JPH0629122B2 - Method for manufacturing ceramic microspheres - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention removes water and oil by heating a water-in-oil emulsion produced by mixing oil with an aqueous solution of a water-soluble metal compound and ultrasonically vibrating the mixture. To produce ceramic microspheres. More specifically, it relates to a method for adjusting the average particle size of ceramic microspheres.

[Prior Art] As a method for producing this type of ceramic microspheres, the present applicant does not require fine ceramic fine powder as a starting material, and has a narrow particle size distribution width and average particle size on the order of submicron. Filed a patent for a method with a diameter
63-36239, JP-A-1-301502), and the frequency of ultrasonic waves in this method is selected from the range of 10 kHz to 100 kHz to reduce the average particle size of the microspheres at high frequencies and to reduce the low frequency. At that time, a patent application was filed for a method of increasing the average particle size (Japanese Patent Application No. 63-317123, Japanese Patent Laid-Open No.
-301502).

[Problems to be Solved by the Invention] In order to adjust the average particle size of the ceramic microspheres by the above-mentioned conventional method, a special ultrasonic generator capable of adjusting the frequency is prepared, or a plurality of units having different frequencies are prepared. It was necessary to prepare an ultrasonic wave generator and select a predetermined frequency or an ultrasonic wave generator for each target average particle diameter of the microspheres.

However, the frequency of the ultrasonic generator is practically limited to a certain range, and it is difficult to finely set the frequency. Therefore, it is not easy in terms of equipment to obtain microspheres having a desired average particle diameter by the conventional method.

The object of the present invention is to prepare a ceramic microsphere having a narrow particle size distribution width and an average particle size on the order of submicron, which is a mixed liquid before forming a water-in-oil emulsion, regardless of a change in the frequency of ultrasonic waves. The object of the present invention is to provide a method for producing ceramic microspheres, which can be adjusted to a desired average particle size by adjusting the viscosity of.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides that an aqueous solution in which a water-soluble metal compound is dissolved is mixed with an oil insoluble in the aqueous solution and having a boiling point higher than that of water. Sonic vibration is applied to form a water-in-oil emulsion, and this emulsion is heated at a temperature lower than the boiling point of water to evaporate the water content of the droplets in which the water-soluble metal compound is dissolved, and to form a spherical water-soluble emulsion in the oil phase. After decomposing the metal compound, the dispersion is heated at a temperature range above the temperature at which the water-soluble metal compound decomposes to form a metal oxide and below the grain growth start temperature of the metal oxide to evaporate or decompose the oil. It is an improvement of the method for producing ceramic microspheres by removing the metal microspheres to obtain metal oxide microspheres.

The feature is that a microsphere having a desired average particle diameter is obtained by mixing a water-soluble viscosity modifier which is insoluble in this oil together with the oil in an aqueous solution in which the aqueous metal compound is dissolved.

The starting material of the present invention is a water-soluble metal compound that constitutes the target ceramics. This water-soluble metal compound is dissolved in water at a predetermined composition ratio of 20 to 50 ° C. to prepare an aqueous solution.

Oil and a viscosity modifier are mixed with this aqueous solution, and ultrasonic vibration is applied to this mixed solution to form a water-in-oil emulsion. The oil is not particularly limited as long as it is insoluble in the above aqueous solution and has a boiling point higher than that of water, and paraffin oil is preferable from the viewpoint of toxicity and cost.

The viscosity modifier is a substance that adjusts the viscosity of the mixed solution and is insoluble in this oil and is water-soluble in order to adjust the droplet size of the emulsion when the mixed solution is formed into an emulsion. There is a need. A low viscosity viscosity modifier,
For example, when methyl alcohol, ethyl alcohol, or the like is added to reduce the viscosity of the mixed solution, the droplets of the emulsion become smaller and the average particle size of the ceramic microspheres becomes smaller. On the other hand, when a viscosity adjusting agent having a high viscosity, for example, a water-soluble polymer such as polyvinyl alcohol or methyl cellulose is added to increase the viscosity of the mixed liquid, the droplets of the emulsion become large and the average particle size of the ceramic microspheres becomes large. From this fact, the average particle diameter can be set to a desired value by appropriately selecting the viscosity of the mixed liquid with this viscosity modifier.

Further, when forming an emulsion, it is preferable to use an emulsifier in order to make the emulsion stably exist for a long time.
This emulsifier may be any emulsifier such as an ionic emulsifier and a nonionic emulsifier. The oil is mixed in an amount of 35 to 100 parts by weight and the emulsifier is mixed in an amount of 1 to 6 parts by weight based on 100 parts by weight of the aqueous solution. It is mixed at a ratio of 10 parts by weight or less with respect to 100 parts by weight.

The mixed liquid is formed into a water-in-oil emulsion by ultrasonic vibration. When the emulsion is generated by means of a stirring homogenizer other than ultrasonic vibration, a pressure homogenizer, etc., the droplet diameter is partially on the order of submicron, but on average it is on the order of submicron. In addition, since the distribution width of the droplet diameter is wide, the average particle diameter of the finally obtained ceramic microspheres is large and uneven. Therefore, methods other than ultrasonic vibration are not suitable for the present invention. The frequency of this ultrasonic wave is selected from the range of 10 kHz to 100 kHz based on the specifications of the ultrasonic wave generator. The ultrasonic wave is generally a sound wave having a frequency above the audible range, that is, a sound wave having a frequency of 20 kHz or more. However, in the present invention, since the average diameter of droplets can be in the order of submicron even at a frequency of 10 kHz, the frequency is 10 kHz. The term “ultrasonic wave” is used for the sound waves of less than 20 kHz.

When the generated emulsion is heated to evaporate the water content of the droplets in which the water-soluble metal compound dissolves, the higher the heating temperature, the faster the water content of the droplets can be removed. Occurs and the emulsion breaks, so 10
The temperature is lower than 0 ° C, preferably 70 to 95 ° C.

Further, the heating temperature for evaporating or decomposing oil and thermally decomposing a water-soluble metal compound is a temperature higher than the temperature at which the water-soluble metal compound decomposes to a metal oxide and lower than the grain growth start temperature of this metal compound. It is necessary.

[Function] When an oil and a viscosity modifier are mixed in an aqueous solution in which a water-soluble metal compound is dissolved, and an emulsifier is added if necessary, and ultrasonic vibration is applied, a powerful cavitation effect by ultrasonic waves is uniformly applied to the entire mixed liquid, The aqueous solution is subdivided into submicron-order droplets and dispersed in the oil phase. Here, if the viscosity modifier is a substance that reduces the viscosity of the mixed liquid, the average diameter of the liquid droplets is small, and if the viscosity modifier is a substance that increases the viscosity of the mixed liquid, the average diameter of the liquid droplets is large. Becomes
As a result, the desired average particle size of the microspheres can be determined.

When the emulsion is heated to evaporate the water content of the droplet in which the water-soluble metal compound is dissolved, the droplet is concentrated and the spherical water-soluble metal compound of submicron order is dispersed in the oil phase.

By heating the oil liquid in which the water-soluble metal compound is dispersed to evaporate or decompose the oil and thermally decompose the water-soluble metal compound, microspheres of a metal oxide in the order of submicrons can be obtained.

[Effects of the Invention] As described above, according to the manufacturing method of the present invention, ceramic microspheres having a narrow particle size distribution width and an average particle size on the order of submicrons can be used regardless of changes in ultrasonic frequency. In addition, by adjusting the viscosity of the mixed solution before forming the water-in-oil emulsion by adding a viscosity modifier, it is possible to adjust to a desired average particle size.

[Examples] Next, examples of the present invention will be described together with comparative examples.

Example 1 10 g of ZrO (NO ₃ ) ₂ .2H ₂ O was dissolved in 25 g of water at 40 ° C. to prepare an aqueous solution. To this aqueous solution, 50 g of paraffin oil, 2 g of methyl alcohol as a viscosity modifier, and 1 g of polyoxyethylene nonylphenyl ether as an emulsifier were added and the viscosity was 2.
A mixed solution of 7 cP was prepared. An ultrasonic generator (Br
Ultrasonic vibration was applied for 15 seconds by anson B-30) to form a water-in-oil emulsion. The frequency of the ultrasonic waves at this time
It was 30 kHz. The emulsion was placed in a dryer and dried at a temperature of 80 ° C. under atmospheric pressure for 8 hours, and water was removed by evaporation. The emulsion became a suspension in which ZrO ₂ particles were dispersed. This suspension was calcined at a temperature of 700 ° C. under atmospheric pressure for 3 hours to decompose and remove the oil to obtain ZrO ₂ spheres. When the particle size of the ZrO ₂ spheres was measured by a scanning electron microscope, the average particle size was 0.
It was an extremely fine ZrO ₂ monodisperse ceramic microsphere with a particle size distribution width of ± 0.02 μm at 08 μm.

Example 2 Similar to Example 1 except that 0.25 g of polyvinyl alcohol as a viscosity modifier was added to the aqueous solution of Example 1 instead of the methyl alcohol of Example 1 and mixed to prepare a mixed solution having a viscosity of 38.0 cP. Then, a ZrO ₂ ball was obtained. As with Example 1, this Zr
When the particle size of the O ₂ sphere was measured, the average particle size was 1.1 μm and the particle size distribution width was ± 0.2 μm. This ZrO ₂ ball was used in Example 1.
The average particle size was wider and the particle size distribution range was wider than that of ZrO ₂ spheres, but they were still monodisperse ceramic micro spheres with finer and less variation.

<Comparative example> The viscosity of the aqueous solution of Example 1 was 3. without adding a viscosity modifier.
Z was prepared in the same manner as in Example 1 except that a mixed solution of 4 cP was prepared.
I got an rO ₂ ball. When the particle size of the ZrO ₂ spheres was measured in the same manner as in Example 1, the average particle size was 0.1 μm and the particle size distribution width was ± 0.2.
It was an extremely fine ZrO ₂ monodisperse ceramic microsphere of μm.

From the results of Example 1, Example 2 and Comparative Example, it was found that the average particle size of the ceramic microspheres was adjusted by adding the viscosity modifier to the aqueous solution to adjust the viscosity of the mixed solution.

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Claims (3)

[Claims] 1. An aqueous solution in which a water-soluble metal compound is dissolved is mixed with an oil insoluble in the aqueous solution and having a boiling point higher than that of water, and ultrasonic vibration is applied to the mixed solution to produce a water-in-oil emulsion,
The emulsion is heated at a temperature lower than the boiling point of water to evaporate the water content of the droplets in which the water-soluble metal compound is dissolved to decompose the spherical water-soluble metal compound in the oil phase, and then the dispersion is mixed with the water-soluble metal compound. A ceramic that obtains metal oxide microspheres by heating at a temperature above the temperature at which a metal compound decomposes to form a metal oxide and below the grain growth start temperature of this metal oxide to evaporate or decompose oil and remove it. A method for producing microspheres, comprising mixing an aqueous solution in which the aqueous metal compound is dissolved with the oil together with a water-soluble viscosity modifier that is insoluble in the oil to obtain microspheres having a desired average particle size. A method for manufacturing a characteristic ceramic microsphere. 2. The method for producing a ceramic microsphere according to claim 1, wherein the oil is paraffin oil and the viscosity modifier is methyl alcohol. 3. The method for producing ceramic microspheres according to claim 1, wherein the viscosity modifier is a water-soluble polymer.