Process for producing spherical silica particles

Abstract

The object is to provide a novel production method of spherical silica particles. It is found that spherical silica particles can be produced by using an alkaline aqueous silicic acid solution as a raw material with an appropriate mixed solvent. The production method of spherical silica particles of the present invention has: a raw material silica particle preparation step of preparing a dispersion liquid of raw material silica particles from a raw material solution in which silicic acid is dissolved, in a mixed solvent of water and an organic solvent, in the presence of an alkaline substance composed of at least one of a quaternary ammonium and a base having a cyclic amidine structure; and a heating step of removing an organic substance contained in the dispersion liquid by heating the dispersion liquid or the raw material silica particles obtained by solid-liquid separation from the dispersion liquid, to produce spherical silica particles. The relative dielectric constant of the mixed solvent is 21 to 40, and the quaternary ammonium from the alkaline substance is coordinated at a coordination ratio of 0.3 to 0.8 in terms of the silicon element from the silicic acid in terms of molar ratio.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for producing spherical silica particles, and particularly to a method for producing spherical silica particles by a so-called wet synthesis method. BACKGROUND

[0002] As a method for producing silica particles having a high degree of sphericity, there are a melting method, a gas phase synthesis method, and a wet synthesis method. Among them, the wet synthesis method represented by the Stober method has a feature that few coarse particles are generated, but has a high degree of uniformity of particle diameter and a low resin filling property.

[0003] In addition, among raw materials used in the Stober method, tetraethoxysilane (TEOS) itself is expensive, and particularly, in order to obtain spherical silica particles having a high degree of purity, TEOS having a high degree of purity at a higher cost is required.

[0004] As a method for obtaining porous spherical silica, an emulsion synthesis method using sodium silicate as a raw material is also implemented, but if sodium contained in the raw material is reduced by washing, there is a problem of an increase in cost.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2021-195275 SUMMARY

[0008] The present application was completed in view of the above-described actual circumstances, and the problem to be solved thereby is to provide a novel method for producing spherical silica particles.

[0009] The present inventors and others have conducted intensive studies in order to solve the above-described problems, and as a result, have found that it is possible to produce spherical silica particles using an aqueous alkali silicate solution (hereinafter referred to as "aqueous alkali silicate solution") as a raw material, and have completed the following application based on this insight.

[0010] That is, the method for producing spherical silica particles of the present application has the following steps:

[0011] a raw material silica particle preparation step of preparing a dispersion liquid of raw material silica particles from a raw material solution in which silicic acid is dissolved, in a mixed solvent of water and an organic solvent, in the presence of an alkali substance composed of at least one of a quaternary ammonium and an alkali having a cyclic amidine structure; and

[0012] The heating step is a step of removing the organic substance contained in the dispersion liquid by heating the dispersion liquid or the raw material silica particles obtained by solid-liquid separation from the dispersion liquid, thereby producing spherical silica particles. Further, the relative dielectric constant of the mixed solvent is 21 to 40, and the quaternary ammonium from the basic substance is compounded at a compounding ratio of 0.3 to 0.8 in terms of the molar ratio of silicon element from the silicic acid.

[0013] The aqueous alkaline silicic acid solution can be prepared from materials such as metallic silicon, silica, TEOS, and the like, and in particular, spherical silica particles can be produced from materials such as metallic silicon, silica, and the like, which are often less expensive than TEOS. In addition, these materials are readily available in high purity, and it is also easy to improve the purity of the spherical silica particles produced. Further, the particle size distribution of the spherical silica particles obtained can be controlled by the reaction conditions, and spherical silica particles having excellent filling properties can be produced. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a histogram showing the particle size distribution of the test sample of Test Examples 3, 5, 11, and 12 in the Examples.

[0015] Figure 2 is an SEM photograph of the test sample of Test Example 3 in the Examples.

[0016] Figure 3 is an SEM photograph of the test sample of Test Example 6 in the Examples.

[0017] Figure 4 is an SEM photograph of the test sample of Test Example 8 in the Examples.

[0018] Figure 5 is an SEM photograph of the test sample of Test Example 10 in the Examples.

[0019] Figure 6 is a cross-sectional SEM photograph of the test sample of Test Example 11 in the Examples.

[0020] Figure 7 is an SEM photograph of the test sample of Test Example 12 in the Examples.

[0021] Figure 8 is an SEM photograph of the test sample of Test Example 14 in the Examples.

[0022] Figure 9 is an SEM photograph of the test sample of Test Example 17 in the Examples.

[0023] Figure 10 is an SEM photograph of the test sample of Test Example 18 in the Examples.

[0024] Figure 11 is a cross-sectional SEM photograph of a test sample of Test Example 19 in the Examples.

[0025] Figure 12 is an SEM photograph of a test sample of Test Example 20 in the Examples. DETAILED DESCRIPTION

[0026] The production method of the spherical silica particles of the present application will be described in detail based on the following embodiments. The spherical silica particles produced by the production method of the spherical silica particles of the present embodiment are particles that are spherical and composed of silica. The spherical silica particles of the present embodiment can be dispersed in a dispersion medium to produce a slurry composition, or dispersed in a resin material to produce a resin composition. These slurry compositions, resin compositions are preferably used for materials for electronic devices such as substrate materials, sealing materials, underfill materials, and the like.

[0027] As the particle diameter of the spherical silica particles of the present embodiment, particles of about 100 nm to 10 μm can be favorably produced. The sphericity of the spherical silica particles is not particularly limited, and is preferably 0.9 or greater, and further preferably 0.95 or greater.

[0028] The spherical silica particles can be solid or hollow. Here, the spherical silica particles being solid means that the density of the particles is 2.3 g / cm 3 or greater. The above, hollow means that the density of the particles is less than 2.3 g / cm 3 . In the measurement of the density of the particles, the volume of the particles is measured by the constant-volume expansion method using nitrogen. The volume of the voids that cannot be invaded by nitrogen can be measured, and the spherical silica particles in which the density of the particles is less than 2.3 g / cm 3 including such voids are provided as hollow particles. The voids present in the interior of the particles can be one or a plurality. Also, in the case where the voids are not observed even by electron microscopy or the like because the voids are formed in a plurality of extremely fine voids, it is still included in the hollow particles.

[0029] The production method of the spherical silica particles of the present embodiment has a raw material silica particle preparation step, a heating step, and other steps as needed.

[0030] (Raw material silica particle preparation step)

[0031] The raw material silica particle preparation step is a step in which the raw material silica particles that are the basis of the spherical silica particles are precipitated from the silicic acid contained in the raw material solution in the presence of an alkaline substance in a mixed solvent of water and an organic solvent to produce a dispersion liquid. The precipitated raw material silica particles are approximately the same as the produced spherical silica particles, but have a high content of moisture, organic matter, and the like.

[0032] The precipitation of the raw material silica particles is preferably performed while stirring. The temperature at the time of precipitation is not particularly limited, and as a lower limit value, 0°C can be exemplified, and as an upper limit value, 40°C, 50°C, 60°C can be exemplified.

[0033] The concentration of silicic acid in the raw material solution is not particularly limited, and as a lower limit value, 1%, 2%, 3%, 5% can be exemplified, and as an upper limit value, 8%, 10%, 15%, 17% can be exemplified, in terms of oxide (SiO2: silica), based on the mass as a whole. In order to make the necessary concentration, it can be diluted with water, an organic solvent, a mixed solvent of water and an organic solvent. Here, the oxide conversion refers to a value calculated assuming that all of the contained silicon element exists in the form of an oxide. Other metal compounds other than silicic acid can be contained in the raw material solution. As the other metal compounds that can be contained, water-soluble compounds, metal oxides having a particle diameter of 100 nm or less (particularly, metal oxides having a particle diameter of 50 nm or less, 30 nm or less, 10 nm or less) can be contained. The other metal oxides can be mixed in at the time of precipitation and particle formation of silicic acid to form a composite oxide or the like.

[0034] In addition, the precipitation of the raw material silica particles is preferably performed in a state adjusted to a prescribed pH. It is preferable to adjust to a prescribed pH by adding a basic substance or adding an organic acid such as acetic acid. As the prescribed pH, 7.0, 7.5, 7.8 can be exemplified as a lower limit value, and 10.0, 9.5, 9.0, 8.5, 8.2 can be exemplified as an upper limit value.

[0035] Here, the relative dielectric constant of the mixed solvent is 21 to 40. As the relative dielectric constant, 38, 35, 33 can be adopted as an upper limit value, and 21.5, 23, 25 can be adopted as a lower limit value. These upper and lower limit values can be arbitrarily combined. Here, the relative dielectric constant of the mixed solvent refers to the relative dielectric constant calculated in the form of a mixed solvent composed only of the contained water and the organic solvent. Specifically, it is the weighted average of the relative dielectric constant of water and the relative dielectric constant of the mixed organic solvent, in terms of the volume ratio.

[0036] As the organic solvent, it can be mixed with water, and after mixing, it is within the above-mentioned range of the relative dielectric constant. As the preferable organic solvent, ketones, esters, alcohols can be exemplified, and particularly, acetone, methyl ethyl ketone, ethyl acetate or the like can be used alone or as a mixture, and further, acetone is preferable. The mixing ratio of the organic solvent to water is set so as to be within the above-mentioned range of the relative dielectric constant at the time of making the mixed solvent.

[0037] The basic substance is constituted of at least one of a quaternary ammonium and a base having a cyclic amidine structure. They are not particularly limited, and the quaternary ammonium is preferably selected from quaternary ammoniums having 4 to 16 carbon atoms, and tetramethylammonium having 4 carbon atoms, tetraethylammonium having 8 carbon atoms, tetrabutylammonium having 16 carbon atoms can be exemplified in particular. The quaternary ammonium generally has some anion as a counter ion. For example, tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrabutylammonium hydroxide (TBAOH) having hydroxide ion, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride having chloride ion can be exemplified. The base having a cyclic amidine structure can exemplify diazabicycloundecene (DBU), diazabicyclononene (DBN).

[0038] The basic substance is contained in a ratio of 0.3 to 0.8 based on the number of moles of silicon element from silicic acid, and the lower limit value thereof can be 0.35, 0.4, and the upper limit value thereof can be 0.75, 0.7, 0.6. These upper and lower limit values can be combined arbitrarily. By making the amount of the basic substance added be the lower limit value or more, the particle diameter of the raw material silica particles produced becomes large and becomes not to form aggregates, or the density of silica in the raw material silica particles produced becomes high. By making the amount of the basic substance added be the upper limit value or less, polymerization can be prevented and particle formation can be performed efficiently. If the density of silica becomes low, there is a tendency that the obtained spherical silica particles shrink due to heating in the heating step described later, or when the obtained spherical silica particles are made into porous particles or hollow particles, the void ratio becomes large.

[0039] The basic substance can be added to the mixed solvent before or after the silicic acid. Furthermore, the entire amount can be added at once or can be added in multiple portions.

[0040] The concentration of silicic acid in the raw material solution is not particularly limited, and the upper limit value thereof is preferably 0.1%, 0.2%, 0.3%, 0.4% and the lower limit value thereof is preferably 1.0%, 1.5%, 2.0%, 3.0% in terms of oxide conversion based on the mass of the raw material solution. The silicic acid is preferably supplied in the form of an aqueous basic silicic acid solution obtained by any one of the following a) to c). These a) to c) are preferably performed while stirring. An appropriate amount of an organic solvent and a basic substance is added to the aqueous basic silicic acid solution obtained in the following procedure to prepare the raw material solution.

[0041] a) Heating and pressurization of silica in an aqueous basic substance solution

[0042] Silica can be derived from substances synthesized from metallic silicon, substances synthesized from silicon compounds, natural products, etc. Substances synthesized from metallic silicon are particularly preferred because they readily provide high-purity metallic silicon as a raw material. For example, granular silica obtained by burning metallic silicon powder (the so-called VMC method) can be used. Here, by using granular silica, the specific surface area increases, thereby increasing its dissolution rate in alkaline aqueous solutions.

[0043] The alkaline substance contained in the aqueous solution of the alkaline substance for dissolving silica can be the aforementioned alkaline substance directly, or it can be any other alkaline substance. If other alkaline substances are used, they are preferably removed after dissolving the silica through washing or ion exchange.

[0044] One method for dissolving silica in an aqueous solution of an alkaline substance involves raising the boiling point of the solution by applying pressure and maintaining it at a temperature above the boiling point under normal pressure. For example, heating at 180°C while applying pressure can be used. The dissolution temperature can be increased to improve the dissolution rate and decreased to reduce the pressure, thus simplifying the dissolution equipment.

[0045] The dissolved silica, based on the overall mass, preferably has an upper limit of 17%, 15%, or 10% and a lower limit of 1%, 3%, or 5%. These upper and lower limits can be combined arbitrarily. The concentration of the alkaline substance in the aqueous solution is not particularly limited, but is preferably a concentration that results in an appropriate alkaline substance concentration when the final raw material solution is prepared.

[0046] b) Removal of Na ions from sodium silicate aqueous solution in the presence of an alkaline substance.

[0047] Aqueous solutions of sodium silicate can be prepared using water glass, which is made by dissolving sodium silicate in water. Alkaline substances can be used. Sodium ions are removed from the aqueous solution of sodium silicate in the presence of an alkaline substance, thus replacing the sodium in the sodium silicate. Sodium ion removal can be performed using ion exchange resins, etc.

[0048] The dissolved sodium silicate, calculated based on the total mass of oxides, preferably has an upper limit of 17%, 15%, or 10%, and a lower limit of 1%, 3%, or 5%. These upper and lower limits can be combined arbitrarily. The concentration of the alkaline substance in the aqueous solution is not particularly limited, but is preferably a concentration that results in an appropriate alkaline substance concentration when the final raw material solution is prepared.

[0049] c) Dissolving metallic silicon in an aqueous solution containing an alkaline substance and / or a second alkaline substance.

[0050] Silicic acid is generated by impregnating and dissolving metallic silicon in an aqueous solution containing the aforementioned alkaline substance and / or a second alkaline substance. The metallic silicon is preferably in powder or granular form. Heating is preferred as the dissolution condition. The heating temperature is not particularly limited, and lower limits such as 30°C, 40°C, 50°C, and 60°C can be used.

[0051] The dissolved metallic silicon, calculated based on the total mass of oxides, preferably has an upper limit of 17%, 15%, or 10% and a lower limit of 1%, 3%, or 5%. These upper and lower limits can be combined arbitrarily.

[0052] The alkaline substance is the alkaline substance described above. The second alkaline substance is not particularly limited, but is preferably composed of an organic compound. Examples of the second alkaline substance include dialkylamines (e.g., amines with 1 to 3 carbon atoms) and trialkylamines (e.g., amines with 1 to 3 carbon atoms).

[0053] The total concentration of the alkaline substance and the second alkaline substance in the aqueous solution containing the alkaline substance and / or the second alkaline substance is not particularly limited. When an alkaline substance is added, it is preferably at a concentration below the amount of the appropriate alkaline substance present when the final raw material solution is prepared.

[0054] (Heating process)

[0055] The heating process involves heating the silica particles contained in the dispersion obtained during the silica particle preparation process to form spherical silica particles. It also removes moisture and organic matter from the silica particles through heating.

[0056] The heating process involves direct heating of the dispersion, heating of the dispersion in a state where the dispersion medium has been replaced with another dispersion medium, and / or solid-liquid separation and heating of the raw silica particles from the dispersion. The raw silica particles can be separated from the dispersion medium by centrifugation or filtration. After separation of the raw silica particles, the dispersion medium can be replaced by adding other dispersion media such as water or organic solvents. By performing multiple replacements of the dispersion medium, organic matter contained in the dispersion can be removed more reliably.

[0057] The heating process removes moisture and organic matter from the raw silica particles by heating them at high temperatures. First, it is preferable to remove moisture and organic solvents at a temperature that does not rapidly remove moisture. Examples include 40°C, 60°C, 80°C, 100°C, 120°C, and 140°C. Pressure reduction or air drying can be performed simultaneously with heating. If a certain degree of moisture is removed, rapid expansion of the moisture will not occur even when heated at high temperatures; therefore, heating can be carried out to a temperature sufficient to remove organic matter. A temperature of 500°C or higher is preferred for removing organic matter.

[0058] In particular, it is preferred that organic matter be removed by oxidation through heating in an oxidizing atmosphere such as air. Lower limits for the heating temperature can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, etc., and upper limits can be 1150℃, 1100℃, 1050℃, etc. It is believed that by heating the raw material silica particles in a state separated from the dispersion medium, the particles shrink and become denser as moisture is removed.

[0059] (Hydrothermal treatment process)

[0060] After the preparation of the raw material silica particles and before the heating step, a hydrothermal treatment step is preferably included, in which the dispersion medium of the dispersion is replaced with water and then heated to carry out a hydrothermal reaction. The hydrothermal reaction is preferably carried out at a temperature of 130°C to 250°C. In particular, the lower limit of the temperature is preferably 100°C, 110°C, or 120°C, and the upper limit is preferably 220°C, 200°C, or 180°C. These upper and lower limits can be combined arbitrarily.

[0061] By conducting a hydrothermal reaction, the final spherical silica particles can also be made into hollow particles and porous particles. That is, through the hydrothermal treatment process, the reaction in which the low density of silanol bonds inside the particles is dissolved by alkaline substances and the reaction in which the particle shell is densified by heat occur in equilibrium. Therefore, it is speculated that hollow particles and porous particles are generated due to the equilibrium of these two reactions.

[0062] In the case of a hydrothermal treatment process, organic matter is removed by heating as described above after separating the raw silica particles from the dispersion medium. In the case of a hydrothermal reaction, it is particularly preferable to solidify the hollow particles or porous particles by heating to 900°C or higher during the heating process.

[0063] (Other processes)

[0064] The method for manufacturing spherical silica particles according to this embodiment can involve crushing or surface-treating the obtained spherical particles. Crushing can be performed using a method similar to conventional pulverization. A jet mill or similar equipment is particularly preferred.

[0065] The spherical silica particles manufactured by the method of this embodiment can be surface-treated using surface treatment agents such as silane compounds. The appropriate surface treatment varies depending on the intended use of the spherical silica particles. When filling the spherical silica particles into a resin, a surface treatment agent capable of introducing functional groups with high affinity for the resin or that are reactive is preferably used.

[0066] Example

[0067] The method for manufacturing spherical silica particles according to the present invention will be described in detail based on the following embodiments.

[0068] <Sample Preparation>

[0069] Test specimens for each test example were prepared under the conditions shown in Table 1. Detailed explanations follow.

[0070] • Experimental Example 1

[0071] (Preparation process of raw material silica particles)

[0072] First, an alkaline silicic acid aqueous solution was prepared. 9.0 g of metallic silicon powder (volume average particle size 20 μm), 27.0 g of ion-exchanged water, and 64.0 g of 25% TMAH aqueous solution were mixed and kept at 40°C for 48 hours to dissolve the metallic silicon, yielding an alkaline silicic acid aqueous solution containing approximately 26.3% silicic acid (converted from silicon dioxide).

[0073] Ion-exchanged water was added to the resulting alkaline silicic acid aqueous solution, with a silicic acid concentration of 4.5% by mass (converted from silica). Based on the silicon element from the contained silicic acid, TMAH, as an alkaline substance, was added in a molar ratio of 0.44. Then, acetone, as an organic solvent, was added in a ratio of 30.6 when mixed with the contained water. Specifically, the water:acetone ratio was 20:80 by mass before mixing.

[0074] After thorough stirring, add 90% acetic acid aqueous solution to adjust the pH to 8, and stir for another 30 minutes, thereby causing the raw material silica particles to precipitate out and become a dispersion.

[0075] (Heating process)

[0076] The resulting dispersion was centrifuged at 5000 rpm for 5 minutes, and the supernatant was removed by decantation to separate the precipitate. Centrifugation was performed using a KUBOTA Model 3700. An equal mass of deionized water was added to the removed supernatant, and the mixture was ultrasonically dispersed. Ultrasonication was performed at 28 kHz and 1000 W for 30 minutes. Centrifugation was repeated under the same conditions. The resulting precipitate was dried at 130°C for 1 hour and then calcined at 500°C for 2 hours. The calcined material was crushed using a mortar until the aggregates were no longer visible. The resulting spherical silica particles were used as the test sample in this experiment.

[0077] • Experimental Examples 2 and 3

[0078] The firing temperature was set to 800℃ (Example 2) and 1000℃ (Example 3). Otherwise, the test specimens of this example were obtained by performing the same operation as in Example 1.

[0079] • Test Examples 4 and 5

[0080] a) Based on silicon from silicic acid, the amount of alkaline substance present is 0.55 in molar ratio; b) The following hydrothermal treatment process is performed: the dispersion obtained by ultrasonic dispersion after the first centrifugation in the heating process is placed in a pressure vessel and subjected to hydrothermal reaction at 175°C for 2 hours; c) The firing temperature is 800°C (Example 4) and 1000°C (Example 5); otherwise, the test sample of this example is obtained by the same operation as in Example 1.

[0081] • Experimental Examples 6–9

[0082] Except for the following differences, the test specimens for this test example were obtained by the same procedure as in Test Example 5.

[0083] a) Based on silicon from silicic acid, the amount of alkaline substance present is 0.44 in molar ratio; b) pH is set to 6 (Example 6), pH is set to 6 and the temperature of the hydrothermal reaction is set to 200°C (Example 7), only a) (Example 8) is changed, pH is set to 6 and the temperature of the hydrothermal reaction is set to 121°C (Example 9).

[0084] • Test Examples 10 and 11

[0085] Based on silicon from silicic acid, the amount of alkaline substance present was 0.35 (Example 10) and 0.79 (Example 11) in molar ratio. Otherwise, the test sample of this example was obtained by the same operation as in Example 3.

[0086] • Experimental Example 12

[0087] (Equivalent to the process of preparing raw material silica particles)

[0088] A mixture of 5.2 g TEOS, 100 g deionized water, and 400 g acetone was prepared. While stirring this mixture, 2.5 g of a 25% (w / w) TMAH aqueous solution was added. Then, a 90% (w / w) acetic acid aqueous solution was rapidly added to adjust the pH to 8, and the mixture was stirred for another 30 minutes, thereby precipitating the silica particles to form a dispersion. Here, the ratio of deionized water to acetone resulted in a relative permittivity of 30.6. The amount of TMAH added was 0.27 molar ratio based on the silicon content from the TEOS.

[0089] (Equivalent to a heating process)

[0090] The resulting dispersion was centrifuged at 5000 rpm for 5 minutes, and the supernatant was removed by decantation to separate the precipitate. Centrifugation was performed using a KUBOTA Model 3700. An equal mass of ion-exchanged water was added to the supernatant, and the mixture was ultrasonically dispersed. Ultrasonic dispersion was performed at 28 kHz and 1000 W for 30 minutes.

[0091] The resulting dispersion was placed in a pressure vessel and subjected to a hydrothermal reaction at 175°C for 2 hours. Then, it was further centrifuged under the same conditions. The resulting precipitate was dried at 130°C for 1 hour and then calcined at 1000°C for 2 hours. The calcined material was crushed using a mortar until the aggregates were no longer visible. The resulting spherical silica particles were used as the test sample for this experiment.

[0092] • Experimental Example 13

[0093] The acetone content was 20% when mixed with the water, and otherwise the same procedures as in Test Example 3 were performed. As a result, no particles were observed to form in the process corresponding to the preparation of the raw material silica particles, and no heating process was performed. Therefore, the test sample of this test example could not be obtained.

[0094] • Test Example 14

[0095] The acetone content was 41.5% when mixed with the water contained therein. Otherwise, the test sample of this test example was obtained by the same procedure as in Test Example 3.

[0096] • Experimental Example 15

[0097] Based on silicon from silicic acid, the amount of alkaline substance present is 0.20 in molar ratio. Otherwise, the test sample of this test example is obtained by the same operation as in Test Example 1.

[0098] • Experimental Example 16

[0099] Based on silicon from silicic acid, the amount of alkaline substance present was 0.85 in molar ratio. Otherwise, the same procedures as in Experimental Example 1 were performed. As a result, no particle formation was observed in the process corresponding to the preparation of raw silica particles, and no heating process was performed. Therefore, the test sample of this experimental example could not be obtained.

[0100] • Test Examples 17 and 18

[0101] As alkaline substances, DBU (Example 17) and DBN (Example 18) were used instead of TMAH. Otherwise, the test sample for this example was obtained through the same procedure as in Example 5. It should be noted that the amounts of DBU and DBN added were the same as those for TMAH. As a result, based on silicon elements from silicic acid, the amount of alkaline substance present was 0.41 in molar ratio.

[0102] • Test Examples 19 and 20

[0103] As alkaline substances, TEAH (Example 19) and TBAOH (Example 20) were used instead of TMAH. Otherwise, the test sample for this example was obtained through the same procedure as in Example 3. It should be noted that the amounts of TEAH and TBAOH added were the same as the concentrations of TMAH. As a result, based on silicon element from silicic acid, the amounts of TEAH and TBAOH added were 0.32 (Example 19) and 0.35 (Example 20) in molar ratio.

[0104] • Experimental Example 21

[0105] Spherical silica particles, prepared by using metallic silicon powder as a raw material for manufacturing an alkaline silicic acid aqueous solution in the silica particle preparation process of Experimental Example 1, were used as test samples in this Experimental Example. The VMC method is a method for producing spherical silica particles by deflagrating metallic silicon powder while it is suspended in air.

[0106] (evaluate)

[0107] For each test sample, particle size distribution, specific surface area, pore volume, true specific gravity, number of coarse particles, and impurity content were determined. The results are shown in Tables 1 and 2.

[0108] Particle size distribution: The test sample was dispersed in water at a concentration of 0.5% by mass, and the particle size distribution was measured using a particle size distribution measuring device (Shimadzu SALD-7500 nano). For test examples 3, 5, 11, and 12, the histograms of the measured particle size distributions were plotted on... Figure 1 .

[0109] Specific surface area and pore volume: The test samples were measured using an automated specific surface area / pore volume distribution measuring device (Shimadzu Tristar 3000). Specific surface area was determined using the BET1 point method with nitrogen. Pore volume was measured using the adsorption value determined by the BJH method.

[0110] True specific gravity: Measured using a dry automatic density meter (Shimadzu Corporation, AccuPycII1345) with nitrogen gas. The density is measured by the volume of particles containing voids within spherical silica particles that nitrogen cannot penetrate. That is, if voids are present, the density of the spherical silica particles decreases only by the volume of those voids.

[0111] Coarse particle count: For each test sample of test examples 3, 5, and 21, the number of particles with a diameter of 3 μm or larger per 1 g was determined using an automated flow particle imaging analyzer (manufactured by Sysmex Corporation, FPIA-3000).

[0112] Impurity content: For each test sample in Test Examples 5 and 21, the impurity content was determined by ICP after the test sample was dissolved in acid.

[0113] Furthermore, SEM images were taken of each test specimen in test examples 3, 6, 8, 10–12, 14, and 17–20. Figures 2 to 12 ).

[0114]

[0115] [Table 2]

[0116]

[0117] As shown in Table 1, in the three groups of a) test examples 1-3, b) test examples 4 and 5, and c) test examples 6-9, the conditions before firing were the same within each group, and the particle size distribution was the same within each group. However, the heating conditions in the subsequent heating process were different within these groups, so the specific surface area values ​​were different.

[0118] That is, under the same conditions in the preparation process of raw silica particles, spherical silica particles with the same particle size distribution can be obtained. The specific surface area differs due to differences in the heating temperature (hydrothermal reaction temperature, firing temperature) after removing the dispersion medium in subsequent processing steps. The reason for the difference in specific surface area is believed to be due to changes in the microporous structure of the manufactured spherical silica particles, particularly the microporous structure of the surface.

[0119] In Test Example 12, where spherical silica particles were manufactured using TEOS, the particle size was uniform. However, in Test Examples 1-11 and 17-20, where spherical silica particles were manufactured using silica, the particle size distribution was wider. Specifically, the particle size of the test sample in Test Example 12 was very uniform. The particle size distribution of the particles in Test Example 12 was approximately 1.26 or D90 / D50. Figure 7 The SEM images shown are confirmed.

[0120] In contrast, in test samples 1-11 and 17-20, even test samples 4 and 5, which had the smallest D90 / D50, contained particles of various sizes, with a ratio of 1.67. Furthermore, from Figures 2 to 6 and Figures 8 to 12 The particle size is clearly uneven.

[0121] Therefore, in the test specimens of Examples 1-11 and 17-20, an improvement in the filling properties of the obtained spherical silica particles in resins, slurries, etc., can be expected. This is from... Figure 1 The histogram shown also shows that the particle size is uniform in the test sample of Test Example 12, which uses TEOS as raw material, but there are deviations in the particle size in the test samples of Test Examples 3, 5, and 11.

[0122] The specific gravity of silicon dioxide is 2.3 g / cm³. 3 The true specific gravity of test examples 1-3, 10, 11, 19, and 20, which did not undergo hydrothermal reaction, is approximately 2.3 g / cm³. 3 It is inferred that there are no voids inside. In contrast, the true specific gravity of experiments 4-6, 17, and 18, which involved hydrothermal reactions, is less than 2.3 g / cm³. 3 This indicates that there are gaps inside that are not connected to the outside.

[0123] It should be noted that in the test specimens undergoing the hydrothermal reaction, the true specific gravity for Test Examples 7–9 was 2.3 g / cm³. 3 While the value is the same as that of particles without pores, it is clear from the fact that in these test samples, due to their respective large pore volume and specific surface area, the true specific gravity becomes the same as that of silicon dioxide because they are connected to the outside through the generated pores.

[0124] The presence or absence of pores (fine holes) communicating with the outside, due to differences in preparation conditions, can also be confirmed using SEM images. For the test specimen in Example 3, [the following text appears to be incomplete and requires further context: "from..."] Figure 2 It can be seen that no voids (pores) communicating with the outside were observed. For the test specimen of Example 6, from... Figure 3 It can be confirmed that although it contains particles with fine pores, the overall sample is largely free of pores. In contrast, for the test sample of Example 8, from... Figure 4 It can be seen that the majority of particles have pores.

[0125] That is, it can be seen that in the test specimen of Example 8, voids are formed inside, just like in hollow particles. However, since these voids are connected to the outside, the true specific gravity becomes the same as that of solid particles. Furthermore, although details are not shown, if the cross-section of the test specimen of Example 5 is examined, it can be seen that a large number of voids are formed, resulting in a porous structure. The density of the fine voids tends to increase as they approach the center of the particle.

[0126] The mechanism by which internal voids are created through a hydrothermal reaction is hypothesized as follows: When raw silica particles are transformed into spherical silica particles through a hydrothermal reaction, moisture slowly escapes from the outside, causing the outer surface of the particles to gradually become dense. Then, as moisture escapes from the inside, voids are created inside. However, if the particles are fired by rapid heating without a hydrothermal reaction, moisture rapidly escapes from the entire particle during firing, resulting in solid particles without internal voids.

[0127] It can be seen that if the relative permittivity of the mixed solvent of water and organic solvent is 20 (Example 13), the silicic acid contained in the raw material solution will dissolve directly without precipitation. Therefore, it can be concluded that the relative permittivity of the mixed solvent must be at least greater than 20.

[0128] If the relative permittivity of the mixed solvent of water and organic solvent is 41.5 (Experimental Example 14), the silica contained in the raw material solution will not precipitate into particles but will only form fine aggregates of silica. Figure 8 Therefore, it can be concluded that the relative permittivity of the mixed solvent must be at least below 41.5.

[0129] In Experiment 15, where the amount of alkaline substance added was 0.20 molar ratio of silicon element from silicic acid, the silicic acid contained in the raw material solution precipitated without particle formation, but only formed fine aggregates of silica. Therefore, it is evident that the amount of alkaline substance added must exceed 0.20 molar ratio of silicon element from silicic acid.

[0130] In Experiment 16, where the amount of alkaline substance added was 0.85 molar ratio of silicon element from silicic acid to silicon element from silicic acid, it was observed that the silicic acid contained in the raw material solution dissolved directly without precipitation. Therefore, it is evident that the amount of alkaline substance added must be less than 0.85 molar ratio of silicon element from silicic acid to silicon element from silicic acid.

[0131] It can be seen that even when DBU (Example 17), DBN (Example 18), TEAH (Example 19), and TBAOH (Example 20) are used instead of TMAH as the alkaline substance, spherical silica particles can be generated in the same way as TMAH. Figures 9 to 12 ).

[0132] The number of coarse particles was measured in Test Examples 3, 5, and 21. The results showed that there were more than 2,000 coarse particles in the spherical silica particles of Test Example 21, which was manufactured by the conventional VMC method. In contrast, very few particles were formed in Test Examples 3 and 5, namely 5 and 36, respectively.

[0133] The impurity content of Test Examples 5 and 21 was measured. The results showed that, compared with the spherical silica particles of Test Example 21 manufactured by the conventional VMC method, the contents of Th and U were reduced to less than 1 / 10, which can reduce the influence of alpha rays when used in electronic devices. In addition, there was also a general trend of reduction for other measured elements. It is speculated that this is because, in Test Example 5, impurities did not precipitate when the metallic silicon powder was dissolved and precipitated in one step.

[0134] (Other tests)

[0135] In the above experimental examples, metallic silicon powder was used as the raw material for preparing alkaline silicic acid aqueous solution. However, it was also confirmed that spherical silicon dioxide particles can be manufactured even when using silicon dioxide particles and water glass (sodium silicate aqueous solution). After preparing alkaline silicic acid aqueous solution from silicon dioxide and sodium silicate aqueous solution, the same spherical silicon dioxide particles as when using metallic silicon powder can be obtained by performing the same operation.

[0136] • Method using silica particles

[0137] 20.0 g of silica powder (product name: SO-E2, manufactured by Yatoma Technology Co., Ltd.), 15.0 g of ion-exchanged water, and 64.0 g of 25% TMAH aqueous solution were mixed and kept in a pressure vessel at 180°C for 1 hour to dissolve the silica, resulting in an alkaline silicic acid aqueous solution containing approximately 20.2% silicic acid based on silica content.

[0138] • Method using sodium silicate aqueous solution

[0139] 10.2 g of sodium silicate aqueous solution (water glass) and 15.0 g of deionized water were mixed and stirred at 40 °C for 4 hours. Then, while adding 64.0 g of 25% by mass TMAH aqueous solution, Na ions were removed by ion exchange. As a result, an alkaline silicic acid aqueous solution containing 10.8% by mass of silicic acid (converted from silica) was obtained.

Claims

1. A method for manufacturing spherical silica particles, comprising: The process for preparing raw silica particles involves preparing a dispersion of raw silica particles from a raw material solution containing dissolved silicic acid in the presence of an alkaline substance composed of at least one of a quaternary ammonium and a base having a cyclic amidine structure, in a mixed solvent of water and an organic solvent; and The heating process involves heating the dispersion or the raw silica particles obtained from the solid-liquid separation of the dispersion to remove organic matter contained in the dispersion and prepare spherical silica particles. The relative permittivity of the mixed solvent is 21–40. Furthermore, the alkaline substance is formulated in a molar ratio of 0.3 to 0.8 relative to the silicon element from the silicic acid.

2. The method for manufacturing spherical silica particles according to claim 1, wherein, The organic solvent is selected from one or more solvents selected from acetone, methyl ethyl ketone and ethyl acetate.

3. The method for manufacturing spherical silica particles according to claim 1 or 2, wherein, The alkaline substance is one or more compounds selected from quaternary ammonium, diazabicycloundecene, and diazabicyclononene, which have 4 to 16 carbon atoms.

4. The method for manufacturing spherical silica particles according to claim 1 or 2, wherein, The raw material solution is prepared by adding the organic solvent and the required alkaline substance to an alkaline silicic acid aqueous solution in the specified proportions. The alkaline silicic acid aqueous solution is prepared by... a) Heating and pressurizing the silica in the alkaline aqueous solution. b) Removal of Na ions from an aqueous sodium silicate solution in the presence of the alkaline substance, and, c) Obtained by any method of dissolving metallic silicon in an aqueous solution containing the alkaline substance and / or a second alkaline substance.

5. The method for manufacturing spherical silica particles according to claim 1 or 2, wherein, The process for preparing the raw material silica particles involves adjusting the pH of the raw material solution to 7-10.

6. The method for manufacturing spherical silica particles according to claim 1 or 2, wherein, After the raw material silica particle preparation step and before the heating step, there is a hydrothermal treatment step in which the dispersion medium for dispersing the raw material silica particles is replaced with water and then pressurized and heated at 130°C to 250°C. The spherical silica particles manufactured in the heating process are hollow particles.

7. The method for manufacturing spherical silica particles according to claim 6, wherein, The heating process includes heating at or above 900°C.

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