JP4928682B2 - Method for producing fine powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a dry fine powder, and more particularly to a method for producing a fine powder of submicron or less and a fine powder having strong cohesiveness and adhesion.
[0002]
[Prior art]
In the production of fine ceramics and pharmaceuticals, it is required to form a particle size of submicron or less. As a method for forming such a fine powder, a wet pulverization method in which an object to be pulverized is pulverized in a solvent and a dry pulverization method using an airflow pulverizer are known.
[0003]
In the wet pulverization method, an object to be pulverized is dispersed in a liquid, and the object to be pulverized dispersed in the liquid is pulverized by a stirring mill.
[0004]
[Problems to be solved by the invention]
Such a wet pulverization method has the following problems.
{Circle around (1)} If the optimum liquid that uniformly disperses the powder is not selected, the pulverization efficiency decreases.
(2) Liquids that cause dissolution and swelling of powder components cannot be used.
(3) A powder drying step is required after pulverization.
(4) If the powder re-aggregates after drying, a pulverization step is required again.
(5) If a liquid other than water is used, a liquid recovery device is required.
(6) Use of liquids that affect people and the environment is restricted.
[0005]
On the other hand, in a dry pulverization method using an airflow pulverizer (jet mill), particles are supplied into a high-speed airflow and pulverized by collision and friction between particles and between particles and the inner wall of the mill. The dry pulverization method has the following problems.
(1) The airflow type pulverizer has a lot of attached equipment such as a compressor and a raw material hopper, so the initial cost of the whole apparatus is high and a large installation area is required.
(2) Since compressed air is required for pulverization, running costs such as power costs are high.
(3) Productivity per hour is low.
(4) In the case of a powder having strong condensability and adhesion, pulverization may be difficult.
(5) In the case of powder that is easily charged with static electricity, it may harden.
[0006]
This invention pays attention to such a point, and it aims at providing the method which can obtain the dry fine powder efficiently grind | pulverized with the small scale machine.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention pulverizes a suspension in which a material to be pulverized is dispersed in a liquefied inert gas with a medium stirring mill, and then vaporizes the liquefied inert gas to obtain a dry powder. It is characterized by that.
[0008]
[Effects of the Invention]
In the present invention, a low temperature liquefied inert gas is injected into a medium agitating mill together with normally used medium balls, and the liquefied inert gas and the material to be crushed are wet pulverized in a suspension state. Then, after pulverization, the liquefied inert gas spontaneously evaporates and a dry powder similar to dry pulverization can be obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
When a fine powder is produced by pulverization, the production volume decreases as it becomes finer, and approaches the limit particle size. And it is known that the particles change from primary particles to secondary particles or higher-order particles as they become finer, and the cohesiveness and adhesion become stronger.
[0010]
And if these powder characteristics depend on temperature, it can be improved by lowering the temperature, and if the agglomerated particles can be dispersed into uniform primary particles, they are pulverized into finer particles. be able to. For this reason, a powder suspension is formed with liquefied gas, and this suspension is pulverized by a medium stirring mill. After this pulverization, when the liquefied gas is vaporized, a dry fine powder can be formed.
[0011]
In the case of reaggregation in a naturally dried state due to vaporization of the liquefied gas, reaggregation can be prevented by vaporizing the liquefied gas while vibrating the powder.
[0012]
Sugar and liquefied nitrogen as a liquefied inert gas are introduced into a medium stirring mill using a stirring ball formed of beads having a particle diameter of 500 μm to 1 mm so that the concentration is in the range of 0.5 to 0.6. After adjusting and making it into the state of a suspension and grind | pulverizing for 15 minutes in a medium stirring mill, liquid nitrogen was vaporized. As a result, a dry powder having an average particle size of 0.5 μm could be obtained.
[0013]
Similarly, toner powder having an average particle diameter of 8 μm and liquefied nitrogen as a liquefied inert gas are introduced into a medium stirring mill using a stirring ball formed of beads having a particle diameter of 500 μm to 1 mm, and the concentration is 0.50 to The mixture was adjusted to be in the range of 0.60, and after making it into a suspension state and pulverizing in a medium stirring mill for 30 minutes, liquid nitrogen was vaporized. As a result, a dry powder having an average particle size of 2.5 μm could be obtained.
[0014]
In the above embodiment, liquid nitrogen is used as the liquefied inert gas used together with the stirring ball. However, a liquid rare gas such as liquid helium, liquid neon, liquid argon, liquid krypton, or liquid xenon may be used. .
[0015]
In this way, when liquefied inert gas is used as a dispersion medium to make a suspension and pulverize with a medium agitation mill, the temperature dependence of the powder characteristics using the cold heat of the liquefied inert gas. In addition, the influence of frictional heat and the like during the pulverization operation can be reduced. Furthermore, when pulverizing a suspension using a liquefied inert gas as a dispersion medium, the material to be crushed does not dissolve in the liquefied inert gas or react with the liquefied inert gas. Thus, it is possible to make a fine powder while maintaining the above properties.
[0016]
【Effect of the invention】
In the present invention, a suspension in which a material to be ground (powder) is dispersed in a liquefied inert gas is pulverized by a medium stirring mill, and then the liquefied inert gas is vaporized to obtain a dry powder. Therefore, it is possible to obtain a fine powder in a dry state without requiring a special drying step, while exhibiting the advantages of wetness during the pulverization operation.
[0017]
Further, since the liquefied inert gas is used as the dispersion medium for dispersing the object to be crushed (powder), the powder component does not dissolve or react in the liquefied inert gas.
[0018]
Since the dispersion medium is a liquefied inert gas, a special device for collecting the dispersion medium is not required, and the influence on people and the environment can be reduced even when released to the atmosphere. In addition, since the pulverizer for fine pulverization functions as a single unit, the entire apparatus can be simplified and running costs such as power costs can be reduced.
[0019]
Since the powder can be finely pulverized in a low-temperature atmosphere of the liquefied inert gas, static electricity generated by friction between the powders during pulverization is reduced, and re-aggregation due to static electricity is reduced.

Claims (2)

A method for producing a fine powder, characterized in that a suspension in which a material to be pulverized is dispersed in a liquefied inert gas is pulverized by a medium stirring mill, and then the liquefied inert gas is vaporized to obtain a dry powder. The method for producing fine powder according to claim 1, wherein the liquefied inert gas is one kind of liquefied gas selected from liquid helium, liquid neon, liquid nitrogen, liquid argon, liquid krypton, and liquid xenon.