TW202432345A - Metal-plastic hybrid materials with aluminum and/or alloys thereof as metal component - Google Patents

Abstract

The present invention relates to a method for preparing a metal-plastic hybrid material, said material comprising at least one substrate having at least one metallic surface made at least partially of aluminum and/or of an alloy thereof and at least one thermoplastic material applied onto said metallic surface of the substrate, inter alia by making use of an acidic aqueous composition, a metal-plastic hybrid material obtainable by this method, a use of the acidic aqueous composition for adhering the substrate to the plastic, a metal-plastic hybrid material as such, and a use of the metal-plastic hybrid material as component in the automotive, construction or electronic industry.

Description

Metal-plastic composite materials with aluminum and/or its alloys as metal components

The invention relates to a method for preparing a metal-plastic hybrid material comprising at least one substrate and at least one thermoplastic material, the at least one substrate having at least one metal surface at least partially made of aluminum and/or its alloys and the at least one thermoplastic material being applied to the metal surface of the substrate, the application being carried out in particular by using an acidic aqueous composition; a metal-plastic hybrid material obtainable by this method; the use of the acidic aqueous composition for bonding the substrate to the plastic; the metal-plastic hybrid material itself; and the use of the metal-plastic hybrid material as a component in the automotive, construction or electronics industries.

Metal-plastic hybrids are one of the solutions proposed for reducing weight, either in components such as structural parts used in the automotive industry or in other assemblies such as battery covers, powertrain components, control panels, etc. To obtain such components and assemblies, plastic and metal can be joined together in several ways to produce a combined material with an ideal combination of the characteristics of both materials, metal and plastic. However, joining different materials such as metal and plastic together is extremely challenging, not only because of the different chemical properties of the two materials and therefore their surfaces, but also due to the shrinkage of the plastic material such as thermoplastics, observed for example after molding, which is caused by the differences between the two materials.

As is known, adhesives are used to bond metals to thermoplastic materials. However, methods of manufacturing such products using adhesives not only increase the number of manufacturing steps, but also the bonding strength may decrease over time or may not exhibit integrated strength at high temperatures. Therefore, regardless of the associated economic and ecological disadvantages, it is not suitable to apply such methods to technical fields such as the automotive industry, because in such methods, significant heat resistance is usually required due to the electrodeposition and painting processes.

Aluminum is nowadays commonly used as a metal component material for the construction of metal-plastic hybrids, in particular for electric vehicle applications or electronic devices, such as smartphones, mobile devices, etc. Various methods have been reported describing the joining of aluminum to thermoplastic materials, in particular in the electronics industry, wherein the aluminum surface is usually anodized, plasma treated or etched in a controlled manner to produce surface roughness prior to injection molding, for example by using nanomolding technology (NMT).

In general, plastic-metal hybrid materials are usually formed by injection molding of a thermoplastic material on the surface of a metal part, such as an aluminum part, which surface has nano-sized pores, micro-sized pores or both. For example, WO 2020/003208 A1 discloses such a plastic-metal hybrid material, in which the plastic contains polyketones. The pores are usually formed by the aforementioned controlled chemical etching or anodizing process. The adhesion mechanism is based on mechanical interlocking, in which the plastic material in a molten state is directly injected into the pores of the metal surface.

Controlled chemical etching and anodizing processes (also known as flash anodizing) require special equipment and have the disadvantage that additional etching or anodizing steps must be used to produce surface roughness when preparing plastic-metal hybrid materials. Such controlled chemical etching and anodizing processes are disclosed, for example, in EP 2 894 240 A1 and EP 3 854 909 A1 and JP 2021-186993 A: EP 2 894 240 A1 is about a metal-resin composite structure obtained by bonding a metal component and a resin component formed of a thermoplastic resin composition to each other. In order to achieve sufficient adhesion between the metal component and the resin, the surface of the metal component must be roughened. EP 3 854 909 A1 relates to a metal/resin composite structure comprising a metal component and a resin component, which is integrated into the metal component and is formed by a resin composition containing a thermoplastic resin. The metal component has a fine uneven shape, that is, a surface roughness, at least on the surface of the portion integrated with the resin component, which is the result of a surface roughening step. In addition, an inorganic particle layer must be present between the metal and the resin component. JP 2021-186993 A discloses a metal/resin composite comprising a metal component and a cured resin bonded to the metal component. The metal member has a fine concavo-convex structure on the surface of the bonding portion with the cured resin made of a thermosetting polyurethane elastic material, and thus has roughness.

However, the resulting roughened (especially etched or anodized) surfaces of metallic materials (such as aluminum-based materials) have a very limited shelf life. Taking anodization as an example, the application window or treatment of plastic materials is only a few hours, otherwise the pores close naturally and adhesion cannot be achieved. In addition, the aforementioned nanomolding technology (NMT) can only be applied to very clearly defined nanopores and very small components, limiting the application to very small electronic devices. The engineering plastics suitable for this application are also limited: for example, polybutylene and polyethylene terephthalate (PBT and PET) each change color during further processing of the components due to their poor acid resistance. Resin-based materials such as polyamide (PA) and poly(phthalamide) (PPA) also have only poor acid resistance.

Therefore, there is a need to provide metal-plastic hybrid materials and methods for their preparation, which contain aluminum and/or its alloys as metal components and have excellent and permanent or at least long-lasting adhesion properties with respect to adhesion between metal and plastic, but at the same time can be prepared without the use of conventional adhesives and, in addition and in particular, without the need for a separate surface roughening step (such as an anodizing step or chemical etching of the surface), which further allow the use of a wider range of thermoplastic polymers (including PBT and PET) compared to the known processes for the preparation of metal-plastic hybrid materials containing aluminum and/or its alloys and can furthermore be prepared in a flexible, convenient and ecologically and economically favorable manner.

The object of the present invention is therefore to provide metal-plastic hybrid materials and methods for their preparation, which contain aluminum and/or its alloys as metal component and have excellent and permanent or at least long-lasting adhesion properties with regard to the adhesion between metal and plastic, but at the same time can be prepared without the use of conventional adhesives and, moreover, in particular without the need for a separate surface roughening step such as an anodizing step or chemical etching of the surface, which, compared to the known processes for the preparation of metal-plastic hybrid materials containing aluminum and/or its alloys, further allow the use of a wider range of thermoplastic polymers (including PBT and PET) and can furthermore be prepared in a flexible, convenient and ecologically and economically favorable manner.

Solution This object has been solved by the subject matter of the patent scope of this application and by its preferred embodiments disclosed in this specification, that is, by the subject matter described herein.

The first subject matter of the present invention is a method for preparing a metal-plastic hybrid material, which comprises a substrate S1 having at least one metal surface and at least one thermoplastic material applied to the metal surface of the substrate S1, the method comprising at least step 1) and step 2) and optionally step 3a) or 3b), namely 1) applying an aqueous acidic composition at least partially to at least one metal surface of the substrate S1 to at least partially form a film on the surface, wherein the metal surface is at least partially made of aluminum and/or at least one aluminum alloy, and In addition to water, the acidic aqueous composition also contains at least one water-soluble polymer as at least one component a1), the at least one water-soluble polymer has at least one functional group selected from acid groups, hydroxyl groups, amine groups and mixtures thereof, and at least one metal cation selected from the group of titanium, zirconium and cobalt ions and mixtures thereof as at least one component a2), and preferably free fluorine anions as at least one component a3), and and optionally drying or curing the film to form a dried or cured layer, 2) applying at least one thermoplastic polymer material TM1 at least partially to the film or the dried or cured layer obtained after step 1), wherein the at least one thermoplastic polymer material TM1 is i) applied in foil form or ii) applied by injection in a molten state to the film or the dried or solidified layer obtained after step 1) to form the metal-plastic hybrid material, and 3a)   optionally, at least one thermoplastic polymer material TM2 is at least partially injected onto the surface of the foil of the metal-plastic hybrid material obtained after steps 2) and i), the at least one thermoplastic polymer material TM2 being the same or different from the thermoplastic material TM1 applied in step 2) and being in a molten state, or 3b)  Optionally, a further substrate S2 having at least one metallic surface at least partly made of aluminum and/or at least one aluminum alloy and having been treated in method step 1) is applied to the surface of the foil of the metal-plastic hybrid material obtained after steps 2) and i), or vice versa.

Another subject matter of the invention is a metal-plastic hybrid material obtainable by this method.

Another subject matter of the present invention is the use of an acidic aqueous composition as defined above in relation to step 1) of the process according to the invention for bonding a metal surface of a substrate, at least partly made of aluminum and/or at least one aluminum alloy, to a thermoplastic material, such as thermoplastic material TM1, which is present on the surface in the form of a foil or applied to the surface by injection molding.

Another subject of the present invention is the metal-plastic hybrid material itself, that is, a metal-plastic hybrid material comprising: a substrate S1 having at least one metal surface, the at least one metal surface being at least partially made of at least one aluminum and/or at least one aluminum alloy, a film or a dry or cured layer, which is at least partially applied to the metal surface, the film or the dry or cured layer being obtained by at least partially applying the aqueous acidic composition defined in step 1) of the method of the present invention to the metal surface, and at least one thermoplastic polymer material TM1 in the form of a foil or in a form obtainable by injection molding, in each case the at least one thermoplastic polymer material TM1 being at least partially applied to the film or the dried or cured layer, preferably as defined in step 2) of the method of the invention, and, In addition, at least one thermoplastic polymer material TM2, optionally selected, which is identical or different to the thermoplastic polymer material TM1, the at least one thermoplastic polymer material TM2 being at least partially applied to the at least one thermoplastic polymer material TM1 in a form obtainable by injection molding, with the proviso that the thermoplastic polymer material TM1 has been applied in the form of a foil, or Furthermore, a substrate S2 is optionally used, which has at least one metal surface, which is at least partially made of aluminum and/or at least one aluminum alloy, and has a film or a dried or cured layer applied at least partially on the metal surface, which can be obtained by applying an aqueous acidic composition as defined in step 1) of the method of the present invention, wherein the film or dried or cured layer at least partially present on the metal surface of the substrate S2 is located adjacent to the at least one thermoplastic polymer material TM1, with the proviso that the thermoplastic polymer material TM1 has been applied in the form of a foil.

Preferably, when the metal-plastic hybrid material comprises another substrate S2, it can be regarded as a sandwich structure comprising two substrates S1 and S2, wherein each of these substrates is adhered to one surface of the thermoplastic material TM1 in the form of a foil by means of an adhesive film or a dry or cured layer, which can be obtained by applying an aqueous acidic composition as defined in step 1) above with respect to the method of the present invention. Preferably, each of the substrates S1 and S2 is a sheet or a coil made of aluminum and/or its alloy.

Another subject matter of the invention is the use of the metal-plastic hybrid material or the metal-plastic hybrid material obtainable by the method of the invention as a component in the automotive, construction or electronics industry.

It has been found that the acidic aqueous composition used in the present invention is able to provide a conversion coating on the metal surface of the substrate and at the same time, due to the adhesion-promoting properties of the conversion coating film or layer formed, achieve good adhesion between the metal surface and the thermoplastic material TM1 applied to the metal surface. It has been found that sufficient adhesion cannot be obtained without the application of the acidic aqueous composition. It has also been found, particularly surprisingly, that in this regard, the water-soluble polymer present in the acidic aqueous composition acts as an adhesion promoter. Achieving excellent adhesion is particularly significant because it has been found that the strength of the adhesive layer between the metal surface and the thermoplastic material used has a significant impact on the service life of the metal-plastic hybrid material. Furthermore, it has been found that surfaces containing metallic aluminum and/or aluminum alloys can be used with all types of substrates having different shapes, in particular sheets, coils and/or substrates of other shapes.

Furthermore, it has been found that applying the acidic aqueous composition used in the present invention to a metal surface according to step 1) represents a surface treatment of the metal surface which not only provides microstructuring of the surface via an immersion passivation treatment, especially when there is at least one metal cation selected from the group of titanium, zirconium and cobalt ions and mixtures thereof (preferably in combination with molybdenum cations), which is important for the mechanical interlocking of the thermoplastic polymer material TM1, but also achieves a real chemical bonding via the functional groups of the water-soluble polymer used. Since the surface roughness is already produced by applying the acidic aqueous composition used in the present invention to the metal surface according to step 1), it is completely unnecessary to apply any known surface treatments such as plasma treatment, chemical etching and/or anodization to the metal surface, let alone to carry out the surface treatment in a separate method step.

Furthermore, it has been found, surprisingly in particular, that the adhesion difficulties and problems known from the prior art when combining two different materials, namely one thermoplastic polymer TM1 and the other aluminum and/or its alloys, can be overcome by the method of the invention for preparing metal-plastic hybrid materials, in particular by chemically pretreating the metal surface with an acidic aqueous composition as described in step 1) of the method of the invention before carrying out step 2). It has been found that the method for preparing metal-plastic hybrid materials even allows, in particular, the use of thermoplastic polymers with a relatively high melting temperature, such as TM1, such as polyamides, in particular polyamide 6, which are directly applied by injection molding according to step 2) of the method of the invention, and further allows the use of thermoplastic polyesters, such as PET and PBT, despite their poor acid resistance. Injecting the thermoplastic material directly onto the metal surface according to step 2) offers many advantages, including simplicity, robustness and a wide application window. Flexibility of the method can be achieved, for example because step 1) of the method can be used in a coil line by a roller coater or can be sprayed on a work coater, which makes the method highly flexible.

It has also been found that not only is excellent adhesion achieved, but also excellent protection against corrosion can be achieved by applying the acidic aqueous composition used in accordance with the present invention.

It has also surprisingly been found that the process of the invention allows direct thermoplastic injection of the thermoplastic polymer TM1 onto the aluminum-containing metal surface according to step 2), despite the extremely short contact time between the thermoplastic polymer TM1 and the metal surface and despite the significant temperature difference between the molten thermoplastic polymer material TM2 (which can exceed 200°C) and the substrate temperature of the surface (which is typically room temperature, i.e. in the range of 18 to 25°C, but can optionally be heated, e.g. up to 60°C). In particular, it has been found that the functional groups of the water-soluble polymer present in the acidic aqueous composition used allow very rapid bonding of the thermoplastic material after application/injection and before cooling.

Furthermore, it has been found that chemical pretreatment of the metal surface with an acidic aqueous composition, as described in step 1) of the method of the invention, also provides strong adhesion to the thermoplastic material TM1 when applied to the treated metal surface in the form of a foil compound before carrying out step 2). It has also been found that the foil formed by applying TM1 can then further serve as, for example, an adhesive layer or an interface layer, onto which another thermoplastic material TM2, which is the same or different from TM1, can be applied by injection when carrying out the optional step 3a) of the method, in particular when the foil formed from TM1 in step 2) is chemically compatible with the material TM2 applied in the optional step 3a). Similarly, when the metal surface of another substrate has also been subjected to a chemical pretreatment as defined in step 1) of the method of the invention by using the acidic aqueous composition used according to the invention, in particular when TM1 has been applied to the metal surface as a foil, the product obtained after step 2) can also be applied in an optional step 3b) to the metal surface of the other substrate, which surface is also at least partially made of aluminum and/or its alloys, to form a sandwich structure in which the foil made using TM1 is flanked by two metal surfaces of two substrates.

In the sense of the present invention, the term "comprising" preferably has the meaning of "consisting of" for example with respect to an acidic aqueous composition. For example, with respect to an acidic aqueous composition, in addition to all the required components present therein, one or more of the other optional components identified below may also be included therein. All components may in each case be present in their preferred embodiments as identified below.

The proportions and amounts given below of any components present in the acidic aqueous composition as (% by weight (wt %)) total 100 wt %, based in each case on the total weight of the acidic aqueous composition.

Method of the Invention The first subject matter of the present invention is a method for preparing a metal-plastic hybrid material, which comprises a substrate S1 having at least one metal surface and at least one thermoplastic material applied to the metal surface of the substrate S1, and the method comprises at least step 1) and step 2) and optionally step 3a) or 3b).

The method may comprise further steps in addition to step 1) and step 2) and optionally step 3a) or 3b). For example, a cleaning step of the metal surface may be carried out before step 1), for example by means of an acidic, alkaline or pH-neutral, preferably alkaline cleaning composition, wherein in the case of an acidic cleaning composition, the composition is different from the acidic aqueous composition used in step 1).

More specifically, before step 1), one or more of the following steps, as appropriate, may be performed in this order: Step A-1):  Preferably alkaline or acidic cleaning is performed, and the surface of the substrate is subsequently rinsed, as appropriate, Step B-1):  The surface of the substrate is acid-washed (i.e., etched), and the surface of the substrate is subsequently rinsed, Step C-1):  The surface of the substrate is contacted with an aqueous composition comprising at least one inorganic acid, which aqueous composition is different from the acidic aqueous composition used in step 1), or is contacted with an aqueous alkaline composition or a pH-neutral aqueous composition, and Step D-1): Rinse the surface of the substrate obtained after contacting according to step C-1) and/or B-1).

Alternatively, steps A-1) and B-1) may be performed in one step, which is preferred. Preferably, steps A-1) and B-1) are both performed.

The optional step C-1) is used to remove aluminum oxide, undesired alloy components, surface layers, brushing dust, etc. from the surface of the substrate, and thereby activate the surface for subsequent treatment in step 1). This step represents a chemical etching step. Preferably, at least one inorganic acid of the composition in step C-1) is sulfuric acid and/or nitric acid and/or phosphoric acid, more preferably sulfuric acid. The content of the at least one inorganic acid is preferably in the range of 1.5 to 75 g/l, more preferably 2 to 60 g/l and most preferably 3 to 55 g/l. The composition used in step C-1) preferably further comprises one or more metal ions selected from the group of titanium, zirconium, cobalt ions and mixtures thereof, and optionally further comprises molybdenum ions. In the treatment of the parts, the duration of the treatment with the composition in step C-1) is preferably in the range of 30 seconds to 10 minutes, more preferably 40 seconds to 6 minutes and most preferably 45 seconds to 4 minutes. The treatment temperature is preferably in the range of 20 to 55°C, more preferably 25 to 50°C and most preferably 30 to 45°C. In the treatment of the coil, the duration of the treatment is preferably in the range of 3 seconds to 1 minute, most preferably 5 to 20 seconds. However, preferably, step C-1) which is optionally used is not performed.

Preferably, in particular before step 1), the method does not comprise any surface treatment step of the metal surface S1 selected from plasma treatment, chemical etching and/or anodization. Steps B-1) and C-1) as appropriate do not represent chemical etching steps disclosed in the prior art for producing any surface roughness of the substrate. Steps B-1) and/or C-1) as appropriate are in fact only preparation steps for the subsequent deposition of the film obtained by applying the aqueous acidic composition in step 1).

Preferably, deionized water or tap water is used for the rinsing step D-1) and the optional rinsing as part of step A-1). Preferably, deionized water is used for the step D-1).

Preferably, the method does not contain any step involving any treatment with chromium ions, such as Cr(III) and/or Cr(VI) ions.

Substrate The metal surface of substrate S1 is at least partially made of aluminum and/or at least one aluminum alloy. Preferably, the entire metal surface is at least partially made of aluminum and/or at least one aluminum alloy. More preferably, substrate S1 itself is a metal substrate at least partially made of aluminum and/or at least one aluminum alloy. Preferably, the amount of any steel and/or steel alloy contained in the metal surface does not exceed the amount of aluminum and/or its alloy present in the surface. Examples of aluminum alloys are aluminum-magnesium alloys, aluminum-magnesium-silicon alloys, aluminum-copper alloys, aluminum-zinc alloys, and aluminum-zinc-copper alloys.

In the case of an aluminum alloy, the alloy preferably contains more than 50 wt% aluminum, based on the total weight of the alloy. The method is particularly applicable to all aluminum alloys containing more than 50 wt% aluminum, in particular to aluminum-magnesium alloys, including but not limited to AA5005, and to aluminum-magnesium-silicon alloys, including but not limited to AA6014, AA6060 and AA6063, to casting alloys such as AlSi7Mg, AlSi9Mg, AlSi10Mg, AlSi11Mg, AlSi12Mg, and to forging alloys such as AlSiMg. Aluminum-magnesium alloys including AA5005 and aluminum-magnesium-silicon alloys including AA6060 and AA6063 are often used in the field of aluminum processing and/or for the treatment of wheels and/or for other vehicle parts such as electric vehicle parts, such as battery housings. The method is further suitable for all alloys of the so-called AA1000, AA2000, AA3000, AA4000, AA5000, AA6000, AA7000 and AA8000 series. A preferred example of the AA2000 series is AA2024. A preferred example of the AA7000 series is AA7075. AA2024 and AA7075 are often used in the aerospace industry. Other examples are Galvalume® and Galfan®.

All types of substrates with different shapes and geometries can be used. Preferably, the substrate is selected from sheets and coils as well as components, in particular components for the automotive industry, and mixtures thereof.

Step 1) of the method In step 1), an aqueous acidic composition is at least partially applied to at least one metal surface of a substrate S1 to at least partially form a film on the surface. In step 1), the film may be optionally dried or cured to form a dried or cured layer. Preferably, such drying or curing is performed. Drying is preferably performed, for example, at a temperature in the range of 15°C to 100°C, more preferably at a temperature in the range of 18°C to 95°C, and in particular at a temperature in the range of 20°C to 90°C.

Step 1) is preferably a contacting step, wherein the metal surface is contacted with the aqueous acidic composition. "Contacting" includes spraying, dipping, cascade or rolling processes. "Contacting" can also be flooding the surface or even manually wiping or brushing.

When the component, in particular for use in the automotive industry, is used as a substrate, it is preferred that in each case the treatment time, i.e. the period of contact of the surface with the acidic aqueous composition used in step 1), is preferably from 15 seconds to 20 minutes, more preferably from 30 seconds to 10 minutes, and most preferably from 45 seconds to 5 minutes, for example from 1 to 3 minutes. In the case of a coil, the treatment time is preferably less than 1 minute, more preferably less than 30 or 15 seconds, even more preferably less than 10 seconds, and more preferably in the range of 1 to 5 seconds.

The temperature of the acidic aqueous composition used in step 1) is preferably 5 to 50°C, more preferably 15 to 45°C, and most preferably 25 to 40°C.

By performing step 1), a conversion coating film is preferably formed on the metal surface. Preferably, after drying or curing, preferably drying, a coating is formed which has the following coating weight determined by XRF (X-ray fluorescence spectroscopy): due to the presence of component a2) in the acidic aqueous composition, in each case calculated as metal, 0.1 to 50 mg/m ² , preferably 0.2 to 30 mg/m ² , even more preferably 0.5 to 20 mg/m ² , still more preferably 1.0 to 15 mg/m ² , still more preferably 1.5 to 10 mg/m ² , in particular 2.0 to 8 mg/m ² of zirconium and/or titanium and/or arsenic, preferably zirconium and/or titanium, more preferably zirconium. Preferably, the coating has, in the presence also of the optional component a4) as defined below, the following coating weight, determined by XRF (X-ray fluorescence spectroscopy): 0.1 to 40 mg/m ² , better still 0.2 to 30 mg/m ² , even better 0.5 to 20 mg/m ² , still better still 1.0 to 15 mg/m ² , even better still 1.5 to 10 mg/m ² , in particular 2.0 to 8 mg/m ² of molybdenum.

The acidic aqueous composition comprises, in addition to water, at least one water-soluble polymer as at least one component a1), the at least one water-soluble polymer having at least one functional group selected from the group consisting of acid groups, hydroxyl groups, amine groups and mixtures thereof, and at least one metal cation selected from the group consisting of titanium, zirconium and cobalt ions and mixtures thereof as at least one component a2). All components present in the composition are different from each other.

Preferably, the acidic aqueous composition used in step 1) has a pH value in the range of 0.1 to <7.0, more preferably 0.5 to 6.5, still more preferably 1.0 to 6.0, even more preferably 1.5 to 5.5, still more preferably 2.0 to 5.0, still more preferably 2.5 to 4.5, still more preferably 3.0 to 4.0, and most preferably >3.0 to <3.7. Preferably, the pH value is measured at room temperature (23° C.). If necessary, nitric acid, ammonia water and/or sodium carbonate may be preferably used to adjust the pH.

In the sense of the present invention, the term "aqueous" with respect to the acidic aqueous composition used in step 1) preferably means a composition containing at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, in particular at least 80 wt %, and most preferably at least 90 wt % of water, based on the total content of organic and inorganic solvents including water in the composition. Thus, the composition may also contain at least one organic solvent in addition to water, however, the amount of the at least one organic solvent is lower than the amount of water present.

Preferably, the acidic aqueous composition used in step 1) contains at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, in particular at least 80 wt % and most preferably at least 90 wt % of water, based in each case on the total weight of water.

The acidic aqueous composition can be used as a dip coating bath. However, the acidic aqueous composition can also be applied by almost any known coating procedure, such as spraying, rolling, brushing, wiping, etc., as outlined above with respect to step 1). Spraying, dipping, waterfall coating or rolling is preferred.

The acidic aqueous composition used in step 1) is preferably a solution.

Preferably, the acidic aqueous composition used in step 1) has a temperature in the range of 18 to 35°C, more preferably 20 to 35°C, especially 20 to 30°C.

Water-soluble polymer ( component a1)) The acidic aqueous composition comprises, as at least one component a1), at least one water-soluble polymer having at least one functional group selected from the group consisting of an acid group, a hydroxyl group, an amine group and a mixture thereof.

The solubility was determined at a temperature of 20°C and atmospheric pressure (1.013 bar).

Preferably, the at least one water-soluble polymer used as component a1) is present in the acidic aqueous composition in an amount ranging from 0.05 to 2.0 g/L or 0.05 to 5.0 g/L, more preferably 0.10 to 1.8 g/L, even more preferably 0.12 to 1.6 g/L, more preferably 0.14 to 1.5 g/L, more preferably 0.16 to 1.4 g/L, more preferably 0.18 to 1.2 g/L, and most preferably 0.20 to 1.0 g/L. Alternatively, the at least one water-soluble polymer used as component a1) is present in the acidic aqueous composition in an amount ranging from 0.1 to 15.0 g/L, more preferably 0.3 to 12.0 g/L, even more preferably 0.5 to 11.0 g/L, and more preferably 0.7 to 10.0 g/L.

Preferably, the at least one water-soluble polymer used as component a1) has at least one functional group selected from the following: carboxylic acid group, phosphonic acid group, sulfonic acid group, hydroxyl group, amine group and mixtures thereof, more preferably selected from carboxylic acid group, hydroxyl group, amine group and mixtures thereof, even more preferably selected from carboxylic acid group.

Preferably, the at least one water-soluble polymer used as component a1) is a homopolymer or copolymer obtainable from the polymerization of at least one ethylenically unsaturated monomer, at least a portion of which carries at least one functional group selected from acid groups, hydroxyl groups, amine groups and mixtures thereof, more preferably a homopolymer or copolymer obtainable from the polymerization of at least one vinyl monomer and/or (meth)acrylic monomer, at least a portion of which carries at least one functional group selected from acid groups, hydroxyl groups, amine groups and mixtures thereof. In particular, in the case of homopolymers and copolymers of vinylphenol, it is possible to modify these polymers by condensation reaction (especially Mannich reaction) with compounds carrying one or more amine groups, such as ethanolamine and/or N-methylglucosamine.

Examples of monomers containing an acid group are acrylic acid and methacrylic acid and maleic acid. Examples of monomers containing a hydroxyl group are 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 3-phenoxy-2-hydroxypropyl (meth)acrylate, glycerol mono(meth)acrylate, N-(2-hydroxypropyl)(meth)acrylamide, allyl alcohol, hydroxystyrene, hydroxyalkyl vinyl ethers (such as hydroxybutyl vinyl ether) and vinylbenzyl alcohol, vinylphenol and vinyl alcohol. Examples of other nonfunctional monomers which can be used additionally and which in particular do not carry acid groups, hydroxyl groups and mixtures thereof are ethylene, propylene, butylene and (meth)acrylates of aliphatic C ₁ -C ₃₀ monoalcohols, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 3-propylheptyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate and isobornyl (meth)acrylate. However, nonfunctional vinyl monomers are preferred, in particular over nonfunctional (meth)acrylates of aliphatic C ₁ -C ₃₀ monoalcohols.

If the polymer a1) is a homopolymer, it is preferably a poly(meth)acrylic acid. If the polymer a1) is a copolymer and has at least an acid group as a functional group, it is preferably a (meth)acrylic acid copolymer, which preferably comprises a polymer backbone and at least one side chain connected to the polymer backbone, the at least one side chain having an acid group, such as a carboxylic acid group.

The term "(meth)acryl" means "acryl" and/or "methacryl". Similarly, "(meth)acrylate" means acrylate and/or methacrylate, and "(meth)acrylic acid" means acrylic acid and methacrylic acid. "(Meth)acrylic acid polymers" are at least partially formed from "acrylic acid monomers" and/or "methacrylic acid monomers", but if other ethylenically unsaturated monomers (such as vinyl monomers) are additionally used when the polymer a1) is a copolymer, the (meth)acrylic acid polymer may additionally contain non-acryl and non-methacryl monomer units. Preferably, the main chain of such (meth)acrylic acid copolymers is formed from more than 50 mol%, even more preferably more than 75 mol% of (meth)acrylic acid monomers.

Preferably, at least one water-soluble polymer used as component a1) is selected from (meth)acrylic acid homopolymers, especially acrylic acid homopolymers, copolymers of (meth)acrylic acid and at least one olefinically unsaturated monomer different from (meth)acrylic acid, especially copolymers of (meth)acrylic acid and maleic acid, copolymers of maleic acid and at least one olefinically unsaturated monomer different from maleic acid, especially copolymers of maleic acid and ethylene and/or propylene and/or at least one alkyl vinyl ether such as methyl vinyl ether, copolymers of vinylphosphonic acid and at least one olefinically unsaturated monomer different from vinylphosphonic acid, especially copolymers of (meth)acrylic acid and vinylphosphonic acid and copolymers of (meth)acrylic acid, vinylphosphonic acid and maleic acid, homopolymers of vinyl alcohol, Copolymers of vinyl alcohol and at least one olefinically unsaturated monomer different from vinyl alcohol (such as vinyl acetate), homopolymers of vinyl phenol, copolymers of vinyl phenol and at least one olefinically unsaturated monomer different from vinyl phenol, copolymers of vinyl ethanol and at least one olefinically unsaturated monomer different from vinyl ethanol, and homopolymers and copolymers of vinyl phenol, which have been modified with at least one amine, preferably at least one primary amine, such as N-ethanolamine and/or N-methylglucamine, and mixtures thereof. The modification is preferably carried out by a Mannich base reaction based on the condensation of formaldehyde with a primary or secondary amine.

More preferably, the at least one water-soluble polymer used as component a1) is selected from (meth)acrylic acid homopolymers, especially acrylic acid homopolymers; copolymers of (meth)acrylic acid and at least one olefinically unsaturated monomer different from (meth)acrylic acid, especially copolymers of (meth)acrylic acid and maleic acid; copolymers of maleic acid and at least one olefinically unsaturated monomer different from maleic acid, especially copolymers of maleic acid and ethylene and/or propylene and/or at least one alkyl vinyl ether such as methyl vinyl ether; homopolymers of vinyl alcohol; copolymers of vinyl alcohol and at least one olefinically unsaturated monomer different from vinyl alcohol; homopolymers and copolymers of vinylphenol, which homopolymers and copolymers have been modified with at least one amine, preferably at least one primary or secondary amine, such as N-ethanolamine and/or N-methylglucosamine, and mixtures thereof. Particularly preferred polymers are poly(vinyl phenol) modified with N-methyl reduced glucosamine, poly(vinyl phenol) modified with N-ethanolamine, poly(maleic acid-co-vinyl methyl ether), poly(maleic acid-co-acrylic acid), polyacrylic acid, poly(vinyl-phosphonic acid-co-acrylic acid), poly(acrylic acid-co-maleic acid-co-vinylphosphonic acid), poly(acrylic acid-co-vinyl ethanol), poly(acrylic acid-co-maleic acid-co-vinyl ethanol), and mixtures thereof.

Preferably, the weight average molecular weight ( _Mw ) of the at least one water-soluble polymer is in the range of 1000 to 350000 g/mol, preferably 2000 to 325000 g/mol, more preferably 3000 to 300000 g/mol, more preferably 4000 to 375000 g/mol. The weight average molecular weight is determined by the method described below in the "Methods" section.

If the polymer a1) used is a poly(meth)acrylic acid, in particular polyacrylic acid, its weight average molecular weight (M _w ) is preferably in the range of 10,000 to 350,000 g/mol, preferably 50,000 to 325,000 g/mol, more preferably 100,000 to 300,000 g/mol, even more preferably 150,000 or 200,000 to 375,000 g/mol. If the polymer a1) used is a copolymer prepared at least partly from maleic acid, its weight average molecular weight (M _w ) is preferably in the range of 10,000 to 200,000 g/mol, preferably 15,000 to 150,000 g/mol, more preferably 20,000 to 100,000 g/mol, even more preferably 30,000 to 80,000 g/mol. If the polymer a1) used is a homopolymer or copolymer prepared at least partly from vinyl alcohol and/or vinyl phenol, its weight average molecular weight ( _Mw ) is preferably in the range of 500 to 100,000 g/mol, preferably 750 to 50,000 g/mol, more preferably 1,000 to 25,000 g/mol, more preferably 1,000 to 10,000 g/mol.

Component a2) The acidic aqueous composition used in step 1) further comprises at least one metal cation selected from the group consisting of titanium, zirconium and cobalt ions and mixtures thereof as at least one component a2).

Preferably, the aqueous acidic composition used in step 1) comprises at least one component a2) in an amount in the range of 0.1 to 10 g/L, calculated in each case as metal, wherein the component a2) is preferably selected from titanium and zirconium ions and mixtures thereof, most preferably from zirconium ions. The content of component a2) can be monitored and determined by means of ICP-OES (optical emission spectroscopy with inductively coupled plasma). The method is described in detail below. Preferably, when the aqueous acidic composition used in step 1) is applied by spraying, the aqueous acidic composition comprises at least one component a2) in an amount in the range of 0.1 to 1.0 g/L, more preferably 0.2 to 0.6 g/L, even more preferably 0.2 to 0.4 g/L, calculated in each case as metal. Preferably, when the aqueous acidic composition used in step 1) is applied by rolling, the aqueous acidic composition comprises at least one component a2) in an amount in the range of 0.2 to 8.0 g/L, more preferably 0.5 to 7.5 g/L, even more preferably 0.7 to 5.0 g/L, even more preferably 1.0 to 3.0 or 2.0 g/L, calculated in each case as metal.

Preferably, a precursor metal compound is used to generate the metal cations present as component a2) in the composition. Preferably, the precursor metal compound is water-soluble. The solubility is determined at a temperature of 20° C. and atmospheric pressure (1.013 bar).

Particularly preferred zirconium, titanium and/or eum compounds are complex fluorides of these metals. The term "complex fluoride" includes single and multiple protonated forms as well as deprotonated forms. Mixtures of such complex fluorides can also be used. In the sense of the present invention, complex fluorides are complexes of zirconium, titanium and/or eum with fluoride ions in the composition, for example complexes formed by coordination of fluoride anions with zirconium, titanium and/or eum cations in the presence of water. In addition, carbonates and/or complex carbonates and/or lactates and/or in particular nitrates of zirconium, titanium and/or eum can also be used. Preferably, however, the cation is incorporated into the composition in the form of its complex fluoride.

Other optional components ( components a3) , a4) and / or a5)) The aqueous acidic composition may include other components as listed below. In view of the ingredients of the aqueous composition, the term "further includes" as used herein throughout the specification means "in addition to the required components". Therefore, such "other" components include ions different from the above-mentioned metal ions.

Optionally and preferably, the acidic aqueous composition used in step 1) further comprises at least one component a3), i.e. comprises free fluorine anions as at least one component a3). If free fluorine anions are present, they are preferably present in an amount in the range of 1 to 50 mg/L, more preferably 2 to 40 mg/L, even more preferably 3 to 30 mg/L, even more preferably 5 to 25 mg/L, calculated in each case as fluorine.

The acidic aqueous composition used in step 1) optionally and preferably contains free fluorine anions as component a3). These free fluorine anions can be generated by the presence of component a2), that is, in particular when complex fluorides of Ti, Zr and/or Hf are present in the composition, but can also or alternatively be generated by the presence of other optional components as described below, such as by incorporating at least one water-soluble fluorine compound. Examples of such water-soluble fluorine compounds are fluorides (except complex fluorides of Ti, Zr and/or Hf) and hydrofluoric acid. The free fluorine content is determined by means of a fluorine ion sensitive electrode according to the method disclosed in the "Method" section.

Optionally and preferably, the acidic aqueous composition used in step 1) further comprises molybdenum cations as at least one component a4), and the amount of the molybdenum cations is preferably in the range of 0.01 to 8.0 g/L calculated as metal.

Preferably, in particular when the aqueous acidic composition used in step 1) is applied by spraying, the aqueous acidic composition comprises at least one component a4) in an amount in the range of 0.01 to 0.2 g/L, more preferably 0.01 to 0.1 g/L, even more preferably 0.01 to 0.05 or to 0.03 g/L, calculated in each case as metal. Preferably, when the aqueous acidic composition used in step 1) is applied by rolling, the aqueous acidic composition comprises at least one component a4) in an amount in the range of 0.2 to 8.0 g/L, more preferably 0.4 to 7.5 g/L, even more preferably 0.5 to 6.0 g/L, calculated in each case as metal.

Preferably, the amount of component a4) is lower than the amount of component a2).

For the preparation of the aqueous acidic composition, in case the composition contains a4), preferably a water-soluble (at a temperature of 20°C and atmospheric pressure (1.013 bar)) molybdenum salt is used. Preferably, the molybdenum ions are incorporated in the form of at least one molybdenum salt, preferably in the form of at least one ammonium molybdate.

Optionally, the acidic aqueous composition used in step 1) further comprises at least one organosilane as an optional component a5), the content of which is preferably in the range of 10 to 500 ppm, more preferably 20 to 100 ppm.

Examples are, for example, (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, (3-butylenepropyl)trimethoxysilane, (3-butylenepropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane and/or (3-glycidyloxypropyl)triethoxysilane and/or vinyltrimethoxysilane.

Other optional components Optionally, the aqueous acidic composition further comprises at least one metal cation, which is selected from the group of metal cations of the 1st to 3rd subgroups (copper, zinc and carbendazim) and the 5th to 8th subgroups (vanadium, chromium, manganese, iron, cobalt and nickel groups) of the periodic table of the elements, including the chrysogens and the 2nd main group (alkali earth metal group) of the periodic table of the elements, lithium, bismuth and tin. Preferably, however, metal cations of the chromium, cobalt and nickel groups are not used. The metal cations mentioned above are usually introduced in the form of water-soluble compounds, preferably in the form of water-soluble salts. Preferably, the one or more cations are selected from the group consisting of cations of niobium and other niobium elements, iron, calcium, copper, magnesium, niobium, tantalum, yttrium, vanadium, lithium, bismuth and tin.

Optionally, the aqueous acidic composition further comprises at least one substance for adjusting the pH value, which is preferably selected from the group consisting of nitric acid, sulfuric acid, methanesulfonic acid, acetic acid, ammonia water, sodium hydroxide and sodium carbonate, among which nitric acid, ammonia water and sodium carbonate are preferred. Depending on the pH value of the acidic aqueous composition, the above compounds may be in their fully or partially deprotonated form or in their protonated form.

Optionally, the aqueous acidic composition further comprises at least one complexing agent. An example is 1-hydroxyethane-1,1-diphosphonic acid (HEDP).

Optionally, the aqueous acidic composition further comprises at least one corrosion inhibitor. Examples are L-cysteine and other amino acids, benzotriazole and mixtures thereof. Preferably, the at least one corrosion inhibitor does not contain any type of metal ions.

Optionally, the aqueous composition further comprises at least one organic acid, preferably at least one organic acid having at least two carboxylic acid groups and/or at least one organic acid having at least one carboxylic acid group and at least one other functional group having at least one donor atom (such as an OH-group), such as lactic acid, especially when the aqueous composition is alkaline. The presence of such compounds can help stabilize at least one metal ion in the composition, such as a Zr cation.

Optionally, the aqueous acidic composition further comprises phosphate anions, which may be preferably added in the form of phosphoric acid. Preferably, the phosphate anions are present in an amount ranging from 0.5 to 90 g/ _L calculated as _P2O5 .

The aqueous composition may further comprise at least one of the following components: one or more waxes, one or more wetting agents, and one or more defoaming agents.

Optional step 1a) After step 1), the surface of the substrate obtained after contacting according to step 1) can be rinsed with deionized water or tap water (optional step 1a)). If this step is performed, it is preferably performed before any drying or curing performed in step 1).

Step 2) of the method In step 2), at least one thermoplastic polymer material TM1 is at least partially applied to the film or the dried or solidified layer obtained after step 1), wherein the at least one thermoplastic polymer material TM1 is i) applied in foil form (option i)) or ii) applied by injection in a molten state (option (ii)) to the film or the dried or solidified layer obtained after step 1) to form a metal-plastic hybrid material. Preferably, step 2), option i) is not performed by injection molding.

The formed foil obtained from the use of thermoplastic polymer material TM1 in step 2), first option i), preferably serves as a compatibilizer material for the thermoplastic polymer material TM2 which is optionally subsequently injected in step 3a), if applicable.

Step 2), the second option ii) and optionally step 3a) each represent an injection molding step, in which the thermoplastic polymer material TM1 (or in the case of step 3a), TM2) is injected directly onto the metal surface of the substrate, to which the acidic aqueous composition has previously been applied in step 1).

Step 2) may be performed in a continuous or discontinuous manner.

The substrate obtained after step 1) or, as the case may be, after step 1a) is preferably heated before carrying out step 2), preferably to a temperature higher than the melting temperature of the thermoplastic material TM1 used.

Preferably, the thermoplastic polymer material TM1 used in step 2) and/or the thermoplastic polymer material TM2 used in step 3a) as appropriate is applied by applying a vacuum to bring the respective thermoplastic polymer material into contact with at least a portion of the surface of the substrate, but preferably the entire surface of the substrate, which has been in contact with the acidic aqueous composition in step 1), and to remove the air enclosed between the surface of the substrate and the respective thermoplastic polymer material. Preferably, the temperature of the substrate and the respective thermoplastic polymer material applied thereto is maintained above a temperature that promotes the connection of the applied thermoplastic polymer material and the metal substrate. After the aforementioned heating, the substrate is preferably placed in an apparatus in which the respective thermoplastic polymer material can be placed on the surface of the substrate, preferably in a thermoforming apparatus: for example, in which the thermoplastic polymer material TM1 can be applied in foil form. As an alternative, it is also possible to first place the substrate in the apparatus in which the respective thermoplastic polymer material is to be applied and then heat the substrate before placing the thermoplastic polymer material on the substrate. Preferably, after placing the heated substrate in the apparatus or after placing the substrate in the apparatus and subsequently heating, the respective thermoplastic polymer material is placed on the substrate and optionally heated, such as in the case of step 2), option ii), in which the material is injected in the molten state. If the thermoplastic polymer material is heated, the heating can be performed, for example, by infrared radiation.

The heating temperature of the thermoplastic polymer material is preferably chosen so that the thermoplastic material has rubber elasticity. For this purpose, the thermoplastic material is preferably heated to a temperature above the glass transition temperature of the thermoplastic material if it is an amorphous thermoplastic, or to a temperature above the melting temperature of the crystallites if it is a semicrystalline thermoplastic, but preferably below the melting temperature to avoid any damage. After the respective thermoplastic polymer material has been placed on the surface of the substrate and, if appropriate, after the material has been heated, a vacuum is preferably applied as described above.

By applying a vacuum, the thermoplastic polymer material is preferably connected to the surface of the substrate and a strong connection can be achieved. Removing air that may be trapped between the surface of the substrate and the thermoplastic polymer material preferably produces a smooth surface without bubbles. For applying the vacuum, the substrate can include openings through which the air can be extracted. If the substrate should not have any openings, the air between the substrate and the thermoplastic polymer material can also be extracted at the edges of the thermoplastic polymer material. If the air is extracted at the edges, it is preferably extracted at least at two opposite sides and preferably over the entire circumference of the respective thermoplastic polymer material. For applying the vacuum, any suitable vacuum pump can be used. If air is evacuated at the edge of the thermoplastic polymer material, the respective thermoplastic polymer material is preferably fixed in a device for applying vacuum so that a gap is formed between the substrate and the edge of the thermoplastic polymer material and the vacuum is applied through the gap. By applying the vacuum, the thermoplastic polymer material preferably contacts the substrate uniformly over the entire surface of the substrate and thus forms a uniform layer on the surface of the substrate.

After the thermoplastic polymer material has been brought into contact with the entire surface of the preferred substrate, the temperature of the substrate and the respective thermoplastic polymer material is preferably maintained at a temperature that promotes the connection of the thermoplastic material and the substrate, preferably at a temperature that is higher than the melting temperature of the thermoplastic material. By maintaining the temperature, the thermoplastic material preferably chemically reacts at least with the functional groups of the water-soluble polymer initially present in the acidic aqueous composition, thereby achieving a stable connection of the surface of the substrate with the respective thermoplastic polymer material and forming a composite component comprising a "metal layer" (metal surface of the substrate) and a "polymer layer" (applied thermoplastic material).

Preferably, at least before carrying out step 2), option ii), the substrate obtained after step 1), optionally 1a), is placed in a mold, and then carrying out step 3).

Optionally optional step 3a) In an optionally optional step 3a), at least one thermoplastic polymer material TM2 is at least partially injected onto the surface of the foil of the metal-plastic hybrid material obtained after steps 2) and i), the at least one thermoplastic polymer material TM2 being the same or different from the thermoplastic material TM1 applied in step 2) and being present in a molten state.

If optional step 3a) is performed, the thermoplastic polymer material TM2 is preferably different from the thermoplastic polymer material TM1.

Optional step 3b) In an optional step 3b), a further substrate S2 having at least one metallic surface which is at least partially made of aluminum and/or at least one aluminum alloy and has been treated in method step 1), i.e. by using an acidic aqueous composition, or vice versa, is applied to the surface of the foil of the metal-plastic hybrid material obtained after steps 2) and i).

Thermoplastic Polymer Materials TM1 and TM2 Thermoplastic polymer material TM1 may be the same as or different from the thermoplastic material TM2, but is preferably different therefrom.

Preferably, the thermoplastic polymer material TM1 is capable of chemically bonding to the functional groups of the water-soluble polymer initially present in the acidic aqueous composition used in step 1).

Preferably, the thermoplastic polymer material TM1 is selected from polyamide, polyester (such as PET and/or PBT), polyurethane, polycarbonate, polyolefin (such as polypropylene and polyethylene) and mixtures thereof. Recycled thermoplastic polymer materials such as recycled polyamide can be used. Preferably, the polyamide is selected from PA6, PA66, PA66/6, PA6.10, PA6.12, PA12, PA9T, PA6I/6T, PA6T/6I, PA6/6.36 and combinations thereof. The best are polyester (such as PET and/or PBT) and polyamide. Preferably, at least one polyester is applied as at least one thermoplastic polymer material TM1 via step 2) (i) or (ii).

A thermoplastic polymer material TM1 can be used, such as a polyamide in a certain form, in which it has been compounded with at least one additive, such as at least one rubber, such as EPDM (ethylene propylene diene monomer) rubber, in order to improve the properties of the thermoplastic polymer material, in particular so as to reduce its moisture absorption. Alternatively or additionally, the thermoplastic polymer material TM1 and/or TM2, preferably TM2, may optionally comprise (i) at least one fiber, such as glass fiber, carbon fiber, polyarylamide fiber, and combinations thereof, and/or may optionally comprise (ii) a polyether block polyamide, such as a copolymer of a polyether diamine and an aliphatic C ₄ to C ₄₀ dicarboxylic acid and/or a C ₆ to C ₁₂ lactamide (such as caprolactam or lauryl lactamide), a copolymer of an aliphatic C ₄ to C ₁₀ diamine and an aliphatic C ₄ to C ₄₀ dicarboxylic acid, _{... The} present invention may further comprise (iii) at least one impact modifier, such as a maleic anhydride graft copolymer of at least one of α-olefin, (meth)acrylate and (meth)acrylic acid and ethylene, a copolymer of at least one of ethylene and (meth)acrylate and maleic anhydride, styrene maleic anhydride or maleic anhydride grafted polypropylene.

Preferably, the thermoplastic polymer material TM2 is selected from polyamide, polyester (such as PET and/or PBT), polyolefin (such as polypropylene and polyethylene) and mixtures thereof. Preferably, the polyamide is selected from PA6, PA66, PA66/6, PA6.10, PA6.12, PA12, PA9T, PA6I/6T, PA6T/6I, PA6/6.36 and combinations thereof. Recycled thermoplastic polymer materials such as recycled polyamide can be used.

Preferably, the melting temperature of the thermoplastic polymer material TM1 is in the range of 80° C. to 280° C. For example, polyolefin may have a melting temperature of 80° C., while polyamide has a significantly higher melting temperature of, for example, 280° C.

Preferably, the melting temperature of the thermoplastic polymer material TM2 is within the range defined with respect to the thermoplastic polymer material TM1.

Metal - Plastic Hybrid Material Obtainable by the Method of the Invention Another subject matter of the present invention is a metal-plastic hybrid material obtainable by the method of the invention.

All the preferred embodiments described above with respect to the method of the present invention and its preferred embodiments are also preferred embodiments of the metal-plastic hybrid material of the present invention that can be obtained by the method.

Preferably, the dry layer thickness of the layer obtained from the dried or cured film, obtainable by at least partially applying an aqueous acidic composition as defined above in relation to step 1) of the process according to the invention to the metal surface, is in the range of 100 to 1000 nm, more preferably 150 to 750 nm, in particular 250 to 550 nm.

A further subject matter of the present invention is the use of an acidic aqueous composition as defined above in relation to step 1) of the process according to the invention for bonding a metal surface of a substrate at least partially made of aluminum and/or at least one aluminum alloy to a thermoplastic material, such as thermoplastic material TM1, which is present on the surface in foil form or applied to the surface by injection molding, preferably by using the process according to the invention.

All the preferred embodiments described above with respect to the method of the present invention, the metal-plastic hybrid material of the present invention obtainable by the method, and the preferred embodiments thereof are also preferred embodiments of the uses of the present invention.

Metal - Plastic Hybrid Material Another subject matter of the present invention is the metal-plastic hybrid material itself, i.e. a metal-plastic hybrid material comprising the following components: a substrate S1 having at least one metal surface, the at least one metal surface being at least partially made of at least one aluminum and/or at least one aluminum alloy, a film or a dried or cured layer, which is at least partially applied to the metal surface, which film or the dried or cured layer can be obtained by applying at least partially an aqueous acidic composition as defined above in step 1) of the method of the invention to the metal surface, and at least one thermoplastic polymer material TM1, which is in the form of a foil or in a form obtainable by injection molding, in each case, the at least one thermoplastic polymer material TM1 is at least partially applied to the film or the dried or cured layer, which is preferably as defined in step 2) of the method of the invention, and, Furthermore, at least one thermoplastic polymer material TM2, which is the same as or different from the thermoplastic polymer material TM1, is applied at least partially to the at least one thermoplastic polymer material TM1 in a form obtainable by injection molding, with the proviso that the thermoplastic polymer material TM1 has been applied in foil form, Or in addition, optionally, a substrate S2 is selected, which has at least one metal surface, which surface is at least partially made of aluminum and/or at least one aluminum alloy, and the substrate has a film or a dried or cured layer at least partially applied to the metal surface, which film or dried or cured layer can be obtained by applying an aqueous acidic composition as defined in step 1) above with respect to the method of the present invention, wherein the film or dried or cured layer at least partially present on the metal surface of the substrate S2 is located adjacent to the at least one thermoplastic polymer material TM1, with the limitation that the thermoplastic polymer material TM1 has been applied in the form of a foil.

Preferably, a metal-plastic hybrid material can be obtained by the method of the present invention.

Preferably, the total thickness of the thermoplastic polymer material TM1 in the form of a laminate or in a form obtainable by injection molding is in the range of 200 to 800 μm.

All the preferred embodiments described above with respect to the method of the present invention, the metal-plastic hybrid material of the present invention obtainable by the method, the use of the present invention and its preferred embodiments are also preferred embodiments of the metal-plastic hybrid material of the present invention itself.

Preferably, the film or the dried or cured layer, preferably the dried or cured layer, preferably the dried layer, applied at least partially to the metal surface of the metal-plastic hybrid material has the following coating weight determined by XRF (X-ray fluorescence spectroscopy): Due to component a2) present in the acidic aqueous composition used, in each case calculated as metal, 0.1 to 40 mg/m ² , preferably 0.2 to 30 mg/m ² , even more preferably 0.5 to 20 mg/m ² , more preferably 1.0 to 15 mg/m ² , more preferably 1.5 to 10 mg/m ² , in particular 2.0 to 8 mg/m ² of zirconium and/or titanium and/or uranium, preferably zirconium and/or titanium, more preferably zirconium, Calculated as metal, 0 or 0.1 to 40 mg/m ² , more preferably 0 or 0.2 to 30 mg/m ² , even more preferably 0 or 0.5 to 20 mg/m ² , more preferably 0 or 1.0 to 15 mg/m ² , more preferably 0 or 1.5 to 10 mg/m ² , especially 2.0 to 8 mg/m ² of molybdenum.

If at least one thermoplastic polymer TM2 is present in the metal-plastic hybrid material, it is preferred to carry out the optional step 3a) of the method according to the invention. In this case, the thermoplastic polymer TM1 has been applied in the form of a foil in step 2) and in step 3a), the thermoplastic polymer TM2 has been applied on the top by injection molding.

If a further substrate S2 which also has at least one metal surface at least partially made of aluminum and/or at least one aluminum alloy is present in the metal-plastic hybrid material, it is preferred to carry out step 3b) of the method according to the invention, which may be used as appropriate. In this case, the thermoplastic polymer material TM1 has been applied in the form of a foil in step 2) and in step 3b), after at least one metal surface of the substrate S2 has also been treated with an acidic aqueous composition according to step 1), the substrate S2 and its treated surface are applied adjacent to the foil formed from the thermoplastic polymer material TM1, so that a sandwich structure is formed overall, in which the foil made using TM1 is flanked by two metal surfaces of two substrates S1 and S2, each of which carries a coating obtained by treatment step 1). Preferably, when the metal-plastic hybrid material comprises another substrate S2, it can be considered as a sandwich structure comprising two substrates S1 and S2, wherein each of these substrates is adhered to one surface of the thermoplastic material TM1 in the form of a foil by means of an adhesive film or a dry or cured layer, which can be obtained by applying an aqueous acidic composition as defined in step 1) of the method of the invention. Preferably, each of the substrates S1 and S2 is a sheet or coil made of aluminum and/or its alloys. Depending on the desired application, the total thickness of each coil or sheet is in the range of 0.2 mm to 3 mm.

Use of the Metal - Plastic Hybrid Material Another subject matter of the invention is the use of the metal-plastic hybrid material or the metal-plastic hybrid material obtainable by the method of the invention as a component in the automotive, construction or electronics industry.

All the preferred embodiments described above with respect to the method of the present invention, the metal-plastic hybrid material of the present invention obtainable by the method, the aforementioned uses of the present invention, the metal-plastic hybrid material of the present invention itself and its preferred embodiments are also preferred embodiments of the uses of the metal-plastic hybrid material of the present invention.

In particular, the metal-plastic hybrid material can be used for electromobility applications, the manufacture of components for the electronics industry and/or for the manufacture of automotive components, especially where weight reduction is desired, wherein the substrate S1 and optionally the substrate S2 are foils. Other possible uses include lidar and EMI shielding applications, the manufacture of control panels in automobiles, the manufacture of battery housings and protective plates for batteries.

Method 1. Cross-cut test according to DIN EN ISO 2409 (06-2013) The cross-cut test according to DIN EN ISO 2409 (06-2013) is used to determine the strength of the adhesion. The cutter spacing is 3 mm. The evaluation is based on characteristic cross-cut values in the range of 0 (excellent adhesion) to 5 (poor adhesion). Three tests are carried out on each sample and the average value is determined.

2. Determination of the average molecular weight _Mw and _Mn The number-average and weight-average molecular weights ( _Mn and _Mw ), respectively, were determined according to the following protocol: The samples were analyzed by SEC (size exclusion chromatography) equipped with a MALS detector. The absolute molar mass was obtained by choosing a dn/dC value equal to 0.1875 mL/g in order to obtain a recovery mass of about 90%. The polymer sample was dissolved in the mobile phase and the resulting solution was filtered with a Millipore filter 0.45 µm. The dissolution conditions were as follows. Mobile phase: H ₂ O 100 vol%, 0.1 M NaCl, 25 mM NaH ₂ PO ₄ , 25 mM Na ₂ HPO ₄ ; 100 ppm NaN ₃ ; Flow rate: 1 mL/min; Column: Varian Aquagel OH mixed H, 8 µm, 3×30 cm; Detection: RI (concentration detector Agilent) + MALLS (multi-angle laser light scattering) Mini Dawn Tristar + UV at 290 nm; Sample concentration: about 0.5 wt% in the mobile phase; Injection loop: 100 µL. The polydispersity P can be calculated from the obtained M _n and M _w values.

3. Determination of free fluorine content The free fluorine content is determined by means of a fluorine ion selective electrode. The electrode is calibrated using at least three master solutions with known fluorine concentrations. A calibration curve is established by the calibration process. This curve is then used to determine the fluorine content.

4. ICP-OES The amount of certain elements (e.g. zirconium, titanium, columbium, etc.) in the sample being analyzed is determined using inductively coupled plasma atomic emission spectrometry (ICP-OES) according to DIN EN ISO 11885 (date: September 1, 2009). The sample undergoes thermal excitation in an argon plasma generated by a high-frequency field and the light emitted due to the electron transfer becomes visible as spectral lines of the corresponding wavelength and is analyzed using an optical system. There is a linear relationship between the intensity of the emitted light and the concentration of the element in question. Prior to implementation, a calibration measurement is performed using standards of known elements (reference standards) according to the specific sample being analyzed. These calibrations can be used to determine the concentrations of unknown solutions, such as titanium, zirconium, and einsteinium.

5. Tensile Strength The tensile strength is measured according to ISO 527-1:2012.

EXAMPLES The following examples further illustrate the present invention but should not be construed as limiting the scope thereof.

1. Preparation of acidic aqueous coating compositions 1.1 A number of acidic aqueous compositions A1 to A3 (1 L each ₎ have been prepared. All aqueous compositions contain H _{2 ZrF 6} in an amount corresponding to the ppm value of zirconium calculated as metal, as shown in Table 1a below. All aqueous compositions further contain ammonium heptamolybdate in an amount corresponding to the ppm value of molybdenum calculated as metal, as shown in Table 1 below. All compositions are chromium-free and contain free fluorine anions. Each composition further contains one of the following water-soluble polymers P1 to P3: P1: commercially available polyacrylic acid with M _w >150,000 g/mol, P2: copolymer of maleic acid and vinyl methyl ether, P3: copolymer of maleic acid and ethylene. Table 1a: Composition pH Amount of polymer [g/L] Amount of Zr[g/L] Mo content [g/L] A1 3.6 P1: 0.25 0.5 0.05 A2 3.6 P2: 0.50 0.5 0.05 A3 3.6 P3: 0.18 0.5 0.05

1.2 A number of other acidic aqueous compositions A4 to A6 ( ₁ L each) were prepared. All aqueous compositions contained H _{2 ZrF 6} in an amount corresponding to the ppm value of zirconium calculated as metal, as shown in Table 1b below. All aqueous compositions further contained ammonium heptamolybdate in an amount corresponding to the ppm value of molybdenum calculated as metal, as shown in Table 1b below. All compositions were free of chromium and contained free fluorine anions. Each composition further contained one of the water-soluble polymers P1 to P3 as identified above. Table 1b: Composition pH Amount of polymer [g/L] Amount of Zr[g/L] Mo content [g/L] Amount of free fluoride [mg/L] A4 3.8 P1: 1.0 0.5 0.05 12 A5 3.8 P2: 1.0 0.5 0.05 13 A6 3.8 P3:1.0 0.5 0.05 12

2. Pretreatment 2.1 An aluminum alloy substrate (substrate T1; 5754 AlMg3) has been used as a substrate in the form of a coil. 5754 AlMg3 is an aluminum-magnesium alloy substrate.

The substrates were cleaned using the commercial alkaline product Gardoclean® S 5160 (at 60 to 70 °C). Subsequently, rinsing was performed twice with tap water (30 seconds each). Subsequently, an acid cleaning step was performed using the commercial product Gardoclean® S 5240/2. Subsequently, rinsing was performed with tap water (30 seconds) and subsequently with deionized water (30 seconds).

A contacting step is then carried out, i.e. the surface of the substrate is contacted with one of the acidic aqueous compositions A1 to A3 described above in Item 1.1 , in order to form a conversion coating with adhesion-promoting properties on the surface of the substrate. The contacting step is carried out in each case by spraying one of the acidic aqueous compositions onto the surface of the substrate for 60 seconds. Prior to spraying, the acidic aqueous composition is heated to 25° C.

After the contacting step, a drying step (15 min at 60-70°C) was performed after a period of air blowing. The resulting dry layer thickness was in the range of 50-200 nm.

2.2 An aluminum alloy substrate (substrate T2; AA 6060) has been used as the substrate.

The substrates were cleaned using the commercial alkaline product Gardoclean® T 5281 A (at 55°C). Subsequently, they were rinsed twice with tap water (30 seconds each). Subsequently, an acid cleaning step was performed using the commercial product Gardacid® P 4432. Subsequently, they were rinsed three times with tap water (60 seconds each).

A contacting step is then carried out, i.e. the surface of the substrate is contacted with one of the acidic aqueous compositions A4 to A6 described above in Item 1.2 , in order to form a conversion coating with adhesion-promoting properties on the surface of the substrate. The contacting step is carried out in each case by spraying one of the acidic aqueous compositions onto the surface of the substrate for 60 seconds. Prior to spraying, the acidic aqueous composition is heated to 30° C.

After the contacting step, rinse three times with tap water (60 seconds each).

Then, a drying step (8 minutes at 100°C) was performed after a period of air blowing.

3. Preparation of Metal - Plastic Hybrids 3.1 A mixture of polybutylene terephthalate (PBT) and glass fibers (commercial product Tecadur® PBT-GF30) as thermoplastic polymer is applied by injection molding directly to the surface of the substrate obtained after the pretreatment as described in Item 2.1 at a temperature between 180° C. and 240° C. Depending on the desired application, the thickness of the resulting laminate (thickness of the plastic layer) produced by injection molding is in the range of 400 µm to 2 cm.

3.2 A sandwich structure is also produced in the same manner as described in item 3.1 , however, Tecadur® PBT-GF30 is injected between the two surfaces of two substrates, each of which is obtained after the pretreatment described in item 2.1 .

3.3 A mixture of polybutylene terephthalate (PBT) and glass fibers (commercial product Tecadur® PBT-GF30) as thermoplastic polymer is applied by injection molding directly to the surface of the substrate obtained after the pretreatment as described in item 2.2 at a temperature between 180°C and 240°C. The thickness of the resulting laminate (thickness of the plastic layer) produced by injection molding is in the range of 400 µm to 2 cm, depending on the desired application.

4. Properties of the metal - plastic hybrid material obtained 4.1 Various properties of the product obtained by the method described above in Items 3.1 and 3.2 were investigated. These properties were determined according to the test methods described above. The results are shown in Tables 2 and 3. In particular, the adhesive strength was investigated. Table 2: Aqueous compositions for chemical pretreatment Cross-section A1 0 A2 0 A3 0

It is evident from Table 2 that excellent adhesion of PBT to the metal substrate was achieved in all cases. Table 3: Aqueous compositions for chemical pretreatment Tensile strength [MPa] A1 23.7 A2 20.8 A3 15.0

The sandwich structure was subjected to peeling tests. The results showed that peeling was not possible.

4.2 Various properties of the product obtained by the method described above in item 3.3 were investigated. These properties were determined according to the test methods described above. The results are shown in Table 4. In particular, the adhesive strength was investigated. Table 4: Aqueous compositions for chemical pretreatment Cross-section A4 0 A5 0 A6 0

As is evident from Table 4, excellent adhesion of the PBT to the metal substrate was achieved in all cases.

Claims (15)

A method for preparing a metal-plastic hybrid material, the material comprising a substrate S1 having at least one metal surface and at least one thermoplastic material applied to the metal surface of the substrate S1, the method comprising at least step 1) and step 2) and optionally step 3a) or 3b), namely 1) applying an aqueous acidic composition at least partially to at least one metal surface of the substrate S1 to at least partially form a film on the surface, wherein the metal surface is at least partially made of aluminum and/or at least one aluminum alloy, and wherein, in addition to water, the acidic aqueous composition also comprises at least one water-soluble polymer as at least one component a1), the at least one water-soluble polymer having at least one functional group selected from acid groups, hydroxyl groups, amine groups and mixtures thereof, at least one metal cation selected from the group consisting of titanium, zirconium and cobalt ions and mixtures thereof as at least one component a2), and free fluorine anions as at least one component a3), and drying or curing the film as appropriate to form a dried or cured layer, 2) applying at least one thermoplastic polymer material TM1 at least partially to the film or the dried or cured layer obtained after step 1), wherein the at least one thermoplastic polymer material TM1 is i) applied in foil form or ii) applied by injection in a molten state to the film or the dried or solidified layer obtained after step 1) to form the metal-plastic hybrid material, and 3a)   optionally, at least one thermoplastic polymer material TM2 is at least partially injected onto the surface of the foil of the metal-plastic hybrid material obtained after steps 2) and i), the at least one thermoplastic polymer material TM2 being the same or different from the thermoplastic material TM1 applied in step 2) and being in a molten state, or 3b) Optionally, a further substrate S2 having at least one metallic surface at least partially made of aluminum and/or at least one aluminum alloy and having been treated in method step 1) is applied to the surface of the foil of the metal-plastic hybrid material obtained after steps 2) and i) or vice versa. The method of claim 1, wherein the acidic aqueous composition used in step 1) has a pH value in the range of 0.1 to <7.0, preferably 0.5 to 6.5, more preferably 1.0 to 6.0, even more preferably 1.5 to 5.5, still more preferably 2.0 to 5.0, even more preferably 2.5 to 4.5, still more preferably 3.0 to 4.0, and most preferably >3.0 to <3.7. The method of claim 1, wherein the at least one water-soluble polymer used as component a1) is present in the acidic aqueous composition in an amount ranging from 0.05 to 2.0 g/L, preferably 0.10 to 1.8 g/L, more preferably 0.12 to 1.6 g/L, still more preferably 0.14 to 1.5 g/L, even more preferably 0.16 to 1.4 g/L, still more preferably 0.18 to 1.2 g/L, and most preferably 0.20 to 1.0 g/L. The method of claim 1, wherein the at least one water-soluble polymer used as component a1) has at least one functional group selected from the following: carboxylic acid group, phosphonic acid group, sulfonic acid group, hydroxyl group, amine group and mixtures thereof, more preferably selected from carboxylic acid group, hydroxyl group, amine group and mixtures thereof, and even more preferably selected from carboxylic acid group. A method as claimed in any one of claims 1 to 4, wherein the at least one water-soluble polymer used as component a1) is a homopolymer or copolymer obtainable by the polymerization of at least one ethylenically unsaturated monomer, wherein at least a portion of said monomers have at least one functional group as defined in claim 1 or 4, preferably a homopolymer or copolymer obtainable by the polymerization of at least one vinyl monomer and/or (meth)acrylic monomer, wherein at least a portion of said monomers have at least one functional group as defined in claim 1 or 4. The method of any one of claims 1 to 4, wherein the at least one water-soluble polymer used as component a1) is selected from (meth)acrylic acid homopolymers, especially acrylic acid homopolymers; copolymers of (meth)acrylic acid and at least one olefinically unsaturated monomer different from (meth)acrylic acid, especially copolymers of (meth)acrylic acid and maleic acid; copolymers of maleic acid and at least one olefinically unsaturated monomer different from maleic acid, especially copolymers of maleic acid and ethylene and/or propylene and/or at least one alkyl vinyl ether such as methyl vinyl ether; copolymers of vinylphosphonic acid and at least one olefinically unsaturated monomer different from vinylphosphonic acid, especially copolymers of (meth)acrylic acid and maleic acid; The present invention relates to copolymers of (meth)acrylic acid, vinylphosphonic acid and maleic acid; homopolymers of vinyl alcohol; copolymers of vinyl alcohol and at least one ethylenically unsaturated monomer different from vinyl alcohol; homopolymers of vinyl phenol; copolymers of vinyl phenol and at least one ethylenically unsaturated monomer different from vinyl phenol; copolymers of vinyl ethanol and at least one ethylenically unsaturated monomer different from vinyl ethanol; homopolymers and copolymers of vinyl phenol, which have been modified with at least one amine, preferably at least one primary amine, such as N-ethanolamine and/or N-methylglucosamine; and mixtures thereof. A method as claimed in any one of claims 1 to 4, wherein the at least one water-soluble polymer used as component a1) is selected from (meth)acrylic acid homopolymers, especially acrylic acid homopolymers; copolymers of (meth)acrylic acid and at least one olefinically unsaturated monomer different from (meth)acrylic acid, especially copolymers of (meth)acrylic acid and maleic acid; copolymers of maleic acid and at least one olefinically unsaturated monomer different from maleic acid, especially copolymers of maleic acid and ethylene and/or propylene and/or at least one alkyl vinyl ether such as methyl vinyl ether; homopolymers of vinyl alcohol; copolymers of vinyl alcohol and at least one olefinically unsaturated monomer different from vinyl alcohol; homopolymers and copolymers of vinyl phenol, which homopolymers and copolymers have been modified with at least one amine, preferably at least one primary amine, such as N-ethanolamine and/or N-methylglucosamine; and mixtures thereof, Preferably, it is selected from poly(vinyl phenol) modified with N-methyl reduced glucosamine, poly(vinyl phenol) modified with N-ethanolamine, poly(maleic acid-co-vinyl methyl ether), poly(maleic acid-co-acrylic acid), polyacrylic acid, poly(vinyl phosphonic acid-co-acrylic acid), poly(acrylic acid-co-maleic acid-co-vinyl phosphonic acid), poly(acrylic acid-co-maleic acid-co-vinyl alcohol) and mixtures thereof. The method of any one of claims 1 to 4, wherein the aqueous acidic composition used in step 1) comprises the at least one component a2), in each case calculated as metal, the amount of the at least one component a2) is in the range of 0.1 to 10.0 g/L, wherein component a2) is preferably selected from titanium and zirconium ions and mixtures thereof, most preferably selected from zirconium ions, wherein, when the aqueous acidic composition used in step 1) is applied by spraying, it preferably comprises in each case calculated as metal, a content of 0.1 to 1.0 g/L, more preferably 0.2 to 0.6 g/L, even more preferably 0.2 to 0.4 g/L, and wherein, when the aqueous acidic composition used in step 1) is applied by rolling, it contains the at least one component a2) in an amount in the range of 0.2 to 8.0 g/L, preferably 0.5 to 7.5 g/L, even more preferably 0.7 to 5.0 g/L, still more preferably 1.0 to 3.0 or 2.0 g/L, calculated in each case as metal. The method of any one of claims 1 to 4, wherein the aqueous acidic composition used in step 1) further comprises molybdenum cations as at least one component a4), the content of which is preferably in the range of 0.01 to 8.0 g/L, wherein when the aqueous acidic composition used in step 1) is applied by spraying, it contains, in each case, calculated as metal, preferably in a content of 0.01 to 0.2 g/L, more preferably 0.01 to 0.1 g/L, even more preferably 0.01 to 0.05 or to 0.03 g/L, and wherein, when the aqueous acidic composition used in step 1) is applied by rolling, it contains the at least one component a4) in an amount preferably in the range of 0.2 to 8.0 g/L, more preferably 0.4 to 7.5 g/L, even more preferably 0.5 to 6.0 g/L, calculated in each case as metal. A method as claimed in any one of claims 1 to 4, wherein the at least one thermoplastic polymer material TM1 and the at least one thermoplastic polymer material TM2 are independently selected from polyamide; polyester, especially PET and/or PBT; polyurethane; polycarbonate; polyolefin, especially polypropylene and/or polyethylene; and mixtures thereof, wherein the at least one thermoplastic polymer material TM1 is preferably selected from polyester, especially PET and/or PBT. A metal-plastic hybrid material, which can be obtained by the method of any one of claims 1 to 10. A use of an acidic aqueous composition as defined in any one of claims 1 to 9 for bonding a metal surface of a substrate to a thermoplastic polymer material which is present on the surface in foil form or applied to the surface by injection molding, the metal surface being at least partially made of aluminum and/or at least one aluminum alloy. A metal-plastic hybrid material comprising: a substrate S1 having at least one metal surface, the at least one metal surface being at least partially made of at least one aluminum and/or at least one aluminum alloy, a film or a dry or cured layer being at least partially applied to the metal surface, the film or the dry or cured layer being obtainable by at least partially applying the aqueous acidic composition as defined in any one of claims 1 to 9 in relation to the aforementioned step 1) to the metal surface, and at least one thermoplastic polymer material TM1 being in the form of a foil or in a form obtainable by injection molding, in each case the at least one thermoplastic polymer material TM1 being at least partially applied to the film or the dry or cured layer, preferably being as defined in step 2) in any one of claims 1 to 9, and Furthermore, at least one thermoplastic polymer material TM2, which is identical or different to the thermoplastic polymer material TM1, is applied at least partially to the at least one thermoplastic polymer material TM1 in a form obtainable by injection molding, with the proviso that the thermoplastic polymer material TM1 has been applied in foil form, or Furthermore, a substrate S2 is optionally used, which has at least one metal surface, which is at least partially made of aluminum and/or at least one aluminum alloy, and the substrate has a film or a dried or cured layer applied at least partially on the metal surface, which can be obtained by applying the aqueous acidic composition defined in any of claims 1 to 9 in relation to the aforementioned step 1), wherein the film or dried or cured layer at least partially present on the metal surface of the substrate S2 is located adjacent to the at least one thermoplastic polymer material TM1, with the proviso that the thermoplastic polymer material TM1 has been applied in the form of a foil. The metal-plastic hybrid material of claim 11 or 13, wherein at least the film or dried or cured layer (preferably the dried or cured layer) obtainable by applying the aqueous acidic composition to the metal surface of the substrate S1 has a dry layer thickness in the range of 100 to 1000 nm, and/or wherein the film or dried or cured layer (preferably the dried or cured layer) obtainable by applying the aqueous acidic composition to the metal surface of the substrate S1 has the following coating weight measured by XRF (X-ray fluorescence spectroscopy): due to the presence of component a2) in the acidic aqueous composition used, in each case calculated as metal, 0.1 to 50 mg/m ² , preferably 0.2 to 30 mg/m ² , even better 0.5 to 20 mg/m ² , still better 1.0 to 15 mg/m ² , even better 1.5 to 10 mg/m ² , especially 2.0 to 8 mg/m ² of zirconium and/or titanium and/or uranium, preferably zirconium and/or titanium, more preferably zirconium; calculated as metal, 0 or 0.1 to 40 mg/m ² , better 0 or 0.2 to 30 mg/m ² , even better 0 or 0.5 to 20 mg/m ² , still better 0 or 1.0 to 15 mg/m ² , even better 0 or 1.5 to 10 mg/m ² , especially 2.0 to 8 mg/m ² of molybdenum. A use of a metal-plastic hybrid material as claimed in any one of claims 11, 13 or 14, which is used as a component in the automotive, construction or electronics industries.