Method for producing silica particles

Abstract

To produce silica particles having high uniformity of particle diameter with good reproducibility.SOLUTION: There is provided a method for producing silica particles which comprises: a generation step of generating a plurality of small silica particles from a product solution containing a first silicon alkoxide; and a first growth step of growing the particle diameter of first small particles by mixing the first small particles, which are a portion of the small silica particles and a first growth solution containing a second silicon alkoxide to obtain silica particles having a larger particle diameter than the small silica particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing silica particles. [Background technology]

[0002] Silica particles are used as fillers in various resin compositions for electronic materials such as semiconductor encapsulation or for film production, etc. For precise and uniform encapsulation, highly monodisperse silica particles with little particle size variation are required.

[0003] A known method for producing highly monodisperse silica particles is the so-called sol-gel method, in which silica particles are produced by hydrolysis and polycondensation of silicon alkoxide (e.g., Patent Documents 1 to 3). As shown in Patent Document 1, it is known that in the sol-gel method, the particle size and particle size distribution can be adjusted by adjusting the reaction conditions during the reaction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-193950 [Patent Document 2] International Publication No. 2018 / 096876 Brochure [Patent Document 3] Patent Publication No. 2021-116225 Summary of the Invention [Problem to be solved by the invention]

[0005] In the sol-gel method, small silica particles are produced from silicon alkoxide, and then grown to a desired particle size to obtain silica particles. The particle size of the small silica particles is easily affected by production conditions such as reaction temperature and stirring conditions.

[0006] Variations in the particle size of small silica particles caused by slight differences in production conditions significantly affect the particle size of the silica particles after the small silica particles have grown, which has led to the problem of making it difficult to uniformize the particle size of silica particles between production batches.

[0007] An object of one aspect of the present invention is to provide a method for producing silica particles with a highly uniform particle size with good reproducibility. [Means for solving the problem]

[0008] and a first growth step of mixing first small particles, which are a part of the silica small particles, with a first growth liquid containing a second silicon alkoxide to grow the particle size of the first small particles and obtain silica particles having a particle size larger than that of the silica small particles.

[0009] A method for producing silica particles according to one embodiment of the present invention may further include, independent of the first growth step, a second growth step in which at least a portion of second small particles, which are the portion of the silica small particles other than the first small particles, are mixed with a second growth liquid containing a third silicon alkoxide to grow the particle size of the second small particles.

[0010] In one embodiment of the method for producing silica particles of the present invention, the component compositions of the first growth liquid and the second growth liquid may be the same, and the amount ratio and mixing temperature of the second small particles to the second growth liquid in the second growth process may be the same as the amount ratio and mixing temperature of the first small particles to the first growth liquid in the first growth process.

[0011] In the method for producing silica particles according to one aspect of the present invention, the first silicon alkoxide may be tetraethoxysilane, and the second silicon alkoxide may be tetramethoxysilane. [Effects of the Invention]

[0012] According to one aspect of the present invention, a method for producing silica particles with a highly uniform particle size with good reproducibility can be realized. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an outline of a method for producing silica particles according to one embodiment of the present invention. [Figure 2] FIG. 1 is a flow diagram showing an example of a method for producing silica particles according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. Furthermore, in this specification, "A to B" means A or more and B or less, unless otherwise specified.

[0015] 〔overview〕 As shown in Figure 1, a method for producing silica particles according to one embodiment of the present invention first involves a production step for producing small silica particles to be used as seeds for silica particles, followed by a growth step for growing the small silica particles. In one embodiment of the present invention, a larger amount of small silica particles are produced in the production step than the number of small silica particles used in one growth step. This makes it possible to carry out two or more growth steps from the small silica particles produced in one production step. Note that the method for producing silica particles according to one embodiment of the present invention produces spherical silica particles with high sphericity.

[0016] The production liquid in the production step and the growth liquid in the growth step each contain silicon alkoxide and a component that promotes hydrolysis and polycondensation of the silicon alkoxide. That is, the production step and the growth step can be said to be methods for producing silica particles using a so-called sol-gel method.

[0017] Conventionally, the production process and the growth process have been performed as a series of production processes. When the production process is performed separately for each growth process, the particle size of the small silica particles produced in each production process may differ. Therefore, for example, if the particle size of the small silica particles differs between production batches, it is difficult to make the particle size of the silica particles after the growth process uniform between these production batches.

[0018] Furthermore, in order to obtain silica particles with high particle sphericity and particle size uniformity (monodispersity), it is important that the particle size is highly uniform at the initial small silica particle stage. If there is variation in particle size at the small silica particle stage, there will also be variation in the particle size of the silica particles after the growth process.

[0019] In this regard, within a group of highly uniform small silica particles obtained by a single production process, the particle size uniformity is extremely high in each group.Therefore, if the small silica particles obtained by a single production process are used in multiple growth processes, it is easy to make the particle size of the silica particles obtained between these multiple growth processes uniform.In addition, even if silica particles with different particle sizes are produced in multiple growth processes, it is easy to ensure the particle size uniformity of the silica particles in each of these growth processes.

[0020] Therefore, for example, a large amount of small silica particles may be produced in the production step, a portion of which may be used in the growth step, and the remaining small silica particles may be stored and used in the production of another batch of silica particles at a later date. With this configuration, silica particles having a desired particle size can be produced reproducibly in multiple production batches.

[0021] In this way, using the small silica particles after the production step in multiple independent growth steps overturns the conventional technical common sense that the production step and the growth step are performed as a series of steps. The inventors have conducted extensive research based on this new finding and have completed the present invention. Hereinafter, a method for producing silica particles according to one embodiment of the present invention will be described.

[0022] [Method for producing silica particles] A method for producing silica particles according to one embodiment of the present invention includes a generation step for generating small silica particles and a first growth step for growing the small silica particles. The first growth step may be one of the above-described multiple growth steps. In this specification, when the term "growth step" is used, it is intended to collectively refer to both the first growth step and the second growth step described below, unless otherwise specified.

[0023] The method for producing silica particles according to one embodiment of the present invention may be a method for producing silica particles by a sol-gel method. In the sol-gel method, for example, silicon alkoxide is hydrolyzed and polycondensed in a reaction solvent containing water and a catalyst to produce a silica sol containing silica particles (production step and growth step). Alternatively, powdered silica particles may be obtained by gelling the silica sol, removing the produced solid content, and drying the solid content, or the powdered silica particles may be further calcined and crushed. Thus, the method for producing silica particles according to one embodiment of the present invention may include steps other than the production step and growth step.

[0024] (generation process) The production step is a step of producing a plurality of small silica particles from a production solution containing a first silicon alkoxide. In the production step, the small silica particles are produced by hydrolysis and polycondensation of the first silicon alkoxide in the production solution containing the first silicon alkoxide. The small silica particles have a smaller particle size than the silica particles obtained in the growth step performed after the production step. The small silica particles are sometimes called "seed particles" because they serve as seeds for obtaining silica particles in the growth step.

[0025] The first silicon alkoxide is not particularly limited as long as it is a silicon alkoxide (alkoxysilane) that is commonly used in the production of silica particles by the sol-gel method. Examples of the first silicon alkoxide include methyltrimethoxysilane, methyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, and tetrabutoxysilane. Among them, methyltrimethoxysilane, tetramethoxysilane, and tetraethoxysilane are preferred from the viewpoint of ease of availability and handling. These silicon alkoxides may be used alone or in combination of two or more.

[0026] As the first silicon alkoxide, from the viewpoint of easily making the particle size of the produced small silica particles uniform, it is preferable to use a silicon alkoxide having a relatively slow reaction rate alone, and it is particularly preferable to use tetraethoxysilane alone.

[0027] The product liquid containing the first silicon alkoxide is not particularly limited as long as it has a composition that allows the hydrolysis and polycondensation of the first silicon alkoxide to proceed. Such a product liquid may contain, in addition to the first silicon alkoxide, for example, a solvent and a catalyst. Furthermore, since water is required for the hydrolysis of the first silicon alkoxide, at least one of the solvent and the catalyst contains water.

[0028] The solvent is preferably a polar solvent. The polar solvent may be water, an organic solvent capable of dissolving 10 g or more of water per 100 g at room temperature and pressure, or a mixed solvent of water and the organic solvent. When the solvent contains such an organic solvent, the organic solvent may be one type or two or more types. When the solvent contains two or more types of organic solvents, the mixture of organic solvents may satisfy the above-mentioned water solubility requirement.

[0029] Examples of the organic solvent include alcohols, ethers, and amide compounds. Examples of the alcohols include methanol, ethanol, isopropyl alcohol, and butanol. Examples of the ethers include tetrahydrofuran and dioxane. Examples of the amide compounds include dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

[0030] In the formation step and the growth step, alcohol is by-produced by hydrolysis of silicon alkoxide, and therefore, from the viewpoints of reducing impurities in the dispersion of the produced silica particles and facilitating removal by heating, it is preferable that the organic solvent is alcohol.

[0031] The catalyst may be an acidic catalyst or a basic catalyst. From the viewpoint of obtaining spherical particles with a highly uniform particle size, the catalyst is preferably a basic catalyst. The basic catalyst is not particularly limited as long as it is a basic catalyst that is generally used in the production of silica particles by a sol-gel reaction. Examples of the basic catalyst include amine compounds and alkali metal hydroxides.

[0032] From the viewpoint of obtaining high-purity small silica particles, the basic catalyst is preferably an amine compound. Examples of amine compounds include ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine. Because it is highly volatile and easy to remove, the basic catalyst is preferably ammonia. The basic catalyst may be one of these, or may contain two or more of them.

[0033] The catalyst may be used by dissolving it in water or an organic solvent, such as aqueous ammonia. From the viewpoint of adjusting the reaction rate of the production step, it is preferable to use the catalyst as an aqueous solution in which the catalyst is dissolved in water and the concentration is adjusted. When the catalyst is used as an aqueous solution, the concentration of the catalyst in the aqueous solution may be, for example, 1 to 30 mass%.

[0034] The proportions of water, organic solvent, and catalyst in the product liquid may be appropriately determined depending on the reaction rate of the production step, the target particle size of the small silica particles, and the target concentration of the small silica particles in the small silica particle dispersion after the production step.

[0035] The proportion of water in the product liquid is preferably 1 to 30% by mass, more preferably 5 to 20% by mass. When the product liquid contains an organic solvent, the proportion of the organic solvent in the product liquid is preferably 50 to 95% by mass, more preferably 70 to 90% by mass. The amount of catalyst contained in the product liquid is preferably 0.1 to 60% by mass, more preferably 0.5 to 40% by mass, relative to the amount of the first silicon alkoxide.

[0036] The production step may be carried out using a reaction vessel generally used for producing silica particles by a sol-gel reaction, such as a cylindrical vessel equipped with a stirring blade.

[0037] The method for preparing the product solution is not particularly limited, but an example is a method in which a solvent and a catalyst are added to a reaction vessel (S1), and then a first silicon alkoxide is added thereto (S2), as shown in FIG. 2. This method allows for the production of spherical small silica particles with a highly uniform particle size with good reproducibility. In this case, for example, a portion of the first silicon alkoxide may be added to the reaction vessel first, and then the remaining first silicon alkoxide may be added. Alternatively, the first silicon alkoxide and the catalyst may be added approximately simultaneously. Furthermore, when the first silicon alkoxide contains two or more types of silicon alkoxide, they may be added simultaneously or sequentially.

[0038] The reaction temperature for producing small silica particles from the product solution may be appropriately selected depending on the component composition of the product solution and the target particle size of the small silica particles. The reaction temperature may be, for example, in the range of -10 to 60°C. At such a reaction temperature, the hydrolysis and polycondensation of the first silicon alkoxide proceed (S3, production step), thereby producing small silica particles.

[0039] The particle size of the small silica particles produced in the production process is not particularly limited as long as it is smaller than the target particle size of the silica particles after the growth process, but may be, for example, 0.40 μm or less, or 0.30 μm or less, preferably 0.20 μm or less, and more preferably 0.10 μm or less. Furthermore, if the particle size of the small silica particles is too small, even a small difference in particle size will easily affect the particle size of the silica particles after the growth process, and they will easily aggregate, making it difficult to achieve uniform particle size in the growth process. Therefore, the particle size of the small silica particles is preferably 0.05 μm or more.

[0040] Such a particle size makes it easy to obtain a group of small silica particles with a highly uniform particle size, and also prevents the reaction time in the production step from becoming too long, resulting in a decrease in production efficiency.

[0041] The method for measuring the particle size of small silica particles is not particularly limited. For example, the average particle size of a group may be determined by a laser diffraction scattering method, or the particle size of each small silica particle may be determined from an image captured by an electron microscope or the like. This also applies to the particle size of silica particles described below. Note that the "particle size" of small silica particles and silica particles refers to the cumulative 50% diameter on a volume basis.

[0042] (growth process) In a method for producing silica particles according to one embodiment of the present invention, a growth step is carried out to grow the particle size of the small silica particles obtained in the production step. As the growth step, at least a first growth step is carried out. It is also preferable to further carry out a second growth step independently of the first growth step. Both the first growth step and the second growth step are steps for growing small silica particles, and each uses small silica particles obtained in a single production step. The second growth step may be carried out multiple times.

[0043] In the first growth step, the first small particles, which are a part of the multiple small silica particles produced in the production step, are mixed with a first growth solution containing a second silicon alkoxide. This causes the particle size of the first small particles to grow, resulting in silica particles with a particle size larger than that of the small silica particles. In the first growth step, the growth in particle size of the first small particles proceeds through hydrolysis and polycondensation of the second silicon alkoxide, as in the production step.

[0044] In the second growth step, which is independent of the first growth step, at least a portion of the second small particles (i.e., the portion of the small silica particles produced in the production step other than the first small particles) is mixed with a second growth solution containing a third silicon alkoxide to grow the particle size of the second small particles. In the second growth step, the growth of the particle size of the second small particles proceeds by hydrolysis and polycondensation of the third silicon alkoxide, as in the production step.

[0045] "Independently from the first growth step" includes at least both cases where the second growth step is carried out at a different time from the first growth step (for example, later than the first growth step), and cases where the second growth step is carried out approximately simultaneously with the first growth step using a reaction vessel separate from that used for the first growth step.

[0046] In the first growth step, only a portion of the small silica particles obtained in the production step is used, not all of them. This portion of the small silica particles is referred to as "first small particles." Furthermore, the portion of the small silica particles obtained in the production step other than the first small particles is referred to as "second small particles."

[0047] The amount of the first small particles is not particularly limited as long as it is the total amount of the silica small particles produced in the production process. The amount of the first small particles may be 50% by mass or less of the total amount of the silica small particles produced in the production process, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass or less. From the viewpoint of using the silica small particles obtained from one production process in many production batches, the amount of the first small particles is preferably 20% by mass or less of the silica small particles produced in the production process.

[0048] The second small particles are preferably used in the second growth step. The second small particles may be used in their entirety or in part in one second growth step. For example, when the second growth step is performed two or more times, the second small particles may be divided into portions corresponding to the number of times the second growth step is performed, and each portion may be used in each second growth step. For example, when the second growth step is performed nine times (i.e., 10 production batches including the first growth step), the first small particles are used in an amount of 10% by mass of the silica small particles produced in the production step. Then, 1 / 9 of the second small particles (10% by mass of the silica small particles produced in the production step) may be used in each second growth step.

[0049] The total number of the first growth step and the multiple second growth steps is the number of production batches in which silica particles are produced using the small silica particles obtained in one production step. Because the small silica particles before growth have high uniformity in particle size between these production batches, it is easy to obtain high uniformity in particle size between production batches for the silica particles after the growth step as well.

[0050] The second silicon alkoxide and the third silicon alkoxide may each be one or more of the compounds exemplified as the first silicon alkoxide. The first silicon alkoxide, the second silicon alkoxide, and the third silicon alkoxide may all be the same silicon alkoxide, or may be different silicon alkoxides. In order to make the particle size of the silica particles uniform between the first growth step and the second growth step, it is preferable that the second silicon alkoxide and the third silicon alkoxide are the same type of silicon alkoxide.

[0051] The second silicon alkoxide is preferably a silicon alkoxide with a higher reaction efficiency than the first silicon alkoxide. For example, when the first silicon alkoxide is tetraethoxysilane, the second silicon alkoxide is preferably tetramethoxysilane. Tetramethoxysilane has a higher Si content in the molecule than tetraethoxysilane, making it easier to increase the concentration of silica particles in the silica particle dispersion.

[0052] In this way, by using different silicon alkoxides in the generation step and the growth step, the production cost can be reduced by increasing the yield of silica particles while maintaining the uniformity of the particle size of the silica particles.

[0053] The first growth liquid and the second growth liquid may each be a solution containing the second silicon alkoxide or the third silicon alkoxide, as well as the solvent and catalyst exemplified for the production liquid. The component compositions other than the silicon alkoxide in the production liquid, the first growth liquid, and the second growth liquid may be the same or different. For example, in the production liquid, the proportion of water and / or catalyst may be reduced to make the particle size uniform and to allow the reaction to proceed slowly, while in the first growth liquid and the second growth liquid, the proportion of water and / or catalyst may be increased to prioritize reaction efficiency.

[0054] When the particle size of the silica particles is to be uniform between the first growth step and the second growth step, it is preferable that the component compositions of the first growth solution and the second growth solution are the same. In this specification, the term "the same conditions" means that the conditions in the manufacturing plan (manufacturing protocol) are the same, and it is a concept that allows for errors that may occur in the actual manufacturing process.

[0055] The first growth step may be performed in the same reaction vessel as that used in the generation step. Furthermore, the amounts of raw materials, such as silicon alkoxide, used in the generation step and the first growth step may differ. Therefore, the reaction vessel used in the first growth step may have a different capacity from that used in the generation step.

[0056] The method for preparing the first growth solution is not particularly limited, but an example is a method in which the first small particles, solvent, and catalyst are charged into a reaction vessel (S4), and the second silicon alkoxide and catalyst are added approximately simultaneously (S5), as shown in Figure 2. This method allows for the reproducibility of spherical silica particles with a highly uniform particle size. In this case, for example, a portion of the second silicon alkoxide may be added to the reaction vessel first, and then the remaining second silicon alkoxide and catalyst may be added simultaneously.

[0057] When the second silicon alkoxide contains two or more silicon alkoxides, they may be added simultaneously or sequentially. The ratio of each component contained in the first growth liquid may be appropriately selected depending on the target particle size of the silica particles.

[0058] The reaction temperature at which small silica particles are grown from the first growth solution may be appropriately selected depending on the component composition of the first growth solution and the target particle diameter of the silica particles. The reaction temperature may be, for example, in the range of -10 to 60°C. At such a reaction temperature, hydrolysis and polycondensation of the second silicon alkoxide proceed (S6, growth step), thereby growing the particle diameter of the first small particles.

[0059] The reaction vessel, the method for preparing the second growth liquid, and the reaction temperature in the second growth step may be appropriately determined in the same manner as in the first growth step. When the particle size of the silica particles in the first and second growth steps is to be uniform, it is preferable that the quantitative ratio of the second small particles to the second growth liquid and the mixing temperature in the second growth step be the same as the quantitative ratio of the first small particles to the first growth liquid and the mixing temperature in the first growth step. It is also more preferable that the other conditions be the same between the first growth step and the second growth step.

[0060] The particle size of the silica particles obtained by the first growth step is not particularly limited. If the target particle size of the silica particles is relatively large, for example, 1.5 μm or more, an additional growth step may be performed after the first growth step to further grow the silica particles. For example, small silica particles having a particle size of about 0.2 μm produced in the production step are used to obtain silica particles (intermediate particles) having a particle size of about 0.4 μm by the first growth step. Then, an additional growth step may be performed to grow the particle size of the intermediate particles, thereby obtaining silica particles having a particle size of about 1.5 μm or more.

[0061] The additional growth step may be performed after the second growth step. In order to make the particle size of the silica particles uniform between production batches, if an additional growth step is performed after the first growth step, it is preferable to perform a similar additional growth step after the second growth step. Furthermore, the reaction conditions in the additional growth step may be the same as or different from those in the first or second growth step.

[0062] (Second small particle storage) When the second growth step is carried out after the first growth step, the second small particles can be stored until the second growth step is carried out. The storage conditions for the second small particles are not particularly limited.

[0063] When storing the second small particles, a dispersion medium may be added to prevent aggregation of the second small particles. The dispersion medium for dispersing the second small particles during storage is not particularly limited, and may be, for example, the solvents exemplified for the production liquid.

[0064] The second small particles are preferably stored in a storage container that is not reactive with the dispersion medium that disperses the second small particles. Examples of such storage containers include storage containers made of metal such as stainless steel or resin. The storage temperature of the second small particles is preferably room temperature to prevent evaporation of the solvent. Specifically, for example, 30°C or less is preferable, and 20°C or less is more preferable. To prevent solidification of the dispersion medium, the temperature is preferably above the freezing point of the dispersion medium, for example, 0°C or above.

[0065] The atmosphere in which the second small particles are stored is not particularly limited, and may be, for example, air or an inert gas such as nitrogen. Furthermore, from the viewpoint of preventing aggregation of particles, it is preferable to constantly or periodically stir the second small particles. Since the second small particles have a small particle size and a slow settling rate, they can be stored for a sufficiently long period of time even if stirring during storage is omitted.

[0066] The second small particles can generally be stored in a stable dispersed state in the dispersion medium for about six months after the production process, although this depends on the particle size, dispersion medium, etc. The following are the results of an investigation into the sedimentation rate of the second small particles.

[0067] The conditions were particle diameter (d) of 0.06 μm and particle density (ρ s ) to 2000 kg / m 3 , the density of the dispersion medium (ρ L ) at 840 kg / m 3 , the viscosity of the dispersion medium (μ L ) to 0.622 kg / m s, and the acceleration of gravity (g) to 9.8 m / s 2 It was decided.

[0068] The particle density was determined taking into consideration that the second small particles were unsintered silica small particles. The dispersion medium was assumed to be a 2:8 mixed solvent of water and methanol. The second small particles were spherical and had a sufficiently small particle diameter, so Stokes' law was assumed to hold. The settling velocity (u t ) was sought.

[0069] u t =d 2 (ρ s -ρ L )g / (18μ L ) (1) As a result, the settling velocity of the second small particles (u t ) is 3.65 × 10 -12 m / s. This indicates that the settling distance of the second small particles in the dispersion medium is approximately 0.05 mm in six months, and approximately 0.1 mm in one year. This result suggests that the second small particles have an extremely small settling distance, making them less likely to aggregate, and that they can be stored stably for at least six months. However, if the second small particles are constantly or periodically stirred in the storage container, the storage period may be even longer.

[0070] Thus, the second small particles can be stored in a stable state for a long period of time, and therefore, according to the method for producing silica particles according to one embodiment of the present invention, after the first growth step is performed, it is possible to produce silica particles having a uniform particle size between each production batch and good reproducibility in the production of the silica particles. [Example]

[0071] An example of the present invention and a comparative example will be described below.

[0072] (Method according to the embodiment) In the examples, small silica particles obtained in one production step were used to carry out six growth steps (one first growth step and five second growth steps) to obtain six production batches of silica particles.

[0073] Specifically, 1m 3A reactor having an internal volume of 405.7 kg of methanol and 83 kg of 25% aqueous ammonia were charged, and the liquid temperature was adjusted to 40°C. 10.4 kg of tetraethoxysilane was used as the first silicon alkoxide in the production step, and this was mixed with 30.6 kg of methanol and added to the reactor at a rate of 40 kg / min or more. After the addition was completed, a production step was carried out in which the production reaction was allowed to proceed with stirring at a liquid temperature of 40°C for 30 minutes, and approximately 530 kg of a slurry of small silica particles was obtained.

[0074] Next, the slurry of small silica particles was divided into 59.8 kg of the first small particle slurry and the remaining (approximately 470.2 kg) of the second small particle slurry, and the first growth step was carried out using the first small particle slurry. 3 A reactor having an internal volume of 59.8 kg of the first small particle slurry, 108.1 kg of methanol, and 18.2 kg of 25% aqueous ammonia were charged, and the liquid temperature was adjusted to 45°C. As the second silicon alkoxide for the first growth step, 1888.0 kg of tetramethoxysilane was used, which was mixed with 188.8 kg of methanol and charged at a rate of 5 kg / min. At the same time, 840.0 kg of 25% aqueous ammonia was charged at a rate of 2 kg / min. After the start of charging, the first growth step was carried out, in which the growth reaction was allowed to proceed under stirring at a liquid temperature of 45°C for approximately 420 minutes, to obtain silica particles.

[0075] In addition, independently of the first growth step, five portions of 59.8 kg each were taken from the slurry of second small particles, and these were used to carry out five second growth steps. All conditions for the second growth step, such as the amount of each raw material added, reaction temperature, and reaction time, were the same as those for the first growth step. In this way, a total of six production batches of silica particles were produced in the first and second growth steps for one production step.

[0076] (Comparative Example Method) In the comparative example, the production method was repeated six times, in which all of the small silica particles obtained in the production step were used in the growth step according to the comparative example, to obtain six production batches of silica particles.

[0077] Specifically, 45.8 kg of methanol and 9.4 kg of 25% aqueous ammonia were charged into a 500 L reactor, and the liquid temperature was adjusted to 40°C. 1.2 kg of tetraethoxysilane was used as the silicon alkoxide, the raw material for silica particles, and this was mixed with 3.5 kg of methanol and poured into the reactor at a rate of 40 kg / min or more. After the addition was complete, the reaction to produce small silica particles was allowed to proceed with stirring for 30 minutes at a liquid temperature of 40°C, yielding approximately 59.9 kg of a slurry of small silica particles.

[0078] Next, the entire amount of the obtained slurry of small silica particles was used to carry out the growth step. 3 A reactor having an internal volume of 59.9 kg of small silica particle slurry, 108.1 kg of methanol, and 18.2 kg of 25% aqueous ammonia were charged, and the liquid temperature was adjusted to 45°C. 1888.0 kg of tetramethoxysilane was used as the silicon alkoxide for the growth step, and this was mixed with 188.8 kg of methanol and added at a rate of 5 kg / min. 840.0 kg of 25% aqueous ammonia was also added at a rate of 2 kg / min. After the start of addition, the growth reaction was allowed to proceed with stirring at a liquid temperature of 45°C for approximately 420 minutes, yielding silica particles.

[0079] In the comparative example, the above series of production methods was carried out six times to produce six production batches of silica particles.

[0080] (result) The average particle size (50% cumulative diameter on a volume basis) of the small silica particles and silica particles obtained by the methods according to the Examples or Comparative Examples was determined by a laser diffraction scattering method (LS13320, manufactured by Beckman Coulter). The average particle size of the small silica particles according to the Examples was 0.06 μm. The silica particles obtained in six production batches using the small silica particles were each fired at 800°C for 10 hours and then crushed using a swirling flow jet mill (STJ-200, manufactured by Seishin Enterprises). The crushing conditions were a swirling pressure of 0.5 MPa and a swirling air volume of 2.4 m 3The feed rate was 10 kg / h, the compression pressure was 0.6 MPa, and the average particle diameters of the silica particles were 0.765 μm, 0.766 μm, 0.757 μm, 0.761 μm, 0.761 μm, and 0.781 μm, respectively. The sphericity of the silica particles was 0.96, 0.97, 0.97, 0.95, 0.97, and 0.96, respectively.

[0081] The sphericity of the silica particles was determined by observation using a SEM (JSM-6060, manufactured by JEOL Ltd.). Specifically, more than 1,000 silica particles were observed, and the sphericity of each silica particle was measured using an image processing program (AnalySIS, manufactured by Soft Imaging System GmbH), and the average was calculated. The sphericity of each silica particle was calculated using the following formula: Sphericity = 4π×(Area) / (Perimeter) 2 The average particle size of the six production batches according to the example was 0.765 μm, with a standard deviation of 0.008 μm.

[0082] The average particle sizes of the small silica particles obtained from the six production batches of the comparative example were 0.06 μm, 0.08 μm, 0.06 μm, 0.07 μm, 0.06 μm, and 0.07 μm, respectively. Silica particles obtained from these small silica particles were calcined and crushed under the same conditions as in the examples. The average particle sizes of the silica particles were 0.753 μm, 0.784 μm, 0.766 μm, 0.788 μm, 0.759 μm, and 0.779 μm, respectively. The sphericity of the silica particles was 0.95, 0.97, 0.97, 0.96, 0.96, and 0.96, respectively. The average average particle size of the six production batches of the comparative example was 0.772 μm, with a standard deviation of 0.014 μm.

[0083] As described above, the method according to the comparative example had a standard deviation of nearly twice as large as that of the method according to the example, indicating a large variation between the six production batches. From the above, the method according to one embodiment of the present invention was able to produce silica particles with a small variation in particle size between production batches and good reproducibility.

[0084] [Additional Notes] The present invention is not limited to the above-described embodiments / examples, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments / examples are also included in the technical scope of the present invention. [Industrial Applicability]

[0085] The present invention can be utilized, for example, in the production of silica particles used as fillers for various resin compositions for electronic materials such as semiconductor encapsulants or for film production.

Claims

1. a production step of producing a plurality of small silica particles from a production solution containing a first silicon alkoxide; a first growth step of mixing first small particles, which are a portion of the plurality of silica small particles, with a first growth solution containing a second silicon alkoxide to grow the particle size of the first small particles and obtain silica particles having a particle size larger than that of the silica small particles; a second growth step, independent of the first growth step, of mixing at least a portion of second small particles, which are portions of the silica small particles other than the first small particles, with a second growth solution containing a third silicon alkoxide to grow the particle size of the second small particles; The first growth solution and the second growth solution have the same component composition, and A method for producing silica particles, characterized in that the quantitative ratio and mixing temperature of the second small particles to the second growth liquid in the second growth process are the same as the quantitative ratio and mixing temperature of the first small particles to the first growth liquid in the first growth process.

2. the first silicon alkoxide is tetraethoxysilane; The method for producing silica particles according to claim 1 , wherein the second silicon alkoxide is tetramethoxysilane.

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