Spherical silica particles, slurry composition, resin composition, and method for producing spherical silica particles

Abstract

The present invention provides a novel method for producing spherical silica particles having fine voids. The following invention is based on the insight that spherical silica particles having fine voids can be produced using an aqueous alkaline silicate solution as a raw material. That is, the spherical silica particles of the present invention have an average particle diameter of 0.1 to 10.0 μm, a true specific gravity of 0.9 to 1.9 g / cm 3 , a pore volume of 0.1 mL / g or less, a Na content of 10 ppm or less, a true specific gravity retention rate of 80% or more before and after pressurization at 300 MPa for 1 minute, a particle ratio of particles for which the maximum length-diameter of the internal voids is more than half the length-diameter of the particle is 60% or less, and a silica content of more than 50%.

Description

TECHNICAL FIELD

[0001] The present application relates to a spherical silica particle and a method for producing the same, and more particularly to a hollow spherical silica particle having a void inside and a method for producing the same. BACKGROUND

[0002] As a method for producing hollow silica, a wet template method is known. This includes a method in which inorganic particles other than silica are coated with silica on a template and the inside is dissolved or heat-decomposed (Patent Documents 1 and 2); a method in which a hydrophobic organic solvent is emulsified in a hydrophilic solvent, and silica synthesis is performed in the resulting solution (Patent Documents 3 and 4).

[0003] As another method for producing hollow silica, a method in which hollow silica is produced by melting porous silica is included (Patent Document 5).

[0004] In addition, a method in which hollow silica is produced by a spray drying, spray decomposition method is known (Patent Documents 6 and 7).

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2012-140286

[0008] Patent Document 2: International Publication No. WO 2022 / 014130

[0009] Patent Document 3: Japanese Patent Application Laid-Open (JP-A) No. 2014-55082

[0010] Patent Document 4: International Publication No. WO 2019 / 131658

[0011] Patent Document 5: Japanese Patent Application Laid-Open (JP-A) No. 2010-260755

[0012] Patent Document 6: Japanese Patent No. 7008004

[0013] Patent Document 7: Japanese Patent Application Laid-Open (JP-A) No. 2020-83736 SUMMARY

[0014] However, in the methods disclosed in Patent Documents 1 to 4, a structure in which a large void is formed inside the particle is formed, and when the hollow rate is increased, the particle strength easily decreases, and when used as a filler for electronic materials, a large internal void is exposed during via processing, and there are problems in terms of plating reliability and the like.

[0015] Further, in the method disclosed in Patent Literature 5, since the operation of melting porous silica is performed, it is difficult to obtain particles having a particle diameter of 3 μm or less. Similarly, in the methods disclosed in Patent Literatures 6 and 7 which utilize spray drying or the like, it is also difficult to produce particles having a particle diameter of 5 μm or less.

[0016] The present application has been achieved in view of the above-described actual circumstances, and an object thereof is to provide a novel spherical silica particle and a production method thereof.

[0017] The present inventors and others have conducted intensive studies in order to solve the above-described problem, and as a result, have found that spherical silica particles having fine voids inside can be produced using an aqueous alkali silicate solution (hereinafter "aqueous alkali silicate solution") as a raw material, and have completed the following application based on this insight.

[0018] That is, the spherical silica particle of the present application has silica as a main component, an average particle diameter of 0.1 to 10.0 μm, a true specific gravity of 0.9 to 1.9 g / cm3 as measured by nitrogen gas, a fine pore volume of 0.1 mL / g or less, a Na content of 10 ppm or less, a true specific gravity retention rate of 80% or more before and after pressurization at 300 MPa for 1 minute as measured by nitrogen gas, and a particle existence ratio of 60% or less for particles in which the maximum value of the length diameter of the internal voids is more than half the length diameter of the particle. 3

[0019] Further, the production method of the spherical silica particle of the present application which solves the above-described problem has the following steps:

[0020] A raw material silica particle preparation step in which a dispersion liquid of raw material silica particles is prepared from a raw material solution in which silicic acid is dissolved, in a mixed solvent of water and an organic solvent, in the presence of an alkali substance composed of at least one of a quaternary ammonium and a base having a cyclic amidine structure;

[0021] A hydrothermal treatment step in which the dispersion medium in which the raw material silica particles are dispersed in the above-described dispersion liquid is replaced with water, and then pressurized and heated to 130°C to 250°C to produce a dispersion liquid of raw material silica particles after hydrothermal treatment;

[0022] A heating step in which the above-described dispersion liquid or the above-described raw material silica particles obtained by solid-liquid separation from the above-described dispersion liquid is heated to remove the organic substance contained in the above-described dispersion liquid, and spherical silica particles are prepared,

[0023] The relative dielectric constant of the above-described mixed solvent is 21 to 40,

[0024] The quaternary ammonium from the above-described alkali substance is compounded at a compounding ratio of 0.3 to 0.8 in terms of molar ratio with respect to the silicon element from the above-described silicic acid. ​

[0025] The spherical silica particles of the present application are particles having voids that are finer than those of conventional spherical silica particles having voids inside. With conventional spherical silica particles having large voids inside the particles, the shell is easily broken by external force, but the spherical silica particles of the present application have voids that are finer than those of the conventional particles, so even if the same external force is applied, it is difficult for them to be broken. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a histogram showing the particle size distribution of the test sample of Test Examples 4, 5, 9, and 11 in the Examples.

[0027] Figure 2 is an SEM photograph of the test sample of Test Example 3 in the Examples.

[0028] Figure 3 is an SEM photograph of the test sample of Test Example 4 in the Examples.

[0029] Figure 4 is an SEM photograph of the test sample of Test Example 5 in the Examples.

[0030] Figure 5 is an SEM photograph of the test sample of Test Example 6 in the Examples.

[0031] Figure 6 is an SEM photograph of the test sample of Test Example 7 in the Examples.

[0032] Figure 7 is an SEM photograph of the test sample of Test Example 9 in the Examples.

[0033] Figure 8 is an SEM photograph of the test sample of Test Example 11 in the Examples.

[0034] Figure 9 is an SEM photograph of the test sample of Test Example 13 in the Examples.

[0035] Figure 10 is an SEM photograph of the test sample of Test Example 16 in the Examples.

[0036] Figure 11 is an SEM photograph of the test sample of Test Example 17 in the Examples.

[0037] Figure 12 is an SEM photograph of the test sample of Test Example 18 in the Examples.

[0038] Figure 13 is an SEM photograph of the test sample of Test Example 19 in the Examples.

[0039] Figure 14is a cross-sectional TEM photograph of a test sample of Test Example 17 in the Examples.

[0040] Figure 15 is a cross-sectional SEM photograph of a test sample of Test Example 11 in the Examples.

[0041] Figure 16 is a cross-sectional SEM photograph of a test sample of Test Example 17 in the Examples.

[0042] Figure 17 is a cross-sectional SEM photograph of a test sample of Test Example 22 in the Examples.

[0043] Figure 18 is a cross-sectional SEM photograph of a test sample of Test Example 23 in the Examples. DETAILED DESCRIPTION

[0044] The spherical silica particles of the present application and the method for producing the same will be described in detail according to the following embodiments.

[0045] (Spherical silica particles)

[0046] The spherical silica particles of the present embodiment are particles having a high degree of sphericity with a void inside. The spherical silica particles have silica as a main component, and specifically, 50% or more of the entire mass is composed of silica, and as a lower limit value of the silica composition ratio, 60%, 70%, 80%, 90%, 95%, 99% can be given, and it is particularly preferable that the silica is 100% and does not contain impurities other than inevitable impurities. In the case where a substance other than silica is contained, the inside of the spherical silica particles of the present embodiment can contain it in a particulate form, and in addition, it can be contained in a dispersed form at an atomic level within the spherical silica particles.

[0047] The particle diameter of the spherical silica particles is 0.1 to 10 μm, and specifically, as an upper limit value, 7 μm, 5 μm, 3 μm, 2 μm can be used. The degree of sphericity of the spherical silica particles is not particularly limited, and can be preferably 0.9 or more, and further preferably 0.95 or more.

[0048] The spherical silica particles of the present embodiment are so-called hollow particles. Here, the spherical silica particles are hollow means that the density of the particles is 1.9 g / cm 3 Hereinafter, it is particularly preferable that the density is 1.7 g / cm 3 Hereinafter, it is further preferable that the density is 1.6 g / cm 3 Hereinafter. As a lower limit value of the density, 0.9 g / cm 3 , preferably 1.1 g / cm 3 , 1.2 g / cm 3 can be given.

[0049] In the measurement of the density of the particles, the volume of the particles is measured by the constant-volume expansion method using nitrogen gas. The volume of the voids into which nitrogen gas cannot intrude can be measured, and the spherical silica particles having such voids and having a density within the above range are used as the hollow particles. The voids present inside the particles can be one or a plurality of voids.

[0050] In the spherical silica particles of the present embodiment, the existence ratio of the particles in which the maximum value of the length diameter of the internal voids is more than half the length diameter of the particle is 60% or less. The length diameter of the internal voids and the length diameter of the particle are values measured on a cross section obtained by cutting the spherical silica particles in a state in which the spherical silica particles are embedded in a resin.

[0051] That is, the length diameter of the cross section of the particle is taken as the length diameter A of the particle, and when one or more of the length diameters B of the cross section of the internal voids present on the cross section is more than half the length diameter A, it is determined that the particle in which the maximum value of the length diameter of the internal voids is more than half the length diameter of the particle is present. Even if a plurality of internal voids having a length diameter B of more than half the length diameter A is found in one spherical silica particle, the particle in which the maximum value of the length diameter of the internal voids is more than half the length diameter of the particle is one.

[0052] Ten (100 can also be used) of the particles measured are randomly selected. From the number of the particles in which the particle in which the maximum value of the length diameter of the internal voids is more than half the length diameter of the particle is present, the existence ratio can be calculated.

[0053] The inside of the spherical silica particle is preferably a so-called porous structure in which a plurality of fine voids are formed. It is particularly preferable to have fine voids. In the case where the inside of the particle is porous, it is preferable that the structure closer to the surface is denser and the pores present near the center are relatively large in size.

[0054] For example, in the spherical silica particles of the present embodiment, the average void ratio of the central region on the cross section of the particle is 5% to 90%, and the average void ratio of the region other than this, that is, the shell region, is preferably 2% to 80% or less than the average void ratio of the central region.

[0055] As a preferable lower limit value of the average void ratio of the central region, for example, 10%, 20%, or 30% is used, and as a preferable upper limit value, for example, 80%, 70%, or 50% is used. These upper and lower limit values can be combined arbitrarily.

[0056] As a preferable lower limit value of the average void ratio of the outer region, for example, 3%, 4%, or 5% is used, and as a preferable upper limit value, for example, 80%, 70%, or 60% is used. These upper and lower limit values can be combined arbitrarily.

[0057] For the evaluation of the center region and the shell region, in a state where the spherical silica particles of the present embodiment are embedded in a resin, FIB processing was performed using FIB / SEM at a step of 10 nm to 20 nm, and the obtained multiple cross sections were compared, using the image of the largest area cross section (evaluation cross section image). Here, the center region refers to the region of a circle of a size of half the radius of the particle from the center of the particle in the evaluation cross section image. The shell region is the region after the center region is removed from the particle. The calculation of the average void ratio was performed by image processing software (for example, A image kun: manufactured by Asahi Kasei Engineering) using the color difference of the void portion. This calculation was performed on 10 randomly selected particles, and the average value was calculated.

[0058] It is preferable that these voids not communicate with the outside. In particular, the volume of the fine pores that communicate with the outside is 0.1 mL / g or less, preferably 0.08 mL / g or less, and more preferably 0.07 mL / g or less. Here, the volume of the fine pores is measured by the BJH method using nitrogen gas, and the volume of the fine pores having a diameter of 250 nm or less is measured. Here, the voids that do not communicate with the outside are determined based on whether or not the voids are accessible to nitrogen gas.

[0059] In the spherical silica particles of the present embodiment, the walls of the voids present in the interior are difficult to be broken by pressure. Specifically, the values of the true specific gravity retention rate and the dielectric loss tangent retention rate before and after the application of a pressure of 300 MPa for 1 minute are maintained within a certain range.

[0060] The true specific gravity retention rate is a value indicating the proportion of the value of the true specific gravity that is maintained before pressure when the voids are not broken by pressure. If the hollow structure is broken by pressure to make the voids present in the interior communicate with the outside, the true specific gravity becomes larger because the volume of the particle decreases only by the volume of the voids. Therefore, the phrase "the true specific gravity after pressure becomes larger" means that the hollow structure is broken by pressure. The true specific gravity retention rate is calculated from the true specific gravity measured using nitrogen gas and the true specific gravity measured using helium gas by the following equation. (True specific gravity retention rate) = {(true specific gravity measured using helium gas) - (true specific gravity measured using nitrogen gas after pressure test)} / {(true specific gravity measured using helium gas) - (true specific gravity measured using nitrogen gas before pressure test)} x 100 (%)

[0061] Specifically, the true specific gravity retention rate of 100% means that the value of the true specific gravity does not change before and after pressure, and the voids are not broken by pressure. The true specific gravity retention rate of 0% means that the value of the true specific gravity after pressure is the same as the value of the true specific gravity measured using helium gas, and all of the voids accessible to helium gas are broken by pressure. The true specific gravity retention rate is 80% or more, preferably 85% or more, and more preferably 90% or more, with respect to the value before pressure.

[0062] The value of the true specific gravity after pressurization can be calculated according to a weighted average in which the value of the true specific gravity before pressurization and the value of the true specific gravity determined using helium are taken into account. For example, (true specific gravity after pressurization) = {(true specific gravity maintenance rate) x (true specific gravity before pressurization) + (100 - (true specific gravity maintenance rate)) x (true specific gravity determined using helium)} ÷ 100.

[0063] The dielectric loss tangent maintenance rate is calculated according to the values of the dielectric loss tangent before and after pressurization by the following equation. (Dielectric loss tangent maintenance rate) = (dielectric loss tangent after pressurization) / (dielectric loss tangent before pressurization) x 100 (%). The dielectric loss tangent maintenance rate is preferably 500% or less, more preferably 400% or less, and further preferably 300% or less. If the hollow structure of the particles is destroyed, the surface of the voids within the particles is exposed, and thus the dielectric loss tangent becomes large. Therefore, a large dielectric loss tangent maintenance rate means that the destruction of the hollow structure is proceeding.

[0064] The D90 / D10 of the spherical silica particles of the present embodiment is preferably 2.0 to 20.0. In particular, the upper limit value is preferably 18.0, 15.0, 13.0, and the lower limit value is preferably 2.2, 2.4, 2.6. These upper and lower limit values can be combined arbitrarily. Note that D10 is the particle diameter of the particles at the position of 10% in the small particle diameter on a volume basis, and D90 is the particle diameter of the particles at the position of 90% in the small particle diameter on a volume basis.

[0065] Further, in the spherical silica particles of the present embodiment, the true specific gravity determined using helium is preferably 2.2 g / cm 3 Further, 2.25 g / cm 3 or more. Helium can also invade the voids present inside the particles, and thus the specific gravity of the particles without voids can be determined. Here, the specific gravity of silica is 2.3 g / cm 3 It can be inferred that the closer the value is to this value, the less the content of impurities other than silica.

[0066] The spherical silica particles of the present embodiment can be subjected to surface treatment in which an organic functional group is introduced. As the organic functional group to be introduced, there are no particular limitations, and examples that can be given include an anilino group, an amino group, a vinyl group, an epoxy group, a phenyl group, an acryl group, a methacryl group, an alkyl group, and an organic functional group having these organic functional groups at the terminal. As a method of introducing these organic functional groups, surface treatment can be performed using a surface treatment agent having these organic functional groups in the molecular structure. As the surface treatment agent, examples that can be given include a silane compound, a titanium compound, and the like. As the amount of these organic functional groups to be introduced, an appropriate amount can be selected as needed, for example, an amount of 10% to 100% or so based on the total amount of the number of organic functional groups introduced on the surface of the spherical silica particles and the number of OH groups present on the surface, and further, as a lower limit value, 30%, 50%, 60%, or the like can be used, and as an upper limit value, 90% or the like can be used.

[0067] (Slurry composition)

[0068] The slurry composition of the present embodiment has the spherical silica particles of the present embodiment described above and a dispersion medium in which the spherical silica particles are dispersed. As the spherical silica particles, the spherical silica particles described above can be used. The dispersion medium is a liquid, an organic substance, water, or the like. As the organic substance, in addition to general organic solvents, a monomer before curing can be given. It can also be dissolved with a certain solute. The mixing ratio of the spherical silica particles to the dispersion medium is not particularly limited, and the slurry composition can contain 20% or more of the spherical silica particles, and further, 40% or more, 60% or more. Furthermore, other components can also be contained as needed. For example, a dispersant or the like.

[0069] (Resin composition)

[0070] The resin composition of the present embodiment has the spherical silica particles of the present embodiment described above and a resin material in which the spherical silica particles are dispersed. As the spherical silica particles, the spherical silica particles described above can be used. The resin material can be a solid after curing, or a liquid before curing. As the resin material after curing, either one of a thermosetting resin or a thermoplastic resin can be used. As a specific resin material, there are no particular limitations, and examples that can be given include an epoxy resin, a phenol resin, a polyimide resin, a fluororesin, a polyphenylene ether resin, and a monomer or a precursor before curing thereof. The mixing ratio of the spherical silica particles to the resin material is not particularly limited, and the resin composition can contain 20% or more of the spherical silica particles, and further, 40% or more, 60% or more. Furthermore, other components can also be contained as needed. For example, a dispersant or the like. Note that when the resin material is a liquid such as a precursor, the resin composition of the present embodiment can be regarded as the slurry composition described above.

[0071] (Method for manufacturing spherical silica particles)

[0072] The method for producing the spherical silica particles of the present embodiment has a raw material silica particle preparation step, a hydrothermal treatment step, a heating step, and other steps as needed.

[0073] (Raw material silica particle preparation step)

[0074] The raw material silica particle preparation step is a step of forming a dispersion liquid by precipitating raw material silica particles, which are the basis of the spherical silica particles, from silicic acid contained in a raw material solution in the presence of an alkaline substance in a mixed solvent of water and an organic solvent. The precipitated raw material silica particles are roughly the same as the produced spherical silica particles, but the content of moisture and organic matter and the like is increased.

[0075] The precipitation of the raw material silica particles is preferably performed while stirring. The temperature at the time of precipitation is not particularly limited, and, for example, 0°C is set as a lower limit value, and, for example, 40°C, 50°C, or 60°C is set as an upper limit value.

[0076] The concentration of silicic acid in the raw material solution is not particularly limited, and, for example, 1%, 2%, 3%, or 5% is set as a lower limit value in terms of the mass of the whole, and, for example, 8%, 10%, 15%, or 17% is set as an upper limit value in terms of the mass of the whole. In order to achieve the desired concentration, dilution can be performed using water, an organic solvent, or a mixed solvent of water and an organic solvent. Here, the conversion into an oxide (SiO2: silica) refers to a value calculated on the assumption that all of the contained silicon elements are contained in the form of an oxide. Other metal compounds other than silicic acid can be contained in the raw material solution. As the other metal compounds that can be contained, water-soluble compounds and metal oxides having a particle diameter of 100 nm or less (particularly, metal oxides having a particle diameter of 50 nm or less, 30 nm or less, or 10 nm or less) can be contained. The other metal oxides can be added at the time of precipitation of silicic acid and formation of particles, and a composite oxide or the like can be formed.

[0077] In addition, the precipitation of the raw material silica particles is preferably performed in a state adjusted to a prescribed pH. Adjustment to the prescribed pH is preferably performed by adding an alkaline substance or adding an organic acid such as acetic acid. As the prescribed pH, for example, 7.0, 7.5, or 7.8 is set as a lower limit value, and, for example, 10.0, 9.5, 9.0, 8.5, or 8.2 is set as an upper limit value.

[0078] The relative dielectric constant of the mixed solvent is 21 to 40. As the upper limit value of the relative dielectric constant, 38, 35, 33 can be used, and as the lower limit value, 21.5, 23, 25 can be used. These upper and lower limit values can be combined arbitrarily. The relative dielectric constant of the mixed solvent here refers to the relative dielectric constant calculated as a mixed solvent composed only of water and the organic solvent contained. Specifically, it is calculated as a weighted average of the relative dielectric constant of water and the relative dielectric constant of the mixed organic solvent in the volume ratio.

[0079] As the organic solvent, an organic solvent that can be mixed with water and reaches the above-mentioned range of relative dielectric constant after mixing can be used. As the preferred organic solvent, ketones, esters, alcohols can be used, and specifically, acetone, methyl ethyl ketone, ethyl acetate, etc. can be used alone or as a mixture, and further, acetone is preferably used. The mixing ratio of the organic solvent to water is set to be within the above-mentioned range of relative dielectric constant when used as a mixed solvent.

[0080] The basic substance can be composed of at least one of quaternary ammonium and a base having a cyclic amidine structure. They are not particularly limited, and the quaternary ammonium is preferably selected from quaternary ammonium having a carbon atom number of 4 to 16, and specifically, tetramethylammonium having a carbon atom number of 4, tetraethylammonium having a carbon atom number of 8, and tetrabutylammonium having a carbon atom number of 16 can be used. The quaternary ammonium generally has some anion as a counter ion. For example, tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrabutylammonium hydroxide (TBAOH) having a hydroxide ion, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride having a chloride ion can be used. The base having a cyclic amidine structure can be diazabicycloundecene (DBU), diazabicycloundecene (DBN).

[0081] The basic substance contains the silicon element from silicic acid in a ratio of 0.3 to 0.8, and the lower limit value can be 0.35, 0.4, and the upper limit value can be 0.75, 0.7, 0.6. These upper and lower limit values can be combined arbitrarily. By making the addition amount of the basic substance be the lower limit value or more, the particle diameter of the raw material silica particles produced becomes large and does not form agglomerates, or the density of silica in the raw material silica particles produced becomes high. By making the addition amount be the upper limit value or less, oligomerization can be prevented, and the particle can be efficiently performed. If the density of silica becomes low, shrinkage occurs by heating in the heating process described later, or the spherical silica particles obtained have a tendency to have a large void ratio when they are porous particles or hollow particles.

[0082] The basic substance can be added to the mixed solvent before the silicic acid or after the silicic acid. Furthermore, it can also be added in several times instead of all at once.

[0083] The concentration of the raw material solution of silicic acid is not particularly limited, and the upper limit is preferably 0.1%, 0.2%, 0.3%, 0.4%, and the lower limit is preferably 1.0%, 1.5%, 2.0%, 3.0% in terms of oxide conversion based on the mass of the raw material solution. The silicic acid is preferably supplied as an aqueous alkaline silicic acid solution obtained by one of the following a) to c). In these a) to c), it is preferable to perform while stirring. An appropriate amount of an organic solvent and an alkaline substance is added to the aqueous alkaline silicic acid solution obtained by the following process to prepare the raw material solution.

[0084] a) Heating and pressurization of silicon dioxide in an aqueous alkaline substance solution.

[0085] The silicon dioxide can be a substance synthesized from metallic silicon, a substance synthesized from a silicon compound, a natural product, or the like. In particular, a substance synthesized from metallic silicon is preferable because it is easy to obtain high-purity metallic silicon as a raw material. For example, a powder particle composed of silicon dioxide obtained by a method in which metallic silicon powder is burned (so-called VMC method) can be used. Here, by using a powder particle as the silicon dioxide, the specific surface area can be increased, and the dissolution rate in the aqueous alkaline substance solution can be improved.

[0086] The alkaline substance contained in the aqueous alkaline substance solution in which the silicon dioxide is dissolved can be directly used as the above-described alkaline substance, or an alkaline substance other than the above-described alkaline substance (another alkaline substance) can be used. In the case where another alkaline substance is used, the other alkaline substance used is preferably removed by washing or ion exchange after the silicon dioxide is dissolved.

[0087] As a method of dissolving the silicon dioxide in the aqueous alkaline substance solution, the boiling point of the aqueous alkaline substance solution can be increased by pressurization, and the temperature can be maintained at a temperature higher than the boiling point at normal pressure. For example, a condition in which the aqueous alkaline substance solution is heated at 180°C while being pressurized can be used. As the temperature of the dissolution, the dissolution rate is improved by increasing the temperature, and the pressure can be reduced by decreasing the temperature, and thus the dissolution apparatus can be simplified.

[0088] The dissolved silicon dioxide is preferably 17%, 15%, 10% or less in terms of the entire mass, and is preferably 1%, 3%, 5% or more. These upper and lower limits can be combined arbitrarily. The concentration of the alkaline substance in the aqueous alkaline substance solution is not particularly limited, and it is preferable to reach an appropriate concentration of the alkaline substance at the time of finally preparing the raw material solution.

[0089] b) Removal of Na ions from an aqueous sodium silicate solution in the presence of an alkaline substance.

[0090] Sodium silicate aqueous solution can be obtained by dissolving sodium silicate in water or by using water glass. Alkaline substances can be used. Sodium ions are removed from the sodium silicate aqueous solution in the presence of an alkaline substance, replacing the sodium in the sodium silicate with the alkaline substance. Sodium ion removal can be performed using ion exchange resins, etc.

[0091] The dissolved sodium silicate, calculated based on the total mass of oxides, preferably has an upper limit of 17%, 15%, or 10%, and a lower limit of 1%, 3%, or 5%. These upper and lower limits can be combined arbitrarily. The concentration of the alkaline substance in the aqueous solution is not particularly limited, but it is preferable to achieve an appropriate concentration of alkaline substance when finally preparing the raw material solution.

[0092] c) Dissolution of metallic silicon in an aqueous solution containing an alkaline substance and / or a second alkaline substance.

[0093] Metallic silicon is impregnated and dissolved in an aqueous solution containing the aforementioned alkaline substance and / or a second alkaline substance, thereby generating silicic acid. The metallic silicon is preferably in powder or granular form. Heating is preferred as a dissolution condition. The heating temperature is not particularly limited, but 30°C, 40°C, 50°C, 60°C, etc., can be used as a lower limit.

[0094] The dissolved metallic silicon, calculated based on the total mass of oxides, preferably has an upper limit of 17%, 15%, or 10% and a lower limit of 1%, 3%, or 5%. These upper and lower limits can be combined arbitrarily.

[0095] The alkaline substance remains the same as described above. The second alkaline substance is not particularly limited, but is preferably composed of an organic compound. Examples of the second alkaline substance include dialkylamines (e.g., compounds with 1 to 3 carbon atoms) and trialkylamines (e.g., compounds with 1 to 3 carbon atoms).

[0096] The total concentration of the alkaline substance and the second alkaline substance in the aqueous solution containing the alkaline substance and / or the second alkaline substance is not particularly limited. When an alkaline substance is added, it is preferably at a concentration below the amount of the appropriate alkaline substance present in the final preparation of the raw material solution.

[0097] (Hydrothermal treatment process)

[0098] The hydrothermal treatment process involves replacing the dispersion medium of the dispersion obtained from the raw material silica particle preparation process with water and then heating it to carry out a hydrothermal reaction. The hydrothermal reaction is preferably carried out at a temperature of 130°C to 250°C. Specifically, the lower limit of the temperature is preferably 100°C, 110°C, or 120°C, and the upper limit is preferably 220°C, 200°C, or 180°C. These upper and lower limits can be combined arbitrarily.

[0099] By performing the hydrothermal reaction, voids are formed inside the finally manufactured spherical silica particles. That is, by the hydrothermal process, the reaction in which the portion of the particle interior having a low density of silanol bonds is dissolved by the alkaline substance and the reaction in which the particle shell is densified by heat are balanced, and thus it can be inferred that the balance of these two reactions enables the voids generated inside to be controlled.

[0100] (heating step)

[0101] The heating step is a step in which the raw silica particles contained in the dispersion liquid obtained by the hydrothermal treatment step are heated to form spherical silica particles. This is a step in which the moisture and organic substances contained in the raw silica particles are removed by heating.

[0102] In the heating step, the dispersion medium is replaced with another dispersion medium while the dispersion liquid is in a state in which it is directly in the state of the dispersion liquid, and / or the raw silica particles are solid-liquid separated from the dispersion liquid and heated. The raw silica particles can be separated from the dispersion medium by centrifugation or filtration. After the raw silica particles are separated, an operation of adding water, an organic solvent, or another dispersion medium is performed, and thus the dispersion medium can be replaced. By performing the replacement of the dispersion medium multiple times, the organic substances contained in the dispersion liquid can be reliably removed.

[0103] In the heating step, by heating at a high temperature, the moisture and organic substances contained in the raw silica particles can be removed. First, the moisture and organic solvent are preferably removed at a temperature at which the moisture is not sharply removed. For example, 40°C, 60°C, 80°C, 100°C, 120°C, 140°C, or the like. The heating can be performed while being depressurized or air-dried. If a certain degree of moisture can be removed, the moisture does not sharply expand even if the heating is performed at a high temperature, and thus the heating is performed to a temperature at which the organic substances can be removed. As the temperature at which the organic substances can be removed, a temperature of 500°C or higher is preferable. In particular, by performing the heating in an oxidative atmosphere such as air, the organic substances can be oxidized and removed, and thus this is preferable. As a lower limit value of the heating temperature, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or the like can be used, and as an upper limit value, 1150°C, 1100°C, 1050°C, or the like can be used. It can be considered that by heating the raw silica particles in a state in which they are separated from the dispersion medium, the particles are densified by shrinking as the moisture is removed. In particular, by heating to 900°C or higher, hollow particles and porous particles can be stabilized.

[0104] (other steps)

[0105] The method of manufacturing the spherical silica particles of the present embodiment can crush the obtained spherical particles or perform a surface treatment. The crushing can be performed by a method similar to a general pulverization operation. In particular, a jet mill or the like is preferable.

[0106] The spherical silica particles produced by the production method of the spherical silica particles of the present embodiment can be surface-treated with a surface treatment agent such as a silane compound. The surface treatment differs depending on the use form of the spherical silica particles, and the appropriate surface treatment also differs. In the case where the spherical silica particles are filled in a resin, a surface treatment agent capable of introducing a functional group having high affinity with the resin or reactivity is preferably used.

[0107] Example

[0108] The production method of the spherical silica particles of the present invention will be described in detail below according to an example.

[0109] Preparation of Test Samples

[0110] Test samples of each of the test examples were prepared according to the conditions shown in Table 1. Details will be described below.

[0111] Test Example 1

[0112] (Preparation Process of Raw Material Silica Particles)

[0113] First, an alkaline silicic acid aqueous solution was prepared. Metal silicon powder (volume average particle diameter 20 μm) 9.0 g, ion-exchanged water 27.0 g, and 25 mass% TMAH aqueous solution 64.0 g were mixed, and the metal silicon was dissolved by keeping at 40°C for 48 hours to obtain an alkaline silicic acid aqueous solution containing about 26.3% of silicic acid in terms of silica.

[0114] Ion-exchanged water was added to the obtained alkaline silicic acid aqueous solution to achieve a silicic acid concentration of 4.5 mass% in terms of silica. TMAH was added as a basic substance so that the total amount of the contained silicon element from the silicic acid was 0.44 in terms of molar ratio. Then, acetone was added as an organic solvent so that the amount of the contained water was 30.6 when mixed. Specifically, the ratio of water:acetone was 20:80 in terms of mass ratio before mixing.

[0115] After sufficient stirring, 90 mass% acetic acid aqueous solution was added to adjust the pH to 8, and further stirring was performed for 30 minutes, whereby the raw material silica particles were precipitated as a dispersion liquid.

[0116] (Heating Process)

[0117] The obtained dispersion liquid was centrifuged at 5000 rpm for 5 minutes, and the supernatant was removed by decantation to separate the precipitate. The centrifugation was performed using Model 3700 manufactured by KUBOTA. The same amount of ion exchange water as the removed supernatant was added, and ultrasonic dispersion was performed. The ultrasonic wave was applied at a frequency of 28 kHz and a power of 1000 W for 30 minutes. The obtained dispersion liquid was again centrifuged under the above conditions, and the obtained precipitate was dried at 130°C for 1 hour and then fired at 500°C for 2 hours. The obtained fired product was crushed to a state where no agglomerates were observed visually using a mortar, and the obtained spherical silica particles were used as the test sample of the present test example. Note that in Test Example 1, the dispersion liquid obtained in the raw silica particle preparation step was directly subjected to the heating step without the hydrothermal treatment step.

[0118] • Test Examples 2 and 3

[0119] The same operations as in Test Example 1 were performed except that the firing temperature was set to 800°C (Test Example 2) and 1000°C (Test Example 3), whereby the test samples of the present test examples were obtained.

[0120] • Test Example 4

[0121] The same operations as in Test Example 3 were performed except that the hydrothermal treatment step was performed with respect to the dispersion liquid obtained in the raw silica particle preparation step, whereby the test sample of the present test example was obtained.

[0122] The hydrothermal treatment step was performed as follows. The dispersion liquid obtained in the raw silica particle preparation step was centrifuged at 5000 rpm for 5 minutes, and the supernatant was removed by decantation to separate the precipitate. The centrifugation was performed using Model 3700 manufactured by KUBOTA. The same amount of ion exchange water as the removed supernatant was added, and ultrasonic dispersion was performed. The ultrasonic wave was applied at a frequency of 28 kHz and a power of 1000 W for 30 minutes. The obtained dispersion liquid was subjected to a hydrothermal reaction at 175°C for 2 hours after being charged into a pressure vessel.

[0123] • Test Example 5

[0124] The same operations as in Test Example 4 were performed except that the amount of the alkaline substance was set to 0.79 in terms of molar ratio based on silicon element from silicic acid, whereby the test sample of the present test example was obtained.

[0125] • Test Examples 6 to 10

[0126] The same operations as in Test Example 4 were performed except for the following points, whereby the test samples of the present test examples were obtained.

[0127] a) the amount of the alkaline substance was set to 0.55 (Test Examples 6 to 9) or 0.35 (Test Example 10) in terms of molar ratio based on silicon element of silicic acid; b) the hydrothermal treatment temperature was set to 150°C (Test Example 6), 121°C (Test Example 7) or kept constant at 175°C (Test Examples 8 to 10); c) the calcination temperature in the heating step was set to 800°C (Test Example 8) or kept constant at 1000°C (Test Examples 6, 7, 9, 10).

[0128] • Test Example 11

[0129] (Equivalent to the raw silica particle preparation step)

[0130] A mixed solution of TEOS 5.2 g, ion-exchanged water 100 g and acetone 400 g was prepared. To this mixed solution, 25 mass% TMAH aqueous solution 2.5 g was added while stirring. Then, 90 mass% acetic acid aqueous solution was added quickly to adjust the pH to 8, and further stirring was carried out for 30 minutes, whereby the raw silica particles were precipitated as a dispersion. Here, the ratio of ion-exchanged water to acetone was set so that the relative dielectric constant reached 30.6. The amount of TMAH added was 0.27 in terms of molar ratio based on silicon element of silicic acid from TEOS.

[0131] (Equivalent to the hydrothermal treatment step)

[0132] The obtained dispersion was centrifuged at 5000 rpm for 5 minutes, and the supernatant was removed by decantation to separate the precipitate. The centrifugation was carried out using Model 3700 manufactured by KUBOTA. The same amount of ion-exchanged water as the removed supernatant was added, and ultrasonic dispersion was carried out. The ultrasonic wave was applied at a frequency of 28 kHz and a power of 1000 W for 30 minutes. The obtained dispersion was subjected to a hydrothermal reaction at 175°C for 2 hours after being charged into a pressure vessel.

[0133] (Equivalent to the heating step)

[0134] Then, further centrifugation was carried out under the above conditions, and the obtained precipitate was dried at 130°C for 1 hour, and then calcined at 1000°C for 2 hours. The obtained calcined product was crushed to a state where no agglomerates were observed visually using a mortar, and the obtained spherical silica particles were used as the test sample of the present test example.

[0135] • Test Example 12

[0136] The same operation as in Test Example 3 was carried out except that the amount of acetone was 20 when mixed with the contained water. As a result, no particle formation was observed in the step equivalent to the raw silica particle preparation step, and the heating step was not carried out. Therefore, the test sample of the present test example was not obtained.

[0137] • Test Example 13

[0138] The content of acetone was 41.5 in amount when mixed with the contained water, and the same operation as in Test Example 1 was performed. In the raw material silica particle preparation step, no spherical particles were generated, and only agglomerates were obtained.

[0139] • Test Example 14

[0140] The amount of the basic substance was made 0.20 in molar ratio based on the silicon element from silicic acid, and the same operation as in Test Example 1 was performed. In the raw material silica particle preparation step, no spherical particles were generated, and only agglomerates were obtained.

[0141] • Test Example 15

[0142] The amount of the basic substance was made 0.85 in molar ratio based on the silicon element from silicic acid, and the same operation as in Test Example 1 was performed. As a result, in the step corresponding to the raw material silica particle preparation step, no particle generation was found, and the heating step was not performed. Therefore, the test sample of the present test example was not obtained.

[0143] • Test Examples 16, 17

[0144] The amount of the basic substance was made 0.35 (Test Example 16) or 0.54 (Test Example 17) in molar ratio based on the silicon element from silicic acid, and the test sample of the present test example was obtained by the same operation as in Test Example 4.

[0145] • Test Examples 18, 19

[0146] DBU (Test Example 18), DBN (Test Example 19) was used instead of TMAH as the basic substance, and the test sample of the present test example was obtained by the same operation as in Test Example 4. Note that the addition amount of DBU and DBN was set to the same amount as TMAH. As a result, the addition amount of DBU and DBN was made 0.41 in molar ratio based on the silicon element from silicic acid as the amount of the basic substance.

[0147] • Test Examples 20, 21

[0148] TEAH (Test Example 20), TBAOH (Test Example 21) was used instead of TMAH as the basic substance, and the test sample of the present test example was obtained by the same operation as in Test Example 4. Note that the addition amount of TEAH and TBAOH was set to the same concentration as TMAH. As a result, the addition amount of TEAH and TBAOH was made 0.32 (Test Example 20), 0.35 (Test Example 21) in molar ratio based on the silicon element from silicic acid as the amount of the basic substance.

[0149] • Test Example 22

[0150] CELLSPHERES manufactured by TAIHEIYO CEMENT Co. was used as it is. CELLSPHERES is a spherical particle composed of alumina borosilicate glass having a hollow structure with a particle diameter of 10 μm or less.

[0151] • Test Example 23

[0152] The hollow silica particle described in Example 8 of the example of Patent Literature 2 was used. Specifically, the hollow silica particle was prepared according to the description of paragraphs 0088 to 0093 of Patent Literature 2. The volume average particle diameter of the obtained hollow silica particle was 0.5 μm.

[0153] • Test Example 24

[0154] In the raw material silica particle preparation step of Test Example 9, a metal silicon powder used for preparing an alkaline aqueous silicic acid solution was fed into a high-temperature oxidation atmosphere in a state of being dispersed in air as a carrier gas, thereby causing deflagration, and spherical silica particles were produced by a so-called VMC method of rapid cooling, as a test sample of the present test example. The impurity content was measured for the test sample of the present test example and the test sample of Test Example 9. The results are shown in Table 2.

[0155] (Evaluation)

[0156] For the test sample of each test example, the particle size distribution, the specific surface area, the fine pore volume, and the true specific gravity were measured. The results are shown in Table 1

[0157] Particle size distribution: The test sample was dispersed in water at a concentration of 0.5 mass%, and a particle size distribution measuring device (SALD-7500nano manufactured by Shimadzu Corporation) was used to measure the particle size distribution. For Test Examples 4, 5, 9, and 11, a histogram of the measured particle size distribution is shown in Figure 1 .

[0158] Ratios of coarse internal void particles: For the test samples of Test Examples 11, 17, 22, and 23, the ratio of particles having a coarse internal void was measured and is shown in Table 3. Coarseness in the internal void refers to a pore having a length diameter of 50% or more based on the particle diameter (length diameter) of the spherical silica particle.

[0159] The length diameter of the internal void and the length diameter of the particle were measured on a cross section obtained by cutting the spherical silica particle embedded in the resin. First, after mixing the liquid epoxy resin (ZX1059) with the test sample, an appropriate amount of curing agent (ETHACURE 100) was added and mixed, and then heated at 170°C to cure. The obtained resin cured product was cut and the cross section was polished. Further, surface treatment was performed using an ion milling device (Hitachi High-Tech), osmium was coated, and an SEM photograph was taken.

[0160] Ten particles were randomly selected from the particles appearing in the cross section, the length diameter of the cross section of the particle was taken as the length diameter A of the particle, the longest length diameter of the internal void appearing in the cross section was taken as B, and the ratio of the particles for which B / A was 0.5 or more was calculated.

[0161] Particle internal void distribution: For the test samples of Test Examples 11, 17, 22, and 23, the test sample of each test example was cut in a state embedded in the resin using the same method as the embedding of the resin in the coarse internal void particle ratio test described above, and the distribution state of the voids of the cut surface (the proportion of the area of the voids) was evaluated, as shown in Table 3.

[0162] The cross section with the largest area among the multiple cross section images obtained by FIB / SEM with 10 nm steps as described above was taken as the evaluation cross section image. Further, the area proportion of the voids in the central region (a region having a circle with a radius of half the size of the center of the cross section) and the area proportion of the voids in the shell region (a region obtained by removing the central region from the cross section of the particle) were calculated. The proportion of the area was calculated by image processing software (Aikaku-n: Asahi Kasei Engineering). This calculation was performed on 10 randomly selected particles, and the average value was calculated.

[0163] Specific surface area, pore volume: The test sample was measured using an automatic specific surface area / pore distribution measuring device (Shimadzu Tristar 3000). The specific surface area was measured by the BET 1-point method using nitrogen gas. The pore volume was measured using the value at the time of adsorption measured using the BJH method.

[0164] True specific gravity: Measured using a dry automatic densitometer (Shimadzu, ACCUPIC II 1345) with nitrogen gas. The particle volume including the voids inside the spherical silica particles that cannot be invaded by nitrogen gas was used to measure the density. That is, if there is a void, the density of the spherical silica particles will decrease due to the volume of the void.

[0165] Dielectric properties: The relative permittivity and dielectric loss tangent were measured using a device manufactured by KEYCOM under the conditions of a cavity resonance method and 1 GHz.

[0166] Pressurization test: 1.5 g of the test sample was charged into a vacuum bag and degassed, and a cold isostatic press device (manufactured by Nikkiso Co., Ltd.) was used to pressurize in water at a pressure of 300 MPa for 1 minute.

[0167] SEM: SEM photographs were taken for each of the test samples of Test Examples 3 to 7, 9, 11, 13, 16 to 19.

[0168] TEM: For the test sample, embedding in resin and taking TEM photographs were performed. First, after mixing a liquid epoxy resin (ZX1059) with the test sample, an appropriate amount of a curing agent (ETHACURE 100) was added and mixed, and then heating was performed at 170°C to cure it. The resulting resin cured product was cut and the cross section was polished. Further, surface treatment was performed using an ion milling device (manufactured by Hitachi High-Tech), osmium was applied, and TEM photographs were taken. Figure 7

[0169] SEM: The same treatment as that performed using the above-described TEM was performed, and SEM photographs were taken.

[0170]

[0171] As is apparent from Table 1, in Test Examples 4 to 10, 16 to 21 in which the hydrothermal treatment step was performed, the true specific gravity measured by nitrogen gas was significantly smaller than the true specific gravity measured by helium gas (2.3 g / cm 3 ), and voids existed inside the particles. In contrast, with respect to Test Example 3 in which the hydrothermal treatment step was not performed, the true specific gravity measured by nitrogen gas and the true specific gravity measured by helium gas were both substantially consistent with the true specific gravity of silicon dioxide, at 2.3 g / cm 3 , and voids did not exist inside. Therefore, it was found that by performing the hydrothermal treatment step, spherical silicon dioxide particles having voids inside (hollow particles) could be effectively formed. Even when SEM photographs were observed, almost no fine pores were seen on the surface or only a little fine pores were seen. In addition, it was apparent from the SEM photographs that the particle diameters of these test samples were not consistent, and it was also apparent from the particle size distribution shown in Table 1 that the particle diameters were not consistent. Figure 1

[0172] With respect to Test Examples 1 to 3, Test Examples 8 and 9, the firing temperature was different within each group, and other than that, the hollow particles were obtained by performing the treatment under the same conditions. It was found that by changing the firing temperature, the fine pore volume changed.

[0173] ​​For Test Examples 6, 7, and 9, the treatment temperature in the hydrothermal treatment step was changed, and other than that, hollow particles were obtained under the same conditions. It was found that by changing the conditions of the hydrothermal treatment, the particle size distribution and the value of the fine pore volume could be changed. In particular, by changing the temperature in the hydrothermal treatment, the voids formed inside the particles could be controlled. For example, if the temperature in the hydrothermal treatment step was low, there was a tendency for the fine pore volume communicating with the outside to increase.

[0174] For Test Examples 4, 12, and 13, the relative dielectric constant of the mixed solvent of water and the organic solvent was changed, and other than that, spherical silica particles were obtained under the same conditions. It was found that if the relative dielectric constant of the mixed solvent was 20 (Test Example 12) or 41.5 (Test Example 13), spherical silica particles were not obtained. Specifically, in Test Example 12 in which the relative dielectric constant was low, particles were not formed because precipitation did not occur, and in Test Example 13, only aggregates were obtained. It was thus found that the relative dielectric constant of the mixed solvent was required to be greater than 20 and less than 41.5. Figure 9

[0175] For Test Examples 4, 5, 9, 10, 14 to 17, the amount of the basic substance was changed, and other than that, spherical silica particles were obtained under the same conditions. It was found that if the amount of the basic substance was 0.20 (Test Example 14) or 0.85 (Test Example 15) in terms of the molar ratio based on the silicon element from silicic acid, spherical silica particles themselves were not obtained. It was thus found that in Test Example 14 in which the amount of the basic substance was small, only aggregates were formed, and in Test Example 15 in which the amount of the basic substance was large, particles were not formed because precipitation did not occur, and thus the amount of the basic substance was required to be greater than 0.20 and less than 0.85 in terms of the molar ratio based on the silicon element from silicic acid.

[0176] For Test Example 11, it was shown that in the raw silica particle preparation step, raw silica particles were prepared using TEOS as the raw material, and thus, D90 / D10 was a small value, 1.76, and the particle diameter of the obtained hollow particles was not uniform (Examples 10 to 13). In contrast, it was found that in Test Examples 1 to 10 and 16 to 21 in which raw silica particles were prepared using a silicon metal powder as the raw material in the raw silica particle preparation step, even in Test Example 10 which was the smallest, D90 / D10 was 2.78, and hollow particles having a non-uniform particle diameter could be obtained (Examples 10 to 13). Figure 1 8 ). In contrast, it was found that in Test Examples 1 to 10 and 16 to 21 in which raw silica particles were prepared using a silicon metal powder as the raw material in the raw silica particle preparation step, even in Test Example 10 which was the smallest, D90 / D10 was 2.78, and hollow particles having a non-uniform particle diameter could be obtained (Examples 10 to 13). Figures 1 to 7

[0177] ​​​For Test Examples 4, 18 to 21, the kind of the basic substance was changed, but otherwise, the hollow particles were obtained under the same conditions. As a result, it was shown that even if the basic substance was changed to these, spherical silica particles could be produced without any problem.

[0178] In Test Examples 3, 9, 11, 16 to 18, 22, 23, in which the dielectric loss tangent was measured, very small values of the dielectric loss tangent were exhibited. For Test Examples 11, 17, 22, 23 among them, a pressurization test under 300 MPa was performed, and the true specific gravity and the dielectric loss tangent before and after the test were measured by nitrogen. As a result, it was shown that the true specific gravity maintenance rate of Test Examples 11, 17, 23 was 84% (Test Example 11), 100% (Test Example 17), 86% (Test Example 13), all of which were high, while that of Test Example 22 was 0%, and almost all of the hollow structure was destroyed. It was also shown that, for the dielectric loss tangent maintenance rate, although Test Example 23 exhibited a very high value, 600%, Test Example 16 exhibited a very low value, 171%, and Test Example 17 exhibited a very low value, 268%. A high dielectric loss tangent maintenance rate means that the voids are largely destroyed, or that a component having a high dielectric loss tangent exists inside the voids, either of which suggests that the voids are destroyed at a high rate.

[0179] From the cross-sectional SEM photographs and the TEM photographs, it was also possible to see the ease or difficulty of the destruction caused by these pressurization tests. In Test Examples 11 and 17, from the cross-sectional SEM photographs, it was observed that the shell of the particle was composed of a dense structure, and in the vicinity of the center, a plurality of fine voids were formed, ( Figure 15 and 16 ). In addition, from the TEM photograph, it was possible to infer that the density of the test sample of Test Example 17 gradually decreased in the vicinity of the center, and it was possible to infer that fine voids were formed in the vicinity of the center, ( Figure 14 ). Thus, it was possible to infer that the fine voids were not easily destroyed even if an external force was applied, and even if a pressurization test was performed, the internal voids were hardly destroyed. On the contrary, it was possible to infer that in Test Examples 22, 23, the internal voids were large, and the pressurization test caused the voids to be destroyed, ( Figure 17 and 18 ).

[0180] [Table 2]

[0181]

[0182] From Table 2, it was shown that even if the silica particles were produced from the same metal silicon powder, the test sample of Test Example 9 produced by the method of the present application had a lower impurity concentration. This was directly oxidizing the metal silicon powder to silica in Test Example 24, as opposed to Test Example 9, in which the metal silicon powder was dissolved once and then silica was precipitated, and thus it was inferred that no impurities were mixed in at the time of precipitation, and the impurity content was reduced.

[0183] [Table 3]

[0184]

[0185] As is apparent from Table 3, in the test sample of Test Example 17, which is within the scope of the present application, there are no particles having a void of a size of more than half the particle diameter inside, and further, the voids are composed of a plurality of voids, and are present in the off-center region.

[0186] On the other hand, in the test samples of Test Examples 22 and 23, which are commercially available products, there are voids of a size of more than half the particle diameter in all of the particles, and the center region is present as a void. Further, it is apparent that the voids present in the center region have a size extending to the shell region.

[0187] In Test Example 11, which was prepared from TEOS, there were many cases in which the voids were large, and the ratio of the coarse internal void particles was large, at 70%.

[0188] As a result, it is apparent that the true specific gravity maintenance rate was 91% in Test Example 17, and the destruction of the voids was suppressed. Further, in Test Example 23, the dielectric loss tangent maintenance rate was as high as 600%, and on the other hand, the test sample of Test Example 17 exhibited a low value, of 268%.

[0189] (Other Tests)

[0190] In the above test examples, metal silicon powder was used as the raw material for preparing the aqueous alkali silicate solution, and in addition, it was confirmed that spherical silica particles could also be produced using silica particles and water glass (aqueous sodium silicate solution). After preparing the aqueous alkali silicate solution from the respective materials of silica and aqueous sodium silicate solution, the same operations as when using metal silicon powder were performed, and as a result, the same spherical silica particles as when using metal silicon powder were obtained.

[0191] • Method using silica particles

[0192] Silica powder (product name: SO-E2, manufactured by Yamauchi Technos Co., Ltd.) 20.0 g, ion-exchange water 15.0 g, and 25 mass% TMAH aqueous solution 64.0 g were mixed, and the silica was dissolved in a pressure vessel at 180°C for 1 hour, and an aqueous alkali silicate solution containing about 20.2% of silicic acid, calculated as silica, was obtained.

[0193] • Method using aqueous sodium silicate solution

[0194] An aqueous sodium silicate solution (water glass) 10.2 g was mixed with ion-exchanged water 15.0 g, and stirring was performed at 40°C for 4 hours. Then, Na ions were removed by ion exchange while adding dropwise a 25 mass% TMAH aqueous solution 64.0 g. As a result, an alkaline aqueous silicate solution containing 10.8 mass% of silicic acid in terms of silicon dioxide could be obtained.

Claims

1. A spherical silica particle, having an average particle diameter of 0.1 to 10.0 μm, Specific gravity 0.9-1.9 g / cm3 by nitrogen determination 3 , a fine pore volume of 0.1 mL / g or less, a Na content of 10 ppm or less, a true specific gravity retention rate of 80% or more as measured by nitrogen gas before and after pressurization at 300 MPa for 1 minute, a particle existence ratio of a particle for which a maximum value of an aspect ratio of an internal void is more than half of the aspect ratio of the particle is 60% or less, having silica as a main component.

2. The spherical silica particles according to claim 1, wherein, an average void ratio of a central region of a particle cross section is 5 to 90%, an average void ratio of a region other than the central region of the cross section, that is, a shell region is 2 to 80% or less than the average void ratio of the central region.

3. The spherical silica particles according to claim 1 or 2, wherein, a dielectric loss tangent retention rate is 500% or less.

4. The spherical silica particles according to claim 1 or 2, wherein, D90 / D10 is 2.0 to 20.

0.

5. The spherical silica particles according to claim 1 or 2, wherein, Specific gravity 2.2 g / cm3 by helium determination 3 The above.

6. The spherical silica particles according to claim 1 or 2, wherein, an organic functional group is introduced to the surface.

7. A slurry composition, having: the spherical silica particle according to claim 1 or 2, and a dispersion medium in which the spherical silica particle is dispersed.

8. A resin composition, having: the spherical silica particle according to claim 1 or 2, and a resin material in which the spherical silica particle is dispersed.

9. A method for producing a spherical silica particle, comprising the following steps: a raw material silica particle preparation step of preparing a dispersion liquid of a raw material silica particle from a raw material solution in which silicic acid is dissolved in a mixed solvent of water and an organic solvent in the presence of an alkaline substance composed of at least one of a quaternary ammonium and a base having a cyclic amidine structure, a hydrothermal treatment step of replacing a dispersion medium in which the raw material silica particle is dispersed in the dispersion liquid with water, and then performing pressurized heating to 130°C to 250°C to produce a dispersion liquid of a raw material silica particle subjected to hydrothermal treatment, a heating step of removing an organic substance contained in the dispersion liquid by heating the dispersion liquid or the raw material silica particle obtained by solid-liquid separation from the dispersion liquid after the hydrothermal treatment step to produce a spherical silica particle; and a relative dielectric constant of the mixed solvent is 21 to 40, the alkaline substance is compounded at a compounding ratio of 0.3 to 0.8 in terms of molar ratio with respect to silicon element from the silicic acid.

10. The method for producing spherical silica particles according to claim 9, wherein the organic solvent is one or more selected from the group consisting of acetone, methyl ethyl ketone, and ethyl acetate.

11. The method for producing spherical silica particles according to claim 9 or 10, wherein the alkaline substance is one or more selected from the group consisting of quaternary ammonium having a carbon atom number of 4 to 16, diazabicyloundecane, and diazabicyloundecane.

12. The method for producing spherical silica particles according to claim 9 or 10, wherein the heating step is performed at 900°C or more.

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