JP6975575B2 - Oxide hollow particles - Google Patents

Description

The present invention relates to hollow oxide particles useful for electrical insulation, fillers and the like.

Hollow particles made of oxide glass are useful as various fillers because they have excellent heat insulating properties and heat insulating properties. As the hollow particles of these oxide glasses, alumina hollow particles are known (Patent Documents 1 and 2), but a temperature of 1200 to 1300 ° C. is required at the time of thermal decomposition, and a smooth particle surface can be obtained. Was difficult. Further, although glass hollow particles containing no alkali have been reported (Patent Document 3), hollow glass spheres could not be synthesized unless the prepared glass powder was remelted in a flame at 1200 to 2000 ° C. On the other hand, in the aluminate (CaO-Al ₂ O ₃ ) two-component system, there is a narrow vitrification range in the vicinity of CaO 60 to 64 mol%, the viscosity of the liquidus temperature is low, and it is easy to produce hollow particles with a homogeneous shell. it is conceivable that.

Japanese Unexamined Patent Publication No. 2003-160331 Japanese Unexamined Patent Publication No. 2005-126309 Japanese Unexamined Patent Publication No. 2012-36055

However, since the CaO-Al ₂ O ₃ system has a very narrow vitrification composition, it is difficult to synthesize hollow particles having no pores on the shell surface.
Therefore, an object of the present invention is to provide new hollow particles of oxide glass having a high circularity and fineness, which can be used for various purposes.

Therefore, the present inventor has made various studies to produce new hollow oxide glass particles by the spray pyrolysis method. _{First, we examined the addition of alkali metal oxides such as Na 2} O, K ₂ O, and Li ₂ O to the CaO-Al ₂ O ₃ system, but if the amount of alkaline components increases, the chemical durability will be hindered. A part of the alkaline component elutes, which causes deterioration of electrical insulation. In addition, although _{it was considered to add SiO 2} , the vitrification range could be expanded _{, but there were problems such as low electrical resistance, low solubility of the SiO 2} raw material in water, and limited manufacturing conditions. be. Therefore, when B ₂ O ₃ is added to Ca O _{and Al 2 O 3} , the range of synthesizable compositions can be expanded, and the obtained CaO-Al ₂ O _3- B ₂ O ₃ system has excellent electrical insulation. The present invention has been completed by finding that hollow particles having a dense and non-spored shell surface can be obtained.

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

_{[1] CaO-Al 2} O _3- B ₂ O ₃ hollow particles having an average circularity of 0.8 or more and an average particle diameter of 0.5 to 20 μm.
_{[2] CaO-Al 2} O _{3 according to} [1], which has a shell for partitioning a hollow chamber, the thickness of the shell is 0.8 to 18.5% of the average particle size, and the hollow ratio is 25 to 95%. −B ₂ O ₃ Hollow particles.
[3] The CaO-Al according to [1] or [2], which contains 2.5 to 60% by mass of CaO, 2.5 to 55% by mass of Al ₂ O ₃ and 15 to 95% by mass of B ₂ O _{3. 2} O _3- B ₂ O ₃ Hollow particles.
_{[4] The CaO-Al 2} O _3- B ₂ O _{3 according to} any one of [1] to [3], wherein the solution containing the calcium compound, the aluminum compound and the boron compound is subjected to a spray pyrolysis treatment. Method for producing hollow particles.

The CaO-Al ₂ O _3- B ₂ O ₃ hollow particles of the _{present invention have excellent electrical insulation characteristics as the characteristics of CaO-Al 2} O _3- B ₂ O ₃ glass, and are minute and non-pore hollow particles. Therefore, it can be filled as a filler in various materials and is useful as electrically insulating material particles.

The scanning electron microscope (SEM) image of the CaO-Al ₂ O _3- B ₂ O _{3 hollow particles of the present invention is shown.} The transmission electron microscope (TEM) image of the CaO-Al ₂ O _3- B ₂ O _{3 hollow particles of the present invention is shown.}

_{The hollow particles of the present invention are CaO-Al 2} O _3- B ₂ O ₃ hollow particles having an average circularity of 0.8 or more and an average particle diameter of 0.5 to 20 μm.

CaO-Al ₂ O _3- B ₂ O ₃ hollow particles containing CaO, Al ₂ O ₃ and B ₂ O ₃ as main components. It is preferable that it does not contain alkali metal oxides or SiO _2. It contains no ingredients other than unavoidable components, and is preferably composed of _{CaO, Al 2} O ₃ and B ₂ O _3.
The content of CaO-Al ₂ O _3- B ₂ O ₃ is 2.5 to 60% by mass of CaO, 2.5 to 55% by mass of Al ₂ O _3, and 15 to 95% by mass of B ₂ O _3. It is preferable to do so. Further, it is more preferable to contain CaO in an amount of 2.5 to 51% by mass, Al ₂ O ₃ in an amount of 2.5 to 34% by mass, and B ₂ O ₃ in an amount of 15 to 95% by mass. The CaO-Al ₂ O _3- B ₂ O ₃ glass exhibits excellent electrical insulation.

The hollow particles of the present invention are particles having a shell that partitions the hollow chamber, and such a structure can be confirmed by a transmission electron microscope (TEM) image and a scanning electron microscope (SEM) image.
Further, it is preferable that the shell of the hollow particles of the present invention has no pores. The absence of pores can be confirmed by floating on a TEM image and water. By being such hollow particles, the particles of the present invention have excellent heat insulating properties and heat insulating properties.

The hollow particles of the present invention are spherical, and their average circularity is 0.8 or more, preferably 0.83 or more, and more preferably 0.85 or more.
Here, for the circularity, the projected area (A) and the peripheral length (PM) of the particle are measured from the scanning electron micrograph, and the area of a perfect circle with respect to the peripheral length (PM) is (B). The circularity is expressed as A / B. Therefore, assuming a perfect circle having the same perimeter as the perimeter of the sample particles (PM), the perimeter is PM = 2πr and the area is B = πr ² , so B = π × (PM / 2π) ² The circularity of this particle is calculated as circularity = A / B = A × 4π / (PM) ^2. The circularity is measured for 100 particles, and the average value is used as the average circularity.

The average particle size of the hollow particles of the present invention is 0.5 μm to 20 μm, preferably 0.5 μm to 15 μm, and more preferably 0.5 μm to 10 μm. If it exceeds 20 μm, a part of it may not be spherical, which is not preferable. The average particle size can be adjusted by changing the nozzle diameter of the spray nozzle used for spraying or the atomization method, and a two-fluid nozzle, a four-fluid nozzle, an ultrasonic atomization method, or the like can be used. Here, the particle size can be measured by analysis with an electron microscope, and the average thereof is JIS R 1629 "Measurement method of particle size distribution by laser diffraction / scattering method of fine ceramics raw material", Particle size distribution measuring device by laser diffraction / scattering method. For example, it can be calculated by a micro truck (manufactured by Nikkiso Co., Ltd.).

The shell thickness of the hollow particles of the present invention is preferably 0.8 to 18.5%, more preferably 1.7 to 16.6%, and even more preferably 2.6 to 16.6% of the average particle size. If the thickness of the shell is too small, the strength of the particles will not be sufficient, and if the thickness of the shell is too large, the thermal conductivity will increase. The thickness of the shell can be measured from a transmission electron microscope (TEM) image.
Further, the hollow ratio of the hollow particles of the present invention is preferably 25 to 95%, more preferably 30 to 90%, still more preferably 30 to 85% from the viewpoint of strength and thermal conductivity.

The hollow particles of the present invention can be produced, for example, by a spray pyrolysis method. Specifically, it can be produced by a spray thermal decomposition method in which a solution containing a raw material compound (a solution containing a calcium compound, an aluminum compound and a boron compound) is sprayed with a fluid nozzle such as a two-fluid nozzle or a four-fluid nozzle.

The raw materials of calcium, aluminum, boron and the like to be used may be an inorganic salt, an oxide particle, a dispersion liquid of the oxide particles and a sol solution whose composition when the hollow particles are formed becomes the composition of the oxide.

The raw material compound-containing solution can be prepared by mixing the raw material compound with an organic solvent such as water or ethanol. As the solvent, a mixture of water and an organic solvent can also be used. For example, calcium compounds, calcium nitrate, calcium chloride, calcium sulfate and the like can be used. As the aluminum compound, compounds such as aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum isopropoxide, aluminum oxide, and sol of aluminum oxide can be used. Boric acid can be used as the boron compound. The composition of these raw material compounds may be adjusted so as to _{have the composition of CaO-Al 2} O _3- B ₂ O _3.

It is preferable to spray the raw material compound-containing solution with a two-fluid nozzle from the viewpoint of adjusting the particle size and productivity. Here, the two-fluid nozzle method includes an internal mixing method in which air and a raw material compound-containing solution are mixed inside the nozzle, and an external mixing method in which air and a raw material compound-containing aqueous solution are mixed outside the nozzle. can.

The sprayed mist is thermally decomposed into hollow particles by passing through a drying zone at 500 to 800 ° C. and then a thermal decomposition zone at 900 to 1100 ° C. The temperature of the drying zone is preferably 600 to 750 ° C., more preferably 650 to 750 ° C. from the viewpoint of maintaining hollowness. The outside of the mist is dried by this drying zone to form a film of an inorganic compound, and the internal liquid is dried from this as a starting point, so that the particles are formed into a hollow shape.
The temperature of the pyrolysis zone is preferably 900 to 1050 ° C., more preferably 950 to 1050 ° C. from the viewpoint of production cost. In this pyrolysis zone, by rapidly advancing the pyrolysis reaction at a high temperature, the hollow structure formed in the drying zone is strengthened, so that the hollow particles have a shell that divides the hollow chamber, and the shell is formed. Hollow particles of constant thickness are obtained.

The obtained hollow particles may be classified by passing through a filter or the like to adjust the particle size. Since the obtained hollow particles may not be sufficiently degassed depending on the composition and the temperature of the pyrolysis zone, the hollow particles are heated to 900 to 1100 ° C. as necessary in order to depore. You may. By this heat treatment, the oxide on the surface of the shell is melted and the pores are closed, and hollow particles having a poreless shell having the above composition can be obtained.

Next, the present invention will be described in more detail with reference to examples.

Example 1
An aqueous solution prepared by dissolving 5.25 g of calcium nitrate tetrahydrate, 8.34 g of aluminum nitrate nine hydrate and 9.61 g of boric acid in 1 liter of distilled water was put into a solution tank of a spray thermal decomposition apparatus. The injected aqueous solution is sprayed in the form of mist through a two-fluid nozzle by a liquid feed pump, passed through a drying zone (about 750 ° C) and then a pyrolysis zone (about 1000 ° C), and hollow particles are used with a bag filter. Was recovered. The composition of the particles was 16.0% by mass for CaO, 14.5% by mass for _{Al 2} O ₃ , and 69.5% by mass for _{B 2} O _3.
Table 1 shows the characteristics of the hollow particles obtained under the temperature conditions of the drying zone 750 ° C. and the thermal decomposition zone 1000 ° C. The SEM image of the particles is shown in FIG. 1, and the TEM image is shown in FIG.

Example 2
Hollow particles were obtained in the same manner as in Example 1 except that the drying zone was set to 500 ° C and the thermal decomposition zone was set to 950 ° C. The characteristics of the hollow particles are shown in Table 1.

Example 3
Hollow particles were obtained in the same manner as in Example 1 except that the drying zone was set to 750 ° C and the thermal decomposition zone was set to 1050 ° C. The characteristics of the hollow particles are shown in Table 1.

Example 4
An aqueous solution prepared by dissolving 23.9 g of calcium nitrate tetrahydrate, 27.9 g of aluminum nitrate nine hydrate, and 1.5 g of boric acid in 1 liter of distilled water was sprayed in the same manner as in Example 1.
The drying zone was set to 750 ° C. and the thermal decomposition zone was set to 1000 ° C., and hollow particles were recovered in the same manner as in Example 1. The characteristics of the hollow particles are shown in Table 1.

Example 5
An aqueous solution prepared by dissolving 18.0 g of calcium nitrate tetrahydrate, 20.9 g of aluminum nitrate 9 hydrate, and 4.2 g of boric acid in 1 liter of distilled water was sprayed in the same manner as in Example 1.
The drying zone was set to 750 ° C. and the thermal decomposition zone was set to 1000 ° C., and hollow particles were recovered in the same manner as in Example 1. The characteristics of the hollow particles are shown in Table 1.

Example 6
An aqueous solution prepared by dissolving 1.4 g of calcium nitrate tetrahydrate, 2.5 g of aluminum nitrate 9 hydrate, and 11.6 g of boric acid in 1 liter of distilled water was sprayed in the same manner as in Example 1.
The drying zone was set to 750 ° C. and the thermal decomposition zone was set to 1000 ° C., and hollow particles were recovered in the same manner as in Example 1. The characteristics of the hollow particles are shown in Table 1.

Comparative Example 1
An aqueous solution prepared by dissolving 25.1 g of calcium nitrate tetrahydrate, 29.2 g of aluminum nitrate 9 hydrate, and 1.0 g of boric acid in 1 liter of distilled water was sprayed in the same manner as in Example 1.
The drying zone was set to 750 ° C. and the pyrolysis zone was set to 1000 ° C., and the particles were recovered in the same manner as in Example 1.
Under this condition, no poreless particles were obtained. The characteristics of the particles are shown in Table 2.

Comparative Example 2
An aqueous solution prepared by dissolving 0.6 g of calcium nitrate tetrahydrate, 1.0 g of aluminum nitrate 9 hydrate, and 12.0 g of boric acid in 1 liter of distilled water was sprayed in the same manner as in Example 1.
The drying zone was set to 750 ° C. and the thermal decomposition zone was set to 1000 ° C., and the particles were recovered in the same manner as in Example 1.
Under this condition, the average circularity and the hollowness ratio were not calculated because the obtained particles had many cracks and particles having a hollow structure could not be synthesized. The characteristics of the particles are shown in Table 2.

Claims (4)

Average circularity of 0.8 or more, an average particle diameter of Ri 0.5~20μm der, CaO, Al ₂ O ₃ and _{B 2 O 3 CaO-Al 2} O of nonporous Ru Tona ₃ -B ₂ O ₃ The hollow particles child. _{The poreless CaO-Al 2} O _{3 according to} claim 1, which has a shell for partitioning a hollow chamber, the thickness of the shell is 0.8 to 18.5% of the average particle size, and the hollow ratio is 25 to 95%. −B ₂ O ₃ Hollow particles. _{The poreless CaO-Al 2} O according to claim 1 or 2, which contains 2.5 to 60% by mass of CaO, 2.5 to 55% by mass of Al ₂ O ₃ and 15 to 95% by mass of B ₂ O _{3. 3-} B ₂ O ₃ Hollow particles. The poreless CaO according to any one of claims 1 to 3, wherein a solution containing a raw material compound composed of a calcium compound, an aluminum compound and a boron compound is sprayed and treated in a dry zone and a thermal decomposition zone. −Al ₂ O ₃ −B ₂ O ₃ Method for producing hollow particles.

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