JP7741002B2 - Method for producing silica particles - Google Patents

Description

The present invention relates to a method for producing silica particles.

Silica particles are used as a filler in various resin compositions for electronic materials such as semiconductor encapsulation or for film manufacturing. To achieve precise and uniform encapsulation, highly monodisperse silica particles with little variation in particle size are required.

The sol-gel method, in which silica particles are produced by hydrolysis and polycondensation of silicon alkoxide, is known as a method for producing highly monodisperse silica particles (see, for example, 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.

JP 2013-193950 A International Publication No. 2018/096876 Japanese Patent Application Laid-Open No. 2021-116225

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

Variations in the particle size of small silica particles caused by slight differences in production conditions have a significant impact on the particle size of the silica particles after the small silica particles have grown. This has created the problem of making it difficult to standardize the particle size of silica particles between production batches.

One aspect of the present invention aims to realize a method for reproducibly producing silica particles with highly uniform particle size.

The method includes a first growth step in which first small particles, which are a portion of the silica small particles, are mixed 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 the silica small particles.

The 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, is mixed with a second growth solution containing a third silicon alkoxide to grow the particle size of the second small particles.

In one embodiment of the present invention, the method for producing silica particles may be such that the component compositions of the first growth liquid and the second growth liquid are the same, and the quantitative ratio and mixing temperature of the second small particles to the second growth liquid in the second growth step are the same as the quantitative ratio and mixing temperature of the first small particles to the first growth liquid in the first growth step.

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

One aspect of the present invention provides a method for reproducibly producing silica particles with highly uniform particle size.

FIG. 1 is a diagram showing an outline of a method for producing silica particles according to one embodiment of the present invention. FIG. 1 is a flow diagram showing an example of a method for producing silica particles according to an embodiment of the present invention.

One embodiment of the present invention is described below, but the present invention is not limited to this. The present invention is not limited to the 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 greater than or equal to A and less than or equal to B, unless otherwise specified.

〔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 allows for the production of spherical silica particles with high sphericity.

The production liquid in the production process and the growth liquid in the growth process each contain silicon alkoxide and components that promote the hydrolysis and polycondensation of silicon alkoxide. In other words, the production process and growth process can be considered methods for producing silica particles using the so-called sol-gel method.

Conventionally, the production process and growth process have been carried out as a single manufacturing process. When a production process is carried out separately for each growth process, differences in the particle size of the small silica particles produced in each production process can occur. Therefore, for example, if differences in the particle size of the small silica particles occur between production batches, it becomes difficult to ensure that the particle size of the silica particles after the growth process is consistent between these production batches.

In addition, 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.

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

Therefore, for example, a large amount of small silica particles can be produced in the production process, some of which can be used in the growth process, while the remaining small silica particles can be stored and used when producing a different batch of silica particles at a later date. This configuration allows silica particles having the desired particle size to be produced reproducibly across multiple production batches.

In this way, using the small silica particles after the production process in multiple independent growth processes overturns the conventional technical wisdom that the production process and growth process are carried out as a series of steps. Based on this novel finding, the inventors conducted extensive research and eventually completed the present invention. Below, we will explain a method for producing silica particles according to one embodiment of the present invention.

[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 the first growth step and the second growth step described below, unless otherwise specified.

A 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). Powdered silica particles may also be obtained by gelling the silica sol and removing and drying the resulting solid, or the powdered silica particles may be further calcined and crushed. In this way, a method for producing silica particles according to one embodiment of the present invention may include steps other than the production step and growth step.

(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.

The first silicon alkoxide is not particularly limited, as long as it is a silicon alkoxide (alkoxysilane) 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. Of these, methyltrimethoxysilane, tetramethoxysilane, and tetraethoxysilane are preferred from the standpoint of ease of availability and handling. These silicon alkoxides may be used alone or in combination of two or more.

In order to make it easier to produce small silica particles with a uniform particle size, it is preferable to use a silicon alkoxide with a relatively slow reaction rate alone as the first silicon alkoxide, and it is particularly preferable to use tetraethoxysilane alone.

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. In addition to the first silicon alkoxide, such a product liquid may contain, for example, a solvent and a catalyst. Furthermore, because water is required for the hydrolysis of the first silicon alkoxide, at least one of the solvent and the catalyst must contain water.

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 such an 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 should satisfy the above-mentioned water solubility requirements.

Examples of organic solvents include alcohols, ethers, and amide compounds. Examples of alcohols include methanol, ethanol, isopropyl alcohol, and butanol. Examples of ethers include tetrahydrofuran and dioxane. Examples of amide compounds include dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

During the production and growth processes, alcohol is produced as a by-product due to the hydrolysis of silicon alkoxide. Therefore, from the standpoint of reducing impurities in the dispersion of the produced silica particles and making it easier to remove by heating, it is preferable that the organic solvent be alcohol.

The catalyst may be an acidic catalyst or a basic catalyst. From the perspective of obtaining spherical particles with a highly uniform particle size, the catalyst is preferably a basic catalyst. There are no particular restrictions on the basic catalyst, as long as it is a basic catalyst commonly used in the production of silica particles by a sol-gel reaction. Examples of basic catalysts include amine compounds and alkali metal hydroxides.

From the perspective 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.

The catalyst may be used dissolved in water or an organic solvent, such as aqueous ammonia. From the perspective of adjusting the reaction rate of the production process, it is preferable to use the catalyst as an aqueous solution in which the catalyst has been dissolved in water and the concentration has been adjusted. When using the catalyst as an aqueous solution, the catalyst concentration in the aqueous solution may be, for example, 1 to 30% by mass.

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

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

The production process may be carried out using a reaction vessel commonly used for producing silica particles by sol-gel reactions. Such a reaction vessel may be, for example, a cylindrical vessel equipped with a stirring blade.

The method for preparing the product solution is not particularly limited, but an example is a method in which a solvent and catalyst are added to a reaction vessel (S1), and then a first silicon alkoxide is added thereto (S2), as shown in Figure 2. This method allows for the reproducible production of small spherical silica particles with a highly uniform particle size. 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 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.

The reaction temperature for producing small silica particles from the product solution can be selected appropriately 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.

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. For example, it may be 0.40 μm or less, 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 excessively small, even minute differences in particle size will likely affect the particle size of the silica particles after the growth process, and they will be more likely to aggregate, making it difficult to achieve uniform particle size in the growth process. Therefore, it is preferable that the particle size of the small silica particles be 0.05 μm or more.

With such a particle size, it is easy to obtain a group of small silica particles with a highly uniform particle size, and it is also possible to prevent the reaction time in the production process from becoming too long and reducing production efficiency.

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 laser diffraction scattering, 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, which will be described later. Note that the "particle size" of small silica particles and silica particles refers to the cumulative 50% diameter on a volume basis.

(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.

In the first growth process, the first small particles, which are part of the multiple small silica particles produced in the production process, 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 larger particle size than the small silica particles. In the first growth process, the growth in particle size of the first small particles proceeds through hydrolysis and polycondensation of the second silicon alkoxide, just as in the production process.

In the second growth process, which is independent of the first growth process, at least a portion of the second small particles (i.e., the portion of the small silica particles produced in the production process 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 process, the growth in particle size of the second small particles proceeds through hydrolysis and polycondensation of the third silicon alkoxide, just as in the production process.

"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 substantially simultaneously with the first growth step using a separate reaction vessel from the first growth step.

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

The amount of the first small particles is not particularly limited, as long as it is equal to 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 perspective of using the silica small particles obtained from a single production process in many production batches, it is preferable that the amount of the first small particles be 20% by mass or less of the silica small particles produced in the production process.

The second small particles are preferably used in the second growth process. The second small particles may be used in their entirety in one second growth process, or only a portion may be used. For example, if the second growth process is performed two or more times, the second small particles may be divided into portions corresponding to the number of second growth processes performed, and each portion may be used in each second growth process. For example, if the second growth process is performed nine times (i.e., 10 production batches including the first growth process), the first small particles should be 10% by mass of the silica small particles produced in the production process. Then, 1/9 of the second small particles (10% by mass of the silica small particles produced in the production process) should be used in each second growth process.

The total number of the first growth process and multiple second growth processes is the number of production batches in which silica particles are produced using the small silica particles obtained in a single production process. Because the particle size of the small silica particles before growth is highly uniform between these production batches, it is easy to achieve high uniformity in particle size between production batches for the silica particles after the growth process as well.

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 they may each be different silicon alkoxides. In order to ensure that the particle size of the silica particles is consistent between the first and second growth steps, it is preferable that the second silicon alkoxide and the third silicon alkoxide are the same type of silicon alkoxide.

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

In this way, by using different silicon alkoxides in the generation process and the growth process, it is possible to reduce production costs by increasing the yield of silica particles while maintaining uniformity in the particle size of the silica particles.

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 product liquid. The component compositions other than the silicon alkoxide in the product liquid, the first growth liquid, and the second growth liquid may be the same or different. For example, in the product liquid, the proportion of water and/or catalyst may be reduced to ensure a consistent particle size, allowing 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.

When the particle size of the silica particles is to be consistent between the first and second growth steps, it is preferable that the component compositions of the first and second growth solutions be the same. Note that, in this specification, "the same conditions" refers to the same conditions in the manufacturing plan (manufacturing protocol), and is a concept that allows for errors that may occur during manufacturing.

The first growth step may be carried out in a reaction vessel similar to that used in the production step. Furthermore, the amounts of raw materials, such as silicon alkoxide, used in the production step and the first growth step may differ. Therefore, the reaction vessel used in the first growth step may have a different capacity from the reaction vessel used in the production step.

The method for preparing the first growth solution is not particularly limited, but an example is a method as shown in Figure 2, 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 at approximately the same time (S5). 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.

Furthermore, when the second silicon alkoxide contains two or more types of silicon alkoxide, they may be added simultaneously or sequentially. The proportions of each component contained in the first growth solution may be selected appropriately depending on the target particle size of the silica particles.

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

The reaction vessel, method for preparing the second growth liquid, and reaction temperature in the second growth step may be determined appropriately, as in the first growth step. When the particle size of the silica particles is to be consistent between the first and second growth steps, 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 all other conditions be the same between the first and second growth steps.

The particle size of the silica particles obtained by the first growth process 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 process may be performed after the first growth process to further grow the silica particles. For example, small silica particles having a particle size of approximately 0.2 μm produced in the production process are used to obtain silica particles (intermediate particles) having a particle size of approximately 0.4 μm by the first growth process. Then, an additional growth process may be performed to grow the particle size of the intermediate particles, resulting in silica particles having a particle size of approximately 1.5 μm or more.

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.

(Storage of second small particles)
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.

When storing the second small particles, a dispersant may be added to prevent aggregation of the second small particles. The dispersant used to disperse the second small particles during storage is not particularly limited, but may be, for example, the solvents exemplified for the production liquid.

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

The atmosphere in which the second small particles are stored is not particularly limited, but may be, for example, air or an inert gas such as nitrogen. Furthermore, from the perspective 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.

The second small particles can generally be stored in a stable dispersed state in the dispersion medium for approximately six months after the production process, although this depends on conditions such as particle size and dispersion medium. The following are the results of an investigation into the sedimentation rate of the second small particles.

The conditions were particle diameter (d) of 0.06 μm, particle density (ρ _s ) of 2000 kg/m ³ , dispersion medium density (ρ _L ) of 840 kg/m ³ , dispersion medium viscosity (μ _L ) of 0.622 kg/m·s, and gravitational acceleration (g) of 9.8 m/s ² .

The particle density was determined taking into account 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. Since the second small particles were spherical and had sufficiently small particle diameters, it was assumed that Stokes' law held true, and the settling velocity (u _t ) of the second small particles was calculated using the following formula (1):

u _t =d ² (ρ _s −ρ _L )g/(18 μ _L ) (1)
As a result, the settling velocity (u _t ) of the second small particles under the above conditions was 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. Note that if the second small particles in the storage container are constantly or periodically stirred, the storage period may be even longer.

In this way, the second small particles can be stored in a stable state for a long period of time. Therefore, according to the method for producing silica particles of one embodiment of the present invention, after the first growth step is performed, it is possible to produce silica particles with good reproducibility, with consistent particle diameters between each production batch, in multiple production batches carried out over a long period of time.

An example of the present invention and a comparative example are described below.

(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.

Specifically, 405.7 kg of methanol and 83 kg of 25% aqueous ammonia were charged into a reaction vessel having a capacity of 1 ^m3 , 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 reaction vessel at a rate of 40 kg/min or more. After completion of the addition, 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, yielding approximately 530 kg of a slurry of small silica particles.

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 small particle slurry was used to carry out the first growth step. In the first growth step, 59.8 kg of the first small particle slurry, 108.1 kg of methanol, and 18.2 kg of 25% aqueous ammonia were charged into a reaction vessel with a capacity of 4 ^m3 , and the liquid temperature was adjusted to 45 ° C. As the second silicon alkoxide in the first growth step, 1888.0 kg of tetramethoxysilane was used, which was mixed with 188.8 kg of methanol at a rate of 5 kg/min, and 840.0 kg of 25% aqueous ammonia was simultaneously added to the reaction vessel at a rate of 2 kg/min. After the start of addition, the first growth step was carried out at a liquid temperature of 45 ° C. for approximately 420 minutes, during which the growth reaction proceeded under stirring, to obtain silica particles.

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

(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.

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 the silica particles. This was mixed with 3.5 kg of methanol and added to the reactor at a rate of 40 kg/min or more. After addition, 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 small silica particle slurry.

Next, the entire amount of the obtained small silica particle slurry was used to carry out the growth step. In the growth step, 59.9 kg of the small silica particle slurry, 108.1 kg of methanol, and 18.2 kg of 25% aqueous ammonia were charged into a reaction vessel with an internal volume of 4 ^m3 , and the liquid temperature was adjusted to 45°C. As the silicon alkoxide for the growth step, 1888.0 kg of tetramethoxysilane was used, which was mixed with 188.8 kg of methanol and added at a rate of 5 kg/min, and 840.0 kg of 25% aqueous ammonia was added at a rate of 2 kg/min to the reaction vessel simultaneously. 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.

In the comparative example, the above series of manufacturing methods was repeated six times to produce six batches of silica particles.

(result)
The average particle diameter (volume-based cumulative 50% diameter) of the small silica particles and silica particles obtained by the methods according to the Examples and Comparative Examples was determined by a laser diffraction scattering method (LS13320, manufactured by Beckman Coulter). The average particle diameter of the small silica particles according to the Examples was 0.06 μm. Silica particles obtained in six production batches using the small silica particles were each fired at 800°C for 10 hours and subjected to a swirl-type jet mill (STJ-200, manufactured by Seishin Enterprises). The swirl pressure was 0.5 MPa, the amount of swirl air was 2.4 m ³ /min, the compression pressure was 0.6 MPa, and the feed rate was 10 kg/h. 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.

The sphericity of the silica particles was determined by observation using a SEM (JSM-6060, manufactured by JEOL Ltd.). Specifically, 1,000 or more 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 x (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.

The average particle diameters 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 fired and crushed under the same conditions as in the examples. The average particle diameters 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 particle diameter of the six production batches of the comparative example was 0.772 μm, with a standard deviation of 0.014 μm.

As such, compared to the method for producing silica particles according to the example, the method according to the comparative example had a standard deviation between the six production batches that was nearly twice as high, meaning there was a large variation between production batches. From the above, the method for producing silica particles according to one embodiment of the present invention made it possible to produce silica particles with good reproducibility and small variation in particle size between production batches.

[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.

The present invention can be used, for example, to produce silica particles used as fillers in various resin compositions for electronic materials such as semiconductor encapsulants or for film manufacturing.

Claims (2)

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