Atmospheric-pressure plasma jet

The present invention relates to a plasma treatment apparatus for use in plasma cleaning, surface modification and surface coating. The present invention relates in particular to the novel plasma nozzle.

State of the art [0002] Plasma nozzles operating at atmospheric pressure are known in the prior art, for example described in EP 0 921 713 A2, WO 98/35379 and WO 99/20809. These jet plasma devices comprise two coaxial electrodes creating a plasma discharge space located between the outer diameter of the centrally located electrode and the inner diameter of the outer electrode. The plasma jet can be generated at the open end of the device by introducing a gas stream at the closed end of the device and applying a sufficiently high voltage between the electrodes. To prevent arcing, a dielectric material may be provided between said electrodes. The plasma jet can be used to etch, clean or coat the surface. In the case of devices known from the prior art, it is difficult to obtain a satisfactorily efficient plasma nozzle, which is due to several limitations regarding currently known devices. At present, for example, it is not possible to activate the rubber with a conventional plasma jet known from the current state of the art and having an acceptable size due to the insufficient energy of exitingaspects of the problem. In most plasma jet devices, therefore, jets concentrating the plasma jet are used to obtain higher plasma densities. This solution, however, has the disadvantage that the area under treatment is smaller, so it is necessary to use more devices, larger devices or take more time to process the surface.

Objects of the Invention [0003] The present invention aims to provide a plasma jet device more efficient than devices known in the art.

Summary of the Invention [0004] The present invention relates to a plasma nozzle operating at atmospheric pressure constituting a cylindrical two-electrode device or a parallel three electrode device. The two-electrode device may be in the form of a tubular device comprising a central metal cylindrical electrode and an outer metal cylindrical electrode, said metal cylindrical electrodes arranged coaxially to form a plasma discharge gap, said device having an open (proximal) end and a closed (distal) end, said discharge gap the plasma is open to the atmosphere at said open end and has an opening for introducing the gas stream at said closed end,

that said dielectric barrier is extended outwardly at said open end. In a particular embodiment, the outer electrodes are connected by their sides to form one electrode that is concentric with respect to the central electrode. This embodiment and tubular embodiment are therefore two variants of a cylindrical device comprising one inner electrode and one outer electrode.

[0006] Therefore, the present invention relates to a plasma jet apparatus for performing plasma treatment of an object. The cylindrical two-electrode configuration and the parallel three-electrode configuration are described here. The cylindrical jet plasma device includes:

wherein said electrical insulator extends in a radially positioned ring at said proximal end outside the outer surface of said outer electrode. The electrodes may be tubular and coaxial, having a circular cross-section, or the central electrode may be a flat, plate-shaped electrode, the outer electrode then having a front side and a back side that are substantially parallel to the central electrode. Instead of a flat electrode, the parallel device may have a central electrode having at the proximal end a round extension extending along the length of the electrode, wherein the front surface and the back surface of the outer electrode remain parallel to said central electrode.

[0007] In a preferred embodiment, the central electrode passes a supply channel for introducing reactive chemical compounds directly into the plasma phosphorescence site at the proximal end.

[0008] The three-electrode parallel plasma jet devices according to the invention comprises:

• a central electrode, e.g. a flat plate electrode, • 2 external electrodes on both sides of said central electrode and substantially parallel to said central electrode, • 2 electrical insulators located substantially parallel between said external electrodes and said central electrode, between said a gas discharge gap is formed between the central electrode and said electrical insulators, which has a distal end and a proximal end, a supply opening located at the distal end of said discharge slot for introducing a gas used for plasma generation into said discharge slot;a feed channel passing through the central electrode for introducing reactive chemicals directly into the plasma phosphorescence at the proximal end, • a power source to provide voltage between the central electrode and the outer electrodes, said electrical insulators extending outwardly at the proximal end outside the outer surface of the outer electrode .

[0009] In the plasma jet apparatus of the present invention, the electric insulator advantageously extends further towards the distal end at the outer surface of the outer electrode. The distance between the outer surface of the central electrode and the inner surface of the electrical insulator is preferably in the range of 0.1 to 10 mm. The power supply is preferably provided for supplying alternating voltage or constant voltage pulses of 1 to 10 kV in the case of a tubular configuration and from 1 to 100 kV in the case of a parallel configuration.

[0010] Another aspect of the present invention relates to a method for generating a plasma stream that comprises the following steps:

• providing a plasma jet apparatus according to the present invention, • providing plasma gas flow through the supply opening, • providing a flow of a reactive chemical compound (e.g. a monomer) through a feed opening and / or a central electrode for introducing a reactive chemical compound for plasma discharge at the open end plasma, and • supplying a voltage between 1 and 100 kV between the central electrode and the external electrode.

Brief Description of the Drawings [0011] Fig. 1 illustrates the construction of a plasma jet apparatus known in the art.

[0012] Fig. 2 schematically illustrates a jet plasma device according to the present invention.

[0013] Fig. 3 schematically illustrates a parallel plasma jet apparatus according to the present invention.

[0014] Fig. 4 schematically shows a particular configuration of an embodiment with parallel electrodes.

[0015] Fig. 5 shows a number of possible cross sections of plasma jetting devices according to the invention.

DETAILED DESCRIPTION OF THE INVENTION [0016] Plasma nozzles known from the prior art, as shown in Figure 1, typically comprise an outer electrode 11, an inner electrode 12 and a dielectric material 13 disposed therebetween.

[0017] Figure 2 shows a tubular embodiment of the present invention which relates to a plasma nozzle operating at atmospheric pressure, comprising 2 coaxial tubular electrodes (1, 2) and a special electric insulator in the form of a dielectric material 3. The dielectric barrier is extended at the proximal end of the plasma jet, preferably in the form of a U-shaped extension. The plasma nozzle operates at a temperature of 30 ° C to 600 ° C and may be used for plasma cleaning, surface modification and surface coating. The U-shaped dielectric material has great advantages in all these applications. A preferred embodiment is also a ring, i.e. simply a radial expansion of the tubular structure (without the backward branch 21 of the letter U). At the distal end of the device there is a supply opening 6 for supplying plasma gas to the gap formed between the central electrode and the dielectric material 3. The central electrode 2 is preferably connected to ground 8, while the outer electrode is connected to a voltage source 9. An embodiment is also possible, in which electrode 1 is connected to ground and electrode 2 is connected to a voltage source. The present invention also includes an embodiment in which both electrodes are connected to a voltage source. It is possible to use a feed channel 7 extending through central electrode 2, which is designed to introduce reactive chemical compounds directly into the plasma phosphorescence site at the open end. The distance 4 between the outer surface of the central electrode and the inner surface of the electrical insulator is in the range of 0.1 to 10 mm. The distance 5 is the diameter of the homogenous plasma zone. The distance 50 is the height of said uniform plasma zone corresponding to the height of the outer electrode 1.

[0018] The central electrode 2 and the outer electrode 1 may have a cylindrical shape with a circular cross-section, i.e. tubular. Alternatively, the central electrode may be a flat electrode 2, while the outer electrode 1 then has a front side and a back side 70, 71 (see Fig. 5A) connected at the sides 72 to form a cylindrical outer electrode 1. The insulator 3 also has in this case in the case of the front side and back side 73, 74 which are parallel to the central electrode and connected 75 at the sides to form one cylindrical insulator 3.

[0019] Fig. 3 shows a plasma jet device according to the invention provided with 3 parallel electrodes. The device comprises a central electrode 15 and two parallel electrodes 16, 17 located on each side of the central electrode. The drawing shows the device in section. In fact, the device is obviously closed on both sides. Figs. 5B to 5D show possible cross-sections. The devices shown in Figs. 5B to 5D are closed on both sides using suitable insulating materials (not shown). The parallel device shown in Fig. 3 comprises two dielectric parts 18, 19, which are arranged substantially parallel to the electrodes. At the distal end of the device there is a supply opening 6 for supplying gas for generating plasma to the discharge gap, which is formed between the central electrode and the insulators. It is possible to use a feed channel 7 extending through a central electrode 15 and intended for introducing reactive chemical compounds directly into the plasma phosphorescence site at the open end. The central electrode 15 is connected to ground 8, while the outer electrodes 16, 17 are connected to the voltage source 9. The present invention also includes an embodiment in which the outer electrodes 16, 17 are connected to ground and the central electrode 15 is connected to a voltage source. . The present invention also includes an embodiment in which both the central electrode 15 and the outer electrodes 16, 17 are connected to a voltage source. At the proximal end of the device, dielectric parts with external extension 40 are formed, which are preferably U-shaped or with a flat outer extension, i.e. free of the reverse branch 41 of the U-letter. The distance 4 between the outer surface of the central electrode and the inner surface of the electrical insulator is in the range of 0.1 to 10 mm. Distance 5 is the width of the homogeneous plasma zone. The distance 60 is the height of said uniform plasma zone corresponding to the height of the outer electrodes. Distance 61 is the length of the plasma zone that corresponds to the length (depth) of the device. Distance 5 is the width of the homogeneous plasma zone. The distance 60 is the height of said uniform plasma zone corresponding to the height of the outer electrodes. Distance 61 is the length of the plasma zone that corresponds to the length (depth) of the device. Distance 5 is the width of the homogeneous plasma zone. The distance 60 is the height of said uniform plasma zone corresponding to the height of the outer electrodes. Distance 61 is the length of the plasma zone that corresponds to the length (depth) of the device.

[0020] Fig. 4 shows a possible configuration of a similar plasma jet device according to the invention. In this configuration, a round extension 30 along the entire length of the metal central electrode 16 is provided at the open end of the plasma nozzle. As can be seen in FIG. 4, both the dielectric material (18, 19) and the metal outer electrodes (16, 17) in particular shape have a special shape to ensure a constant (± 1 mm) distance between the outer the surface of the central electrode and the inner surface of the electrical insulator. Reference numeral 60 indicates the height of the plasma nozzle, reference numeral 5 indicates the width of uniform effective plasma phosphorescence, and reference numeral 61 denotes the length of the plasma zone between the parallel electrodes.

[0021] When using the plasma nozzle according to the present invention, the following operating characteristics can generally be used:

- Electric power of a tubular device with a height of 50 electrodes equal to 10 cm (hereinafter referred to as a pipe device): 20 - 750 W.

- Electrical power of the parallel device (including the parallel device with one external electrode) with a height (50, 60) of the electrode equal to 10 cm and the length (61) of the electrode equal to 10 cm (hereinafter referred to as the parallel device): 100 5000 W. The delivered power depends on from application.

- Electrical voltage (8): 1 - 100 kV.

- Plasma gas flow (6): 1 - 400 l / min for a pipe device, 10,000 l / min for a parallel device.

- Preheated plasma gas temperature: 20 - 400 ° C (this means that the plasma gas can be preheated up to 400 ° C before being introduced into the plasma nozzle).

- Plasma gases: N2, air, He, Ar, CO2 + mixtures of these gases with H2, O2, SF /, CF4, saturated and unsaturated gaseous hydrocarbons, fluorine gas hydrocarbons ...

- Monomer flow: 1 - 2000 g / min (through channel 7 running through the central electrode directly to the plasma phosphorescence site).

- Supply gas flow: 0.1 - 30 l / min (through channel 7 running through the central electrode directly to the plasma phosphorescence site).

- Internal gap (4): 0.1 - 10 mm (depending on plasma gas and use).

- Diameter (in the case of a pipe device) or width (5) (in the case of a parallel device) of a homogeneous plasma zone: 6 - 80 mm.

- Length of effective plasma phosphorescence. 5 - 100 mm (depending on the application).

[0022] When a high voltage or pulsed DC voltage is applied to one of the electrodes, a dielectric discharge occurs between the dielectric and the internal electrode. The active components originating from the plasma are blown from the butt-shaped musk in the Musk-gas stagnation. phosphorescence is directed to the sample, thanks to which it is possible to carry out plasma treatment of three-dimensional objects. When using pulsed DC power, the frequency preferably ranges from 1 to 200 kHz, preferably from 50 to 100 kHz.

[0023] The advantages of a dielectric extending radially or outward from the plasma jet apparatus of the present invention can be summarized in the following 3 concepts: distance from the plasma source, activation width and use of plasma gases.

Distance from the Plasma Source [0024] It should be noted that the radicals, and in particular ions, contained in the plasma discharge are extremely short lived and can not in principle be moved beyond the discharge area. On the other hand, the metastable components generated in plasma have a longer life span at atmospheric pressure, which is usually a time of hundreds of milliseconds. This longer lifespan allows them to be moved beyond the volume of the plasma with the plasma gas stream. The most reactive metastable components will of course be lost the fastest. The closer the plasma source is, the more reactive is plasma phosphorescence. Thanks to the novel plasma jet apparatus of the present invention, samples can be brought closer to a distance of 2 mm from the actual plasma source. The tests have shown

[0025] With the traditional concept, it is impossible to sufficiently activate the rubber: the distance rubber / plasma source is probably too large. The most reactive, and in this case also the most desirable, plasmas components are lost before they hit the rubber sample.

[0026] When using a U-shaped dielectric as shown in Figure 2, a more reactive plasma phosphorescence is obtained. parameters:

Examples

Plasma activation of the rubber

- Power: 400 W

- Frequency: 70 kHz

- Plasma gas: 65 liters of air per minute

- Precursor: missing

- Plasma phosphorescence temperature: 65 ° C

- Distance rubber / plasma source: 4 mm

- Surface energy before plasma activation: ± 20 dyn

- Surface energy after plasma activation:> 75 dynes

- Surface energy 1 week after plasma activation: 62 dyna

Plasma activation of PVC (polyvinyl chloride) [0027] PVC is a material sensitive to temperature. Activation carried out in the traditional sense is not stable over time. After a few hours, the activation effects disappear completely.

[0028] When using a U-shaped dielectric, a more reactive plasma phosphorescence is obtained.

- Power: 300 W

- Frequency: 32 kHz

- Plasma gas: 60 L N2 per minute

- Precursor: missing

- Plasma phosphorescence temperature: 60 ° C

- PVC distance / plasma source: 5-7 mm

- Surface energy before plasma activation: 45 dynes

- Surface energy after plasma activation:> 75 dynes

- Surface energy 1 week after plasma activation: 64 dyna

- Surface energy 1 month after plasma activation: 56 dynes

- Surface energy 4 months after plasma activation: 54 dyna

Activation Width [0029] If the flat samples are placed close to the plasma phosphorescence, the active components contained in the plasma phosphorescence are spread in a certain area between the plasma nozzle and the samples. This means that the activated space must be much wider than the diameter of the plasma nozzle. The more samples are located closer to the actual plasma source, the wider the activated site is. The tests have confirmed that when using the plasma nozzle according to the invention (with a U-shaped dielectric), the activated site is much wider for the same plasma parameters than in the traditional concept.

Examples

Plasmid activation of polyethylene [0030] Increasing the width of the activated site reduces the total operating costs of the plasma nozzle (plasma nozzles). When using a plasma jet according to the present invention, a more reactive plasma phosphorescence is obtained, and the active ingredients are spread over a wider area.

- Power: 200 W

- Frequency: 50 kHz

- Plasma gas: 50 l N2 per minute

- Precursor: missing

- Plasma phosphorescence temperature: 65 ° C

- Diameter of the plasma nozzle: 15 mm

- Surface energy before plasma activation: 32 dyna

- Surface energy after plasma activation: 62 dyna

<td>Sample distance / plasma source (mm):</td><td>The width of the homogeneously activated space (mm) (62 dyne):</td>

<td>2.5</td><td>45</td>

<td>4</td><td>41</td>

<td>6</td><td>25</td>

<td>8</td><td>22</td>

<td>10</td><td>22</td>

<td>12.5</td><td>22</td>

<td>15</td><td>22</td>

<td>20</td><td>18</td>

<td>thirty</td><td>7</td>

<td>35</td><td>3</td>

[0031] In the traditional concept, the width of the homogeneously activated place was a maximum of 32 mm at a sample / plasma nozzle distance of 1.5 mm.

Plasmid activation of polypropylene [0030] Increasing the width of the activated site reduces the total operating costs of the plasma nozzle (plasma nozzles). In the case of using a plasma jet according to the present invention, more plasma phosphorescence is obtained and the active ingredients are spread over a wider area.

- Power: 200 W

- Frequency: 50 kHz

- Plasma gas: 50 liters of air per minute

- Precursor: missing

- Plasma phosphorescence temperature: 65 ° C

- Diameter of the plasma nozzle: 15 mm

- Surface energy before plasma activation: 36 dynes

- Surface energy after plasma activation: 70 dynes

<td>Sample distance / plasma source (mm):</td><td>Width of a homogeneously activated space (mm) (70 dynes):</td>

<td>2.5</td><td>48</td>

<td>4</td><td>45</td>

<td>6</td><td>26</td>

<td>8</td><td>22</td>

<td>10</td><td>22</td>

<td>12.5</td><td>22</td>

<td>15</td><td>22</td>

<td>20</td><td>20</td>

<td>thirty</td><td>12</td>

<td>35</td><td>4</td>

In the traditional concept, the width of the homogeneously activated place was a maximum of 33 mm at a sample / plasma nozzle distance of 1.5 mm.

Plasma Gas Consumption / Plasma Power [0034] As the samples can be located closer to the actual plasma zone, less reactive components are lost in phosphorescence. Thus, compared to a conventional plasma nozzle, it is possible to achieve the same results with less gas and / or energy consumption. This last advantage can be treated as indirectly resulting from the two previous advantages.

[0035] It has been shown experimentally that less gas and / or energy is required to achieve the same plasma activation results. Such tests may be carried out by a specialist in the field.