JPH0817953B2 - Method of dry grinding of graphite - Google Patents

Description

The present invention relates to a method for efficiently pulverizing graphite powder with a vibration mill.

[Conventional technology]

Graphite is industrially widely used as a solid lubricant, a conductive paint for cathode ray tubes, a pencil lead, and the like, but when used for these, it is required to be a fine powder having a finest flow as possible.

Conventionally, graphite powder is pulverized using a jet mill or the like to primarily pulverize the raw ore powder so that the average particles become several microns to several tens of microns, and then it is generally pulverized using a vibration mill. It

When producing fine powder using a vibrating mill, a method of crushing in a dry state by putting media such as steel balls and graphite to be crushed in a crushing chamber, a wet crushing method of crushing graphite to be crushed in a slurry state by adding water etc. When dry pulverizing, there is a method of exhausting with a vacuum pump into the pulverizing chamber and pulverizing while maintaining a vacuum state.

Each of these methods is a publicly-used technique that is adopted as necessary, and the features of each are as follows.

The dry pulverization method has a drawback in pulverization efficiency because graphite powders are easily attached to each other to form agglomerated powders.

Although the wet pulverization method solves the problem of agglomeration, it has drawbacks in the treatment method, such as the need to remove water and the like after pulverization and the type of medium being limited depending on the application of graphite.

On the other hand, according to the pulverization method in vacuum, the adhesive force of the graphite powder is weakened under vacuum, and it is possible to efficiently perform fine pulverization by a dry method. Documents related to this vacuum pulverization include, for example, Japanese Patent Publication No. 40-22099 and Japanese Patent Laid-Open No. 63-1.
6052 publication is mentioned.

[Problems to be Solved by the Invention]

According to the above-mentioned vacuum pulverizing method, it is possible to efficiently pulverize by a dry method, but on the other hand, it takes a pretreatment time to vacuum the pulverizing chamber, and a special device that does not release graphite powder from the pulverizing chamber during evacuation. There is a problem in that the cost is increased due to the troublesome maintenance of the device.

The present invention has been made in the light of the above-described method of the prior art, and is aimed at a fine pulverization means of graphite which is a dry pulverization, has a high pulverization efficiency and a low total cost.

[Means for solving the problem]

The present invention is to put graphite powder to be pulverized into a medium into a pulverizing chamber of a vibration mill, to close the pulverizing chamber, to start pulverizing graphite fine powder at a normal pressure in a sealed state, and to pulverize the pulverizing chamber as the pulverization progresses. The dry pulverization method for graphite is characterized in that the gas of (1) is adsorbed on graphite and pulverized under original pressure.

[Action]

When graphite powder to be crushed is put together with media such as steel balls into the crushing chamber of the vibration mill and the crushing chamber is closed and vibration is applied, the graphite powder is crushed by the shearing and cutting action of the media and the specific surface area increases. . Then, the gas adsorption capacity of the powder increases. As a result, the air in the crushing chamber is adsorbed by the graphite powder,
The crushing chamber is in a reduced pressure state. When further crushing, the air and the like in the crushing chamber are diluted, so there is not enough air and the like to adsorb on the graphite powder, that is, the crushing form similar to that in vacuum crushing is exhibited, and the crushing efficiency is the same as the vacuum crushing method. Indicates the same degree.

The shape of the crushed graphite powder is characterized in that it is relatively agglomerated as compared with the flat shape in the case of dry crushing under normal pressure or wet crushing.

The particle size of the pulverized graphite powder (starting graphite powder) is not particularly limited as long as it is the same as the commercially available general one, but it is not limited to a coarse powder having an average particle size of more than 100 μm. Since the amount of change in the specific surface area is large, the above-described depressurizing effect is exerted, and it is efficient as a vibration mill crushing, but industrially, after being made to be about 5 to 50 μm by another high efficiency crushing method such as a jet mill, It is more rational to apply the method of the present invention. On the other hand, using a starting graphite powder having a finished average particle diameter of 2 μm or 3 μm, which is close to the average particle diameter, results in a low yield and high cost even with other pulverizing means. Since it decreases, it is uneconomical and not preferable.

In addition, the average particle diameter in the present invention means an average value of a distribution in which the particle size is measured by an electric resistance method called a Coulter counter.

〔Example〕

Using a vibration mill, commercially available natural scaly graphite powder having an average particle diameter of 8.8 μm was finely pulverized by the method of the present invention.

The vibration mill used is a mechanism that gives vibration by eccentrically rotating a cylindrical crushing chamber axially mounted in the circumferential direction, and a steel ball is contained in the cylindrical chamber. There is a material access port at the top of the grinding chamber, which can be covered with a valved lid and opened and sealed. A vacuum pump can be connected via a hose to reduce the pressure in the crushing chamber.

Under the pulverization conditions shown below, three types of pulverization were performed, with the pulverization chamber being in an open state, a closed state, and a state in which the pressure was reduced to 1 to 10 Torr by a vacuum pump, and the average particle diameter and specific surface area of the pulverized powder were measured. .

 As the specific surface area, the specific surface area measured by the BET method was used.

Inner volume of crushing container: 3.4 liter Diameter of steel ball: 10 mm Filling amount of steel ball: 68% Graphite powder input amount: 600 g Vibration frequency: 1600 cpm Amplitude: 7 mm Grinding time: 5, 10, 15 hours Figure 1 shows the crushing container The internal pressure is shown. In the case of a sealed container, the crushing time is 100 Torr in 5 hours and 1 in 15 hours.
It showed 6 Torr.

FIG. 2 shows the average particle size of pulverized graphite powder with the pulverization time as the horizontal axis. The sealed pulverization of the present invention is slightly inferior to decompression pulverization in pulverization efficiency, but is far superior to open pulverization. I understand.

This measured value is measured by a Coulter counter as described above, and tends to show a value about 2.4 times larger than that measured by the light transmission method.

Similarly, FIG. 3 shows the specific surface area and shows the same tendency as in the case of the particle size.

〔The invention's effect〕

As described above, the graphite crushing method of the present invention uses a normal vibration mill, the internal pressure is lowered by closing the crushing chamber and crushing, and the crushing is promoted.
It is possible to efficiently pulverize into fine powder in a short time without requiring a complicated pulverizing device and operation.

[Brief description of drawings]

FIG. 1 is a graph showing the pressure inside the crushing chamber in the example, FIG. 2 is a graph showing the relationship between the crushing time and the average particle size of the crushed graphite powder, and FIG. 3 is a relationship between the crushing time and the specific surface area of the crushed graphite powder. It is a graph shown.

Claims (1)

[Claims] 1. A medium and a graphite powder to be crushed are put into a crushing chamber of a vibration mill, the crushing chamber is sealed, and pulverization of fine graphite powder is started in a sealed state at normal pressure. A dry pulverization method of graphite, characterized in that gas in a pulverization chamber is adsorbed to graphite and pulverized under reduced pressure.