High-purity fused spherical silica, resin composition for electronic device containing same, and cosmetic containing same

Abstract

Provided are: high-purity fused spherical silica which reduces the amount of impurities contained in silica particles serving as a filler to be added to a sealing material, enhances kneading properties with respect to a resin serving as the sealing material, and suppresses hollow parts in the particles in view of controlling the conductivity of the silica particles themselves; and a resin composition for an electronic device and a cosmetic which contain the same. The content of uranium in the spherical silica particles is at most 5 ppb, the content of thorium in the spherical silica particles is at most 5 ppb, the circularity of the spherical silica particles is at least 0.98, the crystal residual ratio of silicon oxide in the spherical silica particles is at most 0.01%, and the number of hollow parts, which have a diameter of at least 5 μm and are present in each particle of the spherical silica particles, is at most two in an observation range of 9 mm2 as observed by means of an electron microscope.

Description

High-purity fused spherical silica, resin composition for electronic devices containing the same, and cosmetics containing the same

[0001] The present invention relates to high-purity fused spherical silica, a resin composition for electronic devices containing the same, and cosmetics containing the same, and in particular to high-purity fused spherical silica with a reduced impurity content and improved mixability with resin materials, as well as a resin composition and cosmetics containing the same.

[0002] Inorganic fillers are added to resin compositions to seal precision electronic components such as semiconductors. Fillers are required to have insulating properties and a low thermal expansion coefficient. Silica (silicon oxide) is commonly used.

[0003] Silica is processed into fillers by crushing natural high-purity ores to a predetermined particle size. That is, even if the silica is highly pure, it is derived from natural ores, so the presence of impurities other than silicon oxide is inevitable. In particular, in the case of silica derived from natural products, uranium and thorium elements are present. To reduce these impurities, a method for producing spherical silica powder that combines crushing and exposure to flame has been proposed (see Patent Document 1).

[0004] According to the manufacturing method of Patent Document 1, pulverization and exposure to flame contribute to the reduction of uranium elements. Here, processing precision and integration are further promoted in order to improve the processing speed of semiconductors. Therefore, the impact of external electromagnetic noise on semiconductors is becoming a greater concern than ever before. In the case of silica derived from natural products, it is known that alpha rays and the like are generated by the radioactive decay of uranium and thorium elements, which are thought to be the cause of malfunctions. In addition, since it is possible to reduce natural radiation, it can be said that the impact of exposure on the human body is also small.

[0005] Furthermore, silica particles used as fillers must be easily mixed with resins, and they must also have fewer voids (hollow spaces within the particles) to reduce the conductivity of the silica particles themselves.

[0006] JP 2012-206870 A

[0007] After further research, the inventors have discovered a method that makes it possible to more effectively remove uranium and thorium elements from natural, high-purity ores, thereby reducing alpha rays and other radiation generated by the raw materials.

[0008] The present invention has been made in consideration of the above points, and provides high-purity fused spherical silica and a resin composition for electronic devices, which reduce the amount of impurities contained in silica particles used as a filler in encapsulants, improve the kneadability of the silica particles into encapsulant resins, and further suppress the formation of hollow spaces within the particles in order to control the electrical conductivity of the silica particles themselves. It also provides a material for cosmetic applications that reduces natural radiation and thereby reduces radiation exposure.

[0009] That is, in the high-purity fused spherical silica of the embodiment, the uranium content in the spherical silica particles is 5 ppb or less, and the thorium content in the spherical silica particles is 5 ppb or less, the circularity of the spherical silica particles is 0.98 or more, the residual silicon oxide crystal content in the spherical silica particles is 0.01% or less, and the number of hollows with a diameter of 5 μm or more present in each spherical silica particle is 0.98 or more when measured by an electron microscope at 9 mm ２ The present invention is characterized in that there are two or less such particles in the observation range.

[0010] Furthermore, in the high-purity fused spherical silica, the content of sodium element in the spherical silica particles may be 10 ppm or less.

[0011] Furthermore, in the high-purity fused spherical silica, the spherical silica particles may be made from metallic silicon as a raw material.

[0012] Furthermore, in the high-purity fused spherical silica, the spherical silica particles may be dissolved in a basic solution of metallic silicon.

[0013] Furthermore, in the high-purity fused spherical silica, the spherical silica particles may be exposed to a flame.

[0014] The resin composition for electronic devices according to the embodiment is characterized by including high-purity fused spherical silica and a resin composition.

[0015] In addition, the cosmetic product of the embodiment is characterized by containing high-purity fused spherical silica.

[0016] Additionally, the cosmetic product may be a powder, an ointment, or a lotion.

[0017] According to the high-purity fused spherical silica of the present invention, the uranium content in the spherical silica particles is 5 ppb or less, and the thorium content in the spherical silica particles is 5 ppb or less, the circularity of the spherical silica particles is 0.98 or more, the residual silicon oxide crystal content in the spherical silica particles is 0.01% or less, and the number of hollows with a diameter of 5 μm or more present in each spherical silica particle is 0.98 or less when measured by an electron microscope at 9 mm ２ Since there are two or less particles in the observation range, the amount of impurities contained in the silica particles to be added as a filler to the encapsulant can be reduced, the kneadability of the silica particles into the resin to be used as the encapsulant can be improved, and furthermore, hollow portions within the particles can be suppressed in order to control the conductivity of the silica particles themselves.

[0018] Furthermore, the resin composition for electronic devices makes it possible to reduce the dose of particle radiation and electromagnetic waves emitted from the spherical particles contained in the resin composition, suppressing disturbance factors such as noise and thereby reducing malfunctions of devices, etc. In addition, when the high-purity fused spherical silica of the present invention is used as an additive in cosmetics, it is also possible to reduce natural radiation, thereby further reducing the effects of exposure to radiation on the human body, and further the effects of crystalline silica.

[0019] 1A is an electron microscope photograph of a pulverized product obtained through a pulverization step in Test Example 4, and (B) is an electron microscope photograph of spherical particles obtained through a melt-spheroidization step in Test Example 4. 1B is an electron microscope photograph of high-purity fused spherical silica obtained through Test Example 6. 1C is an electron microscope photograph of silica particles obtained through Test Example 13.

[0020] The following processing method is used to obtain the high-purity fused spherical silica of the embodiment: The high-purity fused spherical silica will now be described starting with the manufacturing method.

[0021] First, a raw material of metallic silicon is prepared and dissolved in a basic solution. In the examples described below, metallic silicon is dissolved in a basic solution to prepare a raw material solution in which the metallic silicon raw material is dissolved ("dissolving step").

[0022] When dissolving the raw material of metallic silicon in a basic solution, the basic solution is a solution that does not contain alkali metals or alkaline earth metals. Generally, aqueous solutions of alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide are strongly basic. However, if the alkali metals remain in the basic solution, it will lower the purity of the final silica particles, which is undesirable.

[0023] Therefore, aqueous solutions of amine compounds are used as solutions that do not contain alkali metals or alkaline earth metals. Examples of amine compounds include ammonia, primary amines, secondary amines, tertiary amines, quaternary ammonium hydroxides (ammonium salts), arylamines, silazanes, and hydrazines.

[0024] More specifically, the amine compound is one or more compounds selected from ammonia, methylamine, ethylamine, propylamine, dimethylamine, diethylamine, pyrrolidine, trimethylamine, triethylamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, methyltriamylammonium hydroxide, methyltributylammonium hydroxide, pyrrolidine, piperidine, pyridine, quinoline, imidazole, indole, pyrimidine, hexamethyldisilazane, hydrazine, diazabicycloundecene, diazabicyclononene, etc. When preparing the aqueous solution, the amine compound may be a single type or a mixture of two or more types.

[0025] When an amine compound, which is an organic compound, is used, the compound molecules volatilize and decompose during subsequent processing steps. Therefore, it is desirable that almost no amine compound remains in the final silica particles. Of course, the concentration of the amine compound in the aqueous solution is set to an optimal concentration and pH depending on the type of raw material, and the solution is stirred. Furthermore, the liquid temperature during dissolution is also adjusted. Furthermore, since some of the compound remains undissolved during dissolution, filtration is also performed as necessary.

[0026] The dissolved components of the raw material solution prepared by dissolving them in a basic solution are solidified to prepare a solidified product ("solidification process"). In the solidification process, an acidic solution is added to prepare a solidified product. The raw material solution is basic, and adding the acidic solution to it promotes neutralization of the acid and base, resulting in the formation of a precipitate. This precipitate becomes the target solidified product. The resulting solidified product is washed with water and dried. Examples of acidic solutions that can be used include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, formic acid, and organic acids such as citric acid. Among these, acetic acid is preferred as the acidic solution because it is easily volatilized and decomposed in subsequent processes.

[0027] After drying, the solidified material is calcined to form a calcined product, and excess moisture such as bound water is removed ("calcination step"). The calcination temperature is 300 to 1200°C, and the calcination time is 1 to 3 hours. Specifically, silicon hydroxide produced by precipitation is oxidized to silicon oxide (silica) through calcination.

[0028] The fired product produced in the firing step is pulverized to prepare a pulverized product ("pulverization step"). Either wet pulverization or dry pulverization may be used for pulverization. Furthermore, known devices for pulverizing solids, such as a ball mill, vibration mill, jet mill, or atomizer, are used as the pulverizer. In this embodiment, the solidified product and alumina balls are placed in a pulverization pod, and the pod is rotated to perform wet pulverization. The rotation time of the pod (pulverization time) is adjusted depending on the target particle size. After wet pulverization, the pulverized product recovered from the pod is dried by spray drying or the like.

[0029] The purpose of the pulverization process is to control the particle size prior to the subsequent melt-spheroidization process. At the stage of the calcination process, the calcined product is irregular in shape and not uniform in size due to the fusion of particles. If the product is directly subjected to the melt-spheroidization process, particles with varying particle sizes will be produced. Furthermore, the non-uniform shape makes it difficult to obtain a spherical shape. This results in a high yield during the process (a decrease in yield).

[0030] Here, the average particle size of the pulverized material is the median diameter (D) measured by a known particle size measurement method such as a laser diffraction scattering method or a dynamic scattering method. ５０ ) and the average particle diameter (D ５０ The particle size is preferably 30 μm or less, more preferably 20 μm or less. By making the particle size smaller, melting in the melt-spheroidizing step becomes easier.

[0031] The pulverized material prepared in the pulverization step is thrown into a flame, and the pulverized material flies through the flame. The pulverized material, i.e., spherical silica particles, melts when exposed to the flame, and the surface tension during melting promotes spheroidization, resulting in spherical particles ("melt-spheroidization step"). The spherical particles thus obtained are the target oxide particles. The spherical particles also have a specified suitable particle size. Specifically, the average particle size (D ５０ The average particle diameter (D) of the spherical particles is 30 μm or less, and more preferably 20 μm or less. ５０ ) is also a median diameter (D) measured by a known particle size measurement method such as a laser diffraction scattering method or a dynamic scattering method. ５０ ) means

[0032] The flame in the melting and spheroidizing process is formed by mixing a combustible gas with a combustion supporting gas containing oxygen and burning it. As an indicator of the furnace temperature, the temperature of the furnace's refractory structure at its highest point (furnace body temperature) is in the range of 900°C to 1500°C. The furnace body temperature preferably has a lower limit of 900°C to 1100°C and an upper limit of 1300°C to 1500°C. Air or oxygen is used as the combustion supporting gas. When the combustible gas and the combustion supporting gas are supplied to the furnace, they may be supplied separately or in a pre-mixed state.

[0033] The flow velocity of the combustible gas is preferably 10 m / s or more, more preferably 15 m / s or more, and even more preferably 20 m / s or more. The flow velocity of the combustion supporting gas is preferably 10 m / s or more, more preferably 15 m / s or more, and even more preferably 20 m / s or more. The flow velocity ratio of combustible gas / combustion supporting gas is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less. The supply amounts of combustible gas and combustion supporting gas are determined by the amount of combustible gas that can form a flame large enough to sufficiently heat the raw material particles being supplied, and the amount of combustion supporting gas that can sufficiently combust the combustible gas. For example, the amount of combustible gas per unit weight of the pulverized material to be processed is 0.5 Nm ３ / kg to 5Nm ３ / kg, and oxygen as a combustion support gas is 1 Nm ３ / kg to 5Nm ３ It is said to be about / kg.

[0034] The method for supplying the raw material particles into the flame is not particularly limited, and the raw material particles are supplied to the flame in a dispersed state in a carrier gas, such as air, oxygen, or nitrogen.

[0035] After the pulverization step and the melt-spheroidization step, the mixture is sieved to obtain particles of a desired size. For sieving, a method of centrifugal separation using a cyclone or the like is used.

[0036] As explained above, the spherical silica particles produced from metallic silicon through the melting, solidifying, firing, pulverizing, and melt-spheroidizing processes have a significantly reduced total amount of uranium and thorium elements compared to the raw material stage.

[0037] In the spherical silica particles that are the substance of the high-purity fused spherical silica of the embodiment, the content of uranium (U) in the spherical silica particles is 5 ppb or less, and the content of thorium (Th) in the spherical silica particles is 5 ppb or less. This content is reduced to 1 / 10 or less, or even 5 / 100 or less, of the total amount of uranium and thorium contained in the raw material. Therefore, it is possible to further reduce the dose of particle rays such as alpha rays and beta rays, and electromagnetic waves such as gamma rays, emitted from the nuclides in the spherical silica particles, thereby reducing the impact on electronic components, etc.

[0038] When the metallic silicon raw material is dissolved in a basic solution, the original raw material changes from metal to hydroxide. At this point, the amount of impurities contained in the raw material is thought to be less than the amount of metallic silicon dissolved in the basic solution. Heavy elements such as U (uranium) and Th (thorium) are not amphoteric elements, so they are difficult to dissolve in the basic solution and remain as insoluble components. This ease of dissolution in the basic solution makes it possible to separate impurity components such as uranium and thorium. Therefore, it is possible to further reduce impurity components compared to the preparation of oxides for conventional fillers.

[0039] In addition, the content of sodium element (Na) in the spherical silica particles is 10 ppm or less. The reason why the content of sodium element is taken up is that it is a representative impurity component, and if the content of sodium element is low, it can be determined that the amount of other impurity components is also low. Since an amine compound is used when dissolving the raw material silicon metal in a basic solution, almost no alkali metal residue such as sodium hydroxide is generated. Furthermore, since the raw material silicon metal has been dissolved in a basic solution, as mentioned above, the dissolution of impurity components is suppressed and the purity is increased.

[0040] Furthermore, the circularity of each spherical silica particle is 0.98 or more, and the shape is extremely similar to a sphere. The circularity of a perfect sphere (true sphere) is 1.0. The circularity is evaluated by calculating the ratio of the length of the minor axis to the major axis (aspect ratio), the ratio of the circle-equivalent diameter to the maximum diameter, etc. In the embodiment described below, the measurement was performed using a flow-type particle image analyzer. The closer the circularity of the spherical silica particles is to a true sphere, the easier it is to fill the coating material into a circuit board, etc. after mixing them with a resin to prepare a sealing material, etc.

[0041] In addition, the silicon oxide (silicon dioxide: SiO ２ The residual crystalline content of the spherical silica particles is 0.01% or less, preferably below the detection limit. Spherical silica particles are mainly composed of amorphous silicon oxide. A small amount of crystalline silicon oxide may be present within the spherical silica particles. In other words, the residual crystalline content refers to the weight ratio of crystalline silicon oxide to the total weight of the spherical silica particles. The presence of crystalline silicon oxide affects the conductivity of the particles as a filler. Furthermore, in recent years, findings suggesting the carcinogenicity of crystalline silicon oxide (silica) have been reported, and therefore, it is desirable to minimize the amount of crystalline silicon oxide in order to mitigate its effects.

[0042] The presence of crystalline silicon oxide (crystalline silica) was confirmed by the intensity of the peak at 2θ=26.6° in X-ray crystallography (XRD). The intensity value of this peak was divided by the intensity value of quartz (crystalline silicon dioxide) to obtain a quotient. The numerical value of this quotient represents the residual crystalline fraction.

[0043] In addition, the number of hollows with a diameter of 5 μm or more present in each spherical silica particle was measured by an electron microscope. ２ The number of hollows in the observation area is two or less, preferably one or less, and more preferably zero. If extremely large hollows (voids, bubbles) exist in the spherical silica particles, the conductivity of the spherical silica particles near the hollows will change. In other words, the hollows may reduce the insulating properties and reduce the performance as a filler used in a sealing material. Therefore, it is desirable to reduce the hollows in the spherical silica particles as much as possible to densify the particles themselves.

[0044] The number and size (diameter) of hollow portions in the spherical silica particles were observed under magnification using an electron microscope. Note that, when observing the number of hollow portions with a diameter of 5 μm or more, the magnification of the electron microscope was set to 2000 times.

[0045] The high-purity fused spherical silica (spherical silica particles) of the embodiments described so far is primarily used as a filler for electronic materials. The high-purity fused spherical silica (spherical silica particles) is added to a resin to prepare a resin composition for electronic devices (a filler-containing resin composition for electronic materials). Examples of resins to which the silica can be added include thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene, other olefin resins, polyimide resins, and liquid crystal polymers; fluororesins, urea resins, phenolic resins, and thermosetting resins such as polyphenylene ether and bismaleimide. The silica can also be added to elastic resins such as styrene-butadiene rubber and isoprene rubber, silicone resins, and the like. For example, epoxy resins are used as resins when producing resin substrates such as electronic component packaging substrates and interlayer insulating films.

[0046] Examples of epoxy resins used in the resin composition include bisphenol A epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, phenol novolac epoxy resins, naphthalene epoxy resins, and phenoxy epoxy resins. The weight of high-purity fused spherical silica (spherical silica particles) incorporated into the resin composition is preferably large from the viewpoints of heat resistance and thermal expansion coefficient. It is desirable to add 80 mass% or more of high-purity fused spherical silica (spherical silica particles) to the total mass of the resin composition.

[0047] Furthermore, the high-purity fused spherical silica (spherical silica particles), i.e., filler for electronic materials, according to the embodiment can be dispersed in a liquid dispersion medium substantially free of water to prepare a slurry for electronic materials. Examples of the dispersion medium include methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, toluene, N-methylpyrrolidone, γ-butyrolactone, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate. The dispersion medium can be used alone or in combination. An appropriate dispersant can also be used.

[0048] As explained above, a characteristic feature of resin compositions for electronic devices (resin compositions containing fillers for electronic materials) is that they can reduce the dose of particle radiation and electromagnetic waves emitted from the silica particles contained in the resin composition. This reduces the impact of particle radiation and electromagnetic waves on electronic components and other devices from the processed portion of the resin composition. As a result, external disturbance factors such as noise are suppressed, and malfunctions and other problems with the equipment are expected to be reduced. Furthermore, the properties of the high-purity fused spherical silica (spherical silica particles) themselves enable them to be easily mixed with resins and also to have satisfactory effects in suppressing electrical conductivity.

[0049] In addition, the high-purity fused spherical silica (spherical silica particles) of the embodiment is also suitable for use as an additive to cosmetics. As explained above, the high-purity fused spherical silica (spherical silica particles) contains extremely low amounts of heavy elements such as U (uranium) and Th (thorium), thereby reducing the dose of natural radiation caused by the high-purity fused spherical silica (spherical silica particles) and thereby reducing the effects of exposure to the human body. This effect of reducing impact is particularly significant because it is applied directly to the skin, as in cosmetics. Furthermore, in recent years, the properties of crystalline silicon oxide (silica) have begun to be viewed as problematic. Therefore, the high-purity fused spherical silica (spherical silica particles) of the embodiment is highly effective in reducing impact due to its reduced crystalline content, making it a promising alternative to existing cosmetic additives such as microplastics.

[0050] When the high-purity fused spherical silica (spherical silica particles) of the embodiment is added to and blended into cosmetics, the cosmetics are not particularly limited as long as they are in a form that can be applied to the skin, such as a powder, ointment, emulsion, or cream. When the cosmetics are ointments, the high-purity fused spherical silica is added to and kneaded with a base material containing oils and fats, such as petrolatum. When the cosmetics are emulsions or creams, the high-purity fused spherical silica is added to a base material containing water, alcohol, glycerin, various oils and fats, and homogenized. When the cosmetics are powders, they are intended for addition to foundations, for example, and are added to and kneaded with oils and fats, wax, moisturizers, water, and the like. Of course, when preparing cosmetics, surfactants, preservatives such as parabens, fragrances, and the like may be blended as needed.

[0051] To demonstrate high-purity fused spherical silica (spherical silica particles), Test Examples 1 to 15 were prepared and the physical properties of each Test Example were evaluated. The following describes the raw materials used, the preparation method, and the measurement and evaluation methods in that order. For details of each prototype, see Tables 1 to 4 below.

[0052] [Raw materials used] Metallic silicon and silicon oxide powders (silica powder, crystalline silica) were used as raw materials. The raw materials used for each test example are shown in the table. In test examples 1 to 10, metallic silicon powder with an average particle size of 20 μm was used. In test examples 11 to 15, crystalline silica with an average particle size of 30 μm was used.

[0053] The following amine compounds were used in preparing the basic solution: Dimethylamine: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Tetramethylammonium hydroxide (hereinafter referred to as TMAH): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Diazabicycloundecene (hereinafter referred to as DBU): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0054] [Preparation of Spherical Silica Particles] Test Examples 1 to 8 9.0 g of metallic silicon powder (Si powder in the table below), 315 g of ion-exchanged water, and 32 g of a 50 wt % aqueous dimethylamine solution were mixed and stirred for 48 hours while heating to 40° C. As a result, a 6.0 wt % aqueous solution of basic silicic acid was obtained in terms of oxide.

[0055] A 90% aqueous acetic acid solution was added dropwise to the basic silicic acid solution while stirring to adjust the pH, and stirring was continued. The precipitate was recovered, dried at 120°C, and calcined at 800°C for 2 hours. Note that calcination was omitted for Test Example 3. The resulting calcined product, an appropriate amount of silica powder and water, and alumina balls with a particle size of 5 mm were placed in a high-purity alumina milling pod and milled until the target particle size was reached. The milled product was then collected through a 4 mm sieve and appropriately dried. The difference between each test example was the particle size during milling, which was achieved by adjusting the milling time.

[0056] 5Nm in a furnace lined with fireproof material (cylindrical, 5m high x 0.5m inner diameter) ３ / hour and 25 Nm ３ The pulverized material of each test example was dispersed in air at a rate of 10 kg / hour into a flame generated by combustion with oxygen gas supplied at a rate of 10 kg / hour, and then melted by heating and recovered. In this way, spherical silica particles of each test example were prepared.

[0057] Test Examples 9 and 10 In Test Example 9, dimethylamine was replaced with TMAH, and the amounts of reagents and treatment were the same as in Test Example 6. In Test Example 10, dimethylamine was replaced with DBU, and the amounts of reagents and treatment were the same as in Test Example 6.

[0058] Test Examples 11 to 15 Test Examples 11 to 15 are control groups in which the steps of dissolving in a basic solution and neutralizing were omitted, and the raw material was pulverized and exposed to flame, unlike the above-mentioned Test Examples 1 to 10. The pulverization method was the same as when using the high-purity alumina pot described above, and the pulverization time was adjusted to produce different samples. The exposure to flame was also the same. Test Example 16 listed in Table 4 is a sample prepared from silicon metal powder by a method known as the VMC method (Vaporized Metal Combustion Method), which produces spherical oxide microparticles by utilizing the deflagration phenomenon of metal powder.

[0059] [Measurement and evaluation methods] Particle size distribution The particle diameters of the spherical silica particles of each test example after pulverization and after melting were measured in an aqueous solvent using a laser diffraction particle size distribution analyzer SALD-7500 nano manufactured by Shimadzu Corporation.１０ , D ５０ (Median diameter), D ９０ The particle size distribution was calculated.

[0060] Measurement of BET specific surface area 1.0 g of spherical silica particles of each test example was weighed and placed in a measurement cell. After pretreatment, the BET specific surface area value was measured by nitrogen adsorption. For the measurement, an automatic specific surface area and pore distribution measuring device TriStar (registered trademark)-II3020 manufactured by Shimadzu Corporation was used. The pretreatment conditions were as follows: Degassing temperature: 200°C Degassing time: 30 minutes Cooling time: 4 minutes

[0061] Component Analysis The atomic composition of the spherical silica particles of each test example was analyzed using ICP-MS (inductively coupled plasma optical emission spectroscopy) instruments (for U and Th), ICP-OES (for silica and other impurities), and ICP-AES (for alumina and other impurities), all manufactured by Shimadzu Corporation. For the measurement, the spherical silica particles of each test example were completely dissolved in a mixed solution of nitric acid and hydrofluoric acid to form a solution, which was then fed to the instrument.

[0062] Circularity measurement: A flow particle image analyzer (FPIA-3000) manufactured by Sysmex Corporation was used. Sodium hexametaphosphate was dissolved in sheath liquid (particle sheath "PSE-900A") to prepare a solution, and the spherical silica particles of each test example were mixed with this solution and subjected to ultrasonic dispersion before measurement. The measurement was performed using the H mode of the same analyzer.

[0063] Crystalline Silica Content: A SmartLab (registered trademark) manufactured by Rigaku Corporation was used as an X-ray crystal structure analyzer (XRD). The peak intensity at 2θ = 26.6° was determined for each spherical silica particle sample. In parallel, the peak intensity at 2θ = 26.6° for 100% crystalline silica was determined. The peak intensity for each sample was then divided by the peak intensity for crystalline silica to obtain a quotient, which was expressed as a percentage.

[0064] - Proportion of hollows of 5 μm or more The spherical silica particles of each test example were added to an epoxy resin, and a curing agent was added and mixed to prepare a resin mixture. At this time, the spherical silica particles (i.e., the filler component) were equivalent to 75% by weight of the resin mixture. The resin mixture of each test example was heated to 170°C and cured. After curing, the resin was cut and the cut surface was polished.

[0065] An ion milling device (IM4000Plus, manufactured by Hitachi High-Tech Corporation) was used to polish the cut surfaces. After polishing, osmium oxide gas was introduced to apply an osmium coating to the polished surface of each test example. Thereafter, the polished surface of each test example was observed using an electron microscope (SEM). The observation range of the electron microscope was 9 mm. ２ The number of spherical silica particles having a diameter (major axis) of 5 μm or more within the same range, which contained hollow portions (voids), was counted. The number of spherical silica particles having a diameter (major axis) of 5 μm or more within the same range, which contained hollow portions (voids), was counted.

[0066] [Results] The results of Test Examples 1 to 15 are shown in Tables 1 to 3. In each table, from the top to bottom, the raw material type, the amount of uranium and thorium in the raw material (ppb), the type of base, the ratio of base to silicon (mol), the yield (%), the firing temperature (°C), the particle diameter after pulverization and after melting (D １０ , D ５０ , D ９０ μm), specific surface area (m ２ / g), amount of sodium after melting (ppm), amount of uranium and thorium after melting (ppb), circularity, residual crystal rate (%), number of hollows of 5 μm or more when magnified 2000 times by electron microscope (number / 9 mm ２ ) is shown. Table 4 shows the composition analysis of the contained elements (expressed in ppb and ppm).

[0067] Additionally, electron microscope (SEM) photographs are presented. Figure 1 shows Test Example 4 after crushing (5000x magnification) and after melting (10000x magnification). Figure 2 shows a cross section of Test Example 6, with electron microscope photographs (2000x magnification) of different observation areas. Figure 3 shows a cross section of Test Example 13, with electron microscope photographs (2000x magnification) of different observation areas.

[0068]

[0069]

[0070]

[0071]

[0072] [Discussion] As can be seen from the photograph in Figure 1, even if the crushed material was irregular in shape, it was confirmed that it became spherical particles when exposed to flames after crushing. Although Figure 2 is difficult to see due to the overall blackness, there were almost no hollow spaces (voids) within the spherical silica particles exposing the cut surface. In Figure 3, hollow spaces large compared to the particle diameter were present within each particle. Actual measurements revealed diameters of 5 to 10 μm. In Test Example 6 in Figure 2 and Test Example 13 in Figure 3, the raw material was dissolved in a basic solution in Test Example 6. In contrast, dissolution in a basic solution was omitted in Test Example 13. From this, dissolving the raw material in a basic solution has the great advantage of reducing hollow spaces.

[0073] Focusing on the amounts (ppb) of uranium and thorium in Test Examples 1 to 10 (excluding Test Example 3), comparing the amounts at the raw material stage and after melting, the amounts were significantly reduced to less than 1 / 10 and less than 6 / 100 after melting. Specifically, the amount of uranium was 1 ppb, and the amount of thorium was 2 ppb. The amount of sodium (ppm) was also low at 1 ppm after melting. In addition, a comparison of all components in Table 4 confirmed the reduction of not only uranium and thorium, but also other impurity components. This demonstrates that the method of combining dissolution in a basic solution and exposure to flame is effective in reducing impurity components. Furthermore, even if the raw material for producing spherical silica particles is inexpensive to procure but has a low purity, it is possible to reduce the impurity components, thereby making it possible to reduce production costs overall.

[0074] Test Examples 9 and 10 show that the types of amine compounds that can be used to prepare a basic solution can be expanded. Selection can be made taking into consideration the type of raw material to be dissolved, ease of solubility (reactivity), raw material costs, etc.

[0075] The circularity of Test Examples 1 to 10 (excluding Test Example 3) and Test Examples 11 to 15 was 0.98, which is a shape extremely close to a perfect sphere. In particular, Test Examples 1 to 10 confirmed that a high circularity could be achieved from an amorphous state by dissolving in a basic solution. As a filler, a more spherical shape is preferable because it improves the fluidity of the coating material.

[0076] The residual silicon oxide crystal rate was below the measurement limit in Test Examples 1 to 10 (except Test Example 3), and can be considered to be substantially non-existent. Furthermore, the proportion of hollow spaces of 5 μm or more was below the measurement limit in Test Examples 1 to 10 (except Test Example 3), and can be considered to be virtually non-existent. These results support the superiority of the preparation method involving dissolution in a basic solution.

[0077] Therefore, as a filler for use in resin compositions for electronic devices, high-purity fused spherical silica contains few impurities, including uranium and thorium, making it possible to reduce the radiation source associated with radioactive decay. It also has extremely nearly perfect spheres, which helps ensure the fluidity of coatings. Furthermore, the absence of relatively large hollow spaces (voids) within the particles ensures performance such as insulation. Additionally, as high-purity fused spherical silica for use in cosmetics, it contains few impurities, including uranium and thorium, and also contains little crystalline silica, making it highly valuable as an additive for cosmetics that are applied directly to the skin.

Claims

1. The uranium content in spherical silica particles is 5 ppb or less, and the thorium content in said spherical silica particles is 5 ppb or less, the circularity of said spherical silica particles is 0.98 or more, the residual silicon oxide crystal rate in said spherical silica particles is 0.01% or less, and the number of hollow parts with a diameter of 5 μm or more present in each particle of said spherical silica particles is 0.01% or less when measured by an electron microscope at 9 mm ２ 2 or less particles in an observation range of said high purity fused spherical silica.

2. The high-purity fused spherical silica according to claim 1, wherein the content of sodium element in said spherical silica particles is 10 ppm or less.

3. The high-purity fused spherical silica according to claim 1, wherein the spherical silica particles are made from metallic silicon.

4. The high-purity fused spherical silica according to claim 3, wherein the spherical silica particles have been dissolved in a basic solution of metallic silicon.

5. The high purity fused spherical silica according to claim 1, wherein said spherical silica particles have been exposed to a flame.

6. A resin composition for electronic devices, comprising the high purity fused spherical silica according to claim 1 and a resin composition.

7. A cosmetic comprising the high purity fused spherical silica according to claim 1.

8. The cosmetic product according to claim 7, which is a powder, an ointment, or a lotion.

Images