactured by Chukoh Chemical Industry Co., Ltd.: PTFE tube, inner diameter 1.5 mm, outer diameter 2.5 mm) with hollow silica particles having organic groups on their surfaces so that all were within the measurement range (6.75 mm to 36.35 mm from the bottom). The weight of the hollow silica particles having organic groups on their surfaces was calculated by measuring the weight before and after filling, and the volume of the hollow silica particles having organic groups on their surfaces filled in the Teflon tube was calculated from the filling weight and specific gravity of the hollow silica particles having organic groups on their surfaces. The relative dielectric constant and the dielectric loss tangent were calculated from the difference between the measured values of an empty Teflon tube not filled with hollow silica particles having organic groups on its surface and the measured values of a Teflon tube filled with hollow silica particles having organic groups on its surface, which was used as the blank.
[0060] (Measurement of BET specific surface area of hollow silica particles having organic groups on the surface) The BET specific surface area of the hollow silica particles having organic groups on the surface was measured using a specific surface area measuring device (Shimadzu Corporation, product name "Flowsorb III2305") The sample was pretreated by heating at 200°C for 15 minutes.
[0061] (Measurement of porosity of hollow silica particles having organic groups on the surface) The true density of the silica particles was calculated according to the following formula using the density measured with a density measuring device (ULTRAPYCNMETER1200e manufactured by Quantachrome) and nitrogen as the measurement gas. 3 It was decided. Porosity (%) = [1 - (true density of hollow silica particles having organic groups on their surface / true density of silica particles)] x 100
[0062] (Measuring the average particle size of droplets containing hydrophobic liquid in emulsions) Approximately 1 mL of emulsion A was placed in a square cell with an optical path length of 10 mm, and the volume average particle diameter was calculated by measuring the particle diameter of droplets containing the hydrophobic liquid using a light scattering device "Zetasizer Nano ZS" (Malvern Panalytical).
[0063] Example 1 [Production of hollow silica particles having organic groups on the surface] 342.2 g of ion-exchanged water, 150 g of dodecane (Kishida Chemical Co., Ltd.: primary n-dodecane), and 7.8 g of Coatamin 2285E (Kao Corporation: containing 58% by mass of behenyl trimethyl ammonium chloride) were mixed and stirred to obtain emulsion A containing dodecane as a hydrophobic liquid. The volume average particle size of the particles in the obtained emulsion A was 0.5 μm. In a reaction vessel, 13146.5 g of ion-exchanged water, 184.1 g of emulsion A, 125.6 g of Kotamin 24P (manufactured by Kao Corporation: containing 27.5% by mass of lauryl trimethyl ammonium chloride), and 3120.8 g of orthosilicate ethyl ester (manufactured by Asahi Kasei Wacker Silicone Corporation: TEOS999) were added and heated to 40°C while stirring, and then stirred for 10 minutes to obtain preparation B. Next, 221.5 g of AH212-CS (manufactured by Yokkaichi Synthetic Co., Ltd.: containing 50% by mass of dimethyl bis(2-hydroxyethyl) ammonium hydroxide) and 711.6 g of Kotamin 24P were uniformly mixed to obtain preparation C. Preparation C was added to preparation B at a constant rate, and then stirred at 40°C for 3 hours to obtain a cloudy white liquid D. Next, the obtained cloudy liquid D was filtered using filter paper No. 5C (manufactured by Advantec Toyo Kaisha, Ltd.), washed with water, and then dried at 110° C. to obtain white hollow silica particle precursors. The obtained hollow silica particle precursor was calcined at 1100° C. for 1 hour to obtain hollow silica particles. In a 500 mL glass beaker, 26.7 g of ion-exchanged water, 240.0 g of ethanol, 2.1 g of 25% ammonia water (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 30.0 g of the obtained hollow silica particles, and 1.2 g of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.: KBM-403) were added and stirred at room temperature for 12 hours. Thereafter, the surface-treated hollow silica particles were filtered and dried at 130°C for 3 hours to obtain hollow silica particles 1 having organic groups on the surface. The physical properties of the obtained hollow silica particles 1 having organic groups on the surface are shown in Table 1.
[0064] [Production of Resin Composition Precursor] 23.7 g of epoxy resin monomer (Mitsubishi Chemical Corporation: jER (trademark) 828), 28.8 g of acid anhydride curing agent (Mitsubishi Chemical Corporation: YH-306), and 0.3 g of imidazole curing agent (Mitsubishi Chemical Corporation: EMI24) were kneaded using a kneader (Thinky Corporation: Planetary Vacuum Mixer) at atmospheric pressure for 1 minute at 1400 rpm and at reduced pressure of 0.3 kPa for 5 minutes at 2000 rpm to obtain an epoxy resin monomer mixed liquid. The obtained epoxy resin monomer mixture (2 g) and hollow silica particles 1 (0.5 g) having organic groups on their surfaces were kneaded in a kneader (Thinky Corporation: Planetary Vacuum Mixer) at atmospheric pressure at 1,400 rpm for 1 minute and at a reduced pressure of 0.3 kPa at 2,000 rpm for 5 minutes to obtain a resin composition precursor 1.
[0065] (Measurement of Shear Viscosity of Resin Composition Precursor) Resin composition precursor 1 was allowed to stand for 1 hour in a thermostatic chamber set at 25° C., and then the shear viscosity of resin composition precursor 1 was evaluated at 25° C. using a B-type viscometer (TVB-10M manufactured by Toki Sangyo Co., Ltd.) and an M4 rotor at a rotation speed of 10 rpm. The results are shown in Table 1.
[0066] [Production of resin composition] The obtained resin composition precursor 1 was poured into a Teflon tube (manufactured by AS ONE Corporation, inner diameter 2.5 mm, outer diameter 4.0 mm), heated in a dryer at 80°C for 3 hours, and then heated at 160°C for 6 hours to obtain a resin composition 1. The relative dielectric constant and dielectric loss tangent of the resin composition 1 were measured in the same manner as for the hollow silica particles having an organic group. The results are shown in Table 1.
[0067] Example 2 Hollow silica particles 2 having an organic group on the surface were obtained in the same manner as in Example 1, except that 3-glycidoxypropyltrimethoxysilane was changed to N-phenylaminopropyltrimethoxysilane (KBM-573 manufactured by Shin-Etsu Chemical Co., Ltd.). The physical properties of the obtained hollow silica particles 2 having an organic group on the surface are shown in Table 1. Resin composition precursor 2 was produced in the same manner as in Example 1, except that hollow silica particles 2 having organic groups on their surfaces were used instead of hollow silica particles 1 having organic groups on their surfaces, and the shear viscosity of resin composition precursor 2 was evaluated in the same manner as in Example 1. Furthermore, resin composition 2 was produced using resin composition precursor 2 in the same manner as in Example 1, and the relative dielectric constant and dielectric loss tangent were measured. The results are shown in Table 1.
[0068] Example 3 388.6 g of ion-exchanged water, 200 g of dodecane (Kishida Chemical Co., Ltd.: primary n-dodecane), and 11.4 g of Coatamin 86W (Kao Corporation: containing 28% by mass of stearyl trimethyl ammonium chloride) were mixed and stirred to obtain emulsion A. The volume average particle size of the particles in the obtained emulsion A was 0.9 μm. The subsequent operations were carried out in the same manner as in Example 1, except that the amount of ion-exchanged water was changed to 13,192.5 g and the amount of emulsion A was changed to 138.1 g, to obtain hollow silica particles 3 having organic groups on their surfaces. The physical properties of the obtained hollow silica particles 3 having organic groups on their surfaces are shown in Table 1. A resin composition precursor 3 and a resin composition 3 were produced in the same manner as in Example 1, except that hollow silica particles 1 having an organic group on the surface were changed to hollow silica particles 3 having an organic group on the surface, and the shear viscosity of the resin composition precursor 3 and the relative dielectric constant and dielectric loss tangent of the resin composition 3 were evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0069] Example 4 Hollow silica particles 4 having organic groups on their surfaces were obtained by the same procedure except that 3-glycidoxypropyltrimethoxysilane was replaced with N-phenylaminopropyltrimethoxysilane (KBM-573, manufactured by Shin-Etsu Chemical Co., Ltd.). The physical properties of the obtained hollow silica particles 4 having organic groups on their surfaces are shown in Table 1. Resin composition precursor 4 and resin composition 4 were produced in the same manner as in Example 1, except that hollow silica particles 1 having an organic group on the surface were changed to hollow silica particles 4 having an organic group on the surface, and the shear viscosity of resin composition precursor 4 and the relative dielectric constant and dielectric loss tangent of resin composition 4 were evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0070] Comparative Example 1 Hollow silica particles 11 were obtained in the same manner as in Example 1, except that the surface treatment was not performed. The physical properties of the obtained hollow silica particles 11 are shown in Table 1. A resin composition precursor 11 was produced in the same manner as in Example 1, except that hollow silica particles 1 having an organic group on the surface were replaced with hollow silica particles 11 having an organic group on the surface, and the shear viscosity of the resin composition precursor 11 was evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0071] Comparative Example 2 Hollow silica particles 12 were obtained in the same manner as in Example 3, except that the surface treatment was not performed. The physical properties of the obtained hollow silica particles 12 are shown in Table 1. A resin composition precursor 12 was produced in the same manner as in Example 1, except that hollow silica particles 1 having an organic group on the surface were replaced with hollow silica particles 12 having an organic group on the surface, and the shear viscosity of the resin composition precursor 12 was evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0072] Comparative Example 3 Resin composition precursor 13 and resin composition 13 were produced in the same manner as in Example 1, except that hollow silica particles were not blended, and the shear viscosity of resin composition precursor 13 and the relative dielectric constant and dielectric loss tangent of resin composition 13 were evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0073] [Table 1]
[0074] As shown in the results in Table 1, the hollow silica particles 1 to 4 having an organic group on the surface produced by the production method of the present invention were able to reduce the relative dielectric constant and dielectric loss tangent at a measurement frequency of 10 GHz even when the average particle size was reduced and the total content of alkali metals and alkaline earth metals relative to the content of silica in the hollow silica particles was reduced. The resin composition precursors 1 to 4 in which the hollow silica particles 1 to 4 having an organic group were blended with a resin monomer had a low viscosity comparable to that of the resin composition precursor 13 of Comparative Example 3 not containing hollow silica particles, and were excellent in handleability. Therefore, the resin compositions 1 to 4 obtained by curing the resin composition precursors 1 to 4 were resin compositions having a low relative dielectric constant and dielectric loss tangent compared to the resin composition 13 of Comparative Example 3 not containing hollow silica particles. On the other hand, the hollow silica particles 11 and 12 having no organic groups on the surface produced in Comparative Examples 1 and 2 were able to reduce the relative dielectric constant and dielectric tangent at a measurement frequency of 10 GHz, but were unable to suppress the increase in viscosity of the resin composition precursors 11 and 12 mixed with the resin monomer.
Claims
1. A method for producing hollow silica particles having organic groups on their surface, comprising the following steps. Step A: A step to prepare an aqueous emulsion of a hydrophobic liquid using cationic surfactant A. Step B: A step to generate hollow silica particle precursors by adding a silanol precursor, an alkaline substance, and cationic surfactant B to the aqueous emulsion obtained in Step A. Step C: A process in which the hollow silica particle precursor obtained in Step B is heat-treated at a temperature exceeding 1000°C but not exceeding 1200°C for at least one hour. Step D: A step in which the surface of the hollow silica particles obtained in Step C is surface-treated with a silane coupling agent.
2. A method for producing hollow silica particles according to claim 1, wherein the addition in step B is carried out by adding a silanol precursor to the aqueous emulsion obtained in step A, and then adding an alkaline substance and a cationic surfactant B.
3. The method for producing hollow silica particles according to claim 2, wherein the addition in step B is carried out by contacting an aqueous emulsion containing a silanol precursor with a mixture of an alkaline substance and a cationic surfactant B.
4. A method for producing hollow silica particles according to claim 1, wherein the addition in step B is performed by adding a silanol precursor and cationic surfactant B to the aqueous emulsion obtained in step A, and then adding an alkaline substance.
5. A method for producing hollow silica particles according to claim 1 or 2, wherein the alkaline substance is a quaternary ammonium hydroxide salt.
6. A method for producing hollow silica particles according to claim 1 or 2, wherein both cationic surfactant A and cationic surfactant B are salts of quaternary ammonium.
7. A method for producing hollow silica particles according to claim 1 or 2, wherein the silanol precursor is selected from alkyl orthosilicate and alkyl pyrosilicate.
8. A method for producing hollow silica particles according to claim 1 or 2, wherein the silane coupling agent is selected from 3-glycidoxypropyltrimethoxysilane and N-phenylaminopropyltrimethoxysilane.
9. Hollow silica particles having organic groups on their surface, wherein the total content of alkali metals and alkaline earth metals relative to the silica content in the particles is 50 ppm by mass or less, the relative permittivity is 2.5 or less, and the dielectric loss tangent is 0.0050 or less at a measurement frequency of 10 GHz.
10. Hollow silica particles according to claim 9, wherein the porosity is 50 volume% or more and 80 volume% or less.
11. BET specific surface area is 30 m² ２ Hollow silica particles according to claim 9 or 10, wherein the amount is less than or equal to / g.
12. Hollow silica particles according to claim 9 or 10, wherein the coefficient of variation of the average particle diameter is 15% or more and 300% or less.
13. Hollow silica particles according to claim 9 or 10, wherein the maximum particle diameter is 5.0 μm or less.
14. A resin composition comprising hollow silica particles as described in claim 9 or 10.
15. The resin composition according to claim 14, wherein the relative permittivity at a measurement frequency of 10 GHz is 2.8 or less, and the dielectric loss tangent is 0.029 or less.