Method for producing surface-treated hollow silica particles

Abstract

The present invention provides a method for producing surface-treated hollow silica particles with a low dielectric loss tangent, and also relates to surface-treated hollow silica particles having a specific residual state of silanol groups, a resin composition containing the hollow silica particles, and an insulating material. [Solution] A method for producing surface-treated hollow silica particles, comprising the following steps. Step 1: A step of preparing a mixture consisting of hollow silica particles (I), a silane coupling agent, and a solvent (S) that satisfies the following conditions (1) to (3). Condition (1) The freezing point at atmospheric pressure is 0°C or lower. Condition (2) Boiling point at atmospheric pressure is 120°C or lower Condition (3) Composed of two or more elements selected from hydrogen, carbon, and oxygen. Step 2: The mixture obtained in Step 1 is subjected to a reduced pressure and at a temperature of 60°C or lower to remove the solvent (S) to obtain hollow silica particles (II) consisting of hollow silica particles (I) and a silane coupling agent. Step 3: A step in which the hollow silica particles (II) obtained in Step 2 are heated to over 100°C.

Description

[Technical Field]

[0001] The present invention relates to a method for producing surface-treated hollow silica particles, surface-treated hollow silica particles having a specific residual state of silanol groups, 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 the same requirements apply to silica particles incorporated into insulating materials to improve thermal properties. Therefore, the use of hollow silica particles is currently being considered to lower the dielectric constant and dielectric loss tangent of insulating materials. Furthermore, in the even faster 6G communication technology currently under development, the use of radio waves with even higher frequencies is being considered, and it is anticipated that the requirements for lower dielectric constant and dielectric loss tangent of insulating materials will become even stricter.

[0003] To improve the dielectric properties of hollow silica particles, particularly reducing the dielectric loss tangent, it is necessary to densify the outer shell of the hollow silica particles and reduce the number of silanol groups on the surface of the hollow silica particles. For the latter, a surface treatment that reacts the silanol groups on the surface of the hollow silica particles with a silane coupling agent to form siloxane bonds is effective. Patent Document 1 describes a method for producing hollow silica particles, which is less likely to thicken a resin composition, and includes the steps of: (1) spray-drying a silica solution obtained by dissolving silica in an organic alkaline aqueous solution to obtain a hollow silica precursor; (2) calcining the hollow silica precursor to obtain hollow silica particles; and (3) surface-treating the hollow silica with a nitrogen-containing silane coupling agent. Furthermore, Patent Document 2 aims to provide a new hollow silica particle that has sufficiently low relative permittivity and dielectric loss tangent, as well as excellent dispersibility, comprising a shell layer containing silica and having a space inside the shell layer, wherein the wavenumber measured by infrared spectroscopy is 3746 cm⁻¹. -1 Hollow silica particles are described 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. The shell layer of these hollow silica particles is described as being surface-treated with hexamethyldisilazane. Furthermore, Patent Document 3 describes a curable resin composition for which a curable resin composition having a sufficiently low dielectric constant and, as a result, a cured product having high insulating properties, is obtained. This composition is characterized by having a curing component (A) consisting of a self-curing resin (a1) and / or a combination of a curable thermoplastic resin and a curing agent (a2), and a hollow nanosilica structure (B) having an aspect ratio (maximum diameter r1 / minimum diameter r2) of 2 or more when observed in a two-dimensional image by a transmission electron microscope. The hollow nanosilica structure (B) is described as being surface-treated with an alkyl group-containing silane coupling agent or an amino group-containing silane coupling agent, with a minimum diameter of 14 nm and an aspect ratio of 14 to 15. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-83736 [Patent Document 2] International Publication No. 2021 / 172294 [Patent Document 3] Japanese Patent Publication No. 2015-67739 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the method for producing hollow silica particles described in Patent Document 1 has the problem that, because an alkaline catalyst is used for the hydrolysis of the silane coupling agent in the surface treatment step, the siloxane bonds on the hollow silica surface are hydrolyzed by the alkaline catalyst to produce silanols, making it impossible to reduce the amount of silanol groups on the hollow silica surface and thus preventing the dielectric loss tangent from being sufficiently lowered. Furthermore, the methods for producing hollow silica particles described in Patent Documents 2 and 3 have the problem that the amount of silanol groups in the hollow silica particles cannot be reduced because the hollow silica particles and the silane coupling agent do not react sufficiently, resulting in a high dielectric loss tangent for the resulting hollow silica particles. The present invention provides a method for producing surface-treated hollow silica particles with low dielectric loss tangent, and also relates to surface-treated hollow silica particles having a specific residual state of silanol groups, a resin composition containing the surface-treated hollow silica particles, and an insulating material. [Means for solving the problem]

[0006] The inventors have found that surface-treated hollow silica, obtained by preparing a mixture consisting of hollow silica particles as raw materials, a silane coupling agent, and a specific solvent, removing the solvent from the mixture under specific temperature and pressure conditions, and then heating it to 100°C or higher, can solve the above problems. The present invention relates to the following [1] to [4]. [1] A method for producing surface-treated hollow silica particles, including the following steps. Step 1: A step of preparing a mixture consisting of hollow silica particles (I), a silane coupling agent, and a solvent (S) that satisfies the following conditions (1) to (3). Condition (1) The freezing point at atmospheric pressure is 0°C or lower. Condition (2) Boiling point at atmospheric pressure is 120°C or lower Condition (3) Composed of two or more elements selected from hydrogen, carbon, and oxygen. Step 2: A step of obtaining hollow silica particles (II) composed of hollow silica particles (I) and a silane coupling agent by distilling off the solvent (S) from the mixture obtained in Step 1 under reduced pressure at 60°C or lower. Step 3: A step of heating the hollow silica particles (II) obtained in Step 2 to 100°C or higher. [2] Surface-treated hollow silica particles in which the ratio (titration value (II) / titration value (I)) of the titration value (II) to the titration value (I) when measured by the following measurement procedure is 0.20 or less. (Measurement procedure) In a surface-treated hollow silica particle suspension prepared so that the concentration of the surface-treated hollow silica particles in a 2% by mass sodium chloride water-ethanol mixed solvent solution is 1% by mass, after adjusting the pH to 4 or lower with a 0.01N-HCl aqueous solution, the following titration values (I) and titration values (II) are determined from the titration curve and the differential curve of the titration curve when a 0.1N-NaOH aqueous solution is dropped at a rate of 0.005 mL / 10 seconds. Titration value (I): The volume of the 0.1N-NaOH aqueous solution dropped from when the pH is 4 to the pH at the point where the slope of the differential curve of the titration curve changes from decreasing to increasing. Titration value (II): The volume of the 0.1N-NaOH aqueous solution dropped from the pH at the point where the slope of the differential curve of the titration curve changes from decreasing to increasing to when the pH becomes 9. [3] A resin composition containing the surface-treated hollow silica particles described in [2]. [4] An insulating material containing the resin composition described in [3].

Advantages of the Invention

[0007] According to the present invention, a method for producing surface-treated hollow silica particles with a low dielectric tangent can be provided, and surface-treated hollow silica particles having a specific residual state of silanol groups, a resin composition containing the surface-treated hollow silica particles, and an insulating material can be provided.

Brief Description of the Drawings

[0008] [Figure 1]This graph shows the titration curve, the differential curve of the titration curve, and the titration values ​​(I) and (II) in Example 1. [Modes for carrying out the invention]

[0009] [Method for producing surface-treated hollow silica particles] The method for producing surface-treated hollow silica particles of the present invention includes the following steps. Step 1: A step to obtain a mixture consisting of hollow silica particles (I), a silane coupling agent, and a solvent (S) that satisfies the following conditions (1) to (3). Condition (1) The freezing point at atmospheric pressure is 0°C or lower. Condition (2) Boiling point at atmospheric pressure is 120°C or lower Condition (3) Composed of two or more elements selected from hydrogen, carbon, and oxygen. Step 2: The mixture obtained in Step 1 is subjected to reduced pressure and at a temperature of 60°C or lower to remove the solvent (S) to obtain hollow silica particles (II) consisting of hollow silica particles (I) and a silane coupling agent. Step 3: A step in which the hollow silica particles (II) obtained in Step 2 are heated to over 100°C. Hereinafter, the method for producing surface-treated 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 method for producing surface-treated hollow silica particles according to the present invention yields surface-treated hollow silica particles with a low dielectric loss tangent. The reason for this is not entirely clear, but it is thought to be as follows. A technique is known to reduce the dielectric loss tangent of hollow silica particles by reacting the silanol groups on the surface of the hollow silica particles with a silane coupling agent. However, if a component that promotes the cleavage of siloxane bonds is used, the cleavage of siloxane bonds on the surface of the hollow silica particles is also promoted, and the reaction that generates silanols on the surface of the hollow silica particles is also promoted. Therefore, the amount of silanol does not decrease according to the stoichiometry of the silane coupling agent. On the other hand, if a component that promotes the cleavage of siloxane bonds is not used, the cleavage of siloxane bonds on the surface of hollow silica particles will not be promoted, but the reactivity between the silane coupling agent and the silanol on the surface of the hollow silica particles will be poor. Therefore, if a dispersion of hollow silica particles containing a silane coupling agent is treated at high temperature to advance the reaction, the silane coupling agents undergo a condensation reaction with each other and do not react sufficiently with the silanol on the surface of the hollow silica particles, so the amount of silanol on the surface of the hollow silica particles does not decrease. Furthermore, while excessive use of silane coupling agents can increase the reaction rate between silanol on the surface of hollow silica particles and the silane coupling agent, the excess silane coupling agent undergoes a condensation reaction, forming fine particles that adversely affect dielectric properties and other characteristics. The present invention provides a method for producing surface-treated hollow silica particles. This method involves preparing a mixture consisting of hollow silica particles (I), a silane coupling agent, and a specific solvent (S). The solvent (S) is then removed under reduced pressure at a temperature of 60°C or lower. The hollow silica particles (II) to which the silane coupling agent is attached are then heated to a temperature of 100°C or higher. This process prevents condensation reactions between the silane coupling agents and does not break the siloxane bonds on the surface of the hollow silica particles (I). This reduces the silanol content on the particle surface, thereby obtaining surface-treated hollow silica particles with a low dielectric loss tangent.

[0011] <Process 1> Step 1 of the manufacturing method of the present invention is a step of preparing a mixture consisting of hollow silica particles (I), a silane coupling agent, and a solvent (S) that satisfies the following conditions (1) to (3). Condition (1) The freezing point at atmospheric pressure is 0°C or lower. Condition (2) Boiling point at atmospheric pressure is 120°C or lower Condition (3) Composed of two or more elements selected from hydrogen, carbon, and oxygen.

[0012] (Hollow silica particles (I)) In step 1, there are no particular restrictions on the hollow silica particles (I), and known hollow silica particles can be used.

[0013] In the manufacturing method of the present invention, the dielectric loss tangent of the hollow silica particles (I) at a measurement frequency of 10 GHz is preferably 0.0100 or less, more preferably 0.0080 or less, and even more preferably 0.0050 or less, from the viewpoint of further lowering the dielectric loss tangent and relative permittivity of the surface-treated hollow silica particles. Furthermore, in the manufacturing method of the present invention, a lower dielectric loss tangent of the hollow silica particles (I) at a measurement frequency of 10 GHz is preferable, but from the viewpoint of productivity, it is preferably 0.0010 or more, more preferably 0.0020 or more, and even more preferably 0.0023 or more. Furthermore, in the manufacturing method of the present invention, the relative permittivity of the hollow silica particles (I) at a measurement frequency of 10 GHz is preferably 2.5 or less, more preferably 2.0 or less, and even more preferably 1.7 or less, from the viewpoint of further lowering the dielectric loss tangent and relative permittivity of the surface-treated hollow silica particles. Furthermore, in the manufacturing method of the present invention, a lower relative permittivity of the hollow silica particles (I) at a measurement frequency of 10 GHz is preferable, but from the viewpoint of productivity, it is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more. The dielectric loss tangent and relative permittivity of hollow silica particles (I) at a measurement frequency of 10 GHz are determined by the method described in the examples.

[0014] In the manufacturing method of the present invention, the average particle diameter of the hollow silica particles (I) is preferably 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and even more preferably 3 μm or less, from the viewpoint of setting the average particle diameter of the surface-treated hollow silica particles obtained in the manufacturing method of the present invention to a suitable range described later, and from the viewpoint of further lowering the dielectric loss tangent and relative permittivity of the surface-treated hollow silica particles obtained in the manufacturing method of the present invention. Furthermore, from the viewpoint of productivity, it is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. The average particle size of the hollow silica particles (I) can be determined by the method described in the examples.

[0015] In the manufacturing method of the present invention, the total content of alkali metals and alkaline earth metals in the hollow silica particles (I) 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 reducing the total content of alkali metals and alkaline earth metals in the resulting surface-treated hollow silica particles and being suitable for use as an insulating material, and from the viewpoint of productivity, preferably 1 ppb by mass or more, and more preferably 5 ppb by mass or more. The total content of alkali metals and alkaline earth metals in hollow silica particles (I) can be determined by the method described in the examples.

[0016] (Manufacturing of hollow silica particles (I)) In the manufacturing method of the present invention, hollow silica particles (I) can be obtained by known methods, but more preferably by a method comprising the following steps A-1 to A-3. Step A-1: ​​Step to prepare an aqueous emulsion of a hydrophobic liquid using cationic surfactant A. Step A-2: A step to generate hollow silica particle (I) precursors by adding a silanol precursor, an alkaline substance, and a cationic surfactant B to the aqueous emulsion of the hydrophobic liquid obtained in Step A-1. Step A-3: A step in which the hollow silica particle (I) precursor obtained in Step A-2 is heat-treated at a temperature between 1000°C and 1200°C for at least one hour.

[0017] [Process A-1] In step A-1, a water-containing liquid A is mixed and stirred with a cationic surfactant A and a hydrophobic liquid to create an aqueous emulsion of the hydrophobic liquid in which droplets of the hydrophobic liquid are dispersed. The preparation of the aqueous emulsion of the hydrophobic liquid can be carried out by a general method.

[0018] Examples of the water contained in liquid A include distilled water, ion-exchanged water, ultrapure water, and the like. Further, from the viewpoint of more uniformly and stably generating the emulsion of the hydrophobic liquid, liquid A may contain an organic solvent compatible with water. Examples of the organic solvent compatible with water include lower alcohols such as methanol, ethanol, and isopropyl alcohol, and acetone. From the viewpoint of instantaneously reducing the solubility of the hydrophobic liquid in liquid A, the water content in liquid A is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 98% by mass or more, and even more preferably 100% by mass.

[0019] ≪Cationic surfactant A≫ From the viewpoints of facilitating the formation of micelles composed of a silanol precursor and a cationic surfactant B in step A-2 described later and decomposing / volatilizing in step A-3 described later, the cationic surfactant A is preferably a quaternary ammonium salt, more preferably at least one selected from alkyltrimethylammonium salts and dialkyldimethylammonium salts, and still 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)

[0020] 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 a plurality of R 3 may be different groups, and X ― represents 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, various eicosyl groups, and various docosyl 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 From the standpoint of availability, it is preferable that it be a methyl group.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The quaternary ammonium salt is preferably lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, and behenyltrimethylammonium chloride, more preferably stearyltrimethylammonium chloride and behenyltrimethylammonium chloride, from the viewpoint of facilitating the formation of micelles consisting of a silanol precursor and cationic surfactant B in step A-2, and from the viewpoint of facilitating decomposition and volatilization in step A-3.

[0025] Hydrophobic liquids The hydrophobic liquid is preferably one that can form emulsified droplets (emulsified oil droplets) in water. Furthermore, considering the use of liquid A containing water as the dispersion medium, and the improvement of the utilization efficiency of the hydrophobic liquid, the temperature range in which the liquid is in its 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, hydrocarbons having 6 to 18 carbon atoms are preferred, hydrocarbons having 8 to 14 carbon atoms are more preferred, and dodecane is even more preferred, from the viewpoint of ease of preparing aqueous dispersions of hydrophobic liquids.

[0026] In step A-1, the mass ratio of the hydrophobic liquid to water [hydrophobic liquid / water] is preferably 0.3 or higher, more preferably 0.35 or higher, even more preferably 0.4 or higher, and preferably 0.8 or lower, more preferably 0.75 or lower, and even more preferably 0.7 or lower, from the viewpoint of ensuring that the particle size of the resulting hydrophobic liquid droplets is within an appropriate range.

[0027] In step A-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 0.03 or higher, and even more preferably 0.04 or higher, from the viewpoint of dispersing the hydrophobic liquid in liquid A, and from the viewpoint of controlling the particle size of the dispersion of the hydrophobic liquid in the aqueous medium, it is preferably 0.08 or lower, more preferably 0.07 or lower, and even more preferably 0.06 or lower.

[0028] In step A-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 A-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 0.1 μm or more, more preferably 0.3 μm or more, even more preferably 0.5 μm or more, and preferably 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and even more preferably 3 μm or less, from the viewpoint of setting the average particle diameter of the surface-treated hollow silica particles obtained by the manufacturing method of the present invention to a suitable range described later. The volume-average particle size of a droplet containing a hydrophobic liquid can be determined by the method described in the examples.

[0029] [Process A-2] In step A-2, the aqueous emulsion of the hydrophobic liquid obtained in step A-1 is mixed with a silanol precursor, an alkaline substance, and a cationic surfactant B to produce a hollow silica particle (I) precursor. Specifically, first, micelles consisting of cationic surfactant B and the silanol precursor accumulate on the surface of the droplets of the hydrophobic liquid. Then, the silanol precursor is hydrolyzed by the alkaline substance 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 droplets of the hydrophobic liquid. The silanol compound in this complex condenses in the presence of the alkaline substance to form silica, and a hollow silica particle (I) precursor is formed on the surface of the droplets of the hydrophobic liquid, having an outer shell containing silica and cationic surfactant B, and containing the hydrophobic liquid inside. The hollow silica particle (I) precursor also contains cationic surfactant A used in step A-1. The mixture of a hydrophobic liquid aqueous emulsion, a silanol precursor, an alkaline substance, and cationic surfactant B may be prepared by simultaneously or separately mixing the silanol precursor and cationic surfactant B into the hydrophobic liquid aqueous emulsion, or by mixing the hydrophobic liquid aqueous emulsion with either the silanol precursor or cationic surfactant B first, and then mixing the other.

[0030] Step A-2 may include, after the formation of the hollow silica particle (I) precursor and before step A-3, a step of isolating the hollow silica particle (I) precursor and a step of drying the hollow silica particle (I) precursor. The isolation of the hollow silica particle (I) precursor can be carried out, for example, by filtration. The drying of the hollow silica particle (I) precursor can be carried out, for example, by heating to a temperature of 100°C or higher and below the boiling point of the hydrophobic liquid contained in the hollow silica particle (I) precursor, if the boiling point of the hydrophobic liquid contained in the hollow silica particle (I) precursor is higher than 100°C. If the boiling point of the hydrophobic liquid contained in the hollow silica particle (I) precursor is 100°C or lower, the hollow silica particle (I) precursor can be dried, for example, by freeze-drying.

[0031] ≪Silanol precursor≫ Silanol precursors are compounds that produce silanol compounds through hydrolysis of alkoxysilanes, 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)

[0032] 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.

[0033] 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 (I) precursor to become dense, resulting in large shrinkage during calcination, and thus the relative permittivity and dielectric loss tangent of the resulting hollow silica particle (I) tend to be high. Conversely, alkoxy groups having 5 or more carbon atoms result in a slower hydrolysis rate.

[0034] 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, alkyl orthosilicate and alkyl pyrosilicate are preferred, and ethyl orthosilicate and ethyl pyrosilicate are more preferred. Silanol precursors can be used alone or in combination of two or more types.

[0035] The mass ratio of the silanol precursor to the hydrophobic liquid [silanol precursor / hydrophobic liquid] is preferably 10 or more, more preferably 20 or more, even more preferably 25 or more, and preferably 90 or less, more preferably 80 or less, and even more preferably 75 or less, from the viewpoint of keeping the porosity of the hollow silica particles (I) within an appropriate range.

[0036] ≪Cationic surfactant B≫ As cationic surfactant B, the same cationic surfactant B as cationic surfactant A shown in step A-1 can be used. From the viewpoint of facilitating the formation of silanol precursor micelles and facilitating decomposition and volatilization in step A-3, cationic surfactant B is preferably a salt of a quaternary ammonium, more preferably lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, and behenyltrimethylammonium chloride, and even more preferably lauryltrimethylammonium chloride. The cationic surfactant B used in this process may be the same as or different from the cationic surfactant A used in process A-1. Furthermore, cationic surfactant B can be used alone or as a mixture of two or more types.

[0037] 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, and even more preferably 6 or more, from the viewpoint of suppressing the formation of non-hollow particles, and from the viewpoint of the dispersibility of the hollow silica particle (I) precursor, it is preferably 25 or less, more preferably 20 or less, and even more preferably 18 or less.

[0038] Alkaline substances Silanol precursors are hydrolyzed to silanol by alkaline substances, and then undergo dehydration condensation to form silica. Specific examples of alkaline substances include those described in paragraph

[0014] of Japanese Patent Publication No. 2016-121060. Among these, quaternary ammonium hydroxide salts are preferred. Specific examples of quaternary ammonium hydroxide salts include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tributylmethylammonium hydroxide, trimethylhydroxyethylammonium hydroxide (choline), tetraethanolammonium hydroxide, methyltriethanolammonium hydroxide, and dimethylbis(2-hydroxyethyl)ammonium hydroxide. From the viewpoint of densifying the outer shell of the hollow silica particle (I) precursor, tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylhydroxyethylammonium hydroxide, methyltriethanolammonium hydroxide, and dimethylbis(2-hydroxyethyl)ammonium hydroxide are preferred, and tetramethylammonium hydroxide and dimethylbis(2-hydroxyethyl)ammonium hydroxide are more preferred.

[0039] The mass ratio of the silanol precursor to the alkaline substance [silanol precursor / alkaline substance] is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more, from the viewpoint of densifying the outer shell of the hollow silica particle (I) precursor, and from the viewpoint of efficiently carrying out the condensation reaction of the silanol precursor, it is preferably 100 or less, more preferably 80 or less, even more preferably 60 or less, and even more preferably 40 or less.

[0040] The alkaline substance may include, in addition to the quaternary ammonium hydroxide salt mentioned above, alkali metal salts, alkaline earth metal salts, etc. However, in order to reduce the content of alkali metals and alkaline earth metals in the resulting hollow silica particles (I), the total content of alkali metals and alkaline earth metals in the silanol precursor is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, and even more preferably 10 ppm by mass or less.

[0041] It is preferable to mix the alkaline substance with cationic surfactant B and contact it with the silanol precursor to obtain hollow silica particles (I) that are suitable for use in the production method of the present invention. Contact between the mixture of the alkaline substance and cationic surfactant B and the silanol precursor may be carried out by adding the mixture of the alkaline substance and cationic surfactant B to the reaction system containing the silanol precursor, or by adding the silanol precursor to the reaction system containing the mixture of the alkaline substance and cationic surfactant B. However, from the viewpoint of increasing porosity and increasing synthesis concentration to improve productivity, it is preferable to add the mixture of the alkaline substance and cationic surfactant B to the reaction system containing the silanol precursor.

[0042] The temperature at which step A-2 is carried out can be appropriately adjusted depending on the type and amount of silanol precursor and alkaline substance used, and is preferably 0°C to 100°C from the viewpoint of densifying the outer shell of the hollow silica particle (I) 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, it is preferable to use ethyl orthosilicate or ethyl pyrosilicate from the viewpoint of reaction control.

[0043] The duration for performing step A-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 (I) 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.

[0044] ≪Hollow Silica Particle (I) Precursor≫ The hollow silica particle (I) precursor is a composite silica particle having a silica-containing outer shell and containing a hydrophobic liquid inside the outer shell. The outer shell has pores formed radially toward the particle center, using a cationic surfactant as a template.

[0045] [Process A-3] In step A-3, the hollow silica particle (I) precursor obtained in step A-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 (I) precursor, and after volatilizing the hydrophobic liquid inside, the pores present in the outer shell are sealed by calcination to obtain hollow silica particles (I) with a uniform outer shell.

[0046] The heat treatment temperature in step A-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 (I), 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 (I).

[0047] The heat treatment time in step A-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 (I), 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 (I).

[0048] (Silane coupling agent) Known silane coupling agents can be used in step 1, for example, vinylsilane-based silane coupling agents, (meth)acrylic-based silane coupling agents, aminosilane-based silane coupling agents, epoxysilane-based silane coupling agents, mercaptosilane-based silane coupling agents, imidazolesilane-based silane coupling agents, ureido-based silane coupling agents, isocyanate-based silane coupling agents, triazinethiol-based silane coupling agents, organosilazane compound-based silane coupling agents, organohalogenated silane-based silane coupling agents, alkylalkoxysilanes, etc.

[0049] Examples of vinylsilane-based silane coupling agents include vinyltrimethoxysilane and vinyltriethoxysilane. Examples of (meth)acrylic silane coupling agents include 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane. Examples of aminosilane-based silane coupling agents include aminopropyltrimethoxysilane, aminopropyltriethoxysilane, N-phenylaminopropyltrimethoxysilane, and 3-(2-aminoethylamino)propyltrimethoxysilane. Examples of epoxysilane-based silane coupling agents include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, glycidylbutyltrimethoxysilane, and (3,4-epoxycyclohexyl)ethyltrimethoxysilane. Examples of mercaptosilane-based silane coupling agents include 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane. Examples of imidazole-silane silane coupling agents include triethoxy-3-(2-imidazolin-1-yl)propylsilane. Examples of ureido-based silane coupling agents include 3-ureidopropyltrialkoxysilane. Examples of isocyanate-based silane coupling agents include 3-isocyanatetopropyltriethoxysilane. Examples of triazinethiol-based silane coupling agents include 6-triethoxysilylpropylamino-1,3,5-triazine-2,4-dithiol monosodium salt. Examples of organodisilazane compound-based silane coupling agents include hexamethyldisilazane. Examples of organohalogenated silane coupling agents include methyltrichlorosilane and phenyltrichlorosilane. Examples of alkylalkoxysilanes include methyltrimethoxysilane, dodecyltrimethoxysilane, dimethyldimethoxysilane, and trimethylmethoxysilane.

[0050] In the manufacturing method of the present invention, the silane coupling agent used in step 1 is preferably one or more selected from aminosilane-based silane coupling agents and epoxysilane-based silane coupling agents, more preferably one or more selected from N-phenylaminopropyltrimethoxysilane and glycidoxypropyltrimethoxysilane, and even more preferably N-phenylaminopropyltrimethoxysilane, from the viewpoint of improving the handling of the precursor of the resin composition when adding surface-treated hollow silica particles to the resin composition. In the manufacturing method of the present invention, the silane coupling agent used in step 1 is not included in the solvent (S) described later.

[0051] In the manufacturing method of the present invention, the amount of silane coupling agent mixed in step 1 is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 0.8 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of hollow silica particles (I), from the viewpoint of sufficiently reducing the silanol on the surface of the surface-treated hollow silica particles and lowering the dielectric loss tangent. Furthermore, from the viewpoint of avoiding deterioration of the dielectric loss tangent and relative permittivity due to excessive silane coupling agent, the amount is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, even more preferably 4 parts by mass or less, and even more preferably 1.5 parts by mass or less, per 100 parts by mass of hollow silica particles (I).

[0052] In the manufacturing method of the present invention, the boiling point of the silane coupling agent in step 1 is preferably 100°C or higher, more preferably 150°C or higher, and even more preferably 200°C or higher, from the viewpoint of efficiently adsorbing the silane coupling agent onto the surface of the hollow silica particles (II) obtained in step 2, and from the viewpoint of productivity, it is preferably 400°C or lower, more preferably 350°C or lower, and even more preferably 320°C or lower.

[0053] (Solvent (S)) In step 1, the solvent (S) satisfies the following conditions (1) to (3). Condition (1) The freezing point at atmospheric pressure is 0°C or lower. Condition (2) Boiling point at atmospheric pressure is 120°C or lower Condition (3) Composed of two or more elements selected from hydrogen, carbon, and oxygen.

[0054] Condition (1) specifies the freezing point of the solvent (S). Condition (1) allows the mixture obtained in step 1 to be treated as a fluid at temperatures above 0°C, which is the temperature range in which the manufacturing method of the present invention is normally carried out. The freezing point of solvent (S) under atmospheric pressure in condition (2) is preferably -10°C or lower, more preferably -20°C or lower, from the viewpoint of efficiently preparing the mixture in step 1. Also, from the viewpoint of availability, it is preferably -140°C or higher, more preferably -130°C or higher, and even more preferably -120°C or higher.

[0055] Condition (2) specifies the boiling point of the solvent (S). Condition (2) allows step 2 of the manufacturing method of the present invention to be carried out smoothly. The boiling point of the solvent (S) under atmospheric pressure in condition (2) is preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 85°C or lower, from the viewpoint of facilitating the distillation of the solvent (S) in step 2. Furthermore, from the viewpoint of facilitating the work in step 1 and preventing the unintentional release of the solvent (S) into the environment, it is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher.

[0056] Condition (3) is that the solvent (S) does not have properties that promote the cleavage of siloxane bonds. Structures that give properties that promote the cleavage of siloxane bonds include those having amino groups, sulfonic acid groups, and phosphate groups as functional groups that impart alkalinity or acidity, but the solvent (S) that satisfies condition (3) is a compound that does not have these amino groups, sulfonic acid groups, and phosphate groups.

[0057] In the present invention, preferred examples of the solvent (S) include one or more selected from alcohols, ethers, esters, ketones, hydrocarbons, and water. Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, and isobutanol. Examples of ethers include diethyl ether, di-n-propyl ether, diisopropyl ether, tetrahydrofuran, and tetrahydropyran. Examples of esters include methyl acetate and ethyl acetate. Examples of ketones include acetone and methyl ethyl ketone. Examples of hydrocarbons include n-hexane, cyclohexane, and toluene.

[0058] Among these, the solvent (S) is preferably one or more selected from alcohols, ketones, and hydrocarbons, more preferably one or more selected from ethanol, methanol, isopropanol, acetone, methyl ethyl ketone, and hexane, even more preferably one or more selected from ethanol, isopropanol, methyl ethyl ketone, and hexane, and still more preferably ethanol.

[0059] The solvent (S) may be a mixture of compounds that satisfy conditions (1) to (3). Furthermore, since step 1 is a step of preparing a mixture consisting of hollow silica particles (I), a silane coupling agent, and a solvent (S) that satisfies the above conditions (1) to (3), it is possible to make it free of components that have properties that promote the cleavage of siloxane bonds.

[0060] In the manufacturing method of the present invention, the amount of solvent (S) mixed in step 1 is preferably 500 parts by mass or more, more preferably 600 parts by mass or more, even more preferably 700 parts by mass or more, and even more preferably 800 parts by mass or more, per 100 parts by mass of hollow silica particles (I), from the viewpoint of preventing aggregation of hollow silica particles (I) and uniformly treating the hollow silica particles (I) with the silane coupling agent, and from the viewpoint of productivity, it is preferably 1200 parts by mass or less, more preferably 1100 parts by mass or less, and even more preferably 1000 parts by mass or less, per 100 parts by mass of hollow silica particles (I).

[0061] <Process 2> Step 2 is a step in which the solvent (S) is removed from the dispersion of hollow silica particles (I) obtained in Step 1 under reduced pressure at a temperature of 60°C or lower to obtain hollow silica particles (II). In this invention, distillation refers to the operation of converting a liquid substance into a gaseous state and removing it from the system. When the solvent (S) is distilled off, some of the components other than the solvent (S) may also be distilled off along with the solvent (S). In step 2, by distilling off the solvent (S) under reduced pressure at a temperature of 60°C or lower, it is possible to prevent the silane coupling agents from condensing during the distillation of the solvent (S). This reduces the amount of silanol groups on the surface of the resulting surface-treated hollow silica particles, thereby lowering the dielectric loss tangent.

[0062] In step 2, the removal of solvent (S) is preferably carried out under reduced pressure, that is, at a pressure lower than atmospheric pressure. Examples of apparatus for performing the operation of removing solvent (S) under reduced pressure in step 2 include a rotary evaporator, a vacuum dryer, and a vacuum spray dryer. In this invention, atmospheric pressure is defined as an absolute pressure of 1013 hPa.

[0063] In step 2, the pressure used to remove the solvent (S) by distillation can be appropriately adjusted depending on the type and amount of silane coupling agent and solvent (S) used in step 1. From the viewpoint of lowering the boiling point of the solvent (S) and increasing the distillation efficiency, the absolute pressure is preferably 300 hPa or less, more preferably 270 hPa or less, even more preferably 140 hPa or less, and even more preferably 120 hPa or less. Furthermore, from the viewpoint of preventing the volatilization of the silane coupling agent, the pressure is preferably 1 hPa or more, more preferably 10 hPa or more, even more preferably 50 hPa or more, even more preferably 80 hPa or more, and even more preferably 90 hPa or more.

[0064] In step 2, the temperature at which the solvent (S) is removed by distillation is 60°C or lower, preferably 55°C or lower, more preferably 40°C or lower, even more preferably 35°C or lower, and even more preferably 30°C or lower, from the viewpoint of preventing condensation reactions between the silane coupling agents during the removal of the solvent (S). Furthermore, from the viewpoint of economy and productivity, it is preferably 20°C or higher. In the manufacturing method of the present invention, the temperature at which the solvent (S) is distilled off in step 2 refers to the temperature of the vapor of the solvent (S) when the solvent (S) is evaporated.

[0065] In step 2, the degree of solvent (S) removal is determined by the amount of solvent (S) present in the hollow silica particles (II) obtained in step 2. The solvent (S) content in the hollow silica particles (II) obtained in step 2 is preferably 10 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.7 parts by mass or less, and even more preferably 0.5 parts by mass or less, per 100 parts by mass of hollow silica particles (II), from the viewpoint of improving the productivity of step 3 and lowering the dielectric loss tangent of the surface-treated hollow silica particles. A lower content of the mixed solvent (S) is preferable, but from the viewpoint of efficiency in step 2, it is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.3 parts by mass or more.

[0066] <Process 3> Step 3 is a step in which the hollow silica particles (II) obtained in Step 2 are heated to a temperature of 100°C or higher. In step 3, the heating temperature for heating the hollow silica particles (II) is 100°C or higher, preferably 110°C or higher, more preferably 115°C or higher, and even more preferably 120°C or higher, from the viewpoint of allowing sufficient reaction between the silane coupling agent and the silanol groups on the surface of the hollow silica particles (II), and from the viewpoint of avoiding decomposition of the silane coupling agent, preferably 200°C or lower, more preferably 180°C or lower, even more preferably 160°C or lower, and even more preferably 140°C or lower. The heating temperature for the hollow silica particles (II) in step 3 is the surface temperature of the hollow silica particles (II) in step 3.

[0067] In step 3, the heating time for heating the hollow silica particles (II) is preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 1 hour or more, even more preferably 3 hours or more, and even more preferably 4 hours or more, from the viewpoint of allowing sufficient reaction between the silane coupling agent and the silanol groups on the surface of the hollow silica particles (II), and from the viewpoint of productivity, preferably 10 hours or less, more preferably 8 hours or less, and even more preferably 6 hours or less.

[0068] [Surface-treated hollow silica particles] The surface-treated hollow silica particles of the present invention have a ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) of 0.20 or less when measured using the following measurement procedure. The surface-treated hollow silica particles of the present invention can be obtained by the method for producing surface-treated hollow silica particles of the present invention described above. (Measurement procedure) In a suspension of surface-treated hollow silica particles prepared so that the concentration of surface-treated hollow silica particles in a 2% by mass sodium chloride aqueous-ethanol mixed solvent was 1% by mass, the pH was adjusted to 4 or less with a 0.01N-HCl aqueous solution, and then a 0.1N-NaOH aqueous solution was added dropwise at a rate of 0.005 mL / 10 seconds. The titration values ​​(I) and (II) below were determined from the titration curve and the differential curve of the titration curve. Titration value (I): Volume of 0.1N NaOH aqueous solution added dropwise from pH 4 to the pH at which the slope of the differential curve of the titration curve changes from decreasing to increasing. Titration value (II): The volume of 0.1N NaOH aqueous solution added dropwise from the pH point where the slope of the differential curve of the titration curve changes from decreasing to increasing until the pH reaches 9.

[0069] Figure 1 shows the titration curve, the differential curve of the titration curve, and the titration values ​​(I) and (II) in Example 1 as specific examples of titration values ​​(I) and (II). In the present invention, "the point at which the slope of the differential curve of the titration curve changes from decreasing to increasing" means the point at which, in the differential curve of the titration curve of the suspension with a 0.1N-NaOH aqueous solution obtained by the above measurement procedure, the slope on the differential curve of the titration polarity changes from decreasing to increasing, as illustrated in Figure 1. Furthermore, in the present invention, "the pH at the point where the slope of the differential curve of the titration curve changes from decreasing to increasing" means the pH on the titration curve that corresponds to the amount of 0.1N-NaOH aqueous solution added (volume of 0.1N-NaOH aqueous solution) at the point where "the slope of the differential curve of the titration curve changes from decreasing to increasing," as illustrated in Figure 1.

[0070] The surface-treated hollow silica particles of the present invention have a ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) of 0.20 or less, thereby lowering the dielectric loss tangent at a measurement frequency of 10 GHz. The reason why the dielectric loss tangent is lower when the surface-treated hollow silica particles of the present invention satisfy the above conditions is not entirely clear, but it is thought to be as follows. Generally, it is known that the silanol groups on the surface of hollow silica particles include hydrogen-bonded silanols, which are adjacent to and associated with other silanol groups, and isolated silanols, which are isolated and not surrounded by other silanol groups. Of these, isolated silanols, in particular, oscillate under high-frequency electric fields, easily dissipating the energy of the electric field, and their effect on increasing the dielectric loss tangent of hollow silica particles is greater than that of hydrogen-bonded silanols. As disclosed in J. Chem. Theory Comput., 8, 1037-1047 (2012), it is generally known that the pKa of hydrogen-bonded silanols is 4.5-5.5, and the pKa of isolated silanols is 8.5-9.9. Typically, when neutralization titration is performed on the silanol groups of hollow silica particles, the peak of hydrogen-bonded silanols can be observed as the lower pH peak and the peak of isolated silanols as the higher pH peak in the differential curve of the titration curve. In the present invention, the titration value (I) measured by the above measurement method corresponds to the amount of 0.1N-NaOH aqueous solution added, which corresponds to the amount of hydrogen-bonded silanol on the surface of the surface-treated hollow silica particles. On the other hand, the titration value (II) measured by the above measurement method corresponds to the amount of 0.1N-NaOH aqueous solution added, which corresponds to the amount of isolated silanol on the surface of the surface-treated hollow silica particles. In this invention, the ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) is an index that corresponds to the ratio of the amount of isolated silanols to the amount of hydrogen-bonding silanols (isolated silanols / hydrogen-bonding silanols) on the surface of surface-treated hollow silica particles. The surface-treated hollow silica particles of the present invention have a ratio (titration value (II) / titration value (I)) of 0.20 or less, that is, a low proportion of isolated silanols. This is thought to suppress the vibration and energy dissipation of silanols on the surface of the surface-treated hollow silica particles due to a high-frequency electric field, thereby lowering the dielectric loss tangent.

[0071] In the surface-treated hollow silica particles of the present invention, the ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) is 0.20 or less from the viewpoint of lowering the dielectric loss tangent. Furthermore, from the viewpoint of productivity, the ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) is preferably 0.05 or more, more preferably 0.06 or more, even more preferably 0.07 or more, and even more preferably 0.08 or more. The ratio of the titration value (II) to the titration value (I) of surface-treated hollow silica particles (titration value (II) / titration value (I)) is determined more specifically by the method described in the examples.

[0072] In step 1, which is the step of preparing a mixture consisting of hollow silica particles (I), a silane coupling agent, and a solvent (S) for the manufacturing method of the present invention described above, it is preferable that the solvent (S) does not have properties that promote the cleavage of siloxane bonds, and that no components that have properties that promote the cleavage of siloxane bonds are used, thereby suppressing the formation of isolated silanols. Furthermore, in step 2 of the manufacturing method of the present invention described above, removing the solvent (S) at a temperature of 60°C or lower is preferable because it prevents the silane coupling agents from condensing during the removal of the solvent (S), thereby suppressing the formation of isolated silanols. Furthermore, in step 3 of the manufacturing method of the present invention, the hollow silica particles (II) obtained in step 2 are heated to 100°C or higher, which allows the silane coupling agent to react sufficiently with the isolated silanol groups on the surface of the hollow silica particles (II), thereby reducing the amount of isolated silanol, and is therefore preferable. In the manufacturing method of the present invention, it is preferable not to use any components that have properties that promote the cleavage of siloxane bonds in steps other than (1), (2), and (3). From the above, the surface-treated hollow silica particles of the present invention can be efficiently obtained by the manufacturing method of the present invention, which allows the ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) to be within a desired range.

[0073] The dielectric loss tangent of the surface-treated hollow silica particles of the present invention at a measurement frequency of 10 GHz is preferably 0.0040 or less, more preferably 0.0035 or less, even more preferably 0.0030 or less, even more preferably 0.0028 or less, and even more preferably 0.0027 or less, from the viewpoint of lowering the dielectric loss tangent of the resin composition containing the surface-treated hollow silica particles, and preferably 0.0001 or more, more preferably 0.0010 or more, even more preferably 0.0020 or more, and even more preferably 0.0023 or more, from the viewpoint of the strength of the surface-treated hollow silica particles. The dielectric loss tangent of surface-treated hollow silica particles can be determined by the method described in the examples.

[0074] The dielectric constant of the surface-treated hollow silica particles of the present invention at a measurement frequency of 10 GHz is preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.0 or less, from the viewpoint of lowering the dielectric constant of the resin composition containing the surface-treated hollow silica particles, and from the viewpoint of the strength of the surface-treated hollow silica particles, it is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and even more preferably 1.5 or more. The relative permittivity of surface-treated hollow silica particles can be determined by the method described in the examples.

[0075] From the viewpoint of lowering the dielectric loss tangent, the BET specific surface area of ​​the surface-treated hollow silica particles of the present invention is preferably 40 m². 2 / g or less, more preferably 30m 2 / g or less, more preferably 20m 2It is less than or equal to / g, and from the viewpoint of increasing the porosity of the surface-treated hollow silica particles and lowering the dielectric constant, it is preferably 5m 2 / g or more, more preferably 8m 2 / g or more, more preferably 10m 2 / g or more, more preferably 12m 2 It is 1 / g or more. The BET specific surface area of ​​surface-treated hollow silica particles can be determined by the method described in the examples.

[0076] The average particle diameter of the surface-treated hollow silica particles of the present invention is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more as a volume-average particle diameter, from the viewpoint of reducing the specific surface area, reducing surface silanol, and lowering the dielectric loss tangent. Furthermore, from the viewpoint of improving the surface properties of the resin composition containing the surface-treated hollow silica particles, it is preferably 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and even more preferably 3 μm or less. The average particle diameter (volume average particle diameter) of surface-treated hollow silica particles can be determined by the method described in the examples.

[0077] The porosity of the surface-treated hollow silica particles of the present invention is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more, from the viewpoint of lowering the dielectric loss tangent and relative permittivity, and from the viewpoint of strength, it is preferably 85% or less, more preferably 80% or less, and even more preferably 75% or less. The porosity of surface-treated hollow silica particles can be determined by the method described in the examples.

[0078] The sphericity of the surface-treated hollow silica particles of the present invention is preferably 0.70 or higher, more preferably 0.75 or higher, and even more preferably 0.80 or higher, from the viewpoint of strength, and 1.00 or lower, preferably 0.95 or lower, from the viewpoint of productivity. The sphericity of surface-treated hollow silica particles can be determined by the method described in the examples.

[0079] The average thickness of the outer shell of the surface-treated 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, and from the viewpoint of strength, it is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, even more preferably 30 nm or more, and even more preferably 40 nm or more. The average thickness of the outer shell of surface-treated hollow silica particles can be determined by the method described in the examples.

[0080] The total content of alkali metals and alkaline earth metals in the surface-treated 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 from the viewpoint of productivity, preferably 1 ppb by mass or more, more preferably 5 ppb by mass or more. The total content of alkali metals and alkaline earth metals in the surface-treated hollow silica particles can be determined by the method described in the examples.

[0081] From the viewpoint of lowering the dielectric loss tangent, the total amount of silanol groups in the surface-treated hollow silica particles of the present invention is preferably 0.10 mmol / g or less, more preferably 0.09 mmol / g or less, and even more preferably 0.08 mmol / g or less. From the viewpoint of productivity, it is preferably 0.01 mmol / g or more, more preferably 0.015 mmol / g or more, and even more preferably 0.02 mmol / g or less. The total amount of silanol groups in surface-treated hollow silica particles can be determined by the method described in the examples.

[0082] [Resin composition] The resin composition of the present invention contains the surface-treated hollow silica particles of the present invention described above. Since the resin composition of the present invention contains the surface-treated hollow silica particles of the present invention described above, the dielectric loss tangent can be reduced.

[0083] The resins constituting the resin composition of the present invention are not particularly limited, but in order to lower the dielectric loss tangent of the resin composition, poly(p-phenylene) resins, liquid crystal polymer resins, epoxy resins, bismaleimide resins, cycloolefin resins, fluororesins, and derivatives thereof are preferred.

[0084] The amount of surface-treated hollow silica particles of the present invention blended 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 processability of the resin composition.

[0085] The dielectric loss tangent of the resin composition of the present invention at a measurement frequency of 10 GHz is preferably 0.0110 or less, more preferably 0.0100 or less, and even more preferably 0.0090 or less, from the viewpoint of suitability as an insulating material for high-frequency circuit boards. A lower dielectric loss tangent of the resin composition of the present invention at a measurement frequency of 10 GHz is preferable, but from the viewpoint of productivity, it is preferably 0.0020 or more, more preferably 0.0040 or more, and even more preferably 0.0060 or more. The dielectric loss tangent of the resin composition can be determined by the method described in the examples.

[0086] The relative permittivity of the resin composition of the present invention at a measurement frequency of 10 GHz is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.5 or less, 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 as low as possible, but from the viewpoint of productivity, it is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and even more preferably 1.5 or more. The dielectric constant of the resin composition can be determined by the method described in the examples.

[0087] [Insulating materials] The insulating material of the present invention includes the resin composition of the present invention described above. The insulating material of the present invention, by containing the resin composition of the present invention, can be made into an insulating material that can reduce transmission loss and transmission delay. The insulating material can be used, for example, in build-up insulating films, insulating layers of copper-clad laminates, prepregs, sealing materials, insulating members of connectors, and insulation materials for electric wires. [Examples]

[0088] In the examples and comparative examples described later, various measurements of hollow silica particles and surface-treated hollow silica particles were performed by the following methods.

[0089] [Measurement method] <Measurement and evaluation of hollow silica particles (I) and surface-treated hollow silica particles used in Step 1> (Volume-average particle diameter of hollow silica particles (I) and surface-treated hollow silica particles used in step 1) The volume-average particle diameter of the hollow silica particles (I) used in step 1 and the surface-treated 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), and the volume-based average particle diameter was determined.

[0090] (Total content of alkali metals and alkaline earth metals in hollow silica particles (I) used in step 1 and in surface-treated hollow silica particles) 100 mg of hollow silica particles (I) or surface-treated hollow silica particles were placed in a platinum crucible, and 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).

[0091] (Dielectric loss tangent and relative permittivity of hollow silica particles (I) used in step 1 and surface-treated hollow silica particles) The relative permittivity and dielectric loss tangent of hollow silica particles (I) and surface-treated 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 (I) or surface-treated hollow silica particles so that they were all within the measurement range (6.75 mm to 21.25 mm from the bottom). The mass of the hollow silica particles filled was calculated from the mass measurements of the hollow silica particles (I) or surface-treated hollow silica particles before and after filling, and the volume of the hollow silica particles (I) or surface-treated hollow silica particles filled in the Teflon tube was determined from the filling mass and specific gravity of the hollow silica particles (I) or surface-treated hollow silica particles. The dielectric loss tangent and relative permittivity were determined by using the measurements of an empty Teflon tube as a blank and calculating the difference between those measurements and those of a Teflon tube filled with hollow silica particles (I) or surface-treated hollow silica particles.

[0092] (BET specific surface area of ​​surface-treated hollow silica particles) The BET specific surface area of ​​surface-treated hollow silica particles was measured using a specific surface area measuring device (Shimadzu Corporation, product name "Flowsorb III 2305"). The samples were pre-treated by heating at 200°C for 15 minutes.

[0093] (Porosity of surface-treated hollow silica particles) The true density of the silica particles was calculated using the following formula based on the density of the surface-treated hollow silica particles of the present invention, 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 surface-treated hollow silica particles (g / cm³)] 3 ) / True density of silica particles (g / cm³) 3)) × 100

[0094] (Average thickness of the outer shell of surface-treated hollow silica particles) Using elastic carbon ELS-C10 (manufactured by Stem Co., Ltd.) and an electrolytic emission scanning electron microscope (Hitachi High-Tech Corporation: S-4800), STEM images of surface-treated hollow silica particles were obtained by observation with an acceleration voltage of 30kV. For 10 surface-treated 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, which was then used as the average thickness of the outer shell of the surface-treated hollow silica particles.

[0095] (Sphericity of surface-treated 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.

[0096] (Ratio of titration value (II) to titration value (I) for surface-treated hollow silica particles (titration value (II) / titration value (I)) and total amount of silanol groups) [Preparation of surface-treated hollow silica particle dispersions for measurement] After taking 1 g of surface-treated hollow silica particles, a solvent (a water-ethanol mixed solvent of NaCl (water:ethanol = 1:1 (mass ratio), NaCl concentration: 2 mass%)) was added to obtain a 1 mass% slurry of surface-treated hollow silica particles. Next, the slurry was stirred with a stirrer at a rotation speed of 250 rpm for 10 minutes, and then dispersed with ultrasound for 5 minutes to obtain a dispersion of surface-treated hollow silica particles for measurement. [Titration of surface-treated hollow silica particle dispersions for measurement] In the obtained surface-treated hollow silica particle dispersion for measurement, a 0.01N-HCl aqueous solution was added to adjust the pH to 3.4. Then, a potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., AT-710) was used to dropwise add a 0.1N-NaOH aqueous solution at a rate of 0.005 mL / 10 seconds. The pH change of the surface-treated hollow silica particle dispersion during titration was recorded, and the total amount of silanol groups (mmol / g) on ​​the surface of the surface-treated hollow silica particles was determined from the volume (mL) of 0.1N-NaOH aqueous solution added dropwise from pH 4 to 9 using the following formula. The total amount of silanol groups (mmol / g) on ​​the surface of surface-treated hollow silica particles = Volume (mL) of 0.1N-NaOH aqueous solution added dropwise from pH 4 to 9 × 0.1 The titration value (I) was defined as the volume of 0.1N NaOH aqueous solution added dropwise from pH 4 to the pH at which the slope of the differential curve of the titration curve changed from decreasing to increasing. The titration value (II) was defined as the volume of 0.1N NaOH aqueous solution added dropwise until the pH reached 9, starting from the pH at which the slope of the differential curve of the titration curve changed from decreasing to increasing. The above procedure was performed three times for each sample, and the average values ​​were taken as the measured value (I) and titration value (II) for each sample. The ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) was then calculated. Figure 1 shows the titration curve, the differential curve of the titration curve, and the titration values ​​(I) and (II) in Example 1. The pH was measured at 20°C.

[0097] <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. Three g of the obtained epoxy resin mixture and two g of surface-treated hollow silica particles obtained in the examples and comparative examples were mixed using a Planetary Vacuum Mixer (manufactured by Thinky Co., Ltd.) 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.

[0098] (Measurement of dielectric loss tangent and relative permittivity 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 samples for measurement, the dielectric loss tangent and relative permittivity of the resin composition were measured in the same manner as "dielectric loss tangent and relative permittivity of hollow silica particles (I) and surface-treated hollow silica particles used in Step 1".

[0099] [Preparation of hollow silica particles (I)] Manufacturing Example 1 Emulsion A (an aqueous dispersion of dodecane with behenyltrimethylammonium chloride as a dispersant) was obtained by mixing and stirring 342.2 g of deionized water, 150 g of dodecane (manufactured by Kishida Chemical Co., Ltd.: reagent grade 1 n-dodecane), and 7.8 g of Cortamin 2285E (manufactured by Kao Corporation: containing 58% by mass of behenyltrimethylammonium chloride). The volume-average particle size of the particles in the obtained emulsion A was 0.5 μm. The particle size of the particles in emulsion A was measured using a dynamic light scattering particle size analyzer "Zetasizer Nano ZS" (manufactured by Malvern Panalytical Corporation) with a square cell with a path length of 10 mm. 13146.5g of deionized water, 184.1g of emulsion A, 125.6g of Cotamin 24P (manufactured by Kao Corporation: containing 27.5% by mass of lauryltrimethylammonium chloride) (in its original form), and 3120.8g of ethyl orthosilicate (manufactured by Asahi Kasei Wacker Silicone Co., Ltd.: TEOS999) were added to a reaction vessel. The mixture was heated to 40°C while stirring, and then stirred for 10 minutes to obtain prepared solution B. Next, 221.5 g (in its original form) of AH212-CS (manufactured by Yokkaichi Synthetic Co., Ltd.: containing 50% by mass of dimethylbis(2-hydroxyethyl)ammonium hydroxide) and 711.6 g (in its original form) of Cortamin 24P were uniformly mixed to obtain prepared solution C. Preparation solution B and preparation solution C were mixed at 25°C, 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 (I) precursor. The obtained hollow silica particle (I) precursor was calcined at 1100°C for 1 hour to obtain hollow silica particle (I). The average particle size of the obtained hollow silica particles (I) was 1.0 μm, the total content of alkali metals and alkaline earth metals was 10 ppm, the relative permittivity at a measurement frequency of 10 GHz was 1.6, and the dielectric loss tangent at a measurement frequency of 10 GHz was 0.0045.

[0100] [Preparation of surface-treated hollow silica particles] Example 1 (Process 1) In a 500 mL flask, 90 g of ethanol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as solvent (S), and 10 g of hollow silica particles (I) obtained in Production Example 1 was added as hollow silica particles (I). After stirring for 30 minutes, ultrasonic dispersion treatment was performed for 30 minutes. Next, 0.2 g of N-phenyl-3-aminopropyltrimethoxysilane (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was added as a silane coupling agent, and the mixture was stirred for 1 hour to obtain an ethanol dispersion of hollow silica particles (I). (Process 2) In step 1, the ethanol dispersion of hollow silica particles (I) was used to obtain hollow silica particles (II) by distilling off the ethanol (solvent (S)) in a rotary evaporator (N-1300E (manufactured by Tokyo Rikakikai Co., Ltd.), NVP-1000 (diaphragm-type vacuum pump, manufactured by Tokyo Rikakikai Co., Ltd.), NVC-3000 (vacuum controller, with vapor temperature sensor kit TS-V, manufactured by Tokyo Rikakikai Co., Ltd.)) under conditions where the vapor temperature was 30°C. At this time, the pressure was 100 hPa (absolute pressure), and the temperature of the water bath used to heat the 500 mL flask was 55°C. The amount of ethanol (solvent (S)) mixed in the obtained hollow silica particles (II) was 0.5 parts by mass per 100 parts by mass of hollow silica particles (II). The amount of ethanol (solvent (S)) mixed in the obtained hollow silica particles (II) was determined using an infrared moisture meter (FD-230, manufactured by Kett Scientific Research Institute Co., Ltd.) with a 5g sample, dried at a temperature of 150°C, and measured in mode 96 (monitoring time 2.5 min / moisture content fluctuation range 0.05%). (Step 3) The obtained hollow silica particles (II) were placed in a rectangular stainless steel (SUS304) tray and heated at 130°C for 5 hours in a constant-temperature drying oven (DKN302, manufactured by Yamato Scientific Co., Ltd.) to obtain surface-treated hollow silica particles.

[0101] Example 2 Surface-treated hollow silica particles were obtained in the same manner as in Example 1, except that the amount of N-phenyl-3-aminopropyltrimethoxysilane added in Step 1 was 0.4 g. The amount of ethanol (solvent (S)) mixed in the obtained hollow silica particles (II) was 0.5 parts by mass per 100 parts by mass of hollow silica particles (II).

[0102] Example 3 Surface-treated hollow silica particles were obtained in the same manner as in Example 1, except that the amount of N-phenyl-3-aminopropyltrimethoxysilane added in Step 1 was 0.1 g. The content of ethanol (solvent (S)) mixed in the obtained hollow silica particles (II) was 0.5 parts by mass per 100 parts by mass of hollow silica particles (II).

[0103] Example 4 In step 1, the ethanol in solvent (S) was changed to isopropanol (reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and in step 2, the pressure during the distillation of isopropanol (solvent (S)) was set to 80 hPa. Surface-treated hollow silica particles were obtained in the same manner as in Example 1. The isopropanol (solvent (S)) content in the obtained hollow silica particles (II) was 0.5 parts by mass per 100 parts by mass of hollow silica particles (II).

[0104] Example 5 In step 1, ethanol in the solvent (S) was replaced with hexane (a reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and in step 2, the pressure during the distillation of hexane (solvent (S)) was set to 270 hPa. Except for these changes, surface-treated hollow silica particles were obtained in the same manner as in Example 1. The hexane (solvent (S)) content in the obtained hollow silica particles (II) was 0.5 parts by mass per 100 parts by mass of hollow silica particles (II).

[0105] Example 6 In step 1, ethanol in solvent (S) was replaced with methyl ethyl ketone (a reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and in step 2, the pressure during the distillation removal of methyl ethyl ketone (solvent (S)) was set to 150 hPa. Surface-treated hollow silica particles were obtained in the same manner as in Example 1. The content of methyl ethyl ketone (solvent (S)) mixed in the obtained hollow silica particles (II) was 0.5 parts by mass per 100 parts by mass of hollow silica particles (II).

[0106] Example 7 In step 3, surface-treated hollow silica particles were obtained in the same manner as in Example 1, except that the heating conditions for the obtained hollow silica particles (II) were set to 150°C for 5 hours.

[0107] Comparative Example 1 The hollow silica particles (I) obtained in Production Example 1 were used as the hollow silica particles in Comparative Example 1. In other words, the hollow silica particles in Comparative Example 1 are hollow silica particles that have not undergone surface treatment.

[0108] Comparative Example 2 Hollow silica particles for Comparative Example 2 were obtained in the same manner as in Example 1, except that Step 1 was performed as described below. The amount of ethanol (solvent (S)) present in the hollow silica particles (II) after the distillation of ethanol (solvent (S)) in Step 2 was 0.5 parts by mass per 100 parts by mass of hollow silica particles (II). (Process 1) In a 500 mL flask, 80.0 g of ethanol, 8.9 g of deionized water, and 10 g of hollow silica particles (I) obtained in Production Example 1 were added and stirred for 15 minutes, followed by ultrasonic dispersion treatment for 30 minutes. Subsequently, 0.6 g of 29% aqueous ammonia (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a component that promotes the cleavage of siloxane bonds, and 0.2 g of N-phenyl-3-aminopropyltrimethoxysilane as a silane coupling agent were added and stirred for 1 hour to obtain an ethanol dispersion of hollow silica particles.

[0109] Comparative Example 3 In Step 2, hollow silica particles of Comparative Example 3 were obtained in the same manner as in Example 1, except that the conditions of the rotary evaporator were set to such that the vapor temperature of the ethanol dispersion of hollow silica particles (I) was 70°C. In Step 2, the pressure during the distillation of ethanol (solvent (S)) was 700 hPa, and the temperature of the water bath used to heat the 500 mL flask was 90°C. The content of ethanol (solvent (S)) mixed in the hollow silica particles (II) after the distillation of ethanol (solvent (S)) in Step 2 was 0.5 parts by mass per 100 parts by mass of hollow silica particles (II).

[0110] Comparative Example 4 Hollow silica particles for Comparative Example 4 were obtained in the same manner as in Example 1, except that step 2 was omitted.

[0111] Comparative Example 5 In step 3, hollow silica particles for Comparative Example 5 were obtained in the same manner as in Example 1, except that the conditions of the constant-temperature dryer were set to 80°C.

[0112] Table 1 shows the conditions for steps 1 to 3, the measurement and evaluation results of the surface-treated hollow silica particles obtained in the examples, and the hollow silica particles obtained in the comparative examples.

[0113] [Table 1]

[0114] As shown in the results in Table 1, the surface-treated hollow silica particles obtained in Examples 1 to 7, which are the manufacturing methods of the present invention, were obtained by preparing a mixture consisting of hollow silica particles (I), a silane coupling agent, and a solvent (S) in step 1, removing the solvent (S) under reduced pressure at a temperature of 60°C or lower in step 2, and further heating at a temperature of 100°C or higher in step 3. As a result, the ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) was 0.20 or less, and the dielectric loss tangent was reduced. On the other hand, in Comparative Example 1, where steps 1 to 3 were not performed; in Comparative Example 2, ammonia was used in addition to hollow silica particles (I), silane coupling agent, and solvent (S) in step 1; in Comparative Example 3, step 1 was the same procedure as in Example 1, but the temperature during the removal of solvent (S) in step 2 exceeded 60°C; in Comparative Example 4, step 2 was not performed; and in Comparative Example 5, the heating temperature in step 3 was less than 100°C was used for the hollow silica particles obtained, and the ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) exceeded 0.20, indicating a high dielectric loss tangent. Therefore, it is considered that a resin composition containing surface-treated 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 surface-treated hollow silica particles, including the following steps. Step 1: A step of preparing a mixture consisting of hollow silica particles (I), a silane coupling agent, and a solvent (S) that satisfies the following conditions (1) to (3). Condition (1) The freezing point at atmospheric pressure is 0°C or lower. Condition (2) Boiling point at atmospheric pressure is 120°C or lower. Condition (3) Composed of two or more elements selected from hydrogen, carbon, and oxygen. Step 2: The mixture obtained in Step 1 is subjected to reduced pressure and at a temperature of 60°C or lower to remove the solvent (S) to obtain hollow silica particles (I) and hollow silica particles (II) consisting of a silane coupling agent. Step 3: A step of heating the hollow silica particles (II) obtained in Step 2 to 100°C or higher.

2. A method for producing surface-treated hollow silica particles according to claim 1, wherein the dielectric loss tangent of the hollow silica particle (I) at a measurement frequency of 10 GHz is 0.0100 or less.

3. A method for producing surface-treated hollow silica particles according to claim 1, wherein the relative permittivity of the hollow silica particles (I) at a measurement frequency of 10 GHz is 2.5 or less.

4. A method for producing surface-treated hollow silica particles according to claim 1, wherein the total content of alkali metals and alkaline earth metals in the hollow silica particles (I) is 50 ppm by mass or less.

5. A method for producing surface-treated hollow silica particles, wherein the amount of silane coupling agent mixed in step 1 is 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of hollow silica particles (I).

6. A method for producing surface-treated hollow silica particles according to claim 1, wherein the silane coupling agent is one or more selected from aminosilane-based silane coupling agents and epoxysilane-based silane coupling agents.

7. Surface-treated hollow silica particles in which the ratio of titration value (II) to titration value (I) (titration value (II) / titration value (I)) when measured using the measurement procedure below is 0.20 or less. (Measurement procedure) In a suspension of surface-treated hollow silica particles prepared so that the concentration of surface-treated hollow silica particles in a 2% by mass sodium chloride aqueous-ethanol mixed solvent solution is 1% by mass, the pH is adjusted to 4 or less with a 0.01 N HCl aqueous solution, and then a 0.1 N NaOH aqueous solution is added dropwise at a rate of 0.005 mL / 10 sec. The titration values ​​(I) and (II) below are determined from the titration curve and the differential curve of the titration curve. Titration value (I): Volume of 0.1 N NaOH aqueous solution added dropwise from pH 4 to the pH at which the slope of the differential curve of the titration curve changes from decreasing to increasing. Titration value (II): The volume of 0.1 N NaOH aqueous solution added dropwise from the pH at which the slope of the differential curve of the titration curve changes from decreasing to increasing until the pH reaches 9.

8. The surface-treated hollow silica particles according to claim 7, wherein the dielectric loss tangent at a measurement frequency of 10 GHz is 0.0040 or less.

9. The surface-treated hollow silica particles according to claim 7, wherein the relative permittivity at a measurement frequency of 10 GHz is 2.5 or less.

10. The BET specific surface area is 40 m². ２ Surface-treated hollow silica particles according to claim 7, wherein the particle size is less than or equal to / g.

11. The surface-treated hollow silica particles according to claim 7, wherein the average particle diameter is 0.1 μm or more and 20 μm or less.

12. A resin composition comprising surface-treated hollow silica particles as described in claim 7.

13. An insulating material comprising the resin composition according to claim 12.

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