USE OF A PLASMA POLYMER LAYER AS A SEPARATION LAYER IN NON-FERROUS METAL CASTING

Description

[0001] The invention relates to the use of a plasma-polymerized separating layer as a separating layer for the separation between 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 non-ferrous metal casting.

[0002] Die casting of non-ferrous metals such as zinc, magnesium, and aluminum is becoming increasingly important, especially for lightweight applications. To prevent the component from sticking to the surface of the die-casting tool during the casting process, release agents and associated equipment have been required. However, their use is costly, and thermal quenching can lead to cracking in the tool and thus increased wear.

[0003] Gravity die casting processes are also important, and in particular the low-pressure casting process, as this promotes castings with few pores and defects.

[0004] The use of release agents from the prior art still regularly leads to an irregular surface of the manufactured components in terms of composition and topography, which usually has to be laboriously removed and / or reworked before further processing or use.

[0005] Therefore, in this application area as well, the elimination of release agents through a permanent coating is desirable. However, no solutions are currently known on the market that allow for die casting without release agents, coolants, or lubricants.

[0006] Components made from materials such as zinc die-casting are now high-tech products used in many areas of daily life, including automotive, mechanical engineering, electrical engineering and electronics, construction, and furniture manufacturing. A large proportion of these are decorative zinc die-cast parts, meaning the surface of the zinc component is electroplated (e.g., with high-gloss chrome). In zinc die-casting, liquid zinc alloy is injected into a temperature-controlled (approx. 150–180 °C) mold under high pressure and speed (30–50 m / s) [cf. Ernst Brunhuber, Praxis der Druckgußfertigung, 1991, Berlin, Schiele & Schöne]. Zinc has a low melting point (419.5 °C), and zinc die-casting alloys have a melting range that, depending on their composition, lies within the temperature range of approximately 379 to 404 °C. This enables die-casting tools to have a service life of 500,000 to 2 million castings (see, for example,[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 now highly automated, including the ejection of the castings from the mold, removal, and the routine application of a release agent before the casting cycle. Molds must be equipped with ejectors that push the casting out of the mold before significant thermal shrinkage occurs and the components can no longer be demolded without damage. The application of a release agent before each casting cycle is essential, because otherwise reliable separation of the casting and the metallic mold is not possible.

[0007] The use of release agents remains indispensable to this day, but it has negative effects on the solidification of the molten metal and the quality of the castings. The release agent itself mixes with the molten metal, which is injected turbulently under high pressure, resulting in an uneven distribution of release agent residue across the metal surface.

[0008] The application of liquid mold release agents is fraught with significant problems. After the casting cycle or demolding, the hot mold wall, at temperatures between 140 and 300 °C, is treated with the release agent, preferably by spray application. Due to the hot mold surface, the solvent evaporates rapidly, leaving only a portion of the sprayed release agent (Leidenfrost phenomenon) on the surface. Furthermore, the mold surface cools down. Upon entry of the molten metal, usually several hundred degrees hot, the organic component of the release agent thermally decomposes, forming a gas cushion between the mold wall and the molten metal. While this gas cushion, due to its insulating effect, does lengthen the pouring path as desired, it also dissolves large quantities of gas into the workpiece.These dissolved gases can lead to the formation of pores and thus a negative influence on the mechanical properties of the casting, especially in near-surface areas.

[0009] Typical casting defects resulting from the use of release agents include pores, streaks, roughness, and flow lines on the casting surface. In decorative castings, near-surface defects are only revealed and detected during subsequent grinding and polishing processes. Some defects even become visible only after electroplating (e.g., chrome plating) on ​​the now shiny, reflective surface, leading to scrap, or so-called "high-quality scrap," only at the end of the complex process and value chain. Scrap rates per process step range from 1% to 30% and depend on the casting geometry and specific requirements. For select small production runs with the highest quality standards, total scrap rates of up to 50% can occur. Despite the use of release agents, the formation of an approximately 2 µm thick zinc layer on the mold surface is known to occur.This leads to a significant reduction in surface quality after approximately 20,000 casting cycles, necessitating maintenance of the mold. The residues require extensive mechanical reworking of the tool [cf. Ernst Brunhuber, Praxis der Druckgussfertigung, 1991, Berlin, Schiele & Schöne; Boris Nogowizin, Theorie und Praxis des Druckgusses, 2011, Berlin, Schiele & Schön].

[0010] Reducing the thermally decomposable components by using inorganic release agents has the advantage that these do not decompose under the influence of high temperatures. However, when incorporated into the workpiece, these release agents can negatively affect the surface properties of the castings, leading to discoloration, impaired wettability or paintability, or even defects within the casting. The use of inorganic release agents becomes problematic when the organic components decompose incompletely, as this can result in firmly adhering deposits on the tool surfaces. These deposits are particularly disadvantageous in complex, thin-walled components.

[0011] Durable wear-resistant coatings, such as those produced using CVD and PVD processes, offer a potential solution. These coatings utilize materials like CrN, TiAlN, Al₂O₃, ZrO₂, TiO₂, as well as nitrides and borides. They already allow for a significant reduction in the amount of release agent required. However, applying them to complex shapes with good adhesion is technically challenging. Furthermore, they are typically brittle, exhibit internal stresses, and their coefficient of thermal expansion differs significantly from that of the substrate material. This necessitates complex adhesion promoter layers. Consequently, their use is subject to technical limitations and economic obstacles. For example, CrVN hard coatings have enabled release agent- and coolant-free production of up to 100 pieces in aluminum die casting.

[0012] The state of the art includes the use of plasma-polymer release layers for reactive plastics (PUR, EP, UP), hot melts, and waxes. Such release layers simplify the production process, increase process reliability, and, in particular, reduce cleaning costs. Typical processing temperatures generally do not exceed 190 °C. This also corresponds to the temperature range in which such release layers do not change, for example, through oxidation or thermal degradation.

[0013] Plasma-cured polymer thin films can be used not only as dry release layers on molding tools, but also to coat everyday objects or machine parts, making them easier or even possible to clean. These properties are of particular interest for sensor products, sanitary ware, food and pharmaceutical processing equipment, and molding tools.

[0014] DE 100 34 737 C2 discloses a process for producing a permanent demolding layer by plasma polymerization. The coating is characterized by its gradient structure.

[0015] 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. No information is provided on how to determine the hydrogen content, nor on the crosslinking situation or density determination. However, general information on density and hydrogen content is given. A density range of 0.9–1.15 g / cm³ is specified. From this, a person skilled in the art infers a rather weakly crosslinked layer system. The H / C ratio ranges from 2.25 to 3:1. The examples also fail to provide information on how to determine this ratio. Additionally, information is given on the shift of the Si 2p peak in the XPS spectrum. This value provides information about the close bonding of the silicon. A significant shift compared to PDMS indicates a high number of Si-O bonds.The mechanical properties are described as elastic and crack-free, elongating up to 50%. This further suggests that the coating is soft and could be classified as a plasma-polymerized PDMS. Regarding the production of the layer, it is stated 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 keep internal leakage from residual water to a minimum. No value for the total leakage rate is given. The power required for the process is approximately 7.25 W / sccm. It is kept low to achieve the desired mechanical properties of the layer and to ensure that the operating regime remains within the range of precursor excess.

[0016] WO 2015 / 044247 A1 is a further development with regard to mechanical properties. It describes a plasma-polymer solid that can primarily be used as a release layer in a mold. The plasma-polymer solid is characterized by a high Young's modulus, which depends on the carbon / oxygen ratio. The surface energy, and consequently its polar component, is low, but also significantly dependent on the Young's modulus.

[0017] This application also starts from the premise that the hardness of plasma-polymerized layers is influenced by the ratio of oxygen to organosilicon precursors in the plasma process, and consequently by the ratio of oxygen to carbon in the coating. Accordingly, the teaching of this patent is that, with an organosilicon precursor to oxygen ratio of 2:1, it is possible to increase the Young's modulus, or hardness, by varying the power without significantly affecting the surface energy. This is evident, among other things, from the fact that the maximum position of the Si₂p peak shifts to higher energy levels with increasing Young's modulus. This is a clear indication of a more pronounced Si-O network.

[0018] For coating production, it is specified that plasma systems with RF coupling should preferably be used, designed such that the self-bias remains close to zero. The total leakage rate is specified as less than 0.3 mbar l / s. This corresponds to a limit of 17.75 sccm, which is approximately 50% of the oxygen quantity supplied in the example. The power required for the process can be derived from the examples with values ​​starting at 10.5 W / sccm.

[0019] DE 10 2017 1310851 A1: It is known from the prior art that the crosslinking network of organosilicon PE-CVD layers is a Si-O network which can be continuously modified starting from a PDMS-like layer, ultimately resulting in an amorphous SiOz film. This involves the incorporation of increasing amounts of oxygen into the coating and the removal of hydrocarbons. The process progresses from silicon atoms with two oxygen atoms in close proximity (secondary Si; PDMS) through an increasing number of tertiary and quaternary Si compounds (3 and 4 oxygen atoms in close proximity, respectively) to coatings with purely quaternary Si compounds (SiOz).

[0020] Regarding the materials described, insofar as they have not yet been used for non-ferrous metal casting, there is no indication in the prior art that they can meet the requirements of this specific casting process. This applies in particular to the plasma-polymerized layers described.

[0021] Against this background, the object of the present invention was to provide an improvement for producing a casting in non-ferrous metal casting. Preferably, contamination or surface deterioration of the casting by release agents should be avoided, and long-term usability of the mold should ideally be achieved without repeated application of release agents.

[0022] This problem is solved by using a plasma polymer layer as a separating layer for the separation between mold and casting in non-ferrous metal casting, wherein the plasma polymer layer comprises silicon, hydrogen and carbon.

[0023] In the context of the present invention, the term "mold" encompasses both a classic forming tool and molds and crucibles. A casting mold, casting form, or simply mold, is a hollow body in a foundry into which the molten metal is poured, solidifies, and thus subsequently assumes the inner contour as its outer shape. Permanent molds are preferred for coating.

[0024] A separating layer within the meaning of the present invention is a layer that is provided here between the mold and the casting to enable and / or facilitate the removal of the casting from the mold.

[0025] A casting within the meaning of the present invention is the target product in non-ferrous metal casting.

[0026] Preferably, within the scope of the invention, the non-ferrous metal casting is a non-ferrous metal die casting.

[0027] Surprisingly, it has been found that plasma-polymerized layers, provided they contain silicon and carbon, are also suitable for use in non-ferrous metal casting. This was not apparent from the prior art. For example, it is possible to use separating layers 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. While not bound to any specific theory, the presence of a hydrocarbon network within the plasma-polymerized layer appears to be of particular importance. Separating layers with a relatively large number of CH₂ or CH₂-CH₂ bridges are especially suitable. Such a layer design generally appears to increase temperature resistance and, in particular, mechanical stability.Furthermore, the density of each layer increases.

[0028] Also without being bound to any theory, it is assumed that the surprising stability of the separating layer used according to the invention with respect to the hot metal melt is made possible by three essential aspects: On the one hand, the exclusion of oxygen at the time of highest thermal stress through the direct contact of the plasma-polymer separating layer with the metal melt, so that no oxidation can take place, appears to have a stability-enhancing effect. This subsequently derived assumption can help explain the surprising stability.

[0029] Furthermore, it is common practice in non-ferrous metal casting to temper the mold wall. For example, temperatures in the range of 140 °C to 180 °C are typical in zinc die casting. This causes the molten metal to solidify relatively quickly in the contact area with the parting line, without the parting line being heated to significantly higher temperatures for an extended period, typically less than one second. Thus, the parting line is not exposed to extreme temperature differences for any length of time. In the case of zinc die casting, where very high gate filling speeds of up to 20–60 m / s are used, the literature even indicates that this results in the parting line being exposed to the temperature of the melt for only 10–20 ms.

[0030] Furthermore, 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 which the component is ejected, thus allowing oxygen access to the separating layer, are below the temperature at which the separating layer would thermally oxidize under normal circumstances.

[0031] Thus, it is clear that, presumably due to the process itself, the separating layer exhibits surprisingly high thermal stability under the specific conditions of casting non-ferrous metals, possibly due to the consistent exclusion of oxygen, and also possesses a good heat transfer coefficient. In die casting, high surface qualities are produced using casting techniques, which, depending on the mold condition, can exhibit the following roughness values ​​(Ra values): aluminum alloys 3.0 to 20 µm, magnesium alloys 3.0 to 18 µm, and zinc alloys 2.5 to 18 µm [Association of German Die Casting Foundries (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 to consistently avoid casting defects caused by release agents and to further significantly improve the surface quality.According to the invention, components with roughness classes N1 to N4 can be produced directly, i.e., without post-processing, where N1 corresponds to a roughness value Ra of up to 0.025 µm and N4 to Ra of up to 0.2 µm (surface finish according to DIN ISO 1302). The roughness classes specify value ranges for Ra (average roughness) and Rz (average roughness depth), which are determined according to DIN EN ISO 4287. See https: / / www.messmittel.tools / Messmittel---Messwerkzeuge / 15--Vergleichsmuster---Haertepruefer---Lupen / Oberflaechen-Vergleichsmuster / Oberflaechen-Vergleichsplatten-Satz-fuer-Rauheit--Ra-0-05 --- 12-5 --- m.html.

[0032] The use according to the invention includes coating the mold with the plasma polymer layer.

[0033] It is self-evident that the plasma polymer layer only needs to be applied to the mold once, while subsequently a multitude of inserts in the coated mold are possible in successive castings in non-ferrous metal casting. Logically, the invention also includes the use of a mold or casting tool coated with a plasma polymer layer in non-ferrous metal casting, wherein the plasma polymer layer comprises silicon, hydrogen, and carbon.A preferred use according to the invention is wherein the coated mold, in partial areas of the cavity or even the entire cavity, has a roughness value Ra of ≤ 1.6 µm, preferably ≤ 0.2 µm, more preferably ≤ 0.05 µm, and even more preferably ≤ 0.025 µm on the side facing away from the mold coated with the plasma polymer layer, and / or a roughness depth Rz of ≤ 10 µm, preferably ≤ 1.6 µm, more preferably ≤ 0.63 µm, and even more preferably ≤ 0.25 µm, and / or wherein a casting separated from the coated mold has a roughness value Ra of ≤ 3.2 µm, preferably ≤ 0.4 µm, on its surface (in the area of ​​the mold coated according to the required use). ≤ 0.1 µm, more preferably ≤ 0.05 µm and / or a roughness depth Rz of ≤ 25 µm, preferably ≤ 6.3 µm, more preferably ≤ 2.5 µm, more preferably ≤ 0.63 µm.

[0034] The roughness values, or roughness depths, that are preferred here can be achieved particularly well with the plasma-polymer layers to be used according to the invention, especially with the preferred ones. Those skilled in the art will note that, since the plasma-polymer layers are themselves contour-following, they are applied to suitable prepared substrates, in this case, the mold. In other words, it is self-evident that the mold to be coated must have a suitable roughness depth or roughness value, otherwise the plasma-polymer layer cannot compensate for excessively high values ​​during the standard application process. On the other hand, the plasma-polymer layer to be used according to the invention has the significant advantage that it itself contributes virtually nothing to a change in the corresponding roughness parameters. It does not form any structures itself.

[0035] Because it is possible to achieve very good surface properties with regard to roughness value or roughness depth using the plasma polymer layer to be used according to the invention, it is possible to directly produce castings with a high surface quality.

[0036] A preferred use according to the invention involves the casting of metals selected from the group consisting of lead, tin, zinc, magnesium and their alloys.

[0037] In principle, "non-ferrous metal casting" within the meaning of the present invention is a process in which castings are produced from liquid metals or alloys that do not contain iron. The preferred elements or their alloys have been listed in the preceding paragraph. The aforementioned metals have the following melting points: magnesium 650°C, zinc 419.53°C, lead 327.43°C, and tin 231.93°C. The maximum temperature for casting processes within the meaning of the present invention depends on the specific alloy used and its specific processing temperature at the start of the casting cycle and is referred to as the casting temperature. The highest casting temperature of the listed main alloying elements occurs with magnesium casting alloys and is in the range of 620°C to 730°C. The casting temperature of zinc casting alloys is in the range of 420°C to 580°C, depending on the alloy selected.For the metals tin and lead, the casting temperatures are correspondingly lower, even for their alloys, due to the low melting point of the pure metals.

[0038] The pressure in the die-casting process according to the present invention is in the range of 50 bar to 2000 bar, preferably <500 bar for hot-chamber die-casting. The pressure in the low-pressure die-casting process is in the range of 0.05 bar to 25 bar, preferably <1 bar. In gravity die-casting, no additional pressure is applied due to the nature of the process.

[0039] The preferred materials, as mentioned above, within the meaning of the present invention, are either in their pure form or as an alloy. An alloy of the respective material exists when at least 50 atomic percent consists of the respective material (metal). A preferred alloy within the meaning of this text made from the preferred non-ferrous metals is also one in which the sum of the atomic percent of the preferred metals exceeds 50 percent.

[0040] A preferred use according to the present invention is one in which the plasma polymer layer comprises oxygen.

[0041] Although in some cases it may be preferable to deposit the plasma-polymerized layers without the additional addition of oxygen, oxygen provides a good basis for adjusting desired layer properties, such as hardness, surface energies, etc. Therefore, the layers preferably used according to the invention also include oxygen.

[0042] A preferred use according to the invention is 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.

[0043] With these layer thicknesses, it is possible, on the one hand, to replicate the contours of even complex surface conditions within the mold (which are then of course transferred to the casting), and on the other hand, the preferred layer thickness also exhibits very good heat transfer behavior and sufficient mechanical stability.

[0044] A preferred use according to the invention is wherein the amount-of-substance ratios on the surface of the plasma-polymer layer are measured by means of XPS or microelemental 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: 2.2 - 3.0 measured by microelemental analysis.

[0045] These preferred layer compositions allow for particularly good results in the context of the invention.

[0046] A preferred use according to the invention is wherein the mole fractions of the substance on the surface of the plasma-polymer layer are measured using XPS as follows: 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 excluding H.

[0047] Overall, it should be emphasized that the molar ratios and the absolute molar 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.

[0048] The immediate surroundings of the silicon atoms in the plasma polymer layer are also important for the use according to the invention: It is advantageous in the sense of the present invention if the total degree of crosslinking of the silicon atoms is between 60 and 90%, 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 contained.

[0049] For the purposes of the present invention, the total degree of silicon crosslinking is understood to be the sum of the crosslinkings 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 ).

[0050] A use according to the invention is preferred, wherein the following applies to the plasma polymer layer: Thermal resistance ≤ 100 mm²K / W and / or thermal conductivity ≥ 0.1 W / mK and / or linear coefficient of thermal expansion ≤ 5 E⁻⁴ and / or modulus of elasticity 1–30 GPa, preferably 4–28 GPa, more preferably 8–25 GPa and / or density 0.7–1.9 g / cm³, more preferably 0.8–1.7 g / cm³, more preferably 1.0–1.7 g / cm³ and / or surface energy 22–35 mN / m, more preferably 24–32 mN / m, more preferably 26–32 mN / m.

[0051] In some cases, the interface surface may exhibit surface energies exceeding the values ​​specified here due to use. This is associated with slight oxidation of the interface, resulting in a slight change in the measured elemental ratios.

[0052] In principle, DE 10 2017 131 085 A1 describes how the separating layers for this application are to be produced and provides guidance on how the preferred, aforementioned characteristics can be achieved. However, for applications in non-ferrous metal casting, it may be advisable to increase the Young's modulus and the associated carbon-to-oxygen ratio to provide the necessary mechanical stability. This is possible because the restriction to a maximum surface energy of 30 mN / m is not required. Rather, a surface energy of up to 35 mN / m can also be permitted. Thus, the separating layer remains low-energy.

[0053] In this context, it should be noted that, in addition to the Si-O network known for organosilicon substances, an additional hydrocarbon network is deliberately sought. This is necessary to increase the layer's density and, in particular, to adjust and improve its mechanical wear resistance. The Young's modulus, in conjunction with the surface energy, provides valuable insights here. Ultimately, this approach is crucial for achieving the optimal layer properties and the low-energy, organic character of the dense, highly cross-linked coating.

[0054] A preferred use according to the invention is wherein a high-gloss casting is produced directly by separating it from the mold.

[0055] A high-gloss casting according to the present invention has a roughness class N4 (Ra≤0.2 µm, Rz≤1.6 µm), preferably N2 (Ra≤0.05 µm, Rz≤0.63 µm) and more preferably N1 (Ra≤0.025 µm, Rz≤0.25 µm) or better.

[0056] Due to the use according to the invention, it is possible, with suitable coordination of the shape with the plasma polymer layer to be used according to the invention, to produce castings with an immediately outstanding high-gloss shank.

[0057] Part of the invention also includes a method for preparing a mold for non-ferrous metal casting, comprising the steps of: a) Providing the mold and b) coating in the mold with a plasma polymer coating as defined above, preferably in the preferred embodiments.

[0058] Similarly, the invention also includes a method for producing a casting in a non-ferrous metal casting process, comprising the steps a) Preparing a mold as described above, b) Providing casting compound for the casting, preferably in a mold made of the preferred metals / alloys described above, c) Pouring the casting compound for the casting into the mold, and d) Separating the at least partially hardened casting from the mold.

[0059] With this method according to the invention, it is possible to produce castings of the quality described above.

[0060] A method according to the invention is preferred, comprehensively prior to step c) ba) evacuating the mold cavity of the closed mold to inhibit oxidation of the coating with oxygen from the air and / or bb) flooding the mold with a protective gas to displace atmospheric oxygen so that oxidative damage to the coating is prevented and / or performing step c.), so that surfaces of the plasma polymer coating in contact with atmospheric oxygen do not exceed a temperature of 200°C and / or opening the mold only when the surface temperature of the plasma polymer coating is ≤ 200°C.

[0061] Step ba) and / or step bb) is particularly well suited to avoid possible oxidation damage to the casting.

[0062] 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-polymer coating to be used according to the invention does not exceed a temperature of 200°C. This ensures particularly well that the coating does not degrade and is therefore available for many further cycles. For the same reasons, it may be preferable or additionally advantageous to open the mold only when the surface temperature of the plasma-polymer coating no longer exceeds 200°C.

[0063] However, a method according to the invention is preferred in which the temperature of the surface of the mold is ≤ 300°C, preferably ≤ 200°C.

[0064] These temperature limits ensure that the plasma polymer layer does not degrade. Example:

[0065] The plasma reactor used for the production of the layers according to the invention is a large-volume reactor of approximately 1.2 m³, which is operated with capacitive radio frequency excitation (13.56 MHz). This reactor was built in-house by the Fraunhofer Institute for Applied Molecular Biotechnology (IFAM) in Bremen. The special feature of the system used is that a self-bias close to zero can be reliably achieved for many hexamethyldisiloxane (HMDSO)-based processes, and a very homogeneous plasma is formed throughout the entire free reactor space. The low self-bias is determined by the geometry of the plasma system, whereby the areas of the electrodes and the grounded surfaces are approximately equal in size. Fig. 1 The plasma system used is shown schematically with its most important components.

[0066] The Figure 1represents a diagram of the plasma system used (the electrode forms a U, the remaining wall, not equipped with the electrode, represents the electrical ground for the plasma, which is also U-shaped).

[0067] In the Fig. 1 The reference symbols mean: 1 Grounded reactor chamber 3 Pressure regulating valve 5 Suction to pump station 7 Baffle plate 9 RF electrode 11 Insulation (PE) 13 Gas supply 15 RF feed 17 Match box 19 RF generator

[0068] The process pressure is regulated by an exhaust system with an adjustable butterfly valve. During the process, gas is continuously introduced via the gas inlets (13), and the adjustable exhaust system (5) ensures a constant process pressure. The power is generated by the RF generator (19) and coupled into the plasma via the matchbox (17). The matchbox (17) serves to compensate for the discontinuous ohmic resistance of the plasma. At the same time, the RF generator (19) is protected from backscattered power.

[0069] The self-bias is a DC voltage value measured between the RF input (15) and the grounded reactor. For this purpose, the RF component present at the input (15) is filtered via a coil. The remaining DC voltage is then measured relative to the grounded reactor wall. Along with the process pressure and the applied power, the self-bias value significantly characterizes the plasma process. At a high bias value, the faster electrons migrate towards the grounded reactor surfaces. As a result, the ions are accelerated towards the electrodes and strike the substrate with increased energy. This increases the deposition rate but also affects the layer formation. The fact that layer deposition occurs even in plasma processes with a self-bias of nearly zero volts is due, among other things, to the plasma potential.For energetic reasons, this plasma potential must be the most positive in the equilibrium between the plasma, the electrode, and the grounded wall. This results in a voltage difference typically on the order of 10–150 V. This difference causes a net drift of the ions towards the electrode.

[0070] The total leakage rate was determined to be 0.065 mbar l / s. The pressure rise method was used over 1 hour. A base pressure of 8 x 10⁻³ mbar was chosen.

[0071] To ensure the most consistent initial conditions possible within the plasma system, conditioning was performed prior to layer production. This involved a 3400W process under the conditions specified above for at least one hour. This conditioning ensures that all surfaces within the plasma system are already coated with a plasma-polymerized separation layer, preventing uncontrolled contamination of the samples from previous processes.

[0072] All substrates were placed on the base electrode. To ensure sufficient adhesion of the plasma polymer layer to the test substrates for the subsequent analytical investigations, the substrates underwent a 10-minute oxygen activation (400 sccm oxygen, 1500 W, 0.02 mbar). Depending on the measurement method, the substrates were silicon wafers, aluminum plates, or glass slides, and of course, an insert for the zinc die-casting machine.

[0073] To produce the coating according to the invention, the person skilled in the art will generally prefer to 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 leak rate is ≤ 0.1 mbar l / s, preferably ≤ 0.075 mbar l / s; the ratio of total leak rate to supplied oz flow is ≤ 0.12, preferably ≤ 0.09, further preferably ≤ 0.07; such a high total gas flow is achieved 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 organosilicon precursor to oxygen is ≥ 0.8, preferably approximately 0.8.1 to a maximum of 1.25; the selected organosilicon precursor has a CH3 / Si ratio of ≥ 2.7, preferably ≥ 3, and simultaneously its O / Si ratio based on the total gas volume is ≤ 1.5, preferably ≤ 1.1; the selected organosilicon precursor preferably does not contain silazane compounds; the electrodes are designed so that there are no exposed electrode edges, so that the plasma discharge is visually uniform and of equal intensity throughout the entire space; local, more intense discharges are avoided and / or, in particular, local discharges in the extraction flange are avoided; the system is designed to be large-volume such that a.) the sample arranged on the electrode can be at least 15 cm, preferably 20 to 25 cm, away from the nearest wall, and b.) the clear distance between the chamber walls is at least 50 cm; Large, flat electrodes are used (with capacitive coupling).Their freely accessible area relative to the plasma preferably corresponds approximately to the free area of ​​the electrical mass, so that a self-bias close to zero results during operation and a plasma potential > 20 V, preferably > 50 V, particularly preferably > 100 V. In this context, one speaks of a geometrically symmetrical discharge.

[0074] Further technical information (which, like the preceding information, applies generally and not only to the present example) can be found in DE 102017131085A1. Example of separating layer application:

[0075] 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.

[0076] The substrate used was a mirror sheet (type: SM-SUPER ACHT Classic silver) with a thickness of 1.5 mm from SM STRUKTURMETALL GmbH & Co. KG.

[0077] This coating has an E-modulus of 21 GPa (LaWave measurement) and a surface energy of 29.2 mN / m.

[0078] The following element ratios were obtained using XPS: O: Si: 1.33 C: Si: 1.47 C: O: 1.11

[0079] The H:C ratio was determined to be 2.6 using microelemental analysis.

[0080] This results in the following stoichiometry: Si : O : C : H of 1 : 1.33 : 1.47 : 3.82.

[0081] Regarding the oxidation state of silicon, the following picture was obtained using a peak fitting of the Si(2p) peak: 6.7% primary, 62.3% secondary, 31% tertiary and 0% quaternary compounds.

[0082] From this, a total Si crosslinking degree of 77.4% is calculated, with a proportion of 56.1% Si-O-Si crosslinks (see 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).

[0083] The plasma-polymer layer produced in the exemplary embodiment exhibited heat resistance up to 200°C under the influence of oxygen, whereas under nitrogen purging (exclusion of oxygen), heat resistance up to over 300°C was observed. These properties can be determined very sensitively using an ellipsometer, which measures the layer thickness or refractive index under the respective conditions. The layer thickness decreases if the layers are not stable under the respective gas and temperature influences. Changes in the layer can be detected more easily using XPS, FTIR, or contact angle measurement in the form of oxidation. Example of the use of the separating layer in zinc casting Description of the casting trials:

[0084] The die-casting tests were carried out using a horizontal cold-chamber die-casting machine, type Bühler SC / N 66, and the fine zinc alloy ZAMAK ZL0410 (ZnAl4Cu) was used as the casting alloy. Mirror-coated steel sheets (from the exemplary embodiment of the separating layer application) with dimensions of 100 mm x 40 mm x 1.5 mm were used for the tests. The coated sheets were cast in a die-casting mold to produce composite castings (see [reference]). Fig. 2 ).

[0085] In Fig. 2 : Movable side of the die-casting mold for the production of composite casting specimens.

[0086] In Fig. 2 Reference symbol 1 designates the cavities used.

[0087] As in Fig. 2 As can be seen, the die-casting mold has a four-cavity design. For geometric reasons, only the cavities on the left and right sides of the die-casting mold were used in the present tests.

[0088] After the die-casting mold was fully assembled, the molten zinc was prepared, and the melt feed system was set up, initial casting trials were conducted without sheet metal inserts to determine suitable manufacturing parameters. These trials included a visual assessment to ensure complete filling and a flawless surface. The parameters determined for conducting the casting trials are summarized in Table 1 below. Table 1: Overview of manufacturing parameters parameter Value piston pressure 600 bar piston speed 2.6 m / s, (→ cutting speed: 40 m / s) Melting point 450°C (warming oven) Molding temperature 180°C Casting chamber temperature 200°C (heating cartridge setting) Solidification period 15 sec

[0089] The manufacturing parameters listed in Table 1 were kept constant during the casting trials.

[0090] Before the casting process begins, the entire mold is first sprayed with a water-diluted release agent (Safety-Lube 7477, 1:60, Chem-Trend) and then dried with compressed air. Only then are the coated mirror sheets inserted. By closing the die-casting mold, the sheets are held securely in position by the compression of the two mold halves and cannot slip during the casting process.

[0091] After the closing process is complete, the dosing robot [Pomac Multilink Ladler] 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 completed the dosing process, the die-casting machine's plunger is released to inject the molten metal into the mold cavity. The movement of the plunger, and thus the filling of the mold cavity, can be divided into three phases.

[0092] In the first phase (pre-filling phase), the molten metal is brought relatively slowly (without turbulence) to the gate area. In the second phase (filling phase), the plunger speed is significantly increased so that the molten metal reaches a velocity of approximately 40 m / s at the gate, ensuring that even thin-walled mold contours are completely filled. In the third phase (holding phase), after the mold is completely filled, increased holding pressure is applied to close any porosities that may have formed. After a cooling period of 15 seconds, the component with the molten metal sheets was removed, and the sheets were separated from the component.

[0093] In general, the user will ensure that the mold is easily temperature-controlled and has good heat distribution and dissipation of the heat introduced during the casting process, so that no hot spots are created. The mold material has a sufficiently high thermal coefficient (>25 W / mK), and is possibly operated under reduced pressure, particularly using a vacuum pressure casting process, or the surface temperature at the time of demolding (demolition temperature) is <300°C, preferably <200°C. The mold and casting system for supplying the molten metal are designed for the production of decorative, high-quality surface castings, possibly...A completely separating and lubricant-free ejection system is used to eject the castings. To avoid contamination or to ensure the functionality of the ejector system, 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 (flint) are removed from the surface of the mold before each casting cycle. Measurement example

[0094] The zinc die-cast components manufactured with the coated mirror sheets were examined with regard to their topography.

[0095] The following surface roughness values ​​(values ​​in µm) were obtained using an optical profilometer (Sensofar Plu Neox / measurement method according to DIN EN ISO 4288 / 3 measurements / line measurements): Mirror sheet metal, uncoated Ra: 0.0030 + / -0 Rz: 0.020 + / - 0.002 Mirror sheet metal, coated Ra: 0.0032 + / -0 Rz: 0.020 + / - 0.002

[0096] The cast zinc die-cast component exhibited the following surface roughness values ​​(values ​​in µm) with 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

[0097] Additionally, the achieved roughness classes are indicated on the right.

[0098] The cast mirror-like surface is also reflected in high gloss values ​​(GlossTools gloss meter / average values ​​from 5 measurements). The value increases from 463 (with release agent) to 1483 (with the release layer according to the invention).

[0099] Subsequent investigations using a scanning electron microscope (SEM) revealed the following: Fig. 3 The comparison images shown: In the element contrast, aluminum (black) can be seen embedded in zinc (white).

[0100] With the use of a release agent, a jagged surface with a multitude of holes (pores) is visible, whereas in the case according to the invention, virtually no defects can be found.

Claims

1. Use of a plasma-polymeric layer as release layer for the release between mould and casting in the casting of non-ferrous metals, wherein the plasma-polymeric layer comprises silicon, hydrogen and carbon, and wherein the coating of the mould with the plasma-polymeric layer is included.

2. Use of a mould or casting tool coated with a plasma-polymeric layer in the casting of non-ferrous metals, wherein the plasma-polymeric layer comprises silicon, hydrogen and carbon.

3. Use according to Claim 1 or Claim 2, wherein the coated mould, on the side of the plasma-polymeric layer facing away from the mould, has a roughness value Ra of ≤ 1.6 µm, preferably ≤ 0.2 µm, more preferably ≤ 0.05 µm, more preferably still ≤ 0.025 µm and / or a roughness depth Rz of ≤ 1.0 µm, preferably ≤ 1.6 µm, more preferably ≤ 0.63 µm, more preferably still ≤ 0.25 µm and / or wherein the surface of a casting released from the coated mould possesses a roughness value Ra of ≤ 3.2 µm, preferably ≤ 0.4 µm, more preferably ≤ 0.05 µm and particularly preferably 0.01 µm and / or a roughness depth Rz of ≤ 2.5 µm, preferably ≤ 6.3 µm, more preferably ≤ 2.5 µm and particularly preferably 0.01 µm.

4. Use according to any of the preceding claims, wherein the casting involved is the casting of metals selected from the group consisting of lead, tin, zinc, magnesium and alloys thereof.

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

6. Use according to any of the preceding claims, wherein the plasma-polymeric layer possesses a layer thickness of 5 nm to 20 µm, preferably 200 nm to 10 µm and particularly preferably 400 nm to 5 µm.

7. Use according to any of the preceding claims, wherein the amount-of-substance ratios on the surface of the plasma-polymeric layer, measured via XPS or micro-elemental analysis, are C:O: 0.8-2.0, preferably 0.9-1.6 measured via XPS and / or C:Si: 0.9-1.7, preferably 1.1-1.7 measured via XPS and / or C:Si: 1.0-2.5, preferably 1.2-2.2 measured via XPS and / or H:C 2.0-3.0, preferably H:C 2.0-2.8 measured via micro-elemental analysis.

8. Use according to any of the preceding claims, wherein for the amount-of-substance fractions on the surface of the plasma-polymeric layer, measured via XPS: C: 25-50 at%, preferably 28-47 at% Si: 22-30 at%, preferably 24-30 at% C: 30-65 at%, preferably 32-50 at% based in each case on the total number of atoms in the layer, excluding H.

9. Use according to any of the preceding claims, wherein for the plasma-polymeric layer: - heat resistance ≤ 100 mm2 K / W and / or - thermal conductivity ≥ 0.1 W / mK and / or - linear thermal expansion coefficient ≤ 5 E-4 and / or - elasticity modulus 1-30 GPa, preferably 4-28 GPa, more preferably 8-25 GPa and / or density 0.7-1.9 g / cm3, preferably 0.8-1.7 g / cm3, more preferably 1.0-1.7 g / cm3 and / or - surface energy 22-35 mN / m, preferably 24-32 mN / m, more preferably 26-32 mN / m.

10. Use according to any of the preceding claims for generating a high-gloss casting directly through release from the mould.

11. Method for readying a mould for the casting of non-ferrous metals, comprising the steps of: a) providing the mould and b) coating the mould with a plasma-polymeric coating as defined in any of the preceding claims.

12. Method for producing a casting in the casting of non-ferrous metals, comprising the steps of: a) readying a mould as described in Claim 11, b) providing casting compound for the casting, c) introducing the casting compound for the casting into the mould, and d) releasing the at least partly cured casting from the mould.

13. Method according to Claim 12, comprising before step c) ba) evacuating the mould cavity of the closed mould to inhibit oxidation of the coating with oxygen from the air, and / or bb) flooding the mould with an inert gas to displace the atmospheric oxygen, thereby preventing oxidative damage to the coating, and / or performing step c) so that surfaces of the plasma-polymeric coating that are contacted by atmospheric oxygen do not exceed a temperature of 200°C, and / or opening the mould only when the surface temperature of the plasma-polymeric coating is ≤ 200°C.

14. Method according to Claim 12 or 13, wherein the temperature at the surface of the mould is ≤ 300°C, preferably ≤ 200°C.