Method for producing a painted flat metal product

Abstract

The invention relates to a method for producing a painted metal flat product (6) according to claim 1.

Description

[0001] The invention relates to a method for producing a painted metal flat product.

[0002] The process for painting flat metal products, for example steel or aluminum flat products, as well as corresponding coil painting systems for carrying out the process, are state of the art.

[0003] Furthermore, it is also known to crosslink coating materials, particularly solvent-based, especially aqueous, but also solvent-free coating materials, by means of UV and / or electron beam (EB) irradiation after application to a flat metal product. This crosslinking can occur very quickly and very efficiently compared to conventional drying ovens; see, for example, DE 10 2008 029 580, WO 2023 / 053107A1 A1. In this process, EB irradiation is the final step in the coating curing process. This corresponds to the prevailing opinion that radiation crosslinking takes place after shaping as the final processing step in the process chain.

[0004] From DE 43 02 124 A1, a method for elasticizing coatings obtained from coating materials based on radically or cationically polymerizable binders by curing with high-energy radiation is known, characterized in that, after curing, a heat treatment, preferably at 200 to 230 °C for 5 to 5 minutes, is carried out. This allows coatings to be elasticized that have been fully cured by high-energy radiation, such as UV radiation or electron beam radiation, and contain no thermosetting components.

[0005] On the so-called primer coater, either a liquid primer is applied to one or both sides, or a primer is applied to one side of the metal flat product and a backcoat to the other. An adhesion promoter is used as an alternative or in addition to the primer. Primer, adhesion promoter, and other primers can be used interchangeably. Typical layer thicknesses are 5 to 10 µm, but thicknesses up to 30 µm are also possible. On the so-called topcoat coater, liquid topcoats are applied to one or both sides, or alternatively, clearcoats, with typical layer thicknesses between 15 and 25 µm. Alternatively, liquid adhesives used for composite / sandwich production can also be applied on both coaters, with layer thicknesses between 5 and 40 µm. Primerless coatings are also possible, meaning that topcoats are applied directly to the metal.Liquid paints (wet paints) are typically dried and thermally cross-linked in gas-fired drying ovens.

[0006] Primers or backcoats are typically in direct contact with preconditioned, i.e., cleaned and / or pretreated, flat metal products, preferably steel strips with a zinc-based coating, also containing aluminum and optionally magnesium. In strip coating, primers or backcoats therefore form the base adhesion to the steel strip surface. The primer protects the surface of the flat metal product from corrosion and simultaneously improves the adhesion of subsequent layers. The primer also evens out surface irregularities. Due to changing coating compositions (primers, paints, etc.), the elimination of chromium-containing pretreatments, and / or the use of novel zinc coatings, particular challenges arise to prevent delamination, especially the separation of the entire coating system from the substrate.

[0007] The process window for cleaning and / or conversion treatment is so narrow in today's coil coating process that, for example, the introduction of novel binder chemistry, which is already demanding with regard to its application, does not completely eliminate the risk of paint delamination / flaking.

[0008] As part of efforts to decarbonize coil coating products, solvent-free, radiation-curing coating materials (adhesion promoters, primers, topcoats, clearcoats, etc.) are seen as an effective approach. The resulting modification of the binder chemistry and the altered crosslinking kinetics of the coating materials pose a significant challenge to switching from solvent-based coating materials, especially primers, and is currently assessed as having high risks to product quality. It is particularly well known that metal adhesion is critical with UV-curing coating materials with regard to adhesion and embrittlement; in particular, post-production embrittlement can lead to problems during subsequent processing into the final product or throughout the product's service life.

[0009] The object of the present invention is to provide a generic method that enables technical resource savings and / or decarbonization potential, while also reducing, and in particular minimizing, the risk of paint delamination / flaking. Resource savings are to be achieved at least partially by reducing the energy consumption of fossil fuels. Additionally, the emission of organic solvents, so-called VOCs (volatile organic compounds), is to be prevented or at least minimized. Furthermore, the thermal crosslinking of coatings is to be carried out in a fuel-flexible and, as far as possible, energy-independent manner.

[0010] This problem is solved by a method having the features of claim 1. Further embodiments are described in the dependent claims.

[0011] The teaching concerns a process for manufacturing an organically coated metal flat product, comprising the following steps: Providing a metal flat product; optionally pretreating the metal flat product; applying a liquid base coat to at least one side of the metal flat product; at least partially crosslinking the liquid-applied base coat on the metal flat product; applying a liquid top coat to at least one side of the metal flat product; at least partially crosslinking the liquid-applied top coat on the metal flat product.

[0012] In one version, a pretreatment, i.e., surface pretreatment of the flat metal product, is carried out, including cleaning and / or conversion treatment. The surface of the flat metal product is prepared so that the base coating adheres sufficiently. Alternatively, the removal of oil, grease, scale (oxide layer), rust, metallic chips, and / or existing coatings takes place. This involves mechanical pretreatment processes (e.g., blasting), cleaning and degreasing, rinsing, and the application of inorganic conversion or passivation layers.

[0013] For cleaning, aqueous cleaners are preferably used, which typically contain builders, complexing agents, and / or surfactants. Cleaning is preferably carried out by spraying or immersion, with ultrasound or electrolysis being used additionally in the case of immersion cleaning. The cleaning process can optionally be combined with pickling and / or the formation of a new, targeted surface structure. For the formation of an inorganic conversion or passivation layer, for example, phosphating, chromating, or chromate-free systems are used, such as aqueous pretreatment dispersions or solutions containing titanium / zirconium fluoride or molybdate complexes or silane-containing compounds.

[0014] Chemical pretreatment may include at least one rinsing step to prevent adhesion. If necessary, a drying step is performed before applying the base coat. So-called "no-rinse" or "rinse" pretreatment dispersions or solutions, familiar to experts, are used.

[0015] In one version, a liquid base coating and / or a liquid topcoat is applied to both sides of the metal flat product.

[0016] In another embodiment, a liquid topcoat is applied to at least one side of the at least partially cross-linked basecoat.

[0017] For the purposes of the invention, the term "topcoat" generally includes the final coating layer in the coating structure, whether topcoats, basecoats, and / or clearcoats. In one embodiment, the flat metal product has the following coating structure on at least one side: a thermally curing basecoat, a radiation-curing intermediate layer, and a thermally or radiation-curing clearcoat.

[0018] Essential to the invention is that the at least partial crosslinking of the liquid-applied base coating is carried out by thermal curing using thermal radiation with a thermal radiation unit in the form of a porous gas burner. Within the scope of the present invention, the term "thermal curing" means the heat-initiated crosslinking of a base layer, in which either a separately provided crosslinking agent and / or self-crosslinking binders are used with the aid of a thermally unblocking catalyst or initiator.

[0019] The crosslinking agent contains reactive functional groups that are complementary to the reactive functional groups present in the binders. This is referred to as crosslinking. If the complementary reactive functional groups or autoreactive functional groups (i.e., groups that react "with themselves") are already present in the binder molecules, the binders are self-crosslinking. Examples of suitable complementary reactive functional groups and autoreactive functional groups are known from German patent application DE 199 30 665 A1, page 7, line 28 to page 8, line 59.

[0020] Porous gas burners and their operating principle are well-known in the field. Due to their high surface temperature, they emit more infrared radiation into the environment than conventional radiant burners. The high-intensity IR radiation from these burners (porous gas burners) increases the heat flow to the coated metal flat product compared to conventional convection ovens, allowing the necessary curing temperatures at the metal surface to be reached more than 2 to 7 times faster, preferably 3 to 5 times faster. Crucial for thermal curing is the temperature of the base coating, which essentially corresponds to the temperature of the metal surface, while the heating of the metal flat product can be considered an energy loss path with respect to the desired cross-linking of the base coating.

[0021] The curing oven is operated well above the upper explosive limit (UEL), so that the crosslinking of the base coating takes place in an atmosphere consisting primarily of solvent vapors, preferably with a residual oxygen content of <4%. These vapors are recirculated to generate an additional convective heat flow within the oven. In the case of organic solvents, these vapors can be returned to the pore gas burners in the gas phase, thus ensuring a highly energy-independent, high-intensity infrared radiation that is fuel-flexible, meaning it can use vapors from different solvents. In addition to conventional fuel gas, especially in light of the planned decarbonization, "green" or "greenly produced" energy carriers, such as biogas, hydrogen, or hydrogen mixtures, can also be increasingly used to operate the pore gas burners.

[0022] Depending on the operating mode and derived process parameters, porous gas burners can save an estimated 30 to 50% of primary energy, which is conventionally supplied with natural gas or, if the coating systems are part of an integrated smelting plant network, with blast furnace gases. This is partly due to the fact that conventionally used convection furnaces must be operated with high volumes of fresh air to avoid exceeding the lower explosive limit (LEL) of the solvents.

[0023] In the case of water as a solvent, water vapor is removed and the heat energy contained therein can be used as an energy source.

[0024] For the purposes of the invention, the term "essentially" or "essentially corresponding" means identical or equivalent statements, a deviation from a specific, predetermined value, or a difference between two values ​​of a maximum of 50%, 45%, 40%, preferably 30%, 25%, particularly preferably 20%, 19%, 18%, 17%, 16%, 15%, 14%, 15%, 12%, 11%, and in particular 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or 0.5%, 0.1%.

[0025] For the purposes of the invention, a base coating is understood to be an adhesion promoter, a primer, a base coat, a filler or a backcoat which is chemically different from the topcoat.

[0026] The process for applying a liquid base coat, a liquid top coat, optionally as a dispersion, particularly an aqueous dispersion, and the associated suitable application units, is state of the art and thus familiar to those skilled in the art. Application can be carried out by spraying, dipping, or preferably by roller application in a coil coating process.

[0027] The invention encompasses not only the application of a base coating and a top coating to one side, but also the application to both sides, whereby the process according to the invention is carried out either simultaneously on both sides of the flat metal product or at different times.

[0028] It is preferable to continue using existing solvent-based basecoat compositions, which are known and thus used as standard practice. The advantage of this is that the solvents driven off from the liquid basecoat during at least partial crosslinking can be used as an additive for firing the porous gas burners or otherwise as an energy source, thereby reducing CO2 emissions and thus promoting the targeted decarbonization.

[0029] In one version, the liquid base coating contains or consists of prepolymers, precopolymers, copolymers and / or polymers as starting materials, which, after hardening or cross-linking, are selected from the group containing or consisting of polyesters, alkyds, aminoplast resins, polyurethanes, polylactones, polycarbonates, polyethers, epoxy resin amine adducts or polyureas after curing or cross-linking to form a product, i.e., as a fully reacted end product.

[0030] In the case of an adhesion promoter, the liquid base coating contains a component comprising at least one R-SiX3 group, wherein R is an organically functionalized residue and X is a hydrolyzable group, such as an alkoxy group, and / or a component comprising at least one functional group selected from thio, amino, hydroxyl, carbamate, allophanate, carboxy, (meth)acrylate groups, hydroxyl groups, anhydride, carboxy, epoxy, blocked isocyanate, urethane, methylol, methylol ether, siloxane, amino, hydroxy and / or beta-hydroxyalkylamide groups.

[0031] The liquid base coating can contain two, more, or combinations of the aforementioned functional groups.

[0032] In addition, the liquid base coating may contain at least one additive or any combination of two or more additives, in particular silane-based additives, crosslinkers, initiators, stabilizers, pigments, fillers, other binders, crosslinking agents, organic solvents, reactive diluents, molecularly dispersed soluble dyes, nanoparticles, light stabilizers, antioxidants, emulsifiers, slip additives, leveling agents, film-forming aids, sag control agents (SCAs), flame retardants, corrosion inhibitors, waxes, driers, biocides and / or matting agents.

[0033] The invention essentially enables a resource-efficient process with regard to the use of solvents in the liquid base coating and a reduction of CO2 emissions, particularly in comparison to the previous conventional coil coating process with convection ovens.

[0034] The at least partial crosslinking of the liquid base coating can be carried out using a PMT between 180 °C and 350 °C. The PMT can be at least 200 °C, preferably at least 210 °C, preferably at least 220 °C, and can be at most 260 °C, preferably at most 250 °C, preferably at most 240 °C.

[0035] The so-called PMT (Peak Metal Temperature) represents the highest temperature reached on the metal surface and is preferably determined using a pyrometer or other suitable means.

[0036] Preferably, a solvent-free topcoat is used in one embodiment. This prevents the release of harmful emissions through evaporation, thus enabling a more environmentally friendly process compared to conventional strip coating with solvent-based topcoats. "Solvent-free" refers, for example, to volatile organic compounds (VOCs) in the coating material with a content of < 5.0 wt.%, particularly < 2.50 wt.%, preferably < 1.50 wt.%, more preferably < 0.50 wt.%, and more preferably < 0.20 wt.%, including 0. A water-based topcoat is also preferably used. In these cases, the process includes an additional step for driving off the solvents or water, preferably in an oven for heating the metal strip and, in particular, the applied coating.

[0037] In an alternative approach, liquid topcoats are preferably used that contain essentially no solvent or water. Appropriate monomers or reactive diluents are used to adjust the viscosity. Since, for example, compared to the conventional solvent-based process, VOC evaporation due to heating is avoided, strict safety measures are not required, and a reduction in so-called "Scope 1" CO₂ emissions is also possible.

[0038] The at least partial crosslinking of the topcoat can be carried out using a PMT between 190 °C and 350 °C. The PMT can be at least 200 °C, preferably at least 210 °C, preferably at least 220 °C, and can be at most 270 °C, preferably at most 260 °C, preferably at most 250 °C.

[0039] Preferably, the at least partial crosslinking of the liquid-applied topcoat is carried out using actinic radiation. Actinic radiation is defined as electromagnetic radiation such as UV radiation (UV-A, UV-B, and UV-C) or shorter-wavelength X-rays or gamma radiation and / or corpuscular radiation, such as electron radiation, beta radiation, alpha radiation, proton radiation, or neutron radiation, in particular electron radiation (EB irradiation). Therefore, the at least partial crosslinking of the liquid-applied topcoat using actinic radiation is carried out with a radiation unit in the form of a UV or corpuscular, preferably EB, emitter.

[0040] If irradiation with UV radiation is carried out, the liquid-applied topcoat contains radical or cationic photoinitiators that initiate crosslinking (curing), wherein the actinically activatable group preferably has at least one C=C double bond. Suitable starting materials include, for example, (meth)acrylate, ethacrylate, crotonate, cinnamate, vinyl ether, vinyl ester, ethenylarylene, dicyclopentadienyl, norbornenyl, isoprenyl, isoprenyl, isoprenyl, isopropenyl, allyl, or butenyl groups; ethenylarylene, dicyclopentadienyl, norbornenyl, isoprenyl, isopropenyl, allyl, or butenyl ether groups; or ethenylarylene, dicyclopentadienyl, norbornenyl, isoprenyl, isopropenyl, allyl, or butenyl ester groups. Of these, (meth)acrylate groups, especially acrylate groups, are particularly advantageous and are therefore especially preferred.In one embodiment, the liquid-applied topcoat contains or consists of prepolymers, precopolymers, copolymers, and / or polymers as starting materials, which, after curing or crosslinking, form a product—i.e., a fully reacted end product—selected from the group containing or consisting of polyacrylates, polyester acrylates, polyurethane acrylates, and / or polyepoxide acrylates. Examples of radically polymerizable materials are described in DE 43 02 124 A1, page 2, line 65 to page 3, line 10.

[0041] Examples of photoinitiators are described in DE 43 02 124 A1, page 3, line 21 to page 3, line 36. Cationically polymerizable material comprises compounds which, in one embodiment, contain a mixture of components containing epoxy groups and hydroxyl groups. Examples are described in DE 43 02 124 A1, page 2, line 50 to page 3, line 57.

[0042] When using particle radiation, chemical bonds of at least one component are cleaved, generating free radicals. These radicals then form new molecular compounds, resulting in at least partial cross-linking of the coating. Ionic and, in particular, radical polymerization proceeds rapidly until no reactants remain in close proximity. However, the use of copolymers can leave reactive groups even after polymerization, which are available for polycondensation or polyaddition reactions, leading to polyester acrylate or polyurethane acrylate, respectively. Ideally, the actinic radiation cross-links only the acrylate.

[0043] Therefore, the liquid topcoat can contain at least one component selected from the group consisting of low-molecular-weight, oligomeric, and polymeric organic compounds, each containing or consisting of at least one actinically activatable group. This component can consist of chemically identical or chemically different organic compounds.

[0044] To promote decarbonization, binders and / or solvents from a) biogenic sources, b) recycled sources or c) from CO2 capture and utilization (CCU) can be used.

[0045] To achieve improved adhesion of the topcoat to the at least partially cross-linked basecoat, the cross-linking of the basecoat can be influenced, for example, by at least partially cooling the at least partially cross-linked basecoat in a cooling unit. The cooling unit can be of a known design, for example, air cooling with optional additional water cooling.

[0046] Partial cooling can be used to prevent complete thermal curing of the base coating. This ensures that reactive functional groups in the base coating remain available for further reactions.

[0047] In addition to or as an alternative to cooling, at least partial activation of the at least partially cross-linked base coating can be carried out in an activation unit using an open flame or plasma. Activating the at least partially cross-linked base coating can have a positive effect on the adhesion of the topcoat to the base coating.

[0048] According to one embodiment, at least partial activation of the liquid topcoat can be achieved using thermal radiation with an activation unit in the form of an IR or NIR emitter or an induction unit. This activation can advantageously influence the topcoat, its flow, and / or its properties; for example, a paint can be gently heated to improve its flow or adjust its properties. Additionally, this can further crosslink or fully cure the basecoat. Post-crosslinking of the basecoat can be achieved by at least partially crosslinking the liquid topcoat using actinic radiation, utilizing the heat generated by the actinic curing process as an external thermal source.

[0049] To activate the liquid topcoat, at least the surface, or even deeper layers or the entire coating material, can be heated to a temperature above the glass transition temperature and above the maximum service temperature of the topcoat. The PMT (Process Mean Temperature) for activating the at least partially cross-linked topcoat on the flat metal product is essentially between 100 and 300 °C, particularly between 120 and 270 °C, preferably between 150 and 250 °C, and more preferably between 180 and 250 °C. Activation takes place between 100 and 300 °C, particularly at least 110 °C, preferably at least 120 °C and a maximum of 250 °C, preferably a maximum of 200 °C, and most preferably a maximum of 180 °C.The activation duration in one embodiment is at least 0.1 s, preferably at least 0.3 s, particularly preferably at least 0.5 s, in particular at least 1.0 s and at most 60 s, preferably at most 30.0 s, in particular at most 20.0 s, in particular at most 10.0 s.

[0050] In one embodiment, the metal flat product, in particular as a strip, is moved at a speed (strip speed) of at least 20 m / min, preferably at least 30 m / min, particularly preferably at least 40 m / min, in particular at least 50 m / min and at most 160 m / min, preferably at most 140 m / min, particularly preferably at most 120 m / min, in particular at most 100 m / min.

[0051] The term "metal flat product" refers to manufactured sheets or similarly constructed strips as rolled products made from an aluminum alloy (aluminum flat product) or a steel alloy (steel flat product), which can be either hot-rolled, essentially a hot-rolled strip, or preferably cold-rolled, essentially a cold-rolled strip. If, for example, a steel flat product is used, it can preferably be provided with a metallic coating. Preferably, the steel flat product can be coated with a zinc-based coating, particularly preferably by hot-dip coating. In this process, the metallic melt bath can contain, in addition to zinc and unavoidable impurities, additional elements such as aluminum with a content of up to 15 wt.%, in particular up to 10 wt.%, preferably up to 8 wt.%, preferably up to 5 wt.%, and / or magnesium with a content of up to 15 wt.%, in particular up to 10 wt.%, preferably up to 8 wt.%, preferably up to 5 wt.%.-% contained in or consisting of the coating. The metallic melt bath may contain or consist of magnesium with a content of at least 0.3 wt.%, in particular at least 0.6 wt.%, preferably at least 0.9 wt.%. Additionally or alternatively, aluminum may be present in addition to magnesium with a content of at least 0.1 wt.%, in particular at least 0.3 wt.%.

[0052] If the metallic melt bath contains or consists of magnesium within the aforementioned limits, aluminum within the aforementioned limits and the remainder being zinc along with unavoidable impurities, the resulting metallic coating on the steel flat product is known in the trade as zinc-magnesium (ZM) or Zn-Al-Mg.

[0053] The zinc coating, applied by hot-dip coating, comprises a zinc alloy containing, in addition to zinc (residual) and unavoidable impurities, additional elements such as aluminum with a content between 0.1 and 8.0 wt.% and magnesium with a content between 0.1 and 8.0 wt.%. Impurities in the melt bath may include elements from the group consisting of Si, Sb, Bi, Zr, Ni, Cr, Pb, Ti, Ca, Mn, Sn, La, Ce, Fe, and Cr in contents individually or cumulatively up to 0.5 wt.%, in particular up to 0.4 wt.%, preferably up to 0.3 wt.%. Impurities in the coating may include elements from the group consisting of Si, Sb, Bi, Zr, Ni, Cr, Pb, Ti, Ca, Mn, Sn, La, Ce, Fe, and Cr in concentrations individually or cumulatively up to 0.5 wt.%, in particular up to 0.4 wt.%, preferably up to 0.3 wt.%, whereby, alternatively, the concentration of Fe may be higher due to the diffusion described above. The remainder is zinc. Steel sheets, separated from flat steel products, or...Steel strips and sheet steel components manufactured from them with a zinc-based corrosion protection coating offer very good cathodic corrosion protection and have been used in automotive manufacturing for many years. If improved corrosion protection is required, the coating contains magnesium with a content of at least 0.8 wt.%, in particular at least 1.0 wt.%, preferably at least 1.1 wt.%, and aluminum with a content of at least 0.8 wt.%, in particular at least 1.0 wt.%. The coating contains magnesium with a content of up to 8.0 wt.%, preferably up to 7 wt.%, particularly preferably 5.0 wt.%, in particular up to 4.0 wt.%, and aluminum with a content of up to 8.0 wt.%, preferably up to 7 wt.%, in particular up to 5.0 wt.%, in particular up to 4.0 wt.%.

[0054] The coating can also consist solely of zinc with small amounts of aluminum, in particular up to 1.0 wt.%, preferably up to 0.70 wt.%, preferably up to 0.50 wt.% and > 0 wt.%, in addition to unavoidable impurities, also known in the trade as "Z". Unavoidable impurities may include, for example, elements from the group consisting of silicon, antimony, lead, titanium, calcium, manganese, tin, lanthanum, cerium, and chromium, individually or in combination, totaling up to 0.5 wt.%, in particular up to 0.3 wt.%, in the metallic melt bath.

[0055] In particular, to achieve a predetermined thickness of a Z or ZM coating, which in the solid state can range from 1.0 µm to 60.0 µm per side, the molten metal applied to the steel flat product or steel strip while still liquid is stripped off. This is accomplished by passing the coated steel flat product or steel strip through a stripping device after it has left the melt bath. The stripping device includes means, such as nozzles, especially slot nozzles, which apply a gaseous stripping medium to both sides of the steel flat product or steel strip to remove the liquid molten metal. This allows for an asymmetrical coating, i.e., different coating thicknesses on each side.The thickness of the Z or ZM coating can be adjusted, in particular, between at least 4.0 µm, preferably at least 5.0 µm and a maximum of 58.0 µm, preferably between 5.0 and a maximum of 55.0 µm, independently of each other on each side.

[0056] In a particular embodiment, the thickness of the Z or ZM coating is at least 1.0 µm, preferably at least 2.0 µm, particularly preferably at least 3.0 µm, in particular at least 5.0 µm and a maximum of 25.0 µm, preferably a maximum of 20.0 µm and particularly preferably a maximum of 15.0 µm, in particular a maximum of 10.0 µm, independently of each other on each side.

[0057] Alternatively, the flat steel product can be coated with a zinc-based coating by electrolytic deposition, known in the trade as "ZE" or "EG". The thickness of the metallic ZE coating on each side can be set between 1.0 and 25 µm, in particular between 1.5 and 20.0 µm, preferably between 2.0 and 15.0 µm.

[0058] The invention further relates to a painted metal flat product with two different coatings, wherein at least one side has at least one thermally cured coating and at least one actinically cured coating arranged thereon. Preferably, the painted metal flat product can be manufactured or is manufactured using the inventive method as described above.

[0059] Furthermore, the present invention relates to a painted metal flat product with two different coatings, wherein one side has at least one thermally cured coating and the other side of the metal flat product has at least one actinically cured coating. Preferably, the painted metal flat product can be manufactured or is manufactured using the inventive method as described above.

[0060] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the drawing.

[0061] The drawing shows the invention using a schematic illustration as an example. Figure 1Figure 1 shows a schematic diagram of a coil coating plant (100) for producing a painted metal flat product (6). A metal flat product (1) in the form of a coil is provided. This can be an aluminum flat product or, preferably, a steel flat product, preferably coated with a zinc-based coating. The metal flat product (1) thus provided in coil form is placed on a unwinder (10) in the coil coating plant (100) and unwound. The subsequent process chain is shown in a simple configuration; depending on the plant configuration,The rolled-out metal flat product (1) may pass through a straightening machine known to those skilled in the art and not shown. The rolled-out metal flat product (1) may pass through a cleaning and conversion unit (11) for cleaning and pretreating for bonding the base coating to the metallic surfaces. Furthermore, the metal flat product passes through: an application unit (12), for example in the form of a roller application unit, for applying a liquid base coating (2), for example a primer, to the metal flat product; a thermal radiation unit (15) in the form of a porous gas burner for at least partially crosslinking the liquid-applied base coating (3) on the metal flat product; optionally a cooling unit (14), for example air cooling, optionally additionally water cooling, for cooling the at least partially crosslinked base coating (3) on the metal flat product; optionally an activation unit (15).for example, in the form of an open flame or plasma, for at least partially activating the base coating (3) on the metal flat product; an application unit (16), for example, in the form of a roller application unit, for applying a liquid topcoat (4) to the metal flat product; optionally, an oven (17) for heating the metal strip and, in particular, the applied coating, for example, in the form of an IR and / or NIR radiation unit or induction unit, for at least partially activating the liquid topcoat (4) on the metal flat product; a radiation unit (18), for example, a UV and / or EB radiation unit, for at least partially crosslinking the liquid topcoat (5) on the metal flat product; a reeler (70) for reeling the painted metal flat product (6).

[0062] The coating process can, of course, be carried out on one or both sides; that is, the flat metal product (1) to be coated can be coated only on the top side, only on the bottom side, or on both sides in a coil coating system (100). Double-sided application can be carried out either simultaneously or at different times.

[0063] (Not shown) in a further step a liquid clear coat can be applied, which is then at least partially cross-linked by means of thermal or actinic radiation.

Claims

1. Method for producing a painted metal flat product (6), comprising the steps of: - providing a metal flat product (1); - applying a liquid base coating (2) to at least one side of the metal flat product; - at least partially crosslinking the liquid-applied base coating (2) to form an at least partially crosslinked base coating (3) on the metal flat product; - applying a liquid topcoat (4) to at least one side of the metal flat product; - at least partially crosslinking the liquid-applied topcoat (4) to form an at least partially crosslinked topcoat (5) on the metal flat product; characterized by the fact that the at least partial crosslinking of the liquid-applied base coating (2) is carried out by thermal curing using thermal radiation with a radiation unit (13) in the form of a pore gas burner.

2. The method of claim 1, wherein a liquid solvent-containing base coating (2) is used.

3. Method according to one of the preceding claims, wherein the at least partial crosslinking of the liquid-applied base coating (2) is carried out with a PMT between 180 °C and 350 °C.

4. Method according to one of the preceding claims, wherein a liquid solvent-free topcoat (4) is used.

5. Method according to one of the preceding claims, wherein the at least partial crosslinking of the liquid-applied topcoat (4) is carried out with a PMT between 190 °C and 350 °C.

6. Method according to one of the preceding claims, wherein the at least partial crosslinking of the liquid-applied topcoat (4) is carried out by means of actinic radiation with a radiation unit (18) in the form of a UV or corpuscular, preferably EB emitter.

7. Method according to one of the preceding claims, wherein at least partial cooling of the at least partially cross-linked base coating (3) is carried out in a cooling unit (14).

8. Method according to one of the preceding claims, wherein at least partial activation of the at least partially cross-linked base coating (3) is carried out in an activation unit (15) by means of an open flame or plasma.

9. Method according to one of the preceding claims, wherein at least partial activation of the liquid-applied topcoat (4) is carried out by means of thermal radiation with an activation unit (17) in the form of an IR or NIR emitter or induction unit.

10. Method according to any of the preceding claims, wherein the metal flat product (1) is a steel flat product.

11. The method of claim 10, wherein the steel flat product is coated with a zinc-based coating.

12. Method according to claim 11, wherein the steel flat product is hot-dip coated or electrolytically coated.

13. Method according to any one of claims 1 to 9, wherein the metal flat product (1) is an aluminum flat product.

14. Painted metal flat product (6) with two different coatings, wherein at least one side has at least one thermally hardened coating and at least one actinically hardened coating arranged thereon.

15. Painted metal flat product (6) with two different coatings, wherein one side has at least a thermally hardened coating and the other side of the metal flat product has at least an actinic radiation hardened coating.

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