Silica powder and its manufacturing method

Abstract

In a silica powder according to the present invention, the number of metallic silicon particles per 10 g of silica powder is no higher than 30 particles, and the dielectric loss tangent is no higher than 0.004. A silica powder production method according the present invention comprises a heating step for heating a silica powder in the presence of chlorine. The present invention makes it possible to provide a silica powder having a low dielectric loss tangent and a low metallic silicon content, and a production method for such a silica powder.

Description

[Technical field]

[0001] The present invention relates to a silica powder to be mixed with a resin and a method for producing the silica powder. [Background technology]

[0002] In 5G (fifth generation mobile communication system), data communication will be large-volume and high-speed, so it is preferable that materials used in 5G can speed up signal propagation and reduce signal transmission loss. Examples of materials used in 5G include composite materials containing silica powder and resin. Since silica powder has a low dielectric constant and dielectric tangent, composite materials containing silica powder and resin may be able to speed up signal propagation and reduce signal transmission loss. However, if the silica powder contains magnetizable foreign matter, the dielectric tangent of the silica powder increases. For this reason, silica powder with a low content of magnetizable foreign matter is desired. As a silica powder with a low content of magnetizable foreign matter, for example, the silica powder described in Patent Document 1 is known as a conventional technology. In the silica powder described in Patent Document 1, the number of magnetizable particles of 45 μm or more measured by a specific method is 0. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 146454 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] However, even if the magnetizable foreign matter is removed from the silica powder, metallic silicon may remain in the silica powder. Metallic silicon is not magnetizable, so it is more difficult to remove from the silica powder than magnetizable foreign matter. If metallic silicon is present in the silica powder, it may cause short circuit defects in the wiring. For this reason, a silica powder with a low content of metallic silicon is desired. [Means for solving the problem]

[0005] As a result of intensive research, the present inventors have found that metallic silicon can be removed from silica powder by heating the silica powder in the presence of chlorine. The present invention is based on the above findings and has the following gist. [1] A silica powder having a dielectric tangent of 0.004 or less and a number of metallic silicon particles per 10 g of the silica powder being 30 or less. [2] The silica powder according to the above [1], having a chlorine content of 0.05% by mass or less. [3] The silica powder according to the above [1] or [2], having an average particle size of 0.5 to 10 μm. [4] Specific surface area is 1 to 8 m 2 The silica powder according to any one of the above [1] to [3], wherein the silica powder has a molecular weight of 1000 or more and a molecular weight of 1000 or more. [5] A method for producing silica powder, comprising a heating step of heating silica powder in the presence of chlorine. [6] The method for producing a silica powder according to the above [5], further comprising a cooling step of cooling the silica powder heated in the heating step under an inert gas atmosphere. Effect of the Invention

[0006] According to the present invention, it is possible to provide a silica powder having a low dielectric tangent and a low content of metallic silicon, and a method for producing the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The silica powder of the present invention will be described below. The silica powder of the present invention has a number of metal silicon particles of 30 or less per 10 g of the silica powder, and a dielectric loss tangent of 0.004 or less.

[0008] (Number of metal silicon particles in 10g of silica powder) When metal silicon particles are used as the silica powder raw material, metal silicon particles may remain in the silica powder. In this case, the number of metal silicon particles in 10g of the silica powder of the present invention is 30 pieces / 10g or less. If the number of metal silicon particles in 10g of the silica powder is greater than 30 pieces / 10g, when the silica powder is used as a semiconductor encapsulant, short circuit defects may occur between leads. From this viewpoint, the number of metal silicon particles in 10g of the silica powder of the present invention is more preferably 5 pieces / 10g or less, and even more preferably 2 pieces / 10g or less. The number of metal silicon particles in 10g of the silica powder can be measured by the method described in the examples below. The number of metal silicon particles in 10g of the silica powder can be easily reduced to 30 pieces / 10g or less, and even 2 pieces / 10g or less, by heating the silica powder in the presence of chlorine. The lower limit of the range of the number of metal silicon particles in 10g of the silica powder of the present invention is not particularly limited, but may be 0 pieces / 10g or 1 piece / 10g.

[0009] (Dielectric tangent) The dielectric loss tangent of the silica powder of the present invention is 0.004 or less. If the dielectric loss tangent of the silica powder is greater than 0.004, when a material containing the silica powder is used in a mobile communication system, the transmission loss may not be sufficiently reduced. From this viewpoint, the dielectric loss tangent of the silica powder is preferably 0.003 or less, more preferably 0.001 or less. The dielectric loss tangent of the silica powder can be measured by the method described in the Examples below. The dielectric loss tangent of the silica powder of the present invention may be 0.00005 or more, or may be 0.0001 or more.

[0010] (Chlorine content) The chlorine content in the silica powder of the present invention is preferably 0.06 mass% or less. It may be 0.05 mass% or less, or 0.04 mass% or less. When the chlorine content in the silica powder is 0.05 mass% or less, the occurrence of corrosion caused by chlorine in the silica powder can be suppressed. The chlorine content in the silica powder can be measured by the method described in the Examples below. It is to be noted that, by cooling the silica powder heated in the presence of chlorine under an inert gas atmosphere, it is further easy to make the chlorine content in the silica powder 0.05 mass% or less. It is to be noted that, from the viewpoint of productivity, the chlorine content in the silica powder may be 50 mass ppm or more.

[0011] (Average particle size) The average particle size of the silica powder of the present invention is preferably 0.5 to 10 μm. When the average particle size of the silica powder is 0.5 μm or more, the adhesion of particles occurring in the chlorine treatment process can be suppressed, and the compatibility of the silica powder with the resin can be further improved. When the average particle size of the silica powder is 10 μm or less, the filling property of the silica powder in the resin can be further improved. From this viewpoint, the average particle size of the silica powder of the present invention is more preferably 0.7 to 8 μm, and further preferably 0.8 to 5 μm. The average particle size of the silica powder is the median size of the particle size distribution measured by a laser diffraction scattering method.

[0012] (specific surface area) The specific surface area of ​​the silica powder of the present invention is preferably 1 to 8 m 2 / g. The specific surface area of ​​silica powder is 1m 2 When the specific surface area of ​​the silica powder is 8 m / g or more, the filling property of the silica powder in the resin can be further improved. 2 When the specific surface area of ​​the silica powder of the present invention is less than 2, the silica particles can be prevented from adhering to each other, and the compatibility of the silica powder with the resin can be further improved. 2 / g, and more preferably 3 to 6m 2 The specific surface area of ​​the silica powder can be measured by the method described in the Examples below.

[0013] (Method of producing silica powder of the present invention) An example of the method for producing the silica powder of the present invention will be described below. However, the method for producing the silica powder of the present invention is not limited to the method described below as long as the silica powder of the present invention can be produced. The method for producing silica powder of the present invention includes, for example, a step (A) of preparing silica powder, and a step (B) of heating the silica powder, maintaining the heat in the presence of chlorine, and cooling it.

[0014] (Process (A)) In step (A), a silica powder is prepared. For example, a commercially available silica powder may be used to prepare the silica powder. Alternatively, a silica powder may be produced to prepare the silica powder. Furthermore, a silica powder taken out during the production of a commercially available silica powder may be used to prepare the silica powder.

[0015] The average particle size of the silica powder prepared in step (A) is preferably 0.5 to 10 μm. When the average particle size of the silica powder is 0.5 μm or more, it is possible to suppress the silica particles from coalescing with each other when the silica powder is heated in the presence of chlorine. When the average particle size of the silica powder is 10 μm or less, the compatibility of the silica powder with the resin is further improved. From this viewpoint, the average particle size of the silica powder prepared in step (A) is more preferably 0.7 to 8 μm, and further preferably 0.8 to 5 μm. The average particle size of the silica powder is the median size of the particle size distribution measured by a laser diffraction scattering method.

[0016] (specific surface area) The specific surface area of ​​the silica powder prepared in step (A) is preferably 1 to 8 m 2 / g. The specific surface area of ​​silica powder is 1m 2 When the specific surface area of ​​the silica powder is 8m / g or more, the silica powder becomes more compatible with the resin. 2 When the silica powder is heated in the presence of chlorine, the silica particles can be prevented from coalescing with each other when the silica powder is heated in the presence of chlorine. From this viewpoint, the specific surface area of ​​the silica powder prepared in step (A) is more preferably 2 to 7 m 2 / g, and more preferably 3 to 6m 2 The specific surface area of ​​the silica powder can be measured by the method described in the Examples below.

[0017] The silica powder prepared in step (A) can be produced, for example, as follows. The method for producing the silica powder prepared in step (A) includes, for example, a step (a) of preparing a silica powder raw material, a step (b) of melting and spheroidizing the silica powder raw material to prepare an unclassified fused spherical silica powder, a step (c) of classifying the unclassified fused spherical silica powder to prepare fused spherical silica powders of different particle sizes, and a step (d) of blending the fused spherical silica powders of different particle sizes to prepare a blend of fused spherical silica powders.

[0018] (Step (a)) In step (a), a silica powder raw material is prepared. Examples of the silica powder raw material include silica powder obtained by crushing high-purity natural silica stone, silica gel synthesized by wet reaction of alkali silicate and mineral acid, crushed gel obtained by sol-gel method from alkoxysilane, metal silicon particles, etc. Among these silica powder raw materials, silica powder of high-purity natural silica stone and metal silicon particles are preferred in terms of production cost and ease of particle size adjustment of the raw material powder.

[0019] Silica powder, which is a raw material for silica powder, is produced, for example, as follows: After washing silica with water, it is pulverized using a pulverizer such as a vibration mill or a ball mill to produce silica powder. Then, the particle size distribution of the produced silica powder is adjusted using a vibration sieve or a classifier.

[0020] (Step (b)) In step (b), the silica powder raw material is melted and spheroidized to produce unclassified fused spherical silica powder. For example, the silica powder raw material is sprayed into a flame. As a result, the silica powder raw material melts and is simultaneously spheroidized by surface tension. The droplets of the silica powder raw material that pass through the flame are rapidly cooled, and become unclassified fused spherical silica powder, which is amorphous spherical silica. As the fuel gas for forming the flame, for example, propane, butane, propylene, acetylene, hydrogen, etc. are used, and as the supporting gas, for example, air, oxygen, etc. are used.

[0021] (Process (c)) In step (c), the unclassified fused spherical silica powder is classified to produce fused spherical silica powders classified by particle size. For example, when collecting the unclassified fused spherical silica powder obtained by passing the silica powder raw material through a flame, it is classified according to particle size before collection. Coarse particles may be collected using a gravity settling chamber, a cyclone, etc., and fine particles may be collected using a bag filter, an electric dust collector, etc. The classified fused spherical silica powder may then be further classified according to particle size using a classifier such as an air flow classifier, a vibrating sieve, or a cylindrical sieve.

[0022] (Step (d)) In step (d), fused spherical silica powders of different particle sizes are blended to produce a blend of fused spherical silica powders. For example, the fused spherical silica powders of different particle sizes are mixed in a ratio such that the fused spherical silica powders of different particle sizes are combined to form the closest packing. The mixed fused spherical silica powders are then mixed using a mixer such as a V-type blender, a double cone blender, or an air blender. This produces a blend of fused spherical silica powders with good packing properties. This blend can be used as the silica powder prepared in step (A).

[0023] (Process (B)) Step (B) is a step of raising the temperature of silica powder, maintaining the temperature in the presence of chlorine, and then cooling. It is preferable that the temperature is increased at a rate of 1 to 10° C. / min in an inert atmosphere during the temperature increase. In the heating and holding step after the temperature is raised, the silica powder is heated in the presence of chlorine. As a result, the metal silicon particles in the silica powder react with chlorine to become silicon tetrachloride. The silicon tetrachloride is sublimated by heating, and the metal silicon particles are removed from the silicon powder. This makes it easy to reduce the number of metal silicon particles in 10 g of silica powder to 30 particles / 10 g or less, or even 2 particles / 10 g or less. Note that when metal silicon particles are used as the silica powder raw material, there is a risk that metal silicon particles will remain in the silica powder.

[0024] From the viewpoint of removing metal silicon in the silica powder and suppressing adhesion between silica particles, the heating temperature in the heating and holding after the temperature increase is preferably 800 to 1200°C, more preferably 800 to 1050°C, and even more preferably 800 to 1000°C. From the viewpoint of more completely removing metal silicon in the silica powder and the efficiency of step (B), the heating time in step (B) is preferably 30 minutes to 10 hours, more preferably 70 minutes to 4 hours, and even more preferably 90 minutes to 2 hours. From the viewpoint of sublimating silicon tetrachloride generated by chlorinating metal silicon and the amount of chlorine in the atmosphere, chlorine treatment in a vacuum atmosphere in which the atmospheric gas can be sucked in by a vacuum pump or the like is desirable. However, from the viewpoint of productivity and cost, heat treatment in a normal pressure atmosphere is desirable. Since chlorine is corrosive, it is preferable to supply chlorine by mixing it with an inert gas such as nitrogen, argon, or dry air. From the viewpoint of removing metallic silicon from the silica powder and from the viewpoint of the corrosiveness of chlorine, the chlorine content in the atmosphere surrounding the silica powder is preferably 5 to 35 volume %, more preferably 10 to 25 volume %. Note that dry air is air with a moisture content of 3500 mass ppm or less. The flow rate of chlorine gas is preferably 50 to 200 L / hr.

[0025] After the heating, the powder is cooled in the same inert gas atmosphere as in the heating, preferably at a temperature drop rate of 1 to 10° C. / min. Lowering the temperature in the presence of chlorine is not preferred because chlorine adheres to the powder surface and the chlorine content increases too much.

[0026] (Other processes) The method for producing a silica powder of the present invention may further include a step of performing a surface treatment with a silane coupling agent on the silica powder heated in step (B) in order to suppress the aggregation of the silica powder. The method for producing a silica powder of the present invention may further include a step of performing a classification treatment to precisely remove coarse particles. EXAMPLES

[0027] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0028] The silica powders of the Examples and Comparative Examples were evaluated as follows.

[0029] (Dielectric tangent) The dielectric loss tangent of the silica powder was measured at a frequency of 1.0 GHz using a perturbation type cavity resonator measurement system (manufactured by Keyence Corporation).

[0030] (Average particle size) The particle size (d50) at which the cumulative frequency of the particle size distribution of the silica powder is 50% was measured as the average particle size using a laser particle size distribution analyzer (product name "MT-3300EX", manufactured by Nikkiso Co., Ltd.).

[0031] (specific surface area) The specific surface area of ​​the silica powder was measured by the BET method using a specific surface area measuring device (product name "Macsorb HM model-1208", manufactured by MACSORB).

[0032] (Chlorine content) 1 g of silica powder was heated using an automatic sample combustion device (trade name "AQF-2100H type", manufactured by Nitto Seiko Analytech Co., Ltd.), and the generated gas was dissolved in water. The concentration of chlorine dissolved in water was measured using an ion chromatograph (trade name "ICS-2100", manufactured by Thermo Fisher Scientific Co., Ltd.) according to JIS R 1603:2007. Based on this measurement value, the content of chlorine contained in the silica powder was calculated.

[0033] (Number of metal silicon particles in 10g of silica powder) 10 g of silica powder was placed in a 50 mL centrifuge tube, and then 40 mL of ion-exchanged water was placed in the centrifuge tube. The centrifuge tube containing the silica powder and ion-exchanged water was placed in a plastic container containing water. The inner diameter of the plastic container was 150 mm, and the water level in the plastic container was the same as that in the centrifuge tube. The plastic container containing the centrifuge tube was set in a homogenizer, and the silica powder and ion-exchanged water in the centrifuge tube were stirred for 2 minutes at an output of 700 W to prepare a slurry of silica powder and ion-exchanged water. The obtained slurry was poured into a resin tray with a depth of 0.2 mm. A bar magnet with a magnetic force of 12,000 gauss was used to collect the magnetizable foreign matter in the slurry poured into the tray. The slurry from which the magnetizable foreign matter had been collected was returned to the centrifuge tube, and the centrifuge tube was placed in a plastic container containing water, and the homogenizer was used to stir the slurry for 2 minutes at an output of 700 W. The stirred slurry was poured into a resin tray with a depth of 0.2 mm. A bar magnet with a magnetic force of 12,000 gauss was used to collect the magnetizable foreign matter in the slurry. This process of stirring the slurry and collecting the magnetizable foreign matter in the slurry was repeated 10 times. The slurry after collecting the magnetizable foreign matter was filtered using a suction filter (product name "JAWP04700", manufactured by Millopore, pore size: 1 μm). The entire area on the filter was observed using an optical microscope at 100x magnification, and the number of black particles was counted. Note that since the magnetizable foreign matter had been collected from the slurry, the black particles were only metallic silicon particles.

[0034] The following silica powders were prepared: (Silica powder A) Commercially available silica powder (average particle size: 0.8 μm, specific surface area: 6.2 m 2 / g, chlorine content: 0.4 mass ppm) was filled into a mullite container. The mullite container filled with silica powder was set in an alumina tubular furnace. The atmosphere in the furnace was replaced with argon gas until the oxygen concentration in the furnace became 0.0%. The temperature was raised to a heating temperature of 1000 ° C. at a heating rate of 5 ° C. / min. The mullite container was heated for 120 minutes at a heating temperature of 1000 ° C. while supplying a mixed gas of chlorine gas and argon gas with a chlorine gas concentration of 20 volume % at a flow rate of 500 L / h. Thereafter, the gas supplied was changed to argon gas only, and the atmosphere of the mixed gas of chlorine gas and argon gas was replaced with an atmosphere of argon gas only. Then, while replacing with an atmosphere of argon gas only, the mullite container was cooled to room temperature at a temperature drop rate of 2 ° C. / min to obtain silica powder A. The chlorine content in the atmosphere replaced with an atmosphere of argon gas only was finally 0.1 mass ppm or less.

[0035] (Silica powder B) Silica powder B was prepared in the same manner as silica powder A, except that the heating temperature was changed from 1000°C to 820°C.

[0036] (Silica powder C) Silica powder C was prepared in the same manner as silica powder A, except that the heating temperature was changed from 1000°C to 900°C.

[0037] (Silica powder D) Silica powder D was prepared in the same manner as silica powder A, except that the concentration of chlorine gas was changed from 20% by volume to 10% by volume.

[0038] (Silica Powder E) Silica powder E was prepared in the same manner as silica powder A, except that chlorine gas was not supplied.

[0039] The results are shown in Table 1. [Table 1]

[0040] From the results of the examples, it was found that a silica powder having a number of metal silicon particles of 30 or less per 10 g of silica powder and a dielectric loss tangent of 0.004 or less can be produced by a method for producing a silica powder including a heating step of heating the silica powder in the presence of chlorine. The dielectric loss tangent of the silica powder E, which is a comparative example, was low. This is believed to be due to the low content of magnetizable impurities in the silica powder E. However, the number of metal silicon particles in 10 g of the silica powder E was high. This shows that it is easy to remove magnetizable foreign matter from the silica powder, but difficult to remove the metal silicon.

Claims

1. The number of metal silicon particles in 10 g of fused spherical silica powder is 30 or less, A fused spherical silica powder having a dielectric tangent of 0.004 or less.

2. 2. The fused spherical silica powder according to claim 1, wherein the chlorine content is 0.05% by mass or less.

3. The fused spherical silica powder according to claim 1 or 2, having an average particle size of 0.5 to 10 μm.

4. Specific surface area is 1 to 8 m ２ The fused spherical silica powder according to any one of claims 1 to 3, wherein the molecular weight of the fused spherical silica powder is 1 / g.

5. A method for producing silica powder, comprising a heating step of heating fused spherical silica powder in the presence of chlorine.

6. The method for producing a silica powder according to claim 5, further comprising a cooling step of cooling the fused spherical silica powder heated in the heating step under an inert gas atmosphere.

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