WO2022090027A1

WO2022090027A1 - Use of a plasma polymer layer as a separating layer in non-ferrous metal casting

Info

Publication number: WO2022090027A1
Application number: PCT/EP2021/079091
Authority: WO
Inventors: Klaus-Dieter Vissing; Michael Heuser
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung eingetragener Verein
Priority date: 2020-10-26
Filing date: 2021-10-20
Publication date: 2022-05-05
Also published as: DE102020128125A1; EP4232213A1

Abstract

Use of a plasma polymer layer as a separating layer for separating the mold from the cast piece in non-ferrous metal casting, the plasma polymer layer comprising silicon, hydrogen and carbon.

Description

Use of a plasma polymer layer as a separating layer in non-ferrous metal casting

The invention relates to the use of a plasma-polymer separating layer as a separating layer for separating the mold and the casting in non-ferrous metal casting. It also relates to a method for preparing a mold for non-ferrous metal casting and a method for producing a casting in a non-ferrous metal casting.

Die casting for non-ferrous metals such as zinc, magnesium and aluminum is becoming increasingly important, especially for lightweight applications. In order to prevent the component from sticking to the surface of the die-casting tool during the casting process, release agents and the associated equipment have been required up to now. However, their use is cost-intensive and thermal quenching can lead to fire cracking in the

tool and thus to increased wear.

Die casting processes in gravity casting are also important, and in particular the low-pressure casting process, because this favors low-pore and low-defect casting.

The use of the release agents from the prior art also regularly leads to an irregular surface of the components produced in terms of composition and topography, which is usually difficult to remove and/or rework before further processing or use. Therefore, in this area of application, too, there is a desire to eliminate the release agents by means of a permanent coating. However, there are still no known solutions on the market that allow die casting to be carried out without the need for parting, coolant or lubricants.

components from e.g. Zinc die-casts, for example, are high-tech products today that are used in many areas of everyday life, in automobile, mechanical and apparatus engineering, in electrical engineering and electronics as well as in construction and furniture making. The majority are decorative zinc die-cast parts, i. H. the surface of the zinc component is z. B. galvanized (e.g. with high-gloss chrome). In zinc die casting, liquid zinc alloy is cast under high pressure and speed (30 - 50 m/s) [cf. Ernst Brunhuber, Die casting production practice, 1991, Berlin, Schiele & Schöne] injected into the tempered (approx. 150 - 180 °C) mold. Zinc has a low melting point (419.5°C) and zinc die cast alloys have a melting range that is within the temperature range of approximately 379 to 404°C depending on composition. This enables die-casting tools to have a service life of 500,000 to 2 million castings (cf. e.g. Association of German Die-Casting Foundries (VDD) and Federal Association of the German Foundry Industry (BDG) Die-Casting from Non-Ferrous Metals, Technical Guidelines, 2016], zinc die-casting is today highly automated, including the ejection of the cast parts from the mold, removal and the regular application of a release agent before the casting cycle.Casting molds must be provided with ejectors that eject the cast part from the mold before a relevant temperature shrinkage sets in and components and no longer free of damage The application of a release agent before each casting cycle is essential, because otherwise a reliable separation of the cast part and the metal mold is not possible.

The use of release agents is therefore still indispensable today, but has negative effects on the solidification of the molten metal and the quality of the cast part. The separating agent itself mixes with the turbulently injected molten metal under high pressure, so that the volume of the metal surface is unevenly mixed with separating agent residues.

The application of liquid mold release agents is associated with significant problems. After the casting cycle or after demoulding of the casting, the hot mold wall is exposed to the release agent at temperatures in the range of 140 - 300 °C, preferably by spray application. Due to the hot mold surface, the solvent evaporates quickly, leaving only part of the sprayed release agent (Leidenfrost phenomenon) on the surface. In addition, the mold surface cools down. With the onset of the molten metal, which is usually several hundred degrees hot the organic part of the release agent is thermally decomposed and forms a gas cushion between the mold wall and the cast metal. Due to the insulating effect, this gas cushion leads to the desired lengthening of the casting paths, but on the other hand large quantities of gas are released in the workpiece. These dissolved gases can lead to the formation of pores and thus have a negative impact on the mechanical properties of the casting, especially in areas close to the surface.

Typical casting defects caused by the use of release agents are, for example, pores, streaks, roughness and flow lines on the surface of the casting. In the case of decorative castings, defects close to the surface are only exposed and detected in the subsequent process steps of grinding and polishing. Some defects only become visible after the galvanic coating (e.g. chrome plating) on the then shiny, reflective surface and only lead to scrap at the end of the complex process and value chain, the so-called "precious scrap". The scrap rates per process step are in a wide range of 1 - 30% and depend on the casting geometry and the respective requirements. For selected small series with the highest quality requirements, total reject rates of up to 50% can occur. Despite the use of release agents, the build-up of an approx. 2 μm thick zinc layer on the Mold surface known. This already leads to a significant reduction in surface quality after about 20,000 casting cycles, which requires maintenance of the mold. The residues require a complex mechanical revision of the tool [cf. Ernst Brunhuber, Praxis der Druckgußfertigung, 1991, Berlin, Schiele & Schöne, Boris Nogowizin, Theory and Practice of die-casting, 201 1 , Berlin, Schiele & Schön],

Reducing the thermally decomposable proportions by using inorganic release agents has the advantage that they do not decompose under the influence of high temperatures, but these release agents can have a negative impact on the surface properties of the cast body, such as discoloration, when embedded in the workpiece the wettability or paintability or lead to defects in the interior of the casting. The use of inorganic release agents becomes problematic if the organic components do not decompose completely, which can then lead to caking on the tool surfaces. In the case of complex, thin-walled components in particular, this caking is a disadvantage.

Permanent anti-wear coatings, such as those produced using CVD and PVD processes, represent a possible solution. CrN, TiAIN, AI2O3, ZrÜ2, T1O2, as well as nitrides and borides are used. They already allow a significant reduction in the amount of release agent. However, it is technically not trivial to apply them firmly to complex shapes. In addition, they are mostly brittle, have residual stresses and differ significantly from the substrate material in terms of thermal expansion coefficients. This requires expensive adhesion promoter layers. In this respect, there are technical limitations and economic obstacles to their use. CrVN hard material layers could e.g. For example, in the case of aluminum die-casting, up to 100 pieces can be produced without the need for any parting or coolant.

The state of the art includes the use of plasma polymer separating layers for reactive plastics (PUR, EP, UP), for hot melts and for waxes. Such separating layers simplify the production process, increase the reliability of the process and, in particular, save on cleaning costs. However, the usual processing temperatures generally do not exceed 190 °C. This also corresponds to the temperature range in which such separating layers do not change, e.g. B. by oxidation or by thermal degradation.

Plasma polymer thin layers can not only be used as a dry separating layer on shaping tools, but also to equip commodities or machine parts to facilitate or enable their cleaning. Such properties are of particular interest for sensor products, for sanitary products, for articles in food and pharmaceutical processing, as well as e.g. B. for shaping tools.

DE 100 34 737 C2 discloses a method for producing a permanent release layer by plasma polymerisation. The coating is characterized by its gradient structure.

DE 10 2006 018 491 A1 discloses a flexible plasma polymer product with a PDMS-like layer structure and thus a soft and sensitive product. A specific layer composition is claimed here. Information on determining the hydrogen content is not given, nor is any information on the crosslinking situation or on determining the density. However, general information on density and hydrogen content can be found. A range of 0.9-1.15 g/cm ³ is given for the density. From this, the person skilled in the art concludes that the layer system is rather weakly crosslinked. The H/C ratio is in the range from 2.25 to 3:1. The examples also contain no information on how the ratio is to be determined. In addition, information on Shift of the Si 2p peak in the XPS spectrum. This value provides information about the local bonding conditions of the silicon. A large shift from PDMS is indicative of a high number of Si-O bonds. The mechanical properties are described as elastic and stretchable up to 50% without cracking. This is another indication that the coating is soft and could be called plasma polymeric PDMS. When creating the layer, it is pointed out that the total external leakage rate should be less than 1% of the amount of oxygen supplied to the process, and that care must be taken to ensure that the internal leakage from residual water is kept small. There is no value for the overall leak rate. The power required for the process is around 7.25 W/sccm. It is kept small in order to be able to achieve the mechanical properties of the layer and to ensure that the working regime is in the range of the precursor excess.

WO 2015/044247 A1 is a further development with regard to the mechanical properties. It describes a plasma polymer solid that can be used primarily as a separating layer in a mold. The plasma polymer solid is characterized by a high modulus of elasticity, with the modulus of elasticity being dependent on the C/O ratio. The surface energy and consequently the polar part thereof are low, but also clearly dependent on the modulus of elasticity.

In this application, too, the starting point is that the hardness of plasma polymer layers is influenced by the ratio of oxygen to silicon-organic precursors in the plasma process and, as a result, the ratio of oxygen to carbon in the coating. Accordingly, the teaching of this patent specification is that it is possible, with a ratio of silicon-organic precursor to oxygen of 2 to 1, to increase the modulus of elasticity or the hardness by varying the power without having too great an influence on the surface energy. This circumstance can be recognized, among other things, by the fact that the maximum position of the Si2p peak shifts to higher energy levels as the Young's modulus increases. This is a clear indication of a more pronounced Si-O network.

To produce the coating, it is stated that plasma systems with HF coupling should preferably be used, which are designed in such a way that the self-bias remains close to zero. The overall leak rate is specified as less than 0.3 mbar l/s. This corresponds to a limit value of 17.75 sccm and is therefore about 50% of the amount of oxygen supplied in the example. The power required for the process can be derived from the examples with values from 10.5 W/sccm. DE 10 2017 1310851 A1: It is known from the prior art that the crosslinking network of silicon-organic PE-CVD layers is a Si-O network, which can be continuously modified starting from a PDMS-like layer, so that in the end an amorphous SiC >2 film is created. More and more oxygen is thus built into the coating and, in return, hydrocarbons are removed. Starting with silicon atoms, which have two oxygen atoms in the immediate vicinity (secondary Si; PDMS), through an increasing number of tertiary and quaternary Si compounds (3 or 4 oxygen atoms in the immediate vicinity) to coatings with purely quaternary Si compounds ( SiO?).

With regard to the materials described, provided they have not yet been used for non-ferrous metal casting, there are no indications in the prior art that they can meet the demands that this special casting process entails. This also applies in particular to the plasma polymer layers described.

Against this background, it was the object of the present invention to specify an improvement for the production of a casting in non-ferrous metal casting. Contamination or deterioration of the surface of the casting due to release agents should preferably be avoided and long-term usability of the mold should ideally be achieved without repeated application of release agents.

This object is achieved by using a plasma polymeric layer as a separating layer for separating the mold and the casting in non-ferrous metal casting, the plasma polymeric layer comprising silicon, hydrogen and carbon.

In the context of the present invention, the term “mold” includes both a classic shaping tool and molds and crucibles. In the foundry, a casting mould, casting mold or mold for short is a hollow body into which the liquid melt is poured, where it solidifies and the inner contour then takes on the outer shape. Permanent forms are to be preferred for the coating.

A separating layer within the meaning of the present invention is a layer that is provided here between the mold and the casting in order to enable and/or facilitate the removal of the casting from the mold.

A casting within the meaning of the present invention is the target product in non-ferrous metal casting. Within the scope of the invention, the non-ferrous metal casting is preferably non-ferrous metal die-casting

Surprisingly, it has been found that plasma polymer layers, if they include silicon and carbon, are also suitable for use in non-ferrous metal casting. This was not recognizable from the prior art. For example, it is possible to use separating layers, which are described in WO 2015/044247 A1 or DE 10 2017 1310851 A1, in non-ferrous metal casting. This also applies in particular to the layers and layer compositions described in more detail below. It seems - without being bound to a theory - the presence of a hydrocarbon network within the plasma polymer layer to be of particular importance. Separating layers that have a relatively large number of CH2 or CH2-CH2 bridges are particularly suitable. Layer configurations of this kind generally appear to increase temperature resistance and, in particular, mechanical stability. In addition, there is an increase in the density of the respective layer.

Also without being bound to a theory, it is assumed that the surprising stability of the separating layer to be used according to the invention in relation to the hot metal melt is made possible by three essential aspects: On the one hand, the exclusion of oxygen at the time of maximum thermal stress appears due to the direct contact of the plasma polymer separating layer with the Molten metal so that oxidation can no longer take place, to increase stability. This assumption, obtained in hindsight, can help explain the surprising stability.

In addition, it is regularly the case that the mold wall is often tempered in non-ferrous metal casting. Temperatures in the range of 140 °C - 180 °C are typical for zinc die-casting, for example. This means that the molten metal solidifies relatively quickly directly in the contact area with the separating layer, without the separating layer being heated to significantly higher temperatures over a longer period of time, i.e. usually a period of less than 1 second, and thus the separating layer not for a longer period of time exposed to extreme temperature differences. For the example of zinc die casting, in which very high gate filling speeds of up to 20 - 60 m/s are used, this leads to a temperature load on the separating layer at the level of the melt temperature for only 10 - 20 ms, even according to the literature.

In addition, it is possible that a large amount of heat is dissipated via the already solidified metal layer and also via the separating layer itself. The temperature ranges in at which the component is ejected and thus allows oxygen access to the separating layer are below the temperature at which the separating layer thermally oxidizes under normal circumstances.

It is thus clear that, presumably due to the process, the separating layer has a surprisingly high thermal stability under the special process conditions of casting non-ferrous metals, possibly because of the consequent lack of oxygen, and on the other hand has a good heat transfer coefficient.

In the die-casting process, high surface qualities are produced by casting, which can have the following roughnesses (Ra values) depending on the mold condition: aluminum alloys 3.0 to 20 pm, magnesium alloys 3.0 to 18 pm and zinc alloys 2.5 to 18 pm [Association of German Die Casting Shops (VDD) and Federal Association of the German Foundry Industry (BDG) Die-casting of non-ferrous metals Technical Guidelines], the use according to the invention makes it possible that casting defects based on release agents can be consistently avoided and the surface quality can be significantly improved again. According to the invention, components can be produced directly, i.e. without post-treatment, which have roughness classes N1-N4, with N1 corresponding to a roughness value Ra of up to 0.025 μm and N4 to an Ra of up to 0.2 μm (surface quality according to DIN ISO 1302). The roughness classes specify value ranges for Ra (average roughness value) and Rz (average roughness depth), which are determined according to DIN EN ISO 4287. See https://www.messmittel.tools/Messmittel— Messtools/15-- Benchmarks— Hardness testers— Lupen/Oberflaechen-Vergleichsmuster/Oberflaechen-Vergleichsplat- ten-Satz-fuer-Rauheit--Ra-0-05— 12- 5—m.html

Consequently, it is preferred according to the invention if the use according to the invention also includes the coating of the mold with the plasma polymer layer. It is of course clear that the plasma polymeric layer only has to be applied to the mold once, while a large number of uses in the coated mold in subsequent castings in non-ferrous metal casting are subsequently possible.

As a logical consequence, part of the invention is also the use of a mold or a casting tool coated with a plasma polymer layer in non-ferrous metal casting, the plasma polymer layer comprising silicon, hydrogen and carbon.

Preferred is a use according to the invention, wherein the coated form, in partial areas of the cavity or the entire cavity on the side facing away from the mold plasma polymeric layer has a roughness value R _a of <1.6 μm, preferably <0.2 μm, more preferably <0.05 μm, even more preferably <0.025 μm and/or a roughness depth R _z of <10 μm, preferably <1, 6 μm, more preferably <0.63 μm, even more preferably <0.25 μm and/or wherein a casting separated from the coated mold has a roughness value on its surface (in the area of the mold coated according to the required preferred use). R _a of <3.2 μm, preferably <0.4 μm, more preferably <0.1 μm, even more preferably <0.05 μm and/or a surface roughness R _z of <25 μm, preferably <6.3 μm , more preferably <2.5 pm, even more preferably <0.63 pm.

The roughness values that are preferred here, or the roughness depths, can be achieved particularly well with the plasma polymer layers to be used according to the invention, in particular with the preferred ones. In this context, the person skilled in the art will note that the plasma polymer layers, since they themselves reproduce contours, are applied to suitably prepared substrates, in this case the mold. In other words, this means that it goes without saying that the form to be coated must have a suitable peak-to-valley height or a suitable peak-to-valley height, since otherwise the plasma polymer layer cannot compensate for values that are too high when applied as a rule. On the other hand, the plasma polymeric layer to be used according to the invention has the great advantage that it hardly contributes to a change in the corresponding roughness parameters. It does not form any structures itself.

Because it is possible to achieve very good surface characteristics with regard to the roughness value or roughness depth with the plasma polymer layer to be used according to the invention, it is possible to directly produce castings with a high surface quality.

A use according to the invention is preferred, which involves the casting of metals selected from the group consisting of lead, tin, zinc, magnesium and their alloys.

Basically, "non-ferrous metal casting" in the sense of the present invention is a process in which castings are produced from liquid metals or alloys that do not contain iron. The elements to be used with preference and their alloys have been listed in the previous paragraph. The metals mentioned have the following melting temperatures: magnesium 650° C., zinc 419.53° C., lead 327.43° C. and tin 231.93° C. have the following melting temperatures. The maximum temperature for casting processes within the meaning of the present invention depends on the particular alloy used and its specific processing temperature at the start of the casting cycle and is called the pouring temperature. The highest casting temperature of the main alloying elements listed occurs in magnesium casting alloys and is in the range from 620°C to 730°C. The casting temperature of cast zinc alloys is between 420°C and 580°C, depending on the alloy selected. For the metals tin and lead, due to the low melting temperature of the pure metals, the casting temperatures are also correspondingly lower for their alloys.

The pressure in the die-casting process within the meaning of the present invention is in the range from 50 bar to 2000 bar, preferably <500 bar for hot-chamber die-casting. The pressure in the low-pressure casting process is in the range from 0.05 bar to 25 bar, preferably in the range <1 bar. Due to the process involved, no additional pressure is applied during gravity casting.

The preferred materials, as mentioned above, for the purposes of the present invention are present either as a pure substance or as an alloy. An alloy of the corresponding material is present if at least 50 atom % consists of the respective material (metal). A preferred alloy within the meaning of this text from the preferred non-ferrous metals is one in which the sum of the atomic percentages of the preferred metals exceeds 50%.

A use in which the plasma polymeric layer comprises oxygen is preferred within the meaning of the present invention.

Even though it may be preferable in some cases to deposit the plasma polymer layers without the additional addition of oxygen, the oxygen forms a good basis for desired layer properties, such as e.g. B. hardness, surface energies, etc. set. The layers to be used with preference according to the invention therefore preferably also comprise oxygen.

A use according to the invention is preferred in which the plasma polymer layer has a layer thickness of 5 nm to 20 μm, preferably 200 nm to 10 μm and particularly preferably 400 nm to 5 μm.

With these layer thicknesses, it is on the one hand easily possible to reproduce the contours of even complicated surface conditions within the mold (which are of course then transferred to the casting), on the other hand the preferred layer thickness also shows very good heat transport behavior and sufficient mechanical stability. Preference is given to a use according to the invention, in which the substance quantity ratios on the surface of the plasma-polymer layer are measured by means of XPS or elementary microanalysis

C:O: 0.8-2.0, preferably 0.9-1.6 measured by XPS and/or

O:Si: 0.9-1.7, preferably 1.1-1.7 measured by XPS and/or

C:Si: 1.0-2.5, preferably 1.2-2.2 measured by XPS and/or

H:C 2.0 - 3.0, preferably H:C 2.2 - 3.0 measured by micro elemental analysis.

With these preferred layer compositions, particularly good results can be achieved in terms of the use according to the invention.

A use according to the invention is preferred, in which case the proportions of amounts of substance on the surface of the plasma polymer layer measured by means of XPS apply:

O: 25 - 50 at%, preferably 28 - 47 at%

Si: 22 - 30 at%, preferably 24 - 30 at%

C: 30-65 at%, preferably 32-50 at%, each based on the total number of atoms contained in the layer without H.

Overall, it should be emphasized that the substance amount ratios and the absolute substance amount fractions are important for the layer properties of the separating layer to be used, but they alone are not decisive for achieving all layer properties.

The vicinity of the silicon atoms in the plasma polymer layer is also important for the use according to the invention: it is advantageous in the context of the present invention if the overall degree of crosslinking of the silicon atoms is between 60 and 90%, is preferably between 65 and 85% and at the same time the degree of silicon crosslinking via hydrocarbon bridges is between 5 and 50%, preferably between 10 and 40%, based on the total number of silicon atoms present.

For the purposes of the present invention, the overall degree of silicon crosslinking is to be understood as the sum of the crosslinks by means of Si-O-Si and Si-alkyl-Si-like bridges (cf. Brenner T., Vissing K. "New insight into organosilicon plasma-enhanced chemical vapor deposition layers and their crosslinking behavior by calculating the degree of Si-networking", Plasma Process Polym. 2020; e1900202. https://doi.org/10.1002/ppap.201900202).

A use according to the invention is preferred, where the following applies to the plasma polymer layer:

- Thermal resistance < 100 mm ² K/W and/or

- Thermal conductivity > 0.1 W/mK and/or

- coefficient of linear thermal expansion < 5 E-4 and/or

- Modulus of elasticity 1-30 GPa, preferably from 4-28 GPa, more preferably 8-25 GPa and/or

Density 0.7-1.9 g/cm ³ , preferably 0.8-1.7 g/cm ³ , more preferably 1.0-1.7 g/cm ³ and/or

- Surface energy 22-35 mN/m, preferably 24-32 mN/m, more preferably 26-32 mN/m.

In some cases it is possible that the surface of the separating layer has surface energies that are higher than the values given here. Associated with this is a slight oxidation of the separating layer, so that the measured element ratios change slightly.

In principle, DE 10 2017 131 085 A1 describes how the separating layers are to be produced for this application and provides information on how the preferred, aforementioned features can be achieved. However, for use in non-ferrous metal casting, it may be advisable to increase the modulus of elasticity and the associated C/O substance ratio, to provide the necessary mechanical stability. This is possible because the restriction to a maximum surface energy of 30 mN/m is not necessary. Rather, a surface energy of up to 35 mN/m can also be permitted. Thus, the separating layer still remains low-energy.

In this context it should be pointed out that in addition to the Si-O network known for organosilicon substances, an additional hydrocarbon network is deliberately sought. This is necessary in order to increase the density of the layer and, in particular, to adjust and improve mechanical wear resistance. The modulus of elasticity with the surface energy provides good information here. Ultimately, this approach is important for adjusting the optimal layer properties in order to achieve the low-energy, organic character of the dense, highly crosslinked coating.

A use according to the invention is preferred, in which case a high-gloss casting is produced directly by separation from the mold.

A high-gloss casting within the meaning of the present invention has a roughness class N4 (Ra<0.2 pm, Rz<1.6 pm), preferably N2 (Ra<0.05 pm, Rz<0.63 pm) and more preferably N1 (Ra <0.025 pm, Rz<0.25 pm) or better.

Due to the use according to the invention, it is possible, if the mold is suitably matched to the plasma polymer layer to be used according to the invention, to produce castings with an immediately outstanding high-gloss property.

Part of the invention is also a method for preparing a mold for non-ferrous metal casting, comprising the steps: a) providing the mold and b) coating in the mold with a plasma polymeric coating as defined above, preferably in the preferred embodiments.

Analogously, part of the invention is also a method for producing a casting in a non-ferrous metal casting, comprising the steps a) preparing a mold as described above, b) providing casting compound for the casting, preferably in the mold in the preferred ones described above metals/alloys, c) pouring the casting compound for the casting into the mold and d) separating the at least partially hardened casting from the mold.

With this method according to the invention, it is possible to produce castings in the quality described above.

Preference is given to a method according to the invention, comprising, before step c), ba) evacuating the mold cavity of the closed mold in order to inhibit oxidation of the coating with oxygen from the air and/or bb) flooding the mold with an inert gas in order to displace the oxygen in the air, so that oxidative damage to the coating is prevented and/or

Carrying out step c.) so that surfaces of the plasma polymer coating that come into contact with atmospheric oxygen do not exceed the temperature of 200° C. and/or

Do not open the mold until the surface temperature of the plasma polymer coating is < 200°C.

In this case, step ba) and/or step bb) is particularly well suited to avoiding possible oxidation damage to the casting.

Alternatively or additionally, it is advantageous to carry out the step according to the invention in such a way that, in combination with oxygen, the plasma polymeric coating to be used according to the invention does not exceed a temperature of 200°C. This is a particularly good guarantee that the coating does not degrade and is therefore available for many more cycles. For the same reasons, it can be preferable or additionally useful to open the mold only when the surface temperature of the plasma polymer coating no longer exceeds 200°C.

However, preference is given to a method according to the invention in which the temperature of the surface of the mold is <300° C., preferably <200° C.

These temperature limits ensure that the plasma polymer layer does not degrade. Example:

The plasma reactor used to produce the layers to be used according to the invention is a large-volume reactor of approximately 1.2 m 3 which is operated with capacitive radio frequency excitation (13.56 MHz). This is a self-construction of the Fraunhofer - IFAM, Bremen. What is special about the system used is that for many hexamethyldisiloxane (HMDSO)-based processes, a self-bias close to zero can be reliably achieved and a very homogeneous plasma is formed in the entire free reactor space. The low self-bias is determined by the geometry of the plasma system, with the areas of the electrodes and the grounded surfaces being approximately the same. In Fig. 1, the plasma system used is shown schematically with its most important components.

FIG. 1 shows a schematic of the plasma system used (the electrode forms a U, the remaining wall not provided with the electrode represents the electrical ground for the plasma, which is also U-shaped accordingly).

In FIG. 1, the reference symbols mean:

I Grounded reactor chamber

3 pressure control valve

5 Suction to the pump stand

7 baffle plate

9 HF electrode

I I Insulation (PE)

13 gas supply

15 RF feed

17 matchbox

19 HF generator The suction with an adjustable butterfly valve is used to control the process pressure. During the process, gas is fed in continuously via the gas supply lines (13) and the adjustable suction (5) ensures a constant process pressure. The power is generated by the HF generator (19) and coupled into the plasma via the matchbox (17). The Matchbox (17) is used to compensate for the discontinuous ohmic resistance of the plasma. At the same time, the HF generator (19) is protected from backscattered power.

The self-bias is a DC voltage value, which is measured between the HF feed (15) and the grounded reactor. For this purpose, the HF component present at the feed (15) is filtered via a coil. The remaining DC component is related to the grounded reactor wall. The value of the self-bias significantly characterizes the plasma process in addition to the process pressure and the irradiated power. With a high bias value, the fast electrons have migrated to the grounded reactor surfaces. As a result, the ions are accelerated in the direction of the electrodes and hit the substrate with increased energy. This increases the deposition rate, but also influences the layer formation. The fact that layers are deposited even in plasma processes with a self-bias of almost zero volts can be attributed to the plasma potential, among other things. For energetic reasons, this plasma potential must be the most positive in the balance between plasma, electrode and grounded wall. This results in a voltage difference of typically 10 - 150 V. This difference ensures a net drift of the ions towards the electrode.

The overall leak rate was determined to be 0.065 mbar l/s. The pressure rise method over 1 hour was used. 8*10-03 mbar was chosen as the base pressure.

In order to be able to show the same initial conditions in the plasma system as possible, the plasma system was conditioned before the layers were produced. This is the process with 3400W of power under the conditions indicated above for a period of at least one hour. This conditioning ensures that all surfaces within the plasma system are already provided with a plasma polymer separating layer and that there is no uncontrolled contamination of the samples from previous processes.

All substrates rested on the base electrode. In order to obtain sufficient adhesion of the plasma polymer layer for the following analytical investigations on the test substrates, the substrates were activated with oxygen (400 sccm oxygen, 1500 W, 0.02 mbar) for 10 minutes. The substrates are different Measuring method for silicon wafers, aluminum plates or glass slides and of course for an insert for the zinc die-casting system.

To produce the coating according to the invention, the person skilled in the art will generally preferably observe some or all of the process instructions in DE 102013219331 and/or observe one or more or all of the following measures, namely that

- the total leakage rate is <0.1 mbar l/s, preferably <0.075 mbar l/s;

- the ratio of the total leak rate to the O 2 flow supplied is <0.12, preferably <0.09, more preferably <0.07;

- such a high total gas flow is realized that the calculated total residence time in the plasma is >10 s and <30 s (preferably <20 s);

- a working pressure (with plasma discharge) of <0.03 mbar, preferably <0.02 mbar and >0.01 mbar is used;

- the flow ratio of silicon-organic precursor to oxygen> 0.8, preferably about 1 to a maximum of 1, 25 is;

- the selected organosilicon precursor has a CHs/Si ratio of >2.7, preferably >3, and at the same time its O/Si ratio, based on the total amount of gas, is <1.5, preferably <1.1;

- If possible, the selected organosilicon precursor does not have silazane compounds;

- the electrodes are designed in such a way that there are no exposed electrode edges, so that the plasma discharge is visually uniform and equally strong throughout the room;

- Local, more intense discharges are avoided and/or

- In particular, local discharges in the suction flange are avoided.

- the system is designed with a large volume so that a.) the sample arranged on the electrode can have a distance of at least 15 cm, preferably 20 to 25 cm, from the nearest wall and b.) the clear distance between the chamber walls is at least 50 cm;

- Large-area, flat electrodes are used (with capacitive coupling). Its freely accessible area compared to the plasma preferably corresponds approximately to the free area of the electrical ground, so that during operation there is a self-bias close to zero and preferably a plasma potential >20 V, preferably >50 V, particularly preferably >100 V connection one speaks of a geometrically symmetrical discharge.

Further technical information (which, like the previous ones, applies generally and not only to the present example) can be found in DE 102017131085A1.

Exemplary application of the separating layer:

A coating according to the invention was produced under the above conditions with an HMDSO flow of 77 sccm and an admixture of oxygen of 68 sccm at a power of 3400 W and a pressure of 0.016 mbar.

A mirror sheet (type: SM-SUPER EIGHT Classic Silver) with a thickness of 1.5 mm from SM STRUKTURMETALL GmbH & Co. KG was used as the substrate

This coating has a Young's modulus of 21 GPa (LaWave measurement) and a surface energy of 29.2 mN/m.

The following element ratios were obtained using XPS:

O: Si: 1.33

C: Si: 1.47

C:O:1.11

The H:C ratio was determined to be 2.6 by means of elementary microanalysis.

This results in the following stoichiometry: Si:O:C:H of 1:1.33:1.47:3.82.

With regard to the oxidation state of the silicon, the following picture resulted with the help of a peak fitting of the Si(2p) peak:

6.7% primary, 62.3% secondary, 31% tertiary and 0% quaternary compounds. From this, an overall degree of Si crosslinking of 77.4% is calculated, with a proportion of 56.1% Si-O-Si crosslinking (cf. Brenner T, Vissing K. New insight into organosilicon plasma-enhanced chemical vapor deposition layers and their crosslinking behavior by calculating the degree of Si-networking. Plasma Process Polym. 2020;e1900202. https://doi.org/10.1002/ppap.201900202).

The plasma polymer layer produced in the exemplary embodiment had a heat resistance of up to 200° C. under the influence of oxygen, whereas heat resistance of up to more than 300° C. was determined under nitrogen gassing (oxygen exclusion). These properties can be determined very sensitively with the help of an ellipsometer, which measures the layer thickness or the refractive index under the respective conditions. The layer thickness decreases if the layers are not stable under the respective gas and temperature influence. It is easier to find changes in the layer using XPS, FTIR or using the contact angle measurement in the sense of oxidation.

Example Use of the separating layer in cast zinc

Description of the casting tests:

The die-casting tests were carried out with a Bühler SC/N 66 horizontal cold-chamber die-casting machine and the fine zinc alloy ZAMAK ZL0410 (ZnAI4Cu) was used as the casting alloy. For the tests, mirror steel sheets (from the exemplary embodiment of the separating layer application) measuring 100 mm×40 mm×1.5 mm were used. The coated panels were cast in a die to produce composite casting samples (see FIG. 2).

In Fig. 2: Movable side of the die for the production of composite casting samples.

In FIG. 2, reference number 1 designates the cavities used.

As can be seen in FIG. 2, the die-casting mold has a 4-cavity cavity. For geometric reasons, only the cavities on the left and right side of the die were used in the present tests.

After the complete assembly of the die casting mold, the provision of the molten zinc and the installation of the molten metal feed, casting tests were carried out without sheet metal inserts in order to determine suitable production parameters. For this purpose, an optical assessment was made with regard to complete filling and a flawless surface performed. The parameters determined for carrying out the casting tests are summarized in Table 1 below.

Table 1: Overview of manufacturing parameters

The manufacturing parameters listed in Table 1 were kept constant during the casting tests.

Before the start of a casting process, the entire mold is first sprayed with a water-diluted release agent (Saefty-Lube 7477, 1:60, from Chem-Trend) and then dried with compressed air. Only then are the coated mirror sheets inserted. By closing the die, the metal sheets are held securely in their position by pressing the two mold halves together and cannot slip during the casting process.

After completion of the closing process, the dosing robot [Pomac Multilink Lädier] is released and the molten zinc is poured into the casting chamber of the cold chamber die casting machine using a ceramic melting spoon. Once the robot has completely completed the dosing process, the movement of the pouring plunger is released Die casting machine that presses the melt into the mold cavity. The movement of the plunger or the filling of the mold cavity can be divided into 3 phases.

In phase 1 (pre-run phase), the melt is brought relatively slowly (without turbulence) to the gate area. In the 2nd phase (filling phase), the plunger speed is greatly increased so that the melt at the gate reaches a speed of approx. 40m/s, so that even thin-walled mold contours can be completely filled. In phase 3 (holding pressure phase), after the mold has been completely filled, increased holding pressure is applied in order to close any porosities that may have occurred. After a cooling time of 15 seconds, the component with the metal sheets poured over it was removed and the metal sheets were detached from the component.

In general, the user will ensure that the mold can be easily temperature controlled and has good heat distribution and dissipation of the heat introduced from the casting process, so that no hot spots arise.

- the material of the casting mold has a sufficiently high thermal coefficient (>25 W/mK),

- If necessary, work is carried out under negative pressure, in particular in the form of a vacuum pressure casting process/or

- The surface temperature at the time of demolding the casting (demolition temperature) is <300°C, preferably <200°C.

- the casting mold and the casting system for feeding the molten metal are designed for the production of decorative high-quality surface castings,

- if necessary, an ejection system that works completely free of separating agents and lubricants is used to eject the cast parts in order to avoid contamination or

- to ensure the functionality of the ejector system, the lubricants are reduced to a minimum and their use is limited locally to the area of the moving guide surfaces (ejector pin and bore),

- the coated mold surface is not damaged by improper use of hard tools, - small metal residues (flakes) are removed from the surface of the mold before each casting cycle.

measurement example

The cast zinc components produced with the coated mirror sheets were examined with regard to their topography.

Using an optical profilometer (Sensofar Plu Neox / measurement method according to DIN EN ISO 4288 / triple measurements / line measurements), the following surface roughness values (data in pm) were obtained:

Mirror sheet, uncoated Ra: 0.0030 +/-0 Rz: 0.020 +/- 0.002

Mirror sheet, coated Ra: 0.0032 +/-0 Rz: 0.020 +/- 0.002

The cast zinc die-cast component had the following surface roughness values (in μm) with a release agent or with the release layer according to the invention:

Cast component, with release agent Ra: 0.16 +/- 0.07 Rz: 1.84 +/- 0.56 N4

Cast component, with separating layer Ra: 0.02 +/- 0.00 Rz: 0.19 +/- 0.11 N1

In addition, the roughness value classes achieved are indicated on the right.

The cast mirror finish surface is also expressed in high gloss values (GlossTools gloss meter / mean values from 5-fold determination). The value increases from 463 (with release agent) to 1483 (with release layer according to the invention).

Subsequent examinations in the scanning electron microscope (SEM) resulted in the comparison images shown in Fig. 3:

In the element contrast, aluminum (black) embedded in zinc (white) can be seen.

With a release agent, a jagged surface with a large number of holes (pores) appears, whereas in the case according to the invention there are almost no more defects to be found.

Claims

- 23 - Claims:

1 . Use of a plasma polymer layer as a separating layer for the separation between mold and casting in non-ferrous metal casting, the plasma polymer layer comprising silicon, hydrogen and carbon.

2. Use according to claim 1, wherein the coating of the mold with the plasma polymer layer is included.

3. Use of a mold or a casting tool coated with a plasma polymer layer in non-ferrous metal casting, the plasma polymer layer comprising silicon, hydrogen and carbon.

4. Use according to claim 2 or claim 3, wherein the coated mold on the side of the plasma polymer layer facing away from the mold has a roughness value R _a of <1.6 μm, preferably <0.2 μm, more preferably <0.05 μm, even more preferably <0.025 μm and/or a surface roughness R _z of <1.0 μm, preferably <1.6 μm, more preferably <0.63 μm, even more preferably <0.25 μm and/or wherein a from the coated form separate casting on its surface a roughness value R _a of <3.2 μm, preferably <0.4 μm, more preferably <0.05 μm and particularly preferably 0.01 μm and/or a surface roughness Rz of <2.5 μm, preferably <6.3 μm, more preferably <2.5 μm and particularly preferably 0.01 μm.

5. Use according to one of the preceding claims, wherein the casting is the casting of metals selected from the group consisting of lead, tin, zinc, magnesium and their alloys.

6. Use according to any one of the preceding claims, wherein the plasma polymeric layer comprises oxygen.

7. Use according to one of the preceding claims, wherein the plasma polymer layer has a layer thickness of 5 nm to 20 μm, preferably 200 nm to 10 μm and particularly preferably 400 nm to 5 μm.

8. Use according to one of the preceding claims, wherein the substance quantity ratios on the surface of the plasma-polymer layer are measured using XPS or micro-elemental analysis C:O: 0.8-2.0, preferably 0.9-1.6 measured by XPS and/or

O:Si: 0.9-1.7, preferably 1.1-1.7 measured by XPS and/or

C:Si: 1.0-2.5, preferably 1.2-2.2 measured by XPS and/or

H:C 2.0 - 3.0, preferably H:C 2.0 - 2.8 measured by micro elemental analysis.

9. Use according to one of the preceding claims, wherein the following applies to the proportions of amounts of substance on the surface of the plasma polymer layer measured by means of XPS:

O: 25 - 50 at%, preferably 28 - 47 at%

Si: 22 - 30 at%, preferably 24 - 30 at%

10. Use according to one of the preceding claims, wherein the following applies to the plasma polymer layer:

- Thermal resistance < 100 mm ² K/W and/or

- Thermal conductivity > 0.1 W/mK and/or

- coefficient of linear thermal expansion < 5 E-4 and/or

E modulus 1-30 GPa, preferably 4-28 GPa, more preferably 8-25 GPa and/or density 0.7-1.9 g/cm ³ , preferably 0.8-1.7 g/cm ³ , more preferably 1.0-1.7 g/cm ³ and/or

- Surface energy 22-35 mN/m, preferably 24-32 mN/m, more preferably 26-32 mN/m.

11 . Use according to one of the preceding claims for producing a high-gloss casting directly by separation from the mould.

12. A method of preparing a mold for non-ferrous metal casting, comprising the steps of: a) providing the mold and b) coating the mold with a plasma polymeric coating as defined in any one of the preceding claims.

13. A method for producing a casting in a non-ferrous metal casting, comprising the steps: a) preparing a mold as described in claim 12, b) providing casting compound for the casting, c) filling the casting compound for the casting into the mold and d) separating the at least partially solidified casting from the mold.

14. The method according to claim 13, comprising before step c) ba) evacuating the mold cavity of the closed mold in order to inhibit oxidation of the coating with oxygen from the air and/or bb) flooding the mold with an inert gas in order to displace the atmospheric oxygen , so that oxidative damage to the coating is prevented and / or

Do not open the mold until the surface temperature of the plasma polymer coating is < 200°C. - 26 -

15. The method according to claim 13 or 14, wherein the temperature at the surface of the mold is <300°C, preferably <200°C.