Method for manufacturing hollow silica particles

Abstract

The present invention relates to a method for producing hollow silica particles with low dielectric loss tangent, the hollow silica particles, a resin composition containing the hollow silica particles, and an insulating material containing the resin composition. [Solution] A method for producing hollow silica particles, comprising the following steps. Step 1: A process for preparing an aqueous dispersion containing polymer particles with an average particle size of 0.10 μm or more and 3.00 μm or less, and a cationic surfactant A. Step 2: A step to produce hollow silica particle precursors by mixing the aqueous dispersion obtained in Step 1 with a silanol precursor, ammonia, and cationic surfactant B. 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, said hollow silica particles, a resin composition containing said hollow silica particles, and an insulating material containing said resin composition. [Background technology]

[0002] High-speed communication technologies such as 5G utilize high frequencies of several 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. Currently, low dielectric constant and low dielectric loss tangent are also required for silica particles incorporated into insulating materials to improve thermal properties. Furthermore, miniaturization of high-frequency circuits is desired, and there is a need to reduce the particle size of silica particles incorporated into insulating materials, as well as narrow the particle size distribution to prevent performance degradation of insulating materials due to coarse or fine particles. Currently, the use of hollow silica particles is being considered to lower the dielectric constant and dielectric loss tangent of insulating materials.

[0003] For example, Patent Document 1 discloses a method for producing hollow silica particles in which the average particle diameter is 0.5 μm or more and 3.0 μm or less, and the total content of alkali metals and alkaline earth metals relative to the silica content in the particles is 50 ppm by mass or less, wherein the relative permittivity of the hollow silica particles at a measurement frequency of 5.8 GHz is 2.5 or less, and the dielectric loss tangent is 0.0050 or less. In the silica particle production method of Patent Document 1, an aqueous emulsion of a hydrophobic liquid such as dodecane is used as a template for the hollow silica particles. Furthermore, Patent Document 2 describes hollow silica particles comprising a shell layer containing silica, with a space inside the shell layer, and having a wavenumber of 3746 cm² as measured by infrared spectroscopy. -1Hollow silica particles are disclosed having a peak intensity of 0.60 or less derived from nearby SiOH, a relative permittivity of 1.3 to 5.0 at 1 GHz, and a dielectric loss tangent of 0.0001 to 0.05 at 1 GHz. Patent Document 2 describes a method for producing hollow silica particles in which alkali metal silicates are used as the silica raw material, and an oil-in-water emulsion containing an organic liquid such as dodecane as the oil phase is used as the template for the hollow silica particles. Furthermore, Patent Document 3 describes a particle with an average particle diameter of 0.05 to 1 μm, in which more than 80% of the particles have a particle diameter within ±30% of the average particle diameter, and a BET specific surface area of ​​30 m². 2 Hollow silica particles with a weight of less than / g are disclosed. In the method for producing hollow silica particles described in Patent Document 3, polymer particles are used as templates for the hollow silica particles, and sodium hydroxide is used as a hydrolysis catalyst for alkoxysilanes and other silica sources. Furthermore, Patent Document 4 describes a spherical hollow particle having a single space inside, with a specific surface area of ​​50 m² measured by gas adsorption using nitrogen gas. 2 Hollow inorganic particles are disclosed that have a weight of less than / g and a water absorption rate of 0.2 to 20%. Patent Document 4 discloses a method for producing hollow inorganic particles in which core particles such as polystyrene are used as a template for the hollow inorganic particles, and ammonia and a silicon compound are dropped into a dispersion of the core particles as catalysts to coat the core particles with the silicon compound, and then calcined in the range of 200°C to 1200°C. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2023 / 140378 [Patent Document 2] International Publication No. 2021 / 172294 [Patent Document 3] Japanese Patent Publication No. 2009-203115 [Patent Document 4] Japanese Patent Publication No. 2023-128890 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In Patent Document 1, the silica raw material is dissolved in an aqueous emulsion of a hydrophobic liquid such as dodecane, and because the particle size of the emulsion increases, the average particle size of the resulting hollow silica particles becomes large, and the coefficient of variation of particle size also becomes large. As a result, the proportion of coarse particles increases, and the appearance of the resin composition containing the hollow silica may be poor. In addition, because the template is an aqueous emulsion of a hydrophobic liquid, collisions between particles during the synthesis of hollow silica particles tend to cause deformation of the template, and there was a problem that hollow silica particles that were not perfectly spherical and had a lot of distortion tended to be produced. Furthermore, in Patent Document 2, since alkali metal silicates are used as the silica raw material, the dissolution of the silica raw material into the oil-in-water emulsion template is suppressed, and hollow silica particles with a relatively small average particle size are obtained. However, because a large amount of alkali metal derived from the silica raw material is present, there is a problem that the insulating properties deteriorate when used as a filler for insulating materials. Furthermore, in Patent Document 3, polymer particles are used as templates for hollow silica particles, resulting in a relatively small coefficient of variation in particle size. This makes it difficult for the template to deform due to collisions between particles during the synthesis of hollow silica particles, thus yielding hollow silica particles with less distortion. However, when sodium hydroxide is used as a hydrolysis catalyst for the silica source, a problem arises in that the strength of the hollow silica particles decreases during heat treatment to obtain hollow silica particles for insulating materials, making it impossible to obtain the desired hollow silica for insulating materials. Furthermore, in Patent Document 4, the surfactant is only used as a dispersant for the core particles, which presents a problem as the outer shell of the hollow silica particles is not dense and the dielectric loss tangent is high.

[0006] The present invention relates to a method for producing hollow silica particles with low dielectric loss tangent, the hollow silica particles, a resin composition containing the hollow silica particles, and an insulating material containing the resin composition. [Means for solving the problem]

[0007] The inventors of the present invention have found that the above problems can be solved by using polymer particles having a specific average particle diameter, a cationic surfactant, and further ammonia as a hydrolysis catalyst for a silanol precursor. 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 preparing an aqueous dispersion containing polymer particles having an average particle diameter of 0.10 μm or more and 3.00 μm or less and a cationic surfactant A Step 2: A step of mixing the aqueous dispersion obtained in Step 1, a silanol precursor, ammonia, and a cationic surfactant B to produce 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 1200 °C or lower [2] Having an average particle diameter of 0.10 μm or more and 3.00 μm or less, Hollow silica particles having a relative permittivity of 2.5 or less and a dielectric loss tangent of 0.0050 or less at a measurement frequency of 5.8 GHz. [3] A resin composition containing the hollow silica particles described in [2] above. [4] An insulating material containing the resin composition described in [3] above.

Advantages of the Invention

[0008] According to the present invention, there are provided a method for producing hollow silica particles having a low dielectric loss tangent, the hollow silica particles, a resin composition containing the hollow silica particles, and an insulating material containing the resin composition.

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 process for preparing an aqueous dispersion containing polymer particles with an average particle size of 0.10 μm or more and 3.00 μm or less, and a cationic surfactant A. Step 2: A step to produce hollow silica particle precursors by mixing the aqueous dispersion obtained in Step 1 with a silanol precursor, ammonia, and cationic surfactant B. 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.

[0010] The method for producing hollow silica according to the present invention can produce hollow silica particles with a low dielectric loss tangent. The reasons for this are not entirely clear, but they are thought to be as follows. In the manufacturing method of the present invention, in step 2, a silanol precursor, ammonia, and cationic surfactant B are mixed into an aqueous dispersion containing polymer particles having a specific average particle size and cationic surfactant A, obtained in step 1. It is believed that the complex formed by micelles of cationic surfactant B and the silanol precursor, as well as the polymer particles, accumulate on the surface of the polymer particles due to the interaction with cationic surfactant A adsorbed on the polymer particles, thereby generating hollow silica particle precursors with a uniform outer shell. Furthermore, by using ammonia, which is weakly alkaline, as a hydrolysis catalyst for the silanol precursor, the affinity between the polymer particles and the complex can be optimized, making the adhesion state of the complex to the polymer particles uniform, and thus making it possible to make the thickness of the silica layer on the outer shell thinner. Next, in step 3, the hollow silica particle precursor is heat-treated at a temperature between 1000°C and 1200°C. During this process, in the initial stage, the cationic surfactant incorporated into the outer shell of the hollow silica particle precursor decomposes and volatilizes, forming uniform pores of a few nanometers in size in the outer shell. Subsequently, the polymer particles decompose and volatilize through these pores, so no large pores are formed in the outer shell of the hollow silica particle precursor. Once the decomposition and volatilization of the polymer particles are complete, the hollow silica particle precursor reaches a high temperature during heat treatment. However, because the pores are very small, only a few nanometers in size, these pores easily close at this high temperature, resulting in a uniform and dense outer shell for the resulting hollow silica particles, which is expected to have a low dielectric loss tangent.

[0011] <Project 1> Project 1 is a process for producing an aqueous dispersion containing polymer particles having an average particle diameter of 0.10 μm or more and 3.00 μm or less and a cationic surfactant A.

[0012] The dispersion medium contained in the aqueous dispersion contains water, and examples of the water include distilled water, ion-exchanged water, ultrapure water, etc. Further, the dispersion medium of the aqueous dispersion may contain an organic solvent compatible with water from the viewpoint of more uniformly and stably generating the dispersion of the polymer particles. Examples of the organic solvent compatible with water include lower alcohols such as methanol, ethanol, isopropyl alcohol, and acetone. From the viewpoint of ease of treatment of the waste liquid after production, the water content in the dispersion medium contained in the aqueous dispersion is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 98% by mass or more, and even more preferably 100% by mass.

[0013] (Cationic surfactant A) From the viewpoint of facilitating the interaction with the complex of the micelle of the cationic surfactant B produced in Step 2 described below and silanol, and from the viewpoint of decomposition and volatilization in Step 3 described below, 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)<000012​​​​​​​​This represents an alkyl group having 1 to 3 carbon atoms, and multiple R 3 Each of these may be a different group, X ― This 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 alkyl groups having 1 to 3 carbon atoms include methyl, ethyl, n-propyl, and isopropyl groups. In general formulas (1) and (2), R 3 It is preferable that it be a methyl group.

[0015] X in general formulas (1) and (2) ― From the viewpoint of readily decomposing and volatilizing during the heat treatment described later, it is preferably at least one selected from monovalent anions such as halide ions and nitrate ions. ― More preferably, these are halide ions, and even more preferably chloride ions.

[0016] Preferred quaternary ammonium 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] Preferred quaternary ammonium salts represented by general formula (2) include dibutyldimethylammonium chloride, dihexyldimethylammonium chloride, dioctyldimethylammonium chloride, dihexyldimethylammonium bromide, dioctyldimethylammonium bromide, dilauryldimethylammonium bromide, and ditetradecyldimethylammonium bromide.

[0018] The quaternary ammonium salt is preferably one or more selected from lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, and behenyltrimethylammonium chloride, and more preferably lauryltrimethylammonium chloride, from the viewpoint of facilitating the formation of a complex with the silanol condensed in step 2 and facilitating decomposition and volatilization in step 3.

[0019] (Polymer particles) The polymer particles used in step 1 include one or more polymer particles selected from cationic polymer particles, nonionic polymer particles, and amphoteric polymer particles, with cationic polymer particles being preferred among these. Furthermore, the polymer constituting the polymer particles is preferably a water-insoluble polymer. In this invention, a water-insoluble polymer means a polymer in which, when a polymer that has been dried at 105°C for 2 hours to reach a constant weight is dissolved in 100g of water at 25°C, the amount dissolved is less than 10g.

[0020] The average particle size of the polymer particles is between 0.10 μm and 3.00 μm. This allows for a smaller average particle size of the resulting hollow silica particles. Specifically, the average particle size of the resulting hollow silica particles can be reduced to between 0.10 μm and 3.00 μm. The average particle diameter of the polymer particles is preferably 0.20 μm or more, more preferably 0.30 μm or more, even more preferably 0.40 μm or more, and preferably 2.00 μm or less, more preferably 1.00 μm or less, and even more preferably 0.60 μm or less, from the viewpoint of keeping the average particle diameter of the resulting hollow silica particles within a certain range. The average particle diameter of polymer particles can be determined as the volume-based average particle diameter by the method described in the examples.

[0021] The coefficient of variation of the particle size of the polymer particles is preferably 20% or less, more preferably 18% or less, even more preferably 15% or less, and even more preferably 10% or less, from the viewpoint of reducing the coefficient of variation of the particle size of the hollow silica particles. The coefficient of variation of the particle size of polymer particles can be determined by the method described in the examples.

[0022] [Cationic polymers] In the present invention, when the polymer particles are cationic polymer particles, the cationic polymer constituting the polymer particles is preferably one obtained by polymerizing a monomer mixture containing an ethylenically unsaturated monomer having a cationic group in an aqueous medium using a known method, that is, a polymer containing constituent units derived from an ethylenically unsaturated monomer having a cationic group. Suitable examples of ethylenically unsaturated monomers having a cationic group include methacroyloxyethyltrimethylammonium chloride, N-[3-(dimethylamino)propyl]acrylamide-methyl quaternary chloride, and 2-(dimethylamino)ethyl acrylate-benzyl quaternary chloride. Among these, methacroyloxyethyltrimethylammonium chloride is preferred as the ethylenically unsaturated monomer having a cationic group.

[0023] Furthermore, it is preferable that the cationic polymer has constituent units derived from ethylenically unsaturated monomers other than those derived from ethylenically unsaturated monomers having cationic groups. Other suitable examples of ethylenically unsaturated monomers include alkyl (meth)acrylates, aromatic ring-containing monomers, and vinyl esters. Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms, more preferably alkyl (meth)acrylates having an alkyl group with 1 to 8 carbon atoms, even more preferably alkyl (meth)acrylates having an alkyl group with 1 to 3 carbon atoms, even more preferably methyl (meth)acrylate, and even more preferably methyl methacrylate. Preferred aromatic ring-containing monomers include styrene and styrene-based monomers such as 2-methylstyrene; aryl esters of (meth)acrylic acid such as benzyl (meth)acrylate; and vinyl monomers containing aromatic groups with 6 to 22 carbon atoms. Vinyl acetate is a preferred example of a vinyl ester. Among these, other ethylenically unsaturated monomers are preferably one or more selected from alkyl (meth)acrylates having an alkyl group with 1 to 3 carbon atoms and styrene, more preferably alkyl (meth)acrylates having an alkyl group with 1 to 3 carbon atoms, even more preferably methyl (meth)acrylate, and even more preferably methyl methacrylate.

[0024] Furthermore, other ethylenically unsaturated monomers are preferred if they have low solubility in water and form a phase separation with water. The LogP value of the ethylenically unsaturated monomer is preferably 0 or higher, more preferably 0.5 or higher, and preferably 25 or lower. Here, LogP refers to the logarithm of the 1-octanol / water partition coefficient of the chemical substance, and is a value calculated using the fragment approach by SRC's LOGKOW / KOWWIN Program. Specifically, it is obtained by decomposing the chemical structure of the chemical substance into its constituent elements and accumulating the hydrophobic fragment constants of each fragment (see Meylan, WM and PH Howard. 1995. Atom / fragment contribution method for estimating octanol-water partition coefficients. J. Pharm. Sci. 84: 83-92).

[0025] Furthermore, the cationic polymer may be one obtained by emulsion polymerization of a monomer mixture containing an ethylenically unsaturated monomer in an aqueous medium in the presence of a cationic surfactant, that is, a polymer having constituent units derived from a cationic surfactant and constituent units derived from an ethylenically unsaturated monomer. When the cationic polymer is a polymer having constituent units derived from a cationic surfactant and constituent units derived from an ethylenically unsaturated monomer, the cationic surfactant may be the same as the cationic surfactant A described above, or it may be different from the cationic surfactant A, but it is preferable that it be the same as the cationic surfactant A. When a cationic polymer is a polymer having structural units derived from a cationic surfactant and structural units derived from an ethylenically unsaturated monomer, the ethylenically unsaturated monomer is preferably the same as the other ethylenically unsaturated monomers in the polymer containing structural units derived from the cationic group-derived ethylenically unsaturated monomer mentioned above.

[0026] The thermal decomposition temperature of the polymer particles is preferably 200°C or higher, more preferably 250°C or higher, and even more preferably 300°C or higher, from the viewpoint of suppressing the decomposition of polymer particles in the drying step when step 2 includes a drying step for hollow silica particle precursors, and in step 3, from the viewpoint of decomposing and volatilizing the polymer particles to remove them before the pores of the hollow silica particle precursors disappear during heat treatment, it is preferably 500°C or lower, more preferably 450°C or lower, and even more preferably 400°C or lower. The thermal decomposition temperature of polymer particles can be measured by the method described in the examples.

[0027] Furthermore, it is preferable that the thermal decomposition temperature of the polymer particles is higher than that of the cationic surfactant B, which will be described later. Because the thermal decomposition temperature of the polymer particles is higher than that of the cationic surfactant B, in the heat treatment in step 3, surfactant B contained in the hollow silica particle precursor can be thermally decomposed before the polymer particles. As a result, volatile components generated by the thermal decomposition of the polymer can be removed from the particles without damaging the outer shell of the hollow silica, making the outer shell of the resulting hollow silica particles more uniform and denser, improving the porosity of the hollow silica particles, and consequently lowering the dielectric loss tangent of the resulting hollow silica particles. The thermal decomposition temperature of the polymer particles is more preferably 20°C or more higher than the thermal decomposition temperature of surfactant B, even more preferably 50°C or more higher than the thermal decomposition temperature of surfactant B, and even more preferably 100°C or more higher than the thermal decomposition temperature of surfactant B, for the same reasons as described above.

[0028] In step 1, the mass ratio of polymer particles to water in the aqueous dispersion [polymer particles / water] is preferably 0.01 or higher, more preferably 0.03 or higher, and even more preferably 0.05 or higher, from the viewpoint of productivity of hollow silica particles, and preferably 0.5 or lower, more preferably 0.4 or lower, and even more preferably 0.3 or lower, from the viewpoint of preventing aggregation of polymer particles.

[0029] In step 1, the mass ratio of cationic surfactant A to polymer particles in the aqueous dispersion [cationic surfactant A / polymer particles] is preferably 0.0005 or higher, more preferably 0.001 or higher, and even more preferably 0.0015 or higher, from the viewpoint of dispersing the polymer particles in water, and from the viewpoint of preventing excess cationic surfactant from adversely affecting the synthesis of the hollow silica particle precursor in step 2, it is preferably 0.1 or lower, more preferably 0.08 or lower, and even more preferably 0.06 or lower.

[0030] In step 1, the aqueous dispersion may contain a hydrophobic liquid. In step 1, the hydrophobic liquid that may be contained in the aqueous dispersion is preferably a hydrocarbon having 6 to 18 carbon atoms, more preferably a hydrocarbon having 8 to 14 carbon atoms, and even more preferably dodecane. In step 1, the content of the hydrophobic liquid in the aqueous dispersion is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 1% by mass or less, and even more preferably 0% by mass, from the viewpoint of reducing the coefficient of variation of the particle size of the resulting hollow silica.

[0031] <Process 2> Step 2 is a step in which the aqueous dispersion obtained in Step 1 is mixed with a silanol precursor, ammonia, and cationic surfactant B to produce hollow silica particle precursors. More specifically, first, the silanol precursor is hydrolyzed with ammonia to obtain silanol. Then, the micelles of the obtained silanol and cationic surfactant B form a complex, and this complex accumulates on the surface of the polymer particles contained in the aqueous dispersion obtained in step 1, causing the silanol to condense and form a hollow silica particle precursor having an outer shell containing silica and cationic surfactant B, and containing polymer particles inside. Furthermore, since ammonia is less alkaline than various amines, there is a risk that the silanol precursor may not be sufficiently hydrolyzed if ammonia is added together with cationic surfactant B. Therefore, it is preferable to mix ammonia with the aqueous dispersion obtained in step 1 before adding cationic surfactant B. In other words, it is preferable that step 2 comprises the following steps 2-1 and 2-2. Step 2-1: A step in which the aqueous dispersion obtained in Step 1 is mixed with a silanol precursor and ammonia. Step 2-2: A step in which cationic surfactant B is mixed with the mixture obtained in Step 2-1.

[0032] Step 2 may include, after the formation of the hollow silica particle precursor and before step 3, a step of isolating the hollow silica particle precursor and a step of drying the hollow silica particle precursor. The isolation of the hollow silica particles can be carried out, for example, by filtration. The drying of the hollow silica particle precursor can be carried out, for example, by heating to a temperature of 100°C or higher.

[0033] (Silanol precursor) Silanol precursors are compounds that produce silanol compounds by hydrolysis of alkoxysilanes, etc., and are preferably selected from alkyl orthosilicates and alkyl pyrosilicates. Specifically, compounds represented by the following general formulas (3) to (7), or combinations thereof, can be mentioned. SiY4(3) R 4 SiY3(4) R 4 2SiY2(5) R 4 3SiY (6) Y3Si-O-SiY3(7)

[0034] In general formulas (4) to (6), R 4 Each of these is independently a C1-C22 hydrocarbon group, preferably one in which some of the hydrogen atoms are substituted with fluorine atoms; more preferably a C1-C22 alkyl group, a C4-C18 alkyl group, a C8-C16 alkyl group, a phenyl group, or a benzyl group. 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 heat treatment and a tendency for the dielectric loss tangent of the hollow silica particles to increase. Conversely, alkoxy groups having 5 or more carbon atoms result in a slower hydrolysis rate.

[0035] 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 the reactivity of hydrolysis, the silanol precursor is preferably one or more compounds selected from compounds represented by general formulas (3) and (7) in which Y is an alkoxy group having 2 to 4 carbon atoms, more preferably one or more compounds selected from compounds represented by general formulas (3) and (7) in which Y is an ethoxy group, and even more preferably a compound represented by general formula (3) in which Y is an ethoxy group. The silanol precursor can be used alone or as a mixture of two or more.

[0036] The mass ratio of silanol precursor to polymer particles [silanol precursor / polymer particles] is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and even more preferably 4 or more, and preferably 50 or less, more preferably 20 or less, even more preferably 10 or less, and even more preferably 8 or less, from the viewpoint of keeping the porosity of the hollow silica particles within an appropriate range.

[0037] (Cationic surfactant B) As cationic surfactant B, the same cationic surfactant A as shown in step 1 can be used. In the present invention, it is preferable that cationic surfactant A and cationic surfactant B are the same compound. As cationic surfactant B, from the viewpoint of facilitating the formation of a complex with silanol and facilitating decomposition and volatilization in step 3, it is preferably a salt of a quaternary ammonium, more preferably lauryltrimethylammonium chloride (dodecyltrimethylammonium chloride), stearyltrimethylammonium chloride, and 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 1, but from the same viewpoint as above, it is preferable that it be the same as cationic surfactant A. Furthermore, from the same viewpoint as above, it is more preferable that both cationic surfactant A and cationic surfactant B are salts of quaternary ammonium. Furthermore, cationic surfactant B can be used alone or in a mixture of two or more types.

[0038] The thermal decomposition temperature of cationic surfactant B in step 3 is preferably 100°C or higher, more preferably 150°C or higher, and even more preferably 180°C or higher, from the viewpoint of suppressing damage to the outer shell due to thermal decomposition in the drying step, and preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 220°C or lower, from the viewpoint of thermal decomposition occurring before the polymer particles. Furthermore, from the same viewpoint as above, the thermal decomposition temperature of cationic surfactant B is preferably lower than the decomposition temperature of polymer particles, more preferably 20°C or more lower than the decomposition temperature of polymer particles, even more preferably 50°C or more lower than the decomposition temperature of polymer particles, and even more preferably 100°C or more lower than the decomposition temperature of polymer particles. The thermal decomposition temperature of cationic surfactant B can be measured by the method described in the examples.

[0039] The mass ratio of silanol precursor to cationic surfactant B [silanol precursor / cationic surfactant B] is preferably 3 or more, more preferably 5 or more, even more preferably 6 or more, and preferably 25 or less, more preferably 20 or less, and even more preferably 18 or less, from the viewpoint of the dispersibility of the hollow silica particle precursor.

[0040] (ammonia) In step 2, ammonia is used as a hydrolysis catalyst for the silanol precursor. That is, in step 2, the silanol precursor is hydrolyzed to silanol by ammonia, and then dehydrated and condensed to form silica.

[0041] The mass ratio of the silanol precursor to ammonia [silanol precursor / ammonia] is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more, from the viewpoint of densifying the outer shell of the hollow silica particle precursor, and from the viewpoint of efficiently carrying out the condensation reaction of the silanol precursor, it is preferably 500 or less, more preferably 400 or less, and even more preferably 350 or less.

[0042] The temperature at which step 2 is carried out can be appropriately adjusted 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. Among these, ethyl orthosilicate or ethyl pyrosilicate is preferred from the viewpoint of reaction control.

[0043] 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, and even more preferably 16 hours or less, from the viewpoint of manufacturing efficiency.

[0044] (Hollow silica particle precursor) The hollow silica particle precursor is a composite silica particle having a silica-containing outer shell and polymer particles inside the outer shell. The outer shell has pores formed radially toward the particle center, using a cationic surfactant as a template.

[0045] [Step 3] In step 3, the hollow silica particle precursor obtained in step 2 is heat-treated at a temperature between 1000°C and 1200°C to decompose and volatilize the cationic surfactant present in the outer shell of the hollow silica particle precursor and the polymer particles inside. Then, the pores in the outer shell are sealed by heat treatment to obtain hollow silica particles with a uniform outer shell.

[0046] 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 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.

[0047] The heat treatment time in the process 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.

[0048] [Hollow silica particles] The hollow silica particles of the present invention have an average particle diameter of 0.10 μm or more and 3.00 μm or less, a relative permittivity of 2.5 or less, and a dielectric loss tangent of 0.0050 or less at a measurement frequency of 5.8 GHz. The hollow silica particles of the present invention can be efficiently obtained by the method for producing hollow silica of the present invention described above.

[0049] The average particle diameter of the hollow silica particles of the present invention is 0.10 μm or more, preferably 0.20 μm or more, more preferably 0.25 μm or more, and even more preferably 0.30 μm or more, from the viewpoint of reducing surface silanols that adversely affect the dielectric loss tangent by reducing the specific surface area, and from the viewpoint of improving the appearance of the resin composition and preventing a decrease in insulation performance through the surface of coarse particles, it is 3.00 μm or less, preferably 2.00 μm or less, more preferably 1.00 μm or less, and even more preferably 0.60 μm or less. The average particle diameter of hollow silica particles can be determined as the volume-based average particle diameter by the method described in the examples.

[0050] The coefficient of variation of particle size of the hollow silica particles of the present invention is preferably 20% or less, more preferably 18% or less, even more preferably 15% or less, and even more preferably 10% or less, from the viewpoint of reducing the proportion of fine particles to reduce the viscosity of the resin composition and improve handling properties, and from the viewpoint of reducing the proportion of coarse particles to improve the appearance of the resin composition. The coefficient of variation of the particle size of hollow silica particles can be determined by the method described in the examples.

[0051] Generally, hollow silica with a larger average particle diameter has a smaller specific surface area, resulting in fewer surface silanols that negatively affect the dielectric loss tangent. Since the maximum particle diameter of hollow silica particles is limited by the degree of miniaturization of the circuit in which the insulating material is used, a smaller coefficient of variation allows for a larger average particle diameter, which is preferable from the viewpoint of reducing the dielectric loss tangent.

[0052] The dielectric constant of the hollow silica particles of the present invention at a measurement frequency of 5.8 GHz is 2.5 or less, preferably 2.4 or less, more preferably 2.3 or less, and even more preferably 2.2 or less, from the viewpoint of sufficiently lowering the dielectric constant of the resin composition containing the hollow silica particles, and from the viewpoint of the strength of the hollow silica particles, it is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more. The relative permittivity of hollow silica particles can be determined by the method described in the examples.

[0053] The dielectric loss tangent of the hollow silica particles of the present invention at a measurement frequency of 5.8 GHz is preferably 0.0050 or less, more preferably 0.0045 or less, and more preferably 0.0040 or less, from the viewpoint of sufficiently lowering the dielectric loss tangent of the resin composition containing the hollow silica particles, and from the viewpoint of the strength of the hollow silica particles, it is preferably 0.0001 or more, more preferably 0.0005 or more, and even more preferably 0.0010 or more. The dielectric loss tangent of hollow silica particles can be determined by the method described in the examples.

[0054] The sphericity of the hollow silica particles of the present invention is preferably 0.85 or higher, more preferably 0.90 or higher, even more preferably 0.95 or higher, and preferably 1.00 or lower, from the viewpoint that the hollow silica particles have sufficient strength. The sphericity of hollow silica particles can be determined by the method described in the examples.

[0055] The porosity of the hollow silica particles of the present invention is preferably 20% or more, more preferably 30% or more, and even more preferably 45% or more, from the viewpoint of lowering the dielectric loss tangent of the hollow silica particles, and preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less, from the viewpoint of the hollow silica particles having sufficient strength. The porosity of hollow silica particles can be determined by the method described in the examples.

[0056] The average thickness of the outer shell of the hollow silica particles of the present invention is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, and even more preferably 60 nm or less, from the viewpoint of lowering the dielectric loss tangent of the hollow silica particles, and preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, and even more preferably 30 nm or more, from the viewpoint of ensuring sufficient strength of the hollow silica particles. The average thickness of the outer shell of hollow silica particles can be determined by the method described in the examples.

[0057] The BET specific surface area of ​​the hollow silica particles of the present invention is preferably 40 m², from the viewpoint of lowering the dielectric loss tangent of the hollow silica particles and reducing the amount of surface treatment agent used when compounding with resin, thereby lowering the dielectric loss tangent of the resin composition. 2 / g or less, more preferably 30m 2 / g or less, more preferably 25m 2 The amount is less than or equal to / g, and from the viewpoint of improving the surface smoothness of the resin when compounded into the resin, it is preferably 5m 2 / g or more, more preferably 8m 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.

[0058] The total content of alkali metals and alkaline earth metals relative to the silica content in the hollow silica particles of the present invention is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, even 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 alkali metal content and alkaline earth metal content in hollow silica particles can be determined by the method described in the examples.

[0059] [Resin composition] The resin composition of the present invention is formulated with the hollow silica particles of the present invention described above. The resin used to form the resin composition is not particularly limited, but for the sake of low dielectric properties of the resin composition, it is preferable to use resins with low relative permittivity and dielectric loss tangent, such as epoxy resins, bismaleimide resins, cycloolefin resins, and fluorine-based resins, which use one or more curing agents selected from poly(p-phenylene) resins, liquid crystal polymer resins, ester or ether-based curing agents, acid anhydride-based curing agents, and imidazole-based curing agents, or derivatives of these resins.

[0060] The amount of hollow silica particles of the present invention incorporated into 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 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.

[0061] [Insulating materials] The insulating material of the present invention includes the resin composition of the present invention described above. Therefore, by including the resin composition of the present invention, the insulating material of the present invention can be made capable of reducing transmission loss and transmission delay. The insulating material can be suitably used, for example, in build-up insulating films, insulating layers of copper-clad laminates, prepregs, sealing materials, insulating members of connectors, and covering materials for electric wires. [Examples]

[0062] The present invention will be described in more detail below with reference to examples. In the following examples, each physical property was measured and evaluated by the following methods. In the following examples and comparative examples, unless otherwise specified, parts and percentages are based on mass.

[0063] [Measurement method] <Measurement of physical properties of hollow silica particles> (Measurement of the average particle size of hollow silica particles) The average particle size of hollow silica particles was measured using the Coulter counter method with a Multisizer 3 (manufactured by Beckman Coulter, Inc., using a 20 μm aperture tube) to determine the volume-based average particle size, which was then used as the average particle size of hollow silica particles in the examples and comparative examples.

[0064] (Measurement of the coefficient of variation of particle size of hollow silica particles) The coefficient of variation of hollow silica particles was determined from scanning electron microscope images using the following method. Multiple scanning electron microscope images taken at an accelerating voltage of 10kV were used to measure the particle diameter of 3000 arbitrarily selected particles. The average particle diameter and its standard deviation were determined, and the coefficient of variation was calculated using the following formula. The software "A-Zou-kun" manufactured by Asahi Kasei Engineering Corporation was used to measure the particle diameter. (Coefficient of variation) (%) = (Standard deviation of particle size) / (Mean of particle size) × 100

[0065] (Measurement of 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 5.8 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 they all fit within the measurement range (6.75 mm to 36.35 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.

[0066] (Measurement of sphericity of hollow silica particles) Multiple scanning electron microscope images taken at an accelerating voltage of 10kV were used to check for deformation in 100 randomly selected particles. The proportion of undeformed particles was defined as sphericity. Here, particles were considered deformed if they showed indentations.

[0067] (Measurement of alkali metal and alkaline earth metal 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).

[0068] (Measurement of porosity of hollow silica particles) The true density of the silica particles was calculated using the following formula based on the density of hollow silica particles measured with nitrogen as the measurement gas using a density measuring device (Quantachrome: ULTRAPYCNMETER1200e). The true density of the silica particles is 2.2 g / cm³. 3 That's what I decided. Porosity (%) = [1 - (Density of hollow silica particles / True density of silica particles)] × 100

[0069] (Measurement of the average thickness of the outer shell of hollow silica particles) Using elastic carbon ELS-C10 (manufactured by Stem Co., Ltd.) and an electrolytic emission scanning electron microscope (manufactured by Hitachi High-Tech Corporation: S-4800), STEM images of hollow silica particles were obtained by observing them at an accelerating voltage of 30kV. For 10 hollow silica particles in these images, the outer shell portion was identified by the intensity of the color, and the average value was calculated for the darker portion as the outer shell portion. This was then used as the average thickness of the outer shell of the hollow silica particles in the examples and comparative examples.

[0070] (Measurement of 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") with nitrogen as the adsorbent gas. The samples were pre-treated by heating at 200°C for 15 minutes.

[0071] <Measurement of the physical properties of polymer particles> (Measurement of the average particle diameter of polymer particles and the coefficient of variation of the particle diameter of polymer particles) The measurements were taken using the same methods as described above for "Measurement of the average particle diameter of hollow silica particles" and "Measurement of the coefficient of variation of the particle diameter of hollow silica particles."

[0072] <Measurement of thermal decomposition temperature of polymer particles and cationic surfactants> 50 mg of polymer particles or cationic surfactant were placed in an aluminum pan (manufactured by Rigaku Corporation), and measured using a differential thermogravimetric analyzer (manufactured by Hitachi High-Tech Science Corporation: STA7200) under the following conditions. The inflection point when temperature (°C) was plotted on the x-axis and the thermogravimetric loss rate (%) on the y-axis was defined as the thermal decomposition temperature. [Measurement conditions] Measurement temperature range: 30~500℃ Heating rate: 5°C / min Measurement atmosphere: Nitrogen flow

[0073] <Measurement and evaluation of the physical properties and characteristics 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. 30 g of the obtained epoxy resin mixture and 20 g of 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.

[0074] (Evaluation of surface smoothness of resin composition) The obtained resin composition precursor was applied onto PET resin (Toray Industries, Inc.: Lumirror S10 (film thickness 25 μm)) using an applicator (Coating Tester Co., Ltd.: 4-sided film applicator (NO.350FA4)). Subsequently, curing treatment was performed by heating at 80°C for 3 hours, followed by further heating at 120°C for 6 hours to prepare a resin composition sample for surface smoothness evaluation. Thin films of resin composition with thicknesses of 50 μm or 20 μm were prepared, and the presence or absence of granular shapes on the surface of each resin composition sample for surface smoothness evaluation was confirmed visually and evaluated based on the following evaluation criteria. [Evaluation Criteria] A: No granular structure was observed on the surface of the resin composition. B: Slight granular structure was observed on the surface of the resin composition. C: Granular structures were observed on the surface of the resin composition.

[0075] (Measurement of 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 cured by heating 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 samples for measurement, the dielectric constant and dielectric loss tangent of the resin composition were measured in the same manner as described above in "Measurement of relative permittivity and dielectric loss tangent of hollow silica particles".

[0076] [Manufacturing of polymer particles] <Manufacturing Example 1> In a 1 L Separful flask, 600 parts of deionized water, 99.5 parts of methyl methacrylate (LogP value 1.38), and 0.5 parts of methacroyloxyethyltrimethylammonium chloride were added, and the internal temperature was raised to 70°C. Next, a solution of 0.5 parts of 2,2'-azobis(2-amidinopropane) dihydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.: V-50) dissolved in 5 parts of deionized water was added as a water-soluble initiator, and the mixture was heated and stirred for 3 hours. After that, the mixture was stirred further at 75°C for 3 hours to obtain a suspension of polymer particles (solid content (effective content): 13.8%). The polymer particles obtained in Production Example 1 had the following properties: average particle size: 0.30 μm, coefficient of variation of particle size: 9%, and thermal decomposition temperature: 331°C.

[0077] <Manufacturing Example 2> In a 1 L Separful flask, 600 parts of deionized water and a solution of 0.5 parts of 2,2'-azobis(2-amidinopropane) dihydrochloride (V-50, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) dissolved in 5 parts of deionized water were added as a water-soluble initiator, and the temperature was raised to 70°C. Next, 99.5 parts of methyl methacrylate (LogP value 1.38) and 0.5 parts of methacroyloxyethyltrimethylammonium chloride were added over 60 minutes, and the mixture was heated and stirred for 3 hours. After that, the mixture was stirred at 75°C for another 3 hours to obtain a suspension of polymer particles (solid content (effective content): 13.8%). The polymer particles obtained in Production Example 2 had the following properties: average particle size 0.50 μm, coefficient of variation of particle size 9%, and thermal decomposition temperature 331°C.

[0078] [Manufacturing of hollow silica particles] <Example 1> [Process 1] In a reaction vessel, 7040.07 g of deionized water, 4550.72 g of a suspension of polymer particles obtained in Production Example 1, and 125.6 g of Cotamine 24P (manufactured by Kao Corporation: containing 27.5% by mass of lauryltrimethylammonium chloride (thermal decomposition temperature 209°C)) as cationic surfactant A were added and stirred to obtain an aqueous dispersion of polymer particles. [Process 2] To the aqueous dispersion obtained in step 1, 3120.8 g of ethyl orthosilicate (manufactured by Asahi Kasei Wacker Silicone Co., Ltd.: TEOS999) was added, and the mixture was heated to 40°C while stirring, then stirred for another 10 minutes to obtain a mixture. Next, 34.8 g of aqueous ammonia (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., effective content: 27.0%) was added. Subsequently, 711.6 g of co-tamine 24P was added as cationic surfactant B, and the mixture was stirred at 40°C for 3 hours to obtain a turbid liquid. The obtained turbid liquid was then 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 hollow silica particle precursor obtained in step 2 was heat-treated at 1100°C for 1 hour to obtain hollow silica particles. The physical properties of the obtained hollow silica particles are shown in Table 1.

[0079] <Example 2> Hollow silica particles were obtained in the same manner as in Example 1, except that in Step 1 of Example 1, the polymer particle suspension was changed to the polymer particle suspension obtained in Production Example 2. The physical properties of the obtained hollow silica particles are shown in Table 1.

[0080] <Comparative Example 1> In a 10L flask, 6000g of deionized water, 2000g of methanol, 45g of 1M sodium hydroxide aqueous solution, 127g of Cotamine 24P, and 33g of a suspension of polymer particles obtained in Production Example 2 were added and stirred. Then, 46.5g of ethyl orthosilicate was slowly added, stirred for 5 hours, and then aged for 12 hours. Next, the obtained white precipitate was filtered through a membrane filter with a pore size of 0.2 μm, washed with 10 L of water, and dried at a temperature of 100°C for 5 hours to obtain hollow silica particle precursors. Subsequently, the obtained hollow silica particle precursor was heat-treated at 1100°C, but the particles melted during the heat treatment, and hollow silica particles could not be obtained.

[0081] <Comparative Example 2> 7040.07 g of deionized water, 4550.72 g of the polymer particle suspension obtained in Production Example 2, and 125.6 g of Cotamine 24P were added to a reaction vessel and stirred to obtain aqueous dispersion A of polymer particles. Next, 3120.8 g of ethyl orthosilicate was added to the aqueous dispersion A, and the mixture was heated to 40°C while stirring, and then stirred for a further 10 minutes to obtain mixture B. Next, 221.5 g of AH212-CS (manufactured by Yokkaichi Synthetic Co., Ltd.: containing 50% by mass of dimethylbis(2-hydroxyethyl)ammonium hydroxide) and 711.6 g of Cortamin 24P were uniformly mixed to obtain preparation solution C. Preparation solution C was added to mixture B at a constant rate, and then stirred at 40°C for 3 hours to obtain turbid liquid D. Next, the obtained turbid liquid D 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. The obtained hollow silica particle precursor was heat-treated at 1100°C for 1 hour to obtain hollow silica particles. The physical properties of the obtained hollow silica particles are shown in Table 1.

[0082] [Table 1]

[0083] As shown in the results in Table 1, the manufacturing method of the present invention was able to produce hollow silica particles with a small dielectric loss tangent at a measurement frequency of 5.8 GHz. On the other hand, in Comparative Example 1, where sodium hydroxide, a strong alkali, was used as the hydrolysis catalyst for the silanol precursor, hollow silica particles could not be obtained, possibly because the hollow silica particle precursor contained a large amount of sodium, resulting in low strength. Furthermore, in Comparative Example 2, where dimethylbis(2-hydroxyethyl)ammonium hydroxide was used as the hydrolysis catalyst for the silanol precursor, the hollow silica particles obtained showed a high dielectric loss tangent.

[0084] As described above, the method for producing hollow silica particles of the present invention can produce hollow silica particles with a low dielectric loss tangent. 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, comprising the following steps. Step 1: A process for preparing an aqueous dispersion containing polymer particles with an average particle size of 0.10 μm or more and 3.00 μm or less, and a cationic surfactant A. Step 2: A step to produce hollow silica particle precursors by mixing the aqueous dispersion obtained in Step 1 with a silanol precursor, ammonia, and cationic surfactant B. 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 thermal decomposition temperature of the polymer particles is higher than the thermal decomposition temperature of the cationic surfactant B.

3. A method for producing hollow silica particles according to claim 1 or 2, wherein the thermal decomposition temperature of the polymer particles is 200°C or higher and 500°C or lower.

4. A method for producing hollow silica particles according to claim 1 or 2, wherein the coefficient of variation of the particle size of the polymer particles is 20% or less.

5. A method for producing hollow silica particles according to claim 1 or 2, wherein the polymer particles are cationic polymer particles.

6. A method for producing hollow silica particles according to claim 1 or 2, wherein both cationic surfactant A and cationic surfactant B are salts of quaternary ammonium.

7. The average particle size is 0.10 μm or more and 3.00 μm or less. Hollow silica particles having a relative permittivity of 2.5 or less and a dielectric loss tangent of 0.0050 or less at a measurement frequency of 5.8 GHz.

8. The hollow silica particles according to claim 7, wherein the coefficient of variation of particle size is 20% or less.

9. The hollow silica particles according to claim 7, wherein the sphericity is 0.85 or more and 1.00 or less.

10. Hollow silica particles according to claim 7, wherein the porosity is 20% or more and 80% or less.

11. The hollow silica particles according to claim 7, wherein the average thickness of the outer shell of the hollow silica particles is 100 nm or less.

12. The hollow silica particles according to claim 7, wherein the total content of alkali metals and alkaline earth metals relative to the silica content in the hollow silica particles is 50 ppm by mass or less.

13. A resin composition comprising hollow silica particles according to any one of claims 7 to 12.

14. An insulating material comprising the resin composition described in claim 13.

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