EP2424683A1

EP2424683A1 - Metal substrates having a scratch-proof and extensible corrosion protection layer and method for the production thereof

Info

Publication number: EP2424683A1
Application number: EP10718958A
Authority: EP
Inventors: Dirk Salz; Klaus-Dieter Vissing; Matthias Ott; Uwe Bultmann
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Impreglon Beschichtungen GmbH Landsberg am Lech
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Aalberts Surface Technologies GmbH Landsberg am Lech
Priority date: 2009-04-30
Filing date: 2010-04-30
Publication date: 2012-03-07
Anticipated expiration: 2030-04-30
Also published as: DE102009002780A1; EP2424683B1; EP2424683B2; WO2010125178A1

Abstract

The invention relates to a method for coating the surface of a metal substrate, comprising the following steps: A. providing the metal substrate an optionally cleaning the substrate surface to be coated, B. coating the substrate surface optionally cleaned in step A in a plasma polymerization reactor by means of plasma polymerization, - in step B, one or more organosilicon compounds and (a) no further or (b) further compounds being used as precursor(s) for the plasma, and in step B, the metal substrate being arranged in the plasma polymerization reactor in such a way that the metal substrate is connected as a cathode, characterized in that the method is conducted in such a way that the coating produced by the method has - an elongation to microcracking ≥ 1.5%, preferably ≥ 2.5%, - a yellow index determined according to ASTM D 1925 ≤ 4, preferably ≤ 3, further preferred ≤ 2.5, and - a hardness to be measured by means of nanoindentation in the range of 2.5 to 10 GPA, preferably 3.1 to 10 GPa, further preferred 3.1 to 6 GPa, and preferably - a thermal conductivity ≤ 5 W/m-K, preferably ≤ 2.5 W/m-K, and/or - a dielectric strength of 10 to 100 kV/mm, preferably ≥ 40 kV/mm, with the stipulation that the metal substrate is not a light metal substrate and with the stipulation that for the case of an elongation to microcracking of the coating ≤ 2.2%, the hardness to be measured by means of nanoindentation is ≥ 6 GPa.

Description

Metal substrates with a scratch-resistant and elastic corrosion protection layer and process for their production

The invention relates to a method of coating the surface of a metal substrate which is not a light metal substrate. The metal substrate may in particular comprise non-ferrous metal, such as e.g. Brass, nickel silver, bronzes or precious metal, such as silver or gold alloys, but also steel material, e.g. Be stainless steel or tool steel. The layer to be applied is characterized by an advantageous combination of scratch and abrasion resistance, extensibility, possibly transparency and corrosion protection effect. Further layer properties are very good specific electrical insulation effect, chemical and thermal stability, as well as barrier properties. The invention further relates to coated metal substrates.

Untreated surfaces of articles (for example semi-finished products, sanitary articles, metal strips, in particular steel and brass and copper, instruments, in particular percussion instruments or basins, food processing articles such as pans or baking molds, (stainless steel) containers, for example for the chemical industry, Jewelery, fittings) made of non-light metals, especially brass, copper, steel have a strong susceptibility to corrosion, especially in certain media, such as alkalis or acids, in an aqueous environment, or in contact with finger sweat. In addition, her Scratch resistance comparatively low. Therefore, for. B. brass surfaces often refined by powder coatings or PVD coatings. The scratch resistance and corrosion protection of PVD coatings based on silicon oxide is sufficient, but in practice, the directional coating process can not provide a complex 3D component such as door handles or taps with a protective layer. Powder coatings overcome this problem, but not as high scratch resistance is achieved in this method as in vacuum-based coating processes. Furthermore, the high gloss of the metallic component is lost slightly. Due to the disadvantages listed, metallic protective layers are applied galvanically to the metallic components, for example, in the sanitary sector. In tools of plastics processing, in particular of injection molding tools, abrasion-resistant, thermally insulating coatings can improve the mobility of the polymer melt on the tool surface, since the melt does not solidify so quickly due to the lower heat transfer.

Often, corresponding surface property improvements are produced by PVD coatings. However, a disadvantage of PVD coatings is their low extensibility. Typical is a crack elongation (crack-onset strain, elongation to microcracking) of max. 1 to 1.5%, which is thus worse than the metal substrate. This means in the processing of corresponding semi-finished products and components made of non-light metals, for example in the case of metal strips, plate-shaped products or extruded profiles a strong limitation. Cracks or hairline cracks are also observed when heated to about 100 ⁰ C, as they regularly occur when welding or hot bending. In addition, the residual stresses in the boundary layer region between the layer and the substrate are increased. The liability is charged. In the places where R isseb zw. H aarrisseverlaufen, ve rs agtinsb es onde re the corrosion protection effect of the PVD coating.

In other cases, the surface is improved, for example by ceramic spray coatings in mechanical wear behavior. In addition, this achieves a thermal insulation that can be used for forms of plastics processing. A disadvantage, however, is their granular surface, so that no high-quality components can be produced.

In the case of the use of a layer of protective lacquer, lacquer infiltration often occurs when a surface finish is damaged. The defect increases rapidly. The corrosion protection effect is lost. In addition, strong visual impairments occur. It was an object of the present invention to provide a method with which a protective layer can be produced on a metal substrate which is not light metal, which does not or at least only to a reduced extent have some or all of the disadvantages of the prior art described above. In particular, such a layer should have improved crack elongation and low residual stresses, so that cold or hot deformation is better possible. Furthermore, an improved chemical stability to alkaline media and generally a good corrosion protection effect is desirable. Such a layer should preferably have a high abrasion and scratch resistance, so that it can also be applied with layer thicknesses of more than 20 μm. In addition, the coating process should be economical, preferably also be carried out in a continuous process.

Surprisingly, it has been found that this object is achieved by a method for coating the surface of a metal substrate, with the following steps:

A. Provision of the metal substrate and optionally cleaning of the substrate surface to be coated,

B. coating the optionally cleaned in step A substrate surface in a plasma polymerization reactor by plasma polymerization, wherein

one or more organosilicon and (a) no further or (b) further compounds are used in step B as precursor (s) for the plasma and in step B the metal substrate is arranged in the plasma polymerization reactor so that it is connected as a cathode,

characterized in that the process is conducted so that the coating produced by the process

an elongation to microcracking of> 1.5%, preferably> 2.5%, a yellow index of <4 preferably <3, more preferably <2.5, determined according to ASTM D 1925, and a hardness to be measured by means of nanoindentation in the range from 2.5 to 10 GPa, preferably from 3.1 to 10 GPa, more preferably from 3.1 to 6 GPa, and preferably

a thermal conductivity <5 W / m ° K, preferably <2.5 W / m ° K and / or - A -

an electrical breakdown strength of 10 - 100 kV / mm, preferably of

> 40 kV / mm, with the proviso that the metal substrate is not a light metal substrate and provided that in case of elongation to micro crack of the coating of <2.2%, the hardness to be measured by nano identification is> 6 GPa.

Metal in the context of the present invention is a metallic material having a density of> 4.5 g / cm ³ at 2O ⁰ C. These include in particular iron, nickel, copper, zinc, nickel, lead, chromium and precious metals and their alloys such as Steel, brass and bronze. Preferred metal substrates are brass and copper substrates, and especially steel substrates. A light metal is a metallic material according to the present invention with a maximum density of 4.5 g / cm ³ at 2O ⁰ C. For metal substrates, the density of the region is crucial for the classification as light metal, on which the coating rests.

The metal substrate is preferably a semifinished product which is subsequently deformed in further preferred processes according to the invention.

A coating produced by the process according to the invention is characterized by a hitherto unknown advantageous combination of properties which were hitherto considered incompatible, namely good scratch and corrosion resistance with high ductility (crack elongation preferably greater than or equal to 2%, in particular greater or equal 2.5%). In addition, a good substrate adhesion, good optical transparency in the visible range and / or high layer thickness homogeneity can be achieved by the method according to the invention. In addition, the coating preferably has a thermal conductivity of <5 W / m ⁰ K and preferably an electrical breakdown strength according to DIN 53841 of 10 - 100 kV / mm.

Coatings with a yellow index of 2.5 or below generally have no yellowing discernible to the human eye. For coatings provided as transparent protective layers, however, even a minimum yellowing is tolerable, as with a yellow index in the range of over 2.5 to 3. The yellow index is further determined substantially by the proportion of Si-H bonds in the coating produced by the process according to the invention, which, as explained below, is crucial for achieving favorable ranges of hardness and elasticity and thus for achieving the advantageous property combination. If you want to increase the hardness of the coating and / or a slightly yellowish color, which ultimately can lead to an intense gold tone, allowed, so restrictions in the elongation to micro crack must be accepted. The yellow index can be adjusted to 4 without losing the corrosion protection effect. To do this, you can increase the self-bias by increasing performance.

Another important parameter is the carbon content in the coating produced by the process according to the invention, which is influenced by the proportion of organic groups. This in turn is just as important for the hardness and elasticity of the coating, which is also desirable for achieving the advantageous property combination. Due to a high elasticity of the coating, this can e.g. be stretched together with the coated article without causing cracking. With very high elasticity of the coating, the substrate can even be plastically deformed without the coating being damaged. As a result, forming processes of the coated material are possible to some extent.

In the case of the coatings which can be produced by the process according to the invention, the scratch resistance of the layers is in many cases comparatively easy to that of glass surfaces. It turned out, surprisingly, that it is possible by use of the inventive (dry chemical) method, for. B. completely to renounce the (wet chemical) chrome plating (decorative chrome plating). This is advantageous because the chromium plating is an expensive and environmentally problematic process because of the high energy input. In addition, the surface properties can be adjusted at the same time as the surface properties of the surface (s). The achievable layer property function is not only of interest as a chromating substitute, but also for the general coating of non-light metals.

DE 197 48 240 A1 discloses a method for the corrosion-resistant coating of metal substrates, in particular of aluminum or aluminum alloys, by means of plasma polymerization. As precursor (s) at least one hydrocarbon or organosilicon compound is used. DE 197 48 240 A1 does not contain information on the proportion of carbon atoms in the plasma polymer coatings produced or on their yellowness index. The layers disclosed there protect the surface well against corrosion without changing it visually. One limitation, however, is their low scratch resistance. The method disclosed there is not suitable for the low deposition rates, but is economically higher Produce layer thicknesses, as they are necessary for scratch-resistant coatings. For putting in, it places very high demands on the surface roughness of the substrate.

WO 03/002269 A2 discloses articles comprising a substrate and a plasma-polymer coating comprising O, C and Si, which are surface-bonded to the substrate, in which the molar ratios of O to Si and C to Si are determined in each case

Areas and that is easy to clean. However, the coatings disclosed therein have at least 25 atomic% of a higher carbon content than the coatings produced by the process according to the invention and do not have the above-mentioned combination of favorable properties. Also, nothing is said about the yellow index to be set.

Domingues et al. (2002) Electrochimica Acta 47, 2253-2258 discloses an aluminum alloy with a plasma polymer coating that provides some corrosion protection (as detected by electrochemical impedance spectroscopy). However, the disclosed coating lacks, in particular, the good scratch resistance and the high ductility which are inherent in the coating according to the invention. Furthermore, they indicate a high water absorption, comparable with that of organic coatings. Domingues et al. contains no information regarding yellowing or carbon content. Due to the procedure (ratio of the gas flows of oxygen to the organosilicon precursor about 23: 1, for details on the influence of these parameters see below) has the in Domingues et al. disclosed coating a lower carbon content than the coating produced by the inventive method.

EP 0 748 259 B1 discloses coatings for soft substrates. It is not disclosed that the coatings could be suitable for protecting metal substrates from corrosion. However, the coatings disclosed in EP 0 748 259 B1, which have a yellow index of <3, have a nanoindentation hardness of less than 2.5 GPa.

Furthermore, there is no teaching to reduce the excess of silicon and thus the formation of Si-H to produce particularly hard (well-crosslinked), elastic layers with little yellowing. The inventively optimized crosslinking ensures optimized corrosion protection behavior. Although thick-film processes, for example the application of paints or sol-gel coatings, can achieve the necessary corrosion resistance, they change the visual appearance. This effect is exacerbated in the case of irregularities such as mechanical damage or lack of adhesion of the thick films.

The method according to the invention is able to meet the demand for a cost-effective method for producing a thin layer which does not change the surface color of the metal (no intrinsic color and thus has a sufficiently high transmission in the visible range), which polishes the surface structure (eg. grinded, matted) simulates, so that no "gloss lacquer" is formed, which in addition to a high corrosion resistance has a high mechanical resistance (scratch resistance, ductility) and which, even with complex geometries has a high layer thickness uniformity.

By varying process parameters, the layer properties can be set within wide limits as described below.

An increase in the self-bias increases the hardness of the layer, its optical absorption in the visible range (and thus the yellow index) and its corrosion protection.

By adjusting the hardness and the thickness of the coatings which can be produced by the process according to the invention, it is possible for a person skilled in the art to achieve an optimum with regard to the scratch resistance of the coating. If the hardness is too low, the deposited plasma polymer layer is not sufficiently scratch-resistant. However, if the hardness is too high, the scratch resistance will also decrease because the layer will then become too brittle. This can be recognized, for example, in the microscopic assessment of the defect image. Generally, the scratch resistance of the layer is determined by the appropriate choice of layer thickness and composition.

Preferred is a method according to the invention, which is conducted so that the coating produced by the method has a pencil hardness of 4H or higher, determined according to ASTM D 3362. The measurement of the hardness by means of nanoindentation is explained in Example 2.

When adjusting the self-bias, the composition of the gas mixture from which the plasma is generated must also be taken into account. For example, with a high molecular weight of a precursor, a lower self-bias is generally to be chosen than at a low. The more readily a precursor can be ionized, the lower the plasma power must be to achieve a given self-bias. With a high electrical conductivity of the plasma, a low plasma power is needed to achieve a given self-bias.

Preference is given to a method according to the invention, wherein a control takes place during step B, so that the self-bias is in the range from 50 to 1000 V, preferably in the range from 100 to 400 V, preferably in the range from 100 to 300 V.

The self-bias can e.g. be reduced with constant plasma power by the plasma excitation frequency is increased. However, alternatively and / or preferably, it can be set or adjusted by applying an additional DC voltage to the electrode, so that it can be adjusted in accordance with the process parameters.

An increase in the self-bias also causes an improvement in the layer thickness homogeneity. For example, it could be determined in own experiments that on a round substrate with a diameter of 10 cm, the maximum layer thickness can differ from the minimum layer thickness at 100 V self-bias by a factor of 1. 1, while this factor at 200 V self -Bias can be 1, 005.

In the method according to the invention, in step B, the metal substrate in the plasma polymerization reactor is arranged so that it is connected as a cathode. As the cathode, the metal substrate acts when in direct electrically conductive contact with the portion of the cathode which is distinguishable from the metal substrate. This facilitates the achievement of a high rate of deposition of the positively charged ions of the plasma attracted to the cathode. When the substrate itself acts as a cathode, the kinetic energy at which the positively charged ions impinge on the surface is increased. As a result, the structure of the layer changes in the direction of a smaller proportion of organic (usually consisting mainly of C and H) groups and a correspondingly higher proportion of Si and O. The same effect also occurs (possibly reduced) when the substrate Although not acting as a cathode, but is arranged in the acceleration path of the cations.

Preferably according to the invention, no separate ion source is used in the process according to the invention. Without wishing to be bound by any particular theory, it is believed that increased kinetic energy of the ions facilitates the knocking off of organic groups in both the layering ions and the resulting coating, with the cleaved groups having a low probability of being trapped Layer to be installed. In addition, the high kinetic energy of the impacting ions reduces the internal stress (residual stresses) of the layer, which increases the strain to microcracking of the layer. As a result, it has also become possible to produce layer thickness ranges of considerably more than 30 μm with this method. For measuring the elongation to microcrack (crack elongation), compare Example 1.

The same observations (higher deposition rate, lower organic content, lower internal stress, higher crack elongation) are made as self-bias is increased. For this reason, hard coatings may have a higher crack elongation than soft ones. With very low self-bias, there is a lack of sufficient force (im pact) that the coating relaxes, which may lead to soft (for example, by nanoindentation to be measured hardness of 1 GPa) and at the same time crack-sensitive coatings.

If, however, the self-bias is increased beyond a favorable range (see also above), coatings are formed which contain too little organic group and too high a proportion of Si-H bonds (see also below). which makes them too hard and too brittle and reduces their scratch resistance. The aim is therefore to be optimum with regard to the hardness and elasticity of the coating produced by the process according to the invention at an acceptable yellow index (see also below).

An increase in the self-bias causes in the resulting layer, on the one hand, the reduction of residual stresses and thus a crack-increasing effect, on the other hand, an increase in hardness and modulus of elasticity and thus a crack-reducing effect. Due to the fact that two opposing effects partially cancel each other out, there is an optimum of crack elongation as a function of self-bias, so that an excellent combination of respectively relatively high hardness and high crack formation can be produced.

In addition, an increase in self-bias leads to an increased deposition rate and improved corrosion resistance in the resulting layer. The layers which can be produced by the process according to the invention are organically modified SiO ₂ frameworks. The organic components can be detected in the IR spectrum by bands at about 2950 cm ^-1 and at about 1275 cm ^-1 . In addition, they can be detected by measuring the surface energy with test inks. The higher the proportion of organic groups, the lower the surface energy. Therefore, the higher the self-bias is set, the greater the surface energy.

Preferably, in a method according to the invention, during step B the self-bias is set on the substrate. The dependence of the deposition rate and the layer properties of self-bias has already been explained. If the self-bias is set directly on the substrate and thus on the object to be coated, this facilitates the achievement of a layer with the desired precisely defined properties.

In a method according to the invention, a regulation is preferably carried out during step B, so that the self-bias is constant. As a result, the structure of the layer can be precisely controlled. Advantages of a self-bias which is as constant as possible are a homogeneous layer structure and a simple process transfer to a variety of substrates or a plurality of substrates. Preferably, during step B, the self-bias is controlled directly. If the plasma power is regulated, the self-bias will generally not be completely constant, but will fluctuate by a certain amount. In such a case, it is preferable that the total fluctuation width of the self-bias is at most 5% of the time average, preferably at most 3%.

Particular preference is given to a method according to the invention (in particular in combination with one or more features of another method described as preferred or particularly preferred), wherein a regulation takes place during step B so that the self-bias on the substrate is in the range from 50 to 1000 V. , preferably in the range of 100 to 400 V, more preferably in the range of 100 to 300 V, in particular such that the self-bias is constant.

For a roll-to-roll process, it is preferred that an AC voltage be applied to the metallic substrate so that a self-bias is formed on the metallic ribbon. In addition, a microwave discharge in spatial proximity to the unwound strip can burn and thus provide the necessary high number of ions. Furthermore, a method according to the invention is particularly preferred (in particular in combination with one or more features of another method described as preferred or particularly preferred), wherein the bias applied to the electrode is not determined solely by the plasma process parameters, but increased by an additional external DC voltage or is lowered. This is particularly important if the electrode surface is chosen to be large and a DC voltage increase becomes necessary for this reason.

An increase in the inflow of the organosilicon precursor (s) (in relation to optionally also inflowing O _2, in particular keeping the total inflow constant) generally causes a reduction in the hardness, an increase in the visible absorption (increase in the yellow index) Deterioration of the corrosion protection effect and an improvement in crack elongation.

With a high number of Si-H bonds in a layer according to the invention, an increased absorption of light of the ultraviolet and blue spectral range can be detected in the UV / Vis spectrum. This leads to an undesirable yellowing (increase in the yellow index). It is therefore desirable not to make the proportion of Si-H bonds too large. A reduction in self-bias prevents the formation of Si-H bonds in the coating. Likewise, the formation of Si-H bonds can be inhibited by a suitable selection of the amount and / or type of precursor (s). This is usually achieved by a reduction in the inflow of organosilicon precursors, which also reduces the proportion of organic groups in the coating. The occurrence of Si-H bonds can also be detected in the IR spectrum (2150 to 2250 cm ^-1 ).

The formation of Si-H bonds in the coating is also reduced when a sufficient amount of oxygen is added to the plasma, which also reduces the level of organic groups in the coating. Preference is given to a process according to the invention wherein oxygen (in the form of O ₂ ) is fed to the plasma in step B and preferably all the substances supplied to the plasma in step B are gaseous before they enter the plasma polymerization reactor. A procedure in the manner that the substances supplied to the plasma are gaseous not only under the conditions of the plasma, but even before entering the reactor, facilitates the exact coordination of the dosage of the substances. An increase in the oxygen supply leads to an increase in hardness, a reduction in visible absorption (reduction in yellowness index), an improvement in the corrosion protection effect, a reduction in the content of organic groups in the coating and a reduction in crack elongation.

In a preferred method according to the invention, oxygen (O ₂ ) is supplied to the plasma, all the substances supplied to the plasma in step B are gaseous before entering the plasma polymerization reactor and the ratio of the oxygen and other precursor gas flows supplied to the plasma in step B is greater (s) (in particular organosilicon precursors) in the range of 1: 1 to 6: 1, preferably 3: 1 to 5: 1. In this area, it is particularly easy according to the invention to adjust the desired proportion of carbon in the coating produced by the process and to achieve the desired properties of the coating.

If a yellow coating is obtained for a given parameter set, the O ₂ flux can be increased. Alternatively, the inflow of the organosilicon precursor (s) or the self-bias can be reduced. If the coating is too hard and therefore too brittle, the self-bias can be reduced or the inflow of the organosilicon precursor (s) can be increased.

The thermal conductivity, as well as the electrical conductivity is only slightly changed by the change in the actual plasma parameters within the claimed coating. Only the layer thickness is an essential parameter, so that it is possible to adapt the mechanical requirements of the coating as well as possible to the problem.

Preference is given to a process according to the invention, in particular in one of the preferred embodiments, wherein in step B as precursor (s) for the plasma one or more siloxanes, optionally oxygen (O ₂ ) and preferably no further compounds are used. Siloxanes, in particular hexamethyldisiloxane (HMDSO), have proven to be particularly suitable precursors for carrying out a process according to the invention with which coatings having the advantageous property combination can be prepared. Preferably, in a method according to the invention in step B, the precursor (s) used for the plasma are HMDSO, optionally oxygen, and preferably no further compound. An increase of the inflow of HMDSO in relation to oxygen causes inter alia Lowering of the hardness, an increase of the absorption in the visible range and a deterioration of the corrosion protection effect.

Particularly preferred is a method according to the invention, in which oxygen is supplied to the plasma in step B, all substances supplied to the plasma in step B are gaseous before entering the plasma polymerization reactor, the ratio of the gas flows of oxygen and further precursor supplied to the plasma in step B. en) is in the range from 1: 1 to 6: 1 and is used as precursor (s) for the plasma HMDSO, oxygen and in particular no further compound.

Preferably, in the method according to the invention, the plasma polymerization at a temperature of less than 200 ⁰ C, preferably less than 18O ⁰ C and / or a

Pressure of less than 1 mbar, preferably carried out in the range of 10 ³ to 10 ^{~ 1} mbar.

If the pressure during the deposition is too high, an undesirable PPuullvveerrbbiilldduunngg ddeess aabbggeesscchhiieeddeennennennennen MMaatteerriiaallsstrue. At a pressure of less than 10 ³ mbar, the plasma can no longer be ignited.

In a method according to the invention, step B is preferably up to a thickness of the deposited coating of greater than or equal to 2 .mu.m, preferably greater than or equal to 4 .mu.m. For specific applica tion, if z. B. extremely abrasion resistance, high dielectric strength or even a good thermal insulation is desired, a higher thickness of> 4 microns, preferably> 50 microns to about 100 microns is possible and preferred due to the low residual stresses of the coating.

Preference is given to a method according to the invention, wherein in step B the deposition rate is set to a value of greater than or equal to 0.2 μm / min, preferably greater than or equal to 0.3 μm / min. For example, a value of 0.5 μm / min can be selected. On the one hand, high deposition rates increase the economic efficiency of the process according to the invention and also facilitate the adjustment of the desired layer properties.

Preferably, in a method according to the invention, the metal substrate is a non-ferrous metal substrate selected from the group of substrates consisting of: brass, copper or bronze with a cleaned, uncoated surface. The substrate surfaces are optionally mechanically and / or electrically glazed and / or luster-etched or refined by a chemical, electrochemical or mechanical pretreatment, for example, luster-bleached, electropolished or polished. It is advantageous to carry out the method according to the invention such that in step A the substrate surface to be coated is cleaned by means of a plasma. Such a report greatly improves the adherence. Preferably, in the method according to the invention in step A d the plasma is added to the plasma cleaning a gas or gas mixture, wherein the gas or gas mixture is selected from the group consisting of: argon, argon-hydrogen mixture, oxygen.

In some cases, it is advantageous to carry out the process according to the invention such that, following step B, non-fragmented organosilicon compounds are present within the plasma polymerization reactor which react with reactive sites on the surface of the coating to form a hydrophobic surface. This can be achieved by first leaving the un-fragmented organosilicon precursor (s) in the reactor after switching off the plasma source in order to react with the surface radical of the plasma polymer layer. As a result, layers can be produced that are particularly easy to clean. The formation of a near-surface hydrophobic layer can be detected by XPS.

Here, the signals C1s, Si2p and O1s are used to quantify the carbon, silicon and oxygen content. To calibrate the stoichiometry measurements, a trimethylsiloxy-terminated polydimethylsiloxane (PDMS) with a kinematic viscosity of 350 mm ² / s at 25 ⁰ C and a density of 0.970 g / mL at 25 ⁰ C is examined. An example of this is the product DMS-T23E Gelest. The relative atomic sensitivity factors are adjusted so that the determined atomic stoichiometric ratio between silicon and oxygen is 1.00 ± 0.05 and the atomic stoichiometric ratio between silicon and carbon is 0.50 ± 0.03.

For a preferred method according to the invention for carrying out the XPS examination, compare Example 1 below.

In the mentioned procedure, a layer produced by the method according to the invention preferably contains in the upper (5 nm away from the substrate) a carbon content of 40-55 atomic%, a silicon content of 15-25 atomic% and an oxygen content of 20-35 atom %, based on the total number of Si, C and O atoms contained in the coating. It is clear to the person skilled in the art that this superficial area is applied only after carrying out the steps essential to the invention.

In the method according to the invention, the plasma is preferably not generated by means of DC voltage, but preferably by means of high frequency (HF) and in special preferred cases (s.v.) with microwaves. High-frequency plasmas lead to higher deposition rates with the same self-bias than lower-frequency plasmas.

Radio frequency should be understood to mean frequencies greater than or equal to 100 kHz.

For a very particularly preferred method according to the invention:

in step B, oxygen is supplied to the plasma; all the substances supplied to the plasma in step B are in front of them

Plasma polymerization reactor gaseous; the ratio of the gas fluxes of oxygen and further precursor (s) supplied to the plasma in step B in the range from 1: 1 to 6: 1; during step B, a control is performed so that the self-bias on the substrate is in the range of 100 to 400 V, preferably such that the self-bias is constant; hexamethyldisiloxane (HMDSO), oxygen and preferably no further compound is used as precursor (s) for the plasma; in step B, the metal substrate is in contact with a portion of the cathode which is distinguishable from the metal substrate; the plasma polymerization is carried out at a temperature of less than 200 ⁰ C and a pressure in the range of 10 ³ to 10 ^{~ 1} mbar; in step B, the deposition rate is set to a value of greater than or equal to 0.2 μm / min; Step B is carried out to a thickness of the deposited coating of greater than or equal to 2 μm; the metal substrate consists of transition metals (preferably atomic numbers of 22 to 30, 39 to 42, 44 to 48 and 57 to 79), gallium, germanium, indium, tin, antimony, bismuth or their alloys; most preferably it consists of alloys containing titanium, iron, copper and / or zinc in step A, the substrate surface to be coated is cleaned by means of a plasma, wherein the plasma for performing the plasma cleaning, a gas or gas mixture is added, which is selected from the group consisting of: argon, argon-hydrogen mixture, oxygen; - The plasma is generated by means of high frequency.

According to a further aspect, the present invention also relates to a coated metal substrate preparable by the process according to the invention, preferably in one of the embodiments described above as preferred.

A metal substrate coated according to the invention comprises a metal substrate and, arranged thereon, a plasma-polymer coating having the following features:

a crack elongation of> 1.5%, preferably> 2.5% a yellow index of <4 preferably <3, more preferably <2.5 and a hardness to be measured by means of nanoindentation in the range of 2 determined according to ASTM D 1925 , 5 to 10 GPa, preferably 3.1 to 10 GPa, more preferably 3.1 to 6 GPa and preferably a thermal conductivity <5 W / m ° K, preferably <2.5 W / m ° K and / or an electrical breakdown strength from 10 to 100 kV / mm, preferably from>

40 kV / mm with the proviso that the metal substrate is not a light metal substrate and with the proviso that for the case of an elongation to micro crack of the coating of <2.2%, the hardness to be measured by nano identification is> 6 GPa.

Preferred coated metal substrates according to the invention comprising the substrates and / or coatings described above as being preferably characterized.

Thus, in a coated metal substrate according to the invention, the coating preferably has determinable proportions of 5 to 30 atomic%, preferably 10 to 25 atomic% silicon and 30 to 70 atomic%, preferably 40 to 60 atomic% oxygen, by measurement by XPS, based on the total number of carbon, silicon and oxygen atoms contained in the coating. Irrespective of the abovementioned atomic% values for silicon and oxygen, but preferably in combination with these values, the coating preferably has a fraction of carbon which can be determined by measurement by means of XPS of from 3 to 28 atomic%, preferably from 5 to 28 atomic % more preferably 7 to 28 atom% based on the total number of carbon, silicon and oxygen atoms contained in the coating. In these atomic percentages Areas, the setting of the desired property combination is particularly well possible. The dependence of the proportions of carbon, silicon and oxygen on the arrangement of the substrate and on the self-bias has already been explained above. In addition, these proportions can be influenced by choosing suitable precursors.

In a preferred coated metal substrate according to the invention, an IR spectrum recorded by the coating has one or more, preferably all of the following bands (peaks) with a respective maximum in the following ranges: CH stretching vibration in the range from 2950 to 2970 cm ^-1 , Si-H vibration in the range of 2150 to 2250 cm ^-1 , Si-CH ₂ -Si vibration in the range of 1350 to 1370 cm ^-1 , Si-CH ₃ deformation vibration in the range of 1250 to 1280 cm ^-1 and Si -O vibration greater than or equal to 1 150 cm ^"1 .

The location of the maximum of the Si-O-Si oscillation gives information about the degree of crosslinking of the layer. The higher its wave number, the higher the degree of crosslinking. Layers in which this maximum is greater than or equal to 1200 cm ^"1 , preferably greater than or equal to 1250 cm ^{" 1} , have a high degree of crosslinking, while about non-stick layers with this maximum at typically about 1100 cm ^{"1 have} a low degree of crosslinking.

A detectable Si-CH ₂ -Si vibrational band indicates that in addition to Si-O-Si linkages, Si-CH ₂ -Si linkages are present in the coating. Such a material regularly has increased flexibility and elasticity.

To characterize the coating, the ratio of the intensity of the Si-H band to the intensity of the Si-CH ₃ band can serve. Coatings where this ratio is less than or equal to about 0.2 are colorless. At a ratio greater than about 0.3, the coatings are yellowish. Preference is given to a coated metal substrate according to the invention, wherein in an IR spectrum recorded by the coating, the ratio of the intensity of the Si-H band to the intensity of the Si-CH ₃ band is less than or equal to 0.3, preferably less than or equal to 0.2 is.

Preferably, an inventive coated metal substrate, wherein the coating has an absorption constant k _3O o _nm of less than or equal to 0.05 and / or an absorption constant k ^ o _nm of klei ner or facilitated g 0, 01. The relationship between the number of Si-H bonds which cause ultraviolet and blue light absorption, self-bias, plasma oxygenation and the amount and type of precursor (s) has already been explained above. Preferably, the coating of a coated metal substrate according to the invention has a surface energy in the range of 20 to 40 inN / m, preferably 25 to 35 inN / m. The surface energy is determined by the proportions of organic groups and thus by the amount of self-bias, as stated above.

As already stated, the anti-corrosion properties of the coating by z. For example, self-biasing, infiltration of the organosilicon precursor (s) and oxygen may be adjusted. Preferably, an inventive coated metal substrate for a 15-minute corrosive attack of NaOH at pH 14 and 3O ⁰ C no visible with the naked eye traces of corrosion.

As stated above, the crack elongation u. a. determined by the setting of the self-bias. In a preferred metal substrate according to the invention, the coating has an elongation to microcracking (crack elongation) of greater than or equal to 1.5%, preferably greater than or equal to 2.5%.

The self-bias influences the layer thickness homogeneity in the above manner. In the case of larger reactors, however, the gas flows are also of great importance. H ieru nter, for example, those reactors are to be understood, in which the reactor chamber (recipient) 2 m ³ or greater. The layer thickness homogeneity, inter alia, is defined by the electric fields generated on the substrate, ie a high field strength means a high deposition rate. Homogeneity can only be achieved if the electric field strength on the substrate is largely the same everywhere. In general, the layer thickness homogeneity on the arbitrary three-dimensional substrate obeys the Laplace equation, which indicates the solution for the electric field strength on the substrate. Preferably, in a coated metal substrate according to the invention, the maximum layer thickness differs from the minimum layer thickness by a factor of 1, 1 or less.

According to a further aspect, the present invention also relates to the use of a coating which can be produced or produced by a method according to the invention (in particular in a configuration marked as preferred) as a protective or functional layer on metals.

Other aspects of the present invention will become apparent from the following examples, the drawings and the claims. Example 1: XPS

XPS measurements (ESCA measurements) were carried out using the KRATOS AXIS Ultra spectrometer from Kratos Analytical. The calibration of the meter was made so that the aliphatic portion of the C 1s peak is 285.00 eV. Due to charging effects, it will usually be necessary to shift the energy axis to this fixed value without further modification. The analysis chamber was equipped with an X-ray source for monochromatized AI K _α radiation, an electron source as neutralizer and a quadrupole mass spectrometer. Furthermore, the system had a magnetic lens, which focused the photoelectrons via an entrance slit in a hemispherical analyzer. During the measurement, the surface normal pointed to the entrance slot of the hemisphere analyzer. The pass energy was 160 eV when determining the molar ratios. In determining the peak parameters, the pass energy was 20 eV each.

The measurement conditions mentioned are preferred in order to enable a high degree of independence from the spectrometer type and to identify plasma-polymer products according to the invention.

The reference material used was the polydimethylsiloxane silicone oil DMS-T23E from Gelest Inc. (Morrisville, USA). This trimethylsiloxy-terminated silicone oil has a kinematic viscosity of 350 mm ² / s (± 10%) and a density of 0.970 g / mL at 25 ⁰ C and an average molecular weight of about 13 650 g / mol. The selected material is characterized by an extremely low level of volatiles: after 24 hours at 125 ^° C. and 10 ^{~ 5} Torr vacuum, less than 0.01% volatiles were detected (according to ASTM-E595-85 and NASA SP-R0022A ). It was applied as a 40 or 50 nm thick layer to a silicon wafer by means of a spin coating process; In this case, hexamethyldisiloxane was used as the solvent or diluent.

With the procedure described above, the following atomic composition results for the silicone oil DMS-T23E. The binding energies of the electrons are also listed.

Table 1: Chemical composition and binding energy of silicone oil DMS-T23E

Example 2: Measurement of hardness by means of nanoindentation

The nanoindentation hardness of a sample was determined using a Berkovich indenter (manufacturer: Hysitron Inc. Minneapolis, USA). The calibration and evaluation was done according to the established method of Oliver & Pharr (J.Mos.Res., 7, 1564 (1992)). The machine rigidity and area function of the indenter were calibrated prior to measurement. In the indentation, the "multiple partial unloading" method (Schiffmann & Küster, Z. Metallkunde 95, 31 1 (2004)) was used to obtain depth-dependent hardness values and thus to exclude a substrate influence.

Example 3: Elongation to microcracking (crack elongation)

To determine the value of the elongation of the microcrack, a 0.5 mm thin and 10 cm long steel sheet (ST 37) is coated analogously and stretched until optical cracks are visible. The crack extension limit is equal to the quotient of elongation to the original total length of the steel.

Example 4 IR spectroscopy and determination of the intensity ratio of two bands in the IR spectrum

The measurements were carried out using an IFS 66 / S IR spectrometer from Bruker. As a method, the IRRAS technique was used, with the help of which even the thinnest coatings can be measured. The spectra were recorded in the wavenumber range of 700 to 4000 cm ^-1 using small platelets of very clean and particularly even aluminum as the substrate material, the angle of incidence of the IR light was 50 ° during the measurement while the sample was in the IR spectrometer The sample chamber was continuously purged with dry air and the spectrum was recorded under such conditions that the water vapor content in the sample chamber was so small that no rotation bands of water were found in the IR spectrum One used aluminum plate. The intensity ratio of two bands (peaks) is determined as follows: The baseline in the region of a peak is defined by the two minima which include the maximum of the band and corresponds to the distance between them. It is assumed that the absorption bands are Gaussian. The intensity of a band corresponds to the area between the baseline and the measurement curve, bounded by the two minima which include the maximum, and can easily be determined by the person skilled in the art according to known methods. The determination of the intensity ratio of two bands is done by taking the quotient of their intensities. The basic prerequisite for the comparison of two samples is that the coatings have the same thickness and that the angle of incidence is not changed.

Exemplary embodiments 1 to 4

A zinc sheet is additionally provided with a transparent, elastic scratch and corrosion resistant coating.

The substrate is mounted on or in the immediate vicinity of the HF (13.56 MHz) operated cathode (area approximately 15 x 15 cm), so that the substrate itself acts as a cathode. After the rectangular low-pressure reactor with a volume of approximately 360 l and an installed nominal suction capacity of 4500 m ³ / h has been evacuated to a pressure of less than 0.02 mbar, oxygen is introduced into the reactor with a flow of 280 sccm. Using a high-frequency plasma discharge (13.56 MHz), a self-bias voltage of 250 V is set on the substrate. Under these conditions, a Sputterätzprozess takes place, in which in particular organic impurities are efficiently degraded. This step as step A of the method according to the invention has a duration of 5 min. The plasma coating is then deposited on the prepurified substrate surface in step B of the method according to the invention. For this purpose, hexamethyldisiloxane (HMDSO) is introduced into the reactor at a flow of 66 sccm and oxygen at a flow of 280 sccm. The self-bias voltage is controlled to set a value of 100V, 250V, 300V and 400V respectively. An approximately 4 micron thick layer on the substrate is deposited after a coating time of 20 min, which greatly improves the scratch resistance and the corrosion protective effect against alkaline media: a corrosive attack of NaOH (pH 14, 5 min, 3O ⁰ C) does not cause visible to the naked eye visible traces of corrosion. In particular, coatings 1 to 3 (see Table 2) are transparent in the visible and UVA range. This is reflected in the very low absorption constant k at 300 or 400 nm. The absorption constants were obtained from the ellipsometric data calculated according to the manual of the WVASE32 spectrometer from JA Woolam Co, Inc.

Table 2: Optical constants of the coating at the variation of the BIAS voltage.

Embodiment 5

A stainless steel sheet (1.4544) was treated by plasma polymerization under the process parameters listed in Example 2 (66 sccm H MDSO and 280 sccm O ₂ , Self-bias = 250 V). The coating proved to be more scratch-resistant than a compacted anodized coating with a layer thickness of about 8 μm, but a significantly higher crack elongation of 2.8% was observed. By contrast, the crack elongation for the anodized coating was only 0.5%.

In order to determine the scratch resistance on the substrate, an eccentric device (Starnberger) was used. In this case, an approximately 8 μm thick anodized surface (not according to the invention), an approximately 500 nm thick plasma-polymer coating produced by a process of the prior art (not according to the invention), was applied to a felt plate loaded with a 1 kg weight. exemplified by TW Jelinek, surface treatment of aluminum, Eugen G. Leuze Verlag, Saulgau, 1996) and a 4 μm thick plasma-polymer coating according to the invention were investigated. The anodization surface was already visibly scratched after about 300 strokes after about 300 double strokes and the non-inventive plasma polymer coating after about 500 strokes. In the case of the plasma-polymer coating according to the invention, no visually noticeable scratches could be detected even after 10,000 strokes.

D iegu ts Korros io nss chutzeigenschaften of the coating produced by plasma polymerization according to the invention are in the acid (20% sulfuric acid, 45 min, 65 ⁰ C), such as in basic (NaOH, pH 14, 5 min, 3O ⁰ C) media. After these Corrosion tests showed no visible damage or no infiltration of coating edges.

The infrared spectrum of this coating are shown in Figure 1. Clearly to see CH stretching vibrations at 2966 cm ^"1, the Si-H vibration at 2238 ^{cm" 1,} the Si-CH ₂ -Si vibration at about 1360 cm ^"1 , the Si-CH ₃ deformation vibration at 1273 cm ^"

The Si-O vibrations at 1 192 cm ^-1 or 820 cm ^-1 . The band ratio (according to

Example 4) between Si-H and Si-CH ₃ is about 1: 5. The IR spectrum shows a small peak at 1360 cm-1. This band is correlated with a Si-CH ₂ -Si vibration.

Thus, in addition to the Si-O-Si network, there is an Si-CH ₂ -Si network in the coating.

The hardness of the coating was determined according to Example 2. It is 3 GPa. The pencil hardness is 4H.

The coating is homogeneous in depth. The proportions of carbon are about 10%, silicon about 10%, hydrogen about 30% and oxygen about 50%. A more in fl uent co m p u c t i o n c e m e n t o f e a tio n the plasma polymer layer shows on the one hand a shaggy fracture known for brittle materials (glass) and on the other hand small step-like fractures expected for crystalline materials.

Embodiment 6

The experiment is performed as in Embodiment 5, but to increase the deposition rate and thus to shorten the process time, a plasma generator oscillating at a frequency of 27.12 MHz was used. For equal gas flows (HMDSO: 66 sccm, O ₂ : 280 sccm) and self-bias voltage (250 V), the deposition rate is increased by a factor of 1.5. The coating properties change only insignificantly and are very similar to those of the coating of Example 5.

Embodiment 7

The dependence of the scratch and abrasion protection properties were determined as a function of the layer thickness. The substrate used was 600 μm thick stainless steel sheet (1.4544). The layer thickness was defined by the coating time. The scratch protection was achieved by particle bombardment (50 μm corundum, speed 100 km / h, time 3 min, Particle flow 33 g / min / cm ² ). The coating parameters are shown in Table 3.

The coatings whose layer thickness is less than 10 microns are completely removed, i. the layer thickness after the scratch protection test was 0 nm. From a layer thickness of about 17 μm, no appreciable erosion could be detected, i. the layer thickness remained unchanged.

Table 3: Coating Parameters for Scratch and Abrasion Protective Coatings

Embodiment 8

To determine the thermal conductivity of stainless steel sheets were provided with a 15μm thick layer. The plasma parameters are listed in Table 4.

Table 4 Coating Parameters for Samples 1 and 2.

The thermal parameters were determined by the flash method. Its principle is to suddenly heat the front of a sample by a short pulse of light and then measure how much time the heat front reaches the back of the sample. Flash methods provide as a primary measure the thermal diffusivity (α) of the temperature, which can be converted from the heat (p) and heat capacity (Cp) into the thermal conductivity (λ). The measuring principle image is shown in FIG. 2.

λ [W / m K] = α [mm ² / s] ^■ Cp [J / gK] ^■ p [g / cm ³ ]

The method can also be applied to multi-layered samples. Here, the thermal conductivity of an unknown layer can be determined if the thermophysical parameters (α, Cp, p) of all other layers are known.

The data for the uncoated stainless steel sample can be found in Table 6:

Table 5

With plasma polymer coating, the data of Table 6 were measured. In addition to the thermal conductivity, information is given on the thermal diffusivity and thermal conductivity.

Table 6

The layers measured here are particularly suitable for the coating of injection molds.

Example 9

A brass door handle was equipped with a corrosion and scratch resistant coating. The door handle has been switched as a cathode, so that during the

Deposition a constant self-bias voltage of -250 V prevailed. After a

Coating time of 20 min and an HMDSO or O ₂ flow of 66 sccm and 280 sccm was on the handle a transparent and interference-free layer of about 5 microns.

The color impression of the handle was unchanged. The resistance of the coating to sweat was measured by immersion in artificial sweat for 96 hours. The handle showed no visible change, the layer adhesion was not reduced.

Claims

claims:

1. A method for coating the surface of a metal substrate, comprising the following steps:

A. Provision of the metal substrate and optionally cleaning the substrate surface to be coated,

an elongation to microcracking of> 1.5%, preferably> 2.5%, a yellow index of <4 preferably <3, more preferably <2.5 determined according to ASTM D 1925 and a hardness to be measured by means of nanoindentation Range of 2.5 to 10 GPa, preferably 3.1 to 10 GPa, more preferably 3.1 to 6 GPa, and preferably - a thermal conductivity <5 W / m ° K, preferably <2.5 W / m ° K and / or has an electrical breakdown strength of 10 - 100 kV / mm, preferably of> 40 kV / mm,

with the proviso that the metal substrate is not a light metal substrate

and with the proviso that for the case of an elongation to micro crack of the coating of <2.2%, the hardness to be measured by means of nanoindentation is> 6 GPa.

2. The method of claim 1, wherein the method is performed so that the coating produced a determinable by measurement by XPS fraction of carbon from 3 to 28 atomic%, preferably 5 to 28 atomic%, more preferably 7 to 28 atomic %, based on the total number of carbon, silicon and oxygen atoms contained in the coating.

3. The method of claim 1, wherein the metal substrate is a brass, bronze or copper substrate.

4. The method of claim 1, wherein the metal substrate is a semi-finished product.

5. The method of claim 1 or 2, wherein the method is performed so that the coating produced by the method has a pencil hardness of 4H or higher.

6. The method according to any one of the preceding claims, wherein in step B, the plasma oxygen is supplied and preferably all the plasma in step B supplied substances before entering the plasma polymerization reactor are gaseous.

7. The method of claim 6, wherein all of the plasma in step B supplied materials before entering the plasma polymerization reactor are gaseous and the ratio of the plasma in step B supplied gas flows of oxygen and other precursor (s) in the range of 1: 1 to 6 : 1, preferably 3: 1 to 5: 1.

8. The method according to any one of the preceding claims, wherein in step B as precursor (s) for the plasma one or more siloxanes, optionally oxygen and preferably no further compounds are used.

9. The method according to claim 8, wherein in step B as the precursor (s) for the plasma hexamethyldisiloxane (HMDSO), optionally oxygen and preferably no further compound is used.

10. The method according to any one of the preceding claims, wherein during step B, a regulation takes place, so that the self-bias in the range of 50 to 1000 V, preferably in the range of 100 to 400 V, preferably in the range of 100 to 300 V. ,

11. The method according to any one of the preceding claims, wherein during step B, the self-bias is set on the substrate, preferably using an external DC voltage source.

12. The method according to any one of the preceding claims, wherein during step B, a regulation takes place, so that the total fluctuation width of the self-bias is a maximum of 5%, preferably a maximum of 3% of the time average.

13. The method of claim 1, wherein in step B the metal substrate is in spatial contact with (i) the cathode or (ii) a portion of the cathode which is distinguishable from the metal substrate.

14 Ve rfa h after re n ei ne md he vorang eh end en Ans Che ch e where IThe be plasma polymerization at a temperature of less than 200 ⁰ C and / or

Pressure of less than 1 mbar, preferably in the range of 10 ³ to 1 0 ^{~ 1} mbar is performed.

15. The method according to any one of the preceding claims, wherein in step B, the deposition rate to a value of greater than or equal to 0.2 microns / min, preferably greater than or equal to 0.3 microns / min, is set.

16. The method according to any one of the preceding claims, wherein step B is carried out to a thickness of the deposited layer of greater than or equal to 2 microns, preferably greater than or equal to 4 microns.

17. The method according to any one of the preceding claims, wherein the metal substrate is selected from the group of substrates consisting of brass or

Brass alloys with a cleaned, uncoated surface, copper, nickel silver, bronze, silver, gold or their alloys, in each case possibly with superficial oxide layer.

18. The method according to any one of the preceding claims, wherein in step A, the substrate surface to be coated is cleaned by means of a plasma.

19. The method of claim 18, wherein in step A the plasma for performing the plasma cleaning a gas or gas mixture is added, wherein the gas or gas mixture is selected from the group consisting of: argon, argon-hydrogen mixture, oxygen and oxygen-hydrogen -Mixture.

20. The method according to any one of the preceding claims, wherein the method is performed so that following step B within the

Plasma polymerisation reactor non-fragmented organosilicon compounds, which react with reactive sites on the surface of the coating to form a hydrophobic surface.

21. The method according to any one of the preceding claims, wherein the plasma is generated by means of high frequency.

22. A coated metal substrate comprising a metal substrate and having thereon a plasma polymer coating as defined in any one of claims 1 to 21, with the proviso that the metal substrate is not a light metal substrate.

23. Coated metal substrate according to claim 22, wherein the coating can be determined by measurement by means of XPS determinable proportions of 5 to 30 atom%, preferably 10 to 25

Atomic% of silicon and 30 to 70 atomic%, preferably 40 to 60 atomic% of oxygen, based on the total number of carbon, silicon and oxygen atoms contained in the coating.

24. A coated metal substrate according to claim 22 or 23, wherein an IR spectrum recorded by the coating has one or more, preferably all, of the following bands with a respective maximum in the following ranges: CH stretching vibration in the range of 2950 to 2970 cm ^-1 , Si-H vibration in the range of 2150 to 2250 cm ^-1 , Si-CH ₂ -Si vibration in the range of 1350 to 1370 cm ^-1 , Si-CH ₃ deformation vibration in the range of 1250 to 1280 cm ^-1 and Si-O vibration greater than or equal to 1 150 cm ^"1 .

25. Coated metal substrate according to one of claims 22 to 24, wherein in an IR spectrum recorded by the coating, the ratio of the intensity of the Si-H band to the intensity of the Si-CH ₃ band is less than or equal to 0.3, preferably smaller or equal to 0.2.

26. A coated metal substrate according to any one of claims 22 to 25, wherein the coating has an absorption _constant k _3O o _nm of less than or equal to 0.05 and / or an absorption constant ^ _{00 nm} of less than or equal to 0.01.

27. A coated metal substrate according to any one of claims 22 to 26, wherein the coating has a surface energy in the range of 20 to 40 mN / m, preferably 25 to 35 mN / m.

28. A coated metal substrate according to any one of claims 22 to 27, which after a 15-minute corrosive attack of NaOH at pH 13.5 and 30O ⁰ C has no traces visible to the naked eye traces of corrosion.

A coated metal substrate according to any one of claims 22 to 28, wherein the coating has an elongation to microcrack of greater than or equal to 1.5%, preferably greater than or equal to 2.5%.

30. A coated metal substrate according to any one of claims 22 to 29, wherein the maximum layer thickness differs from the minimum layer thickness by a factor of 1, 1 or less.

31. Use of a producible or prepared by a method according to any one of claims 1 to 21 plasma polymer coating or a plasma polymer coating as defined in any one of claims 23 to 30 as a protective or functional layer on metals, with the proviso that it is no Light metals acts.

Use according to claim 31, wherein the substrate is an injection mold or a part thereof.