Porous aggregate, method of manufacturing the same, and use thereof

Abstract

To provide a novel porous aggregate made of silica nanoparticles which are useful mainly as abrasive grains and have an average crushing strength controlled within in a specific range.SOLUTION: The present invention relates to a porous aggregate made of metal oxide, which satisfies an average crushing strength Cs of 0.02 to 1 MPa, an average circularity of 0.5 or more, and an equivalent circle diameter (D50) 1 to 100 μm. The porous aggregate of the present invention preferably has a mode of pore diameter of 5 to 50 nm. Further, the porous aggregate of the present invention preferably has a pore volume of 0.5 to 5 ml / g. Further, the porous aggregate of the present invention preferably has a specific surface area of 50 to 800 m2 / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel, easily disintegrable porous aggregate suitable for use as an ultra-precision polishing wheel, a cosmetic additive, etc., and a method for producing the same. [Background technology]

[0002] In the polishing process of semiconductor wafers, when using a loose abrasive lapping method, a constant supply of lapping agent (a mixed slurry of abrasive grains and processing fluid) is required to maintain a stable processing state at all times. Normally, a highly viscous oil-based liquid is used, and the disposal of used lapping agent and cleaning of the equipment takes time and money, making automation difficult.

[0003] Examples of fixed abrasive machining tools that can perform mirror polishing in a relatively short time without polluting the surrounding environment and that can improve productivity by enabling automation between the devices used in the preceding and following processes are described in Patent Documents 1 and 2.

[0004] The polishing wheel, which is essential for this polishing method, is made of an agglomerate of ultrafine abrasive grains solidified with resin and held on a hard base.It can be attached to an appropriate polishing device, so polishing can be performed without using loose abrasive grains (lapping agent) (Patent Document 1).

[0005] In particular, there has been a recent demand for ultra-precision machining that achieves surface roughness on the nanometer order. The abrasive grains used in these grinding wheels are primary particles of inorganic oxides with diameters ranging from a few nanometers to several tens of nanometers. However, during grinding wheel formation, the primary particles aggregate, and it is impossible to control the aggregation force. If the aggregation force is strong, it becomes impossible to avoid scratches on the polished surface (Patent Document 2).

[0006] Therefore, it is recommended to use aggregates that are easy to control particle size and have good dispersibility in resin. During polishing and grinding, it is important that the aggregates quickly disintegrate due to shear forces, evenly distributing the nanometer-order primary particles that become abrasive grains.

[0007] On the other hand, regarding the polishing pressure (substrate load) in the lapping process, according to multiple literature information (Patent Documents 3 to 5), using a pressure of 0.02 MPa or less is suitable for achieving both high processing efficiency and high quality.

[0008] In light of the above, the characteristics of the agglomerates suitable for the grinding wheels are that they have as weak a cohesive force as possible, as long as they do not break down during production, transportation, or pad formation. Furthermore, it is preferable that they undergo moderate deformation and have high adhesion to the substrate without breaking down under pressure of 0.02 MPa or less and generating micron-order fragments.

[0009] According to Patent Document 6, porous agglomerated particles having an average crushing strength of 1.8 MPa can be obtained while maintaining a spherical shape, but the average crushing strength is not sufficiently low.

[0010] The reason why the average crushing strength cannot be reduced is presumably due to the manufacturing method.

[0011] Among methods for granulating porous aggregates using metal oxide nanoparticles as raw materials, the spray drying method is the most commonly known method (Patent Document 7).

[0012] However, because the particle size distribution of the spray liquid must be as monodisperse as possible, it is necessary to separate coarse particles by using strong centrifugal force or disperse them by using high shear force. This requires pretreatment using so-called physical methods. This raises concerns about the high energy consumption and quality stability due to the increased number of production steps.

[0013] In the case of spray drying, it is common to perform a heat treatment at a temperature range of 150°C to 600°C to increase the bonding stability of the fine particles, which increases the average crushing strength of the aggregates. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Patent Publication No. 2000-198073 [Patent Document 2] Patent Publication No. 2000-190228 [Patent Document 3] Patent Publication No. 2007-208220 [Patent Document 4] Patent Publication No. 2016-092045 [Patent Document 5] Patent Publication No. 2018-145225 [Patent Document 6] WO2019 / 131873 [Patent Document 7] Patent Publication No. 2010-138021 Summary of the Invention [Problem to be solved by the invention]

[0015] In light of the above background, an object of the present invention is to provide a novel porous aggregate of silica nanoparticles, which is useful primarily as abrasive grains and has an average crushing strength controlled within a specific range. [Means for solving the problem]

[0016] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that porous aggregate particles made of silica nanoparticles with an average crushing strength controlled within a specific range can be prepared by using the following original techniques in a process for producing porous aggregates made of silica nanoparticles, thereby completing the present invention.

[0017] That is, the present invention relates to a porous aggregate made of a metal oxide, which has an average crushing strength Cs of 0.02 to 1 MPa, a circularity of 0.5 or more, and a circle-equivalent diameter (D50) of 1 to 100 μm. , specific surface area is 50 to 800 m 2 / g The porous aggregate is characterized by satisfying the following:

[0018] In another aspect, the present invention provides a method suitable for producing the porous aggregate of the present invention, comprising: a dispersing step of mixing metal oxide particles with a hydrophobic solvent to obtain a dispersion; an extraction step of mixing the dispersion liquid with ammonia water having a pH of 12 or higher and containing 1 to 30 mass % ammonia in a ratio of 0.1 to 1 part by weight of ammonia water to 1 part by weight of the hydrophobic solvent, thereby extracting the metal oxide particles from the hydrophobic solvent into the ammonia water, thereby obtaining a mixed liquid consisting of an upper layer of hydrophobic solvent and a lower layer of ammonia water containing the metal oxide particles; an emulsification step of adding a surfactant to the mixed liquid to prepare a W / O emulsion; an aggregation step of feeding the W / O emulsion to 0.5 to 5 parts by weight of an alcohol having 4 or less carbon atoms per 1 part by weight of the W / O emulsion to form an upper O phase and a lower W phase, and generating water-insoluble aggregates in the W phase; a solid-liquid separation step of obtaining the agglomerate by solid-liquid separation; a washing step of washing the aggregate to obtain a washed product from which the surfactant has been removed; a drying step of drying the washed material to obtain a porous aggregate; The present invention provides a method for producing a porous aggregate, comprising: [Effects of the Invention]

[0019] When the porous aggregates of the present invention are dispersed in a resin and solidified to form a grinding wheel, they have a weak average crushing strength, which is also controllable. Therefore, during ultra-high precision polishing and grinding, the porous aggregates are expected to quickly disintegrate due to shear forces, enabling the uniform supply of primary particles on the nanometer order (nm size) that will become abrasive grains.

[0020] Furthermore, because the raw material fumed silica forms a network structure, the porous aggregates can have a large internal pore volume while maintaining the high specific surface area of ​​fumed silica, making them suitable for a variety of carriers, including cosmetic additives, carriers for active pharmaceutical ingredients, and chromatography packings. DETAILED DESCRIPTION OF THE INVENTION

[0021] <Porous aggregate> The porous aggregate of the present invention is a porous aggregate made of a metal oxide, characterized by an average crushing strength Cs of 0.02 to 1 MPa, a circularity of 0.5 or more, and a circle-equivalent diameter (D50) of 1 to 100 μm. Therefore, because the average crushing strength is in a weak range and can be controlled, it is believed that during ultra-high precision polishing and grinding, the aggregates quickly disintegrate due to shear force, allowing for an even supply of primary particles on the order of nanometers (nm) that become abrasive grains.

[0022] (average crushing strength) The porous aggregate of the present invention has an arithmetic mean value of the "pressure at which sample destruction is observed" ("average crushing strength Cs") of 0.02 to 1.0 MPa, determined according to the method specified in JIS Z8844:2019. An average crushing strength within this range results in particles with excellent pressure disintegration properties. That is, the particles disintegrate when a specific load is applied. When used as an abrasive for industrial products, the particles are less likely to scratch the object being polished, and when used as a scrubbing agent for cosmetic products, the particles can reduce the burden on the skin. If the average crushing strength is less than 0.02 MPa, the particles will disintegrate under vertical polishing pressure (substrate load), resulting in poor adhesion between the polishing pad and the substrate and reduced processing efficiency. Furthermore, the internal space required for a carrier cannot be maintained. If the average crushing strength is 1.0 MPa or higher, the desired disintegration properties cannot be achieved. The average crushing strength is preferably 0.02 to 1.0 MPa, and more preferably 0.2 to 1.0 MPa.

[0023] (average circularity) The "average circularity" is a value obtained by determining the value C (circularity) defined by the following formula (10) for each particle from an SEM image observed using a scanning electron microscope (SEM) (image analysis), and calculating this circularity C as the arithmetic mean value for, for example, 1500 to 2000 particles (image analysis method). Note that in this case, a group of particles forming one aggregate particle is counted as one particle. C=4πS / L 2 (1) [In formula (1), S represents the area (projected area) that the particle occupies in the image, and L represents the length (perimeter) of the outer periphery of the particle in the image.] As the average circularity increases from 0.8 and approaches 1, the individual particles constituting the metal oxide become closer to a perfect sphere and the number of agglomerated particles decreases. Therefore, a high average circularity improves rolling properties when used as a filler, resulting in excellent packing properties. If the circularity of the porous aggregate of the present invention is less than 0.5, the flowability, packing density, and dispersibility are poor, making it impractical. Furthermore, horizontal scratches are likely to occur during polishing. The circularity is preferably 0.5 to 1.0, more preferably 0.8 to 1.0.

[0024] (circle equivalent diameter) The "equivalent circle diameter" is a value obtained by converting the area S (projected area) of 1,500 to 2,000 particles in the SEM image into the diameter of a circle equivalent to the area S (projected area) of the image (image analysis method). From the obtained particle size distribution, the cumulative 50% diameter based on the number is defined as the equivalent circle diameter. If the equivalent circle diameter of the porous aggregate of the present invention exceeds 100 μm, the packing density will be poor and it will not be practical. On the other hand, if it is less than 1 μm, the powder will have poor fluidity and workability will be poor. The equivalent circle diameter is preferably 1 to 100 μm, more preferably 5 to 30 μm. Such particles are particularly suitable for use as abrasive grains for polishing pads or as materials for cosmetics.

[0025] In order to achieve both measurement accuracy and calculation efficiency in the average circularity and the equivalent circle diameter, the number of particles used is preferably 500 to 5,000, and more preferably 1,500 to 2,000.

[0026] (Measurement of specific surface area, pore volume, and mode of pore diameter) The specific surface area, pore volume, and mode (peak) of pore diameter can be measured using a specific surface area / pore size distribution measuring device. (Most frequent pore size) The mode of pore diameter is the value of the pore diameter at which the cumulative pore volume (volume distribution curve) based on the logarithm of the pore diameter takes the most frequent peak value. The porous aggregate of the present invention preferably has a pore size mode of 5 to 50 nm, more preferably 15 to 50 nm. When the pore size mode is within the above range, the particle's own easy disintegration property, the particle-resin bond strength, and the particle's internal supporting capacity are all optimal. If the pore size mode is less than 5 nm, the particles may not have the desired disintegration property, and the resin may not easily penetrate into the particle, resulting in poor interlocking between the particles and the resin. On the other hand, if the pore size mode exceeds 50 nm, the support's supporting capacity tends to be poor.

[0027] (pore volume) The porous aggregate of the present invention preferably has a pore volume measured by the BJH method of 0.5 to 5 ml / g, more preferably 1.0 to 4.0 ml / g. When the pore volume is within the above range, the desired crushing strength is easily obtained. (specific surface area) The porous aggregate of the present invention has a specific surface area of ​​50 to 800 m by the BET method. 2 / g, and 100 to 400m 2 / g. When the specific surface area is within the above range, particles that are easily disintegrable and have a good surface adsorption ability are easily obtained. 2 / g or more becomes difficult to obtain, and 50m 2 If the value is less than 1 / g, the strength increases and the surface adhesion tends to decrease.

[0028] <Method of manufacturing porous aggregate> According to the manufacturing method of the present invention, the process of manufacturing a porous aggregate does not require a mechanical pretreatment step of the dispersion (such as filtration or classification to prevent nozzle clogging). Furthermore, the process of insolubilizing the aggregate by heating at a high temperature, i.e., a calcination step, is also not required. This allows for easy manufacturing of porous aggregates.

[0029] The following embodiments are examples of the present invention, and the present invention is not limited to these embodiments. Furthermore, unless otherwise specified, the expression "A to B" for a numerical range means "A or more and B or less." In such expressions, when a unit is assigned only to the numerical value B, the unit also applies to the numerical value A. Below, the manufacturing method of the present invention will be explained step by step.

[0030] (Dispersion process) In the dispersion step, metal oxide particles and a hydrophobic solvent are mixed to obtain a dispersion.

[0031] The metal oxide particles are ultrafine particles produced by a gas phase method, and those with an average particle size of several nanometers (several nm) to several tens of nanometers (several tens of nm) are preferably used. For example, metal oxide nanoparticles SiO2, TiO2, ZnO, and Al2O3 manufactured by Kanto Chemical Co., Ltd., various hydrophilic grades of Reolosil manufactured by Tokuyama Corporation, various hydrophilic grades of Aerosil manufactured by Nippon Aerosil Co., Ltd., various hydrophilic grades of dry silica HDK manufactured by Wacker Asahi Kasei Silicone Co., Ltd., zirconia powders Zirconeo-Cp and Zirconeo-Rp manufactured by ITEC Co., Ltd., and gallium oxide nanoparticles manufactured by Rare Metal Materials Research Institute Co., Ltd. can be used.

[0032] Furthermore, fumed silica is highly pure and contains almost no impurities such as alkali metals, and is therefore preferred because it allows the produced porous aggregate to have an extremely low alkali metal content.

[0033] The hydrophobic solvent used to prepare the dispersion preferably has a solubility in water at 20°C of 20 g / L or less, more preferably 5 g / L or less. Any solvent may be used as long as it is hydrophobic enough to form an emulsion with the alkaline aqueous solution. Examples of such solvents include organic solvents such as saturated or unsaturated hydrocarbons with linear or cyclic skeletons, and halogenated hydrocarbons. More specific examples include pentane, hexane, cyclohexane, heptane, octane, nonane, decane, dichloromethane, dichloroethane, chloroform, carbon tetrachloride, dichloropropane, liquid paraffin, toluene, xylene, and mesitylene. Among these, hexane, heptane, and decane, which have appropriate viscosities, are preferred. If necessary, multiple solvents may be used in combination.

[0034] The method for preparing the dispersion is not particularly limited, and can be carried out before or after adding the particles and solvent (particles to liquid, particles to liquid, or simultaneous addition), as long as no powdery particles remain after moderate stirring or vibration. Commercially available powder-liquid mixers and dispersers can also be used. The amount of hydrophobic solvent used is preferably 4.5 to 45 parts by weight, and more preferably 8 to 25 parts by weight, per part by weight of metal oxide particles. If the amount is less than 4.5 parts by weight, the dispersion will lose fluidity and may not proceed to subsequent processes. If more than 45 parts by weight is used, production efficiency will be poor.

[0035] (extraction process) In the extraction step, 0.1 to 1 part by weight of an aqueous ammonia solution having a pH of 12 or higher and containing 1 to 30 mass % ammonia per 1 part by weight of the hydrophobic solvent is added to the dispersion liquid to extract the metal oxide particles from the hydrophobic solvent into the aqueous ammonia, thereby obtaining a mixed liquid consisting of an upper layer of hydrophobic solvent and a lower layer of aqueous ammonia solution containing the metal oxide particles.

[0036] The concentration of metal oxide particles in the mixed solution is preferably 2 to 10% by mass, and more preferably 3 to 7% by mass. If the particle concentration is 2% by mass or less, the dissolution-precipitation equilibrium concentration is low, and aggregates may not be obtained in the aggregation step described below. If the concentration is 10% by mass or more, the dissolution-precipitation equilibrium concentration is high, and the W phase of the W / O emulsion thickens quickly in the emulsification step described below. This results in a large difference in surface tension between the W phase and the O phase, and the W / O emulsion may not be formed even if a surfactant is added.

[0037] In the extraction step, it is preferable to stir and mix the metal oxide particles in the hydrophobic solvent until the concentration of the metal oxide particles in the hydrophobic solvent is 2% by mass or less. If the concentration of the metal oxide particles is 2% by mass or more, extraction will be insufficient, and a large amount of undissolved metal oxide will remain, which may interfere with subsequent steps.

[0038] The method for preparing the mixture is to add an aqueous ammonia solution to the dispersion and mix it using any suitable method, including a stirrer, disperser, or static mixer. The amount of aqueous ammonia solution used is preferably 0.1 to 1 part by weight, more preferably 0.3 to 0.6 parts by weight, per 1 part by weight of the hydrophobic solvent. If the amount is less than 0.1 part by weight, the metal oxide particles will easily solidify, causing the mixture to lose fluidity and potentially preventing it from proceeding to subsequent steps. If more than 1 part by weight is used, production efficiency will be poor.

[0039] The solute of the aqueous ammonia solution used to prepare the mixture may be at least one selected from those that cannot be extracted with a hydrophobic organic solvent, such as alkali metal hydroxides and ammonia. In addition, when a commercially available product such as aqueous ammonia (aqueous ammonia solution) is used, it may be used as is or after dilution.

[0040] The above mixing is carried out by adding an aqueous ammonia solution and stirring until the upper layer (hydrophobic solvent) is transparent and the lower layer is a slurry (uniform in color, fluid, and can be picked up with a dropper) when the stirring is stopped, and the concentration of metal oxide particles in the hydrophobic solvent is 2 mass% or less, which can be used to determine the end point of the extraction process.

[0041] Here, we will describe the mechanism and advantages of this process. Whether spray-drying a colloidal solution of metal oxides or agglomerating and then calcining the resulting aggregates, the colloidal solution of metal oxides is an essential starting material. However, concerns about the stability of colloidal solutions (agglomeration stability) are known. Commercially available products contain alkali to prevent agglomeration, and the silica concentration is limited to a low range. However, there are concerns about the quality of the products varying over time.

[0042] On the other hand, in a dispersion of metal oxide particles prepared from starting materials, the metal oxide particles aggregate during production and storage. Therefore, a classification process must be performed after the dispersion is produced to control the quality of the aggregated product. Furthermore, when the primary particle size of metal oxide particles is smaller, the bulk density is lower, resulting in a large particle volume relative to the dispersion. This necessitates a long dispersion production process in which the particles are added little by little while stirring the dispersion.

[0043] The manufacturing method of the present invention is a solvent extraction method (liquid-liquid extraction), i.e., a dispersion method that utilizes the phenomenon of solute partitioning (which one is more soluble in which) between two immiscible liquids, such as water and oil. Specifically, the metal oxide particles dispersed in the hydrophobic solvent (oil phase) in the dispersion process described above migrate to the aqueous phase due to their overwhelmingly high affinity (solubility) with the alkaline aqueous solution (aqueous phase) with a pH of 12 or higher added in this process. As a result, because the particles migrate between liquids, the process time is extremely fast, regardless of the volume of the particles (solutes).

[0044] The reason why the pH of the aqueous ammonia solution used to prepare the above-mentioned mixed solution must be 12 or higher is that, in an alkaline environment of pH 12 or higher, the elements of the metal oxides used, such as the aforementioned metals Si, Ti, Zr, Zn, Al, and Ga, are thought to become their hydroxides or ions, based on the potential-pH diagram. In other words, in a strongly alkaline environment, the oxides of these metals are thought to be able to maintain an equilibrium between dissolution and precipitation. At pH levels below 12, some of the metals are not in an ionic dissociated state, but rather their oxides or oxide hydrates are stable. Therefore, it is thought that the conversion to the oxides or oxide hydrates (gelation) of aqueous dispersions with a pH below 12 begins shortly after preparation. This causes the entire solution to become a single mass, making it impossible to proceed to subsequent processes.

[0045] Furthermore, since the above-mentioned equilibrium between dissolution and precipitation occurs on the surface of the primary particles, it is thought that weak aggregation of metal oxide particle solids during storage is resolved by dissolution. Moreover, since the degree of dissolution, or the imbalance between dissolution and precipitation equilibrium, depends on pH and concentration, quality control can be simplified by controlling pH and particle concentration. For these reasons, adopting the process of the present invention eliminates the need for mechanical force in the dispersion and classification processes, thereby simplifying the process and reducing the risk of foreign matter contamination.

[0046] (emulsification process) A surfactant is added to the mixture to prepare a W / O emulsion. In the production method of the present invention, a surfactant is added when forming the above-mentioned W / O emulsion. The surfactant to be used may be any of anionic surfactants, cationic surfactants, and nonionic surfactants. Among these, nonionic surfactants are preferred because they are easy to form a W / O emulsion.

[0047] The amount of surfactant used is the same as the amount typically used to form a W / O emulsion. Specifically, a range of 0.025 g to 10 g per 100 g of hydrophobic solvent can be suitably used. If a large amount of surfactant is used, the W / O emulsion droplets tend to become finer; conversely, if a small amount of surfactant is used, the W / O emulsion droplets tend to become larger. Therefore, the average particle size of the porous aggregates can be adjusted by increasing or decreasing the amount of surfactant used.

[0048] When forming a W / O emulsion, known methods for forming W / O emulsions can be used to disperse alkaline water containing dispersed metal oxide particles in a hydrophobic solvent. From the standpoint of ease of industrial production, emulsion formation by mechanical emulsification is preferred, and specific examples include methods using a mixer, homogenizer, etc. Preferably, a homogenizer can be used. Since the particle size of the dispersed metal oxide sol droplets is related to the particle size of the porous aggregates, it is preferable to adjust the particle size of the sol droplets to achieve the desired particle size.

[0049] In the above-mentioned production method, the particle size of the resulting porous aggregates is approximately equal to the droplet size (W phase) of the dispersion liquid in the W / O emulsion prepared in the emulsification step. Therefore, it is necessary to set the dispersion conditions so that the droplet size falls within the desired range. Various methods for controlling the droplet size in W / O emulsions are known, and these techniques can be selected and applied as appropriate.

[0050] The purpose of the emulsification step is to form an emulsion using the hydrophobic solvent in the above-mentioned mixed solution as the dispersion medium and the alkaline water in which the metal oxide particles are dispersed as the W phase of the W / O emulsion. By forming such a W / O emulsion, the dispersoids become spherical due to surface tension, etc., and by gelling them in this spherical shape, spherical gelled bodies can be obtained. In this way, by going through the W / O emulsion preparation step of forming a W / O emulsion, it is possible to produce porous aggregates with a high degree of circularity.

[0051] (agglomeration process) The W / O emulsion is fed to an alcohol having 4 or less carbon atoms in an amount of 0.5 to 5 parts by weight per 1 part by weight of the W / O emulsion to form an upper O phase and a lower W phase, and water-insoluble aggregates are formed (precipitated) in the W phase.

[0052] The alcohol used in this step may have a carbon number of 4 or less, as long as it does not dissolve the metal oxide particles, and examples thereof include methanol, ethanol, and propanol. Of these, 2-propanol is preferred because it is easy to handle.

[0053] The amount of alcohol used in this step is preferably 0.5 to 5 parts by weight per 1 part by weight of the W / O emulsion. If the amount is less than 0.5 parts by weight, sufficient dilution may not be achieved, and spherical aggregates may not be obtained. If more than 5 parts by weight is used, the solvent is wasted and subsequent steps become a burden.

[0054] The embodiment of this step is not particularly limited, and the W / O emulsion may be added dropwise or poured while stirring the alcohol, and any mixing method such as a stirrer or static mixer may be used.

[0055] The mechanism of this process is described below. As mentioned above, in a strongly alkaline environment with a pH of 12 or higher, metal oxides reach an equilibrium state between dissolution and precipitation. If this equilibrium state is broken, that is, if the water in the W phase of the W / O emulsion is removed, the ion-dissociated metal species present in the aqueous solution will precipitate as their oxides, forming new cross-linked structures between the primary particles and resulting in the formation of aggregates.

[0056] Therefore, in this process, we focused on the technique of dilution. When the W / O emulsion is fed to alcohol, the W / O emulsion breaks down, and the water in the micron-order W-phase micelles is rapidly diluted by the alcohol. Taking advantage of this decrease in water content, ion-dissociated metal species precipitate as their oxides, forming new cross-linked structures between primary particles, resulting in the formation of aggregates.

[0057] (Solid-liquid separation process) The upper O phase and the lower W phase containing the aggregates are subjected to solid-liquid separation to obtain the aggregates. The solid-liquid separation is preferably carried out by filtration or centrifugation, from the viewpoint of preventing the aggregates from being broken down.

[0058] (ripening process) Here, between the aggregation step and the solid-liquid separation step, the W phase can be heated to 10 to 90°C to age the aggregates in the W phase. Ageing tends to reduce the average crushing strength of the final porous aggregate. The higher the temperature and the longer the ageing time, the more pronounced the effect. To obtain the desired average crushing strength, the ageing time is preferably 0 to 180 minutes, more preferably 0 to 60 minutes. The ageing temperature is preferably 10 to 90°C, more preferably 30 to 80°C. However, the aggregates will not dissolve and disappear even after ageing for at least several days.

[0059] The aging process involves a chemical equilibrium between silica and hydroxide ions on the surface of the silica, which is the primary particle that makes up the precipitated aggregates (secondary particles). The higher the aging temperature, the shorter the time it takes to reach equilibrium. On the other hand, the higher the hydroxide ion concentration, the more favorable the equilibrium becomes for the reaction to proceed. Therefore, in the case of the present invention, it is believed that as aging progresses, more silica reacts to become ions, the skeleton of the primary particles becomes thinner, and the average crushing strength decreases.

[0060] (Cleaning process) The aggregate is washed to obtain a washed product from which the nonionic surfactant has been removed. After the above-mentioned aggregates are obtained, the aggregates are preferably washed with at least one selected from water, a hydrophobic solvent, and an alcohol having 4 or less carbon atoms in order to remove salts, surfactants, and the like contained in the aggregates. This washing operation can be carried out by a known method. In order to improve the washing efficiency, it is preferable to use an aqueous solution of about several tens of mass % of isopropyl alcohol after washing with the hydrophobic solvent. Furthermore, raising the temperature to a level not exceeding the boiling point of the hydrophobic organic solvent can sometimes improve the washing efficiency. Typically, the washing can be carried out at a temperature in the range of 30 to 70°C.

[0061] (drying process) The washed material is dried to obtain a porous aggregate. In the production method of the present invention, if the above washing step has been carried out, this step can be carried out subsequently. That is, the washed product dispersed in an aqueous solution of about several tens of mass % isopropyl alcohol is filtered, and the solvent is removed (dried). The temperature during drying is preferably above the boiling point of the solvent and below 150°C, and the pressure is preferably normal pressure or reduced pressure. [Example]

[0062] Examples are given below to specifically explain the present invention, but the present invention is not limited to these examples.

[0063] <Evaluation method> The produced porous aggregates were evaluated for the following items.

[0064] (Measurement of average circularity and equivalent circle diameter by SEM image analysis) First, a scanning electron microscope (SEM: Hitachi High-Technologies Corporation, SU-3500) was used to obtain SEM images at a secondary electron detection, low acceleration voltage (20 kV), and magnification of 270x. The obtained SEM images were analyzed using image analysis software (Mitani Corporation, WINROOF2018) to calculate the average circularity and equivalent circle diameter. The average circularity is the arithmetic mean value of the value C (circularity) defined by the following formula (1) obtained for 1500 to 2000 particles. C=4πS / L 2 (1) [In formula (1), S represents the area (projected area) that the particle occupies in the image, and L represents the length (perimeter) of the outer periphery of the particle in the image.] The equivalent circle diameter is the cumulative 50% diameter based on the number of particles, based on the particle size distribution evaluated by evaluating the diameter of a circle equivalent to the area S (projected area) occupied by 1500 to 2000 particles in the image. In this case, a group of particles forming one aggregate particle is counted as one particle.

[0065] (Measurement of specific surface area, pore volume, and mode of pore diameter) The specific surface area, pore volume, and mode of pore diameter were measured using a specific surface area / pore distribution analyzer (BELSORP-mini, manufactured by BEL Japan Co., Ltd.). As a pretreatment for the measurement, the sample to be measured was dried at 150°C for at least 2 hours under a vacuum of 1 kPa or less. Then, an adsorption isotherm was obtained for only the nitrogen adsorption side at liquid nitrogen temperature. Analysis was then performed using the BET method and the BJH method. The mode of pore diameter is the pore diameter value at which the cumulative pore volume (volume distribution curve) of the logarithm of the pore diameter reaches the most frequent peak value.

[0066] (average crushing strength) The average crushing strength was measured using a microcompression tester (Shimadzu Corporation, MCT-W510-J) according to the definition above. The test was performed under the following conditions: test force 9.81 mN, loading rate 9.81 mN / sec, and load holding time 0 sec. An indenter with a diameter of 200 μm was used for the measurement.

[0067] Example 1 (Dispersion process) Rheoloseal QS-30 (Tokuyama Corporation, specific surface area 300±30m 240 g of decane was added to 2.0 g of cellulose acetate (0.1% w / g, average primary particle size 7 nm, SiO2 purity >99.9%, Cl <50 ppm, Fe <20 ppm, Al <20 ppm), and the mixture was stirred with a spoon until no powdery particles remained, yielding a creamy dispersion. (extraction process) 16.0 g of 9.38% by mass ammonia water, pH 13.0 (prepared by diluting 25% by mass ammonia water manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the above dispersion, and then the mixture was stirred for 30 seconds at 7000 rpm using a homogenizer (manufactured by IKA, T25BS1) to obtain a mixed solution. (emulsification process) 3 g of decane containing 0.3 g of sorbitan monooleate (Kao Corporation, Rheodol SP-010V) dispersed therein was added all at once, and the mixture was stirred at 7000 rpm for 15 seconds using a homogenizer, as in the previous step, to obtain a W / O emulsion. (agglomeration process) The W / O emulsion obtained in the previous step was immediately added to 40 g of 2-propanol (Fujifilm Wako Pure Chemical Industries, Ltd.) while stirring with a magnetic stirrer. After that, the mixture was allowed to stand, and separated into two layers: an upper O phase and a lower W phase containing aggregates. (solid-liquid separation, washing process) The resulting aggregate was filtered off from the W phase using a suction filter, and washed with decane, water, and 2-propanol while being suctioned to obtain a washed product. (drying process) The washed product was transferred to a beaker and dried in a vacuum dryer for 3 hours at 120° C. The physical properties of the porous aggregate thus obtained are shown in Table 1.

[0068] <Example 2> In the dispersion step, 3.0 g of Reolosil QS-30 was used. Following the aggregation step and prior to the solid-liquid separation step, the two-layer liquid, consisting of an upper O phase and a lower W phase containing aggregates, was allowed to stand at 70°C for 20 minutes. Other than that, the procedure was the same as in Example 1. The physical properties of the resulting porous aggregates are shown in Table 1 (the same applies below).

[0069] Example 3 After the aggregation step and before the solid-liquid separation step, the two-layer liquid consisting of an upper layer O phase and a lower layer W phase containing aggregates was allowed to stand at 70°C for 75 minutes. Otherwise, the same operation as in Example 3 was carried out.

[0070] Example 4 In the dispersion process, Rheoloseal QS-102 (manufactured by Tokuyama Corporation, specific surface area 200±20 m 2 / g, average primary particle size 12 nm, SiO2 purity >99.9%, Cl <50 ppm, Fe <20 ppm, Al <20 ppm) was used. Otherwise, the same operation as in Example 1 was carried out.

[0071] <Comparative Example 1> (Dispersion process) 40 g of decane was added to 4.0 g of Reolosil QS-30, and the mixture was stirred with a spoon until no powdery particles remained, to obtain a creamy dispersion. (extraction process) To the dispersion was added 16.0 g of 9.38% by mass aqueous ammonia at pH 13.0, and the mixture was stirred for 30 seconds at 7000 rpm using a homogenizer to obtain a mixed liquid. (emulsification process) 3 g of decane in which 0.3 g of sorbitan monooleate had been dispersed was added all at once, and the mixture was stirred for 15 seconds at 7,000 rpm using the homogenizer as in the previous step to obtain a W / O emulsion. (agglomeration process) The obtained W / O emulsion was transferred to a shallow tray and dried in a vacuum dryer at 150°C for 2 hours to obtain an aggregate. (solid-liquid separation, washing process) The resulting aggregates were dispersed in 40 g of 2-propanol for 30 minutes with stirring, then filtered from the solvent using a suction filter, and washed with decane, water, and 2-propanol while suctioning to obtain washed products. (drying process) The washed product was transferred to a beaker and dried in a vacuum dryer at 150°C for 3 hours.

[0072] <Comparative Example 2> The dispersion step and extraction step were carried out in the same manner as in Example 2, except that 21.2 g of 0.12% by mass aqueous ammonia, pH 11.8, was used in the extraction step. The W phase thickened rapidly, and a mixed liquid could not be obtained. Further work was no longer possible.

[0073] <Comparative Example 3> (Dispersion liquid preparation process) To 200 ml of ion-exchanged water containing 6.65 g of urea, 66 g of Reolosil QS-30 was added while stirring with a homogenizer, and the fumed silica was pre-dispersed. After that, the mixture was finely dispersed using an ultrasonic homogenizer (Sonifier SFX250, manufactured by Branson) to obtain a fumed silica dispersion. The dispersion preparation process was carried out in a chiller cooled to 10°C. (W / O emulsion preparation process) 65.5 g of the fumed silica dispersion prepared by the above method was taken, and 129 g of decane in which 0.75 g of sorbitan monooleate had been dispersed was added. The mixture was then stirred for 3 minutes at 8,600 rpm using a homogenizer to obtain a W / O emulsion. (Gelling process) The resulting W / O emulsion was stirred at 300 rpm using a four-paddle impeller with a blade diameter of 60 mm, a blade width of 20 mm, and an oblique angle of 45 degrees, and was kept in a water bath at 80°C for 3 hours to cause gelation. (Gelated body recovery process) 77 g of isopropyl alcohol and 52 g of water were added, and the mixture was stirred with a stirring blade while maintaining the temperature at 70° C. for 30 minutes. After that, the mixture was allowed to stand, whereby it separated into two layers: an upper O phase and a lower W phase. Then, the O phase and the W phase were separated by decantation, and the W phase was recovered. The resulting gel was filtered using a suction filter and separated from phase W. The collected gel was dried in a vacuum dryer at 150°C for 12 hours.

[0074] [Table 1]

Claims

1. A porous aggregate of metal oxide, A porous aggregate characterized by satisfying the following (1) to (4): (1) Average crushing strength Cs is 0.02 to 1 MPa (2) Average circularity of 0.5 or more (3) Equivalent circle diameter (D50) is 1 to 100 μm (4) A specific surface area of ​​50 to 800 m 2 / g

2. 2. The porous aggregate according to claim 1, wherein the mode of the pore diameter is 5 to 50 nm.

3. 3. The porous aggregate according to claim 1, wherein the pore volume is 0.5 to 5 ml / g.

4. An abrasive comprising the porous aggregate according to any one of claims 1 to 3.

5. A cosmetic comprising the porous aggregate according to any one of claims 1 to 3.

6. A drug carrier comprising the porous aggregate according to any one of claims 1 to 3.

7. A chromatography carrier comprising the porous aggregate according to any one of claims 1 to 3.

8. A resin composition comprising the porous aggregate according to any one of claims 1 to 3.

9. a dispersing step of mixing metal oxide particles with a hydrophobic solvent to obtain a dispersion; an extraction step of mixing the dispersion liquid with ammonia water having a pH of 12 or higher and containing 1 to 30% by mass of ammonia in a ratio of 0.1 to 1 part by weight of ammonia water to 1 part by weight of the hydrophobic solvent, thereby extracting the metal oxide particles from the hydrophobic solvent into the ammonia water, thereby obtaining a mixed liquid consisting of an upper layer of hydrophobic solvent and a lower layer of ammonia water containing the metal oxide particles; an emulsification step of adding a surfactant to the mixed solution to prepare a W / O emulsion; an aggregation step of feeding the W / O emulsion to 0.5 to 5 parts by weight of an alcohol having 4 or less carbon atoms per 1 part by weight of the W / O emulsion to form an upper O phase and a lower W phase, and generating water-insoluble aggregates in the W phase; a solid-liquid separation step of obtaining the agglomerate by solid-liquid separation; a washing step of washing the aggregate to obtain a washed product from which the surfactant has been removed; a drying step of drying the washed material to obtain a porous aggregate; A method for producing a porous aggregate, comprising:

10. The method for producing a porous aggregate according to claim 9, further comprising, between the aggregation step and the solid-liquid separation step, a maturation step of heating the W phase to 10 to 90°C to mature the aggregate.

11. The method for producing a porous aggregate according to claim 9 or 10, wherein the hydrophobic solvent has a solubility in water at 20°C of 20 g / L or less.

12. 11. The method for producing a porous aggregate according to claim 9, wherein in the extraction step, the concentration of the metal oxide in the mixed solution is 2 to 10 mass %.

13. The method for producing a porous aggregate according to claim 9 or 10, wherein in the extraction step, the hydrophobic solvent is stirred and mixed until the concentration of the metal oxide particles in the hydrophobic solvent becomes 2 mass % or less.

14. The method for producing a porous aggregate according to claim 9 or 10, wherein in the washing step, washing is carried out with at least one washing liquid selected from water, a hydrophobic solvent, and an alcohol having 4 or less carbon atoms.

15. The method for producing a porous aggregate according to claim 9 or 10, wherein in the solid-liquid separation step, solid-liquid separation is carried out by filtration or centrifugation.

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