JP2023150589A - Porous aggregate and manufacturing method thereof as well as usage thereof - Google Patents

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

The present invention relates to a novel easily disintegrating porous aggregate suitable for use as ultra-precision grinding wheels, cosmetic additives, etc., and a method for producing the same.

When polishing semiconductor wafers during wafer making, when lapping using a free abrasive method, it is necessary to constantly supply lapping agent (a mixed slurry of abrasive grains and processing liquid) to maintain stable processing conditions at all times. be. Normally, a highly viscous oil-based liquid is used, and it takes time and cost to dispose of the used wrap agent and clean the equipment, making it difficult to automate.

In order to perform mirror polishing in a relatively short time without contaminating the surrounding environment, and to improve productivity by enabling automation with equipment used in the previous and subsequent processes, fixing methods such as those described in Patent Documents 1 and 2 are used. Examples include abrasive processing tools.

The grinding wheel, which is indispensable for this polishing method, has a structure in which a grindstone made of agglomerated ultra-fine abrasive grains hardened with resin is held on a hard base, and can be attached to an appropriate polishing device. , polishing can be performed without using free abrasive grains (lap agent) (Patent Document 1).

In particular, recently there has been a demand for ultra-precision processing that can achieve surface roughness on the order of nanometers. The abrasive grains used in these polishing wheels are inorganic oxide primary particles with a diameter of several nanometers to several tens of nanometers. However, agglomeration of primary particles occurs during the grindstone forming process, and it is impossible to control the cohesive force.If the cohesive force is strong, it is impossible to avoid scratches on the polished surface (patent Reference 2).

Therefore, it is proposed to use aggregates whose particle size can be easily controlled and whose dispersibility in the resin is good. During polishing and grinding, it is important that the aggregates are quickly disintegrated by shear force and that nanometer-order primary particles, which become abrasive grains, are evenly supplied.

On the other hand, regarding the polishing pressure (substrate load) in the lapping process, multiple documents (Patent Documents 3 to 5) indicate that it is preferable to use a pressure of 0.02 MPa or less in order to achieve both processing efficiency and high quality. be.

Based on the above background, it is preferable that the agglomerate has as weak a cohesive force as possible as long as the agglomerate does not collapse during manufacturing, transportation, and pad-forming as a characteristic of the agglomerate that is compatible with the above-mentioned grindstone. Furthermore, it is preferable that appropriate deformation occurs without breaking under a pressure of 0.02 MPa or less and generating micron-order fragments, thereby increasing adhesion to the substrate.

According to Patent Document 6, porous aggregated 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.

It is presumed that the reason why the average crushing strength cannot be reduced is due to the manufacturing method.

Among methods for granulating porous aggregates using metal oxide nanoparticles as a raw material, spray drying is the most popular method known (Patent Document 7).

However, since the particle size distribution of the spray liquid must be made as monodisperse as possible, it is necessary to separate the aggregated coarse particles using strong centrifugal force or to disperse the aggregated coarse particles using high shear force. Pretreatment using a so-called physical method is required. There are concerns about quality stability due to the high energy consumption and increased number of production processes.

Furthermore, in the case of spray drying, it is common to perform heat treatment in a temperature range of 150° C. to 600° C. in order to increase the bonding stability between fine particles. This increases the average crushing strength of the aggregates.

JP2000-198073 JP2000-190228 JP2007-208220 JP2016-092045 JP2018-145225 WO2019/131873 JP2010-138021

Based on the above background, an object of the present invention is to provide a novel porous aggregate made of silica nanoparticles whose average crushing strength is controlled within a specific range and which is mainly useful as an abrasive grain.

The present inventors have made extensive studies to solve the above problems. As a result, in the production process of porous aggregates made of silica nanoparticles, by using the following several original methods, it was possible to prepare porous aggregate particles made of silica nanoparticles with an average crushing strength controlled within a specific range. The inventors have discovered that this can be done, and have completed the present invention.

That is, the present invention provides a porous aggregate made of metal oxide, which satisfies an average crushing strength Cs of 0.02 to 1 MPa, a circularity of 0.5 or more, and an equivalent circle diameter (D50) of 1 to 100 μm. A porous aggregate is provided.

From another aspect, the present invention provides, as a method suitable for producing the porous aggregate according to the present invention,
a dispersion step of mixing metal oxide particles and a hydrophobic solvent to obtain a dispersion;
Mixing the dispersion liquid and ammonia water having a pH of 12 or more and containing 1 to 30% by weight of ammonia at a ratio of 0.1 to 1 part by weight of ammonia water to 1 part by weight of the hydrophobic solvent, an extraction step of extracting the metal oxide particles from the hydrophobic solvent into the ammonia water to obtain a mixed solution consisting of an upper layer of the hydrophobic solvent and a lower layer of the ammonia aqueous solution containing the metal oxide particles;
an emulsification step of adding a surfactant to the mixed liquid to prepare a W/O emulsion;
The W/O emulsion is supplied to an alcohol containing 0.5 to 5 parts by weight based on 1 part by weight of the W/O emulsion and having a carbon number of 4 or less to form an upper O phase and a lower W phase. , a coagulation step of producing water-insoluble aggregates in the W phase;
a solid-liquid separation step to obtain the aggregate through 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;
Provided is a method for producing a porous aggregate, the method comprising:

When the porous aggregate of the present invention is dispersed in a resin and hardened to form a grindstone, the average crushing strength is in the region of low and controllable. It is expected that the particles will quickly disintegrate due to shear force, and that it will be possible to evenly supply nanometer-order (nm-sized) primary particles that will become abrasive grains.

Further, since the fumed silica as a raw material forms a network structure, the porous aggregate can maintain a high specific surface area of the fumed silica and obtain a high internal pore volume. Therefore, it can be used as a variety of carriers, such as additives for cosmetics, carriers for active ingredients in drugs, and chromatography packings.

<Porous aggregate>
The porous aggregate of the present invention is a porous aggregate made of metal oxide, and has an average crushing strength Cs of 0.02 to 1 MPa, a circularity of 0.5 or more, and an equivalent circle diameter (D50) of 1 to 1 MPa. It is a porous aggregate characterized by filling 100 μm.
Therefore, the average crushing strength is in a region where it is weak and can be controlled, so during ultra-high precision polishing and grinding, the aggregates quickly disintegrate due to shear force, producing nanometer (nm) order primary particles that become abrasive grains. I think it is possible to supply it evenly.

(Average crushing strength)
The porous aggregate of the present invention has an arithmetic mean value ("average crushing strength Cs") of "pressure at which sample fracture is observed" determined according to the method specified in JIS Z8844:2019 from 0.02 to It is 1.0 MPa. When the average crushing strength is within this range, the particles will have excellent pressure disintegration properties. In other words, 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 cause scratches on the object to be polished, and when used as a scrubbing material for cosmetics, they are less likely to damage the skin. It becomes possible to reduce the burden. If the average crushing strength is less than 0.02 MPa, it will collapse under vertical polishing pressure (substrate load), poor adhesion between the polishing pad and the substrate, and processing efficiency will decrease. Moreover, it becomes impossible to maintain the internal space as a carrier. At 1.0 MPa or more, the desired disintegrability cannot be obtained. The average crushing strength is preferably 0.02 to 1.0 MPa, more preferably 0.2 to 1.0 MPa.

(Average circularity)
"Average circularity" refers to the value C (circularity) defined by the following formula (10) for each particle from the observed SEM image using a scanning electron microscope (SEM) (image analysis) , this circularity C is, for example, a value obtained as an arithmetic average value of 1500 to 2000 particles (image analysis method). At this time, a particle group forming one aggregated 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. L represents the length of the outer periphery (perimeter length) of the particle in the image. ]
As the average circularity becomes larger than 0.8 and closer to 1, the individual particles constituting the metal oxide have a shape closer to a perfect sphere, and the number of agglomerated particles decreases. Therefore, if the average circularity is high, rolling properties will be improved when used as a filler, and excellent filling properties will be obtained. When the circularity of the porous aggregate of the present invention is less than 0.5, the fluidity, packing density, and dispersibility are poor and it is not practical. Furthermore, horizontal scratch marks are likely to occur during polishing. The circularity is preferably 0.5 to 1.0, more preferably 0.8 to 1.0.

(Equivalent circle diameter)
"Equivalent circle diameter" is a value converted from the above SEM image into the diameter of a circle equivalent to the area S (projected area) occupied by 1,500 to 2,000 individual particles in the image (image analysis method). . From the obtained particle size distribution, the cumulative 50% diameter based on the number of particles is defined as the equivalent circle diameter. When the equivalent circle diameter of the porous aggregate of the present invention exceeds 100 μm, the packing density is poor and it is not practical. On the other hand, if it is less than 1 μm, the fluidity of the powder will be low 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 materials for cosmetics.

In order to achieve both measurement accuracy and calculation efficiency in terms of average circularity and equivalent circle diameter, the number of particles used is preferably 500 to 5000, more preferably 1500 to 2000.

(Measurement of the mode of specific surface area, pore volume, and pore diameter)
The specific surface area, pore volume, and mode (peak) of the pore diameter can be measured using a specific surface area/pore distribution measuring device.
(Mode of pore diameter)
The mode of the 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 mode of pore diameter of 5 to 50 nm, more preferably 15 to 50 nm. When the mode of the pore diameter is within the above range, the easy disintegration of the particles themselves, the bonding strength between the particles and the resin, and the carrying capacity inside the particles are all optimal. If the mode of the pore diameter is less than 5 nm, there is a risk that the particles will not have the desired disintegrability, and the resin will be difficult to penetrate into the particles, resulting in poor interlocking between the particles and the resin. On the other hand, if it exceeds 50 nm, the retention ability as a carrier tends to deteriorate.

(pore volume)
The porous aggregate of the present invention preferably has a pore volume of 0.5 to 5 ml/g, more preferably 1.0 to 4.0 ml/g, according to the BJH method. When the pore volume is within the above range, desired crushing strength can be easily obtained.
(Specific surface area)
The porous aggregate of the present invention preferably has a specific surface area of 50 to 800 m ² /g, more preferably 100 to 400 m ² /g, as determined by the BET method. When the specific surface area is within the above range, it is easy to obtain particles that have both easy disintegration and surface adsorption ability. It is difficult to obtain a specific surface area of 800 m ² /g or more, and if it is 50 m ² /g or less, the strength tends to increase and the surface adhesion tends to deteriorate.

<Method for producing porous aggregate>
According to the production method of the present invention, mechanical pretreatment of the dispersion (filtration, classification, etc. to prevent nozzle clogging) is not necessary in the process of producing porous aggregates. In addition, there is no need for a process of insolubilizing the aggregates by heating them at a high temperature, that is, a baking process. Porous aggregates can be easily produced.

The forms shown below are examples of the present invention, and the present invention is not limited to these forms. Furthermore, unless otherwise specified, the notation "A to B" in a numerical range means "above A and below B." In such a notation, if a unit is attached only to the numerical value B, the unit shall also be applied to the numerical value A. The manufacturing method of the present invention will be explained step by step below.

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

The metal oxide particles are ultrafine particles produced by a vapor phase method, and those having an average particle diameter of several nanometers (several nm) to several tens of nanometers (several tens of nanometers) are preferably used. For example, metal oxide nanoparticles SiO ₂ , TiO ₂ , ZnO, Al ₂ O ₃ manufactured by Kanto Kagaku Co., Ltd., various hydrophilic grades of Rheolo Seal manufactured by Tokuyama Co., Ltd., various hydrophilic grades of Aerosil manufactured by Nippon Aerosil Co., Ltd., Various hydrophilic grades of dry silica HDK manufactured by Asahi Kasei Wacker Silicone Co., Ltd., zirconia powders Zirconeo-Cp and Zirconeo-Rp manufactured by ITEC Co., Ltd., gallium oxide nanoparticles manufactured by Rare Metal Materials Research Institute Co., Ltd., etc. can be used.

Further, since fumed silica is highly pure and contains almost no impurities such as alkali metals, it is preferable because the alkali metal content of the produced porous aggregate can be extremely reduced.

The hydrophobic solvent for preparing the above 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 has enough hydrophobicity to form an emulsion with an alkaline aqueous solution. As such a solvent, it is possible to use, for example, an organic solvent such as saturated or unsaturated hydrocarbons having a linear or cyclic skeleton, or 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 having appropriate viscosity can be preferably used. Note that, if necessary, a plurality of solvents may be used in combination.

The method for preparing the dispersion liquid is not particularly limited, and regardless of whether the particles and the solvent are added before or after (adding the liquid to the particles, or the particles to the liquid at the same time), moderate stirring or vibration can be used to ensure that no powder particles remain. It's fine if you don't have it. Furthermore, commercially available powder/liquid mixers and dispersers can also be used. The amount of the hydrophobic solvent used is preferably 4.5 to 45 parts by weight, more preferably 8 to 25 parts by weight, per 1 part by weight of the metal oxide particles. If the amount is less than 4.5 parts by weight, the fluidity of the dispersion may be lost and it may not proceed to the subsequent process, and if it is more than 45 parts by weight, the production efficiency will be poor.

(Extraction process)
In the extraction step, 0.1 to 1 part by weight of an ammonia aqueous solution having a pH of 12 or more and containing 1 to 30% by mass of ammonia is added to the dispersion liquid, based on 1 part by weight of the hydrophobic solvent, to perform metal oxidation. The metal oxide particles are extracted from the hydrophobic solvent into aqueous ammonia to obtain a liquid mixture consisting of the hydrophobic solvent in the upper layer and the ammonia aqueous solution containing the metal oxide particles in the lower layer.

The concentration of metal oxide particles in the liquid mixture is preferably 2 to 10% by mass, more preferably 3 to 7% by mass. If it is less than 2% by mass, the particle concentration is low, so the above-mentioned dissolution/precipitation equilibrium concentration is low, and aggregates may not be obtained in the aggregation step described below. If it exceeds 10% by mass, the dissolution/precipitation equilibrium concentration is high, and in the emulsification process described below, the W phase of the W/O emulsion thickens quickly, resulting in a large difference in surface tension between the W phase and the O phase. Even if a surfactant is added, a W/O emulsion may not be formed.

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

As a method for preparing the above-mentioned liquid mixture, an ammonia aqueous solution is added to the above-mentioned dispersion liquid, and a mixing method such as a stirrer, a disperser, or a static mixer is used, which is not particularly limited. The amount of the ammonia aqueous solution is preferably 0.1 to 1 part by weight, more preferably 0.3 to 0.6 part 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, the fluidity of the mixture will be lost, and the subsequent process may not proceed. If it is used more than 1 part by weight, the manufacturing efficiency will decrease. bad.

The solute in the ammonia aqueous solution used to prepare the above-mentioned liquid mixture may be at least one selected from those that are not extracted by hydrophobic organic solvents, such as alkali metal hydroxides and ammonia. In addition, if it is a commercially available product such as ammonium water (ammonia aqueous solution), it may be used as it is or after being diluted.

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

Here, the mechanism and advantages of this process will be described. In either method, a colloidal solution of a metal oxide is used as an indispensable starting material in any of the methods of producing an aggregate by spray drying or aggregation and then firing from a colloidal solution of a metal oxide. However, there are known concerns about the stability of colloidal solutions (aggregation stability), and commercially available products have an alkali added to prevent coagulation, and the silica concentration is limited to a low range. There is a concern that quality may vary depending on the period.

On the other hand, in a dispersion of metal oxide particles prepared from starting materials, the metal oxide particles aggregate during the manufacturing and storage process. Therefore, in order to control the quality of the aggregate product, a classification process must be performed after producing the dispersion. Furthermore, if the primary particle diameter of the metal oxide particles is smaller, the bulk density is lower, so the volumetric volume of the particles relative to the dispersion is huge, and it takes a long time to add the particles little by little while stirring the dispersion. The dispersion manufacturing process is unavoidable.

The production method of the present invention is a solvent extraction method (liquid-liquid extraction), that is, a dispersion method that utilizes the phenomenon of distribution of solutes between two immiscible liquids such as water and oil (which one is easier to dissolve in). . Specifically, the above dispersion process improves the affinity (solubility) of the metal oxide particles dispersed in the hydrophobic solvent (oil phase) with the alkaline aqueous solution (aqueous phase) with a pH of 12 or higher, which is added in this process. Because the ease of transport is overwhelmingly high, we took advantage of the fact that it migrates to the aqueous phase by itself. As a result, since particles move between liquids, the time required for the process is extremely fast regardless of the volume of the particles (solute).

The reason why it is necessary that the pH of the ammonia aqueous solution used to prepare the above-mentioned mixed solution is 12 or higher is that in an alkaline environment with a pH of 12 or higher, the potential-pH diagram shows that the elements of the metal oxide used above, for example, The listed metals such as Si, Ti, Zr, Zn, Al, and Ga are considered to be in their hydroxide or ionic state. That is, it is considered that in a strongly alkaline environment, the oxides of the above metals can maintain a balance between dissolution and precipitation. When the pH is lower than 12, some of the metals mentioned above are not in an ion-dissociated state and their oxides or hydrates of the oxides are stable. It is thought that the change to a hydrate (gelation) begins. If this happens, the entire solution will become one lump, making it impossible to proceed to the subsequent steps.

Further, since the above-mentioned equilibrium between dissolution and precipitation occurs on the surface of the primary particles, it is thought that weak agglomeration of the metal oxide particle solids during storage is eliminated by dissolution. Furthermore, since the degree of dissolution, so-called bias in dissolution and precipitation equilibrium, depends on pH and concentration, quality control can be simplified by controlling pH and particle concentration. Based on the above, it is believed that if the process of the present invention is adopted, mechanical force is not required in the dispersion and classification process, and the process can be simplified and the risk of foreign matter contamination can be reduced.

(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 W/O emulsion. As the surfactant to be used, any of anionic surfactants, cationic surfactants, and nonionic surfactants can be used. Among these, nonionic surfactants are preferred because they easily form a W/O emulsion.

The amount of surfactant used is the same as the amount typically used when forming a W/O emulsion. Specifically, a range of 0.025 g or more and 10 g or less can be suitably employed per 100 g of the hydrophobic solvent. When the amount of the surfactant used is large, the droplets of the W/O emulsion tend to become finer, and conversely, when the amount of the surfactant used is small, the droplets of the W/O emulsion tend to become larger. Therefore, by increasing or decreasing the amount of surfactant used, it is possible to adjust the average particle size of the porous aggregate.

When forming a W/O emulsion, a known method for forming a W/O emulsion can be adopted as a method for dispersing alkaline water in which metal oxide particles are dispersed in a hydrophobic solvent. From the viewpoint of ease of industrial production, emulsion formation by mechanical emulsification is preferred, and specific examples include methods using mixers, homogenizers, 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 aggregate, it is preferable to adjust the particle size of the sol droplets so that the particle size becomes the desired particle size.

In the above production method, the particle size of the porous aggregates obtained almost corresponds to the droplet (W phase) size of the dispersion in the W/O emulsion prepared in the emulsification step. Therefore, it is necessary to set the dispersion conditions so that the target diameter range is achieved. Various methods for controlling the droplet diameter in W/O emulsions are known, and these techniques may be appropriately selected and applied.

The purpose of the emulsification step is to form an emulsion by using the hydrophobic solvent in the above-mentioned liquid mixture as a dispersion medium and using the alkaline water in which metal oxide particles are dispersed as W phase of a W/O emulsion. By forming such a W/O emulsion, the dispersoid becomes spherical due to surface tension or the like, and by gelling the dispersoid in the spherical shape, a spherical gelled body can be obtained. In this way, by going through the W/O emulsion preparation step of forming a W/O emulsion, it becomes possible to produce a porous aggregate having a high degree of circularity.

(Agglomeration process)
The W/O emulsion is supplied to an alcohol containing 0.5 to 5 parts by weight based on 1 part by weight of the W/O emulsion and having a carbon number of 4 or less to form an upper O phase and a lower W phase. , a water-insoluble aggregate is produced (precipitated) in the W phase.

The alcohol having 4 or less carbon atoms used in this step may be used as long as the metal oxide particles are insoluble, and examples thereof include methanol, ethanol, and propanol. Among these, 2-propanol is preferred because it is easy to handle.

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 possible and spherical aggregates may not be obtained. Even if more than 5 parts by weight is used, the solvent will be wasted and the subsequent steps will be burdened.

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

The mechanism of this process will be described below. As mentioned above, in a strongly alkaline environment with a pH of 12 or more, metal oxides are in an equilibrium state of 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 metal species in the ion-dissociated state existing in the aqueous solution will precipitate as oxides, creating a new cross-linked structure between the primary particles. It is thought that aggregates are obtained.

Therefore, in this process, we focused on the method of dilution. When the W/O emulsion is supplied to alcohol, the water in the W-phase micelles on the order of microns can be rapidly diluted by the alcohol as the W/O emulsion is thawed. It is thought that by utilizing this decrease in water content, metal species in an ion-dissociated state precipitate as their oxides, create a new crosslinked structure between primary particles, and obtain aggregates.

(Solid-liquid separation process)
The upper O phase and the lower W phase containing aggregates are subjected to solid-liquid separation to obtain the aggregates.
The solid-liquid separation is preferably performed by filtration or centrifugation from the viewpoint of preventing aggregates from breaking.

(Aging process)
Here, between the aggregation step and the solid-liquid separation step, the W phase can be heated to 10 to 90° C. to ripen the aggregates in the W phase. There is a tendency for the average crushing strength of the final porous aggregate to decrease with aging. The higher the temperature and the longer the aging time, the more pronounced the effect. In order to obtain the desired average crushing strength, the aging time is preferably 0 to 180 minutes, more preferably 0 to 60 minutes. The aging temperature is preferably 10 to 90°C, more preferably 30 to 80°C. However, the aggregates do not dissolve and disappear even after aging for at least several days.

The above-mentioned aging means that a chemical equilibrium exists between silica and hydroxide ions on the surface of silica, which is a primary particle constituting the precipitated aggregate (secondary particle). The higher the ripening temperature, the shorter the time to reach equilibrium. On the other hand, the higher the hydroxide ion concentration, the more favorable the equilibrium is for the direction of reaction progress. Therefore, in the case of the present invention, it is thought that as aging progresses, more silica reacts and becomes ions, the skeleton of the primary particles becomes thinner, and the average crushing strength decreases.

(Washing 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, in order to remove salts, surfactants, etc. contained in the aggregates, the aggregates are washed with at least one solvent selected from water, a hydrophobic solvent, and an alcohol having a carbon number of 4 or less. It is preferable to carry out this by two methods. This washing operation can be performed by a known method. In order to increase the cleaning efficiency, it is preferable to use an aqueous solution of isopropyl alcohol of about several tens of mass % after cleaning with the hydrophobizing solvent. In addition, cleaning efficiency may be improved by increasing the temperature to a level that does not exceed the boiling point of the hydrophobic organic solvent. Usually, it can be carried out at a temperature in the range of 30 to 70°C.

(drying process)
The washed material is dried to obtain a porous aggregate.
In the manufacturing method of the present invention, when the above-mentioned washing step is performed, this step can be performed subsequently. That is, the washed material dispersed in an aqueous solution of about several tens of mass % of isopropyl alcohol is filtered and the solvent is removed (drying). The temperature during drying is preferably higher than the boiling point of the solvent and lower than 150° C., and the pressure is preferably normal pressure to reduced pressure.

Examples for specifically explaining the present invention are shown below. However, the present invention is not limited to these examples.

<Evaluation method>
The produced porous aggregates were evaluated on the following items.

(Measurement of average circularity and circle equivalent diameter by SEM image analysis)
First, a SEM image is obtained using a scanning electron microscope (SEM: SU-3500, manufactured by Hitachi High-Technologies Corporation) with secondary electron detection, low acceleration voltage (20 kV), and 270x magnification. Image analysis is performed on the obtained SEM using image analysis software (WINROOF2018, manufactured by Mitani Shoji Co., Ltd.), and the average circularity and equivalent circle diameter are calculated.
The average circularity is a value obtained by calculating the value C (circularity) defined by the following formula (1) for 1,500 to 2,000 particles and calculating the arithmetic average value.
C=4πS/L ² (1)
[In formula (1), S represents the area (projected area) that the particle occupies in the image. L represents the length of the outer periphery (perimeter length) 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 that evaluates the diameter of a circle equivalent to the area S (projected area) occupied by 1,500 to 2,000 individual particles in the image. At this time, a particle group forming one aggregated particle is counted as one particle.

(Measurement of the mode of specific surface area, pore volume, and pore diameter)
The mode values of the specific surface area, pore volume, and pore diameter were measured using a specific surface area/pore distribution measuring device (BELSORP-mini, manufactured by Bell Japan Co., Ltd.). As pretreatment for measurement, the sample to be measured was dried at a temperature of 150° C. for 2 hours or more under a vacuum of 1 kPa or less. Thereafter, an adsorption isotherm only on the nitrogen adsorption side at liquid nitrogen temperature was obtained. Thereafter, analysis was performed using the BET method and the BJH method. The mode of the 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.

(Average crushing strength)
The average crushing strength was measured using a micro compression tester (manufactured by Shimadzu Corporation, MCT-W510-J) according to the above definition. Note that the measurement was performed under the conditions of a test force of 9.81 mN, a loading rate of 9.81 mN/sec, and a load holding time of 0 sec. Further, an indenter with a diameter of 200 μm was used for the measurement.

<Example 1>
(Dispersion process)
Rheolo Seal QS-30 (manufactured by Tokuyama Co., Ltd., specific surface area 300 ± 30 m ² /g, average primary particle size 7 nm, SiO ₂ purity >99.9%, Cl < 50 ppm, Fe < 20 ppm, Al < 20 ppm) to 2.0 g 40 g of decane was added and stirred with a spoon until there were no powder particles left, to obtain a creamy dispersion.
(Extraction process)
After adding 16.0 g of 9.38% by mass, pH 13.0 ammonia water (made by diluting 25% by mass ammonia water manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) to the above dispersion, a homogenizer (manufactured by IKA) was added. , T25BS1) at 7000 rpm for 30 seconds to obtain a mixed solution.
(Emulsification process)
By adding 3 g of decane in which 0.3 g of sorbitan monooleate (manufactured by Kao Corporation, Rheodor SP-010V) was dispersed at once, and stirring for 15 seconds at 7000 rpm using a homogenizer as in the previous step. , a W/O emulsion was obtained.
(Agglomeration process)
The W/O emulsion obtained in the previous step was immediately added to 40 g of 2-propanol (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) and stirred with a magnetic stirrer. Thereafter, by allowing the mixture to stand still, it was separated into two layers: an upper layer consisting of an O phase and a lower layer containing a W phase containing aggregates.
(solid-liquid separation, washing process)
The resulting aggregate was filtered from the W phase using a suction filter, and washed with decane, water, and 2-propanol while suctioning as it was, to obtain a washed product.
(drying process)
The obtained washed product was transferred to a beaker and dried in a vacuum dryer at 120° C. for 3 hours. Table 1 shows the physical properties of the porous aggregate thus obtained.

<Example 2>
In the dispersion step, 3.0 g of Rheolosil QS-30 was used. Further, after the aggregation step and before the solid-liquid separation step, the two-layer liquid with the upper layer being the O phase and the lower layer being the W phase containing aggregates was allowed to stand at 70° C. for 20 minutes. Other than that, the operation was performed in the same manner as in Example 1. The physical properties of the obtained porous aggregate are shown in Table 1 (the same applies below).

<Example 3>
After the aggregation step and before the solid-liquid separation step, the two-layer liquid with the upper layer being the O phase and the lower layer being the W phase containing the aggregates was allowed to stand at 70° C. for 75 minutes. Other than that, the operation was performed in the same manner as in Example 3.

<Example 4>
In the dispersion process, Rheolo Seal QS-102 (manufactured by Tokuyama Co., Ltd., specific surface area 200 ± 20 m ² /g, average primary particle diameter 12 nm, SiO ₂ purity >99.9%, Cl < 50 ppm, Fe < 20 ppm, Al < 20 ppm) was used. 4.0g of was used. Other than that, the operation was performed in the same manner as in Example 1.

<Comparative example 1>
(Dispersion process)
40 g of decane was added to 4.0 g of Rheolosil QS-30, and the mixture was stirred with a spoon until there were no powder particles left, to obtain a creamy dispersion.
(Extraction process)
After adding 16.0 g of aqueous ammonia of 9.38% by mass and pH 13.0 to the above dispersion, the mixture was stirred for 30 seconds at 7000 rpm using a homogenizer to obtain a mixed solution.
(Emulsification process)
A W/O emulsion was obtained by adding 3 g of decane in which 0.3 g of sorbitan monooleate was dispersed all at once, and stirring the mixture for 15 seconds at 7000 rpm using the same homogenizer as in the previous step.
(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 aggregate was dispersed in 40 g of 2-propanol for 30 minutes with stirring. Thereafter, the solvent was filtered off using a suction filter, and while the solvent was being suctioned, the product was washed with decane, water, and 2-propanol, respectively, to obtain a washed product.
(drying process)
The obtained washed product was transferred to a beaker and dried in a vacuum dryer at 150° C. for 3 hours.

<Comparative example 2>
The dispersion step and the extraction step were performed in the same manner as in Example 2, and in the extraction step, 21.2 g of ammonia water having a concentration of 0.12% by mass and a pH of 11.8 was used. The W phase thickened quickly and a mixed liquid could not be obtained. After that, it became impossible to implement.

<Comparative example 3>
(Dispersion liquid preparation process)
To 200 ml of ion-exchanged water in which 6.65 g of urea was dissolved, 66 g of Rheolosil QS-30 was added while stirring with a homogenizer, and after predispersing the fumed silica, an ultrasonic homogenizer (manufactured by BRANSON, Sonifier SFX250) was used. A fumed silica dispersion liquid was obtained by finely dispersing the mixture. Note that the dispersion liquid preparation step was performed in a chiller cooled to 10°C.
(W/O emulsion preparation process)
65.5g was taken from the fumed silica dispersion prepared in the above method, 129g of decane in which 0.75g of sorbitan monooleate was dispersed was added, and then using a homogenizer at 8600 rpm for 3 minutes. By stirring, a W/O emulsion was obtained.
(gelation process)
The obtained W/O emulsion was stirred at 300 rpm using four paddle blades 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 form a gel. .
(Gel collection process)
77 g of isopropyl alcohol and 52 g of water were added and stirred with a stirring blade while maintaining the temperature at 70° C. for 30 minutes. Thereafter, by allowing the mixture to stand still, it was separated into two layers, the O phase as an upper layer and the W phase as a lower layer.
Then, the O phase and the W phase were separated by decantation, and the W phase was recovered.
The obtained gelled product was filtered from the W phase using a suction filter. The recovered gelled product was dried in a vacuum dryer at 150° C. for 12 hours.

Claims (16)

A porous aggregate made of metal oxide,
A porous aggregate characterized by satisfying the following (1) to (3).
(1) Average crushing strength Cs is 0.02 to 1 MPa
(2) Average circularity is 0.5 or more (3) Circle equivalent diameter (D50) is 1 to 100 μm The porous aggregate according to claim 1, wherein the mode of the pore diameter is 5 to 50 nm. The porous aggregate according to claim 1 or 2, characterized in that the pore volume is 0.5 to 5 ml/g. The porous aggregate according to claim 1, having a specific surface area of 50 to 800 m ² /g. An abrasive comprising the porous aggregate according to any one of claims 1 to 4. A cosmetic comprising the porous aggregate according to any one of claims 1 to 4. A drug carrier comprising the porous aggregate according to any one of claims 1 to 4. A chromatography carrier comprising the porous aggregate according to any one of claims 1 to 4. A resin composition comprising the porous aggregate according to any one of claims 1 to 4. a dispersion step of mixing metal oxide particles and a hydrophobic solvent to obtain a dispersion;
Mixing the dispersion liquid and ammonia water having a pH of 12 or more and containing 1 to 30% by weight of ammonia at a ratio of 0.1 to 1 part by weight of ammonia water to 1 part by weight of the hydrophobic solvent, an extraction step of extracting the metal oxide particles from the hydrophobic solvent into the ammonia water to obtain a mixed solution consisting of an upper layer of the hydrophobic solvent and a lower layer of the ammonia aqueous solution containing the metal oxide particles;
an emulsification step of adding a surfactant to the mixed liquid to prepare a W/O emulsion;
The W/O emulsion is supplied to an alcohol containing 0.5 to 5 parts by weight based on 1 part by weight of the W/O emulsion and having a carbon number of 4 or less to form an upper O phase and a lower W phase. , a coagulation step of producing water-insoluble aggregates in the W phase;
a solid-liquid separation step to obtain the aggregate through 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: The method for producing a porous aggregate according to claim 10, comprising, between the aggregation step and the solid-liquid separation step, an aging step of heating the W phase to 10 to 90° C. to age the aggregate. . The method for producing a porous aggregate according to claim 10 or 11, wherein the hydrophobic solvent has a solubility in water at 20°C of 20 g/L or less. The method for producing a porous aggregate according to any one of claims 10 to 12, wherein in the extraction step, the concentration of the metal oxide in the mixed liquid is 2 to 10% by mass. The method for producing a porous aggregate according to any one of claims 10 to 13, wherein in the extraction step, the metal oxide particles in the hydrophobic solvent are mixed by stirring until the concentration becomes 2% by mass or less. The method for producing a porous aggregate according to any one of claims 10 to 14, wherein in the cleaning step, the porous aggregate is cleaned with at least one cleaning liquid selected from water, a hydrophobic solvent, and an alcohol having 4 or less carbon atoms. The method for producing a porous aggregate according to any one of claims 10 to 15, wherein in the solid-liquid separation step, solid-liquid separation is performed by filtration or centrifugation.