DE20321042U1 - Device for applying electro-spray coatings to electrically non-conducting surfaces has electrospray capillary for introducing, electrically charging electrospray onto surfaces, periodically repeats compensation, dissipation of charges - Google Patents

Abstract

Device for applying electrospray coatings on electrically non-conductive surfaces, comprising
a) a motor-driven about a rotational axis (1) rotating sample carrier (2) with an electrically non-conductive target area (5) for receiving the electrically non-conductive surfaces,
b) an electrospray capillary (3) for introducing and electrically charging an electrospray (4) on the electrically non-conductive surfaces and
c) means (7) for periodically recurring compensation or dissipation of electrical charges on the surfaces, wherein
d) an insulating partition wall (6) is provided, which is arranged in the space above the target area (5) and subdivided into a first and a second subspace, wherein the means (i) in the first and the electrospray capillary (3) in second subspace are arranged.

Description

The An innovation relates to a device for applying electrospray coatings on electrically non-conductive surfaces according to the first Protection claim.

Electrospray coating process are essentially spray coating processes in which a liquid or solid coating material over a nozzle or finely atomize a capillary or atomized on a surface to be coated is injected. In this case, the liquid coating material and the surface to be coated electrically charged opposite. The so electrochemically charged liquid atomized at atmospheric pressure at the open end of the capillary or nozzle electrodynamically over a Jet into an aerosol of small charged drops, taking it to a electrostatic attraction of the mist comes to the surface. Due to the Coulomb repulsion between the same name charged drops or the resulting particles (e.g., nanoparticles by evaporation of solvent fractions) in the electrospray mist the spray aspires conical from the capillary opening Direction of the counter electrode (surface to be coated) and meets there. For the achievement of a uniform coating thickness as well as a high coating rate is a good electrical conductivity the surface is essential.

During electrospray coatings of electrically conductive surfaces often To date, the electrospray coating of non-conductive surfaces has been poor common. Become non-conductive surfaces of charged drops or nanoparticles from an electrospray met, the entrained Charge over the non-electrically conductive surface do not drain. The surface invites Electrostatic for as long as possible, until further drops approach each other or nanoparticles due to the decreasing potential difference to the charged surface even repelled become. this leads to to that by conventional Electrospray coating on non-conductive surfaces only vanishingly thin Layers can be applied which are not usable in practice.

at mixed surfaces (Subareas conductive and e.g. connected to ground, other subregions not conductive), separates depending on the design, the coating is exclusive or preferably on the conductive Areas of the surface from. For example, in SAW sensors by conventional Electrospray coating only the comb fingers of the IDTs (Interdigital Transducer) coated. Also, the inactive SAW elements, d. H. the SAW resonators are not coated because they are not electrically conductive with the IDTs are connected or grounded. As in the production of functional coatings often, as here in SAW production, the need for a complete Coating of a substrate, be electrospray coating process due to the limitations mentioned for the Production of layer thickness sensitive functional layers only not at all drawn.

task The innovation is therefore a device for applying electrospray coatings to propose, which in particular for the application of layer thickness sensitive Functional layers on electrically non-conductive surfaces is suitable.

The solution The object can be found in the features of claim 1 again. Subordinate claims preferred embodiments the innovation again.

The essential feature of the innovation includes means by which a Charge on the non-electrically conductive surface quickly compensated, i. derived becomes. As part of this change the actual electrospray coating and the compensation periodically. The original state of charge of the surface will be back regularly produced, which allows subsequent charged drops or nanoparticles Favorable way with approximately constant electrostatic conditions are deposited on the surface.

The aforementioned periodic change between the two areas compensation and electrospray coating, i. Discharge (compensation or overcompensation a charge) and more contrary Charging in the kV range, is achieved preferably by the fact that the surface arranged eccentrically on a rotationally driven sample carrier is, taking each point of the surface between the two areas swinging in and out.

at compensation (or overcompensation) an electrical charge on the electrically non-conductive surface takes place a discharge to the electrical neutrality or above (overcompensation with the goal one possible huge Potential difference to electrospray) on the means, which a deviating from the charge and for skipping the electrical Charge sufficiently different electrical potential.

For the purposes of an efficient coating, the periodic discharge / charging of the surface must occur so frequently that the surface charge is not already within the control of the Spray coating is so high that other charged drops or particles are repelled. An optimal residence time in the coating region can be adjusted by the rotational speed of the sample carrier.

The capillary stream, ie the stream which flows off the capillary by spraying charged drops out of the capillary, lies in the nano-ampere range. It is helpful to observe this capillary flow when adjusting the electrospray and during the coating as it is a measure of how efficiently the existing electrospray atomizes the fluid. A sufficient charge of the electrospray is only possible if there are enough components in the coating solution, which can be implemented electrochemically. In addition, a certain conductivity must prevail in the solution of the electrospray in order to allow the electrochemical processes and the spray formation. The choice of solvent for the coating substance has an influence on the conductivity and sprayability of the coating solution. Polar solvents such as alcohols (methanol, ethanol) or water have a higher conductivity than ethers (eg tetrahydrofuran). However, even with polar solvents, the majority of the conductivity is due to the impurities normally contained therein. Extremely pure solvents, such as those used in semiconductor technology, regardless of whether they are polar or non-polar, have too low a conductivity to be sprayed without additives with electrospray. In the case of reagent grade methanol, on the other hand, the conductivity of the salts contained therein is sufficient to produce a very fine and efficient electrospray. Optimum conductivities, which enable a fine and stable electrospray, are about 10 ^-4 -10 ^-2 S / m, which are also with additives, such as electrolytes such as salts, but also acids such as acetic acid or formic acid or bases. Likewise conductive electrolytes come into consideration, as they are also used in electrochemistry. If it is a non-volatile additive such as a salt, this must be chosen so that it does not affect the function of the layer formed, because it will remain in the layer. In the case of volatile additives, such as acetic acid or formic acid, these may not remain completely in the coating, but care must be taken that undesirable chemical reactions between the additive and the coating substance do not occur in the solution.

is the capillary current is too low, not enough charge carriers in the to be atomized liquid generated. The drops produced are then comparatively large and / or The spray process is unstable and uneven. In this case, that must be Potential increased at the capillary be or have to Additives to improve the conductivity and / or the electrochemical Chargeability of the liquid be added.

Increases the capillary flow when increasing of the potential disproportionately on, is often in addition to Spray process a corona discharge at the capillary end. The case resulting corona products discharge the already formed drops and thus counteract the formation of very small drops. In this In the case, the potential applied to the sprayer must be reduced.

varies the capillary flow is very strong, often the flow rate is not suitable selected. Also a too low conductivity the coating solution and unwanted Corona discharges lead to Swaying of the capillary flow.

Next Observing the spray stream is also a visual check the electrospray helpful. This is for example by a Microscope or a camera over be positioned to the electrospray, facilitates. The electrospray must be suitably illuminated for observation (e.g., from diagonally below with a cold light bulb with gooseneck light guide). By optical Observation of the spray can be checked, whether the spray evenly and fine, or if instabilities or too large drops occur.

at Start the coating process and set the optimum Spray parameters may be temporary Tear off of big ones liquid drops come. So that they do not hit the surface to be coated, the spray device is not directly on the to be coated surface directed but at an angle of about 30 ° to 90 ° to it. The spray device is ideally on a partition between coating region and discharge region. Eventually formed big drops fly because of their inertia not on the sample to be coated but rather on the screen. For optimal adjustment of the sprayer in relation to the coating to be coated surface is the spray device in height and position.

The means, with which a charge on the non-electric conductive surface quickly compensated, i. for example, include a serving as an electrically conductive sliding contact wire, a Plasma or a charge cloud with electrically charged accordingly Corona ions.

The Innovation is based on four possible embodiments closer with the following figures explained. Show it

1 a first embodiment of the device with a periodic discharge via a non-abrasive parallel to the surface arranged and rotating discharge wire,

2 a second embodiment of the device with a periodic discharge via a grinding discharge wire,

3 a third embodiment of the device with a periodic discharge via a non-abrasive, U-shaped bent discharge wire,

4 a fourth embodiment of the device with a periodic discharge via a discharge on a rotating disc discharge wire and

5 a fifth embodiment of the device with a periodic discharge with a corona.

All figures show devices, each with a motor-driven, about a rotation axis 1 rotatable sample carrier 2 and an electrospray capillary 3 (For example, stainless steel capillary with about 110 microns inside and about 240 microns outside diameter) for the introduction and atomization of an electrospray 4 (Flow rates, for example, 1 to 5 μl / min). The electrospray capillary 3 comprises an electrode with direct contact to the electrospray, which via a charge source to a certain electrical potential (for example, 2 to 4 kV with capillary 20 to 80 nA) set the electrical charge of the drops and / or the resulting charged particles of electrospray serves. The sample carrier 2 also includes a target area 5 on which the components with the surfaces to be coated (not shown in the figures) are placed. The positioning of the electrospray capillary 3 is in three spatial axes, shown in the figures as directional arrows, above the sample carrier 2 displaceable. Furthermore, all figures each contain an insulating partition 6 , which is arranged above the sample tray and divides the space above the sample carrier into a first and a second subspace and means 7 to compensate for the electrical charges on the surfaces to be coated, which have a deviating from the charge and sufficient to skip the electrical charge electrical potential.

Embodiment 1

1 shows the first embodiment, in which the partition 6 between sample carriers 2 and electrospray capillary 3 parallel to the target area 5 is arranged. The partition 6 points to the passage of the electrospray 4 a window 8th on. As the aforementioned means for compensating the electric charges on the surfaces to be coated rotates a grounded discharge wire 9 For example, tungsten with 50 microns thickness, in parallel in front of the non-conductive surface to be coated or the target area. The discharge wire rotates in this case with a high number of revolutions, preferably in the range of about 10,000 revolutions per minute. Without the insulating partition, the charged electrospray would constantly see the discharge wire as a direct counterpotential, preferring to coat this wire. As a result of the discharge wire periodically discharging the target area such as the one, the electrospray is forwarded exactly in that direction.

Preferably, the discharge wire 9 as close as possible over the target surface or the surface to be coated. Ideal distance is about 1-2 mm. To avoid damage to the partition, coating or surfaces to be coated is an exact adjustment or retractable spacers or guides especially during speed changes, eg when starting or when parking, or essential. As an alternative, a pivoting device is provided for the entire means for compensating the electric charges on the surfaces to be coated (discharge wire and rotation axis), pivoting taking place exclusively at high constant rotational speeds. In the production of SAW sensors, such damage by the discharge wire preferably also extends to a destruction of the bonding wires for the coating necessary for contacting the IDTs.

experiments with different length discharge wires have shown that in Trap one over Although the target area rotating wire tip while overpassed in contact Area a discharge of the surface takes place, but preferred in the areas below the wire tip. This can be explained by the fact that the field line density is greatest at the wire tip. For a uniform coating It is therefore necessary that the wire end outside of the to be coated Range and thus the field strength of the wire above the Target area is uniform.

An increase in the field line density can be achieved with discharge wires with particularly small diameters (eg tungsten wires with a diameter of 10 to 25 μm). Due to their low tensile strength, however, such wires break off very rapidly, especially at high rotational speeds, which is why such wires can only be used up to a comparatively low rotational speed. However, this increases the dwell time of the discharge wire under the window, with much of the electrospray increasingly being deposited on the wire. That causes, that the discharge wire is very quickly covered by the coating substance and thus isolated and loses its charge-discharging function increasingly.

As part of an application example, the described first embodiment is used for the coating of SAW sensors. The speed of discharge wire and sample carrier were specified at 10,000 or 1400 revolutions per minute, with a distance between the discharge wire and the coating surface was set to a value between 1 and 3 mm. The coating time was 30 minutes, the flow rate for the electrospray 1 μL / min. To the electrospray capillary 3 a potential of 4 kV was applied, whereby a capillary flow of 20 to 30 nA was established during the coating process with grounded sample carrier.

The coating substance used was 4-tert-butyl-calix [4] tetraethyltetraacetate (molecular weight M _r = 993.29 g / mol), hereinafter referred to as calixarene. Calixarene is readily soluble in THF (tetrahydrofuran) and is dissolved at a concentration c = 10 ^-2 mol / l in a mixture of 90% THF with 10% methanol and 1% formic acid as additives. The additives do not adversely affect the solubility of the calixarene, but significantly improve the electrospray properties by increasing the electrical conductivity of the THF solution.

Embodiment 2

In the second embodiment, an electrical discharge of the sample carrier takes place via a on the target area 5 grinding grounded discharge wire 9 ( 2 ). The insulating partition 6 , Which is located just above the sample carrier and divides the space above the sample carrier in a first and a second compartment (Compartment), is preferential, perpendicular to the target area 5 and aligned with the axis of rotation 1 arranged. In the first compartment takes place during the coating process via the electrospray on the surface to be coated or the electrically non-conductive target area an electric charge. By rotation of the sample tray, the surface to be coated or the target area passes under the second compartment, in which the discharge of the surface takes place via the discharge wire.

The means 7 To compensate for the electrical charges on the surfaces to be coated of this embodiment, ie the abrasive discharge wire, require a wiper track on the target area, whereby the grounding effect of the means on the target area decreases with increasing distance to this wiper track. The compensation of the electrical charges on the surfaces to be coated thus takes place with locally different effectiveness, which limits the advantage of this embodiment, namely the high absolute effectiveness of the compensation. It forms a narrow ring very high coating, followed by the inside and outside areas with a smaller layer thickness. With this method, it is not possible to homogeneously coat larger areas. Although larger surfaces are reliably, but not uniformly coated in this embodiment.

The Parameters for a coating process for the successful production of SAW sensors with this embodiment correspond to those in the first embodiment aforementioned parameters (speed of the sample carrier, potential at the electrospray capillary, Capillary flow, coating time, flow rate).

Embodiment 3

The third embodiment ( 3 ) differs from the second embodiment in the design of the means for compensating the electric charges on the surfaces to be coated. The grounded discharge wire 9 is bent in this embodiment U-shaped, wherein the legs 10 are isolated and the non-insulated wire section 11 with a minimum distance parallel to the target area.

By the isolation of the U-thighs 10 is achieved that the parallel to the sample wire section 11 and the electrically charged target surface or surface to be coated behave like a capacitor. He is to the surface to be coated by an independent gas discharge (dark discharge), in which the field lines evenly between surface and wire section 11 are distributed, unloaded. Ideally, the wire section completely overflows the target area during one revolution of the sample carrier.

The parameters for a coating process for the successful production of SAW sensors with this embodiment also correspond to the aforementioned parameters in the first embodiment (speed of the sample carrier, potential at the electrospray capillary, capillary flow, coating time, flow rate). The distance between the wire section 11 and to be coated surface was about 1 mm

Embodiment 4

As in 4 shown is the discharge wire 9 in the fourth embodiment on a disc 12 applied (preferably glued) and on this around a disc axis 13 rotatably mounted. The disc 12 and the target area 5 tighten an angle 15 , preferably between 10 and 70 °, with the disc 12 in the target area 5 , preferably in the middle or pivot point of the target area 5 , shows. During operation, ie when the disk is rotating, the end of the discharge wire projecting beyond the disk approximates to a minimum of approximately 1 mm against the surface or target area to be coated, wherein it must be ensured that no contact is made with the discharge wire.

The insulating partition 6 is preferably parallel to the target area 5 and in alignment with the electrospray capillary 3 aligned and ends at a small distance above the disc 12 (see. 4 ). In this way, the electrospray can be 4 by positioning the unloading wire on the target area 5 or via the insulating partition. Alternatively, the insulating partition wall 6 in the context of this embodiment also can not be aligned with the electrospray capillary 3 Arrange so that they serve as a shield for the pane 12 with the discharge wire 9 serves. This offers a parallel positioning of the partition 6 to the disc 12 , wherein the partition at a certain distance above the target area 5 ends.

In contrast to the described embodiments 2, 3, and 5 exists for the electrospray 4 an unobstructed spatial connection between discharge wire and electrospray capillary 3 ,

Consequently, there is also an insulating partition 6 not necessarily required for the function of this embodiment.

Regarding the Experimental parameter in the coating of SAW sensors is based on the aforementioned embodiments directed.

Embodiment 5

The basic structure of the fifth embodiment shown in FIG 5 , substantially corresponds to that of the second embodiment 2 , The difference in principle lies on average 7 to compensate for the electrical charges on the surfaces to be coated, which use corona plasma ions in the function as a charge carrier.

The means comprise a corona discharge cone which can be positioned in three axes 14 in which a sufficiently high electrospray-charged electrical potential is applied to a corona gas discharge. With the gas discharge, charged particles (eg electrons or negatively charged ions) are created for the charge transport from the corona discharge cone to the surface to be coated, whereby the particles basically also cover larger distances.

A Corona gas discharge consists of a light zone and a dark zone. The light zone is located directly around the lying on potential Tip around and light up. The dark zone is further away from the top. A corona gas discharge starts by removing a charge carrier (e.g. by natural radioactivity or UV radiation generated ion) from a peak that is at opposite high Potential lies, is attracted. Immediately around the top is the field strength so high that the charge carrier is strongly accelerated towards the top while using gas molecules the environment encounters. there arise further ions, electrons and electromagnetic radiation (visible light = corona lights and UV radiation). The resulting Ions move away from the tip or up depending on the polarity the summit. to. Generate the ions accelerated to the top turn inside pairs and electromagnetic radiation, leaving a collision cascade arises. It is believed that the generated UV radiation again charge carrier generated, which are accelerated to the top, so that the collision cascade is maintained.

The Tension for the onset of a corona discharge depends mainly on the field strength, the surrounding gas and gas pressure. Preferably, the corona discharge operated in air at normal pressure. The sharper a corona discharge cone, the higher is at its peak for a given applied potential the field strength. at Very pointed discharge cones already contribute to the corona discharge moderate adjacent Potentials, because then the field strengths around the apex already are high enough to charge carriers enough for the triggering to a collision cascade accelerate. Furthermore Is it possible, to position very pointed discharge cone very close to the target (until about 2-3 mm), without causing an undesirable Flashover instead of the desired Corona gas discharge comes. As a corona discharge cone are, for example, electrochemical etched Tungsten tips, if possible with a tip radius of less than 1 μm. The threshold voltage for Corona discharge is for such peaks under atmospheric conditions at intervals from about 5 mm to the counter electrode at just under 1000 V.

The charged corona products strike the surface to be coated (target area), first neutralize the charge located there and, in the event of overcompensation, charge the surface opposite to the electrospray. The surface thus charged in opposite directions subsequently returns to the coating region through the rotation of the sample carrier. The charged trop From the electrospray are attracted by the now oppositely charged surface, so that the actually directed to the partition spray of charged drops on the surface to be coated (target area) is deflected. In the starting phase, the dividing wall, which is made of non-conductive material, charges itself through the first impinging drops with the same polarity as the electrospray, until the charges of the same name that have been repelled by the electrospray and the dividing wall repel each other. From this point on, the charged drops preferably fly onto the target area to be coated. Only very large drops can not follow this change of direction due to their inertia and impinge on the partition wall.

ever stronger the target area to be coated (surface) in the discharge zone opposite charged to the electrospray mist, the more drops or particles can hit in the target area, before this again as strong with the same polarity as the Spray is charged, that he is approaching subsequent drops or repels particles.

The Extent, in which the target area to be coated is charged in opposite directions to the spray polarity will hang from the potential with which the corona discharge is operated and from the threshold voltage at which the corona discharge starts.

The Corona needle is powered by a high voltage power supply to a fixed potential placed. This is with the spray device via a chain of high impedance safety resistors connected, which prevent the user from accidental Touch the potential of the spray capillary reaches dangerously high electric shocks. The Corona discharge persists for so long and dumps charge the surface to be coated, as the potential difference between the corona needle and the surface to be coated greater than the threshold voltage for the occurrence of corona discharge is. When so many loaded corona products the surface have taken that the potential difference is the threshold voltage falls below, the corona discharge collapses and it finds no further charging of the sample surface more. The lower the threshold voltage is applied, the more charge can be brought to the surface. For that reason are possible tip corona discharge cone (eg needles) to be preferred. Besides, very much tip discharge cone, as described above, positioned closer to the surface be unwanted without it Sparking Corona gas discharge comes.

The charged products of corona gas discharge and the charged drops or particles preferably strike the previously oppositely charged regions the surface to be coated on. Ideally, the spray current and corona current are therefore the same size. If Corona products and / or charged drops or particles undesirable Discharges are different.

The Koronakegelspitze is directly on the places to be coated the surface (Target area) aligned. The area covered by the Koronaprodukten is taken by the course of the field lines between Koronakegelspitze and Tar getbereich determined. The distance to the sample is in the present Case when coating small objects about 5 mm. If a more spacious area is to be coated, the distance to the sample is chosen larger.

With rotating sample carrier 2 Now an interplay between positive and negative charging of the surface to be coated in the target area develops 5 , If the surface in one compartment is below the electrospray capillary, it is coated and simultaneously positively charged. In the second compartment below the discharge cone 14 , this positive charge is not only compensated, but overcompensated, the surface charges negatively. This leads to; that the electrospray first encounters a negative potential when the sample has rotated further, and therefore is focused particularly effectively in this direction in an advantageous manner.

One Another advantage of this embodiment is in that the corona ions are uniform over the entire target area act. As a result receives a very wide range of homogeneity the target area, a uniform coating speeds and thus coatings of particularly high quality and reproducibility.

in the One example of an application becomes the fifth embodiment described for the Coating used by SAW sensors. The speed of sample carrier was at 1400 revolutions per minute, the distance between discharge cone tip, to which a negative potential (corona charge) of 1000 V is applied, and coating surface at about 10 mm. The other parameters as well as the coating material correspond to those mentioned in the context of embodiment 1.

The Mounting and contacting the corona tip is preferably carried out in an electrically insulating PEEK holder, which is a simple Replacement of the corona tip permitted.

Embodiment 6

It is advisable to charge compensation instead of a corona gas discharge according to the off Guide 5 another, the first spray source 3 contrary to use charged electrospray. Used eg as a spray source 3 sprays a coating solution with positive electrical potential, and thus the target area or the surface to be coated positively charged, a negatively charged electrospray is used for charge compensation. This electrospray for charge compensation may also contribute to the coating of the target (optionally with the same coating substance as in the first spray source 3 contained, or else with another coating substance, which then on the target with the coating substance from spray source 3 forms a mixed layer). But it can also contain only volatile components that do not remain on the functional layer, but only serve for charge compensation and / or overcompensation. Incidentally, the same statements apply as with the use of a corona gas discharge source for charge compensation or overcompensation.

1

axis of rotation

2

sample carrier

3

Electrospray capillary

4

electrospray

5

target area

6

partition wall

7

medium for compensation of an electric charge

8th

window

9

discharge wire

10

leg

11

wire section

12

disc

13

wheel axis

14

Corona discharge cone

15

angle

Claims (9)

Device for applying electrospray coatings on electrically nonconductive surfaces, comprising a) a motor-driven drive about an axis of rotation ( 1 ) rotating sample carrier ( 2 ) with an electrically non-conductive target area ( 5 ) for receiving the electrically non-conductive surfaces, b) an electrospray capillary ( 3 ) for introducing and electrically charging an electrospray ( 4 ) on the electrically non-conductive surfaces and c) means ( 7 ) for the periodically recurring compensation or discharge of electrical charges on the surfaces, wherein d) an insulating partition wall ( 6 ) is provided, which in the space above the target area ( 5 ) and divides it into a first and a second subspace, wherein the means (i) in the first and the electrospray capillary ( 3 ) are arranged in the second subspace. Device according to claim 1, characterized in that a) the partition wall ( 6 ) between sample carriers ( 2 ) and electrospray capillary ( 3 ) parallel to the target area ( 5 ) and a window ( 8th ) as passage for the electrospray ( 4 ) and b) the funds ( 7 ) a discharge wire ( 9 ), which between partition ( 6 ) and target area ( 5 ) projecting radially from an axis parallel to the axis of rotation about the axis parallel to the axis of rotation and in peri odisch distances the target area ( 5 ) covered. Device according to claim 1, characterized in that the partition wall ( 6 ) perpendicular to the target area ( 5 ) and just above this ends. Device according to claim 3, characterized in that the means ( 7 ) one over the target area ( 5 ) grounded grounded discharge wire ( 9 ). Device according to claim 3, characterized in that the means ( 7 ) a positionable in three axes corona discharge cone ( 14 ) to which an electric potential opposite to that of the electrospray for a corona gas discharge is applied. Device according to claim 3, characterized in that the means ( 7 ) comprise a further electrospray capillary for introducing and electrically charging a further electrospray onto the electrically non-conductive surfaces, wherein the further electrospray after electrical charging instructs an electrical potential opposite the electrospray. Device according to claim 3, characterized in that the means ( 7 ) one in the first subspace over the target area ( 5 ) arranged earthed U-shaped discharge wire with two mutually parallel electrically insulated legs ( 10 ) and one parallel to the target area ( 5 ), the legs connecting wire section ( 11 ). Device according to claim 1, characterized in that the means comprise a discharge wire ( 9 ), which on a round disc ( 12 ) radially to a disk axis ( 13 ) over the disc edge of the round disc ( 12 ) is erstreckingly applied and rotated with the disc, the disc axis ( 13 ) and the axis of rotation ( 1 ) are arranged at an angle between 10 and 70 ° to each other are and the distal end of the discharge wire ( 9 ) with a rotation of the disc to a distance below 2 mm the target area ( 5 ) approaches. Coating device for coating SAW sensors, comprising a device according to one of the preceding claims.