Method for adjusting particle size of silica particles and method for producing silica particles

Abstract

To provide a method for simply adjusting silica particles to a desired particle diameter.SOLUTION: There is provided a method for adjusting the particle diameter of silica particles, which comprises hydrolysis and polycondensation of a silicon alkoxide in the presence of a basic catalyst, water and an organic solvent. The average particle diameter (volume-based cumulative 50% diameter) of silica particles by laser diffraction scattering method is adjusted to 0.05 μm or more and 0.60 μm or less by adjusting the mass ratio of methanol to an alcohol having 2 or more and 4 or less carbon atoms in an organic solvent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for adjusting the particle size of silica particles and a method for producing silica particles. [Background technology]

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

[0003] As a method for producing highly monodisperse silica particles, the so-called sol-gel method, in which silica particles are produced by hydrolysis and polycondensation of silicon alkoxide, is known (e.g., Patent Documents 1 to 3). For example, Patent Document 1 describes that highly monodisperse silica particles can be obtained by setting the supply rate of a raw material metal alkoxide to a reaction solution in a specific range. [Prior art documents] [Patent documents]

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

[0005] On the other hand, it is not easy to maintain the monodispersity of silica particles obtained by the silica powder manufacturing methods described in Patent Documents 1 to 3 and adjust the particle size to a desired size. In order to obtain silica particles with a 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 a desired particle size.

[0006] An object of one aspect of the present invention is to provide a method for easily adjusting silica particles to a desired particle size. [Means for solving the problem]

[0007] In order to solve the above problems, a method for adjusting the particle size of silica particles according to one embodiment of the present invention includes a step of 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.

[0008] In the method for adjusting the particle size of silica particles according to one aspect of the present invention, the alcohol having 2 to 4 carbon atoms may be ethanol, n-propanol, isopropanol, 1-butanol, or 2-butanol.

[0009] In order to solve the above problems, 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, 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. [Effects of the Invention]

[0010] According to one aspect of the present invention, a method for easily adjusting silica particles to a desired particle size can be realized. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a graph showing the relationship between the mixing ratio of methanol and isopropanol and the silica particle size. [Figure 2] 1 is a graph showing the relationship between the mixture ratio of methanol and isopropanol and the particle size after growth. [Figure 3] 1 is a graph showing the relationship between the mixing ratio of methanol and ethanol and the silica particle size. [Figure 4] 1 is a graph showing the relationship between the mixture ratio of methanol and ethanol and the particle size after growth. [Figure 5] 1 is a graph showing the relationship between the mixing ratio of methanol and 2-butanol and the silica particle size. [Figure 6] 1 is a graph showing the relationship between the mixing ratio of methanol and 2-butanol and the particle size after growth. DETAILED DESCRIPTION OF THE INVENTION

[0012] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. Furthermore, in this specification, "A to B" means A or more and B or less, unless otherwise specified.

[0013] [Method for adjusting particle size of silica particles] A method for adjusting the particle size of silica particles according to one embodiment 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.

[0014] The present inventors have conducted extensive research into the control of silica particle size and have succeeded in obtaining a new finding: that is, they have independently discovered that the particle size of silica particles can be easily controlled by adjusting the organic solvent used in the hydrolysis and polycondensation of silicon alkoxide to a specific composition.

[0015] (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) commonly 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.

[0016] (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 preferred. The basic catalyst may be one of these, or may contain two or more of them.

[0017] The basic 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, it is preferable to use the basic catalyst as an aqueous solution in which the concentration is adjusted by dissolving it in water. When the basic catalyst is used as an aqueous solution, the concentration of the basic catalyst in the aqueous solution may be, for example, 1 to 30 mass%.

[0018] (organic solvent) The organic solvent used in the preparation method of this embodiment is adjusted such that the mass ratio of methanol to 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.

[0019] By adjusting the mixing ratio of methanol to an alcohol having 2 to 4 carbon atoms, silica particles having an average particle size of 0.05 μm to 0.60 μm can be obtained. The higher 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 a laser diffraction scattering method. In this specification, the average particle size of silica particles refers to the cumulative 50% diameter based on volume.

[0020] Examples of alcohols having 2 to 4 carbon atoms include ethanol, n-propanol, isopropanol, 1-butanol, and 2-butanol. The alcohols having 2 to 4 carbon atoms may be one of these, or may contain two or more of these. The alcohols having 2 to 4 carbon atoms are preferably ethanol, isopropanol, or 2-butanol, and more preferably isopropanol.

[0021] The amount of the basic catalyst used in the preparation method of this embodiment may be appropriately selected taking into consideration the reaction rates of the hydrolysis and polycondensation reactions of the silicon alkoxide, etc. The amount of the basic catalyst used is preferably 0.1 to 60 mass % and more preferably 0.5 to 40 mass % relative to the amount of the silicon alkoxide.

[0022] 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, based on 100% by mass of the total reaction solution. 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, based on 100% by mass of the total reaction solution. The total amount of the reaction solution refers to the total amount of raw materials used in the reaction, such as silicon alkoxide, basic catalyst, organic solvent, and water.

[0023] 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 a reaction vessel include a reaction vessel equipped with a stirrer. Examples of the stirring blades of the stirrer include an inclined paddle blade, a turbine blade, a triple-swept blade, an anchor blade, a full zone blade, a twin star blade, and a max blend blade.

[0024] The reaction vessel having a stirrer may be a hemispherical or cylindrical reaction vessel with a flat or round bottom, or a reaction vessel having a baffle plate installed therein. 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.

[0025] It is preferable to use a reaction vessel equipped with an agitator with a dimensionless mixing time (n × θm) of 100 or less, as this will result in silica particles with a more uniform particle size and a narrow particle size distribution. 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 and rotation speed of the agitator impeller, and the viscoelastic properties of the liquid being mixed.

[0026] The order of addition to the reaction vessel is not particularly limited, but 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. When the silicon alkoxide contains two or more types of silicon alkoxide, they may be added simultaneously or sequentially.

[0027] The reaction temperature may be appropriately selected depending on the types of silicon alkoxide, basic catalyst, and organic catalyst, etc. The reaction temperature may be, for example, in the range of -10 to 60°C.

[0028] [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.

[0029] The organic solvent used in the above production method includes methanol and isopropanol, and the mass ratio of isopropanol to methanol (isopropanol / methanol) is 3 / 7 or more.

[0030] 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 ratio of methanol in the organic solvent, the smaller the average particle size of silica particles can be obtained. The average particle size of silica particles is measured by laser diffraction scattering method.

[0031] Another aspect of the present invention is a method for producing silica particles, which 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, wherein the organic solvent includes methanol and ethanol. By adjusting the mixing ratio of methanol and ethanol, silica particles having 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 can be obtained. The average particle size of the silica particles is measured by laser diffraction scattering.

[0032] Another aspect of the present invention is a method for producing silica particles, which 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, wherein the organic solvent includes methanol and 2-butanol. By adjusting the mixing ratio of methanol and ethanol, silica particles with an average particle size of more 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 obtained silica particles. The average particle size of the silica particles is measured by a laser diffraction scattering method.

[0033] The silica particles obtained by the method for producing silica particles according to one embodiment of the present invention and 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 silica particles. That is, hydrolysis and polycondensation of silicon alkoxide may be performed in two stages.

[0034] When the hydrolysis and polycondensation of silicon alkoxide are carried out in two stages, the reaction conditions for the first stage are as described above, and the composition of the organic solvent must be adjusted to obtain silica particles with 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 the 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.

[0035] In the method for producing silica particles according to one embodiment of the present invention, after the hydrolysis and polycondensation of silicon alkoxide, a treatment generally performed in the production of silica particles by a sol-gel reaction may be carried out. Examples of such treatments include a filtration step, a surface treatment step, a coagulation step, a separation step, a drying step, a calcination step, and a crushing step. Each step will be described below.

[0036] <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 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 falls within the above range.

[0037] As the filter medium, a wet filtration filter having a mesh size of 5 μm or less can be used without any particular limitation on the type, and preferably a filter having a mesh size of 3 μm or less can also be used.

[0038] The material of the filter is not particularly limited, but examples include resin (polypropylene, PTFE, etc.) and metal. From the viewpoint of preventing the inclusion of metal impurities, it is preferable to use a resin filter.

[0039] <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 treatment agent selected from the group consisting of silicone oil, a silane coupling agent, and a silazane.

[0040] The surface treatment can efficiently carry out the separation step described below. Furthermore, since the formation of strong agglomerates during drying can be suppressed, the silica particles can be used for various purposes without any special crushing treatment.

[0041] The surface treatment step may be carried out before the coagulation step in the dispersion of silica particles, and may be carried out either before or after the filtration step of the dispersion, but is preferably carried out before the filtration step of the dispersion in order to accurately reduce reaction residues, adhered particles, or agglomerates. By carrying out the surface treatment step before the filtration step, it is possible to remove agglomerates or residues of the surface treatment agent generated during the surface treatment in the filtration step of the dispersion.

[0042] As the silicone oil, any known silicone oil that is normally used for surface treatment of silica particles can be used without any particular restrictions, and may be appropriately selected and used depending on the required performance of the surface-treated silica particles, etc.

[0043] 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.

[0044] The proportion of silicone oil used is not particularly limited, but if it is too little, the surface treatment will be insufficient, and if it is too much, post-treatment will be complicated. Therefore, the proportion is preferably 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.

[0045] As the silane coupling agent, any known silane coupling agent commonly used for surface treatment can be used without any particular restrictions, and may be appropriately selected and used depending on the required performance of the surface-treated silica particles, etc.

[0046] 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.

[0047] The proportion of the silane coupling agent used is not particularly limited, but if it is too small, the surface treatment will be insufficient, and if it is too large, post-treatment will be complicated. Therefore, the proportion is preferably 0.05 to 80 parts by mass, and more preferably 0.1 to 40 parts by mass, per 100 parts by mass of the silica particles used.

[0048] As the silazane, any known silazane that is usually used for surface treatment can be used without any particular limitation.

[0049] Specific examples of silazanes include tetramethyldisilazane, hexamethyldisilazane, heptamethyldisilazane, etc. Among these, hexamethyldisilazane is preferred for its reactivity and ease of handling.

[0050] The proportion of silazane used is not particularly limited, but if it is too small, the surface treatment will be insufficient, and if it is too large, the post-treatment will be complicated. Therefore, the proportion is preferably 0.1 to 150 parts by mass, and more preferably 1 to 120 parts by mass, per 100 parts by mass of the silica particles used.

[0051] The above surface treatment agents may be used alone or in combination of two or more.

[0052] Among the above-mentioned surface treatment agents, 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, since the resulting surface-treated silica particles have good fluidity.

[0053] The method of adding the surface treatment agent is not particularly limited. When the surface treatment agent is a low-viscosity liquid at room temperature and normal pressure, it can be added dropwise to the dispersion. When 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 in the case of a low-viscosity liquid. Examples of the organic solvent used here include the same polar solvents as those mentioned above. Furthermore, when 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.

[0054] The treatment temperature when performing the surface treatment may be determined taking into consideration the reactivity of the surface treatment agent used, etc. However, if the treatment temperature is too low, the reaction will proceed slowly, and if it is too high, the operation will be complicated. Therefore, the treatment temperature is preferably 10 to 100°C, and more preferably 20 to 80°C.

[0055] The treatment time for the surface treatment is not particularly limited and may be determined taking into consideration the reactivity of the surface treatment agent used, etc. Taking into consideration both the sufficient progress of the surface treatment reaction and shortening the process time, the treatment time is preferably set to 0.1 to 48 hours, and more preferably 0.5 to 24 hours.

[0056] <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.

[0057] Examples of the coagulant include carbon dioxide, ammonium carbonate, ammonium hydrogen carbonate, ammonium carbamate, etc. The coagulant may be used alone or in combination of two or more kinds.

[0058] The use rate and addition method of coagulant can be set as follows according to the type of coagulant used.The use rate of coagulant is set by considering the balance between the degree of formation of weak aggregates of silica particles in dispersion and the waste of using an unreasonably large amount of raw material.The mass of silica particles used as the basis for the use rate of coagulant below is the converted value when it is assumed that all the silicon alkoxide used is hydrolyzed and polycondensed to form silica particles.

[0059] When carbon dioxide is used as the coagulant, the proportion of carbon dioxide used is preferably 0.005 parts by mass or more, 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, particularly preferably 0.05 to 300 parts by mass, and particularly preferably 0.25 to 200 parts by mass, per 100 parts by mass of silica particles. When the silica particles are surface-treated, the proportion of carbon dioxide used is more preferably 15 parts by mass or more, particularly preferably 15 to 300 parts by mass, and particularly preferably 17 to 200 parts by mass, per 100 parts by mass of silica particles.

[0060] Examples of methods for adding carbon dioxide include blowing it into the dispersion in a gaseous state and adding it in a solid state (dry ice). Adding it in a solid state is preferred because it is easier to operate.

[0061] When ammonium carbonate, ammonium bicarbonate, or ammonium carbamate is used as the coagulant, the proportion thereof is preferably 0.001 parts by mass or more, 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 is more preferably 0.001 to 15 parts by mass, particularly preferably 0.001 to 10 parts by mass, per 100 parts by mass of silica particles. When the silica particles are surface-treated, the proportion of ammonium carbonate, ammonium bicarbonate, or ammonium carbamate is more preferably 15 parts by mass or more, particularly preferably 15 to 80 parts by mass, 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.

[0062] Ammonium carbonate, ammonium bicarbonate, or ammonium carbamate may be added in a solid state or in a solution state dissolved in an appropriate solvent. When adding these in a solution state, the solvent used is not particularly limited as long as it dissolves these compounds, but water is preferred from the viewpoints of high dissolving ability and ease of removal after filtration. The concentration of the ammonium carbonate, ammonium bicarbonate, or ammonium carbamate solution is not particularly limited as long as it is within a range in which these compounds can be dissolved, but 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, and particularly 5 to 12% by mass, is preferred.

[0063] In particular, a mixture of ammonium hydrogen carbonate and ammonium carbamate, commercially available as so-called "ammonium carbonate," can be used as is or as a solution dissolved in a suitable solvent. In this case, the total proportion of ammonium hydrogen carbonate 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 those for ammonium carbonate, ammonium hydrogen carbonate, or ammonium carbamate.

[0064] The pH of the silica particle dispersion when adding the coagulant is preferably set within a pH range that does not cause undesirable decomposition of the coagulant in the dispersion. From this perspective, the pH of the dispersion is preferably alkaline, more preferably pH 9 or higher.

[0065] When adding coagulant, the temperature of the dispersion of silica particles is desired to be selected and set at the temperature that can stably exist the weak aggregate of silica particles that is generated by adding coagulant.From this point of view, the temperature of dispersion is preferably -10 to 60 ℃, which is the same as the reaction temperature during the hydrolysis and polycondensation of silicon alkoxide, and more preferably 10 to 40 ℃.

[0066] After the addition of the coagulant, it is preferable to carry out aging, i.e., to wait a while before the next step of filtration. By carrying out aging after the addition of the coagulant, the formation of the weak aggregates of silica particles described above 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 aggregates 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 the coagulant is added, and it is sufficient to carry out the aging at the same temperature as when the coagulant is added.

[0067] <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.

[0068] The silica particles that have formed weak aggregates by the addition of the coagulant can be easily recovered by filtration to separate the solid and liquid. The filtration method is not particularly limited, and known methods such as vacuum filtration, pressure filtration, and centrifugal filtration can be used.

[0069] The filter paper, filters, filter cloth, etc. (hereinafter collectively referred to as "filter paper, etc.") used in filtration can be any industrially available material without particular restrictions, and can be selected appropriately depending on the scale of the separation device (filter). Because the silica particles are weakly aggregated into agglomerates due to the addition of a coagulant, a pore size of approximately 5 μm, for example, is sufficient for the filter paper, etc. In this way, a large pore size is sufficient for the filter paper, etc., allowing for rapid filtration.

[0070] The silica particles are recovered as a cake by filtration.

[0071] When an aqueous ammonium bicarbonate solution is used as the coagulant in the coagulation step, the resulting cake may be rinsed with an appropriate solvent, such as water, alcohol, etc. This treatment allows 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.

[0072] <Drying process> In the drying step, the silica particles recovered in the above separation step may be dried.

[0073] In order to improve the crushability of the cake of silica particles recovered in the above separation step, the drying temperature in the drying step is preferably 35° C. or higher. By heating at this temperature, the coagulant remaining in the cake without being removed by the above filtration, rinsing, etc. can be easily removed by thermal decomposition.

[0074] The drying method is not particularly limited, and known methods such as air drying or vacuum drying can be used. In order to improve the crushability of the cake of silica particles recovered by the above separation step, drying by vacuum drying is preferred.

[0075] Increasing the temperature during drying is advantageous from the viewpoint of the decomposition efficiency of coagulant and the viewpoint of making silica particles more easily disintegrated.However, if the drying temperature is too high, the reactive substituent introduced on the surface of silica particles by surface treatment may cause the formation of agglomerates, which is not preferable.Therefore, in order to achieve the above balance, the drying temperature is preferably 35 to 200 ° C, more preferably 50 to 200 ° C, particularly preferably 80 to 200 ° C, and particularly preferably 120 to 200 ° C.

[0076] The drying time is not particularly limited, but by setting it to about 2 to 48 hours, the silica particles can be dried sufficiently.

[0077] In addition, the removal of dispersion medium from the dispersion of silica particles can be carried out continuously during concentration and drying.For example, the dispersion of silica particles can be carried out by the method of volatilizing dispersion medium by heating concentration or vacuum concentration etc., so that the silica particles from which dispersion medium is removed can be directly obtained from the dispersion of silica particles.In this case, when removing dispersion medium by heating, there is a risk that the salt derived from coagulant will disappear, so that the concentrate of silica dispersion during concentration and drying can be appropriately added with coagulant, so that the salt derived from coagulant will not disappear in the concentrate.

[0078] Through the above process, the silica particles are obtained as a dry powder in the form of agglomerates formed by weak aggregation of individual particles. These silica particles are excellent in dispersibility and can be easily disintegrated without forming agglomerates that are difficult to disintegrate. They can be easily disintegrated by the shear of a disperser when dispersed in a resin or solvent, without requiring any special disintegration treatment, and can be uniformly dispersed in the resin or solvent.

[0079] <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.

[0080] If the firing temperature in the firing step is too low, it is difficult to remove the dispersion medium components, and if it is too high, fusion of the silica particles occurs. Therefore, the firing step is preferably carried out at 300 to 1300°C, more preferably 600 to 1200°C.

[0081] The calcination time in the calcination step is not particularly limited as long as the remaining dispersion medium is removed. If the calcination time is too long, productivity will decrease, so it is sufficient to calcinate the mixture by heating it to the desired calcination temperature for 0.5 to 48 hours, more preferably 2 to 24 hours.

[0082] The atmosphere during firing is not particularly limited, and firing can be carried out in an inert gas such as argon or nitrogen, or in the air.

[0083] As described above, the silica particles obtained after the calcination step are also obtained as a dry powder in the form of aggregates in which the individual particles are weakly aggregated.

[0084] <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.

[0085] Examples of known disintegration means include a ball mill, a jet mill, etc. Furthermore, when silica particles are used by being dispersed in a resin or a solvent, etc., even without using known disintegration means, the silica particles can be disperse in the resin or the solvent and disintegrated at the same time by using a high-shear disperser. [Example]

[0086] [Production Example 1] Production of silica particles The reaction vessel used was a 10 L jacketed glass reaction vessel equipped with a Max Blend impeller. 207.6 g of methanol, isopropanol, 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 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.

[0087] Next, 25.9 g of tetraethoxysilane (TEOS), methanol, and isopropanol were added to the initial reaction mixture at a rate of 300 g / min or more to produce silica particles. Hydrolysis and polycondensation of TEOS were carried out to produce silica particles. The amounts (g) of methanol (MeOH, C) and isopropanol (IPA, D) in the silica particle production mixture are shown in Table 1. The IPA concentration (mass%) in the organic solvents (MeOH and IPA) contained in the silica particle production mixture is also shown in Table 1.

[0088] The average particle size (50% cumulative volume diameter) of the obtained silica particles was measured by a laser diffraction scattering method (LS13 320, manufactured by Beckman Coulter). The measurement results for the silica particles (X) are shown in Table 1. Figure 1 shows a graph in which the vertical axis represents the average particle size (μm) of the silica particles and the horizontal axis represents the IPA concentration (mass%). The IPA concentration is the IPA concentration in the organic solvent used to generate the silica particles.

[0089] [Table 1]

[0090] As shown in Table 1 and FIG. 1, it was found that the particle size of the silica particles can be adjusted depending on the mixing ratio of methanol and IPA.

[0091] Furthermore, 4150 g of tetramethoxysilane (TMOS) and 415 g of methanol were fed into the silica particle solution at a discharge rate of 20 g / min. Simultaneously with this feed, 1830 g of ammonia water (25% by mass) was fed at a discharge rate of 8 g / min to carry out hydrolysis and polycondensation of TMOS, thereby growing silica particles. After the feed was completed, stirring was continued for 1 hour.

[0092] 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.

[0093] 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 in generating the silica particles. Furthermore, each grown particle was spherical.

[0094] [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.

[0095] 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. The EtOH concentration (mass%) in the organic solvents (MeOH and EtOH) contained in the silica particle production mixture is also shown in Table 2.

[0096] The average particle size of the obtained silica particles was measured by a laser diffraction scattering method. The measurement results for silica particles (X) are shown in Table 2. Figure 3 shows a graph in which the vertical axis represents the average particle size (μm) of the silica particles and the horizontal axis represents the EtOH concentration (mass%). The EtOH concentration is the EtOH concentration in the organic solvent used in producing the silica particles.

[0097] [Table 2]

[0098] As shown in Table 2 and FIG. 3, it was found that the particle size of the silica particles can be adjusted depending on the mixing ratio of methanol and ethanol.

[0099] Furthermore, 4150 g of TMOS and 415 g of methanol were fed into the silica particle solution at a discharge rate of 20 g / min. Simultaneously with this feed, 1830 g of ammonia water (25% by mass) was fed at a discharge rate of 8 g / min to carry out hydrolysis and polycondensation of TMOS, thereby growing silica particles and obtaining grown particles. After the feed was completed, stirring was continued for 1 hour.

[0100] The average particle size and coefficient of variation of the grown particles were measured using a laser diffraction scattering method. The measurement results for the grown particles (Y) are shown in Table 2. Figure 4 shows a graph plotting the average particle size (μm) of the 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.

[0101] 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 in producing the silica particles.

[0102] [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) 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 2-butanol (BuOH, B) in the initial reaction solution are shown in Table 3. Table 3 also shows the BuOH concentration (% by mass) in the organic solvents (MeOH and BuOH) contained in the initial reaction solution.

[0103] Next, a silica particle-producing 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-producing mixture are shown in Table 3. The BuOH concentration (mass%) in the organic solvents (MeOH and BuOH) contained in the silica particle-producing mixture is also shown in Table 3.

[0104] The average particle size of the obtained silica particles was measured by a laser diffraction scattering method. The measurement results for silica particles (X) are shown in Table 3. Figure 5 shows a graph in which the vertical axis represents the average particle size (μm) of the silica particles and the horizontal axis represents the BuOH concentration (mass%). The BuOH concentration is the BuOH concentration in the organic solvent used in producing the silica particles.

[0105] [Table 3]

[0106] As shown in Table 3 and FIG. 5, it was found that the particle size of the silica particles could be adjusted depending on the mixing ratio of methanol and 2-butanol.

[0107] Furthermore, 4150 g of TMOS and 415 g of methanol were fed into the silica particle solution at a discharge rate of 20 g / min. Simultaneously with this feed, 1830 g of ammonia water (25% by mass) was fed at a discharge rate of 8 g / min to carry out hydrolysis and polycondensation of TMOS, thereby growing silica particles and obtaining grown particles. After the feed was completed, stirring was continued for 1 hour.

[0108] The average particle size and coefficient of variation of the grown particles were measured by laser diffraction scattering. The measurement results for the grown particles (Y) are shown in Table 3. Figure 6 shows a graph plotting the average particle size (μm) of the 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.

[0109] 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 in producing the silica particles.

[0110] [Additional Notes] The present invention is not limited to the above-described embodiments / examples, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments / examples are also included in the technical scope of the present invention. [Industrial Applicability]

[0111] The present invention can be utilized, for example, in the production of silica particles used as fillers for various resin compositions for electronic materials such as semiconductor encapsulants or for film production.

Claims

1. 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.

2. A method for producing silica particles, comprising the steps of: hydrolyzing and polycondensing a 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.

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 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.

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