JP7114231B2 - inorganic particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to inorganic particles containing air bubbles.

Oxide hollow particles and oxide porous materials are used in fields such as heat-insulating materials, heat-shielding materials, catalyst carriers, and building materials. For example, shirasu balloons (Patent Document 1) and perlite (Patent Document 2), which are hollow particles using volcanic vitreous sediment fine powder (shirasu), are widely known. It has not been applied in the fields of heat insulating materials, plastic fillers, sensitizers, etc. that require Silica hollow particles using calcium carbonate as a template have also been reported (Patent Document 3). Expensive. Ceramic particles having a plurality of open pores on the outer surface have also been reported (Patent Document 4). not sexual enough. Patent document 5 also describes a metal oxide powder, but this powder is also spongy and has pores on the outer surface, so the specific surface area is large and the heat shielding and heat insulating properties are not sufficient.
In addition, composite particles in which a thin film containing silica as a main component is formed on the outer shell of a carbon core particle (Patent Document 6), spherical polymer-metal compound composite particles in which the core is a polymer and the shell is a metal compound (Patent Document 6). Document 7) and particles obtained by removing central carbon and polymer from these particles have been reported, but all of them have one hollow pore, and the manufacturing process is complicated.

JP-A-8-73232 JP 2012-136402 A JP-A-2005-263550 JP 2010-100502 A WO2012/147812 JP 2010-105868 A JP-A-6-7670

However, there have been no reports of inorganic particles that are fine hollow particles, have a plurality of air bubbles inside, each air bubble is sealed with an inorganic material that constitutes the hollow particles, and have a dense particle surface.
Accordingly, an object of the present invention is to provide novel inorganic particles contained inside a plurality of cells that can be widely used as a heat insulating material or the like.

Therefore, the present inventor made various studies to solve the above problems, and found that droplets were produced by slurrying colloidal carbon spheres (colloidal carbon spheres) together with inorganic particle raw materials instead of solid carbon particles. However, if this is heat treated, the colloidal carbon spheres do not evaporate to the temperature at which the solvent evaporates and the inorganic particle raw material solidifies, so the shape of the cells is maintained, and a plurality of closed cells exist inside and each cell is sealed with an inorganic material that constitutes the hollow particles, fine inorganic particles with a dense particle surface can be easily produced, and the obtained particles are excellent in heat insulation and lightweight, and completed the present invention. did.

That is, the present invention provides the following [1] to [4].

[1] An inorganic particle with an average particle size of 0.1 μm to 20 μm, which contains a plurality of closed cells with an average particle size of 50 nm to 500 nm, each of which is sealed with an inorganic material that constitutes the hollow particles, and has a dense particle surface.
[2] The inorganic particles of [1], wherein the inorganic particles are inorganic oxide particles.
[3] The method for producing inorganic particles according to [1] or [2], which comprises heat-treating water-based slurry liquid droplets containing colloidal carbon spheres and a particle raw material inorganic compound.
[4] The production method according to [3], wherein the heat treatment of the water-based slurry droplets is a means of granulating the water-based slurry droplets followed by heat treatment or a means of spray pyrolysis of the water-based slurry.

The inorganic particles of the present invention have a plurality of closed cells inside, each cell is sealed with an inorganic material that constitutes the hollow particles, and the surface of the particles is dense. It is possible to maintain excellent heat insulation without impregnation, and the light weight is not compromised. Therefore, it is useful as a wide range of heat insulating materials, heat shielding materials and building materials. Also, colloidal carbon spheres can be produced by autoclaving using a water-soluble organic substance, and the particle size can be controlled by the carbon source and heat treatment temperature.

SEM images of colloidal carbon spheres are shown. 1 shows an SEM image of the inorganic particles obtained in Example 1. FIG. 1 shows an SEM image of the inorganic particles obtained in Example 1. FIG. 1 shows an SEM image of the inorganic particles obtained in Example 1. FIG. 2 shows an SEM image of the inorganic particles obtained in Example 2. FIG. 2 shows an SEM image of the inorganic particles obtained in Example 2. FIG.

The inorganic particles of the present invention contain a plurality of closed cells with an average particle diameter of 50 nm to 500 nm, each bubble is sealed with an inorganic material that constitutes the hollow particles, and the particle surface is dense. 20 μm particles.

Closed cells mean that a plurality of cells in the inorganic particles exist independently. The particle size of closed cells means the inner diameter of each cell.
The average particle size of the closed cells is 50 nm to 500 nm, preferably 50 nm to 300 nm, more preferably 100 nm to 200 nm. Closed cells are cells generated by decomposing and removing colloidal carbon spheres used as a raw material. Therefore, the particle size of closed cells depends on the particle size of colloidal carbon spheres used as a raw material. The average particle diameter of the closed cells can be measured by scanning electron microscopy (SEM) of the cross section of the particles. Become.

The number of closed cells included in the inorganic particles is plural, and the number is appropriately determined according to the particle size of the colloidal carbon spheres used and the droplet size of the aqueous slurry during particle production. The number of closed cells is preferably adjusted in consideration of the relationship between the heat insulating property and lightness of the inorganic particles to be obtained and the strength. Specifically, the number is preferably 2 to 50, more preferably 4 to 27, even more preferably 5 to 14.

The inorganic particles have a dense particle surface, with each internal bubble sealed with an inorganic material forming the hollow particles. In other words, the internal air bubbles are independent and the particle surface is dense, so even if it is mixed with resin etc., the resin will not be impregnated in the air bubbles. is not damaged. After the colloidal carbon spheres are decomposed and removed by heat treatment, the bubbles are sealed by further heating to melt the inorganic material.

The inorganic particles of the present invention have an average particle size of 0.1 μm to 20 μm. It is preferably 0.1 μm to 10 μm, more preferably 0.1 μm to 5 μm, still more preferably 0.1 μm to 1 μm.
The average particle size of the inorganic particles can be measured by JIS R 1629 "Method for measuring particle size distribution of fine ceramic raw materials by laser diffraction/scattering method", a particle size distribution measuring device by laser diffraction/scattering method, SEM, or the like.

As the inorganic particles, inorganic oxide fine particles or water-soluble inorganic substances are preferable. Specifically, aluminum oxide, titanium oxide, magnesium oxide, calcium oxide, silica, aluminum nitrate, titanyl nitrate, magnesium nitrate, aluminosilicate, soda. Materials that soften with high temperature heat treatment include glass, borosilicate glass, and the like.

The compressive strength of the inorganic particles of the present invention is preferably 1 to 800 MPa, more preferably 10 to 800 MPa, even more preferably 30 to 800 MPa. Here, the compressive strength can be measured with a microcompression tester MCT-510 (manufactured by Shimadzu Corporation).

The thermal conductivity of the inorganic particles of the present invention is preferably 0.01 to 0.2 W/m·k, more preferably 0.01 to 0.1 W/m·k, and more preferably 0.01 to 0.05 W/m·k. k is more preferred. The thermal conductivity can be measured by the unsteady hot wire method using a rapid thermal conductivity meter QTM-500 (manufactured by Tokyo Denshi Kogyo Co., Ltd.).

The relative density of the inorganic particles of the present invention is preferably 0.2 to 0.8, more preferably 0.4 to 0.7. Lower relative densities lead to lower compressive strengths, while higher relative densities lead to higher thermal conductivity. The relative density is obtained by dividing the value measured by the gas replacement method of JIS R 1620 "Method for measuring particle density of fine ceramic powder", such as dry automatic densitometer Accupic II 1340, by the density of solid particles of the same composition. Desired.

The inorganic particles of the present invention can be produced by heat-treating aqueous slurry liquid droplets containing colloidal carbon spheres (hereinafter referred to as "CCS") and a particle raw material inorganic compound. Here, the means for heat-treating the water-based slurry droplets is preferably a means for heat-treating the water-based slurry droplets after granulating them, or a means for spray-pyrolyzing the water-based slurry.

More specifically, granules obtained by drying water-based slurry droplets containing raw materials of inorganic particles and CCS, or inorganic particles containing CCS are produced by heat-treating droplets of the water-based slurry. Then, the CCS inside is burned or decomposed to disappear, and the inorganic components are fired to seal the pores, and the traces of CCS are closed cells.
When a water-soluble organic substance such as ethyl cellulose or glucose is dissolved in water and treated in an autoclave at 140 to 200° C. for 3 to 24 hours, the organic substance aggregates to form micellar spherical fine particles. This is the colloidal carbon sphere (CCS). CCS is not completely carbonized, leaving many hydrophilic groups on the surface and showing hydrophilicity. When the heat treatment of CCS is further advanced, the organic matter is completely carbonized and becomes hydrophobic amorphous carbon spheres (ACS) (Materials Letters 61 (2007) 4199-4203, Carbohydrate Research 346 (2011) 999-1004).
Thus, CCS is a colloidal spherical organic substance and has hydrophilicity. Due to its hydrophilicity, it has high dispersibility in water and does not easily agglomerate, so it is possible to attach a component that becomes a compound of inorganic particles in water to the surface of each CCS particle. Since CCS has high dispersibility and does not agglomerate, closed cells can be formed in fine particles obtained by decomposing and removing CCS by heat treatment.
CCS can be produced by hydrothermally reacting an aqueous solution in which glucose, methylcellulose, etc. are dissolved in water. Since the particle diameter of CCS can be adjusted by adjusting conditions such as the type of raw material and the temperature of hydrothermal treatment, the diameter of closed cells in the fine particles can be controlled.
Since it is possible to produce CCS with fine particles having a particle size of 50 nm to 1 μm, even inorganic fine particles having a small particle size can form a plurality of closed cells.

The component that becomes the compound of the inorganic particles may be a compound that contains an element that constitutes an oxide and is dissolved in water, or a fine particle that is dispersed in water. powder. More specifically, aluminum salts, titanium salts, magnesium salts, calcium salts, sodium salts, potassium salts, lithium salts, borates, phosphates, aluminosilicates, aluminum alkoxides, tetraethoxysilane, tetramethoxysilane, etc. and fine powders of alumina, titania, zinc oxide and the like.

An aqueous slurry containing CCS is mixed with a component that will form a compound of inorganic particles. For mixing, there is a method of mixing and dissolving a component that becomes a compound of inorganic particles into an aqueous slurry containing CCS, and a method of mixing an aqueous slurry containing CCS with an aqueous solution or slurry in which a component that becomes a compound of inorganic particles is dissolved. , is not particularly limited.

Inorganic fine particles can be produced by heat-treating slurry droplets containing a component that forms a compound of CCS and inorganic particles, decomposing and removing CCS, and converting the material compound into an inorganic oxide by firing.
Heat treatment includes a method of heat-treating granules obtained by drying slurry droplets containing components that form compounds of CCS and inorganic particles, and a method of heat-treating slurry containing components that form compounds of CCS and inorganic particles by spray pyrolysis. is mentioned. These methods can be selected according to the particle size, shape, and the like.
In the method of heat-treating granules obtained by drying slurry droplets containing components that form compounds of CCS and inorganic particles, granules are produced by drying the slurry with a spray dryer or the like. The granules are calcined to decompose and calcine the CCS.
In the method of heat-treating a slurry containing a component that forms a compound of CCS and inorganic particles by spray pyrolysis, the slurry is sprayed with a nozzle or the like and introduced into a heating furnace, where CCS is decomposed and removed and calcined.
The heat treatment temperature may be 400° C. or higher at which CCS can be decomposed and removed. Furthermore, by increasing the heat treatment temperature, the compound of the inorganic fine particles can be converted into the desired oxide. Furthermore, by heating to a softening point of the oxide of the inorganic fine particles or higher, the pores can be sealed and the particle surfaces can be densified.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Reference example (production of CCS)
20 g of glucose was added to 250 mL of distilled water and dissolved. Next, this solution was heat-treated at 160° C. for 6 hours in a pressure vessel.
A SEM photograph of the obtained CCS is shown in FIG. CCS with a diameter of about 200-300 nm were obtained.

Example 1
12 g of sodium borate, 15 g of calcium nitrate, 25 g of aluminum nitrate and 100 g of colloidal silica (10% solids) were added to CCS and stirred to obtain a solution. Using an ultrasonic atomizer, the solution was sprayed into an air stream, introduced into a tubular furnace at 1000° C., and passed through for about 5 seconds for heat treatment.
SEM photographs of the resulting bubble-containing microparticles are shown in FIGS.

Microparticles with closed cells could be obtained by greatly reducing the amount of chemicals used.

The produced particles had a diameter of about 1 μm, a particle density (JIS R 1620 “Method for measuring particle density of fine ceramic powder” gas replacement method) of 1.2 g/cm ³ , and a BET specific surface area of 2.5 m ² /g. rice field. The particle size of the closed cells was 150-200 nm (measured by cross-sectional measurement with SEM).

For particle density, a solution without CCS (12 g sodium borate, 15 g calcium nitrate, 25 g aluminum nitrate, 100 g colloidal silica (10% solids) was added to 250 mL distilled water, stirred to obtain a clear solution, This was heat-treated in the same manner as described above, and the solid particle density produced was 2.5 g/cm ^3. The particle density of Example 1 was 1.2 g/cm ³ and the relative density was 0.48. This suggests that closed cells are formed in the particles, and the small BET specific surface area indicates that closed cells are formed.

Example 2
The same solution as that prepared in Example 1 was sprayed into an air stream using a two-fluid nozzle, introduced into a tubular furnace at 1000° C., and passed through for about 15 seconds for heat treatment.
SEM photographs of the resulting bubble-containing microparticles are shown in FIGS. Larger droplets resulted in larger particles.
The produced particles had a diameter of about 10 μm, a particle density (according to JIS R 1620 “Method for measuring particle density of fine ceramic powder” gas replacement method) of 1.2 g/cm ³ , and a BET specific surface area of 2 m ² /g. The particle size of the closed cells was 150 to 200 nm as in Example 1.
The particle density of Example 2 was 1.5 g/cm ³ and the relative density was 0.6, suggesting that closed cells were formed in the particles. In addition, the BET specific surface area is small, so it can be seen that closed cells are formed.

Claims (2)

Inorganic oxide hollow particles containing a plurality of closed cells with an average cell inner diameter of 50 nm to 500 nm, characterized by heat-treating an aqueous slurry droplet containing colloidal carbon spheres and a raw material inorganic compound for the inorganic oxide hollow particles. , an inorganic oxide having an average particle size of 0.1 μm to 20 μm in which each bubble is sealed with an inorganic oxide that constitutes the inorganic oxide hollow particle, and the surface of the inorganic oxide hollow particle is more dense than before the heat treatment A method for producing hollow particles, comprising:
The inorganic oxide is an inorganic oxide containing a component selected from aluminum oxide, titanium oxide, magnesium oxide, calcium oxide, silica, aluminosilicate, soda glass and borosilicate glass, and the starting inorganic compound constitutes the inorganic oxide. A method for producing inorganic salts, metal alkoxides or oxide fine powders containing soot elements . 2. The production method according to claim 1, wherein the heat treatment of the water-based slurry droplets is a means of granulating the water-based slurry droplets followed by heat treatment or a means of spray pyrolysis of the water-based slurry.

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