Low dielectric loss tangent silica particle and method for producing the same

Abstract

To provide silica particles having a dielectric loss tangent of 0.002 or less at a frequency of 1 GHz.SOLUTION: Silica particles and a dispersion thereof having a dielectric loss tangent of 0.002 or less at a frequency of 1 GHz satisfy the following conditions: (i) an average primary particle diameter of 5 nm to 120 nm; (ii) a content of polyvalent metal element M in a molar ratio of M / Si from 0.00001 to 0.002; and (iii) an amorphous structure. In preferred embodiments, the particles further satisfy either (iv) a carbon content of less than 0.1 mass% and a hydrogen content of 0.001 mass% to 0.1 mass% as measured by CHN elemental analysis, or (v) a carbon content of 0.1 mass% or more and a hydrogen content of 0.01 mass% to 10 mass% as measured by CHN elemental analysis.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to nano-order silica particles having a low dielectric loss tangent and a method for producing the same. [Background technology]

[0002] In recent years, with the increase in the amount of information and communication traffic in the field of communications such as 5G, the use of high frequency bands has become widespread in electronic devices and communications equipment.

[0003] The application of high frequency bands poses the problem of increased transmission loss of circuit signals, so materials with low dielectric dissipation factors are generally used for the insulators that make up electrical and electronic components such as antennas, circuits, and circuit boards. Polymer materials used as insulators generally have low relative permittivity but high dielectric dissipation factors. On the other hand, ceramic materials often have the opposite characteristics. For this reason, ceramic-filled polymer materials that combine these materials to achieve both low dielectric constant and low dielectric dissipation factor have become popular (Patent Document 1, Patent Document 2).

[0004] Fused silica, which has a micron-order size, is generally widely used as the ceramic filler (inorganic filler). However, since coarse particles generated during manufacturing have a significant impact on the performance of molded products, separating and removing the coarse particles has become an issue (Non-Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4).

[0005] On the other hand, silica particles with an average particle size on the nano-order are considered to have an advantage in that they are less likely to produce coarse particles during production, and because they can be filtered or centrifuged, even if coarse particles do occur, they are easy to separate and remove. Nano-order size particles are also considered to have various advantages, such as being applicable to transparent polymer materials and having a greater composite effect than micro-order size fillers (Patent Document 5, Patent Document 6). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-24916 [Patent Document 2] Patent No. 6793282 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-269636 [Patent Document 4] Patent No. 6546386 [Patent Document 5] Patent No. 5862886 [Patent Document 6] Patent No. 6813815 [Non-patent literature]

[0007] [Non-Patent Document 1] Fuji Chimera Research Institute, December 2019, No. 831906736, Extensive research into next-generation novel low-dielectric materials targeting 2020-2030 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, nano-sized particles have various advantages in ceramic fillers. However, existing nano-sized particles have a high dielectric loss tangent, making them difficult to apply to materials for electronic devices and the like that operate in high frequency bands.

[0009] The present invention has been made in view of the above circumstances, and aims to provide nano-order particles having a low dielectric loss tangent, specifically, a dielectric loss tangent of 0.002 at a frequency of 1 GHz. The object of the present invention is to provide silica particles that are: [Means for solving the problem]

[0010] As a result of intensive research into solving the above problems, the present inventors have found that silica particles having an average primary particle diameter of 5 nm to 120 nm, a content of polyvalent metal element M of 0.00001 to 0.002 as an M / Si molar ratio, and a content of hydrogen atoms of less than 0.1 mass % as measured by CHN elemental analysis, exhibit low dielectric properties, with a dielectric loss tangent of 0.002 or less at a frequency of 1 GHz, and have completed the present invention.

[0011] That is, in a first aspect, the present invention provides silica particles having a dielectric loss tangent of 0.002 or less at a frequency of 1 GHz, which satisfy the following items (i), (ii), and (iii): (i) the average primary particle size is 5 nm to 120 nm; (ii) the content of the polyvalent metal element M is 0.00001 to 0.002 in terms of the M / Si molar ratio; (iii) is amorphous; According to a second aspect, the silica particles according to the first aspect further satisfy the requirement (iV): (iV) The carbon element content measured by CHN elemental analysis is less than 0.1% by mass, and the hydrogen element content measured by CHN elemental analysis is 0.001% by mass to 0.1% by mass. According to a third aspect, there is provided the silica particles according to the first aspect, which further satisfy the requirement (V): (V) The carbon element content measured by CHN elemental analysis is 0.1% by mass or more, and the hydrogen element content measured by CHN elemental analysis is 0.01% by mass to 10% by mass. As a fourth aspect, a silica powder containing the silica particles according to any one of the first to third aspects. According to a fifth aspect, there is provided a mixed liquid comprising the silica particles according to any one of the first to third aspects and water or an organic solvent; According to a sixth aspect, there is provided a composite material comprising the silica particles according to any one of the first to third aspects and a polysiloxane resin or an organic resin material. According to a seventh aspect, there is provided a composite material according to the sixth aspect, in which the organic resin material is at least one selected from the group consisting of a styrene resin, an epoxy resin, a cyanate resin, a phenolic resin, an acrylic resin, a maleimide resin, a urethane resin, a polyurethane, a polyimide, a polytetrafluoroethylene, a cycloolefin polymer, an unsaturated polyester, a vinyl triazine, a polyphenylene sulfide, a crosslinkable polyphenylene oxide, and a curable polyphenylene ether. As an eighth aspect, the composite material according to the sixth aspect has an application selected from the group consisting of a semiconductor device material, a copper-clad laminate, a flexible wiring material, a flexible display material, an antenna material, an optical wiring material, and a sensing material. As a ninth aspect, the present invention provides a method for producing a pharmaceutical composition comprising the following steps (i) and (ii): Step (i): preparing amorphous silica particles having an average primary particle diameter of 5 nm to 120 nm, a content of a polyvalent metal element M in terms of an M / Si molar ratio of 0.00001 to 0.002; (ii) Step: firing at 700°C to 1200°C; The present invention relates to a method for producing silica particles according to the first aspect, comprising: [Effects of the Invention]

[0012] The silica particles of the present invention have the effect of exhibiting low dielectric properties. Furthermore, since the silica particles of the present invention can be combined with organic resin materials to form composite materials, they are expected to be used in the production of semiconductor device materials, etc. [Brief explanation of the drawings]

[0013] [Figure 1] XRD pattern of silica particles A. [Figure 2] XRD pattern of silica particle C. [Figure 3] XRD pattern of silica particles F. [Figure 4] XRD pattern of silica particle G. [Figure 5] XRD pattern of silica particles H. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Silica particles> The silica particles of the present invention are silica particles that satisfy the following requirements (i), (ii), and (iii) and have a dielectric loss tangent of 0.002 or less at a frequency of 1 GHz. As long as the silica particles satisfy the following requirements (i) to (iii), there are no limitations on their shape, and they may be, for example, spherical particles, chain particles, or hollow particles. (i) the average primary particle size is 5 nm to 120 nm; (ii) the content of the polyvalent metal element M is 0.00001 to 0.002 in terms of the M / Si molar ratio; (iii) It is amorphous.

[0015] Nano-sized crystalline silica particles are generally known to be carcinogenic, and therefore amorphous is preferable from a safety perspective. The silica particles of the present invention are also preferably amorphous. While silica is generally known to be amorphous, alkali metals and other elements can be partially incorporated into the silica particles to maintain the amorphous nature of the silica. The inclusion of alkali metals in the silica particles promotes rearrangement of Si-O-Si bonds, making it easier to reduce the dielectric tangent of the silica particles while maintaining their amorphous nature. Examples of alkali metals include one or more elements selected from Na, K, Li, and the like. For example, the alkali metals can be incorporated in the range of 1 ppm to 5,000 ppm, 1 ppm to 4,000 ppm, 1 ppm to 3,000 ppm, 1 ppm to 2,500 ppm, 1 ppm to 1,000 ppm, 1 ppm to 100 ppm, 1 ppm to 50 ppm, or 1 ppm to 25 ppm relative to the Si content of the silica particles. By setting the alkali metal content to 1 ppm or more relative to the Si contained in the silica particles, the crystallinity of the silica particles can be made amorphous, thereby reducing the dielectric loss tangent.By setting the alkali metal content to 5,000 ppm or less relative to the Si contained in the silica particles, the dielectric loss and dielectric loss tangent during high frequency application due to ionic polarization derived from the alkali metal can be reduced.

[0016] <Average primary particle diameter> The average primary particle size of the silica particles according to the present invention is determined by the specific surface area (S N2 ) can be used.

[0017] The specific surface area diameter (average primary particle diameter: D (nm)) is the specific surface area S measured by the nitrogen adsorption method (BET method). N2 (m 2 The primary particle diameter is calculated from the particle diameter (nm) of the silica nanoparticles (wt. / g) by the formula D(nm)=2720 / S, and means the particle diameter converted into that of spherical silica particles.

[0018] The average primary particle diameter of silica particles can also be calculated by observing a micrograph taken with a transmission electron microscope or the like, and can be treated as a value equivalent to the specific surface area diameter.

[0019] The silica particles according to the present invention have an average primary particle diameter in the range of 5 nm to 120 nm, for example, in the range of 5 nm to 100 nm, 10 to 100 nm, or 20 to 80 nm.

[0020] By using silica particles with an average primary particle size of 5 nm to 120 nm, defects can be suppressed and high transparency can be achieved when a composite material using the silica particles is molded. Furthermore, the viscosity of the resin composition containing the silica particles can be reduced, and handling can be improved during the production process.

[0021] <Specific surface area by nitrogen adsorption (S N2 )> The silica particles according to the present invention have a specific surface area (S N2 ) is 25~550m 2 / g, or 25 to 300m 2 / g, or 25 to 250 m 2 / g range can be used. Specific surface area (S N2 ) for 25 to 250 m 2 / g, a low dielectric tangent is exhibited, and when a composite material using the silica particles is molded, the contact area between the particles and the resin increases, thereby reducing particle dropout.

[0022] <Content of polyvalent metal element M> The content of polyvalent metal element M in silica particles can be quantified by analysis using inductively coupled plasma optical emission spectroscopy (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AA), X-ray fluorescence spectrometry (XRF), or the like after performing a known appropriate pretreatment. The polyvalent metal element M refers to a metal element whose ionic valence can be divalent or greater, and includes, for example, at least one element selected from the group consisting of Fe, Al, Ca, Mg, Ti, Zr, Cu, Ni, Cr, Zn, and Pb, and may be a combination of two or more elements. The polyvalent metal element M may be contained in silica particles as an impurity derived from natural products or as a result of contamination during particle production.

[0023] The silica particles according to the present invention have a content of a polyvalent metal element M as measured by ICP-OES, expressed as an M / Si molar ratio, which is a range represented by a combination of a lower limit of 0.00001, 0.00005, 0.00008, or 0.0001 and an upper limit of 0.002, 0.001, or 0.0005. For example, silica particles having a content of 0.00001 to 0.002, 0.00001 to 0.001, or 0.00005 to 0.0001 can be used.

[0024] By setting the content of the polyvalent metal element M in the silica particles according to the present invention within the above range, the dielectric loss and dielectric loss tangent due to ionic polarization resulting from the polyvalent metal element M when a high frequency is applied can be reduced.

[0025] The above-mentioned predetermined content of the polyvalent metal element M (M / Si molar ratio) can be achieved by a method for producing silica particles from activated silicic acid from which cations have been removed, or a method for producing silica particles from which metal elements have been removed by acid leaching.

[0026] In a method for producing silica particles from activated silicic acid from which cations have been removed, for example, an aqueous solution of alkali silicate is first treated with a cation exchange resin to obtain an aqueous solution of activated silicic acid from which cations have been removed. Then, a strong acid (e.g., nitric acid, hydrochloric acid, sulfuric acid) is added to the aqueous solution of activated silicic acid from which cations have been removed, and the resulting solution is brought into contact with a cation exchange resin and an anion exchange resin to remove impurity ions. After that, an alkaline substance (e.g., metal hydroxide, ammonia) is added and the mixture is heated with stirring to obtain silica particles with a reduced content of polyvalent metal element M in the form of a silica sol in which the particles are dispersed.

[0027] In the leaching method, the polyvalent metal element M present on the surface of silica particles is leached (eluted) as a polyvalent metal element M salt, polyvalent metal element M oxide, or polyvalent metal element M hydroxide using an aqueous solution of at least one mineral acid selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid, thereby obtaining silica particles with a reduced content of the polyvalent metal element M. In particular, a method of leaching (eluting) the polyvalent metal element M using an aqueous nitric acid solution is preferably used. The aqueous nitric acid solution used for leaching can be used at a pH in the range of 0.5 to 4.0, 0.5 to 3.0, 0.5 to 2.0, or 1.0 to 1.5, and is typically pH 1.0. For example, 100 mL of the above nitric acid aqueous solution can be added to 1 g of silica, and the polyvalent metal element M compound can be eluted from the surface of the silica particles by maintaining the mixture at a temperature of 20 to 70°C or 40 to 60°C for 10 to 24 hours.

[0028] <Hydrogen element content> The hydrogen content is an index of the amount of silanol groups contained in silica particles, and the higher this value, the greater the amount of silanol groups. The hydrogen content can be measured by CHN elemental analysis.

[0029] The silica particles according to the present invention can be used that have a hydrogen element content measured by CHN elemental analysis within a predetermined range.The hydrogen element can include hydrogen elements derived from silica particles and hydrogen elements other than silica particles, such as hydrogen elements derived from additives such as silane coupling agents and stabilizers.One method for distinguishing between hydrogen elements derived from silica particles and hydrogen elements other than silica particles is, for example, to measure the carbon elements derived from additives such as silane coupling agents and stabilizers, thereby considering the amount of hydrogen elements bonded to carbon. More specifically, if the carbon content measured by CHN elemental analysis is less than 0.1% by mass, silica particles with a hydrogen content of 0.001% to 0.1% by mass, 0.005% to 0.1% by mass, or 0.005% to 0.05% by mass can be used. If the carbon content measured by CHN elemental analysis is 0.1% by mass or greater, silica particles with a hydrogen content of 0.01% to 10% by mass, 0.01% to 5% by mass, 0.01% to 3% by mass, or 0.1% to 3% by mass can be used. Using silica particles with such hydrogen content can reduce the dielectric loss and dielectric dissipation factor during high-frequency application due to orientation polarization caused by silanol groups. Furthermore, silica particles with such hydrogen content have a reduced amount of polar silanol groups, which reduces the particle surface polarity, thereby improving compatibility with low-polarity resins.

[0030] Furthermore, the form of the silica particles of the present invention is not particularly limited, and they can be used as silica powder, a silica particle aqueous dispersion, a silica particle organic solvent dispersion, a silica particle-containing mixed liquid, or a silica particle dispersion monomer (liquid). Examples of organic solvents used in the silica particle organic solvent dispersion include alcohols having 1 to 10 carbon atoms, ketones having 1 to 10 carbon atoms, ethers having 1 to 10 carbon atoms, esters and amides having 1 to 10 carbon atoms. Furthermore, examples of the monomer (liquid) used in the silica particle-containing dispersed monomer (liquid) include, but are not limited to, a monomer solution of an organic resin material in the <composite material> described below.

[0031] Furthermore, the silica particles of the present invention can be produced by any method, including, for example, (i) a step of preparing amorphous silica particles having an average primary particle size of 5 nm to 120 nm, a content of polyvalent metal element M of 0.00001 to 0.002 in terms of M / Si molar ratio, and (ii) a step of firing the particles at 700°C to 1200°C. The step (i) can be carried out by using silica particles having the above average primary particle diameter as a raw material and by a method in which the polyvalent metal element M is contained at the above-mentioned predetermined content (M / Si molar ratio), for example, by a method of producing silica particles from activated silicic acid from which cations have been removed, or a method of producing silica particles from which metal elements have been removed by acid leaching. The calcination (heating) temperature in the above step (ii) can be 700°C to 1200°C, 700°C to 1100°C, 700°C to 1000°C, or 800°C to 1000°C. The heating time can be 0.1 to 10 hours, 0.5 to 5 hours, or 1 to 3 hours. By producing silica particles at the above heating temperature and heating time, the silanol groups contained in the silica particles, which cause dielectric loss during high frequency application due to orientation polarization, can be reduced by dehydration condensation, thereby reducing the dielectric loss tangent. Furthermore, when the heating temperature is set to 700°C to 1200°C, By doing so, it is possible to suppress the generation of crystalline silica, which is a carcinogenic substance. The heat treatment is not particularly limited, but can be carried out using, for example, an electric furnace.

[0032] <Measurement of dielectric properties> The dielectric constant and dielectric loss tangent of the silica particles can be measured using a dry powder of the silica particles by, for example, a perturbation cavity resonance method using a dedicated device, such as a cavity resonator jig for a measurement frequency of 1 GHz (product name: TMR-1A, manufactured by Keycom Corporation) and a vector network analyzer (product name: N5227A, manufactured by Keysight Technologies).

[0033] When silica particles are composited with an organic resin material and used as an insulator, the dielectric loss tangent of the silica particles at a frequency of 1 GHz is preferably 0.002 or less, particularly 0.0015 or less. The lower limit of the dielectric loss tangent is preferably as low as possible, and can be, for example, 0.00001 or more, 0.00005 or more, 0.0001 or more, or 0.0005 or more.

[0034] <Composite materials> The composite material according to the present invention is a composite material containing the silica particles according to the present invention and a polysiloxane resin or an organic resin material.

[0035] The organic resin material can be at least one selected from the group consisting of styrene resin, epoxy resin, cyanate resin, phenol resin, acrylic resin, maleimide resin, urethane resin, polyurethane, polyimide, polytetrafluoroethylene, cycloolefin polymer, unsaturated polyester, vinyl triazine, polyphenylene sulfide, crosslinkable polyphenylene oxide, and curable polyphenylene ether.

[0036] The method for producing the composite material is not particularly limited. For example, the composite material can be obtained by mixing silica particles with a monomer solution or a polymer solution of the organic resin material to prepare a polymerizable composition, removing excess solvent, and then photocuring or thermal curing the composition.

[0037] The mixing ratio of the silica particles to the monomer solution or polymer solution of the organic resin material in the polymerizable composition can be such that the mass ratio of silica particles to the monomer solution or polymer solution of the organic resin material is 1:0.1 to 100, for example 1:0.1 to 20.

[0038] The polymerizable composition can be cured by light or heat by using a polymerization initiator. Examples of the photopolymerization initiator include a photoradical polymerization initiator or a photocationic polymerization initiator, and examples of the thermal polymerization initiator include a thermal radical polymerization initiator or a thermal cationic polymerization initiator. The polymerization initiator can be used in an amount ranging from 0.01 to 50 parts by mass relative to 100 parts by mass of the polymerizable composition.

[0039] Furthermore, as optional components, various additives commonly used in conventional polymerizable compositions and composite materials, such as catalysts and pigments for curing acceleration, radical scavengers (quenchers), leveling agents, viscosity modifiers, antioxidants, ultraviolet absorbers, stabilizers, plasticizers, surfactants, and other additives used in the relevant technical fields, may also be mixed and used.

[0040] By selecting an appropriate organic resin material depending on the intended use, the composite material of the present invention can be used as a semiconductor device material, a copper-clad laminate, a flexible wiring material, a flexible display material, an antenna material, an optical wiring material, or a sensing material. [Example]

[0041] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0042] [Water-dispersed silica sol] The water-dispersed silica sols used in the examples and comparative examples are as follows: The properties of the silica particles in water-dispersed silica sols A to E are shown in Table 1. Water-dispersed silica sol A (Synthesis Example 1) Water-dispersed silica sol B (Synthesis Example 2) Water-dispersed silica sol C (Synthesis Example 3) Water-dispersed silica sol D (see Comparative Example 2) Water-dispersed silica sol E (see Comparative Example 3)

[0043] [Table 1]

[0044] According to the following methods, the physical properties of the water-dispersed silica sols A to E and the silica particles prepared in the examples and comparative examples were measured and evaluated.

[0045] [Silica concentration measurement] The silica concentration of the water-dispersed silica sol was calculated by placing the dispersion in a crucible, removing the solvent by heating, calcining at 1000°C for 30 minutes, and weighing the calcination residue. [pH measurement] The pH of the water-dispersed silica sol was measured using a pH meter (manufactured by DKK Toa Corporation, trade name: MM-43X). [Viscosity measurement] The viscosity of the water-dispersed silica sol was measured using an Ostwald viscometer (Shibata Scientific Co., Ltd., product name: Viscometer Measurements were taken at 25°C using an Ostwald method.

[0046] [Specific surface area by nitrogen adsorption method (S N2 ) Measurement The specific surface area (S N2 ) was measured by removing water-soluble cations in the water-dispersed silica sol with a cation exchange resin (Dow Chemical Company, trade name: Amberlite IR-120B), drying the silica sol at 290°C to prepare a measurement sample, and measuring the specific surface area using a nitrogen adsorption method specific surface area measuring device trade name: Monosorb (Quantachrome Instruments Japan, LLC). The specific surface area of ​​the silica particles obtained in the examples and comparative examples was measured using a specific surface area measuring device in the same manner as above, using a measurement sample prepared by drying the obtained silica particles at 290°C.

[0047] [Average primary particle size] The average primary particle diameter is calculated by the specific surface area S obtained by the nitrogen adsorption method described above. N2 (m 2 / g) was converted into spherical particles using the following formula: Average primary particle diameter (nm)=2720 / S N2 (m 2 / g)

[0048] [Measurement of M / Si molar ratio] 2.5 ml of nitric acid (manufactured by Kanto Chemical Co., Inc., trade name: nitric acid 1.38, purity 60.0%) and 2.5 ml of 38% hydrofluoric acid (manufactured by Tama Chemicals Co., Ltd., trade name: hydrofluoric acid) were added to 250 mg of silica particles to dissolve them, and the content of the polyvalent metal element M in the resulting aqueous solution was measured using an ICP-OES analyzer (manufactured by Rigaku Corporation, trade name: CIROS120 E0P). The content, M / Si molar ratio, of the polyvalent metal element M in the entire silica particles was determined by dividing the result by the content of Si.

[0049] [Measurement of carbon and hydrogen element content] The silica particles were stored in an electric furnace maintained at 150°C for 1 hour to remove adsorbed water from the particle surface, and then the carbon and hydrogen element contents of the obtained silica particles were measured using a CHN elemental analyzer (trade name: PerkinElmer 2400II, manufactured by PerkinElmer Co., Ltd.).

[0050] [Measurement of relative permittivity and dielectric loss tangent] Using a cavity resonator jig for measuring frequency 1 GHz (trade name: TMR-1A, manufactured by Keycom Corporation), silica particles (powder samples obtained in Examples 1 and 2, and Comparative Examples 1 to 5 described below) were filled into a PTFE sample tube (length 30 mm, inner diameter 3 mm) using a cavity resonator jig for measuring frequency 1 GHz (trade name: TMR-1A, manufactured by Keycom Corporation), and the relative permittivity and dielectric loss tangent of the silica particles were measured using a vector network analyzer (trade name: N5227A, manufactured by Keysight Technologies). Samples with a dielectric loss tangent of 0.002 or less were evaluated as OK, and samples with a dielectric loss tangent of more than 0.002 were evaluated as NG.

[0051] [Crystallinity measurement] The silica particles were measured by powder X-ray diffraction (product name: MiniFlex600, manufactured by Rigaku Corporation). When the obtained X-ray diffraction results showed no specific crystalline peaks, such as clear X-ray diffraction patterns derived from quartz, tridymite, or cristobalite, and only broad peaks (halo patterns) were observed, the crystallinity of the silica particles measured was determined to be "amorphous."

[0052] (Synthesis Example 1) Water-dispersed silica sol A Step (a): A JIS No. 3 aqueous sodium silicate solution was prepared as a raw material water-soluble alkali metal silicate. The SiO2 concentration, which was the main component other than water, of this sodium silicate solution was 28.8 mass % and the Na2O concentration was 9.47 mass %. The sodium silicate solution was diluted with pure water to prepare a sodium silicate aqueous solution (a) with an SiO2 concentration of 4 mass %. Next, the sodium silicate aqueous solution (a) was immersed in a hydrogen-type strongly acidic cation exchange resin (Da). An activated silicic acid solution was prepared by passing the solution through a column packed with Amberlite IR-120B (manufactured by Woo Chemical Co., Ltd.) at a space velocity of 4.5 per hour to remove cations. A 10% aqueous solution of sodium hydroxide was added to the resulting activated silicic acid solution to adjust the pH to 8.5-9.5, yielding a stabilized activated silicic acid solution. The SiO2 concentration of the resulting stabilized activated silicic acid solution was 3.2% by mass.

[0053] 2400 g of the stabilized activated silicic acid aqueous solution obtained above was placed in a 3 L stainless steel pressure vessel equipped with a stirrer and heater, and the temperature of the liquid in the vessel was adjusted to 130-150°C by heating. After the temperature in the vessel reached 130-150°C, the vessel was heated for 2 hours and 30 minutes while maintaining the temperature at 130-150°C, yielding a colloidal silica dispersion with an average primary particle size of 10-15 nm. The resulting colloidal silica dispersion was concentrated at room temperature using a commercially available ultrafiltration device equipped with a polysulfone ultrafiltration membrane (Advantec Co., Ltd., product name Q2000 150E) with a molecular weight cutoff of 200,000, to an SiO2 concentration of 33% by mass, yielding a precursor colloidal silica dispersion.

[0054] The precursor colloidal silica dispersion was passed through a column packed with a hydrogen-type strongly acidic cation exchange resin (trade name) Amberlite IR-120B at a space velocity of 10 per hour to remove cations, and a 10% by mass aqueous solution of sodium hydroxide was added to the resulting dispersion to adjust the pH to 7 to 8.

[0055] Step (b): The colloidal silica dispersion as a precursor with the pH adjusted obtained above was placed in a reactor equipped with a stirrer, a heater, etc., in a 3 L stainless steel pressure vessel, and the liquid temperature in the vessel was adjusted to 250-260°C by heating. After the temperature in the vessel reached 250°C, the vessel was heated for 9 hours while maintaining the temperature at 250-260°C, thereby obtaining water-dispersed silica sol A.

[0056] (Synthesis Example 2) Water-dispersed silica sol B The pH-adjusted colloidal silica dispersion as a precursor obtained in step (a) of Synthesis Example 1 was placed in a reactor equipped with a stirrer, a heater, etc., in a 3 L stainless steel pressure vessel, and the liquid temperature in the vessel was adjusted to 220 to 240° C. by heating. After the temperature in the vessel reached 220 to 240° C., the vessel was heated for 2 hours and 20 minutes while maintaining the temperature at 220 to 240° C., thereby obtaining water-dispersed silica sol B.

[0057] (Synthesis Example 3) Water-dispersed silica sol C A water-dispersed silica sol with an average primary particle diameter of 10 nm (Nissan Chemical Industries, Ltd., trade name: ST-OS, pH 3, silica concentration 20% by mass) was prepared. This water-dispersed silica sol was passed through an ultrafiltration membrane made of polysulfone with a molecular weight cutoff of 200,000 (Advantec Co., Ltd., trade name: Q2000 The sol was concentrated at room temperature using a commercially available ultrafiltration device equipped with a filter (150E) until the SiO2 concentration reached 31% by mass. A 10% by mass aqueous solution of sodium hydroxide was added to the concentrated water-dispersed silica sol to adjust the pH to 8-9, thereby obtaining water-dispersed silica sol C.

[0058] [Example 1] Step (i): 100 g of water-dispersed silica sol A was mixed with 30 g of cation exchange resin (Amberlite IR-120B, Organo Corporation), stirred for 30 minutes, and then the supernatant water-dispersed silica sol was collected by decantation. This mixture was then mixed with 30 g of anion exchange resin (Amberlite IRA400J, Dow Chemical Company), stirred for 30 minutes, and then the supernatant water-dispersed silica sol was collected by decantation. This mixture was then mixed with 30 g of cation exchange resin (Amberlite IR-120B, Organo Corporation), stirred for 30 minutes, and then filtered to obtain an acidic silica sol (pH 3-4, SiO2 concentration 21% by mass, viscosity 4.7 mPa s). Step (ii): The acidic silica sol obtained in step (i) was heated at 150°C for 1 hour to remove moisture, and the resulting silica gel was then pulverized in a mortar and heated at 1000°C for 1 hour to obtain silica particles A (average primary particle diameter 87 nm, hydrogen atom content 0.02% by mass). The XRD pattern of silica particles A obtained by powder X-ray diffraction is shown in Figure 1. Since the XRD pattern in Figure 1 was broad, it was determined that these silica particles A were amorphous.

[0059] [Example 2] The same operations as in steps (i) to (ii) of Example 1 were carried out, except that heating was performed at 700°C for 1 hour instead of 1000°C for 1 hour in step (ii) of Example 1, to obtain silica particles B (average primary particle diameter 77 nm).

[0060] [Example 3] The same operations as in steps (i) and (ii) of Example 1 were carried out, except that water-dispersed silica sol B was used instead of water-dispersed silica sol A in step (i) of Example 1, to obtain silica particles C (average primary particle size 47 nm, hydrogen atom content 0.01% by mass). The XRD pattern of silica particles C obtained by powder X-ray diffraction is shown in Figure 2. As can be seen from Figure 2, the XRD pattern of silica particles C was broad, and therefore it was determined that these silica particles C were amorphous.

[0061] [Comparative Example 1] The same operations as in steps (i) to (ii) of Example 1 were carried out, except that in step (ii) of Example 1, heating was performed at 500°C for 1 hour instead of 1000°C for 1 hour, to obtain silica particles D (average primary particle diameter 77 nm).

[0062] Comparative Example 2 The same operations as in steps (i) to (ii) of Example 1 were carried out, except that heating was performed at 600°C for 1 hour instead of 1000°C for 1 hour in step (ii) of Example 1, to obtain silica particles E (average primary particle diameter 76 nm).

[0063] Comparative Example 3 Silica particles F (average primary particle size: 15 nm, hydrogen atom content: 0.11 mass%) were obtained by performing the same operations as in steps (i) and (ii) of Example 1, except that water-dispersed silica sol C was used instead of water-dispersed silica sol A in step (i) of Example 1. The XRD pattern of silica particles F obtained by powder X-ray diffraction is shown in Figure 3. As can be seen from Figure 3, the XRD pattern of silica particles F was broad, and therefore it was determined that these silica particles F were amorphous.

[0064] Comparative Example 4 2500 g of water-dispersed silica sol B was added to a 3 L stainless steel autoclave reactor and subjected to hydrothermal treatment at 250 ± 20 °C for 2 to 3 hours to obtain water-dispersed silica sol D (average primary particle size 46 nm, pH 10.9, SiO2 concentration 30 mass%, viscosity 1.8 mPa·s). Thereafter, steps (i) and (ii) of Example 1 were repeated except that water-dispersed silica sol D was used instead of water-dispersed silica sol A in step (i) of Example 1, to obtain silica particles G (average primary particle size 52 nm, hydrogen atom content 0.03 mass%). The XRD pattern of silica particles G obtained by powder X-ray diffraction is shown in FIG. 4. As shown in FIG. 4, the XRD pattern of silica particles G was broad, and therefore it was determined that these silica particles G were amorphous.

[0065] Comparative Example 5 1000 g of water-dispersed silica sol C was mixed with 300 g of cation exchange resin (trade name Amberlite IR-120B, Organo Corporation), stirred for 30 minutes, and then filtered to obtain an acidic silica sol (pH 2.4, SiO2 mass concentration 31%, viscosity 2.3 mPa s). 1260 g of the acidic silica sol of the obtained water-dispersed silica sol C and 1300 g of water-dispersed silica sol D were added to a 3 L stainless steel autoclave reactor and subjected to hydrothermal treatment at 260 ± 20 °C for 2 to 3 hours to obtain water-dispersed silica sol E (pH 10.0, SiO2 concentration 30 mass%, average primary particle diameter 75 nm, viscosity 1.6 mPa·s). Thereafter, steps (i) and (ii) of Example 1 were repeated except that water-dispersed silica sol E was used instead of water-dispersed silica sol A in step (i) of Example 1, to obtain silica particles H (average primary particle size: 79 nm, hydrogen atom content: 0.02 mass%). The XRD pattern of silica particles H obtained by powder X-ray diffraction measurement is shown in FIG. 5. As shown in FIG. 5, the XRD pattern of silica particles H was broad, and therefore it was determined that silica particles H were amorphous.

[0066] [Physical properties of silica powder] The average primary particle size, crystalline structure, hydrogen element content, M / Si molar ratio, relative permittivity at 23°C and a frequency of 1 GHz, and dielectric loss tangent were measured for the silica powders obtained in Examples 1 to 3 and Comparative Examples 1 to 5. The physical properties of the silica particles are shown in Table 2.

[0067] [Test Example 1] A 20 mL glass bottle was charged with 0.05 g of silica particles A obtained in Example 1, 0.5 g of hexamethyldisilazane (Shin-Etsu Chemical Co., Ltd., product name: SZ-31), 0.05 g of pure water, and 4.5 g of methyl ethyl ketone, and the mixture was sonicated at 40 kHz for 10 minutes. The resulting mixture was filtered through a 0.5 μm nylon syringe filter to obtain a translucent, colloidal-colored methyl ethyl ketone dispersion of silica particles A obtained in Example 1. The resulting methyl ethyl ketone dispersion of silica particles A had an average primary particle diameter of 87 nm and an SiO2 concentration of 0.2 mass%, and exhibited good dispersibility with no sediment.

[0068] [Table 2]

[0069] As shown in Table 2, silica particles A to C of Examples 1 to 3 are silica particles having an average primary particle size of 5 nm to 120 nm, a carbon element content of less than 0.1 mass % as measured by CHN elemental analysis, a hydrogen content of 0.001 mass % to 0.1 mass %, and a polyvalent metal element M content of 0.00001 to 0.002 in terms of M / Si molar ratio. The dielectric loss tangent value at several 1 GHz was 0.002 or less, confirming that the silica particles exhibited excellent low dielectric properties.

[0070] The silica particles D and E of Comparative Examples 1 and 2 were silica particles having an average primary particle diameter of 5 nm to 120 nm and a content of polyvalent metal element M of 0.00001 to 0.002 in terms of M / Si molar ratio. However, when the heating temperature in step (ii) was 500°C or 600°C, the dielectric loss tangent was greater than 0.002, and the silica particles were inferior in low dielectric properties to the particles of the above Examples.

[0071] The silica particles F to H of Comparative Examples 3 to 5 had an average primary particle diameter of 5 nm to 120 nm, the heating temperature in step (ii) was 1000°C, and the carbon element content measured by CHN elemental analysis was less than 0.1 mass% and the hydrogen element content was 0.1 mass% or more. However, when the content of the polyvalent metal element M was 0.003 as the M / Si molar ratio, the dielectric loss tangent was greater than 0.002, and the silica particles were inferior in low dielectric properties compared to the particles of the above Examples.

[0072] The present invention reduces the dielectric loss tangent value of conventional silica particles to less than half, and is expected to be applicable to high frequency applications. [Industrial Applicability]

[0073] The present invention provides silica particles with a reduced dielectric loss tangent, which are expected to be applicable to high frequency applications.

Claims

1. Silica particles having a dielectric loss tangent of 0.002 or less at a frequency of 1 GHz, which satisfy the following items (i), (ii), and (iii): (i) the average primary particle size is 5 nm to 120 nm; (ii) the content of the polyvalent metal element M is 0.00001 to 0.002 in terms of the M / Si molar ratio; (iii) It is amorphous.

2. The silica particles according to claim 1, further satisfying the requirement (iv): (iv) The carbon element content measured by CHN elemental analysis is less than 0.1% by mass, and the hydrogen element content measured by CHN elemental analysis is 0.001% by mass to 0.1% by mass.

3. The silica particles according to claim 1, further satisfying the requirement (V): (V) The carbon element content measured by CHN elemental analysis is 0.1% by mass or more, and the hydrogen element content measured by CHN elemental analysis is 0.01% by mass to 10% by mass.

4. A silica powder comprising the silica particles according to any one of claims 1 to 3.

5. A mixed liquid comprising the silica particles according to any one of claims 1 to 3 and water or an organic solvent.

6. A composite material comprising the silica particles according to any one of claims 1 to 3 and a polysiloxane resin or an organic resin material.

7. 7. The composite material according to claim 6, wherein the organic resin material is at least one selected from the group consisting of a styrene resin, an epoxy resin, a cyanate resin, a phenolic resin, an acrylic resin, a maleimide resin, a urethane resin, a polyurethane, a polyimide, a polytetrafluoroethylene, a cycloolefin polymer, an unsaturated polyester, a vinyl triazine, a polyphenylene sulfide, a crosslinkable polyphenylene oxide, and a curable polyphenylene ether.

8. 7. The composite material according to claim 6, having an application selected from the group consisting of semiconductor device materials, copper clad laminates, flexible wiring materials, flexible display materials, antenna materials, optical wiring materials, and sensing materials.

9. The following steps (i) and (ii): Step (i): preparing amorphous silica particles having an average primary particle size of 5 nm to 120 nm, a content of a polyvalent metal element M in terms of M / Si molar ratio of 0.00001 to 0.002; (ii) step: firing at 700°C to 1200°C; The method for producing silica particles according to claim 1 , comprising:

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