WO2024257788A1 - High-purity fused spherical silica, resin composition for electronic device containing same, and cosmetic containing same - Google Patents

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 same, and cosmetic product containing same

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 reduced impurity content and improved mixability with resin materials, as well as the resin composition and cosmetics containing the same.

Insulating materials used to seal precision electronic parts such as semiconductors contain inorganic fillers added to the resin composition. Fillers are required to have insulating properties and a low coefficient of thermal expansion. Generally, silica (silicon oxide) is used.

Silica is processed into fillers by crushing natural high-purity ores to a specified particle size. In other words, even if it is highly pure, since it is derived from natural ores, 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. In order to reduce such impurities, a method for producing spherical silica powder that combines crushing and exposure to flame has been proposed (see Patent Document 1).

The manufacturing method described in Patent Document 1 contributes to the reduction of uranium elements through pulverization and exposure to flame. Here, processing precision and integration are being further promoted with the aim of improving the processing speed of semiconductors. As a result, the impact of external electromagnetic noise on semiconductors is becoming more of a problem 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, and are thought to be the cause of malfunctions. In addition, since it is possible to reduce natural radiation, it can be said that there is also less impact of exposure on the human body.

In addition, silica particles used as a filler must be easily mixed with resin. Furthermore, there is a demand for the suppression of voids (hollow spaces within the particles) in order to reduce the electrical conductivity of the silica particles themselves.

JP 2012-206870 A

Subsequently, the inventors conducted extensive research and have now discovered a method to more effectively remove uranium and thorium elements from high-purity natural ores, thereby reducing alpha rays and other emissions that originate from the raw materials.

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 that reduce the amount of impurities contained in silica particles that serve as a filler to be added to encapsulants, improves the kneadability of the particles into the encapsulant resin, and further suppresses hollow spaces within the particles in order to control the electrical conductivity of the silica particles themselves. In addition, it also provides a material for cosmetic applications that reduces natural radiation and thus reduces radiation exposure.

That is, the high-purity fused spherical silica of an embodiment is characterized in that 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 rate in the spherical silica particles is 0.01% or less, and the number of hollow portions having a diameter of 5 μm or more present in each spherical silica particle is 2 or less within an observation area of 9 ^mm2 using an electron microscope.

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

Furthermore, in high-purity fused spherical silica, the spherical silica particles may be made from metallic silicon.

Furthermore, in the high purity fused spherical silica, the spherical silica particles may have been dissolved in a basic solution of metallic silicon.

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

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

In addition, the cosmetic of the embodiment is characterized in that it contains high-purity fused spherical silica.

Furthermore, the cosmetic product may be a powder, an ointment, or a lotion.

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, 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 rate in the 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 spherical silica particle is 2 or less within an observation area of 9 ^mm2 using an electron microscope. Therefore, the amount of impurities contained in the silica particles to be used as a filler in a sealant is reduced, the kneadability with the sealant resin is improved, and further, the hollow parts within the particles can be suppressed in terms of controlling the electrical conductivity of the silica particles themselves.

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 reducing malfunctions of equipment. In addition, the high-purity fused spherical silica of the present invention can also be used as an additive in cosmetics to reduce natural radiation, thereby further reducing the effects of exposure to the human body, and even the effects of crystalline silica.

1A is an electron microscope photograph of a pulverized product after a pulverization process in Test Example 4, and FIG. 1B is an electron microscope photograph of spherical particles after a melt-spheroidization process. 1 is an electron microscope photograph of the high-purity fused spherical silica of Test Example 6. 1 is an electron microscope photograph of silica particles of Test Example 13.

The following processing method is used to obtain the high-purity fused spherical silica of the embodiment. Therefore, the high-purity fused spherical silica will be explained starting from the manufacturing method.

First, the raw silicon metal material is prepared and dissolved in a basic solution. In the examples described below, the silicon metal is dissolved in a basic solution to prepare a raw material solution in which the raw silicon metal material is dissolved (the "dissolving process").

When the raw material for silicon metal is dissolved in a basic solution, the basic solution is a solution that does not contain alkali metals or alkaline earth metals. In general, aqueous solutions of alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide are strongly alkaline. However, if any alkali metal remains in the basic solution, it will lower the purity of the final silica particles, which is undesirable.

Aqueous solutions of amine compounds are therefore 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.

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.

When using an amine compound, which is an organic compound, the compound molecules volatilize and decompose during subsequent processing steps. For this reason, it is desirable for almost no amine compound to remain 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. In addition, the liquid temperature during dissolution is also adjusted. Since some of the compound remains undissolved during dissolution, filtration is also added as necessary.

The dissolved components of the raw material solution, which is prepared by dissolving them in a basic solution, are solidified to prepare a solidified product (the "solidification process"). In the solidification process, an acidic solution is added to prepare a solidified product. The raw material solution is basic, and adding an acidic solution to it promotes neutralization of the acid and base, resulting in the formation of a precipitate. This precipitate becomes the desired 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. Of these, acetic acid is preferred as the acidic solution due to its tendency to volatilize and decompose in subsequent processes.

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

The fired product produced by the firing process is pulverized to prepare a pulverized product (the "pulverization process"). Either wet pulverization or dry pulverization may be used for pulverization. Furthermore, known devices for pulverizing solids, such as ball mills, vibration mills, jet mills, and atomizers, are used as pulverizers. 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 according to the target particle size. After wet pulverization, the pulverized product collected from the pod is dried by spray drying or the like.

The purpose of the crushing process is to control the particle size before the subsequent melt-spheroidizing process. After the sintering process, the sintered product is amorphous and not uniform in size due to the fusion of particles. If the product is sent to the melt-spheroidizing process in this state, particles with a wide range of particle sizes will be produced. In addition, it will be difficult to obtain a spherical shape due to the non-uniform shape. This results in a high yield during the process (a decrease in yield).

Here, the average particle size of the pulverized material means the median diameter ( _D50 ) measured by a known particle size measurement method such as a laser diffraction scattering method or a dynamic scattering method. Therefore, the average particle size ( _D50 ) of the pulverized material is preferably 30 μm or less, more preferably 20 μm or less. By making the particle size finer, melting in the melt-spheroidizing step becomes easier.

The pulverized material prepared in the pulverization process is put 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 to obtain spherical particles ("melt spheroidization process"). The spherical particles thus obtained are the oxide particles. The spherical particles also have a suitable particle size. Specifically, the average particle size ( _D50 ) of the spherical particles is 30 μm or less, more preferably 20 μm or less. The average particle size (D50) of the spherical particles also means the median size ( _D50 ) measured by a known particle size measurement method such as a _laser diffraction scattering method or a dynamic scattering method.

The flame in the melting and spheroidizing process is formed by mixing combustible gas with a combustion supporting gas containing oxygen and burning it. As an indicator of the temperature inside the furnace, the temperature of the furnace's refractory structure is in the range of 900°C to 1500°C at the highest point (furnace body temperature). 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 and oxygen are 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 premixed state.

The flow rate 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 rate 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 rate 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 the combustible gas and the combustion supporting gas are determined by the amount of the combustible gas that can form a flame large enough to sufficiently heat the raw material particles to be supplied, and the amount of the combustion supporting gas that can sufficiently combust the combustible gas. For example, the amount of the combustible gas is 0.5 Nm ³ /kg to 5 Nm ³ /kg per unit weight of the pulverized material to be processed, and the amount of oxygen as the combustion supporting gas is about 1 Nm ³ /kg to 5 Nm ³ /kg.

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. Examples of the carrier gas include air, oxygen, and nitrogen.

After the crushing process and the melt-spheroidizing process, appropriate sieving is performed to select the desired particle size. In addition to sieving, centrifugal separation using a cyclone or other method is also used for sieving.

As explained above, the spherical silica particles produced from the raw material silicon metal through the melting, solidification, firing, crushing, and melt-spheroidizing processes have a significantly reduced total amount of uranium and thorium elements compared to the raw material stage.

The spherical silica particles that are the embodiment of the high purity fused spherical silica of the embodiment have a uranium (U) content of 5 ppb or less, and a thorium (Th) content of 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. This makes it 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.

When the raw silicon metal is dissolved in the 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 silicon metal that dissolves in the basic solution. Heavy elements such as U (uranium) and Th (thorium) are not amphoteric elements, so they are difficult to dissolve in basic solutions and remain as insoluble components. This ease of dissolution in basic solutions makes it possible to separate impurity components such as uranium and thorium elements. This makes it possible to reduce impurities even further than in the previous preparation of oxides for fillers.

In addition, the sodium (Na) content in the spherical silica particles is 10 ppm or less. The sodium content is mentioned because it is a representative impurity component, and if the sodium content is low, it can be determined that the amounts of other impurities are also low. Because an amine compound is used when dissolving the raw silicon metal in a basic solution, there is almost no residual alkali metal such as sodium hydroxide. Also, because the raw silicon metal is dissolved in a basic solution, the dissolution of impurities is suppressed and the purity is increased, as mentioned above.

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 short axis to the long axis (aspect ratio), the ratio of the circle equivalent diameter to the maximum diameter, and the like. In the embodiment described below, measurements were taken 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 circuit boards, etc. after mixing with resin and preparing it into a sealing material, etc.

In addition, the residual crystal rate of silicon oxide (silicon dioxide: SiO ₂ ) in the spherical silica particles is 0.01% or less, preferably below the detection limit. The spherical silica particles are mainly formed of amorphous silicon oxide. A small amount of crystalline silicon oxide may be present in the particles. In other words, the residual crystal rate indicates 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 as a filler. In addition, in recent years, findings suggesting the carcinogenicity of crystalline silicon oxide (silica) have been reported, so it is desirable to suppress crystalline silicon oxide as much as possible in order to reduce the impact.

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 (silicon dioxide crystals) to obtain a quotient. This quotient represents the crystal residual rate.

In addition, the number of hollows with a diameter of 5 μm or more present in each spherical silica particle is 2 or less, preferably 1 or less, more preferably 0, in an observation area of 9 ^mm2 by an electron microscope. If an extremely large hollow part (void, bubble) exists in a spherical silica particle, the conductivity of the spherical silica particle near the hollow part will change. In other words, the insulating property may be reduced by the hollow part, and the performance as a filler used in a sealing material may be reduced. Therefore, it is desirable to reduce the hollow part in the spherical silica particle as much as possible to densify the particle itself.

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

The high-purity fused spherical silica (spherical silica particles) of the embodiments described so far is mainly 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 (resin composition containing filler for electronic materials). Resins to which it 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. It 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 manufacturing resin substrates such as packaging substrates for electronic components and interlayer insulating films.

Epoxy resins used in the resin composition include, for example, bisphenol A type epoxy resins, bisphenol F type epoxy resins, biphenyl type epoxy resins, phenol novolac type epoxy resins, naphthalene type epoxy resins, and phenoxy type epoxy resins. The weight of high-purity fused spherical silica (spherical silica particles) blended 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.

Furthermore, the high purity fused spherical silica (spherical silica particles) of the embodiment, i.e., the filler for electronic materials, can be prepared as a slurry for electronic materials by dispersing the filler for electronic materials and having a liquid dispersion medium that is substantially free of moisture. As the dispersion medium, for example, a solvent such as 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, propylene glycol monomethyl ether acetate, etc. can be used. The dispersion medium can also be used alone or in combination. It is also possible to use an appropriate dispersant.

As explained in the description of high-purity fused spherical silica (spherical silica particles), the characteristic property of the resin composition for electronic devices (resin composition containing fillers for electronic materials) is that it is possible to reduce the dose of particle rays and electromagnetic waves emitted from the silica particles contained in the resin composition. This makes it possible to reduce the effects of particle rays and electromagnetic waves on electronic components and the like from the processed parts of the resin composition. As a result, it is expected that disturbance factors such as noise will be suppressed and problems such as malfunctions of equipment will be reduced. In addition, the properties of the high-purity fused spherical silica (spherical silica particles) itself make it possible to satisfy the effects of kneading with resin and suppressing electrical conductivity.

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 content of heavy elements such as U (uranium) and Th (thorium) is extremely low, so the dose of natural radiation caused by the high-purity fused spherical silica (spherical silica particles) is suppressed, and the impact of exposure to the human body is suppressed. In particular, since it is applied directly to the skin like cosmetics, the effect of reducing the impact is great. Furthermore, in recent years, the properties of crystalline silicon oxide (silica) have begun to be viewed as problematic, so the high-purity fused spherical silica (spherical silica particles) of the embodiment is highly effective in reducing the impact due to the reduction in crystallinity, and is promising as an alternative material to existing cosmetic additives such as microplastics.

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, lotion, cream, etc. When the cosmetic is an ointment, the high-purity fused spherical silica is added to and kneaded with a base material of oil and fat components such as petrolatum. When the cosmetic is an lotion or cream, the high-purity fused spherical silica is added to a base material of water, alcohol, glycerin, various oils and fats, etc., and homogenized. When the cosmetic is a powder, it is assumed that it will be added to, for example, a foundation, and it is added to and kneaded with oils and fats, wax, moisturizers, water, etc. Of course, when preparing it as a cosmetic, surfactants, preservatives such as paraben, fragrances, etc. are blended as necessary.

In order 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 production method, and the measurement and evaluation methods in that order. For details of each prototype example, see Tables 1 to 4 below.

[Ingredients used]
Metallic silicon and silicon oxide powder (silica powder, crystalline silica) were used as raw materials. The raw materials used in each test example are shown in the table.
The metallic silicon powder used in Test Examples 1 to 10 had an average particle size of 20 μm.
The crystalline silica used in Test Examples 11 to 15 had an average particle size of 30 μm.

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.

[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, an aqueous solution of basic silicic acid having a concentration of 6.0 wt % in terms of oxide was obtained.

The pH was adjusted by adding 90% acetic acid solution dropwise to the basic silicic acid solution while stirring, and stirring was continued. The precipitate was collected and dried at 120°C, then fired at 800°C for 2 hours. Note that firing was omitted for test example 3. The resulting fired product, an appropriate amount of silica powder and water, and alumina balls with a particle size of 5 mm were placed in a grinding pod made of high-purity alumina, and grinding continued until the target particle size was reached. The ground product was then collected using a 4 mm sieve and appropriately dried. The difference between each test example was the particle size during grinding, which was created by adjusting the grinding time.

In a furnace (cylindrical, 5 m high x 0.5 m inside diameter) lined with fireproof material, LPG gas supplied at 5 ^Nm3 /h and oxygen gas supplied at 25 ^Nm3 /h were combusted, and the pulverized material of each test example was dispersed in air at a rate of 10 kg/h into the flame generated by the combustion, heated and melted, and then collected. In this way, the spherical silica particles of each test example were prepared.

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

Test Examples 11 to 15
Unlike the above-mentioned Test Examples 1 to 10, Test Examples 11 to 15 are control groups in which the process of dissolving in a basic solution and neutralizing is omitted, and the raw material is crushed and exposed to flame. The crushing method is the same as when the high-purity alumina pot described above is used, and the crushing time is adjusted to produce different samples. The exposure to flame is also the same. Test Example 16 described in Table 4 is a sample prepared from silicon metal powder by a method of producing spherical oxide fine particles by utilizing the deflagration phenomenon of metal powder, known as the VMC method (Vaporized Metal Combustion Method).

[Measurement and evaluation methods]
Particle size distribution The particle sizes of the spherical silica particles of each test example after crushing and after melting were measured in an aqueous solvent using a laser diffraction particle size distribution analyzer SALD-7500 nano manufactured by Shimadzu Corporation. Additionally, the particle size distributions _D10 , _D50 (median diameter), and _D90 were calculated.

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

Component Analysis When analyzing the atomic composition contained in the spherical silica particles of each test example, IPC (inductively coupled plasma atomic emission spectrometry) devices ICP-MS (for U and Th), ICP-OES (for silica and other impurities), and ICP-AES (for alumina and other impurities), manufactured by Shimadzu Corporation, were used.
For the measurement, the spherical silica particles of each test example were completely dissolved in a mixture of nitric acid and hydrofluoric acid to prepare a solution, which was then fed into the apparatus.

Circularity Measurement: A flow type 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 into the solution, and after ultrasonic dispersion, the solution was subjected to measurement. The measurement was performed using the H mode of the same device.

Crystalline silica content: SmartLab (registered trademark) manufactured by Rigaku Corporation was used as an X-ray crystal structure analyzer (XRD). The peak intensity value at 2θ = 26.6 ° was obtained for the spherical silica particle samples of each test example. In parallel, the peak intensity value at 2θ = 26.6 ° of 100% crystalline silica was obtained. The peak intensity value of each test example sample was then divided by the peak intensity value of crystalline silica to obtain a quotient, which was expressed as a percentage.

- Proportion of hollows of 5 μm or more The spherical silica particles of each test example were added to an epoxy resin, and a hardener 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 hardened. After hardening, the resin was cut and the cut surface was polished.

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 coat to the polished surfaces of each test example. Then, the polished surfaces of each test example were observed using an electron microscope (SEM). The observation range of the electron microscope was 9 ^mm2 , and the number of particles containing hollows (voids) in spherical silica particles with a diameter (major axis) of 5 μm or more within the same range was counted. Then, the number of particles containing hollows (voids) in spherical silica particles with a diameter (major axis) of 5 μm or more was counted.

[result]
The results of Test Examples 1 to 15 are shown in Tables 1 to 3. In each table, from the top, the type of raw material, 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 calcination temperature (°C), the particle size after grinding and after melting ( _D10 , _D50 , _D90 in μm), the specific surface area ( ^m2 /g), the amount of sodium after melting (ppm), the amount of uranium and thorium after melting (ppb), the circularity, the crystal residual rate (%), and the number of hollows of 5 μm or more when magnified 2000 times by an electron microscope (pieces/9 ^mm2 ) are shown. Table 4 shows the composition analysis of the contained elements (expressed in ppb and ppm).

In addition, we present photographs taken with an electron microscope (SEM). Figure 1 shows Test Example 4 after crushing (5,000x) and after melting (10,000x). Figure 2 shows a cross section of Test Example 6, with electron microscope photographs (2,000x) of different observation areas. Figure 3 shows a cross section of Test Example 13, with electron microscope photographs (2,000x) of different observation areas.

[Discussion]
As can be seen from the photograph in FIG. 1, even if the crushed material is of an irregular shape, it was confirmed that it was granulated into spherical particles by exposure to flames after crushing. Although FIG. 2 is hard to see because it is black overall, there are almost no hollows (voids) in the spherical silica particles that expose the cut surface. In FIG. 3, there are hollows in each particle that are large compared to the particle diameter. When actually measured, the diameter was 5 to 10 μm. In Test Example 6 in FIG. 2 and Test Example 13 in FIG. 3, Test Example 6 dissolves the raw material in a basic solution. In contrast, Test Example 13 omits dissolving in a basic solution. From this, dissolving the raw material in a basic solution has a great advantage in reducing hollows.

Focusing on the amount (ppb) of uranium and thorium elements in Test Examples 1 to 10 (excluding Test Example 3), comparing the amount at the raw material stage with that after melting, the amount was greatly reduced to 1/10 or less and 6/100 or less after melting. Specifically, the amount of uranium was 1 ppb, and the amount of thorium was 2 ppb. The amount of sodium element (ppm) was also at a low level of 1 ppm after melting. In addition, a comparison of all components in Table 4 confirmed the reduction of not only uranium and thorium elements but also other impurity components. From this, the method of combining dissolution in a basic solution and exposure to flame is effective in reducing impurity components. In addition, even if the raw material for manufacturing spherical silica particles is inexpensive to procure but has a low purity, it is possible to reduce the impurity components, which makes it possible to suppress manufacturing costs overall.

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

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

The residual rate of silicon oxide crystals was below the measurement limit in Test Examples 1 to 10 (except Test Example 3), and can be considered to be practically non-existent. In addition, the rate 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 practically non-existent. These facts support the superiority of the preparation method involving dissolution in a basic solution.

Therefore, as high-purity fused spherical silica for use as a filler in resin compositions for electronic devices, it contains few impurities, including uranium and thorium, making it possible to reduce the radiation source associated with radioactive decay. It is also extremely nearly spherical, making it easier to ensure the fluidity of the coating. Furthermore, there are no relatively large hollow spaces (voids) in the particles, so insulation and other performance properties are also guaranteed. In addition, 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 (8)

The content of uranium element in the spherical silica particles is 5 ppb or less, and the content of thorium element in the spherical silica particles is 5 ppb or less,
The circularity of the spherical silica particles is 0.98 or more;
the residual rate of silicon oxide crystals in the spherical silica particles is 0.01% or less;
1. A high-purity fused spherical silica, characterized in that the number of hollow parts having a diameter of 5 μm or more present in each spherical silica particle is 2 or less within an observation area of 9 ^mm2 under an electron microscope. The high-purity fused spherical silica according to claim 1, wherein the sodium content in the spherical silica particles is 10 ppm or less. The spherical silica particles are high-purity fused spherical silica according to claim 1, which is made from metallic silicon. The high-purity fused spherical silica according to claim 3, wherein the spherical silica particles have been dissolved in a basic solution of metal silicon. The high-purity fused spherical silica of claim 1, wherein the spherical silica particles are exposed to a flame. A resin composition for electronic devices, comprising the high purity fused spherical silica according to claim 1 and a resin composition. A cosmetic comprising the high-purity fused spherical silica according to claim 1. The cosmetic product according to claim 7, which is a powder, an ointment, or a lotion.