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 water content of at most 500 ppm, as measured by the Karl Fischer method, generated until the temperature reaches 200°C; a specific surface area of 0.2 m2 / g-5.4 m2 / g, as measured by the BET 1-point method using nitrogen gas adsorption; and a D90 of 3.0 μm-75 μm where D90 is defined as the particle diameter at the point at which the cumulative volume is 90% from the small particle side in a volume frequency particle size distribution as measured by a wet laser diffraction scattering method.

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] The present inventors have further studied and found that, in silica powder, the "BET specific surface area" and the "particle diameter D at 90% cumulative volume measured by a wet laser method" are determined in addition to the predetermined "water content measured by the Karl Fischer method." ９０ The inventors have found that by appropriately adjusting the particle size characteristics such as ", the dielectric tangent when blended into a resin can be reduced while improving the 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, wherein the amount of moisture generated by the time the temperature reaches 200°C as measured by the Karl Fischer method is 500 ppm or less, and the specific surface area as measured by the BET single-point method using nitrogen gas adsorption is 0.2 m or less. ２ / g or more 5.4m ２ / g or less, and 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 ９０A silica powder having a specific surface area of ​​3.0 μm or more and 75 μm or less. (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 in the particle size frequency distribution measured by a wet laser diffraction scattering method is 2.5 μm or more and 40 μm or less. 3. The silica powder according to 1. or 2., wherein the frequency of the maximum peak in the particle size frequency distribution measured by a wet laser diffraction scattering method is 10% or less. 4. The silica powder according to any one of 1. to 3., wherein the value of the mode diameter in the particle size frequency distribution measured by a wet laser diffraction scattering method is Dm (μm), and the value of the specific surface area is S (m ２ / g), Dm / S is 0.6 or more. 5. The silica powder according to any one of 1. to 4., wherein the frequency of particles having a particle diameter of 15.7 μm or more in the particle diameter frequency distribution measured by a wet laser diffraction scattering method is 50% or less. 6. The silica powder according to any one of 1. to 5., wherein the frequency of particles having a particle diameter of less than 0.5 μm in the particle diameter frequency distribution measured by a wet laser diffraction scattering method is 15% or less. 7. The silica powder according to any one of 1. to 6., wherein the particle diameters at which the cumulative volume from the small particle side in the volume frequency particle size distribution measured by a wet laser diffraction scattering method are 10%, 50%, and 100% are respectively represented by D １０ , D ５０ , D ９０ When this is done, (D ９０ -D １０ ) / D ５０A silica powder having an average sphericity of 0.85 or more. 8. A silica powder according to any one of 1. to 7., having an average sphericity of 0.85 or more. 9. A silica powder according to any one of 1. to 8., having an amorphous fraction of 95.0% or more. 10. A silica powder according to any one of 1. to 9., having an uranium and thorium content 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 the following characteristics: the amount of moisture generated by the temperature reaching 200°C is 500 ppm or less as measured by the Karl Fischer method; and the specific surface area is 0.2 m as measured by the BET single-point method using nitrogen gas adsorption. ２ / g or more 5.4m ２ / g or less, and 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 is 3.0 μm or more and 75 μm or less.

[0013] According to the findings of the present inventors, in silica powder, the "BET specific surface area" and the "particle diameter D at 90% cumulative volume measured by a wet laser method" are determined in addition to the predetermined "water content measured by the Karl Fischer method." ９０It has been found that by appropriately adjusting particle size characteristics such as ", it is possible to reduce the dielectric loss tangent when blended into a resin and improve the fillability of the resin. While blending ultrafine powder can improve the filling state of silica powder in a resin, the large specific surface area of ​​the ultrafine powder may increase the dielectric loss tangent of the resin sheet. After extensive research, the inventors have found that using ultrafine powder that has been thoroughly heat-treated can achieve both good fillability and a low dielectric loss tangent. Furthermore, a resin composition containing silica powder with appropriate particle size characteristics as described above can improve the fillability into narrow gaps during molding, allowing for high silica powder loading. This makes it possible to reduce the dielectric loss tangent of a thin molded body of the resin composition.

[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 ​​silica powder is 5.4 m ２ / g or less, preferably 5.0m 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 mode diameter in the particle size frequency distribution of the silica powder is, for example, 40 μm or less, preferably 30 μm or less, and more preferably 20 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, 2.5 μm or more, preferably 3.0 μm or more, and more preferably 4.0 μm or more. This can suppress an increase in viscosity of the resin material containing the silica powder.

[0027] 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, 10% or less, preferably 9.5% or less, and more preferably 9.0% or less. On the other hand, the lower limit of the frequency of the maximum peak is, for example, 2.0% or more, preferably 3.5% or more, and more preferably 4.0% or more. A particle size frequency distribution that satisfies the upper limit of the frequency of the maximum peak has a relatively broad profile. This can improve the filling property of a resin material containing silica powder.

[0028] 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, for example, 0.5 or more, preferably 1.2 or more, and more preferably 1.6 or more. This can improve the filling property of a resin material containing silica powder.

[0029] In addition, the number of peaks showing a frequency maximum within the range of 2.5 μm to 40 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."

[0030] The upper limit of the frequency of particles having a particle size of 15.7 μm or more in the particle size frequency distribution of the silica powder is, for example, 50% or less, preferably 20% or less, more preferably 10% or less, and even 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 15.7 μm or more is not particularly limited, but may be 0% or more or 0.1% or more.

[0031] The upper limit of the frequency of particles having a particle size of less than 0.5 μm in the particle size frequency distribution of the silica powder is, for example, 15% or less, preferably 6.0% or less, and more preferably 1.0% 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 less than 0.5 μm is not particularly limited, but may be 0% or more, or 0.1% 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%, and 90% are defined as D １０ , D ５０ , D ９０ Let's say.

[0033] D ９０ The upper limit of D is 75 μm or less, preferably 50 μm or less, and more preferably 30 μm or less. This can further improve the filling property of the resin material containing silica powder. ９０ The lower limit of the particle size is 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 ９０ -D １０ ) / D ５０ The upper limit of (D) is, for example, 10 or less, preferably 5 or less, and more preferably 3.0 or less. This makes it possible to suppress an increase in viscosity of the resin material containing the silica powder. ９０ -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 500 ppm or less, preferably 490 ppm or less, and more preferably 480 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, dry classification, blending with heat-treated ultrafine powder, etc. can be cited as elements for adjusting 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 to 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 classifying raw silica powder produced by a dry method and then blending it with ultrafine powder. 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 ultrafine powder blending process is a process in which ultrafine silica powder having a particle size smaller than that of the classified silica powder is blended in a predetermined ratio. The particle size of the ultrafine silica powder may be, for example, D50 of 2 μm or less, and preferably 0.1 μm to 1.5 μm. The blending amount of the ultrafine silica powder is preferably, for example, 5% to 35% by mass, when the total silica powder is taken as 100% by mass. The ultrafine silica powder is preferably subjected to the above-mentioned heat treatment before blending.

[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 5] 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 2.5 to 40.0 μm.

[0052] (Dry Classification) First, the raw material silica powder was subjected to dry classification using a precision air classifier in order to remove particles with large diameters. The particle diameter frequency distribution showed the frequencies of particles with diameters of 15.7 μm or more as shown in Table 1.

[0053] (Ultrafine Powder Blending) Next, a predetermined amount of ultrafine silica powder having a D50 of 2 μm or less was blended with the silica powder after dry classification. The particle size frequency distribution showed the frequency of particles with a particle size of less than 0.5 μm as shown in Table 1.

[0054] (Post-treatment 1: Heat Treatment) In Examples 1 and 3, the silica powder after dry classification was heat-treated before blending with the ultrafine powder. 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: Heat Treatment) In Examples 1 to 5, ultrafine silica powder having a D50 of 2 μm or less was heat-treated before being mixed with the ultrafine powder. 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 mixture 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 ultrafine silica powder was recovered.

[0056] [Comparative Example 1] Silica powder B, a commercially available product produced by a dry method, was obtained by carrying out the above-mentioned (dry classification) and (post-treatment 1: heat treatment). Silica powder B had no mode diameter peak in the range of 2.5 to 40.0 μm, and one mode diameter peak in the range exceeding 40.0 μm.

[0057] [Comparative Example 2] As a raw material, commercially available silica powder C produced by a dry method was used, and only the above-mentioned (dry classification) was carried out to obtain a silica powder. Silica powder C used as a raw material had no mode diameter peak in the range of 2.5 to 40.0 μm, and one mode diameter peak in the range of less than 2.5 μm.

[0058] [Comparative Example 3] As a raw material, commercially available silica powder D produced by a dry method was used, and only the above-mentioned (dry classification) and (post-treatment 1: heat treatment) were carried out to obtain a silica powder. Silica powder D used as a raw material had no mode diameter peak in the range of 2.5 to 40.0 μm, and one mode diameter peak in the range of less than 2.5 μm.

[0059] [Comparative Example 4] As a raw material, commercially available silica powder E produced by a dry method was used, and only the above-mentioned (dry classification), (post-treatment 1: heat treatment), and (ultrafine powder blending) were carried out to obtain the above silica powder. Silica powder E used as the raw material had one mode diameter peak in the range of 2.5 to 40.0 μm.

[0060] [Comparative Example 5] As a raw material, commercially available silica powder F produced by a dry method was used, and the above-mentioned (post-treatment 2: heat treatment) was not carried out, but only the above-mentioned (dry classification) and (post-treatment 1: heat treatment) were carried out to obtain a silica powder. The silica powder F used as the raw material had one mode diameter peak in the range of 2.5 to 40.0 μm.

[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 pretreatment was performed by dispersing the powder for 120 seconds or more using a homogenizer at 500 W output. 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," and "frequency of particle sizes 15.7 μm or greater" 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] <Spiral Flow: Evaluation of Fluidity> 85.0% by mass of the silica powder obtained above, 8.04% by mass of epoxy resin (NC-3000P, manufactured by Nippon Kayaku Co., Ltd.), 6.08% by mass of phenolic resin (MEH-7851SS, manufactured by Meiwa Kasei Co., Ltd.), 0.35% by mass of silane coupling agent (KBM-573, manufactured by Shin-Etsu Chemical Co., Ltd.), 0.26% by mass of curing accelerator (triphenylphosphine, TPP), and 0.27% by mass of ester wax (Lico-WAX E, manufactured by Clariant Chemicals) were mixed and homogenized, and then heated and kneaded using a twin-roll mill heated to 80°C. The mixture was extruded, cooled to solidify, and then pulverized to a predetermined particle size using a pulverizer to obtain a powdered epoxy resin composition (measurement sample) that was solid at room temperature. The resulting measurement sample was transfer molded under the following conditions, and the spiral flow (cm) was measured. The results are shown in Table 1. (Conditions) Mold size: φ3 mm spiral shape Mold temperature: 175°C Injection pressure: 65 kgf / cm ２ Molding time: 90 seconds When the obtained spiral flow was 40 cm or more, the fluidity was judged to be excellent, and when it was less than 40 cm, the fluidity was judged to be poor.

[0072] <Narrow Gap Filling Length: Evaluation of Filling Property> Using the measurement sample obtained above, the narrow gap filling length (cm) was measured when transfer molding was performed under the following conditions. The results are shown in Table 1. (Conditions) Mold size: 5 mm x 60 mm x 0.03 mm (width x length x thickness) Mold temperature: 175°C Injection pressure: 65 kgf / cm ２ Molding time: 90 seconds When the obtained narrow gap filling length was 20 cm or more, the narrow gap filling property was judged to be excellent, and when it was less than 20 cm, the narrow gap filling property was judged to be poor.

[0073] The silica powders of Examples 1 to 5 were able to reduce the dielectric loss tangent when blended with a resin compared to Comparative Examples 2 and 5, and showed superior narrow gap filling properties when blended with a resin compared to Comparative Examples 1 to 4.

[0074] This application claims priority based on Japanese Patent Application No. 2023-137030, filed 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 The silica powder has a specific surface area of ​​0.2 m or less, the amount of moisture generated by the time the temperature reaches 200° C. as measured by the Karl Fischer method being 500 ppm or less, and the specific surface area measured by the BET single point method using nitrogen gas adsorption being 0.2 m or less. ２ / g or more 5.4m ２ / g or less, and 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 D ９０ When this is done, D ９０ Silica powder having a particle size of 3.0 μm or more and 75 μm or less. (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 in the particle size frequency distribution measured by a wet laser diffraction scattering method is 2.5 μm or more and 40 μm or less.

3. The silica powder according to claim 1 or 2, wherein the frequency of the maximum peak in the particle size frequency distribution measured by a wet laser diffraction scattering method is 10% or less.

4. The silica powder according to claim 1 or 2, wherein the value of the most frequent diameter in the particle size frequency distribution measured by a wet laser diffraction scattering method is Dm (μm), and the value of the specific surface area is S (m ２ / g), Dm / S is 0.6 or more, 5. A silica powder according to claim 1 or 2, in which the frequency of particles having a particle size of 15.7 μm or more in the particle size frequency distribution measured by a wet laser diffraction scattering method is 50% or less.

6. A silica powder according to claim 1 or 2, in which the frequency of particles having a particle size of less than 0.5 μm in the particle size frequency distribution measured by a wet laser diffraction scattering method is 15% or less.

7. 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 ９０ When this is done, (D ９０ -D １０ ) / D ５０ The silica powder has a molecular weight of 10 or less.

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

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

10. 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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