EP2016809A2 - Cold plasma implement for plasma treatment of surfaces - Google Patents

Abstract

A plasma tool for generating a cold plasma beam (10) is described. The plasma tool is defined by the fact that it has a plasma nozzle, in particular a plasma nozzle which is dimensioned for operation by hand, wherein at least the coil (6) of the adaptation network is integrated into the plasma nozzle, for operation with a high frequency generator in addition to the capacitor C2, while the capacitor C1 can be arranged in the generator itself or in its vicinity.

Description

 Cold plasma hand-held device for the plasma treatment of surfaces

Reference to related applications

This application claims priority to German Patent Application No. 10 2006 019 664.3, filed on Apr. 27, 2006, the entire disclosure of which is hereby incorporated by reference.

Technical area

The invention relates to a plasma tool for the plasma-assisted treatment, modification and coating of inner and outer surfaces of materials in air by means of a cold plasma jet according to the preamble of claim 1.

State of the art

Plasma technology, especially at high temperatures and high gas pressures, has long been known and described many times, e.g. in US Pat. No. 3,648,015, US Pat. No. 4,626,648, DE 41 08 499 A1 and DE 10.1 40 298 B4.

In WO 03/026365 Al a device is described which allows to generate a plasma by means of microwaves, wherein it allows the device described in WO 03/026365, despite any pressure fluctuations in the process gas to produce a stable plasma flame.

Another plasma generator that produces a plasma at high temperatures is described in German Auslegeschrift 1 639 257. It is a high-frequency plasma jet generator with a cylindrical tube, on one end side of which to gas to be ionized and at the other end side of the generated plasma flows out, an induction coil whose one end is connected to ground and the other end is connected to a high-frequency generator. Between the two ends of the coil, a tap is arranged. The high-frequency voltage generated in the induction coil is higher than the excitation voltage. The tube in the area of the plasma outlet is made of metal and placed on the high-voltage end of the induction coil. The tube is concentrically and electrically isolated surrounded by a metallic housing. Due to the special arrangement, the gas discharge between the two adjacent ends of tube and housing takes place due to a capacitive coupling between these two components.

However, this generator is not suitable for the generation of a cold normal pressure plasma at least due to its electrode shape.

Low-temperature plasmas are also known and successfully used in numerous surface treatment applications for the purpose of surface activation (changes in the

Adhesion properties, hydrophobing, hydrophilization) of the etching, the polymerization, for layer deposition, for cleaning and for the reduction of bacteria used. However, low-pressure plasmas have been used to date for these processes, in which the radicals, excited atoms, ions, electrons and UV radiation required for these applications can be generated to a defined extent by the selection of suitable process parameters. Low-pressure plasma processes, however, are not suitable for numerous industrial processes in which a corresponding surface modification is required, both for cost reasons and for procedural reasons.

A normal pressure plasma process that ionizes water vapor at a relatively low temperature vermag is described in EP 0 124 623. However, this method is hardly applicable in industrial production.

To plasma technological procedures of the

To make surface treatment available to potential users of these industrial sectors, it is necessary to develop suitable non-thermal normal pressure plasma processes which are significantly less expensive and can be integrated into corresponding production lines. An essential requirement for the applicability of atmospheric pressure plasmas for this application is the generation of homogeneous plasmas. One way to achieve the required homogeneity is to generate a plasma jet outside the discharge space by a directed flow of the working gas (process gas).

All known types of discharge plasmas generated under normal pressure conditions, such as RF arc discharges, spark, corona, and barrier discharges, can be used to produce anisotropic normal pressure jet plasmas by implementing suitable process gas flows. Beamplasmas produced on this basis are the subject of various patents. Thus, for example, in the patent DE 3733492 a device for generating a jet plasma means

Corona discharge, which is suitable for the plasma treatment of surfaces. In this case, a gas stream is passed through a corona discharge gap between a rod-shaped inner and a tubular outer electrode. In the patent DE 19532412 a process for the plasma treatment of surfaces is described, which is based on the generation of a plasma jet by arc discharge with non-transferred arc. The subject matter of US Pat. Nos. 6,194,036 and 6,262,523 are arrangements based on the RF excitation of atmospheric pressure plasmas. In another patent document (US 2002/122896) are various Arrangements for producing normal pressure plasmas based on RF excited discharges in tubes of insulating material are described. In the field of medicine, plasmas of this type are used for argon plasma coagulation (US 4,781,175, US 4,060,088, DE 19513338), for coatings on artificial implants to increase their biocompatibility, for controlling cell adhesion to surfaces, for disinfecting medical instruments (M. Laroussi: IEEE Trans. Plasma. 30: 4 (2002), 1409) and for the treatment of biological cells and tissues (E. Stoffels et al.: Plasma Sources Sei. Technol., 11 (2002), 383).

The arrangements and methods for surface treatment by means of normal pressure plasma described hitherto in the technical or patent literature are solutions for limited tasks, which can not or only partially be adapted to the requirements of other applications due to their special construction and operation. Since the tasks and objectives of the plasma treatment of surfaces are very diverse, a solution is to be sought, which allows such an adaptation to different requirements with regard to the material or product to be treated or the desired effect on the surface to be treated. Arrangements for generating

Normal-pressure plasmas based on RF-excited discharges have the advantage that they can be operated at fixed frequencies (13, 56 MHz, 27.12 MHz, 40.68 MHz), which are released for industrial applications, and on the other hand at smaller

Voltages can be generated. However, they also have a significant disadvantage, which will be explained below.

High-frequency operated plasma reactors require a matching network (matchbox) for maximum power transmission from their RF generator. An often used circuit in the Matchbox is the π circuit. It consists of two capacitors C1 and C2 and a coil (see Fig. 1). In order to keep losses in the matchbox low, capacitors with air as a dielectric are used, which occupy a large volume. Since the current transport at these frequencies takes place mainly on the surface of an electrical conductor (skin effect), the coil and all other electrical leads consist of a relatively thick metal wire with high electrical conductivity on the surface (silver wire, silver-plated copper wire). As a result, such a matchbox is generally very voluminous. To ignite and maintain a gas discharge in the plasma reactor, high voltages are needed. These are achieved in the matchbox by the fact that the coil and the capacitor C2 form a series resonant circuit, which must be matched to the particular frequency of the RF generator used. To prevent losses, the supply line Z2 should consist of an unshielded cable and should be kept as short as possible. As a result, the matchbox and the plasma reactor actually form a relatively rigid, unwieldy unit. If you want to realize a handy plasma nozzle as a plasma reactor, which can be performed for example by a robot, such a bulky plasma reactor is useless.

The invention is therefore based on the object to realize a handy plasma nozzle, which can also be performed by hand and / or by robots.

Presentation of the invention

In the context of the present invention, it has now been found that a very handy plasma nozzle can be obtained if an adaptation network in the form of a separate matchbox is dispensed with. According to the invention, therefore, the coil and optionally the capacitor C2 is integrated into the plasma nozzle. A possibly required capacitor Cl may be located anywhere between the generator and the plasma nozzle, but preferably the capacitor Cl is positioned directly on the generator outside (short lead) or directly inside. This achieves the following improvements:

1. The supply line Zl (coaxial cable) from the generator to the plasma nozzle can be designed much more flexible and longer than would ever have been possible for the lead Z2 according to the prior art.

2. Changes in the length of the lead Z1 are associated with changes in the cable capacitance, which can be compensated by changing Cl.

3. The supply line Z2 is formed by the coil end to the electrode El and can therefore be made extremely short. 4. The formed between the electrodes El and E2

Capacity is parallel to C2. Changes in this capacity due to tolerances in the production of the plasma nozzle or upon ignition of the plasma can be compensated for by changing C2, so that the resonance condition is maintained. 5. Due to the very short lead Z2, the total capacity, formed by the capacitance C2 and the capacitance between El and E2, is automatically kept small, so that the inductance L can be maximally selected according to the fixed frequency and thus a high quality of the series resonant circuit (generation a high voltage overshoot) can be achieved.

The plasma tool according to the invention for producing a cold plasma jet comprises a

Plasma nozzle with a hollow body for the supply of a process gas or a process gas mixture, a Frequency generator and consisting of at least one coil or containing a coil

Adaptation network for generating the required voltage and is characterized in that the matching network at least the coil is integrated into the plasma nozzle.

In particular, in a plasma nozzle operated with a fixed frequency RF generator (13.56 MHz, 27.12 MHz, 40.68 MHz), the matching network integrates the coil L and the capacitor C2 into the plasma nozzle.

The capacitor Cl of the matching network can be arranged directly on or in the frequency generator and it is advantageously arranged there. In a specific embodiment, the plasma nozzle contains a capillary made of insulating material and the coil is arranged around this capillary.

In a particularly preferred embodiment, where the frequency generator is a high frequency generator, the matching network (matchbox) consists of one coil and two capacitors C1 and C2 with their connections. The coil and the capacitor C2 are integrated in the plasma nozzle and the capacitor Cl is arranged directly on or in the generator. In another specially preferred

Embodiment, the generator is a frequency-tunable RF generator and the matching network consists of a coil with leads, the coil being integrated into the plasma nozzle. Although this description only two

Capacitors C1 and C2, it is clearly stated here that the capacitors C1 and C2 can be made up of several partial capacitors and that capacitors constructed from partial capacitors are likewise referred to as C1 and C2 in the context of this invention. In another embodiment, the plasma reactor may be configured such that the matching network consists of a coil and either capacitor C1 or capacitor C2 and the corresponding lines.

Also subject of the present

Invention is a plasma nozzle, in which at least one coil, preferably a coil and a capacitor C2 are integrated. These can, as described above and in the embodiments resp. the figures shown to be installed.

Also subject of the present

The invention is a frequency generator in which either a capacitor suitable as a capacitor Cl of a matching network is integrated or mounted directly at the output of the generator.

As already described above, the embodiment with a capacitor Cl and a capacitor C2 relates in particular to commercially available RF generators having a fixed frequency, as described e.g. in Germany are released by the post office for technical concerns. A simplification, and therefore cheaper, of the combination RF generator - plasma nozzle results in the transition to lower frequencies (e.g., 3 MHz) and using a

Generator with variable frequency. In such an embodiment, both capacitors Cl and C2 can be dispensed with, so that apart from a part of the lines, only the coil which forms a series resonant circuit together with the capacitor formed by the electrodes El and E2 is present in the matching network in the plasma nozzle. In this embodiment, the resonance state can be adjusted by varying the generator frequency. A plasma nozzle according to the invention generally comprises a body side, ie on the plasma respectively. the nozzle facing away from the plasma nozzle, with a hollow body connected to a process gas supply. This hollow body is preferably made of insulating material. In a particularly space-saving variant, the coil forming part of the matching network is arranged around a part of this hollow body. The dimensions of the hollow body, or these dimensions together with another body, preferably an insulating body, are to be chosen such that the coil with the desired winding diameter can be arranged thereon. This coil must - if the hollow body or other body on which it is arranged, not made of insulating material, be self-insulated. This coil is connected to the nozzle side with an electrode El and optionally a variable capacitor C2. The electrode E1 may optionally be a ring electrode disposed around the insulating hollow body or a rod electrode disposed in the hollow body. The capacitor C2 and the coil are connected in series, so that it can adjust the voltage required at a given frequency. On the side facing away from the coil, the capacitor C2 is connected to the grounded housing. In a suitable distance for plasma generation from the first electrode El and at the nozzle-side end of the hollow body is arranged on this, a ring electrode E2, which is connected to the grounded housing. This housing has feeds for the electric current and feed openings for the process gas and a discharge opening for the plasma within the second electrode E2. Between the coil and the grounded housing there is a further insulating layer, which is important in particular with a small clearance between the coil and the housing. The connecting line between the electrode El and the capacitor C2 is usually on the coil side on the housing shielding insulation and in turn is provided with an insulating layer. For the generation of a cold plasma, it is important that the two electrodes El and E2 are well insulated from each other. As a result, the formation of an arc discharge is prevented, which would lead to an unwanted heating of the plasma.

Examples of suitable insulating materials are plastic, quartz glass, ceramics, etc., which may be used singly or in combination.

Since the current in the coil primarily flows over the surface, is a material with high

Conductivity preferred at least on the surface, such as silver-plated copper wire or pure silver wire.

Brief description of the drawings

Further embodiments, advantages and applications of the invention will become apparent from the dependent claims and from the following description with reference to FIGS.

FIG. 1 shows the general connection of an RF-operated, capacitively coupled plasma tool, FIG. 1a) representing the plasma reactor in general and FIG. 1b) the plasma nozzle. FIG. 2 shows an inventive device

Embodiment in which the coil L and the capacitor C2 in the generator resp. the nozzle are integrated.

FIG. 3 shows a further embodiment according to the invention with a variable frequency generator in which the capacitors C 1 and C 2 can be dispensed with.

FIG. 4 shows a plasma nozzle according to the invention with an RF ring electrode.

FIG. 5 shows a plasma nozzle according to the invention with an RF rod electrode.

FIG. 6 shows a plasma broad-jet nozzle with an RF ring electrode according to the invention. Figure Legend

The reference numbers in the figures generally have the following meaning:

1 capillary discharge

2 electrode

3 RF electrode 4 hollow body (capillary), preferably made of

insulating material

5 insulator

6 coil (also called L)

7 RF input 8 housing

9 process gas

10 jet plasma / plasma zone

11 RF generator

12 Matchbox 13 plasma reactor

14 plasma nozzle (plasma reactor)

Way (s) for carrying out the invention

The illustrated in Figure 1

Embodiments of the prior art relate in particular to commercially available RF generators having a fixed frequency.

In the embodiment according to the invention shown in FIG. 2, the matching network, the matchbox, has been separated, the capacitor C1 in the RF generator and the capacitor C2 and the coil being integrated in the plasma nozzle. A simplification, and thus a more cost-effective variant of the RF generator-plasma nozzle combination, results in the transition to lower frequencies (e.g., 3 MHz) and using a variable-frequency generator

Frequency. This variant, in which both capacitors C 1 and C 2 can be dispensed with, so that only the coil is still present in the plasma nozzle, which forms a series resonant circuit together with the capacitor formed by the electrodes E 1 and E 2, is shown in FIG. In this embodiment, the resonance state is adjusted by varying the generator frequency.

FIG. 4 shows an exemplary embodiment of a plasma nozzle with a capacitively coupled capillary discharge 1. Two metallic ones

Ring electrodes 2, 3 are mounted at a suitable distance on a hollow body made of insulating material (dielectric) 4. On one, the hollow body 4 enclosing insulator 5, a coil 6 is wound, which is connected at one end to the RF electrode 3 and at the other end to the RF input 7 of the plasma nozzle. The RF electrode 3 is connected to the grounded case 8 via a rotary air capacitor C2. Via the hollow body 4, the process gas 9 (preferably noble gas) is fed to the discharge zone between the two electrodes 2 and 3. Both electrodes 2 and 3 and the dielectric 4 form a capacitance (a few pF), the parallel to C2. The coil 6 forms a series resonant circuit with these capacitances and can be adjusted via C2 to maximum voltage at the electrode 3. If a sufficiently high voltage at the electrode 3 has been achieved via the adjustment with C2, the electric field built up between the electrodes 3 and 2 leads to a capillary discharge whose plasma is driven outwards by the gas flow 9 and forms a jet plasma 10. To the voltage drop across the capacitor, formed from the electrode 3, the

Dielectric 4 and the plasma within the capillary to keep small, a dielectric with the highest possible dielectric constant should be selected.

Suitable dimensions and materials for the embodiment described in FIG. 4 are:

Width of metallic ring electrodes: 5mm

Distance between the metallic ring electrodes: 5 mm

Material of metallic ring electrodes: stainless steel

Dimensions of the hollow body

Insulating material (capillary): outer diameter 3mm, inner diameter lmm

Gas flow: 2 to 10 slm (standard liters per minute).

Examples of process gases: noble gases, such as argon and helium

Examples of admixtures to process gases: Nitrogen, oxygen Dielectric with the highest possible

Dielectric constant, e.g. quartz glass

Values suitable / preferred for an RF generator with a fixed frequency of eg 27.12 MHz: strength of the capacitance formed by both electrodes 2 and 3 as well as the dielectric 4 and lying parallel to C2: a few pF Inductance of the coil 1.9 μH Capacitor C2: Tunable in the range of 5 to 30 pF.

Capacitor Cl: 350 pF In Fig. 5 is another

Embodiment of a plasma nozzle with a capillary discharge 1 shown. In contrast to the variant described above, here the RF energy is coupled via a rod electrode 3 into the capillary discharge. The rod electrode should be made of low work function materials to minimize the voltage needed for capillary discharge. She should also be pointed forward, so as to achieve a high field strength. Between the tip and the grounded electrode 2, at sufficiently high voltages, a capillary discharge is formed, the plasma of which is in turn blown outward by the gas flow.

Essential dimensions / materials other than in the embodiment described above and in FIG. 4 are:

Hollow body made of insulating material (capillary) 4: outer diameter 6mm, inner diameter 2mm.

Distance tip of the rod electrode to the end of the capillary 4: lmm

Diameter of the rod electrode: lmm

Material of the rod electrode: Tungsten.

FIG. 6 shows a modified variant of the plasma nozzle. The discharge is again generated between the electrodes 2 and 3 and passes through a

Slot into the atmosphere. With a slot of 0.8 mm width and 4 cm length can be generated with this arrangement, a linearly expanded plasma of 4 cm width. In all examples described, in a hollow body through which a process gas flows, insulating material, such as, for example, plastic, Quartz glass, ceramics, etc. (referred to in the above description as "plasma nozzle") by means of an RF discharge generated by a nozzle, directed normal pressure blasting plasma with the desired properties (for example, non-thermal, floating, homogeneous and reactive) to which the In order to achieve their desired physicochemical change, the conditions in the jet plasma region may be changed by changing the geometric arrangements and dimensions within the plasma nozzle, by using other process gases, their admixtures and flow rates be controlled by the arrangement and choice of electrodes, by the type of ignition and / or by varying the electrical parameters of the discharge.

The physical principles for the choice of dimensions within the nozzle as well as the definition of suitable operating conditions are known to those skilled in the field of plasma technology.

While preferred embodiments of the invention are described in the present application, it is to be understood that the invention is not limited thereto and may be embodied otherwise within the scope of the following claims.

Claims

claims 1. Plasma tool for generating a cold plasma jet with a plasma nozzle comprising a hollow body (4) for the supply of process gas, a frequency generator and at least one coil (6) existing or a coil (6) containing matching network for generating the required voltage, characterized in that at least the coil (6) is integrated into the plasma nozzle of the matching network. 2. Plasma tool according to claim 1, with a plasma nozzle comprising two electrodes, El and E2, wherein the electrode El is either a ring around an insulating hollow body arranged round electrode or arranged in the hollow body rod electrode and that the electrode E2 at the nozzle end of the hollow body (4) and is disposed thereon at a suitable distance for plasma generation from the first electrode El ring electrode which is connected to the grounded housing. 3. Plasma tool according to claim 1 or 2, characterized in that the matching network, the coil (6) and the capacitor C2 are integrated into the plasma nozzle. 4. Plasma tool according to one of the preceding claims, characterized in that the capacitor Cl of the matching network is arranged directly on or in the frequency generator. 5. Plasma tool according to one of the preceding claims, characterized in that the coil (6) around the hollow body (4) is arranged around and preferably rests on this hollow body or this hollow body additionally enclosing insulating body (5). 6. Plasma tool according to one of the preceding claims, characterized in that the Generator is a fixed frequency RF generator, that the matching network consists of a coil (6) and two capacitors Cl and C2 with their connections and that the coil (6) and the capacitor C2 are integrated into the plasma nozzle and that the capacitor Cl am or arranged in the generator. 7. Plasma tool according to one of the preceding claims, characterized in that the frequency generator is a frequency-tunable generator and the matching network consists of a coil (6) with lines, wherein the coil (6) is integrated into the plasma nozzle. 8. Plasma tool according to one of the preceding claims, characterized in that the matching network consists of a coil (6), the lines and either capacitor Cl or capacitor C2. 9. Plasma tool according to one of the preceding claims, characterized in that the plasma nozzle is dimensioned so that it can be held in use in one hand, in particular a plasma nozzle with the following dimensions: diameter: 2 cm, length: 17 cm, Length of the plasma zone: up to 1 cm 10. Plasma tool according to one of the preceding claims, characterized in that the hollow body consists of insulating material. Plasma nozzle, in particular a plasma nozzle for manual operation, characterized in that it contains part of a matching network as described in one of the preceding claims. 12. Frequency generator, characterized in that a capacitor suitable as a capacitor Cl of a matching capacitor is integrated into it or mounted directly at its output.