EP2424683B2 - Metal substrates having a scratch-proof and extensible corrosion protection layer and method for the production thereof - Google Patents

Description

The invention relates to a method as defined in the claims for coating the surface of a metal substrate that is not a light metal substrate. The metal substrate can in particular be non-ferrous metals such as brass, nickel silver, bronzes or precious metals such as silver or gold alloys, but also steel material such as stainless steel or tool steel. The layer to be applied is characterized by an advantageous combination of scratch and abrasion resistance, elasticity, transparency and, if necessary, corrosion protection. Further layer properties are very good specific electrical insulation properties, chemical and thermal stability, as well as barrier properties. The invention also relates to coated metal substrates as defined in the claims

Untreated surfaces of objects (for example semi-finished products, sanitary articles, metal strips, especially made of steel and brass and copper, instruments, especially percussion instruments or basins, objects for food processing such as pans or baking molds, (stainless steel) containers for example for the chemical industry, jewelry, Fittings) made of non-light metals, in particular made of brass, copper, steel are particularly susceptible to corrosion in certain media, such as alkalis or acids, in an aqueous environment, or in contact with finger sweat. In addition, their scratch resistance is comparatively low. Therefore z. B. brass surfaces are often refined with powder paints 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 cannot provide complex 3D components such as door handles or faucets with a protective layer. Powder coatings overcome this problem, but this process does not achieve as high a scratch resistance as vacuum-assisted coating processes. Furthermore, the high gloss of the metallic component is somewhat lost. Because of the disadvantages listed, metallic protective layers are applied to the metallic components by electroplating, for example in the sanitary sector. In tools used in plastics processing, in particular 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 as quickly due to the lower heat transfer.

Corresponding improvements in surface properties are often produced by PVD coatings. However, a disadvantage of PVD coatings is their low extensibility. Typical is a crack-onset-strain of max. 1 to 1.5%, which is therefore worse than with the metal substrate. This means a severe restriction 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. Cracks or hairline cracks are also observed when heated to over approx. 100 ° C, as they regularly occur during welding or hot bending, for example. In addition, the internal stresses in the boundary layer area between the layer and the substrate are increased. The liability is charged. At the points where cracks or hairline cracks run, the corrosion protection effect of the PVD coating fails in particular.

In other cases, the mechanical wear behavior of the surface is improved, for example by ceramic spray coatings. In addition, this creates thermal insulation that can be used for forms of plastics processing. However, their grainy surface is disadvantageous, so that no high-quality components can be produced.

If a layer of protective lacquer is used, if a surface lacquer is damaged, there is often infiltration of the lacquer. The defect increases rapidly. The anti-corrosion effect is lost. In addition, there are strong visual impairments.

EP 0 752 483 A1 discloses a method for coating objects made of metal, metal alloys, plastics or with corresponding surfaces with a protective layer after prior cleaning by means of a plasma-assisted CVD process by electrical plasma excitation at reduced gas pressure with the introduction of a gas mixture with reactive, layer-forming gases and control of the Working pressure, with the vapor of an easily vaporizable organosilicon compound containing the element silicon in organic compound or a silicon-containing gas being introduced as the reactive gases in addition to oxygen, characterized in that the reactive gases are introduced in such a mixture, that the proportion of reactive oxygen is not sufficient for the quantitative conversion to silicon dioxide, and that the deposition parameters of the electrical gas discharge are controlled in such a way that a quartz-like This layer forms which, in addition to silicon and oxygen, also contains organic, plasma-polymerized components in a homogeneous distribution.

DE 195 23 442 A1 discloses a method for coating objects made of metal or metal alloys or with corresponding surfaces with a protective layer after prior cleaning by means of a plasma-assisted CVD process by means of an electrical high-frequency discharge at reduced gas pressure with the introduction of a gas mixture with reactive, layer-forming gases and control of the working pressure, characterized in that for the formation of a quartz-like layer as the reactive gases, in addition to oxygen, the vapor of an easily vaporizable organosilicon compound containing the element silicon in an organic compound or a silicon-containing gas can be introduced in such a mixture that the proportion of reactive oxygen is not sufficient for the quantitative conversion to silicon dioxide, and that the self-bias voltage of the electrical gas discharge is controlled so that a layer with a mixed structure of quartz with embedded organic Forms structural components.

• Bereitstellen eines Substrates mit einer glatten Oberfläche, insbesondere mit einer Oberflächenrauhigkeit Rqvon höchstens 10 nm,
• Plasmavorbehandlung des Substrates im Vakuum,
• Aufbringen einer Basisschicht aus einem zumindest Silizium, Sauerstoff und Kohlenstoff umfassenden Polymer mittels Plasmapolymerisation im Vakuum,
• Aufbringen einer Glanzschicht aus einem Metall, einer Metalllegierung oder Metallverbindung mittels Sputtern im Vakuum und
• Aufbringen einer zumindest teiltransparenten, verschleißfesten Lackdeckschicht.

DE 10 2004 049111 A1 discloses a method for high-gloss coating of substrates, at least comprising the steps

• Providing a substrate with a smooth surface, in particular with a surface roughness Rq of at most 10 nm,
• Plasma pretreatment of the substrate in a vacuum,
• Application of a base layer made of a polymer comprising at least silicon, oxygen and carbon by means of plasma polymerisation in a vacuum,
• Application of a glossy layer of a metal, a metal alloy or metal compound by means of sputtering in a vacuum and
• Application of an at least partially transparent, wear-resistant top coat of paint.

The object of the present invention was to provide a method with which a protective layer can be produced on a metal substrate that is not a light metal, which does not have some or all of the disadvantages of the prior art described above, or at least only to a reduced extent. In particular, such a layer should have improved elongation at break and low internal stresses, so that cold or hot deformation is better possible. Furthermore, improved chemical stability with respect to alkaline media and, in general, a good anti-corrosion effect are desirable. Such a layer should preferably have a high resistance to abrasion and scratching, so that it can also be applied with layer thicknesses of over 20 μm. In addition, it should be possible to carry out the coating process economically, preferably also in a continuous process.

1. A. Bereitstellen des Metallsubstrates und gegebenenfalls Säubern der zu beschichtenden Substratoberfläche,
2. B. Beschichten der gegebenenfalls in Schritt A gesäuberten Substratoberfläche in einem Plasmapolymerisationsreaktor mittels Plasmapolymerisation, wobei
   • in Schritt B für das Plasma (a) Precursoren bestehend aus einer oder mehreren siliciumorganischen Verbindungen oder (b) Precursor(en) bestehend aus einer oder mehreren siliciumorganischen Verbindungen und weiteren Verbindungen eingesetzt werden und
   • in Schritt B das Metallsubstrates im Plasmapolymerisationsreaktor so angeordnet wird, dass es als Kathode geschaltet ist,
   dadurch gekennzeichnet, dass das Verfahren so geführt wird, dass die durch das Verfahren hergestellte Beschichtung
   • eine Dehnung bis Mikroriss von ≥ 1,5 %, vorzugsweise ≥ 2,5 %
   • einen nach ASTM D 1925 bestimmten Gelbindex (Yellow Index) von ≤ 4, vorzugsweise ≤ 3, weiter bevorzugt ≤ 2,5 und
   • eine mittels Nanoindentation zu messende Härte im Bereich von 2,5 bis 10 GPa, vorzugsweise 3,1 bis 10 GPa, weiter bevorzugt 3,1 bis 6 GPa,
   • einen durch Messung mittels XPS bestimmbaren Anteil von Kohlenstoff von 3 bis 28 Atom-%, vorzugsweise 5 bis 28 Atom-%, weiter vorzugsweise 7 bis 28 Atom-%,
     bezogen auf die Gesamtzahl der in der Beschichtung enthaltenen Kohlenstoff-, Silicium- und Sauerstoffatome
   sowie bevorzugt
   • eine Wärmeleitfähigkeit ≤ 5 W / m°K, vorzugsweise ≤ 2,5 W / m°K und/oder
   • eine elektrische Durchschlagsfestigkeit von 10 - 100 kV/mm, vorzugsweise von ≥ 40 kV/mm
   aufweist,
   mit der Maßgabe, dass das Metallsubstrat kein Leichtmetallsubstrat und kein Titan ist und mit der Maßgabe, dass für den Fall
   einer Dehnung bis Mikroriss der Beschichtung von ≤ 2,2 % die mittels Nanoidentation zu messende Härte ≥ 6 GPa beträgt,
   wobei
   • das Verhältnis der dem Plasma in Schritt B zugeführten Gasflüsse von Sauerstoff und den Precursor(en) im Bereich von 1:1 bis 6:1 liegt
     und
   • während Schritt B eine Regelung erfolgt, so dass der Self-Bias im Bereich von 50 bis 1000 V liegt.

Surprisingly, it has been shown that this object is achieved by a method for coating the surface of a metal substrate as defined in claim 1, with the following steps:

1. A. Provision of the metal substrate and, if necessary, cleaning of the substrate surface to be coated,
2. B. Coating of the optionally cleaned substrate surface in step A in a plasma polymerization reactor by means of plasma polymerization, wherein
   • in step B for the plasma (a) precursors consisting of one or more organosilicon compounds or (b) precursor (s) consisting of one or more organosilicon compounds and further compounds are used and
   • in step B the metal substrate is arranged in the plasma polymerization reactor in such a way that it is connected as a cathode,
   characterized in that the method is carried out in such a way that the coating produced by the method
   • an expansion to micro-cracks of ≥ 1.5%, preferably ≥ 2.5%
   • a yellow index determined according to ASTM D 1925 of 4, preferably 3, more preferably 2.5 and
   • a hardness to be measured by means of nanoindentation in the range from 2.5 to 10 GPa, preferably 3.1 to 10 GPa, more preferably 3.1 to 6 GPa,
   • a carbon content of 3 to 28 atom%, preferably 5 to 28 atom%, more preferably 7 to 28 atom%, which can be determined by measurement by means of XPS,
     based on the total number of carbon, silicon and oxygen atoms contained in the coating
   as well as preferred
   • a thermal conductivity 5 W / m ° K, preferably 2.5 W / m ° K and / or
   • an electrical breakdown strength of 10-100 kV / mm, preferably ≥ 40 kV / mm
   having,
   with the proviso that the metal substrate is not a light metal substrate and not titanium and with the proviso that for the case
   an elongation up to a micro-crack of the coating of ≤ 2.2% the hardness to be measured by means of nanoidentation is ≥ 6 GPa,
   whereby
   • the ratio of the gas flows of oxygen supplied to the plasma in step B and the precursor (s) is in the range from 1: 1 to 6: 1
     and
   • control takes place during step B so that the self-bias is in the range from 50 to 1000 V.

For the purposes of the present invention, metal is a metallic material with a density of> 4.5 g / cm ³ at 20 ° C., titanium being excluded. 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 within the meaning of the present invention with a maximum density of 4.5 g / cm ³ at 20 ° C. For metal substrates, the density of the area on which the coating rests is decisive for classification as a light metal.

The metal substrate is preferably a semi-finished product which is subsequently further deformed in further preferred methods according to the invention.

A coating produced according to the method according to the invention is characterized by a previously unknown advantageous combination of properties that were previously considered incompatible, namely good scratch and corrosion resistance with high elasticity (elongation at break preferably greater than or equal to 2%, in particular greater than or equal to) 2.5%). In addition, the method according to the invention can also achieve good substrate adhesion, good optical transparency in the visible range and / or high layer thickness homogeneity. In addition, the coating preferably has a thermal conductivity of 5 W / m ° 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 yellow discoloration that can be detected by the human eye. In the case of coatings that are intended as transparent protective layers, however, a minimal yellow coloration, such as with a yellow index in the range of over 2.5 to 3, can also be tolerated. The yellowness index is also essentially determined by the proportion of Si-H bonds in the coating produced by the method according to the invention, which, as explained below, is decisive for achieving favorable areas of hardness and elasticity and thus for achieving the advantageous combination of properties. If you want to increase the hardness of the coating and / or if a slightly yellowish color, which can ultimately lead to an intense gold tone, is allowed, then restrictions in the elongation up to micro-cracks must be accepted. The yellow index can be set up to 4 without losing the anti-corrosion effect. To do this, you can increase the self-bias by increasing performance.

Another important parameter is the carbon content in the coating produced with the method according to the invention, which is influenced by the content 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 combination of properties. Due to the high elasticity of the coating, it can be stretched together with the coated object, for example, without cracking. If the coating is very elastic, the substrate can even be plastically deformed without the coating being damaged. This enables forming processes of the coated material to a certain extent.

In the case of the coatings that can be produced by the process according to the invention, the scratch resistance of the layers is in many cases comparable to that of glass surfaces. It turned out, surprisingly, that it is possible by using the (dry chemical) method according to the invention, for. B. to completely dispense with the (wet chemical) chrome plating (decorative chrome plating). This is advantageous because chrome plating is an expensive process due to the high energy consumption and is problematic from an environmental point of view. In addition, dirt-repellent (low-energy) surface properties can be set on the coating surface. The layer property function that can be achieved is not only of interest as a substitute for chromating, but also for the general coating of non-light metals.

From the DE 197 48 240 A1 a method for the corrosion-resistant coating of metal substrates, in particular made of aluminum or aluminum alloys, by means of plasma polymerisation is known. At least one hydrocarbon or organosilicon compound is used as precursor (s). In the DE 197 48 240 A1 there is no information on the proportion of carbon atoms in the plasma polymer coatings produced or on their yellow index. The layers disclosed there protect the surface well against corrosion without changing its appearance. One limitation, however, is their poor scratch resistance. Because of the low deposition rates, the method disclosed there is not suitable for economically producing higher layer thicknesses, as are necessary for scratch protection coatings. In addition, it places very high demands on the surface roughness of the substrate.

In the WO 03/002269 A2 Articles are disclosed comprising a substrate and a plasma polymeric coating comprising O, C and Si, which is connected flatly to the substrate, in which the molar ratios of O to Si and C to Si are each in certain ranges and which can be easily cleaned. However, the coatings disclosed there have a higher carbon content of at least 25 atom% than the coatings which can be produced by the process according to the invention and do not have the abovementioned combination of favorable properties. 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 which effects a certain protection against corrosion (verified by electrochemical impedance spectroscopy). However, the coating disclosed lacks in particular the good scratch resistance and the high extensibility which are inherent in the coating produced according to the invention. It is also characterized by high water absorption, comparable to that of organic coatings. Domingues, et al. does not contain any information regarding yellow coloration or regarding the carbon content. Due to the way the process is carried out (ratio of the gas flows of oxygen to the organosilicon precursor approx. 23: 1; for more information on the influence of these parameters see below), the method described in Domingues et al. The coating disclosed has a lower carbon content than the coating produced by the method according to the invention.

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

Furthermore, no teaching is given to reduce the excess of silicon and thus the formation of Si-H in order to produce particularly hard (well cross-linked), stretchable layers with a low yellow color. The inventive optimized crosslinking ensures optimized corrosion protection behavior.

Thick-film processes, e.g. the application of paints or sol-gel coatings, can achieve the necessary corrosion resistance, but they change the visual appearance. This effect is reinforced in the case of irregularities such as mechanical damage or poor adhesion of the thick layers.

The method according to the invention is able to meet the need for an inexpensive 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 the surface structure (e.g. polishes, sanded, matt), so that no "lacquer gloss" arises, which, in addition to high corrosion stability, has high mechanical resistance (scratch resistance, elasticity) and which has a high level of layer thickness uniformity even with complex geometries.

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 anti-corrosion effect.

By adjusting the hardness and the thickness of the coatings that can be produced by the method according to the invention, it is possible for the 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. If the hardness is too great, the scratch resistance also decreases, since the layer then becomes too brittle. This can be seen, for example, in the microscopic assessment of the defect image. In general, the scratch resistance of the layer is determined by the appropriate selection of layer thickness and composition.

A method according to the invention is preferred which is carried out in such a way that the coating produced by the method has a pencil hardness of 4H or higher, determined in accordance with ASTM D 3362.

When setting 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 should generally be selected than with a low one. The easier it is to ionize a precursor, the lower the plasma power has to be in order to achieve a certain self-bias. With a high electrical conductivity of the plasma, a low plasma power is required in order to achieve a given self-bias.

A method according to the invention is preferred, with regulation taking place during step B so that the self-bias is in the range from 100 to 400 V, preferably in the range from 100 to 300 V.

The self-bias can be reduced, for example, with the plasma power remaining the same, by increasing the plasma excitation frequency. However, it can alternatively and / or preferably by applying an additional DC voltage the electrode can be adjusted or influenced so that it can be adjusted independently of other process parameters.

An increase in the self-bias also leads to an improvement in the homogeneity of the layer thickness. In our own experiments it was found 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 is arranged in the plasma polymerization reactor in such a way that it is connected as a cathode. The metal substrate acts as a cathode when it is in direct electrically conductive contact with that part of the cathode which can be distinguished from the metal substrate. This makes it easier to achieve a high deposition rate of the positively charged ions of the plasma, which are attracted to the cathode. When the substrate itself acts as a cathode, the kinetic energy with which the positively charged ions collide with the surface is increased. This changes the structure of the layer in the direction of a lower proportion of organic groups (usually consisting predominantly of C and H) and a correspondingly higher proportion of Si and O. The same effect also occurs (possibly reduced) when the substrate although it does not act as a cathode, it is arranged in the acceleration path of the cations.

Preferably, according to the invention, no separate ion source is used in the method according to the invention.

Without wishing to be bound by a specific theory, it is assumed that an increased kinetic energy of the ions facilitates the knocking off of organic groups both in the layer-forming ions and in the coating that is formed, with the cleaved groups having a low probability of being converted into 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 elongation up to micro-cracks in the layer. This also made it possible to use this method to produce layer thickness ranges of well over 30 µm. For the measurement of the elongation up to a micro-crack (elongation at break) see example 1.

The same observations (higher separation rate, lower proportion of organic groups, lower internal stress, higher crack elongation) are made when the self-bias is increased. For this reason, hard coatings can have a higher elongation at break than soft ones. In the case of very low self-bias, there is insufficient impact (impact) to relax the coating, which can lead to coatings that are soft (e.g. hardness of 1 GPa measured by nanoindentation) and at the same time crack-sensitive coatings.

However, if the self-bias is increased beyond an advantageous range (see also above), coatings are created that contain too low a proportion of organic groups and too high a proportion of Si-H bonds (see also below), whereby they become too hard and too brittle and their scratch resistance decreases. The aim is therefore to achieve an optimum with regard to the hardness and elasticity of the coating produced by the method according to the invention with an acceptable yellow index (see also below).

An increase in the self-bias in the resulting layer causes, on the one hand, the reduction of internal stresses and thus an effect that increases the elongation at break, and, on the other hand, an increase in hardness and the modulus of elasticity and thus an effect that reduces the elongation at break. Because two opposing effects partially cancel each other out, there is an optimum crack elongation depending on the self-bias, so that an excellent combination of relatively high hardness and high crack formation can be produced.

In addition, an increase in the self-bias leads to an increased deposition rate and improved corrosion resistance in the resulting layer.

The layers that can be produced with the method _{according to the invention are organically modified SiO 2} frameworks. The organic components can be detected in the IR spectrum by bands at approx. 2950 cm ^-1 and at approx. 1275 cm ^-1. They can also 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, the greater the surface energy.

In a method according to the invention, the self-bias is preferably set on the substrate during step B. The dependence of the deposition rate and the layer properties on the 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 makes it easier to achieve a layer with the desired, precisely defined properties.

In a method according to the invention, regulation preferably takes place during step B so that the self-bias is constant. In this way, the structure of the layer can be precisely controlled. Advantages of a self-bias that is as constant as possible are a homogeneous layer structure and simple process transfer to different types of substrates or a plurality of substrates. The self-bias is preferably regulated directly during step B. If the plasma power is regulated, the self-bias will usually not be completely constant, but will fluctuate around a certain value. In such a case, it is preferred if the total fluctuation range of the self-bias is a maximum of 5% of the mean value over time, preferably a maximum of 3%.

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 during In step B, regulation takes place so that the self-bias on the substrate is in the range from 100 to 400 V, more preferably in the range from 100 to 300 V, in particular such that the self-bias is constant.

For a roll-to-roll method, it is preferred that an alternating voltage is applied to the metallic substrate, so that a self-bias is formed on the metallic strip. A microwave discharge can also burn in close proximity to the unwound strip and thus provide the necessary high number of ions.

A method according to the invention is also 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 is increased or increased by an additional external DC voltage is humiliated. This is particularly important if the electrode area is selected to be large and an increase in DC voltage is necessary for this reason.

An increase in the inflow of the organosilicon precursor (s) for the plasma (in relation to possibly also inflowing O _2, in particular while keeping the total inflow constant) generally causes a decrease in hardness, an increase in absorption in the visible range (increase in yellow index), a Deterioration in the anti-corrosion effect and an improvement in the elongation at break.

In the case of a high number of Si — H bonds in a layer produced according to the invention, an increased absorption of light in the ultraviolet and blue spectral range can be determined in the UV / Vis spectrum. This leads to an undesirable yellow coloration (increase in the yellow index). It is therefore desirable not to let the proportion of Si-H bonds become too large. A reduction in the self-bias prevents the formation of Si-H bonds in the coating. The formation of Si-H bonds can also be inhibited by a suitable selection of the amount and / or type of precursor (s). This is usually achieved by reducing the inflow of organosilicon precursors, which in addition 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 if a sufficient amount of oxygen is supplied to the plasma, which in addition also reduces the proportion of organic groups in the coating. A method according to the invention is preferred, in which oxygen (in the form of O ₂ ) is supplied to the plasma in step B and preferably all of the substances supplied to the plasma in step B are gaseous before entry into the plasma polymerization reactor. Conducting the process in such a way that the substances supplied to the plasma are not only gaseous under the conditions of the plasma, but also before they enter the reactor, facilitates the precise adjustment of the dosage of the substances.

An increase in the flow of oxygen leads to an increase in hardness, a reduction in absorption in the visible range (reduction in the yellow index), an improvement in the corrosion protection effect, a reduction in the proportion of organic groups in the coating and a reduction in elongation at break.

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

If a yellow coating is obtained for a given set of parameters, the O ₂ flow can be increased. Alternatively, the inflow to the organosilicon precursor or precursors 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 to the organosilicon precursor or precursors can be increased.

The thermal conductivity as well as the electrical conductivity is only slightly changed by changing the actual plasma parameters in the context of 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 at hand.

A method according to the invention is preferred, in particular in one of the embodiments designated as preferred, with one or more siloxanes, optionally oxygen (O ₂ ) and preferably no further compounds being used as precursor (s) for the plasma in step B. Siloxanes, in particular hexamethyldisiloxane (HMDSO), have proven to be particularly suitable precursors for carrying out a method according to the invention with which coatings with the advantageous combination of properties can be produced. In a method according to the invention, HMDSO, optionally oxygen and preferably no further compound is used as precursor (s) for the plasma in step B. An increase in the inflow of HMDSO in relation to oxygen causes, among other things, a reduction in hardness, an increase in absorption in the visible range and a deterioration in the anti-corrosion effect.

A method according to the invention is particularly preferred 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 precursor (s) supplied to the plasma in step B 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.

In the process according to the invention, the plasma polymerization is preferably carried out at a temperature of less than 200 ° C., preferably less than 180 ° C. and / or a pressure of less than 1 mbar, preferably in the range from 10 ^-3 to 10 ^-1 mbar. If the pressure is too high during the deposition, undesirable powder formation of the deposited material can occur. If the pressure is less than 10 ^-3 mbar, the plasma can no longer be ignited.

In a method according to the invention, step B is preferably carried out up to a thickness of the deposited coating of greater than or equal to 2 μm, preferably greater than or equal to 4 μm. For certain applications, e.g. if extreme abrasion resistance, high dielectric strength or good thermal insulation is required, a higher thickness of> 4 µm, preferably> 50 µm to approx. 100 µm, is possible and also preferred due to the low internal stresses of the coating.

A method according to the invention is preferred, the deposition rate being set to a value greater than or equal to 0.2 μm / min, preferably greater than or equal to 0.3 μm / min, in step B. For example, a value of 0.5 µm / min can be selected. On the one hand, high deposition rates increase the economic viability of the method according to the invention and also make it easier to set the desired layer properties.

In a method according to the invention, the metal substrate is preferably 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 polished and / or gloss-pickled or refined by a chemical, electrochemical or mechanical pretreatment, for example gloss-pickled, electropolished or polished.

It is advantageous to carry out the method according to the invention in such a way that in step A the substrate surface to be coated is cleaned by means of a plasma. Such a plasma cleaning improves the layer adhesion. In the method according to the invention, a gas or gas mixture is preferably added to the plasma in step A to carry out the plasma cleaning, the gas or gas mixture being 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 in such a way that following step B there are non-fragmented organosilicon compounds 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 in that the unfragmented organosilicon precursor or precursors are initially left in the reactor after the plasma source has been switched off and are thus given the opportunity to react with the surface radicals of the plasma polymer layer. This allows layers to be created that are particularly easy to clean. The formation of a near-surface hydrophobic layer can be detected by means of XPS.

The signals C1s, Si2p and O1s are used to quantify the carbon, silicon and oxygen content. To calibrate the stoichiometric measured values, a trimethylsiloxy-terminated polydimethylsiloxane (PDMS) with a kinematic viscosity of 350 mm ² / s at 25 ° C and a density of 0.970 g / mL at 25 ° C is investigated. An example of this is the product DMS-T23E from 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 method preferred according to the invention for carrying out the XPS investigation, see Example 1 below.

In the process mentioned, a layer produced by the process according to the invention preferably contains in the upper 5 nm (facing away from the substrate) a carbon content of 40-55 atom%, a silicon content of 15-25 atom% 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 only applied after the steps essential to the invention have been carried out.

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

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

• in Schritt B wird dem Plasma Sauerstoff zugeführt;
• alle dem Plasma in Schritt B zugeführten Stoffe sind vor Eintritt in den Plasmapolymerisationsreaktor gasförmig;
• das Verhältnis der dem Plasma in Schritt B zugeführten Gasflüsse von Sauerstoff und Precursor(en) im Bereich von 1:1 bis 6:1;
• während Schritt B erfolgt eine Regelung, so dass der Self-Bias auf dem Substrat im Bereich von 100 bis 400 V liegt, vorzugsweise so, dass der Self-Bias konstant ist;
• als Precursor(en) für das Plasma wird Hexamethyldisiloxan (HMDSO), Sauerstoff und vorzugsweise keine weitere Verbindung eingesetzt;
• in Schritt B befindet sich das Metallsubstrat im Kontakt mit einem Teil der Kathode, der vom Metallsubstrat unterscheidbar ist;
• die Plasmapolymerisation wird bei einer Temperatur von weniger als 200°C und einem Druck im Bereich von 10^-3 bis 10^-1 mbar durchgeführt;
• in Schritt B wird die Abscheiderate auf einen Wert von größer oder gleich 0,2 mm/min eingestellt;
• Schritt B wird bis zu einer Dicke der abgeschiedenen Beschichtung von größer oder gleich 2 mm durchgeführt;
• das Metallsubstrat besteht aus Übergangsmetallen wobei Titan ausgeschlossen ist (bevorzugt Ordnungszahlen von 22 bis 30, 39 bis 42, 44 bis 48 und 57 bis 79), Gallium, Germanium, Indium, Zinn, Antimon, Bismut oder deren Legierungen; besonders bevorzugt besteht es aus Legierungen, die Titan, Eisen, Kupfer und/oder Zink enthalten
• in Schritt A wird die zu beschichtende Substratoberfläche mittels eines Plasmas gereinigt, wobei dem Plasma zur Durchführung der Plasmareinigung ein Gas oder Gasgemisch zugesetzt wird, das ausgewählt ist aus der Gruppe bestehend aus: Argon, Argon-Wasserstoff-Gemisch, Sauerstoff;
• das Plasma wird mittels Hochfrequenz erzeugt.

The following applies to a particularly preferred method according to the invention:

• in step B, oxygen is supplied to the plasma;
• all substances fed to the plasma in step B are gaseous before entering the plasma polymerization reactor;
• the ratio of the gas flows of oxygen and precursor (s) supplied to the plasma in step B in the range from 1: 1 to 6: 1;
• control takes place during step B so that the self-bias on the substrate is in the range from 100 to 400 V, preferably such that the self-bias is constant;
• hexamethyldisiloxane (HMDSO), oxygen and preferably no other compound are used as precursor (s) for the plasma;
• in step B the metal substrate is in contact with a part of the cathode which is distinguishable from the metal substrate;
• the plasma polymerization is carried out at a temperature of less than 200 ° C. and a pressure in the range from 10 ^-3 to 10 ^-1 mbar;
• in step B the deposition rate is set to a value greater than or equal to 0.2 mm / min;
• Step B is carried out up to a thickness of the deposited coating of greater than or equal to 2 mm;
• the metal substrate consists of transition metals, titanium being excluded (preferably atomic numbers from 22 to 30, 39 to 42, 44 to 48 and 57 to 79), gallium, germanium, indium, tin, antimony, bismuth or their alloys; it is particularly preferably composed of alloys which contain titanium, iron, copper and / or zinc
• In step A, the substrate surface to be coated is cleaned by means of a plasma, a gas or gas mixture selected from the group consisting of: argon, argon-hydrogen mixture, oxygen being added to the plasma to carry out the plasma cleaning;
• the plasma is generated by means of high frequency.

According to a further aspect, the present invention also relates to a coated metal substrate as defined in the claims, which can be produced by the method according to the invention, preferably in one of the configurations described above as preferred.

• eine Rissdehnung von ≥ 1,5 %, bevorzugt ≥ 2,5 %
• einen nach ASTM D 1925 bestimmten Gelbindex (Yellow Index) von ≤ 4 vorzugsweise ≤ 3, weiter bevorzugt ≤ 2,5 und
• eine mittels Nanoindentation zu messende Härte im Bereich von 2,5 bis 10 GPa, vorzugsweise 3,1 bis 10 GPa, weiter bevorzugt 3,1 bis 6 GPa
• einen durch Messung mittels XPS bestimmbaren Anteil von Kohlenstoff von 3 bis 28 Atom-% bezogen auf die Gesamtzahl der in der Beschichtung enthaltenen Kohlenstoff-, Silicium- und Sauerstoffatome
  sowie bevorzugt
• eine Wärmeleitfähigkeit ≤ 5 W / m°K, vorzugsweise ≤ 2,5 W / m°K und/oder
• eine elektrische Durchschlagsfestigkeit von 10 - 100 kV/mm, vorzugsweise von ≥ 40 kV/mm,

mit der Maßgabe, dass das Metallsubstrat kein Leichtmetallsubstrat und kein Titan ist und mit der Maßgabe, dass für den Fall einer Dehnung bis Mikroriss der Beschichtung von ≤ 2,2 % die mittels Nanoidentation zu messende Härte ≥ 6 GPa beträgt.A metal substrate coated according to the invention as defined in claim 11 comprises a metal substrate and, arranged thereon, a plasma polymer coating with the following features:

• a tear elongation of ≥ 1.5%, preferably ≥ 2.5%
• a yellow index determined in accordance with ASTM D 1925 of 4, preferably 3, more preferably 2.5 and
• a hardness to be measured by means of nanoindentation in the range from 2.5 to 10 GPa, preferably 3.1 to 10 GPa, more preferably 3.1 to 6 GPa
• a carbon content of 3 to 28 atomic%, which can be determined by measurement using XPS, based on the total number of carbon, silicon and oxygen atoms contained in the coating
  as well as preferred
• a thermal conductivity 5 W / m ° K, preferably 2.5 W / m ° K and / or
• a dielectric strength of 10 - 100 kV / mm, preferably ≥ 40 kV / mm,

with the proviso that the metal substrate is not a light metal substrate and not titanium and with the proviso that in the event that the coating is stretched to a micro-crack of ≤ 2.2%, the hardness to be measured by means of nanoidentation is ≥ 6 GPa.

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

In the case of a coated metal substrate according to the invention as defined in the claims, the coating preferably has proportions of 5 to 30 atom%, preferably 10 to 25 atom%, and 30 to 70 atom%, preferably 40 to 60 atom, which can be determined by measurement using XPS -% oxygen, based on the total number of carbon, silicon and oxygen atoms contained in the coating. Regardless of the atom% values mentioned for silicon and oxygen, but preferably in combination with these values, the coating has a carbon content of 3 to 28 atom%, preferably 5 to 28 atom%, more preferably 7 to 28 atom%, based on the total number, which can be determined by measurement using XPS of the carbon, silicon and oxygen atoms contained in the coating. It is particularly easy to set the desired combination of properties in these atomic percent ranges. 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 from 2150 to 2250 cm ^-1 , Si-CH ₂ -Si vibration in the range from 1350 to 1370 cm ^-1 , Si-CH ₃ deformation vibration in the range from 1250 to 1280 cm ^-1 and Si -O oscillation at greater than or equal to 1150 cm ^-1 .

The position of the maximum of the Si-O-Si oscillation provides information about the degree of crosslinking of the layer. The higher its wave number, the higher the degree of networking. 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 anti-stick layers with this maximum typically have a low degree of crosslinking ^{at approximately 1100 cm -1.}

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

The ratio of the intensity of the Si-H band to the intensity of the Si-CH ₃ band can be used to characterize the coating. Coatings in which this ratio is less than or equal to approx. 0.2 are colorless. If the ratio is greater than about 0.3, the coatings are yellowish. A coated metal substrate according to the invention is preferred, the ratio of the intensity of the Si-H band to the intensity of the Si-CH ₃ band being less than or equal to 0.3, preferably less than or equal to 0.2, in an IR spectrum recorded by the coating is.

A coated metal substrate according to the invention is preferred, the coating having an absorption _{constant k 300 nm} of less than or equal to 0.05 and / or an absorption _{constant k 400 nm} of less than or equal to 0.01. The relationship between the number of Si-H bonds, which cause light absorption in the ultraviolet and blue range, with the self-bias, an oxygen supply to the plasma and the amount and type of precursor (s) has already been explained above. The coating of a coated metal substrate according to the invention preferably has a surface energy in the range from 20 to 40 mN / m, preferably 25 to 35 mN / m. As explained above, the surface energy is determined by the proportions of organic groups and thus by the amount of self-bias.

As already stated, the anti-corrosion properties of the coating can be achieved by z. B. Adjustment of the self-bias, the inflows to the organosilicon precursor or precursors and to oxygen. A coated metal substrate according to the invention preferably shows no traces of corrosion that are visible to the naked eye after a 15-minute corrosive attack by NaOH at pH 14 and 30 ° C.

As stated above, the elongation at break is inter alia. determined by setting the self-bias. In the case of a preferred metal substrate according to the invention, the coating has an elongation up to a microcrack (tear 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-mentioned way. In the case of larger reactors, however, the gas flows are also of great importance. This is to be understood as meaning, for example, those reactors in which the reactor chamber (recipient) is 2 m ³ or larger. The homogeneity of the layer thickness, among other things, is defined by the electrical fields generated on the substrate, ie a high field strength means a high deposition rate. Homogeneity can only be achieved if the electrical field strength on the substrate is largely the same everywhere. In general, the following applies: The layer thickness homogeneity on any three-dimensional substrate obeys the Laplace equation, which gives the solution for the electrical field strength on the substrate. In a coated metal substrate according to the invention, the maximum layer thickness preferably 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 that can be produced or produced by a method according to the invention (in particular in an embodiment characterized as preferred) as a protective or functional layer on metals as defined in claim 15.

Further aspects of the present invention as defined in the claims emerge from the following examples, the drawings and the claims.

Example 1: XPS

XPS measurements (ESCA measurements) were carried out with the KRATOS AXIS Ultra spectrometer from Kratos Analytical. The calibration of the measuring device was carried out in such a way that the aliphatic content of the C 1s peaks at 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 Al K _α radiation, an electron source as a neutralizer and a quadrupole mass spectrometer. The system also had a magnetic lens that focused the photoelectrons into a hemisphere analyzer through an entry slot. During the measurement, the surface normal pointed to the entry slit of the hemispherical analyzer. The passenger energy in the determination of the molar ratios was 160 eV in each case. When determining the peak parameters, the pass energy was 20 eV in each case.

The measurement conditions mentioned are preferred in order to enable extensive independence from the spectrometer type and in order to identify plasma polymer products produced according to the invention.

The polydimethylsiloxane silicone oil DMS-T23E from Gelest Inc. (Morrisville, USA) was used as the reference material. 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 ° C and an average molecular weight of approx. 13,650 g / mol. The selected material is characterized by an extremely low proportion of vaporizable components: after 24 hours at 125 ° C and 10 ^-5 Torr vacuum, less than 0.01% volatile components were detected (according to ASTM-E595-85 and NASA SP-R0022A ). It was applied to a silicon wafer as a 40 or 50 nm thick layer with the aid of a spin coating process; 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 element Si O C. Concentration [atom%] 24.76 25.40 49.84 Binding energy [eV] 102.39 532.04 285.00

Example 2: Measurement of hardness using nanoindentation

The nanoindentation hardness of a sample was determined with the aid of a Berkovich indenter (manufacturer: Hysitron Inc. Minneapolis, USA). The calibration and evaluation took place according to the established procedure of Oliver & Pharr (J. Mater. Res. 7, 1564 (1992 )). The machine stiffness and the area function of the indenter were calibrated before the measurement. The "multiple partial unloading" method ( Schiffmann & Küster, Z. Metallkunde 95, 311 (2004 )) is used to obtain depth-dependent hardness values and thus exclude the influence of the substrate.

Example 3: elongation to micro-cracks (elongation at cracks)

To determine the value of the elongation of the microcrack, a 0.5 mm thin and 10 cm long sheet steel (ST 37) is coated in the same way and stretched until optical cracks are visible. The elongation at break is equal to the quotient of the 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 with an IFS 66 / S IR spectrometer from Bruker. The IRRAS technique was used as a method, with the help of which even the thinnest coatings can be measured. The spectra were recorded in the wavenumber range from 700 to 4000 cm ^-1 . Small platelets of very clean and particularly flat aluminum were used 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 flushed with dry air. The spectrum was recorded under such conditions that the water vapor content in the sample chamber was so small that no rotational bands of the water could be seen in the IR spectrum. An uncoated aluminum plate was used as a reference.

The intensity ratio of two bands (peaks) is determined as follows: The baseline (baseline) in the area 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, limited by the two minima which include the maximum, and can easily be determined by a person skilled in the art using known methods. The intensity ratio of two bands is determined by forming the quotient of their intensities. The basic requirement for the comparison of two samples is that the coatings have the same thickness and that the angle of incidence is not is changed.

Embodiments 1 to 4

A zinc sheet is also provided with a transparent, stretchable, scratch-resistant and corrosion-resistant coating.

The substrate is attached to or in the immediate vicinity of the cathode operated with HF (13.56 MHz) (area approx. 15 x 15 cm) so that the substrate itself acts as a cathode. After the rectangular low-pressure reactor with a volume of approx. 360 l and an installed nominal suction capacity of 4500 m ³ / h has been evacuated to a pressure less than 0.02 mbar, oxygen is admitted into the reactor at a flow of 280 sccm. A self-bias voltage of 250 V is set on the substrate with the aid of a high-frequency plasma discharge (13.56 MHz). A sputter etching process takes place under these conditions, in which organic contaminants in particular are efficiently broken down. This step as step A of the method according to the invention has a duration of 5 minutes. The plasma coating is now deposited on the pre-cleaned substrate surface in step B of the method according to the invention. For this purpose, hexamethyldisiloxane (HMDSO) is let into the reactor with a flow of 66 sccm and oxygen with a flow of 280 sccm. The self-bias voltage is regulated in such a way that a value of 100 V, 250 V, 300 V or 400 V is set. After a coating time of 20 minutes, an approx. 4 µm thick layer has deposited on the substrate, which greatly improves the scratch resistance and corrosion protection against alkaline media: Corrosive attack by NaOH (pH 14, 5 minutes, 30 ° C) does not cause any traces of corrosion visible to the naked eye. Coatings 1 to 3 in particular (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 calculated from the ellipsometric data in accordance with the manual for the WVASE32 spectrometer from JA Woolam Co, Inc. Table 2: Optical constants of the coating with the variation of the BIAS voltage. Self-bias n _{250 nm} n _{300 nm} n _{400 nm} k _{250 nm} k _{300 nm} k _{400 nm} 1 100 V 1.58 1.52 1.50 0.015 0.00 0 2 250 V 1.62 1.58 1.54 0.040 0.01 0 3 300 V 1.85 1.76 1.58 0.110 0.06 0.01 4th 400 V 2.20 1.93 1.85 0.210 0.12 0.03

Embodiment 5

A stainless steel sheet (1.4544) was treated by plasma polymerization under the process parameters listed in embodiment 2 (66 sccm HMDSO 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 approx. 8 µm, but a significantly higher elongation at break of 2.8% was observed. The elongation at break for the anodized coating, on the other hand, was only 0.5%.

An eccentric device (Starnberger) was used to determine the scratch resistance on the substrate. Here, an anodized surface approx. 8 µm thick (not according to the invention), an approx. 500 nm thick plasma polymer coating produced according to a prior art method (not according to the invention, exemplarily manufactured according to TW Jelinek, surface treatment of aluminum, Eugen G. Leuze Verlag, Saulgau, 1996 ) and investigated a 4 μm thick plasma polymer coating produced according to the invention. The anodized surface was scratched in a visually perceptible manner after approx. 300 double rubs and the plasma polymer coating not according to the invention after approx. 500 rubs. In the case of the plasma polymer coating produced according to the invention, no optically perceptible scratches could be found even after 10,000 strokes.

The good corrosion protection properties of the coating according to the invention produced by means of plasma polymerization apply in acidic (20% sulfuric acid, 45 min, 65 ° C.) as well as in basic (NaOH, pH 14, 5 min, 30 ° C.) media. After these corrosion tests, no visible damage or infiltration could be found on the coating edges.

The infrared spectrum from this coating shows Figure 1 . The CH stretching vibrations at 2966 cm ^-1 , the Si-H vibration at 2238 cm ^-1 , the Si-CH ₂ -Si vibration at approx. 1360 cm ^-1 , the Si-CH ₃ deformation vibration at can clearly be seen 1273 cm ^-1 , the Si-O oscillations at 1192 cm ^-1 and 820 cm ^-1 . The band ratio (according to Example 4) between Si-H and Si-CH ₃ is approximately 1: 5. The IR spectrum shows a small peak at 1360 cm-1. This band is correlated with a Si-CH ₂ -Si vibration. In addition to the Si-O-Si network, there is thus a 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 approx. 10%, silicon approx. 10%, hydrogen approx. 30% and oxygen approx. 50%. A scanning electron microscope examination of the break edge of the plasma polymer layer shows, on the one hand, a mussel-like break, as is known for brittle materials (glass), and, on the other hand, small, step-like breaks, which are more likely to be expected for crystalline materials.

Embodiment 6

The experiment is carried out as in exemplary embodiment 5, but to increase the deposition rate and thus to shorten the process time, a plasma generator that oscillates at a frequency of 27.12 MHz was used. With the same gas flows (HMDSO: 66 sccm, O ₂ : 280 sccm) and self-BIAS voltage (250 V), the separation rate is increased by a factor of 1.5. The coating properties change only insignificantly and are very similar to those of the coating from embodiment 5.

Embodiment 7

The dependence of the scratch and abrasion protection properties were determined as a function of the layer thickness. 600 µm thick stainless steel sheet (1.4544) was used as the substrate. The layer thickness was defined by the coating time. The scratch protection was checked 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, the layer thickness of which is less than 10 μm, are completely removed, ie the layer thickness after the scratch protection test was 0 nm. From a layer thickness of approx. 17 μm, no significant removal was found, ie the layer thickness remained unchanged. Table 3: Coating parameters for scratch and abrasion protection coatings Bias [V] HMDSO [sccm] O ₂ [sccm] Time [min] Thickness [µm] 200 60 60 5 0.7 200 60 60 10 1.6 200 60 60 20th 3.4 200 60 60 40 7.7 200 60 60 80 17.5 200 60 60 160 36

Embodiment 8

To determine the thermal conductivity, stainless steel sheets were provided with a 15 µm thick layer. The plasma parameters are listed in Table 4. Table 4 Coating parameters for samples 1 and 2. sample BIAS [V] HMDSO [sccm] O ₂ [sccm] Time [min] Thickness [µm] 1 300 60 60 80 15th 2 300 60 180 80 15th

The thermal parameters were determined using the flash method. Its principle is based on suddenly heating the front of a sample with a short pulse of light and then measuring the time delay with which the heated front reaches the back of the sample. Flash methods provide the thermal diffusivity (α) of the sample as the primary measured variable, which can be converted into the thermal conductivity (λ) if the density (p) and heat capacity (Cp) are known. The principle of measurement is in Fig. 2 shown. $$\mathrm{\lambda }\left[\mathrm{W.}/\mathrm{mK}\right]=\mathrm{<figure-callout\; id="2"\; label="\alpha \; mm"\; filenames="imgf0002.png"\; state="\{\{state\}\}">\alpha </figure-callout>}\left[{\mathrm{mm}}^{}\right]\left[{}^{\mathrm{2}}/\mathrm{s}\right]\cdot \mathrm{Cp}\left[\mathrm{J\; /\; gK}\right]\cdot \mathrm{\rho }\left[\mathrm{G}/{\mathrm{<figure-callout\; id="3"\; label="cm"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">cm</figure-callout>}}^{\mathrm{3}}\right]$$

The method can also be used on 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 5: Table 5 Density (density balance based on the buoyancy principle, carrier medium: water, 24 ° C) 7.93 g / cm ³ Heat capacity (power-compensated DSC, 25 ° C) 0.47 J / gK Dimensions of the test specimen for the flash measurement (outside micrometer) 12.7 x 12.7 x 0.58mm ³ Thermal diffusivity 3.85 ± 0.02 mm ² / s (Netzsch Nanoflash LFA 447, 25 ° C) Thermal conductivity (25 ° C) 14.3 W / mK (approx. ± 10%)

The data in Table 6 were measured with a plasma polymer coating. In addition to the thermal conductivity, there is information on the thermal conductivity and thermal resistance. Table 6 Sample ID Thickness [µm] Thermal diffusivity [mm ² / s] Thermal conductivity [W / mK] average thermal conductivity [W / mK] thermal resistance [mm ² K / W] 1st sample position 1 15th 0.124 0.20 0.18 83 1. Sample position 2 0.097 0.16 2nd sample position 1 15th 0.107 0.17 0.18 83 2nd sample position 2 0.110 0.18

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

Example 9

A brass door handle was given a corrosion- and scratch-resistant coating. The door handle was connected as a cathode, so that a constant self-bias voltage of -250 V prevailed during the deposition. After a coating time of 20 minutes and an HMDSO or O ₂ flow of 66 sccm and 280 sccm, a transparent and interference-free layer of approx. 5 µm was created on the handle. The color impression of the handle was unchanged. The resistance of the coating to perspiration was investigated by immersing it in artificial perspiration for 96 hours. The handle showed no visible change, and the layer adhesion was not reduced.

Claims (15)

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

   A. providing the metal substrate,

   B. coating the substrate surface in a plasma polymerisation reactor by means of plasma polymerisation, wherein

   - in step B, (a) precursor(s) consisting of one or more organosilicon compounds or (b) precursor(s) consisting of one or more organosilicon compounds and further compounds are used for the plasma, and

   - in step B, the metal substrate is arranged in the plasma polymerisation reactor in such a way that the metal substrate is connected as a cathode,

   characterised in that the method is conducted in such a way that the coating produced by the method has

   - a strain to microcracking of ≥ 1.5%,

   - a yellow index determined according to ASTM D 1925 of ≤ 4 and

   - a hardness to be measured by means of nanoindentation in the range of 2.5 to 10 GPa,

   - a carbon content, determinable by measurement using XPS, of 3 to 28 atom%, based on the total number of carbon, silicon and oxygen atoms contained in the coating,

   with the proviso that the metal substrate is not a light metal substrate and not titanium
   and with the proviso that in the case of a strain to microcracking of the coating of ≤ 2.2%, the hardness to be measured by means of nanoindentation is ≥ 6 GPa,
   wherein

   - the ratio of the gas flows of oxygen and the precursor(s) supplied to the plasma in step B lies in the range of 1:1 to 6:1

   and

   - during step B, a control is performed, so that the self-bias lies in the range of 50 to 1000 V.
2. Method according to claim 1, wherein the metal substrate is

   - a semi-finished product,

   and/or

   - selected from the group of substrates consisting of brass or brass alloys with cleaned, uncoated surface, copper, nickel silver, bronze, silver, gold or their alloys in each case if necessary with a superficial oxide layer.
3. Method according to claim 1, wherein the method is conducted in such a way that the coating produced by the method has a pencil hardness of 4H or higher.
4. Method according to one of the preceding claims, wherein in step B

   - one or more siloxanes are used as precursor(s) for the plasma.
5. Method according to one of the preceding claims, wherein during step B

   - a control is performed, so that the self-bias lies in the range of 100 to 400 V

   and/or

   - the self-bias is adjusted to the substrate.
6. Method according to one of the preceding claims, wherein the plasma polymerisation is carried out at a temperature of less than 200°C and/or a pressure of less than 1 mbar.
7. Method according to one of the preceding claims, wherein in step B the deposition rate is set to a value of greater than or equal to 0.2 µm/min.
8. Method according to one of the preceding claims, wherein step B is carried out up to a thickness of the deposited layer of greater than or equal to 2 µm.
9. Method according to one of the preceding claims, wherein in step A the substrate surface to be coated is cleaned by means of a plasma.
10. Method according to one of the preceding claims, wherein the plasma is produced by means of high frequency.
11. Coated metal substrate, comprising a metal substrate and arranged thereon a plasma polymer coating, wherein the coating has

    - a strain to microcracking of ≥ 1.5%,

    - a yellow index determined according to ASTM D 1925 of ≤ 4 and

    - a hardness to be measured by means of nanoindentation in the range of 2.5 to 10 GPa,

    - a carbon content, determinable by measurement using XPS, of 3 to 28 atom%, based on the total number of carbon, silicon and oxygen atoms contained in the coating,

    with the proviso that the metal substrate is not a light metal substrate and not titanium
    and with the proviso that in the case of a strain to microcracking of the coating of ≤ 2.2%, the hardness to be measured by means of nanoindentation is ≥ 6 GPa.
12. Coated metal substrate according to claim 11, wherein the coating has one, a plurality of or all the features from the group consisting of:

    - oxygen contents, determinable by measurement using XPS, of 5 to 30 atom%, based on the total number of carbon, silicon and oxygen atoms contained in the coating,

    - an absorption constant k_{300 nm} of less than or equal to 0.05,

    - an absorption constant k_{400 nm} of less than or equal to 0.01,

    - a surface energy in the range of 20 to 40 mN/m

    - a maximum layer thickness which differs from the minimum layer thickness by a factor of 1.1 or less.
13. Coated metal substrate according to claim 11 or 12, wherein an IR spectrum taken of the coating has one or more of the following bands with a respective maximum in the following ranges: C-H stretching vibration in the range of 2950 to 2970 cm^-1, Si-H vibration in the range of 2150 to 2250 cm^-1, Si-CH₂-Si vibration in the range of 1350 to 1370 cm^-1, SiCH₃ scissoring vibration in the range of 1250 to 1280 cm^-1 and Si-O vibration at greater than or equal to 1150 cm^-1.
14. Coated metal substrate according to one of claims 11 to 13, which shows no signs of corrosion visible to the naked eye after a 15-minute corrosive attack of NaOH pH 13.5 and 30°C.
15. Use of a plasma polymer coating producible or produced by a method according to one of claims 1 to 10 or of a plasma polymer coating as defined in one of claims 11 to 14

    - as a protective or functional layer on metals, with the proviso that the metals are not light metals and not titanium,

    and/or

    - wherein the substrate is an injection mould or a part thereof.

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