Hollow Silica Particles

Abstract

To provide hollow silica particles having a small average particle size and a small change in relative permittivity and dielectric tangent with time under high temperature and high humidity, as well as a resin composition and an insulating material formulated with the same.SOLUTION: The hollow silica particles have an average particle size of 0.5 μm or more and 3.0 μm or less and an increase in particle density of 8% or less when heat-treated at 1100°C for 1 hour.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to hollow silica particles, and to a resin composition and an insulating material 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. High-frequency circuits that handle such high-frequency radio waves require insulating materials with low dielectric constants and low dielectric dissipation factors to reduce transmission loss and delays. Silica particles, which are currently incorporated into insulating materials to improve thermal properties, are also required to have low dielectric constants and low dielectric dissipation factors. Furthermore, miniaturization of high-frequency circuits is desired, and the silica particles incorporated into insulating materials must also have smaller particle sizes. Currently, hollow silica particles are being investigated as a way to lower the dielectric constant of silica particles.

[0003] For example, Patent Document 1 describes a low dielectric constant film in which mesoporous silica particles having a hollow structure are dispersed in a matrix resin. Furthermore, Patent Document 2 describes silica-based particles having cavities inside a non-porous outer silica shell layer, a porosity in the range of 20 to 95% by volume, and an average particle size in the range of 0.1 to 50 μm. Furthermore, Patent Document 3 describes hollow silica particles that have a shell layer containing silica and have a space inside the shell layer, and that have a relative dielectric constant of 1.3 to 5.0 at 1 GHz and a dielectric loss tangent of 0.0001 to 0.05 at 1 GHz. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-93876 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-103850 [Patent Document 3] International Publication No. 2021 / 172294 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although Patent Document 1 achieves a resin with a low dielectric constant by dispersing hollow mesoporous silica in a matrix resin, the mesopores in the outer shell of the hollow mesoporous silica have high hygroscopicity, which causes a problem of low stability of the dielectric constant over time under high temperature and high humidity conditions. In Patent Document 2, hollow silica particles are synthesized by spray-drying an aqueous alkali silicate solution, and the pores in the outer shell are sealed by hydrothermal treatment to improve the stability over time of the dielectric constant and dielectric loss tangent under high temperature and high humidity conditions. However, the hydrothermal treatment generates a large number of silanols in the particles, so the dielectric loss tangent itself is high and is still not at a satisfactory level. Furthermore, in Patent Document 3, hollow silica is treated with a silane coupling agent to make it hydrophobic, thereby reducing its hygroscopicity. However, since alkali metals and the like are contained in order to effectively reduce the dielectric loss tangent in high-temperature treatment, the silica tends to crystallize in the high-temperature treatment, increasing the density and relative dielectric constant, and also increasing its hygroscopicity, resulting in a problem of poor stability of the relative dielectric constant and dielectric loss tangent over time under high temperature and high humidity. Therefore, an object of the present invention is to provide hollow silica particles that have a small average particle size and exhibit little change over time in dielectric constant and dielectric loss tangent under high temperature and high humidity conditions, as well as a resin composition and an insulating material containing the hollow silica particles. [Means for solving the problem]

[0006] The present invention relates to the following [1] to [3]. [1] The average particle size is 0.5 μm or more and 3.0 μm or less, Hollow silica particles whose particle density increases by 8% or less when heat treated at 1100°C for 1 hour. [2] A resin composition containing the hollow silica particles described in [1] above. [3] An insulating material containing the resin composition according to [2] above. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide hollow silica particles having a small average particle size and exhibiting little change over time in the dielectric constant and dielectric loss tangent under high temperature and high humidity conditions, as well as a resin composition and an insulating material containing the hollow silica particles. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Hollow silica particles] The hollow silica particles of the present invention are characterized by having an average particle diameter of 0.5 μm or more and 3.0 μm or less, and exhibiting an increase in particle density of 8% or less when heat-treated at 1100° C. for 1 hour.

[0009] The present inventors have considered that reducing the hygroscopicity of silica particles is important for improving the stability of their dielectric constant and dielectric loss tangent. They have found that reducing the hygroscopicity of silica particles effectively involves reducing the amount of silanol groups on the silica particle surface and the fine structures, such as pores (mesopores) that easily adsorb water. They have also found that hollow silica particles with an average particle size of 0.5 μm to 3.0 μm show small changes over time in their dielectric constant and dielectric loss tangent under high temperature and high humidity conditions when the particle density increases by 8% or less after heat treatment at 1100°C for 1 hour. The above-mentioned mechanism regarding the effects of the present invention is only a supposition, and the present invention is not limited to this.

[0010] The hollow silica particles have a volume average particle size of 0.5 μm or more, preferably 0.7 μm or more, and more preferably 0.9 μm or more, from the viewpoints of reducing the viscosity when blended into a resin composition and maintaining processability, and the volume average particle size is 3.0 μm or less, preferably 2.8 μm or less, and more preferably 2.6 μm or less, from the viewpoints of improving the appearance of the resin composition. Furthermore, from the viewpoint of incorporating a large number of hollow silica particles into a resin composition and reducing the relative dielectric constant and dielectric loss tangent of the resin composition, the coefficient of variation of the average particle size of the hollow silica particles 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 is, in terms of volume average particle size, 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 4.5 μm or less, even more preferably 4.0 μm or less. The volume average particle size of the hollow silica particles can be determined by the method described in the Examples.

[0011] The increase rate of particle density of hollow silica particles when heat-treated at 1100°C for 1 hour is 8% or less, preferably 7% or less, more preferably 6% or less, and preferably 0% or more, more preferably 0%, from the viewpoint of minimizing changes over time in the dielectric constant and dielectric loss tangent under high temperature and high humidity conditions. The heat treatment is carried out by increasing the temperature from room temperature at a rate of 500°C / h and maintaining the temperature at 1100°C for 1 hour. The density of the hollow silica particles can be determined by the method described in the Examples.

[0012] When the dielectric constant of the hollow silica particles at a measurement frequency of 5.8 GHz is 2.5 or less, the dielectric constant of a resin composition containing the hollow silica particles can be sufficiently low. From the viewpoint of the strength of the hollow silica, the dielectric constant at a measurement frequency of 5.8 GHz is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more, and from the viewpoint of sufficiently lowing the dielectric constant of the resin composition, it is preferably 2.4 or less, more preferably 2.2 or less, and even more preferably 2.1 or less. Furthermore, if the increase in dielectric constant at a measurement frequency of 5.8 GHz when hollow silica particles are stored at a temperature of 60°C and a humidity of 90% for 5 days is 0.15 or less, it can be said that the change in the dielectric constant of the hollow silica particles over time under high temperature and high humidity is small, and the increase is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.0. The relative dielectric constant of the hollow silica particles can be determined by the method described in the Examples.

[0013] When the hollow silica particles have a dielectric loss tangent of 0.0070 or less at a measurement frequency of 5.8 GHz, the dielectric loss tangent of a resin composition containing the hollow silica particles can be sufficiently low. From the viewpoint of the strength of the hollow silica, the dielectric loss tangent at a measurement frequency of 5.8 GHz is preferably 0.0001 or more, more preferably 0.0005 or more, and even more preferably 0.001 or more, and from the viewpoint of sufficiently low dielectric loss tangent of the resin composition, it is preferably 0.0060 or less, more preferably 0.0055 or less, and even more preferably 0.0050 or less. Furthermore, if the increase in the dielectric loss tangent at a measurement frequency of 5.8 GHz when hollow silica particles are stored at a temperature of 60°C and a humidity of 90% for 5 days is 0.0020 or less, it can be said that the change in the dielectric loss tangent of the hollow silica particles over time under high temperature and high humidity is small, and the increase is preferably 0.0010 or less, more preferably 0.0005 or less, and even more preferably 0.0000. The dielectric loss tangent of the hollow silica particles can be determined by the method described in the Examples.

[0014] When the hollow silica particles are stored at a temperature of 60°C and a humidity of 90% for 5 days, the moisture absorption amount of the hollow silica particles is preferably 1.0% by mass or less, since this reduces the changes over time in the dielectric constant and dielectric loss tangent of the hollow silica particles under high temperature and high humidity. The moisture absorption amount is more preferably 0.5% by mass or less, even more preferably 0.2% by mass or less, and even more preferably 0.1% by mass or less.

[0015] The porosity of the hollow silica particles is preferably 45 vol% or more, more preferably 47 vol% or more, and even more preferably 48 vol% or more from the viewpoint of reducing the dielectric constant of the hollow silica particles, 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 ensuring sufficient strength of the hollow silica particles. The porosity of the hollow silica particles can be determined by the method described in the Examples.

[0016] The BET specific surface area of ​​the hollow silica particles 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 loss tangent of the hollow silica particles and reducing the amount of surface treatment agent used when compounded with a resin, thereby lowering the dielectric loss 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 can be determined by the method described in the Examples.

[0017] [Method for manufacturing hollow silica particles] The method for producing hollow silica particles of the present invention is not particularly limited, but may, for example, include: step A of preparing an aqueous emulsion of a hydrophobic liquid using a cationic surfactant A; step B of adding a silanol precursor and a cationic surfactant B to the aqueous emulsion obtained in step A, hydrolyzing the silanol precursor to obtain silanol, and subjecting the resulting silanol to a condensation reaction to produce hollow silica particle precursors; and step C of heat-treating the hollow silica particle precursor obtained in step B.

[0018] [Process A] In step A, an aqueous emulsion of a hydrophobic liquid may be prepared by mixing and stirring a cationic surfactant A and a hydrophobic liquid with a water-containing liquid A to disperse the hydrophobic liquid droplets in step A1, or by mixing and stirring a cationic surfactant A, a hydrophobic liquid, and the water-compatible organic solvent to prepare a solution containing the hydrophobic liquid droplets, and then mixing the solution with water while stirring in step A2 to prepare an aqueous emulsion of a hydrophobic liquid. Preparation of an aqueous emulsion of a hydrophobic liquid can also be performed by other common methods.

[0019] In step A1, examples of the water contained in liquid A include distilled water, ion-exchanged water, and ultrapure water. Liquid A may also contain a water-compatible organic solvent to produce a more uniform and stable emulsion of the hydrophobic liquid. Examples of water-compatible organic solvents 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 content of water 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. In step A2, the water content in the aqueous emulsion is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, from the viewpoint of instantly reducing the solubility of the hydrophobic liquid in liquid A.

[0020] (cationic surfactant A) From the viewpoint of dispersibility of the emulsion and 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 3N] + X ― (2)

[0021] In general formula (1) and 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 be different groups, and X ― indicates a monovalent anion. Examples of alkyl groups 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.

[0022] X in general formulas (1) and (2) ― From the viewpoint of easy decomposition and volatilization during firing, X is preferably at least one type selected from monovalent anions such as halogen ions, hydroxide ions, and nitrate ions. ― The cation is more preferably a halide ion, and even more preferably a chloride ion.

[0023] Examples of the alkyltrimethylammonium salt represented by general formula (1) include butyltrimethylammonium chloride, hexyltrimethylammonium chloride, octyltrimethylammonium chloride, decyltrimethylammonium chloride, lauryltrimethylammonium chloride (dodecyltrimethylammonium chloride), tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, stearyltrimethylammonium chloride, behenyltrimethylammonium chloride, butyltrimethylammonium bromide, hexyltrimethylammonium bromide, octyltrimethylammonium bromide, decyltrimethylammonium bromide, lauryltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, stearyltrimethylammonium bromide, and behenyltrimethylammonium bromide.

[0024] 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.

[0025] The quaternary ammonium salt is preferably lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, or behenyltrimethylammonium chloride, 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.

[0026] (hydrophobic liquid) The hydrophobic liquid is preferably one that can form emulsified droplets (emulsified oil droplets) in water. In addition, because liquid A containing water is used as the dispersion medium and in terms of 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 JP 2016-121060 A. Among these, hydrocarbons having 6 to 18 carbon atoms are preferred, hydrocarbon groups having 6 to 14 carbon atoms are more preferred, and hexane and dodecane are more preferred.

[0027] In step A1, 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 within an appropriate range, and is preferably 0.7 or less, more preferably 0.65 or less, even more preferably 0.6 or less. In step A2, the mass ratio of the hydrophobic liquid to water [hydrophobic liquid / water] is preferably 0.001 or more, more preferably 0.003 or more, even more preferably 0.005 or more, from the viewpoint of keeping the particle size of the resulting hydrophobic liquid droplets within an appropriate range, and is preferably 0.1 or less, more preferably 0.05 or less, even more preferably 0.02 or less.

[0028] In step A1, the mass ratio of cationic surfactant A to the hydrophobic liquid [cationic surfactant A / hydrophobic liquid] is, from the viewpoint of dispersing the hydrophobic liquid in liquid A, 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. In step A2, the mass ratio of cationic surfactant A to hydrophobic liquid [cationic surfactant A / hydrophobic liquid] is preferably 0.8 or more, more preferably 0.85 or more, even more preferably 0.9 or more, from the viewpoint of preparing a uniform solution containing hydrophobic liquid droplets, and is preferably 1.2 or less, more preferably 1.1 or less, even more preferably 1 or less.

[0029] 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 0°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 keeping the average particle diameter of the hollow silica particles within the above range. The volume average particle size of droplets containing a hydrophobic liquid can be determined by the method described in the Examples.

[0030] [Process B] In step B, a silanol precursor is added to the aqueous emulsion obtained in step A, and the silanol precursor present on the surface of the hydrophobic liquid droplets is hydrolyzed in the presence of an alkaline substance to obtain silanols. The obtained silanols condense in the presence of the alkaline substance to form hollow silica particle precursors that have an outer shell containing silica and a cationic surfactant on the surface of the hydrophobic liquid droplets and contain the hydrophobic liquid inside. When the silanol precursor is added to the aqueous emulsion, a cationic surfactant B may also be added. The cationic surfactant B may be added to the aqueous emulsion either simultaneously with or separately from the silanol precursor and the cationic surfactant B, or the aqueous emulsion may be added to either the silanol precursor or the cationic surfactant B, and then the other may be added.

[0031] 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. Furthermore, if the boiling point of the hydrophobic liquid contained in 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 or the like.

[0032] (Silanol precursor) The silanol precursor is a compound that generates a silanol compound by hydrolysis of an alkoxysilane or the like, and is preferably selected from alkyl orthosilicate esters and alkyl pyrosilicate 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)

[0033] 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 hydroxy group upon hydrolysis.

[0034] In the general formulas (4) to (6), R 3 are each independently a hydrocarbon group preferably 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 formulae (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 1 to 4 carbon atoms.

[0035] 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 acids 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 1 to 4 carbon atoms, more preferably selected from compounds represented by general formula (3) and general formula (7) in which Y is a methoxy group and / or an ethoxy group, and even more preferably selected from methyl orthosilicate and methyl pyrosilicate, and ethyl orthosilicate and ethyl pyrosilicate. The silanol precursors can be used alone or in combination of two or more. When using a silanol precursor in which Y is a methoxy group, the hydrolysis reaction rate is too fast at room temperature (25°C), making it difficult to form a dense outer shell of the hollow silica precursor. Therefore, it is preferable to carry out step B at a temperature of 15°C or lower.

[0036] 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 within an appropriate range.

[0037] (cationic surfactant B) As the cationic surfactant B, the same cationic surfactant 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 preferred, more preferably lauryltrimethylammonium chloride (dodecyltrimethylammonium chloride), stearyltrimethylammonium chloride, or behenyltrimethylammonium chloride, and even more preferably lauryltrimethylammonium 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. The cationic surfactant B may be used alone or in combination of two or more.

[0038] From the viewpoint of dispersibility of the hollow silica particle precursor, the mass ratio of the silanol precursor to the cationic surfactant B [silanol precursor / cationic surfactant B] is preferably 1 or more, more preferably 1.5 or more, even more preferably 2 or more, and is preferably 30 or less, more preferably 25 or less, even more preferably 23 or less.

[0039] (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 alkaline substances include those described in paragraph

[0014] of JP 2016-121060 A. Among these, quaternary ammonium hydroxide salts are preferred. Specific examples of quaternary ammonium hydroxide salts 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 densifying the outer shell of the hollow silica particle precursor, preferred are tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylhydroxyethylammonium hydroxide, methyltriethanolammonium hydroxide, and dimethylbis(2-hydroxyethyl)ammonium hydroxide, and more preferred are tetramethylammonium hydroxide and dimethylbis(2-hydroxyethyl)ammonium hydroxide.

[0040] The mass ratio of the silanol precursor to the alkaline substance [silanol precursor / alkaline substance] is preferably 5 or more, more preferably 8 or more, even more preferably 10 or more, from the viewpoint of densifying the outer shell of the hollow silica particle precursor, and is preferably 40 or less, more preferably 35 or less, even more preferably 31 or less, even more preferably 29 or less.

[0041] The alkaline substance may contain, in addition to the hydroxide salt of the quaternary ammonium, for example, an alkali metal salt or an alkaline earth metal salt. In order to reduce the content of alkali metals and alkaline earth metals in the resulting hollow silica particles, the total content of alkali metals and alkaline earth metals relative to the silanol precursor is 50 ppm by mass or less, preferably 30 ppm by mass or less, and more preferably 10 ppm by mass or less, calculated as silica (SiO).

[0042] By mixing an alkaline substance with cationic surfactant B and contacting it with a silanol precursor, hollow silica particles with a small maximum particle size and an appropriate coefficient of variation can be obtained. The contact of the mixture of alkaline substance and cationic surfactant B with the silanol precursor may be carried out by adding the mixture of 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 alkaline substance and cationic surfactant B. However, from the viewpoints of increasing porosity and productivity by increasing the synthesis concentration, it is preferable to add the mixture of alkaline substance and cationic surfactant B to a reaction system containing the silanol precursor.

[0043] 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 from the viewpoint of densifying the outer shell of the hollow silica particle precursor, from 0° C. to 100° C. For example, when orthosilicate ethyl ester or pyrosilicate ethyl ester is used as the silanol precursor, the temperature is preferably from 20° C. to 45° C., and when orthosilicate methyl ester or pyrosilicate methyl ester is used, the temperature is preferably from 0° C. to 20° C.

[0044] 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.

[0045] (Hollow silica particle precursor) The hollow silica particle precursor is a composite silica particle having a silica-containing shell and a hydrophobic liquid inside the shell, in which surfactant-templated pores are formed radially toward the particle center.

[0046] [Process C] In step C, the hollow silica particle precursor obtained in step B is heat-treated to decompose and volatilize the cationic surfactant present in the outer shell of the hollow silica particle precursor, volatilize the internal hydrophobic liquid, and then close the pores present in the outer shell by calcination to obtain hollow silica particles with a uniform outer shell.

[0047] The heat treatment temperature in step C is preferably 1000°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 preferably 1200°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.

[0048] The heat treatment time in step C is preferably 15 minutes or longer, more preferably 30 minutes or longer, and even more preferably 45 minutes or longer, from the viewpoint of reducing silanol groups on the surface of the hollow silica particles, and is preferably 3 hours or shorter, more preferably 2 hours or shorter, and even more preferably 1.5 hours or shorter, from the viewpoint of avoiding aggregation of the hollow silica particles.

[0049] [Resin composition] The hollow silica particles of the present invention can be blended with a resin to form a resin composition. The resin to be blended with hollow silica is not particularly limited, but in order to provide a resin composition with low dielectric constant, it is preferable to use resins with low relative dielectric constant and dielectric loss tangent, such as polyparaphenylene resin, liquid crystal polymer resin, epoxy resin using a curing agent selected from ester- or ether-based curing agents, acid anhydride-based curing agents, and imidazole-based curing agents, bismaleimide resin, cycloolefin resin, and fluorine-based resin, or derivatives of these resins.

[0050] The amount of hollow silica particles 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 loss 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 the viscosity and processability of the resin composition.

[0051] In order to be 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 5.8 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 2.7 or less, even more preferably 2.65 or less. Furthermore, when the increase in the dielectric constant at a measurement frequency of 5.8 GHz when the resin composition is stored at a temperature of 60°C and a humidity of 90% for 5 days is 0.15 or less, it can be said that the change in the dielectric constant of the resin composition over time under high temperature and high humidity conditions is small, and the increase is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.0. The relative dielectric constant of the resin composition can be determined by the method described in the examples.

[0052] In order to be 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 5.8 GHz of preferably 0.0001 or more, more preferably 0.005 or more, even more preferably 0.001 or more, and preferably 0.0090 or less, more preferably 0.0089 or less, even more preferably 0.0088 or less. Furthermore, when the resin composition is stored at a temperature of 60°C and a humidity of 90% for 5 days, if the increase in the dielectric loss tangent at a measurement frequency of 5.8 GHz is 0.0020 or less, it can be said that the change over time in the dielectric loss tangent of the resin composition under high temperature and high humidity conditions is small, and the increase is preferably 0.0010 or less, more preferably 0.0005 or less, and even more preferably 0.0000. The dielectric loss tangent of the resin composition can be determined by the method described in the examples.

[0053] [Insulating material] By including the resin composition of the present invention in an insulating material, it is possible to obtain an insulating material that can reduce 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 for connectors, and coating materials for electric wires. [Example]

[0054] In the examples and comparative examples described later, various measurements of hollow silica particles and resin compositions were carried out by the following methods.

[0055] [Measurement method] (Measurement of average particle size and coefficient of variation of hollow silica particles) The average particle size of the hollow silica particles 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) × 100 The maximum particle size was defined as the particle size at 99% of the cumulative frequency distribution.

[0056] (Measurement of the density of hollow silica particles) The measurement was carried out using a true density measuring device (Quantachrome: ULTRAPYCNMETER1200e) with nitrogen as the measurement gas.

[0057] (Measurement of porosity of hollow silica particles) The true density of the silica particles was calculated using the density measured by the above method according to the following formula: 3 It was decided. Porosity (%) = [1 - (true density of hollow silica particles / true density of silica particles)] x 100

[0058] (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 (Shimadzu Corporation, product name "Flowsorb III2305") The sample was pretreated by heating at 200°C for 15 minutes.

[0059] (Measurement of moisture absorption amount after storage under high temperature and humidity conditions) The weight of an empty 24 mL weighing bottle was measured, and hollow silica particles were added and the weight was then measured. The weighing bottle containing the measured hollow silica particles was placed in a thermo-hygrostat (manufactured by Espec Corporation, product name "Small Environmental Tester SH-241") maintained at a temperature of 60°C and a humidity of 90% RH and stored for 5 days. After 5 days of storage, the weighing bottle containing the hollow silica particles was removed from the thermo-hygrostat and cooled to 25°C in a desiccator, and its weight was measured. The amount of moisture absorption was calculated from the weight of the weighing bottle containing the hollow silica particles before and after storage and the weight of the empty weighing bottle. Weight of hollow silica particles before moisture absorption = Weight of weighing bottle containing hollow silica before storage - Weight of empty weighing bottle Weight of hollow silica particles after moisture absorption = Weight of weighing bottle containing hollow silica after storage - Weight of empty weighing bottle Moisture absorption amount (%) = {(weight of hollow silica particles after moisture absorption / weight of hollow silica particles before moisture absorption) - 1} * 100

[0060] (Measurement of the relative permittivity 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 5.8 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 immediately after production so that they were all within the measurement range (6.75 mm to 36.35 mm from the bottom). The weight of the hollow silica particles was calculated by measuring the weight before and after filling, and the volume of the hollow silica particles filled in the Teflon tube was determined from the filling weight and specific gravity of the hollow silica particles. The relative dielectric constant and dielectric loss tangent were determined from the difference between the measurement value of an empty Teflon tube not filled with hollow silica particles and the measurement value of a Teflon tube filled with hollow silica particles, which was used as a blank. The relative dielectric constant and dielectric loss tangent were also measured for hollow silica particles stored for 5 days in a thermo-hygrostat (manufactured by Espec Corporation, product name "Small Environmental Tester SH-241") maintained at a temperature of 60°C and a humidity of 90% Rh.

[0061] (Measurement of relative permittivity and dielectric loss tangent of resin composition) The relative permittivity and dielectric loss tangent of the resin composition were measured at a frequency of 5.8 GHz by the cavity resonator perturbation method immediately after molding the resin composition into a diameter of 2.5 mm and a length of 4 mm, in the same manner as in "Measurement of relative permittivity and dielectric loss tangent of hollow silica particles." The resin composition molded into a size of 2.5 mm in diameter and 4 mm in length was placed in a thermo-hygrostat (manufactured by Espec Corporation, product name "Small Environmental Tester SH-241") maintained at a temperature of 60°C and a humidity of 90% Rh and stored for 5 days. The relative dielectric constant and dielectric loss tangent of this resin composition were also measured in the same manner.

[0062] (Evaluation of Appearance of Resin Composition) The presence or absence of granular shapes on the surface of the resin composition was confirmed by visual inspection. In Table 2, the resin composition for which no granular shapes were observed on the surface is indicated by "◯", and the resin composition for which granular shapes were observed is indicated by "X".

[0063] (Measuring the mean particle size of droplets containing hydrophobic liquid in emulsion) 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 determined by measuring the particle diameter of droplets containing the hydrophobic liquid using a light scattering device, Zetasizer Nano ZS (Malvern Panalytical).

[0064] [Production of hollow silica particles] Example 1 388.6 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 trimethylammonium 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. Next, 13192.5 g of ion-exchanged water, 138.1 g of emulsion A, 125.6 g of Courtamine 24P (manufactured by Kao Corporation; containing 27.5% by weight of lauryltrimethylammonium chloride), and 3120.8 g of orthosilicate ethyl ester (manufactured by Asahi Kasei Silicones Co., Ltd.; TEOS999) were added to a reaction vessel and heated to 40°C with stirring. After stirring for 10 minutes, preparation B was obtained. Next, 221.5 g of AH212-CS (manufactured by Yokkaichi Synthetic Co., Ltd.; containing 50% by weight of dimethylbis(2-hydroxyethyl)ammonium hydroxide) and 711.6 g of Courtamine 24P were uniformly mixed to obtain preparation C. Preparation C was added to preparation B at a constant rate, and then the mixture was stirred at 40°C for 3 hours to obtain a cloudy white liquid D. Next, the resulting cloudy liquid D was filtered using 5C filter paper (manufactured by Advantec Toyo Co., 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 for 1 hour at 1100° C. to obtain hollow silica particles. The physical properties of the obtained hollow silica particles are shown in Tables 1 and 2.

[0065] Example 2 342.2 g of ion-exchanged water, 150 g of dodecane (Kishida Chemical Co., Ltd.: primary n-dodecane), and 7.8 g of Kotamin 2285 (Kao Corporation: containing 58% by mass of behenyltrimethylammonium chloride) were mixed and stirred to obtain emulsion A. The volume average particle size of the particles in the obtained emulsion A was 0.5 μm. Hollow silica particles were obtained by the same procedures as in Example 1, except that the amount of ion-exchanged water was 13,146.5 g and the amount of emulsion A was 184.1 g. The physical properties of the obtained hollow silica particles are shown in Tables 1 and 2.

[0066] Example 3 A reaction vessel equipped with a stirrer was charged with 2670 g of methanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 248 g of Catiogen TML (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.: containing 30% by mass of dodecyltrimethylammonium chloride), 80 g of hexane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 52.7 g of a 25% aqueous solution of tetramethylammonium (manufactured by Seichem Asia Co., Ltd.), and the temperature was adjusted to 10°C while stirring to prepare solution A. Then, 8000 g of ion-exchanged water adjusted to 15°C was added to solution A while stirring, and the mixture was then stirred at 15°C for 10 minutes to obtain an O / W emulsion. Next, 170 g of tetramethoxysilane (manufactured by Tama Chemicals Co., Ltd.) was added to the O / W emulsion, and then the mixture was stirred at 15° C. for 10 minutes to obtain a cloudy liquid. The resulting cloudy liquid was then filtered using 5C filter paper (manufactured by Advantec Toyo Co., Ltd.), washed with water, and dried at 110° C. to obtain white hollow silica particle precursors. The obtained hollow silica particle precursor was calcined for 1 hour at 1100° C. to obtain hollow silica particles. The physical properties of the obtained hollow silica particles are shown in Tables 1 and 2.

[0067] Comparative Example 1 A 2L separable flask was charged with 600 g of ion-exchanged water, 99.5 g of methyl methacrylate, and 0.5 g of methacryloyloxyethyltrimethylammonium chloride, and the internal temperature was raised to 70° C. Next, a solution prepared by dissolving 0.5 g of 2,2′-azobis(2-amidinopropane) dihydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-50) as a water-soluble polymerization initiator in 5 parts of ion-exchanged water was added, followed by heating and stirring at 75° C. for 3 hours and cooling. After cooling, the aggregates were filtered from the resulting mixture using a 200-mesh sieve (openings approximately 75 μm) to obtain a suspension of cationic polymer particles (solid content (active content) 14% by mass, average primary particle diameter 270 nm). Next, 6 kg of water, 2 kg of methanol, 45 g of a 1 M aqueous solution of sodium hydroxide, 35 g of dodecyltrimethylammonium bromide, and 33 g of the suspension of cationic polymer particles obtained above were placed in a 10 L flask and stirred, and 34 g of tetramethoxysilane was slowly added to the aqueous solution, followed by stirring for 5 hours and then aging for 12 hours. The resulting white precipitate was then filtered through a membrane filter with a pore size of 0.2 μm, washed with 10 L of water, and dried at 100° C. for 5 hours. The resulting dried powder was calcined at 600° C. for 2 hours to obtain hollow silica particles. The physical properties of the resulting hollow silica particles are shown in Tables 1 and 2. The obtained hollow silica particles had micropores in the silica shell that allowed nitrogen gas to pass through, and the porosity could not be measured using a true density measuring device. Therefore, the porosity values ​​shown in Table 1 were estimated from transmission electron microscope images.

[0068] Comparative Example 2 A reaction vessel equipped with a stirrer (Taiatsu Glass Kogyo Co., Ltd.: TEM-D1500M) was charged with 200 g of silica (Admafine SO-C2, manufactured by Admatechs Co., Ltd.), 640 g of a 25% aqueous solution of tetramethylammonium hydroxide (Sachem Asia Co., Ltd.: pH 14), and 160 g of ion-exchanged water, 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, yielding a silica solution (silica concentration: 20% by mass, silica / organic alkali (molar ratio) = 1.9). Next, 1000 g of the prepared silica solution and 1000 g of ion-exchanged water were mixed until homogeneous, yielding a diluted silica solution. The resulting diluted silica solution was spray-dried using a spray dryer (Fujisaki Electric Co., Ltd.: Micromist Spray Dryer) (spray-drying conditions: hot air inlet temperature: 130°C, nozzle flow rate: 100 L / min, spray volume: 25 mL / min) to obtain a dried powder. The dried powder obtained by spray drying was then calcined at 1100°C for 1 hour to obtain hollow silica particles. The physical properties of the resulting hollow silica particles are shown in Tables 1 and 2.

[0069] Comparative Example 3 Hollow silica particles were synthesized in the same manner as in Example 1, except that AH212-CS was replaced with an aqueous sodium hydroxide solution (13.2% by mass, 22.2 mL, 73.1 mmol) and the firing temperature was changed to 1000°C. The physical properties of the obtained hollow silica particles are shown in Tables 1 and 2. The obtained hollow silica particles contained 820 ppm of sodium.

[0070] In all of the hollow silica particles of Examples 1 to 3 and Comparative Examples 1 to 3, no diffraction peaks derived from crystalline silica were observed in powder X-ray diffraction, and the particles were amorphous.

[0071] [Table 1]

[0072] [Table 2]

[0073] As shown in the results in Table 1, the hollow silica particles of the present invention showed a low increase in particle density of 8% or less when heat-treated at 1100°C for 1 hour, and the moisture absorption amount of the hollow silica particles when stored for 5 days at a temperature of 60°C and a humidity of 90% was 1.0% by mass or less. On the other hand, the hollow silica particles of Comparative Examples 1 to 3 showed a high increase in particle density when heat-treated at 1100°C for 1 hour, and a large moisture absorption amount when stored for 5 days at a temperature of 60°C and a humidity of 90%. Furthermore, as shown in the results in Table 2, the dielectric constant and dielectric loss tangent of the hollow silica particles of the present invention after storage for 5 days at a temperature of 60°C and a humidity of 90% remained low compared to those immediately after production, and changes over time were very small. In contrast, the hollow silica particles of Comparative Examples 1 to 3 had a low dielectric constant, but the dielectric loss tangent of the resin compositions of Comparative Examples 1 and 2 was high. Furthermore, the dielectric loss tangent of the resin compositions of Comparative Examples 1 to 3 after storage for 5 days at a temperature of 60°C and a humidity of 90% was significantly high.

[0074] [Production of Resin Composition] Example 4 23.7 g of epoxy resin (manufactured by Mitsubishi Chemical Corporation: jER™ 828), 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) at 1400 rpm under atmospheric pressure for 1 minute and at 2000 rpm under a reduced pressure of 0.3 kPa for 5 minutes to obtain an epoxy resin kneaded liquid. 2 g of the obtained epoxy resin kneaded liquid and 1.2 g of the hollow silica particles obtained in Example 1 were kneaded in a kneader (Thinky Corporation: Planetary Vacuum Mixer) at atmospheric pressure for 1 minute at 1400 rpm and then at a reduced pressure of 0.3 kPa for 5 minutes at 2000 rpm to obtain an epoxy resin hollow silica particle kneaded liquid. The obtained epoxy resin / hollow silica particle mixture was cured at 160° C. for 6 hours to obtain a resin composition. The physical properties of the obtained resin composition are shown in Table 3.

[0075] Example 5 A resin composition was obtained in the same manner as in Example 4, except that 1.2 g of the hollow silica particles obtained in Example 2 was used instead of 1.2 g of the hollow silica particles obtained in Example 1. The physical properties of the obtained resin composition are shown in Table 3.

[0076] Example 6 A resin composition was obtained in the same manner as in Example 4, except that 2.0 g of the hollow silica particles obtained in Example 3 was used instead of 1.2 g of the hollow silica particles obtained in Example 1. The physical properties of the obtained resin composition are shown in Table 3.

[0077] Comparative Example 4 A resin composition was obtained in the same manner as in Example 4, except that 3.4 g of the hollow silica particles obtained in Comparative Example 1 was used instead of 1.2 g of the hollow silica particles obtained in Example 1. The physical properties of the obtained resin composition are shown in Table 3.

[0078] Comparative Example 5 A resin composition was obtained in the same manner as in Example 4, except that 2.7 g of the hollow silica particles obtained in Comparative Example 2 was used instead of 1.2 g of the hollow silica particles obtained in Example 1. The physical properties of the obtained resin composition are shown in Table 3.

[0079] Comparative Example 6 A resin composition was obtained in the same manner as in Example 4, except that 2.4 g of the hollow silica particles obtained in Comparative Example 3 was used instead of 1.2 g of the hollow silica particles obtained in Example 1. The physical properties of the obtained resin composition are shown in Table 3.

[0080] In Examples 4 to 6 and Comparative Examples 4 to 6, the volume ratio of the resin to the hollow silica particles is the same.

[0081] [Table 3]

[0082] As shown in Table 3, the resin composition containing the hollow silica particles of the present invention was able to reduce the dielectric constant and dielectric loss tangent at a measurement frequency of 5.8 GHz. Furthermore, the dielectric constant and dielectric loss tangent remained unchanged after storage for 5 days at a temperature of 60°C and a humidity of 90%. Furthermore, because the average particle diameter of the hollow silica particles was small, a resin composition with excellent appearance was obtained. On the other hand, the resin compositions of Comparative Examples 4 to 6 containing the hollow silica particles of Comparative Examples 1 to 3 had low relative dielectric constants, but the resin compositions of Comparative Examples 4 and 5 had high dielectric loss tangents. Furthermore, the resin compositions of Comparative Examples 4 to 6 had significantly high dielectric loss tangents after being stored at a temperature of 60°C and a humidity of 90% for 5 days. From the above, it is believed that an insulating material containing the resin composition of the present invention can be used as an insulating material that changes little over time in high frequency circuits that handle high frequency radio waves.

Claims

1. The average particle size is 0.5 μm or more and 3.0 μm or less, The increase rate of particle density when heat treated at 1100°C for 1 hour is 8% or less, Hollow silica particles having a coefficient of variation of an average particle size of 15% or more and 300% or less.

2. 2. The hollow silica particles according to claim 1, wherein the hollow silica particles have a dielectric constant of 2.5 or less and a dielectric dissipation factor of 0.0070 or less at a measurement frequency of 5.8 GHz, and when stored at a temperature of 60°C and a humidity of 90% for 5 days, an increase in the dielectric constant is 0.15 or less and an increase in the dielectric dissipation factor is 0.0020 or less.

3. The hollow silica particles according to claim 1 or 2, having a porosity of 45% by volume or more and 80% by volume or less.

4. 4. The hollow silica particles according to claim 1, wherein the amount of moisture absorbed after storage for 5 days at a temperature of 60° C. and a humidity of 90% is 1.0 mass % or less of the weight of the silica particles.

5. BET specific surface area is 30m ２ The hollow silica particles according to any one of claims 1 to 4, wherein the average molecular weight of the hollow silica particles is 1 / g or less.

6. The hollow silica particles according to any one of claims 1 to 5, wherein the maximum particle size is 5.0 µm or less.

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

8. 8. The resin composition according to claim 7, wherein the resin composition has a dielectric constant of 2.8 or less and a dielectric dissipation factor of 0.0090 or less at a measurement frequency of 5.8 GHz, and when stored at a temperature of 60°C and a humidity of 90% for 5 days, an increase in the dielectric constant is 0.15 or less and an increase in the dielectric dissipation factor is 0.0020 or less.

9. An insulating material comprising the resin composition according to claim 7 or 8.

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