JP2023110668A - Method for producing silica particles - Google Patents

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

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

BACKGROUND ART Silica particles are used as fillers for various resin compositions such as electronic materials such as semiconductor encapsulants or films. For precise and uniform sealing, highly monodisperse silica particles with little variation in particle size are required.

As a method for producing highly monodisperse silica particles, a so-called sol-gel method is known, in which silica particles are produced by hydrolysis and polycondensation of silicon alkoxide (eg, 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 pamphlet Japanese Patent Application Laid-Open No. 2021-116225

In the sol-gel method, fine silica particles are produced from silicon alkoxide, and then the silica particles are grown to a desired particle size to obtain silica particles. Here, the particle diameter of the small silica particles is likely to be affected by reaction temperature, stirring conditions, and other production conditions.

Fluctuations in the particle size of the small silica particles caused by slight differences in production conditions greatly affect the particle size of the silica particles after growing the small silica particles. Therefore, there has been a problem that it is difficult to make the particle size of the silica particles uniform between production batches.

An object of one aspect of the present invention is to realize a method for producing silica particles having a highly uniform particle size with good reproducibility.

First small particles that are part of the silica small particles and a first growth liquid containing a second silicon alkoxide are mixed to grow the particle diameter of the first small particles so that the particle diameter is larger than that of the silica small particles. and a first growth step to obtain silica particles with a large .

In the method for producing silica particles according to an aspect of the present invention, independently of the first growth step, at least part of second small particles, which are portions other than the first small particles in the silica small particles, A second growth step may be further included in which a second growth liquid containing a tertiary silicon alkoxide is mixed to grow the particle size of the second small particles.

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

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.

ADVANTAGE OF THE INVENTION According to one aspect of the present invention, it is possible to realize a method for producing silica particles having a highly uniform particle size with good reproducibility.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the outline|summary of the manufacturing method of the silica particle which concerns on one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows an example of the manufacturing method of the silica particle which concerns on one Embodiment of this invention.

An embodiment of the invention will be described below, but the invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope of the claims. In addition, the technical scope of the present invention also includes embodiments and examples obtained by appropriately combining technical means disclosed in different embodiments and examples. Further, in the present specification, "A to B" means from A to B, unless otherwise specified.

〔overview〕
As shown in FIG. 1, in the method for producing silica particles according to one embodiment of the present invention, first, a production step is performed to produce small silica particles used as seeds for silica particles, and then the small silica particles are grown. Carry out the growth process. In one embodiment of the present invention, the forming step produces a larger amount of small silica particles than the small silica particles used in one growing step. This makes it possible to carry out two or more growth steps from the small silica particles produced in one production step. According to the method for producing silica particles according to one embodiment of the present invention, spherical silica particles having a high degree of sphericity can be obtained.

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

Conventionally, the production process and the growth process were performed as a series of manufacturing processes. When the production step is carried out for each growth step, the particle size of the small silica particles produced in each production step may differ. Therefore, for example, when there is a difference in the particle size of the small silica particles between production batches, it is difficult to uniform the particle size of the silica particles after the growth step between these production batches.

In addition, in order to obtain silica particles having high uniformity (monodispersity) in particle sphericity and particle diameter, it is important that the initial small silica particles have high uniformity in particle diameter. If the particle size varies in the small silica particle stage, the particle size of the silica particles after the growing process also varies.

In this regard, within a population of silica small particles with high uniformity obtained by one generation step, the uniformity of particle size is extremely high in any population. Therefore, by using small silica particles obtained in one generation step in each of a plurality of growth steps, it becomes easy to uniformize the particle diameters of the silica particles obtained in these plurality of growth steps. In addition, even when silica particles having different particle sizes are produced in a plurality of growth steps, it is easy to ensure uniformity in particle size of the silica particles in each of these growth steps.

Therefore, for example, a large amount of small silica particles are produced in the production process, part of which is used in the growth process, and the remaining small silica particles are stored, and when producing another batch of silica particles at a later date, The stored small silica particles may be used. According to such a configuration, silica particles having a desired particle size can be produced with good reproducibility in a plurality of production batches.

Using the small silica particles after the production step in a plurality of independent growth steps in this way overturns the conventional technical common sense that the production step and the growth step are performed as a series of steps. The present inventors have completed the present invention as a result of extensive studies based on such new knowledge. Hereinafter, a method for producing silica particles according to one embodiment of the present invention will be described.

[Method for producing silica particles]
A method for producing silica particles according to an embodiment of the present invention includes a production step of producing small silica particles and a first growth step of growing the small silica particles. The first growth step may be one of the plurality of growth steps described above. In this specification, the term "growth step" is intended to collectively refer to the first growth step and the second growth step, which will be described later, unless otherwise specified.

A method for producing silica particles according to an 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). Further, powdery silica particles may be obtained through a step of removing and drying the solid content produced by gelling the silica sol, or the powdery silica particles may be further subjected to a step of firing and pulverizing. may Thus, the method for producing silica particles according to one embodiment of the present invention may include steps other than the production step and the growth step.

(Generation process)
The production step is a step of producing a plurality of small silica particles from a production liquid containing the first silicon alkoxide. In the production step, small silica particles are produced by hydrolyzing and polycondensing the first silicon alkoxide in a production liquid containing the first silicon alkoxide. The small silica particles have a smaller particle diameter than the silica particles obtained by the growth step performed after the formation step. Small silica particles are sometimes called "seed particles" because they serve as seeds for obtaining silica particles in the growth process.

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

As the first silicon alkoxide, it is preferable to use silicon alkoxide alone, which has a relatively low reaction rate, and it is particularly preferable to use tetraethoxysilane alone, from the viewpoint of facilitating uniformity of the particle size of the small silica particles to be produced.

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

Preferably, the solvent is a polar solvent. The polar solvent may be water, an organic solvent capable of dissolving 10 g or more of water per 100 g under normal temperature and pressure, or a mixed solvent of water and the organic solvent. When the solvent contains such an organic solvent, the number of organic solvents may be one, or two or more. When the solvent contains two or more organic solvents, the above water-solubility requirements may be met as a mixture of organic solvents.

Organic solvents can include, for example, alcohols, ethers and amide compounds. Alcohols include, for example, methanol, ethanol, isopropyl alcohol and butanol. Ethers include, for example, tetrahydrofuran and dioxane. Amide compounds include, for example, dimethylformamide, dimethylacetamide and N-methylpyrrolidone.

Alcohol is by-produced by hydrolysis of silicon alkoxide in the production step and the growth step. Therefore, the organic solvent is preferably alcohol from the viewpoints of reducing contamination of impurities in the manufactured silica particle dispersion and ease of removal by heating.

The catalyst may be an acidic catalyst or a basic catalyst. From the viewpoint of obtaining spherical particles having 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 generally used for producing silica particles by a sol-gel reaction. Basic catalysts can include, for example, amine compounds and alkali metal hydroxides.

From the viewpoint of obtaining high-purity small silica particles, the basic catalyst is preferably an amine compound. Amine compounds include, for example, ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine and triethylamine. Preferably, the basic catalyst is ammonia because of its high volatility and ease of removal. The basic catalyst may be one of these, or may contain two or more.

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 concentration is adjusted by dissolving it in water. When the catalyst is used as an aqueous solution, the concentration of the catalyst in the aqueous solution can be, for example, 1-30% by weight.

The proportions of water, organic solvent, and catalyst in the product solution are appropriately determined according to the reaction rate of the production process, 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 process. good.

The proportion of water in the generated liquid is preferably 1 to 30% by mass, more preferably 5 to 20% by mass. Further, when the generated liquid contains an organic solvent, the ratio of the organic solvent in the generated liquid is preferably 50 to 95% by mass, more preferably 70 to 90% by mass. Also, the amount of the 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.

The production step may be performed using a reaction vessel generally used for producing silica particles by a sol-gel reaction. Such a reaction vessel may be, for example, a cylindrical vessel equipped with stirring blades.

The method of preparing the product liquid is not particularly limited, but for example, as shown in FIG. 2, a method of adding a solvent and a catalyst to a reaction vessel (S1) and then adding the first silicon alkoxide (S2) can be mentioned. According to this method, spherical silica small particles with high uniformity in particle size can be produced with good reproducibility. In this case, for example, part of the first silicon alkoxide may be added to the reaction vessel first, and then the rest of the first silicon alkoxide may be added. Also, the first silicon alkoxide and the catalyst may be added substantially simultaneously. Furthermore, when the first silicon alkoxide contains two or more silicon alkoxides, each may be added simultaneously or each may be added sequentially.

The reaction temperature for producing small silica particles from the product solution may be appropriately selected according to the component composition of the product solution and the target particle size of the small silica particles. The reaction temperature may range, for example, from -10 to 60°C. Small silica particles can be produced by advancing the hydrolysis and polycondensation of the first silicon alkoxide at such a reaction temperature (S3, production step).

The particle size of the small silica particles produced in the production step is not particularly limited as long as it is smaller than the target particle size of the silica particles after the growth step. However, it is preferably 0.20 μm or less, more preferably 0.10 μm or less. In addition, if the particle size of the small silica particles is excessively small, a very small difference in particle size tends to affect the particle size of the silica particles after the growth process, and the silica particles tend to aggregate. uniformity is difficult to obtain. Therefore, the particle size of the small silica particles is preferably 0.05 μm or more.

With such a particle size, it is easy to obtain a group of small silica particles with high uniformity in particle size, and it is possible to prevent the production efficiency from being lowered due to excessive reaction time in the production step.

The method for measuring the particle size of the 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 is determined from an image captured by an electron microscope or the like. may This also applies to the particle size of silica particles, which will be described later. The "particle diameter" of the small silica particles and the silica particles intends the volume-based cumulative 50% diameter.

(Growth process)
In the method for producing silica particles according to one embodiment of the present invention, a growing step is performed to grow the particle size of the small silica particles obtained in the forming step. At least the first growth step is performed as the growth step. Moreover, it is preferable to further perform the 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 use small silica particles obtained by one generation step. The second growth step may be performed in multiple steps.

In the first growth step, first small particles that are part of the plurality of small silica particles produced in the production step are mixed with a first growth liquid containing a second silicon alkoxide. Thereby, the particle diameter of the first small particles is increased to obtain silica particles having a particle diameter larger than that of the small silica particles. In the first growth step, growth of the particle size of the first small particles proceeds by hydrolysis and polycondensation of the second silicon alkoxide, as in the generation step.

In the second growth step, independently of the first growth step, at least part of the second small particles, which are portions other than the first small particles in the silica small particles produced in the production step, and a tertiary silicon alkoxide are combined. The particle size of the second small particles is grown by mixing with the second growth liquid containing the second small particles. In the second growth step, growth of the particle size of the second small particles proceeds by hydrolysis and polycondensation of the tertiary silicon alkoxide, as in the generation step.

“Independently of the first growth step” means the case where the second growth step is performed at a different time from the first growth step (for example, after the first growth step), or substantially simultaneously with the first growth step. , and a case where the second growth step is performed using a reaction vessel separate from the first growth step.

In the first growing step, only some, but not all, of the small silica particles obtained in the growing step are used. This portion of the silica small particles is referred to as the "first small particles". In addition, among the silica small particles obtained in the production step, portions other than the first small particles are referred to as "second small particles".

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

The second small particles are preferably used in the second growth step. The second small particles may be used entirely or only partially 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 the number of times the second growth step is performed, and each portion may be used in each of the second growth steps. For example, if the second growth step is performed 9 times (that is, 10 production batches including the first growth step), the first small particles are 10 mass % of the silica small particles produced in the production step. Then, in each second growth step, 1/9 amount of the second small particles (10% by mass of the silica small particles produced in the production step) may be used.

The total number of the first growth step and the number of second growth steps is the number of manufacturing batches for manufacturing silica particles using the small silica particles obtained by one generation step. Since the particle size of the small silica particles before growth is highly uniform between these production batches, it is possible to obtain high uniformity in particle size between production batches also for the silica particles after the growth process. is easy.

Each of the second silicon alkoxide and the tertiary silicon alkoxide may be one or more of the compounds exemplified as the first silicon alkoxide. The first silicon alkoxide, the second silicon alkoxide and the tertiary silicon alkoxide may all be the same silicon alkoxide, or they 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, the second silicon alkoxide and the tertiary silicon alkoxide are preferably the same type of silicon alkoxide.

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

In this way, according to the configuration in which different silicon alkoxides are used in the formation 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.

Each of the first growth liquid and the second growth liquid may be a solution containing the second silicon alkoxide or the tertiary silicon alkoxide, as well as the solvent and catalyst exemplified in the production liquid. The component compositions other than the silicon alkoxide in the generation liquid, the first growth liquid, and the second growth liquid may be the same or different. For example, in the production liquid, the ratio of water and/or catalyst is reduced to make the particle size uniform, and the reaction proceeds slowly. may be increased.

When the particle size of the silica particles is uniform between the first growth process and the second growth process, it is preferable that the component compositions of the first growth liquid and the second growth liquid are the same. In this specification, the term "same conditions" means that the conditions in the manufacturing plan (manufacturing protocol) are the same, and any error that may occur in the manufacturing process is acceptable.

The first growth step may be performed in a reaction vessel similar to the reaction vessel used in the formation step. In addition, the amount of raw materials such as silicon alkoxide used may differ between the generation step and the first growth step. Therefore, the reaction vessel used in the first growth step may be a reaction vessel having a different capacity from the reaction vessel used in the formation step.

Although the method for preparing the first growth liquid is not particularly limited, for example, as shown in FIG. 2, the reaction vessel is charged with the first small particles, the solvent and the catalyst (S4), and the second silicon alkoxide and the catalyst are added substantially simultaneously. (S5) method. According to this method, spherical silica particles having a highly uniform particle size can be produced with good reproducibility. In this case, for example, after part of the second silicon alkoxide is first added to the reaction vessel, the remaining second silicon alkoxide and the catalyst may be added at the same time.

Moreover, when the second silicon alkoxide contains two or more silicon alkoxides, each may be added simultaneously, or each may be added sequentially. The ratio of each component contained in the first growth liquid may be appropriately selected according to the target particle size of the silica particles.

The reaction temperature for growing the small silica particles from the first growth liquid may be appropriately selected according to the composition of the first growth liquid and the target particle size of the silica particles. The reaction temperature may range, for example, from -10 to 60°C. At such a reaction temperature, the 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, the method of adjusting 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 is uniform between the first growth step and the second growth step, the amount ratio and mixing temperature of the second small particles and the second growth liquid in the second growth step are adjusted to It is preferable to set the same conditions as the quantitative ratio of the first small particles and the first growth liquid and the mixing temperature in . Further, it is more preferable to set the same conditions between the first growth step and the second growth step for each condition other than these.

The particle size of the silica particles obtained in the first growth step is not particularly limited. When 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, silica particles (intermediate particles) having a particle diameter of about 0.4 μm are obtained in the first growth step using small silica particles having a particle diameter of about 0.2 μm produced in the production step. After that, an additional growth step for growing the particle size of the intermediate particles may be performed to obtain silica particles having a particle size of about 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, when the additional growth process is performed after the first growth process, it is preferable to perform the same additional growth process after the second growth process. Moreover, the reaction conditions in the additional growth step may be the same conditions as those in the first growth step or the second growth step, or may be different conditions.

(Storage of second small particles)
If the second growth step is performed after the first growth step, the second small particles can be stored until the second growth step. Storage conditions for the second small particles are not particularly limited.

When storing the second small particles, a dispersion medium may be added from the viewpoint of preventing aggregation of the second small particles. The dispersion medium for dispersing the second small particles during storage of the second small particles is not particularly limited, but may be, for example, the solvent exemplified for the generated liquid.

The second small particles are preferably stored in a storage container that is non-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. Further, the storage temperature of the second small particles is preferably room temperature from the viewpoint of preventing evaporation of the solvent. Specifically, for example, the temperature is preferably 30° C. or lower, and more preferably 20° C. or lower. From the viewpoint of preventing solidification of the dispersion medium, the temperature is preferably equal to or higher than the solidification point of the dispersion medium, for example, 0° C. or higher.

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. Moreover, from the viewpoint of preventing aggregation of the particles, it is preferable to stir the second small particles all the time or periodically. Since the second small particles have a small particle diameter and a slow sedimentation velocity, 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 state of being stably dispersed in the dispersion medium for about half a year after the production process, although this depends on the conditions such as the particle size and the dispersion medium. The following is the result of examining the sedimentation velocity of the second small particles.

The conditions are a particle diameter (d) of 0.06 μm, a particle density (ρ _s ) of 2000 kg/m ³ , a dispersion medium density (ρ _L ) of 840 kg/m ³ , and a dispersion medium viscosity (μ _L ) of 0. .622 kg/m·s, gravitational acceleration (g) was 9.8 m/s ² .

The density of the particles was determined taking into consideration that the second small particles were unfired small silica particles. Also, the dispersion medium was assumed to be a 2:8 mixed solvent of water and methanol. The sedimentation velocity (u _t ) of the second small particles was determined by the following formula (1), assuming that Stokes' law holds because the second small particles are spherical and have sufficiently small particle diameters.

u _t =d ² (ρ _s −ρ _L )g/(18 μ _L ) (1)
As a result, the sedimentation velocity (u _t ) of the second small particles under the above conditions was 3.65×10 ⁻¹² m/s. This indicates that the sedimentation distance of the second small particles in the dispersion medium is about 0.05 mm in half a year and about 0.1 mm in one year. This result suggests that since the sedimentation distance of the second small particles is very small, aggregation of the particles is unlikely to occur, and that the particles can be stably stored for at least half a year. In addition, when the second small particles in the storage container are constantly or periodically stirred, the storage period may be longer.

Thus, the second small particles can be stored for a long period of time in a stable state. Therefore, according to the method for producing silica particles according to one embodiment of the present invention, in production batches that are performed multiple times over a long period of time after the first growth step, the particle diameters are uniform between each production batch. It is possible to produce silica particles with good reproducibility.

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

(Method according to Example)
In the example, using silica small particles obtained in one production step, six growth steps (one first growth step and five second growth steps) were performed to produce six production batches of silica particles. got

Specifically, 405.7 kg of methanol and 83 kg of 25% aqueous ammonia were charged into a reaction vessel having a capacity of 1 m ³ 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, mixed with 30.6 kg of methanol, and charged into the reactor at a rate of 40 kg/min or higher. After the completion of the addition, a forming step was carried out at a liquid temperature of 40° C. for 30 minutes to advance the forming reaction under stirring, and about 530 kg of slurry of small silica particles was obtained.

Next, the silica small particle slurry is divided into 59.8 kg of the first small particle slurry and the remainder (approximately 470.2 kg) of the second small particle slurry, and the first small particle slurry is used to prepare the first slurry. performed the growth process. In the first growth step, 59.8 kg of slurry of the first small particles, 108.1 kg of methanol and 18.2 kg of 25% aqueous ammonia were charged into a reaction vessel having an internal volume 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 and mixed with 188.8 kg of methanol at a rate of 5 kg/min. were charged into the reaction vessel at the same speed. After the start of charging, a first growth step was performed at a liquid temperature of 45° C. for about 420 minutes to allow the growth reaction to proceed under stirring to obtain silica particles.

In addition, independently of the first growth step, five portions of 59.8 kg each were taken from the slurry of the second small particles, and these were used to perform the second growth step five times. The conditions of the second growth process, such as the input amount of each raw material, the reaction temperature and the reaction time, were all the same as those of the first growth process. In this way, six production batches of silica particles were produced in total in the first growth step and the second growth step for one generation step.

(Method according to Comparative Example)
In the comparative example, the manufacturing method in which the entire amount of the silica small particles obtained in the production step is used in the growth step according to the comparative example was performed six times to obtain six manufacturing batches of silica particles.

Specifically, 45.8 kg of methanol and 9.4 kg of 25% aqueous ammonia were charged into a reaction vessel having a capacity of 500 L, and the liquid temperature was adjusted to 40°C. 1.2 kg of tetraethoxysilane was used as a silicon alkoxide as a raw material for silica particles, mixed with 3.5 kg of methanol, and charged into a reactor at a rate of 40 kg/min or higher. After the completion of the addition, the reaction for producing small silica particles was allowed to proceed under stirring at a liquid temperature of 40° C. for 30 minutes, and about 59.9 kg of slurry of small silica particles was obtained.

Next, a growth step was performed using the entire amount of the resulting slurry of small silica particles. In the growth step, 59.9 kg of slurry of small silica particles, 108.1 kg of methanol and 18.2 kg of 25% aqueous ammonia were charged into a reaction vessel having a capacity of 4 m ³ and the liquid temperature was adjusted to 45°C. 1888.0 kg of tetramethoxysilane was used as the silicon alkoxide in the growth step, mixed with 188.8 kg of methanol and reacted at a rate of 5 kg/min, and 840.0 kg of 25% aqueous ammonia was reacted at a rate of 2 kg/min. were put into the container at the same time. After the start of charging, the growth reaction was allowed to proceed under stirring at a liquid temperature of 45° C. for about 420 minutes to obtain silica particles.

In a comparative example, six production batches of silica particles were produced by performing the series of production methods described above six times.

(result)
The average particle size (volume-based cumulative 50% diameter) of the small silica particles and silica particles obtained by the method according to Examples or Comparative Examples was determined by a laser diffraction scattering method (LS13320 manufactured by Beckman Coulter). The average particle size of the silica small particles according to the example was 0.06 μm. Silica particles obtained from 6 production batches using the silica small particles were each calcined at 800° C. for 10 hours and pulverized using a swirling jet mill (STJ-200, manufactured by Seishin Enterprises). . The crushing conditions were a swirl pressure of 0.5 MPa, a swirl air amount of 2.4 m ³ /min, a pushing pressure of 0.6 MPa, and a feed rate of 10 kg/h. The average particle sizes of 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 with an SEM (JSM-6060, manufactured by JEOL Ltd.). Specifically, 1000 or more silica particles were observed, the sphericity of each silica particle was measured using an image processing program (Soft Imaging System GmbH, AnalySIS), and the average was determined. The sphericity of each silica particle was calculated by the following formula;
Sphericality = 4π × (area) / (perimeter) ²
The average mean particle size of the 6 production batches according to the example was 0.765 μm with a standard deviation of 0.008 μm.

In addition, the average particle sizes of the small silica particles obtained from the six production batches according to 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 pulverized under the same conditions as in 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, 0.96, respectively. The average particle size of the six production batches according to the comparative example was 0.772 μm, and the standard deviation was 0.014 μm.

Thus, compared with the method for producing silica particles according to the example, in the method according to the comparative example, the standard deviation among the six production batches was nearly double, and the variation among the production batches was large. As described above, according to the method for producing silica particles according to one embodiment of the present invention, it was possible to produce silica particles with good reproducibility and small variations in particle size between production batches.

[Additional notes]
The present invention is not limited to the above-described embodiments/examples, and can be modified in various ways within the scope of the claims. Embodiments obtained by appropriately combining technical means disclosed in different embodiments/examples are also included in the technical scope of the present invention.

INDUSTRIAL APPLICABILITY The present invention can be used, for example, in the production of silica particles used as fillers for electronic materials such as semiconductor encapsulating materials or various resin compositions for producing films.

Claims (4)

a production step of producing a plurality of small silica particles from a production liquid containing the first silicon alkoxide;
First small particles that are part of the plurality of small silica particles and a first growth liquid containing a second silicon alkoxide are mixed to grow the particle diameter of the first small particles to a size larger than that of the small silica particles. and a first growth step for obtaining silica particles having a large particle size. Independently of the first growth step, at least a part of the second small particles of the silica small particles other than the first small particles is mixed with a second growth liquid containing a tertiary silicon alkoxide. 2. The method for producing silica particles according to claim 1, further comprising a second growing step of growing the particle size of said second small particles. The component compositions of the first growth liquid and the second growth liquid are the same, and
The quantity ratio and mixing temperature of the second small particles and the second growth liquid in the second growth step are the same as the quantity ratio and mixing temperature of the first small particles and the first growth liquid in the first growth step. 3. The method for producing silica particles according to claim 2, wherein the same conditions are used. the first silicon alkoxide is tetraethoxysilane;
4. The method for producing silica particles according to claim 1, wherein the second silicon alkoxide is tetramethoxysilane.

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