WO2025027860A1 - Plasma head and plasma processing machine - Google Patents

Abstract

This plasma head comprises: a main body which is formed in a cylindrical shape and to one side of which a process gas is supplied; an electrode which is housed in the main body and discharges to at least a part of the process gas by being supplied with electric power to generate plasma gas; and a nozzle which has an inlet which is in communication with the other end side of the main body and into which the process gas or the plasma gas flows, a tapered portion in which the inner diameter gradually decreases as proceeding in the axial direction from the inlet, and an outlet which is positioned at the small diameter side end portion of the tapered portion and jets the plasma gas, wherein the hole diameter of the outlet and the taper angle of the tapered portion are determined so that the plasma gas which has reached a position separated from the outlet by a certain distance has a predetermined temperature or higher.

Description

Plasma head and plasma treatment machine

This specification relates to a plasma head that generates and ejects plasma gas, and a plasma processing machine that includes the plasma head.

Plasma treatment machines are known that perform plasma treatment using plasma gas generated from a process gas. Plasma treatment machines are widely used in industries such as welding and cutting solid workpieces and surface treatment, as well as in environmental protection and medical applications such as sterilization and purification of liquids and gases. When first developed, plasma treatment machines maintained the quality of the plasma gas by using a vacuum pump or the like to keep the process gas at low pressure (negative pressure) and stabilize the discharge. In recent years, atmospheric pressure plasma treatment machines that use atmospheric pressure process gas have been put into practical use, and it has become possible to obtain a high plasma density. One technical example of this type of plasma treatment machine is disclosed in Patent Document 1.

Patent Document 1 discloses a device for generating an atmospheric plasma beam. This device comprises a tubular housing having an axis, an internal electrode disposed inside the housing, a nozzle that is rotatable about the axis and has an opening that extends obliquely to the axis and emits the plasma beam, and a shield that surrounds the nozzle and changes the strength of the interaction between the plasma beam and the surface of the workpiece (work) depending on the rotation angle of the nozzle. It is said that this makes it possible to control the intensity of the plasma treatment and to treat the surface of the workpiece more uniformly than before.

Special table 2019-501505 publication

In general plasma processing machines, not just the device of Patent Document 1, when the temperature of the generated plasma gas is low, the lifespan tends to be shortened and the plasma density also tends to decrease. As a result, the effectiveness of the plasma processing sometimes decreases. In the configuration of Patent Document 1, the temperature of the plasma gas depends on the structure of the housing and internal electrode, and is also affected by the amount of process gas supplied. Furthermore, the temperature of the plasma gas that reaches the surface of the workpiece changes depending on the shape of the nozzle that sprays the plasma gas. From another perspective, it is possible to improve the efficiency of plasma processing by improving the shape of the nozzle to increase the generation and utilization efficiency of the plasma gas. Among the components of a plasma processing machine, the part that generates plasma gas and sprays it from the nozzle is called the plasma head.

The problem to be solved in this specification is to provide a plasma head that enhances the effectiveness of plasma processing by improving the nozzle shape, and a plasma processing machine that includes this plasma head.

This specification discloses a plasma head comprising: a body formed in a cylindrical shape, one end of which is supplied with a process gas; an electrode housed in the body, which generates plasma gas by discharging at least a portion of the process gas when power is supplied; and a nozzle having an inlet communicating with the other end of the body through which the plasma gas flows, a tapered section whose inner diameter gradually decreases as it advances axially from the inlet, and an outlet located at the small diameter end of the tapered section for ejecting the plasma gas, the hole diameter of the outlet and the taper angle of the tapered section being determined so that the plasma gas reaching a position a certain distance away from the outlet is at or above a predetermined temperature.

This specification also discloses a plasma processing machine that includes the plasma head described above, a gas supply unit that supplies the process gas to the main body, and a power supply unit that supplies the power to the electrode.

This specification discloses the technical idea of changing "the plasma head according to claim 1" in claim 3 originally filed to "the plasma head according to claim 1 or 2," and the technical idea of changing "the plasma head according to claim 4" in claim 5 originally filed to "the plasma head according to any one of claims 1 to 4." This specification also discloses the technical idea of changing "a plasma processing machine equipped with a plasma head according to any one of claims 1 to 6" in claim 8 originally filed to "a plasma processing machine equipped with a plasma head according to any one of claims 1 to 7."

In the disclosed plasma head and plasma processing machine, the nozzle shape can be improved by determining the hole diameter of the nozzle outlet and the taper angle of the tapered section so that the plasma gas that reaches a position a certain distance away from the nozzle outlet reaches a predetermined temperature or higher. This makes it possible to raise the temperature of the plasma gas higher than before, thereby improving the effectiveness of plasma processing.

1 is a perspective view showing a schematic overall configuration of a plasma processing apparatus; FIG. 2 is a perspective cross-sectional view showing a configuration of a plasma head. 1 is a front cross-sectional view illustrating the shape of a nozzle, a processing limit distance, and a fixed distance. FIG. 13 is a diagram showing the results of a gas supply amount experiment carried out using a conventional plasma head, showing the relationship between the supply amount of process gas and the effect of plasma processing (contact angle). FIG. 13 is a diagram showing the results of a first basic experiment carried out to improve the effect of plasma processing, showing the relationship between the nozzle outlet hole diameter and the plasma gas temperature. FIG. 11 is another diagram showing the results of the first basic experiment, illustrating the relationship between the nozzle outlet hole diameter and the effect of plasma treatment (contact angle). FIG. 13 is a diagram showing the results of a second basic experiment carried out to improve the effect of plasma processing, showing the relationship between the taper angle of the tapered portion of the nozzle and the temperature of the plasma gas. FIG. 11 is another diagram showing the results of the second basic experiment, illustrating the relationship between the taper angle of the tapered portion of the nozzle and the effect of plasma treatment (contact angle).

1. Overall Configuration of Plasma Processing Machine 10 First, the overall configuration of the plasma processing machine 10 including the plasma head 11 of the embodiment will be described with reference to Fig. 1. The plasma processing machine 10 performs plasma processing on the surface by ejecting plasma gas GP (see Fig. 2) generated under atmospheric pressure toward the surface of a solid workpiece W. An example of the plasma processing is, but is not limited to, a modification process for modifying the surface of the workpiece W from hydrophobic to hydrophilic.

The plasma processing machine 10 is composed of a plasma head 11, a robot 13, a control box 15, and other components. The plasma head 11 generates and ejects plasma gas GP from process gas GS (see Figure 2). The robot 13 moves the plasma head 11 in three dimensions and changes its posture. The control box 15 supplies the process gas GS and power to the plasma head 11, and provides overall control over the operation of the plasma processing machine 10.

For example, a serial link type robot (which can also be called an articulated robot) is used as the robot 13. More specifically, the robot 13 is composed of a base 131, a body 132, three arms (133, 134, 135), and a bracket 12. The base 131 is fixed to the floor. The body 132 is provided above the base 131 and rotates within a horizontal plane. The three arms (133, 134, 135) are mutually swingable and connected in series. The base end arm 133 is swingably supported by the body 132. The distal end arm 135 is provided with a bracket 12 at its tip. The bracket 12 holds the outer periphery of the plasma head 11.

Without being limited to the above, the robot 13 may be configured such that the plasma head 11 is swingably mounted on the tip of an arm that can extend and rotate, or may be configured such that the plasma head 11 is driven by a three-way independent drive mechanism. The robot 13 may also have a camera (not shown) to check the exact position and posture of the workpiece W placed on the work table 17 on the floor. Alternatively, a fixed camera may be provided above the work table 17. Furthermore, instead of the work table 17, a conveyor device (not shown) that sequentially transports multiple workpieces W may be used.

The control box 15 has a power supply unit 15A, a gas supply unit 15B, a display operation unit 15C, and a control unit 15D. The power supply unit 15A is connected to the plasma head 11 via a power cable (not shown). The power supply unit 15A is configured, for example, by a power supply circuit including a power semiconductor. The power supply unit 15A transforms the sine wave voltage of a commercial power supply (not shown) to generate a voltage waveform of the power to be supplied to the plasma head 11. A high-frequency voltage waveform can be used as this voltage waveform, and for example, a rectangular pulse voltage waveform with a frequency of 20 kHz and an adjustable duty ratio can be used. The duty ratio and voltage value of the rectangular pulse voltage waveform are appropriately controlled so that the plasma gas GP is efficiently generated. Without being limited to the above, the frequency of the supplied power can be changed, and the voltage waveform can be a triangular wave or other shape.

The gas supply unit 15B supplies the process gas GS to the plasma head 11 via a gas tube 19. Examples of the type of process gas GS include, but are not limited to, nitrogen and dry air. The gas supply unit 15B has a function of compressing the process gas GS and a function of adjusting the supply amount of the process gas GS. The gas tube 19 is pulled out from the housing of the control box 15 and is bridged so as to pass through guide rings (191, 192) provided on each of the two arms (133, 134), and is connected to the plasma head 11.

In this embodiment, the gas supply unit 15B supplies a predetermined supply amount of process gas GS at room temperature. A reference value of 40 L/min (40 liters per minute) converted to atmospheric pressure is set as the predetermined supply amount. The gas supply unit 15B may be provided with a heater (not shown) to supply heated process gas GS. The gas supply unit 15B may also be provided with a tank (not shown) for storing the process gas GS, or an air purifier (not shown) for dehumidifying and purifying the air to produce the process gas GS.

The control unit 15D is configured using a computer. The control unit 15D controls the operation of the robot 13, the power supply unit 15A, and the gas supply unit 15B. The control unit 15D is provided with a display operation unit 15C. The display operation unit 15C is configured, for example, by a touch panel, or by a combination of a display and various switches. The display operation unit 15C displays various setting screens and the operating status of the plasma processing device 10. The display operation unit 15C also accepts various information input by the operator.

The plasma treatment machine 10 operates as follows under the control of the control unit 15D. First, the robot 13 moves the plasma head 11 to approach and directly face the workpiece W on the work table 17. While the plasma head 11 is approaching the workpiece W or after it has directly faced the workpiece W, the power supply unit 15A and the gas supply unit 15B start operating. This causes the plasma head 11 to generate plasma gas GP inside. Furthermore, the plasma head 11 sprays the plasma gas GP toward the surface of the workpiece W, thereby performing plasma treatment on the surface of the workpiece W. Thereafter, the plasma head 11 moves parallel to the surface of the workpiece W and performs plasma treatment on the entire surface or the area to be treated as instructed.

2. Configuration of the Plasma Head 11 of the Embodiment Next, the configuration of the plasma head 11 of the embodiment will be described with reference to Figs. 2 and 3. As shown in Fig. 2, the plasma head 11 is configured to be approximately symmetrical about the central axis, and is formed long in the axial direction. In Figs. 2 and 3, the central axis extends in the vertical direction. In practice, the plasma head 11 may be used tilted, and the extension direction of the central axis changes. In the following description, the upper end of the member extending in the axial direction in Fig. 2 will be referred to as one end, and the lower end as the other end. The plasma head 11 is composed of a main body 20, an internal cable 22, a rectifying member 26, an electrode holder 28, an electrode 30, a nozzle 32, and the like.

The main body 20 is formed long in the axial direction using a metal material such as iron or aluminum. Most of the axial length, including one end of the main body 20 (the upper end in Figure 2), is formed in a roughly cylindrical shape. A portion of the main body 20 near the other end (near the lower end in Figure 2) is conically shaped and tapers toward the other end. The low-voltage line of the power cable wired from the power supply unit 15A is connected to the main body 20. A nozzle 32 is attached to the other end of the main body 20. The nozzle 32 is formed using a metal material. Therefore, the nozzle 32 is electrically conductive with the main body 20.

Nozzle 32 has an inlet 321, a tapered section 322, and an outlet 323. The inner diameter of tapered section 322 gradually decreases as it progresses in the axial direction (downward in Figures 2 and 3), in other words it is formed into a cone shape. The large diameter end on one end of tapered section 322 corresponds to inlet 321. Inlet 321 is attached in communication with the other end of main body 20 to ensure airtightness. Process gas GS or plasma gas GP flows in from main body 20 through inlet 321. The small diameter end on the other end of tapered section 322 corresponds to outlet 323. Outlet 323 ejects plasma gas GP.

The internal cable 22, conductor 62, crimp terminal 56, and electrode 30 are arranged in order on the central axis of the main body 20 from one end to the other end. The internal cable 22 extends from a position near one end of the central axis of the main body 20 to approximately the middle position of the axial length of the main body 20. The internal cable 22 consists of a central conductor (not shown) and an insulating layer covering the outer periphery of the central conductor. The internal cable 22 is held by a roughly cylindrical cable holder 24 that is fitted into the inner peripheral surface of the main body 20. The high-voltage line of the power cable is connected to one end of the internal cable 22. One end of the conductor 62 is connected to the center of the other end of the internal cable 22. The conductor 62 is formed in a round bar shape with a smaller diameter than the internal cable 22. One end of the crimp terminal 56 is crimped and attached to the other end of the conductor 62.

A gap 36 extending in the axial direction is formed between the internal cable 22 and the cable holder 24. A gas tube 19 is connected to the gap 36 from the gas supply unit 15B via the robot 13. This allows the process gas GS to be supplied to the gap 36 on one end side of the main body 20. The supplied process gas GS becomes an axial flow that flows through the gap 36 toward the other end.

The rectifying member 26 is formed in a ring shape using an insulating material such as plastic. The rectifying member 26 is positioned outside and spaced from the outer peripheral surface of the crimp terminal 56 located on the central axis of the main body 20. The outer peripheral edge of the rectifying member 26 is fitted into and fixed in a recess formed on the inner peripheral surface of the main body 20. The annular space between the rectifying member 26 and the crimp terminal 56 is the attachment position for the electrode holder 28. A female thread is formed on the inner peripheral surface of the rectifying member 26.

A number of straightening plates 38 are provided near the outer periphery of the straightening member 26 and are arranged in the circumferential direction. The straightening plates 38 are arranged parallel to one another while being inclined with respect to the axial direction. As a result, a number of inclined flow paths inclined with respect to the axial direction are formed between the straightening plates 38. The straightening member 26 changes the axial flow into a spiral flow by directing the process gas GS descending from the gap 36 into the inclined flow paths. In other words, in the internal space from the straightening member 26 to the nozzle 32 within the main body 20, the process gas GS becomes a spiral flow that advances in the axial direction while rotating around the central axis.

The electrode holder 28 is formed into a cylindrical shape using a metal material. The outer surface of the electrode holder 28 consists of a thin-diameter portion at one end that is short in the axial direction, and a tapered portion at the other end that is long in the axial direction. A male thread is formed on the outer surface of the thin-diameter portion. The tapered portion is formed into a cone shape tapered at the other end in the axial direction. The inner surface of the electrode holder 28 is formed with a step, and consists of a small-diameter inner surface 50 at one end, and a large-diameter inner surface 52 at the other end. The small-diameter inner surface 50 is located on the inner side of a part of the thin-diameter portion and the tapered portion near one end. The inner diameter of the small-diameter inner surface 50 is slightly larger than the outer diameter of the other end of the crimp terminal 56. The large-diameter inner surface 52 is located on the inner side of the remaining part near the other end of the tapered portion. The inner diameter of the large-diameter inner surface 52 is slightly larger than the outer diameter of the round bar-shaped electrode 30.

A horizontal hole 60 that communicates with the small diameter inner surface 50 is formed near one end of the tapered portion of the electrode holder 28. An enamel bolt 58 (enameled bolt) can be screwed and embedded in the horizontal hole 60. A horizontal hole 68 that communicates with the large diameter inner surface 52 is formed near the other end of the tapered portion. An enamel bolt 66 can be screwed and embedded in the horizontal hole 68. The enamel bolts (58, 66) do not become the starting point of a discharge path due to the action of the sintered material on their surface and the effect of being embedded.

The worker screws the male thread of the small diameter part of the electrode holder 28 into the female thread of the rectifying member 26, and attaches it by screwing. Therefore, the rectifying member 26 also serves as a structural member for attaching the electrode holder 28. When screwing, the other end of the crimp terminal 56 enters the small diameter inner circumferential surface 50 of the electrode holder 28 and passes through the horizontal hole 60. Next, the worker screws the hollow bolt 58 into the horizontal hole 60 to press the crimp terminal 56 and press it against the small diameter inner circumferential surface 50. This prevents the screw connection of the electrode holder 28 from loosening, and stabilizes the installation position. In addition, low resistance conduction between the crimp terminal 56 and the electrode holder 28 is ensured.

The electrode 30 is formed in a round bar shape using a metal material with excellent heat resistance. The worker inserts one end of the electrode 30 from the underside of the electrode holder 28 into the large diameter inner surface 52 and passes it through the horizontal hole 68 to attach it. When attaching, the worker adjusts the position of the electrode 30 so that the tip (other end) of the electrode 30 extends a predetermined amount (for example, 3 to 5 mm) from the other end of the electrode holder 28. The tip of the electrode 30 is located inside the main body 20 and does not reach the nozzle 32. Next, the worker screws the hollow bolt 66 into the horizontal hole 68 to press the electrode 30 and press it against the large diameter inner surface 52. As a result, the electrode 30 is housed in the center of the main body 20 and extends in the axial direction, and rotation and axial movement are restricted, stabilizing the attachment posture. In addition, low resistance conduction between the electrode holder 28 and the electrode 30 is ensured. When the tip of the electrode 30 becomes worn due to repeated discharges, maintenance such as cleaning, position adjustment, and replacement are performed as necessary.

In the above configuration, the voltage waveform output by the power supply unit 15A is applied to the electrode 30 via the high-voltage line of the power cable, the internal cable 22, the conductor 62, the crimp terminal 56, and the electrode holder 28. Therefore, the internal cable 22, the conductor 62, the crimp terminal 56, and the electrode holder 28 may be considered as part of the electrode 30 to which the voltage waveform is applied. On the other hand, the low-voltage line of the power cable is connected to the main body 20 and the nozzle 32. Therefore, power is supplied between the electrode 30 and the main body 20 and the nozzle 32. In this way, the space between the electrode 30 and the main body 20 and the nozzle 32 becomes the generation region RM where the plasma gas GP is generated by discharge. In addition, the process gas GS supplied from the gas supply unit 15B flows in the form of a spiral flow within the generation region RM.

Here, the tip of the electrode 30 is more likely to be the starting point of the discharge path than other parts because the electric field generated by the application of the voltage waveform is concentrated there. On the other hand, the main body 20 and the nozzle 32 can be the end points of the discharge path. The discharge path can move along with the flow of the process gas GS, so the state of the discharge changes over time. In either case, energy is injected into the process gas GS by the discharge, and plasma gas GP is generated. Furthermore, the temperature and plasma density of the plasma gas GP increase as multiple discharges are repeated. The generation efficiency of the plasma gas GP depends on the shapes and relative positional relationship (shape of the generation region RM) of the electrode 30, the main body 20, and the nozzle 32, as well as on the applied voltage waveform and voltage value, and the state and flow rate of the spiral flow of the process gas GS.

The generated plasma gas GP is ejected from the outlet 323 of the nozzle 32 and reaches the surface of the workpiece W to perform plasma processing. At this time, the plasma gas GP flows in the ejection direction while expanding in a conical shape, so the area to be processed on the surface of the workpiece W can be made larger than the hole diameter D of the outlet 323. Since the plasma gas GP generally has a short life, some of it returns to the original process gas GS before reaching the workpiece W. The utilization efficiency of the plasma gas GP depends on the temperature and plasma density of the ejected plasma gas GP, the flow speed and flow direction of the plasma gas GP after it is ejected, and the distance and opposing angle between the nozzle 32 and the workpiece W.

3. Conventional Plasma Head Here, the dimensional specifications and the like of a conventional plasma head will be explained with reference to Fig. 3. The hole diameter D (diameter) of the outlet 323 of the conventional nozzle 32 is 4.5 mm, and the taper angle AT of the tapered portion 322 is 28°. The machining accuracy of the hole diameter D is controlled to an error of ±0.02 mm or less, and the machining accuracy of the taper angle AT is controlled to an error of ±0.5° or less.

　A conventional plasma head manufactured based on the above specifications has a predetermined processing limit distance LM as shown in Figure 3. In other words, a conventional plasma head is capable of plasma processing when the surface of the workpiece W is positioned within the processing limit distance LM from the outlet 323. In other words, when the surface of the workpiece W is positioned at a position beyond the processing limit distance LM from the outlet 323, at least one of the temperature and plasma density of the arriving plasma gas GP decreases, reducing the effectiveness of the plasma processing. In other words, at a position beyond the processing limit distance LM, it is practically impossible to perform good plasma processing. Specifically, the processing limit distance LM is set to 25 mm.

General plasma heads, including conventional ones, rarely perform plasma processing at the processing limit distance LM. In other words, under normal circumstances, plasma heads often perform plasma processing at a distance closer than the processing limit distance LM. Therefore, a position that is a fixed distance LC away from the outlet 323 that is less than the processing limit distance LM is set as a representative position for evaluating at least one of the temperature of the plasma gas GP and the effect of the plasma processing using the plasma gas GP. Specifically, the fixed distance LC is 20 mm.

When experimentally evaluating the temperature of the plasma gas GP, the workpiece W is not used. Instead, the temperature sensor's temperature sensing part is placed at a central position PC on the central axis a certain distance LC away from the outlet 323 of the nozzle 32, and the plasma gas GP is ejected into the plasma head to actually measure its temperature. A thermocouple can be used as the temperature sensor, but is not limited to this. This experimental method is used in the first and second basic experiments described below.

When experimentally evaluating the effect of plasma treatment, the surface of the workpiece W is positioned at a certain distance LC from the outlet 323 so as to be perpendicular to the central axis, and the plasma head is caused to perform plasma treatment. In addition, a modification process is performed as an example of plasma treatment, and a quantitative evaluation is performed. Specifically, a glass plate is used for the workpiece W. The effect of the plasma treatment, which modifies the surface of the glass plate from hydrophobic to hydrophilic, is expressed by the contact angle AC of water on the glass. In other words, the higher the effect of the plasma treatment, the better the hydrophilicity obtained, and the smaller the contact angle AC. In this embodiment, the effect of the plasma treatment is determined to be sufficient when the contact angle AC of water on the glass is 10° or less. This experimental method is used in the gas supply amount experiment described next, and the first and second basic experiments described below.

In a conventional plasma head, a gas supply rate experiment was conducted to determine the supply rate Q of the process gas GS. In the gas supply rate experiment, a glass plate was placed at the central position PC, and the supply rate Q of the process gas GS was increased or decreased in 1 L increments from a reference value of 40 L/min, and the contact angle AC was measured after plasma processing was performed. This resulted in the experimental results shown in Figure 4, which show the relationship between the supply rate Q of the process gas GS and the effect of plasma processing (contact angle AC). In Figure 4, the horizontal axis shows the supply rate Q (L/min) of the process gas GS converted to atmospheric pressure. The vertical axis shows the measured contact angle AC (°).

According to the experimental results, it was found that when the supply rate Q was in the range of 37 to 42 L/min, the contact angle AC was 10° or less, and the plasma treatment was effective enough. It was also found that when the supply rate Q was 36 L/min or less and 43 L/min or more, the contact angle AC exceeded 10°, and the plasma treatment was not effective enough. As a result, conventional plasma heads allowed the supply rate Q of the process gas GS to vary within a range of 37 to 42 L/min, converted to atmospheric pressure conditions.

If the supply amount Q of the process gas GS is too large, it is estimated that the residence time in the generation region RM will be shortened, and the temperature of the plasma gas GP and the plasma density will not increase sufficiently. Conversely, if the supply amount Q of the process gas GS is too small, it is estimated that the amount and flow rate of the plasma gas GP ejected from the nozzle 32 will decrease, and good plasma processing cannot be performed. Thus, there is an appropriate allowable range of fluctuation for the supply amount Q.

4. Basic Experiments for Improving the Effect of Plasma Processing The inventors of the present application conducted the first and second basic experiments, focusing on improving the shape of the nozzle 32, in order to improve the effect of the plasma processing of the plasma processing machine 10 and the plasma head 11. As a prerequisite for the improvement, the condition was that the nozzle 32 should not be changed from the current model except for its dimensional specifications. In addition, the processing limit distance LM of 25 mm, the constant distance LC of 20 mm, and the allowable fluctuation range of the supply amount Q of 37 to 42 L/min were also considered to be equivalent to those of the current model. In the first and second basic experiments, multiple types of nozzles 32 with different hole diameters D of the outlet 323 and taper angles AT of the taper portion 322 were prototyped and assembled into the plasma head 11, and actual measurements were performed.

In the first basic experiment shown in Figures 5 and 6, the hole diameter D of the outlet 323 of the nozzle 32 is 4.0 mm, 4.5 mm (current product), and 5.0 mm. The taper angle AT of the tapered portion 322 is 28° (current product), and the supply amount Q of the process gas GS is 40 L/min (reference value). Figure 5 shows the temperature TG of the plasma gas GP measured at the center position PC without using the workpiece W. Specifically, when the hole diameter D is 4.0 mm, the temperature TG is 455°C, when the hole diameter D is 4.5 mm, the temperature TG is 505°C, and when the hole diameter D is 5.0 mm, the temperature TG is 650°C. According to this, it was found that the shape of the nozzle 32 can be improved by changing the hole diameter D of the outlet 323 of the nozzle 32 from 4.5 mm of the current product to 5.0 mm, and the temperature TG of the plasma gas GP can be increased by 145°C.

In addition, in FIG. 6, a glass plate is used as the workpiece W, and the contact angles AC measured at seven points arranged in a straight line at a pitch of 2 mm around the center position PC are shown. Specifically, when the hole diameter D is 4.0 mm, the contact angles AC exceed 10° at five points, and it is found that the effect of the plasma treatment is insufficient. When the hole diameter D is 4.5 mm, the contact angles AC slightly exceed 10° at two points, and it is found that the effect of the plasma treatment of the current product is not necessarily sufficient. When the hole diameter D is 5.0 mm, the contact angles AC are 10° or less at all seven points, and it is found that the effect of the plasma treatment is sufficient. This is consistent with the experimental results in FIG. 5, and it is found that the shape of the nozzle 32 can be improved by changing the hole diameter D of the outlet 323 of the nozzle 32 from 4.5 mm to 5.0 mm, and the effect of the plasma treatment can be increased.

Next, in the second basic experiment shown in Figures 7 and 8, the taper angle AT of the taper portion 322 is 24°, 28° (current product), and 30°. The hole diameter D of the outlet 323 of the nozzle 32 is 4.5 mm (current product), and the supply amount Q of the process gas GS is 40 L/min (reference value). In Figure 7, the temperature TG of the plasma gas GP measured at the center position PC without using the workpiece W is shown. Specifically, when the taper angle AT is 24°, the temperature TG is 630°C, when the taper angle AT is 28°, the temperature TG is 455°C, and when the taper angle AT is 30°, the temperature TG is 470°C. According to this, it was found that the shape of the nozzle 32 can be improved by changing the taper angle AT of the taper portion 322 of the nozzle 32 from 28° of the current product to 24°, and the temperature TG of the plasma gas GP can be increased by 175°C.

In addition, in FIG. 8, a glass plate is used as the workpiece W, and the contact angles AC are shown as being measured at seven points arranged in a straight line at a pitch of 2 mm with the central position PC as the center. Specifically, when the taper angle AT is 24°, the contact angles AC are 10° or less at all seven points, and it is found that the effect of the plasma treatment is sufficient. When the taper angle AT is 28°, the contact angles AC exceed 10° at two points, and it is found that the effect of the plasma treatment of the current product is not necessarily sufficient. When the taper angle AT is 30°, the contact angles AC exceed 10° at all seven points, and it is found that the effect of the plasma treatment is not necessarily sufficient. According to this, in agreement with the experimental results in FIG. 7, it is found that the shape of the nozzle 32 can be improved by changing the taper angle AT of the taper portion 322 from 28° to 24°, and the effect of the plasma treatment can be increased.

5. Improvement of the Shape of the Nozzle 32 The mechanism by which the shape of the nozzle 32 affects the temperature TG of the plasma gas GP and the effect of the plasma processing is complex, and is believed to involve the following factors (1) to (8).
(1) As the taper angle AT of the tapered portion 322 is changed, the shape and internal volume of the generation region RM where the plasma gas GP is generated change, and the residence time of the process gas GS changes.
(2) As the taper angle AT is changed, the discharge characteristics (discharge path, discharge intensity, discharge duration, etc.) change.
(3) As the taper angle AT is changed, the state of the spiral flows of the process gas GS and the plasma gas GP changes.
(4) The temperature and plasma density of the generated plasma gas GP change due to the combined effects of the above (1) to (3).
(5) Depending on the temperature and plasma density of the generated plasma gas GP, the life of the plasma gas GP after being ejected and the time-dependent decrease characteristic of the plasma density change.
(6) The average flow velocity of the plasma gas GP changes as the hole diameter D of the outlet 323 changes.
(7) As the hole diameter D and the taper angle AT are changed, the way in which the ejected plasma gas GP flows in the ejection direction while expanding in a cone shape (flow state) changes.
(8) The combined effects of (4) to (7) above cause changes in the temperature, plasma density, and flow rate of the plasma gas GP that reaches the surface of the workpiece W, thereby affecting the effectiveness of the plasma processing.

As described above, the mechanism is complex, but based on the results of the first basic experiment, the shape of the nozzle 32 can be improved by changing the hole diameter D of the outlet 323 of the nozzle 32 from 4.5 mm to 5.0 mm. Also, based on the results of the second basic experiment, the shape of the nozzle 32 can be improved by changing the taper angle AT of the tapered portion 322 from 28° to 24°. Ultimately, the inventors determined the hole diameter D of the outlet 323 of the nozzle 32 of the embodiment of the plasma head 11 to be 5.0 mm, and the taper angle AT of the tapered portion 322 to be 24°, resulting in an improved shape.

Furthermore, the inventors have additionally carried out technical studies and considerations regarding the temperature of the plasma gas GP, as well as simulations of the flow velocity distribution of the plasma gas GP, in relation to the plasma head 11 of the embodiment (improved product). As a result, it was concluded that, according to the plasma head 11 of the embodiment, even when taking into account the allowable fluctuation range of the supply amount Q and the variation in operation during plasma processing, the plasma gas GP becomes 600°C or higher at the central position PC. In other words, in the plasma head 11 of the embodiment, the hole diameter D of the outlet 323 is set to 5.0 mm, and the taper angle AT of the tapered portion 322 is set to 24° so that the plasma gas GP that reaches the central position PC, which is a certain distance LC away from the outlet 323 of the nozzle 32, becomes 600°C or higher. This allows the temperature TG of the plasma gas GP to be 600°C or higher, which is significantly higher than the temperatures of the current product (505°C, 455°C). It was also found that when the hole diameter D of the outlet 323 was set to 5.0 mm, the taper angle AT of the tapered portion 322 should be set in the range of 24±2°.

In the plasma head 11 of the embodiment, the appropriate average flow velocity of the plasma gas GP sprayed from the outlet 323 can be derived. When deriving, the hole diameter D of 5.0 mm is taken into consideration with a processing accuracy error of ±0.02 mm, and the allowable fluctuation range of the supply amount Q of 37 to 42 L/min is taken into consideration. Then, the maximum and minimum values of the appropriate average flow velocity of the plasma gas GP are derived as follows. Here, π represents the circular constant.

Maximum value = (42 x 10 ⁶ / 60) / (π ・ 4.98 ² / 4) = 35838 mm/sec
= 35.8 m/sec
Minimum value = (37 x 10 ⁶ / 60) / (π ・ 5.02 ² / 4) = 31157 mm/sec
= 31.2 m/sec
In other words, the constant distance LC is set to 20 mm, and the hole diameter D of the outlet 323 is set to 5.0 mm so that the average flow velocity of the plasma gas GP ejected from the outlet 323 of the nozzle 32 falls within the range of 31.2 to 35.8 m/sec.

Furthermore, in the plasma head 11 of the embodiment, the hole diameter D of the outlet 323 of the nozzle 32 may be changed from 4.5 mm to 5.0 mm, and the taper angle AT of the tapered portion 322 may be maintained at 28°. Furthermore, in the plasma head 11 of the embodiment, the hole diameter D of the outlet 323 of the nozzle 32 may be maintained at 4.5 mm, and the taper angle AT of the tapered portion 322 may be changed from 28° to 24°. In this way, even with an improvement that changes only one of the hole diameter D of the outlet 323 of the nozzle 32 of the current product and the taper angle AT of the tapered portion 322, the temperature TG of the plasma gas GP at the center position PC can be made 600°C or higher.

In the plasma head 11 and plasma processing machine 10 of the embodiment, the shape of the nozzle 32 can be improved by determining the hole diameter D of the outlet 323 of the nozzle 32 and the taper angle AT of the tapered portion 322 so that the plasma gas GP that reaches a central position PC a certain distance LC away from the outlet 323 of the nozzle 32 is at or above a predetermined temperature. This makes it possible to raise the temperature TG of the plasma gas GP higher than in the past, thereby improving the effectiveness of the plasma processing.

6. Application and modification of the embodiment The temperature of 600°C shown in the embodiment is an example and can be changed. However, if the lower limit of the temperature TG of the plasma gas GP at the center position PC is set to a value other than 600°C, it becomes necessary to reconsider the appropriate values of the hole diameter D of the outlet 323 and the taper angle AT of the tapered portion 322. In addition, the detailed configuration inside the main body 20, for example, the number and shape of a plurality of members to which a voltage waveform is applied, can be modified, and the generation region RM and the state of the discharge can change with the modification. Furthermore, the shape of the rectifying member 26 can be modified to change the state (flow) of the spiral flow of the process gas GS. When these modifications are made, it is considered that the generation efficiency and utilization efficiency of the plasma gas GP change, so it becomes necessary to reconsider the appropriate values of the hole diameter D of the outlet 323 and the taper angle AT of the tapered portion 322. In addition, the embodiment can be applied and modified in various ways.

10: Plasma treatment machine 11: Plasma head 13: Robot 15: Control box 15A: Power supply unit 15B: Gas supply unit 20: Main body 22: Internal cable 26: Rectifier 28: Electrode holder 30: Electrode 32: Nozzle 321: Inlet 322: Taper section 323: Outlet GS: Process gas GP: Plasma gas D: Hole diameter AT: Taper angle LC: Fixed distance LM: Processing limit distance PC: Center position Q: Supply amount TG: Temperature AC: Contact angle W: Workpiece

Claims (8)

a main body formed in a cylindrical shape, one end of which is supplied with a process gas;
an electrode housed in the body and configured to discharge electricity in at least a portion of the process gas to generate a plasma gas;
a nozzle having an inlet communicating with the other end side of the body and through which the process gas or the plasma gas flows, a tapered section whose inner diameter gradually decreases as it advances in the axial direction from the inlet, and an outlet located at the small diameter end of the tapered section and for ejecting the plasma gas, the hole diameter of the outlet and the taper angle of the tapered section being determined so that the plasma gas reaching a position a certain distance away from the outlet has a predetermined temperature or higher;
A plasma head comprising: The electrode is housed in the center of the body and extends in an axial direction, and the power is supplied between the metallic body and the metallic nozzle;
The plasma head is formed in an annular shape and disposed between the body and the electrode, and includes a flow straightening member for making the supplied process gas flow in a spiral direction.
2. The plasma head according to claim 1. The plasma head of claim 2 performs plasma treatment on a workpiece surface by ejecting the plasma gas toward the workpiece surface. The plasma head is capable of performing the plasma processing when the surface of the workpiece is positioned within a predetermined processing limit distance from the outlet,
The certain distance is equal to or less than the processing limit distance.
4. The plasma head according to claim 3. The plasma head of claim 4, wherein the hole diameter of the outlet is set so that the average flow velocity of the plasma gas ejected from the outlet falls within the range of 31.2 to 35.8 m/sec. The plasma head according to claim 5, wherein the process gas is supplied to the main body at a rate of 37 to 42 L/min, calculated at room temperature and atmospheric pressure. The plasma head according to any one of claims 1 to 6, wherein the taper angle of the taper portion is set within the range of 24±2°. The plasma head according to any one of claims 1 to 6,
a gas supply unit for supplying the process gas to the main body;
a power supply unit for supplying the power to the electrodes;
A plasma processing apparatus comprising:

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