Silica powder

Abstract

A silica powder according to the present invention has: a dielectric loss tangent of at most 2.0×10-3 at 40 GHz in a resin sheet sample, as measured by a resonance method; a specific surface area of 0.2 m2 / g-5.0 m2 / g, as measured by the BET 1-point method using nitrogen gas adsorption; a frequency of at least 5.5% for the maximum peak in a particle diameter frequency distribution as measured by a wet laser diffraction scattering method; a frequency of at most 6.0% for particles having a particle diameter of at least 20.7 μm; a Dm / S that reaches at least 1.50 where the value of the mode diameter in the particle size frequency distribution is Dm (μm), and the value of the specific surface area is S (m2 / g).

Description

Silica powder

[0001] The present invention relates to a silica powder.

[0002] In recent years, with the increase in the amount of information and communication in the field of communication, the use of high frequency bands has been expanding in electronic devices and communication devices. High frequency bands have characteristics such as wide bandwidth, straightness, and transparency. ９ The GHz band or higher is being used extensively.

[0003] The application of high frequencies has led to the problem of increased transmission loss of circuit signals. 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 devices are required to have low dielectric constants and dielectric loss tangents.

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

[0005] In contrast to this, Non-Patent Document 1 investigates a method of surface treatment with a silane coupling agent as a method of reducing adsorbed water and polar functional groups on the surface of filler particles, but the dielectric loss tangent is hardly reduced at 1 to 10 MHz, and the effect is insufficient, and the effect in the GHz band is not clearly stated.

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

[0007] However, as a result of investigations by the present inventors, it has been found that the silica powder described in Non-Patent Document 1 has room for improvement in terms of low dielectric tangent and packing properties when blended with a resin.

[0008] As a result of further investigation, the present inventors have found that by appropriately adjusting the particle size characteristics of the "frequency of the maximum peak," "frequency of particles with a particle diameter of 20.7 μm or more," and "mode diameter / specific surface area" in the particle diameter frequency distribution of a silica powder having a predetermined "specific surface area," it is possible to lower the dielectric tangent of the silica powder when blended with a resin while improving its fillability into the resin, and have completed the present invention.

[0009] According to one aspect of the present invention, there is provided the following silica powder: 1. A resin sheet sample has a dielectric loss tangent of 2.0×10 at 40 GHz, as measured according to the following procedure. －３ A silica powder having a specific surface area of ​​0.2 m or less as measured by a BET single-point method using nitrogen gas adsorption. ２ / g or more 5.0m ２ / g or less, the frequency of the maximum peak in the particle size frequency distribution measured by a wet laser diffraction scattering method is 5.5% or more, the frequency of particles having a particle size of 20.7 μm or more in the particle size frequency distribution is 6.0% or less, and the value of the most frequent diameter in the particle size frequency distribution is Dm (μm), the value of the specific surface area is S (m ２ / g), a silica powder having a Dm / S of 1.50 or more. (Procedure) The silica powder is mixed with polyethylene powder so that the filling amount is 40 volume %, and the resulting mixed powder is used to mold the resin sheet sample. The resulting resin sheet sample is used to measure the dielectric loss tangent at 40 GHz by a resonance method. 2. The silica powder according to 1., wherein the mode diameter is 1.0 μm or more and 15.0 μm or less. 3. The silica powder according to 1. or 2., wherein the frequency of particles having a particle diameter of 2.01 μm or less in the particle diameter frequency distribution is 2.0% or less. 4. The silica powder according to any one of 1. to 3., wherein D is the particle diameter at a point where the cumulative volume from the small particle side in the volume frequency particle size distribution measured by a wet laser diffraction scattering method is 90%.９０ When this is done, D ９０ 5. The silica powder according to any one of 1. to 4., wherein the particle diameters at the points where the cumulative volume from the small particle side in the volume frequency particle size distribution measured by a wet laser diffraction scattering method is 10%, 50%, and 100% are D １０ , D ５０ , D １００ When this is done, (D １００ -D １０ ) / D ５０ A silica powder having a moisture content of 5.0 or less. 6. The silica powder according to any one of 1. to 5., wherein the silica powder according to 1. or 2. has an amount of moisture generated by the time the temperature reaches 200°C, as measured by an estimated method using the Karl Fischer method, of 700 ppm or less. 7. The silica powder according to any one of 1. to 6., having an average sphericity of 0.85 or more. 8. The silica powder according to any one of 1. to 7., having an amorphous fraction of 95.0% or more. 9. The silica powder according to any one of 1. to 8., having an amorphous fraction of 20 ppb or less.

[0010] According to the present invention, there is provided a silica powder which has a low dielectric loss tangent and excellent filling properties when blended with a resin.

[0011] An outline of the silica powder of this embodiment will be described.

[0012] The silica powder of this embodiment has a specific surface area of ​​0.2 m2 measured by the BET single-point method using nitrogen gas adsorption. ２ / g or more 5.0m ２ / g or less, the frequency of the maximum peak in the particle size frequency distribution measured by a wet laser diffraction scattering method is 5.5% or more, the frequency of particles having a particle size of 20.7 μm or more in the particle size frequency distribution is 6.0% or less, and the value of the most frequent diameter in the particle size frequency distribution is Dm (μm) and the value of the specific surface area is S (m ２ / g), Dm / S satisfies 1.50 or more.

[0013] The inventors have discovered that by selecting silica powder having a predetermined "specific surface area," and by appropriately adjusting particle size characteristics such as the "frequency of the maximum peak" in the particle size frequency distribution, the "frequency of particles with a particle size of 20.7 μm or more," and the "modal diameter / specific surface area" in the particle size frequency distribution, it is possible to reduce the dielectric loss tangent when compounded with a resin and improve its fillability in the resin. While the detailed mechanism is unclear, it is presumed that appropriately controlling the particle size characteristics as described above improves the fillability of the silica powder in the resin, thereby reducing the dielectric loss tangent of the resin sheet. Furthermore, resin compositions containing silica powder with appropriate particle size characteristics as described above can increase the resin's penetration into narrow gaps, allowing for high silica powder loading. This allows for a low dielectric loss tangent in thin molded resin compositions.

[0014] The silica powder of this embodiment has a dielectric loss tangent of 2.0 × 10 at 40 GHz of the resin sheet measured by the following procedure. －３ The upper limit of the dielectric loss tangent at 40 GHz is 2.0 × 10 －３ or less, preferably 1.9 × 10 －３ or less, more preferably 1.5 × 10 －３ More preferably, 0.5 × 10 －３ The lower limit of the dielectric loss tangent at 40 GHz is not particularly limited, but is, for example, 1.0 × 10 －６ It may be more than that.

[0015] (Procedure for measuring dielectric loss tangent) Silica powder is mixed with polyethylene powder so that the filling amount is 40 volume %, and the resulting mixed powder is used to mold a resin sheet sample. Using the resulting resin sheet sample, the dielectric loss tangent at 40 GHz is measured by a resonance method.

[0016] The silica powder of this embodiment can be suitably used as a filler to be blended into resin materials such as resins or resin compositions. This resin material can be used for various purposes, for example, as a resin material for high frequency bands.

[0017] The composition of the silica powder of this embodiment will be described in detail below.

[0018] <Silica Powder> The silica powder is silica (SiO ２ The main component is silica (SiO) in terms of mass in the total amount of silica powder. ２ ) in an amount of, for example, 50% or more, preferably 80% or more, and more preferably 90% or more. The silica powder preferably has a high purity, but the presence of impurities inevitably mixed in from the raw materials or during the production process is acceptable.

[0019] The silica powder contains either or both of amorphous and crystalline silica. The amorphous content of the silica powder is, for example, 95.0% or more, preferably 97.0% or more, and more preferably 99.0% or more.

[0020] The amorphous fraction of silica powder is measured by X-ray diffraction analysis using a powder X-ray diffractometer (e.g., RIGAKU Corporation, product name "Model MiniFlex") in the 2θ range of 26° to 27.5° with CuKα radiation, and the intensity ratio of specific diffraction peaks is used to determine the amorphous fraction. In the case of siliceous powder, crystalline silica exhibits a main peak at 26.7°, while amorphous silica exhibits no peak. When amorphous silica and crystalline silica are mixed, a peak height of 26.7° corresponding to the proportion of crystalline silica is obtained. Then, the crystalline silica mixing ratio (X-ray diffraction intensity of 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 a crystalline silica standard sample, and the amorphous fraction (%) can be calculated from the formula: amorphous fraction (%) = (1 - crystalline silica mixing ratio) x 100.

[0021] The shape of the silica powder may be any of spherical, crushed, needle-like, flake-like, etc., but spherical is preferred.

[0022] The average circularity of the silica powder is, for example, 0.85 or more, preferably 0.90 or more, and more preferably 0.95 or more, which can suppress an increase in viscosity and a decrease in flowability when the silica powder is mixed with a resin.

[0023] The average sphericity of silica powder is measured as follows. Particle images taken with a stereomicroscope (for example, Nikon Model "SMZ-10"), a scanning electron microscope, or the like are imported into an image analyzer (for example, a Nippon Avionics Co., Ltd. product). The projected area (A) and perimeter (PM) of the particle are measured from the photograph. If 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 with the same perimeter as the perimeter (PM) of the sample particle, PM = 2πr and B = πr ２ Therefore, B = π × (PM / 2π) ２ The sphericity of each particle is given by: Sphericity = A / B = A x 4π / (PM) ２ The circularity of 200 randomly selected particles thus obtained was determined, and the average value was taken as the average sphericity.

[0024] The upper limit of the specific surface area of ​​the silica powder is 5.0 m ２ / g or less, preferably 4.5m ２ / g or less, more preferably 4.0 m ２ / g or less. This allows the dielectric loss tangent to be reduced when blended with a resin. On the other hand, the lower limit of the BET specific surface area is 0.2 m ２ / g or more, preferably 0.3m ２ / g or more, more preferably 0.4m ２ This makes it possible to suppress a decrease in fluidity when blended into a resin.

[0025] The specific surface area of ​​silica powder can be measured by the BET single-point method using nitrogen gas adsorption. Specifically, a specific surface area measuring device (manufactured by Anton Paar, device name: NOVA 800 BET) is used, and nitrogen gas is transported as the adsorption gas using a vacuum pump. 0.1 to 5.0 g of the sample is dried and degassed at 300°C for 30 minutes, and then the measurement is performed.

[0026] The upper limit of the frequency of the maximum peak in the particle size frequency distribution of the silica powder is not particularly limited, but is, for example, 20% or less, preferably 18% or less, and more preferably 15% or less. On the other hand, the lower limit of the frequency of the maximum peak is 5.5% or more, preferably 5.6% or more, and more preferably 5.7% or more. A particle size frequency distribution that satisfies the lower limit of the frequency of the maximum peak has a relatively sharp profile. This can improve the filling ability of resin materials containing silica powder.

[0027] In addition, the number of peaks showing a frequency maximum within the range of 1.0 μm to 15.0 μm in the particle size frequency distribution of the silica powder may be one or more. When the silica powder has multiple peaks, the peak with the highest frequency is defined as the "maximum peak."

[0028] The upper limit of the mode diameter in the particle size frequency distribution of the silica powder is, for example, 15.0 μm or less, preferably 14.0 μm or less, and more preferably 13.0 μm or less. This can further improve the filling ability of the resin material containing the silica powder. On the other hand, the lower limit of the mode diameter is, for example, 1.0 μm or more, preferably 2.0 μm or more, and more preferably 3.0 μm or more. This can suppress an increase in viscosity of the resin material containing the silica powder.

[0029] The value of the most frequent diameter in the particle size frequency distribution of the silica powder is Dm (μm), and the value of the specific surface area of ​​the silica powder is S (m ２ / g), and the value of the mode diameter / specific surface area is defined as Dm / S. The upper limit of Dm / S in silica powder is not particularly limited, but is, for example, 50 or less, preferably 40 or less, and more preferably 30 or less. This can further improve the filling property of a resin material containing silica powder. On the other hand, the lower limit of Dm / S is 1.50 or more, preferably 1.60 or more, and more preferably 1.70 or more. This can improve the filling property of a resin material containing silica powder.

[0030] The upper limit of the frequency of particles having a particle size of 20.7 μm or more in the particle size frequency distribution of the silica powder is 6.0% or less, preferably 3.0% or less, and more preferably 1.0% or less. This improves the filling property of the resin material containing the silica powder. On the other hand, the lower limit of the frequency of particles having a particle size of 20.7 μm or more is not particularly limited, but may be 0% or more.

[0031] The upper limit of the frequency of particles having a particle size of 2.01 μm or less in the particle size frequency distribution of the silica powder is, for example, 2.0% or less, preferably 1.0% or less, and more preferably 0.8% or less. This can suppress an increase in viscosity of the resin material containing the silica powder. On the other hand, the lower limit of the frequency of particles having a particle size of 2.01 μm or less is not particularly limited, but may be 0% or more.

[0032] The particle diameters at the points where the cumulative volume from the small particle side in the volume frequency particle size distribution of silica particles is 10%, 50%, 90%, and 100% are defined as D １０ , D ５０ , D ９０ , D １００ Let's say.

[0033] D ９０ The upper limit of D is, for example, 25.0 μm or less, preferably 21.0 μm or less, and more preferably 18.0 μm or less. This can further improve the filling property of the resin material containing the silica powder. ９０ The lower limit of the particle size is, for example, 3.0 μm or more, preferably 4.0 μm or more, and more preferably 5.0 μm or more. This makes it possible to suppress an increase in viscosity of the resin material containing the silica powder.

[0034] (D １００ -D １０ ) / D ５０ The upper limit of (D) is, for example, 5.0 or less, preferably 4.5 or less, and more preferably 4.0 or less. This makes it possible to suppress an increase in viscosity of the resin material containing the silica powder. １００ -D １０ ) / D ５０ The lower limit of is, for example, 0.3 or more, preferably 0.7 or more, and more preferably 1.0 or more.

[0035] The particle size frequency distribution and volume frequency particle size distribution of silica powder are values ​​based on particle size measurement using a wet laser diffraction light scattering method. Measurements can be performed using a particle size distribution analyzer, such as a Coulter LS13 320. For measurement, water is used as the solvent, and pretreatment involves dispersion treatment using a homogenizer at 500 W output for 120 seconds or more. The PIDS (Polarization Intensity Differential Scattering) concentration is adjusted to 45-55%. The refractive index of water is set to 1.33, while the refractive index of the powder is determined by taking into account the refractive index of the powder material. For example, measurement is performed using a refractive index of 1.50 for amorphous silica.

[0036] The upper limit of the amount of moisture (physically adsorbed water) generated in the silica powder by the time the temperature reaches 200°C, as measured by the Karl Fischer method, is, for example, 700 ppm or less, preferably 600 ppm or less, and more preferably 500 ppm or less. This allows the dielectric loss tangent to be further reduced when the silica powder is blended with a resin. On the other hand, the lower limit of the physically adsorbed water is not particularly limited, but may be 0 ppm or more or 1 ppm or more.

[0037] The moisture content in the silica powder is measured by the Karl Fischer method. Specifically, a trace moisture analyzer (Model CA-05, manufactured by Mitsubishi Chemical Corporation) is used. The powder is placed in a quartz tube in a moisture vaporization mechanism, and while heating from room temperature to 900°C with an electric heater, dehydrated argon gas is supplied as a carrier gas. The water vapor volatilized from the powder surface is introduced into the moisture measurement mechanism, and the moisture content is measured. The moisture generated before the heating temperature of the electric heater reaches 200°C is considered to be physically adsorbed water.

[0038] The upper limit of the content of uranium and thorium elements in the silica powder is, for example, 20 ppb or less, preferably 10 ppb or less, and more preferably 1.0 ppb or less. This can suppress the occurrence of defects in devices such as memories. On the other hand, the lower limit of the content of uranium and thorium elements is not particularly limited, but may be, for example, 0.1 ppb or more.

[0039] The contents of uranium and thorium in the silica powder are measured using an inductively coupled plasma mass spectrometer (ICP-MS).

[0040] In this embodiment, it is possible to control the above-mentioned dielectric loss tangent, specific surface area, various values ​​calculated from particle size frequency distribution, and various values ​​calculated from volume frequency particle size distribution by appropriately selecting, for example, the raw material components of the silica powder, the manufacturing method of the silica powder, etc. Among these, for example, using silica powder manufactured by a dry method, and combining removal of coarse powder and removal of fine powder are cited as factors for setting the above-mentioned dielectric loss tangent, specific surface area, various values ​​calculated from particle size frequency distribution, and various values ​​calculated from volume frequency particle size distribution within desired numerical ranges.

[0041] <Method for Producing Silica Powder> In one example of the manufacturing method of this embodiment, silica powder can be obtained by subjecting raw silica powder produced by a dry method to coarse particle classification followed by fine particle classification. The classification can be performed by mixing or classifying appropriate amounts of silica powders with different particle size compositions. Industrially, classification using a classifier such as a sieve or precision air classifier is desirable, and a dry method is preferred for the classification operation. Dry classification of raw silica powder produced by a dry method can suppress aggregation of the silica powder compared to raw silica powder produced by a wet method and / or wet classification, thereby improving handleability, etc. It is desirable to store the obtained silica powder in a moisture-proof bag.

[0042] The classified silica powder may also be subjected to a heat treatment as a post-treatment. The heat treatment is carried out in a hot air or electric furnace at a temperature of 500 to 1100°C for a predetermined time (e.g., about 1 to 52 hours) such that the heating temperature (°C) × heating time (h) is 1000 to 26400 (°C·h), preferably 1800 to 17600 (°C·h) (e.g., about 2 to 35 hours). Since the specific surface area and average particle size do not change before and after heating at a heating temperature of 500 to 1100°C, it is desirable to carry out the classification step before heating, and then adjust the specific surface area and average particle size to the desired value before heat treatment. After the heat treatment, the silica powder is allowed to cool naturally in an electric furnace, and then collected at 110 to 300°C. It is then further cooled to 25°C in an environment with a humidity of 40% RH or less, and stored at 15 to 25°C. It may also be collected and stored in a moisture-proof aluminum bag.

[0043] The classified silica powder may be subjected to a surface treatment as a post-treatment. Surface treatment with a surface treatment agent can further reduce the polar groups on the surface and reduce the dielectric loss tangent. A surface treatment agent that does not leave polar functional groups after surface treatment is preferred, such as hexamethyldisilazane. After surface treatment, it is desirable to collect the powder again in a moisture-proof aluminum bag.

[0044] The silica powder was stored in a container with a moisture permeability of 0.1 (g / m) under condition B of JIS Z 0208-1976 (temperature 40°C - relative humidity 90%). ２ It is preferable to store the product in a moisture-proof bag, such as a moisture-proof aluminum bag or a PET / AL / PE laminate bag, for a storage time of 24 hours or less.

[0045] Next, the resin composition of this embodiment will be described. A resin composition containing the silica powder of this embodiment can be suitably used as a resin material. The resin composition contains, in addition to the silica powder of this embodiment, a resin and known resin additives.

[0046] In the resin composition, silica powder may be used alone or in a mixture with other fillers. The resin composition may contain 10 to 99% by mass of silica powder, or 10 to 99% by mass of a mixed inorganic powder containing silica powder and other fillers. The content of other fillers in the mixed inorganic powder 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, the symbol "to" indicates that the range includes both the upper and lower limits, unless otherwise specified.

[0047] Examples of other fillers include silica other than the 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 is about 5 to 100 μm, and there are no particular restrictions on the particle size configuration and shape.

[0048] Examples of the resin include epoxy resin, silicone resin, phenol resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyamide such as polyimide, polyamideimide, polyetherimide, polyester such as polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, etc. These may be used alone or in combination of two or more.

[0049] The resin composition can be produced, for example, by blending raw material components in a predetermined ratio using a blender, a Henschel mixer, or the like, kneading the mixture using a heated roll, a kneader, a single-screw or twin-screw extruder, or the like, cooling the mixture, and then pulverizing it.

[0050] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0051] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the description of these examples. <Preparation of Silica Powder> [Examples 1 to 10] Silica powder was prepared by the following procedure. Commercially available silica powder A produced by a dry method was used as the raw material. Silica powder A used as the raw material had one mode diameter peak in the range of 1.0 to 15.0 μm.

[0052] (Coarse particle classification) First, the raw material silica powder was subjected to coarse particle classification using sieves with various mesh sizes in order to remove large particle diameters. The particle diameter frequency distribution showed the frequencies of particles with diameters of 20.7 μm or more as shown in Table 1.

[0053] (Fine Powder Classification) Next, the silica powder after the coarse particle classification was subjected to fine powder classification using a precision air classifier to cut off the fine powder side. The particle size frequency distribution showed the frequency of particles with a particle size of 2.01 μm or less, as shown in Table 1.

[0054] (Post-treatment 1: Heat Treatment) After fine powder classification, the silica powders of Examples 3, 8, and 10 were further subjected to heat treatment. In the heat treatment, the silica powder was filled into an alumina crucible and heat-treated in the atmosphere at a temperature of 1000°C in an electric furnace for 4 hours. After the heat treatment, the silica powder was cooled to 200°C in the furnace and then cooled to room temperature in a desiccator (23°C, 10% RH), and the heat-treated silica powder was recovered.

[0055] (Post-treatment 2: Surface treatment) After fine powder classification, the silica powder of Example 9 was further subjected to a surface treatment. In the surface treatment, 1 part by mass of methacrylsilane (manufactured by Shin-Etsu Silicones Co., Ltd.) was added to 100 parts by mass of the silica powder, and the mixture was mixed in a vibration mixer (manufactured by Resodyn), followed by drying at 200°C for 4 hours, and the surface-treated silica powder was recovered.

[0056] Comparative Example 1: Commercially available silica powder B produced by a dry method was used. Silica powder B had no mode diameter peak in the range of 1.0 to 15.0 μm, and one mode diameter peak in the range exceeding 15.0 μm.

[0057] [Comparative Example 2] Commercially available silica powder C produced by a dry method was used as the raw material. Silica powder C had one mode diameter peak in the range of 1.0 to 15.0 μm. Silica powder C was used and only the above-mentioned (coarse powder classification) was carried out to obtain a silica powder.

[0058] Comparative Example 3 Silica powder C was used and only the above-mentioned (coarse particle classification) and (post-treatment 1: heat treatment) were carried out to obtain a silica powder.

[0059] [Comparative Example 4] Commercially available silica powder D produced by a dry method was used as the raw material. Silica powder D had one mode diameter peak in the range of 1.0 to 15.0 μm. Silica powder D was used and only the above-mentioned (coarse powder classification) was carried out to obtain a silica powder.

[0060] Comparative Example 5 Silica powder D was used and only the above-mentioned (coarse particle classification) and (post-treatment 1: heat treatment) were carried out to obtain silica powder.

[0061] The silica powder obtained in each of the Examples and Comparative Examples was stored in an aluminum pack until immediately before various evaluations.

[0062]

[0063] The obtained silica powder was evaluated for the following items.

[0064] <Dielectric loss tangent measured by resonance method> Silica powder was mixed with polyethylene powder (Flothen UF-20S, manufactured by Sumitomo Seika Chemicals Co., Ltd.) to a filling level of 40% by volume using a vibration mixer (manufactured by Resodyn Corporation) under conditions of an acceleration of 60 g and a processing time of 2 minutes. The resulting mixed powder was weighed to a predetermined volume (so as to have a thickness of approximately 0.3 mm), placed in a metal frame with a diameter of 3 cm, and molded in a heat press (Imoto Machinery Works, Ltd., "IMC-1674-A Model") under molding conditions of 140°C, 10 MPa, and 15 minutes to form a resin sheet sample measuring 1.5 cm square and 0.3 mm thick. 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, a 40 GHz cavity resonator (manufactured by Samtec) was connected to a vector network analyzer (85107, manufactured by Keysight Technologies), and the 10 mm diameter hole in the resonator was set to be blocked, and the resonant frequency (f0) and unloaded Q value (Qu) were measured. The sample was rotated for each measurement, and the measurement was repeated five times in the same manner. The obtained f0 and Qu values ​​were averaged and used as the measured value. The dielectric constant was calculated from f0, and the dielectric loss tangent (tan δc) was calculated from Qu using analysis software (manufactured by Samtec). The measurement temperature was 20°C and the humidity was 60% RH. The obtained tan δc was used as the dielectric loss tangent of the resin sheet sample.

[0065] <Specific Surface Area> The specific surface area of ​​the silica powder was measured by the BET single-point method using nitrogen gas adsorption. Specifically, using a specific surface area measuring device (manufactured by Anton Paar, device name: NOVA 800 BET), nitrogen gas was transported using 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.

[0066] <Particle Size> The particle size frequency distribution and volume frequency particle size distribution of the silica powder were determined by a wet laser diffraction scattering method using a particle size distribution analyzer (Coulter, LS13 320). Water was used as the solvent, and the powder was pre-dispersed for 120 seconds or more using a homogenizer at 500 W output for measurement. The PIDS (Polarization Intensity Differential Scattering) concentration was adjusted to 45-55% for measurement. The refractive index of water was 1.33, and the refractive index of the powder was determined taking into account the refractive index of the powder material. For example, amorphous silica was measured with a refractive index of 1.50. Based on the obtained particle size frequency distribution, the "mode diameter," "maximum peak frequency," "frequency of particle sizes less than 0.5 μm," "frequency of particle sizes 0.5 μm to 13 μm," and "frequency of particle sizes 13 μm or more" were calculated. Based on the obtained volume frequency particle size distribution, the particle diameter (D Ｘ ) was calculated.

[0067] <Average Sphericity> The average sphericity of silica powder is measured as follows by capturing particle images taken with a stereomicroscope (for example, Nikon Model "SMZ-10"), a scanning electron microscope, or the like, into an image analyzer (for example, Nippon Avionics Co., Ltd.). That is, the projected area (A) and perimeter (PM) of the particle are measured from the photograph. If 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 with the same perimeter as the perimeter (PM) of the sample particle, PM = 2πr and B = πr ２ Therefore, B = π × (PM / 2π) ２ The sphericity of each particle is given by: Sphericity = A / B = A x 4π / (PM) ２ The circularity of 200 randomly selected particles thus obtained was determined, and the average value was taken as the average sphericity.

[0068] <Moisture Content> The moisture content in the silica powder was measured by the Karl Fischer method. Specifically, a trace moisture analyzer (Mitsubishi Chemical Corporation, Model CA-05) was used. The powder was placed in a quartz tube in a moisture vaporization mechanism, and heated from room temperature to 900°C with an electric heater while dehydrated argon gas was supplied as a carrier gas. Water vapor volatilized from the powder surface was introduced into the moisture measurement mechanism to measure the moisture content. Moisture generated by the time the heating temperature of the electric heater reached 200°C was considered to be physically adsorbed water, moisture generated between 200°C and 550°C was considered to be water derived from hydrogen-bonded OH groups, and moisture generated between 550°C and 900°C was considered to be water resulting from dehydration condensation of isolated OH groups.

[0069] <Amorphous Ratio> The amorphous ratio of the silica powder was measured from the intensity ratio of specific diffraction peaks by performing X-ray diffraction analysis using a powder X-ray diffractometer (manufactured by RIGAKU Corporation under the trade name "Model MiniFlex") with CuKα radiation in the 2θ range of 26° to 27.5°. Specifically, the crystalline silica mixing ratio (X-ray diffraction intensity of sample / X-ray diffraction intensity of crystalline silica) was calculated from the ratio of the X-ray intensity of the sample (obtained silica powder) to the X-ray intensity of a crystalline silica standard sample, and the amorphous ratio (%) was calculated from the formula: amorphous ratio (%) = (1 - crystalline silica mixing ratio) × 100.

[0070] <Contents of Uranium and Thorium> The contents (ppb) of uranium and thorium in the silica powder were measured using an inductively coupled plasma mass spectrometer (ICP-MS).

[0071] <Viscosity> 35% by mass of the obtained silica powder and 65% by mass of a liquid epoxy resin (bisphenol F type resin, JER807, manufactured by Mitsubishi Chemical Corporation) were mixed to obtain a resin sample. The viscosity (Pa s) of the obtained resin sample was measured at 25°C and a shear rate of 1 [1 / s] using a rheometer (Modular Compact Rheometer MCR 102, manufactured by Anton Paar) equipped with a conical cone (3 degrees). The results are shown in Table 1.

[0072] <Evaluation of Filling Properties in Narrow Gap> 60 g of the obtained silica powder, 40 g of liquid epoxy resin (bisphenol F-type resin, JER807, manufactured by Mitsubishi Chemical Corporation), and 0.06 g of silane coupling agent (phenylaminotrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain a liquid filling sample. Two cleaned glass plates were placed facing each other and fixed to a jig so that the gap thickness was 50 μm. The jig was placed on a horizontal table so that the two glass plates were horizontal. Next, the glass plates were placed on a hot plate, heated, and maintained at approximately 95°C. 0.2 mL of the above filling sample was dropped into the gap opening of the glass plate (thickness: 50 μm, width: 30 mm). The dropped filling sample gradually penetrated from the gap opening toward the interior of the glass plate. Photographs of the penetration state were taken 5 minutes after the start of dropping. From the photographs, the percentage of the filling sample filled in an area of ​​3 mm widthwise × 3 mm inward near the center of the gap opening was quantified to calculate the resin penetration rate. When the obtained resin penetration rate was 40% or more, the filling was judged to be excellent, when it was 10% or more but less than 40%, the filling was judged to be poor, and when it was less than 10%, the filling was judged to be very poor.

[0073] The silica powders of Examples 1 to 10 were able to reduce the dielectric loss tangent when blended with a resin, and showed superior narrow gap filling properties when blended with a resin compared to Comparative Examples 1 to 5.

[0074] This application claims priority based on Japanese Patent Application No. 2023-137028, filed on August 25, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. The dielectric loss tangent of a resin sheet sample at 40 GHz measured according to the following procedure is 2.0 x 10 －３ A silica powder having a particle size frequency distribution measured by a wet laser diffraction scattering method, in which the frequency of a maximum peak is 5.5% or more, the frequency of particles having a particle size of 20.7 μm or more in the particle size frequency distribution is 6.0% or less, and the specific surface area measured by a BET single point method using nitrogen gas adsorption is 0.2 m ２ / g or more 5.0m ２ / g or less, and the value of the most frequent diameter in the particle size frequency distribution is Dm (μm), and the value of the specific surface area is S (m ２ / g), Dm / S is 1.50 or more. (Procedure) The silica powder is mixed with polyethylene powder so that the filling amount is 40 volume %, and the resin sheet sample is molded using the obtained mixed powder. The dielectric loss tangent at 40 GHz is measured using the obtained resin sheet sample by a resonance method.

2. The silica powder according to claim 1, wherein the most frequent diameter is 1.0 μm or more and 15.0 μm or less.

3. A silica powder according to claim 1 or 2, wherein the frequency of particles having a particle size of 2.01 μm or less in the particle size frequency distribution is 2.0% or less.

4. The silica powder according to claim 1 or 2, wherein the particle diameter at the point where the cumulative volume from the small particle side in the volume frequency particle size distribution measured by a wet laser diffraction scattering method is 90% is defined as D ９０ When this is done, D ９０ The silica powder has a particle size of 3.0 μm or more and 25.0 μm or less.

5. The silica powder according to claim 1 or 2, wherein the particle diameters at the points where the cumulative volume from the small particle side in the volume frequency particle size distribution measured by a wet laser diffraction scattering method is 10%, 50%, and 100% are respectively defined as D １０ , D ５０ , D １００ When this is done, (D １００ -D １０ ) / D ５０ The silica powder has a molecular weight of 5.0 or less.

6. The silica powder according to claim 1 or 2, wherein the amount of moisture generated by the temperature reaching 200°C is 700 ppm or less as measured by the Karl Fischer method.

7. The silica powder according to claim 1 or 2, having an average sphericity of 0.85 or more.

8. The silica powder according to claim 1 or 2, wherein the amorphous ratio is 95.0% or more.

9. The silica powder according to claim 1 or 2, wherein the content of uranium and thorium elements is 20 ppb or less.

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