JPH09141087A - Treatment of powder by atmospheric pressure glow discharge plasma and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the hydrophilicity of hydrophobic powder having poor dispersibility by supplying the powder between disk-shaped electrodes which face each other and at least one of which rotate, imparting centrifugal force to the powder and impressing a high-frequency voltage between the electrodes, thereby generating atm. glow discharge plasma. SOLUTION: Dielectric substances 3, 3 are stuck to the electrodes 2, 2 arranged in a reaction vessel 2. These dielectric substances 3, 3 are disposed to face each other at a specified spacing. The air in this reaction vessel 1 is replaced with a gaseous mixture and the high-frequency voltage is impressed between the electrodes 2 and 2 from a high-frequency power source 11 to generate the glow discharge. The upper part of the reaction vessel 1 is provided with a powder tank 5 and the powder material to be treated is dropped from the lower part of this tank through a rotary metering valve 6 into the raw material supplying port of the upper electrode 2 so as to be supplied into the glow discharge atmosphere. As a result, the powder is moved by imparting the kinetic energy to the powder and is simultaneously subjected to the plasma treatment, by which the surfaces of the powder are uniformly treated and the hydrophilicity thereof is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a treatment method and apparatus for rendering hydrophobic powder having poor dispersibility hydrophilic by atmospheric pressure glow discharge plasma treatment.

[0002]

2. Description of the Related Art Recently, it has become known that a film or a fiber is treated by plasma excitation by an atmospheric pressure glow discharge so that the surface of an object to be treated is made hydrophilic to improve the wetting of the surface and enhance the adhesive effect. I came. Then, the present inventors have found that the plasma treatment is also applied to powder, and the surface of the powder is made hydrophilic or hydrophobic by plasma treatment to improve dispersibility in water, oil or solvent, The application was filed earlier (see JP-A-4-135638). Subsequently, the present inventors proposed a further improved method and apparatus for plasma processing of powder (Japanese Patent Laid-Open No. 4-13563).
No. 8, JP-A-6-365 or JP-A-6-134296.
issue). And, by using these methods and devices, the plasma treatment of the powder surface has achieved some results, but depending on the type of powder to be treated, uniform treatment may not be possible or the electrode gap may not be uniform. In some cases, fine powder was clogged, and the work was difficult if the gap between the electrodes was not always cleaned and kept clean.

That is, since a high energy field is present in the glow discharge and a barrier generated around the electric field acts on the powder like a wall, the fine powder has a bulk specific gravity. Since it was small and light, it did not enter the plasma and could not be processed only by the weight of the powder itself. For that reason, first, a considerable amount of force was required to put the powder fine particles into the plasma. Also, some of the particles that have entered the plasma are significantly charged depending on the powder, so electrostatic adhesion occurs and it may be difficult to take them out. The surface area of the powder is extremely large compared to the surface area of a film or the like, and is several hundred times larger. Therefore, plasma must act uniformly on the entire surface of the powder in order to uniformly process the entire surface. For that reason,
Although there is a method of using a gas flow for feeding powder into plasma at a high speed together with the processing gas, this method has a huge amount of processing gas and is not economical.

The method described in JP-A-6-134296 is a method in which powder is placed thinly in a container such as a dish, and the powder is placed between electrodes, glow discharge is performed, and the plasma is treated with excited plasma. However, even in this case, if the powder is not treated while being made to flow while being vibrated, only the surface of the powder layer is treated and the entire surface cannot be treated. As a result, the powder flowing due to vibration scatters and drifts into the reaction vessel, mixing unprocessed powder and treated powder, and the effect is not sufficiently exerted, and the powder acts as one type of dielectric. To achieve this, the result is similar to attaching a thick dielectric to the electrodes. Therefore, glow discharge is unlikely to occur unless the voltage is increased. This is also difficult to use industrially in terms of economy and safety.

[0005]

As a result of repeated research to solve the above-mentioned various problems, the present inventor has sent the powder to the central portion between the disk-shaped upper and lower electrodes in which both or one of them rotates. Put in, give kinetic energy to the powder by centrifugal force,
The present invention has been completed by finding that the entire surface of the powder can be continuously and completely processed by moving in the plasma, and the object of the present invention is to increase the surface of the powder with high yield. A method and an apparatus for performing atmospheric pressure glow discharge plasma treatment are provided.

[0006]

Means for Solving the Problems The gist of the present invention is to provide a powder from a raw material supply port provided at the center of one electrode between at least one of the rotating disc-shaped opposing electrodes. It is supplied between the electrodes, and a centrifugal force based on the rotating electrode is applied to the powder, and a high frequency high voltage is applied between the electrodes to generate an atmospheric pressure glow discharge plasma, and the powder surface is treated by the atmospheric pressure glow discharge plasma. A method for treating powder by atmospheric pressure glow discharge plasma, characterized in that a powder supply port is provided at the center of at least one electrode arranged in a plasma reaction container having a gas inlet and a gas outlet. And a disk-shaped pair of opposing electrodes, a glow discharge plasma generator for generating an atmospheric pressure glow discharge plasma between the electrodes, and a rotating device for rotating the electrodes. A processing apparatus of the powder by the plasma.

The plasma reactor of the present invention has been conventionally used as an atmospheric pressure glow discharge plasma generator, and has a gas inlet and outlet and a plasma generating electrode. As the plasma generating electrode, at least one of the metal electrodes is covered with a dielectric, and the dielectric is preferably a hard synthetic resin or ceramic capable of maintaining a flat surface. The heat resistance is preferably such that it does not deform even when heated to 100 ° C. or higher, and thermosetting resins such as melamine, urea and bakelite, and thermoplastic resins such as methacryl, polycarbonate, polyester and polyimide are preferable. The high-frequency wavelength applied to the electrodes is not particularly limited. About 1K
Although a high frequency of 13.56 MHz, which is used in vacuum low-pressure plasma processing, can be used, it is preferably about 1 KHz to 100 KHz in order to suppress heat generation in atmospheric pressure glow discharge. At 1 KHz or less, the transformer becomes large at high output, 100 KHz
Above, the efficiency is good, but it becomes more difficult to match the output transformer as heat is generated and the frequency becomes higher. Voltage about 2
It is about 000 to 7,000 V, and varies depending on the type of gas introduced into the reaction vessel. The gap between the electrodes is about 5 to 40 mm, and this gap also differs depending on the type of gas introduced.

Further, in the case of imparting lipophilicity to the particle surface together with the inert gas for plasma generation in the reaction vessel, the kinds of gas introduced are, for example, propane, butanepentane, hexane, ethylene, butene, trimethylpentane. , Trimethylolpropane aliphatic hydrocarbons and their derivatives, or aromatic hydrocarbons such as benzene, toluene, xylene, styreneethylbenben, cumene and their substituted products, or alicyclic hydrocarbons such as cyclopentene and cyclohexene and their substituted products. In the case of imparting hydrophilicity to the particle surface, a mixed gas of argon and helium, a ketone compound such as acetone and methyl ethyl ketone, an alcohol such as ethanol and propanol, an ether such as 1,4-dioxane and methyl cellosolve. , Tetramethylsilane, trimethyl chloride There silane compounds such Roshiran, these conditions are not different from conventional atmospheric pressure glow discharge plasma generating conditions (see JP-A-4-135638 and JP-A-6-134296).

Next, as the processing gas, as the gas for exciting plasma in the atmospheric pressure glow discharge, helium gas, a mixed gas of helium and argon, or a mixture of argon gas and a slight amount of ketone vapor has been invented by the inventors. Known by. Usually, the treatment of the powder is mainly intended to improve the dispersion performance, and therefore, the treatment for increasing the hydrophilicity is performed so that the powder is finely dispersed in water or a polar solvent. If the surface is slightly etched by passing it through the plasma of the above-mentioned inert gas, or if it is passed through the plasma of a gas in which a gas such as CF ₃ is mixed with a trace amount of the inert gas, a remarkable hydrophilic property is obtained. Especially in the case of the present invention, the gas is only necessary to create an atmosphere of atmospheric pressure, and when treating with only inert gas, the leak is replenished or the effect of air still adhering to the powder is A small amount of inflow that does not come out is acceptable. That is, it suffices to allow the glow discharge to flow in a stable manner. The powder to be treated is not particularly limited, but for example, carbon, aluminum oxide, titanium oxide,
Zinc white or the like, and the particle size thereof may be any of the range from ordinary powder to ultrafine particles.

In the present invention, the powder is supplied to the central portion between the rotating electrodes, and the powder is given kinetic energy by the centrifugal force by the rotating force of the rotating electrode.
Centrifugal force is the weight of powder (W) and radius of rotating disk (γ)
Furthermore, the product of the squares of the angular velocities (ω) of rotation, that is, f = Wγ
Since it is represented by ω ² , even if the rotation speed is increased, the weight of the powder is light, but the powder moves while being processed in the glow discharge with extremely large centrifugal energy, and is blown out of the disk. Therefore, all powders are uniformly processed and released on all surfaces without loss. Since it is necessary to change the rotation speed depending on the specific gravity of the powder to be processed, it is preferable that the rotation speed of the motor be variable. Therefore, in the case of an induction motor, it is preferable to use an inverter, or to use a continuously variable transmission, or a direct winding motor that can freely change the number of rotations by using a sliderac.

Next, the apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view of an atmospheric pressure glow discharge plasma generator according to the present invention, and FIG. 2 is a perspective view of a metal electrode,
FIG. 3 is a side view of an example in which the upper and lower electrodes are simultaneously rotated,
FIG. 4 is a side view and a plan view of another electrode, and FIG. 5 is a side view of a heat dissipation plate provided on the electrode. In FIG. 1, a plasma reaction gas is introduced into a plasma reaction vessel 1 through an introduction pipe 7
Through a discharge port provided in the reaction vessel 1 and discharged to the outside of the reaction vessel through a discharge pipe 8. The dielectrics 3 and 3'are attached to the disk-shaped metal electrodes 2 and 2'arranged vertically in the reaction vessel 1, and the dielectrics 3 and 3'are opposed to each other with a constant interval. As shown in FIG. 2, this electrode is composed of an upper metal electrode 2 having a raw material supply port 4 in the center and a lower metal electrode 2 ′ directly connected to a rotating shaft 9, and each metal electrode has a dielectric layer. Covered by bodies 3, 3 ', dielectrics 3, 3'oppose each other with a constant gap. The rotating shaft 9 is connected to a rotating device 10, and the rotating device 10 rotates the lower electrode. A metal film to be an electrode may be attached to the front surface of the dielectric as the upper electrode and a back surface of the dielectric as the lower electrode. Even if you stick metal foil with adhesive,
Alternatively, plating, vacuum deposition, or sputtering may be used. However, in such a planar electrode, the metal foil needs to have a radius smaller than that of the dielectric, and this is to prevent sparks and arcs from directly flowing between the metals when a high voltage is applied.

Further, as shown in FIG. 3, if the upper and lower electrodes are connected with an electrically insulating screw or bolt or nut 11 such as epoxy resin and the upper and lower electrodes are rotated together, the processing gas therein also moves due to centrifugal force. It is even more effective. When a large amount of powder is processed for a long period of time, electric power is large, and as a result, a large amount of heat is generated, and therefore a dielectric made of synthetic resin may be deformed. In such a case, a disk-shaped metal electrode made of glass or enamel is used as a dielectric. Further, in order to dissipate heat, a heat sink (radiating plate) provided with a discharge slit may be used as an electrode. This is the same as the one used for power transistors for high power, but it requires special consideration for rotation.

FIG. 4 is a side view and a top view of the special electrode.
In the figure, 2 is a metal to be an electrode, and 3 is a dielectric enamel provided on the surface thereof. The periphery and the center are provided with edges so that spark discharge does not occur, and are wider than the gap where glow discharge occurs. The electrodes are provided with concentric slit ridges so that the heat generated by the inflowing gas can be taken away. The electrode can be used as a heat sink only with the upper electrode, and any shape of heat sink may be used when it is not rotated, but if it is rotated together with the lower electrode, a well-balanced one can be used for smooth rotation. is necessary. In addition, grooves are made more finely in the raised portion (partial view in Fig. 5) to maximize the heat radiation area.

Next, a plasma processing method using such an apparatus will be described. The processing gas is introduced little by little as shown by the arrow in FIG. 1, but the powder moves by centrifugal force and does not need to be carried in the gas flow, so the flow rate of the processing gas introduced is very small. In addition, if the powder tank is replaced with the processing gas in advance, there is no inflow of air and the processing can always be performed under the same conditions. When the air in the reaction vessel 1 is replaced with helium or a mixed gas of helium and argon, and a high frequency voltage of, for example, 10 KHz and 2500 V is applied between the upper and lower electrodes from the high frequency power source 11, glow discharge occurs in the gap between the dielectrics, and this glow discharge is It continues even if the lower electrode 2 ′ is rotated via the rotation shaft 9. A powder tank 5 is provided on the upper part of the reaction vessel 1, and a powder to be treated is supplied from the lower part of the powder tank 5 through a rotary metering valve 6 to the upper electrode in the reaction vessel 1 by a fixed amount. It is dropped into the mouth 4 and supplied into the glow discharge atmosphere. The powder to be treated is put into the powder tank 5 in advance. Since not only the powder tank 5 but also the powder contains a lot of air, helium or a mixed gas of helium and argon is used first. It is preferable to replace the plasma treatment gas. If necessary, the powder tank 5 is evacuated to remove air and then replaced with a gas such as helium to obtain a better result. It is preferable to be able to supply.

In the case of processing by atmospheric pressure glow discharge, unlike vacuum low-pressure plasma processing, it is characterized by room temperature processing up to 100 ° C. Further, since the gas always flows, the processing gas also serves as a cooling gas and cooling by a heat sink is also efficient. You can do well. Further, when treating organic powder having a low melting point, a method using a Peltier effect in which a semiconductor is used and cooling is performed with an electric current is also possible if heat radiation cooling is not sufficient. Under such conditions, when the powder is dropped from the raw material supply part 4 of the upper electrode 2 to the center of the rotating lower electrode 2 ', each powder particle is given a strong kinetic energy by centrifugal force. The gas discharged from the reaction vessel can be reused and is extremely economical. Next, the effect will be described by implementation.

[0016]

[Examples and Comparative Examples]

Example 1 In the apparatus shown in the figure, a disc electrode having a diameter of 30 cm was used, and a synthetic mica having a thickness of 1.5 mm as a dielectric and a stainless steel thin plate having a diameter of 26 cm as an electrode were attached to the disc. Therefore, the radius of the dielectric is increased by 20 mm and sparks do not wrap around. The upper disk electrode was fixed, the shaft of a small direct-winding motor was connected to the center of the lower electrode for direct drive, and the rotation speed was changed by changing the voltage with a slidac. At the center of the upper electrode there is an opening for the powder, all of which are contained in the reaction vessel. The upper electrode and the lower electrode are each connected to a high frequency power source, and the lower electrode is grounded for safety. The distance between the electrodes is 10 mm. B-2 carbon manufactured by Toyo Tanso Co., Ltd. was selected as the powder to be hydrophilized, and it was confirmed in advance that the powder floated in water without being dispersed. Next, the air in the reaction vessel is replaced with argon 60 and helium 3
The gas is replaced with a mixed gas of 9.5 and 0.5 parts by volume of carbon tetrafluoride, and a voltage of 5 KHz and 3500 V is applied between the electrodes.
A beautiful orange glow discharge occurs. Next, the glow discharge is stably maintained even if the lower electrode is rotated. The rotation speed is 100 times / minute. Next, by gradually adding carbon powder from the opening of the upper electrode, a small pyramid is formed in the center of the rotating lower electrode, and the lower side of the pyramid collapses as the number of revolutions increases, and is blown into the glow discharge. The rotation speed at this time was 1500 times / minute. When the number of revolutions exceeds 1500 times, the pyramid becomes small and is immediately blown during the glow discharge, continuously treated with the plasma excited by the glow discharge, and hits the wall of the container to accumulate at the bottom.
The untreated carbon powder that has been treated does not disperse in water at all and floats on water, whereas the treated carbon powder disperses well in water and very few floats, improving hydrophilicity. It had a great effect.

Example 2 Rutile titanium oxide was used as powder in the same apparatus as in Example 1. Argon: helium = 5 in the reaction vessel
10m when mixed gas of 0:50 volume ratio was added to replace air
A high-frequency voltage of 3 KHz 4000 V was applied to the electrodes at m intervals to perform glow discharge, and the rotation number of the lower rotating electrode was 150.
Titanium oxide powder was added from the opening of the upper electrode at 0 times / minute, and the same treatment as in Example 1 was performed. The treated titanium oxide powder has improved hydrophilicity and has significantly better dispersibility than untreated titanium oxide powder. The results of the comparative test are shown below.
1 g of untreated titanium oxide and 1 g of plasma-treated titanium oxide were placed in separate test tubes, respectively, and distilled water was added.
Add cc and shake well. Next, this test tube was stood upright and allowed to stand, and the time required for the dispersed titanium oxide powder to settle and the top to become transparent was measured. The untreated sample completely settled in 23 seconds, while the sample treated in Example 2 had a fine powder floating and slowed to settle, and it took 3 minutes or more to completely settle. Therefore, it is clear that the formation of secondary particles hydrophilized by plasma is prevented, and a great effect was recognized.

[0018]

As described above, according to the present invention, the powder is supplied to the central portion of the rotating atmospheric pressure glow discharge plasma generating electrode, and kinetic energy based on the centrifugal force is applied to the powder. Since the plasma treatment is carried out while moving, the surface of the powder can be uniformly treated, and the workability can be greatly improved compared to the conventional atmospheric pressure glow discharge plasma treatment of the powder. .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a plasma processing reactor according to the present invention.

FIG. 2 is a perspective view of an electrode used in the present invention.

FIG. 3 is a side view of an example in which the upper and lower electrodes are simultaneously rotated.

FIG. 4 is a side view and a plan view of another special electrode.

FIG. 5 is a side view of a heat dissipation plate provided on an electrode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Plasma reaction container 2 Metal electrode 3 Dielectric 4 Raw material supply port 5 Powder tank 6 Rotating metering valve 7 Gas inlet port 8 Gas discharge port 9 Rotating shaft 10 Rotating device 11 Electrode connecting bolts and nuts

Claims (2)

[Claims] 1. At least one electrode is rotated between disk-shaped opposing electrodes, and powder is supplied between the electrodes through a raw material supply port provided at the center of one electrode to rotate the powder. Applying a centrifugal force based on the electrodes and applying a high frequency high voltage between the electrodes to generate atmospheric pressure glow discharge plasma,
A method for treating powder with atmospheric pressure glow discharge plasma, comprising treating the surface of the powder with the atmospheric pressure glow discharge plasma. 2. A pair of disc-shaped opposing electrodes provided with a powder supply port at the center of at least one electrode arranged in a plasma reaction container having a gas inlet and a gas outlet.
An apparatus for treating powder with atmospheric pressure glow discharge plasma, comprising: a glow discharge plasma generator for generating atmospheric pressure glow discharge plasma between the electrodes; and a rotating device for rotating the electrodes.