JP6605304B2 - Manufacturing method of micro magnesium oxide hollow particles - Google Patents

Description

  The present invention relates to a method for producing fine magnesium oxide hollow particles.

  Metal oxide micro hollow bodies are excellent in heat resistance and also have heat insulation, and are therefore used as fillers such as resins, refractories, various fillers, and the like. Among the metal oxides, magnesium oxide hollow particles are particularly useful as inorganic fillers for coating film fillers, heat insulating films and the like because they are excellent in heat resistance and heat insulation.

  As a method for producing such metal oxide hollow particles, there are an emulsion method (Patent Documents 1 to 3), a method of baking after forming a film on the resin surface (Patent Document 4), and a spray pyrolysis method (Patent Document 5). Are known.

JP-A-4-250842 JP-A-11-116211 JP 2000-203810 A JP 2011-16718 A JP-A-7-96165

  However, the emulsion method and the resin template method have disadvantages that the operation is complicated, the production amount per unit time is small, and it is not suitable for industrial production. On the other hand, the spray pyrolysis method is an excellent method that does not use a template such as a resin. However, according to Patent Document 5, high temperature conditions of 1500 to 1650 ° C. are required to produce magnesium oxide hollow particles. In addition, there were restrictions on the electric furnace equipment, and it was not possible to manufacture at low cost. Moreover, when spraying on high temperature conditions, the subject that a hollow particle became easy to break by rapid heating occurred.

  Accordingly, an object of the present invention is to provide a method for producing high-quality magnesium oxide hollow particles at a low temperature and with ordinary equipment.

  Therefore, as a result of various investigations on the manufacturing conditions of the magnesium oxide hollow particles, the present inventor used an organic acid magnesium salt solution as a raw material, and if this was dried and pyrolyzed under specific temperature conditions, the maximum temperature could be obtained. The inventors have found that fine magnesium oxide hollow particles can be obtained efficiently and stably under conditions of 1200 ° C. or lower, and the present invention has been completed.

  That is, the present invention provides the following [1] to [3].

[1] A fine magnesium oxide hollow particle characterized by subjecting droplets of an organic acid magnesium salt solution to a spray pyrolysis treatment in which a droplet is passed through a drying temperature zone of 100 to 450 ° C. and a pyrolysis zone of 450 to 1200 ° C. or more. Manufacturing method.
[2] The production method according to [1], wherein the obtained fine magnesium oxide hollow particles are fine magnesium oxide hollow particles having an average circularity of 0.85 or more and an average particle diameter of 0.5 μm to 20 μm.
[3] The obtained micro magnesium oxide hollow particles have a shell having a hollow chamber, the shell thickness is 1.6 to 20.7% of the average particle diameter, and the micro magnesium oxide hollow has a hollow ratio of 20 to 90%. The production method according to [1] or [2], which is a particle.

  According to the method of the present invention, magnesium oxide hollow particles having high sphericity, small average particle diameter, and stable quality can be stably and efficiently obtained under low temperature conditions without requiring special equipment. .

The SEM image of the magnesium oxide hollow particle obtained in Example 1 is shown. 2 shows XRD of magnesium oxide hollow particles obtained in Example 1. FIG. The XRD of the magnesium oxide hollow particle obtained in Example 2 is shown. The XRD of the magnesium oxide hollow particle obtained in Example 3 is shown. 3 shows XRD of magnesium oxide hollow particles obtained in Comparative Example 1. FIG.

  The method for producing fine magnesium oxide hollow particles of the present invention uses an organic acid magnesium salt solution as a raw material, and sprays the droplets through a drying temperature zone of 100 to 450 ° C and a thermal decomposition zone of 450 to 1200 ° C. It is characterized by decomposing.

Examples of the organic acid magnesium salt used as the raw material include organic carboxylic acid magnesium salts such as magnesium acetate and magnesium propionate. Examples of the organic acids, organic carboxylic acids, especially fatty acids are preferred, C ₁ -C ₃₆ fatty acid is more preferable. The organic acid magnesium salt solution is preferably an organic acid magnesium salt aqueous solution.
Inorganic acid magnesium such as magnesium sulfate has a high decomposition temperature.

  The organic acid magnesium salt concentration in the organic acid magnesium salt solution is preferably 0.01 to 2.0 mol / L, and more preferably 0.1 to 2.0 mol / L.

  The organic acid magnesium salt solution is preferably sprayed with a spray nozzle, particularly a two-fluid nozzle, in terms of particle diameter adjustment and productivity. Here, the two-fluid nozzle method includes an internal mixing method in which air and an organic acid magnesium salt solution are mixed inside the nozzle, and an external mixing method in which air and the organic acid magnesium salt solution are mixed outside the nozzle. Can also be adopted.

  The sprayed mist (droplet) is thermally decomposed by passing through a drying zone at 100 to 450 ° C. and then a thermal decomposition zone at 450 to 1200 ° C. to form magnesium oxide hollow particles. When the temperature of the drying zone is less than 100 ° C., rapid drying cannot be performed, and when it exceeds 450 ° C., evaporation of moisture and precipitation reaction of the outer shell occur at the same time, so that the particles easily break. The temperature of the drying zone is preferably 150 to 450 ° C., more preferably 200 to 450 ° C. from the viewpoint of maintaining hollowness and preventing cracking. In this drying zone, the outside of the mist is dried to form an organic acid magnesium film, and the internal liquid is dried starting from the film, so that the particles are formed in a hollow shape.

  The temperature of the pyrolysis zone is preferably 450 to 1200 ° C., more preferably 500 to 1200 ° C., more preferably 600 to 1200 ° C. from the viewpoint of thermally decomposing organic acid magnesium into magnesium oxide and not efficiently decomposing magnesium oxide and obtaining hollow particles efficiently. More preferably, ˜1200 ° C. When the temperature of the pyrolysis zone is less than 450 ° C., a sufficient pyrolysis reaction does not occur. In this thermal decomposition zone, the hollow structure formed in the drying zone is strengthened by advancing the thermal decomposition reaction at a high temperature at a stretch, whereby magnesium oxide hollow particles having shells defining the hollow chamber, Thin hollow particles are obtained.

  The obtained magnesium oxide hollow particles can be adjusted in particle size by passing through a filter after cooling.

  The fine magnesium oxide hollow particles obtained by the method of the present invention preferably have an average circularity of 0.85 or more and an average particle diameter of 0.5 μm to 20 μm.

  The fine magnesium oxide hollow particles obtained by the method of the present invention have a substantially spherical shape, preferably an average circularity of 0.85 or more, and more preferably an average circularity of 0.90 or more.

Here, the circularity is determined by measuring the projected area (A) and the perimeter (PM) of a particle from a scanning electron micrograph, and assuming that the area of a perfect circle with respect to the perimeter (PM) is (B). Circularity is expressed as A / B. Therefore, the circumference and area of a perfect circle having the same circumference as the sample particle (PM) are PM = 2πr and B = πr ² , respectively, so that B = π × (PM / 2π) ² . The circularity of the particles is calculated as circularity = A / B = A × 4π / (PM) ² . The circularity is measured for 100 particles, and the average value is defined as the average circularity.

  The average particle size of the fine magnesium oxide hollow particles obtained by the method of the present invention is preferably 0.5 μm to 20 μm, more preferably 1 μm to 20 μm, still more preferably 1 μm to 15 μm, and further preferably 2 μm to 12 μm. And more preferably 3 μm to 10 μm. Hollow particles having an average particle size of less than 0.5 μm require the use of a special device such as ultrasonic irradiation, and when the particle size exceeds 20 μm, some of the particles may be incomplete spheres, which is not preferable. In addition, adjustment of an average particle diameter can be performed by adjustment of the diameter of the fluid nozzle used for spraying. Here, the particle size can be measured by analysis with an electron microscope, and the average is JIS R 1629 “Method for measuring particle size distribution by laser diffraction / scattering method of fine ceramic 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 particle size distribution (particle size distribution) of the fine magnesium oxide hollow particles obtained by the method of the present invention is so small that 80% or more of the particles are preferably within ± 5.0 μm of the average particle diameter, and 80% or more of the particles. Is more preferably within ± 4.5 μm of the average particle diameter, and more preferably 80% or more of the particles are within ± 4.0 μm of the average particle diameter.

The fine magnesium oxide hollow particles obtained by the method of the present invention preferably have a shell having a hollow chamber, and the thickness of the shell is preferably 1.6 to 20.7% of the average particle diameter. Moreover, it is preferable that a hollow rate is 20 to 90%. The hollow particles having a hollow chamber can be confirmed from the SEM image and the TEM image.
The thickness of the shell is preferably from 1.6 to 20.7%, more preferably from 3.6 to 20.7%, more preferably from 3.6 to 16% of the average particle diameter from the viewpoints of strength, weight reduction and thermal conductivity. 4% is more preferable. Moreover, 20 to 90% is preferable, 20 to 80% is more preferable, and 30 to 80% is more preferable. The thickness of the shell can be measured from an SEM image and a TEM image. The thickness of the shell was measured for 50 particles, and the average value was taken as the shell thickness. The hollow ratio is calculated as follows. The particles and the voids within the particles are assumed to be true spheres. When the particle diameter is (A) and the shell thickness obtained from the SEM image and TEM image is (B), the void radius of the particle is expressed as A / 2-B. The volume of a perfect circle having the same volume as the sample particle is V ₁ = 4/3 × π × (A / 2) ³ . The void volume is V ₂ = 4/3 × π × (A / 2-B) ³ , and the hollowness of the particles can be calculated as hollowness = V ₂ / V ₁ × 100.

The bulk density of the fine magnesium oxide hollow particles obtained by the method of the present invention is preferably from 0.01~0.4g / cm ^3, more preferably from 0.02~0.4g / cm ^3, 0 More preferably, it is 0.03-0.4 g / cm ³ . The bulk density can be measured by a measurement method of JIS R 1628 “Measurement Method of Bulk Density of Fine Ceramics Powder” or a powder mechanical property measurement device such as a powder tester (manufactured by Hosokawa Micron).

Apparent density of the fine magnesium oxide hollow particles obtained by the method of the present invention is preferably from 0.36~2.92g / cm ^3, more preferably from 0.73~2.92g / cm ^3, 0 More preferably, it is 0.73 to 2.56 g / cm ³ . The apparent density can be measured by JIS R 1620 “Method of measuring particle density of fine ceramic powder”, a dry automatic densimeter of AccuPick (manufactured by Shimadzu Corporation), or the like.

  The fine magnesium oxide hollow particles obtained by the method of the present invention preferably have a compressive strength of 0.3 to 150 MPa, more preferably 1 to 150 MPa, and even more preferably 3 to 150 MPa. The compressive strength can be measured by a micro compression tester MCT-510 (manufactured by Shimadzu Corporation).

BET specific surface area of fine magnesium oxide hollow particles obtained by the method of the present invention is preferably from 0.6~5m ² / g, more preferably 0.7~5m ² / g, 0.7~2.6m ² / g is more preferable. The BET specific surface area can be measured by JIS Z 8830 “Method for measuring specific surface area of powder (solid) by gas adsorption”, Flow Soap II 2300 (manufactured by Shimadzu Corporation) BET specific surface area meter or the like.

  Since the fine magnesium oxide hollow particles obtained by the method of the present invention have a hollow spherical shape, the filling property to a film or sheet is good, and weight reduction can be achieved. Moreover, since heat conductivity is low, characteristics, such as heat insulation and heat insulation, can be provided.

  EXAMPLES Next, an Example is given and this invention is demonstrated still in detail.

Example 1
A magnesium acetate aqueous solution in which 0.1 mol of magnesium acetate was dissolved in 1 liter of distilled water was put into a solution tank of a spray pyrolysis apparatus. The introduced aqueous solution was sprayed in a mist form via a two-fluid nozzle by a liquid feed pump, and passed through a drying zone (about 400 ° C.) and then a thermal decomposition zone (about 1000 ° C.). Magnesium oxide hollow particles were recovered using a bag filter.

  Table 1 shows the characteristics of the magnesium oxide hollow particles obtained under the temperature conditions of the drying zone of 400 ° C and the thermal decomposition zone of 1000 ° C. An SEM image is shown in FIG. 1 and an XRD is shown in FIG.

Examples 2 and 3
The 0.1 mol / L magnesium acetate aqueous solution prepared in Example 1 was sprayed with a two-fluid nozzle, passed through a drying zone and a thermal decomposition zone at different temperatures, and magnesium oxide was recovered using a bag filter.
In Example 2, the drying zone was 400 ° C and the pyrolysis zone was 600 ° C. In Example 3, the drying zone was 400 ° C and the pyrolysis zone was 800 ° C.
FIG. 3 shows XRD of magnesium oxide hollow particles obtained by spray pyrolysis in the same manner as in Example 1 with the drying zone set at 400 ° C. and the pyrolysis zone set at 600 ° C. FIG. 4 shows XRD of magnesium oxide hollow particles obtained by spray pyrolysis with the drying zone set at 400 ° C. and the pyrolysis zone set at 800 ° C.
3 and 4, magnesium oxide hollow particles were obtained even by spray pyrolysis in a drying zone of 400 ° C and a pyrolysis zone of 600 to 800 ° C.

Comparative Example 1
Spray pyrolysis was performed in the same manner as in Example 1 with the drying zone set at 400 ° C. and the thermal decomposition zone set at 400 ° C. The XRD of the obtained particles is shown in FIG.
From FIG. 5, not only magnesium oxide but also magnesium carbonate was generated.

Claims (3)

An average particle, characterized by subjecting droplets of an organic acid magnesium salt solution sprayed by a two-fluid nozzle to a spray pyrolysis treatment in which the droplets pass through a drying temperature zone of 100 to 450 ° C. and a pyrolysis zone of 450 to 1200 ° C. A method for producing fine magnesium oxide hollow particles having a diameter of 1 μm to 15 μm . The resulting fine magnesium oxide hollow particles, The process of Claim 1 average is small magnesium oxide hollow particles of circularity 0.85 on more than.   The obtained micro magnesium oxide hollow particles are micro magnesium oxide hollow particles having a shell having a hollow chamber, the shell thickness being 1.6 to 20.7% of the average particle diameter, and the hollow ratio being 20 to 90%. The production method according to claim 1 or 2.