Surface-treated silica powder and method for producing surface-treated silica powder

Abstract

A surface-treated silica powder according to the present invention comprises silica particles surface-treated with a vinyl silane, and when the carbon content measured according to a predetermined procedure is defined as C (mass%) and the specific surface area measured by the BET one-point method using nitrogen gas adsorption is defined as S(m2 / g), C and S satisfy 0.001≤C / S≤0.025, and S is at least 0.8 m2 / g and at most 5.0 m2 / g.

Description

Surface-treated silica powder, method for producing surface-treated silica powder

[0001] This invention relates to surface-treated silica powder and a method for producing surface-treated silica powder.

[0002] In recent years, with the increase in the volume of information and communication in the telecommunications field, the use of high-frequency bands in electronic devices and communication equipment has been expanding. High frequencies have characteristics such as broad bandwidth, directivity, and transparency, and in particular, frequencies of 10 ９ The use of the GHz band, as described above, is widespread.

[0003] With the application of high-frequency bands, a problem arises in which the transmission loss of circuit signals increases. Transmission loss can be broadly classified into conductor loss due to the skin effect of wiring and dielectric loss due to the properties of the dielectric material of the insulator constituting electrical and electronic components such as substrates. Since dielectric loss is proportional to the first power of frequency, the square root of the dielectric constant of the insulator, and the first power of the dielectric loss tangent, materials used in high-frequency band devices are required to have low dielectric constant and dielectric loss tangent.

[0004] Silica (SiO ２ Silica has a low dielectric constant (3.7) and a quality factor index Qf (the product of the reciprocal of the dielectric loss tangent and the measurement frequency) of approximately 120,000, making it a promising filler material with a low dielectric constant and a predetermined dielectric loss tangent. However, the surface of silica particles contains many polar functional groups such as adsorbed water and silanol groups, and in particular, there is a problem that the dielectric loss tangent deteriorates compared to the properties of the sintered substrate.

[0005] In contrast, Non-Patent Document 1 investigates a method of surface treatment using a silane coupling agent as a way to reduce adsorbed water and polar functional groups on the surface of filler particles. However, the dielectric loss tangent is hardly reduced in the 1-10 MHz range, and the effect is insufficient. The effect in the GHz band is not specified.

[0006] IEEE Transactions on Dielectrics and Electrical Insulation Vol. 17, No. 6 (2010)

[0007] However, as a result of the inventors' study, it has been found that there is room for improvement in suppressing the change in the dielectric tangent before and after storage in a high-temperature and high-humidity environment in the silica powder described in the above Non-Patent Document 1.

[0008] As a result of further study by the inventors, it has been found that in silica powder having a predetermined specific surface area, by vinyl silane treatment, the carbon content on the powder surface can be reduced compared with methacryl silane. Based on such findings, as a result of intensive study, it has been found that by setting the carbon content per unit area to a predetermined value or less, the change in the dielectric tangent before and after storage in a high-temperature and high-humidity environment can be suppressed in the surface-treated silica powder.

[0009] According to one aspect of the present invention, the following surface-treated silica powder and method for producing a surface-treated silica powder are provided. 1. A surface-treated silica powder containing silica particles surface-treated with vinyl silane, where the carbon content measured according to the following procedure is C (mass%), and the specific surface area measured by the BET one-point method by nitrogen gas adsorption is S (m ２ / g), when C and S satisfy 0.001 ≦ C / S ≦ 0.025, and S satisfies 0.8 m ２ / g or more and 5.0 m ２ / g or less, the surface-treated silica powder. (Procedure) Add 3 g of the surface-treated silica powder to 37 g of acetone and stir for 30 minutes. Then, operate the slurry liquid in a centrifuge at 3500 rpm for 10 minutes to separate the surface-treated silica powder and acetone, and discard the supernatant solution of acetone. Perform this washing operation with acetone twice and dry at 120 °C for 2 hours. Measure the carbon content (mass%) in 0.3 g of the washed surface-treated silica powder with a carbon / sulfur simultaneous analyzer and quantify it by the calibration curve method. 2. The surface-treated silica powder according to 1., where when the particle diameters at the points where the cumulative volume from the small particle side in the volume-based cumulative distribution measured by the wet laser diffraction scattering method is 10%, 50%, and 90% are D １０ 、D ５０ 、D ９０ , when (D ９０ - D １０ ) / D ５０Surface-treated silica powder having a ratio of 1.0 to 5.0. 3. Surface-treated silica powder as described in 1. or 2., wherein the particle diameter at the points where the cumulative volume from the small particle side in the volume-based cumulative distribution measured by wet laser diffraction scattering is 10% and 50% is D. １０ , D ５０ In that case, D ５０ / D １０ Surface-treated silica powder having a ratio of 1.5 to 10.0. 4. Surface-treated silica powder according to any one of 1. to 3., wherein the average sphericity is 0.80 or higher. 5. Surface-treated silica powder having a specific surface area of ​​0.8 m² measured by the BET one-point method by nitrogen gas adsorption. ２ / g or more 5.0m ２ A method for producing surface-treated silica powder, comprising the step of heat-treating silica powder at a density of 1000°C·h or more and 26400°C·h or less, and then surface-treating it with vinylsilane.

[0010] According to the present invention, a surface-treated silica powder that is excellent at suppressing fluctuations in dielectric loss tangent before and after storage in a high-temperature and high-humidity environment, a packaging body using the same, and a storage method are provided.

[0011] The outline of the surface-treated silica powder of this embodiment will be described.

[0012] The surface-treated silica powder of this embodiment is a surface-treated silica powder containing silica particles surface-treated with vinylsilane, wherein the carbon content measured according to the following procedure is defined as C (mass%), and the specific surface area measured by the BET 1-point method by nitrogen gas adsorption is defined as S (m²). ２ When ( / g), C and S satisfy 0.001 ≤ C / S ≤ 0.025, and S is 0.8 m ２ / g or more 5.0m ２Surface-treated silica powder satisfying the requirement of 0.5 / g or less. (Procedure) Add 3 g of the surface-treated silica powder to 37 g of acetone and stir for 30 minutes. Then, run the slurry liquid in a centrifuge at 3500 rpm for 10 minutes to separate the surface-treated silica powder from the acetone, and discard the supernatant solution of acetone. Repeat this washing operation with acetone twice and dry at 120°C for 2 hours. Measure the carbon content (mass%) in 0.3 g of the washed surface-treated silica powder using a carbon / sulfur simultaneous analyzer and quantify it using the calibration curve method.

[0013] According to the inventors' findings, it has been found that by keeping the carbon content per unit area (C / S) below the above upper limit, it is possible to realize a surface-treated silica powder that can suppress large fluctuations in the dielectric loss tangent between before and after storage in high-temperature and high-humidity environments. Furthermore, it is possible to realize a surface-treated silica powder with a low dielectric loss tangent immediately after manufacturing.

[0014] By using a silane coupling agent having a nonpolar functional group that does not contain O and / or N, and keeping the C / S ratio below the above upper limit, a surface-treated silica powder with minimal change in dielectric loss tangent over time before and after storage can be realized. Although the detailed mechanism is not clear, it is presumed that by using vinylsilane that does not contain O and N and has a low-polarity vinyl group as a functional group, a surface-treated silica powder with superior suppression of fluctuations in dielectric loss tangent before and after storage in high-temperature and high-humidity environments can be realized compared to using (meth)acrylicsilane that contains O and has a polar (meth)acrylic group (including acrylic group and methacrylic group) as a functional group. Furthermore, regarding the functional group of vinylsilane, it may be used if the functional group has a small number of carbon atoms, but it has also been found that by using one with a large number of carbon atoms, the amount of vinylsilane added can be reduced.

[0015] The lower limit of C / S is, for example, 0.001 or higher, preferably 0.005 or higher, and more preferably 0.010 or higher. This improves adhesion with the resin. The upper limit of C / S is, for example, 0.025 or lower, preferably 0.015 or lower, and more preferably 0.010 or lower. Keeping it below the upper limit suppresses fluctuations in dielectric loss tangent before and after storage in high-temperature and high-humidity environments, for example, at 40°C and 90% RH.

[0016] In this embodiment, for example, by appropriately selecting a method for adjusting raw material silica powder, a method for surface treatment of raw material silica powder, etc., it is possible to control the specific surface area, carbon content, and particle size distribution. Among these, for example, appropriately adjusting the specific surface area by classifying the raw material silica powder, performing surface treatment with vinyl silane after classification treatment and heat treatment, etc. can be cited as elements for setting the specific surface area, carbon content, and particle size distribution within a desired numerical range.

[0017] The silica powder of this embodiment can be suitably used as a filler for blending with resin materials such as resins or resin compositions. This resin material can be applied to various uses, for example, it can be used for resin materials for high-frequency bands, etc.

[0018] Hereinafter, the configuration of the surface-treated silica powder of this embodiment will be described in detail.

[0019] The surface-treated silica powder may contain silica (SiO ２ ) as a main component. The main component means that, in terms of mass conversion in the total amount of the surface-treated silica powder, silica (SiO ２ ) is contained, for example, at 50% or more, preferably 80% or more, more preferably 90% or more. Although it is preferable that the silica has a high purity, the presence of impurities inevitably mixed in during the raw materials and the manufacturing process is tolerated.

[0020] The surface-treated silica powder contains either or both of amorphous and crystalline forms. The amorphous ratio of the surface-treated silica powder is, for example, 95.0% or more, preferably 97.0% or more, more preferably 99.0% or more.

[0021] The amorphous ratio of the surface-treated silica powder is measured from the intensity ratio of specific diffraction peaks by performing X-ray diffraction analysis using a powder X-ray diffractometer (for example, the product name "Model MiniFlex" manufactured by Rigaku Corporation) in the range of 2θ of CuKα ray from 26° to 27.5°. In the case of silica-based powder, crystalline silica (α-quartz) has a main peak at 26.7°, but there is no peak in amorphous silica. When amorphous silica and crystalline silica are mixed, a peak height of 26.7° corresponding to the ratio of crystalline silica is obtained. Then, the mixed ratio of crystalline silica (X-ray diffraction intensity of the sample / X-ray diffraction intensity of crystalline silica) is calculated from the ratio of the X-ray intensity of the sample to the X-ray intensity of the crystalline silica standard sample, and the amorphous ratio (%) can be calculated from the formula: amorphous ratio (%) = (1 - mixed ratio of crystalline silica) × 100. When there are crystal phases other than α-quartz, it may be calculated similarly for the main peaks of each crystal phase.

[0022] The shape of the silica particles contained in the surface-treated silica powder may be any of spherical, crushed, needle-like, flaky, etc., but spherical is preferred.

[0023] The average sphericity of the surface-treated silica powder is, for example, 0.80 or more, preferably 0.90 or more, more preferably 0.95 or more. Thereby, when mixed with a resin, an increase in the viscosity and a decrease in the fluidity of the obtained resin composition can be suppressed.

[0024] The average sphericity of the surface-treated silica powder is measured as follows. Particle images taken with a stereomicroscope (for example, the model "SMZ-10 type" manufactured by Nikon Corporation), a scanning electron microscope, etc. are imported into an image analysis device (for example, manufactured by Nippon Avionics Co., Ltd., etc.). The projected area (A) and the perimeter (PM) of the particles are measured from the photograph. Assuming the area of a perfect circle corresponding to the perimeter (PM) is (B), the circularity of the particle can be expressed as A / B. Therefore, assuming a perfect circle having the same perimeter as the perimeter (PM) of the sample particles, PM = 2πr and B = πr ２ so B = π × (PM / 2π) ２ and the sphericity of each particle is sphericity = A / B = A × 4π / (PM) ２It can be calculated as follows. The roundness of 200 arbitrary particles obtained in this way was determined, and the average value was taken as the average sphericity.

[0025] The vinylsilanes used for surface treatment of silica particles are silanes having at least one vinyl group in their molecule. These may be included individually or in any combination of two or more.

[0026] The silanes described above have one or more hydrolyzable groups in their molecules, in addition to functional groups such as vinyl groups. Examples of hydrolyzable groups include alkoxy groups such as methoxy groups and ethoxy groups. These alkoxy groups generate silanol groups through hydrolysis. These silanol groups chemically react with OH groups (reaction sites) present on the surface of the silica particles, causing the silane coupling agent to chemically bond to the surface of the silica particles.

[0027] The vinylsilane described above contains a functional group and a hydrolyzable group, and it is preferable that the functional group contains a vinyl group. In this case, the functional group may be a silane having a hydrocarbon group with a terminal vinyl, or a silane having a vinyl group or an alkenyl group. However, the hydrocarbon group with a terminal vinyl, vinyl group, and alkenyl group shall be low-polarity groups that do not contain O and / or N. The hydrocarbon group contains -C=CH ２ The number of carbon atoms other than the one in the first position is not particularly limited, but may be 0 to 12, 0 to 11, 0 to 10, or 0 to 8. Furthermore, the silane having a vinyl group may be a low-polarity silane that does not contain O and / or N in the vinyl group or other functional groups. Specifically, examples include vinyltrimethoxysilane, vinyltriethoxysilane, and 7-octenyltrimethoxysilane.

[0028] The upper limit of the specific surface area (S) of surface-treated silica powder is 5.0 m². ２ / g or less, preferably 4.5m ２ / g or less, more preferably 4.0m ２ It is less than / g. This allows for a further reduction in the dielectric loss tangent when compounded into the resin. On the other hand, the lower limit of the specific surface area (S) is 0.8 m². ２ / g or more, preferably 1.0m ２ / g or more, more preferably 1.4m ２ The concentration is 1 / g or more. This improves the filler properties of the composition when it is incorporated into the resin.

[0029] The specific surface area of ​​silica powder can be measured by the BET single-point method using nitrogen gas adsorption. Specifically, using a specific surface area analyzer (Anton Paar, model name: NOVA 800 BET), nitrogen gas is transported as the adsorption gas by a vacuum pump, and 0.1 to 5.0 g of the sample is dried and degassed at 300°C for 30 minutes before measurement.

[0030] In the volume-based cumulative distribution of particle size in surface-treated silica powder, the particle size at the points where the cumulative volume from the smallest particle side reaches 10%, 50%, and 90% is D. １０ , D ５０ , D ９０ The volume-based cumulative distribution of surface-treated silica powder is a value based on particle size measurement by wet laser diffraction scattering, and can be measured using, for example, a Coulter LS13 320 particle size analyzer. For measurement, water is used as the solvent, and as a pretreatment, dispersion treatment can be performed using a homogenizer with an output of 500W for 120 seconds or more. In addition, the PIDS (Polarization Intensity Differential Scattering) concentration is adjusted to 45-55%. The refractive index of water is set to 1.33, and the refractive index of the powder material is taken into consideration. For example, amorphous silica is measured with a refractive index of 1.50.

[0031] (D ９０ -D １０ ) / D ５０ The lower limit is, for example, 1.0 or higher, preferably 1.4 or higher, and more preferably 1.8 or higher. This improves the fillability of the composition when it is compounded with resin. (D ９０ -D １０ ) / D ５０ The upper limit is, for example, 5.0 or less, preferably 4.0 or less, and more preferably 3.0 or less. By keeping it below the upper limit, moldability can be improved by reducing coarse particles.

[0032] D ５０ / D １０ The lower limit is, for example, 1.5 or higher, preferably 2.0 or higher, and more preferably 2.5 or higher. This further improves the fillability of the composition when it is compounded with resin. D ５０ / D １０ The upper limit is, for example, 10.0 or less, preferably 9.0 or less, and more preferably 8.0 or less. By keeping it below the upper limit, the dielectric loss tangent in the resin composition containing surface-treated silica powder can be reduced.

[0033] <Method for producing surface-treated silica powder> As an example of the method for producing surface-treated silica powder in this embodiment, surface-treated silica powder can be obtained by classification, heat treatment, and surface treatment using vinylsilane. A specific manufacturing method is, for example, when the specific surface area measured by the BET 1-point method using nitrogen gas adsorption is 0.8 m². ２ / g or more 5.0m ２ The process may include heating silica powder at a concentration of 1000°C·h or less at a temperature of 26400°C·h or higher, followed by surface treatment with the vinylsilane described above. In the above manufacturing method, one or more vinylsilanes may be used alone, and vinylsilane may be used in combination with other silanes or silazanes as long as the effects of the present invention are not impaired. Here, the content of vinylsilane in the silane coupling agent used in the surface treatment is, for example, 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. Furthermore, by reducing the content of silazane (hexamethyldisilazane, etc.) in the silane coupling agent used in the surface treatment, ammonia (NH) can be reduced in the blended resin. ３ This suppresses the occurrence of (the phenomenon described above), thereby reducing the impact on changes in resin properties such as curing behavior.

[0034] The following describes each process in detail. First, the raw silica powder is produced by a dry process. An example of a dry process is the powder melting method, which involves passing the powder through a high-temperature range above its melting point to create spheroids. An example of a high-temperature range above the melting point is a flame. The flame temperature may be, for example, 1700°C. The raw silica powder produced by the dry process is subjected to a classification process, including coarse powder classification and / or fine powder classification, to obtain classified silica powder. It may be collected and stored in moisture-proof aluminum bags. Classification can also be performed by mixing or classifying appropriate amounts of silica powder with different particle size configurations. Industrially, classification using a classifier such as a sieve or a precision wind classifier is desirable, and the classification operation is preferably performed by a dry process. By dry classifying the raw silica powder produced by the dry process, aggregation of the silica powder can be suppressed and handling properties can be improved compared to using raw silica powder produced by a wet process and / or wet classification.

[0035] Next, the classified silica powder is heat-treated. The heat treatment is performed at a temperature of 500 to 1100°C for a predetermined time (for example, about 1 to 52 hours) where the heating temperature (°C) × heating time (h) is 1000 to 26400 (°C·h), preferably 1800 to 17600 (°C·h) for a predetermined time (for example, about 2 to 35 hours), using hot air or an electric furnace. If the heating temperature is 500 to 1100°C, the specific surface area and average particle size do not change before and after heating, so it is desirable to perform the classification process before heating, adjust to the desired specific surface area and average particle size, and then perform the heat treatment. After the heat treatment, the silica powder is allowed to cool naturally in an electric furnace, recovered at a temperature of 110°C to 300°C, further cooled to 25°C in an environment with a humidity of 40% RH or less, stored at 15 to 25°C, and may be recovered and stored in moisture-proof aluminum bags.

[0036] Next, the heat-treated silica powder is surface-treated with the silane coupling agent described above.

[0037] In the method for producing surface-treated silica powder, the treated material may be collected and stored in a bag after at least one of the following treatments: classification, heat treatment, and surface treatment.

[0038] In this embodiment, the treated material and / or surface-treated silica powder can be stored in a resin bag or a moisture-proof aluminum bag. Examples of resin bags include, but are not limited to, PET film bags, PE film bags, and PP film bags. The moisture-proof aluminum bag has a moisture permeability of 0.1 g / m³ under JIS Z 0208-1976 condition B (temperature 40°C - relative humidity 90%). ２ Examples of moisture-proof bags include those with a moisture-proof barrier of 24 hours or less, such as moisture-proof aluminum bags or PET / AL / PE laminated bags.

[0039] The packaging of this embodiment may comprise the above-mentioned surface-treated silica powder and a resin bag containing the surface-treated silica powder. The resin bag may be sealed to contain the surface-treated silica powder, and the sealed space may be degassed or replaced with a known inert gas.

[0040] Furthermore, the storage method of this embodiment may include the step of storing the surface-treated silica powder in a resin bag. In the storage method, the external environment during storage and the storage period are not particularly limited. Because the surface-treated silica powder of this embodiment itself exhibits little change in dielectric loss tangent over time, the dielectric loss tangent of the surface-treated silica powder can be kept low after storage even without using a moisture-proof bag.

[0041] Next, the resin composition of this embodiment will be described. The surface-treated silica powder of this embodiment can be suitably used as a resin material when incorporated into a resin composition. In addition to the surface-treated silica powder of this embodiment, the resin composition includes a resin and known resin additives.

[0042] In the resin composition, the surface-treated silica powder may be used alone or mixed with other fillers. The resin composition may contain 10 to 99% by mass of the surface-treated silica powder, or 10 to 99% by mass of a mixed inorganic powder containing the surface-treated silica powder and other fillers. In the mixed inorganic powder, the content of other fillers may be, for example, 1 to 20% by mass or 3 to 15% by mass, relative to 100% by mass of the silica powder. In this specification, "~" indicates that the upper and lower limits are included unless otherwise specified.

[0043] Other fillers include, for example, silica other than the surface-treated silica powder of this embodiment, alumina, titania, silicon nitride, aluminum nitride, silicon carbide, talc, calcium carbonate, etc. The average particle size of the other fillers used is approximately 5 to 100 μm, and there are no particular restrictions on their particle size composition and shape.

[0044] Examples of the resins mentioned above include epoxy resins, silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyimides, polyamideimides, polyetherimides and other polyimides, polyesters such as polybutylene terephthalate and polyethylene terephthalate, polyphenylene sulfide, fully aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins. These may be used individually or in combination of two or more.

[0045] Resin compositions can be manufactured, for example, by blending raw material components in predetermined ratios using a blender or Henschel mixer, then kneading them using a heated roll, kneader, single-screw or twin-screw extruder, cooling, and then grinding the mixture.

[0046] The embodiments of the present invention have been described above, but these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention.

[0047] The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way to the descriptions of these examples.

[0048] <Preparation of Silica Powder> [Example 1] A raw silica powder manufactured by the dry method was used as the raw material. The raw silica powder had one peak with the most frequent diameter in the range of 1.0 to 15.0 μm. The fine and coarse powders were removed from the raw silica powder using cyclone collection and a precision wind classifier, and through this classification process, silica powder with the particle size distribution and specific surface area shown in Table 1 was obtained. Next, the classified silica powder was packed into an alumina crucible and heat-treated under atmospheric conditions at an electric furnace temperature of 980°C for 4 hours. After the heat treatment, it was cooled to 200°C in the furnace, cooled to room temperature in a desiccator (23°C, 10% RH), and the heat-treated silica powder was recovered. To 100 parts by mass of heat-treated silica powder, 0.15 parts by mass of vinylsilane (KBM-1003, manufactured by Shin-Etsu Silicone Co., Ltd.) was added and mixed for 30 minutes in a vibrating mixer (manufactured by Resodyn Co., Ltd.). After that, the mixture was dried at 120°C for 4 hours. This surface treatment yielded surface-treated silica powder.

[0049] [Example 2] Surface-treated silica powder was obtained in the same manner as in Example 1, except that 0.10 parts by mass of vinylsilane (KBM-1003 manufactured by Shin-Etsu Silicone Co., Ltd.) was added to 100 parts by mass of heat-treated silica powder in the surface treatment described above. [Comparative Example 1] Silica powder that had not undergone surface treatment was recovered in the same manner as in Example 1, except that the above surface treatment was not performed.

[0050] [Comparative Example 2] Surface-treated silica powder was obtained in the same manner as in Example 1, except that 0.2 parts by mass of methacrylic silane (KBM-503 manufactured by Shin-Etsu Silicone Co., Ltd.) was added to 100 parts by mass of heat-treated silica powder in the surface treatment described above.

[0051] [Reference Example 1] The above raw material silica powder was added to 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 put into a classifier and wet classification was performed. The classification conditions were rotor peripheral speed: 26 m / s and fine particle discharge rate: 10 L / hr. The supernatant liquid was removed from the slurry from which the fine particles had been removed by decantation, and the obtained silica powder was dried at 110°C for 24 hours. The dried silica powder was crushed in a mortar. The crushed silica powder was placed in an alumina crucible and heated in an electric furnace under a nitrogen atmosphere at an electric furnace temperature of 1000°C for 4 hours. After that, the furnace was allowed to cool naturally until it reached room temperature, and the silica powder was recovered. 1 part by mass of vinylsilane (KBM-1003, manufactured by Shin-Etsu Silicone Co., Ltd.) was added to 100 parts by mass of the recovered silica powder. Subsequently, the mixture was mixed for 2 minutes at an acceleration of 60G using a vibrating mixer (manufactured by Resodyn), and then dried in a mixed powder vacuum dryer at 120°C and under a pressure of less than -133 Pa for 24 hours to obtain surface-treated silica powder.

[0052] The silica powder obtained as described above was stored in a plastic bag until immediately before each evaluation.

[0053]

[0054] The following items were evaluated for the obtained silica powder.

[0055] <Specific Surface Area> The specific surface area of ​​silica powder was measured using the BET single-point method with nitrogen gas adsorption. Specifically, using a specific surface area analyzer (Anton Paar, name: NOVA 800 BET), nitrogen gas was transported by a vacuum pump, and 0.1 to 5.0 g of the sample was dried and degassed at 300°C for 30 minutes before measurement.

[0056] <Particle Size> The volume-based frequency distribution and volume-based cumulative distribution of silica powder particle size were determined by wet laser diffraction scattering using a particle size distribution analyzer (Culturer LS13 320). Water was used as the solvent, and as a pretreatment, the powder was dispersed using a homogenizer at a power of 500 W for 120 seconds or more before measurement. The PIDS (Polarization Intensity Differential Scattering) concentration was adjusted to 45-55% for measurement. A refractive index of 1.33 was used for water, and the refractive index of the powder material was considered. For example, amorphous silica was measured with a refractive index of 1.50. Based on the obtained volume-based cumulative distribution, the particle size (D) at which the cumulative value from the smallest particle size side reaches X% was determined. Ｘ ) was calculated.

[0057] <Average Sphericity> The average sphericity of silica powder was measured by taking particle images with a stereomicroscope (for example, Nikon's SMZ-10 model) or scanning electron microscope, and inputting the images into an image analysis device (for example, one manufactured by Japan Avionics Co., Ltd.) as follows: The projected area (A) and perimeter (PM) of the particle were measured from the photograph. If (B) is the area of ​​a perfect circle corresponding to the perimeter (PM), then the roundness of the particle can be expressed as A / B. Therefore, assuming a perfect circle with the same perimeter (PM) as the sample particle, PM = 2πr and B = πr ２ Therefore, B = π × (PM / 2π) ２ Therefore, the sphericity of each particle is given by: Sphericity = A / B = A × 4π / (PM) ２ It can be calculated as follows. The roundness of 200 arbitrary particles obtained in this way was determined and the average value was taken as the average sphericity. The average sphericity of the silica powders in Examples 1 and 2 was 0.90 or higher in both cases.

[0058] <Carbon Content After Acetone Washing> 3 g of the obtained silica powder was added to 37 g of acetone and stirred for 30 minutes to obtain a slurry. The slurry was then centrifuged at 3500 rpm for 10 minutes to separate the silica powder from the acetone, and the supernatant solution of the acetone was discarded. This acetone washing operation was performed twice, and the mixture was dried at 120°C for 2 hours. The carbon content (mass%) in 0.3 g of the washed silica powder was measured using a carbon / sulfur simultaneous analyzer "CS-444LS" (manufactured by LECO Corporation) and quantified using the calibration curve method.

[0059] <Viscosity> A resin sample was obtained by mixing 35% by mass of the obtained silica powder with 65% by mass of liquid epoxy resin (Mitsubishi Chemical Corporation, bisphenol F type resin, JER807). The viscosity (Pa·s) of the obtained resin sample was measured at 25°C and a shear rate of 100 [1 / s] using a rheometer (Anton Paar Corporation, model Modular Compact Rheometer MCR 102) equipped with a conical cone (3 degrees). The results are shown in Table 1. When the viscosity was less than 200 Pa·s, the packing performance was judged as "good", when it was between 200 and 300 Pa·s, the packing performance was judged as "poor", and when it exceeded 300 Pa·s, the packing performance was judged as "very poor".

[0060] <Dielectric Loss Tangent Measured by Resonance Method> The obtained silica powder was mixed with polyethylene powder (Sumitomo Seika Co., Ltd., Flowsen UF-20S) at a filling volume of 40 volume percent using a vibrating mixer (Resodyn Co., Ltd.) under conditions of acceleration of 60 g and processing time of 2 minutes. The obtained mixed powder was weighed to a predetermined volume (to a thickness of approximately 0.3 mm), placed in a 3 cm diameter metal frame, and molded using a nanoimprint apparatus (SCIVAX "X-300") under conditions of 140°C-5 min-30000 N to form a resin sheet sample of 3.0 cmΦ and 0.3 mm thickness. Note that the shape and size of the resin sheet sample do not affect the evaluation results as long as it can be mounted on the measuring instrument. Using the obtained resin sheet sample, the dielectric constant and dielectric loss tangent were measured using a 40 GHz split cylinder resonator (EM Lab Co., Ltd.) with the sample set in the resonator. The same sheet was measured twice under the same processing conditions, with n=2 measurements, and the average of the four measurements was calculated. The measurement temperature was 20°C and the humidity was 60% RH. The obtained tanδ was defined as the dielectric loss tangent of the resin sheet sample. Furthermore, the obtained silica powder was stored for 6 months under the conditions of (temperature 40°C, humidity 90% RH, in a high-temperature, high-humidity chamber, in an atmospheric environment, with a storage amount of silica of 20 g, in a glass petri dish with a diameter of 12 cm), and then a resin sheet sample was manufactured in the same manner as above, and the dielectric loss tangent of the resin sheet sample was measured. Table 1 shows the ratio of the dielectric loss tangent of the resin sheet using silica powder after 6 months of storage to the dielectric loss tangent of the resin sheet using silica powder before storage, with the dielectric loss tangent of the resin sheet using silica powder before storage being used as the reference.

[0061] The surface-treated silica powders of Examples 1 and 2 showed that, compared to Comparative Examples 1 and 2, they could suppress the increase in the degree of change in dielectric loss tangent when compounded with resin, both before and after storage in high-temperature and high-humidity environments. Furthermore, the surface-treated silica powders of Examples 1 and 2 showed superior filling performance compared to Reference Example 1, which had a smaller specific surface area.

[0062] This application claims priority based on Japanese Patent Application No. 2024-173420, filed on 2 October 2024, and incorporates all of its disclosures herein.

Claims

1. A surface-treated silica powder containing silica particles surface-treated with vinylsilane, wherein the carbon content measured according to the following procedure is defined as C (mass%), and the specific surface area measured by the BET one-point method by nitrogen gas adsorption is defined as S (m²). ２ When ( / g), C and S satisfy 0.001 ≤ C / S ≤ 0.025, and S is 0.8 m ２ / g or more 5.0m ２ Surface-treated silica powder satisfying the requirement of 0.5 / g or less. (Procedure) Add 3 g of the surface-treated silica powder to 37 g of acetone and stir for 30 minutes. Then, run the slurry liquid in a centrifuge at 3500 rpm for 10 minutes to separate the surface-treated silica powder from the acetone, and discard the supernatant solution of acetone. Repeat this washing operation with acetone twice and dry at 120°C for 2 hours. Measure the carbon content (mass%) in 0.3 g of the washed surface-treated silica powder using a carbon / sulfur simultaneous analyzer and quantify it using the calibration curve method.

2. The surface-treated silica powder according to claim 1, wherein the particle diameters of the respective points at which the cumulative volume from the small particle side in the volume-based cumulative distribution measured by the wet laser diffraction scattering method is 10%, 50%, and 90% are D １０ , D ５０ , D ９０ , and when they are denoted as D ９０ , D １０ , and D ５０ respectively, (D ９０ - D １０ ) / D ５０ is 1.0 or more and 5.0 or less. The surface-treated silica powder.

3. A surface-treated silica powder according to claim 1 or 2, wherein the particle diameter at the points where the cumulative volume from the small particle side in the volume-based cumulative distribution measured by wet laser diffraction scattering is 10% and 50% is D. １０ , D ５０ In that case, D ５０ / D １０ Surface-treated silica powder having a value of 1.5 or more and 10.0 or less.

4. Surface-treated silica powder according to claim 1 or 2, wherein the average sphericity is 0.80 or higher.

5. The specific surface area measured by the BET one-point method using nitrogen gas adsorption is 0.8 m². ２ / g or more 5.0m ２ A method for producing surface-treated silica powder, comprising the step of heat-treating silica powder at a density of 1000°C·h or more and 26400°C·h or less, and then surface-treating it with vinylsilane.

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