Connection arrangement for a pressure vessel, pressure vessel having connection arrangement and method for manufacturing a connection arrangement

Abstract

The present invention relates to a method for manufacturing a sealing assembly for gases, the method comprising the following steps: providing a metal part which has an assembly contact surface, heating the assembly contact surface of the metal part and coating the assembly contact surface with a first thermoplastic material, wherein the assembly contact surface reaches a predefined first temperature above the melting temperature of the first thermoplastic material in order to produce an integral connection between the assembly contact surface and the first thermoplastic material, applying a second thermoplastic material as a gas-tight layer and integrally connecting same to the coating which has the first thermoplastic material, and cross-linking the first thermoplastic material and the second thermoplastic material by way of heating to a second temperature.

Description

[0001]1 263 867 t3 Connection arrangement for a pressure vessel, pressure vessel with connection arrangement, and manufacturing method for a connection arrangement. TECHNICAL FIELD The present subject matter relates to a manufacturing method for a sealing assembly for gas, a gas-tight sealing assembly, and a connection arrangement for a pressure vessel. BACKGROUND OF THE INVENTION The storage, transport, and use of gases place specific demands on lines and containers for handling these gases. The first two requirements apply to mobile compressed gas storage, while in a fuel storage system (e.g., in a ship or a truck), all three requirements must be taken into account in order to use the respective gas safely and efficiently.The pipes and containers used for storage, processing, and transport are typically made of different materials, such as metals and / or polymers. It is important to ensure a permanently sealed connection between the different materials so that the gas can be stored and transported under high pressure. Furthermore, energy-efficient transport requires that the containers be as lightweight as possible. One example in which different materials are combined to form a sealed assembly is so-called fiber-encased gas pressure storage tanks. These typically have a metallic connector (a so-called "boss"), while the remaining pressure vessel is formed by a fiber sheath with an internal, gas-tight liner.Particularly at the connection points between the metallic connector for supplying and / or discharging gas and the gas-tight polymer liner, several materials are combined, making it particularly challenging to create a substantially gas-tight and structurally resilient connection between these materials. Hydrogen poses a particularly significant challenge in this context. Due to its size, the gas diffuses most quickly through materials and thus sets the standard for tightness in compressed gas containers. SUMMARY OF THE INVENTION The connection between these different materials therefore represents a crucial challenge for the transport of gases and their storage in compressed gas containers, which forms the basis of the present application.The object is, in particular, to provide a sealing connection that improves pressure resistance, leak resistance, and operational reliability, as well as a connection arrangement having such a sealing connection. A further object was to provide a manufacturing method for this purpose. In view of these objects, the subject matter defined in the independent claims is presented as a solution, with the dependent claims specifying preferred embodiments. Thus, a method for producing a gas-tight connection is defined, which comprises the following steps. First, a metal part is provided that has a connection contact surface. The connection contact surface of the metal part, and preferably the entire metal part, is heated to a predetermined first temperature above the melting temperature of a first thermoplastic.Furthermore, before, during, and / or after heating the composite contact surface, the first thermoplastic is applied to form a coating that is integrally bonded to the composite contact surface. In a further step, a second thermoplastic is applied as a gas-tight layer, which is bonded to the previously applied coating, which comprises the first thermoplastic. Furthermore, the first thermoplastic and the second thermoplastic are cross-linked by heating to a second temperature. By first applying a first thermoplastic to the metal part as an intermediate layer, it is possible to form an improved gas-tight seal over the second thermoplastic.The bond thus created between the metal surface of the metal part, the first thermoplastic, and the second thermoplastic is not only gas-tight, but also exhibits greater structural strength than if the second thermoplastic, which can form a gas-tight liner, were applied directly to the metal part. It has been found that initially coating the metal part with a first thermoplastic by melting it results in a surprisingly stable and strong bond. This observation is also attributed to the comparatively high heat capacity of the metal part, which is heated above the melting temperature of the first thermoplastic for the coating. It is assumed that this makes the melting process of the coating particularly uniform. Furthermore, the coating process is limited in particular to the composite contact surface of the metal part.If this were not the case, uneven heating and cooling would occur outside the metal part, possibly leading to different material properties. This is prevented by the second thermoplastic acting as a gas-tight liner, which only requires a bond to the first thermoplastic, not to the metal part, for it to function properly. This bond is achieved on the one hand by melting the first and second thermoplastics and on the other hand by crosslinking the two thermoplastics. By using a first temperature for coating, while crosslinking takes place at a different, second temperature, reliable and mutually independent process control can be achieved when creating the bond between the metal part and the first thermoplastic, on the one hand, and between the first thermoplastic and the second thermoplastic, on the other.In the above method, the composite contact surface is a surface designed for a material-to-material connection with a thermoplastic. In particular, the composite contact surface has an (average) surface roughness in a range from Rz = 40 µm to Rz = 60 µm, in a range from Rz = 45 µm to Rz = 55 µm, or essentially Rz = 50 µm. The composite contact surface preferably has recesses, such as elongated pockets. In addition to the material connection described above, these recesses also enable a positive connection. Such a positive connection makes it possible to apply higher forces in the plane of the composite contact surface (without the recesses). The metal part can be inserted into a mold before the application of the second thermoplastic, wherein the second thermoplastic is preferably applied using a shaping process, such as rotational molding (in particular a rotational sintering process).It is possible to coat the metal part with the first thermoplastic before or after insertion into the mold. The rotational sintering process makes it particularly possible to form larger parts, such as containers or tanks. These parts are created during the application of the second thermoplastic to the first thermoplastic. In other words, the second thermoplastic extends beyond the first thermoplastic and forms a solid body in addition to the gas-tight wall. Particularly preferably, a first additive is added to the first thermoplastic for coating the metal part, and the first thermoplastic is heated to the reaction temperature of the first additive in order to bond with the composite contact surface of the metal part. The first additive is thus designed to support and strengthen a material-to-material bond between the coating and the metal part.For this purpose, the reaction temperature of the first additive is preferably above the melting temperature of the first thermoplastic. The first additive preferably has a structure with the chemical formula 1 described in more detail below. In addition, in the method, preferably for applying the gas-tight layer, a second additive is added to the second thermoplastic and the second thermoplastic is heated to the reaction temperature of the second additive. The second additive is designed to crosslink the second thermoplastic and improve the material bond between the second thermoplastic and the first thermoplastic. The reaction temperature of the second additive is preferably above the reaction temperature of the first additive and / or above the melting temperature of the first thermoplastic. Particularly preferably, the second additive heated above its reaction temperature also causes crosslinking of the second thermoplastic with the first thermoplastic.The reaction temperature for the second additive is in particular selected such that the first thermoplastic melts at least in one contact area with the second thermoplastic, thus causing crosslinking with the first thermoplastic in this area in addition to internal crosslinking of the second thermoplastic. An additive, such as the second additive, can also be provided in the first thermoplastic in order to promote stronger crosslinking between the first thermoplastic and the second thermoplastic. The first thermoplastic preferably comprises or consists of polyethylene, polypropylene and / or polyamide. The gas-tight layer preferably comprises or consists of X-polyethylene, X-polypropylene and / or X-polyamide. The first thermoplastic and the second thermoplastic are particularly preferably based on the same polymer (i.e. in particular polyethylene, polypropylene and / or polyamide).The metal part preferably comprises or consists of an aluminum alloy and / or a steel alloy, in particular a stainless steel alloy. Furthermore, the method may further comprise a step of applying a reinforcement layer, in which a reinforcement layer made of a material is applied that has a higher tensile strength and a higher modulus of elasticity than the gas-tight layer. Particularly preferably, the reinforcement layer is formed by applying a filament, in particular a polymer filament. In particular, the reinforcement layer has the filament embedded in a matrix. In other words, the reinforcement layer may comprise a filament-reinforced polymer. The filament may be at least one so-called continuous fiber, a plurality of short fiber filaments, and / or a fabric made from filaments. Furthermore, the present disclosure provides a gas-impermeable sealing composite.This sealing composite comprises a metal part, an intermediate layer made of a first thermoplastic, which is designed as a material-to-material coating of a composite contact surface of the metal part, and a gas-tight layer made of a second thermoplastic, which is material-to-material bonded to the first thermoplastic. A sealing composite designed in this way makes it possible to ensure a permanently gas-tight and mechanically strong connection between a metal part and a section of a gas device made of a polymer. In the sealing composite, a first additive is preferably bound in the coating comprising the first thermoplastic, which increases the hydrogen bonds between the metal part and the coating. This improvement in the hydrogen bond enables an increase in the strength of the material-to-material bond between the metal part and the coating.Preferably, the first additive is also provided to increase the wettability of the composite contact surface of the metal part with the first thermoplastic during the coating process. Furthermore, the material-to-material bond between the coating comprising the first thermoplastic and the gas-tight layer comprising the second thermoplastic preferably comprises crosslinking, wherein the crosslinking is based on a second additive and in particular promotes intramolecular chemical bonds. The crosslinking between the first thermoplastic and the second thermoplastic increases the strength of the material-to-material bond between the coating and the gas-tight layer. Furthermore, the present disclosure provides a connection arrangement for a pressure vessel, in which the metal part is designed for a detachable connection to a gas device and is part of a sealing assembly.The sealing connection is preferably designed and / or manufactured as described above. The connection arrangement thus makes it possible to create a firm and gas-tight connection between a metal part and a polymer part within a gas device. It thus supports the purpose-optimized design of a gas device in that polymer materials and metals can be used advantageously depending on the task of a section of the gas device. BRIEF DESCRIPTION OF THE FIGURES The following figures illustrate preferred embodiments. These embodiments are not to be understood as limiting, but instead serve to better understand the claimed subject matter. In the figures, like reference numerals refer to features that have a substantially similar function and / or structure. Figure 1 illustrates a preferred embodiment of the method in accordance with the present disclosure.Figure 2 illustrates a metal part inserted into a mold with a coated composite contact surface. Figure 3 illustrates the metal part of Figure 2 inserted into the mold after the application of the second thermoplastic. DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS Figure 1 illustrates steps a to e, which a method for producing a sealing composite for gases in accordance with the present disclosure may comprise. Step (a) is a schematic illustration of a provision of a metal part 10. As described above, the metal part 10 may be made, for example, from an aluminum alloy or a steel alloy. In a device intended for gas (hereinafter referred to as a gas device), such metal parts 10 may be used, for example, where increased mechanical or thermal stress exists.This is particularly the case at connection points between different components of a gas device, especially when the connection points are detachable. However, if, for example, the weight of a device intended for gas plays a role, such as in the transport of gas or in a mobile fuel storage system, the use of polymer materials is preferred. The latter can also be produced cost-effectively. However, these polymer materials may not be suitable for the connection points mentioned above or for locations where they are exposed to high thermal stress. In such cases, it is advantageous to combine such polymer materials with metal parts, such as the metal part 10, to form a sealed composite.The example of a metal part 10 illustrated in the figures is a connecting part that is used in a gas pressure storage system to create a connection to a part of a gas device. Such a connection can be a permanently installed connection or a detachable connection. The connecting part illustrated in the figures is also referred to as a "boss" and is used to connect a gas tank to a gas device. Such metal parts 10 have a correspondingly high specific gravity. To save weight, these metal parts for a gas device are therefore preferably joined with polymer materials. This forms a sealed bond in which different materials are combined or joined in such a way that they meet the requirements for a specified gas tightness (see, for example, the technical rules for operational safety TRBS 2141-3).For this purpose, a metal part 10 in accordance with the present disclosure has a composite contact surface 11. The surface of the composite contact surface 11 is preferably not polished. It preferably has a roughness that is achieved by the machining itself (e.g., turning or milling) or by a corresponding treatment (e.g., grinding, sandblasting, etching, anodizing). The mean roughness Ra is preferably in a range from 0.2 µm to 50 µm, and the roughness depth Rz is particularly in a range from 1 µm to 250 µm or in the range already specified above. In addition, the metal part 10 can have recesses 14 in the composite contact surface 11 that are designed for a positive connection with the polymer part to be connected (see Figures 2 and 3). Such recesses 14 can, for example, be elongated pockets whose longitudinal direction is arranged transversely to a direction of a force to be applied to the sealing connection.The provision of such recesses 14 in addition to the material-to-material connection with the first thermoplastic has the advantage that, in particular, shear forces can be better absorbed or transmitted by the sealing composite. After the metal part 10 has been provided, the coating 20 with the first thermoplastic takes place (step (b) in Figure 1). For this purpose, the metal part 10 is preferably coated with a coating material containing the first thermoplastic (for example, a powder). The metal part 10 is preferably electrostatically charged and / or masked for the application of the coating material in order to coat the metal part and in particular the composite contact surface 11 in a targeted and defined manner. To create a material-to-material connection between the coating 20 comprising the first thermoplastic and the composite contact surface 11, the metal part is heated to or above the melting temperature of the first thermoplastic.Heating can occur before, during, or after the application of the coating material. The melting of the first thermoplastic caused by the heating results in the creation of a material bond with the metallic composite contact surface (for example, when using a powdered coating material in a sintering process). In this context, it is assumed that, in particular, the heat capacity of the metal part 10 and the associated uniform temperature distribution and longer-lasting temperature retention result in a stronger bond between the metal part 10 and the coating 20. The first thermoplastic preferably comprises or consists of polyethylene, polypropylene, and / or polyamide.Taking into account the melting temperature of the polymer and assuming atmospheric pressure, the metal part is heated for a coating with polyethylene to a temperature in the range of 100°C to 140°C, with polypropylene to a temperature in the range of 130°C to 170°C, and with polyamide to a temperature in the range of 175°C to 275°C. The temperature can be measured non-contact (for example, via infrared temperature measurement) and / or via contact measurement (for example, with a thermocouple) of the material to be measured (metal or thermoplastic). The coating resulting from the coating step preferably has a thickness in the range of 100 µm to 2 mm, preferably 500 µm to 1 mm. To further improve the material bond between the coating 20 and the composite contact surface 11 of the metal part 10, an additive can be added to the first thermoplastic.Such an additive contains at least one functional group that increases the adhesion of the first thermoplastic to the metal surface of the metal part 10 (in particular through increased hydrogen bonding). For example, the first additive can have a carbonyl group as a functional group. Other or further functional groups that the first additive can have are alcohols, thiols, amines and / or imines. In particular, functional groups that change the surface energy and polarity are advantageous in such a way that the first additive increases the wettability of the first thermoplastic on metal surfaces. As a result, it has surprisingly been found that it also functions very well as an adhesion promoter in the first thermoplastic for the bond between the metal of the metal part 10 and the second thermoplastic of the gas-tight layer 40.In particular, the first additive may have a structure having the following chemical formula 1. [Chemical Formula 1]. In chemical formula 1, n can be 1 or 2, where n is preferably 1. Y can be O or S, where Y is preferably O. R1 and R2 can each independently be hydrogen, deuterium, halogen, cyano, C 1-10 -Alkyl, C 1-10 -Alkenyl, C 3-10 -aryl or a C 3-10 -Heteroaryl having at least one heteroatom selected from N, O and S. When n is 1, R1 and R2 may optionally be joined together to form a C 3-10 -Cycloalkyl, a C 3-10 -aryl or a C 3-10 -Heteroaryl containing at least one heteroatom selected from N, O and S. Preferably, R1 and R2 each independently represent hydrogen, C 1-10 -Alkyl, C 1-10-alkenyl, C6-aryl or C6-heteroaryl having at least one heteroatom selected from N and O. Preferably, the additive is selected from the group consisting of furan-2,5-dione, 3,4-dihydrofuran-2,5-dione and thiophene-2,5-dione, each having one or two C 1-4 -alkyl groups in position 3. Even more preferred is the additive furan-2,5-dione, which is substituted with one or two C 1-4-Alkyl groups can be substituted in position 3. Without being bound to any theory, it is suspected that the functional groups, such as furan-2,5-dione, can be bound to the polymer chain and react with metal surfaces to form chemical bonds that improve the adhesion between polymer and metal. Furthermore, it should be noted that alkyl and alkenyl groups can be linear or branched. Furthermore, alkyl, alkenyl, cycloalkyl, aryl or heteroaryl can each independently be substituted with one or more substituents selected from the group consisting of deuterium, a halogen group, a cyano group, a nitro group, a hydroxy group, a carbonyl group, an ester group, an imide group, an amine group, a phosphine group, an alkoxy group, a silyl group, an alkyl group, a cycloalkyl group, an alkenyl group, an aryl group or a heteroaryl group.To activate the bonding capacity of the first additive, the metal part 10 provided with the coating 20 is heated to a temperature of at least 150°C and preferably at least 190°C, and to a maximum of 215°C and preferably to a maximum of 205°C. As a result, in step (b) of Figure 1, the metal part 10 is coated with the first thermoplastic 20, wherein the optional first additive can surprisingly further improve the bond between the coating 20 and the composite contact surface 11 of the metal part 10, which is attributed in particular to increased or stronger hydrogen bonds 21 caused by the first additive. The metal part coated in this way can be cooled and temporarily stored, or it can be fed directly to the following or further process steps.In process steps (c) and (d) illustrated in Figure 1, a second thermoplastic 41 is then applied to form a gas-tight layer (“liner”) (40) onto the coating 20 of the metal part 10, thereby increasing the impermeability to gases and thus establishing the sealed connection. For this purpose, the metal part 10 can be inserted into a mold 30. Using the mold, at least part of the polymer body can be produced, which is to be connected to the metal part 10 via the sealed connection. The mold 30 in step (c) is, by way of example, the shape of a gas tank, in particular a rotationally symmetrical gas tank. The result of step (c) from Figure 1 is illustrated enlarged in Figure 2. There, as an example of the metal part 10, a boss is shown, which establishes the connection between a gas device (not illustrated) and a gas tank via a flow path (12).This metal part 10 has been inserted into the mold 30 and has the first coating 20 on its composite contact surface 11. Furthermore, Figure 2 shows recesses 14 in the composite contact surface 11, which can increase the shear strength between the coating 20 and the metal part 10 through a positive connection. The mold 30 illustrated in Figures 1 and 2 is preferably a mold for a rotational molding process (in particular, a rotational sintering process). This process can also be used to produce large bodies with a uniform wall thickness. As shown in step (c) of Figure 1, after the coated metal part 10 has been inserted into the mold 30, the second thermoplastic 41 is added to the mold via a feed device 42. Other molding processes can also be used to apply the second thermoplastic 41, such as, for example, an injection molding process, an extrusion process, or an injection blow molding process.The second thermoplastic 41 forms a gas-tight layer 40 and preferably comprises or consists of polyethylene, polypropylene, and / or polyamide. More preferably, the thermoplastic of the produced sealing composite is or consists of X-polyethylene (PE-X), X-polypropylene (PP-X), and / or X-polyamide (PA-X). Preferably, the coating 20 and the gas-tight layer 40 are based on the same polymer. However, they can also be based on different polymers, such as the polymers mentioned above. Preferably, the melting temperature of the polymer of the coating 20 and the polymer of the gas-tight layer 40 is in a similar temperature range (±50°C, ±40°C, ±30°C, ±20°C, or ±10°C). Preferably, the melting temperature of the polymer of the gas-tight layer 40 is substantially the same as or higher than the melting temperature of the polymer of the coating 20.This promotes a bond at the interface between coating 20 and gas-tight layer 40. The supplied second thermoplastic 41 is also heated to at least its melting temperature and distributed in the mold 30. The distribution of the second thermoplastic 41 over the wall of the mold 30 and the coated side of the metal part 10 is carried out, for example, by rotational molding or rotational casting, i.e. the mold 30 is rotated with the inserted metal part 10 about one or two axes so that the heated second thermoplastic 41 spreads as a melt over the inner surface of the mold 30 and the coating 20 of the metal part 10. This results in the uniform distribution of the second thermoplastic shown in step (d) of Figure 1, which acts as a gas-tight layer 40.Depending on the underlying polymer used, the second thermoplastic 41 is heated for shaping, in particular to a temperature in the temperature ranges already described above in connection with the first thermoplastic. The heating of the second thermoplastic 41 and the associated heating of the first thermoplastic results in the first thermoplastic and the second thermoplastic 41 bonding together in the boundary region between the two thermoplastics in the molten state. The bonding created can be formed by intermolecular and intramolecular bonding forces. This is also illustrated on an enlarged scale in Figure 3. There, the gas-tight layer 40 is distributed over the inner surface of the mold 30 and over the area of ​​the composite contact surface 11 of the metal part 10 or the coating 20.The wall thickness of the second thermoplastic 41 of the produced sealing composite is 5 to 20 mm, preferably 6 to 15 mm. The first thermoplastic and the second thermoplastic 41 are then heated to a second temperature in order to induce a crosslinking reaction in the region of the material-to-material connection between the first thermoplastic and the second thermoplastic 41. The second temperature is, for example, in a range from 190°C to 300°C, preferably in a range from 220°C to 280°C. The crosslinking improves both the strength and the permeation properties of the sealing composite. The second temperature is preferably above the melting temperature of the first thermoplastic and the second thermoplastic 41. This can in particular prevent a crosslinking reaction that starts too early, which could otherwise have a detrimental effect on the shape of the second thermoplastic 41.As illustrated in step (e) of Figure 1, the sealing composite thus obtains the above-described, strong, material-to-material connection 21 between the connection contact surface 11 of the metal part 10 and the first thermoplastic 20, as well as a likewise material-to-material connection between the first thermoplastic 20 and the second thermoplastic 41, which is particularly resistant due to the crosslinking 43. Particularly preferably, the second thermoplastic 40 is crosslinked throughout during the manufacturing process (i.e., not only in the area of, and preferably with, the coating 20). Suitable methods known from the prior art for inducing internal crosslinking and, in particular, also crosslinking between the first and second thermoplastics can be used here. This crosslinking can be achieved by adding a crosslinking agent, such as, for example, peroxide (for example, dicumyl peroxide or di-tert-butyl peroxide).Crosslinking with the first thermoplastic can also be achieved using this crosslinking agent or by adding a second additive containing a crosslinking agent. Such a second additive is particularly intended for crosslinking the second thermoplastic, which preferably also interacts with the first thermoplastic, i.e., crosslinks it. In order to increase the gas pressure resistance in the case of a container or gas tank as a molded body, the outer side is preferably provided with a reinforcing layer (not shown). A composite material is preferably used for this purpose. For example, a polymer fiber in a matrix, preferably made of a resin, such as epoxy resin, can be used. During production of the reinforcing layer, the polymer fiber is preferably wound around the container so that it can absorb tensile forces during operation of the container. This significantly increases the gas pressure resistance.Thus, the present disclosure provides a functional division or weighting of individual functions for the different materials joined together in the sealing assembly. The metal part 10 is intended in particular for areas subject to greater mechanical and / or thermal stress. The coating 20 with the first thermoplastic serves in particular as an adhesion promoter between the metal part 10 and the second thermoplastic 41, which in turn forms a gas-tight layer (liner) and can also define the shape of a part of a gas device (such as the aforementioned gas tank). The reinforcement layer, in turn, absorbs the force exerted by the gas on the structure of the sealing assembly and the part of the gas device, thus increasing the gas pressure resistance.It is thus possible to produce and provide a sealing connection that improves compressive strength and operational reliability, as well as a connection arrangement that has such a sealing connection. REFERENCE SYMBOL 10 Metal part 11 Composite contact surface 12 Opening 14 Recess 20 Coating with a first thermoplastic 21 Metal-thermoplastic connection (in particular hydrogen bonding) 30 Mold Gas-tight layer with a second thermoplastic Second thermoplastic Feed device for second thermoplastic Crosslinking.

Claims

CLAIMS 1. A method for producing a sealing composite for gases, the method comprising the steps of: providing a metal part (10) having a composite contact surface (11), heating the composite contact surface (11) of the metal part (10) to a predetermined first temperature which is above the melting temperature of a first thermoplastic, applying the first thermoplastic to form a material-to-material coating of the composite contact surface (11) with the first thermoplastic, wherein the first thermoplastic is applied before, during and / or after heating the composite contact surface, applying a second thermoplastic (41) as a gas-tight layer (40) and material-to-material bonding to the coating (20) having the first thermoplastic, crosslinking the first thermoplastic and the second thermoplastic with one another by heating to a second temperature.Method according to claim 1, wherein the metal part (10) is placed in a mold (30) before the application of the second thermoplastic, and the second thermoplastic is preferably applied using a rotational molding process.

3. Method according to one of the preceding claims, wherein, for the coating of the metal part (10), a first additive is added to the first thermoplastic, and the first thermoplastic is heated to the reaction temperature of the first additive in order to bond with the composite contact surface (11) of the metal part (10).

4. Method according to one of the preceding claims, wherein, for the application of the gas-tight layer (40), a second additive is added to the second thermoplastic, and the second thermoplastic is heated to the reaction temperature of the second additive.

5. The method according to claim 4, wherein the second additive causes crosslinking (43) of the second thermoplastic with the first thermoplastic.

6. The method according to any one of the preceding claims, wherein the first thermoplastic comprises or consists of polyethylene, polypropylene, and / or polyamide.

7. The method according to any one of the preceding claims, wherein the gas-tight layer (40) comprises or consists of X-polyethylene, X-polypropylene, and / or X-polyamide.

8. The method according to any one of the preceding claims, wherein the metal part (10) comprises or consists of an aluminum alloy and / or a steel alloy, in particular a stainless steel alloy.

9. The method according to any one of the preceding claims, further comprising a step of applying a reinforcing layer, in which a reinforcing layer made of a material is applied that has a higher tensile strength and a higher modulus of elasticity than the gas-tight layer (40).A gas-impermeable sealing composite comprising: a metal part (10), an intermediate layer made of a first thermoplastic, which is formed as a cohesive coating (20) of a composite contact surface (11) of the metal part (10), and a gas-tight layer (40) made of a second thermoplastic, which is cohesively bonded to the first thermoplastic.

11. The sealing composite according to claim 10, wherein a first additive is bound in the coating (20) comprising the first thermoplastic, which increases the hydrogen bonds between the metal part (10) and the coating (20).

12. A sealing assembly according to claim 10 or 11, wherein the material connection between the coating (20) comprising the first thermoplastic and the gas-tight layer (40) comprising the second thermoplastic comprises crosslinking, the crosslinking being based on a second additive.

13. A connection arrangement for a pressure vessel, wherein the metal part (10) is designed for a detachable connection to a gas device and is part of a sealing assembly according to one of claims 10 to 12.

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