Methods and systems for producing coated metal

Abstract

A method of coating a metal substrate 4 comprises applying a first coating layer 8 to the substrate, spraying a second coating layer 10 on top of the first coating layer whilst the first coating layer

Description

Field The present application relates to methods and systems for producing coated metal. Background Coated metals find application in a number of areas, including as a building material, in appliances (for example as a housing for home appliances) and for many other purposes. By coating a metal substrate with one or more layers, additional functionality and properties can be added to the metal. For example, each layer may provide one or more of corrosion resistance, scratch resistance, colour, gloss and adhesion. It may be beneficial to provide for additional functionality of a metal substrate without requiring significant additional steps in a manufacturing process and / or significant additional manufacturing equipment. For example, it may be beneficial to provide for additional functionality of a coated metal product without requiring extensive changes to existing production lines. Summary In a first aspect of the present invention there is provided a method of coating a metal substrate. The method comprises: - applying a first coating layer to the metal substrate; - spraying a second coating layer on top of the first coating layer while the first coating layer is wet; and - curing the first and second coating layers simultaneously. On some existing production lines, coating apparatuses (e.g. roller-coaters) are used to apply a series of coatings to a metal substrate using a continuous coil coating method. Each layer is applied and cured in turn. Multilayer coatings are produced with each individual layer providing its own key properties, including, corrosion resistance, scratch resistance, colour, gloss and adhesion. To further develop products with additional functionality it may be required to add additional layers to such a product. Due to production line restrictions such as space, it may not be possible to add additional roller-coaters and curing ovens (for example) into the production line. The methods and systems described herein provide a way of applying such coatings incorporating additional functionality using wet-on-wet spray coating. Through incorporation of spray coaters following, e.g. immediately following, the coating (for example roller-coating) of a previous layer, it is possible to add an additional layer with the additional functionality incorporated wet-on-wet. Both the previous layer and the additional layer can then be cured at the same time to create a multi-layered product. It should be noted that is not necessary that the first coating layer is applied directly onto the metal of the metal substrate. Instead, one or more coating layers may have already been applied (by any suitable method) before the first coating layer is applied. For example, the first coating layer may be a penultimate coating layer in a set of three of more coating layers which are applied onto the metal substrate and the second coating layer may be a final coating layer, i.e. a top coat. Each of the first and second coating layers may be any suitable material, e.g. paint, primer or any liquid. It should be understood that use of the term ‘wet’ is intended to not only refer to a layer in a state of being completely uncured but also to a state of being partially but not fully cured. For example, the first coating layer may be tacky and / or have a skin and this may still be described as being ‘wet’. Generally, the present application is directed to wet-on-wet application methods and systems using such methods. The term curing should be understood to referred to the conversion of a wet, liquid layer (including layers which are tacky, and / or have a skin, as explained above), to a dry, solid layer. For example, curing may refer to the conversion of a wet, liquid layer of paint to a dry, solid layer of paint. In some embodiments, the second coating layer has antimicrobial properties. For example, the second coating layer may comprise one or more additives which have antimicrobial properties. Such additives may be silver-based additives, for example. Antimicrobial properties may be particularly advantageous when the final product (i.e. the coated metal) is to be used in scenarios in which it is likely to be touched regularly and / or by numerous different people. This may include as a building material for interiors of buildings and / or as a material for the housing of home appliances. Alternatively or additionally, the second coating layer may have one or more different properties. For example the second coating layer may be one or more of the following: decorative, reflective and / or mattifying. In some embodiments, curing the first and second coating layers comprises oven-curing the first and second coating layers, i.e. curing the first and second coating layers in a curing oven. In some embodiments, curing the first and second coating layers simultaneously comprises curing (e.g. in a curing oven) the first and second coating layers for one minute or less. In other words, the total curing time for the curing of the two coating layers simultaneously may be one minute or less. This curing may result in the two layers being fully cured. In some embodiments, curing the first and second coating layers simultaneously comprises curing the first and second coating layers (e.g. in a curing oven) for a shorter time, for example 45 seconds or less, 30 seconds or less, 25 seconds or less, or 15 seconds or less. The curing time may be between 20 and 25 seconds, for example. Such a short curing time may be advantageous because an overall production time of the coated metal may be reduced. In some embodiments, curing the first and second coating layers simultaneously comprises curing the first and second coating layers in a curing oven at a peak metal temperature of 200°C or higher. Such a high temperature may enable a faster curing time. In other embodiments, different temperatures may be used. For example, in some embodiments curing the first and second coating layers simultaneously comprises curing the first and second coating layers in a curing oven at 180°C or higher, 220°C or higher, 240°C or higher or 250°C or higher. These temperatures each refer to the peak metal temperature. Peak metal temperature is the minimum temperature to which the metal substrate is heated during curing. Curing the first and second coating layers simultaneously may comprise curing the first and second coating layers in a curing oven with peak metal temperature between 180°C and 250°C. In some embodiments, curing the first and second coating layers simultaneously comprises electron-beam (or ‘e-beam’) curing the first and second coating layers, i.e. curing the first and second coating layers by exposure to one or more electron beams (e.g. high-energy electron beams). E-beam curing may be carried out at room temperature up to around 50°C. In some embodiments, curing the first and second coating layers simultaneously comprises UV (‘ultraviolet’) curing the first and second coating layers, i.e. curing the first and second coating layers by exposure to UV radiation. UV curing may be carried out at room temperature up to around 50°C. In some embodiments, the method comprises partially curing the first coating layer before spraying the second coating layer on top of the first coating layer. Advantageously, this may reduce mixing between the first and second coating layers and may provide for better adhesion between the first and second coating layers. After the partial cure, the first coating layer may still be described as being wet. As described above, it should be understood that use of the term ‘wet’ is intended to also refer to a state of being partially but not fully cured, for example tacky. The partial cure of the first coating layer may be performed by a first curing apparatus and the simultaneous, full cure of the first and second coating layers may be performed by a second, different curing apparatus. Alternatively, the partial cure and the full cure may be performed by the same curing apparatus. In embodiments in which both a first and second curing apparatus are present, the first and second apparatuses may be of the same type (e.g. curing oven, e-beam or UV curing apparatus) or of different types. In other words, the partial cure may be carried out by any suitable curing method, e.g. any of oven curing, heat gun curing, e-beam curing or UV curing, and the simultaneous, full cure may be carried out by any suitable curing method, e.g. any of oven curing, e-beam curing or UV curing. In some embodiments, applying the first coating layer comprises applying the first coating layer by roller coating. In other embodiments, applying the first coating layer comprises spraying the first coating layer onto the metal substrate. Any other suitable application method may be used to apply the first coating layer to the metal substrate. In some embodiments, the metal substrate is a steel substrate, for example a steel plate or strip. In some embodiments, the metal substrate is steel coil. The methods described herein may be part of a continuous coil coating process. In a continuous coil coating process, a strip of metal (e.g. steel) may be uncoiled, passed through the various stages of a production line (including coating and curing stages as described herein but optionally also additional steps such as pre-cleaning) at a constant speed and then re-coiled. In some embodiments, the second coating layer is transparent or substantially transparent. This may be advantageous in embodiments in which a previous layer (for example the first coating layer) has a desired colour. In some embodiments, the second coating layer is a top-coat. In other words, in some embodiments the second coating layer may be a final layer applied to the metal substrate and no other layers are applied on top of the second coating layer. In a second aspect of the present invention there is provided a system for coating a metal substrate. The system comprises: - a first coating apparatus configured to apply a first coating layer to the metal substrate; - a second coating apparatus configured to spray a second coating layer on top of the first coating layer while the first coating layer is wet; and - a curing apparatus configured to cure the first and second coating layers simultaneously. This system has advantages corresponding to those as described for the method explained above. In summary, the system may provide for incorporation of additional functionality into a coated metal product without requiring significant additional manufacturing equipment and / or extensive changes to existing production lines. The system may be described as being configured to coat a metal substrate. Features described with reference to the method above may also be applied to the system, as will now be explained. In some embodiments, the second coating layer has antimicrobial properties. For example, the second coating layer may comprise one or more additives which have antimicrobial properties. Such additives may be silver-based additives, for example. Antimicrobial properties may be particularly advantageous when the final product (i.e. the coated metal) is to be used in scenarios in which it is likely to be touched regularly and / or by numerous different people. This may include as a building product for interiors of buildings and / or as a material for the housing of home appliances. Alternatively or additionally, the second coating layer may have one or more different properties, for example the second coating layer may be one or more of the following: decorative, reflective and / or mattifying. In some embodiments, the curing apparatus may comprise a curing oven. In some embodiments, the curing apparatus may be configured to cure the first and second coating layers simultaneously (e.g. in a curing oven) for one minute or less. In other words, the total curing time for the curing of the two coating layers simultaneously may be one minute or less. In some embodiments, the curing apparatus (which may comprise a curing oven) may be configured to cure the first and second coating layers for a shorter time, for example 45 seconds or less, 30 seconds or less, 25 seconds or less, or 15 seconds or less. The curing time may be between 20 and 25 seconds, for example. This may be advantageous because an overall production time of the coated metal may be reduced. In some embodiments in which the curing apparatus comprises a curing oven, the curing apparatus may be configured to cure the first and second coating layers simultaneously at a peak metal temperature of 200°C or higher. Such a high temperature may enable a faster curing time. In other embodiments, different temperatures may be used. For example, in some embodiments the curing apparatus may be configured to cure the first and second coating layers at 180°C or higher, 220°C or higher, 240°C or higher or 250°C or higher. These temperatures each refer to the peak metal temperature. The peak metal temperature is the minimum temperature to which the metal substrate is heated during curing. In some embodiments, the curing apparatus may be configured to cure the first and second coating layers by electron beam (‘e-beam’) curing. In other words, the curing apparatus may be configured to cure the first and second coating layers by exposure to one or more electron beams (e.g. high-energy electron beams). In some embodiments, the curing apparatus may be configured to cure the first and second coating layers by UV (ultraviolet) curing. In other words, the curing apparatus may be configured to cure the first and second coating layers by exposure to UV radiation. In some embodiments, the system may comprise a further curing apparatus which is configured to partially cure the first coating layer before the second coating apparatus sprays the second coating layer on top of the first coating layer. This partial curing may reduce mixing between the two layers and / or improve adhesion between the two layers. After the partial cure, the first coating layer may still be described as being wet. As described above, it should be understood that use of the term ‘wet’ is intended to also refer to a state of being partially but not fully cured, for example tacky. In some embodiments, the system may not comprise a further curing apparatus and the partial pre-cure of the first coating layer and the simultaneous cure of the first and second coating layers may be performed by the same curing apparatus (e.g. the curing apparatus referred to above). The curing apparatus and / or the further curing apparatus may comprise any suitable arrangement for curing the relevant layers for example each may comprise any of a curing oven, an e-beam curing apparatus, or a UV curing apparatus. The further curing apparatus may comprise or be a heat gun, for example. In embodiments in which a further curing apparatus is present, the curing apparatus and the further curing apparatus may be of the same type (e.g. curing oven, e-beam or UV curing apparatus) or of different types. In other words, the partial cure may be carried out by any suitable curing apparatus and the simultaneous, full cure may be carried out by any suitable curing apparatus. In some embodiments, the first coating apparatus may be configured to apply the first coating layer by roller-coating. In other words, the first coating apparatus may comprise one or more rollers. In other embodiments, the first coating apparatus may be configured to spray the first coating layer onto the metal substrate. Any other suitable application method may be used to apply the first coating layer. In some embodiments, the metal substrate is a steel substrate, for example a steel plate or strip. In some embodiments, the metal substrate is steel coil. In some embodiments, the second coating layer is transparent or substantially transparent. This may be advantageous in embodiments in which a previous layer (for example the first coating layer) has a desired colour. In some embodiments, the second coating layer is a top-coat. In other words, in some embodiments the second coating layer may be a final layer applied to the metal substrate and no other layers are applied on top of the second coating layer. Any of the systems described herein may be a continuous coil coating system. Methods and systems have been described above with reference to the application of two layers, followed by simultaneous curing of the two layers. The present invention may also extend to the application of three or even more layers, followed by simultaneous curing of the three or more layers. For example, the following method is disclosed: - applying a first coating layer to a metal substrate; - spraying a second coating layer on top of the first coating layer while the first coating layer is wet; - spraying a third coating layer on top of the second coating layer while the second coating layer is wet; and - curing the first, second and third coating layers simultaneously. The method may comprise optional steps of partially curing the first coating layer before the second coating layer is applied and / or partially curing the second coating layer (and optionally the first coating layer) before the third coating layer is applied. A corresponding system is also disclosed, comprising a first coating apparatus, a second coating apparatus, a third coating apparatus and a curing apparatus, each configured to carry out a respective step of the method detailed above. Brief description of the drawings Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic, exploded view of a piece of coated metal; Figure 2 is a flow diagram illustrating a method of coating a metal substrate; Figure 3A is a schematic diagram illustrating a method of coating a metal substrate; Figure 3B is a schematic diagram illustrating an alternative method of coating a metal substrate; Figure 3C is a schematic diagram illustrating a further alternative method of coating a metal substrate; Figure 3D is a schematic diagram illustrating a further alternative method of coating a metal substrate; Figure 4 is a schematic diagram illustrating a system for coating a metal substrate; and Figure 5 is a schematic diagram illustrating a production line suitable for implementing a system and / or method as described herein. Detailed description The methods and systems described herein are for producing coated metal. With reference to Figure 1, an example of such a coated metal is shown in an exploded view. The coated metal 2 comprises a metal substrate 4, for example steel coil or a steel plate. It will be appreciated that other metals could also be used. The coated metal 2 also comprises three mid-layers 6, 7a, 7b. The first mid-layer 6 may comprise a metallic coating comprising an alloy of two or more metals, for example. This layer may provide corrosion resistance, for example. The second mid-layer 7a may be a pre-treatment layer. The pre-treatment layer may be applied to create a thin inorganic layer which improves corrosion resistance and adhesion to subsequent layers (e.g. the third-mid layer 7b). The third mid-layer 7b may be a primer layer. Such a primer layer may have properties selected to provide a good foundation (e.g. good adhesion, chemically inert) for subsequent layers. The first mid-layer 6 is directly on top of the metal substrate 4 and the second and third mid-layers 7a, 7b are stacked on top of the first mid-layer 6. In the example shown in Figure 1, three mid-layers 6, 7a 7b are present but other numbers of mid-layers are also possible. The three mid-layers may each provide one or more properties to the overall product, for example corrosion resistance, scratch resistance, colour, gloss and / or adhesion. Equally, the coated metal 2 may not comprise a primer and / or any mid-layers. The coated metal 2 also comprises a first coating layer 8 and a second coating layer 10. The first coating layer 8 may provide one or more properties to the overall product, for example one or more of the properties listed above. The second coating layer 10 may have antimicrobial properties, for example. A method of applying the first and second coating layers to the metal substrate will now be described with reference to Figure 2. It will be appreciated that the first and second coating layers may have any desired position within the stack of layers shown in Figure 1: they may be the first two layers applied directly to the metal substrate 4 (i.e. they may take the places of the first mid-layer 6 and the second mid-layer 7a, with the first and second mid-layers being positioned elsewhere within the stack), they could be intermediate layers, coming after one or more layers applied directly to the metal substrate (i.e. they could take the place of mid-layers 7a and 7b) or, as described above, they could be the penultimate and final layers respectively. In other words, the methods and systems described herein may be used to apply any two (or more) layers in a stack of layers applied to a metal substrate. With reference to Figure 2, a method 12 of coating a metal substrate is described. The method 12 comprises a first step 14 which comprises applying a first coating layer to the metal substrate. The first coating layer may be applied by roller-coating for example. As described above, the first coating layer 8 may be applied directly onto the metal substrate 4 or on top of one or more layers which have already been applied to the metal substrate. The method 12 comprises an optional second step 14a in which the first coating layer is partially cured. This partial cure may be carried out using a heat gun. This may prevent or reduce mixing between the first coating layer and a second coating layer (which is subsequently applied on top of the first coating layer, see below). However, this second step 14a may be omitted. The method 12 comprises a third step 16, carried out subsequently to the first step 14 and optionally the second step 14a, in which a second coating layer is sprayed on top of the first coating layer while the first coating layer is still wet (i.e. completely uncured or only partially cured). Next, in a fourth step 18, the first and second coating layers are cured simultaneously. For example, the first and second coating layers may be cured for 20 seconds in a curing oven, with a peak metal temperature of 200°C. As explained above, other curing methods may be used for the optional partial cure of the first coating layer and / or the simultaneous, full cure of the first and second coating layers. One example of another curing method is e-beam curing. Typical values for curing the coating layers with e-beam curing are: - Dose 20-70 kGy - Inerting with Nitrogen to less than 350ppm of O2 - Accelerating voltage of electrons: 100 - 300 kV - Air gap (between coating layers and beam source): 10-60 mm - Temperature: ambient to 50°C Another example of a curing method is UV curing. Typical values for curing the coating layers with UV curing are: - Type: Any bulb (H, H+, D, V) or LED - Either carried out in air or inerting with Nitrogen to less than 350ppm of O2 - Dose: 150 - 750 mJ / cm2 - Irradiance: 3000 - 10000 mW / cm2 - Temperature: ambient to 50°C It will be appreciated that additional processing steps may come before the first step 14 and / or after the fourth step 18 or even in between the steps shown in Figure 2. For example, the method may comprise a step of applying, e.g. by roller coating or spraying, one or more previous layers onto the metal substrate and curing the one or more previous layers before the first coating layer is applied. Alternatively or additionally, the method may comprise applying one or more subsequent layers on top of the second coating layer and curing the one or more subsequent layers. The method may be part of a continuous coil coating layer, in which a strip of metal (e.g. steel) may be uncoiled, passed through the various stages of a production line (including coating and curing stages as described herein but optionally also additional steps such as pre-cleaning) at a constant speed and then re-coiled. Various options for applying the first and second coating layers and also for how the first and second coating layers are cured are provided. With reference to Figures 3A-D, four possible options are provided. In each figure, the first coating layer 8 and the second coating layer 10 are illustrated schematically on top of the metal substrate 4. With reference to Figure 3A, in a first example the first coating layer 8 is roller-coated onto the metal substrate 4 and the second coating layer 10 is then sprayed on top of the first coating layer 8 (without any partial curing of the first coating layer 8 in between). The first and second coating layers are then cured simultaneously by a curing apparatus 22, as indicated by arrows 24. With reference to Figure 3B, in a second example the first coating layer 8 is sprayed onto the metal substrate 4 and the second coating layer 10 is then sprayed on top of the first coating layer 8 (without any partial curing of the first coating layer 8 in between). The first and second coating layers are then cured simultaneously by a curing apparatus 22, as indicated by arrows 24. With reference to Figure 3C, in a third example the first coating layer 8 is roller-coated onto the metal substrate 4. The first coating layer 8 is then partially cured, as indicated by arrows 26. The second coating layer 10 is then sprayed on top of the first coating layer 8 once the first coating layer 8 has been partially cured. The first and second coating layers are then cured fully simultaneously by a curing apparatus 22, as indicated by arrows 24. The same curing apparatus may be used for both the partial cure of the first coating layer 8 and the simultaneous cure of the first and second coating layers. Alternatively, separate curing apparatuses (e.g. ovens) may be used. With reference to Figure 3D, in a fourth example the first coating layer 8 is spray coated onto the metal substrate 4. The first coating layer 8 is then partially cured, as indicated by arrows 26. The second coating layer 10 is then sprayed on top of the first coating layer 8 once the first coating layer 8 has been partially cured. The first and second coating layers are then cured simultaneously by a curing apparatus 22, as indicated by arrows 24. The same curing apparatus may be used for both the partial cure of the first coating layer 8 and the simultaneous cure of the first and second coating layers. Alternatively, separate curing apparatuses (e.g. ovens) may be used. With reference to Figure 4, a system for coating a metal substrate is described. This system may be used to implement a method of coating a metal substrate as described herein, for example a method as described with reference to Figure 2. A system 32 for coating a metal substrate is provided. The system 32 comprises a first coating apparatus 34 which is configured to apply a first coating layer to the metal substrate. The first coating apparatus 34 may comprise one or more rollers for roller-coating the metal substrate. The system 32 further comprises a second coating apparatus 36 which is configured to spray a second coating layer on top of the first coating layer while the first coating layer is wet. The second coating apparatus 36 comprises an automatic spray nozzle which is used to spray on the second coating layer. The automatic spray nozzle is positioned above the metal substrate. The spray nozzle is connected to a pressure pot in which the coating is placed. The pressure pot is connected to a source of compressed air, with a regulator affixed to control the pressure of the air within the pot. Tubing is connected directly between the pressure pot and the automatic spray nozzle for transportation of the coating. The atomizing pressure and fan pressure can be controlled via regulators to control the rate of coating deposition and application width of the coating. The system 32 further comprises a curing apparatus 38 which is configured to cure the first and second coating layers simultaneously. The curing apparatus 38 may comprise an oven, for example. The system 32 may, in some embodiments, comprise a further curing apparatus 35 which is configured to partially cure the first coating layer once it has been applied to the metal substrate before the second coating apparatus 36 applies the second coating layer on top of the first coating layer. The system 32 may, in some embodiments, also comprise a substrate transport apparatus 40 which is configured to transport the metal substrate between the first coating apparatus, the second coating apparatus and the curing apparatus(es). For example, the metal substrate may be a steel coil or a portion of a steel coil and the portion of the steel coil being coated at any one time may be moved between the various parts of the system 32 by the substrate transport apparatus 40, which may include one or more rollers configured to rotate and uncoil a coil of steel, for example. An example of a complete production line for coating a coil of steel with multiple layers is illustrated schematically in Figure 5. With reference to Figure 5, the production line 25 comprises a first stage 26 in which steel coil is cleaned and pre-treated. In a second stage 28, a primer is applied to the steel coil (e.g. by roller- 5 coating) and then cured. The production line 25 also comprises a third stage 30 comprising two sub-stages 30a and 30b. In a first sub-stage 30a, the first and second coating layers are applied. In a second sub-stage 30b, the first and second coating layers are cured simultaneously. In other words, a method such as that described with reference to Figure 2 is performed in stage 30. In a fourth stage 32, 10 the coated steel is re-coiled for shipment. It will be appreciated that there may be many variations of the examples described above.

Claims

1. A method of coating a metal substrate, the method comprising:applying a first coating layer to the metal substrate;spraying a second coating layer on top of the first coating layer while the first coating layer is wet; andcuring the first and second coating layers simultaneously.

2. A method according to claim 1, wherein the second coating layer has antimicrobial properties.

3. A method according to claim 1 or claim 2, wherein curing the first and second coating layers simultaneously comprises oven-curing the first and second coating layers.

4. A method according to claim 3, wherein curing the first and second coating layers simultaneously comprises curing the first and second coating layers for one minute or less.

5. A method according to claim 3 or claim 4, wherein curing the first and second coating layers simultaneously comprises curing the first and second coating layers at 200 degrees centigrade or higher.

6. A method according to claim 1 or claim 2, wherein curing the first and second coating layers simultaneously comprises electron-beam curing or UV curing the first and second coating layers.

7. A method according to any preceding claim comprising partially curing the first coating layer before spraying the second coating layer on top of the first coating layer.

8. A method according to any preceding claim, wherein applying the first coating layer comprises applying the first coating layer by roller coating.

9. A method according to any of claims 1 to 7, wherein applying the first coating layer comprises spraying the first coating layer onto the metal substrate.

10. A method according to any preceding claim, wherein the metal substrate is a steel substrate.

11. A method according to any preceding claim, wherein the metal substrate is steel coil.

12. A method according to any preceding claim, wherein the second coating layer is a top-coat.

13. A method according to any preceding claim, wherein applying the first coating layer comprises applying the first coating layer onto one or more previous coating layers which are on the metal substrate.

14. A system for coating a metal substrate, the system comprising:a first coating apparatus configured to apply a first coating layer to the metal substrate;a second coating apparatus configured to spray a second coating layer on top of the first coating layer while the first coating layer is wet; anda curing apparatus configured to cure the first and second coating layers simultaneously.

15. A system according to claim 14, wherein the second coating layer has antimicrobial properties.

16. A system according to claim 14 or claim 15, wherein the curing apparatus comprises a curing oven.

17. A system according to claim 16, wherein the curing apparatus is configured to cure the first and second coating layers simultaneously for one minute or less.

18. A system according to claim 16 or 17, wherein the first curing apparatus is configured to cure the first and second coating layers simultaneously at 200 degrees centigrade or higher.

19. A system according to claim 14 or claim 15, wherein the curing apparatus is configured to cure the first and second coating layers by electron beam curing or UV curing.

20. A system according to any of claims 14 to 19 comprising a further curing apparatus which is configured to partially cure the first coating layer before the second coating apparatus sprays the second coating layer on top of the first coating layer.

21. A system according to any of claims 14 to 20, wherein the first coating apparatus is configured to apply the first coating layer by roller coating.

22. A system according to any of claims 14 to 20, wherein the first coating apparatus is configured to spray the first coating layer onto the metal substrate.

23. A system according to any of claims 14 to 22, wherein the metal substrate is a steel plate or strip, optionally wherein the metal substrate is steel coil.

24. A system according to any of claims 14 to 23, wherein the second coating layer is a top-coat.

25. A system according to any of claims 14 to 24, wherein the first coating apparatus is configured to apply the first coating layer onto a previous coating layer which is on the metal substrate.s

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