Semi-finished product, method for producing a semi-finished product and its use

Description

[0001] The invention relates to a method for producing a sheet- or strip-shaped semi-finished product by providing a strip-shaped coil comprising at least one first metal layer and at least one plastic layer, which are fully bonded together to form a metal / plastic composite, wherein the material thickness of the metal layer is at most 1.5 mm and the material thickness of the plastic layer is at least 0.2 mm, and coating the visible surface of the metal layer of the metal / plastic composite in a coil-coating process, as well as its use.

[0002] Metal / plastic / metal composites are particularly well-known in the prior art. The applicant markets sandwich panels under the trade name Litecor®, consisting of two steel sheet facings with a material thickness between 0.2 and 0.3 mm and a plastic core layer with a material thickness of at least 0.3 mm arranged between the steel sheet facings, which are ideally suited as exterior and / or interior parts, particularly for passenger cars. WO 2014 / 114370 discloses a process for producing galvanized thin or ultra-thin sheet metal with high corrosion resistance from a hot-rolled steel strip, comprising the steps of electroplating the steel strip with zinc, temper rolling the zinc-coated surface of the steel strip, and applying a polymer coating or an organic lacquer to one or both sides of the zinc-coated surface of the steel strip.

[0003] Furthermore, components made of metal sandwich panels, particularly for the cladding of commercial vehicles, especially trailers, and in particular box bodies for refrigerated transport, are known from the prior art. For example, the outer surface consists of a coil-coated steel sheet hot-dip galvanized on both sides, the inner surface of a steel sheet hot-dip galvanized on both sides and coated with a food-grade plastic, and a polyurethane foam core layer in between (product information for "ISOPLUS II vario" from Rohr Nutzfahrzeuge). The steel sheets used for the box body have a material thickness of at least 0.6 mm. To ensure sufficient stability of the body and due to the particularly high loads occurring during transport, the specified thickness cannot be reduced further, at least for this type of body.The potential for lightweight construction, particularly in this application area, has not yet been fully exploited. Further weight savings are also possible in other applications, for example in garage doors, by using coil-coated sheets with material thicknesses of up to 3.0 mm.

[0004] Furthermore, coil coating, also known as "coil coating" in technical circles, is state of the art. An example can be found at the link. http: / / de.wikipedia.org / wiki / Coil_Coating Information on the coating process is available. Typically, steel strips, especially hot-dip galvanized steel strips, and aluminum strips with material thicknesses between 0.4 and 3.0 mm are coated. Material thicknesses below 0.4 mm prove extremely difficult to process in coil coating lines, as a complete coating, particularly with a constant thickness, cannot be guaranteed on such thin material.

[0005] Based on the prior art, the invention was based on the objective of providing a semi-finished product which is significantly lighter than the semi-finished products used in the prior art, in particular specifying a method for its manufacture and its use.

[0006] The problem is solved by applying a coil coating to the visible surface of the metal layer of the metal / plastic composite.

[0007] The inventors have found that the combination of at least one metal layer and at least one plastic layer to form a metal / plastic composite, which, compared to a solid metal material with at least the same material thickness, wherein the metal layer has a thickness of at most 1.5 mm, in particular at most 1.0 mm, preferably at most 0.5 mm and particularly preferably at most 0.35 mm and the thickness of the plastic layer is at least 0.2 mm, in particular at least 0.3 mm, preferably at least 0.4 mm, leads, on the one hand, to a reduced mass and, on the other hand, can now be easily coated in the coil-coating process even with metal layer thicknesses below the minimum thickness disclosed in the prior art.

[0008] According to a first embodiment, the metal layer is formed from a steel material. While steel materials are somewhat heavier than other metals, especially light metals, they are inexpensive to obtain and easy to process, particularly cold forming. Specifically, metal-coated steel materials, preferably coated on both sides, are used. Zinc- or aluminum-based systems are suitable as coatings, with galvanized steel materials being particularly preferred due to their cost-effectiveness.

[0009] According to a further embodiment, the semi-finished product comprises a second metal layer that is fully bonded to the free surface of the plastic layer to form a metal / plastic / metal composite. This sandwich-like semi-finished product possesses high bending and buckling stiffness, which, with an adapted thickness, essentially corresponds to that of a solid material while simultaneously reducing mass. To ensure the lightweight potential, the material thickness of the second metal layer is at most 1.5 mm, particularly at most 1.0 mm, preferably at most 0.5 mm, and most preferably at most 0.35 mm. The second metal layer can preferably have the same properties as the first metal layer, or, depending on the application, a coil coating or alternatively other coating systems. Depending on the application, the metal layers can also be of different thicknesses.

[0010] According to another embodiment, the visible surface of the first and / or second metal layer is textured. The texturing can be applied to the metal layer as raised areas during coil coating. This can be achieved, for example, using appropriately modified application rollers. Because at least the first metal layer has a thin material thickness, irregularities may be present in the material. Depending on the application, for example, with large components, especially cladding parts, these irregularities can create a negative appearance under poor lighting and visibility conditions. To counteract this disadvantage, the raised areas can compensate for the poor appearance by, for example, using repeating patterns, or even provide an improved appearance.Alternatively or cumulatively, embossing can be applied to at least the first metal layer after coil coating or the curing process, for example, using an embossing roller. This is advantageous, firstly, as with raised areas, for example, to give the first metal layer an improved appearance, and secondly, it can also cause a slight hardening of the metal layer. In particular, the embossing force must be adjusted so that no flow or reduction in thickness of the plastic layer occurs within the composite.

[0011] According to another embodiment, the plastic layer is made of a temperature-resistant plastic. This is advantageous because the metal / plastic composite or metal / plastic / metal composite is temporarily exposed to high temperatures during the coil-coating process, particularly during the curing of a previously applied adhesion promoter (primer) and the coil-coating layer or the lacquer applied to the metal layer. To prevent the plastic from decomposing or melting, a plastic that is temperature-resistant up to at least 200°C, and particularly up to at least 220°C, is preferably used. Preferred plastics include, for example, systems based on PA, PE, and / or mixtures thereof.

[0012] To improve the stiffness and / or strength of the semi-finished product, or to transfer the load-bearing function within the semi-finished product to the plastic layer, a fiber-reinforced plastic can be used according to a further embodiment. Plastic systems containing glass, carbon, and / or natural fibers, particularly biodegradable fibers, are especially preferred, whereby the strength and / or stiffness of the plastic can be influenced depending on the type of fiber, particularly by the filler content. The fibers used are preferably temperature-resistant up to at least 200°C, and particularly up to at least 220°C.According to one embodiment of the inventive method, a second metal layer is arranged which is fully bonded to the free surface of the plastic layer to form a metal / plastic / metal composite, wherein the free surface of the second metal layer of the metal / plastic / metal composite is coated by coil coating. To avoid repetition, reference is made to the foregoing, in particular to the descriptions concerning the semi-finished product.

[0013] According to a further embodiment of the inventive method, the curing temperature, which is particularly used for curing a previously applied adhesion promoter (primer) and for curing the coil coating or the lacquer applied to the metal layer, is adjusted to the plastic in such a way as to ensure the temperature resistance of the plastic, whereby a temperature of particularly a maximum of 220°C, preferably a maximum of 200°C, is set.

[0014] According to a further embodiment of the inventive method, the visible surface of the first and / or second metal layer is textured. This can be achieved either by applying a raised texture to the at least first and / or second metal layer during the coil coating process, or by forming indentations into the metal layer after the coil coating or after the curing process.

[0015] According to a further aspect, the invention relates to the use of the semi-finished product as a component, in particular as a cladding part for, for example, commercial vehicles, trailers, or white goods (household appliances). To avoid repetition, reference is made to the foregoing.

[0016] The invention will now be explained in more detail with reference to a drawing illustrating an embodiment. Identical parts are identified by the same reference numerals. It shows Figure 1: a cross-section through a part of a box body for deep-freeze transport from the prior art, Figure 2a): a section through a first example of a semi-finished product that can be used as a paneling part, Figure 2b): a section through a second example of a semi-finished product that can be used as a paneling part, and Figure 3: a schematic sequence of steps of a first example of a method according to the invention.

[0017] In Figure 1As an example, a cross-section through a section of a box body for refrigerated transport made of metal sandwich panels, as currently implemented in the prior art, is shown. The metal sandwich panel 1 has, for example, a first steel sheet 2 arranged on the outer surface A, which is provided on both sides of the steel sheet 2 with a metallic coating 3, in particular a zinc coating. On the outer surface A, a further coating in the form of a coil coating 4 is applied to the visible surface of the steel sheet 2.On the inner side I of the metal sandwich panel 1, a second steel sheet 2' is arranged. This second sheet is provided on both sides of the steel sheet 2' with a metallic coating 3', in particular a zinc coating, and with a further food-resistant organic layer 5 facing the inner side I. The second sheet has a material thickness that, for example, is equal to that of the first steel sheet 2. A plastic core 6, for example a foamed plastic, is arranged between the steel sheets 2 and 2', completing the metal sandwich panel 1. The material thickness of the steel sheets 2 and 2', in particular that of the first steel sheet 2, is, for example, 0.6 mm and cannot be reduced further for reasons of stability and due to the high loads that occur during transport.

[0018] The first embodiment of a semi-finished product is in Figure 2aA semi-finished product 7 in the form of a metal / plastic composite is described. The semi-finished product 7 comprises a metal layer 8, preferably made of a steel material, which is metallically coated 9 on both sides, in particular galvanized, preferably electrolytically galvanized, and has a material thickness of, for example, 0.3 mm. The preferably electrolytically coated steel material 8 is bonded on one side over its entire surface to a plastic layer 10, which is temperature-resistant up to at least 200°C, in particular up to at least 220°C, and has a material thickness of, for example, 0.5 mm. On the side opposite the plastic layer, the visible side of the metal layer 8 is provided with a coil coating 11. The semi-finished product 7 is ideally suited as a component, in particular as a paneling part for commercial vehicles or trailers.Although the material thickness of semi-finished product 7 is somewhat greater than that of steel sheet 2, mass can be saved by reducing the metal content in semi-finished product 7, for example, when it is used as cladding as part of a box body for refrigerated transport. Furthermore, the relatively thin metal layer, combined with a plastic layer, can be easily processed into a metal / plastic composite using coil coating lines (not shown here). Also not shown here, the plastic layer can be fiber-reinforced, which in turn can improve the stiffness and / or strength of the semi-finished product. Depending on the application, it may well be possible to further reduce the thickness of the metal layer when using fiber-reinforced plastic.

[0019] As a second embodiment of a semi-finished product, in Figure 2bA semi-finished product 7' is represented in the form of a metal / plastic / metal composite. In contrast to semi-finished product 7, semi-finished product 7' has a second metal layer 8', preferably made of a steel material, which is coated on both sides with a metal coating 9', in particular galvanized, preferably electrolytically galvanized, and is fully bonded to the free surface of the plastic layer 10'. The individual material thicknesses of semi-finished product 7' are, for example, 0.2 mm for the first and second metal layers 8, 8' and, for example, 0.3 mm for the plastic layer 10'. The advantages mentioned for semi-finished product 7 can also be transferred to semi-finished product 7'.

[0020] Not shown, for example, the visible surface of at least the first metal layer 8 may be textured to give the later use of the semi-finished product 7, 7' an improved appearance.

[0021] In Figure 3is a schematic sequence of steps for the production of at least one-sided coated, circuit board- or strip-shaped semi-finished products, especially in a coil coating plant.In step 12, a ribbon-shaped coil is preferably provided, comprising either a aforementioned metal / plastic composite, which is preferably provided on the plastic side with a protective film to protect the plastic surface and to prevent adhesion to the metal side in the coiled state, which is subsequently removed or peeled off, or a metal / plastic / metal composite, wherein the thickness of the metal layer is at most 0.5 mm, in particular at most 0.4 mm, preferably at most 0.35 mm and particularly preferably at most 0.3 mm, wherein the metal layer is preferably made of a steel material and is preferably electrolytically coated on both sides, and the thickness of the plastic layer is at least 0.2 mm, in particular at least 0.3 mm, preferably at least 0.4 mm, wherein the plastic is temperature-resistant up to at least 200°C, in particular up to at least 220°C.The ribbon-shaped coil is unwound and continuously fed to step 13 for cleaning the first metal layer. Passivation / activation of the first metal layer takes place in step 14, after which an adhesion promoter (primer) is applied to the first metal layer using an applicator roller (step 15). This primer is then baked on at a temperature (step 16) that is specifically tailored to the plastic to ensure its temperature resistance within the composite, with a temperature of, in particular, a maximum of 220°C, preferably a maximum of 200°C. In the next step, 17, a coil coating is applied to the first metal layer, which already has the adhesion promoter baked on, using an applicator roller. This coating is then baked on at a temperature (step 18) that essentially corresponds to the temperature in step 16.In step 19, either the coil is wound onto a coil to form a strip-shaped semi-finished product, with the coil coating being covered with a protective film, or it is cut to length to form sheet-shaped semi-finished products.

[0022] Not shown here, the first metal layer can be textured. The texturing can be applied to the first metal layer as a raised area during the coil coating process, for example in step 18. This can be achieved, for instance, using appropriately modified application rollers. Alternatively or cumulatively, indentations can be formed into the first metal layer after the coil coating process or after the curing process, for example using an embossing roller as described in step 19, whereby the embossing force is specifically adjusted to prevent flow or a reduction in the thickness of the plastic layer within the composite. The material thickness of the metal layer (8, 8') is at least 0.05 mm, particularly at least 0.1 mm, and preferably at least 0.15 mm.The material thickness of the plastic layer (10, 10') is at most 3.0 mm, in particular at most 2.5 mm and preferably at most 2.0 mm.

[0023] The invention is not limited to the embodiments shown in the drawing; rather, semi-finished products can be used in all areas and replace existing solutions (coil-coated sheets) where weight reduction plays an important role, e.g., in the area of ​​doors, industrial doors, garage doors, etc. Its use is not limited to vehicle construction or white goods. Reference symbol list

[0024] 1 Metal sandwich panel 2, 2' Steel sheet 3, 3' Metallic coating 4 Coil coating 5 Food-resistant organic coating 6 Plastic core 7 Metal / plastic composite, semi-finished product 7' Metal / plastic / metal composite, semi-finished product 8, 8' Metal layer 9, 9' Metallic coating 10, 10' Plastic layer 11 Coil coating 12 Provision of a ribbon-shaped coil 13 Cleaning 14 Activation / Passivation 15 Application of adhesion promoter 16 Curing of the adhesion promoter 17 Coil coating application 18 Curing of the coil coating 19 Winding / Cutting to length

Claims

1. Method for producing a single-sided coated plate or strip-shaped semi-finished product, characterized by providing a strip-shaped coil comprising a first metal layer and a plastic layer, which are bonded together over the entire surface to form a metal / plastic composite, wherein the material thickness of the metal layer is at most 1.5 mm and the material thickness of the plastic layer is at least 0.2 mm, coating the visible surface of the metal layer of the metal / plastic composite using the coil coating process and baking the coil coating, winding into a strip-shaped semi-finished product or cutting to length into plate-shaped semi-finished products.

2. Method according to claim 2, characterized in that a second metal layer is arranged, which is bonded over its entire surface to the free surface of the plastic layer to form a metal / plastic / metal composite, wherein the visible surface of the second metal layer of the metal / plastic / metal composite is coated using the coil coating process.

3. Method according to one of the preceding claims, characterized in that the baking temperature is adjusted to the plastic in such a way that the temperature resistance of the plastic is ensured, whereby a temperature of, in particular, a maximum of 220°C, preferably a maximum of 200°C, is set.

4. Method according to one of the preceding claims, characterized in that the visible surface of the first and / or second metal layer is textured.

5. Method according to one of the preceding claims, characterized in that the metal layer is formed from a steel material, in particular from a steel material coated with metal on both sides.

6. Use of the semi-finished product according to one of claims 1 to 5 as a component for commercial vehicles, trailers, or white goods.