JP7311258B2 - Method for producing spherical particles - Google Patents

Description

The present invention relates to a method for producing spherical particles composed of inorganic components.

Spherical particles of inorganic components are used in various industries and support modern convenient life. Particles vary in size and composition, and are manufactured in a variety of ways. For example, it is known to spray-dry a colloidal liquid containing an inorganic oxide to produce spherical porous silica particles having an average particle size of 1 to 10 μm (see, for example, Patent Document 1). It is also known to produce hollow silica particles by removing alkali from precursor particles obtained by spray-drying an aqueous alkali silicate solution (see, for example, Patent Document 2). Further, it is known to produce silica particles having acicular projections by an emulsion method (see, for example, Patent Document 3). In addition, a method of producing hollow glass microbodies by foaming glass frit in a flame is known (see, for example, Patent Document 4).

JP-A-61-270201 JP 2011-256098 A Japanese Patent Application Laid-Open No. 2009-242115 JP-A-2006-256895

Various methods for producing spherical particles with various structures have been proposed, but it has been necessary to apply different methods depending on the constituent components even for spherical particles with the same structure. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for relatively easily controlling the structure of spherical particles composed of an inorganic component.

The method for producing spherical fine particles of the present invention includes an emulsification step of mixing an aqueous dispersion containing an inorganic component, an emulsifier, and a non-aqueous solvent to prepare a water-in-oil emulsion containing emulsified droplets. , a freezing step of cooling the emulsified liquid to −50 to 0° C. to freeze emulsified droplets, and a dehydration step of removing water from the emulsified droplets after the freezing step.

Further, by adjusting the conditions of the freezing step, it is possible to obtain porous spherical particles having pores inside the particles or hollow spherical particles having cavities inside the outer shell. That is, hollow spherical particles can be produced by freezing emulsified droplets in a temperature range of -10 to 0°C.

Furthermore, hollow spherical particles with porous outer shells and hollow spherical particles with non-porous outer shells can be produced by selecting constituent components of the spherical particles.

According to the method for producing spherical particles of the present invention, the internal structure of spherical particles made of inorganic components can be controlled relatively easily. Specifically, porous particles, hollow particles with a porous outer shell, and hollow particles with a non-porous outer shell can be produced.

A method for producing spherical particles according to the present invention comprises the following steps. First, a dispersion in which an inorganic component is dispersed in water, an emulsifier, and a non-aqueous solvent are mixed, and a water-in-oil type emulsion containing emulsified droplets is prepared from this mixed solution (emulsification step). This emulsified liquid is cooled to freeze emulsified droplets (freezing step). Next, water is removed from the emulsified droplets (dehydration step). As a result, spherical particles composed mainly of the inorganic component contained in the aqueous dispersion are obtained. The dispersion liquid may contain a solvent other than water. Also, an emulsifier and a non-aqueous solvent are added to form water-in-oil emulsified droplets. Next, each step will be described in detail.

[Emulsification process]
First, an aqueous dispersion of inorganic components is prepared. At this time, it is preferable to adjust the solid content concentration of the aqueous dispersion to be in the range of 0.5 to 80%. In general, when the solid content concentration exceeds 80%, the viscosity of the dispersion increases, and there is a risk that uniformity of emulsified droplets cannot be obtained. If the solid content concentration is less than 0.5%, the particles are too dilute and the spherical particles are not shaped properly.

This aqueous dispersion is mixed with a non-aqueous solvent and an emulsifier. The non-aqueous solvent is necessary for emulsification and should be incompatible with water. Common hydrocarbon solvents can be used as non-aqueous solvents. Any emulsifier may be used as long as it can form water-in-oil emulsified droplets. Surfactants are suitable as emulsifiers. The HLB value of the surfactant is preferably in the range of 1-10. An optimum HLB value may be selected according to the polarity of the non-aqueous solvent. The HLB value is particularly preferably in the range of 1-5. Also, surfactants with different HLB values may be combined.

Next, this mixed solution is emulsified by an emulsifier. At this time, emulsification conditions are set so as to obtain an emulsified liquid containing emulsified droplets of a desired average diameter. The mean diameter of the emulsified droplets approximately corresponds to the mean diameter of the spherical particles. Therefore, in the emulsification step, an emulsified liquid containing emulsified droplets having an average diameter of 10 nm to 1000 μm is generally prepared. A common high-speed shearing device can be used for the emulsifying device. In addition, known devices such as a high-pressure emulsifier capable of obtaining finer emulsified droplets, a membrane emulsifier capable of obtaining more uniform emulsified droplets, and a microchannel emulsifier can be selected depending on the purpose.

It is industrially difficult to prepare an emulsified liquid containing emulsified droplets with an average diameter of less than 10 nm. On the other hand, although it is easy to prepare emulsified droplets with an average diameter exceeding 1000 μm, there are not many examples of industrial application of spherical particles exceeding 1000 μm at present.

[Freezing process]
Next, the emulsified liquid obtained in the emulsification step is cooled in the range of -50 to 0°C. As a result, a frozen emulsion is obtained by freezing the water in the droplets. Here, when the freezing temperature is -50° C. to -10° C., the inorganic components in the droplets are expelled as the ice crystals grow rapidly. Therefore, porous spherical particles can be prepared. In the case of −10 to 0° C., the inorganic component in the droplet is expelled to the periphery of the droplet as ice crystals grow slowly. Therefore, it is possible to prepare hollow-structured spherical particles having cavities inside the outer shell.

When the emulsified droplets are frozen, their volume expands by about 10%, but spherical particles that maintain the particle diameter of the frozen emulsified droplets can be obtained even after dehydration in the dehydration step described later.

[Dehydration process]
After the freezing step, the emulsion is dehydrated. The dehydration treatment removes water from the emulsified droplets to obtain a non-aqueous solvent dispersion containing spherical particles with a desired particle size.

Dehydration can be done in various ways. For example, after heating the frozen emulsion to room temperature, water can be evaporated by heating under normal pressure or reduced pressure. As a result, a non-aqueous solvent dispersion containing spherical particles is obtained. In the heat dehydration method under normal pressure, a separable flask equipped with a cooling tube is heated, and dehydration is performed while recovering the non-aqueous solvent. In the heat dehydration method under reduced pressure, dehydration is performed by heating under reduced pressure using a rotary evaporator, an evaporator, or the like, while recovering the non-aqueous solvent.

Alternatively, the emulsified liquid droplets can be dehydrated during the solid-liquid separation of the emulsified liquid. That is, after raising the temperature of the frozen emulsion obtained in the freezing step to room temperature, the solid content is separated by a known method such as filtration or centrifugation. As a result, the water of the emulsified droplets can be removed together with the non-aqueous solvent. A cake of spherical particles is thus obtained. Furthermore, by heating the cake-like substance under normal pressure or under reduced pressure (drying step), water is evaporated together with the non-aqueous solvent to obtain a dry powder of spherical particles.

Also, if necessary, the cake-like substance can be washed to reduce the surfactant. It is preferable that the residual amount of the surfactant is 500 ppm or less with respect to the spherical particles. This improves the long-term stability when the spherical particles are incorporated into a liquid formulation such as an emulsion. In order to reduce surfactant, it is preferable to wash with an organic solvent.

When it is desired to obtain spherical particles in the form of an aqueous dispersion, water is substituted for the cake-like substance obtained by the solid-liquid separation treatment. Thereby, an aqueous dispersion of spherical particles is obtained.

Inorganic components used in the present invention include compounds containing at least one element of silicon, aluminum, titanium, iron, zinc, strontium, zirconium, barium, and cerium.

These inorganic ingredients must be dispersed in water. That is, a dispersion obtained by dispersing a water-soluble inorganic compound in water, a sol obtained by previously dispersing a solid in water, or a dispersion obtained by dispersing a powder of titanium oxide or the like in water is used. Moreover, you may use these in combination.

Hollow spherical particles having a non-porous outer shell can be obtained by cooling an emulsified liquid prepared using a water-soluble inorganic compound such as a silicic acid liquid in the range of -10 to 0°C.

Water-soluble inorganic compounds include alkali metal salts, organic alkali metal salts, peroxo compounds, and salts thereof. Examples of alkali metal salts include sodium silicate, potassium titanate, and those treated with a cation exchange resin to dealkalize (remove alkali ions, etc.). Examples of organic alkali metal salts include quaternary ammonium silicates and quaternary ammonium silicates treated with a cation exchange resin to dealkalize (remove alkali ions, etc.). Further, examples of peroxo compounds include titanium or zirconium peroxo compounds.

Examples of sols in which solids are previously dispersed in water include silica sols, alumina sols, titania sols, iron oxide sols, zinc oxide sols, strontium oxide sols, zirconium oxide sols, barium sulfate sols, and cerium oxide sols. Also, the average particle diameter _d3 of various particles is preferably 2 nm to 100 μm. If the average particle size exceeds 100 μm, spherical particles may not be obtained. When the average particle size is less than 2 nm, the stability as particles is low, which is not preferable from an industrial point of view. A range of 10 nm to 10 μm is particularly desirable.

When dispersing the powder in water, after adding the powder to the water, a submerged disperser such as a high-speed line shearing stirrer, colloid mill, roll mill, high-pressure jet disperser, ultrasonic disperser, volumetric drive mill, medium It is preferable to disperse using a stirring mill or the like. The average particle diameter _d3 of various particles after dispersion is preferably 2 nm to 100 μm.

When an alkali metal salt, an organic alkali metal salt, or a peroxo compound salt is used as the inorganic component, it is necessary to perform a desalting operation after the dehydration step. When the salt is an alkaline component, it is neutralized with a mineral, organic acid, carbonic acid, or the like. When the salt is an acid component, it is neutralized with an alkali, an organic base, or the like. After neutralization, it is desirable to purify by washing with water.

Examples of the present invention will be specifically described below.

[Example 1]
First, an aqueous dispersion of inorganic components is prepared. In this example, 3333 g of pure water was added to 1667 g of silica sol (Cataloid SI-30 manufactured by Nikki Shokubai Kasei Co., Ltd., solid concentration: 30%) to prepare an aqueous dispersion with a solid concentration of 10%.

This aqueous dispersion, a water-insoluble solvent and a surfactant are mixed. In this example, 200 g of the aqueous dispersion was added to a mixed solution of 3346 g of heptane (manufactured by Kanto Chemical Co., Ltd.) and 25 g of surfactant AO-10V (manufactured by Kao Corporation). This mixed solution was stirred at 10000 rpm for 10 minutes to emulsify using an emulsifying disperser (TK Robomix manufactured by Primix). The emulsified liquid thus obtained was allowed to stand in a constant temperature bath at -25°C for 72 hours to freeze the water in the emulsified droplets. After that, the temperature was raised to room temperature. Furthermore, it was filtered with quantitative filter paper (No. 2, manufactured by Advantech Toyo Co., Ltd.) using a Buchner funnel (3.2 L, manufactured by Sekiya Rika Glass Instruments Co., Ltd.). This filtration method removes water from the emulsified droplets. After that, washing was repeated with heptane to remove the surfactant. The resulting cake-like material was dried at 120° C. for 12 hours. This drying process also removes the water in the emulsified droplets. The obtained dried powder was calcined at 500° C. for 4 hours, and the calcined powder was sieved with a 250-mesh sieve (JIS test standard sieve) to obtain a powder of spherical particles.

Table 1 shows the preparation conditions of the spherical particles. Further, the physical properties of the powder of spherical particles were measured by the following methods. Table 2 shows the results.

(1) Average Particle Size of Each Particle The particle size distribution of each particle was measured using a laser diffraction method. The median value was obtained from this particle size distribution and used as the average particle size. Thus, the average particle size d ₁ of the spherical particles and the average particle size d ₃ of the inorganic component were determined. Here, the particle size distribution was measured using a laser diffraction/scattering particle size distribution analyzer LA-950v2 (manufactured by HORIBA, Ltd.). However, for the average particle size _d1 of Examples 10 and 11, the particle size distribution was measured by the dynamic light scattering method using Microtrac UPA (manufactured by Nikkiso Co., Ltd.).

(2) Average Particle Size Ratio Before and After Ultrasonic Dispersion Dispersion was carried out using a laser diffraction/scattering particle size distribution analyzer (LA-950v2) with the dispersion condition set to "ultrasonic for 60 minutes". The particle size distribution of spherical particles after dispersion was measured. The median value of this particle size distribution was defined as the average particle size _d2 after ultrasonic dispersion. From this, the ratio (d ₂ /d ₁ ) of the average particle size before and after ultrasonic dispersion was determined.

(3) Sphericality of Spherical Particles Using a transmission electron microscope (manufactured by Hitachi, Ltd., H-8000), photographs are taken at a magnification of 2000 to 250,000 times to obtain photographic projections. Arbitrarily selected 50 particles from this photographic projection, the maximum diameter DL and the short diameter DS perpendicular thereto were measured to obtain the ratio (DS/DL). Their average value was taken as the degree of sphericity.

(4) Specific Surface Area of Spherical Particles About 30 ml of the powder of spherical particles was collected in a magnetic crucible (B-2 type), dried at 105° C. for 2 hours, placed in a desiccator and cooled to room temperature. Next, 1 g of the sample was taken, and the specific surface area (m ² /g) was measured by the BET method using a fully automatic surface area measuring device (manufactured by Yuasa Ionics, Multisorb Model 12). The density (1.5 g/cm ³ ) of the type I crystalline cellulose blended in the spherical particles was converted into a specific surface area per unit volume. As for the aqueous dispersions of spherical particles of Examples 10 and 11, the powder obtained by drying the dispersions at 120° C. for 12 hours was used as a sample.

(5) Pore Volume and Pore Diameter of Spherical Particles 10 g of powder of spherical particles was placed in a crucible, dried at 105° C. for 1 hour, placed in a desiccator and cooled to room temperature. Next, a 0.15 g sample is placed in the cleaned cell, and nitrogen gas is adsorbed onto the sample while vacuum deaeration is performed using Belsorp mini II (manufactured by Bell Japan), followed by desorption. From the obtained adsorption isotherm, the average pore diameter is calculated by the BJH method. Also, the pore volume was calculated from the formula “pore volume (ml/g)=(0.001567×(V−Vc)/W)”. Here, V is the standard adsorption amount (ml) at a pressure of 735 mmHg, Vc is the cell blank capacity (ml) at a pressure of 735 mmHg, and W is the mass of the sample (g). Also, the density ratio of nitrogen gas to liquid nitrogen was set to 0.001567. As for the aqueous dispersions of spherical particles of Examples 10 and 11, the powder obtained by drying the dispersions at 120° C. for 12 hours was used as a sample.

(6) Average Diameter of Emulsified Droplets Using a laser diffraction method, the particle size distribution of emulsified droplets was measured. A median value was obtained from this particle size distribution and used as an average diameter. Thus, the average diameter of emulsified droplets was obtained. Here, the particle size distribution was measured using a laser diffraction/scattering particle size distribution analyzer SALD-2000 (manufactured by Shimadzu Corporation). However, for the average diameter of the emulsified droplets in Examples 10 and 11, the particle size distribution was measured by the dynamic light scattering method using ELS-Z (manufactured by Otsuka Electronics Co., Ltd.).

[Example 2]
An emulsion was prepared in the same manner as in Example 1. This emulsion was allowed to stand in a freezer at -5°C for 72 hours. After that, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

The structure of the spherical particles obtained in this example was investigated. After uniformly mixing 0.1 g of powder with about 1 g of epoxy resin (EPO-KWICK manufactured by BUEHLHER) and curing at room temperature, the sample was processed using an FIB processing device (FB-2100 manufactured by Hitachi, Ltd.). made. Using a transmission electron microscope (HF-2200, manufactured by Hitachi, Ltd.), an SEM image of this sample was taken under the condition of an acceleration voltage of 200 kV. As a result, the particles had a hollow structure in which a cavity was formed inside the outer shell. From this SEM image, the thickness T and the outer diameter OD of the outer shell were measured to obtain the outer shell thickness ratio (T/OD).

[Example 3]
USBB-120 (solid concentration: 10%) manufactured by Nikki Shokubai Kasei Co., Ltd. was used instead of the aqueous dispersion of inorganic components used in Example 1. Therefore, the inorganic component in this example is silica alumina. Except for this, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 4]
In this example, 500 g of FINEX-50 (manufactured by Sakai Chemical Industry Co., Ltd.) was suspended in 4500 g of pure water, and this suspension was passed through a microfluidizer (M-7250-30, manufactured by Microfluidex Co., Ltd.) 10 times. , an aqueous dispersion having a solid content concentration of 10% was prepared. Using this as an aqueous dispersion of an inorganic component, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 5]
In place of the aqueous dispersion of inorganic components used in Example 1, Neosanver PW-1010A-20 (solid concentration: 10%) manufactured by Nikki Shokubai Kasei Co., Ltd. was used. Except for this, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 6]
In place of the aqueous dispersion of inorganic components used in Example 1, Neosanver A (solid concentration: 10%) manufactured by Nikki Shokubai Kasei Co., Ltd. was used. Except for this, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 7]
In place of the aqueous dispersion of inorganic components used in Example 1, Neosanver F (solid concentration: 10%) manufactured by Nikki Shokubai Kasei Co., Ltd. was used. Except for this, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 8]
In this example, 4138 g of pure water was added to 862 g of BF-20FW (solid concentration: 58%) manufactured by Sakai Chemical Industry Co., Ltd. to prepare an aqueous dispersion with a solid concentration of 10%. Using this as an aqueous dispersion of an inorganic component, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 9]
In this example, 3333 g of pure water was added to 1667 g of SZR-W (solid concentration: 30%) manufactured by Sakai Chemical Industry Co., Ltd. to prepare an aqueous dispersion with a solid concentration of 10%. Using this as an aqueous dispersion of an inorganic component, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 10]
A silicic acid solution (solid concentration: 4.5%) was used as an aqueous dispersion of inorganic components. 200 g of this silicic acid solution was added to a mixed solution of 3346 g of heptane (manufactured by Kanto Chemical Co., Ltd.) and 25 g of surfactant AO-10V (manufactured by Kao Corporation). This mixed solution was passed through a microfluidizer three times at a pressure of 100 MPa. This resulted in an emulsified liquid containing emulsified droplets. The emulsified liquid thus obtained was allowed to stand in a constant temperature bath at -25°C for 72 hours to freeze the water in the emulsified droplets. After that, the temperature was raised to room temperature. Furthermore, centrifugation treatment was performed at 10000 G for 10 minutes to separate solid and liquid. The sediment thus obtained was again dispersed in heptane and centrifuged. This operation was repeated three times to remove the surfactant. Further, the obtained sediment was dispersed in ethanol and centrifuged at 10000 G for 10 minutes for solid-liquid separation. The sediment thus obtained was again dispersed in ethanol and centrifuged. This operation was repeated 5 times. Further, the obtained sediment was dispersed in pure water and subjected to centrifugal separation at 10000 G for 10 minutes to separate solid and liquid. The sediment thus obtained was again dispersed in pure water and subjected to centrifugal separation. This operation was repeated 10 times to obtain an aqueous dispersion of spherical particles. Physical properties of an aqueous dispersion of the spherical particles were measured.

[Example 11]
In this example, 178 g of pure water was added to 22 g of a silicic acid solution (solid concentration: 4.5%) to prepare an aqueous dispersion of inorganic components with a solid concentration of 0.5%. 200 g of this aqueous dispersion was added to a mixed solution of 3346 g of heptane (manufactured by Kanto Chemical Co., Ltd.) and 25 g of surfactant AO-10V (manufactured by Kao Corporation). This mixed solution was passed through a microfluidizer 10 times at a pressure of 170 MPa. Thereafter, an aqueous dispersion of spherical particles was prepared in the same manner as in Example 10, and its physical properties were measured. In this example, since the solid content concentration was lower than in Example 10 and the conditions of the microfluidizer were changed, small spherical particles were obtained.

[Example 12]
Spherical particles were prepared in the same manner as in Example 1, except that the emulsification conditions were 100 rpm for 10 minutes, and their physical properties were measured.

[Example 13]
Spherical particles were prepared in the same manner as in Example 1, except that the emulsification conditions were 2000 rpm for 10 minutes, and their physical properties were measured.

[Example 14]
The silica sol (Cataloid SI-30) used in Example 1 was used as an aqueous dispersion of an inorganic component without diluting it at a solid concentration of 30%. Except for this, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 15]
A silicic acid solution (solid concentration: 4.5%) was used as an aqueous dispersion of inorganic components. Except for this, spherical particles were prepared in the same manner as in Example 1, and their physical properties were measured.

[Example 16]
A silicic acid solution (solid concentration: 4.5%) was used as an aqueous dispersion of inorganic components. Spherical particles were prepared in the same manner as in Example 2 except for this, and their physical properties were measured.

[Comparative Example 1]
An emulsion was prepared in the same manner as in Example 1. This emulsion was placed in a glass beaker and frozen by immersing it in liquid nitrogen (-196° C.) in a Dewar bottle for 1 minute. After that, the temperature was raised to room temperature. Furthermore, it was filtered with quantitative filter paper (No. 2, manufactured by Advantech Toyo Co., Ltd.) using a Buchner funnel (3.2 L, manufactured by Sekiya Rika Glass Instruments Co., Ltd.). After that, washing was repeated with heptane to remove the surfactant. The resulting cake-like material was dried at 120° C. for 12 hours. Moisture in the emulsified droplets was removed by this drying process. The dried powder was calcined at 500° C. for 4 hours, and the calcined powder was sieved with a 250-mesh sieve (JIS test standard sieve) to obtain a powder of inorganic particles. Physical properties of the inorganic particles were measured.

Claims (4)

A mixed liquid containing an aqueous dispersion containing an inorganic component, an emulsifier, and a non-aqueous solvent is emulsified so that the solid content concentration is 0.5 to 80%, to form emulsified droplets encapsulating the aqueous dispersion. an emulsification step of preparing a water-in-oil emulsion containing
a freezing step of forming spherical particles from the emulsified droplets by cooling the emulsified liquid to −50 to 0° C. to expel the inorganic component as ice crystals grow in the emulsified droplets;
a dehydration step of returning the emulsified droplets to room temperature after the freezing step and removing water from the emulsified droplets. In the freezing step, the emulsified liquid is cooled to −50° C. or more and less than −10° C. to freeze the emulsified liquid droplets, thereby manufacturing porous spherical particles having pores in the particles. Item 1. A method for producing spherical particles according to item 1 . 1. The method according to claim 1 , wherein in the freezing step, the emulsified liquid is cooled to -10 to 0.degree. 3. The method for producing spherical particles according to 1 . 4. A compound according to any one of claims 1 to 3 , characterized in that said inorganic component is a compound containing at least one element of silicon, aluminum, titanium, iron, zinc, strontium, zirconium, barium, and cerium. A method for producing spherical particles of