Method for producing spherical silica particles

Abstract

A method for producing spherical silica particles that can achieve a lower dielectric loss tangent when filled in a resin is provided. [Solution] A method for producing spherical silica particles (X) includes classifying amorphous spherical silica particles (A) and then heat-treating the particles at 800 to 1200°C. The classification step preferably includes wet classification. The classification step preferably includes removing foreign matter from the surfaces of the spherical silica particles (A). The spherical silica particles (A) are preferably amorphous spherical silica particles obtained by a powder fusion method.

Description

[Technical Field]

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

[0002] In recent years, with the increase in the volume of information traffic in the communications field, the use of high-frequency signals has become widespread in electronic devices and communication equipment. However, the application of high-frequency signals to such equipment has also led to the problem of increased transmission loss of circuit signals. Therefore, materials with low dielectric loss tangents are required for devices used in high-frequency bands. Transmission loss can be broadly divided into conductor loss due to the skin effect of wiring and dielectric loss due to the characteristics of the dielectric material of the insulators that make up electrical and electronic components such as circuit boards. Dielectric loss is proportional to the first power of frequency, the half-power of the dielectric constant of the insulator, and the first power of the dielectric loss tangent. Therefore, materials used in high-frequency band devices are required to have low dielectric constants and dielectric loss tangents.

[0003] The dielectric properties of ceramic materials in the GHz band are described in, for example, Non-Patent Document 1, but these are the properties of sintered substrates. Silica particles have a relatively small dielectric constant and a quality factor index Qf (the value obtained by multiplying the reciprocal of the dielectric tangent by the measurement frequency) of approximately 120,000, making them promising as a ceramic filler with low dielectric constant and low dielectric tangent. From the perspective of facilitating incorporation into resins, the closer their shape is to a sphere, the more preferable. Spherical silica particles can be produced, for example, by a flame fusion method (Patent Document 1). Spherical silica particles synthesized by this method are expected to be applied to the above-mentioned high-frequency devices.

[0004] However, there is a problem that the surface of spherical silica particles contains a large amount of adsorbed water and polar functional groups such as silanol groups, which tends to deteriorate the dielectric loss tangent. Methods for reducing the amount of adsorbed water and silanol groups on the surface of spherical silica particles are described in, for example, Patent Documents 2 to 4, but the spherical silica particles obtained by these methods do not have a sufficient effect of reducing the dielectric loss tangent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 031823 [Patent Document 2] Patent No. 2926348 [Patent Document 3] Japanese Patent Application Publication No. 2020-097498 [Patent Document 4] Japanese Patent Application Publication No. 2020-138880 [Non-patent literature]

[0006] [Non-Patent Document 1] International Materials Reviews vol.60 No.70 Supplementary data (2015) Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, an object of the present invention is to provide a method for producing spherical silica particles that can achieve a lower dielectric loss tangent when filled into a resin. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have discovered that spherical silica particles that can achieve the above-mentioned object can be obtained by removing fine particles from amorphous spherical silica particles and then heat-treating the spherical silica particles under high-temperature conditions, and have thus completed the present invention. That is, the present invention has the following aspects. [1] A method for producing spherical silica particles (X), comprising classifying amorphous spherical silica particles (A) and then heat-treating the particles at 800 to 1200°C. [2] The method for producing spherical silica particles (X) according to [1], wherein the classification step includes wet classification. [3] The method for producing spherical silica particles (X) according to [1] or [2], wherein the classification step comprises classifying the spherical silica particles (A) to prepare spherical silica particles (B) having a surface fractal dimension of 1.0 to 2.3. [4] The method for producing spherical silica particles (X) according to any one of [1] to [3], wherein the classification step includes removing foreign matter from the surface of the spherical silica particles (A). [5] The method for producing spherical silica particles (X) according to any one of [1] to [4], wherein the spherical silica particles (A) are amorphous spherical silica particles obtained by a powder fusion method. [6] The method for producing spherical silica particles (X) according to any one of [1] to [5], wherein the classification step is wet classification, and the wet classification is carried out using a slurry containing a dispersion medium containing at least water and the spherical silica particles (A). [7] The specific surface area of ​​the spherical silica particles (X) is 0.1 to 2.0 m 2 The method for producing spherical silica particles (X) according to any one of [1] to [6], wherein the silica particle (X) has a molecular weight of 1000 or more. [8] The method for producing spherical silica particles according to any one of [1] to [7], wherein the average particle size and specific surface area of ​​the spherical silica particles (A) and the spherical silica particles (X) satisfy the following conditions (1) and (2): Condition (1): The ratio of the average particle diameter (Dx50) of the spherical silica particles (X) to the average particle diameter (Da50) of the spherical silica particles (A) ((Dx50) / (Da50)) is 0.8 or more and 1.2 or less. Condition (2): The ratio of the specific surface area (Sx) of the spherical silica particles (X) to the specific surface area (Sa) of the spherical silica particles (A) ((Sx) / (Sa)) is 0.2 or more and 0.6 or less. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for producing spherical silica particles that can achieve a lower dielectric loss tangent when filled into a resin. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an electron microscope photograph showing one embodiment of spherical silica particles (X) obtained by the production method of the present invention. [Figure 2] 1 is an electron microscope photograph of amorphous spherical silica particles (A) before classification treatment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below, but the present invention is not limited to the following embodiments. In this specification, the term "to" means "not less than or equal to." For example, "800 to 1200°C" means 800°C or higher and 1200°C or lower.

[0012] [Method for producing spherical silica particles (X)] The method for producing spherical silica particles (X) according to the present invention comprises classifying amorphous spherical silica particles (A) (step (i)) and then heat-treating them at 800 to 1200°C (step (ii)). The spherical silica particles (X) produced by such a method can achieve a lower dielectric tangent when filled in a resin. The method for producing spherical silica particles according to the present invention may also comprise preparing amorphous spherical silica particles (A) (step (i')).

[0013] <Preparation process: Process (i')> The method for producing spherical silica particles (X) according to the present invention may include a step (i') of preparing amorphous spherical silica particles (A) (hereinafter referred to as "spherical silica particles (A)"). The spherical silica particles (A) may be prepared by a conventionally known method. From the viewpoint of productivity, those prepared by a powder fusion method are preferred. In the production method according to the present invention, step (i') may be a step of preparing the spherical silica particles (A) by a powder fusion method. In the present invention, "amorphous spherical silica particles" refers to spherical silica particles having a silica purity of 98% or more and containing an amorphous phase of 95% by mass or more of the total. Furthermore, "spherical" silica particles refers to silica particles whose projection view (including a three-dimensional view and a plan view) when observed under a microscope or the like has a shape that is close to a circle. The powder melting method is a method in which pulverized materials such as silica sand and silica stone (hereinafter sometimes referred to as "raw materials") are melted and spheroidized at high temperatures above the melting point of the raw materials using flame, plasma, an electric furnace, a gas furnace, or the like. The melting atmosphere is not particularly limited, but from an economical standpoint, it is preferable to carry out the process in an air atmosphere. The average particle size of the raw materials is preferably 0.1 to 100 μm, more preferably 0.2 to 50 μm, and even more preferably 0.3 to 10 μm. In this specification, "average particle size" refers to the particle size (D50) corresponding to the cumulative value of 50% in the volume-based cumulative particle size distribution measured using a laser diffraction particle size analyzer.

[0014] The average particle diameter (D50) of the spherical silica particles (A) (hereinafter referred to as "average particle diameter (Da50)") is preferably 1 to 30 μm, more preferably 1 to 15 μm. The average circularity is preferably 0.85 or more, from the viewpoint that spherical silica particles (X) whose shape is closer to a perfect circle (i.e., spherical silica particles (X) having a preferred average circularity of 0.85 or more) can be easily obtained. The specific surface area of ​​the spherical silica particles (A) (hereinafter referred to as "specific surface area (Sa)") is not particularly limited, but may be, for example, 0.1 to 10 m 2 The average particle size (Da50), average circularity, and specific surface area (Sa) of the spherical silica particles (A) can be measured by the methods described below. If necessary, step (i') is carried out to obtain spherical silica particles (A), and then the spherical silica particles (A) are classified as follows.

[0015] <Classification process: Process (i)> The method for producing spherical silica particles (X) according to the present invention includes a step (i) of classifying spherical silica particles (A). In step (i), the spherical silica particles (A) are introduced into a classifier and centrifuged at a constant peripheral speed to remove fine particles from the spherical silica particles (A). Examples of the classifier that can be used include a gravity field classifier and a centrifugal field classifier. In this specification, the silica particles obtained after step (i) are referred to as "spherical silica particles (B)." Step (i) is preferably a step of removing fine particles of 0.9 μm or less contained in the spherical silica particles (A). Step (i) also preferably includes removing foreign matter from the surfaces of the spherical silica particles (A). "Foreign matter on the surfaces of the spherical silica particles (A)" refers to fine particles attached to the surfaces of the spherical silica particles (A), as shown in FIG. 2, for example. By removing fine particles and the like attached to the surfaces of the spherical silica particles (A) in step (i), spherical silica particles (X) with minimal surface irregularities and a small specific surface area can be obtained. Such spherical silica particles (X) have a reduced absolute amount of adsorbed water and polar functional groups such as silanol groups, and can achieve a lower dielectric tangent. Step (i) may be a step of removing foreign matter from the surfaces of the spherical silica particles (A) to reduce the specific surface area of ​​the spherical silica particles (A). In one embodiment, the ratio of the specific surface area (Sb) of the spherical silica particles (B) obtained after step (i) to the specific surface area (Sa) of the spherical silica particles (A) ((Sb) / (Sa)) may be 0.2 or more and 0.6 or less, or 0.3 or more and 0.6 or less.

[0016] In the production method according to the present invention, step (i) may be a step of classifying spherical silica particles (A) to obtain spherical silica particles (B) having a surface fractal dimension of 1.0 to 2.3. "Surface fractal dimension" is an index indicating the degree of surface roughness of a particle. The lower the surface fractal dimension (Ds), the less surface roughness there is on the particle, meaning the particle has a smoother surface. In the production method for spherical silica particles (X) according to the present invention, the surface fractal dimension of the spherical silica particles (B) after classification is preferably 1.0 to 2.3, more preferably 1.0 to 2.1, and even more preferably 1.0 to 1.9. The surface fractal dimension of the spherical silica particles can be measured by the following method. <Method for measuring surface fractal dimension> The spherical silica particles are placed in the transmittance measurement sample cell of an X-ray diffraction analyzer (Rigaku Corporation, product name: SmartLab) and the particles are measured using ultra-small angle X-ray scattering (USAXS) under the following conditions. Furthermore, background removal and desmearing processing are performed during analysis. Desmearing processing is performed using analysis software (Rigaku Corporation, product name: Particle size and pore size analysis software NANO-Solver). X-ray tube: Cu Kα, Tube voltage / current: 45kV-200mA, Detector: scintillation counter, Scan range: 0.00~0.50deg, Scan step: 0.0006deg, Scan speed: 0.03deg / min, Incident side analyzing crystal: Ge(220)×2, Receiving crystal: Ge(220) × 2. <Calculation method of surface fractal dimension> The surface fractal dimension is calculated as follows: First, the scattering angle 2θ is converted into a scattering vector q using the following formula (2): The measurement X-ray wavelength λ was set to 0.154 nm. q=4πsinθ / λ (2) Next, a log-log graph showing the relationship between the scattering vector q and the intensity I(q) was created for the USAXS pattern after background subtraction and desmearing processing. -1 Power approximation is performed at (2θ=0.174 to 0.0882°). The exponent α in the approximation formula is substituted into the following formula (3) to calculate the surface fractal dimension (Ds). Ds=6+α (3)

[0017] Step (i) may be a step of removing fine particles from the spherical silica particles (A) by dry classification, or a step of removing fine particles from the spherical silica particles (A) by wet classification. From the viewpoint of efficiently removing particles of 0.9 μm or less, wet classification is preferred.

[0018] (Wet classification) Step (i) may be a step of removing fine particles from the spherical silica particles (A) by wet classification. Conventionally, methods for producing silica particles with reduced amounts of adsorbed water and silanol groups have been proposed as a method for improving the dielectric loss tangent of silica particles (e.g., Patent Documents 2 to 4, etc.). These production methods require steps to minimize contact with moisture during the production process or to control the amount of moisture. The present inventors have found that removing fine particles from raw silica particles, particularly fine particles attached to the silica particle surface, can reduce the absolute amount of adsorbed water and polar functional groups such as silanol groups. Surprisingly, they have also found that performing this fine particle removal step under wet conditions does not deteriorate the dielectric loss tangent of the final spherical silica particles (X), and instead facilitates the production of spherical silica particles (X) with a lower dielectric loss tangent. When step (i) is wet classification, a slurry containing the spherical silica particles (A) and a dispersion medium is introduced into a classifier to remove fine particles from the spherical silica particles (A). As the classifier, for example, a gravity field classifier, a centrifugal field classifier, etc. can be used. Examples of the dispersion medium include water (including pure water, ion-exchanged water, etc.), and organic solvents such as ethanol, acetone, etc. Among these, from the viewpoint of ease of dispersion of the spherical silica particles (A) and economical aspects, it is preferable that the dispersion medium contains at least water. The proportion of water in the dispersion medium is more preferably 50 to 100% by mass relative to the total mass of the dispersion medium, and the concentration of the spherical silica particles (A) in the slurry is preferably 1 to 50% by mass, more preferably 20 to 40% by mass, relative to the total mass of the slurry. The slurry can be prepared, for example, by adding the spherical silica particles (A) to a dispersion medium so as to have a desired solid content, followed by stirring at room temperature for 1 to 24 hours.

[0019] When using the classifier described in the examples below, the rotor peripheral speed during wet classification is preferably 10 to 30 m / s, more preferably 20 to 30 m / s, from the viewpoint of efficiently classifying fine particles. The temperature during wet classification is not particularly limited, but from an economical point of view, room temperature is preferred. When step (i) is wet classification, the classified slurry is allowed to stand and the supernatant liquid is removed to obtain spherical silica particles (B). Then, as described below, the spherical silica particles (X) are prepared by further heat treatment. Before step (ii), the spherical silica particles (B) may be dried at 40 to 200°C for 1 to 24 hours. They may also be dried under vacuum.

[0020] <Heat treatment step: step (ii)> The method for producing spherical silica particles (X) according to the present invention further includes heat treatment at a temperature of 800 to 1200°C after step (i). In step (ii), the heating temperature of the spherical silica particles (B) is 800 to 1200°C, preferably 900 to 1100°C. By performing heat treatment at a high temperature of 800 to 1200°C, adsorbed water and the like can be removed from the spherical silica particles (B), thereby obtaining spherical silica particles (X) that can achieve a low dielectric loss tangent. On the other hand, if the heat treatment temperature exceeds 1200°C, the dispersibility of the spherical silica particles (X) in the resin decreases due to particle fusion, and defects in the silica structure increase, which tends to deteriorate the dielectric loss tangent. In one embodiment, the spherical silica particles (X) obtained by the production method according to the present invention may have an amount of water molecules desorbed (molecular weight of desorbed water) of 0.010 mmol / g or less when heated from 50°C to 1000°C at a heating rate of 25°C / min. The lower limit of the molecular weight of the desorbed water can be set to 0.001 mmol / g or more. The amount of water molecules desorbed from the spherical silica particles (X) can be measured by the following method. <Method for measuring the number of desorbed water molecules> Using a gas chromatograph mass spectrometer (JEOL Ltd., product name: JMS-Q1500GC) and a pyrolyzer (Frontier Labs, product name: PY-3030D), 15 μg of spherical silica particles were heated from 50 to 1000 °C at a heating rate of 25 °C / min under a helium atmosphere. The area value of the resulting mass chromatogram (m / z = 18) in the range from 50 to 1000 °C was calculated, and the number of desorbed water molecules was calculated from the calibration curve. The calibration curve was created by precisely weighing 23 μg, 122 μg, and 270 μg of aluminum hydroxide sample using a microbalance, heating the sample under the same conditions as above, and measuring the area value of the water molecules desorbed from the aluminum hydroxide. The water content of aluminum hydroxide here is a value calculated from the amount of mass loss at temperatures from 200°C to 320°C using a high-sensitivity differential thermobalance.

[0021] In step (ii), for example, an electric furnace or a gas furnace can be used as the heating device. From the viewpoint of reducing the dielectric loss tangent, step (ii) is preferably carried out in a nitrogen, argon, or vacuum atmosphere. The heating time is preferably 1 to 24 hours, more preferably 2 to 8 hours. If the heating time is 1 to 24 hours, productivity is likely to be good.

[0022] Spherical silica particles (X) are prepared by a method including the above-mentioned steps (i) and (ii) (or, if necessary, by a method including step (i'), step (i), and step (ii)). After step (ii), the spherical silica particles (X) may be surface-treated with a surface treatment agent, if necessary. By surface-treating the spherical silica particles (X) with a surface treatment agent, the spherical silica particles (X) tend to have better fillability in resin. In addition, polar functional groups on the particle surface tend to be reduced, making it easier to obtain spherical silica particles (X) with a lower dielectric tangent. Examples of surface treatment agents include silane coupling agents and aluminate coupling agents. These may be used alone or in combination of two or more. Among these, from the viewpoint of easily reducing polar functional groups on the particle surface, treatment with a silane coupling agent is preferred, and silazanes such as hexamethyldisilazane (HMDS) and silane coupling agents having a vinyl group such as vinyltrimethoxysilane are more preferred.

[0023] The spherical silica particles (X) obtained after step (i) or step (ii), or after any surface treatment step, may be in the form of aggregates. Therefore, after these steps, a crushing treatment may be carried out as necessary. The crushing method is preferably carried out under dry conditions without contact with moisture, and for example, an agate mortar, a ball mill, a vibration mill, a jet mill, etc. can be used.

[0024] The spherical silica particles (X) obtained by the production method according to the present invention have a surface structure as shown in FIG. 1, for example. Meanwhile, FIG. 2 is an electron microscope photograph showing one embodiment of amorphous spherical silica particles (spherical silica particles (A)) before classification. As is clear from a comparison between FIGS. 1 and 2, a large amount of very fine foreign matter (fine particles) adheres to the surface of the spherical silica particles (A), and these fine foreign matter increase the specific surface area (Sa) of the spherical silica particles (A). According to the production method according to the present invention, the fine foreign matter on the surface of the spherical silica particles (A) is easily removed by step (i), and as a result, spherical silica particles (X) with a small amount of surface foreign matter and a small specific surface area, as shown in FIG. 1, can be obtained. In one embodiment, the specific surface area (Sx) of the spherical silica particles (X) is 0.1 to 2.0 m. 2 / g, and 0.5 to 2.0 m 2 / g. The spherical silica particles (X) having such a small specific surface area and a small amount of surface foreign matter have a small absolute number of adsorbed water and polar functional groups on the particle surface, and therefore, when filled into a resin, they are likely to achieve a low dielectric loss tangent. That is, it is more preferable that the production method according to the present invention is a method that satisfies the following conditions (1) and (2). Condition (1): The ratio of the average particle diameter (Dx50) of the spherical silica particles (X) to the average particle diameter (Da50) of the spherical silica particles (A), i.e., (Dx50) / (Da50), is 0.8 or more and 1.2 or less. Condition (2): The ratio of the specific surface area (Sx) of the spherical silica particles (X) to the specific surface area (Sa) of the spherical silica particles (A), i.e., (Sx) / (Sa), is 0.2 or more and 0.6 or less. By satisfying the conditions (1) and (2), it becomes easier to obtain spherical silica particles (X) having a small specific surface area while maintaining the average particle size (Da50) of the spherical silica particles (A) within the range.

[0025] [Spherical silica particles (X)] The production method according to the present invention can provide spherical silica particles (X) that can achieve a lower dielectric loss tangent. In one embodiment, the resin sheet containing the spherical silica particles (X) produced by the method described below preferably has a dielectric constant of 3.0 or less at 35 GHz. The dielectric loss tangent of the resin sheet at 35 GHz is preferably 4.8×10 -4 Preferably, it is less than 4.5 x 10 -4 More preferably, it is 4.0×10 or less. -4 It is even more preferable that:

[0026] The spherical silica particles (X) obtained by the production method according to the present invention can have an average particle diameter (Dx50) in the range of 1 to 30 μm, an average circularity of 0.85 or more, and an average particle density of 1.8 to 2.4 g / cm. 3 The methods for measuring the average circularity and the average particle density will be described later.

[0027] [Application] The spherical silica particles (X) obtained by the production method according to the present invention can achieve a lower dielectric loss tangent when filled into a resin, and therefore can be suitably used as a filler for resin materials.

[0028] [Resin composition] The resin composition according to the present invention contains the spherical silica particles (X) prepared by the above-described production method and at least one resin selected from thermoplastic resins and thermosetting resins. The content of the spherical silica particles (X) in the resin composition is not particularly limited and can be adjusted appropriately depending on the purpose. For example, when used as a high-frequency substrate material or an insulating material, the content may be in the range of 1 to 95 mass % relative to the total mass of the resin composition, and more preferably in the range of 10 to 80 mass %.

[0029] <Resin> The resin composition according to the present invention contains at least one resin selected from thermoplastic resins and thermosetting resins. More specifically, examples of the resin include polyethylene resins, polypropylene resins, epoxy resins, silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyester resins, fluororesins, polyamide-based resins such as polyimide resins, polyamide-imide resins, and polyetherimide resins, polyester-based resins such as polybutylene terephthalate resins and polyethylene terephthalate resins, polyphenylene sulfide resins, wholly aromatic polyester resins, polysulfone resins, liquid crystal polymer resins, polyethersulfone resins, polycarbonate resins, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins, hydrocarbon-based elastomer resins, polyphenylene ether resins, and aromatic polyene-based resins. These resins may be used alone or in combination of two or more.

[0030] When the resin composition according to the present invention is used as a substrate material for high frequency bands or as an insulating material, a known low dielectric resin used for this purpose can be used. Specifically, the low dielectric resin can be at least one resin selected from a hydrocarbon-based elastomer resin, a polyphenylene ether resin, and an aromatic polyene-based resin. Of these, a hydrocarbon-based elastomer resin or a polyphenylene ether resin is preferred.

[0031] The resin composition according to the present invention may contain a curing agent, a curing accelerator, a release agent, a coupling agent, a colorant, a flame retardant, an ion scavenger, etc., within the range that does not impair the effects of the present invention.

[0032] <Method of manufacturing resin composition> The method for producing the resin composition is not particularly limited, and the resin composition can be produced by stirring, dissolving, mixing, and dispersing predetermined amounts of each material. The apparatus for mixing, stirring, dispersing, etc., of these mixtures is not particularly limited, and examples that can be used include a mortar and pestle machine equipped with a stirring and heating device, a three-roll mill, a ball mill, and a planetary mixer. These apparatuses may also be used in appropriate combination.

[0033] As described above, the resin composition containing the spherical silica particles (X) can achieve a low dielectric constant and a lower dielectric loss tangent. Furthermore, the resin composition containing the spherical silica particles (X) according to the present invention has a low viscosity, and therefore has good flowability and excellent moldability. [Example]

[0034] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description.

[0035] As the spherical silica particles (A), spherical silica particles (A-1) shown in Table 1 (manufactured by Denka Co., Ltd., trade name: FB-5D, specific surface area: 2.3 m) were used. 2 / g), and spherical silica particles (A-2) (manufactured by Denka Co., Ltd., trade name: FB-3SDC, specific surface area 3.3 m 2 The average circularity, average particle density, average particle diameter, specific surface area, and amount of desorbed water of the spherical silica particles (A-1) and (A-2), as well as the dielectric constant and dielectric loss tangent when formed into a resin sheet, were measured according to the methods described below.

[0036] [Table 1]

[0037] [Example 1] 2 kg of spherical silica particles (A-1) shown in Table 1 was added to 3 kg of pure water and stirred at room temperature for 6 hours to prepare a slurry with a particle concentration of 40% by mass. This slurry was then placed in a classification device (manufactured by Satake Chemical Machinery Co., Ltd., product name: SATAKE i Classifier (registered trademark) standard machine) and subjected to wet classification. The classification conditions were a rotor peripheral speed of 26 m / s and a fine particle discharge rate of 10 L / hr. The supernatant liquid from the slurry from which the fine particles had been removed was removed by decantation, and the resulting spherical silica particles (B) were dried at 110°C for 24 hours. The dried spherical silica particles (B) were crushed in a mortar and placed in a 50 g alumina crucible and heat-treated in an electric furnace (manufactured by Fuji Radio Engineering Co., Ltd., product name: Hi-Multi (registered trademark) 10000) under a nitrogen atmosphere at an electric furnace temperature of 1000°C for 4 hours. The furnace was then allowed to cool naturally to room temperature, and the spherical silica particles (X) were then recovered. The specific surface area, desorbed water molecular weight, average particle size, average circularity, surface fractal dimension, and average particle density of the obtained spherical silica particles (X) were measured using the following methods. The surface condition of the spherical silica particles (X) was also observed using the following method to confirm the presence or absence of fine particles on the surface. The results are shown in Table 2.

[0038] <Method for measuring the number of desorbed water molecules> Using a gas chromatograph mass spectrometer (JEOL Ltd., product name: JMS-Q1500GC) and a pyrolyzer (Frontier Labs, product name: PY-3030D), 15 μg of spherical silica particles were heated from 50°C to 1000°C at a heating rate of 25°C / min under a helium atmosphere. The area value of the resulting mass chromatogram (m / z = 18) in the range of 50°C to 1000°C was calculated, and the number of desorbed water molecules was calculated from the calibration curve. The calibration curve was prepared using the area value of the number of desorbed water molecules (m / z = 18) of an aluminum hydroxide sample (Kojundo Chemical Laboratory Co., Ltd., product name: Aluminum Hydroxide) as a standard sample. Specifically, 23 μg, 122 μg, and 270 μg of aluminum hydroxide standard samples were precisely weighed using a microbalance and heated under the same conditions as above. The area of ​​the water molecules desorbed from the aluminum hydroxide was measured to create a calibration curve. The water content of the aluminum hydroxide was calculated using the following method. A high-sensitivity differential thermobalance (NETZSCH, product name: STA 2500 Regulus) was used to measure the mass loss of aluminum hydroxide particles (Kojundo Chemical Laboratory, product name: Aluminum Hydroxide, ALI06PB) from 200 °C to 320 °C (heating conditions: room temperature (23 °C) to 800 °C at a heating rate of 10 °C / min, carrier gas: air, measurement container: platinum pan, sample amount: 13 mg).

[0039] <Method for measuring specific surface area> The measurement cell was filled with 1 g of spherical silica particles, and the specific surface area of ​​the spherical silica particles was measured using a fully automatic specific surface area diameter measuring device (Mountech, product name: Macsorb HM model-1201 (BET one-point method)). The degassing conditions before the measurement were 200°C and 10 minutes.

[0040] <Method for measuring average circularity> Spherical silica particles were fixed to a sample stage with carbon tape and then coated with osmium. Images were then taken with a scanning electron microscope (JEOL Ltd., JSM-7001F SHL) at 500-50,000x magnification and a resolution of 1280 x 1024 pixels and imported into a personal computer. The images were analyzed using an image analyzer (Nippon Roper Co., Ltd., product name: Image-Pro Premier Ver. 9.3) to calculate the projected area (S) and projected perimeter (L) of the powder, and then the circularity was calculated using the following formula (I). The circularity was calculated for 200 randomly selected particles, and the average value was used as the average circularity. Circularity = 4πS / L 2 (I)

[0041] <Method for measuring average particle size> The average particle size was measured using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: LS 13 320). 3 0.1 g of pure water and 0.1 g of spherical silica particles were added and dispersed for 1 minute using an ultrasonic homogenizer (BRANSON, product name: SFX250). The dispersed spherical silica particle dispersion was added dropwise to a laser diffraction particle size analyzer using a dropper, and measurements were taken 30 seconds after the specified amount was added. The particle size distribution was calculated from the light intensity distribution data of the diffracted / scattered light of the spherical silica particles detected by the sensor in the laser diffraction particle size analyzer. The average particle size was calculated from the particle size corresponding to a cumulative value of 50% in the volume-based cumulative particle size distribution of the particle sizes being measured.

[0042] <Method for measuring average particle density> 2.0 g of spherical silica particles were placed in a measurement sample cell, and the average particle density was measured by the gas (helium) substitution method using a dry density meter (Shimadzu Corporation, product name: Accupyc II 1340).

[0043] <Method for measuring surface fractal dimension> The spherical silica particles were placed in their original form in the sample cell for transmission measurement of an X-ray diffraction analyzer (Rigaku Corporation, product name: SmartLab), and the particles were measured using ultra-small angle X-ray scattering (USAXS) under the following conditions. During analysis, background removal and desmearing processing were performed. Desmearing processing was performed using analysis software (Rigaku Corporation, product name: Particle size and pore size analysis software NANO-Solver). X-ray tube: Cu Kα, Tube voltage / current: 45kV-200mA, Detector: scintillation counter, Scan range: 0.00~0.50deg, Scan step: 0.0006deg, Scan speed: 0.03deg / min. Incident side analyzing crystal: Ge(220)×2, Receiving crystal: Ge(220) × 2. <Calculation method of surface fractal dimension> The surface fractal dimension was calculated as follows: First, the scattering angle 2θ was converted into a scattering vector q using the following formula (2): The measurement X-ray wavelength λ was set to 0.154 nm. q=4πsinθ / λ (2) Next, a log-log graph showing the relationship between the scattering vector q and the intensity I(q) was created for the USAXS pattern after background subtraction and desmearing processing. -1 Power approximation was performed at 2θ=0.174 to 0.0882°. The exponent α in the approximation formula was substituted into the following formula (3) to calculate the surface fractal dimension (Ds). Ds=6+α (3)

[0044] <Observation of particle surfaces> The surfaces of the spherical silica particles (X) were observed under an electron microscope to evaluate the presence or absence of fine particles on the particle surface. (Evaluation criteria) Passed: Fine particles were removed from the surface of the spherical silica particles (X), and the surface irregularities were reduced. Failed: A large amount of fine particles was found attached to the surface of the spherical silica particles (X).

[0045] The obtained spherical silica particles (X) were filled into a resin, and the dielectric properties were evaluated by the following method. <Evaluation of dielectric properties (dielectric constant and dielectric loss tangent)> The spherical silica particles (X) and polyethylene resin powder (manufactured by Sumitomo Seika Chemicals Co., Ltd., trade name: FLOTHEN® UF-20S) were weighed so that the loading of the spherical silica particles (X) was 40% by volume, and mixed using a vibration mixer (manufactured by Resodyn) at an acceleration of 60 G for a processing time of 2 minutes to obtain a resin composition. The obtained resin composition was placed in a metal frame with a diameter of 3 cm in an amount to give a thickness of approximately 0.3 mm, and sheeted using a nanoimprinting device (manufactured by SCIVAX, trade name: X-300) under conditions of 140°C, 5 minutes, and 30,000 N. The obtained sheet was cut into a size of 1.5 cm x 1.5 cm to obtain an evaluation sample. Next, a 36 GHz cavity resonator (manufactured by SAMTECH) was connected to a vector network analyzer (manufactured by Keysight Technologies, product name: 85107), and the evaluation sample was placed so as to cover the 10 mm diameter hole in the cavity resonator. The resonant frequency (f0) and unloaded Q value (Qu) were measured. The evaluation sample was rotated 60 degrees after each measurement, and the same measurement was repeated five times. The average values ​​of f0 and Qu were used as the measured values, and analysis software (manufactured by SAMTECH) was used to calculate the dielectric constant from f0 and the dielectric loss tangent (tan δc) from Qu. The measurements were performed at a temperature of 20°C and a humidity of 60% RH. The obtained dielectric constant and dielectric loss tangent values ​​were evaluated according to the following criteria. The results are shown in Table 2. (Evaluation criteria) <Dielectric constant> 3 points: Dielectric constant is 3.0 or less 2 points: Dielectric constant is greater than 3.0 and less than 3.2 1 point: Dielectric constant is greater than 3.2 and less than 3.4 0 points: Dielectric constant is greater than 3.4 <Dielectric loss tangent> 3 points: Dielectric tangent is 4.0 x 10 -4 less than 2 points: Dielectric tangent is 4.0 x 10 -4That's it, 4.5 x 10 -4 less than 1 point: Dielectric tangent is 4.5 x 10 -4 That's it, 5.0 x 10 -4 less than 0 points: Dielectric tangent is 5.0 x 10 -4 End <Overall rating> The scores of the dielectric constant and the dielectric loss tangent were totaled, and the dielectric properties were evaluated according to the following criteria. Excellent: The dielectric constant and dielectric loss tangent both score 3 points (total score 6 points). Good: Either the dielectric constant or the dielectric dissipation factor is 3 points, and the other is 2 points (total score is 5 points). Pass: The dielectric constant and dielectric tangent both receive 2 points (total score is 4 points). Unacceptable: The score for either the dielectric constant or the dielectric loss tangent is less than 2 points (total score is 4 points or less).

[0046] [Examples 2 to 3 and Comparative Examples 1 to 4] Spherical silica particles (X) were prepared under the production conditions shown in Table 2. Comparative Examples 1 to 4 are examples in which spherical silica particles were produced without performing step (i) (classification step). The spherical silica particles (X) of each example were measured for specific surface area, molecular weight of desorbed water, average particle size, average circularity, surface fractal dimension, and average particle density using the same methods as in Example 1. The surface condition and dielectric properties of the particles were also evaluated using the same methods as in Example 1. The results are shown in Table 2.

[0047] [Example 4] Spherical silica particles (X) were produced under the production conditions shown in Table 2. To 100 parts by mass of the obtained spherical silica particles (X), 1 part by mass of hexamethyldisilazane (referred to as "HMDS" in Table 2) (manufactured by Shin-Etsu Chemical Co., Ltd., product name: SZ-31) was added as a surface treatment agent. The mixture was then mixed for 2 minutes at an acceleration of 60 G using a vibration mixer (manufactured by Resodyn, product name: LabRAM II), and then dried for 24 hours in a mixed powder vacuum dryer at 120°C and less than -133 Pa to obtain surface-treated spherical silica particles (X). The specific surface area, molecular weight of desorbed water, average particle diameter, average circularity, surface fractal dimension, and average particle density of the obtained spherical silica particles (X) were measured using the same methods as in Example 1. The surface condition and dielectric properties of the particles were also evaluated using the same methods as in Example 1. The results are shown in Table 2.

[0048] [Example 5] Spherical silica particles (X) were produced under the production conditions shown in Table 2. To 100 parts by mass of the obtained spherical silica particles (X), 1 part by mass of vinyltriethoxysilane (represented as "vinyl" in Table 2) (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBE-1003) was added as a surface treatment agent. The mixture was then mixed for 2 minutes at an acceleration of 60 G using a vibration mixer (manufactured by Resodyn, product name: LabRAM II), and then dried for 24 hours in a mixed powder vacuum dryer at 120°C and less than -133 Pa to obtain surface-treated spherical silica particles (X). The specific surface area, molecular weight of desorbed water, average particle diameter, average circularity, surface fractal dimension, and average particle density of the obtained spherical silica particles (X) were measured using the same methods as in Example 1. The particle surface condition and dielectric properties were also evaluated using the same methods as in Example 1. The results are shown in Table 2.

[0049] [Table 2]

[0050] As shown in Table 1, the spherical silica particles (X) of Examples 1 to 5 obtained by the production method according to the present invention had lower dielectric loss tangents than the spherical silica particles of the comparative examples. Furthermore, electron microscope observation of the spherical silica particles (X) of Examples 1 to 5 revealed that fine particles had been removed from the particle surfaces. On the other hand, in Comparative Examples 1 and 2, in which step (i) was not performed, the resin sheet had a high dielectric loss tangent. In Comparative Examples 1 and 2, the absence of step (i) meant that the fine particles of the spherical silica particles could not be removed. From these findings, it is presumed that the reduction of adsorbed water and polar functional groups was insufficient, resulting in a deterioration in the dielectric loss tangent. Furthermore, in Comparative Example 3, in which step (ii) was performed at 1300°C, the resin sheet also had a high dielectric loss tangent. It is presumed that the deterioration in the dielectric loss tangent of Comparative Example 3 was due to poorer dispersion within the resin sheet compared to the examples and an increase in defects due to the high treatment temperature. Furthermore, the spherical silica particles of Comparative Example 4, which were produced by heat-treating spherical silica particles (A) at a high temperature of 1200°C for 8 hours instead of performing step (i), also had a high dielectric loss tangent value for the resin sheet. Comparative Example 4 has a large specific surface area, and a high treatment temperature is required to reduce the amount of adsorbed water and functional groups. As a result, as with Comparative Example 3, the dispersion within the resin sheet was poorer than in the Examples, and the high treatment temperature increased defects within the particles. From these results, it was confirmed that the spherical silica particles (X) obtained by the production method according to the present invention can achieve a lower dielectric loss tangent when filled into a resin.

Claims

1. A method for producing spherical silica particles (X), comprising: The manufacturing method includes: The method comprises wet classifying amorphous spherical silica particles (A) and then heat-treating the particles at 800 to 1200°C, The average particle size and specific surface area of ​​the spherical silica particles (A) and the spherical silica particles (X) satisfy the following conditions (1) to (2): Condition (1): The ratio of the average particle diameter (Da50) of the spherical silica particles (A) to the average particle diameter (Da50) of the spherical silica particles (A) The average particle size (Dx50) ((Dx50) / (Da50)) of the silica particles (X) is 0.8 is equal to or greater than 1.2, Condition (2): The ratio of the specific surface area (Sa) of the spherical silica particles (A) to the specific surface area (Sa) of the spherical silica particles (A) The specific surface area (Sx) of the particles (X) ((Sx) / (Sa)) is 0.2 or more and 0.6 or less. A method for producing spherical silica particles (X), which satisfies the above.

2. 2. The method for producing spherical silica particles (X) according to claim 1, wherein the classification step comprises wet-classifying the amorphous spherical silica particles (A) at a rotor peripheral speed of 10 to 30 m / s.

3. 3. The method for producing spherical silica particles (X) according to claim 1 or 2, wherein the classification step comprises removing foreign matter from the surface of the spherical silica particles (A).

4. The method for producing spherical silica particles (X) according to any one of claims 1 to 3, wherein the spherical silica particles (A) are amorphous spherical silica particles obtained by a powder fusion method.

5. 5. The method for producing spherical silica particles (X) according to claim 1, wherein the classification step is wet classification, and the wet classification is carried out using a slurry containing a dispersion medium containing at least water and the spherical silica particles (A).

6. The specific surface area of ​​the spherical silica particles (X) is 0.1 to 2.0 m ２ The method for producing spherical silica particles (X) according to any one of claims 1 to 5, wherein the saturation energy of the spherical silica particles (X) is 0.1 wt. / g.

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