JP2015024941A - Hollow particle and production method thereof - Google Patents

Abstract

To provide hollow particles by a simple manufacturing process without using a core material such as polymer particles, etc. SOLUTION: Layered silicate and inorganic phosphoric acid formed by evaporation spray drying Hollow particles made of salt, characterized in that the ratio of diameter to partition wall thickness (diameter / partition wall thickness) is 3/1 to 20/1.
[Selection] Figure 1

Description

  The present invention relates to hollow particles having nanosheet partition walls and a method for producing the same.

  Since hollow particles having inorganic partition walls can be expected to have a wide range of applications as composite materials, catalysts, pharmaceuticals, etc., synthesis has been attempted using various methods. Conventionally, it has been reported that a polymer sphere is used as a template to coat the surface with nanoparticles or the like to synthesize a core / shell structure, and that the core is removed to induce a hollow shell material (Patent Document 1). ). Patent Document 2 proposes a method for producing hollow nanoparticles in which the core portion of solid nanoparticles is hollow.

JP 2004-130429 A WO2011-058976

However, the synthesis method using a polymer sphere template has a drawback in that a process of removing the polymer is required after coating the inorganic nanosheet, which makes the process complicated. Furthermore, when removing the core particles by the solvent, it is impossible to completely remove the partition walls formed by the inorganic nanosheets without breaking them. In the case of the method by heat treatment, the inorganic nanosheets themselves are oxides. There is a possibility that the properties of the original inorganic nanosheet may be impaired by the alteration.
An object of this invention is to implement | achieve the hollow particle comprised by the partition which consists only of nanosheets, and its manufacturing method in view of such a situation.

[1] Hollow particles made of layered silicate and inorganic phosphate formed by evaporation spray drying, wherein the ratio of diameter to partition wall thickness (diameter / partition wall thickness) is 3/1 to Hollow particles characterized by being 20/1.

[2] Swelling synthetic mica (mica) such as montmorillonite, beidellite, nontronite, saponite, hectorite, smectites represented by stevensite, Na-tetrasilicon mica, Na-teniolite, [1] The hollow particles according to [1], which are monolayer silicates selected from the group of vermiculites such as 2-octahedral vermiculite and 3-octahedral vermiculite.

[3] The phosphate is a primary phosphate ion (H ₂ PO ₄ ⁻ ), a secondary phosphate ion (HPO ₄ ²⁻ ), a tertiary phosphate ion (PO ₄ ³⁻ ), or a diphosphate ion. It is a salt of at least one of (P ₂ O ₇ ⁴⁻ ), triphosphate (P ₃ O ₁₀ ⁵⁻ ), polyphosphate ion (P _n O _{3n + 1} ^{(n + 2) −} ) and a cation. The hollow particles according to [1] or [2].

[4] The hollow particles according to any one of [1] to [3], wherein the layered silicate raw material primary particle diameter is in the range of 5 nm or more and 1 μm or less.

[5] The hollow particles according to any one of [1] to [4], wherein an average particle diameter of the hollow particles is 20 nm or more and 500 nm or less.

[6] The mixing ratio of the (A) layered silicate and the (B) inorganic phosphate is 1 to 20 (B) inorganic phosphate with respect to 100 parts by mass of the (A) layered silicate. The hollow particle according to any one of [1] to [5], wherein the hollow particle is a mass part.

[7] A method for producing the hollow particles, wherein the dispersion liquid in which the layered silicate and the phosphate are dispersed is dispersed by centrifugal spraying in an atmosphere in which the dispersion medium evaporates to evaporate the dispersion medium. A method for producing hollow particles, comprising removing the particles.

  The hollow particles of the present invention are those in which hollow particles are formed by spray-drying a colloidal layered silicate dispersion, and since no core substance, such as polymer particles, is used, only the drying process is performed. It is possible to provide hollow particles. Moreover, since the manufacturing method of the hollow particle of this invention does not require a solvent washing | cleaning process and a heating combustion process, it can anticipate as a low environmental impact process.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the centrifugal spray-drying apparatus for implementing this invention. The transmission electron micrograph which shows the hollow particle in Example 1 of Table 1. FIG. Transmission electron micrograph showing hollow particles in Example 2 of Table 1 Transmission electron micrograph showing hollow particles in Example 3 of Table 1 2 is a transmission electron micrograph of a powder sample in Comparative Example 1 of Table 1.

  The present invention is to obtain hollow particles by spray-drying a colloidal layered silicate dispersion, and a composite of an inorganic phosphate and a swellable layered silicate in which the dispersion is dispersed The first feature of the present invention is that Furthermore, the second feature is that the colloidal layered silicate dispersion is subjected to centrifugal spray drying. Swellability (swellability means that water penetrates between crystal layers in water and swells in water). Details of layered silicates, phosphates, solvents, and centrifugal spray drying are as follows. Shown in

  The layered silicate according to the present invention is not particularly limited as long as it swells in a solvent. Specifically, smectite represented by montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, Na-4 Swelling synthetic mica (mica) such as silicon mica and Na-teniolite, vermiculite such as 2-octahedral vermiculite and 3-octahedral vermiculite are suitable. These layered silicates may be natural minerals or may be synthesized by hydrothermal synthesis, melting method, solid phase method or the like. Moreover, in this invention, 1 type in said layered clay mineral may be used independently, and may be used in combination of 2 or more type.

The phosphate is composed of a first phosphate ion (H ₂ PO ₄ ⁻ ), a second phosphate ion (HPO ₄ ²⁻ ), a third phosphate ion (PO ₄ ³⁻ ), a diphosphate ion (P _2). Inclusion hydration using a salt of at least one of O ₇ ⁴⁻ ), triphosphate (P ₃ O ₁₀ ⁵⁻ ), and polyphosphate ion (P _n O _{3n + 1} ^{(n + 2) −} ) and a cation as a guest compound It is characterized by being at least 1 type selected from the thing. Although it is not specifically limited, inorganic phosphate is monopotassium phosphate, dipotassium phosphate, tripotassium phosphate, potassium pyrophosphate, pentapotassium triphosphate, potassium tripolyphosphate, potassium metaphosphate. , Monocalcium phosphate, dicalcium phosphate, tricalcium phosphate, calcium acid pyrophosphate, calcium pyrophosphate, monosodium phosphate, disodium phosphate, trisodium phosphate, sodium pyrophosphate, pentasodium triphosphate, acidic pyrolin Sodium phosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, sodium pentapolyphosphate, sodium metaphosphate, acidic sodium metaphosphate, sodium phosphite, sodium hypophosphite, primary magnesium phosphate, secondary magnesium phosphate, Magnetriphosphate , Magnesium pyrophosphate, magnesium metaphosphate, primary aluminum phosphate, secondary aluminum phosphate, tertiary aluminum phosphate, aluminum metaphosphate, monoammonium phosphate, diammonium phosphate, triammonium phosphate, ammonium pyrophosphate , One or more selected from the group consisting of ammonium tripolyphosphate, ammonium metaphosphate, and bitumenite.

  Hollow particles characterized in that the ratio of diameter to partition wall thickness (diameter / wall thickness) is 3/1 or more and 20/1 or less, more preferably 5/1 or more, 10 / 1 or less. Hollow particles in this range can be produced more stably.

  The primary particle size and the average particle size of the layered silicate used as a raw material for the production of hollow particles should be statistically processed by directly observing images with a laser diffraction particle size measuring device or an electron microscope. Can be obtained. In the measurement with the laser diffraction particle size meter, there is no significant difference between the diffraction behavior of the incident laser beam due to the aggregated particles and the diffraction behavior of the isolated primary particles, so the measured particle size exists as a single primary particle. There is no distinction between the particle size or the size of the aggregated secondary particles. Therefore, the average particle size measured by this method is an average value reflecting the average particle size of the secondary particles including the isolated primary particles that have not been agglomerated in a broad sense. It is preferable to use together with the method of observing and obtaining by statistical processing.

  The raw material primary particle size is preferably in the range of 5 nm to 1 μm, and more preferably in the range of 10 nm to 100 nm. If it is less than 5 nm, it becomes difficult to form a hollow shape because the particles are difficult to form a shell in the evaporation spraying process, and if it is more than 1 μm, it is difficult to form a spherical shape in the evaporation process, and anisotropic particles are formed after drying. There is a fear.

  The particle size of the hollow particles can be controlled by the concentration of the layered silicate dispersion, the drying temperature, and the production apparatus, but is formed in the range of 20 nm to 500 nm. The particle diameter is 10 to 100 times, preferably about 10 to 50 times the partition wall thickness. When the particle diameter is excessively larger than the partition wall thickness, the specific surface area is reduced, so that the functional characteristics are reduced. In addition, when the particle diameter is excessively small compared to the partition wall thickness, it does not change from solid particles.

The blending ratio of (A) layered silicate and (B) inorganic phosphate is preferably 1 to 20 parts by mass of (B) inorganic phosphate with respect to 100 parts by mass of (A) layered silicate. More preferably, (A) inorganic phosphate is in the range of 3 to 10 parts by mass with respect to 100 parts by mass of (A) layered silicate. When the inorganic phosphate is less than 1 part by mass and over 20 parts by mass with respect to 100 parts by mass of the layered silicate, the crosslinked structure between the layered silicate particles in the dispersion becomes unstable and solid particles are formed. There is a risk.

  The solvent used for dispersion of the layered silicate and phosphate is based on water, but alcohol (lower alcohol such as methanol, ethanol, propanol, etc.) and / or polyhydric alcohol may be mixed therewith. .

  The basic configuration of the centrifugal spray device used in the production method of the present invention will be described (FIG. 1). This apparatus has a cylindrical chamber (10) in which the spraying process is performed, a centrifugal disk structure (30) disposed therein for centrifugally spraying the raw material, and the raw material is supplied to the centrifugal disk structure (30). It is comprised by the raw material supply mechanism (20).

  The raw material supply mechanism (20) is arranged above the chamber (10), and has a raw material tank (23) having a flow-down port (23) at the lower end for flowing the raw material toward the rotation center of the receiving surface (34). 21) and a gas spray nozzle (22) for injecting the raw material flowing down from the flow down port (23) toward the receiving surface (34).

  In this way, the liquid raw material flowing down from the flow outlet (23) of the raw material tank (21) is made into droplets of several microns to 10 microns by the gas ejected from the gas spray nozzle (22), and high speed Spray onto the rotating receiving surface (34). The raw material sprayed on the receiving surface (34) becomes a thin film (50), and is scattered as fine droplets from the outer periphery to the chamber (10) by centrifugal force due to rotation, as indicated by (35) in the figure. Is done. The raw material scattered as fine droplets in the chamber (10) is heated to a temperature controlled by the heaters (41), (42), and (43) in the middle of falling to the bottom of the chamber (10). Depending on the temperature, the liquid component is removed by evaporation. The particles thus obtained together with the gas injected from the gas spray nozzle (22) are taken out through the outlet (44) to the outside of the chamber (10) and collected.

  The thickness of the thin film (50) is determined by the feed rate of raw materials, the gas injection speed, and the rotational speed of the disk (33). The faster the rotational speed, the thinner the thin film (50) and the smaller the size of the resulting atomized particles. As the gas injection speed increases, the size of the droplets sprayed on the receiving surface (34) decreases. If the rotational speed of the receiving surface (34) is constant, if it is ejected at an excessively high speed, it will be reflected from the receiving surface (34) and a thin film (50) cannot be formed. It is necessary to maintain a certain relationship with the gas injection speed.

Further, as the feed rate of the raw material increases, the droplets become larger and the thin film (50) becomes thicker. For this reason, it is possible to adjust the thickness of the thin film (50) and the size of the atomized particles by adjusting these three elements with emphasis. Further, as to how the raw material is denatured, the temperature (T ₁ ) at the receiving surface (34) and the region (A ₁ ) above the receiving surface (34), and the region (A and ambient temperature (T ₂₎ at _2), is determined by the relationship between the volatilization temperature of the volatile components in the raw material (T _b). Further, the temperature (T _1), so can affect the fluidity of the raw material, it is necessary to exceed the temperature (Ta) to maintain fluidity capable of forming the thin film (50).
Furthermore, the temperature (T ₂ ) needs to be lower than such a modification temperature (T ₀ ) so that the nanosheet is not modified and the partition walls are not broken. When producing hollow particles as in the present invention, it is necessary to maintain a liquid state until atomization, and to evaporate volatile components after atomization to solidify, so the relationship between the three temperatures is The following formula 1 needs to be satisfied.

And the temperature of a raw material and injection gas, and the heating conditions by said heater (41), (42), (43) will be set so that it may become such temperature conditions. The atomized particles flow downward in the chamber (10) together with the propellant gas. Therefore, the upper heater (41) having the region (A ₁ ) as the heating range is adjusted so that the temperature (T ₁ ) satisfies the above-described formula 1 also depending on the temperature of the raw material and the temperature of the injection gas. Further, the middle heater (42) and the lower heater (43) having the region (A ₂ ) as a heating range move along with the gas flow, and the dispersion medium is moved while moving in the region (A ₂ ). Will be adjusted to the temperature (T ₂ ) so that is removed by evaporation.

The temperatures T ₁ and T ₂ as described above, and the rotational speed of the rotating disk disc are the solvent, the type of solid components and the concentration and viscosity of the solution as the raw material, the area of the silica-receiving surface, the thickness of the thin film and the desired solid particles. It is determined in consideration of the particle size of the material. In addition, the rotational speed of the rotating disk is not particularly defined, but generally, it operates within a range of 10,000 rpm to 60000 rpm.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[Evaluation item]
-Appearance and particle size measurement Observation was performed at an acceleration voltage of 160 kV using a transmission electron microscope (manufactured by JEOL Ltd.) JEM-2000FX, and the partition wall thickness and average particle size were measured from the number distribution.

[Example 1]
Synthetic saponite (Kunimine Kogyo Co., Ltd.) smecton (5 g) was added as a layered silicate to distilled water in 500 mL and stirred to prepare a suspension. Further, 0.3 g of sodium diphosphate (manufactured by Wako Pure Chemical Industries, Ltd.) was added as a phosphate and stirred at room temperature for 24 hours to prepare a uniform dispersion.
A sample was prepared from the dispersion using the centrifugal spray dryer of FIG. 1 under the following production conditions. FIG. 2 shows an observation image of the obtained sample, and Table 1 shows the evaluation result. FIG. 2 is a transmission electron micrograph showing hollow particles in Example 1 of Table 1.

[Production conditions]
Injection hole pore diameter: 1.5mm diameter
Raw material supply rate: adjusted between 1.5 ml / s and 1.8 ml / s Gas spraying pressure: 2 MPa
Injection gas: Nitrogen gas Rotating disk used: Material: Mild steel (Fe)
Turntable diameter: 70mm
Rotation speed: 30000rpm
Chamber atmosphere: atmospheric pressure

[Example 2]
Evaluation was conducted in the same manner as in Example 1 except that pentasodium triphosphate was used as the phosphate salt of Example 1. The evaluation results of the obtained powder sample are shown in Table 1. FIG. 3 is a transmission electron micrograph showing hollow particles in Example 2 of Table 1. The powder formed in Example 2 was a hollow particle having a partition wall thickness of 2 to 4 layers and an average particle diameter of 40 nm.

[Example 3]
Evaluation was conducted in the same manner as in Example 1 except that synthetic hectorite (Laponte RDS manufactured by Laporte) containing 4.5% by mass of sodium diphosphate was used for the layered silicate. FIG. 4 is a transmission electron micrograph showing hollow particles in Example 3 of Table 1. The evaluation results of the obtained powder sample are shown in Table 1. Moreover, the powder formed in Example 3 was a hollow particle having a partition wall thickness of 3 to 9 layers and an average particle diameter of 40 nm.

[Comparative Example 1]
Evaluation was performed in the same manner as in Example 1 except that no phosphate was added to the dispersion. A transmission electron micrograph of the powder sample obtained in Comparative Example 1 is shown in FIG. The evaluation results are shown in Table 1. All solid particles were obtained.

  The hollow particles of the present invention are expected to be applied in various fields such as composite materials, catalysts, and pharmaceuticals, and are expected to be useful for technological advancement in material design in various fields.

10 Chamber 20 Raw Material Supply Mechanism 21 Raw Material Tank 22 Gas Spray Nozzle 23 Downstream Port 30 Centrifugal Disc Structure 31 Cover 32 Rotating Motor 33 Disc 34 Receiving Surface 35 Atomized Particle 41 Upper Heater 42 Middle Heater 43 Lower Heater 44 Outlet 50 Thin Film A ₁ Upper region A ₂ Outer region T _b Volatilization temperature T ₁ Upper region ambient temperature T ₂ Outer region ambient temperature

Claims (7)

  Hollow particles made of layered silicate and inorganic phosphate formed by evaporation spray drying, the ratio of the diameter to the partition wall thickness (diameter / partition wall thickness) of 3/1 to 20/1 Hollow particles characterized by the above.   The layered silicate is composed of montmorillonite, beidellite, nontronite, saponite, hectorite, smectites represented by stevensite, swellable synthetic mica (mica) such as Na-tetrasilicon mica, Na-teniolite, 2-8 2. The hollow particle according to claim 1, wherein the hollow particle is a monolayer silicate selected from the group of vermiculites such as a tetrahedral vermiculite and a 3-octahedral vermiculite. The phosphate is composed of a first phosphate ion (H ₂ PO ₄ ⁻ ), a second phosphate ion (HPO ₄ ²⁻ ), a third phosphate ion (PO ₄ ³⁻ ), a diphosphate ion (P _2). A salt of at least one of O ₇ ⁴⁻ ), triphosphate (P ₃ O ₁₀ ⁵⁻ ), and polyphosphate ion (P _n O _{3n + 1} ^{(n + 2) −} ) and a cation. The hollow particles according to 1 to 2.   The hollow particle according to any one of claims 1 to 3, wherein the primary particle diameter of the raw material of the layered silicate is in the range of 5 nm to 1 µm.   The hollow particles according to any one of claims 1 to 4, wherein an average particle diameter of the hollow particles is 20 nm or more and 500 nm or less.   The blending ratio of the (A) layered silicate and the (B) inorganic phosphate is 1 to 20 parts by mass of the (B) inorganic phosphate with respect to 100 parts by mass of the (A) layered silicate. The hollow particles according to any one of claims 1 to 5, wherein the hollow particles are present.   A method for producing the hollow particles, wherein the dispersion liquid in which the layered silicate and the phosphate are dispersed is dispersed by centrifugal spraying in an atmosphere in which the dispersion medium evaporates, and the dispersion medium is removed by evaporation. A process for producing hollow particles characterized by the above.