Plasma head and plasma processing machine

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

[0001] The present specification relates to a plasma head that generates and ejects plasma gas, and a plasma processing apparatus that includes the plasma head.

[0002] Plasma treatment machines are known that perform plasma treatment using plasma gas generated from a process gas. Plasma treatment machines are widely used in industrial applications such as welding, cutting, and surface treatment of solid workpieces, as well as in environmental protection and medical applications such as sterilizing and purifying liquids and gases. Initially, plasma treatment machines used vacuum pumps or other devices to maintain the quality of the process gas by stabilizing the discharge. In recent years, atmospheric-pressure plasma treatment machines using atmospheric-pressure process gas have been put into practical use, achieving high plasma density. One technical example of this type of plasma treatment machine is disclosed in Patent Document 1.

[0003] Patent Document 1 discloses a device for generating an atmospheric plasma beam. The device includes a tubular housing having an axis, an internal electrode disposed inside the housing, a nozzle rotatable about the axis and having an opening extending obliquely relative to the axis through which the plasma beam is emitted, and a shield surrounding the nozzle and changing the strength of the interaction between the plasma beam and the surface of a workpiece (workpiece) depending on the rotation angle of the nozzle. The device is said to be able to control the intensity of the plasma treatment and to treat the surface of the workpiece more uniformly than conventional methods.

[0004] Special table 2019-501505 publication

[0005] Incidentally, in general plasma processing devices, not just the device described in Patent Document 1, low plasma gas temperatures tend to shorten the device's lifespan and reduce plasma density. As a result, the effectiveness of plasma processing sometimes declines. In the configuration described in 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 reaching the workpiece surface varies depending on the shape of the nozzle that ejects the plasma gas. From another perspective, improving the nozzle shape may increase the generation and utilization efficiency of the plasma gas, thereby improving the effectiveness of plasma processing. Among the components of a plasma processing device, the part that generates plasma gas and ejects it from the nozzle is called the plasma head.

[0006] The problem to be solved in this specification is to provide a plasma head in which the effect of plasma processing is enhanced by improving the shape of the nozzle, and a plasma processing machine including this plasma head.

[0007] This specification discloses a plasma head comprising: a main body formed in a cylindrical shape and having a process gas supplied to one end thereof; an electrode housed in the main body and supplied with power to discharge at least a portion of the process gas to generate plasma gas; and a nozzle having an inlet communicating with the other end of the main body and through which the plasma gas flows in, 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 spraying 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.

[0008] This specification also discloses a plasma processing apparatus including 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.

[0009] 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."

[0010] In the disclosed plasma head and plasma processing device, the nozzle shape can be improved by determining the nozzle outlet hole diameter and the taper angle of the tapered portion so that the plasma gas reaching a position a certain distance from the nozzle outlet reaches a predetermined temperature or higher. This makes it possible to raise the temperature of the plasma gas more than before, thereby improving the effectiveness of plasma processing.

[0011] 1 is a perspective view schematically illustrating the overall configuration of a plasma processing machine; 2 is a perspective cross-sectional view illustrating the configuration of a plasma head; 3 is a front cross-sectional view illustrating the nozzle shape, processing limit distance, and fixed distance; 4 is a diagram illustrating the results of a gas supply amount experiment conducted with a conventional plasma head, showing the relationship between the supply amount of process gas and the effect of plasma processing (contact angle); 5 is a diagram illustrating the results of a first basic experiment conducted to improve the effect of plasma processing, showing the relationship between the nozzle outlet hole diameter and the plasma gas temperature; 6 is another diagram illustrating the results of the first basic experiment, showing the relationship between the nozzle outlet hole diameter and the effect of plasma processing (contact angle); 7 is a diagram illustrating the results of a second basic experiment conducted to improve the effect of plasma processing, showing the relationship between the taper angle of the tapered portion of the nozzle and the plasma gas temperature; 8 is another diagram illustrating the results of the second basic experiment, showing the relationship between the taper angle of the tapered portion of the nozzle and the plasma gas temperature;

[0012] 1. Overall Configuration of Plasma Treatment Machine 10 First, the overall configuration of the plasma treatment machine 10 including the plasma head 11 of the embodiment will be described with reference to Figure 1. The plasma treatment machine 10 performs plasma treatment on the surface of a solid workpiece W by spraying plasma gas GP (see Figure 2) generated under atmospheric pressure toward the surface of the workpiece W. An example of plasma treatment is, but is not limited to, a modification treatment that modifies the surface of the workpiece W from hydrophobic to hydrophilic.

[0013] In addition to the plasma head 11, the plasma processing machine 10 is composed of a robot 13 and a control box 15. The plasma head 11 generates and ejects a plasma gas GP from a process gas GS (see FIG. 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 controls the overall operation of the plasma processing machine 10.

[0014] The robot 13 may be, for example, a serial link robot (which may also be called an articulated robot). 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 connected in series and can swing relative to one another. The base-end arm 133 is swingably supported by the body 132. The distal-end arm 135 has a bracket 12 attached to its tip. The bracket 12 holds the outer periphery of the plasma head 11.

[0015] 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 extendable and swiveling arm, or such that the plasma head 11 is driven by a three-way independent drive mechanism. Furthermore, the robot 13 may 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 loads and unloads multiple workpieces W may be used.

[0016] The control box 15 includes 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 circuit including a power semiconductor. The power supply unit 15A transforms a sine wave voltage from a commercial power source (not shown) to generate a voltage waveform of power supplied to the plasma head 11. This voltage waveform can be a high-frequency voltage waveform, for example, a rectangular pulse voltage waveform with a frequency of 20 kHz and an adjustable duty ratio. The duty ratio and voltage value of the rectangular pulse voltage waveform are appropriately controlled to efficiently generate plasma gas GP. The above is not a limitation; the frequency of the supplied power can be changed, and the voltage waveform can be a triangular wave or other waveforms.

[0017] The gas supply unit 15B supplies a 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 drawn out from the housing of the control box 15, stretched so as to pass through guide rings (191, 192) provided on two arms (133, 134), and connected to the plasma head 11.

[0018] In this embodiment, the gas supply unit 15B supplies a predetermined supply amount of process gas GS at room temperature. The predetermined supply amount is set to a reference value of 40 L / min (40 liters per minute) converted to atmospheric pressure. The gas supply unit 15B may be equipped with a heater (not shown) to supply heated process gas GS. The gas supply unit 15B may also be equipped 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.

[0019] The control unit 15D is configured using a computer. The control unit 15D controls the operations of the robot 13, the power supply unit 15A, and the gas supply unit 15B. The control unit 15D is equipped 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.

[0020] The plasma treatment machine 10 operates as follows under 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 begin operating. This causes the plasma head 11 to generate plasma gas GP therein. 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 specified treatment range.

[0021] 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 approximately symmetrically about a central axis and is formed long in the axial direction. In FIGS. 2 and 3, the central axis extends vertically. In practice, the plasma head 11 may be used tilted, which changes the direction of extension of the central axis. In the following description, the upper end of the axially extending member in FIG. 2 will be referred to as one end, and the lower end will be referred to 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.

[0022] 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 of the main body 20, including one end (the upper end in FIG. 2 ), is formed in a generally cylindrical shape. A portion of the main body 20 near the other end (the lower end in FIG. 2 ) is tapered into a conical shape. A low-voltage line of a 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 connected to the main body 20.

[0023] The nozzle 32 has an inlet 321, a tapered portion 322, and an outlet 323. The inner diameter of the tapered portion 322 gradually decreases in the axial direction (downward in FIGS. 2 and 3 ), in other words, it is formed into a conical shape. The large-diameter end on one end of the tapered portion 322 corresponds to the inlet 321. The inlet 321 is attached to and communicates with the other end of the main body 20, ensuring airtightness. The process gas GS or plasma gas GP flows into the inlet 321 from the main body 20. The small-diameter end on the other end of the tapered portion 322 corresponds to the outlet 323. The plasma gas GP is ejected from the outlet 323.

[0024] The internal cable 22, conductor 62, crimp terminal 56, and electrode 30 are arranged along the central axis of the main body 20 in this order from one end to the other. The internal cable 22 extends from a position near one end of the central axis of the main body 20 to approximately the middle of the axial length of the main body 20. The internal cable 22 consists of a center conductor (not shown) and an insulating layer covering the outer periphery of the center conductor. The internal cable 22 is held by a generally cylindrical cable holder 24 fitted to the inner surface of the main body 20. A high-voltage line of a 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 rod 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.

[0025] 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 passes through the gap 36 toward the other end.

[0026] The rectifying member 26 is formed in a ring shape using an insulating material such as plastic. The rectifying member 26 is disposed outside and spaced apart from the outer circumferential surface of the crimp terminal 56 located on the central axis of the main body 20. The outer circumferential edge of the rectifying member 26 is fitted into and fixed in a recess formed on the inner circumferential 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 circumferential surface of the rectifying member 26.

[0027] A plurality of rectifying plates 38 are provided near the outer periphery of the rectifying member 26 and are arranged in the circumferential direction. The plurality of rectifying plates 38 are arranged parallel to one another and inclined with respect to the axial direction. As a result, a plurality of inclined flow paths inclined with respect to the axial direction are formed between the plurality of rectifying plates 38. The rectifying member 26 directs the process gas GS descending from the gap 36 into the inclined flow paths, thereby changing the axial flow into a spiral flow. In other words, in the internal space within the main body 20 from the rectifying member 26 to the nozzle 32, the process gas GS becomes a spiral flow that advances in the axial direction while rotating around the central axis.

[0028] The electrode holder 28 is made of metal and has a cylindrical shape. The outer surface of the electrode holder 28 consists of a narrow-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 narrow-diameter portion. The tapered portion is formed into a conical shape that tapers toward the other end in the axial direction. The inner surface of the electrode holder 28 is stepped 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 periphery of a portion of the narrow-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 periphery of the remaining portion of the tapered portion near the other end. The inner diameter of the large-diameter inner surface 52 is slightly larger than the outer diameter of the rod-shaped electrode 30.

[0029] A horizontal hole 60 that communicates with the small-diameter inner circumferential 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 or embedded in the horizontal hole 60. A horizontal hole 68 that communicates with the large-diameter inner circumferential surface 52 is formed near the other end of the tapered portion. An enamel bolt 66 can be screwed or embedded in the horizontal hole 68. The enamel bolts (58, 66) do not become the starting point of a discharge path due to the effect of the sintered material on their surfaces and the effect of being embedded.

[0030] The worker threads the male threads of the small-diameter portion of the electrode holder 28 into the female threads of the rectifying member 26 to attach the electrode holder 28 by screwing them together. Therefore, the rectifying member 26 also serves as a structural member for attaching the electrode holder 28. During the 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 threads the hollow bolt 58 into the horizontal hole 60 to press the crimp terminal 56 against the small-diameter inner circumferential surface 50. This prevents the electrode holder 28 from loosening and stabilizes its installation position. Furthermore, low-resistance electrical continuity is ensured between the crimp terminal 56 and the electrode holder 28.

[0031] The electrode 30 is formed in a round rod shape using a metal material with excellent heat resistance. The worker inserts one end of the electrode 30 from the bottom of the electrode holder 28 into the large-diameter inner circumferential surface 52 and passes it through the horizontal hole 68 to attach it. During attachment, the worker adjusts the position of the electrode 30 so that its tip (other end) extends a predetermined amount (e.g., 3 to 5 mm) from the other end of the electrode holder 28. The tip of the electrode 30 is positioned within the main body 20 and does not reach the nozzle 32. Next, the worker threads the hollow bolt 66 into the horizontal hole 68 to press the electrode 30 against the large-diameter inner circumferential surface 52. This allows the electrode 30 to be housed in the center of the main body 20 and extend axially, while restricting rotation and axial movement, stabilizing the attachment position. Furthermore, low-resistance electrical continuity is ensured between the electrode holder 28 and the electrode 30. When the tip of the electrode 30 is worn down due to repeated discharge, maintenance such as cleaning, position adjustment, and replacement is carried out as necessary.

[0032] In the above-described 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 part of the electrode 30 to which the voltage waveform is applied. Meanwhile, 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. The space between the electrode 30 and the main body 20 and the nozzle 32 constitutes a generation region RM where plasma gas GP is generated by discharge. Furthermore, the process gas GS supplied from the gas supply unit 15B flows in the form of a spiral flow within the generation region RM.

[0033] Here, the tip of the electrode 30 is more likely to be the starting point of the discharge path than other locations 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 discharge behavior changes over time. In either case, the discharge injects energy into the process gas GS, generating plasma gas GP. Furthermore, multiple discharges increase the temperature and plasma density of the plasma gas GP. The generation efficiency of the plasma gas GP depends on the shapes and relative positions of the electrode 30, main body 20, and nozzle 32 (the shape of the generation region RM), as well as the applied voltage waveform and voltage value, and the behavior and flow velocity of the spiral flow of the process gas GS.

[0034] 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 wider than the hole diameter D of the outlet 323. Since the plasma gas GP generally has a short life, a portion 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 velocity and flow pattern of the plasma gas GP after being ejected, the separation distance and opposing angle between the nozzle 32 and the workpiece W, etc.

[0035] 3. Conventional Plasma Head The dimensions and specifications of a conventional plasma head will now be described with reference to Figure 3. The hole diameter D 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.

[0036] Conventional plasma heads manufactured based on the above specifications have a predetermined processing limit distance LM as shown in FIG. 3 . In other words, conventional plasma heads are 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 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, it becomes virtually impossible to perform good plasma processing at a position beyond the processing limit distance LM. Specifically, the processing limit distance LM is set to 25 mm.

[0037] Conventional and general plasma heads rarely perform plasma processing at the processing limit distance LM. That is, plasma heads usually perform plasma processing at a distance closer than the processing limit distance LM in most cases. Therefore, a representative position for evaluating at least one of the temperature of the plasma gas GP and the effect of plasma processing using the plasma gas GP is set at a position a certain distance LC away from the outlet 323 that is less than the processing limit distance LM. Specifically, the certain distance LC is 20 mm.

[0038] When experimentally evaluating the temperature of the plasma gas GP, no workpiece W is used. Instead, the temperature sensor's temperature-sensing part is placed at a central position PC on the central axis, a fixed distance LC from the outlet 323 of the nozzle 32, and the plasma gas GP is ejected into the plasma head to 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.

[0039] Furthermore, when experimentally evaluating the effectiveness of plasma treatment, the surface of the workpiece W is positioned a certain distance LC from the outlet 323, perpendicular to the central axis, and the plasma head is used to perform plasma treatment. Furthermore, a modification process is performed as an example of plasma treatment, and a quantitative evaluation is performed. Specifically, a glass plate is used as the workpiece W. The effectiveness 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 more effective the plasma treatment, the better the hydrophilicity, and the smaller the contact angle AC. In this embodiment, the effectiveness 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 rate experiment described below, as well as the first and second basic experiments described below.

[0040] A gas supply rate experiment was conducted on a conventional plasma head to determine the supply rate Q of the process gas GS. In the gas supply rate experiment, a glass plate was placed at the center 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. After plasma processing, the contact angle AC was measured. 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 represents the supply rate Q (L / min) of the process gas GS converted to atmospheric pressure. The vertical axis represents the measured contact angle AC (°).

[0041] Experimental results showed 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. Furthermore, when the supply rate Q was 36 L / min or less or 43 L / min or more, the contact angle AC exceeded 10°, and the plasma treatment was ineffective. Therefore, conventional plasma heads allowed the supply rate Q of the process gas GS to fluctuate within a range of 37 to 42 L / min, converted to atmospheric pressure conditions.

[0042] If the supply rate Q of the process gas GS is too high, 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 rate Q of the process gas GS is too low, the amount and flow rate of the plasma gas GP ejected from the nozzle 32 will decrease, and good plasma processing will not be possible. Thus, there is an appropriate allowable fluctuation range for the supply rate Q.

[0043] 4. Basic Experiments to Enhance Plasma Treatment Effect The inventors of the present application conducted first and second basic experiments, focusing on improving the shape of the nozzle 32 in order to enhance the plasma treatment effect of the plasma treatment device 10 and plasma head 11. The premise for the improvement was that the nozzle 32 would remain unchanged from the current model except for its dimensional specifications. Furthermore, the processing limit distance LM of 25 mm, the constant distance LC of 20 mm, and the allowable fluctuation range of the supply rate Q of 37 to 42 L / min were also considered to be equivalent to the current model. In the first and second basic experiments, several types of nozzles 32 with different hole diameters D of the outlet 323 and taper angles AT of the tapered portion 322 were prototyped and incorporated into the plasma head 11, and actual measurements were performed.

[0044] In the first basic experiment shown in Figures 5 and 6, the hole diameter D of the outlet 323 of the nozzle 32 was 4.0 mm, 4.5 mm (current model), and 5.0 mm. The taper angle AT of the tapered portion 322 was 28° (current model), and the supply rate Q of the process gas GS was 40 L / min (reference value). Figure 5 shows the temperature T of the plasma gas GP measured at the center position PC without using a workpiece W. Specifically, when the hole diameter D was 4.0 mm, the temperature T was 455°C, when the hole diameter D was 4.5 mm, the temperature T was 505°C, and when the hole diameter D was 5.0 mm, the temperature T was 650°C. This result demonstrated that the shape of the nozzle 32 could be improved by changing the hole diameter D of the outlet 323 of the nozzle 32 from 4.5 mm (current model) to 5.0 mm, and the temperature T of the plasma gas GP could be increased by 145°C.

[0045] FIG. 6 shows the contact angles AC measured at seven points on a glass plate, arranged in a line with a 2-mm pitch around the center position PC. Specifically, when the hole diameter D was 4.0 mm, the contact angles AC exceeded 10° at five points, indicating that the plasma treatment was insufficient. When the hole diameter D was 4.5 mm, the contact angles AC slightly exceeded 10° at two points, indicating that the current plasma treatment was not necessarily effective. When the hole diameter D was 5.0 mm, the contact angles AC were 10° or less at all seven points, indicating that the plasma treatment was effective. This, consistent with the experimental results shown in FIG. 5, indicates that the nozzle 32 could be improved by changing the hole diameter D of the outlet 323 of the nozzle 32 from 4.5 mm to 5.0 mm, thereby enhancing the effectiveness of the plasma treatment.

[0046] Next, in a second basic experiment shown in FIGS. 7 and 8 , the taper angle AT of the tapered portion 322 was 24°, 28° (current model), and 30°. The hole diameter D of the outlet 323 of the nozzle 32 was 4.5 mm (current model), and the supply rate Q of the process gas GS was 40 L / min (reference value). FIG. 7 shows the temperature TG of the plasma gas GP measured at the center position PC without using a workpiece W. Specifically, when the taper angle AT was 24°, the temperature TG was 630°C, when the taper angle AT was 28°, the temperature TG was 455°C, and when the taper angle AT was 30°, the temperature TG was 470°C. This result demonstrated that the shape of the nozzle 32 could be improved by changing the taper angle AT of the tapered portion 322 of the nozzle 32 from 28° (current model) to 24°, and that the temperature TG of the plasma gas GP could be increased by 175°C.

[0047] FIG. 8 also shows the contact angles AC measured at seven points on a glass plate, arranged in a straight line at 2 mm intervals around the center position PC. Specifically, when the taper angle AT was 24°, the contact angles AC were 10° or less at all seven points, demonstrating sufficient plasma treatment effectiveness. When the taper angle AT was 28°, the contact angles AC exceeded 10° at two points, demonstrating insufficient plasma treatment effectiveness. When the taper angle AT was 30°, the contact angles AC exceeded 10° at all seven points, demonstrating insufficient plasma treatment effectiveness. This result, consistent with the experimental results shown in FIG. 7, demonstrates that the shape of the nozzle 32 can be improved by changing the taper angle AT of the tapered portion 322 from 28° to 24°, thereby enhancing the effectiveness of plasma treatment.

[0048] 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 effectiveness of the plasma processing is complex, and the following factors (1) to (8) are thought to be involved. (1) Changing the taper angle AT of the tapered portion 322 changes the shape and internal volume of the generation region RM where the plasma gas GP is generated, thereby changing the residence time of the process gas GS. (2) Changing the taper angle AT changes the discharge characteristics (discharge path, discharge intensity, discharge duration, etc.). (3) Changing the taper angle AT changes the spiral flow characteristics of the process gas GS and plasma gas GP. (4) The combined effects of factors (1) to (3) above change the temperature and plasma density of the generated plasma gas GP. (5) Depending on the temperature and plasma density of the generated plasma gas GP, the lifespan of the plasma gas GP after ejection and the time-dependent decrease in plasma density change. (6) Changing the hole diameter D of the outlet 323 changes the average flow velocity of the plasma gas GP. (7) As the hole diameter D and the taper angle AT are changed, the flow pattern (flow aspect) of the ejected plasma gas GP, which expands in a conical shape and flows in the ejection direction, changes. (8) The combined effects of (4) to (7) above change the temperature, plasma density, and flow velocity of the plasma gas GP that reaches the surface of the workpiece W, affecting the effectiveness of the plasma processing.

[0049] As described above, the mechanism is complex, but based on the results of the first basic experiment, it is possible to improve the shape of the nozzle 32 by changing the hole diameter D of the outlet 323 of the nozzle 32 from 4.5 mm to 5.0 mm. Furthermore, based on the results of the second basic experiment, it is possible to improve the shape of the nozzle 32 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 plasma head 11 of the embodiment to be 5.0 mm and the taper angle AT of the tapered portion 322 to be 24°, resulting in an improved shape.

[0050] Furthermore, the inventors conducted technical studies and considerations regarding the temperature of the plasma gas GP and 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, they concluded that with the plasma head 11 of the embodiment, the plasma gas GP reaches 600°C or higher at the center position PC, even when taking into account the allowable fluctuation range of the supply rate Q and operational variations during plasma processing. That is, in the plasma head 11 of the embodiment, the hole diameter D of the outlet 323 of the nozzle 32 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 reaching the center position PC, a certain distance LC away from the outlet 323, reaches 600°C or higher. This allows the temperature TG of the plasma gas GP to reach 600°C or higher, significantly higher than the temperatures (505°C, 455°C) of the current product. It was also found that when the hole diameter D of the outlet 323 was determined to be 5.0 mm, the taper angle AT of the tapered portion 322 should be set within the range of 24±2°.

[0051] In the plasma head 11 of this embodiment, the appropriate average flow velocity of the plasma gas GP ejected from the outlet 323 can be derived. When deriving, the hole diameter D of 5.0 mm is taken into account, with a processing accuracy error of ±0.02 mm, and the allowable fluctuation range of the supply rate Q of 37 to 42 L / min is also taken into account. Then, the maximum and minimum values ​​of the appropriate average flow velocity of the plasma gas GP are derived as follows, where π represents the circular constant.

[0052] 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 fixed 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.

[0053] In addition, 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, while maintaining the taper angle AT of the tapered portion 322 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, while 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 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 increased to 600°C or higher.

[0054] 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 reaches a predetermined temperature or higher when it reaches a central position PC a certain distance LC away from the outlet 323 of the nozzle 32. 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.

[0055] 6. Applications and Modifications of the Embodiments The 600°C shown in the embodiment is merely 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 will be necessary to reconsider the appropriate values ​​for the hole diameter D of the outlet 323 and the taper angle AT of the tapered portion 322. Furthermore, the detailed configuration of the main body 20, such as the number and shape of multiple components to which a voltage waveform is applied, can be modified, and such modifications may change the generation region RM and the discharge characteristics. Furthermore, the shape of the rectifying member 26 can be modified to change the spiral flow characteristics (flow pattern) of the process gas GS. Since these modifications are likely to change the generation efficiency and utilization efficiency of the plasma gas GP, it will be necessary to reconsider the appropriate values ​​for the hole diameter D of the outlet 323 and the taper angle AT of the tapered portion 322. Various other applications and modifications are possible for the embodiment.

[0056] 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 member 28: Electrode holder 30: Electrode 32: Nozzle 321: Inlet 322: Tapered portion 323: Outlet GS: Process gas GP: Plasma gas D: Hole diameter AT: Taper angle LC: Constant distance LM: Processing limit distance PC: Center position Q: Supply amount TG: Temperature AC: Contact angle W: Workpiece

Claims

1. A plasma head comprising: a main body formed in a cylindrical shape, one end of which is supplied with a process gas; an electrode contained in the main body and which generates a 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 main body and through which the process gas or the plasma gas flows in, 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 for spraying 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.

2. The plasma head according to claim 1, wherein the electrode is housed in the center of the body and extends in the axial direction, and the power is supplied between the metallic body and the metallic nozzle, and the plasma head is provided with a straightening member formed in a ring shape and disposed between the body and the electrode, for making the supplied process gas into a spiral flow.

3. A plasma head according to claim 2, which performs plasma processing on a surface of a workpiece by ejecting the plasma gas toward the surface.

4. The plasma head according to claim 3, wherein the plasma processing is possible when the surface of the workpiece is positioned within a predetermined processing limit distance from the outlet, and the certain distance is equal to or less than the processing limit distance.

5. A plasma head according to claim 4, wherein the hole diameter of the outlet is determined 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.

6. 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 when converted to atmospheric pressure at room temperature.

7. A plasma head according to any one of claims 1 to 6, wherein the taper angle of the tapered portion is set in the range of 24±2°.

8. A plasma processing apparatus comprising: the plasma head according to any one of claims 1 to 6; 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.

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