Hollow silica particle

Abstract

To provide a hollow silica particle capable of preventing the viscosity of a resin composition precursor from increasing upon preparing a resin composition and improving the surface smoothness of the resin composition, and a resin composition and an insulation material using the same.SOLUTION: There are provided, [1] hollow silica particles having a mean particle diameter measured by a Coulter counter method, of 0.1 μm or more and 3.0 μm or less, in which the number ratio of particles having a particle diameter of more than 4.0 μm measured by the Coulter counter method, relative to the whole hollow silica particles is 20000 ppm or less, [2] a resin composition containing the hollow silica particles as described in [1], and [3] an insulation material including the resin composition as described in [2].SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to hollow silica particles, a resin composition, and an insulating material. [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 excellent dielectric properties such as low dielectric constant and low dielectric tangent are required to reduce transmission loss and transmission delay, and similar performance is required for silica particles that are blended as a filler in the insulating material to improve the dielectric properties. In response to these requirements, the use of hollow silica particles has been considered to improve the dielectric properties of silica particles. In addition, miniaturization of high-frequency circuits is desired, and the silica particles are also required to have a smaller particle size.

[0003] Patent Document 1 describes silica-based hollow particles having a cavity inside a non-porous outer shell and an average particle size (D50) of 0.1 to 10 μm, which are characterized in that when suspended in water, the floating particles comprise 0.5 to 7.0 mass%, the suspended particles comprise 0 to 4.0 mass%, and the settling particles comprise 89.0 to 99.5 mass%. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-103683 A Summary of the Invention [Problem to be solved by the invention]

[0005] When hollow silica particles are used as a filler for insulating materials in high-frequency circuits, etc., the average particle size is required to be 3.0 μm or less in order to accommodate miniaturization and thinning of the material. In addition, the hollow silica particles are required to have a high porosity in order to improve the dielectric properties of the insulating material. However, since the silica-based hollow particles of Patent Document 1 have an average particle diameter (D50) of 0.1 to 10 μm, when used as a filler in a resin composition used in an insulating material for high-frequency circuits, etc., there is a problem that the viscosity of the resin composition precursor increases during preparation of the resin composition, resulting in reduced processability. In addition, since the silica-based hollow particles contain a large number of particles (coarse particles) with a large particle diameter, voids (defects caused by particles) are generated in the resulting resin composition, which impairs the surface smoothness of the resin composition. The present invention relates to hollow silica particles that can suppress an increase in the viscosity of a resin composition precursor during preparation of the resin composition and improve the surface smoothness of the resin composition, and to a resin composition and an insulating material using the same. [Means for solving the problem]

[0006] The present inventors have found that the above problem can be solved by using hollow silica particles having an average particle size within a specific range as measured by a Coulter counter method and a low percentage of particles larger than the specific particle size. The present invention relates to the following [1] to [3]. [1] Hollow silica particles having an average particle diameter of 0.1 μm or more and 3.0 μm or less, as measured by the Coulter counter method, and the number ratio of particles having a particle diameter of more than 4.0 μm, as measured by the Coulter counter method, to the total number of hollow silica particles is 20,000 ppm or less. [2] A resin composition containing the hollow silica particles described in [1] above. [3] An insulating material comprising the resin composition described in [2] above. Effect of the Invention

[0007] According to the present invention, it is possible to provide hollow silica particles that can suppress an increase in the viscosity of a resin composition precursor during preparation of a resin composition and further improve the surface smoothness of the obtained resin composition, as well as a resin composition and an insulating material using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Hollow silica particles] The hollow silica particles of the present invention have an average particle diameter of 0.1 μm or more and 3.0 μm or less as measured by the Coulter counter method, and the proportion of particles having a particle diameter of more than 4.0 μm as measured by the Coulter counter method to the total number of hollow silica particles is 20,000 ppm or less. When the hollow silica particles of the present invention are used as a filler in a resin composition constituting an insulating material, they can suppress an increase in viscosity of the resin composition precursor during its preparation and further improve the surface smoothness of the resulting resin composition.

[0009] Usually, the particle size of silica particles used as filler of resin composition is measured by laser diffraction particle size distribution measurement.However, in the case of hollow silica particles having a hollow structure, it cannot be said that it represents the actual situation because it causes multiple scattering of laser light in the hollow part, and when hollow silica particles having a suitable particle size range in this measurement are mixed into a resin composition, the surface smoothness may be inferior to that estimated from the particle size.In other words, it is suggested that particles (coarse particles) with a particle size larger than the measured value by laser diffraction particle size distribution measurement are included. On the other hand, the hollow silica particles of the present invention are characterized in that the proportion of particles having a particle diameter of more than 4.0 μm relative to the total number of hollow silica particles, as measured by the Coulter counter method, is 20,000 ppm or less. In the Coulter counter method, the change in electrical resistance when passing through an aperture (pore) is proportional to the volume of the particle, so that all particles can be detected. That is, the hollow silica particles of the present invention can accurately determine that the number ratio of particles exceeding 4.0 μm to the total number of hollow silica particles is 20000 ppm or less by specifying the number ratio of particles with a large particle diameter measured by the Coulter counter method. As a result, it is considered that the hollow silica particles of the present invention can improve the surface smoothness of a resin composition when used as a filler in the resin composition.

[0010] The average particle size (volume-based average particle size) of the hollow silica particles of the present invention is 0.1 μm or more and 3.0 μm or less when measured by the Coulter counter method. Hereinafter, in the present invention, "average particle size of hollow silica particles" means the volume-based average particle size calculated by the Coulter counter method (the sum of (each particle size calculated by measurement by the Coulter counter method) x (the volume ratio of each particle size)). The volume-based average particle size by the Coulter counter method is measured by the method described in the Examples. In the present invention, when the hollow silica particles have an average particle size of 0.1 μm or more and 3.0 μm or less as measured by a Coulter counter method, when the hollow silica particles are used as a filler for a resin composition, an increase in the viscosity of a resin composition precursor during preparation of the resin composition can be suppressed. The average particle size of the hollow silica particles of the present invention measured by the Coulter counter method is, from the same viewpoints as above, 0.1 μm or more, preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, still more preferably 1.0 μm or more, still more preferably 1.5 μm or more, and is 3.0 μm or less, preferably 2.8 μm or less, more preferably 2.5 μm or less, and even more preferably 2.2 μm or less.

[0011] The maximum particle diameter (maximum particle diameter on a volume basis) of the hollow silica particles measured by a Coulter counter method is preferably 15.0 μm or less, more preferably 10.0 μm or less, even more preferably 8.0 μm or less, and still more preferably 5.0 μm or less, from the viewpoint of further suppressing an increase in the viscosity of the resin composition precursor when used in a resin composition and from the viewpoint of further improving the surface smoothness of the obtained resin composition. In the present invention, the maximum particle size of the hollow silica particles measured by the Coulter counter method is the particle size at 99% (D99) of the cumulative frequency distribution on a volume basis measured by the Coulter counter method, as measured by the method described in the Examples.

[0012] In the present invention, the number ratio of the hollow silica particles having a particle diameter of more than 4.0 μm to the total number of hollow silica particles, as measured by the Coulter Counter method, is 20,000 ppm or less (hereinafter, the "number ratio of the hollow silica particles having a particle diameter of more than 4.0 μm to the total number of hollow silica particles, as measured by the Coulter Counter method" is also simply referred to as the "number ratio of particles having a particle diameter of more than 4.0 μm."). When the number ratio of the particles having a particle diameter of more than 4.0 μm is 20,000 ppm, the surface smoothness of the resin composition can be improved when the hollow silica particles are used as a filler for the resin composition. From the same viewpoints as above, the number ratio of hollow silica particles having a particle diameter exceeding 4.0 μm is preferably 10,000 ppm or less, more preferably 6,000 ppm or less, even more preferably 4,000 ppm or less, still more preferably 2,000 ppm or less, still more preferably 500 ppm or less, and still more preferably 200 ppm or less.

[0013] In the present invention, the number ratio of particles having a particle diameter of more than 5.0 μm to the total number of hollow silica particles, as measured by the Coulter counter method, is preferably 10,000 ppm or less, more preferably 5,000 ppm or less, even more preferably 1,000 ppm or less, even more preferably 500 ppm or less, even more preferably 200 ppm or less, and even more preferably 100 ppm or less, from the viewpoint of further improving the surface smoothness of a resin composition when used as a filler in the resin composition (hereinafter, "the number ratio of particles having a particle diameter of more than 5.0 μm to the total number of hollow silica particles, as measured by the Coulter counter method" is also simply referred to as "the number ratio of particles having a particle diameter of more than 5.0 μm").

[0014] In the present invention, the number ratio of particles having a particle diameter exceeding 8.0 μm to the total number of hollow silica particles, as measured by the Coulter counter method, is preferably 1000 ppm or less, more preferably 500 ppm or less, even more preferably 100 ppm or less, even more preferably 50 ppm or less, even more preferably 20 ppm or less, and even more preferably 0 ppm, from the viewpoint of further improving the surface smoothness of a resin composition when used as a filler in the resin composition (hereinafter, "the number ratio of particles having a particle diameter exceeding 8.0 μm to the total number of hollow silica particles, as measured by the Coulter counter method" is also simply referred to as "the number ratio of particles having a particle diameter exceeding 8.0 μm"). In the number ratio of the particles exceeding each particle size to the whole hollow silica particles, each particle size is the volume-based particle size measured by Coulter counter method.The number ratio of the particles exceeding each particle size to the whole hollow silica particles is calculated from the volume-based number distribution measured by Coulter counter method, which is the ratio of the number of particles exceeding each particle size to the whole number of hollow silica particles.These are specifically measured by the method described in the examples.

[0015] In the hollow silica particles of the present invention, the dielectric tangent at a measurement frequency of 10 GHz is preferably 0.0050 or less, more preferably 0.0048 or less, even more preferably 0.0046 or less, and even more preferably 0.0040 or less, from the viewpoint of sufficiently low dielectric tangent when used in a resin composition such as an insulating material, and is preferably 0.0001 or more, more preferably 0.0005 or more, even more preferably 0.0010 or more, and even more preferably 0.0015 or more, from the viewpoint of sufficient strength of the hollow silica particles. The dielectric loss tangent of the hollow silica particles is measured by the method in the Examples.

[0016] In the hollow silica particles of the present invention, the dielectric constant at a measurement frequency of 10 GHz is preferably 2.5 or less, more preferably 2.4 or less, even more preferably 2.2 or less, and still more preferably 2.0 or less, from the viewpoint of sufficiently low dielectric constant when used in a resin composition such as an insulating material, and is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and still more preferably 1.5 or more, from the viewpoint of sufficient strength of the hollow silica particles. The relative dielectric constant of the hollow silica particles is measured by the method described in the Examples.

[0017] The porosity of the hollow silica particles of the present invention is preferably 45% or more, more preferably 50% or more, and even more preferably 55% or more, from the viewpoint of lowering the dielectric constant of the hollow silica particles, and is preferably 80% or less, more preferably 77% or less, even more preferably 74% or less, and even more preferably 72% or less, from the viewpoint of ensuring sufficient strength of the hollow silica particles. The porosity of the hollow silica particles is determined by the method described in the Examples.

[0018] The average thickness of the shell of the hollow silica particles of the present invention is, from the viewpoint of lowering the dielectric constant and dielectric tangent of the hollow silica particles, preferably 200 nm or less, more preferably 160 nm or less, even more preferably 140 nm or less, and still more preferably 120 nm or less, and from the viewpoint of ensuring sufficient strength of the hollow silica particles, is preferably 40 nm or more, more preferably 60 nm or more, even more preferably 80 nm or more, and still more preferably 90 nm or more. The average thickness of the shell of the hollow silica particles is measured by the method described in the Examples.

[0019] The BET specific surface area of ​​the hollow silica particles of the present invention is preferably 5 m from the viewpoint of increasing the porosity of the hollow silica particles and decreasing the relative dielectric constant. 2 / g or more, more preferably 8m 2 / g or more, more preferably 10m 2 / g or more, and from the viewpoint of lowering the dielectric tangent, it is preferably 30m 2 / g or less, more preferably 25m 2 / g or less, more preferably 20m 2 / g or less, and even more preferably 18m 2 / g or less, and even more preferably 14m 2 / g or less. The BET specific surface area of ​​the hollow silica particles is measured by the method in the Examples.

[0020] <Method of manufacturing hollow silica particles> In the present invention, the hollow silica particles are preferably produced by a production method including the following steps 1 to 4. Step 1: preparing an aqueous emulsion A of a hydrophobic liquid using a cationic surfactant A. Step 2: A step of adding a silanol precursor, a cationic surfactant B, and an agent exhibiting alkalinity to the obtained aqueous emulsion A, and subjecting the silanol obtained by hydrolyzing the silanol precursor to a condensation reaction to produce hollow silica particle precursors. Step 3: A step of calcining the obtained hollow silica particle precursor at 1000° C. or higher to obtain silica particle aggregates. Step 4: A step of crushing and classifying the obtained hollow silica particle agglomerates.

[0021] [Process 1] In step 1, an aqueous medium, a cationic surfactant A, and a hydrophobic liquid are mixed and stirred to obtain an aqueous emulsion of the hydrophobic liquid in which droplets of the hydrophobic liquid are emulsified in the aqueous medium. The aqueous emulsion of the hydrophobic liquid can be prepared by a general method.

[0022] The aqueous medium preferably contains water. Examples of the water contained in the aqueous medium include distilled water, ion-exchanged water, and ultrapure water. In addition, the aqueous medium may 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 the aqueous medium, the water content in the aqueous medium 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.

[0023] [Cationic surfactant A] From the viewpoint of facilitating the formation of a complex with the condensed silanol in step 2 described below, and from the viewpoint of decomposition and volatilization in step 3 described below, the cationic surfactant A is preferably a quaternary ammonium salt, more preferably one or more types selected from the group consisting of quaternary ammonium salts represented by the following general formula (1) or general formula (2), and even more preferably one or more types selected from alkyltrimethylammonium salts and dialkyldimethylammonium salts. [R 1 R 3 3N] + X ― (1) [R 1 R 2 R 3 2N] + X ― (2)

[0024] 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 24 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 24 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, various eicosyl groups, various docosyl groups, and various tetracosyl 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.

[0025] 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.

[0026] 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.

[0027] From the viewpoint of facilitating the formation of a complex with the condensed silanol in step 2, and facilitating decomposition and volatilization in step 3, the quaternary ammonium salt is preferably one or more selected from lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, and behenyltrimethylammonium chloride, more preferably one or more selected from lauryltrimethylammonium chloride and behenyltrimethylammonium chloride, and even more preferably behenyltrimethylammonium chloride.

[0028] (hydrophobic liquid) The hydrophobic liquid is preferably capable of forming emulsified droplets (emulsified oil droplets) in an aqueous medium. In view of using the aqueous medium as a dispersion medium and improving the utilization efficiency of the hydrophobic liquid, the temperature range in which the hydrophobic 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.

[0029] In step 1, the mass ratio of the hydrophobic liquid to the aqueous medium [hydrophobic liquid / aqueous medium] is, from the viewpoint of keeping the volume average particle size of the hydrophobic liquid particles in the resulting aqueous emulsion of the hydrophobic liquid within an appropriate range, preferably 0.2 or more, more preferably 0.25 or more, even more preferably 0.3 or more, and is preferably 0.8 or less, more preferably 0.75 or less, even more preferably 0.7 or less. Furthermore, when the aqueous medium consists of water only, in step 1, the mass ratio of the hydrophobic liquid to water [hydrophobic liquid / water] is, from the viewpoint of keeping the particle size of the resulting droplets of the hydrophobic liquid within an appropriate range, preferably 0.3 or more, more preferably 0.35 or more, even more preferably 0.4 or more, and is preferably 0.8 or less, more preferably 0.75 or less, even more preferably 0.7 or less.

[0030] In step 1, the mass ratio of cationic surfactant A to the hydrophobic liquid [cationic surfactant A / hydrophobic liquid] is, from the viewpoint of emulsifying the hydrophobic liquid in an aqueous medium, preferably 0.001 or more, more preferably 0.005 or more, even more preferably 0.01 or more, and is preferably 0.05 or less, more preferably 0.04 or less, even more preferably 0.035 or less.

[0031] In step 1, 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 1 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 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 setting the average particle diameter of the hollow silica particles in the above range. The volume average particle size of droplets containing a hydrophobic liquid can be determined by the method described in the Examples.

[0032] [Process 2] In step 2, a silanol precursor, cationic surfactant B, and an agent exhibiting alkalinity are added to the aqueous emulsion obtained in step 1, and the silanol precursor present on the surface of the hydrophobic liquid droplets is hydrolyzed to obtain silanols. The silanols condense to form hollow silica particle precursors 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 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 obtained in step 1, or the aqueous emulsion may be added to either the silanol precursor or the cationic surfactant B, and then the remaining one may be added. The addition of the agent exhibiting alkalinity to the aqueous emulsion may be performed by adding the silanol precursor and / or the cationic surfactant B simultaneously to the aqueous emulsion, or by adding a mixture of the agent exhibiting alkalinity with either or both of the silanol precursor and the cationic surfactant B to the aqueous emulsion.

[0033] (Silanol precursor) The silanol precursor is a compound that generates a silanol compound by hydrolysis of alkoxysilane or the like, and is preferably one or more 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 4 SiY3(4) R 4 2SiY2(5) R 4 3SiY (6) Y3Si-O-SiY3(7)

[0034] In general formulas (3) to (7), R 4each independently represents a hydrocarbon 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.

[0035] In the general formulas (4) to (6), R 4 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.

[0036] The silanol precursor is preferably one or more selected from the compounds represented by general formula (3) and general formula (7). Among them, from the viewpoint of suppressing the generation of metal-corrosive acid and from the viewpoint of hydrolysis reactivity, the silanol precursor is preferably one or more selected from the 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 one or more selected from the compounds represented by general formula (3) and general formula (7) in which Y is an ethoxy group. The silanol precursor can be used alone or in combination of two or more.

[0037] 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, and is preferably 90 or less, more preferably 80 or less, even more preferably 75 or less, from the viewpoint of keeping the porosity of the hollow silica particles in an appropriate range.

[0038] (Cationic Surfactant B) As the cationic surfactant B, the same cationic surfactant B as the cationic surfactant A shown in step 1 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 3, it is preferably a quaternary ammonium salt, more preferably one or more selected from 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 1. In addition, the cationic surfactant B may be used alone or in combination of two or more kinds.

[0039] 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.

[0040] (Alkaline substances) When the system is made alkaline by the addition of an alkaline agent, the silanol precursor is hydrolyzed to silanol, which is then dehydrated and condensed to form silica. Specific examples of the alkaline agent (hereinafter also referred to as "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, dimethylbis(2-hydroxyethyl)ammonium hydroxide, etc., and from the viewpoint of making the outer shell of the hollow silica particle precursor dense, it is preferably one or more selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylhydroxyethylammonium hydroxide, methyltriethanolammonium hydroxide, and dimethylbis(2-hydroxyethyl)ammonium hydroxide, more preferably one or more selected from tetramethylammonium hydroxide and dimethylbis(2-hydroxyethyl)ammonium hydroxide, and even more preferably dimethylbis(2-hydroxyethyl)ammonium hydroxide.

[0041] 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.

[0042] In addition to the above-mentioned quaternary ammonium hydroxide salt, the alkaline substance may contain, for example, an alkali metal salt, an alkaline earth metal salt, etc., but in order to reduce the content of alkali metal and alkaline earth metal in the obtained hollow silica particles, the total content of alkali metal and alkaline earth metal is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, even more preferably 10 ppm by mass or less, and even more preferably 0 ppm by mass, relative to the mass of the obtained hollow silica particles.

[0043] The alkaline substance is preferably mixed with cationic surfactant B and contacted with the silanol precursor, since it is possible to obtain hollow silica particles having a small maximum particle size and a suitable particle size. The contact between the mixture of the alkaline substance and cationic surfactant B and the silanol precursor may be performed by adding the mixture of the alkaline substance and 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 cationic surfactant B. However, from the viewpoint of making the average particle size of the obtained hollow silica particles appropriate and from the viewpoint of reducing the number ratio of particles having a particle size of more than 4.0 μm, it is preferable to add the mixture of the alkaline substance and cationic surfactant B to a reaction system containing the silanol precursor.

[0044] The temperature at which step 2 is carried out can be appropriately adjusted depending on the type and amount of the silanol precursor and alkaline substance used, and is preferably from 0° C. to 100° C. in terms of making the outer shell of the hollow silica particle precursor dense. For example, when orthosilicate tetraethyl ester or pyrosilicate hexaethyl ester is used as the silanol precursor, the temperature is preferably from 20° C. to 45° C., and when orthosilicate tetramethyl ester or pyrosilicate hexamethyl ester is used, the temperature is preferably from 0° C. to 20° C.

[0045] The time for carrying out step 2 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.

[0046] Step 2 may include, after the formation of the hollow silica particle precursor and before step 3, a step of aggregating the hollow silica particle precursor, a step of isolating the hollow silica particle precursor, and a step of drying the hollow silica particle precursor, as necessary.

[0047] (Step of aggregating hollow silica particle precursor) The step of aggregating the hollow silica particle precursor is a step of aggregating the hollow silica particle precursor in a liquid phase after forming the hollow silica particle precursor in step 2. It is considered that the inclusion of this step can cause weak aggregation (flocculation) that maintains a certain distance between the particles of the hollow silica particle precursor. As a result, in step 3, the distance between the particles in the obtained hollow silica particle aggregate can be kept constant, and the hollow silica particles can be easily disintegrated even with a weak disintegration force that does not easily break the hollow silica particles, and the breakage of the hollow silica particles can be easily suppressed. Furthermore, since the obtained hollow silica particle precursor becomes an aggregate and has a certain particle diameter, it is easy to efficiently recover the hollow silica particle precursor by an operation such as filtration in the step of isolating the hollow silica particle precursor described later. The step of aggregating the hollow silica particle precursor is preferably a step of adding an aggregating agent to the liquid phase containing the hollow silica particle precursor obtained in step 2.

[0048] <Flocculant> The flocculant is preferably an anionic polymer, and an anionic polymer that can cause particle flocculation by adding it to the hollow silica particle precursor in a liquid phase can be suitably selected. As the anionic polymer, from the viewpoint of obtaining hollow silica particles that can easily cause weak aggregation between particles of the hollow silica particle precursor, can suppress cracking even when crushed, and can maintain low relative dielectric constant and dielectric tangent, polycarboxylates and polysulfonates are preferable. The polycarboxylate is preferably a salt of polyacrylic acid and a salt of an acrylic acid-maleic acid copolymer, and is preferably a metal salt (salt of an alkali metal such as sodium or potassium), an amine salt, or an ammonium salt of polyacrylic acid and an acrylic acid-maleic acid copolymer. Among these, from the viewpoint of obtaining hollow silica particles that can be prevented from cracking even when crushed and can maintain a low relative dielectric constant and dielectric loss tangent, one or more selected from ammonium polyacrylate and ammonium salt of an acrylic acid-maleic acid copolymer are preferred. The polysulfonate is preferably a salt of a formalin condensate of an aromatic sulfonic acid and a salt of a formalin condensate of a lignin sulfonic acid. The salt of the formalin condensate of aromatic sulfonic acid may be a salt of condensed naphthalene sulfonic acid. The salt of condensed naphthalene sulfonic acid is preferably a metal salt (sodium, potassium, or other alkali metal salt), an amine salt, or an ammonium salt of condensed naphthalene sulfonic acid. Among these, the ammonium salt of condensed naphthalene sulfonic acid is preferred from the viewpoint of obtaining hollow silica particles that can suppress cracking even when crushed and can maintain low relative dielectric constant and dielectric loss tangent. Among the above, from the viewpoint of obtaining hollow silica particles that can be prevented from cracking even when crushed and can maintain a low relative dielectric constant and dielectric loss tangent, the anionic polymer is more preferably one or more selected from ammonium polyacrylate, ammonium salt of acrylic acid-maleic acid copolymer, and ammonium salt of condensed naphthalenesulfonic acid, and even more preferably ammonium polyacrylate. Furthermore, using the above ammonium salt as the anionic polymer is also preferable from the viewpoint of use in insulating materials, etc., and from the viewpoint of reducing the content of metal ions in the obtained hollow silica particles.

[0049] The temperature at which the step of aggregating the hollow silica particle precursor is carried out is preferably 0°C or higher and 100°C or lower, more preferably 10°C or higher and 80°C or lower, even more preferably 15°C or higher and 60°C or lower, and still more preferably 20°C or higher and 45°C or lower, from the viewpoint of adjusting the agglomeration strength of the hollow silica particles, suppressing cracking even when crushed, and obtaining hollow silica particles that can maintain a low relative dielectric constant and dielectric tangent. In addition, the process of aggregating the hollow silica particle precursor is preferably performed by stirring after adding the aggregating agent. In the process of aggregating the hollow silica particle precursor, the stirring time is preferably 1 minute or more, more preferably 3 minutes or more, even more preferably 5 minutes or more, even more preferably 8 minutes or more, and is preferably 60 minutes or less, more preferably 45 minutes or less, even more preferably 30 minutes or less, even more preferably 15 minutes or less, from the viewpoint of adjusting the aggregation strength of the hollow silica particle precursor, suppressing cracking even when crushed, and obtaining hollow silica particles that can maintain low relative dielectric constant and dielectric loss tangent.

[0050] (Step of isolating hollow silica particle precursor and step of drying hollow silica particle precursor) The hollow silica particle precursor can be isolated, for example, by filtration. If the boiling point of the hydrophobic liquid containing the hollow silica particle precursor is higher than 100°C, 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 100°C or lower, the hollow silica particle precursor can be dried, for example, by freeze-drying.

[0051] (Hollow silica particle precursor) The hollow silica particle precursor is a composite silica particle having an outer shell containing silica and a hydrophobic liquid inside the outer shell, in which a cationic surfactant is radially oriented toward the center of the particle.

[0052] [Step 3] In step 3, the hollow silica particle precursor obtained in step 2 is calcined at 1000°C or higher to decompose and volatilize the cationic surfactant present in the outer shell of the hollow silica particle precursor and volatilize the internal hydrophobic liquid, and then the pores present in the outer shell are closed by calcination to obtain hollow silica particle aggregates having uniform outer shells.

[0053] The calcination temperature in step 3 is, from the viewpoint of reducing silanol groups on the surface of the hollow silica particles, 1000°C or higher, preferably 1010°C or higher, more preferably 1030°C or higher, and even more preferably 1050°C or higher, and, from the viewpoint of suppressing aggregation of the hollow silica particles, is preferably 1200°C or lower, more preferably 1190°C or lower, even more preferably 1180°C or lower, and even more preferably 1160°C or lower.

[0054] The calcination time in step 3 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 suppressing aggregation of the hollow silica particles. [Step 4] In step 4, the hollow silica particle agglomerates obtained in step 3 are crushed and classified to loosen the agglomerates of hollow silica particles to obtain hollow silica particles, and hollow silica particles having a large particle size are removed from the agglomerates. In step 4, the ratio of components having a large particle diameter contained in the hollow silica particles can be reduced by adjusting the intensity of classification by the classifier.

[0055] In step 4, the apparatus used for disintegration can be appropriately selected from known apparatuses, and examples thereof include a hammer mill, an atomizer, a rotoplex, and a jet mill. Examples of the jet mill include a swirling airflow jet mill, a fluidized bed jet mill, a collision plate jet mill, and a rotary mechanical mill. Among these, from the viewpoint of reducing the rate of cracking of the hollow silica particles after disintegration, a jet mill is preferred, and a swirling airflow jet mill is more preferred. In step 4, the device used for classification can be appropriately selected from known devices, and preferably includes a gravity classifier, a centrifugal classifier, and an inertial classifier. Among these, the inertial classifier is preferred from the viewpoint of efficiently reducing the components with large particle diameters contained in the hollow silica particles.

[0056] (Measured using the Coulter counter method) After the hollow silica particles of the present invention are produced by the above-mentioned production method, they are preferably measured by the Coulter counter method. The physical properties measured by the Coulter counter method include the above-mentioned average particle size and the number ratio of particles having a particle size of more than 4.0 μm to the total number of hollow silica particles. In addition, it is preferable to further measure the maximum particle size, the number ratio of particles having a particle size of more than 5.0 μm to the total number of hollow silica particles, and the number ratio of particles having a particle size of more than 8.0 μm to the total number of hollow silica particles. As the Coulter counter used for the measurement, a known Coulter counter can be appropriately selected and used, and preferable examples include "Multisizer 3" and "Multisizer 4e" manufactured by Beckman Coulter, Inc. In addition, it is preferable to use an aperture of 20 μm for the measurement by the Coulter counter method.

[0057] [Resin composition] The resin composition of the present invention contains the hollow silica particles of the present invention described above. The resin composition contains the hollow silica particles of the present invention, so that the dielectric constant and the dielectric loss tangent can be reduced. Since the resin composition of the present invention has a low dielectric constant and a low dielectric loss tangent, it can be suitably used as an insulating material that can reduce transmission loss and transmission delay.

[0058] The resin to be mixed with the hollow silica particles is not particularly limited, but from the viewpoint of lowering the relative dielectric constant and the dielectric loss tangent of the resin composition and improving the moldability, a curable resin is preferable. Suitable examples of the curable resin include epoxy resin, bismaleimide resin, cycloolefin resin, fluorine-based resin, and derivatives of these resins. In the present disclosure, the resin composition precursor means, when the resin to be mixed with the hollow silica particles is a curable resin, the resin composition precursor means the resin before curing.

[0059] In the resin composition, from the viewpoint of suitable use as an insulating material for high-frequency circuit boards and the like, the relative dielectric constant at a measurement frequency of 10 GHz is preferably 3.5 or less, more preferably 3.0 or less, even more preferably 2.8 or less, still more preferably 2.6 or less, and from the viewpoint of production, it is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, still more preferably 1.5 or more. In the resin composition, the dielectric loss tangent at a measurement frequency of 10 GHz is preferably 0.0350 or less, more preferably 0.0300 or less, even more preferably 0.0280 or less, and even more preferably 0.0260 or less from the viewpoint of suitable use as an insulating material for high-frequency circuit boards, etc., and is preferably 0.0150 or more, more preferably 0.0180 or more, even more preferably 0.0200 or more, and even more preferably 0.0230 or more from the viewpoint of production. The relative dielectric constant and dielectric loss tangent of the resin composition are measured by the method described in the Examples.

[0060] The amount of hollow silica particles in the resin composition is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 18% by mass or more, from the viewpoint of reducing the relative dielectric constant and dielectric tangent of the resin composition, and is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of reducing the viscosity of the resin composition precursor and improving the processability.

[0061] [Insulating material] The insulating material of the present invention contains the above-mentioned resin composition of the present invention. 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

[0062] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples in any way.

[0063] [Measurement and evaluation method] <Measurement of the volume average particle size of droplets containing hydrophobic liquid in water-based emulsion A> The volume average particle size of the particles in the aqueous emulsion A was measured using a particle size measuring device "Zetasizer Nano ZS" (manufactured by Malvern Panalytical) by dynamic light scattering method, using a square cell with an optical path length of 10 mm.

[0064] <Measurement of the physical properties and characteristics of hollow silica particles> The hollow silica particles obtained in the examples and comparative examples were measured by the following methods. The measurement results are shown in Table 1. (Measurement of the average particle size, maximum particle size, and the percentage of particles exceeding each particle size in the total number of hollow silica particles using the Coulter counter method) The average particle size, maximum particle size, and the percentage of particles exceeding each particle size relative to the total number of hollow silica particles were measured using a particle size measuring device (Beckman Coulter, Inc., Multisizer 3 (using a 20 μm aperture tube)) using the Coulter counter method. The average particle size of the hollow silica particles measured by the Coulter counter method was taken as the volume-based average particle size calculated by the Coulter counter method (the sum of (each particle size calculated by measurement using the Coulter counter method) x (the volume ratio of each particle size)). The maximum particle size of the hollow silica particles measured by the Coulter counter method was determined to be the particle size at 99% (D99) of the cumulative frequency distribution on a volume basis. The number ratios of particles exceeding 4.0 μm to all hollow silica particles, the number ratios of particles exceeding 5.0 μm to all hollow silica particles, and the number ratios of particles exceeding 8.0 μm to all hollow silica particles, as measured by the Coulter Counter method, were calculated in parts per million by dividing the number of particles exceeding these sizes by the number of all hollow silica particles from the volume-based particle size number distribution.

[0065] (Measurement of porosity of hollow silica particles) The true density of the silica particles was calculated according to the following formula using the density measured with a density measuring device (ULTRAPYC1200e manufactured by Quantachrome Corp.) and nitrogen as the measurement gas. 3 It was decided. Porosity (%) = [1-(true density of hollow silica particles / true density of silica particles)] x 100

[0066] (Measurement of BET specific surface area of ​​hollow silica particles) The BET specific surface area of ​​the hollow silica particles was measured using a specific surface area measuring device (manufactured by Shimadzu Corporation, product name "Flowsorb III2305") The sample was pretreated by heating at 200°C for 15 minutes.

[0067] (Measurement of the average shell thickness of hollow silica particles) Using Elastic Carbon ELS-C10 (made by Stem Corp.) and a field emission scanning electron microscope (made by Hitachi High-Tech Corp.: S-4800), observation was performed at an acceleration voltage of 30 kV to obtain a STEM image of the hollow silica particles. For 10 hollow silica particles in the image, the outer shell portions were identified based on the shade of color, and the darker portions were taken as the outer shell portions to calculate the average value, which was used as the average thickness of the outer shell of the hollow silica particles of the present invention.

[0068] (Measurement of the dielectric constant and dielectric loss tangent of hollow silica particles) The dielectric constant and dielectric loss tangent of the hollow silica particles were measured at a temperature of 25°C and a 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 (registered trademark) tube (manufactured by Chukoh Chemical Industry Co., Ltd.: PTFE tube, inner diameter 1.5 mm, outer diameter 2.5 mm) with hollow silica particles so that all of them were within the measurement range (between 6.75 mm and 36.35 mm from the bottom). The mass of the Teflon tube before and after filling with the hollow silica particles was measured to calculate the filling mass of the hollow silica particles, and the volume of the hollow silica particles filled in the Teflon tube was calculated from the filling mass and specific gravity of the hollow silica particles. 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 and the measured values ​​of a Teflon tube filled with hollow silica particles, which was used as a blank.

[0069] <Measurement and evaluation of the physical properties and characteristics of resin compositions> (Preparation of Resin Composition Precursor) 23.7 g of epoxy resin (manufactured by Mitsubishi Chemical Corporation: jER828), 28.8 g of acid anhydride curing agent (manufactured by Mitsubishi Chemical Corporation: YH-306), and 0.3 g of imidazole curing agent (manufactured by Mitsubishi Chemical Corporation: EMI24) were kneaded using a kneader (manufactured by Thinky Corporation: Planetary Vacuum Mixer) under atmospheric pressure at 1400 rpm for 1 minute, and then further kneaded under reduced pressure of 0.3 kPa at 2000 rpm for 5 minutes to obtain an epoxy resin kneaded liquid. 40 g of the obtained epoxy resin kneaded liquid and 10 g of the hollow silica particles obtained in the Examples and Comparative Examples were kneaded using a kneader (Planetary Vacuum Mixer manufactured by Thinky Corporation) under conditions of 1400 rpm at atmospheric pressure for 1 minute, and then continuously kneaded under conditions of 2000 rpm at reduced pressure of 0.3 kPa for 5 minutes to obtain a resin composition precursor.

[0070] The obtained resin composition precursor was allowed to stand for 1 hour in a thermostatic chamber set at 25° C., and then the viscosity was evaluated 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 evaluation results are shown in Table 1.

[0071] (Evaluation of Surface Smoothness of Resin Composition) The obtained resin composition precursor was applied onto a PET resin (Lumirror S10, Toray Industries, Inc., film thickness 25 μm) using an applicator (4-sided film applicator (NO. 350FA4), Coating Tester Co., Ltd.). At this time, the resin composition precursor was applied so that the thickness of the obtained resin composition precursor was a thin film of 50 μm. After that, a curing treatment was performed at 80°C for 3 hours and at 120°C for 6 hours to prepare a resin composition sample for evaluating surface smoothness. The presence or absence of granular shapes on the surface of the resin composition sample for evaluating surface smoothness was confirmed by visual inspection, and the surface smoothness was evaluated based on the following evaluation criteria. The evaluation results are shown in Table 1. (Evaluation Criteria) A: No granular shape was found on the surface of the resin composition. B: A small amount of granular shape was observed on the surface of the resin composition. C: Granular shapes were observed on the surface of the resin composition.

[0072] (Measurement of relative dielectric constant and dielectric loss tangent of resin composition) The obtained resin composition precursor was poured into a Teflon tube (manufactured by AS ONE Corporation, inner diameter 2.5 mm, outer diameter 4.0 mm) and heated in a dryer at 80°C for 3 hours, and then heated at 160°C for 6 hours to prepare a resin composition sample for measuring the relative dielectric constant and dielectric tangent. The obtained resin composition sample for measurement was used to measure the dielectric constant and dielectric loss tangent of the resin composition in the same manner as in "Measurement of relative dielectric constant and dielectric loss tangent of hollow silica particles." The evaluation results are shown in Table 1.

[0073] <Example 1> (Process 1) 342.2 g of ion-exchanged water as an aqueous medium, 150 g of dodecane (reagent manufactured by Kishida Chemical Co., Ltd.: primary n-dodecane) as a hydrophobic liquid, and 7.8 g of Coatamin 2285E (manufactured by Kao Corporation: containing 58% by mass of behenyl trimethyl ammonium chloride) as a cationic surfactant A were mixed and stirred to obtain aqueous emulsion A. The volume average particle size of the particles in the obtained aqueous emulsion A was 0.8 μm. (Process 2) A reaction vessel was charged with 13,157.6 g of ion-exchanged water, 173.0 g of aqueous emulsion A, 125.6 g of Coatamin 24P (manufactured by Kao Corporation: containing 27.5% by mass of lauryl trimethyl ammonium chloride) as cationic surfactant B, and 3,120.8 g of orthosilicate ethyl ester (manufactured by Wacker Asahi Kasei Silicones Corporation: SEMICOSIL TEOS999-LB) as a silanol precursor, and the mixture was heated to 40° C. with stirring and then stirred for 10 minutes to obtain preparation solution B. Next, 221.5 g of AH212-CS (manufactured by Yokkaichi Synthetic Co., Ltd.: containing 50% by mass of dimethylbis(2-hydroxyethyl)ammonium hydroxide) as an alkaline agent and 711.6 g of Courtamin 24P as a cationic surfactant B were mixed uniformly to obtain preparation C. Preparation liquid C was added to preparation liquid B at a constant rate, and then the mixture was stirred at 40° C. for 3 hours to obtain a cloudy white liquid D. The cloudy white liquid D contains hollow silica particle precursors. The obtained cloudy liquid D was filtered using 5C filter paper (manufactured by Advantec Toyo Kaisha, Ltd.) and then dried at 110° C. to obtain white dried hollow silica particle precursors. (Step 3) The obtained dried hollow silica particle precursor was calcined at 1100° C. for 1 hour to obtain hollow silica particle aggregates. (Step 4) The obtained hollow silica particle agglomerates were crushed in a swirling air jet mill (CO-JET SYSTEM α MARK III, manufactured by Seishin Enterprise Co., Ltd.) at a P NOZZLE pressure of 0.5 MPa, a G NOZZLE pressure of 0.5 MPa, and a sample supply rate of 10 g / min to obtain a crushed product of hollow silica particle agglomerates. The crushed product of hollow silica particle agglomerates was classified into a classification point of 1:3 μm, a classification point of 2:5 μm, and a specific gravity of 1.3 g / cm using an inertial classifier (ELBOW-JET L-3, manufactured by Nittetsu Mining Co., Ltd.). 3 The classification treatment was carried out under the conditions of a sample supply rate of 10 g / min, and hollow silica particles were obtained by collecting particles below the classification point of 1:3 μm. The percentage of the number of particles exceeding each particle size of the obtained hollow silica particles relative to the total number of hollow silica particles was measured by the Coulter counter method as described above. The measurement results are shown in Table 1.

[0074] <Example 2> Hollow silica particles were obtained in the same manner as in Example 1, except that step 4 was changed as follows. (Step 4) The obtained hollow silica particle agglomerates were disintegrated in a swirling airflow jet mill (Seishin Enterprise Co., Ltd.: CO-JET SYSTEM α MARK III) at a P NOZZLE pressure of 0.5 MPa, a G NOZZLE pressure of 0.4 MPa, and a sample supply rate of 10 g / min to obtain hollow silica particles.

[0075] <Example 3> Hollow silica particles were obtained in the same manner as in Example 1, except that step 4 was changed as follows. (Step 4) The obtained hollow silica particle aggregates were pulverized using a rotor speed mill (Retsch: ZM200) at a rotation speed of 18,000 rpm to obtain hollow silica particles.

[0076] <Comparative Example 1> Hollow silica particles were obtained in the same manner as in Example 1, except that step 4 was changed as follows. (Step 4) The obtained hollow silica particle aggregates were pulverized using a rotor speed mill (Retsch: ZM200) at a rotation speed of 6000 rpm to obtain hollow silica particles.

[0077] <Comparative Example 2> 200 g of silica (Admafine SO-C2, manufactured by Admatechs Co., Ltd.), 640 g of a 25% aqueous solution of tetramethylammonium hydroxide (pH 14, manufactured by Seichem Asia Co., Ltd.), and 160 g of ion-exchanged water were placed in a reaction vessel equipped with a stirrer (TEM-D1500M, manufactured by Taiatsu Glass Industry Co., Ltd.), and the mixture was heated to 180°C over 1 hour and 30 minutes with stirring, and then stirred at 180°C for 1 hour to obtain a silica solution (silica concentration: 20% by mass, silica / organic alkali (molar ratio) = 1.9). Next, 1000 g of the prepared silica solution was mixed with 1000 g of ion-exchanged water until homogeneous, to obtain a diluted solution of silica solution. The diluted solution of silica solution obtained was spray-dried using a spray dryer (Micromist Spray Dryer manufactured by Fujisaki Electric Co., Ltd.) (spray-drying conditions: hot air inlet temperature: 130°C, nozzle flow rate: 100 L / min, spray amount: 25 mL / min) to obtain a dry powder. Next, the dried powder obtained by spray drying was calcined at 1100° C. for 1 hour to obtain hollow silica particle aggregates. The obtained hollow silica particle aggregates were disintegrated in a jet mill ("CO-JET SYSTEM α MARKIII" manufactured by Seishin Enterprise Co., Ltd.) at a P. NOZZLE pressure of 0.2 MPa, a G. NOZZLE pressure of 0.2 MPa, and a sample supply rate of 5 g / min to obtain hollow silica particles.

[0078] [Table 1]

[0079] From Table 1, it is confirmed that the hollow silica particles of Examples 1 to 3 have a low viscosity of the resin composition precursor when used in a resin composition. Furthermore, it is confirmed that the resin composition containing the hollow silica particles of Examples 1 to 3 has no granular shape on the surface, and the surface smoothness of the resin composition can be improved.

Claims

1. Hollow silica particles having an average particle diameter of 0.1 μm or more and 3.0 μm or less as measured by the Coulter counter method, and the number ratio of particles with a particle diameter exceeding 4.0 μm to the total number of hollow silica particles as measured by the Coulter counter method being 20,000 ppm or less.

2. The hollow silica particle according to claim 1, wherein the dielectric loss tangent at a measurement frequency of 10 GHz is 0.0050 or less.

3. Hollow silica particles according to claim 1, wherein the porosity is 45% or more and 80% or less.

4. The hollow silica particles according to claim 1, wherein the average thickness of the outer shell of the hollow silica particles is 200 nm or less.

5. The BET specific surface area is 5 m ２ / g or more 30m ２ Hollow silica particles according to claim 1, wherein the amount is less than or equal to / g.

6. The hollow silica particle according to claim 1, wherein the relative permittivity at a measurement frequency of 10 GHz is 2.5 or less.

7. A resin composition containing hollow silica particles according to any one of claims 1 to 6.

8. An insulating material comprising the resin composition described in claim 7.