Method for manufacturing hollow silica particles

Abstract

The present invention relates to a method for producing hollow silica particles having a small average particle diameter, a low content of non-hollow silica fine particles, and low relative permittivity and dielectric loss tangent, as well as hollow silica particles obtained by the production method, a resin composition containing the hollow silica particles, and an insulating material. [Solution] A method for producing hollow silica particles, comprising the following steps. Step 1: A step to obtain an aqueous dispersion of a hydrophobic liquid by mixing an aqueous solvent, a hydrophobic liquid, and cationic surfactant A. Step 2: A step to produce a hollow silica particle precursor by mixing the aqueous dispersion of the hydrophobic liquid obtained in Step 1, a silanol precursor, a cationic surfactant B containing a cationic surfactant b having an alkyl group with 14 to 16 carbon atoms, and ammonia. Step 3: A process of heat-treating the hollow silica particle precursor obtained in Step 2 at a temperature between 1000°C and 1200°C.

Description

[Technical Field]

[0001] The present invention relates to a method for producing hollow silica particles, hollow silica particles, a resin composition containing the same, and an insulating material. [Background technology]

[0002] High-speed communication technologies such as 5G and radar used in autonomous driving are considering the use of high frequencies of several tens of GHz. In high-frequency circuits that handle such high-frequency radio waves, insulating materials with low dielectric constant and low dielectric loss tangent are required to reduce transmission loss and transmission delay, and similar requirements are also placed on silica particles incorporated into insulating materials to improve thermal properties. Therefore, the use of hollow silica particles is currently being considered as a way to reduce the dielectric constant of silica particles. Furthermore, miniaturization of high-frequency circuits is desired, and therefore, smaller particle sizes are also required for these silica particles.

[0003] For example, Patent Document 1 describes a method for producing hollow silica particles, in which a mixture containing a hydrophobic organic compound, polyvinyl alcohol, and an aqueous solvent is pressurized by a high-pressure emulsification method, and an emulsified oil droplet aqueous dispersion containing the hydrophobic organic compound is mixed with a silica source in the presence of a cationic surfactant, and hollow silica particles with an average particle diameter of 500 to 700 nm produced by this method are described. Furthermore, Patent Document 2 describes a method for producing hollow silica particles, comprising preparing an aqueous emulsion of a hydrophobic liquid using cationic surfactant A, synthesizing a hollow silica particle precursor by adding a silanol precursor, an alkaline substance, and cationic surfactant B, and heat-treating the obtained hollow silica particle precursor; and hollow silica particles produced by this method having an average particle diameter of 0.5 μm or more and 3.0 μm or less, a total content of alkali metals and alkaline earth metals of 50 ppm or less, a relative permittivity of 2.5 or less at 5.8 GHz, and a dielectric loss tangent of 0.0050 or less. Furthermore, Patent Document 3 describes hollow silica particles comprising a shell layer containing silica and having a space inside the shell layer, wherein the relative permittivity at 1 GHz is 1.3 to 5.0 and the dielectric loss tangent at 1 GHz is 0.0001 to 0.05. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-55082 [Patent Document 2] International Publication No. 2023 / 140378 [Patent Document 3] International Publication No. 2021 / 172294 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the hollow silica particles described in Patent Document 1 contain silica microparticles with zero or low porosity. As the porosity decreases, the relative permittivity increases, and the number of silanols on the particle surface increases, which leads to a problem of high dielectric loss tangent. Furthermore, although the hollow silica particles described in Patent Document 2 have a small average particle diameter and low relative permittivity and dielectric loss tangent, they contain non-hollow silica microparticles such as perfectly spherical solid microparticles and crushed fragments. Due to the influence of these particles, the silanol number increases, and therefore the dielectric loss tangent is not yet at a satisfactory level. Furthermore, Patent Document 3 describes how hollow silica particles containing a metal selected from alkali metals or alkaline earth metals are fired, causing the specific surface area to decrease, promoting the condensation of silanol groups, and reducing the dielectric loss tangent by decreasing the number of silanol groups contained in the hollow silica particles. However, as described in Japanese Patent Application Publication No. 2016-94527, for example, alkali metals are known to reduce the insulating properties of resin compositions, and the hollow silica particles described in Patent Document 3 cannot be used as insulating materials. Moreover, particles with promoted silanol group condensation have poor crushability, and the smoothness of the resin composition is impaired due to the remaining coarse particles. On the other hand, reducing the content of alkali metals or alkaline earth metals presents the problem that the dielectric constant of the insulating material cannot be sufficiently reduced.

[0006] In other words, to the best of our knowledge, hollow silica particles with a small particle size, few non-hollow silica microparticles, and sufficiently low relative permittivity and dielectric loss tangent have not been obtained to date, suitable for use as insulating material in fine high-frequency circuits. The present invention relates to a method for producing hollow silica particles having a small average particle diameter, a low content of non-hollow silica fine particles, and low relative permittivity and dielectric loss tangent, as well as hollow silica particles obtained by the production method, a resin composition containing the hollow silica particles, and an insulating material. [Means for solving the problem]

[0007] As a result of diligent research, the inventors have found that by using a cationic surfactant having a specific structure as a surfactant to generate hollow silica particle precursors, and by using ammonia as a hydrolysis catalyst when generating silanol compounds from silanol precursors, the generation of particles without internal cavities can be suppressed, thereby achieving the above objective. Furthermore, the inventors have found that hollow silica particles having a specific average particle size and a low proportion of non-hollow silica particles within a specific particle size range, and a resin composition containing these hollow silica particles, achieve the above objective, and that this resin composition serves as a good insulating material. The present invention relates to the following [1] to [4]. [1] A method for producing hollow silica particles, comprising the following steps. Step 1: A step of mixing an aqueous solvent, a hydrophobic liquid, and a cationic surfactant A to obtain an aqueous dispersion of the hydrophobic liquid Step 2: A step of mixing the aqueous dispersion of the hydrophobic liquid obtained in Step 1, a silanol precursor, a cationic surfactant B containing a cationic surfactant b having an alkyl group with 14 or more and 16 or less carbon atoms, and ammonia to generate a hollow silica particle precursor Step 3: A step of heat-treating the hollow silica particle precursor obtained in Step 2 at a temperature exceeding 1000 °C and not exceeding 1200 °C [2] Hollow silica particles satisfying the following conditions (1) to (2). Condition (1): When the volume-based average particle diameter of the hollow silica particles is (d), the standard deviation of the volume-based particle size distribution is (σ), and the particle diameter smaller than the volume-based average particle diameter (d) by the standard deviation (σ) of the volume-based particle size distribution is (D), the number ratio (R) of the particles having a porosity of 10% or less among the particles having a particle diameter of (D) or less in the hollow silica particles is 0.5 or less Condition (2): The volume-based average particle diameter (d) measured by the Coulter counter method is 0.05 μm or more and 3.0 μm or less [3] A resin composition containing the hollow silica particles described in [2]. [4] An insulating material containing the resin composition described in [3].

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a method for producing hollow silica particles having a small average particle diameter, a small content of non-hollow silica fine particles, and low relative permittivity and dielectric loss tangent, hollow silica particles obtained by the production method, a resin composition containing the hollow silica particles, and an insulating material.

Embodiments for Carrying Out the Invention

[0009] [Method for Producing Hollow Silica Particles] The method for producing hollow silica particles of the present invention includes the following steps. Step 1: A step to obtain an aqueous dispersion of a hydrophobic liquid by mixing an aqueous solvent, a hydrophobic liquid, and cationic surfactant A. Step 2: A step to produce a hollow silica particle precursor by mixing the aqueous dispersion of the hydrophobic liquid obtained in Step 1, a silanol precursor, a cationic surfactant B containing a cationic surfactant b having an alkyl group with 14 to 16 carbon atoms, and ammonia. Step 3: A process of heat-treating the hollow silica particle precursor obtained in Step 2 at a temperature between 1000°C and 1200°C. Hereinafter, the method for producing hollow silica particles, including steps 1 to 3 described above, will also be referred to as the manufacturing method of the present invention.

[0010] The manufacturing method of the present invention yields hollow silica particles with a small average particle size, a low content of non-hollow silica fine particles, and low relative permittivity and dielectric loss tangent. The reason for this is not entirely clear, but it is thought to be as follows. Typically, when strong alkalis such as quaternary ammonium salts, alkali hydroxides, and various amines are used as hydrolysis catalysts to promote the hydrolysis of alkoxysilane compounds, which are silanol precursors, the pH in the reaction solution becomes locally high. This excessively promotes the hydrolysis of the silanol precursor, causing condensation reactions to occur not only on the surface of the dispersion of hydrophobic liquid dispersed by cationic surfactant A, which is the source of hollow silica particle precursors. This makes it easier for silica particles that do not contain hydrophobic liquid to be generated, and these become non-hollow silica microparticles. On the other hand, the manufacturing method of the present invention uses ammonia, a weakly alkaline compound, as a hydrolysis catalyst added to obtain hollow silica particle precursors by hydrolyzing the silanol precursor. This suppresses the local rise in pH of the reaction solution and controls the hydrolysis of the silanol precursor, thereby suppressing the generation of silica particles that do not contain hydrophobic liquids. Furthermore, when a cationic surfactant with fewer than 14 C atoms in its alkyl group is typically used as the cationic surfactant mixed with the silanol precursor, the critical micelle concentration increases, requiring a larger amount of surfactant for the reaction. Conversely, when a cationic surfactant with more than 16 C atoms is used, the solubility of the surfactant in the reaction solution decreases. In both cases, the surfactant concentration becomes locally excessive upon addition, which is thought to be a factor in the condensation reaction of the silanol precursor hydrolyzed around the surfactant micelles, thus making it easier for non-hollow silica microparticles to be generated. On the other hand, in the manufacturing method of the present invention, since a cationic surfactant B containing a cationic surfactant b having an alkyl group with 14 to 16 carbon atoms is used as the cationic surfactant to be mixed with the silanol precursor, the amount and solubility of the surfactant used in the reaction solution can be controlled to an appropriate range, and the generation of non-hollow silica fine particles can be suppressed. As a result of the above, the manufacturing method of the present invention can reduce the content of non-hollow silica fine particles, thereby enabling the production of hollow silica particles with low relative permittivity and dielectric loss tangent.

[0011] <Process 1> Step 1 is a step of mixing an aqueous solvent, a hydrophobic liquid, and cationic surfactant A to obtain an aqueous dispersion of the hydrophobic liquid.

[0012] (aqueous medium) The aqueous medium mixed in step 1 contains water. Examples of water contained in aqueous media include distilled water, deionized water, and ultrapure water. Furthermore, from the viewpoint of more uniform and stable dispersion of hydrophobic liquids, aqueous media may also contain organic solvents that are compatible with water. Examples of organic solvents that are compatible with water include lower alcohols such as methanol, ethanol, and isopropyl alcohol, and low molecular weight ketones such as acetone and methyl ethyl ketone. From the viewpoint of reducing the solubility of hydrophobic liquids 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.

[0013] (Cationic surfactant A) From the viewpoints of facilitating the accumulation of the micelles of the silanol precursor and the cationic surfactant B on the surface of the aqueous dispersion of the hydrophobic liquid in Step 2 and decomposing and volatilizing the cationic surfactant A in Step 3, the cationic surfactant A is preferably a quaternary ammonium salt, and more preferably at least one selected from the group consisting of quaternary ammonium salts represented by the following general formula (1) or general formula (2). [R 1 R 3 3N] + X ― (1) [R 1 R 2 R 3 2N] + X ― (2)

[0014] In general formula (1) and general formula (2), R 1 and R 2 each independently represent 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 the plurality of R 3 may each be different groups, and X ― represents a monovalent anion. Examples of the alkyl group having 4 to 22 carbon atoms include various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, various tetradecyl groups, various hexadecyl groups, various octadecyl groups, various eicosyl groups, various docosyl groups, and the like. 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. In general formula (1) and general formula (2), R 3 is preferably a methyl group from the viewpoint of availability.

[0015] X in general formulas (1) and (2) ―From the viewpoint of easily decomposing and volatilizing during firing, it is preferably at least one selected from monovalent anions such as halogen ions, hydroxide ions, and nitrate ions. ― From the viewpoint of availability, halide ions are more preferred, and chloride ions are even more preferred.

[0016] Examples of alkyltrimethylammonium salts 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.

[0017] Examples of dialkyldimethylammonium salts represented by general formula (2) include dibutyldimethylammonium chloride, dihexyldimethylammonium chloride, dioctyldimethylammonium chloride, dihexyldimethylammonium bromide, dioctyldimethylammonium bromide, dilauryldimethylammonium bromide, and ditetradecyldimethylammonium bromide.

[0018] Cationic surfactant A preferably contains one or more selected from tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, stearyltrimethylammonium chloride, and behenyltrimethylammonium chloride, more preferably containing one or more selected from stearyltrimethylammonium chloride and behenyltrimethylammonium chloride, and even more preferably containing behenyltrimethylammonium chloride, from the viewpoint of facilitating the accumulation of micelles of the silanol precursor and cationic surfactant B on the surface of the hydrophobic liquid dispersion in step 2, and from the viewpoint of facilitating the decomposition and volatilization of cationic surfactant A in step 3.

[0019] The content of one or more selected from tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, stearyltrimethylammonium chloride, and behenyltrimethylammonium chloride in cationic surfactant A is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and even more preferably 100% by mass, from the viewpoint of facilitating the accumulation of micelles of the silanol precursor and cationic surfactant B on the surface of the hydrophobic liquid dispersion in step 2, and from the viewpoint of facilitating the decomposition and volatilization of cationic surfactant A in step 3.

[0020] (Hydrophobic liquid) The hydrophobic liquid is preferably one that can form emulsion droplets (emulsified oil droplets) in water. Furthermore, from the viewpoint of using an aqueous solvent as a dispersion medium and improving the utilization efficiency of the hydrophobic liquid, the temperature range in which it is in a liquid state is preferably 0 to 100°C, and more preferably 20 to 90°C. Examples of hydrophobic liquids include those described in paragraphs

[0015] to

[0023] of Japanese Patent Publication No. 2016-121060. Among these, from the viewpoint of ease of preparing aqueous dispersions of hydrophobic liquids, hydrocarbons having 6 to 18 carbon atoms are preferred, more preferably hydrocarbons having 8 to 14 carbon atoms, and even more preferably dodecane.

[0021] In step 1, the mass ratio of the hydrophobic liquid to the aqueous medium [hydrophobic liquid / aqueous medium] is preferably 0.1 or higher, more preferably 0.15 or higher, even more preferably 0.2 or higher, and preferably 0.8 or lower, more preferably 0.5 or lower, and even more preferably 0.3 or lower, from the viewpoint of ensuring that the particle size of the resulting hydrophobic liquid droplets is within an appropriate range.

[0022] In step 1, the mass ratio of cationic surfactant A to the hydrophobic liquid [cationic surfactant A / hydrophobic liquid] is preferably 0.01 or higher, more preferably 0.05 or higher, and even more preferably 0.07 or higher, from the viewpoint of improving the dispersion stability of the hydrophobic liquid in an aqueous medium, and from the viewpoint of controlling the particle size of the dispersion of the hydrophobic liquid in an aqueous medium, it is preferably 0.20 or lower, more preferably 0.15 or lower, and even more preferably 0.10 or lower.

[0023] 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 droplets containing a hydrophobic liquid is preferably 0.05 μm or more, more preferably 0.10 μm or more, even more preferably 0.15 μm or more, and preferably 1.00 μm or less, more preferably 0.75 μm or less, and even more preferably 0.50 μm or less, from the viewpoint of ensuring that the average particle diameter of hollow silica particles is within a range suitable for use as an insulating material. The volume-average particle size of a droplet containing a hydrophobic liquid can be determined by the method described in the examples.

[0024] <Process 2> Step 2 is a step in which the aqueous dispersion of the hydrophobic liquid obtained in Step 1, a silanol precursor, a cationic surfactant B containing a cationic surfactant b having an alkyl group with 14 to 16 carbon atoms, and ammonia are mixed to produce a hollow silica particle precursor. In step 2, the silanol precursor and cationic surfactant B form micelles, which accumulate on the surface of the hydrophobic liquid droplets. Then, under an alkaline environment due to ammonia, the silanol precursor hydrolyzes to form a silanol compound, and a complex is obtained in which the silanol compound and cationic surfactant B are present on the surface of the hydrophobic liquid droplets. The silanol compound in this complex is thought to condense into silica under an alkaline environment due to ammonia, forming a hollow silica particle precursor on the surface of the hydrophobic liquid droplets that has an outer shell containing silica and cationic surfactant B, and contains the hydrophobic liquid inside. The hollow silica particle precursor also contains cationic surfactant A used in step 1. Furthermore, since ammonia is less alkaline than various amines, there is a risk that the silanol precursor may not be sufficiently hydrolyzed if added together with cationic surfactant B. Therefore, from the viewpoint of rapidly generating the silanol compound formed from the silanol precursor, it is preferable that step 2 involves mixing the aqueous dispersion of the hydrophobic liquid obtained in step 1, cationic surfactant B, and the silanol precursor, then adding ammonia, and further adding cationic surfactant B.

[0025] Step 2 may include steps for isolating the hollow silica particle precursor and drying the hollow silica particle precursor. The hollow silica particles can be isolated, for example, by filtration. The hollow silica particle precursor can be dried, for example, by heating to a temperature of 100°C or higher but below the boiling point of the hydrophobic liquid contained in the hollow silica particle precursor, if the boiling point of the hydrophobic liquid contained in the hollow silica particle precursor is higher than 100°C. If the boiling point of the hydrophobic liquid contained in the hollow silica particle precursor is 100°C or lower, the hollow silica particle precursor can be dried, for example, by freeze-drying.

[0026] (Silanol precursor) Silanol precursors are compounds that produce silanol compounds through hydrolysis of alkoxysilane compounds, etc. Specifically, these 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)

[0027] In general formulas (3) to (7), R 3 Each of these independently represents an organic group in which a carbon atom is directly bonded to a silicon atom, and Y represents a monovalent hydrolyzable group that becomes a hydroxyl group upon hydrolysis.

[0028] In general formulas (4) to (6), R 3 Each of these is independently a hydrocarbon group having 1 to 22 carbon atoms, preferably in which some of the hydrogen atoms are substituted with fluorine atoms. From the viewpoint of improving the utilization efficiency of hydrophobic organic materials, these are preferably alkyl groups, phenyl groups, or benzyl groups having 1 to 22 carbon atoms, more preferably 4 to 18 carbon atoms, and even more preferably 8 to 16 carbon atoms. In general formulas (3) to (7), Y is preferably an alkoxy group having 1 to 8 carbon atoms or a halogen group excluding fluorine, and more preferably an alkoxy group having 2 to 4 carbon atoms. When Y is an alkoxy group having 1 carbon atom or a halogen group excluding fluorine, the hydrolysis reaction rate is too fast, making it difficult for the outer shell of the hollow silica particle precursor to become dense, resulting in large shrinkage during calcination, and thus tending to increase the relative permittivity and dielectric loss tangent of the hollow silica particles. Conversely, alkoxy groups having 5 or more carbon atoms result in a slower hydrolysis rate.

[0029] The silanol precursor is preferably selected from compounds represented by general formulas (3) and (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 formulas (3) and (7) in which Y is an alkoxy group having 2 to 4 carbon atoms, and more preferably from compounds represented by general formulas (3) and (7) in which Y is an ethoxy group. Among these, the silanol precursor is preferably one or more selected from alkyl orthosilicate and alkyl pyrosilicate, and more preferably ethyl orthosilicate and ethyl pyrosilicate. Silanol precursors can be used alone or in combination of two or more types.

[0030] In step 2, the mass ratio of the silanol precursor to the hydrophobic liquid [silanol precursor / hydrophobic liquid] is preferably 10 or more, more preferably 50 or more, even more preferably 100 or more, and preferably 1000 or less, more preferably 700 or less, and even more preferably 500 or less, from the viewpoint of keeping the porosity of the hollow silica particles within an appropriate range.

[0031] (Cationic surfactant B) In the present invention, cationic surfactant B contains cationic surfactant b (hereinafter also simply referred to as "cationic surfactant b") having an alkyl group with 14 to 16 carbon atoms. By containing cationic surfactant b in cationic surfactant B, the dispersion stability of the silanol precursor in step 2 can be enhanced, and the supply rate of the silanol precursor to the surface of the droplets of hydrophobic liquid dispersed by cationic surfactant A and the hydrolysis rate of the silanol precursor by ammonia are balanced, which is thought to efficiently generate hollow silica particle precursors with small particle sizes and suppress the generation of silica particle precursors that do not contain hydrophobic liquid.

[0032] From the viewpoint of efficiently generating hollow silica particle precursors with small particle size by balancing the supply rate of silanol precursors to the surface of the hydrophobic liquid dispersed by cationic surfactant A and the hydrolysis rate of silanol precursors by ammonia, cationic surfactant b is preferably one or more selected from tetradecyltrimethylammonium chloride, tetradecyltriethylammonium chloride, ditetradecyldimethylammonium chloride, hexadecyltrimethylammonium chloride, hexadecyltriethylammonium chloride, and dihexadecyldimethylammonium chloride, more preferably one or more selected from tetradecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride, and even more preferably hexadecyltrimethylammonium chloride.

[0033] Cationic surfactant B may contain other cationic surfactants besides cationic surfactant b. Other cationic surfactants include cationic surfactants other than those exemplified in cationic surfactant A above, which are salts of quaternary ammonium represented by general formula (1) or general formula (2) above, and which have an alkyl group having 14 to 16 carbon atoms.

[0034] The content of cationic surfactant b in cationic surfactant B is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and even more preferably 100% by mass, from the viewpoint of enhancing the dispersion stability of the silanol precursor in step 2, balancing the supply rate of the silanol precursor to the surface of the droplets of hydrophobic liquid dispersed by cationic surfactant A with the hydrolysis rate of the silanol precursor by ammonia, thereby efficiently generating hollow silica particle precursors with small particle sizes, and suppressing the generation of silica particle precursors that do not contain hydrophobic liquid.

[0035] In step 2, the mass ratio of the silanol precursor to the cationic surfactant B [silanol precursor / cationic surfactant B] is preferably 3 or more, more preferably 5 or more, even more preferably 7 or more, and even more preferably 9 or more, from the viewpoint of suppressing the formation of solid fine particles, and from the viewpoint of improving the dispersibility of the hollow silica particle precursor, it is preferably 25 or less, more preferably 20 or less, and even more preferably 18 or less.

[0036] In step 2, the mass ratio of the silanol precursor to ammonia [silanol precursor / ammonia] is preferably 10 or more, more preferably 80 or more, even more preferably 150 or more, and even more preferably 200 or more, from the viewpoint of densifying the outer shell of the hollow silica particle precursor, and preferably 500 or less, more preferably 400 or less, and even more preferably 350 or less, from the viewpoint of efficiently carrying out the condensation reaction of the silanol precursor.

[0037] The temperature at which step 2 is performed can be adjusted as appropriate depending on the type and amount of silanol precursor used, and is preferably 0°C to 100°C from the viewpoint of densifying the outer shell of the hollow silica particle precursor. For example, when using ethyl orthosilicate or ethyl pyrosilicate as the silanol precursor, it is preferably 20°C to 45°C, and when using methyl orthosilicate or methyl pyrosilicate, it is preferably 0°C to 20°C.

[0038] The time required for 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 preferably 24 hours or less, more preferably 20 hours or less, even more preferably 16 hours or less, even more preferably 10 hours or less, and even more preferably 6 hours or less, from the viewpoint of manufacturing efficiency.

[0039] (Hollow silica particle precursor) The hollow silica particle precursor is a composite silica particle produced in step 2 of the manufacturing method of the present invention, having a silica-containing outer shell and containing a hydrophobic liquid internally. The outer shell is thought to have a structure in which the alkyl group of the cationic surfactant B is formed radially toward the particle center.

[0040] <Process 3> Step 3 is a process of heat-treating the hollow silica particle precursor obtained in Step 2 at a temperature between 1000°C and 1200°C. In step 3, it is believed that the cationic surfactant present in the outer shell of the hollow silica particle precursor decomposes and volatilizes, and the hydrophobic liquid inside volatilizes, blocking the pores in the outer shell, thereby forming hollow silica particles with a uniform outer shell.

[0041] The heat treatment temperature in step 3 is preferably 1010°C or higher, more preferably 1030°C or higher, and even more preferably 1050°C or higher, from the viewpoint of reducing silanol groups on the surface of hollow silica particles, and is 1200°C or lower, preferably 1190°C or lower, more preferably 1180°C or lower, and even more preferably 1160°C or lower, from the viewpoint of avoiding aggregation of hollow silica particles.

[0042] The heat treatment 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 hollow silica particles, and preferably 3 hours or less, more preferably 2 hours or less, and even more preferably 1.5 hours or less, from the viewpoint of avoiding aggregation of hollow silica particles.

[0043] The manufacturing method of the present invention may include a step of mixing the hollow silica particles obtained in step 3 with a silane coupling agent in order to hydrophobize the hollow silica particles and improve their kneadability with the resin. There are no particular restrictions on the silane coupling agent used at this time, and any known silane coupling agent can be appropriately selected considering the physical properties of the resin used to knead the hollow silica particles. Among these, N-phenyl-3-aminopropyltrimethoxysilane is preferred from the viewpoint of reducing the dielectric loss tangent of the hollow silica particles treated with the resulting silane coupling agent.

[0044] [Hollow silica particles] The hollow silica particles of the present invention satisfy the following conditions (1) to (2). It is preferable to obtain the hollow silica particles of the present invention by the manufacturing method described above. Condition (1): When (d) is the volume-based average particle diameter of hollow silica particles, (σ) is the standard deviation of the volume-based particle diameter distribution, and (D) is the particle diameter that is smaller than the volume-based average particle diameter (d) by the standard deviation of the volume-based particle diameter distribution (σ), then the number ratio (R) of particles with a particle diameter of (D) or less in the hollow silica particles that have a porosity of 10% or less is 0.5 or less. Condition (2): The volume-based average particle size (d) measured by the Coulter counter method is between 0.05 μm and 3.0 μm.

[0045] <Condition (1)> Condition (1) is as follows: Condition (1): When (d) is the volume-based average particle diameter of hollow silica particles, (σ) is the standard deviation of the volume-based particle diameter distribution, and (D) is the particle diameter that is smaller than the volume-based average particle diameter (d) by the standard deviation of the volume-based particle diameter distribution (σ), then the number ratio (R) of particles with a particle diameter of (D) or less in the hollow silica particles that have a porosity of 10% or less is 0.5 or less. Here, in condition (1), (D) is specifically a value that satisfies the following relationship between (d) being the volume-based average particle diameter and (σ) being the standard deviation of the volume-based particle diameter distribution. (D) (μm) = Volume-based average particle diameter (d) (μm) - Volume-based standard deviation (σ) (μm)

[0046] In the hollow silica particles of the present invention, by satisfying condition (1), the relative permittivity and dielectric loss tangent can be lowered, and furthermore, the relative permittivity and dielectric loss tangent of the resin composition using the hollow silica particles of the present invention can be lowered. In the hollow silica particles of the present invention, the number ratio (R) under condition (1) is preferably 0.45 or less, more preferably 0.40 or less, from the viewpoint of lowering the relative permittivity and dielectric loss tangent. A lower number ratio (R) is preferable because it allows for lower relative permittivity and dielectric loss tangent of hollow silica particles and resin compositions using hollow silica particles. However, from the viewpoint of productivity of hollow silica particles, it is preferably 0.1 or higher, more preferably 0.15 or higher, and even more preferably 0.2 or higher. In the hollow silica particles of the present invention, the number ratio (R) under condition (1) can be adjusted by the mass ratio of the silanol precursor to the cationic surfactant B when producing the hollow silica particles of the present invention, and the content of cationic surfactant b in the cationic surfactant B.

[0047] <Condition (2)> Condition (2) is as follows: Condition (2): The volume-based average particle size (d) measured by the Coulter counter method is between 0.05 μm and 3.0 μm. In the hollow silica particles of the present invention, by satisfying condition (2), the viscosity when blended into a resin composition can be reduced, processability can be maintained, and the appearance when blended into a resin composition can be improved. In the hollow silica particles of the present invention, the volume-based average particle diameter (d) under condition (2) is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more, from the viewpoint of lowering the viscosity when blended into a resin composition and maintaining processability, and from the viewpoint of improving the appearance when blended into a resin composition, it is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.2 μm or less. In the hollow silica particles of the present invention, the volume-based average particle diameter (d) under condition (2) can be adjusted by controlling the particle size of the dispersion in the aqueous medium of the hydrophobic liquid by the mass ratio of cationic surfactant A to the hydrophobic liquid when producing the hollow silica particles of the present invention.

[0048] In hollow silica particles, the volume-based average particle diameter (d), the standard deviation of the volume-based particle diameter distribution (σ), the particle diameter (D), and the number ratio (R) of particles with a particle diameter of (D) or less that have a porosity of 10% or less can be determined by the method described in the examples.

[0049] <Condition (3)> The hollow silica particles of the present invention are preferably further satisfied with the following condition (3). Condition (3): Dielectric loss tangent at a measurement frequency of 10 GHz is 0.0030 or less. In the hollow silica particles of the present invention, by satisfying condition (3), the dielectric loss tangent of the resin composition containing the hollow silica particles can be further reduced. In the hollow silica particles of the present invention, under condition (3), the dielectric loss tangent at a measurement frequency of 10 GHz is preferably 0.0001 or higher, more preferably 0.0005 or higher, and even more preferably 0.0010 or higher, from the viewpoint of the strength of the hollow silica particles, and more preferably 0.0028 or lower, even more preferably 0.0025 or lower, and even more preferably 0.0023 or lower, from the viewpoint of further lowering the dielectric loss tangent of the resin composition. The dielectric loss tangent of hollow silica particles can be determined by the method described in the examples. In the hollow silica particles of the present invention, the dielectric loss tangent under condition (3) can be adjusted by the heat treatment temperature and heat treatment time in step 3 when manufacturing the hollow silica particles of the present invention.

[0050] <Condition (4)> The hollow silica particles of the present invention are preferably further satisfied with the following condition (4). Condition (4): The total content of alkali metals and alkaline earth metals relative to the silica content in hollow silica particles is 50 ppm by mass or less. By further satisfying condition (4) in the hollow silica particles of the present invention, they can be more suitably used as insulating materials. In the hollow silica particles of the present invention, the total content of alkali metals and alkaline earth metals relative to the silica content in the hollow silica particles under condition (4) is preferably 30 ppm by mass or less, more preferably 20 ppm by mass or less, and even more preferably 15 ppm by mass or less, from the viewpoint of suitability for use as an insulating material, and preferably 1 ppb by mass or more, and more preferably 5 ppb by mass or more, from the viewpoint of productivity of hollow silica particles. The total content of alkali metals and alkaline earth metals relative to the silica content in hollow silica particles can be measured by the method described in US EPA METHOD 3051A, and specifically by the method described in the examples. In the hollow silica particles of the present invention, the total content of alkali metals and alkaline earth metals relative to the silica content in the hollow silica particles under condition (4) can be adjusted by the purity of the raw materials used in steps 1 and 2 when producing the hollow silica particles of the present invention, i.e., the amount of alkali metals and alkaline earth metals contained in surfactant A, hydrophobic liquid, water, surfactant B, silanol precursor, and ammonia.

[0051] <Condition (5)> The hollow silica particles of the present invention are preferably further satisfied with the following condition (5). Condition (5): Relative permittivity at a measurement frequency of 10 GHz is 2.5 or less. In the hollow silica particles of the present invention, by further satisfying condition (5), the dielectric constant of the resin composition containing the hollow silica particles can be sufficiently lowered. In the hollow silica particles of the present invention, under condition (5), the relative permittivity at a measurement frequency of 10 GHz is preferably 1.1 or higher, more preferably 1.2 or higher, and even more preferably 1.3 or higher, from the viewpoint of the strength of the hollow silica particles, and from the viewpoint of sufficiently lowering the relative permittivity of the resin composition, it is preferably 2.2 or lower, more preferably 2.0 or lower, and even more preferably 1.9 or lower. The relative permittivity of hollow silica particles can be determined by the method described in the examples. In the hollow silica particles of the present invention, the relative permittivity under condition (5) can be adjusted by controlling the porosity of the hollow silica particles by the mass ratio of the silanol precursor to the hydrophobic liquid when producing the hollow silica particles of the present invention.

[0052] <Condition (6)> The hollow silica particles of the present invention are preferably further satisfied with the following condition (6). Condition (6): Average porosity is 40% or more and 80% or less. In the hollow silica particles of the present invention, by further satisfying condition (6), the dielectric constant of the resin composition containing the hollow silica particles can be sufficiently lowered. In the hollow silica particles of the present invention, the average porosity under condition (6) is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and even more preferably 65% ​​or more, from the viewpoint of lowering the dielectric constant, and preferably 78% or less, more preferably 76% or less, and even more preferably 74% or less, from the viewpoint of the hollow silica particles having sufficient strength. The average porosity of hollow silica particles can be determined by the method described in the examples. In the hollow silica particles of the present invention, the average porosity under condition (6) can be adjusted by controlling the mass ratio of the silanol precursor to the hydrophobic liquid when producing the hollow silica particles of the present invention.

[0053] <Condition (7)> The hollow silica particles of the present invention are preferably further satisfied with the following condition (7). Condition (7): Maximum particle size is 5.0 μm or less. In the hollow silica particles of the present invention, the appearance of the resin composition containing the hollow silica particles can be improved by further satisfying condition (7). In the hollow silica particles of the present invention, the maximum particle diameter under condition (7) is preferably 4.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.5 μm or less, from the viewpoint of improving the appearance of the resin composition, and preferably 1.2 μm or more, more preferably 1.4 μm or more, and even more preferably 1.6 μm or more, from the viewpoint of lowering the viscosity when blended into the resin composition and maintaining processability. The maximum particle size of hollow silica particles can be determined by the method described in the examples. In the hollow silica particles of the present invention, the maximum particle diameter under condition (7) can be adjusted by the heat treatment temperature and heat treatment time in step 3 when manufacturing the hollow silica particles of the present invention.

[0054] <Condition (8)> The hollow silica particles of the present invention are preferably further satisfied with the following condition (8). Condition (8): BET specific surface area is 40m² 2 / g or less In the hollow silica particles of the present invention, by further satisfying condition (8), the dielectric loss tangent of the hollow silica particles can be lowered, and the amount of surface treatment agent used when compounding with a resin composition can be reduced, thereby further lowering the dielectric loss tangent of the resin composition. In the hollow silica particles of the present invention, the BET specific surface area under condition (8) is preferably 30m, from the viewpoint of lowering the dielectric loss tangent of the hollow silica particles, lowering the viscosity when blended into the resin composition and maintaining processability, and reducing the amount of surface treatment agent used when blending into the resin composition and lowering the dielectric loss tangent of the resin composition. 2 / g or less, more preferably 25m 2 / g or less, more preferably 20m 2 It is less than or equal to / g, and from the viewpoint of increasing porosity and further lowering the relative permittivity, preferably 5m 2 / g or more, more preferably 7m 2 / g or more, more preferably 10m 2 It is 1 / g or more. The BET specific surface area of ​​hollow silica particles can be determined by the method described in the examples. In the hollow silica particles of the present invention, the BET specific surface area under condition (8) can be adjusted by the heat treatment temperature and heat treatment time in step 3 when manufacturing the hollow silica particles of the present invention.

[0055] <Condition (9)> The hollow silica particles of the present invention are preferably further satisfied with the following condition (9). Condition (9): The coefficient of variation of the volume-based particle size distribution is 80% or less. In the hollow silica particles of the present invention, by further satisfying condition (9), more hollow silica particles can be incorporated into the resin composition, and the relative permittivity and dielectric loss tangent of the resin composition can be further reduced. In addition, the appearance of the resin composition containing hollow silica particles can be improved. In the hollow silica particles of the present invention, the coefficient of variation of the volume-based particle size distribution under condition (9) is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more, from the viewpoint of incorporating more hollow silica particles into the resin composition and further reducing the relative permittivity and dielectric loss tangent of the resin composition, and from the viewpoint of incorporating more hollow silica particles into the resin composition and further reducing the relative permittivity and dielectric loss tangent of the resin composition, and from the viewpoint of improving the appearance of the resin composition, it is preferably 80% or less, more preferably 75% or less, and even more preferably 50% or less. The coefficient of variation of the volume-based particle size distribution of hollow silica particles can be determined by the method described in the examples. In the hollow silica particles of the present invention, the coefficient of variation of the volume-based particle size distribution under condition (9) can be adjusted by the type of hydrophobic liquid used to produce the hollow silica particles of the present invention, for example, the number of carbon atoms in the case of a hydrocarbon.

[0056] [Resin composition] The resin composition of the present invention contains the hollow silica particles of the present invention described above. Since the resin composition of the present invention contains the hollow silica particles of the present invention described above, it is possible to lower the relative permittivity and dielectric loss tangent while maintaining viscosity and processability.

[0057] While there are no particular limitations on the resin into which hollow silica particles are incorporated, from the viewpoint of low dielectric properties of the resin composition, resins with low relative permittivity and dielectric loss tangent are preferred. Specifically, resins with low relative permittivity and dielectric loss tangent, such as poly(p-phenylene) resins, liquid crystal polymer resins, epoxy resins using curing agents selected from ester or ether-based curing agents, acid anhydride-based curing agents, and imidazole-based curing agents, as well as bismaleimide resins, cycloolefin resins, and fluoropolymer resins, or derivatives of these resins, are preferred.

[0058] 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 lowering the relative permittivity and dielectric loss tangent of the resin composition, and 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.

[0059] From the viewpoint of suitability as an insulating material for high-frequency circuit boards, the relative permittivity of the resin composition of the present invention at a measurement frequency of 10 GHz is preferably 2.8 or less, and more preferably 2.5 or less. Furthermore, a lower relative permittivity is preferable, but from the viewpoint of productivity of hollow silica particles with low relative permittivity, it is preferably 1.1 or more, more preferably 1.5 or more, and even more preferably 2.0 or more. The dielectric constant of the resin composition can be determined by the method described in the examples.

[0060] From the viewpoint of suitability as an insulating material for high-frequency circuit boards, the resin composition of the present invention preferably has a dielectric loss tangent at a measurement frequency of 10 GHz of 0.0090 or less, more preferably 0.0085 or less, and even more preferably 0.0080 or less. Furthermore, a lower dielectric loss tangent is preferable, but from the viewpoint of productivity of hollow silica particles with a low dielectric loss tangent, it is preferably 0.0010 or more, more preferably 0.0030 or more, and even more preferably 0.0050 or more. The dielectric loss tangent of the resin composition can be determined by the method described in the examples.

[0061] [Insulating materials] The insulating material of the present invention includes the resin composition of the present invention described above. By including the resin composition of the present invention in the insulating material, an insulating material that can reduce transmission loss and transmission delay can be obtained. In other words, the insulating material of the present invention includes the resin composition of the present invention. The insulating material can be used, for example, in build-up insulating films, insulating layers for copper-clad laminates, prepregs, sealing materials, insulating components for connectors, and insulation materials for electric wires. [Examples]

[0062] In the examples and comparative examples described later, various measurements of the hollow silica particles and resin composition were performed by the following methods.

[0063] [Measurement method] <Measurement of aqueous dispersions of hydrophobic liquids> (Average particle size of droplets containing a hydrophobic liquid in an aqueous dispersion of a hydrophobic liquid) Approximately 1 mL of an aqueous dispersion of a hydrophobic liquid was placed in a rectangular cell with a path length of 10 mm, and the volume-average particle size of droplets containing the hydrophobic liquid was measured using a light scattering instrument, "Zetasizer Nano ZS" (Malvern Panalytical).

[0064] <Measurement and evaluation of hollow silica particles> (Volume-based mean particle diameter (d) of hollow silica particles, standard deviation (σ) of volume-based particle diameter distribution, maximum particle diameter, coefficient of variation) The volume-based mean particle size and the standard deviation of the volume-based particle size distribution of hollow silica particles were measured and calculated using the Coulter counter method with a Multisizer 4e (Beckman Coulter, Inc., using a 10 μm aperture tube). The dispersion medium used was a mixture of ISOTON2 electrolyte (Beckman Coulter, Inc.) and ethanol (Fujifilm Wako Pure Chemical Industries, Ltd., product name: Ethanol 99.5) in a mass ratio of 50% each. The maximum particle diameter of hollow silica particles was determined as the particle diameter that accounts for 99% of the cumulative frequency distribution, based on the same measurement method as the volume-based average particle diameter described above. The coefficient of variation of hollow silica particles was calculated from the volume-based mean particle diameter and the standard deviation of the volume-based particle diameter distribution obtained from the above measurements using the following formula. Coefficient of variation (%) = Standard deviation of particle size distribution (μm) / Volume-based average particle size (μm) × 100

[0065] (Number ratio (R) of particles with a porosity of 10% or less) [Preparation of samples for measurement] Hollow silica particles were dispersed in ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: Ethanol 99.5), dropped onto elastic carbon (manufactured by Stem Co., Ltd., product name: Elastic Carbon ELS-C10), and dried to prepare a sample for measurement. [Measurement method] The measurement sample was observed using an electrolytic emission high-resolution scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, product name "S-4800") in transmission mode with an acceleration voltage of 30kV, and with image brightness and contrast that allowed the hollow structure to be confirmed. In any field of view where 200 or more hollow silica particles were observed, 100 particles with a particle diameter of (D) or less were selected. Of these 100 particles, the number (N) of particles with a porosity of 10% or less was determined, and the value obtained by dividing (N) by 100 was defined as the number ratio (R). Note that (D) is the particle diameter that is smaller than the volume-based average particle diameter (d) by the volume-based standard deviation (σ), and was calculated using the following formula. (D) (μm) = Volume-based average particle diameter (d) (μm) - Volume-based standard deviation (σ) (μm) Furthermore, the porosity of each observed particle was determined using the following formula. Porosity of individual particles (%) = (Diameter of cavity (μm) / Diameter of hollow silica particle (μm)) 3 ×100

[0066] (Content of alkali metals and alkaline earth metals relative to the silica content in hollow silica particles) 100 mg of hollow silica particles were placed in a platinum crucible, to which 3 mL of concentrated nitric acid, 1 mL of concentrated hydrofluoric acid, and 1 mL of concentrated hydrochloric acid were added. After heating and evaporation to dryness, the residue in the crucible was diluted with hydrochloric acid and measured using an inductively coupled plasma mass spectrometer (Agilent Technologies, Inc., product name: Agilent 8900).

[0067] (Average porosity of hollow silica particles) The true density of silica particles was calculated using the following formula based on the density measured with nitrogen as the measurement gas using a density measuring device (Quantachrome: ULTRAPYCNMETER1200e). The true density of silica particles is 2.2 g / cm³. 3 That's what I decided. Average porosity (%) = [1 - (True density of hollow silica particles (g / cm³)] 3 ) / True density of silica particles (g / cm³) 3 )) × 100

[0068] (BET specific surface area of ​​hollow silica particles) The specific surface area (BET) of hollow silica particles was measured using a specific surface area analyzer (Shimadzu Corporation, product name "Flowsorb III 2305"). The samples were pre-treated by heating at 200°C for 15 minutes.

[0069] (Relative permittivity and dielectric loss tangent of hollow silica particles) The relative permittivity and dielectric loss tangent of hollow silica particles were measured using the cavity resonator perturbation method (CP-MA dielectric constant measurement software, manufactured by Kanto Electronics Applied Development Co., Ltd.) at a temperature of 25°C and a frequency of 10 GHz, using a network analyzer (Agilent Technologies, Inc., product name: N5221A) connected to a perturbation method cavity resonator (CP-580) manufactured by Kanto Electronics Applied Development Co., Ltd. A sample for measurement was prepared by filling a Teflon tube (manufactured by Chuko Chemical 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 (6.75 mm to 21.25 mm from the bottom). The weight of the hollow silica particles filled was calculated from the weight measurements of the hollow silica particles before and after filling, and the volume of the hollow silica particles filled in the Teflon tube was determined from the weight of the hollow silica particles filled and their specific gravity. The relative permittivity and dielectric loss tangent were determined by using the measurements of an empty Teflon tube (without hollow silica particles) as a blank and calculating the difference between those measurements and those of a Teflon tube filled with hollow silica particles.

[0070] <Measurement and evaluation of resin compositions> (Preparation of resin composition precursors) 23.7g of epoxy resin (Mitsubishi Chemical Corporation: jER828), 28.8g of acid anhydride-based curing agent (Mitsubishi Chemical Corporation: YH-306), and 0.3g of imidazole-based curing agent (Mitsubishi Chemical Corporation: EMI24) were mixed using a kneader (Thinky Co., Ltd.: Planetary Vacuum Mixer) at atmospheric pressure at 1400 rpm for 1 minute, and then continued to be mixed under reduced pressure of 0.3kPa at 2000 rpm for 5 minutes to obtain an epoxy resin mixture. Two g of the obtained epoxy resin mixture and 1.3 g of the hollow silica particles obtained in the examples and comparative examples were mixed using a kneader (Sinky Co., Ltd.: Planetary Vacuum Mixer) at atmospheric pressure at 1400 rpm for 1 minute, and then continued to be mixed under reduced pressure of 0.3 kPa at 2000 rpm for 5 minutes to obtain a resin composition precursor.

[0071] (Relative permittivity and dielectric loss tangent of resin composition) The obtained resin composition precursor was injected into a Teflon tube (manufactured by AS ONE Corporation, inner diameter 2.5 mm, outer diameter 4.0 mm), heated in a dryer at 80°C for 3 hours, and then heated at 160°C for 6 hours to prepare a resin composition sample for measuring relative permittivity and dielectric loss tangent. Using the obtained resin composition sample for measurement, the dielectric constant and dielectric loss tangent of the resin composition were measured in the same manner as for "relative permittivity and dielectric loss tangent of hollow silica particles".

[0072] (Coefficient of linear thermal expansion of resin composition) Using a thermal stress-strain measuring device (manufactured by Hitachi High-Tech Science Co., Ltd., product name "TMA7100"), a cylindrical sample with a diameter of 4 mm and a length of 12 mm was subjected to expansion and compression mode under a nitrogen atmosphere, with the temperature increased at a rate of 5°C per minute, and a load of 9.8 g was measured. The linear thermal expansion coefficient was obtained by calculating the average linear thermal expansion coefficient over a temperature range from 50°C to 100°C.

[0073] (Appearance of the resin composition) The obtained resin composition precursor was spin-coated (1000 rpm, 30 seconds) on an acetone-washed glass slide substrate (manufactured by Matsunami Glass Industry Co., Ltd., product name "S-1111", refractive index 1.52) using a spin coater (manufactured by Able Co., Ltd.), and then dried at 160°C for 6 hours to create a resin composition thin film in which hollow silica particles were dispersed in the resin. The surface of this thin film was observed using an electrolytic emission high-resolution scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, product name "S-4800") to confirm its smoothness. (Evaluation Criteria) A: Smooth B: Slightly uneven surface C: Uneven surface

[0074] [Manufacturing of hollow silica particles] Example 1 (Process 1) 192.6 g of deionized water was used as the aqueous medium, 50 g of dodecane (manufactured by Kishida Chemical Co., Ltd.: primary n-dodecane) as the hydrophobic liquid, and 7.3 g of Kotamine 2285E (manufactured by Kao Corporation: containing 58% by mass of behenyltrimethylammonium chloride) as the surfactant A were mixed and stirred at 25°C to obtain an aqueous dispersion of dodecane. The volume-average particle size of the dodecane particles in the obtained aqueous dispersion of dodecane was 0.50 μm. (Process 2) 11634.6g of deionized water, 32.4g of the aqueous dispersion of dodecane obtained above, 94.2g of a 30% by mass aqueous solution of hexadecyltrimethylammonium chloride (corresponding to cationic surfactant b) (Kachiogen TMP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as cationic surfactant B (in its raw form: 28.3g as hexadecyltrimethylammonium chloride solids), and 2600.7g of ethyl orthosilicate (TEOS999, manufactured by Asahi Kasei Wacker Silicone Co., Ltd.) as a silanol precursor were added to the reaction vessel. After heating to 40°C while stirring, the mixture was stirred for 10 minutes, and 34.8g of aqueous ammonia (25% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. Subsequently, 533.6 g (in morphological form) of cationic surfactant B, equivalent to cationic surfactant b, was added at a constant rate, and the mixture was then stirred at 40°C for 3 hours. The resulting white liquid was filtered using 5C filter paper (manufactured by Advantec Toyo Co., Ltd.), washed with water, and dried at 110°C to obtain a white hollow silica particle precursor. (Step 3) The obtained hollow silica particle precursor was calcined at 1100°C for 1 hour to obtain hollow silica particle 1. The physical properties of hollow silica particle 1 are shown in Table 1.

[0075] Example 2 In a 300 mL glass beaker, 20.0 g of hollow silica particles 1 obtained in Example 1, 177.0 g of ethanol (Fujifilm Wako Pure Chemical Industries: 99.5% concentration), 1.4 g of aqueous ammonia (25% by mass), and 1.6 g of N-phenyl-3-aminopropyltrimethoxysilane (Shin-Etsu Silicone Co., Ltd.: KBM-573) were added and stirred at room temperature for 10 hours. After that, the mixture was filtered using 5C filter paper and dried at 110°C for 2 hours to obtain surface-treated hollow silica particles 2. The physical properties of hollow silica particles 2 are shown in Table 1.

[0076] Comparative Example 1 In step 2 of Example 1, 94.2 g of Cathiogen TMP added to the reaction vessel was replaced with 104.6 g of Cortamin 24P (manufactured by Kao Corporation: containing 27.5% by mass of lauryltrimethylammonium chloride (not equivalent to cationic surfactant b)), and 533.6 g of Cathiogen TMP added immediately after the ammonia was added was replaced with 593.0 g of Cortamin 24P, otherwise the procedure was the same as in Example 1 to obtain hollow silica particles C1. The physical properties of hollow silica particles C1 are shown in Table 1.

[0077] Comparative Example 2 In step 2 of Example 1, 94.2 g of Cathiogen TMP added to the reaction vessel was replaced with 89.0 g of Cortamin 86W (manufactured by Kao Corporation: containing 28% by mass of stearyltrimethylammonium chloride (not equivalent to cationic surfactant b)), and 533.6 g of Cathiogen TMP added immediately after the ammonia was added was replaced with 609.0 g of Cortamin 86W, all other than being replaced with the same procedure as in Example 1 to obtain hollow silica particles C2. The physical properties of the hollow silica particles C2 are shown in Table 1.

[0078] Comparative Example 3 In step 2 of Example 1, instead of adding ammonia all at once, 184.6 g of AH212-CS (manufactured by Yokkaichi Synthetic Co., Ltd.: dimethylbis(2-hydroxyethyl)ammonium hydroxide (in its natural state)) was pre-mixed with Catiogen TMP and slowly added. Hollow silica particles C3 were obtained in the same manner as described above. The physical properties of the hollow silica particles C3 are shown in Table 1.

[0079] [Table 1]

[0080] As shown in Table 1, the hollow silica particles produced by the manufacturing method of the present invention in Examples 1 and 2 have a small average particle size, high porosity, a low proportion of non-hollow silica particles, and a small dielectric loss tangent at a measurement frequency of 10 GHz. Furthermore, the resin composition containing these hollow silica particles exhibited a lower dielectric loss tangent. On the other hand, in Comparative Examples 1 and 2, which did not use a cationic surfactant equivalent to cationic surfactant b, which has 14 to 16 carbon atoms in the alkyl group, and in Comparative Example 3, which used AH212-CS, a strong alkali, as a hydrolysis catalyst for the silanol precursor, the hollow silica particles produced all had low porosity or a high number ratio (R), resulting in a large number of non-hollow silica microparticles and a high dielectric loss tangent for the hollow silica particles. Furthermore, the dielectric loss tangent of the resin composition containing these hollow silica particles also increased. Therefore, a resin composition containing hollow silica particles obtained by the manufacturing method of the present invention, and an insulating material containing the resin composition, can be suitably used as an insulating material in high-frequency circuits corresponding to high-frequency radio waves.

Claims

1. A method for producing hollow silica particles, including the following steps. Step 1: A step to obtain an aqueous dispersion of a hydrophobic liquid by mixing an aqueous solvent, a hydrophobic liquid, and cationic surfactant A. Step 2: A step to produce a hollow silica particle precursor by mixing the aqueous dispersion of the hydrophobic liquid obtained in Step 1, a silanol precursor, a cationic surfactant B containing a cationic surfactant b having an alkyl group with 14 to 16 carbon atoms, and ammonia. Step 3: A process of heat-treating the hollow silica particle precursor obtained in Step 2 at a temperature between 1000°C and 1200°C.

2. A method for producing hollow silica particles according to claim 1, wherein the cationic surfactant A contains one or more selected from tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, stearyltrimethylammonium chloride, and behenyltrimethylammonium chloride.

3. A method for producing hollow silica particles according to claim 1, wherein the cationic surfactant b is one or more selected from tetradecyltrimethylammonium chloride, tetradecyltriethylammonium chloride, ditetradecyldimethylammonium chloride, hexadecyltrimethylammonium chloride, hexadecyltriethylammonium chloride, and dihexadecyldimethylammonium chloride.

4. A method for producing hollow silica particles according to claim 1, wherein the silanol precursor contains one or more selected from alkyl orthosilicates and alkyl pyrosilicates.

5. The method for producing hollow silica particles according to claim 1, wherein in step 2, the mass ratio of the silanol precursor to the cationic surfactant B [silanol precursor / catenic surfactant B] is 3 or more and 25 or less.

6. The method for producing hollow silica particles according to claim 1, wherein in step 2, the mass ratio of the silanol precursor to ammonia [silanol precursor / ammonia] is 10 or more and 500 or less.

7. The method for producing hollow silica particles according to claim 1, wherein in step 2, the mass ratio of the silanol precursor to the hydrophobic liquid [silanol precursor / hydrophobic liquid] is 10 or more and 1000 or less.

8. Hollow silica particles that satisfy the following conditions (1) to (2). Condition (1): When (d) is the volume-based average particle diameter of hollow silica particles, (σ) is the standard deviation of the volume-based particle diameter distribution, and (D) is the particle diameter that is smaller than the volume-based average particle diameter (d) by the standard deviation of the volume-based particle diameter distribution (σ), the number ratio (R) of particles with a particle diameter of (D) or less in the hollow silica particles that have a porosity of 10% or less is 0.5 or less. Condition (2): The volume-based average particle size (d) measured by the Coulter counter method is 0.05 μm or more and 3.0 μm or less.

9. Furthermore, the hollow silica particles according to claim 8 satisfy the following condition (3). Condition (3): Dielectric loss tangent at a measurement frequency of 10 GHz is 0.0030 or less.

10. Furthermore, the hollow silica particles according to claim 8 satisfy the following condition (4). Condition (4): The total content of alkali metals and alkaline earth metals relative to the silica content in hollow silica particles is 50 ppm by mass or less.

11. Furthermore, the hollow silica particles according to claim 8 that satisfy the following condition (5). Condition (5): The relative permittivity at a measurement frequency of 10 GHz is 2.5 or less.

12. Furthermore, the hollow silica particles according to claim 8 satisfy the following condition (6). Condition (6): Average porosity is 40% or more and 80% or less.

13. Furthermore, the hollow silica particles according to claim 8 satisfy the following condition (7). Condition (7): Maximum particle size is 5.0 μm or less.

14. Furthermore, the hollow silica particles according to claim 8 satisfy the following condition (8). Condition (8): BET specific surface area is 40 m² ２ / g or less

15. Furthermore, the hollow silica particles according to claim 8 satisfy the following condition (9). Condition (9): The coefficient of variation of the volume-based particle size distribution is 80% or less.

16. A resin composition comprising hollow silica particles according to any one of claims 8 to 15.

17. An insulating material comprising the resin composition described in claim 16.

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