Method for producing hollow silica particles

Abstract

To provide a method for producing hollow silica particles in which cracking can be prevented even when the hollow silica particles undergo pulverization.SOLUTION: A method for producing hollow silica particles comprises the following steps 1 to 3. Step 1: a step of forming a hollow silica particle precursor in a liquid phase, Step 2: a step of aggregating the hollow silica particle precursor in the liquid phase from Step 1 to provide an aggregate of hollow silica particle precursors, and Step 3: a step of removing the liquid phase from the aggregate of hollow silica particle precursors from Step 2.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing hollow silica particles. [Background technology]

[0002] The use of high frequencies of several tens of GHz is being considered for high-speed communication technologies such as 5G and radars used in autonomous driving. In high-frequency circuits that handle such high-frequency radio waves, insulating materials with excellent dielectric properties such as low dielectric constant and low dielectric tangent are required to reduce transmission loss and transmission delay, and similar performance is required for the silica particles that are mixed into the insulating material to improve the dielectric properties. In response to these demands, the use of hollow silica particles has been considered to improve the dielectric properties of silica particles. In addition, miniaturization of high-frequency circuits is desired, and the silica particles are also required to have a smaller particle size.

[0003] For example, Patent Document 1 describes hollow silica particles that have a shell layer containing silica and have a space inside the shell layer, and that have a relative dielectric constant of 1.3 to 5.0 at 1 GHz and a dielectric tangent of 0.0001 to 0.05 at 1 GHz. Patent Document 2 describes hollow silica particles having an outer shell that forms an internal space, the outer shell being composed of a component containing silica, and the surface of the hollow silica particles being surface-treated with a nitrogen-containing silane coupling agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 172294 [Patent Document 2] JP 2020-83736 A Summary of the Invention [Problem to be solved by the invention]

[0005] The hollow silica particles in Patent Document 1 cannot be incorporated into insulating materials as is because the silanols on the particle surface condense with each other during firing, causing the particles to aggregate. Although it is also disclosed that the hollow silica particles can be crushed as necessary, there is a problem that the hollow silica particles are strongly fused during firing, and if they are crushed by a normal method, the hollow silica particles will crack, causing an increase in the relative dielectric constant and dielectric loss tangent. In addition, in Patent Document 2, hollow silica particles are crushed using a jet mill, but in order to prevent the hollow silica particles from cracking, it was necessary to reduce the crushing force, which resulted in a problem that the crushing took time, lowering productivity, and that when the particle size was small, poor crushing was likely to occur. As described above, in the conventional method for producing hollow silica particles, hollow silica particles aggregated by firing are easily broken in the step of crushing the aggregates, and the productivity of the crushing step is low. An object of the present invention is to provide a method for producing hollow silica particles, which can suppress cracking even when hollow silica particles are crushed. [Means for solving the problem]

[0006] The present inventors have found that by agglomerating hollow silica particle precursors obtained in a liquid phase to form hollow silica particle precursor aggregates, it is possible to prevent the hollow silica particles from strongly fusing together during the subsequent firing, and further to reduce the cracking of the hollow silica particles when the aggregates are subsequently crushed. The present invention relates to the following [1]. [1] A method for producing hollow silica particles, comprising the following steps 1 to 3: Step 1: Obtaining hollow silica particle precursor in a liquid phase Step 2: A step of aggregating the hollow silica particle precursor in the liquid phase obtained in step 1 to obtain a hollow silica particle precursor aggregate. Step 3: Removing the liquid phase from the silica particle precursor aggregate obtained in step 2 Effect of the Invention

[0007] According to the present invention, a method for producing hollow silica particles can be provided that can suppress cracking during the process of crushing hollow silica particle aggregates even if hollow silica particles that have been aggregated by firing are crushed. In addition, the hollow silica obtained by the method for producing hollow silica particles of the present invention can maintain a low relative dielectric constant and dielectric loss tangent because cracking is suppressed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Method of manufacturing hollow silica particles] The method for producing hollow silica particles of the present invention includes the following steps 1 to 3. Step 1: Obtaining hollow silica particle precursor in a liquid phase Step 2: A step of aggregating the hollow silica particle precursor in the liquid phase obtained in step 1 to obtain a hollow silica particle precursor aggregate. Step 3: Removing the liquid phase from the silica particle precursor aggregate obtained in step 2

[0009] According to the method for producing hollow silica particles of the present invention, it is possible to suppress the occurrence of cracks in the process of crushing aggregates of hollow silica particles. In addition, the hollow silica obtained by the method for producing hollow silica particles of the present invention can maintain a low relative dielectric constant and dielectric loss tangent. The reason for this is unclear, but is assumed as follows. It is considered that the hollow silica particle precursor obtained in the liquid phase is aggregated before the step of removing the liquid phase, i.e., when the concentration of the hollow silica particle precursor is low, to form a hollow silica particle precursor aggregate, and the hollow silica particle precursor holds the liquid phase between the hollow silica particle precursors, and some of them come into contact with each other to form a weak aggregate (flocculation). Even if the liquid phase is subsequently removed, the weak aggregate is maintained, and the distance between the hollow silica particle precursors can be maintained even during firing, so that the hollow silica particles generated by firing can be prevented from strongly fusing with each other, and can be kept as hollow silica particle aggregates. Since the hollow silica particle aggregate is only weakly contacted with each other, it is considered that it can be sufficiently disintegrated even if the disintegration force is not strong enough to destroy the hollow structure of the hollow silica. In addition, if the hollow silica particles themselves are broken into fragments and are mixed in with the hollow silica particles, the porosity of the entire hollow silica particle decreases, increasing the relative dielectric constant, and the dielectric loss tangent increases due to the silanol groups present on the cross sections of the broken hollow silica particles. In contrast, the hollow silica particles obtained by the method for producing hollow silica particles of the present invention are prevented from cracking even when crushed, and therefore it is believed that the porosity can be maintained even after crushing, and the relative dielectric constant and dielectric loss tangent can be kept low.

[0010] <Process 1> Step 1 is a step of obtaining hollow silica particle precursors in a liquid phase. In step 1, the liquid phase is a dispersion medium in which the hollow silica particle precursor is dispersed in a particulate state. In step 1, the hollow silica particle precursor is a dispersoid, and the liquid phase is a continuous phase.

[0011] From the viewpoint of decreasing the average particle size of the resulting hollow silica particles and decreasing the relative dielectric constant and dielectric loss tangent of the resulting hollow silica particles, step 1 preferably includes the following steps 1-1, 1-2, and 1-3. Step 1-1: A step of mixing an aqueous medium, a cationic surfactant A, and a hydrophobic liquid to obtain an aqueous emulsion of the hydrophobic liquid. Step 1-2: A step of mixing a silanol precursor with the aqueous emulsion obtained in step 1-1 to obtain a mixture. Step 1-3: A step of adding an alkaline agent to the mixture obtained in step 1-2 to obtain hollow silica particle precursors.

[0012] [Step 1-1] Step 1-1 is a step of mixing an aqueous medium, a cationic surfactant A, and a hydrophobic liquid to obtain an aqueous emulsion of the hydrophobic liquid. In step 1-1, an aqueous emulsion of the hydrophobic liquid is obtained in which the hydrophobic liquid is emulsified in the aqueous medium by the cationic surfactant A. The aqueous emulsion of the hydrophobic liquid can be prepared by a general method.

[0013] (aqueous medium) In step 1-1, the aqueous medium refers to a component that becomes a dispersion medium among the components that constitute the liquid phase in step 1. The aqueous medium preferably contains water. Examples of the water contained in the aqueous medium include distilled water, ion-exchanged water, and ultrapure water. In addition, the aqueous medium may contain an organic solvent that is compatible with water from the viewpoint of more uniform and stable emulsion of the hydrophobic liquid described later. Examples of the organic solvent that is compatible with water include lower alcohols such as methanol, ethanol, and isopropyl alcohol, and acetone. When the aqueous medium contains an organic solvent in addition to water, the aqueous medium is formed by combining the water and the organic solvent. In step 1-1, the water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 98% by mass or more, and even more preferably 100% by mass, from the viewpoint of ensuring appropriate solubility of the hydrophobic liquid in the aqueous medium.

[0014] (Cationic Surfactant A) From the viewpoints of stably producing an aqueous emulsion of a hydrophobic liquid, facilitating the formation of silanols produced from silanol precursors in steps 1-2 and 1-3 and hollow silica particle precursors obtained by condensing the silanols on the surfaces of hydrophobic liquid particles in the aqueous emulsion of the hydrophobic liquid, and of facilitating decomposition and volatilization during firing, the cationic surfactant A is preferably a quaternary ammonium salt, more preferably one or more types selected from the group consisting of quaternary ammonium salts represented by the following general formula (1) or general formula (2), and even more preferably one or more types selected from alkyltrimethylammonium salts and dialkyldimethylammonium salts. [R 1 R 3 3N] + X ― (1) [R 1 R 2 R 3 2N] + X ― (2)

[0015] In the general formula (1) and the general formula (2), R 1 and R 2 each independently represents a linear or branched alkyl group having 4 to 24 carbon atoms; R 3 represents an alkyl group having 1 to 3 carbon atoms, and multiple R 3 may each be a different group, and X ― indicates a monovalent anion. Examples of the alkyl group having 4 to 24 carbon atoms include various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, various tetradecyl groups, various hexadecyl groups, various octadecyl groups, various eicosyl groups, various docosyl groups, and various tetracosyl groups. Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. 3 is preferably a methyl group.

[0016] X in general formulas (1) and (2)― From the viewpoint of being easily decomposed and volatilized during firing, X is preferably at least one type selected from monovalent anions such as halogen ions, hydroxide ions, and nitrate ions. ― More preferably, the cation is a halide ion, and even more preferably, a chloride ion.

[0017] Examples of the alkyl trimethyl ammonium salt represented by the general formula (1) include butyl trimethyl ammonium chloride, hexyl trimethyl ammonium chloride, octyl trimethyl ammonium chloride, decyl trimethyl ammonium chloride, lauryl trimethyl ammonium chloride (dodecyl trimethyl ammonium chloride), tetradecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, butyl trimethyl ammonium bromide, hexyl trimethyl ammonium bromide, octyl trimethyl ammonium bromide, decyl trimethyl ammonium bromide, lauryl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, stearyl trimethyl ammonium bromide, and behenyl trimethyl ammonium bromide.

[0018] Examples of the dialkyldimethylammonium salt represented by the general formula (2) include dibutyldimethylammonium chloride, dihexyldimethylammonium chloride, dioctyldimethylammonium chloride, dihexyldimethylammonium bromide, dioctyldimethylammonium bromide, dilauryldimethylammonium bromide, and ditetradecyldimethylammonium bromide.

[0019] The quaternary ammonium salt as the cationic surfactant A is preferably lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, or behenyltrimethylammonium chloride, from the viewpoints of stably producing an aqueous emulsion of a hydrophobic liquid, facilitating the formation of silanols produced from the silanol precursors in steps 1-2 and 1-3, and hollow silica particle precursors obtained by condensing the silanols on the surfaces of the hydrophobic liquid particles in the aqueous emulsion, and of facilitating decomposition and volatilization during firing, more preferably lauryltrimethylammonium chloride or behenyltrimethylammonium chloride, and even more preferably behenyltrimethylammonium chloride.

[0020] (hydrophobic liquid) The hydrophobic liquid is preferably one that can form stable droplets in an aqueous medium by the cationic surfactant A. In addition, from the viewpoint of using an aqueous medium as a dispersion medium and improving the utilization efficiency of the hydrophobic liquid, the temperature range in which the hydrophobic liquid is in a liquid state is preferably 0 to 100°C, and more preferably 20 to 90°C. Specific examples of hydrophobic liquids include those described in paragraphs

[0015] to

[0023] of JP 2016-121060 A. 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.

[0021] In step 1-1, the mass ratio of the hydrophobic liquid to the aqueous medium [hydrophobic liquid / aqueous medium] is, from the viewpoint of keeping the volume average particle size of the hydrophobic liquid particles in the resulting aqueous emulsion of the hydrophobic liquid within an appropriate range, preferably 0.2 or more, more preferably 0.25 or more, even more preferably 0.3 or more, and is preferably 0.8 or less, more preferably 0.75 or less, even more preferably 0.7 or less. Furthermore, when the aqueous medium consists of only water, the mass ratio of the hydrophobic liquid to water [hydrophobic liquid / water] is, from the same viewpoints as above, preferably 0.2 or more, more preferably 0.25 or more, even more preferably 0.3 or more, and is preferably 0.8 or less, more preferably 0.75 or less, even more preferably 0.7 or less.

[0022] In step 1-1, the mass ratio of cationic surfactant A to the hydrophobic liquid [hydrophobic liquid / cationic surfactant A] is, from the viewpoint of keeping the volume average particle size of the hydrophobic liquid particles in the resulting aqueous emulsion of the hydrophobic liquid within an appropriate range, preferably 5 or more, more preferably 15 or more, even more preferably 20 or more, and is preferably 100 or less, more preferably 75 or less, even more preferably 50 or less.

[0023] In step 1-1, by appropriately adjusting the stirring speed, temperature, etc., it is possible to adjust the volume average particle size of the hydrophobic liquid particles in the resulting aqueous emulsion of the hydrophobic liquid to fall within an appropriate range. Step 1-1 is preferably carried out at a temperature of 15°C to 80°C. In step 1-1, the volume average particle diameter of the hydrophobic liquid particles in the aqueous emulsion of the hydrophobic liquid is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and is preferably 2.5 μm or less, more preferably 2.0 μm or less, even more preferably 1.5 μm or less, from the viewpoint of setting the volume-based average particle diameter and the volume-based maximum particle diameter of the hollow silica particles obtained by the silica particle production method of the present invention within the ranges described below. The volume average particle size of the hydrophobic liquid particles in the aqueous emulsion of the hydrophobic liquid can be determined by the method described in the Examples.

[0024] [Step 1-2] Step 1-2 is a step of mixing a silanol precursor with the aqueous emulsion of a hydrophobic liquid obtained in step 1-1 to obtain a mixture. This operation allows the silanol precursor to be present on the surfaces of the hydrophobic liquid particles in the aqueous emulsion of a hydrophobic liquid. The mixing of the aqueous emulsion of the hydrophobic liquid obtained in step 1-1 with the silanol precursor may be performed by adding the silanol precursor to the aqueous emulsion of the hydrophobic liquid obtained in step 1-1, or by adding the aqueous emulsion of the hydrophobic liquid obtained in step 1-1 to the silanol precursor.

[0025] (Silanol precursor) Examples of the silanol precursor in step 1-2 include compounds that generate a silanol compound upon hydrolysis, such as alkylalkoxysilanes, alkoxysilanes, and alkoxydisiloxanes. Specific examples include compounds represented by the following general formulas (3) to (7), or combinations of these. SiY4(3) R 4 SiY3(4) R 4 2SiY2(5) R 4 3SiY (6) Y3Si-O-SiY3(7)

[0026] In general formulas (3) to (7), R 4 each independently represents a hydrocarbon group in which a carbon atom is directly bonded to a silicon atom, and Y represents a monovalent hydrolyzable group that becomes a hydroxyl group upon hydrolysis.

[0027] In general formulas (4) to (6), R 4 are each independently preferably a hydrocarbon group having 1 to 22 carbon atoms, more preferably a hydrocarbon group having 4 to 18 carbon atoms, even more preferably a hydrocarbon group having 8 to 16 carbon atoms, and still more preferably an alkyl group or aryl group having 8 to 16 carbon atoms. In the general formulas (3) to (7), Y is preferably an alkoxy group or a halogen group having 1 to 8 carbon atoms, more preferably an alkoxy group having 1 to 8 carbon atoms. When Y is an alkoxy group having 1 to 8 carbon atoms, the number of carbon atoms in the alkoxy group is preferably 2 or more and preferably 5 or less, more preferably 4 or less, from the viewpoint of reducing the relative dielectric constant and dielectric loss tangent of the resulting hollow silica.

[0028] The silanol precursor is preferably one or more selected from the compounds represented by general formula (3) and general formula (7). Among them, from the viewpoint of suppressing the generation of metal-corrosive acid and from the viewpoint of hydrolysis reactivity, the silanol precursor is preferably a compound represented by general formula (3) and general formula (7) in which Y is an alkoxy group having 2 to 4 carbon atoms, more preferably a compound represented by general formula (3) and general formula (7) in which Y is one or more selected from an ethoxy group, a propyl group, and an isopropyl group, further preferably one or more selected from tetraethyl orthosilicate and hexaethyl pyrosilicate, and further more preferably tetraethyl orthosilicate. The silanol precursor can be used alone or in a mixture of two or more.

[0029] The mass ratio of the silanol precursor to the hydrophobic liquid [silanol precursor / hydrophobic liquid] is preferably 10 or more, more preferably 20 or more, even more preferably 25 or more, and is preferably 90 or less, more preferably 80 or less, even more preferably 75 or less, from the viewpoint of keeping the porosity of the hollow silica particles in an appropriate range.

[0030] (Cationic Surfactant B) In step 1-2, it is preferable to further mix a cationic surfactant B. The cationic surfactant B may be mixed before the mixing of the aqueous emulsion of the hydrophobic liquid obtained in step 1-1 with the silanol precursor, after the mixing of the aqueous emulsion of the hydrophobic liquid obtained in step 1-1 with the silanol precursor, or simultaneously with the mixing of the aqueous emulsion of the hydrophobic liquid obtained in step 1-1 with the silanol precursor. From the viewpoint of facilitating the formation of a complex with the condensed silanol and facilitating decomposition and volatilization in step 4 described below, the cationic surfactant B is preferably a quaternary ammonium salt, more preferably lauryl trimethyl ammonium chloride (dodecyl trimethyl ammonium chloride), stearyl trimethyl ammonium chloride, and behenyl trimethyl ammonium chloride, and even more preferably lauryl trimethyl ammonium chloride. The cationic surfactant B used in this step may be the same as or different from the cationic surfactant A, but is preferably different from the cationic surfactant A, and more preferably the number of carbon atoms in the longest hydrocarbon group of the cationic surfactant B is smaller than the number of carbon atoms in the longest hydrocarbon group of the cationic surfactant A. The cationic surfactant B may be used alone or in combination of two or more kinds.

[0031] When cationic surfactant B is used in step 1-2, the mass ratio of the silanol precursor to the cationic surfactant B mixed in step 1-2 [silanol precursor / cationic surfactant B] is, from the viewpoint of dispersibility of the hollow silica particle precursor, preferably 3 or more, more preferably 5 or more, even more preferably 6 or more, and is preferably 25 or less, more preferably 20 or less, even more preferably 18 or less.

[0032] [Step 1-3] Step 1-3 is a step of adding an alkaline agent to the mixture obtained in step 1-2. The mixture obtained in step 1-2 contains an aqueous medium, a cationic surfactant A, a hydrophobic liquid, and a silanol precursor, and if necessary, a cationic surfactant B. In step 1-3, an alkaline agent is added to the mixture to make the system alkaline, hydrolyzing the silanol precursor to obtain silanol, which is then condensed on the surface of the hydrophobic liquid particles in the aqueous emulsion of the hydrophobic liquid to obtain hollow silica particle precursors having an outer shell containing silica, a cationic surfactant A, and a cationic surfactant B, and containing a hydrophobic liquid in an inner shell. (Alkaline substances) Specific examples of the alkaline agent (hereinafter also referred to as "alkaline substance") include those described in paragraph

[0014] of JP 2016-121060 A. Among these, hydroxide salts of quaternary ammonium are preferred. Specific examples of hydroxide salts of quaternary ammonium include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tributylmethylammonium hydroxide, trimethylhydroxyethylammonium hydroxide (choline), tetraethanolammonium hydroxide, methyltriethanolammonium hydroxide, and dimethylbis(2-hydroxyethyl)ammonium hydroxide. From the viewpoint of making the outer shell of the hollow silica particle precursor dense, preferred are tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylhydroxyethylammonium hydroxide, and methyltriethanolammonium hydroxide, and dimethylbis(2-hydroxyethyl)ammonium hydroxide, more preferred are tetramethylammonium hydroxide and dimethylbis(2-hydroxyethyl)ammonium hydroxide, and even more preferred is dimethylbis(2-hydroxyethyl)ammonium hydroxide.

[0033] The mass ratio of the silanol precursor to the alkaline substance [silanol precursor / alkaline substance] is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more, from the viewpoint of densely forming the outer shell of the hollow silica particle precursor, and is preferably 100 or less, more preferably 80 or less, and even more preferably 70 or less, from the viewpoint of efficiently carrying out the condensation reaction of the silanol precursor.

[0034] The alkaline substance may contain an alkali metal salt or an alkaline earth metal salt in addition to the above-mentioned quaternary ammonium hydroxide salt. In order to reduce the content of alkali metals and alkaline earth metals in the resulting hollow silica particles, the total content of alkali metals and alkaline earth metals in the silanol precursor is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, even more preferably 10 ppm by mass or less, and even more preferably 0 ppm by mass, relative to the mass of the resulting hollow silica particles.

[0035] In step 1-3, an alkaline substance may be added to the mixture obtained in step 1-2, or the mixture obtained in step 1-2 may be added to a system containing an alkaline substance. From the viewpoint of increasing the porosity and increasing the synthesis concentration to increase productivity, it is preferable to add an alkaline substance to the mixture obtained in step 1-2. From the viewpoint of obtaining hollow silica particles having a small maximum particle size and an appropriate coefficient of variation, it is preferable to mix the alkaline substance with cationic surfactant B to prepare a mixture of the alkaline substance and cationic surfactant B, and then further mix the mixture with the mixture obtained in step 1-2.

[0036] The temperature at which steps 1-2 and 1-3 are carried out can be appropriately adjusted depending on the type and amount of the silanol precursor and alkaline substance used, and is preferably 0° C. or higher and 100° C. or lower from the viewpoint of densifying the outer shell of the hollow silica particle precursor. For example, when tetraethyl orthosilicate or hexaethyl pyrosilicate is used as the silanol precursor, the temperature is preferably 20° C. or higher and 45° C. or lower, and when tetramethyl orthosilicate or hexamethyl pyrosilicate is used, the temperature is preferably 0° C. or higher and 20° C. or lower.

[0037] The time for carrying out steps 1-2 and 1-3 is preferably 30 minutes or more, more preferably 1 hour or more, and even more preferably 2 hours or more, as the combined time for steps 1-2 and 1-3, from the viewpoint of making the outer shell of the hollow silica particle precursor dense, and is preferably 24 hours or less, more preferably 20 hours or less, and even more preferably 16 hours or less, from the viewpoint of production efficiency.

[0038] (Hollow silica particle precursor) The hollow silica particle precursor is a particle having an outer shell containing silica, containing a hydrophobic liquid inside the outer shell, and dispersing in a liquid phase. The outer shell has a cationic surfactant oriented radially toward the center of the particle.

[0039] <Process 2> Step 2 is a step of aggregating the hollow silica particle precursor in the liquid phase obtained in step 1 to obtain hollow silica particle precursor aggregates. The hollow silica particle precursor aggregates are particles in which the hollow silica particle precursors are aggregated but remain dispersed in the liquid phase. The method for producing hollow silica particles of the present invention includes step 2, which can cause weak aggregation (flocculation) that maintains a certain distance between the particles of the hollow silica particle precursor, thereby making it possible to obtain hollow silica particles that can be prevented from cracking even when crushed and can maintain a low relative dielectric constant and dielectric tangent.

[0040] In step 2, the volume average particle diameter of the hollow silica particle precursor aggregate is preferably at least twice the volume average particle diameter of the hollow silica particle precursor. When the volume average particle diameter of the hollow silica particle precursor aggregate is at least twice the volume average particle diameter of the hollow silica particle precursor, some of the particles of the hollow silica particle precursor are weakly bound to each other while maintaining a certain distance from each other, preventing the hollow silica precursors from approaching each other too closely, and preventing the silica particle precursor aggregate from being excessively aggregated in the step of removing the liquid phase and recovering the silica particle precursor aggregate, which will be described later. In step 2, the ratio of the volume average particle diameter of the hollow silica particle precursor agglomerates to the volume average particle diameter of the hollow silica particle precursor [volume average particle diameter of hollow silica particle precursor agglomerates / volume average particle diameter of hollow silica particle precursor] is preferably 2 or more, more preferably 4 or more, and even more preferably 8 or more, from the viewpoint of reducing the average particle diameter of the obtained hollow silica particles and from the viewpoint of obtaining hollow silica particles that can be prevented from cracking even when crushed and can maintain low relative dielectric constant and dielectric tangent, and from the same viewpoints, it is preferably 40 or less, more preferably 30 or less, even more preferably 20 or less, and even more preferably 18 or less. The volume average particle diameter of the hollow silica particle precursor and the hollow silica particle precursor aggregate in the liquid phase can be measured by the method described in the Examples.

[0041] From the viewpoint of reducing the average particle size of the resulting hollow silica particles and obtaining hollow silica particles that can be prevented from cracking even when crushed and can maintain low relative dielectric constant and dielectric loss tangent, it is preferable that Step 2 includes the following Step 2'. Step 2': mixing the liquid phase containing the hollow silica particle precursor obtained in step 1 with an anionic polymer.

[0042] [Step 2'] Step 2' is a step of mixing the liquid phase containing the hollow silica particle precursor obtained in step 1 with an anionic polymer. By adding the hollow silica particle precursor and the anionic polymer, the hollow silica particle precursor is weakly aggregated to obtain a hollow silica particle precursor aggregate. In the step of mixing the liquid phase containing the hollow silica particle precursor obtained in step 1 with the anionic polymer, the anionic polymer may be added to the liquid phase containing the hollow silica particle precursor obtained in step 1, or the liquid phase containing the hollow silica particle precursor obtained in step 1 may be added to a system containing an anionic polymer, but from the viewpoint of lowering the relative dielectric constant and dielectric loss tangent of the obtained hollow silica particles, it is preferable to add the anionic polymer to the liquid phase containing the hollow silica particle precursor obtained in step 1.

[0043] (anionic polymer) In the present invention, the anionic polymer is used as an aggregating agent that weakly aggregates hollow silica particles. In step 2, the anionic polymer causes particle aggregation by being mixed with the liquid phase containing the hollow silica particle precursor obtained in step 1. Whether particle aggregation has occurred can be determined by comparing the volume average particle diameter of the hollow silica particle precursor before mixing with the anionic polymer and the volume average particle diameter of the hollow silica particle precursor aggregate after mixing. The method for producing hollow silica particles of the present invention is preferable because it includes step 2' as step 2, which makes it easier to obtain hollow silica that can suppress cracking even when crushed and maintain low relative dielectric constant and dielectric tangent. The hollow silica particle precursor generated in step 1 has a positively charged surface because cationic surfactant A and cationic surfactant B are used during synthesis. Therefore, by including step 2', it is considered that the anionic polymer is easily adsorbed on the surface of the hollow silica particle precursor, and the hollow silica particle precursor is likely to cause weak aggregation (flocculation) that maintains a certain distance between particles via the anionic polymer. During firing, the anionic polymer decomposes and vaporizes while maintaining the distance between the hollow silica particles, preventing the obtained hollow silica particles from strongly aggregating and fusing with each other due to high temperatures, and therefore it is considered that it is possible to sufficiently disintegrate the hollow silica particles even with a weak disintegration force that does not break the hollow silica particles themselves.

[0044] As the anionic polymer, from the viewpoint of obtaining hollow silica particles capable of suppressing cracking even when the hollow silica particle precursor is weakly aggregated and crushed, and capable of maintaining a low relative dielectric constant and dielectric tangent, polycarboxylates and polysulfonates are preferable.

[0045] The polycarboxylate is preferably a salt of polyacrylic acid and a salt of an acrylic acid-maleic acid copolymer, and is preferably a metal salt (salt of an alkali metal such as sodium or potassium), an amine salt, or an ammonium salt of polyacrylic acid and an acrylic acid-maleic acid copolymer. Among these, from the viewpoint of obtaining hollow silica particles that can be prevented from cracking even when crushed and can maintain a low relative dielectric constant and dielectric loss tangent, one or more selected from ammonium polyacrylate and ammonium salt of an acrylic acid-maleic acid copolymer are preferred. The polysulfonate is preferably a salt of a formalin condensate of an aromatic sulfonic acid and a salt of a formalin condensate of a lignin sulfonic acid. The salt of the formalin condensate of aromatic sulfonic acid may be a salt of condensed naphthalene sulfonic acid. The salt of condensed naphthalene sulfonic acid is preferably a metal salt (sodium, potassium, or other alkali metal salt), an amine salt, or an ammonium salt of condensed naphthalene sulfonic acid. Among these, the ammonium salt of condensed naphthalene sulfonic acid is preferred from the viewpoint of obtaining hollow silica particles that can suppress cracking even when crushed and can maintain low relative dielectric constant and dielectric loss tangent. Among the above, the anionic polymer is more preferably one or more selected from ammonium polyacrylate, ammonium salt of acrylic acid-maleic acid copolymer, and ammonium salt of condensed naphthalenesulfonic acid, from the viewpoint of obtaining hollow silica particles that can suppress cracking even when crushed and can maintain low relative dielectric constant and dielectric loss tangent. In addition, using the above ammonium salt as the anionic polymer is also preferable from the viewpoint of use in insulating materials, etc., and from the viewpoint of reducing the content of metal ions in the obtained hollow silica particles.

[0046] The weight average molecular weight of the anionic polymer is preferably 1,000 to 100,000, more preferably 1,500 to 80,000, even more preferably 1,800 to 60,000, and even more preferably 2,000 to 40,000. When the weight average molecular weight is 1,000 or more, the hollow silica particle precursor can be easily weakly aggregated. Also, when the weight average molecular weight is 100,000 or less, the hollow silica particle precursor can be prevented from being strongly aggregated, so that a strong disintegration force is not required, and the cracking of the hollow silica particles due to disintegration can be prevented. In the method for producing hollow silica particles of the present invention, the weight average molecular weight of the anionic polymer may be a value given in a catalog.

[0047] The temperature at which step 2' is carried out is preferably 0°C or higher and 100°C or lower, more preferably 10°C or higher and 80°C or lower, even more preferably 15°C or higher and 60°C or lower, and even more preferably 20°C or higher and 45°C or lower, from the viewpoint of adjusting the aggregation strength of the hollow silica particles, suppressing cracking even when crushed, and obtaining hollow silica particles that can maintain a low relative dielectric constant and dielectric tangent.

[0048] In addition, it is preferable that step 2' is accompanied by stirring. In step 2', the stirring time is preferably 1 minute or more, more preferably 3 minutes or more, even more preferably 5 minutes or more, even more preferably 8 minutes or more, and is preferably 60 minutes or less, more preferably 45 minutes or less, even more preferably 30 minutes or less, and even more preferably 15 minutes or less, from the viewpoint of adjusting the aggregation strength of the hollow silica particles, suppressing cracking even when crushed, and obtaining hollow silica particles that can maintain low relative dielectric constant and dielectric loss tangent.

[0049] <Process 3> Step 3 is a step of removing the liquid phase from the hollow silica particle precursor aggregate obtained in step 2. In step 3, the liquid phase is preferably removed by, for example, filtration. In addition, it is preferable that step 3 further includes a step of drying the hollow silica particle precursor after removing the liquid phase. If the boiling point of the hydrophobic liquid contained in the hollow silica particle precursor is higher than 100°C under atmospheric pressure, the step of drying the hollow silica particle precursor can be carried out, for example, by maintaining the temperature at a temperature higher than 100°C under atmospheric pressure and lower than the boiling point of the hydrophobic liquid. If the boiling point of the hydrophobic liquid contained in the hollow silica particle precursor is lower than 100°C under atmospheric pressure, the step can be carried out, for example, by freeze-drying.

[0050] <Step 4> The method for producing hollow silica particles of the present invention preferably further includes the following step 4 after step 3. Step 4: Calcining the hollow silica particle precursor aggregate to obtain hollow silica particle aggregate. In step 4, the hollow silica particle precursor aggregate obtained in step 3 is calcined to decompose and volatilize the cationic surfactant present in the outer shell of the hollow silica particle precursor and volatilize the internal hydrophobic liquid, and then the pores present in the outer shell are closed by calcination to obtain an aggregate of hollow silica particles having a uniform outer shell. In step 4, the hollow silica particle precursor agglomerate obtained in step 3 may be a dried hollow silica precursor agglomerate.

[0051] The method for producing hollow silica particles of the present invention includes step 2, which can cause weak aggregation (flocculation) that maintains a certain distance between the particles of the hollow silica particle precursor. Therefore, even if the hollow silica particles undergo a firing step such as step 4 and then a crushing step, it is possible to obtain hollow silica particles that can suppress cracking and maintain a low relative dielectric constant and dielectric tangent.

[0052] The calcination temperature in step 4 is preferably 1000°C or higher, more preferably 1010°C or higher, even more preferably 1030°C or higher, and still more preferably 1050°C or higher, from the viewpoint of reducing silanol groups on the surface of the hollow silica particles, and is preferably 1500°C or lower, more preferably 1400°C or lower, even more preferably 1300°C or lower, and still more preferably 1200°C or lower, from the viewpoint of avoiding fusion of the hollow silica particles.

[0053] The calcination time in step 4 is preferably 15 minutes or more, more preferably 30 minutes or more, and even more preferably 45 minutes or more, from the viewpoint of reducing silanol groups on the surface of the hollow silica particles, and is preferably 3 hours or less, more preferably 2 hours or less, and even more preferably 1.5 hours or less, from the viewpoint of avoiding fusion of the hollow silica particles.

[0054] <Process 5> The method for producing hollow silica particles of the present invention preferably further includes the following step 5 after step 4. Step 5: Disintegrating hollow silica particle agglomerates

[0055] In the present invention, by disintegrating hollow silica particle agglomerates in step 5, the agglomerated hollow silica particles can be disintegrated with a weak force, thereby making it possible to suppress the occurrence of cracks, which is preferable when used as an insulating material, since it makes it easy to blend the hollow silica particles with resins in particular.

[0056] In step 5, the apparatus used for disintegration can be appropriately selected from known apparatuses, and examples thereof include a hammer mill, an atomizer, a rotoplex, and a jet mill. Examples of the jet mill include a swirling air jet mill, a fluidized bed jet mill, a collision plate jet mill, and a rotary mechanical mill. Among these, from the viewpoint of reducing the rate of cracking of the hollow silica particles after disintegration, a jet mill is preferred, and a swirling air jet mill is more preferred.

[0057] [Hollow silica particles] In the present invention, the hollow silica particles can be obtained by a production method including the above steps 1 to 3 and, if necessary, further steps 4 and 5. Since the hollow silica particles in the present invention can be obtained by the above production method, cracking can be suppressed even when crushed, and the relative dielectric constant and dielectric loss tangent can be kept low.

[0058] In the present invention, the hollow silica particles obtained by crushing preferably have a relative dielectric constant of 2.5 or less at a measurement frequency of 10 GHz and a dielectric loss tangent of 0.0050 or less at a measurement frequency of 10 GHz. The dielectric constant at a measurement frequency of 10 GHz is preferably 2.5 or less, more preferably 2.2 or less, even more preferably 2.0 or less, and even more preferably 1.8 or less, from the viewpoint of sufficiently low dielectric constant when used in insulating materials, etc., and is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more, from the viewpoint of sufficient strength of the hollow silica particles after crushing. In addition, the dielectric tangent at a measurement frequency of 10 GHz is preferably 0.0050 or less, more preferably 0.0048 or less, and even more preferably 0.0046 or less, from the viewpoint of sufficiently low dielectric tangent when used in an insulating material or the like, and is preferably 0.0001 or more, more preferably 0.0005 or more, and even more preferably 0.0010 or more, from the viewpoint of sufficient strength of the hollow silica particles after crushing. The dielectric constant and dielectric loss tangent of the hollow silica particles are measured by the method described in the Examples.

[0059] In the present invention, the volume-based average particle size of the hollow silica particles obtained by crushing is, from the viewpoints of facilitating incorporation into insulating materials and maintaining processability, preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 0.7 μm or more, still more preferably 0.9 μm or more, and is preferably 3.0 μm or less, more preferably 2.5 μm or less, even more preferably 2.3 μm or less, and still more preferably 2.0 μm or less. In the present invention, the volume-based average particle size of the hollow silica particles means the volume-based average particle size calculated by the Coulter counter method (the sum of (each particle size calculated by measurement using the Coulter counter method) x (the volume ratio of each particle size)). The volume-based average particle size is measured by the method described in the Examples.

[0060] In the present invention, the maximum particle size on a volume basis of the hollow silica particles obtained by crushing is preferably 1.0 μm or more, more preferably 1.5 μm or more, even more preferably 1.8 μm or more, still more preferably 2.0 μm or more, from the viewpoint of making the particles easily blendable with insulating materials and maintaining processability, and is preferably 5.0 μm or less, more preferably 4.5 μm or less, even more preferably 4.0 μm or less, still more preferably 3.5 μm or less. The maximum volumetric particle size of the hollow silica particles is measured as the particle size at 99% cumulative frequency distribution (D99), and is measured by the method described in the Examples.

[0061] In the present invention, the porosity of the hollow silica particles obtained by crushing is preferably 40% or more, more preferably 45% or more, and even more preferably 50% or more, from the viewpoint of reducing the relative dielectric constant of the hollow silica particles after crushing, and is preferably 80% or less, more preferably 77% or less, and even more preferably 74% or less, from the viewpoint of the hollow silica particles after crushing having sufficient strength.

[0062] In the present invention, the porosity of the hollow silica particle agglomerate (hollow silica particle agglomerate after firing and before being disintegrated) is, from the same viewpoint as above, preferably 40% or more, more preferably 45% or more, even more preferably 50% or more, and is preferably 80% or less, more preferably 77% or less, even more preferably 74% or less. The porosity of the hollow silica particles and the hollow silica particle aggregates can be determined by the method described in the Examples.

[0063] In the present invention, the ratio of broken hollow silica particles among the hollow silica particles obtained by crushing is preferably 20% or less. By making the ratio of broken hollow silica particles among the hollow silica particles after crushing 20% ​​or less, it is easy to keep the relative dielectric constant and dielectric loss tangent low, and it is easy to blend the hollow silica particles into insulating materials, etc., and it is easy to maintain the processability of the insulating materials, etc. In the present invention, the ratio of cracked hollow silica particles among the hollow silica particles obtained by crushing is preferably 20% or less, more preferably 15% or less, still more preferably 10% or less, even more preferably 5% or less, and even more preferably 3% or less, from the viewpoints of keeping the relative permittivity and dielectric loss tangent low and making it easier to blend with insulating materials and the like to improve the processability of the insulating materials. The ratio of cracked hollow silica particles among the hollow silica particles obtained by crushing can be determined from the porosity of the hollow silica particles before crushing and the porosity of the hollow silica particles after crushing, and is determined by the method described in the examples.

[0064] In the present invention, since the hollow silica particles have the above characteristics, the relative permittivity and dielectric loss tangent can be kept low, and also it is easy to blend with insulating materials and the like, and the processability of the insulating materials can be maintained.

Examples

[0065] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by these examples in any way. Each property value was measured and evaluated by the following methods.

[0066] [Measurement method] (1) Measurement of the weight-average molecular weight of an anionic polymer The weight-average molecular weight of the anionic polymer was measured using GPC under the following measurement conditions. <GPC measurement conditions (ammonium polyacrylate, ammonium acrylate-maleic acid copolymer, polyethylene glycol 20,000)> Sample concentration: 1 mg / mL Column: G4000PWXL + G2500SWXL (manufactured by Tosoh Corporation) Eluent: 0.2 mol / L phosphate buffer / acetonitrile = 9 / 1 Flow rate: 1.0 mL / min Column temperature: 40 °C Detector: differential refractometer <GPC measurement conditions (ammonium condensed naphthalenesulfonate)> Sample concentration: 1mg / mL Column: G4000SWXL+G2500SWXL (Tosoh Corporation) Eluent: 30mmol / L sodium acetate aqueous solution, water / acetonitrile = 6 / 4 Flow rate: 1.0mL / min Column temperature: 40℃ Detector: Differential refractometer

[0067] (2) Measurement of particle size of hydrophobic liquid particles in an aqueous emulsion of a hydrophobic liquid, hollow silica particle precursors in the liquid phase, and hollow silica particle precursor aggregates in the liquid phase The particle sizes of the hydrophobic liquid particles in the aqueous emulsion of the hydrophobic liquid, the hollow silica particle precursor in the liquid phase, and the hollow silica particle precursor aggregates were measured by the wet method using a laser diffraction / scattering particle size distribution analyzer (HORIBA, Ltd.: LA-920). The analysis was performed using the HORIBA LA-920 WET (LA-920) Version 3.02 that came with the device, and the range of 0.020 μm to 2000 μm was measured. Water was used as the dispersion medium, and the sample was introduced so that the transmittance was 70 to 95%, and the relative refractive index was set to 1.09, which corresponds to silica / water, and the particle size standard was analyzed as volume to determine the volume average particle size.

[0068] (3) Measurement of the average particle size and maximum particle size of hollow silica particles The average particle size and maximum particle size of the hollow silica particles were measured using a Coulter counter (Beckman Coulter, Inc., Multisizer 3 (using a 20 μm aperture tube)). The average particle size of the hollow silica particles was determined to be the volume-based average particle size calculated by the Coulter counter method (the sum of (each particle size calculated by measurement using the Coulter counter method) x (the volume ratio of each particle size)). The maximum particle size of the hollow silica particles was determined as the particle size at 99% (D99) of the cumulative frequency distribution on a volume basis.

[0069] (4) Measurement of porosity of hollow silica particle aggregates and hollow silica particles The porosity was calculated by measuring the density of samples of hollow silica particle aggregates and hollow silica particles using a true density measuring device (ULTRAPYCNMETER1200e manufactured by Quantachrome Corp.) with nitrogen as the measurement gas, and using the following formula. The true density of the silica particles was 2.2 g / cm 3 It was decided. Porosity (%) = [1-(measured sample density / true density of silica particles)] x 100

[0070] (5) Measurement of the dielectric constant and dielectric tangent of hollow silica particles The dielectric constant and dielectric loss tangent of the hollow silica particles were measured at a temperature of 25°C and a frequency of 10 GHz using a network analyzer (Agilent Technologies, product name: N5221A) connected to a perturbation method cavity resonator (CP-580) manufactured by Kanto Electronics Application Development Co., Ltd., using the cavity resonator perturbation method (CP-MA dielectric constant measurement software, manufactured by Kanto Electronics Application Development Co., Ltd.). A measurement sample was prepared by filling a Teflon (registered trademark) tube (manufactured by Chukoh Chemical Industry Co., Ltd.: PTFE tube, inner diameter 1.5 mm, outer diameter 2.5 mm) with hollow silica particles so that all of them were within the measurement range (between 6.75 mm and 36.35 mm from the bottom). The weight of the Teflon tube before and after filling with the hollow silica particles was measured to calculate the filling weight of the hollow silica particles, and the volume of the hollow silica particles filled in the Teflon tube was calculated from the filling weight and specific gravity of the hollow silica particles. The relative dielectric constant and the dielectric loss tangent were calculated from the difference between the measured values ​​of an empty Teflon tube not filled with hollow silica particles and the measured values ​​of a Teflon tube filled with hollow silica particles, which was used as a blank.

[0071] <Example 1> (Process 1) 342.2 g of ion-exchanged water was used as the aqueous medium, 150 g of dodecane (Kishida Chemical Co., Ltd., Reagent Grade 1: Grade 1 n-dodecane) was used as the hydrophobic liquid, and 7.8 g of Coatamin 2285E (Kao Corporation: containing 58% by mass of behenyl trimethyl ammonium chloride) was used as the cationic surfactant A to obtain aqueous emulsion A1. The volume average particle size of the particles in the obtained aqueous emulsion A1 was 0.4 μm. A reaction vessel was charged with 13,157.6 g of ion-exchanged water, 173.0 g of aqueous emulsion A1, 125.6 g of Coatamin 24P (manufactured by Kao Corporation: containing 27.5% by mass of lauryl trimethyl ammonium chloride) as cationic surfactant B, and 3,120.8 g of tetraethyl orthosilicate (manufactured by Wacker Asahi Kasei Silicones Corporation: SEMICOSIL TEOS999-LB) as a silanol precursor, and the mixture was heated to 40° C. with stirring, and then stirred for 10 minutes to obtain preparation solution B1. Next, 221.5 g of AH212-CS (manufactured by Yokkaichi Chemical Co., Ltd.: containing 50% by mass of dimethylbis(2-hydroxyethyl)ammonium hydroxide) as an alkaline agent and 711.6 g of Courtamin 24P as a cationic surfactant B were mixed uniformly to obtain preparation liquid C1. Preparation liquid C1 was added to preparation liquid B1, and then the mixture was stirred at 40°C for 3 hours to obtain a cloudy liquid D1. The cloudy liquid D1 contained hollow silica particle precursors before the addition of the anionic polymer. The volume average particle diameter of the hollow silica particle precursors in the liquid phase of the cloudy liquid D1 was measured. (Process 2) 25.0 g of ammonium polyacrylate (Kao Corporation: weight average molecular weight 38000, solid content 40% by mass) was added as an anionic polymer to the obtained cloudy liquid D1, and the mixture was stirred at 40°C for 10 minutes to obtain a cloudy liquid E1. The cloudy liquid E1 contains hollow silica particle precursor aggregates after the addition of the anionic polymer additive. The particle diameter of the hollow silica particle precursor aggregates in the liquid phase of this cloudy liquid E1 was measured. (Step 3) The obtained cloudy liquid E1 was filtered using No. 5C filter paper (manufactured by Advantec Toyo Co., Ltd.) and then dried at 110°C to obtain a white dried hollow silica particle precursor agglomerate (hereinafter also referred to as "dried hollow silica particle precursor") 1. (Step 4) The obtained dried hollow silica particle precursor 1 was baked at 1100° C. for 1 hour to obtain hollow silica particle agglomerates 1. The porosity of the obtained hollow silica particle agglomerates 1 before being disintegrated was measured. (Step 5) The obtained hollow silica particle aggregates 1 were disintegrated in a jet mill (CO-JET SYSTEM α MARK III, manufactured by Seishin Enterprise Co., Ltd.) at a P NOZZLE pressure of 0.5 MPa, a G NOZZLE pressure of 0.5 MPa, and a sample supply rate of 10 g / min to obtain disintegrated hollow silica particles 1. From the obtained hollow silica particles 1, the average particle size, maximum particle size, porosity, proportion of broken hollow silica particles, relative dielectric constant, and dielectric loss tangent were each measured.

[0072] <Example 2> In obtaining the cloudy liquid E1 in step 2 of Example 1, 22.7 g of ammonium polyacrylate solution 70-110 (reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.: ammonium polyacrylate, weight average molecular weight 7300, evaporation residue 44 mass%) was added instead of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38000, solid content 40 mass%) added to the cloudy liquid D1, and the same procedure was repeated to obtain a dried hollow silica particle precursor 2, a hollow silica particle agglomerate 2, and disintegrated hollow silica particles 2.

[0073] <Example 3> In obtaining the cloudy liquid E1 in step 2 of Example 1, the same procedure as in Example 1 was repeated except that 25.0 g of Aron A-30SL (manufactured by Toa Gosei Co., Ltd.: containing 40 mass% ammonium polyacrylate (weight average molecular weight 6500)) was added instead of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38,000, solid content 40 mass%) added to the cloudy liquid D1. Thus, a dried hollow silica particle precursor 3, hollow silica particle agglomerates 3, and crushed hollow silica particles 3 were obtained.

[0074] <Example 4> In obtaining the cloudy liquid E1 in step 2 of Example 1, the same procedure as in Example 1 was repeated except that 25.0 g of Roma PWA-40K (manufactured by San Nopco Ltd.: containing 40 mass% of condensed ammonium naphthalenesulfonate (weight average molecular weight 2300)) was added instead of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38,000, solid content 40 mass%) added to the cloudy liquid D1 to obtain the cloudy liquid E1. Thus, a dried hollow silica particle precursor 4, hollow silica particle agglomerates 4, and crushed hollow silica particles 4 were obtained.

[0075] <Example 5> In obtaining the cloudy liquid E1 in step 2 of Example 1, the same procedure as in Example 1 was repeated except that 25.0 g of Caocera 2110 (manufactured by Kao Corporation: containing 40 mass% of acrylic acid-maleic acid ammonium copolymer (weight average molecular weight 11,000)) was added instead of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38,000, solid content 40 mass%) added to the cloudy liquid D1 to obtain the cloudy liquid E1. A hollow silica particle precursor dried material 5, hollow silica particle agglomerates 5, and crushed hollow silica particles 5 were obtained.

[0076] <Example 6> (Process 1) 388.6 g of ion-exchanged water was mixed as an aqueous medium, 200 g of dodecane (Kishida Chemical Co., Ltd. reagent: primary n-dodecane) as a hydrophobic liquid, and 11.4 g of Coatamin 86w (Kao Corporation: containing 28% by mass of stearyl trimethyl ammonium chloride) as a cationic surfactant A to obtain an aqueous emulsion A6. The volume average particle size of the particles in the obtained aqueous emulsion A6 was 0.8 μm. A reaction vessel was charged with 13,192.5 g of ion-exchanged water, 138.1 g of aqueous emulsion A6, and 3,120.8 g of tetraethyl orthosilicate as a silanol precursor, and the mixture was heated to 40° C. with stirring, and then stirred for 10 minutes to obtain preparation liquid B6. Next, in the same manner as in Example 1, preparation liquid C6 and cloudy liquid D6 were prepared. (Process 2) Next, 18.0 g of ammonium polyacrylate (Kao Corporation: weight average molecular weight 38000, solid content 40% by mass) as an anionic polymer was added to the cloudy liquid D6, and the mixture was stirred at 40° C. for 10 minutes to obtain a cloudy liquid E6. (Steps 3~5) The subsequent steps 3 to 5 were carried out in the same manner as in Example 1, and thus a dried hollow silica particle precursor 6, hollow silica particle aggregates 6, and crushed hollow silica particles 6 were obtained.

[0077] <Example 7> In obtaining the cloudy liquid E6 in step 2 of Example 6, 16.4 g of ammonium polyacrylate solution 70-110 (reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added as an anionic polymer instead of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38,000, solid content 40 mass%) added to the cloudy liquid D6, and the same procedure was repeated to obtain the dried hollow silica particle precursor 7, the hollow silica particle agglomerate 7, and the crushed hollow silica particles 7.

[0078] <Example 8> Dry hollow silica particle precursor 8, hollow silica particle agglomerate 8, and crushed hollow silica particles 8 were obtained in the same manner as in Example 6, except that 18.0 g of Aron A-30SL was added as an anionic polymer instead of ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38,000, solid content 40 mass%) added to the cloudy liquid D6 when obtaining the cloudy liquid E6 in step 2 of Example 6.

[0079] <Example 9> Dry hollow silica particle precursor 9, hollow silica particle agglomerate 9, and disintegrated hollow silica particles 9 were obtained in the same manner as in Example 6, except that 18.0 g of Rome PWA-40K was added as an anionic polymer instead of ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38,000, solid content 40 mass%) added to the cloudy liquid D6 when obtaining the cloudy liquid E6 in step 2 of Example 6.

[0080] <Example 10> A dried hollow silica particle precursor 10, hollow silica particle agglomerates 10, and disintegrated hollow silica particles 10 were obtained in the same manner as in Example 6, except that 18.0 g of Kaocera 2110 was added as an anionic polymer instead of ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38,000, solid content 40 mass%) added to the cloudy liquid D6 when obtaining the cloudy liquid E6 in step 2 of Example 6.

[0081] <Comparative Example 1> After step 1 of Example 1, without adding ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38,000, solid content 40% by mass) in step 2, the mixture was filtered using 5C filter paper (manufactured by Advantech Toyo Co., Ltd.) in step 3, and then dried at 110°C to obtain a white hollow silica particle precursor dried product c1. The subsequent operations were carried out in the same manner as in steps 4 and 5 of Example 1, and hollow silica particle agglomerates c1 and disintegrated hollow silica particles c1 were obtained.

[0082] <Comparative Example 2> In obtaining the cloudy liquid E1 in step 2 of Example 1, 25.0 g of a 25.0 wt % aqueous solution of ammonium sulfate (a reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added in place of the anionic polymer in place of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38000, solid content 40 mass%) added to the cloudy liquid D1, and the same procedure as in Example 1 was used to obtain hollow silica particle precursor c2, hollow silica particle precursor dried product c2, hollow silica particle aggregate c2 by firing, and disintegrated hollow silica particles c2. Note that no increase in particle size was observed with ammonium sulfate.

[0083] <Comparative Example 3> In the step 2 of Example 1, when obtaining the cloudy liquid E1, 25.0 g of polyethylene glycol 20,000 (reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., weight average molecular weight 20000) was added in place of the anionic polymer instead of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38000, solid content 40 mass%) added to the cloudy liquid D1, and the same procedure as in Example 1 was used to obtain a dried hollow silica particle precursor c3, a hollow silica particle aggregate c3, and a disintegrated hollow silica particle c3. Note that no increase in particle size was observed with polyethylene glycol.

[0084] <Comparative Example 4> After step 1 of Example 6, ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38000, solid content 40% by mass) was not added in step 2, and the mixture was filtered using 5C filter paper (manufactured by Advantec Toyo Co., Ltd.) in step 3, and then dried at 110° C. to obtain white hollow silica particle precursor c4. Subsequent operations were performed in the same manner as in steps 4 and 5 of Example 6 to obtain dried hollow silica particles c4 and crushed hollow silica particles c4.

[0085] <Comparative Example 5> In the step 2 of Example 6, when obtaining the cloudy liquid E6, 18.0 g of a 25.0 wt % aqueous solution of ammonium sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added in place of the anionic polymer instead of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38000, solid content 40 mass%) added to the cloudy liquid D6 was used in place of the anionic polymer, and the same procedure was followed as in Example 6 to obtain the dried hollow silica particle precursor c5, the hollow silica particle aggregate c5, and the disintegrated hollow silica particles c5. Note that no increase in particle size was observed for the ammonium sulfate.

[0086] <Comparative Example 6> In the step 2 of Example 6, when obtaining the cloudy liquid E6, 18.0 g of polyethylene glycol 20,000 was added in place of the anionic polymer, instead of the ammonium polyacrylate (manufactured by Kao Corporation: weight average molecular weight 38000, solid content 40 mass%) added to the cloudy liquid D6, in place of the anionic polymer, in the same manner as in Example 6, a hollow silica particle precursor dried product c6, a hollow silica particle aggregate c6, and a disintegrated hollow silica particle c6 were obtained. Note that no increase in particle size was observed with polyethylene glycol.

[0087] [Table 1]

[0088] It is seen from Table 1 that the hollow silica particles of Examples 1 to 10 obtained by the hollow silica particle manufacturing method of the present invention can suppress the occurrence of cracks in the crushing step. In addition, the hollow silica particles obtained by the hollow silica particle manufacturing method of the present invention can maintain low relative dielectric constant and dielectric loss tangent because the inclusion of cracks is suppressed.

Claims

1. A method for producing hollow silica particles, comprising the following steps 1 to 3. Step 1: Step to obtain hollow silica particle precursors in a liquid phase. Step 2: A process to aggregate the hollow silica particle precursor in the liquid phase obtained in Step 1 to obtain a hollow silica particle precursor aggregate. Step 3: Step to remove the liquid phase from the silica particle precursor aggregate obtained in Step 2.

2. A method for producing hollow silica particles according to claim 1, wherein the volume-average particle diameter of the hollow silica particle precursor aggregate is at least twice the volume-average particle diameter of the hollow silica particle precursor.

3. A method for producing hollow silica particles according to claim 1 or 2, wherein step 2 includes the following step 2'. Step 2': A step of mixing the liquid phase containing the hollow silica particle precursor obtained in Step 1 with an anionic polymer.

4. A method for producing hollow silica particles according to claim 3, wherein the weight-average molecular weight of the anionic polymer is 1,000 or more and 100,000 or less.

5. The method for producing hollow silica particles according to claim 3, wherein the anionic polymer is one or more selected from ammonium polyacrylate, ammonium salts of acrylic acid-maleic acid copolymers, and ammonium salts of condensed naphthalene sulfonic acid.

6. A method for producing hollow silica particles according to claim 1 or 2, further comprising the following step 4 after step 3. Step 4: A process to obtain hollow silica particle aggregates by calcining the hollow silica particle precursor aggregates.

7. A method for producing hollow silica particles according to claim 6, further comprising the following step 5 after step 4. Step 5: Process for crushing hollow silica particle aggregates

8. A method for producing hollow silica particles according to claim 1 or 2, wherein the relative permittivity of the hollow silica particles at a measurement frequency of 10 GHz is 2.5 or less, and the dielectric loss tangent at a measurement frequency of 10 GHz is 0.0050 or less.

9. A method for producing hollow silica particles according to claim 1 or 2, wherein the average particle diameter of the hollow silica particles is 0.1 μm or more and 3.0 μm or less.

10. A method for producing hollow silica particles according to claim 1 or 2, wherein the maximum particle diameter of the hollow silica particles is 5 μm or less.

11. A method for producing hollow silica particles according to claim 1 or 2, wherein the proportion of broken particles in the hollow silica particles is 20% or less.