JPH0628721B2 - Method for manufacturing ceramic hollow spheres - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing microcapsules made of ceramics. More specifically, it relates to a method for manufacturing a ceramic hollow sphere.

[Prior Art] Generally, a microcapsule is a fine particle composed of a core substance and an outer wall surrounding the core substance. For core substances, cosmetics, pharmaceuticals,
Examples include agriculture, fragrances, fertilizers, and the like. The outer wall has a function of blocking these core substances from the outside and maintaining the stability of the core substances, and a substance having an unpleasant odor or taste. The outer wall has minute pores and has a function of controlling the release rate when the core substance is released to the outside.

Conventionally, there is a hardening emulsification method as one of the methods for microencapsulation. In this method, a core substance is emulsified or suspended in a matrix solution, the emulsion is emulsified in another liquid, and then the droplets are cured.

Further, conventionally, there has been disclosed a hollow ceramic sintered body in which an unsintered ceramic is formed on the outer peripheral portion of a core of a flammable material, and the core is burned down by firing this (Japanese Patent Laid-Open No. 1-1310).
83).

[Problems to be Solved by the Invention] However, since the outer wall of the microcapsule formed by the conventional method is made of a high molecular substance such as gelatin, polyester, polystyrene, etc., it has poor heat resistance and pressure resistance, and the inner wall It was difficult to make a hollow material by filling the core material with the core material.

Further, the hollow ceramic sintered body is excellent in heat resistance and pressure resistance and forms a hollow body. After the core substance is first formed, the outer periphery of the core substance is coated with unfired ceramics to form a hollow body. Since it is fired, there is a problem that it does not become a minute hollow body.

An object of the present invention is to provide a method of manufacturing ceramic hollow spheres having excellent heat resistance and pressure resistance and using a ceramic as an outer wall and having a fine sphere diameter.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method in which an aqueous solution in which a water-soluble metal compound is dissolved is mixed with a first oil that is insoluble in the aqueous solution and has a boiling point higher than that of water. Produces a W-type emulsion,
This O / W type emulsion is mixed with a second oil which is insoluble in the aqueous solution and has a boiling point higher than that of water to form an O / W / O type emulsion, and water is removed from the O / W / O type emulsion. Forming a spherical shell of a metal compound surrounded by the first oil on the inner side and the second oil on the outer side, and
The spherical shell surrounded by the oil is heated above the temperature at which the metal compound decomposes to form a metal oxide and below the grain growth start temperature of the metal oxide, and the first and second oils are evaporated. Alternatively, it is a method of obtaining hollow spheres of metal oxide by decomposing and removing.

Hereinafter, the present invention will be described in more detail.

(a) Formation of O / W Emulsion 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 form an aqueous solution. This aqueous solution is mixed with the first oil to form an O / W type emulsion. Here, the first oil must be insoluble in this aqueous solution and have a boiling point higher than that of water in order to form a spherical shell of ceramics described later. If this condition is satisfied, the first oil is not limited to a specific oil, and linseed oil, paraffin oil, and the like are preferable in terms of toxicity and price.

The emulsion is produced by means of ultrasonic vibration, a stirrer, a stirring homogenizer, a pressure homogenizer, or the like. It is preferable to add a polymeric surfactant, an ionic surfactant, and a nonionic surfactant together with the aqueous solution when forming this emulsion, because the emulsion will remain stable for a long time. 100-1000 parts by weight of the above aqueous solution and 100 parts by weight of the first oil, and 0.1% by weight of the surfactant.
Mix 5 to 5 parts by weight.

(b) Generation of O / W / O type emulsion This O / W type emulsion is mixed with a second oil to form O / W.
/ O type emulsion is produced. The second oil also needs to be insoluble in the aqueous solution and have a boiling point higher than that of water in order to form a spherical shell of ceramics described later. If this condition is satisfied, the second oil may be the same as or different from the first oil. The second oil is not limited to a specific oil like the first oil, and linseed oil, paraffin oil and the like are preferable in terms of toxicity and price.

The emulsion is produced in the same manner as the O / W type emulsion. When forming this emulsion, a polymer type surfactant together with an O / W type emulsion,
It is preferable to add an ionic surfactant or a nonionic surfactant because the emulsion will remain stable for a long time. The second oil is 100 to 1000 parts by weight, and the surfactant is 0.1 to 100 parts by weight of the O / W type emulsion.
Mix 5 to 5 parts by weight.

(c) Drying of O / W / O type emulsion The water is removed from the O / W / O type emulsion to dry it. To remove this water, a method of heating an O / W / O type emulsion at a temperature of room temperature to 100 ° C. is used.
Any one or both of a method of placing the O-type emulsion under a reduced pressure of less than 1 atm and at a pressure at which the aqueous solution boils or higher is adopted. When water is removed from the O / W / O type emulsion, a spherical shell of a metal compound surrounded by a first oil on the inside and a second oil on the outside is formed.

(d) Production of ceramic hollow spheres A spherical shell surrounded by the first and second oils is heated to evaporate or decompose the first and second oils from the spherical shells to remove the hollow metal oxide. Obtain a sphere, a ceramic hollow sphere. The heating temperature for evaporating or decomposing the first and second oils and thermally decomposing the water-soluble metal compound is equal to or higher than the temperature at which the water-soluble metal compound decomposes to form a metal oxide. Is selected from the temperature range below the grain growth start temperature.

[Operation] An aqueous solution in which a water-soluble metal compound is dissolved is added to the first oil,
If necessary, a surfactant is added, and these are mixed by ultrasonic vibration, a homogenizer, or the like, and the first oil becomes fine oil droplets, which are dispersed in the aqueous phase to form an O / W type emulsion.

Then, this O / W type emulsion is added to a second oil, and a surfactant is added if necessary, and they are mixed in the same manner. Then, a layer of the second oil is further provided outside the aqueous solution layer surrounding the oil particles. Are formed to form an O / W / O type emulsion.

By removing water from this O / W / O type emulsion and heating it at a predetermined temperature, all the oil components constituting this emulsion are evaporated or decomposed to obtain ceramic hollow spheres made of metal oxide.

Since the ceramic hollow sphere of the present invention is manufactured from an emulsion, it is possible to make a very small sphere diameter of the order of micron.

[Effects of the Invention] As described above, according to the production method of the present invention, an aqueous solution of a water-soluble metal compound that constitutes a target ceramic is first mixed with oil to form an O / W emulsion.
This emulsion is then mixed with another oil to produce O / W / O
By forming a type emulsion and removing the oil content of this emulsion by heating, it is possible to manufacture fine ceramic hollow spheres having ceramics having heat resistance, pressure resistance and chemical resistance as the outer wall.

In particular, in the present invention, if the constituent elements of the starting material ceramics are substances that are soluble in water, the constituent elements of the ceramics can be arbitrarily selected, and ceramic hollow spheres can be produced at any composition ratio, and a compound can be obtained. The hollow spheres can be manufactured in the form of a mixture without limitation.

Since the ceramic hollow sphere of the present invention has no core substance,
It is used as a filler, heat insulating material, and sound insulation material.

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

<Example _{1> ZrO (NO 3) 2} 2 mole was dissolved in 1 water ZrO (NO ₃₎ was prepared ₂ solution. 50m of linseed oil as the inner oil phase
100m of ZrO (NO ₃ ) ₂ aqueous solution and poly.
1 g of oxyethylene sorbitan monolaurate was added, and ultrasonic vibration was applied for 120 seconds by an ultrasonic generator to form an O / W type emulsion.

As an oil phase on the outside, this O
/ W type emulsion and 4 g of polyoxyethylene nonylphenyl ether as a surfactant were added and stirred by a stirring homogenizer to produce an O / W / O type emulsion.

This O / W / O type emulsion was heated at 70 ° C. under atmospheric pressure to 1
It was dried for 0 hours and the water was removed by evaporation. Then 50
By heating at 0 ° C for 5 hours, linseed oil in the inner oil phase and paraffin oil in the outer oil phase are decomposed and removed.
O ₂ hollow sphere powder was obtained.

The diameter of the ZrO ₂ hollow spheres of this powder was measured by a scanning electron microscope and found to be 4 to 15 μm. Further, when the powder of the hollow spheres was heated to 200 ° C. and then put into liquid nitrogen to break the hollow spheres by thermal contraction, the outer wall thickness was 0.2 to 2 μm.

<Example 2> An O / W / O type emulsion was produced in the same manner as in Example 1 except that paraffin oil was used instead of linseed oil. This O / W / O type emulsion is treated under a pressure of 700 mmHg at 40
It was dried at a temperature of ℃ for 12 hours, and the heating temperature was raised to 1000 ℃ to decompose and remove the paraffin oil in the oil phase inside and outside to obtain ZrO ₂ hollow sphere powder.

The diameter of the ZrO ₂ hollow spheres of this powder was measured by a scanning electron microscope and found to be 4 to 13 μm. Further, when the powder of the hollow spheres was heated to 200 ° C. and then put into liquid nitrogen to break the hollow spheres by thermal contraction, the outer wall thickness was 0.2 to 1.8 μm.

Claims (7)

[Claims] 1. An aqueous solution in which a water-soluble metal compound is dissolved is mixed with a first oil which is insoluble in the aqueous solution and has a boiling point higher than that of water, and O /
A W-type emulsion is formed, and the O / W-type emulsion is mixed with a second oil that is insoluble in the aqueous solution and has a boiling point higher than that of water to form an O / W / O-type emulsion; Removing water from the emulsion to form a spherical shell of a metal compound surrounded by the first oil on the inside and the second oil on the outside, and a spherical shell surrounded by the first and second oils Is heated in a temperature range above the temperature at which the metal compound decomposes to form a metal oxide and below the grain growth start temperature of the metal oxide to evaporate or decompose and remove the first and second oils. A method for producing ceramic hollow spheres for obtaining oxide hollow spheres. 2. The method for producing a ceramic hollow sphere according to claim 1, wherein the first oil and the second oil are the same type of oil. 3. The method for producing a ceramic hollow sphere according to claim 1, wherein the first oil and the second oil are different types of oil. 4. The O / W / O emulsion is at room temperature to 1
The method for producing a ceramic hollow sphere according to claim 1, wherein water is removed from the emulsion by heating at a temperature of 00 ° C. 5. The water is removed from the O / W / O type emulsion by placing the O / W / O type emulsion under a reduced pressure of less than 1 atm and at a pressure not lower than the boiling point of the aqueous solution.
A method for producing the ceramic hollow sphere described. 6. The method for producing a ceramic hollow sphere according to claim 1, wherein a surfactant is added to the first oil together with an aqueous solution in which the aqueous solution metal compound is dissolved to produce an O / W type emulsion. 7. The method for producing a ceramic hollow sphere according to claim 1, wherein a surfactant is added to the second oil together with the O / W type emulsion to form an O / W / O type emulsion.