Metal sheet or strip and method for producing same

Abstract

A method for producing a metal sheet or strip (1, 100), more particularly of steel, and the metal sheet or strip (1, 100) having at least one coating (2) on at least one flat side (1a) of the metal sheet or strip (1, 100), wherein the coating (2) comprises at least one electrically insulating primer coating film (5) with anti-corrosion pigments, at least one electrically insulating clear varnish film (6a, 6b) provided on the primer coating film (5), and at least one electrically insulating coating film (7), pigmented with electrically insulating and inorganic pigments, which is provided on the clear varnish film (6a, 6b) or on the clear varnish films (6a, 6b).

Description

[0001] Metal sheet or strip and process for its manufacture

[0002] Technical area

[0003] The invention relates to a metal sheet or strip, in particular made of steel, with at least one coating on a flat side of the metal sheet or strip and to a method for producing the metal sheet or strip.

[0004] State of the art

[0005] Metal strips made of steel with an organic multi-layer coating for the purpose of corrosion protection are known from the state of the art. Recently, such metal sheets or strips have been subjected to electrical functionalization. These coatings must therefore also ensure sufficient electrical insulation between the electrical functionalization and the metal sheet or strip. Despite a supposedly closed coating, pores and / or other recesses cannot be completely excluded, which significantly reduces the electrical insulation resistance and thus the electrical strength. In addition, such coatings have a comparatively high relative permittivity £r due to pigments, for example for corrosion protection of the metal sheet or strip, which increases or decreases the capacitance between the metal sheet or strip and the functionalized layer.adversely affects the leakage currents (according to ÖNORM EN 60335-1 ) and adversely limits the field of application of such metal sheets or strips.

[0006] Description of the invention

[0007] Based on the prior art described above, the invention therefore sets itself the task of modifying the coating of a metal sheet or strip in such a way that it is more suitable for electrical functionalization. The invention solves this problem by the features of claim 1.

[0008] If the coating comprises at least one electrically insulating primer coat layer with anti-corrosive pigments, at least one electrically insulating clear coat layer provided on the primer coat layer and at least one electrically insulating coat layer provided on the clear coat layer or layers and pigmented with electrically insulating and inorganic pigments, this can significantly increase the electrical strength of the coating.

[0009] In particular, the clear coat layer provided between the primer coat and the paint layer can ensure excellent pore-freeness and dielectric strength of the coating, which can lead to high electrical strength.

[0010] In addition to the comparatively high dielectric strength, the coating structure according to the invention can also ensure low permittivity. The metal sheet or strip according to the invention is therefore particularly stable in terms of electrical functionality.

[0011] This can lead to higher values ​​being achieved under AC voltage, surge and / or withstand voltage loads.

[0012] For example, this could also open up the possibility for the first time of expanding the application range of a final product made from such a semi-finished product to include the mains voltage range, for example, 230 V. Therefore, in contrast to known functionalizable metal sheets or strips, the metal sheet or strip according to the invention can also be suitable for a comparatively broader and more complex range of applications.

[0013] The clear coat layer preferably adjoins the primer coat layer and is thus provided directly on the primer coat layer. The pigmented coat layer preferably adjoins the clear coat layer or the last clear coat layer of the clear coat layers, as seen from the primer coat layer, and is thus provided directly on the clear coat layer or directly on the last clear coat layer. The primer coat layer is preferably polyurethane or polyester based to enable high corrosion resistance. Such a base can also ensure a stable bond to the clear coat layer, which can increase the mechanical stability of the coating.

[0014] For example, the primer coat layer can have a layer thickness in the range of 5 to 30 pm.

[0015] The corrosion resistance of the primer coat can be further increased if the primer coat contains phosphate-containing anti-corrosive pigments, particularly zinc phosphate. Additionally or alternatively, the primer coat can contain inorganic anti-corrosive pigments, particularly amorphous silica. This can achieve high resistance, for example, in outdoor applications with extreme climatic conditions.

[0016] If the clear coat layer, especially the thermally cured one, has a polyurethane or polyester base, this can lead to a stable and also cost-effective coating (for example, one that can be produced using a coil coating process).

[0017] It can also be advantageous if the clear coat layer has a layer thickness in the range of 10 to 30 pm.

[0018] The electrical insulation resistance and dielectric strength can be further increased with structural simplicity by applying multiple clear coat layers. At the same time, this can enable reduced permittivity, which reduces capacitance between the metal sheet or strip and the functionalized layer. This can reduce or even prevent adverse leakage currents (according to ÖNORM EN 60335-1).

[0019] Therefore, even larger areas of the metal sheet or strip can be electrically functionalized according to the invention. For example, heating applications with up to two m 2This allows for the printing of conductor tracks with a width of 0.6 mm, further increasing the stability of the electrical functionalization. Furthermore, these multiple layers of clear varnish can enable higher electrical voltages at the electrical functionalization and / or the use of the metal sheet or strip at higher temperatures.

[0020] For example, this multi-layered clear coat can be achieved by applying the same clear coat multiple times, for example, in a coil-coating process. A two-layer clear coat may be sufficient to achieve the above-mentioned advantage.

[0021] The pigmented lacquer layer preferably has a polyurethane or polyester base in order to be able to bond firmly to the clear lacquer layer.

[0022] Furthermore, the pigmented lacquer layer can be distinguished, which has a layer thickness in the range of 6 to 30 pm.

[0023] This allows the pigmented coating layer to act not only as a color-imparting layer but also as a diffusion barrier, for example, against moisture. This allows moisture to penetrate into the underlying layers at a reduced rate and with a reduced amount. Corrosive degradation, as well as interlayer delamination between the individual coating layers, can be significantly reduced or even completely prevented.

[0024] Preferably, the pigments of the pigmented coating layer are wettable. It is also conceivable for the pigments to have an average particle diameter of < 20 pm, thus enabling comparatively thin coating thicknesses.

[0025] If the pigmented coating layer contains TiO2 as a pigment, this can further improve the stability of the electrical functionalization. A sufficient barrier effect can be ensured, for example, if the proportion of TiO2 in the pigmented coating layer is in the range of 30 to 65 wt.%.

[0026] Additionally or alternatively, the pigmented coating layer can contain barium sulfate (BaSCk) as a pigment. The proportion of barium sulfate (BaSCM) is preferably in the range of 20 to 60 wt.% of the pigmented coating layer. Barium sulfate (BaSCM) can, for example, be distinguished by its reduced permittivity compared to other fillers, such as TiO2, which can reduce the capacitance between the metal sheet or strip and the functionalized layer or reduce adverse leakage currents.

[0027] The electrical functionalizability of the coating can be further improved if the first relative permittivity sr the primer coat > the second relative permittivity s r of the clear coat layer. This is further improved when the second relative permittivity s r of the clear coat layer < the third relative permittivity s r the paint layer.

[0028] Preferably, the first relative permittivity s r in the range of 4 to 6. For example, the second relative permittivity s r < 3. In particular, the third relative permittivity s r in the range of 6 to 7.

[0029] Furthermore, the coating may comprise at least one electrical insulation lacquer layer with an acrylate, epoxy, or styrene base, applied to the pigmented lacquer layer. The coating may also comprise several adjacent layers of this insulation lacquer layer. The electrical insulation lacquer layer is preferably UV-cured and / or solvent-free. Such UV-curing insulation lacquer systems may be characterized, for example, by a reduced tendency to pore formation, which can further improve the dielectric strength of the coating.

[0030] This is especially true if the insulating lacquer layer is intended to have a layer thickness in the range of 10 to 100 pm.

[0031] For example, the insulating lacquer layer is a UV-curing clear lacquer layer. The insulating lacquer layer preferably adjoins the pigmented lacquer layer and is thus provided directly on the pigmented lacquer layer. Stable electrical functionalization can be created if the coating has at least one electrically conductive layer, for example an electrical conductor, wherein the electrically conductive layer is provided on the pigmented lacquer layer and / or on the insulating lacquer layer. For example, this can be achieved with comparatively little effort if the electrically conductive layer is printed. It is also conceivable for the electrically conductive layer to be provided over the entire surface or in certain regions on the pigmented lacquer layer and / or on the insulating lacquer layer.

[0032] Preferably, the electrically conductive layer adjoins the pigmented lacquer layer or the insulating lacquer layer. The electrically conductive layer is thus provided directly on the pigmented lacquer layer or directly on the insulating lacquer layer.

[0033] The stability of an electrical functionalization can be further increased if the coating has a top layer that covers at least the electrically conductive layer. This covering can, for example, be complete.

[0034] Preferably, the primer coat, the clear coat or coats, the pigmented coat and, if applicable, the top coat are provided over the entire surface of the flat side of the metal sheet or strip.

[0035] The electrically conductive layer can be provided in regions on the flat side of the metal sheet or strip, and the insulating varnish layer, if provided, can also be provided in regions on the flat side of the metal sheet or strip.

[0036] The invention also aims to create a method with which an electrically functionalizable metal sheet or strip can be reproducibly produced. Furthermore, the method should be easy to handle.

[0037] The invention solves the problem by the features of claim 16. A metal sheet or strip particularly suitable for electrical functionalization can be produced reproducibly by applying the coating comprising:

[0038] Applying a curable polymeric primer coating to a flat side of the metal sheet using a roller application and thermally curing the primer coating to form the electrically insulating primer coating layer,

[0039] Applying or repeatedly applying a curable polymeric clear coat using a roller application to the primer coat layer (5) and thermally curing the clear coat or thermally curing the applied clear coats to form the electrically insulating clear coat layer or the electrically insulating clear coat layers and

[0040] Application of a curable polymeric and pigmented lacquer to the clear lacquer layer or layers using a roller application and thermal curing of the pigmented lacquer to form the electrically insulating and pigmented lacquer layer.

[0041] In addition, roller application can provide a comparatively easy-to-use process.

[0042] The electrical functionalizability of the metal sheet or strip can be further increased if the process comprises applying a curable, polymeric and electrically insulating insulating lacquer to the pigmented lacquer layer by means of a screen printing application and UV curing of the insulating lacquer to form the insulating lacquer layer.

[0043] The method may include applying a functional layer to electrically functionalize the metal sheet or strip. This can be achieved by applying the coating additionally comprising applying, in particular printing, an electrically conductive layer to the pigmented lacquer layer. This application to the pigmented lacquer layer can be to the pigmented lacquer layer or to the insulating lacquer layer located on the pigmented lacquer layer. The functionalized layer of the metal sheet or strip can be particularly protected if a topcoat is applied to the electrically conductive layer and cured to form the topcoat.

[0044] Short description of the drawing

[0045] The figures show, for example, the subject matter of the invention in more detail using an exemplary embodiment.

[0046] Fig. 1 is a fragmentary sectional view of a first metal strip transverse to the longitudinal direction according to a first embodiment and

[0047] Fig. 2 is a fragmentary sectional view of a second metal strip transverse to the longitudinal direction according to a second embodiment.

[0048] Way to implement the invention

[0049] The first metal strip 1 (often referred to as sheet metal strip) made of steel shown in Fig. 1 has a coating 2 with an electrically conductive layer

[0050] 3 for electrical functionalization, of which a printed electrical conductor

[0051] 4 was made from a paste consisting of conductive silver particles.

[0052] The metal strip 1 or metal sheet can have a sheet thickness of up to 3 mm, for example 0.3 mm. Preferably, the metal strip 1 or metal sheet is a thin sheet.

[0053] The coating 2 is provided in regions on a flat side 1a of the metal strip 1, whereby the opposite flat side 1b is also organically coated, for example for reasons of corrosion protection, which has not been shown in more detail.

[0054] According to the invention, this coating 2 is multi-layered and comprises a primer layer 5, two clear coat layers 6a, 6b, and a pigmented coat layer 7, which acts, for example, as a diffusion barrier. Primer layer 5, clear coat layers 6a, 6b, and pigmented coat layer 7 are provided over the entire surface of the flat side 1a of the metal sheet or strip 1, namely one above the other, as schematically illustrated in Fig. 1 and Fig. 2.

[0055] According to Fig. 1, the electrically conductive and printed layer 3 adjoins the pigmented lacquer layer 7 and is thus provided directly on this pigmented lacquer layer 7 in the exemplary embodiment.

[0056] The primer coating layer 5 adjoins the flat side 1a of the metal strip 1, namely its galvanization (not shown), for example, made of a Zn-Al alloy, and is thus provided in the exemplary embodiment directly on the metal strip 1 or directly on the galvanization (not shown in detail). This primer coating layer 5, which has a layer thickness of 10 μm, comprises phosphate-containing anti-corrosive pigments, made of zinc phosphate, which results in a first relative permittivity s r of approximately 5. Other corrosion protection pigments are conceivable, for example amorphous silica, in order to achieve the first relative permittivity s r the primer coat layer and thus reduce the leakage currents of the coating.

[0057] The primer is made of a polyurethane polymer with a solids content of 60% by weight. The wet film density is 1.18 g / cm 3 with a yield of 52 g / m 2

[0058] This primer coat 5 is followed by the first clear coat 6a. This first clear coat 6a consists of a thermally cured clear coat with a polyurethane base, which enables closed and largely pore-free layers. The electrical breakdown capacity and electrical insulation resistance are achieved by applying a curable polymeric clear coat twice using a roller application to the primer coat and thermally curing the applied clear coat twice, which creates a second clear coat 6b identical to the first clear coat 6a on top of the first clear coat 6a. By applying this multiple times, namely twice, it is possible to reliably prevent pores through the two clear coats 6a, 6b.

[0059] These clear coat layers 6a, 6b, like the primer, are based on a polyurethane binder. The solids content is 45% by weight. The wet paint density is 1.05 g / cm 3 with a yield of 27 g / m 2 Both clear coat layers 6a, 6b are pigment-free and filler-free.

[0060] With a layer thickness of 15 μm for the first clear coat 6a or each clear coat 6a, 6b, a comparatively high dielectric strength can be achieved. This is also possible with a comparatively low second relative permittivity s. r of approx. 2 of each clear coat layer 6a, 6b.

[0061] A pigmented lacquer layer 7 is provided on this second, and thus last, clear lacquer layer 6b as seen from the primer lacquer layer 5. In the exemplary embodiment, it is thus provided directly on the second clear lacquer layer 6b, as can be seen in Fig. 1. The pigmented lacquer layer 7 has a polyurethane base and a layer thickness of 20 μm. Pigments, namely TiO2, with a pigment content of 61 wt.% in the pigmented lacquer layer 7, for example, also form a diffusion barrier.

[0062] Therefore, a relatively low permittivity can be r of approximately 7. The wet layer density is 1.37 g / cm 3 with a yield of 63 g / m 2 .

[0063] The above advantages can be further improved by a second metal strip 100 made of steel, shown in Fig. 2. The layer structure shown here has, in addition to the layer structure of Fig. 1, an electrical insulation lacquer layer 8 on the pigmented lacquer layer 7 and is thus provided directly on the pigmented lacquer layer 7 in the exemplary embodiment. The electrical insulation lacquer layer 8 has a UV-cured acrylate base and a layer thickness of 30 μm and is provided in regions on the flat side 1a of the metal sheet or strip 1, namely underneath the electrically conductive layer 3. As shown in Fig. 2, this electrical insulation lacquer layer 8 protrudes, for example, laterally comparatively slightly from the electrically conductive layer 3. In the exemplary embodiment, the electrically conductive layer 3 adjoins the insulation lacquer layer 8.The electrically conductive layer 3 is thus provided directly on the insulating lacquer layer 8.

[0064] To protect the electrically conductive layer 3, a covering layer 9 made of polyurethane with a layer thickness of 60 μm is provided. This covering layer 9 can be formed by an applied lacquer, a powder coating, a film, etc.

[0065] In contrast to Fig. 2, according to Fig. 1, the electrical conductor 4 is printed as an electrically conductive layer 3 onto the pigmented lacquer layer 7 in Fig. 1 and is thus provided directly on the pigmented lacquer layer 7. Fig. 1 can also have a cover layer 9 (not shown in detail), as shown and described in Fig. 2.

[0066] An electrical conductor 4, an electrical conductor track, an electrical contact, an electrode, a heating resistor, a piezoelectric layer, etc. can be conceived as an electrically conductive layer 3.

[0067] The advantages of the invention can be seen in Tables 1 and 2 in comparison with a steel sheet A from the prior art:

[0068] Steel sheet A (state of the art):

[0069] Steel sheet A has a coating consisting of a primer layer, an electrical conductor 4 made of a paste containing silver particles printed on the primer layer, and a protective lacquer layer provided over the electrical conductor 4. The primer layer consists of a polyester polymer and has a layer thickness of 6 μm. The protective lacquer layer also consists of a polyester polymer and has a layer thickness of 20 μm. This results in a layer thickness of 26 μm between metal sheet 1 and the electrical conductor.

[0070] Steel sheet B (according to the invention): The steel sheet B according to the invention corresponds in structure to the steel metal strip 1 shown in Fig. 1. The layer thickness of the organic section 2a of the coating 2 between the metal sheet 1 and the electrical conductor 4 is 60 pm in this exemplary embodiment.

[0071] Steel sheet C (according to the invention):

[0072] The steel sheet C according to the invention corresponds in structure to the steel metal strip 100 shown in Fig. 2. The layer thickness of the organic sections 2a and 2b of the coating 2 between the metal sheet 1 and the electrical conductor 4 is 90 pm in this exemplary embodiment.

[0073] Table 1

[0074] *1 Test parameters: AC voltage, 50Hz, application time 1 min

[0075] *2 Test parameters: Uimp 1 ,2 / 50ps pulse, 5x positive polarity and 5x negative polarity, time between pulses 15 see.

[0076] As can be seen in Table 1, a significant increase in electrical strength was achieved for steel sheets B and C in the withstand / impulse voltage test and the AC voltage test compared to those of steel sheets A known from the prior art. Thus, the steel sheets B and C according to the invention can be reliably electrically functionalized.

[0077] This is due to the multi-layer coating structure according to the invention. This eliminates open pores and / or potential defects to the extent technically manageable, thus preventing electrical short circuits.

[0078] Furthermore, this inventive multilayer structure, with its comparatively high electrical strength, is characterized by its ability to enable functionalization in the voltage range of a mains voltage (e.g., 230 V). Thus, the inventive structure of the insulation layer, consisting of the primer coat, the additional application of two further clear coat layers 6a, 6b, and a final pigmented coat layer 7, was able to achieve sufficiently high electrical insulation. This was achieved, among other things, by changes in the layer design to reduce the permittivity and increase the dielectric strength.

[0079] The inventive layer structures of the coatings 2 according to Fig. 1 and Fig. 2 provide a significant improvement in dielectric strength. This makes it possible to realize applications with voltages higher than low voltages (e.g., up to 48V). This was made possible, among other things, by a significant reduction in pores in these individual layers.

[0080] The advantageous influence of the inventive sections 2a, 2b of the coatings 2 on the permittivity and thus on the area of ​​the steel sheet that can be used for electrical functionalization (e.g.: for resistance heating) can be seen from Table 2.

[0081] Table 2

[0082] Even using the thermally curing clear coat layer 6 shown in Fig. 1, an area 3.5 times larger than the prior art can be used with conductive structures. If the UV-curing clear coat layer 8 is added as an insulating layer 8 shown in Fig. 2 in a further step, an area 9.2 times larger than the prior art can be used.

[0083] In general, it is noted that "in particular" can be translated into English as "more particularly." A feature preceded by "in particular" is to be considered an optional feature that can be omitted and thus does not constitute a limitation, for example, of the claims. The same applies to "vorzugsweise," translated into English as "preferably."

Claims

Patent claims:

1. Metal sheet or strip, in particular made of steel, with at least one coating (2) on at least one flat side (1a) of the metal sheet or strip (1, 100), wherein the coating (2) has at least one electrically insulating primer coat (5) with anti-corrosive pigments, at least one electrically insulating clear coat (6a, 6b) provided on the primer coat (5) and at least one electrically insulating coat (7) provided on the clear coat (6a, 6b) or on the clear coat layers (6a, 6b) and pigmented with electrically insulating and inorganic pigments.

2. Metal sheet or strip according to claim 1, characterized in that the primer coat (5) has a polyurethane or polyester base and / or a layer thickness in the range of 5 to 30 pm.

3. Metal sheet or strip according to claim 1 or 2, characterized in that the primer coat (5) comprises phosphate-containing anti-corrosive pigments, in particular zinc phosphate, and / or inorganic anti-corrosive pigments, in particular amorphous silica.

4. Metal sheet or strip according to one of claims 1 to 3, characterized in that the, in particular thermally cured, clear lacquer layer (6a, 6b) has a polyurethane or polyester base and / or a layer thickness in the range of 10 to 30 pm.

5. Metal sheet or strip according to one of claims 1 to 4, characterized in that on the primer layer (5) several, in particular two, adjacent subsequent clear lacquer layers (6a, 6b) are provided and / or that the clear lacquer layer (6a, 6b) or the clear lacquer layers (6a, 6b) is or are free of fillers and / or free of pigments, in particular opaque pigments.

6. Metal sheet or strip according to one of claims 1 to 5, characterized in that the pigmented lacquer layer (7) has a polyurethane or polyester base and / or a layer thickness in the range of 6 to 30 pm.

7. Metal sheet or strip according to one of claims 1 to 6, characterized in that the pigments of the pigmented lacquer layer (7) are wettable and / or have an average particle diameter of < 20 pm.

8. Metal sheet or strip according to one of claims 1 to 7, characterized in that the pigmented lacquer layer (7) is used as pigment TiO2, preferably in the range of 30 to 65 wt.%, and / or barium sulfate (BaSCM), preferably in the range of 20 to 60 wt.%.

9. Metal sheet or strip according to one of claims 1 to 8, characterized in that the first relative permittivity s r the primer coat (5) > the second relative permittivity s rthe clear coat layer (6a, 6b) and / or that the second relative permittivity s r the clear coat layer (6a, 6b) < the third relative permittivity s r the pigmented lacquer layer (7).

10. Metal sheet or strip according to claim 9, characterized in that the first relative permittivity s r in the range of 4 to 6 and / or the second relative permittivity s r < 3 and / or the third relative permittivity s r is or are in the range of 6 to 7.

11. Metal sheet or strip according to one of claims 1 to 10, characterized in that the coating (2) comprises at least one, in particular several, electrical insulation lacquer layers (8) provided on the pigmented lacquer layer (7) with a, in particular UV-cured, acrylate or epoxy or styrene base and / or a layer thickness in the range of 10 to 100 pm.

12. Metal sheet or strip according to one of claims 1 to 11, characterized in that the coating (2) has at least one electrically conductive layer (3), in particular an electrical conductor (4), which electrically conductive layer (3) is provided, in particular printed, on the pigmented lacquer layer (7) and / or on the insulating lacquer layer (8).

13. Metal sheet or strip according to claim 12, characterized in that the electrically conductive layer (3) is provided adjacent to the pigmented lacquer layer (7) or to the insulating lacquer layer (8).

14. Metal sheet or strip according to claim 12 or 13, characterized in that the coating (2) has a cover layer (9) which covers at least the electrically conductive layer (3).

15. Metal sheet or strip according to one of claims 1 to 14, characterized in that the primer lacquer layer (5), the clear lacquer layer (6a, 6b), the pigmented lacquer layer (7) and optionally the cover layer (9) are provided over the entire surface of the flat side (1 a) of the metal sheet or strip (1, 100) and / or that the electrically conductive layer (3) and optionally the insulating lacquer layer (8) are provided in regions on the flat side (1 a) of the metal sheet or strip (1, 100).

16. A method for producing a metal sheet or strip according to one of claims 1 to 15, wherein the coating (2) is applied to a flat side (1 a) of the metal sheet or strip (1, 100), wherein the application of the coating (2) comprises: Applying a curable polymeric primer coating to a flat side (1 a) of the metal sheet or strip by means of a roller application and thermally curing the primer coating to form the electrically insulating primer coating layer (5), Applying or repeatedly applying a curable polymeric clear coat using a roller application to the primer coat layer (5) and thermally curing the clear coat or thermally curing the applied clear coats to form the electrically insulating clear coat layer (6a, 6b) or the electrically insulating clear coat layers (6a, 6b) and Applying a curable polymeric and pigmented lacquer to the clear lacquer layer (6a, 6b) or to the clear lacquer layers (6a, 6b) by means of a roller application and thermally curing the pigmented lacquer to form the electrically insulating and pigmented lacquer layer (7).

17. The method according to claim 16, characterized in that the application of the coating (2) additionally comprises: Applying a curable, polymeric and electrically insulating insulating varnish to the pigmented varnish layer (7) by means of a screen printing application and UV curing of the insulating varnish to form the insulating varnish layer (8).

18. Method according to claim 16 or 17, characterized in that the application of the coating (2) additionally comprises: Applying, in particular printing, an electrically conductive layer (3) onto the pigmented lacquer layer (7), in particular onto the pigmented lacquer layer (7) or onto the insulating lacquer layer (8).

19. Method according to claim 18, characterized in that a cover lacquer (9) is applied to the electrically conductive layer (3) and cured to form the cover layer (9).

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