Silica powder, resin composition, and substrate

Abstract

The present invention provides a silica powder which has low frequency dependence of dielectric loss tangent in a high frequency band. The silica powder is characterized in that, when a test composition, which is obtained by kneading the silica powder into a polypropylene resin at a ratio of 30 vol%, is molded into a sheet shape that has a thickness of 0.35 mm to 0.45 mm and the dielectric loss tangent of the sheet is measured by a resonator method, the ratio tanδ91 / tanδ10 of the dielectric loss tangent tanδ91 that is measured at the frequency of 91 GHz to the dielectric loss tangent tanδ10 that is measured at the frequency of 10 GHz is 1.6 or less.

Description

Silica powder, resin composition, and substrate

[0001] The present invention relates to a silica powder, a resin composition, and a substrate.

[0002] Resin compositions in which silica powder is filled into resins are widely used for applications such as substrates, semiconductor encapsulation, and insulating layers for printed wiring boards. In recent years, with the increasing performance and high-speed communication of electronic devices and information terminals, it has become necessary to control the dielectric loss tangent of resin compositions in order to control the dielectric properties of substrates, semiconductor encapsulants, insulating layer materials, etc. One method for lowering the dielectric loss tangent of resin compositions has been considered to be controlling the dielectric loss tangent of the silica powder to be filled, and various studies have been conducted on this matter.

[0003] For example, Patent Document 1 aims to provide silica powder with an extremely small dielectric loss tangent and a resin composition containing the same, and discloses a low dielectric silica powder with a dielectric loss tangent of 0.0005 or less measured at a frequency of 10 GHz.

[0004] For example, Patent Document 2 aims to provide a silica powder that has a sufficiently small dielectric loss tangent and excellent miscibility with a resin composition, and discloses a silica powder that has a dielectric loss tangent of 0.020 or less measured at a frequency of 1 GHz.

[0005] Patent Documents 1 and 2 describe that the dielectric loss tangent of silica powder can be reduced by reducing the number of silanol groups (Si—OH) on the surface of the silica powder. Methods for reducing the number of silanol groups include subjecting the silica powder to high temperature treatment, surface treatment, and controlling the particle size and specific surface area.

[0006] JP 2021-187714 A

[0007] In recent years, with the development of communication technologies such as beyond 5G and 6G, importance has begun to be placed on dielectric properties in high frequency bands of several tens of GHz or more in resin compositions used for substrate applications, semiconductor encapsulation applications, insulating layer applications for printed wiring boards, etc. When a wide range of frequency bands are used, if the dielectric properties change depending on the frequency, the design of the device becomes complicated, so it is preferable that the behavior of the dielectric properties does not change significantly over a wide frequency range.

[0008] However, as described above, while silica powders with low dielectric loss tangents below 10 GHz are known, the behavior of their dielectric properties in high frequency bands above several tens of GHz has not been fully investigated. In particular, the dielectric loss tangent of silica powders generally depends on frequency, and the dielectric loss tangent increases as the frequency increases. However, it cannot be said that any study has focused on the frequency dependence in high frequency bands above several tens of GHz. In fact, when the dielectric properties of existing silica powders, such as EXELICA SE-8 (manufactured by Tokuyama) which is manufactured by a flame fusion method and therefore has few surface silanol groups, and SUNSIL SP-10M (manufactured by Tokuyama) which has been surface-treated and therefore has few surface silanol groups, are evaluated in the high frequency band, as shown in the Reference Examples of the present application, the dielectric loss tangent at 91 GHz is about twice the value of the dielectric loss tangent at 10 GHz, indicating a relatively large frequency dependence of the dielectric loss tangent.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a silica powder having a dielectric loss tangent with small frequency dependency in the high frequency band.

[0010] In order to solve the above problems, the present inventors conducted extensive research and, as a result, succeeded in obtaining a silica powder that has a smaller difference between the dielectric loss tangent measured at a frequency of 10 GHz and the dielectric loss tangent measured at a frequency of 91 GHz, compared to existing silica powders.

[0011] That is, in the present invention, a test composition obtained by kneading silica powder into polypropylene resin at a ratio of 30% by volume is formed into a sheet having a thickness of 0.35 mm to 0.45 mm, and when the dielectric loss tangent of the sheet is measured by the resonator method, the dielectric loss tangent tanδ measured at a frequency of 10 GHz is １０ and the dielectric loss tangent tanδ measured at a frequency of 91 GHz９１ The ratio tan δ ９１ / tanδ １０ The silica powder is characterized by having a dielectric constant of 1.6 or less. When a test composition obtained by kneading the silica powder into a polypropylene resin at a ratio of 30% by volume is formed into a sheet having a thickness of 0.35 mm to 0.45 mm and the dielectric constant of the sheet is measured by a resonator method, the dielectric constant measured at a frequency of 10 GHz is preferably 3.0 or less. In addition, the median diameter D50 is 0.05 to 10 μm and the specific surface area is 0.5 to 50 m. ２ The present invention can be embodied in a resin composition containing the silica powder and a resin, and further in a substrate containing the resin composition or a cured product thereof.

[0012] The silica powder of the present invention makes it possible to provide a resin composition whose dielectric loss tangent has little frequency dependence in the 10 to 91 GHz band. By using such a resin composition for substrates, semiconductor encapsulation, and insulating layers, the behavior of dielectric properties becomes stable over a wide frequency range, making the design of communication devices and the like easier than ever before.

[0013] The silica powder of the present invention is a test composition obtained by kneading silica powder into polypropylene resin at a ratio of 30% by volume, and forming the test composition into a sheet having a thickness of 0.35 mm to 0.45 mm. When the dielectric loss tangent of the sheet is measured by the resonator method, the dielectric loss tangent tanδ measured at a frequency of 10 GHz is １０ and the dielectric loss tangent tanδ measured at a frequency of 91 GHz ９１ The ratio tan δ ９１ / tanδ １０ is 1.6 or less.

[0014] The dielectric loss tangent is a value that indicates the degree of electrical energy loss, and the larger this value, the greater the energy loss and transmission loss. In silica powder, the dielectric loss tangent is generally frequency-dependent, being affected by the frequency of the applied current, and the higher the frequency, the greater the dielectric loss tangent.

[0015] On the other hand, the silica powder of the present invention has a dielectric loss tangent tanδ measured at a frequency of 10 GHz. １０and the dielectric loss tangent tanδ measured at a frequency of 91 GHz ９１ The ratio tan δ ９１ / tanδ １０ The tan δ is 1.6 or less, and the frequency dependency is small. This characteristic enables the resin composition using the silica of the present invention to exhibit stable behavior over a wide frequency range from several GHz to several tens of GHz. ９１ / tanδ １０ is preferably 1.4 or less, and more preferably 1.2 or less. ９１ / tanδ １０ Although there are no particular restrictions on the lower limit of the dielectric loss tangent, as described above, the higher the frequency, the larger the dielectric loss tangent, and the lower limit is usually 1.0 or more.

[0016] The silica powder has a dielectric loss tangent tanδ measured at a frequency of 28 GHz. ２８ , dielectric loss tangent tanδ measured at a frequency of 35 GHz ３５ , dielectric loss tangent tanδ measured at a frequency of 56 GHz ５６ , dielectric loss tangent tanδ measured at a frequency of 74 GHz ７４ The difference between the dielectric loss tangents is small, and the dielectric loss tangent and tanδ １０ and tanδ ９１ It is preferable that the difference between tan δ and ７４ / tanδ １０ , tanδ ５６ / tanδ １０ , tanδ ３５ / tanδ １０ , tanδ ２８ / tanδ １０ , tanδ ９１ / tanδ ２８ , tanδ ５６ / tanδ ２８ , tanδ ３５ / tanδ ２８ , tanδ ９１ / tanδ ３５ , tanδ ７４ / tanδ ３５ , tanδ ５６ / tanδ ３５ , tanδ ９１ / tanδ ５６ and tan δ ７４ / tanδ ５６ are each preferably 1.6 or less, more preferably 1.4 or less, even more preferably 1.2 or less, and generally 1.0 or more. Due to these characteristics, the resin composition using the silica of the present invention is likely to exhibit stable behavior over a wide range of frequencies.

[0017] Also, tan δ １０ , tanδ ２８ , tanδ ３５ , tanδ ５６ , tanδ ７４ , tanδ ９１ are preferably 0.005 or less, more preferably 0.004 or less, and even more preferably 0.003 or less. By being in the above ranges, the transmission loss at each frequency can be reduced. １０ , tanδ ２８ , tanδ ３５ , tanδ ５６ , tanδ ７４ , tanδ ９１ The lower limit of is not particularly limited, but is generally 0.0001 or more.

[0018] The silica powder was mixed with polypropylene resin at a ratio of 30% by volume to obtain a test composition, which was then molded into a sheet having a thickness of 0.35 mm to 0.45 mm. The relative dielectric constant εr was measured at a frequency of 10 GHz by a resonator method. １０ is preferably 3.0 or less, and more preferably 2.7 or less. Similarly, the relative dielectric constant εr measured at a frequency of 28 GHz ２８ , relative permittivity εr measured at a frequency of 35 GHz ３５ , relative permittivity εr measured at a frequency of 56 GHz ５６ , relative permittivity εr measured at a frequency of 74 GHz ７４ , relative permittivity εr measured at a frequency of 91 GHz ９１ The relative dielectric constant at each frequency is also preferably 3.0 or less, and more preferably 2.7 or less. When the relative dielectric constant at each frequency is within the above range, it becomes easy to reduce the transmission loss at each frequency. １０ , εr ２８ , εr３５ , εr ５６ , εr ７４ , εr ９１ The lower limit of is not particularly limited, but is generally 2.0 or more.

[0019] The relative permittivity and dielectric loss tangent in the present invention are measured using an evaluation sample obtained by kneading silica powder into a polypropylene resin at a ratio of 30% by volume and molding the resulting test composition into a sheet having a thickness of 0.35 to 0.45 mm. As the polypropylene resin, for example, Novatec PP MA3 manufactured by Japan Polypropylene Corporation (melt flow rate: 11 g / 10 min, density: 0.90 g / cm at a test temperature of 230°C and a test load of 2.16 kg) is used. ３ ) can be used. The silica powder can be kneaded into the polypropylene resin using a kneading device. The silica powder and polypropylene resin are weighed out so that the silica powder accounts for 30% by volume of the total, and then charged into the heated mixing section of the kneading device and kneaded to obtain a test composition. Specifically, a Labo Plastomill 3S150 from Toyo Seiki Seisaku-sho, Ltd. is used as the kneading device. After heating the mixing section to 200°C, a predetermined amount of polypropylene is charged into the mixing section and dissolved. A predetermined amount of silica powder is then charged into the mixing section, and the mixture is kneaded at 200°C for 10 minutes at a rotation speed of 30 rpm to obtain a test composition. The test composition is then pressed using a 0.4 mm thick SUS mold at 2 tons and 180°C for 2 minutes, and then at 2 tons and 40°C for 2 minutes to form a sheet having a thickness of 0.35 mm to 0.45 mm, thereby obtaining an evaluation sample.

[0020] In the present invention, the dielectric constant and dielectric loss tangent are measured by a resonance method. Specifically, a resonator tuned to a predetermined frequency is connected to a network analyzer, and an evaluation sample is placed on the resonator for measurement, thereby calculating the dielectric constant and dielectric loss tangent. The measurement is performed in a constant temperature and humidity room at a temperature of 25°C and a humidity of 50% RH. Note that, when the evaluation sample is placed on the resonator during measurement, the frequency of the resonator may change slightly due to the influence of the evaluation sample. However, the measurement frequency in this application refers to the frequency of the resonator before the evaluation sample is placed on it. For example, "measured at a frequency of 10 GHz" means that the frequency of the resonator before the evaluation sample is placed on it is 10 GHz, and "measured at a frequency of 91 GHz" means that the frequency of the resonator before the evaluation sample is placed on it is 91 GHz. The frequency of the resonator is strongly affected by the thickness of the evaluation sample, but this effect can be minimized by adjusting the thickness of the evaluation sample to a certain range of 0.35 mm to 0.45 mm.

[0021] The silica powder of the present invention preferably has a median diameter D50 measured by a laser diffraction method of 0.05 to 10 μm, more preferably 0.1 to 6.0 μm. Also, the specific surface area measured by a nitrogen adsorption method is preferably 0.5 to 50 m. ２ / g, and 1.0 to 40m ２ / g is more preferable. If the median diameter D50 is smaller than 0.05 μm, the flow characteristics of the resin composition deteriorate, and the processability decreases, which is not preferable. If the median diameter D50 is larger than 10 μm, the permeability into gaps deteriorates when used as a material for semiconductor packaging, which is becoming increasingly miniaturized. Similarly, if the specific surface area is 50 m ２ If the specific surface area is greater than 0.5 m / g, the flow characteristics of the resin composition deteriorate, and the processability decreases, which is not preferable. ２ If the molecular weight is less than 1 / g, the permeability into gaps will be reduced when the material is used as a material for semiconductor packages, which are becoming increasingly miniaturized.

[0022] The silica powder of the present invention has a surface silanol group count of 5 / nm２ Preferably, the number is 3 or less per nm. ２ It is more preferable that the surface silanol group content is less than 100%. By reducing the surface silanol group content, it becomes easier to reduce the dielectric loss tangent and the relative dielectric constant. The amount of surface silanol groups can be measured by the method described in WO2018 / 096876.

[0023] The silica powder of the present invention can be obtained by performing a surface stabilization treatment under a nitrogen atmosphere after silica synthesis. While the reason for this is unclear, it is presumed that the surface condition of the silica powder affects its dielectric properties, and that this behavior can be controlled by performing the surface stabilization treatment. While the dielectric loss tangent and dielectric constant can be reduced by reducing the surface silanol groups of the silica powder as described above, simply reducing the amount of silanol groups is not enough to sufficiently reduce the frequency dependence of the dielectric loss tangent and dielectric constant. By synthesizing silica with a low amount of silanol groups and then performing a surface stabilization treatment on it, a silica powder can be obtained that has a low dielectric loss tangent and dielectric constant, and also has a low frequency dependence of these.

[0024] The silica powder before the surface stabilization treatment (hereinafter, sometimes referred to as "coarse silica powder") can be produced by a known method, for example, a flame fusion method or a sol-gel method.

[0025] Flame fusion methods include, for example, a method in which raw silica, quartz, an organosilane compound, etc. are supplied to and melted in a flame generated by mixing a gaseous or liquid fuel with a combustion-supporting gas such as oxygen or air and burning it with a burner, thereby producing spherical silica (flame-fused silica). Examples of such methods include those disclosed in WO 2020 / 175160 and JP 2004-002059. This flame fusion method is preferred because it produces silica in a high-temperature flame, reduces the number of surface silanol groups on the silica powder, and lowers the relative dielectric constant and dielectric dissipation factor. Known silica and quartz can be used as the raw silica and quartz without any particular restrictions. Examples of the organosilane compound that can be used include cyclic siloxanes such as octamethylcyclotetrasiloxane, linear siloxanes such as hexamethyldisiloxane, alkoxysilanes such as tetramethoxysilane, and chlorosilanes such as tetrachlorosilane. The flame is preferably an oxyhydrogen flame, and the flame temperature is preferably above the melting point of silica. The flame-fused silica may be used as coarse silica powder as is, or may be used as coarse silica powder after being classified and / or calcined.

[0026] The sol-gel method is a method in which silicon alkoxide is supplied to a reaction medium consisting of water and an organic solvent containing a hydrolysis catalyst, hydrolyzed and polycondensed to produce a silica sol, which is then gelled, and the resulting solid is extracted and dried to obtain a sol-gel silica powder. Known conditions for the sol-gel method can be used without any restrictions, and examples include the method disclosed in WO 2018 / 096876. After drying, classification may be performed. The sol-gel silica powder obtained by the sol-gel method has a large number of silanol groups on the particle surface, making their control difficult, so it must be used as a coarse silica powder after being calcined.

[0027] The firing can be carried out, for example, in an air atmosphere, by maintaining the target temperature for 0.5 to 48 hours, particularly 2 to 24 hours, at 300 to 1300°C, preferably 600 to 1200°C.

[0028] In the production of the silica powder of the present invention, it is important to subject the coarse silica powder to surface stabilization treatment under a nitrogen atmosphere. The surface stabilization treatment can be carried out by leaving the coarse silica powder in a nitrogen atmosphere at 10 to 50°C for at least 12 hours. If the coarse silica powder is stored in air after production, the silica powder of the present invention cannot be obtained even after surface stabilization treatment. Therefore, the surface stabilization treatment must be started within 12 hours of the completion of the production of the coarse silica powder. Here, the completion of the production of the coarse silica powder refers to the point at which the surface silanol groups of the silica particles have decreased. In the case of the flame fusion method, this refers to the point at which silica is generated in a high-temperature flame, and in the case of the sol-gel method, this refers to the point at which calcination is completed (when the temperature in the calcination furnace becomes less than 300°C). However, even in the case of the flame fusion method, if the calcination is performed, the completion of the calcination is considered to be the point at which the production of the coarse silica powder is completed. As long as the surface stabilization treatment is started within 12 hours of the completion of the production of the coarse silica powder, there is no problem even if the end of the treatment exceeds 12 hours from the completion of the production of the coarse silica powder.

[0029] The silica powder of the present invention may be a silica powder that has not been surface-treated with a surface treatment agent, or may be a surface-treated silica powder that has been surface-treated with a surface treatment agent such as a silane coupling agent. Surface treatment with a silane coupling agent makes it easy to increase affinity with resins and reduce the number of silanol groups on the surface, thereby lowering the dielectric loss tangent and relative dielectric constant. Known silane coupling agents can be used, and examples thereof include tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, n-butyltrimethoxysilane, i-butyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, i-butyltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacrylsilane, and the like. Examples of the alkoxysilane include alkoxysilanes such as aryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, and γ-(2-aminoethyl)aminopropylmethyldimethoxysilane; and silazanes such as hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldisilazane, hexapentyldisilazane, hexahexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, and dimethyltetravinyldisilazane.

[0030] When the silica powder of the present invention is a surface-treated silica powder, it is subjected to a surface treatment before the surface stabilization treatment. Known methods can be used for the surface treatment without any particular limitations, and either dry or wet surface treatment can be used. Dry surface treatment is a dry mixing method in which the raw material powder and the surface treatment agent are mixed without the use of a large amount of solvent. Examples include a method in which the surface treatment agent is gasified and mixed with the raw material powder, a method in which a liquid surface treatment agent is sprayed or dropped and mixed with the raw material powder, or a method in which the surface treatment agent is diluted with a small amount of organic solvent to increase the amount of liquid, and then sprayed or dropped. Wet surface treatment is a method in which the raw material powder and the surface treatment agent are mixed with a solvent, for example, a method in which the raw material powder, the surface treatment agent, and the solvent are mixed, and then the solvent is removed by drying or the like. When surface treatment is performed, the completion of the surface treatment is considered to be the completion of the production of the coarse silica powder. Specifically, in the case of a dry surface treatment, the time when mixing of the raw material powder and the surface treatment agent is completed is considered to be the time when the surface treatment is completed, and in the case of a wet surface treatment, the time when the treatment of removing the solvent is completed (for example, when the solvent is removed by reducing pressure or heating, the time when the reduction in pressure or heating is stopped is considered to be the time when the surface treatment is completed).

[0031] The use of the silica powder of the present invention is not particularly limited, but it can be used as a filler for filling resins. When the silica powder of the present invention is used as a filler, a resin composition containing the silica powder of the present invention and a resin can be obtained. Furthermore, compared to when other silica powders are used, the resin composition has a smaller frequency dependency in the high-frequency range, and therefore can be suitably used for substrate applications, semiconductor encapsulation applications, and insulating layer applications for printed wiring boards and package substrates, where dielectric properties are important. Among these applications, its use as a material for substrates such as printed wiring boards and package substrates is particularly preferred, and substrates containing the resin composition or a cured product thereof are suitable examples.

[0032] The resin of the resin composition may be a thermoplastic resin or a thermosetting resin, such as an epoxy resin, a phenolic resin, a melamine resin, a urea resin, an unsaturated polyester resin, an acrylic resin, a methacrylic resin, a silicone resin, a fluororesin, a polyphenylene ether, or an LCP. The resin may have a polymerizable functional group, and may be a cured product obtained by polymerizing and curing a resin composition containing the silica powder of the present invention and a resin having a polymerizable functional group. The amount of the silica powder of the present invention in the resin composition is not particularly limited and can be adjusted appropriately depending on the application. For example, the amount of silica powder may be 1 to 900 parts by weight, preferably 30 to 800 parts by weight, per 100 parts by weight of resin. When the resin composition is used as a substrate material, the resin is preferably an epoxy resin, a polyphenylene ether, or an LCP. The amount of silica powder is preferably 10 to 400 parts by weight, more preferably 30 to 250 parts by weight, per 100 parts by weight of resin.

[0033] The resin composition may contain other components, such as fillers other than silica, flame retardants, rubber particles, thickeners, antifoaming agents, leveling agents, adhesion promoters, antioxidants, ultraviolet degradation inhibitors, and colorants.

[0034] Examples of substrate materials made of the resin composition include build-up films and prepregs, and examples of substrate materials containing the resin composition include copper-clad laminates in which the resin composition and copper are laminated together.

[0035] Examples will be described below to specifically explain the present invention, but the present invention is not limited to these examples. The measurements of the various items in the examples and comparative examples were performed by the following methods.

[0036] <Measurement of median diameter D50> Silica powder was dispersed in a solvent at a concentration of 0.2% by mass, and the resulting sample was dispersed by irradiating it with ultrasonic waves at about 40 W for 10 minutes. The particle size distribution was measured using a laser diffraction scattering particle size distribution analyzer (LS13 320, manufactured by Beckman Coulter, Inc.). In the obtained volume frequency distribution (particle size distribution), the volume frequency was accumulated from the smallest particle size, and the particle size at which the accumulated value reached 50% was taken as the median diameter D50. In the case of silica powder that was not surface-treated with a silane coupling agent, water was used as the solvent, and in the case of surface-treated silica powder that was surface-treated with a silane coupling agent, ethanol was used as the solvent.

[0037] <Measurement of BET Specific Surface Area> The BET specific surface area was determined by the BET method (single-point nitrogen adsorption method) using a rapid surface area measuring device (SA-1000 manufactured by Shibata Scientific Co., Ltd.) For the measurement, 2 g of a powder sample was used, which had been previously dried at 100°C for 1 hour in a nitrogen gas flow.

[0038] <Measurement of Relative Dielectric Constant and Dielectric Loss Tangent> Polypropylene resin (Novatec PP MA3, manufactured by Japan Polypropylene Corporation) and silica powder were each weighed out so that the silica powder accounted for 30% by volume of the total, and then placed in a mixing section of a kneading machine (Labo Plastomill 3S150, manufactured by Toyo Seiki Seisaku-sho, Ltd.) heated to 200°C. The mixture was then kneaded at 200°C for 10 minutes at a rotation speed of 30 rpm to obtain a test composition. The test composition was then pressed using a 0.4 mm thick SUS mold at 2 tons and 180°C for 2 minutes, and then at 2 tons and 40°C for 2 minutes to obtain a sheet-like molded product with a thickness of 0.35 mm to 0.45 mm. The molded product was then cut into pieces according to the size of the resonator to be used depending on the frequency, and evaluation samples were obtained.

[0039] The dielectric properties were measured by connecting a split cylinder resonator of a predetermined frequency to a network analyzer (N5290A for measurements at 10 GHz and 28 GHz, HP8510 for measurements at 35 GHz, and HP8757 for measurements at 56 GHz, 74 GHz, and 91 GHz), setting the evaluation sample in the resonator, and performing measurements in TE011 mode to determine the relative permittivity and dielectric loss tangent from the obtained results. The measurements were performed in a constant temperature and humidity environment room at a temperature of 25°C and a humidity of 50% RH.

[0040] Example 1 Flame-fused silica was obtained by the method described in Example 9 of WO 2020 / 175160. Using the flame-fused silica as coarse silica powder, the atmosphere inside the container was thoroughly replaced with nitrogen within 6 hours from the time the flame-fused silica was obtained, and the mixture was allowed to stand for 15 hours in a nitrogen atmosphere controlled at a temperature of 20 to 30°C for surface stabilization treatment, yielding a silica powder. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0041] [Example 2] A silica powder was obtained in the same manner as in Example 1 of the present application, except that flame-fused silica was obtained by the method described in Comparative Example 2 of WO2020 / 175160. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0042] [Example 3] A silica powder was obtained in the same manner as in Example 1 of the present application, except that flame-fused silica was obtained by the method described in Comparative Example 3 of WO2020 / 175160. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0043] [Example 4] A silica powder was obtained in the same manner as in Example 1 of the present application, except that flame-fused silica was obtained by the method described in Example 6 of JP 2015-086120 A. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0044] [Example 5] Silica powder was obtained in the same manner as in Example 1 of the present application, except that flame-fused silica was obtained by the method described in Example 1 of JP 2015-086120 A. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0045] [Example 6] Sol-gel silica was obtained by the method described in Example 1 of WO2018 / 096876. The sol-gel silica was used as a coarse silica powder, and within 6 hours from the completion of firing, a surface stabilization treatment was carried out in the same manner as in Example 1 of the present application, to obtain a silica powder. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0046] [Example 7] A silica powder was obtained in the same manner as in Example 6 of the present application, except that the sol-gel silica was obtained by the method described in Example 7 of WO2018 / 096876. The results of evaluation of the obtained silica powder are shown in Tables 1 to 3.

[0047] Example 8 The flame-fused silica obtained in Example 2 of the present application was dispersed in a mixed solvent of ethanol and isopropyl alcohol (mass ratio of 7:2), and then 200 μmol / g of HMDS (SZ-31 manufactured by Shin-Etsu Silicones) was added as a surface treatment agent relative to the amount of flame-fused silica and stirred for 2 hours. The solvent was then removed under reduced pressure at 50°C, and the mixture was then dried under reduced pressure at 100°C to perform a surface treatment, yielding a coarse silica powder. The coarse silica powder was subjected to a surface stabilization treatment in the same manner as in Example 1 of the present application within 6 hours from the completion of the surface treatment, yielding a silica powder. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0048] Example 9 The flame-fused silica obtained in Example 5 of the present application was dispersed in a mixed solvent of ethanol and isopropyl alcohol (mass ratio of 7:2), and then 200 μmol / g of HMDS (SZ-31 manufactured by Shin-Etsu Silicones) was added as a surface treatment agent relative to the amount of flame-fused silica, and the mixture was stirred for 2 hours.The solvent was then removed under reduced pressure at 50°C, and the mixture was then dried under reduced pressure at 100°C to perform a surface treatment, yielding a coarse silica powder.The coarse silica powder was subjected to a surface stabilization treatment in the same manner as in Example 1 of the present application within 6 hours from the completion of the surface treatment, yielding a silica powder.The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0049] [Example 10] Sol-gel silica was obtained by the method described in Example 6 of WO2018 / 096876. The sol-gel silica was used as a coarse silica powder, and within 6 hours from the completion of calcination, a surface stabilization treatment was carried out in the same manner as in Example 1 of the present application, to obtain a silica powder. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0050] Example 11 The sol-gel silica obtained in Example 7 of the present application was dispersed in a mixed solvent of ethanol and isopropyl alcohol (mass ratio 7:2), and then 200 μmol / g of HMDS (SZ-31 manufactured by Shin-Etsu Silicones) was added as a surface treatment agent relative to the amount of flame-fused silica, and the mixture was stirred for 2 hours. After that, the solvent was removed under reduced pressure at 50°C, and then the mixture was dried under reduced pressure at 100°C to perform surface treatment, thereby obtaining a coarse silica powder. The coarse silica powder was subjected to a surface stabilization treatment in the same manner as in Example 1 of the present application within 6 hours from the completion of the surface treatment, to obtain a silica powder. The obtained silica powder was evaluated, and the results are shown in Tables 1 to 3.

[0051] Comparative Example 1 The coarse silica powder obtained in Example 2 of the present application was evaluated without being subjected to a surface stabilization treatment. The evaluation results are shown in Tables 1 to 3.

[0052] Comparative Example 2 The coarse silica powder obtained in Example 6 of the present application was evaluated without being subjected to a surface stabilization treatment. The evaluation results are shown in Tables 1 to 3.

[0053] Comparative Example 3 The coarse silica powder obtained in Example 8 of the present application was evaluated without being subjected to a surface stabilization treatment. The evaluation results are shown in Tables 1 to 3.

[0054] Comparative Example 4 The coarse silica powder obtained in Example 10 of the present application was evaluated without being subjected to a surface stabilization treatment. The evaluation results are shown in Tables 1 to 3.

[0055] [Reference Example 1] As a commercially available silica powder, EXELICA SE-8 (manufactured by Tokuyama) was evaluated. EXELICA SE-8 was produced by the flame fusion method and was not surface-treated with a silane coupling agent. The evaluation results are shown in Tables 1 to 3.

[0056] Reference Example 2: As a commercially available silica powder, Sunseal SP-10M (manufactured by Tokuyama) was evaluated. Sunseal SP-10M is manufactured by the sol-gel method and is surface-treated with hexamethyldisilazane. The evaluation results are shown in Tables 1 to 3.

[0057]

[0058]

[0059]

[0060] As shown in Table 1, the silica powders of Examples 1 to 11 that had undergone surface stabilization treatment had a tan δ ９１ / tanδ １０ On the other hand, the silica powder produced by the conventional manufacturing method without surface passivation treatment had a tanδ of 1.6 or less, and the frequency dependence of the dielectric loss tangent was small. ９１ / tanδ １０ The dielectric loss tangent was greater than 1.6, and the frequency dependence of the dielectric loss tangent was large. Note that the silica powders of the above examples and comparative examples all had a silanol group count of 3 / nm ２ It was as follows.

Claims

1. Silica powder, wherein the silica powder is kneaded into polypropylene resin at a ratio of 30 volume % to obtain a test composition, which is formed into a sheet having a thickness of 0.35 mm to 0.45 mm, and the dielectric loss tangent of the sheet is measured by a resonator method. When the dielectric loss tangent tan δ measured at a frequency of 10 GHz is １０ and the dielectric tangent tan δ measured at a frequency of 91 GHz ９１ Ratio tan δ ９１ / tan δ １０ The silica powder is characterized in that the molecular weight is 1.6 or less.

2. The silica powder according to claim 1, wherein the silica powder is mixed into a polypropylene resin at a ratio of 30 volume % to obtain a test composition, which is then molded into a sheet having a thickness of 0.35 mm to 0.45 mm, and the relative dielectric constant of the sheet is measured by a resonator method, and the relative dielectric constant measured at a frequency of 10 GHz is 3.0 or less.

3. The median diameter D50 measured by the laser diffraction method is 0.05 to 10 μm, and the specific surface area measured by the nitrogen adsorption method is 0.5 to 50 m ２ The silica powder according to claim 1, wherein the silica powder has a molecular weight of 1000 or more and a molecular weight of 1000 or more.

4. A resin composition comprising the silica powder according to any one of claims 1 to 3 and a resin.

5. A substrate comprising the resin composition according to claim 4 or a cured product thereof.

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