Porous spherical silica and method for producing the same

Abstract

Provided is porous spherical silica which contains impurities in a reduced amount (has a low alkali metal content), has a narrow particle size distribution, has a D50 (volume-based cumulative 50% diameter) value falling within a specified range, and has a pore volume falling within a specified range, and is useful as a polishing agent or a cosmetic ingredient.　The porous spherical silica has a D50 value of 2 to 200 μm and a D10 / D90 ratio of 0.3 or more when determined by a laser diffraction scattering method, has a pore volume of 0.5 ml / g to 8 ml / g inclusive, has an arithmetic mean value of 1.0×101 to 1.0×102 mN which is determined in a sample fracture test on 10 particles employing a loading rate of 38.7363 mN / sec, and has an alkali metal content of 50 ppm or less. The porous spherical silica can be produced by forming a W / O emulsion using a fumed silica liquid dispersion as an aqueous phase, gelatinizing the W / O emulsion by the adjustment of the pH value thereof, heating or the like, collecting the gelatinized product, and drying the collected product.

Description

[Technical Field]

[0001] This invention relates to a novel porous spherical silica and a method for producing the same. [Background technology]

[0002] Porous silica has been studied extensively, and porous silica with diverse physical properties has been proposed. Porous silica can be produced, for example, by neutralizing an aqueous alkali metal silicate solution with a mineral acid and then separating and recovering the resulting particles (Patent Documents 1 and 2). Porous spherical silica obtained by the above method has the characteristics of having a high pore volume and a narrow particle size distribution. In particular, when used as an abrasive for industrial products, the resin penetrates into the pores, making it easy to fix the silica to the resin on the polishing pad. However, since the above porous spherical silica uses an aqueous alkali metal silicate solution as a raw material, it has the problem of containing impurities such as sodium, making it difficult to use as an abrasive for materials that are sensitive to alkali metals, such as semiconductors.

[0003] Patent Document 3 proposes a method for obtaining porous spherical silica with reduced alkali metal content by spray-drying a fumed silica dispersion. However, the porous spherical silica obtained by the method in Patent Document 3 has the problem of having a wide particle size distribution because it is formed by spray drying. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2004 / 101139 Pamphlet [Patent Document 2] International Publication No. 2012 / 057086 Brochure [Patent Document 3] International Publication No. 2019 / 131873 brochure [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, the object of the present invention is to provide porous spherical silica having a low alkali metal content, a narrow particle size distribution, a D50 (cumulative 50% diameter by volume) within a predetermined range, and a pore volume within a predetermined range, as well as a method for producing the same. [Means for solving the problem]

[0006] The inventors have diligently conducted research to solve the above problems. As a result, they have discovered that in the manufacturing process of porous spherical silica, by forming a fumed silica dispersion by emulsion and then gelling it, it is possible to produce porous spherical silica in which the alkali metal content is reduced, the particle size distribution is narrow, the D50 (cumulative 50% diameter by volume) is within a predetermined range, and the pore volume is within a predetermined range, thus completing the present invention.

[0007] In other words, the present invention is The volume-based cumulative 50% diameter (D50) measured by laser diffraction scattering is in the range of 2 to 200 μm. Similarly, the ratio of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) (D10 / D90) is 0.3 or greater. The pore volume measured by the BJH method is between 0.5 ml / g and 8 ml / g. According to the method specified in JIS Z8844:2019, the arithmetic mean of the "test force at which sample fracture was observed" for 10 particles, calculated at a loading speed of 38.7363 mN / sec, is 1.0 × 10⁻⁶. 1 mN ~ 1.0 × 10 2 mN is, This porous spherical silica is characterized by having an alkali metal content of 50 ppm or less.

[0008] The volume-based cumulative 50% diameter (D50) measured by laser diffraction scattering is in the range of 2 to 200 μm. Similarly, the ratio of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) (D10 / D90) is 0.3 or greater. The pore volume determined by the BJH method is 0.5 ml / g or more and 8 ml / g or less, In accordance with the method specified in JIS Z8844, the arithmetic mean value of "test force at which fracture of a sample is observed" for 10 particles obtained at a loading rate of 0.4462 mN / sec is 1.0×10 -1 ~1.0×10 1 mN, Porous spherical silica characterized in that the alkali metal content is 50 ppm or less.

[0009] The volume-based 50% cumulative diameter (D50) measured by laser diffraction scattering method is in the range of 2 to 200 μm, Similarly, the ratio (D10 / D90) of the 10% cumulative diameter (D10) to the 90% cumulative diameter (D90) is 0.3 or more, The pore volume determined by the BJH method is 0.5 ml / g or more and 8 ml / g or less, The mode value of pore radius determined by the BJH method is 5 nm or more and 50 nm or less, The specific surface area determined by the BET method is 100 m 2 / g or more and 400 m 2 / g or less, Porous spherical silica characterized in that the alkali metal content is 50 ppm or less.

[0010] Further, the above-mentioned porous spherical silica can be produced by forming a W / O emulsion composed of an aqueous phase in which fumed silica is dispersed and an organic phase containing a water-insoluble solvent as a main component, modulation then heating the W / O emulsion to gel the aqueous phase to obtain a porous spherical silica dispersion, and then recovering the produced porous spherical silica from the liquid.

Effect of the Invention

[0011] As indicated by the high D10 / D90 ratio, the porous spherical silica of the present invention has a narrow particle size distribution, a low alkali metal content, a D50 (cumulative 50% diameter by volume) within a predetermined range, and a predetermined pore volume, enabling precise polishing. Therefore, it is extremely useful as an abrasive for materials that are undesirable due to alkali metal content, such as semiconductors. Furthermore, when used as an additive in cosmetics, it can impart a smooth feel.

[0012] Furthermore, the manufacturing method of the present invention allows the use of high-purity fumed silica as a raw material, and by appropriately selecting its specific surface area, the specific surface area of ​​the resulting porous silica can be arbitrarily controlled. In addition, because the fumed silica used as a raw material has a structure, the reduction in pore volume due to drying shrinkage is suppressed, making it possible to obtain porous spherical silica with a high pore volume without surface treatment. Therefore, this method offers many advantages as a way to produce high-purity porous spherical silica that does not contain alkali metals. [Modes for carrying out the invention]

[0013] The embodiments shown below are illustrative examples of the present invention, and the present invention is not limited to these embodiments.

[0014] <Porous spherical silica> The porous spherical silica of the present invention has a volume-based cumulative 50% diameter (D50) in the particle size distribution measured by laser diffraction scattering, which is in the range of 2 to 200 μm, and the ratio of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) (D10 / D90) is 0.3 or greater. The fact that the porous spherical silica is within the above range makes it particularly suitable for use as an abrasive or cosmetic material. D50 is preferably 2 to 100 μm, particularly preferably 5 to 50 μm, and even more preferably 5 to 20 μm. D10 / D90 is preferably 0.4 or greater, and even more preferably 0.5 or greater. Note that D10 / D90 cannot exceed 1.0 and is generally 0.6 or less.

[0015] The porous spherical silica of the present invention has a pore volume measured by the BJH method described below of 0.5 ml / g or more and 8 ml / g or less. It is difficult to obtain a product having a pore volume exceeding 8 ml / g. If the pore volume is 6 ml / g or less, it is easier to produce; if it is 4 ml / g or less, it is even easier to produce; and if it is 2.5 ml / g or less, it is particularly easy to produce. In particular, in order for the porous spherical silica of the present invention to have high oil absorption properties, the pore volume is preferably 1.0 ml / g or more, more preferably 1.6 ml / g or more, and even more preferably 2.0 ml / g or more. Porous spherical silica having such a pore volume can be particularly suitably used as an additive for cosmetics.

[0016] In addition, the mode value of the pore radius is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more. As for the upper limit, it is preferably 50 nm or less, and more preferably 30 nm or less.

[0017] The pore volume and pore radius determined by the BJH method are obtained by the following procedure: a sample to be measured is dried under a vacuum of 1 kPa or less at a temperature of 200°C for 3 hours or more, then an adsorption isotherm only on the adsorption side of nitrogen at liquid nitrogen temperature is obtained, and analyzed by the BJH method (Barrett, E. P. ;Joyner, L. G. ;Halenda, P. P. , J. Am. Chem. Soc. 73, 373 (1951)). The "mode value of pore radius determined by BJH method" refers to the pore radius value at which the pore distribution curve (volume distribution curve) — obtained by analysis with the above BJH method, plotted with the derivative of cumulative pore volume with respect to the logarithm of pore radius as the vertical axis and pore radius as the horizontal axis — reaches its maximum value.

[0018] The porous spherical silica of the present invention has a specific surface area determined by the BET method of 100 m 2 / g or more and 400 m 2 / g or less. The specific surface area is preferably 150 m 2 / g or more, more preferably 200 m 2 / g or more and 350 m 2It is particularly preferable that the value is in the range of less than or equal to / g. The specific surface area of ​​the porous spherical silica obtained by the manufacturing method of the present invention is several tens of m² from the specific surface area of ​​the fumed silica used as a raw material. 2 This value is obtained by subtracting the value per g. Selecting fumed silica as a raw material so that porous spherical silica within the above range can be obtained makes gelation easier and facilitates molding into a spherical shape. Generally, the specific surface area of ​​fumed silica is 400 m². 2 Since it is less than / g, the specific surface area is 400m². 2 It is difficult to obtain porous spherical silica with a density exceeding / g. Note that the specific surface area is the value obtained by the nitrogen adsorption BET multipoint method.

[0019] The porous spherical silica of the present invention, when measured according to the method specified in JIS Z8844:2019 at a loading rate of 38.7363 mN / sec, yields an arithmetic mean of the "test force at which the sample fractures" (hereinafter referred to as "test force at fracture") for 10 particles, which is 1.0 × 10⁻¹⁰. 1 ~1.0×10 2 It is preferable that it be mN. More preferably 5.0 × 10 1 It is less than or equal to mN, and more preferably 3.0 × 10⁻⁶ 1 It is less than or equal to mN. The lower limit is 1.2 × 10⁻⁶. 1 A force of mN or greater is more preferable. When the test force at fracture falls within this range, the particles exhibit excellent pressure disintegration properties. That is, when a specific load is applied to the particles, they disintegrate, and when used as an abrasive for industrial products, they are less likely to scratch the object being polished, and when used as a scrubbing agent for cosmetic materials, they can reduce the burden on the skin. If the test force at fracture is below the lower limit mentioned above, the porous spherical silica disintegrates easily, and its workability deteriorates significantly. On the other hand, if it exceeds the upper limit mentioned above, it does not break even when a strong force is applied, and the above advantages cannot be obtained.

[0020] The porous spherical silica of the present invention, when measured according to the method specified in JIS Z8844:2019 at a loading rate of 0.4462 mN / sec, has an arithmetic mean of the "test force at which the sample was fractured" (hereinafter referred to as "test force at fracture") for 10 particles, which is 1.0 × 10⁻⁶. -1~1.0×10 1 It is preferable that it be mN. More preferably 8.0 × 10 0 It is less than or equal to mN, and more preferably 5.0 × 10⁻⁶ 0 It is less than or equal to mN. Furthermore, the lower limit is more preferably 3.0 × 10⁻⁶. ―1 mN or greater, and more preferably 6.0 × 10⁻⁶ ―1 The test force at fracture is mN or greater. When the test force at fracture falls within this range, the particles exhibit excellent pressure disintegration properties. That is, when a specific load is applied to the particles, they disintegrate. In particular, when used as an abrasive for industrial products, they are less likely to scratch the object being polished, and when used as a scrubbing agent in cosmetics, they can reduce the burden on the skin. If the test force at fracture is below the lower limit mentioned above, the porous spherical silica disintegrates easily, and its workability deteriorates significantly. On the other hand, if it exceeds the upper limit mentioned above, it will not break even under strong force, and the above advantages cannot be obtained.

[0021] 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 30 ppm or less, and more preferably 10 ppm or less. Such porous spherical silica can be suitably used as an abrasive for semiconductor substrate materials.

[0022] The porous silica of the present invention is spherical in shape. Here, "spherical" means that the average circularity, determined by image analysis using a scanning electron microscope (SEM), is 0.8 or higher. "Average circularity determined by image analysis" is the arithmetic mean of circularity obtained by image analysis of SEM images observed at 1000x magnification for 2000 or more porous spherical silica particles. Here, "circularity" is the value obtained by the following formula (1). C = 4πS / L 2 (1)

[0023] In the above formula (1), C represents the circularity, S represents the area (projected area) occupied by the porous spherical silica in the image, and L represents the length of the outer perimeter of the porous spherical silica in the image. The circularity is particularly preferably 0.85 or higher. Furthermore, the porous spherical silica of the present invention typically does not have corners in the particle image obtained by SEM observation at a magnification of 1000x.

[0024] Furthermore, the porous spherical silica of the present invention may be hydrophilic or hydrophobic. Hydrophilic silica can be produced by the manufacturing method described later, while hydrophobic silica can be obtained by adding a surface treatment agent to the reaction system after the gelation step and before the gelled body recovery step in the said manufacturing method, or by drying the gelled body to obtain hydrophilic porous spherical silica and then applying an appropriate silica surface treatment method. Here, "hydrophilic" means that it can be dispersed in water that does not contain organic solvents.

[0025] Because the porous spherical silica of the present invention possesses the above-described properties, it can be suitably used as an abrasive, cosmetic material, and the like. When the porous spherical silica is used as an abrasive, the polishing method is not particularly limited and can be used for both dry and wet polishing. When the porous spherical silica of the present invention is used as an abrasive wheel fixed to a resin pad, the resin penetrates into the pores, making it easy to fix the abrasive grains. Furthermore, when used as a cosmetic material, its high oil absorption properties due to its porous nature and smooth feel due to its spherical shape make it suitable for use as an additive or scrub material in cosmetics such as foundations.

[0026] <Method for producing porous spherical silica> The method for producing the porous spherical silica of the present invention described above is not particularly limited, but the high pore volume and the most frequent pore radius can be easily achieved by using a fumed silica dispersion as a raw material. Generally, fumed silica has a structure in which particulate silica (primary particles) are aggregated. 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, the decrease in pore volume due to drying shrinkage is suppressed, and porous spherical silica with a high pore volume can be obtained without surface treatment.

[0027] More specifically, a W / O emulsion consisting of an aqueous phase in which fumed silica is dispersed and an organic phase mainly composed of a water-insoluble solvent. modulation (W / O emulsion) modulation One method for producing porous spherical silica involves the following steps: first, heating the emulsion to gel the aqueous phase and obtain a porous spherical silica dispersion (gelling step); and second, recovering the resulting porous spherical silica from the liquid (gelled material recovery step). Each step will be described in detail below.

[0028] (W / O emulsion preparation process) A W / O emulsion consisting of an aqueous phase in which fumed silica is dispersed and an organic phase mainly composed of a water-insoluble solvent. modulation The method involves first preparing a dispersion by dispersing fumed silica in the aqueous phase (dispersion preparation step), and then using this with an organic solvent to create an emulsion according to a standard method. modulation It is particularly preferable to employ a method involving emulsification. These will be explained further below.

[0029] (Dispersion liquid preparation process) The dispersion preparation step involves dispersing fumed silica in water to prepare a dispersion.

[0030] The fumed silica used is dispersible in water and can be gelled by heating, pH adjustment, etc. These properties are achieved by having numerous silanol groups on the silica surface; therefore, most fumed silica that has not undergone surface treatment can be used. Furthermore, due to the ease of gelation, a specific surface area of ​​100 m² is sufficient for the fumed silica. 2 / g or more, especially 200m 2 It is preferable to use a product with a value of / g or more. 250m 2 It is even more preferable that the amount is greater than or equal to / g. The larger the specific surface area, the faster the gelation process proceeds, making it easier to gel the droplets (W phase) in which the fumed silica is dispersed. Due to availability, the upper limit is 400m. 2 It is preferable to use a product that is rated at / g. The specific surface area is the value obtained by the nitrogen adsorption BET multipoint method.

[0031] Furthermore, the specific surface area of ​​the porous spherical silica obtained by the method described here can be calculated by subtracting several tens of square meters from the specific surface area of ​​the fumed silica used as the raw material. 2 This value is obtained by subtracting the value per g. Therefore, by appropriately selecting the fumed silica used as a raw material according to the specific surface area of ​​the desired porous spherical silica, the specific surface area of ​​the porous spherical silica can be arbitrarily controlled without changing the manufacturing conditions. In addition, it is possible to use a mixture of fumed silica with different specific surface areas in this invention.

[0032] Fumed silica as described above is commercially available, and for example, various hydrophilic grades of Tokuyama's Rheoroseal, various hydrophilic grades of Nippon Aerosil's Aerosil, and various hydrophilic grades of Asahi Kasei Wacker Silicon's dry silica HDK can be used.

[0033] Furthermore, since fumed silica is generally of high purity and contains almost no impurities such as alkali metals, the alkali metal content of the porous spherical silica produced can also be kept extremely low.

[0034] Water is essential as the solvent in this process, but other solvents may be included as long as they do not inhibit emulsion formation or subsequent gelation. Furthermore, if a latent base is used to promote gelation (as described later), it is advisable to dissolve it in water before dispersing the fumed silica.

[0035] 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 finely disperse it using a crusher or the like. Examples of crushers that can be used for fine dispersion include ball mills, bead mills, vibratory mills, pin mills, atomizers, colloid mills, homogenizers, high-pressure homogenizers, and ultrasonic homogenizers. As for the degree of dispersion after fine dispersion, it is preferable that the D90 value of the dispersion is 0.5 μm or less when the particle size distribution of the dispersion is measured by laser diffraction scattering.

[0036] The silica concentration in the fumed silica dispersion is preferably in the range of 10 wt% to 30 wt%. It is more preferably 15 wt% or higher, and particularly preferably 20 wt% or higher. A higher silica concentration in the fumed silica dispersion leads to a faster gelation rate, but if it is too high, it loses fluidity, making it difficult to form a fumed silica dispersion.

[0037] Furthermore, the gelation of the fumed silica dispersion is accelerated by heating. If gelation of the fumed silica dispersion progresses during the dispersion preparation process, the W phase will have difficulty forming a spherical shape in the subsequent emulsion formation process, and in extreme cases, the emulsion itself may become difficult to form. Therefore, it is preferable to keep the temperature of the fumed silica dispersion at or below room temperature (20°C) during the dispersion preparation process. In cases where the specific surface area or concentration of fumed silica is high and gelation is likely to progress, cooling to a temperature lower than room temperature (preferably 15°C or lower, more preferably 12°C or lower) is also effective.

[0038] (Emulsion process) The W / O emulsion preparation step involves dispersing the fumed silica dispersion obtained in the dispersion preparation step in a water-insoluble solvent to form a W / O emulsion. By forming such a W / O emulsion, the dispersed fumed silica dispersion becomes spherical due to surface tension, etc., and by gelling the fumed silica dispersion dispersed in the water-insoluble solvent in this spherical shape, a spherical gelled body can be obtained.

[0039] The water-insoluble solvent used in this manufacturing method can be any solvent that is hydrophobic enough to form an emulsion with the fumed silica dispersion. Suitable solvents include, for example, organic solvents such as hydrocarbons and halogenated hydrocarbons. More specifically, water-insoluble solvents such as hexane, heptane, octane, nonane, decane, liquid paraffin, dichloromethane, chloroform, carbon tetrachloride, and dichloropropane are examples. Among these, hexane, heptane, and decane, which have appropriate viscosity, are preferable. Multiple solvents may be mixed and used as needed. Furthermore, hydrophilic solvents such as lower alcohols can also be used in combination (as a mixed solvent), as long as they can form an emulsion with the fumed silica dispersion.

[0040] The amount of water-insoluble solvent used is not particularly limited as long as it can form a W / O emulsion, but generally, an amount of 1 to 10 parts by volume of water-insoluble solvent is used per 1 part by volume of fumed silica dispersion.

[0041] In this manufacturing method, it is preferable to add a surfactant when forming the above-mentioned W / O emulsion. Any known surfactant used for W / O emulsion formation can be used without limitation, and anionic surfactants, cationic surfactants, and nonionic surfactants can all be used. Among these, nonionic surfactants are preferred because they facilitate W / O emulsion formation and are less likely to cause alkali metal contamination. In particular, surfactants with an HLB value of 3 or more and 5 or less, which indicates the degree of hydrophilicity and hydrophobicity of the surfactant, can be suitably used. Here, "HLB value" refers to the HLB value by the Griffin method. Specific examples of surfactants that can be suitably used include sorbitan monooleate, sorbitan monostearate, and sorbitan monosesquioleate.

[0042] The amount of surfactant used is no different from the typical amount used to form a W / O emulsion. Specifically, a range of 0.05 g to 10 g per 100 ml of fumed silica dispersion can be suitably used.

[0043] When forming a W / O emulsion, known methods for forming W / O emulsions can be used to disperse the fumed silica dispersion in a water-insoluble solvent. From the viewpoint of ease of industrial production, emulsion formation by mechanical emulsification is preferred, and specifically, methods using a mixer, homogenizer, etc., can be exemplified. Preferably, a homogenizer can be used. This emulsification process yields an emulsion with a sharp particle size distribution of aqueous phase droplets, and therefore the particle size distribution of the final spherical porous silica also becomes sharp.

[0044] (Gelation process) The gelation step, following the W / O emulsion preparation step, is a step in which the fumed silica dispersion is gelled while droplets of the fumed silica dispersion are dispersed in a water-insoluble solvent. This gelation can be carried out by known methods. For example, gelation can be easily promoted by heating to a high temperature or by adjusting the pH of the fumed silica dispersion to a weakly acidic or basic state. The above methods are preferred because they allow for proactive control of the reaction. The pH of a fumed silica dispersion prepared by the above method and without pH adjustment is generally in the range of 3.0 to 4.5.

[0045] When heating is performed, the boiling point of each solvent used should not be exceeded. 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.

[0046] The above pH adjustment can be easily performed by first mixing a substance that exhibits basicity (referred to as a "latent base"), such as urea, into a fumed silica dispersion by thermal decomposition through heating, and then raising the pH by heating during gelation, or by adding a base to the emulsion while maintaining a W / O emulsion formation state by stirring with a mixer or the like.

[0047] Specific examples of the base include ammonia; tetraalkylammonium hydroxides such as tetramethylammonium hydroxide (TMAH); amines such as trimethylamine; alkali hydroxides such as sodium hydroxide; alkali metal carbonates such as sodium carbonate and sodium bicarbonate; and alkali metal silicates. The stirring intensity should be strong enough to cause mixing between the W / O emulsion and the base.

[0048] Among these methods, the thermal decomposition of latent bases such as urea, or the use of ammonia, tetraalkylammonium hydroxides, or amines is preferred because it does not involve the introduction of metal elements. When using ammonia for pH adjustment, it may be blown in as a gas or added as aqueous ammonia. pH adjustment using urea is particularly preferred because it allows for uniform pH adjustment throughout the mixture through heating.

[0049] When adjusting the pH to promote gelation, it is particularly preferable to adjust the amount added so that the pH value of the fumed silica dispersion rises to approximately 4.5 to 8.0. The same applies when using latent bases, but if urea is used, for example, the specific amount added is preferably 1 wt% or more relative to the fumed silica dispersion, and particularly preferably 2 wt% or more. The upper limit is preferably 7 wt% or less, and more preferably 5 wt% or less.

[0050] By adjusting the gelation conditions and gelation time described above, the fracture strength of the porous spherical silica can be controlled. The higher the gelation temperature and the longer the gelation time, the more the gelation progresses, and the stronger the bonds between the particulate silica particles (primary particles), resulting in a stronger fracture strength for the porous spherical silica. When performing the heating and pH adjustment described above, it is preferable to stir the mixture to prevent aggregation of the gels. While known methods are generally used for stirring, a mixer equipped with stirring blades can be used as a specific example.

[0051] Furthermore, after gelation, the dispersed phase changes from a liquid state to a solid state, so the system is not a W / O emulsion, but rather a dispersion (suspension) in which a solid (gelled substance) is dispersed in a hydrophobic solvent.

[0052] (Gelated material recovery process) In this manufacturing method, the gelled material produced as described above is recovered from the liquid. While general solid-liquid separation methods such as filtration and centrifugation can be used to recover the gelled material, WO phase separation may be performed prior to recovery. WO phase separation involves separating the gelled material dispersion into two layers, the O phase and the W phase, and is generally also known as dissolution. Here, the gelled material obtained in the gelation step is present in the separated W phase. Separating this from the O phase facilitates the recovery of the gelled material by solid-liquid separation methods such as filtration.

[0053] As for the WO phase separation method, any known method for demudging can be appropriately selected and implemented, but preferably, a certain amount of water-soluble organic solvent, which is normally used in demudging, is added to the gelled dispersion and heated to separate it into the O phase and the W phase. After this step, generally, the upper layer is the O phase (a layer mainly containing the organic solvent) and the lower layer is the W phase (an aqueous layer containing aqueous organic solvent and the gelled material).

[0054] Examples of the above-mentioned water-soluble organic solvents include acetone, methanol, ethanol, and isopropyl alcohol. Of these, isopropyl alcohol can be used particularly favorably.

[0055] The amount of water-soluble organic solvent added is preferably adjusted according to the type and amount of surfactant with an HLB of 3 to 5 used during emulsion formation. For example, when sorbitan monooleate is used as the surfactant, the water-soluble organic solvent can be added in an amount of about 1 / 6 to 1 / 2 by mass (water-soluble organic solvent / water-insoluble organic solvent) relative to the mass of the water-insoluble organic solvent, and after stirring as necessary, the mixture can be allowed to stand to dissolve the emulsion effectively.

[0056] In WO phase separation, surfactants migrate (are extracted) to the O phase. By removing the O phase, porous spherical silica free from surfactant impurities can be obtained.

[0057] Furthermore, the heating temperature range is 50°C or higher, preferably around 50-80°C, and more preferably around 60-70°C.

[0058] As described above, after adding the water-soluble organic solvent to the gel dispersion, it is preferable to stir to prevent aggregation of the gels. While known methods are generally used for stirring, a mixer with a stirring blade can be used as a specific example. The degree of mixing is not particularly limited, but it should be sufficient for the liquid surface to rotate due to stirring. For example, stirring with a mixer should be 0.1-3.0 kW / m². 3 Preferably 0.5 to 1.5 kW / m² 3 Furthermore, a stirring time of 0.5 to 24 hours, preferably 0.5 to 1 hour, is appropriate.

[0059] After the WO phase separation described above, the W phase containing the gelled material is recovered. Specifically, the O phase (upper layer) can be separated and removed by decantation or the like.

[0060] The porous spherical silica of the present invention can be obtained by recovering the gelled material contained in the recovered W phase through solid-liquid separation and drying. While general drying methods can be used, it is preferable to employ a fluid drying method in particular to suppress the aggregation of particles. Specifically, this includes vibration drying, airflow drying, and spray drying. Furthermore, the aggregation of particles can also be suppressed by replacing the solvent with an organic solvent with low surface tension before drying, or by rinsing the cake after solid-liquid separation with these organic solvents. The organic solvent is preferably water-soluble because it facilitates the replacement of water remaining inside the pores. Specific examples of water-soluble organic solvents include acetone, methanol, ethanol, and isopropyl alcohol. By adjusting the drying shrinkage inside the pores through solvent substitution or rinsing, it is possible to control the pore volume beyond moderate drying shrinkage. When performing solvent substitution, lowering the concentration of the water-soluble organic solvent and increasing the proportion of water will increase drying shrinkage and reduce the pore volume. Conversely, increasing the concentration of the water-soluble organic solvent will suppress drying shrinkage and increase the pore volume. When performing rinsing, reducing the amount of water-soluble organic solvent used will reduce the pore volume. The drying temperature is preferably above the boiling point of the solvent with the highest boiling point among the various solvents used from the preparation to the drying of the fumed silica dispersion, and the drying is preferably carried out under atmospheric pressure or reduced pressure. Note that "above the boiling point" refers to the boiling point of the solvent under the pressure used during drying.

[0061] The porous spherical silica of the present invention may be further calcined after drying. Calcination can remove organic matter and adjust the test force at fracture. If the purpose is to remove organic matter, the calcination temperature should be above the boiling point of each organic matter used in the manufacturing method of the present invention. If the purpose is to adjust the test force at fracture, the calcination conditions should be adjusted to obtain the target value. Generally, the longer the calcination time and the higher the calcination temperature, the higher the test force at fracture. Specifically, calcining at a temperature of 700 to 1000°C for about 10 hours can increase the test force at fracture without causing particle aggregation. The calcination temperature is preferably 750°C or higher, and more preferably 850°C or higher. The calcination time is preferably 8 hours or more, and more preferably 9 hours or more. Note that calcining at temperatures of 1000°C or higher tends to cause particle aggregation.

[0062] Dry porous spherical silica, or dried and calcined porous spherical silica, may be further crushed. Crushing can be carried out using general-purpose pulverizers, and specific methods using ball mills, pin mills, vibratory mills, bead mills, jet mills, and mascolloiders (trade name) are known. The crushing conditions should be adjusted as needed depending on the equipment used, as long as the particles are not destroyed and the aggregates are broken down.

[0063] In the above manufacturing method, the particle size of the porous spherical silica obtained is approximately equal to the droplet (W phase) diameter of the fumed silica dispersion in the W / O emulsion prepared in the emulsion step. Therefore, it is necessary to set the dispersion conditions so that the particle size falls within the desired range. Various methods for controlling droplet diameter in W / O emulsions are known, and these techniques can be appropriately selected and applied. Known methods can be used to adjust the droplet size, and specifically, these include adjusting the amount of surfactant added and adjusting the shear force applied during emulsification by changing the rotation speed, flow rate, etc. When adjusting by 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. Similarly, when adjusting by shear force, a larger shear force tends to result in finer droplets, while a smaller shear force tends to result in larger droplets.

[0064] Furthermore, the pore volume can be controlled by drying shrinkage. Known methods can be used to control drying shrinkage, specifically, by solvent substitution or rinsing as described above, or by modifying the drying process, such as freeze-drying or supercritical drying. In addition, as in the manufacturing method of the present invention, by using fumed silica as a raw material, the most frequent value of the high pore radius is obtained due to the aggregated structure of the fumed silica. The specific surface area can be adjusted by appropriately selecting the specific surface area of ​​the fumed silica used as a raw material, and can also be adjusted by the gelation time. Note that the shorter the gelation time, the higher the specific surface area.

[0065] The test force at fracture increases with higher gelation temperatures during the gelation process, decreases with lower temperatures, increases with longer gelation times, and decreases with shorter gelation times. It can also be controlled by firing conditions; the longer the firing time and the higher the firing temperature, the higher the test force at fracture.

[0066] As mentioned above, the alkali metal content can be easily reduced by using fumed silica that is substantially free of alkali metals as a raw material, and by using other raw materials that are also substantially free of alkali metals, and by having a person skilled in the art take sufficient care to avoid contamination (impurity inclusion) during manufacturing. Furthermore, if the aim is to reduce the alkali metal content even further, the cake may be washed with water or an organic solvent after solid-liquid separation and before drying. [Examples]

[0067] The following are examples illustrating the present invention in detail. However, the present invention is not limited to these examples.

[0068] <Evaluation Method> The following items were evaluated for the manufactured porous spherical silica.

[0069] (Measurement of particle size distribution and volume-based cumulative diameter using laser diffraction) 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, manufactured by BRANSON). The particle size distribution of the dispersion was measured using an LS 13 320, manufactured by Beckman Coulter, Inc. The refractive index of the solvent was set to 1.374, and the refractive index of the particles was set to 1.46. From the obtained particle size distribution, the cumulative 50% diameter, cumulative 10% diameter, and cumulative 90% diameter based on volume were evaluated.

[0070] (Measurement of BJH pore volume, pore radius (mode), and BET specific surface area) BJH pore volume, pore radius (mode), and BET specific surface area were measured using BELSORP-mini (manufactured by Nippon Bell Co., Ltd.) according to the definitions described above.

[0071] (Test force at which sample failure was observed) The "test force at which sample fracture was observed" was measured using a microcompression tester (Shimadzu Corporation, MCT-W510-J) according to the definition described above. Measurements were performed under two conditions: loading speeds of 38.7363 mN / sec and 0.4462 mN / sec. The loading time was 10 seconds in both cases, and a 200 μm diameter indenter was used for measurement.

[0072] (Alkali metal content) 1 g of porous spherical silica was dissolved in 10 ml of nitric acid and 10 ml of hydrofluoric acid. The solution was heated at 180°C for 4 hours and evaporated to dryness. After cooling to room temperature, 2 ml of nitric acid and 18 ml of ultrapure water were added to make up 20 ml to obtain the measurement sample. The alkali metal content of the obtained measurement sample was measured using an inductively coupled plasma emission spectrometer (Thermo Scientific, ICAP650DUO). (Average circularity) For over 2000 porous spherical silica particles, SEM images were observed at a magnification of 1000x using a SEM (Hitachi High-Technologies S-5500, acceleration voltage 3.0kV, secondary electron detection). Image analysis was performed on these images, and the average circularity was calculated according to the definition described above.

[0073] <Example 1> (Dispersion liquid preparation process) To 200 ml of deionized water containing 6.65 g of urea, 66 g of RheoroSeal QS-30 (manufactured by Tokuyama Corporation) was added while stirring in a homogenizer (IKA, T25BS1) to pre-disperse the fumed silica. After pre-dispersion, the fumed silica dispersion was obtained by fine-dispersing it using an ultrasonic homogenizer (BRANSON, Sonifier SFX250). The particle size distribution of the dispersed liquid was measured by laser diffraction scattering, and the D90 value was 0.19 μm. The dispersion preparation process was carried out in a chiller cooled to 10°C.

[0074] (W / O emulsion preparation process) Using the above method modulation65.5 g was taken from the fumed silica dispersion, and 129 g of decane containing 0.75 g of sorbitan monooleate (Kao Corporation, Leodol SP-010V) was added. The mixture was then stirred for 3 minutes at 4000 rpm using a homogenizer to obtain a W / O emulsion.

[0075] (Gelation process) The obtained W / O emulsion was gelled by holding it in an 80°C water bath for 3 hours while stirring at 300 rpm using a four-blade paddle with a diameter of 60 mm, a wingspan of 20 mm, and an angle of 45 degrees.

[0076] (Gelated material recovery process) 77g of isopropyl alcohol and 52g of water were added and stirred with a stirring blade while maintaining a temperature of 70°C for 30 minutes. After that, the mixture was allowed to stand, separating into two layers: the O phase as the upper layer and the W phase as the lower layer.

[0077] Next, the O phase and W phase were separated by decantation, and the W phase was recovered.

[0078] The obtained gelled material was filtered from the W phase using a suction filter. The recovered gelled material was dried in a vacuum dryer at 150°C for 12 hours. The physical properties of the porous spherical silica obtained in this manner are shown in Table 1 (similarly, the physical properties of the porous spherical silica obtained in the following examples and comparative examples are also shown in Table 1).

[0079] <Example 2> Porous spherical silica was obtained in the same manner as in Example 1, except that the rotation speed of the homogenizer in the W / O emulsion preparation step was changed to 8600 rpm, and after drying, it was calcined at 800°C for 10 hours. <Example 3> Porous spherical silica was obtained in the same manner as in Example 2, except that the fumed silica used as the raw material was changed from Rheoloseal QS-30 to Rheoloseal QS-40 (manufactured by Tokuyama Corporation) and the gelation time was set to 1 hour. modulation The D90 value of the fumed silica dispersion after the process was 0.15 μm. <Example 4> In the W / O emulsion preparation step, the homogenizer was replaced with a stirring blade, the rotation speed was set to 400 rpm, and the stirring time to 1 hour. Otherwise, porous spherical silica was obtained in the same manner as in Example 1.

[0080] <Example 5> Porous spherical silica was obtained in the same manner as in Example 1, except that the rotation speed of the homogenizer in the W / O emulsion preparation step was changed to 10,000 rpm, and after drying, it was calcined at 900°C for 10 hours. <Example 6> Porous spherical silica was obtained in the same manner as in Example 2, except that the rotation speed of the homogenizer in the W / O emulsion preparation step was changed to 3000 rpm and the cake was rinsed with 100 g of isopropyl alcohol before drying. <Example 7> Porous spherical silica was obtained in the same manner as in Example 2, except that the firing process involved firing at 600°C for 1 hour.

[0081] <Comparative Example 1> Dispersion of Example 1 modulation In the same way as the process modulation The fumed silica dispersion was spray-dried and then calcined at 600°C for 1 hour to obtain porous spherical silica. <Comparative Example 2> To a sodium silicate aqueous solution with a molar ratio of SiO2 / Na2O of 3.1 (9g / 100mL), 10g / 100mL of sulfuric acid was added to adjust the pH to 2.9, resulting in 500mL of silica sol. modulation The silica sol was then divided into 66.5 g portions, and the fumed silica dispersion was replaced with the silica sol. The W / O emulsion was prepared in the same manner as in Example 2. modulation The process involved a gelation step and a gel recovery step to obtain a gel. The obtained gel was placed in a pressure filter and washed with water until the electrical conductivity of the filtrate was 100 μS / cm or less. At this time, 5 L of deionized water was required until the electrical conductivity of the filtrate reached the aforementioned value. The washed gel was dried in a vacuum dryer at 150°C for 12 hours to obtain porous spherical silica. <Comparative Example 3> To a mixture of 6.4 mL of tetraethyl orthosilicate and 5.26 mL of ethanol, 10.8 mL of deionized water, adjusted to a pH of 2 with hydrochloric acid, is added to form a silica sol. modulation The molar ratio of tetraethyl orthosilicate:exchanged water:ethanol was 1:20:3. 66.5 g of this silica sol was taken out, and porous spherical silica was obtained in the same manner as in Example 2, except that the fumed silica dispersion was replaced with the silica sol.

[0082] [Table 1]

[0083] <Evaluation Results> (Examples 1-7) As shown in Table 1, in Examples 1 to 7, porous spherical silica with a narrow particle size distribution (D10 / D90 of 0.3 or higher) and an alkali metal content reduced to 50 ppm or less was successfully produced. This is due to the use of fumed silica as a raw material and molding by the emulsion method, as in the manufacturing method of the present invention. Furthermore, all porous spherical silica obtained in Examples 1 to 7 had a D50 in the range of 2 to 200 μm, a pore volume in the range of 0.5 to 8 ml / g by the BJH method, a mode of pore radius in the range of 5 nm or more and 50 nm or less by the BJH method, and a specific surface area of ​​100 m² by the BET method. 2 / g or more, 400m 2 The range is less than or equal to / g, and the arithmetic mean of the "test force at which sample fracture was observed" for 10 particles, calculated according to the method specified in JIS Z8844:2019 with a loading rate of 38.7363 mN / sec, is 1.0 × 10 1 ~1.0×10 2 The value is in the range of mN, and the arithmetic mean of the "test force at which sample fracture was observed" for 10 particles, calculated with a loading speed of 0.4462 mN / sec, is 1.0 × 10⁻⁶. -1 ~1.0×10 1 It was in the range of mN. In Examples 1 to 7, porous spherical silica with various D50 values ​​was obtained. In all cases, the D50 value was controlled by adjusting the droplet size of the W / O emulsion by changing the rotation speed during emulsification or the emulsification equipment. The manufacturing method of the present invention makes it possible to easily control the D50 value of porous spherical silica without major changes to the manufacturing process.

[0084] (Example 3) The porous spherical silica of Example 3 exhibits a higher specific surface area compared to Example 1. This is because fumed silica with a higher specific surface area than that of Example 1 was used, and the decrease in specific surface area due to the progression of gelation (maturation) was suppressed by shortening the gelation time. Thus, the specific surface area can be arbitrarily adjusted by appropriately selecting the fumed silica used as a raw material and adjusting the gelation time. (Example 5) The porous spherical silica of Example 5 exhibits a higher fracture force compared to Examples 1 and 2. This is due to the addition of a firing process compared to Example 1, and the higher firing temperature compared to Example 2. Thus, it is possible to control the fracture force by adding a firing process or by adjusting the firing conditions during the firing process.

[0085] (Comparative Example 1) The porous spherical silica of Comparative Example 1, formed by spray drying, has a D10 / D90 ratio of less than 0.3 and exhibits a wide particle size distribution. Thus, it is difficult to obtain porous spherical silica with a narrow particle size distribution and a D10 / D90 ratio greater than 0.3 using spray drying. (Comparative Example 2) The porous spherical silica of Comparative Example 2, which used sodium silicate as a raw material, exhibited a higher alkali metal content compared to Examples 1-7. This high alkali metal content is thought to be due to the residual sodium from the sodium silicate in the porous spherical silica. In Comparative Example 2, after the gelled material recovery process, the gelled material was thoroughly washed with deionized water until the electrical conductivity of the filtrate was 100 μS / cm or less, but the alkali metal content could not be reduced. Thus, it is difficult to obtain porous spherical silica with reduced alkali metal content when using sodium silicate as a raw material. (Comparative Example 3) The porous spherical silica of Comparative Example 3, which used tetraethyl orthosilicate as a raw material, had a circularity of less than 0.8. This is thought to be because tetraethyl orthosilicate generates ethanol during gelation, destabilizing the emulsion and making it difficult to maintain a spherical shape. Due to the above characteristics, tetraethyl orthosilicate is unsuitable for molding into a spherical shape by the emulsion method.

Claims

1. The volume-based cumulative 50% diameter (D50) measured by laser diffraction scattering is in the range of 2 to 200 μm. Similarly, the ratio of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) (D10 / D90) is 0.3 or greater. The pore volume measured by the BJH method is 0.5 ml / g or more and 8 ml / g or less. According to the method specified in JIS Z8844:2019, the arithmetic mean of the "test force at which sample fracture was observed" for 10 particles, calculated at a loading rate of 38.7363 mN / sec, is 1.0 × 10⁻⁶. １ ~1.0 x 10 ２ It is mN, Porous spherical silica characterized by having an alkali metal content of 50 ppm or less.

2. The volume-based cumulative 50% diameter (D50) measured by laser diffraction scattering is in the range of 2 to 200 μm. Similarly, the ratio of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) (D10 / D90) is 0.3 or greater. The pore volume measured by the BJH method is 0.5 ml / g or more and 8 ml / g or less. According to the method specified in JIS Z8844, the arithmetic mean of the "test force at which sample fracture was observed" for 10 particles, calculated at a loading rate of 0.4462 mN / sec, is 1.0 × 10⁻⁶. －１ ~1.0 x 10 １ It is mN, Porous spherical silica characterized by having an alkali metal content of 50 ppm or less.

3. The volume-based cumulative 50% diameter (D50) measured by laser diffraction scattering is in the range of 2 to 200 μm. Similarly, the ratio of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) (D10 / D90) is 0.3 or greater. The pore volume measured by the BJH method is 0.5 ml / g or more and 8 ml / g or less. The most frequent value of the pore radius according to the BJH method is between 5 nm and 50 nm. The specific surface area calculated by the BET method is 100 m². ２ / g or more, 400m ２ / g or less, Porous spherical silica characterized by having an alkali metal content of 50 ppm or less.

4. The porous spherical silica according to any one of claims 1 to 3, wherein the pore volume obtained by the BJH method is 1.4 ml / g or more and 8 ml / g or less.

5. Abrasive containing porous spherical silica as described in any one of claims 1 to 4.

6. A cosmetic product comprising porous spherical silica according to any one of claims 1 to 4.

7. A resin composition comprising porous spherical silica according to any one of claims 1 to 4.

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