JPS6399243A - Plasma treating apparatus - Google Patents

Abstract

PURPOSE:To obtain the titled apparatus, having a detecting means for detecting the vacuum degree in a plasma treating chamber for containing and treating a work and a controlling means for controlling the number of revolutions of a motor in a vacuum producing device and preventing the deterioration in efficiency and useful for treating synthetic resins, etc. CONSTITUTION:A plasma treating apparatus, having an airtight plasma treating chamber 1 for containing and treating a work (W), a plasma producing device 2 for supplying plasma to the plasma treating chamber 1 and a vacuum producing device 3, driven by an electrically-operated motor 20 and sucking a gas intol the plasma treating chamber 1 for containing and treating the work (W), a detecting means 38 for directly or indirectly detecting the vacuum degree in the plasma treating chamber 1 and a controlling means 24 for receiving the output from the detecting means 38 and controlling the electrically-operated motor 20 to increase the number of revolutions thereof according to the increase of the vacuum degree of the plasma treating chamber 1. The surface of the work (W) is subjected to plasma treatment using the above-mentioned plasma treating apparatus.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a plasma treatment apparatus that performs plasma treatment on the surface of synthetic resin products, and in particular, to shorten the treatment cycle by increasing the exhaust speed from the plasma treatment chamber. The present invention relates to a plasma processing apparatus that can perform

(Prior art) Generally, when painting the surface of a workpiece made of synthetic resin such as polypropylene, the surface of the workpiece is often subjected to plasma treatment or electrical discharge machining treatment to ensure coating film adhesion. The plasma processing apparatus for this plasma processing includes an airtight plasma processing chamber that accommodates a workpiece and performs plasma processing, a plasma generator that supplies plasma to the plasma processing chamber, and a plasma processing chamber that is driven by an electric motor and is connected to the plasma processing chamber. It is equipped with a vacuum generator that sucks in gas.

The vacuum generator of the above-mentioned plasma processing equipment generally has a vacuum pump connected in series with a booster and a bypass passage connected in parallel from the upstream side, and the electric motor that drives the vacuum pump and booster generally rotates at a constant rotation speed. controlled. Therefore, even if the degree of vacuum in the plasma processing chamber increases and the load on the motor decreases, the suction ability of the vacuum generator does not decrease, and the current consumption decreases by the amount of the decrease in load.

(Problems to be Solved by the Invention) In the conventional plasma processing apparatus described above, the electric motor of the vacuum generator is controlled at a constant rotation speed, so even if the degree of vacuum increases, the suction capacity does not improve and the There is a problem in that the processing cycle time for suctioning to a vacuum level is extremely long.

That is, as shown by the dotted line in FIG. 2 according to the embodiment, if only the vacuum pump is driven in the initial stage, the current consumption decreases as the degree of vacuum increases, as shown by the curve A0. , if the booster is driven in addition to the vacuum pump in the next step, the current consumption will be curve B. Although it increases by the amount of booster drive, it rapidly decreases as the degree of vacuum increases.

As described above, the conventional apparatus cannot make full use of the evacuation capacity of the vacuum pump or booster, so there is a problem that the plasma processing cycle time becomes long and the plasma processing power is inferior.

(Means for Solving the Problem) A plasma processing apparatus according to the present invention includes an airtight plasma processing chamber that accommodates a workpiece and performs plasma processing, a plasma generator that supplies plasma to the plasma processing chamber, and an electric motor. In the plasma processing apparatus, the plasma processing apparatus is equipped with a vacuum generating device that is driven by a vacuum generating device that sucks gas in the plasma processing chamber, and a detection means for directly or indirectly detecting the degree of vacuum in the plasma processing chamber is provided, and the A control means is provided which receives the output and controls the number of revolutions of the electric motor to increase as the degree of vacuum in the plasma processing chamber increases.

(Function) In the plasma processing apparatus according to the present invention, a workpiece is housed in a plasma processing chamber, the plasma processing chamber is brought into a substantially vacuum state by a vacuum generator, and while this substantially vacuum state is maintained, a workpiece is processed by a plasma generator. Plasma is supplied to the chamber for plasma processing.

When the vacuum generator sucks the gas inside the plasma processing chamber, the detection means directly or indirectly detects the degree of vacuum inside the plasma processing chamber. Then, in response to the output from the detection means, the control means controls to increase the rotational speed of the electric motor that drives the vacuum generator as the degree of vacuum in the plasma processing chamber increases and the load decreases. do. By controlling the rotational speed of the electric motor in this manner, it is possible to prevent a decrease in the load on the vacuum generator and to fully utilize its exhaust capacity.

(Effects of the Invention) According to the plasma processing apparatus according to the present invention, as explained above, the rotation speed of the electric motor that drives the vacuum generator increases as the degree of vacuum in the plasma processing chamber increases. Therefore, with a simple configuration consisting of a detection means and a control means, it is possible to reduce or prevent a decrease in the capacity of the vacuum generator (that is, a decrease in the work efficiency of the electric motor) and to reach a predetermined degree of vacuum in a short time. I can do it.

Furthermore, since the degree of vacuum in the processing chamber and the suction capacity of the vacuum generator are maintained high even during plasma processing, it is possible to speed up the flow of processing gas (plasma) and shorten the plasma processing time.

In this way, the processing cycle time of plasma processing can be significantly shortened.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

This embodiment is an example in which the present invention is applied to a plasma processing apparatus that performs plasma processing on an automobile bumper (hereinafter referred to as a workpiece) made of synthetic resin such as polypropylene as a pre-painting treatment.

As shown in FIG. 1, this plasma processing apparatus includes a plasma processing chamber 1, a plasma generator 2 that supplies plasma to the plasma processing chamber 1, and a vacuum generator 3 that sucks air and plasma from the plasma processing chamber 1. It is equipped with

A cylindrical chamber 4 that forms the plasma processing chamber 1 has an inlet door 5 airtightly attached to one open end, and an outlet door 6 that can be opened and closed to the other open end of the cylindrical chamber 5.
is installed airtight. A net conveyor 7 extending between both doors 5 and 6 is disposed at the bottom of the cylindrical chamber 5, and a workpiece W is placed on the net conveyor 7.

The plasma generator 2 is configured as follows.

Three plasma discharge shower pipes 8 are arranged at the upper end of the cylindrical chamber 5, each shower pipe 8 has a large number of outlet holes facing downward, and the upper part of each shower pipe 8 has a plasma supply pipe. 9 are connected to each plasma supply pipe 9.
extends upward through the earthen wall of the cylindrical chamber 5, the upstream ends of these three supply pipes 9 are connected to raw material gas supply pipes 10, respectively, and the upstream ends of the raw material gas supply pipes 10 are connected to gas cylinders 11. It is connected.

The gas cylinder 11 is filled with, for example, oxygen (or nitrogen) as a raw material gas for plasma, and the oxygen gas can be supplied or stopped via the electromagnetic on-off valve 12.

A flow rate control valve 13 is interposed at the upstream portion of each plasma supply pipe 9, and a microwave oscillator 14, a waveguide 15, and a three-stub tube 16 are provided near each supply pipe 9.
Each supply pipe 9 passes through a corresponding waveguide 15 at a position near the outside of the chamber 5, and oxygen in the supply pipe 9 is transmitted from the microwave oscillator 14 through the waveguide 15. The gas is irradiated with microwaves, thereby generating plasma using oxygen gas as a raw material.The plasma is supplied from each shower pipe 8 into the plasma processing chamber 1, and the surface of the workpiece W is plasma-processed by the plasma. .

The vacuum generator 3 includes a vacuum pump 21 driven by an AC motor 20, a mechanical booster 23 consisting of a Roots blower driven by an AC motor 22, and a mechanical booster 23 that is driven by an AC motor 20.
0, a control device 25 that drives and controls the motor 22, and other suction passages and valves, and is configured as follows.

The bottom wall of the chamber 5 is provided with three exhaust ports 26 and one intake port 27, and the intake port 27 is connected to an atmosphere introduction pipe 28 for introducing the atmosphere. An electromagnetic on-off valve 29 is provided.

Each of the exhaust ports 26 is connected to a merging suction pipe 32 via a branch suction pipe 31 equipped with a flow rate control valve 3o, and this merging suction pipe 32 is connected to the suction port of the booster 23.
The discharge port of the booster 23 is connected to the suction port of the vacuum pump 21 via a confluence suction pipe 32A, and an electromagnetic on-off valve 34 is interposed in a bypass pipe 33 that bypasses the booster 23.

The opening and closing of the electromagnetic valves 12, 29, 3o, and 34 are controlled by control signals from a control unit (not shown).

In the control device 24 , an AC power source 35 is connected to a power input terminal of a frequency converter 36 , and an output terminal of the frequency converter 36 is connected to the motor 20 via an output line 37 . A current detector 38 consisting of an induction coil or the like is interposed in the output wiring 37, and the output from the current detector 38 is supplied to the negative input terminal of the subtracter 4o via a current/voltage converter 39. An output from a current setting device 41 for setting the current of the motor 20 is supplied to the positive input terminal of the subtracter 40, and the output terminal of the subtracter 40 is connected to one input terminal of the adder 42. As a result, the subtracter 40 outputs the difference voltage between the output voltage from the current setter 41 and the output voltage from the current/voltage converter 39 to the adder 42.

A speed setter 43 for setting the rotational speed of the motor 20 is connected to the other input terminal of the adder 42.
The output terminal of is connected to the frequency control input terminal of the frequency converter 36.

As a result, the adder 42 inputs the sum voltage of the output voltage of the subtracter 40 and the output voltage of the speed setter 43 to the frequency converter 36 as a frequency control signal. In the frequency converter 36 configured with an inverter, the adder 42
As the input voltage from the motor increases, the output frequency to the motor 20 is increased to increase the rotation speed of the motor 20.

Note that since the control device 25 is similar to the control device 24,
The explanation will be omitted.

Next, the operation of the plasma processing apparatus described above will be explained.

When plasma-processing an untreated workpiece W, the workpiece W is accommodated in the chamber 5 by the net conveyor 7, and both doors 5 and 6 are closed. Next, close the solenoid valve 29 and close the solenoid valve 3.
0.34 is opened, the vacuum pump 21 is driven by the motor 20 controlled by the control device 24.

The rotational speed of the motor 20 is preset as a voltage value in the speed setter 43, and the current consumption of the motor 20 is preset as a voltage value in the current setter 41. Note that the voltage value set by the current setting device 41 is, for example,
A voltage value obtained by converting the current consumed by the motor 20 at the rotational speed set by the speed setting device 43 by the current/voltage converter 39 when the vacuum pump 21 is driven by the motor 20 in a state where the inside of the chamber 5 is at 1 atm. is set to the same value.

When the vacuum pump 21 starts operating, the voltage value detected by the current detector 38 and input to the subtracter 40 is set by the current setter 41.
Therefore, the frequency converter 36 is controlled only by the output from the speed setting device 43, and the voltage value from the motor 2
A rotation speed of 0 matches the set value.

When the air in the chamber 5 is sucked by the vacuum pump 21, the degree of vacuum gradually increases and the load on the vacuum pump 21 gradually decreases. If the load decreases in this way, the current consumption of the motor 20 starts to decrease, so this is detected by the current detector 38 and input as a voltage value to the subtracter 40, and the difference voltage corresponding to the decrease in current is input to the adder. 42, and the output voltage from the adder 42 increases by the above voltage.

Since the frequency converter 36 increases the output frequency in accordance with the voltage increase from the adder 42, the number of revolutions of the motor 20 increases and the suction capacity of the vacuum pump 21 is prevented from decreasing. This control is performed by feedback control so that no voltage difference occurs in the subtracter 40, so the current consumption of the motor 20 is held substantially constant. The current consumption when the vacuum pump 21 is operated to suck the plasma from the plasma processing chamber 1 as described above is as indicated by the line segment A in FIG.

When the electromagnetic on-off valve 34 is closed and the booster 23 is activated when the pressure inside the chamber 5 has been reduced to about 2 Qtorr, the suction force of the booster 23 is applied, and the degree of vacuum inside the chamber 5 is further increased.

Similarly to the constant current control in the control device 24, the control device 25 also controls the motor 22 with a constant current, and increases the rotation speed of the electric motor 22 as the degree of vacuum increases.
The suction ability of the booster 23 is maintained so as not to decrease.

During this time, the motor 20 of the vacuum pump 21 is also under constant current control. Therefore, the current consumption during control during this period is constant as shown by line segment B in FIG.

When the inside of the chamber 5 drops to about Q, 4 torr, the vacuum pump 21 and booster 23 are stopped, the solenoid valve 12 of the gas cylinder 11 is opened, and the raw material gas is supplied to the plasma processing chamber 1 through the supply pipe 10 and the supply pipe 9. Supply inside. The current consumption at this time is as shown by line C in FIG.

Next, when the microwave transmitter 14 is activated to generate oxygen plasma in the plasma supply pipe 9, the plasma enters the chamber 5 from the shower pipe 8 and plasma-processes the surface of the workpiece W. Chamber 5 due to the above constant current control
Since the degree of vacuum inside the chamber is higher than in conventional equipment, the efficiency of plasma processing is improved and processing time is shortened. The current consumption during this period is as shown by the line segments in FIG.

When the plasma treatment is finished, the solenoid valve 12 of the gas cylinder 11 is closed to stop the microwave transmitter 14, and then the solenoid valve 29 is opened to introduce atmospheric air into the chamber 5. The current consumption during this period is as shown by line E in FIG.

Finally, the outlet side R6 is opened and the plasma-treated workpiece W is taken out from the plasma processing chamber 1 by the net conveyor 7.

In FIG. 2, the dotted lines indicate the current consumption in the conventional device, and the curves or line segments AO, B, , co, Do, and Eo correspond to the line segments A, B, C, D, and E, respectively.

Further, FIG. 3 shows the temporal change in the degree of vacuum in the plasma processing chamber 1, where the solid line indicates the plasma processing apparatus of the present application and the dotted line indicates that of the conventional apparatus, with points P and P.

indicates the point at which plasma generation begins.

As is clear from FIGS. 2 and 3, in the plasma processing apparatus of this embodiment, as a result of constant current control of the motors 20 and 22, the suction capacity of the vacuum generator 3 can be fully utilized. The time it takes to reach the plasma temperature is significantly shortened, and the degree of vacuum that can be reached is also increased, so the plasma flow in the plasma processing chamber 1 becomes faster and the plasma processing time is significantly shortened.

In the above embodiment, the number of revolutions of the electric motors 20 and 22 was controlled by changing the frequency, but the number of revolutions of the motors 20 and 22 may be controlled by adopting a variable pulley ratio configuration. Further, in the above embodiment, the degree of vacuum in the chamber 5 is indirectly detected by the current detector 38, but the degree of vacuum in the plasma processing chamber 1 is directly detected using a pressure sensor, and the rotation is performed based on the pressure signal. The number may be controlled.

Incidentally, constant current control may be applied to only the motor 20 of both the motors 20 and 22.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is an overall configuration diagram of a plasma processing apparatus, FIG. 2 is a diagram showing changes in current consumption of the above device over time, and FIG. 3 is a diagram showing changes in degree of vacuum over time. FIG. W... Work, ■... Plasma processing chamber, 2... Plasma generator, 3... Vacuum generator, 11... Gas cylinder, 14... Microwave transmitter, 15.
・Waveguide, 20 AC motor, 21. Vacuum pump, 22. AC motor, 23. Mechanical booster, 24. Control device, 25. Control device, 38.
...Current detector. Patent applicant Mazda Motor Corporation Figure 2 Figure 3

Claims (1)

[Claims] (1) An airtight plasma processing chamber that accommodates a workpiece and processes it with plasma, a plasma generator that supplies plasma to the plasma processing chamber, and a vacuum generator that is driven by an electric motor and sucks gas in the plasma processing chamber. a detection means for directly or indirectly detecting the degree of vacuum in the plasma processing chamber; and a detection means for directly or indirectly detecting the degree of vacuum in the plasma processing chamber; and control means for controlling the rotation speed of the electric motor to increase.