JP7752064B2 - Method for adjusting particle size of silica particles and method for producing silica particles - Google Patents

Description

The present invention relates to a method for adjusting the particle size of silica particles and 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. For precise and uniform encapsulation, silica particles with controlled particle size are required.

A known method for producing highly monodisperse silica particles is the sol-gel method, in which silica particles are produced by hydrolysis and polycondensation of silicon alkoxide (see, for example, Patent Documents 1 to 3). For example, Patent Document 1 describes that highly monodisperse silica particles can be obtained by adjusting the feed rate of the raw material metal alkoxide to a reaction solution within a specific range.

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

However, it is not easy to maintain the monodispersity of the silica particles obtained by the silica powder manufacturing methods described in Patent Documents 1 to 3 and adjust the particle size to the desired size. To obtain silica particles of the desired particle size, it is necessary to carry out the hydrolysis and polycondensation of silicon alkoxide in two steps. When hydrolysis and polycondensation are carried out in two steps, it takes time to produce silica particles. Therefore, there is a need for a method for easily adjusting silica particles to the desired particle size.

One aspect of the present invention aims to provide a method for easily adjusting silica particles to a desired particle size.

In order to solve the above problems, one embodiment of the present invention provides a method for adjusting the particle size of silica particles, which comprises producing silica particles by hydrolyzing and polycondensing a silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent, and adjusting the mass ratio of methanol to an alcohol having 2 to 4 carbon atoms (methanol:alcohol having 2 to 4 carbon atoms) in the organic solvent to 100:0 to 0:100, thereby adjusting the volume-based cumulative 50% diameter (hereinafter also referred to as the average particle size) of the silica particles as measured by a laser diffraction scattering method to 0.05 μm or more and 0.60 μm or less.

In one embodiment of the method for adjusting the particle size of silica particles according to the present invention, the alcohol having 2 to 4 carbon atoms may be ethanol, n-propanol, isopropanol, 1-butanol, or 2-butanol.

In order to solve the above problems, one embodiment of the present invention provides a method for producing silica particles, which comprises producing silica particles by hydrolyzing and polycondensing a silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent, wherein the organic solvent contains methanol and isopropanol, the mass ratio of the isopropanol to the methanol in the organic solvent (isopropanol/methanol) is 3/7 or more, and the average particle diameter of the silica particles measured by a laser diffraction scattering method is 0.16 μm or more and less than 0.44 μm.

One aspect of the present invention provides a method for easily adjusting silica particles to a desired particle size.

1 is a graph showing the relationship between the mixing ratio of methanol and isopropanol and the silica particle size. 1 is a graph showing the relationship between the mixture ratio of methanol and isopropanol and the particle size after growth. 1 is a graph showing the relationship between the mixing ratio of methanol and ethanol and the silica particle size. 1 is a graph showing the relationship between the mixture ratio of methanol and ethanol and the particle size after growth. 1 is a graph showing the relationship between the mixing ratio of methanol and 2-butanol and the silica particle size. 1 is a graph showing the relationship between the mixing ratio of methanol and 2-butanol and the particle size after growth.

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.

[Method for adjusting particle size of silica particles]
A method for adjusting the particle size of silica particles according to one aspect of the present invention (hereinafter sometimes referred to as the "adjustment method of this embodiment") includes a step of producing silica particles by hydrolysis and polycondensation of silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent.

As a result of extensive research into adjusting the particle size of silica particles, the inventors have succeeded in discovering a new finding. Specifically, they independently discovered that the particle size of silica particles can be easily adjusted by using a specific composition of organic solvent for the hydrolysis and polycondensation of silicon alkoxide.

(Silicon alkoxide)
The silicon alkoxide used in the preparation method of this embodiment is not particularly limited as long as it is a silicon alkoxide (alkoxysilane) that is generally used in the production of silica particles by the sol-gel method. Examples of silicon alkoxides 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.

(Basic catalyst)
The basic catalyst used in the preparation method of this embodiment is not particularly limited 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 viewpoint of obtaining high-purity silica particles, the basic catalyst is preferably an amine compound. Examples of amine compounds include ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine. Because the basic catalyst is highly volatile and easy to remove, ammonia is preferably used. The basic catalyst may be one of these, or may include two or more of them.

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

(organic solvent)
The organic solvent used in the preparation method of this embodiment is adjusted such that the mass ratio of methanol to the alcohol having 2 to 4 carbon atoms (methanol:alcohol having 2 to 4 carbon atoms) is 100:0 to 0:100 depending on the target particle size of the silica particles.

By adjusting the mixing ratio of methanol to an alcohol having 2 to 4 carbon atoms, silica particles with an average particle size of 0.05 μm to 0.60 μm can be obtained. The greater the proportion of methanol in the organic solvent, the smaller the average particle size of silica particles that can be obtained. The average particle size of silica particles is measured by laser diffraction scattering. In this specification, the average particle size of silica particles refers to the cumulative 50% diameter on a volume basis.

Examples of alcohols having 2 to 4 carbon atoms include ethanol, n-propanol, isopropanol, 1-butanol, and 2-butanol. The alcohol having 2 to 4 carbon atoms may be one of these, or may contain two or more of these. The alcohol having 2 to 4 carbon atoms is preferably ethanol, isopropanol, or 2-butanol, with isopropanol being more preferred.

The amount of basic catalyst used in the preparation method of this embodiment may be selected appropriately taking into consideration factors such as the reaction rate of the hydrolysis and polycondensation reactions of the silicon alkoxide. The amount of basic catalyst used is preferably 0.1 to 60 mass% of the amount of silicon alkoxide, and more preferably 0.5 to 40 mass%.

The amount of water used in the preparation method of this embodiment is preferably 1 to 30% by mass, and more preferably 5 to 20% by mass, when the total amount of the reaction solution is 100% by mass. Furthermore, the amount of organic solvent used in the preparation method of this embodiment is preferably 50 to 95% by mass, and more preferably 70 to 90% by mass, when the total amount of the reaction solution is 100% by mass. The total amount of the reaction solution is the total amount of raw materials used in the reaction, such as silicon alkoxide, basic catalyst, organic solvent, and water.

The hydrolysis and polycondensation of silicon alkoxide may be carried out using, for example, a reaction vessel commonly used in the production of silica particles by a sol-gel reaction. Examples of such reaction vessels include a reaction vessel equipped with a stirrer. Examples of the stirring blades of the stirrer include inclined paddle blades, turbine blades, triple-swept blades, anchor blades, full zone blades, twin star blades, and max blend blades.

Reaction vessels equipped with a stirrer may be of the general shape, such as hemispherical or cylindrical with a flat or round bottom, or may have a baffle plate installed inside. The material of the reaction vessel is not particularly limited, and may be made of glass, metal such as stainless steel (which may be glass-coated or resin-coated), or resin.

In order to obtain silica particles with a more uniform particle size and a narrow particle size distribution, it is preferable to use a reaction vessel equipped with an agitator with a dimensionless mixing time (n x θm) of 100 or less. n represents the agitator impeller rotation speed (1/s), and θm represents the mixing time. The mixing time θm generally refers to the time required for the tracer substance to be uniformly mixed, and is affected by factors such as the shape of the reaction vessel, the type or rotation speed of the agitator impeller, and the viscoelastic properties of the liquid being mixed.

The order of addition to the reaction vessel is not particularly limited. For example, the basic catalyst, water, and organic catalyst may be added to the reaction vessel, followed by the silicon alkoxide (or an organic solvent solution of the silicon alkoxide). Alternatively, a portion of the silicon alkoxide may be added to the reaction vessel, and then the remaining silicon alkoxide and the basic catalyst may be added simultaneously. Furthermore, when the silicon alkoxide contains two or more types of silicon alkoxide, they may be added simultaneously or sequentially.

The reaction temperature may be selected appropriately depending on the types of silicon alkoxide, basic catalyst, and organic catalyst. The reaction temperature may be, for example, in the range of -10 to 60°C.

[Method for producing silica particles]
A method for producing silica particles according to one embodiment of the present invention includes a step of producing silica particles by hydrolysis and polycondensation of silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent.

The organic solvent used in the above manufacturing method includes methanol and isopropanol. The mass ratio of isopropanol to methanol (isopropanol/methanol) is 3/7 or more.

By adjusting the mixing ratio of methanol and isopropanol, silica particles with an average particle size of 0.16 μm or more and 0.44 μm or less can be obtained. The higher the proportion of methanol in the organic solvent, the smaller the average particle size of the silica particles obtained. The average particle size of the silica particles is measured by laser diffraction scattering.

Another aspect of the present invention is a method for producing silica particles, which includes the step of producing silica particles by hydrolysis and polycondensation of silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent, where the organic solvent includes methanol and ethanol. By adjusting the mixing ratio of methanol to ethanol, silica particles with an average particle size of more than 0.06 μm and not more than 0.37 μm can be obtained. The greater the proportion of methanol in the organic solvent, the smaller the average particle size of the silica particles that can be obtained. The average particle size of the silica particles is measured by laser diffraction scattering.

Another aspect of the present invention is a method for producing silica particles, which includes the step of producing silica particles by hydrolyzing and polycondensing silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent, where the organic solvent includes methanol and 2-butanol. By adjusting the mixing ratio of methanol to ethanol, silica particles with an average particle size greater than 0.06 μm and less than 0.55 μm can be obtained. The greater the proportion of methanol in the organic solvent, the smaller the average particle size of the silica particles that can be obtained. The average particle size of the silica particles is measured by laser diffraction scattering.

The silica particles obtained by the method for producing silica particles according to one embodiment of the present invention, which have been adjusted to a desired particle size, have a uniform particle size and can be suitably used as raw material or seed particles for growing larger particles. For example, silicon alkoxide (or an organic solvent for silicon alkoxide) and a basic catalyst may be added again to the silica particles obtained by the method for producing silica particles according to one embodiment of the present invention to grow the silica particles. In other words, hydrolysis and polycondensation of silicon alkoxide may be carried out in two stages.

When the hydrolysis and polycondensation of silicon alkoxide are carried out in two stages, the reaction conditions for the first stage, as described above, require adjusting the composition of the organic solvent in order to obtain silica particles adjusted to the desired particle size. Meanwhile, the reaction conditions for the second and subsequent stages may be the same as or different from the reaction conditions for the first stage. The particle size of silica particles reacted in two or more stages can also be adjusted depending on the composition of the organic solvent used in the reaction conditions for the first stage.

In one embodiment of the method for producing silica particles according to the present invention, after the hydrolysis and polycondensation of silicon alkoxide, a process typically performed in the production of silica particles by a sol-gel reaction may be carried out. Examples of such processes include a filtration process, a surface treatment process, a coagulation process, a separation process, a drying process, a calcination process, and a crushing process. Each process is described below.

<Filtration process>
In the filtration step, the dispersion of silica particles adjusted to the desired particle size may be wet filtered to remove reaction residues, coalesced particles, or aggregates contained in the dispersion. The concentration of silica particles in the dispersion of silica particles to be filtered is preferably 1 to 40% by mass, and more preferably 2 to 25% by mass. It is preferable to adjust the amount of polar solvent, particularly polar solvent other than water, used so that the concentration of silica particles is adjusted to the above range.

The filter medium can be any wet filtration filter with a mesh size of 5 μm or less, with no particular restrictions on the type, and preferably a filter with a mesh size of 3 μm or less can be used.

The material of the filter is not particularly limited, but examples include resin (polypropylene, PTFE, etc.) or metal. From the perspective of preventing the inclusion of metal impurities, it is preferable to use a resin filter.

<Surface treatment process>
Prior to the coagulation step described below, the dispersion of silica particles may be surface-treated by adding at least one surface-treating agent selected from the group consisting of silicone oil, silane coupling agent, and silazane.

By applying the surface treatment, the separation process described below can be carried out more efficiently. Furthermore, since the formation of strong agglomerates during drying can be suppressed, the silica particles can be used for a variety of purposes without any special crushing treatment.

The surface treatment process can be performed before the coagulation process in the silica particle dispersion, or either before or after the dispersion filtration process. However, it is preferable to perform the surface treatment process before the dispersion filtration process in order to accurately reduce reaction residues, adhered particles, or agglomerates. By performing the surface treatment process before the filtration process, agglomerates or residues of the surface treatment agent generated during the surface treatment can also be removed in the dispersion filtration process.

The silicone oil can be any known silicone oil typically used for surface treatment of silica particles, without any particular restrictions. It can be selected appropriately depending on the required performance of the surface-treated silica particles.

Specific examples of silicone oils include dimethyl silicone oil, methylphenyl silicone oil, methylhydrogen silicone oil, alkyl-modified silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil, carbinol-modified silicone oil, methacrylic-modified silicone oil, polyether-modified silicone oil, and fluorine-modified silicone oil.

There are no particular restrictions on the proportion of silicone oil used, but if it is too little, the surface treatment will be insufficient, and if it is too much, post-treatment will be complicated. Therefore, it is preferable to use 0.05 to 80 parts by mass, and more preferably 0.1 to 60 parts by mass, per 100 parts by mass of silica particles used.

The silane coupling agent can be any known silane coupling agent commonly used in surface treatment, without any particular restrictions, and can be selected appropriately depending on the required performance of the surface-treated silica particles.

Specific examples of silane coupling agents include methyltrimethoxysilane, methyltriethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 3-acryloyloxytrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N,N-dimethyl-3-aminopropyltrimethoxysilane, N,N-diethyl-3-aminopropyltrimethoxysilane, and 4-styryltrimethoxysilane.

There are no particular restrictions on the proportion of silane coupling agent used, but if it is too small, the surface treatment will be insufficient, and if it is too large, post-treatment will be complicated. Therefore, it is preferable to use 0.05 to 80 parts by mass, and more preferably 0.1 to 40 parts by mass, per 100 parts by mass of silica particles used.

As the silazane, any known silazane commonly used for surface treatment can be used without any particular restrictions.

Specific examples of silazanes include tetramethyldisilazane, hexamethyldisilazane, and heptamethyldisilazane. Of the above, hexamethyldisilazane is preferred due to its high reactivity and ease of handling.

There are no particular restrictions on the proportion of silazane used, but if it is too little, the surface treatment will be insufficient, and if it is too much, post-treatment will be complicated. Therefore, it is preferable to use 0.1 to 150 parts by mass, and more preferably 1 to 120 parts by mass, per 100 parts by mass of silica particles used.

The above surface treatment agents may be used alone or in combination of two or more.

Of the surface treatment agents listed above, it is preferable to use at least one selected from the group consisting of a silane coupling agent and a silazane, and it is more preferable to use a silazane, as this will result in good fluidity for the resulting surface-treated silica particles.

There are no particular restrictions on the method of adding the surface treatment agent. If the surface treatment agent is a low-viscosity liquid at room temperature and normal pressure, it can be added dropwise to the dispersion. If the surface treatment agent is a high-viscosity liquid or solid, it can be added to an appropriate organic solvent to form a solution or dispersion, and then added in the same manner as for a low-viscosity liquid. Examples of organic solvents that can be used here include the same polar solvents as those mentioned above. Furthermore, if the surface treatment agent is in a gaseous state, it can be added by blowing it into the liquid in the form of fine bubbles.

The treatment temperature during surface treatment can be determined taking into consideration the reactivity of the surface treatment agent used, but if the treatment temperature is too low, the reaction will proceed slowly, and if it is too high, the operation will be complicated. Therefore, a temperature of 10 to 100°C is preferred, and a temperature of 20 to 80°C is even more preferred.

There are no particular restrictions on the treatment time when performing surface treatment, and it can be determined taking into account factors such as the reactivity of the surface treatment agent used. Taking into account both the sufficient progress of the surface treatment reaction and shortening the process time, a treatment time of 0.1 to 48 hours is preferred, and 0.5 to 24 hours is even more preferred.

<Coagulation process>
In the coagulation step, a coagulant may be added to the dispersion of silica particles. By adding the coagulant to the dispersion, weak aggregates of silica particles are formed in the dispersion. These aggregates can be stably present in the dispersion due to the presence of the coagulant or its derivatives in the dispersion, and can be easily recovered by filtration.

Examples of coagulants include carbon dioxide, ammonium carbonate, ammonium bicarbonate, and ammonium carbamate. Coagulants may be used singly or in combination of two or more.

The proportion of coagulant used and the method of addition can be set as follows, depending on the type of coagulant used. The proportion of coagulant used is set by considering the balance between the degree of formation of weak aggregates of silica particles in the dispersion and the waste of using an unreasonably large amount of raw material. The mass of silica particles used as the basis for the proportion of coagulant used below is a converted value assuming that all of the silicon alkoxide used has been hydrolyzed and polycondensed to form silica particles.

When carbon dioxide is used as the coagulant, the proportion used is preferably 0.005 parts by mass or more, and more preferably 0.005 to 300 parts by mass, per 100 parts by mass of silica particles contained in the dispersion. When the silica particles are not surface-treated, the proportion of carbon dioxide used is more preferably 0.05 parts by mass or more, and particularly preferably 0.05 to 300 parts by mass, and especially preferably 0.25 to 200 parts by mass, per 100 parts by mass of silica particles. On the other hand, when the silica particles are surface-treated, the proportion of carbon dioxide used is more preferably 15 parts by mass or more, and particularly preferably 15 to 300 parts by mass, and especially preferably 17 to 200 parts by mass, per 100 parts by mass of silica particles.

Methods for adding carbon dioxide include blowing it into the dispersion in gaseous form or adding it in solid form (dry ice), but adding it in solid form is preferred because it is easier to operate.

When ammonium carbonate, ammonium bicarbonate, or ammonium carbamate is used as the coagulant, the proportion used is preferably 0.001 parts by mass or more, and more preferably 0.001 to 80 parts by mass, per 100 parts by mass of silica particles contained in the dispersion. When the silica particles are not surface-treated, the proportion of ammonium carbonate, ammonium bicarbonate, or ammonium carbamate used is more preferably 0.001 to 15 parts by mass, and particularly preferably 0.001 to 10 parts by mass, per 100 parts by mass of silica particles. On the other hand, when the silica particles are surface-treated, the proportion of ammonium carbonate, ammonium bicarbonate, or ammonium carbamate used is more preferably 15 parts by mass or more, and particularly preferably 15 to 80 parts by mass, and particularly preferably 17 to 60 parts by mass, and even more preferably 20 to 50 parts by mass, per 100 parts by mass of silica particles.

Ammonium carbonate, ammonium bicarbonate, or ammonium carbamate may be added in solid form, or in solution form dissolved in an appropriate solvent. When adding these in solution form, there are no particular restrictions on the solvent used, as long as it dissolves them; however, water is preferred from the standpoint of its high dissolving ability and ease of removal after filtration. There are no particular restrictions on the concentration of the ammonium carbonate, ammonium bicarbonate, or ammonium carbamate solution, as long as it is within the range in which they dissolve; however, if the concentration is too low, the amount of solution used will increase, which is uneconomical; therefore, a concentration of 2 to 15% by mass is preferred, and a concentration of 5 to 12% by mass is particularly preferred.

In particular, the mixture of ammonium bicarbonate and ammonium carbamate, commercially available as "ammonium carbonate," can be used as is or as a solution dissolved in an appropriate solvent. In this case, the total proportion of ammonium bicarbonate and ammonium carbamate used, the type of solvent used when adding this as a solution, and the concentration of the solution are the same as for ammonium carbonate, ammonium bicarbonate, or ammonium carbamate.

When adding a coagulant, it is desirable to select and set the pH of the silica particle dispersion within a pH range that does not cause undesirable decomposition of the coagulant in the dispersion. From this perspective, it is preferable for the pH of the dispersion to be alkaline, and more preferably a pH of 9 or higher.

When adding a coagulant, it is desirable to select and set the temperature of the silica particle dispersion at a temperature at which the weak agglomerates of silica particles formed by the addition of the coagulant can remain stable. From this perspective, the temperature of the dispersion is preferably -10 to 60°C, the same as the reaction temperature during the hydrolysis and polycondensation of silicon alkoxide, and more preferably 10 to 40°C.

After adding the coagulant, it is preferable to carry out aging, i.e., to wait a while before the next step, filtration. By carrying out aging after adding the coagulant, the formation of the aforementioned weak agglomerates of silica particles is promoted, which is preferable. The longer the aging time, the better, but too long is uneconomical. On the other hand, if the aging time is too short, the formation of weak agglomerates of silica particles will be insufficient. Therefore, the aging time is preferably 0.5 to 72 hours, and particularly preferably 1 to 48 hours. The temperature of the dispersion during aging is not particularly limited, and can be carried out within the same temperature range as the preferred temperature when adding the coagulant, and it is sufficient to carry out aging at the same temperature as when adding the coagulant.

<Separation process>
In the separation step, a coagulant may be added in the coagulation step, and the silica particles may be recovered by filtration from the dispersion, preferably after aging.

The silica particles that form weak aggregates by adding the coagulant can be easily recovered by filtration, separating the solid and liquid, as a filter cake. There are no particular restrictions on the filtration method, and known methods such as vacuum filtration, pressure filtration, and centrifugal filtration can be used.

The filter paper, filters, filter cloth, etc. (hereinafter collectively referred to as "filter paper, etc.") used in filtration can be any industrially available material, and can be selected appropriately depending on the scale of the separation device (filter). Because the addition of a coagulant causes the silica particles to form weakly aggregated agglomerates, a pore size of approximately 5 μm, for example, is sufficient for the filter paper, etc. Because filter paper, etc. with a large pore size is sufficient, filtration can be carried out quickly.

The silica particles are recovered as a cake by filtration.

If an aqueous ammonium bicarbonate solution is used as the coagulant in the above coagulation step, the resulting cake may be rinsed with an appropriate solvent, such as water or alcohol. This treatment allows for the decomposition or removal of the solvent, basic catalyst, and unreacted surface treatment agent used in the hydrolysis and polycondensation reaction of the silicon alkoxide.

<Drying process>
In the drying step, the silica particles recovered in the above separation step may be dried.

In order to improve the crushability of the cake of silica particles recovered in the above separation process, it is preferable that the drying temperature in the drying process be 35°C or higher. By heating at this temperature, any coagulant remaining in the cake that has not been removed by the above filtration, rinsing, etc. can be easily removed by thermal decomposition.

The drying method is not particularly limited, and known methods such as air drying or vacuum drying can be used. Vacuum drying is preferred in order to improve the crushability of the silica particle cake recovered in the above separation process.

Increasing the drying temperature is advantageous from the standpoint of the decomposition efficiency of the coagulant and making the silica particles more easily disintegrated. However, if the drying temperature is too high, the reactive substituents introduced to the surface of the silica particles by surface treatment may cause the formation of agglomerates, which is undesirable. Therefore, to strike a balance between the above, the drying temperature is preferably 35 to 200°C, more preferably 50 to 200°C, and particularly preferably 80 to 200°C, with 120 to 200°C being especially preferred.

There are no particular restrictions on the drying time, but a drying time of approximately 2 to 48 hours will allow the silica particles to dry sufficiently.

It is also possible to remove the dispersing medium from the silica particle dispersion continuously throughout the concentration and drying processes. For example, by concentrating the silica particle dispersion by heating or concentrating under reduced pressure to volatilize the dispersing medium, it is possible to directly obtain silica particles from which the dispersing medium has been removed. In this case, since there is a risk that salts derived from the coagulant will be lost when the dispersing medium is removed by heating, it is possible to add an appropriate amount of coagulant to the concentrate of the silica dispersion during concentration and drying so as to prevent salts derived from the coagulant from being lost in the concentrate.

Through the above process, silica particles are obtained as a dry powder in the form of agglomerates formed by weakly agglomerating individual particles. These silica particles are easy to disperse and have excellent dispersibility, without forming agglomerates that are difficult to disperse. They can be easily disperse by the shear of a disperser when dispersing in a resin or solvent, without the need for any special dispersing process, and can be uniformly dispersed in the resin or solvent.

<Firing process>
After the drying process, the silica particles have not completely removed the dispersant absorbed in the particles, and silanol groups remain and pores are present. In order to thoroughly remove the dispersant from the particles and reduce the amount of silanol groups on the particle surface to obtain solid silica, it is preferable to further perform a calcination process depending on the application. That is, the silica particles treated in the calcination process are preferable not only because the amount of silanol groups on the particle surface is reduced, but also because the dispersant remaining in the particles is removed. When used as a resin filler, the solvent remaining in the particles generates bubbles upon heating, causing a decrease in yield. This is particularly noticeable in applications such as semiconductor encapsulants or liquid crystal sealants, which have a high filling rate. Therefore, it is preferable to include this calcination process in the production of silica particles, particularly for use as semiconductor encapsulants or liquid crystal sealants.

If the firing temperature in the firing process is too low, it will be difficult to remove the dispersion medium components, and if it is too high, the silica particles will fuse together. Therefore, it is preferable to carry out the firing process at a temperature of 300 to 1300°C, and more preferably 600 to 1200°C.

The firing time in the firing step is not particularly limited as long as the remaining dispersion medium is removed. Since productivity decreases if the firing time is too long, it is sufficient to heat the mixture to the desired firing temperature and then maintain the temperature for 0.5 to 48 hours, more preferably 2 to 24 hours.

The atmosphere during firing is not particularly limited, and firing can be carried out under an inert gas such as argon or nitrogen, or in the air.

As mentioned above, after the firing process, the silica particles are obtained as a dry powder in the form of agglomerates, with the individual particles weakly clumped together.

<Crushing process>
The silica particles after the calcination step can be used for various purposes without any particular crushing treatment, but depending on the purpose, a crushing step may be carried out to further reduce agglomerates. In the crushing step, crushing treatment may be carried out by a known crushing means.

Known disintegration methods include, for example, a ball mill or jet mill. Furthermore, even without using known disintegration methods, when silica particles are used by dispersing them in a resin or solvent, a high-shear disperser can be used to disperse the silica particles in the resin or solvent at the same time.

[Production Example 1] Production of Silica Particles A jacketed glass reactor with an internal volume of 10 L and a Max Blend impeller was used as the reaction vessel. 207.6 g of methanol, isopropanol, and aqueous ammonia (25% by mass) were charged as the initial reaction solution. The reaction temperature was set to 40°C, and the mixture was stirred at 60 rpm. The amounts (g) of methanol (MeOH, A) and isopropanol (IPA, B) in the initial reaction solution are shown in Table 1. The IPA concentration (% by mass) in the organic solvents (MeOH and IPA) contained in the initial reaction solution is also shown in Table 1.

Next, a silica particle generation mixture of 25.9 g of tetraethoxysilane (TEOS), methanol, and isopropanol was added to the initial reaction solution at a discharge rate of 300 g/min or more, and hydrolysis and polycondensation of the TEOS were carried out to produce silica particles. The amounts (g) of methanol (MeOH, C) and isopropanol (IPA, D) in the silica particle generation mixture are shown in Table 1. Table 1 also shows the IPA concentration (mass %) in the organic solvents (MeOH and IPA) contained in the silica particle generation mixture.

The average particle size (50% cumulative diameter on a volume basis) of the resulting silica particles was measured using a laser diffraction scattering method (LS13 320, manufactured by Beckman Coulter). The measurement results for silica particles (X) are shown in Table 1. Figure 1 also shows a graph plotting the average particle size (μm) of silica particles on the vertical axis and the IPA concentration (% by mass) on the horizontal axis. The IPA concentration is the IPA concentration in the organic solvent used to produce the silica particles.

As shown in Table 1 and Figure 1, it was found that the particle size of silica particles can be adjusted depending on the mixing ratio of methanol and IPA.

Furthermore, 4,150 g of tetramethoxysilane (TMOS) and 415 g of methanol were supplied to the silica particle solution at a discharge rate of 20 g/min. Simultaneously with this supply, 1,830 g of ammonia water (25% by mass) was supplied at a discharge rate of 8 g/min, causing hydrolysis and polycondensation of TMOS and growing silica particles. After the supply was completed, stirring was continued for 1 hour.

The average particle size and coefficient of variation of the large particles obtained by growing silica particles (hereinafter sometimes referred to as "grown particles") were measured using a laser diffraction scattering method. The measurement results for the grown particles (Y) are shown in Table 1. Figure 2 is a graph plotting the average particle size (μm) of the grown particles on the vertical axis and the IPA concentration (mass%) in the organic solvent used to generate the silica particles on the horizontal axis.

As shown in Table 1 and Figure 2, it was found that the particle size of the grown silica particles could be adjusted depending on the mixing ratio of methanol and IPA used to generate the silica particles. Furthermore, each grown particle was spherical.

[Production Example 2] Production of Silica Particles The same reaction vessel as in Production Example 1 was used. 207.6 g of methanol, ethanol, and aqueous ammonia (25% by mass) was charged as the initial reaction solution. The reaction temperature was set to 40°C, and the mixture was stirred at 60 rpm. The amounts (g) of methanol (MeOH, A) and ethanol (EtOH, B) in the initial reaction solution are shown in Table 2. Table 2 also shows the EtOH concentration (% by mass) in the organic solvents (MeOH and EtOH) contained in the initial reaction solution.

Next, a silica particle production mixture of 25.9 g of TEOS, methanol, and ethanol was added to the initial reaction solution at a discharge rate of 300 g/min or more, and hydrolysis and polycondensation of TEOS were carried out to produce silica particles. The amounts (g) of methanol (MeOH, C) and ethanol (EtOH, D) in the silica particle production mixture are shown in Table 2. Table 2 also shows the EtOH concentration (mass %) in the organic solvents (MeOH and EtOH) contained in the silica particle production mixture.

The average particle size of the resulting silica particles was measured by laser diffraction scattering. The measurement results for silica particles (X) are shown in Table 2. Figure 3 shows a graph plotting the average particle size (μm) of silica particles on the vertical axis and the EtOH concentration (mass%) on the horizontal axis. The EtOH concentration is the EtOH concentration in the organic solvent used to produce the silica particles.

As shown in Table 2 and Figure 3, it was found that the particle size of silica particles can be adjusted depending on the mixing ratio of methanol and ethanol.

Furthermore, 4,150 g of TMOS and 415 g of methanol were supplied to the silica particle solution at a discharge rate of 20 g/min. Simultaneously with this supply, 1,830 g of ammonia water (25% by mass) was supplied at a discharge rate of 8 g/min, causing hydrolysis and polycondensation of TMOS, growing silica particles, and obtaining grown particles. After the supply was completed, stirring was continued for 1 hour.

The average particle size and coefficient of variation of the grown particles were measured using a laser diffraction scattering method. The measurement results for grown particles (Y) are shown in Table 2. Figure 4 is a graph plotting the average particle size (μm) of grown particles on the vertical axis and the EtOH concentration (mass%) in the organic solvent used to generate the silica particles on the horizontal axis.

As shown in Table 2 and Figure 4, it was found that the particle size of the grown silica particles can be adjusted depending on the mixing ratio of methanol and ethanol used to generate the silica particles.

[Production Example 3] Production of Silica Particles The same reaction vessel as in Production Example 1 was used. 207.6 g of methanol, 2-butanol, and aqueous ammonia (25% by mass) were charged as the initial reaction solution. The reaction temperature was set to 40°C, and the mixture was stirred at 60 rpm. The amounts (g) of methanol (MeOH, A) and 2-butanol (BuOH, B) in the initial reaction solution are shown in Table 3. Table 3 also shows the BuOH concentrations (% by mass) in the organic solvents (MeOH and BuOH) contained in the initial reaction solution.

Next, a silica particle production mixture of 25.9 g of TEOS, methanol, and 2-butanol was added to the initial reaction solution at a discharge rate of 300 g/min or more, and hydrolysis and polycondensation of TEOS were carried out to produce silica particles. The amounts (g) of methanol (MeOH, C) and 2-butanol (BuOH, D) in the silica particle production mixture are shown in Table 3. Table 3 also shows the BuOH concentration (mass %) in the organic solvents (MeOH and BuOH) contained in the silica particle production mixture.

The average particle size of the resulting silica particles was measured by laser diffraction scattering. The measurement results for silica particles (X) are shown in Table 3. Figure 5 shows a graph plotting the average particle size (μm) of silica particles on the vertical axis and the BuOH concentration (mass%) on the horizontal axis. The BuOH concentration is the BuOH concentration in the organic solvent used to produce the silica particles.

As shown in Table 3 and Figure 5, it was found that the particle size of silica particles can be adjusted depending on the mixing ratio of methanol and 2-butanol.

Furthermore, 4,150 g of TMOS and 415 g of methanol were supplied to the silica particle solution at a discharge rate of 20 g/min. Simultaneously with this supply, 1,830 g of ammonia water (25% by mass) was supplied at a discharge rate of 8 g/min, causing hydrolysis and polycondensation of TMOS, growing silica particles, and obtaining grown particles. After the supply was completed, stirring was continued for 1 hour.

The average particle size and coefficient of variation of the grown particles were measured using a laser diffraction scattering method. The measurement results for grown particles (Y) are shown in Table 3. Figure 6 is a graph plotting the average particle size (μm) of grown particles on the vertical axis and the BuOH concentration (mass %) in the organic solvent used to generate the silica particles on the horizontal axis.

As shown in Table 3 and Figure 6, it was found that the particle size of the grown silica particles can be adjusted depending on the mixing ratio of methanol and 2-butanol used to generate the silica particles.

[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 (3)

The method includes the step of producing silica particles by hydrolysis and polycondensation of silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent,
the organic solvent includes methanol and ethanol;
a mass ratio of the ethanol to the methanol in the organic solvent (ethanol/methanol) is 1/9 or more and 1 or less;
The method for producing silica particles, wherein the volume-based cumulative 50% diameter of the silica particles measured by a laser diffraction scattering method is 0.07 μm or more and 0.22 μm or less. The method includes the step of producing silica particles by hydrolysis and polycondensation of silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent,
the organic solvent is an organic solvent containing methanol and 2-butanol, or 2-butanol;
a mass ratio of the 2-butanol to the methanol (2-butanol/methanol) in the organic solvent containing methanol and 2-butanol is 1/9 or more;
The method for producing silica particles, wherein the silica particles have a volume-based cumulative 50% diameter of 0.12 μm or more and 0.55 μm or less, as determined by a laser diffraction scattering method. The method includes the step of producing silica particles by hydrolysis and polycondensation of silicon alkoxide in the presence of a basic catalyst, water, and an organic solvent,
the organic solvent comprises methanol and isopropanol;
a mass ratio of the isopropanol to the methanol (isopropanol/methanol) in the organic solvent is 3/7 or more;
The method for producing silica particles, wherein the volume-based cumulative 50% diameter of the silica particles measured by a laser diffraction scattering method is 0.16 μm or more and less than 0.44 μm.