Porous spherical silica, catalyst carriers, cosmetics, analytical columns, abrasives, resin compositions, and methods for manufacturing porous spherical silica.

Abstract

This invention provides a porous spherical silica with reduced alkali metal content, high particle hardness, and a reduced number of fragmented particles, as well as a method for manufacturing the same. The porous spherical silica has a volume-based cumulative 50% particle size (D50) of 2 μm or more and 200 μm or less, a cumulative 10% particle size (D10) to 90% particle size (D90) ratio (D10 / D90) of 0.3 or more, a pore volume of 0.5 ml / g or more and 8 ml / g or less, a pore radius modulus of 5 nm or more and 50 nm or less, and a specific surface area of ​​50 m² / g. 2 / g or more and 400m 2 For samples below / g, the arithmetic mean of the "test force at which specimen failure is confirmed" calculated according to the method specified in JIS Z8844 is 1.0 × 10⁻⁶. 1 mN or higher and 2.0×10 1 The particle size is below N, the number of particles with a roundness of less than 0.7 is less than 20, and the alkali metal content is less than 50 ppm.

Description

Technical Field

[0001] This invention relates to novel porous spherical silica, catalyst supports, cosmetics, analytical columns, abrasives, resin compositions, and methods for manufacturing porous spherical silica. Background Technology

[0002] Various studies have been conducted on porous silica, and porous silica with multiple physical properties has been proposed. Porous silica can be manufactured, for example, by methods such as: neutralizing an aqueous solution of an alkali metal silicate by adding an inorganic acid, and then separating / recovering the resulting particles (Patent Document 1); spray drying a fumed silica dispersion (Patent Document 2); and gelling a fumed silica dispersion in a liquid (Patent Document 3). Porous silica manufactured using the above methods is characterized by its pore volume and pore size, and is expected to be used as a catalyst support and a packing agent for analytical columns. Furthermore, when used as an abrasive in industrial products, resin penetrates into the pores, making it easy to fix onto the resin of the abrasive pad. When using spherical products in the above applications, it has the advantage of easy particle size adjustment and improved filling rate. In addition, porous spherical silica has a smooth tactile feel derived from its shape, and therefore can also be used as a cosmetic additive.

[0003] Existing technical documents

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2004 / 101139

[0006] Patent Document 2: International Publication No. 2019 / 131873

[0007] Patent Document 3: International Publication No. 2022 / 154014

[0008] Non-patent literature

[0009] Non-patent literature 1: "Sintering of Fine Ceramics", Journal of the Powder Technology Society, Vol. 25, No. 12, (1988), pp. 805-811 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] However, due to the brittle nature of porous silica stemming from its porous structure, durability is a concern in its applications as a catalyst support for long-term use and as a packing material for analytical columns used in fluids. Furthermore, in its application as an abrasive in industrial products, particle shape deformation and breakage occur during the mixing process with resin, leading to decreased processability. Typically, sintering is used to increase the hardness of inorganic materials (Non-Patent Document 1). However, for the porous silica described in Patent Document 1, which uses sodium silicate as a raw material, the presence of sodium from the raw material causes a decrease in melting point, resulting in pore blockage during high-temperature sintering and an inability to maintain the porous structure.

[0012] The porous silica described in Patent Document 2, obtained by spray drying a fumed silica dispersion, cannot produce silica with low compressive strength and high hardness after calcination. The porous silica described in Patent Document 3, obtained by gelling a fumed silica dispersion in a liquid, results in particle aggregation during calcination, requiring a crushing process. This process generates fragmented microparticles, reducing the overall sphericality of the particles. When this porous spherical silica is used as a packing material for analytical columns, the incorporation of these microparticles becomes a major cause of column clogging. Furthermore, when used as a cosmetic additive, its tactile properties deteriorate.

[0013] Therefore, the object of the present invention is to provide an independent spherical porous spherical silica with reduced alkali metal content, high particle hardness, and reduced number of fragmented particles, and a method for manufacturing the same.

[0014] Solution for solving the problem

[0015] To solve the aforementioned problems, the inventors conducted repeated and in-depth research. They discovered that in the manufacturing process of porous spherical silica, by gelling a fumed silica dispersion in a liquid to obtain a gel, followed by spray drying and calcination, it is possible to manufacture independent spherical porous spherical silica with reduced alkali metal content, high particle hardness, and a reduced number of fragmented particles. This led to the completion of the following invention.

[0016] [1] A porous spherical silica, characterized in that: the cumulative 50% particle size (D50) on a volume basis, as measured by the Coulter counting method, is in the range of 2 μm or more and 200 μm or less.

[0017] Similarly, the ratio of the cumulative 10% particle size (D10) to the cumulative 90% particle size (D90) obtained (D10 / D90) is greater than 0.3.

[0018] Based on the BJH method, the pore volume is above 0.5 ml / g and below 8 ml / g.

[0019] The modulus of the aperture radius based on the BJH method is greater than 5 nm and less than 50 nm.

[0020] The specific surface area based on the BET method is 50 m². 2 / g or more and 400m 2 / g or less

[0021] The arithmetic mean of the "test force at which the specimen breaks" for 10 particles, calculated by setting the loading rate to 0.4462 mN / s according to the method specified in JIS Z8844, is 1.0 × 10⁻⁶. 1 mN or higher and 2.0×10 1 Below mN,

[0022] Of the 200 particles observed in the SEM images, fewer than 20 particles had a roundness of less than 0.7.

[0023] The alkali metal content is below 50 ppm.

[0024] [2] A catalyst support comprising the porous spherical silica described in [1].

[0025] [3] A cosmetic product comprising the porous spherical silica described in [1].

[0026] [4] An analytical column comprising the porous spherical silica described in [1].

[0027] [5] An abrasive comprising the porous spherical silica described in [1].

[0028] [6] A resin composition comprising the porous spherical silica described in [1].

[0029] [7] A method for manufacturing porous spherical silica, comprising the following steps:

[0030] The process for preparing a W / O emulsion comprising an aqueous phase in which fumed silica is dispersed and an organic phase in which an insoluble solvent is the main component.

[0031] The process of heating an emulsion to gel the aqueous phase and obtaining a gel dispersion;

[0032] The process of recovering the generated gel from the liquid and spray drying it; and,

[0033] The process involves firing the obtained porous spherical silica at a temperature of 900–1500°C for 10–25 hours.

[0034] [8] The method for manufacturing porous spherical silica according to [7] is characterized in that the spray drying method is a two-fluid nozzle method.

[0035] The effects of the invention

[0036] The porous spherical silica of the present invention has a high pore volume and high hardness, as indicated by the level of the test force at which the sample breaks. Therefore, even with long-term use or use in fluids, particle disintegration or pore blockage will not occur, and the porous structure can be maintained. Thus, using the porous spherical silica of the present invention improves the durability required for catalyst supports, adsorbent materials for carbon dioxide, and packing materials for analytical columns. Furthermore, when used as an abrasive in industrial products, it achieves particle strength capable of withstanding resin mixing, improving processability in the manufacturing process.

[0037] Moreover, as indicated by the high D10 / D90, the particle size distribution is narrow, thus reducing the likelihood of microparticles entering the interparticle spaces and causing blockage when used as a packing material for analytical columns.

[0038] Furthermore, among the 200 particles observed in the SEM image, if fewer than 20 particles have a roundness of 0.7 or less, the number of fragmented particles decreases, and the particles are independent spheres. Therefore, when used as a cosmetic additive, it can impart a smooth tactile feel.

[0039] In addition, when the alkali metal content is below 50 ppm, the purity is high, and it is especially useful as an abrasive for materials such as semiconductors that are not suitable for containing alkali metals.

[0040] The manufacturing method of the present invention suppresses particle aggregation by spray-drying the base material followed by firing, thus enabling manufacturing using a process that does not include a crushing step. Therefore, even when a crushing step is performed, the generation of fragmented particles can be suppressed, and porous spherical silica with the aforementioned characteristics can be manufactured without producing micropowder or reducing the overall sphericality of the particles.

[0041] Furthermore, the manufacturing method of the present invention involves firing under specific conditions, thereby improving the bonding strength between primary particles. As a result, porous spherical silica with high particle hardness can be obtained. Detailed Implementation

[0042] The following are examples of the present invention, but the present invention is not limited to these methods.

[0043] <Porous spherical silica>

[0044] For the porous spherical silica of the present invention, the cumulative 50% particle size (D50) in the particle size distribution measured by the Coulter counting method is in the range of 2 μm or more and 200 μm or less, and similarly, the ratio (D10 / D90) of the cumulative 10% particle size (D10) to the cumulative 90% particle size (D90) is 0.3 or more. If the porous spherical silica is within the above range, the column is less prone to clogging when used as a packing material for analytical columns, and packing becomes easier. D50 is preferably 2 μm or more and 100 μm or less, particularly preferably 5 μm or more and 50 μm or less, and further preferably 5 μm or more and 20 μm or less. In addition, D10 / D90 is preferably 0.4 or more, and more preferably 0.5 or more. It should be noted that D10 / D90 will not exceed 1.0, and is generally 0.6 or less.

[0045] For the porous spherical silica of the present invention, the pore volume, measured by the BJH method described below, is 0.5 ml / g or more and 8 ml / g or less. It is difficult to obtain porous spherical silica with a pore volume exceeding 8 ml / g. It is easier to manufacture if the pore volume is 6 ml / g or less, further easier if it is 4 ml / g or less, and particularly easy to manufacture if it is 2.5 ml / g or less. In particular, when using the porous spherical silica of the present invention as a catalyst support, an adsorbent for carbon dioxide, etc., in order to have a high loading or adsorption capacity, the pore volume is preferably 0.6 ml / g or more, more preferably 0.7 ml / g or more, and more preferably 1.0 ml / g or more.

[0046] Furthermore, the modulus of the aperture radius based on the BJH method is 5 nm or more, preferably 10 nm or more, and more preferably 15 nm or more. Additionally, the upper limit is 50 nm or less, preferably 30 nm or less.

[0047] It should be noted that the pore volume and pore radius based on the BJH method were obtained as follows: the sample of the test object was dried at 200°C for more than 3 hours under a vacuum of less than 1 kPa. After that, the adsorption isotherm of nitrogen adsorption only was obtained at liquid nitrogen temperature, and the results were obtained by analysis using the BJH method (Barrett, EP; Joyner, LG; Halenda, PP, J. Am. Chem. Soc. 73, 373 (1951)). The "mode value of the pore radius based on the BJH method" refers to the pore radius value at which the pore distribution curve (volume distribution curve) obtained by the above BJH method reaches its maximum value, plotted with the differential of the cumulative pore volume based on the logarithm of the pore radius as the vertical axis and the pore radius as the horizontal axis.

[0048] For the porous spherical silica of this invention, the specific surface area based on the BET method is 50 m². 2 / g or more and 400m 2 / g or less. The preferred specific surface area is 100m². 2 / g or more, preferably 120m 2 / g or more and 350m 2 The specific surface area of ​​fumed silica used as a raw material is below / g. The higher the specific surface area of ​​the fumed silica, the higher the specific surface area of ​​the porous spherical silica. Furthermore, the higher the specific surface area of ​​fumed silica, the easier it is to gel and form spherical shapes; however, the specific surface area of ​​fumed silica is typically around 400m². 2 The specific surface area is below / g, making it difficult to obtain a specific surface area exceeding 400m². 2 / g porous spherical silica. It should be noted that the specific surface area is a value obtained based on the nitrogen adsorption BET multi-point method.

[0049] For the porous spherical silica of the present invention, the arithmetic mean of the "test force at which the specimen breaks" (hereinafter referred to as "test force at break") for 10 particles, calculated by setting the loading rate to 0.4462 mN / s according to the method specified in JIS Z8844:2019, is 1.0 × 10⁻⁶. 1 ~2.0×10 1 mN. If the test force at failure exceeds 2.0 × 10 mN. 1 If the pore size is less than mN, it is difficult to obtain porous spherical silica with a pore volume of 0.5 ml / g or more. A pore size of 1.0 × 10⁻⁶ mN is preferred. 1 ~1.8×10 1 mN. If the test force at the time of failure is within the above range, the particles have high hardness, forming porous spherical silica with the target durability.

[0050] The porous spherical silica of the present invention has an alkali metal content of 50 ppm or less (by mass). The alkali metal content is particularly preferably 40 ppm or less, and more preferably 30 ppm or less.

[0051] The porous spherical silica of the present invention is spherical in shape. Here, "spherical" means that the average roundness obtained by image analysis using a scanning electron microscope (SEM) is 0.8 or higher. "Average roundness obtained by image analysis" refers to the sum of the roundness values ​​obtained by observing more than 2000 porous spherical silica particles at 1000x magnification using SEM and performing image analysis on the SEM images. Here, "roundness" is the value obtained by the following formula (1).

[0052] C = 4πS / L 2 (1)

[0053] In the above formula (1), C represents the roundness, S represents the area (projected area) occupied by the porous spherical silica in the image, and L represents the length (perimeter) of the outer periphery of the porous spherical silica in the image. The average roundness is particularly preferably 0.85 or higher.

[0054] For the porous spherical silica of the present invention, among 200 particles observed in the SEM image, the number of fragmented particles is 20 or less. Here, fragmented particles refer to particles with a sphericity of 0.7 or less calculated according to the foregoing definition. The number of fragmented particles is preferably 15 or less, more preferably 10 or less.

[0055] Furthermore, the porous spherical silica of the present invention can be either hydrophilic or hydrophobic. The porous spherical silica of the present invention manufactured using the manufacturing method described later is hydrophilic. Hydrophobic porous spherical silica can be obtained by appropriately applying a silica surface treatment method after obtaining the hydrophilic porous spherical silica using this manufacturing method. It should be noted that "hydrophilic" here means that it can be dispersed in water without organic solvents.

[0056] The porous spherical silica of the present invention has the properties described above, and therefore can be used as a carrier for catalysts or fragrances, an adsorbent for carbon dioxide, a packing material for analytical columns, a cosmetic additive, an abrasive for industrial products, and an additive for various resin compositions.

[0057] <Method for manufacturing porous spherical silica>

[0058] The method for manufacturing the porous spherical silica of the present invention is not particularly limited, and the aforementioned high pore volume and modulo-sized pore radius can be easily achieved by using a fumed silica dispersion as a raw material. Typically, fumed silica has a structure formed by the aggregation of particulate silica (primary particles). Therefore, by using a fumed silica dispersion as a raw material for porous spherical silica and gelling the fumed silica in the dispersion to form a network, thereby suppressing the reduction in pore volume caused by drying shrinkage, porous spherical silica with high pore volume can be obtained.

[0059] More specifically, the method can be described as follows: A W / O emulsion containing an aqueous phase with dispersed fumed silica and an organic phase primarily composed of a non-water-soluble solvent is prepared (W / O emulsion preparation step). Next, the emulsion is heated to gel the aqueous phase, resulting in a porous spherical silica dispersion (gelation step). The generated porous spherical silica is then recovered from the liquid (gel recovery step), followed by spray drying (drying step) and calcination (calcination step), thereby manufacturing porous spherical silica. Each step is described in detail below.

[0060] (W / O emulsion preparation process)

[0061] As a method for preparing a W / O emulsion comprising an aqueous phase containing dispersed fumed silica and an organic phase mainly composed of a non-water-soluble solvent, the following method is particularly preferred: First, a dispersion containing dispersed fumed silica in an aqueous phase is prepared (dispersion preparation step), and an emulsion is prepared using the dispersion and an organic solvent according to conventional methods (emulsification step). These steps will be further explained below.

[0062] (Dispersion preparation process)

[0063] The dispersion preparation process is a process of dispersing fumed silica in water to prepare a dispersion.

[0064] The fumed silica used is dispersible in water and can be gelled by heating or adjusting the pH. This property is achieved by having a large number of silanol groups on the silica surface; therefore, most fumed silica that has not undergone surface treatment can be used. Furthermore, considering ease of gelation, a specific surface area of ​​100 m² is preferred for the fumed silica. 2 / g or more, especially 200m 2 / g or more. Further preferred is 250m. 2 / g or more. The larger the specific surface area, the faster the gelation process and the easier it is to gel droplets (W phase) containing this fumed silica. From the perspective of ease of acquisition, 400m² is preferred. 2 / g is used as the upper limit. It should be noted that the specific surface area is a value obtained based on the nitrogen adsorption BET multi-point method.

[0065] Furthermore, the larger the specific surface area of ​​the fumed silica used as a raw material, the larger the specific surface area of ​​the porous spherical silica obtained by the method described herein. Therefore, by appropriately selecting the fumed silica used as a raw material according to the target specific surface area of ​​the porous spherical silica, the specific surface area of ​​the porous spherical silica can be arbitrarily controlled without changing the manufacturing conditions. It should be noted that the fumed silica used in this invention can also be mixed with those having different specific surface areas.

[0066] The aforementioned fumed silica is commercially available, for example, various hydrophilic grades of Reolosil from Tokuyama Corporation, various hydrophilic grades of AEROSIL from AEROSIL Corporation of Japan, and various hydrophilic grades of HDK dry silica from Asahi Kasei Wacker Silicone Corporation.

[0067] In addition, fumed silica is usually high in purity and basically free of impurities such as alkali metals, so the porous spherical silica produced can also have very low alkali metal content.

[0068] Water is essential as a solvent in this process, but other solvents may be included to the extent that they do not impede emulsion formation and subsequent gelation. Additionally, if a potential base is used to promote the gelation process described later, it can be dissolved in water beforehand to disperse the fumed silica.

[0069] As a method for dispersing fumed silica in a solvent, it is preferable to prepare a dispersion in which fumed silica is pre-dispersed in the solvent, and then perform micro-dispersion using a crusher or the like. Examples of crushers suitable for micro-dispersion include ball mills, bead mills, vibratory mills, pin mills, atomizers, colloid mills, homogenizers, high-pressure homogenizers, and ultrasonic homogenizers. Regarding the degree of dispersion after micro-dispersion, when determining the particle size distribution of the dispersion using laser diffraction scattering, a D90 value of 0.5 μm or less is preferred.

[0070] The silica concentration in the fumed silica dispersion is preferably in the range of 10% to 30% by mass. More preferably, it is 15% by mass or more, and particularly preferably 20% by mass or more. A higher silica concentration in the fumed silica dispersion results in faster gelation, but excessively high concentrations will lead to loss of fluidity, making it difficult to produce a fumed silica dispersion.

[0071] It should be noted that heating accelerates the gelation of the fumed silica dispersion. When the gelation of the fumed silica dispersion occurs during the dispersion preparation step described above, the W phase is difficult to form spherical shapes in the subsequent emulsification step; in extreme cases, emulsion formation itself becomes difficult. Therefore, in the dispersion preparation step, the liquid temperature of the fumed silica dispersion is preferably maintained at around room temperature (20°C) or below. When the specific surface area or concentration of fumed silica is high, and gelation is easy to occur, cooling to a temperature below room temperature (preferably below 15°C, more preferably below 12°C) is also effective.

[0072] (Emulsification process)

[0073] The W / O emulsion preparation process involves dispersing a fumed silica dispersion obtained from the dispersion preparation process in a non-water-soluble solvent to form a W / O emulsion. By forming this W / O emulsion, the fumed silica dispersion, as the dispersed phase, becomes spherical due to surface tension and other factors. Therefore, by gelling the fumed silica dispersion dispersed in the non-water-soluble solvent in this spherical shape, a spherical gel can be obtained.

[0074] The non-aqueous solvent used in this manufacturing method can be any hydrophobic solvent capable of forming an emulsion with the fumed silica dispersion. Examples of such solvents include organic solvents such as hydrocarbons and halogenated hydrocarbons. More specifically, examples include non-aqueous solvents such as hexane, heptane, octane, nonane, decane, liquid paraffin, dichloromethane, chloroform, carbon tetrachloride, and dichloropropane. Hexane, heptane, and decane, which have suitable viscosities, are particularly suitable. It should be noted that multiple solvents can be mixed as needed. Furthermore, hydrophilic solvents such as lower alcohols can also be used in combination (as a mixed solvent), as long as the solvent can form an emulsion with the fumed silica dispersion.

[0075] There is no particular limitation on the amount of non-water-soluble solvent used, as long as it is within the range that can form a W / O emulsion. Generally speaking, the amount of non-water-soluble solvent used is about 1 to 10 parts by volume relative to 1 part by volume of fumed silica dispersion.

[0076] In this manufacturing method, a surfactant is preferably added when forming the aforementioned W / O emulsion. Known surfactants suitable for W / O emulsion formation can be used without limitation; anionic, cationic, and nonionic surfactants are all acceptable. From the viewpoint of facilitating W / O emulsion formation and minimizing the introduction of alkali metals, nonionic surfactants are preferred. In particular, surfactants with an HLB value of 3 or higher and less than 5, representing the degree of hydrophilicity and hydrophobicity, are suitable. It should be noted that "HLB value" here refers to the HLB value obtained by the Griffith method. Specific examples of suitable surfactants include sorbitan monooleate, sorbitan monostearate, and sorbitan monosesquioleate.

[0077] The amount of surfactant used is the same as that used when forming a W / O emulsion. Specifically, a range of 0.05g to 10g is suitable relative to 100ml of fumed silica dispersion.

[0078] When forming a W / O emulsion, known methods for forming W / O emulsions can be used as a method for dispersing a fumed silica dispersion in a non-water-soluble solvent. From the viewpoint of ease of industrial manufacturing, it is preferable to form the emulsion using mechanical emulsification; specifically, methods using mixers, homogenizers, etc., can be exemplified. A homogenizer is suitable for use. Through this emulsification process, an emulsion with a narrow particle size distribution of the aqueous phase droplets can be obtained, and therefore, the particle size distribution of the final obtained spherical porous silica is also narrow. In the case where it is preferable to obtain particles of 1 μm or more and less than 100 μm, and more preferably particles of 8 μm or more and less than 90 μm, the rotation speed of the homogenizer is preferably 1,000 rpm or more and less than 15,000 rpm, more preferably 2,000 rpm or more and less than 12,000 rpm, and even more preferably 4,000 rpm or more and less than 9,000 rpm. The stirring time is preferably 30 seconds or more and less than 1 hour, more preferably 1 minute or more and less than 30 minutes.

[0079] (Gelization process)

[0080] The gelation process is a step performed after the W / O emulsion preparation process, whereby the fumed silica dispersion is gelled in a non-water-soluble solvent while droplets are dispersed in the solution. This gelation can be carried out using known methods. For example, it can be facilitated by heating to a high temperature or by adjusting the pH of the fumed silica dispersion to a weakly acidic or even alkaline state. From the viewpoint of being able to control the reaction effectively, the above methods are preferred. It should be noted that the pH of the fumed silica dispersion prepared by the aforementioned methods without pH adjustment is typically in the range of 3.0 to 4.5.

[0081] When heating is performed, the temperature should not exceed the boiling point of each solvent used. The lower limit of the gelation temperature is preferably 50°C, more preferably 60°C. The upper limit is preferably 100°C or less, more preferably 90°C or less.

[0082] The pH adjustment described above can be easily performed by the following methods: pre-mixing a substance such as urea, which decomposes thermally upon heating and exhibits alkalinity (called a "latent alkali") into a fumed silica dispersion, and then heating it during gelation to raise the pH; or adding alkali to the emulsion while maintaining the W / O emulsion formation state by stirring with a mixer or similar device.

[0083] Specific examples of such alkalis include: ammonia; tetraalkylammonium hydroxides such as tetramethylammonium hydroxide (TMAH); amines such as trimethylamine; alkali metal hydroxides such as sodium hydroxide; alkali metal carbonates such as sodium carbonate and sodium bicarbonate; and alkali metal silicates. It should be noted that the intensity of the stirring can be strong enough to cause mixing between the W / O emulsion and the alkali.

[0084] Among the aforementioned methods for pH adjustment, from the viewpoint of avoiding the introduction of metal elements, methods utilizing the thermal decomposition of potential bases such as urea, or methods using ammonia, tetraalkylammonium hydroxides, or amines as bases, are preferred. When using ammonia for pH adjustment, the ammonia can be introduced either as a gas or added as ammonia water. From the viewpoint of ensuring uniformity when adjusting pH by heating, pH adjustment using urea is particularly preferred.

[0085] As the pH is adjusted to promote gelation, it is particularly preferable to adjust the amount added so that the pH of the fumed silica dispersion rises to about 4.5 to 8.0. The same applies when a potential alkali is used; if a specific amount is shown, for example when urea is used, it is preferably 1% by mass or more, particularly preferably 2% by mass or more, relative to the fumed silica dispersion. The upper limit is preferably 7% by mass or less, more preferably 5% by mass or less.

[0086] During the heating and pH adjustment processes described above, stirring is preferred to prevent the gel from agglomerating. Stirring is typically performed using well-known methods; for example, a mixer with stirring blades may be used.

[0087] In addition, after gelation, the dispersed phase changes from a liquid to a solid state. Therefore, the system becomes a dispersion (suspension) in a hydrophobic solvent containing solids (gels), and is no longer a W / O emulsion.

[0088] (Gel recovery process)

[0089] In this manufacturing method, the gel generated as described above is recovered from the liquid. Conventional solid-liquid separation methods such as filtration and centrifugation can be used to recover the gel, but WO phase separation can also be performed before recovery. WO phase separation refers to separating the aforementioned gel dispersion into two layers: the O phase and the W phase; this operation is commonly referred to as demulsification. Here, the gel obtained from the aforementioned gelation process exists on the separated W phase side. By separating it from the O phase, solid-liquid separation and recovery of the gel can be easily achieved using methods such as filtration.

[0090] As for the aforementioned WO phase separation method, a known method can be appropriately selected as the demulsification method and implemented, but it is preferred to carry it out in the following manner: a certain amount of water-soluble organic solvent, which is usually used for demulsification, is added to the gel dispersion and heated to separate it into O phase and W phase. After this process, the upper layer is usually the O phase (a layer mainly containing organic solvent), and the lower layer is the W phase (a water layer containing aqueous organic solvent and gel).

[0091] Examples of water-soluble organic solvents include acetone, methanol, ethanol, and isopropanol. Isopropanol is particularly suitable for use among these.

[0092] The amount of water-soluble organic solvent added is preferably adjusted according to the type and amount of surfactant with an HLB of 3 or higher and 5 or lower used in forming the emulsion. For example, when using sorbitan monooleate as the surfactant, about 1 / 6 to 1 / 2 times the mass of the water-soluble organic solvent (water-soluble organic solvent / water-insoluble organic solvent) is added relative to the mass of the insoluble organic solvent. After stirring as needed and allowing to stand, demulsification can be appropriately achieved.

[0093] During WO phase separation, the surfactant migrates to the O phase side (extraction). Therefore, by removing the O phase, porous spherical silica free from impurities produced by the surfactant can be obtained.

[0094] In addition, the aforementioned heating temperature range is 50°C or higher, preferably around 50 to 80°C, and more preferably around 60 to 70°C.

[0095] As described above, after adding a water-soluble organic solvent to the gel dispersion, stirring is preferable to prevent the gel particles from agglomerating. Stirring is typically performed using well-known methods; for example, a mixer with stirring blades can be used. The degree of mixing is not particularly limited, as long as the liquid surface is rotated by stirring; for example, stirring using a mixer would be 0.1–3.0 kW / m³. 3 Preferred power is 0.5–1.5 kW / m 3 In addition, a stirring time of 0.5 to 24 hours, preferably around 0.5 to 1 hour, is appropriate.

[0096] After the WO phase separation described above, the aforementioned W phase containing the gel is recovered. Specifically, the O phase (upper layer) can be separated and removed using methods such as decantation.

[0097] (Drying process)

[0098] The gel contained in the recovered W phase is preferably recovered from the W phase. Known methods can be used for recovery, such as filtration and centrifugation. In this case, it is preferable to remove the solvent by using the recovered gel as a filter cake.

[0099] The recovered gel is dried by spray drying. In the manufacturing method of the present invention, when the gel is manufactured using a wet process, capillary forces of the solvent are generated between the gel particles during drying. This leads to particle aggregation, especially during static drying, where the dried powder also aggregates. However, by using spray drying, the diameter of the solvent droplets during drying can be made close to the particle size of the porous spherical silica particles. Ideally, if the diameter of the solvent droplets is equal to the particle size of the porous spherical silica particles, the porous spherical silica particles are contained individually within the solvent droplets during drying. In this state, the porous spherical silica particles are not adjacent during drying; therefore, drying can be performed without solvent-induced capillary forces between the particles, easily resulting in non-aggregated particles. The spray drying method is not particularly limited; known methods such as rotary atomization or nozzle spraying can be used. It is preferable to select a method where the particle size of the target porous spherical silica particles is equal to the droplet diameter of the sprayed solvent. Generally, nozzle methods tend to produce finer droplet diameters compared to rotary atomization methods. From the viewpoint of enabling finer droplet diameters and reducing the likelihood of agglomeration during drying, dual-fluid nozzle methods are particularly preferred.

[0100] From the perspective of minimizing aggregation, the gel during spray drying is preferably dispersed in a water-soluble organic solvent. Specific examples of water-soluble organic solvents include acetone, methanol, ethanol, and isopropanol. Using solvents with lower boiling points can improve drying efficiency.

[0101] Water and non-water-soluble solvents can also be mixed into the aforementioned water-soluble organic solvent. To suppress aggregation during drying, the concentration of the water-soluble organic solvent in the solvent is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and particularly preferably 70% by mass or more. If the concentration of the water-soluble organic solvent is within the above range, aggregation due to poor drying during spray drying is less likely to occur. It should be noted that the drying shrinkage inside the pores can be adjusted according to the concentration of the water-soluble solvent during drying. Therefore, by adjusting the concentration of the aforementioned water-soluble organic solvent, appropriate drying shrinkage can be generated and the pore volume can be controlled. Specifically, by increasing the proportion of water in the solvent and decreasing the concentration of the water-soluble organic solvent, drying shrinkage is more likely to occur, and the pore volume becomes smaller. Conversely, by decreasing the proportion of water in the solvent and increasing the concentration of the water-soluble organic solvent, drying shrinkage is suppressed, and the pore volume becomes larger.

[0102] To prevent particle aggregation in the liquid, it is preferable to stir the water-soluble organic solvent (slurry) in which the gel is dispersed. Commonly known methods can be used for stirring; specific examples include stirring rods and mixers with stirring blades. The degree of mixing is sufficient to prevent the particles from settling in the liquid and from being broken down. The slurry can be added to the spray dryer while stirring, or it can be added after stirring for a certain period of time. From the viewpoint of preventing particle settling, adding the slurry while stirring is more preferable.

[0103] During spray drying, the inlet temperature is preferably adjusted to be above the boiling point of the solvent in the slurry, so that the porous spherical silica forms a dry powder rather than a slurry or filter cake at the outlet of the spray dryer. It should be noted that "above the boiling point" refers to the boiling point of the solvent under drying pressure. More preferably, the inlet temperature is adjusted to be about 20-50°C higher than the boiling point of the solvent in the slurry, and preferably the temperature difference between the inlet and outlet temperatures is in the range of 10-70°C. Typically, the spray dryer only has a heating device at the inlet, and the outlet temperature does not exceed the inlet temperature. The temperature difference between the inlet and outlet temperatures is more preferably in the range of 20-70°C, and particularly preferably in the range of 20-60°C. If the inlet and outlet temperatures are within the above ranges, the drying state during spray drying is good, resulting in porous spherical silica without aggregation.

[0104] During spray drying, the circulating air volume only needs to be adjusted to maintain a stable temperature within the drying chamber, preferably according to the size of the spray dryer. When using a cyclone separator to collect the dried porous spherical silica, the circulating air volume affects the collection efficiency under the cyclone separator; the larger the circulating air volume, the higher the collection efficiency under the cyclone separator.

[0105] The concentration of gel in the slurry should be adjusted to a level that allows the slurry containing the gel to flow freely without causing blockage when fed into the spray dryer. Specifically, the concentration (by mass) of the silica solids after drying is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. There is no particular limitation on the lower limit of the gel concentration, but the lower the concentration, the lower the drying efficiency; therefore, it is preferable to have a concentration that is not extremely low, and more preferably 5% by mass or more.

[0106] During spray drying, the slurry feed rate only needs to be adjusted to ensure stable spraying and that the inlet and outlet temperatures reach the aforementioned values. It is preferable to adjust this rate according to the scale of the spray dryer. The slurry feed rate affects the temperature difference between the inlet and outlet temperatures; a faster feed rate results in a larger temperature difference between the inlet and outlet.

[0107] As a method for collecting dry, porous, spherical silica, generally known methods can be used. Specifically, single-collection methods, two-collection methods, etc., can be cited. In addition, common collectors can be used, such as cyclone separators, bag filters, etc. From the viewpoint of removing coarse particles, it is preferable to use a two-collection method using a cyclone separator.

[0108] (Firing process)

[0109] The porous spherical silica of the present invention is further sintered after drying. Firing increases the test force at the time of destruction. The sintering conditions only need to be adjusted to achieve the target test force at the time of destruction; the longer the sintering time and the higher the sintering temperature, the higher the test force at the time of destruction. The sintering temperature is 900–1500°C, preferably below 1400°C, more preferably below 1300°C. The sintering time is 10–25 hours, preferably 12–23 hours, more preferably 12–20 hours. If the sintering temperature and sintering time are within the above ranges, porous spherical silica with a test force at the time of destruction within the target range can be obtained. The particles, after spray drying without aggregation, will not re-aggregate, and the pores will not become clogged.

[0110] As a firing method, well-known methods can be used, such as placing dry porous spherical silica in a crucible, quartz pot, etc., and heating it in an electric furnace.

[0111] There are no special restrictions on the atmosphere during firing; it can be carried out under inert gases such as argon and nitrogen, or under atmospheric atmosphere.

[0112] The heating rate during firing can be within the acceptable range of temperature rise of the heating device such as the electric furnace. The slower the heating rate, the lower the firing efficiency, so a very low rate is preferred. When using a general electric furnace, a heating rate of 2 to 10°C per minute is suitable.

[0113] The porous spherical silica particles obtained by the above manufacturing method have a particle size that is basically consistent with the droplet (W phase) diameter of the fumed silica dispersion in the W / O emulsion prepared in the emulsification process. Therefore, it is necessary to set the dispersion conditions to achieve the target diameter range. Various methods for controlling the droplet diameter in W / O emulsions are known; appropriate selection and application are sufficient. Known methods for adjusting droplet size include: adjusting the amount of surfactant added; and adjusting the shear force applied during emulsification based on rotation speed, flow rate, etc. When adjusting the amount of surfactant added, a larger amount of surfactant tends to result in finer droplets, while a smaller amount tends to result in larger droplets. Furthermore, when adjusting the shear force, a larger shear force results in finer droplets, while a smaller shear force results in larger droplets.

[0114] Furthermore, pore volume can be controlled by drying shrinkage. Known methods can be used to control drying shrinkage; specifically, adjusting the concentration of the water-soluble solvent before drying is an example. Pore volume can also be controlled by firing conditions; generally, higher firing temperatures and longer firing times result in smaller pore volumes. Additionally, by using fumed silica as a raw material as in the manufacturing method of this invention, the aforementioned high pore radius is achieved due to the aggregated structure of fumed silica. Specific surface area can be adjusted by appropriately selecting the specific surface area of ​​the fumed silica used as a raw material, and also by adjusting the gelation time. It should be noted that shorter gelation times result in higher specific surface areas. Specific surface area can also be adjusted by firing conditions. Generally, higher firing temperatures and longer firing times result in lower specific surface areas.

[0115] By using fumed silica, which is substantially free of alkali metals as described above, as a raw material, and by using other raw materials that are also substantially free of alkali metals, and by taking sufficient care to avoid contamination (impurity contamination) in the manufacturing process, the alkali metal content can be easily reduced. Furthermore, when the goal is to reduce the alkali metal content, the filter cake can be washed with water, organic solvents, etc., after solid-liquid separation and before drying.

[0116] By suppressing particle aggregation during the manufacturing process as described in the manufacturing method of this invention, and without performing a crushing process, the number of fragmented particles can be reduced. Furthermore, care should be taken not to apply excessive load to the particles throughout the manufacturing process to avoid particle damage.

[0117] Example

[0118] The following are embodiments illustrating the present invention. However, the present invention is not limited to these embodiments.

[0119] <Evaluation Methods>

[0120] The following items are evaluated for the manufactured porous spherical silica.

[0121] (Particle size distribution and cumulative particle size based on volume were determined using a Coulter counter)

[0122] 0.1 g of porous spherical silica was added to 40 ml of deionized water and dispersed for 30 minutes using an ultrasonic cleaner (BRANSON IC1510J-DTH). The particle size distribution of the dispersion was determined using a Beckman Coulter Multisizer III. Pores with a pore size of 100 μm were used in the determination. Based on the obtained particle size distribution, the cumulative 50%, 10%, and 90% particle sizes on a volume basis were evaluated.

[0123] (Determination of BJH pore volume, pore radius (mode), and BET specific surface area)

[0124] The BJH pore volume, pore radius (modal), and BET specific surface area were determined according to the aforementioned definitions and using a BLESORP-mini (manufactured by BEL JAPAN Co., Ltd.).

[0125] (Confirm the test force at which the specimen fails)

[0126] The determination of the "test force at which specimen failure is confirmed" was performed according to the aforementioned definition using a micro compression testing machine (Shimadzu MCT-W510-J). The loading rate was set to 0.4462 mN / s, and the loading holding time was set to 10 seconds. A 200 μm diameter indenter was used in the measurement.

[0127] (Alkali metal content)

[0128] 1g of porous spherical silica was dissolved in 10ml of nitric acid and 10ml of hydrofluoric acid. The solution was heated at 180°C for 4 hours to evaporate to dryness. After cooling to room temperature, 2ml of nitric acid and 18ml of ultrapure water were added, and the volume was adjusted to 20ml to obtain the test sample. The alkali metal content of the test sample was determined using an inductively coupled plasma atomic emission spectrometer (Inductively Coupled Plasma Optical Emission Spectrometry, Thermo Scientific, ICAP650DUO).

[0129] (Average roundness)

[0130] For more than 2000 porous spherical silica particles, image analysis was performed on SEM images observed at 1000x magnification using a SEM (Hitachi High Technologies S-5500, accelerating voltage 3.0kV, secondary electron detection), and the average sphericity was calculated according to the aforementioned definition.

[0131] (Number of fragmented particles (number of particles with a roundness of 0.7 or less))

[0132] For porous silica with more than 200 particles, image analysis was performed on SEM images observed at 800x magnification using a SEM (Hitachi High Technologies S-5500, accelerating voltage 3.0kV, secondary electron detection). The roundness of each particle was calculated according to the aforementioned definition, and the number of particles with a roundness of 0.7 or less was counted.

[0133] <Example 1>

[0134] (Dispersion preparation process)

[0135] In 200 ml of ion-exchanged water containing 6.65 g of urea, 66 g of Reolosil QS-30 (manufactured by Tokuyama Corporation) was added while stirring with a homogenizer (IKA T25BS1) to pre-disperse the fumed silica. Then, a micro-dispersion was performed using an ultrasonic homogenizer (BRANSON Sonifier SFX250) to obtain a fumed silica dispersion. The particle size distribution of the dispersed liquid was determined by laser diffraction scattering, and the D90 value was 0.19 μm. It should be noted that the dispersion preparation process was carried out in a cooler cooled to 10°C.

[0136] (W / O emulsion preparation process)

[0137] 65.5g of the fumed silica dispersion prepared by the above method was separated, and 129g of decane containing 0.75g of dehydrated sorbitan monooleate (manufactured by Kao Corporation, Rheodol SP-010V) was added. The mixture was then stirred for 3 minutes at 8600 rpm using a homogenizer to obtain a W / O emulsion.

[0138] (Gelization process)

[0139] The obtained W / O emulsion was gelled by stirring it at 200 rpm with four blades (60 mm in diameter, 20 mm in width, and 45 degrees at an angle) in a water bath at 80°C for 3 hours.

[0140] (Gel recovery process)

[0141] Add 77g of isopropanol and 52g of water, and stir with a stirring blade while maintaining the temperature at 70°C for 30 minutes. After that, let it stand to separate two layers, with the O phase as the upper layer and the W phase as the lower layer.

[0142] Next, the O phase and W phase are separated by decantation, and the W phase is recovered.

[0143] The W phase was filtered to extract the gel.

[0144] (Drying process)

[0145] The resulting gel cake was dispersed in 60g of isopropanol and added to a spray dryer (BUCHI Mini Spray Dryer B-290) while stirring with a stirring rod. At this point, the concentration of dried silica solids in the slurry was 10% by mass. The inlet temperature of the spray dryer was set to 120℃, and the outlet temperature was set to 85℃. The feed rate was set to 15ml / min, and the circulating air volume was set to 35m³ / min. 3 / Hour.

[0146] (Firing process)

[0147] The obtained dry powder was placed in a crucible and heated in an electric furnace (ADVANTEC, FUS722PB) at a heating rate of 5°C / min, and calcined at 1000°C for 20 hours. It should be noted that the calcination atmosphere was not adjusted; instead, it was set to an air atmosphere.

[0148] The properties of the resulting porous spherical silica are shown in Table 1. (The same applies to the following examples and comparative examples; the properties of the resulting porous spherical silica are shown in Table 1.)

[0149] <Example 2>

[0150] In Example 1, the firing conditions were changed to 900°C for 17 hours; otherwise, porous spherical silica was obtained in the same manner as in Example 1. It should be noted that the outlet temperature during spray drying was 85°C.

[0151] <Example 3>

[0152] In Example 1, the rotation speed of the homogenizer in the W / O emulsion preparation process was changed to 3000 rpm. Otherwise, porous spherical silica was obtained in the same manner as in Example 1. It should be noted that the outlet temperature during spray drying was 85°C.

[0153] <Example 4>

[0154] In Example 1, the rotation speed of the homogenizer in the W / O emulsion preparation process was changed to 10,000 rpm. Otherwise, porous spherical silica was obtained in the same manner as in Example 1. It should be noted that the outlet temperature during spray drying was 85°C.

[0155] <Example 5>

[0156] In Example 1, the firing conditions were changed to 1200°C for 15 hours; otherwise, porous spherical silica was obtained in the same manner as in Example 1. It should be noted that the outlet temperature during spray drying was 85°C.

[0157] <Example 6>

[0158] In Example 1, the homogenizer speed in the W / O emulsion preparation process was changed to 6000 rpm, and the firing conditions were changed to 1200°C for 10 hours. Otherwise, porous spherical silica was obtained in the same manner as in Example 1. It should be noted that the outlet temperature during spray drying was 85°C.

[0159] <Comparative Example 1>

[0160] 500 mL of silica sol was prepared by adding 10 g / 100 mL of sulfuric acid to a sodium silicate aqueous solution with a SiO2 / Na2O molar ratio of 3.1 (9 g / 100 mL) to achieve a pH of 2.9. 66.5 g of this silica sol was collected, and the fumed silica dispersion from Example 1 was replaced with this silica sol. The W / O emulsion preparation, gelation, and gel recovery processes were performed in the same manner as in Example 1 to obtain a gel. The obtained gel was dried using a vacuum dryer and calcined at 1000°C for 20 hours to obtain porous spherical silica.

[0161] <Comparative Example 2>

[0162] The fumed silica dispersion prepared in the same manner as the dispersion preparation process in Example 1 was spray-dried and then calcined at 1000°C for 20 hours to obtain porous spherical silica.

[0163] <Comparative Example 3>

[0164] In Example 1, the homogenizer speed in the W / O emulsion preparation process was changed to 5500 rpm, and a gelation and gel recovery process was performed to obtain a gel. The obtained gel was dried using a vacuum dryer and calcined at 1000°C for 20 hours. After calcination, it was crushed using a jet mill to obtain porous spherical silica.

[0165] <Comparative Example 4>

[0166] In Example 1, no firing process was performed; otherwise, porous spherical silica was obtained in the same manner as in Example 1.

[0167] <Comparative Example 5>

[0168] In Example 6, porous spherical silica was obtained by firing at 800°C for 10 hours, otherwise, the process was the same as in Example 6.

[0169] [Table 1]

[0170] (Table 1)

[0171]

[0172] <Evaluation Results>

[0173] (Examples 1-6)

[0174] As shown in Table 1, in Examples 1-6, the hardness was high, and the arithmetic mean of the "test force at which the specimen breaks" for 10 particles, calculated by setting the loading rate to 0.4462 mN / s according to the method specified in JIS Z8844, was 1.0 × 10⁻⁶. 1 ~2.0×10 1 The number of fragmented particles was reduced, with fewer than 20 out of 200 particles observed in the SEM image having a sphericity of 0.7 or less. This can be achieved by gelling a fumed silica dispersion in a liquid to obtain a gel, as described in the manufacturing method of this invention, drying the gel using spray drying under appropriate drying conditions to suppress particle aggregation, and then firing it under appropriate firing conditions.

[0175] Furthermore, the porous spherical silica obtained in Examples 1-6 all had a D50 ranging from 2 to 200 μm, a D10 / D90 ratio of 0.3 or higher, a pore volume ranging from 0.5 to 8 ml / g based on the BJH method, a pore radius modulus ranging from 5 nm to 50 nm based on the BJH method, and a specific surface area of ​​50 m² based on the BET method. 2 / g or more and 400m 2 The range is below / g, and the alkali metal content is below 50ppm.

[0176] In Examples 1-6, porous spherical silica with various D50 values ​​were obtained. However, the control was achieved by adjusting the droplet diameter of the W / O emulsion by changing the rotation speed during emulsification. The manufacturing method of the present invention can easily control the D50 value of porous spherical silica without significant changes to the manufacturing process.

[0177] (Comparative Example 1)

[0178] In Comparative Example 1, where sodium silicate was used as a raw material, the pore volume of the porous spherical silica decreased. This was because sodium residue from the raw material caused a decrease in the melting point during firing, leading to pore blockage. Consequently, when using sodium silicate as a raw material, it is difficult to obtain porous spherical silica with high hardness while maintaining the pore volume.

[0179] (Comparative Example 2)

[0180] The test force at which the porous spherical silica of Comparative Example 2, obtained by spray drying the fumed silica dispersion, was lower. This is because the bonding strength between the primary particles of the matrix material before firing is low. Consequently, it is difficult to obtain porous spherical silica with the target hardness when granulation is performed by spray drying.

[0181] (Comparative Example 3)

[0182] For the porous spherical silica of Comparative Example 3, which was dried in a vacuum dryer after the gel was recovered, the number of fragmented particles increased. This is because the particles aggregated during the drying process and underwent a crushing step, resulting in fragmented particles. Therefore, it is difficult to obtain porous spherical silica with a reduced number of fragmented particles by simply drying in a static environment.

[0183] (Comparative Example 4)

[0184] The porous spherical silica of Comparative Example 4, which did not undergo a firing process, exhibited a low test force upon destruction. Therefore, it is difficult to obtain porous spherical silica with high hardness without a firing process.

[0185] (Comparative Example 5)

[0186] The porous spherical silica in Comparative Example 5 exhibited a low test force upon destruction. Therefore, if the firing conditions are inappropriate, it is difficult to obtain porous spherical silica with high hardness.

Claims

1. A porous spherical silica, characterized in that, The cumulative 50% particle size (D50) on a volumetric basis, measured using the Coulter counting method, is the range of 2 μm or larger and 200 μm or smaller. Similarly, the ratio of the cumulative 10% particle size (D10) to the cumulative 90% particle size (D90) obtained (D10 / D90) is greater than 0.

3. Based on the BJH method, the pore volume is above 0.5 ml / g and below 8 ml / g. The modulus of the aperture radius based on the BJH method is greater than 5 nm and less than 50 nm. The specific surface area based on the BET method is 50 m². 2 / g or more and 400m 2 / g or less The arithmetic mean of the "test force at which specimen failure is confirmed" for 10 particles, calculated by setting the loading rate to 0.4462 mN / s according to the method specified in JIS Z8844, is 1.1 × 10⁻⁶. 1 mN or higher and 2.0×10 1 Below mN, Of the 200 particles observed in the SEM images, fewer than 20 particles had a roundness of less than 0.

7. The alkali metal content is below 50 ppm.

2. A catalyst support comprising the porous spherical silica as described in claim 1.

3. A cosmetic product comprising the porous spherical silica as described in claim 1.

4. An analytical column comprising the porous spherical silica of claim 1.

5. An abrasive comprising the porous spherical silica of claim 1.

6. A resin composition comprising the porous spherical silica of claim 1.

7. A method for manufacturing porous spherical silica according to claim 1, comprising the following steps: The process for preparing a W / O emulsion comprising an aqueous phase in which fumed silica is dispersed and an organic phase in which an insoluble solvent is the main component. The process of heating an emulsion to gel the aqueous phase and obtaining a gel dispersion; The process of recovering the generated gel from the liquid and spray drying it; and, The process involves sintering the obtained porous spherical silica at a temperature of 900–1500°C for 10–25 hours. in, The spray drying process uses a dual-fluid nozzle method.

8. The method for manufacturing porous spherical silica according to claim 7, wherein, The spray drying is carried out within the following range: the inlet temperature of the spray dryer is 20-50°C higher than the boiling point of the solvent in the gel dispersion, and the temperature difference between the inlet and outlet temperatures of the spray dryer reaches 20-70°C.

Images