Coil coating of products for extremely warm and humid environments

Abstract

The invention relates to a method for surface coating a plane metal substrate, the method comprising the steps of: providing a coiled plane metal substrate; unwinding the coiled plane metal substrate; applying one or more adhesive layers onto a top surface of the plane metal substrate; laminating a layered laminate comprising a first PVC layer and a second PVC layer onto the top surface of the plane metal substrate, the first PVC layer contacting the one or more adhesive layers, wherein the first PVC layer has been thermally fused with the second PVC layer, and wherein the second PVC layer comprises antimicrobial particles, thereby forming a laminated assembly with an antimicrobial PVC top layer.

Description

[0001] Coil coating of products for extremely warm and humid environments

[0002] The present invention relates to a method for surface coating a plane metal substrate, to a pre-coated metal substrate obtainable by the method, and to a product comprising the precoated metal substrate.

[0003] Specifically, the present invention relates to pre-coated metal substrates designed to endure extreme environmental conditions, such as in high humidity and / or high temperature atmospheres (e.g. as used in mushroom farms or in water containers). The pre-coated metal substrates are specifically tailored for cleaning at high temperatures and high humidity without the use of further cleaning agents. The invention addresses the challenges encountered when conventional polyester-type coated materials fail due to hydrolysis in environments where surfaces are cleaned not with detergents but through pasteurization processes involving water vapor.

[0004] Background Art

[0005] Controlled environments like slaughterhouses, dairies, and other food growing and processing facilities, are environments where repeated cleaning and decontamination can cause a fast degradation of walls and doors. Sandwich panels are often used to realize walls and partitions in such environments. Sandwich panels are structures made from at least three layers and comprise two facing layers made from a relatively high-density material, enclosing a low-density insulating core. An example of such sandwich panels can be found in WO 2023222894 A1 which discloses sandwich panels comprising polyethylene terephthalate (PET) surfaces. PET surfaces are easy to clean, stain resistant and scratch resistant.

[0006] However, PET surfaces exhibit inherent vulnerabilities to hydrolysis, which under certain circumstances leads to performance failures over time. One notable context where the limitations of existing PET surfaces become pronounced is in environments like mushroom cultivation rooms. Here, the surfaces are subjected to cleaning involving high temperature water vapor for pasteurization. The use of detergents or aggressive chemicals that could adversely affect the cultivated mushrooms is specifically avoided. During pasteurization treatment, the surface of the sandwich panels reaches temperatures of 60 or even 70 °C or higher. The prevalent issue arises when attempting to utilize polyester coatings in these settings, where hydrolysis compromises their integrity, posing a threat to both the protective coating and the delicate mushroom cultivation.

[0007] The present invention addresses the shortcomings of the prior art by introducing a novel material for sandwich panels that is impervious to hydrolysis, eliminating the vulnerabilities associated with polyester-type coatings. The disclosed material enables surfaces to withstand high-temperature and high-humidity environments, facilitating effective cleaning through pasteurization without compromising its structural integrity.

[0008] Description of the invention

[0009] It is an objective of the present invention to overcome one or more of the abovementioned disadvantages, or at least to provide a useful alternative. Thereto, the present invention provides: a method for surface coating a plane metal substrate, the method comprising the steps of:

[0010] - providing a coiled plane metal substrate;

[0011] - unwinding the coiled plane metal substrate;

[0012] - applying one or more adhesive layers onto a top surface of the plane metal substrate;

[0013] - laminating a layered laminate comprising a first PVC layer and a second PVC layer onto the top surface of the plane metal substrate, the first PVC layer contacting the one or more adhesive layers, wherein the first PVC layer has been thermally fused with the second PVC layer, and wherein the second PVC layer comprises antimicrobial particles, thereby forming a laminated assembly with an antimicrobial PVC top layer.

[0014] Thus, the laminated assembly comprises at least four layers in the following order: metal, adhesive(s), a first PVC layer and a second PVC layer.

[0015] The invention further relates to a laminated assembly obtainable by the method of the invention. In particular, the invention relates to a laminated assembly comprising, in the following order and each layer contacting the previous layer: a plane metal substrate, one or more adhesive layers, a first PVC layer, and a second PVC layer comprising antimicrobial particles.

[0016] The invention further provides for a product comprising a laminated assembly according to the invention. Preferably, the product is a sandwich panel.

[0017] Metal layers are more structurally robust and are therefore suitable for creating sandwich panel facing layers. Compared to all-plastic sandwich panels, there is less chance of the panels flexing under their own weight. Coil coating is a continuous and highly automated industrial process for efficiently providing metal with a coating. In a coil coating processes, a metal substrate (usually steel, steel with a metallic coating, stainless steel or aluminium) is delivered in coil form from the rolling mills or galvanizing lines. The weight of the coils varies from 5-6 tonnes for aluminium and up to 20 tonnes for steel. The coil is positioned at the beginning of the coil coating line, and is then unwound at a constant speed, passing through various coating processes before being recoiled. Such process may include cleaning, if necessary, and chemical pre-treatment of the metal surface and either one-side or two-side, single or multiple application of paints or coating powders which are subsequently cured. Laminating with permanent plastic films may be carried out as well. Two strip accumulators which may be found at the beginning and the end of the line enable the work to be continuous, allowing new coils to be added (and finished coils removed) by a metal stitching process without having to slow down or stop the line.

[0018] The method according to the invention is preferably performed in a coil coating line. The coil may have a width of maximally 1 .8 m, typically about 1 .0 to 1 .5 m. The plane metal substrate preferably has a thickness of between 0.17 mm to 3.0 mm. At these thicknesses, the metal can suitably be treated by a coil coating process such as the method according to the invention. More preferably, the plane metal substrate, i.e. metal strip, has a thickness of between 0.30 mm and 1.50 mm, as this is the optimal thickness for a coil coating process. Even more preferably, the plane metal substrate has a thickness of between 0.4 and 0.8 mm, as this is the optimum thickness for use in a sandwich panel, providing the best balance between ease of processing, weight of the sandwich panel and strength of the sandwich panel.

[0019] After the coil coating process, the laminated assembly may be processed, i.e. cut, in slit coils or plane sheets. There are two types of cutting, referred to as slitting, to produce slit coils: log slitting and rewind slitting. In log slitting the coil is treated as a whole (the 'log') and one or more slices are taken from it without an unrolling / re-reeling process. In rewind slitting the web is unwound and run through a machine, passing through knives or lasers, before being rewound on one or more shafts to form narrower rolls. Sheets may be formed by further cutting the rolled metal strip forming the coil or the slit coil in the desired dimensions.

[0020] Typically, after coil coating, the metal is cut and then formed to its final shape in cold bending processes. For example, sheets of coated metal may be cut from the coil by cutting the unwound metal in an axial direction. If the metal coil was first slitted into narrower rolls, sheets of the coated metal are often cut from the coil by cutting the metal in sheets in a radial direction. The plane metal substrate may optionally be pre-treated, for example by degreasing, optionally followed by washing, rinsing, passivation and drying, and / or pre-treatment may comprise chemical pre-treatment based on chrome VI, chrome III or a chrome free passivant. Examples of chrome free passivants are titanium and / or zirconium compounds, particularly complex fluorides of these elements. Additionally or alternatively, a metal substrate primer (i.e., a primer applied on the plane metal substrate, preferably on the top surface of the plane metal substrate) may be used to pre-treat the metal surface before application of the one or more adhesive layers. An anticorrosive primer is however not necessary. Preferably, the method according to the invention does not comprise application of an anticorrosive primer onto the top surface of the plane metal substrate. Thus, the one or more adhesive layers are preferably applied directly onto the top surface of the plane metal substrate. Thus, preferably the one or more adhesive layers are applied onto the plane metal substrate without application of an anticorrosive primer onto the top surface of the plane metal substrate and an adhesive layer is applied directly to the plane metal substrate.

[0021] Because the metal is treated before it is cut and formed, the entire surface is cleaned and treated, providing tightly bonded finishes with reduced effort, cost and use of chemicals. Coil coated metal, or pre-coated metal, is more durable and more corrosion-resistant than post coated metal.

[0022] The plane metal substrate used in the invention may for example comprise or consist of aluminium, cold rolled steel, HDG (hot dip galvanized) steel, stainless steel or austenitic stainless steel.

[0023] Cold rolled steel, also known as cold reduced steel, is produced through controlled cold-rolling of steel after an initial hot-rolling phase. This process refines the steel’s grain structure, improving its mechanical properties such as strength, hardness, and dimensional accuracy.

[0024] Hot dip galvanised steel consists of a cold reduced steel substrate onto which a layer of zinc is coated via a hot dip process to impart enhanced corrosion properties onto the base steel.

[0025] Stainless steels are steel alloys with at least 11 percent (maximum 30%) chromium, which prevents corrosion of iron particles and enhances their ability to withstand higher temperatures. Austenitic stainless steel is especially corrosion resistant and can be used all the way from a cryogenic to a high temperature range due to the ductility, toughness and mechanical strength that is sustained over a wide temperature range. The primary crystalline structure is austenite (face-centered cubic) and the steel is essentially non-magnetic, which makes austenitic stainless steel especially suitable in the construction of buildings where magnetic fields are likely to be produced.

[0026] Preferably, the plane metal substrate consists of hot dip galvanized steel, as it provides the best balance between performance and cost. In fact, an important attribute of the invention, is that relatively inexpensive steel can be used while still obtaining a very good performance.

[0027] Preferably, the one or more adhesive layers comprise a polyester based adhesive, as a polyester based adhesive has proven to result in the strongest adhesion between PVC and a metal substrate or metal substrate primer, thereby providing the best protection against delamination. An adhesive layer may be applied by reverse roller coat or spray coating. A layer is preferably applied by reverse roller coat. An adhesive layer preferably has a thickness of about 5 - 25 pm, more preferably of about 5 - 15 pm, most preferably of about 5 - 10 pm.

[0028] Preferably, at least two adhesive layers are applied onto the top surface of the plane metal substrate, and the first adhesive layer is cured before applying the second layer. It has surprisingly been found that application of two adhesive layers, wherein the first applied adhesive layer is cured before applying the second layer results in improved adhesion and corrosion protection, and therefore improved weathering properties of the obtained assembly. Without wishing to be bound by theory, this is believed to be the result of a reduction of the amount of micro-defects in the combined adhesive layers. Due to evaporation of solvent, an adhesive layer may exhibit porosity. By application of two adhesive layers, the chance of pores in the individual layers overlapping and leading to a direct path from the outer surface of the second adhesive layer through the first adhesive layer to the metal is very low. Furthermore, two layers lead to a smoother and more uniform surface of the adhesive layers as compared to the same adhesive layer thickness applied as a single layer due to a more uniform evaporation.

[0029] With respect to the polyester based adhesive, it is noted that synthesis of polyesters is generally achieved by a polycondensation reaction of an acid component and a hydroxy component, specifically a diacid and a diol. Identical polymers however may be formed by the reactions of acid anhydrides and diols, or by the reactions of dimethylesters with diols. It is therefore to be understood that a polyester that is described as e.g. comprising terephthalic acid and glycol may be formed by a reaction between glycol and terephthalic acid, but also between glycol and dimethyl terephthalate or between glycol and terephthalic anhydride or any other comparable chemical reaction (e.g. condensation of a hydroxy carboxylic acid) leading to the same polymer structure. The polyester based adhesive may comprise a mixture of different polyester polymers. Therefore, it is to be understood that components of the polyester as further described below may be present in the same polyester polymer, or in different polymers in case the adhesive comprises a mixture of different polyester polymers.

[0030] Preferably, the polyester based adhesive comprises an aromatic acid component, more preferably an aromatic acid component chosen from the group consisting of phthalic acid, isophthalic acid, and terephthalic acid, and combinations thereof.

[0031] Preferably, the aromatic acid component comprises a combination of two aromatic acid components, more preferably a combination of terephthalic acid and isophthalic acid.

[0032] Preferably, the weight ratio of terephthalic acid : isophthalic acid is in the range of 1 : 1 to 1 : 2, more preferably 1 : 1.2 - 1 : 2.

[0033] The polyester based adhesive furthermore preferably comprises an aliphatic diol, preferably a C2 - C10, more preferably a C2 - C6 aliphatic diol, most preferably a C2 - C5 aliphatic diol. The aliphatic diol may be linear, such as ethylene glycol, 1 ,3-propylene diol, 1 ,4-butylene diol, etc., or the aliphatic glycol may be branched, such as propylene glycol, butylene glycol, pentylene glycol, neopentyl glycol, hexylene glycol, etc. Preferably, the aliphatic diol is branched, most preferably the aliphatic diol is neopentyl glycol.

[0034] The polyester based adhesive may further comprise a dihydroxy ether, preferably diethylene glycol.

[0035] The polyester based adhesive may further comprise trifunctional components, such as a triacid and / or a triol. The presence of trifunctional components causes cross-linking of the polymer chains, thereby increasing the interlayer adhesion. The triacid is preferably an aromatic triacid, such as trimellitic acid. The triol preferably is an aliphatic triol, such as trimethylol propane or glycerol or a combination of both.

[0036] PVC is very resistant to acids and bases. PVC is also inherently fire resistant. PVC may further comprise pigments. Preferably, the first and / or second PVC layer comprise one or more pigments. Suitable pigments are for example metal oxides, of which titanium dioxide is most preferred, or organic pigments. Common types of organic pigments can include azo pigments, lake pigments, phthalocyanine pigments, quinacridone pigments and carbon black.

[0037] Preferably, the first PVC layer has a thickness of between 50 and 200 pm, more preferably of between 60 and 160 pm, most preferably of between 70 and 110 pm.

[0038] Preferably, the second PVC layer has a thickness of between 50 and 200 pm, more preferably of between 60 and 160 pm, most preferably of between 70 and 110 pm. In this application, the terms film and layer are used interchangeably. The permeability of a polymeric film is inversely proportional to its thickness. Thus, the thicker the films, the less water permeability and the better the adhesion. However, thicker films require more material and thus are more expensive. The thicknesses given above provide the optimum between cost and permeability.

[0039] PVC may be flexible or rigid. Flexible PVC typically comprises a plasticizer, whereas rigid PVC does not contain a plasticizer, or only contains a small amount of plasticizer (e.g., less than 100 ppm by mass, preferably less than 10 ppm by mass, most preferably less than 1 ppm by mass). Plasticizers or dispersants are additives that increase the plasticity or decrease the viscosity of a material. These are the substances, which are added in order to alter the physical properties of a material, and they are either liquids with low volatility or solids. They decrease the attraction between polymer chains to make them more flexible. Over the last 60 years, more than 30,000 different substances have been evaluated for their plasticizing properties. Of these, only a small number - approximately 50 - are in commercial use today. Most commonly phthalate esters are used as plasticizers in PVC. Plasticizers are typically low molecular weight compounds, although polymeric plasticizers exist as well. Nevertheless, plasticizers typically have a molecular weight lower than 5000 g / mol. Over time, low molecular weight plasticizers may migrate through the layers and evaporate. This results in porosity, brittleness and shrinking of the film. In turn, this leads to decreased aesthetics and to corrosion of the underlying metal. Particularly preferably, the PVC of the invention contains less than 100 ppm by weight, preferably less than 10 ppm by weight, most preferably less than 1 ppm by weight plasticizers with a molecular weight lower than 5000 g / mol. Furthermore, rigid PVC has a lower permeability to water vapour because no plasticizers are present in the rigid PVC.

[0040] Preferably, the PVC of the invention is rigid PVC. Thus, preferably the first and / or second PVC layers comprise rigid PVC. Rigid PVC may contain impact modifiers. Impact modifiers are added to plastic materials to improve their durability and toughness. Impact modifiers are generally polymeric compounds. Examples are MBS (methyl butadiene styrene) polymers and polyacrylics.

[0041] Furthermore, the PVC of the invention is preferably food-safe PVC. Thus, preferably the first and / or second PVC layers comprise food-safe PVC. Food-safety of the PVC may be assessed according to Ell regulation 10 / 2011 and subsequent updates. Preferably foodsafety of the PVC is assessed according to Ell regulation 10 / 2011. Preferably, the first PVC layer has been thermally fused with the second PVC layer. The latter may have been accomplished by simultaneously coextruding the two PVC layers, or by thermal lamination of one of the PVC layers with the other PVC layer.

[0042] The second PVC layer comprises antimicrobial particles. The antimicrobial particles may inhibit or destroy the growth of microorganisms, including bacteria, viruses, fungi, or protozoa, thereby limiting their presence and preventing their harmful effects. In combination with a high temperature cleaning regime, the presence of the antimicrobial particles provides for surfaces with a very low risk of fouling by harmful organisms, without the use of harmful chemicals and / or soap.

[0043] Preferably, the second PVC layer comprises 0.2 - 1.0 wt.% of antimicrobial particles, such as between 0.3 - 0.9 wt.%, most preferably between 0.4 - 0.8 wt.%. Preferably, the antimicrobial particles comprise silver, copper, zinc oxide, or combinations thereof. Most preferably, the antimicrobial particles are silver containing particles. Preferably, the silver containing particles are larger than 1 pm, given the health concerns in relation to nanoscale particles (i.e. particles smaller than 1 pm). More preferably the particles have a size in the range of 1 - 100 pm. Most preferably, the silver containing particles are silver doped glass particles.

[0044] A particle may be spherical or non-spherical. In case of a spherical particle, the size refers to the diameter of the particle. In the case of a non-spherical particle, the size may refer to the hypothetical size of a circular opening through which the particle would fit.

[0045] Preferably, the second PVC layer comprises more antimicrobial particles in percent by weight than the first PVC layer. Preferably, the first PVC layer comprises less than 0.2 wt.%, more preferably less than 0.1 wt.%, most preferably less than 0.05 wt.% antimicrobial particles. Preferably, the first PVC layer does not contain antimicrobial particles. Due to this distribution of the particles in the layers, wherein the second (i.e. surface) PVC layer comprises a high number of antimicrobial particles, and the PVC layer that is not exposed to the surface comprises a low number or no antimicrobial particles, a very effective antimicrobial surface is obtained, while reducing production costs related to the costs of the antimicrobial particles.

[0046] Furthermore, polymeric films with a thickness of less than 300 pm have a very low, but inherent risk of comprising through-holes. Due to the presence of two polymeric films on the metal substrate, the danger of holes in a single film leading to attack of the metal substrate through such a hole by water or chemicals is largely avoided. The chances of a hole in the first PVC layer and a hole in the second PVC layer overlapping, leading to a path from the outer surface to the metal is close to 0%. Preferably, the layered laminate and / or the laminated assembly do(es) not comprise any PET.

[0047] Finally, the laminated assembly may further comprise a strippable layer. The strippable layer covers the second PVC layer and may be applied as a final step in the coil coating process, i.e. the method of the invention, before the unwound and laminated coil is rewound, in order to protect the laminated surface of the coated coil during shipment and handling. Thus, in a preferred embodiment, the method according to the invention further comprises applying a strippable layer covering the antimicrobial PVC top layer. The strippable layer is preferably a strippable film.

[0048] The method of the invention may further comprise applying a backing coating to a bottom surface of the plane metal substrate. Different types of back coats can be applied depending on the customer demand and the kind of metal substrate. An epoxy primer is a common choice. Preferably the backing coating is configured to be used in a high temperature, high humidity environment, i.e. is a so called high performance back coat. Although the backing coating is not normally in direct contact with the environment in which the laminated assembly is used, contact of the backing coating with the high temperature, high humidity environment cannot always be avoided. The use of a high performance back coat prevents detachment of the coating and structural collapse of the product in which the laminated assembly is used. The backing coating may for example be applied at the same time as the adhesive.

[0049] Preferably, the method according to the invention further comprises rewinding the laminated assembly resulting in a laminate coil. The method according to the invention may further comprise cutting the laminated assembly to produce slit coils.

[0050] The pre-coated metal coil or slit coil of the invention may be cut into pre-coated metal sheets. These metal sheets may be formed into their final shape by cold bending and applied in a product, such as a sandwich panel. Thus, preferably, the method according to the invention further comprises cutting the laminated assembly to produce pre-coated metal sheets.

[0051] Brief description of the Figures

[0052] Fig. 1: Schematic picture of a coil coating line.

[0053] Fig. 2: Schematic picture of a laminated assembly according to the invention. Detailed description of the Figures

[0054] Fig. 1 depicts a typical coil coating line for carrying out a process according to the invention. In the embodiment shown, a coil 2 of a plane metal substrate 1 is unwound and transported through the line in transport direction 19. The substrate is degreased, washed, rinsed, passivated and dried in washing zone 4. A primer is optionally applied by reverse roller coat in zone 5, cured by heating in primer heating zone 6, and cooled with water in primer cooling zone 7. A first adhesive layer 24 is applied by reverse roller coat in zone 9, cured by heating in adhesive heating zone 10, and cooled with water in adhesive cooling zone 11. In the depicted embodiment, optional second adhesive layer 25 and a back-coat 30 are applied simultaneously in adhesive and back-coat coating zones 12 and 13, respectively. Both the adhesive 24 and back-coat 30 are applied by reverse roller coat. Subsequent heating is performed in adhesive heating zone 14. The film 31 is laminated onto the metal substrate 1 in lamination zone 15. Subsequent cooling is performed by cooling with water in laminate cooling zone 16, followed by drying in laminate drying zone 17. A strippable film 29 is applied in strippable film lamination zone 18. The metal substrate is rewound onto coil 3.

[0055] Fig. 2 depicts an embodiment of a laminated assembly 21 according to the invention. Shown are the plane metal substrate 1 , of which a first surface, or top surface, 32 is subsequently covered by polyester based adhesive layer 24, optional polyester based adhesive layer 25, layered laminate 31 , and strippable film 29. The second surface, or bottom surface, 33 is covered by a backing coating 30.

[0056] Layered laminate 31 comprises in order layer 26, optional layer 34, and layer 27, i.e. PVC layer 26, optional ink layer 34 and antibacterial PVC layer 27.

[0057] Materials

[0058] Polyester based adhesive - Commercially available polyester-based adhesive comprising terephthalic acid, isophthalic acid, (in a ratio of between 1 :1 and 2:1), and neopentyl glycol as main components, according to the most preferred embodiments of the invention.

[0059] Example 1

[0060] A layered laminate of 90 pm food safe rigid PVC and 90 pm food safe, antimicrobial rigid PVC was prepared by thermal lamination of a first 100 pm thick PVC layer with a second 100 pm thick PVC layer, resulting in a layered laminate with a thickness of between 180 - 200 pm.

[0061] A 0.6 mm thick coil of hot dip galvanized steel was unwound, degreased and pretreated by a passivant liquid. A polyester based adhesive layer was applied in a film thickness of 8 pm by using a reverse roll coating process at a line speed of 20 m / min, curing it up to 232°C for a total of 30 sec. After this, a second polyester based adhesive layer was applied in a film thickness of 8 pm by using a reverse roll coating process at a line speed of 20 m / min, curing it up to 232°C for a total of 30 sec.

[0062] Then the film was laminated with the layered laminate of food safe rigid PVC and food safe, antimicrobial rigid PVC immediately outside the oven. The coil was cooled down by water and dried up. A protective film was applied in line and the coil was rewound. The laminated assembly was cut into sheets. The sheets were tested according to various tests.

[0063] NEN-EN 13523-6:2020 determines the adhesion of an organic coating to a metallic substrate after indentation produced by slow deformation (cupping). The standard requires a 1 hour immersion in boiling water. No loss of adhesion was observed. Even after repeating the same test after 4 hours immersion in boiling water, no loss of adhesion was observed.

[0064] NEN-EN 13523-26:2022 specifies a procedure for evaluating the resistance to continuous condensation of an organic coating on a metallic substrate, by means of exposure in a humidity cabinet under controlled conditions. The standard requires a test over a period of 1000 hours. No weathering or corrosion were observed. Even after repeating the same test over a period of 2000 hours, no weathering or corrosion were observed.

[0065] NEN-EN 13523-9:2022 specifies a procedure for determining the resistance to water immersion of an organic coating on a metallic substrate. The standard requires a test of a scratched and punctured sample immersed in a water batch at 40 °C. No alteration or corrosion on the scratch and on the puncture were observed. Even after repeating the same test at 50 °C, no alteration or corrosion on the scratch and on the puncture were observed.

[0066] NEN-EN 13523-27:2017 specifies a procedure for evaluating the resistance of an organic coating on a metallic substrate in conditions of extreme humidity (acid, alkaline and / or neutral). The standard requires a test on a flat sample with cotton and water at 70 °C for 14 days. Excellent adhesion was observed. Even after repeating the same test on a stamped and scratched sample for 21 days, excellent adhesion was observed.

[0067] CEI 1646 1996-11 requires a test cycle to be performed in a climatic chamber. The test subjects a sample to extreme temperature variations. 10 test cycles are required to be performed on a sample. No loss of adhesion was observed.

[0068] A test was designed for the specific intended operating environment. To ensure robustness, the test conditions were more demanding than those expected in actual use. Specimens were placed in a closed bath with water temperature of 70 °C. The atmosphere above reaches water vapor saturation. Each day, the specimens were kept out of the bath for 8 hours at room temperature and put in the bath for the next 16 hours. After 90 cycles, the samples were in perfect condition.

[0069] Example 2

[0070] Sheets are prepared as described above for example 1, using only a single layer of polyester based adhesive. In the test designed for the specific intended operating environment, after 90 cycles only very slight localized delamination is observed.

[0071] Comparative example 1

[0072] Comparative example 1 consists of a pre-coated substrate comprising a polyester primer, polyester paint and a polyester film (PET55). In the test designed for the specific intended operating environment, after 90 cycles severe delamination is observed.

[0073] Comparative example 2

[0074] A 0.6 mm thick coil of austenitic stainless steel was unwound, degreased and pretreated by a passivant liquid. Polyester based adhesive was applied in a film thickness of 8 pm by using a reverse roll coating process at a line speed of 20 m / min, curing it up to 232°C for a total of 30 sec. After this, a second polyester based adhesive layer was applied in a film thickness of 8 pm by using a reverse roll coating process at a line speed of 20 m / min, curing it up to 232°C for a total of 30 sec. Then the film was laminated with a layered laminate of 120 pm rigid PVC, 0.5 pm amorphous PET and 19.5 pm semicrystalline PET immediately outside the oven. Then the coil was cooled down by water and dried up. The laminated assembly was cut into sheets.

[0075] Specimens are placed in a closed bath with water temperature of 70 °C. The atmosphere above reaches water vapor saturation. Each day, the specimens are kept out of the bath for 8 hours at room temperature and put in the bath for the next 16 hours. After 90 cycles, the specimens exhibit slight to minor delamination.

Claims

CLAIMS1. Method for surface coating a plane metal substrate, the method comprising the steps of:- providing a coiled plane metal substrate;- unwinding the coiled plane metal substrate;- applying one or more adhesive layers onto a top surface of the plane metal substrate;- laminating a layered laminate comprising a first PVC layer and a second PVC layer onto the top surface of the plane metal substrate, the first PVC layer contacting the one or more adhesive layers, wherein the first PVC layer has been thermally fused with the second PVC layer, and wherein the second PVC layer comprises antimicrobial particles, thereby forming a laminated assembly with an antimicrobial PVC top layer.

2. Method according to claim 1, wherein the antimicrobial particles comprise silver, copper, zinc oxide, or combinations thereof, preferably wherein the antimicrobial particles are silver containing particles, more preferably silver doped glass particles.

3. Method according to claim 1 or 2, wherein the second PVC layer comprises 0.2 - 1 .0 wt.% of antimicrobial particles, such as between 0.3 - 0.9 wt.%, most preferably between 0.4 - 0.8 wt.%.

4. Method according to any one of the preceding claims, wherein the first PVC layer comprises less than 0.2 wt.%, preferably less than 0.1 wt.%, more preferably less than 0.05 wt.% antimicrobial particles, most preferably wherein the first PVC layer does not comprise antimicrobial particles.

5. Method according to any one of the preceding claims, wherein the first PVC layer has a thickness of between 50 and 200 pm, preferably of between 60 and 160 pm, most preferably of between 70 and 110 pm.

6. Method according to any one of the preceding claims, wherein the second PVC layer has a thickness of between 50 and 200 pm, preferably of between 60 and 160 pm, most preferably of between 70 and 110 pm.

7. Method according to any one of the preceding claims, wherein the one or more adhesive layers comprises a polyester based adhesive.

8. Method according to any one of the preceding claims, wherein at least two adhesive layers are applied onto the top surface of the plane metal substrate, and the first adhesive layer is cured before applying the second layer.

9. Method according to any one of the preceding claims, wherein the first and / or the second PVC layer comprises one or more pigments.

10. Method according to any one of the preceding claims, wherein the one or more adhesive layers are applied directly onto the top surface of the plane metal substrate.

11. Method according to any one of the preceding claims, further comprising applying a strippable layer covering the antimicrobial PVC top layer.

12. Method according to any one of the preceding claims, further comprising applying a backing coating to a bottom surface of the plane metal substrate.

13. Method according to any one of the preceding claims, further comprising rewinding the laminated assembly resulting in a laminate coil.

14. Method according to any one of the preceding claims, further comprising cutting the laminated assembly to produce slit coils.

15. Method according to any one of the preceding claims, further comprising cutting the laminated assembly to produce pre-coated metal sheets.

16. Laminated assembly comprising, in the following order and each layer contacting the previous layer: a plane metal substrate, one or more adhesive layers, a first PVC layer, and a second PVC layer comprising antimicrobial particles.

17. Laminated assembly according to claim 16, obtainable by the method of any one of claims 1 - 15.

18. Product comprising a laminated assembly according to claim 16 or 17.

19. Product according to claim 18, which is a sandwich panel.

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