Coil coating for decorative interior panels

Abstract

The present invention relates to a method for surface coating a plane metal substrate (1), the method comprising the steps of: providing a coiled (2) plane metal substrate (1); unwinding the coiled plane metal substrate (1); applying an adhesive layer (24) onto a top surface of the plane metal substrate (1); laminating a layered laminate (31) comprising a PVC film (25) and a PVF film (27) onto the top surface of the plane metal substrate (1), the PVC film (25) contacting the adhesive layer (24), thereby forming a laminated assembly with a PVF top surface. The invention also provides a laminated assembly produced by the method, and a product comprising the laminated assembly.

Description

[0001] COIL COATING FOR DECORATIVE INTERIOR PANELS

[0002] The present invention relates to a method for surface coating a plane metal substrate, to a laminated assembly, and to a product comprising the laminated assembly.

[0003] Background Art

[0004] In traditional manufacturing processes, steel and other metals arrived at factories in an untreated (besides possibly being oiled or passivated) and unpainted state. Companies would cut and shape the metal and then surface treat and paint the metal components before further assembly. This was costly, time-consuming, and environmentally harmful. Moreover, as formed parts can have many holes, recessed areas, valleys, and hidden areas, they are difficult to clean and uniformly paint. This painting of pre-shaped materials therefore resulted in coatings with defects and thereby low weathering resistance. Coil coating provides a solution to this problem.

[0005] Coil coating is a continuous and highly automated industrial process for efficiently coating coils of metal. The definition of a coil coating process according to EN 10169 : 2010 is a “process in which an (organic or inorganic) coating material is applied on rolled metal strip in a continuous process which includes cleaning, if necessary, and chemical pre-treatment of the metal surface and either one-side or two-side, single or multiple application of (liquid) paints or coating powders which are subsequently cured or / and laminating with permanent plastic films”. The metal substrate (normally steel or aluminum) is delivered as a coil from the rolling mills. Coil weights vary from 5-6 tons for aluminum and up to about 25 tons for steel. The coil is positioned at the beginning of the line, then unwound at a constant speed, passing through the various pre-treatment and coating processes before being recoiled. Two strip accumulators may be placed at the beginning and the end of the line enabling the work to be continuous. This allows new coils to be added (and finished coils removed) by a metal stitching or welding process without having to slow down or stop the line.

[0006] 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 painted metal. Typically, after pre-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. In addition, the metal coil may first be slitted into narrower rolls before sheets of the coated metal are cut from the coil by cutting the metal in sheets in an axial direction. Not all coatings or paints are suitable for use in coil coating. Although the coatings and / or paints may be applied in the process, not all coatings are suitable for use in cold bending processes. Some materials may deform, resulting in visible and invisible faults, such as stress whitening, cracking and / or micro cracking. These faults do not only result in unsatisfactory aesthetics, but also reduce the protective properties of the films, e.g. resulting in premature corrosion. Care should be taken to utilize suitable materials.

[0007] The Venetian blind industry was the first to utilize pre-coated metal. Nowadays, precoated metal is used in a variety of products. It can be formed for many different applications, including those with T bends, without loss of coating quality. Major industries use pre-coated metal in products such as building panels (also known as fagade elements), metal roofs, wall panels, garage doors, office furniture (desks, cubicle divider panels, file cabinets, modular cabinets, etc.), home appliances (refrigerators, dishwashers, freezers, range hoods, microwave ovens, washers, dryers, etc.), heating and air-conditioning outer panels and ductwork, commercial appliances, vending machines, foodservice equipment, cooking tins, beverage cans, and automotive panels and parts (fuel tanks, body panels, bumpers, etc.). The list continues to grow, with new industries making the switch from post-painted to precoated processes each year. For each pre-coated product, the coating may be built up in a number of paint layers. The end product may further be protected with a strippable film.

[0008] Backing coats are applied to the underside (reverse side) of the metal strip (i.e. plane metal substate) with or without the use of a primer. The coating is generally not as thick as the finish coating used for exterior applications. Backing coats are generally not exposed to corrosive environments and not visible in the end application.

[0009] As an alternative to paint systems, the steel, which may comprise an anticorrosive primer, can be laminated with a film onto a suitable adhesive in order to form a laminated assembly. A widely used technology is laminating a PVC (poly vinyl chloride) film on top of the metal coil substrate by use of a polyester based adhesive.

[0010] Such PVC precoated steel may be used in wall panels for interior applications. However, some interior applications are more demanding than others. For example, interior wall panels in public transportation and other unsupervised public locations are often subject to vandalism such as graffiti spraying. Moreover, materials used in public transportation should meet very stringent standards related to VOC (volatile organic compound) emissions and fire resistance. At the same time, pleasing aesthetics are required. Corrosion resistance of the underlying metal is also important.

[0011] The properties of PVC precoated steel are not optimal for such applications. For example, a disadvantage of PVC is its lower solvent resistance. Also, PVC may suffer from alteration of gloss, such as reduced gloss, after it has been processed at high temperatures, such as the high temperatures used in coil coating. US 2023 / 107134 A1 discloses coil coating of a film comprising a base acrylic layer onto a metal substrate with a polyester based adhesive.

[0012] JPH 03126543 A discloses a traditional lamination process involving a steel sheet and PVC.

[0013] There remains a need for precoated steel with improved properties, especially with respect to aesthetics, cleanability, VOC emissions, fire resistance and corrosion resistance.

[0014] Description of the Invention

[0015] 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. It is especially an objective of the present invention to provide precoated steel with pleasing aesthetics, good cleanability, low VOC emissions and excellent fire resistance.

[0016] Thereto, the present invention provides a method for surface coating a plane metal substrate, the method comprising the steps of:

[0017] - providing a coiled plane metal substrate;

[0018] - unwinding the coiled plane metal substrate;

[0019] - applying an adhesive layer onto a top surface of the plane metal substrate;

[0020] - laminating a layered laminate comprising a PVC film and a PVF (poly vinyl fluoride) film onto the top surface of the plane metal substrate, the PVC film contacting the adhesive layer, thereby forming a laminated assembly.

[0021] The invention further provides for a laminated assembly obtainable by the method. Such a laminated assembly thus preferably comprises at least three layers in the following order: metal, PVC, and PVF. In between the consecutive layers, an adhesive layer is preferably present. Most preferably, such a laminated assembly comprises, in the following order:

[0022] - a metal substrate

[0023] - an adhesive layer

[0024] - a PVC layer

[0025] - a laminate adhesive layer

[0026] - a PVF layer.

[0027] In particular, the invention relates to a surface coated metal substrate, comprising:

[0028] - a plane metal substrate;

[0029] - an adhesive layer applied on a top surface of the plane metal substrate;

[0030] - a layered laminate comprising a PVC film and a PVF film on the top surface of the plane metal substrate, the PVC film contacting the adhesive layer. Preferably, the adhesive layer, the PVC layer, the laminate adhesive layer and / or the PVF layer of the invention contain less than 100 ppm, preferably less than 10 ppm, most preferably less than 1 ppm plasticizers with a molecular weight lower than 5000 g / mol. Most preferably, each layer of the layered laminate of the invention contains less than 100 ppm, preferably less than 10 ppm, most preferably less than 1 ppm plasticizers with a molecular weight lower than 5000 g / mol.

[0031] The invention further provides for a product comprising the laminated assembly. Preferably, the product is an interior decorative surface panel.

[0032] 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 decorative surface panel, providing the best balance between ease of processing, weight of the decorative surface panel and strength of the decorative surface panel. The plane metal substrate may for example be aluminum, or steel. In case of steel, the steel may be galvanized on one or both surfaces, i.e. comprising a layer of zinc on one or both surfaces. A zinc layer may be 1 - 10 pm, such as 2 - 9 pm. Preferably, at least the top surface, i.e. the surface to be coated with the layered laminated, is galvanized.

[0033] 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.

[0034] 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.

[0035] 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 adhesive layer. 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 adhesive layer is preferably applied onto the plane metal substrate without application of an anticorrosive primer onto the top surface of the plane metal substrate and the adhesive layer is applied directly to the plane metal substrate.

[0036] 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.

[0037] PVC may be flexible or rigid. Flexible PVC typically comprises a plasticizer, whereas rigid PVC is PVC that does not contain a plasticizer, or only contains a small amount of plasticizer (e.g. less than 100 ppm, preferably less than 10 ppm, most preferably less than 1 ppm). 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, preferably less than 10 ppm, most preferably less than 1 ppm plasticizers with a molecular weight lower than 5000 g / mol. Furthermore, rigid PVC has a lower permeability to water vapor because no plasticizers are present in the rigid PVC.

[0038] Preferably, the PVC used in the invention is rigid PVC. The 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. Preferably, the PVC comprises a polyacrylic impact modifier, as it has been found that PVC with a polyacrylic impact modifier has better UV-light resistance.

[0039] Preferably, the PVC film has a thickness of between 70 and 250 pm, preferably of between 90 and 180 pm, most preferably of between 100 and 135 pm.

[0040] Furthermore, PVC is very resistant to acids and bases. PVC is also inherently fire resistant. PVC may further comprise pigments, which is beneficial for aesthetic purposes. Preferably, the PVC film comprises one or more pigments. Suitable pigments are for example metal oxides, such as titanium dioxide, or organic pigments. Common types of organic pigments can include azo pigments, lake pigments, phthalocyanine pigments and quinacridone pigments. A disadvantage of PVC is its lower solvent resistance. Also, PVC may suffer from alteration of gloss, such as reduced gloss, after it has been processed at high temperatures, such as the high processing temperatures used during coil coating, which are typically between 130 - 250 °C, such as between 200 - 250 °C.

[0041] Preferably, the layered laminate further comprises a laminate adhesive layer for bonding the PVC film to the PVF film, and an optional ink layer between the PVC and the laminate adhesive layer.

[0042] For example, an ink pattern may be applied on the PVC layer, thereby making it possible to apply a wide range of aesthetic images. The ink pattern does not need to fully cover the PVC layer, as a printed design may comprise unprinted areas. Thus, preferably, the ink layer partially or at least partially covers the PVC layer. The ink layer may be applied by rotographic printing.

[0043] Preferably, the laminate adhesive layer comprises an acrylic adhesive.

[0044] The acrylic adhesive may be a copolymer. Suitable adhesives are for example Tedlar 68070 and Tedlar 68080 from DuPont. Solvent resistance and gloss are provided by the PVF (polyvinyl fluoride) film. Due to the PVF layer, the coated metal substrate is very easy to clean, and has very appealing aesthetics. The PVF layer retains its gloss during coil coating.

[0045] Preferably, the PVF film comprises an embossed pattern on the PVF top surface.

[0046] Preferably, the PVF film has a total thickness of between 6 and 50 pm, more preferably of between 8 and 32 pm, most preferably of between 10 and 20 pm.

[0047] 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 PVC layer and a hole in the PVF layer overlapping, leading to a path from the outer surface to the metal is close to 0%.

[0048] For example, the layered laminate comprising the PVC film and the PVF film may be prepared by

[0049] 1. calendering PVC into a film, and optionally printing the film with an ink layer, e.g. by rotographic printing,

[0050] 2. providing a PVF film with a laminate adhesive layer, preferably an acrylic adhesive layer,

[0051] 3. bonding the PVC layer with the laminate adhesive layer of the PVF, such that the ink layer, if present, is in contact with the acrylic adhesive layer and the layered laminate has a PVF top surface,

[0052] 4. optionally embossing the PVF top surface with an embossing pattern. Alternatively, the acrylic adhesive layer may be applied to the PVC in step 2 (onto the ink layer if present) and a PVF film without adhesive layer is provided, after which in step 3 the PVF is bonded with the laminate adhesive layer.

[0053] Preferably, the laminate adhesive layer has a thickness of between 2 - 10 pm, more preferably between 3 - 8 pm, most preferably between 4 - 6 pm.

[0054] Preferably, step 3 is performed at a temperature of between 140 - 210 °C, more preferably between 160 - 200 °C, most preferably between 170 - 190 °C.

[0055] Preferably, step 4 is performed at a temperature of between 120 - 180 °C, more preferably between 130 - 170 °C, most preferably between 140 - 160 °C. By using these embossing temperatures, the PVF may retain its embossing pattern and gloss during coil coating.

[0056] Embossing may for example be performed by pressuring a metal roll with an embossing pattern on the PVF top surface. Thus, the outer surface of the PVF film, i.e. the surface opposite the surface comprising the laminate adhesive layer, may be embossed.

[0057] Preferably, the adhesive layer comprises a polyester based adhesive, as a polyester based adhesive has proven to result in the strongest adhesion between the PVC film and the metal substrate, thereby providing the best protection against delamination. The polyester based adhesive layer may be applied by reverse roller coat or spray coating. The layer is preferably applied by reverse roller coat. The adhesive layer preferably has a thickness of about 2 - 25 pm, more preferably of about 3 - 15 pm, most preferably of about 4 - 10 pm.

[0058] Finally, the laminated assembly may further comprise a strippable film. The strippable film covers the PVF 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 film covering the PVF top layer. Thus, the outer surface of the PVF film, i.e. the surface opposite the surface comprising the laminate adhesive layer, may comprise a strippable film.

[0059] The method of the invention may further comprise applying a backing coating to a bottom surface (opposite the top surface) of the coiled plane metal substrate. Different types of back coats can be applied depending on the customer demand and the kind of metal substrate. A back coat comprising epoxy or polyester is preferred as it promotes polyurethane foam adherence to the metallic support. Polyurethane foam is often used as insulating layer in public transport applications. The backing coating may for example be applied at the same time as the adhesive. Preferably, the backing coating has a thickness of between 2 - 25 pm, more preferably 4 - 10 pm.

[0060] 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. 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.

[0061] Detailed description of the Figures

[0062] 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 in degreasing zone 4, washed in washing zone 5, rinsed in rinsing zone 6, and subsequently passivated and dried in passivation zone 7 and drying zone 8, respectively. A primer 23 is optionally applied by reverse roller coat in zone 9, cured by heating in primer heating zone 10, and cooled with water in primer cooling zone 11. In the depicted embodiment, the adhesive 24 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.

[0063] 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, film 31, and strippable film 29. The second surface, or bottom surface, 33 is covered by a backing coating 30.

[0064] Film 31 comprises in order layers 25, 26, 34 and 27, i.e. PVC layer 25, ink layer 26, laminate adhesive layer 34 and PVF layer 27. The PVF layer 27 comprises an embossing pattern 28 at its top surface.

[0065] Example 1

[0066] A layered laminate of 115 pm rigid PVC, 5 micron of acrylic adhesive and 10 pm of PVF was prepared by

[0067] 1. calendering PVC into a film, and printing the film with an ink layer,

[0068] 2. providing a PVF film with an acrylic adhesive layer,

[0069] 3. bonding the PVC layer with the acrylic adhesive layer of the PVF, such that the ink layer is in contact with the acrylic adhesive layer and the PVF is the top layer,

[0070] 4. embossing the PVF top layer with an embossing pattern. A 0.6 mm thick coil of steel was unwound, degreased and pre-treated by a passivant liquid. The 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. Then the film was laminated with the layered laminate of 115 pm rigid PVC, 5 micron of acrylic adhesive and 10 pm of PVF immediately outside the oven. Then 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, and formed into a decorative surface panel in a cold bending process. The decorative surface panel did not contain visible or invisible faults, such as stress whitening, cracking and / or micro cracking.

[0071] The product complies with the tests T10.01, T10.02 and T11.01 requirements R1 for HL1, HL2 and HL3 of standard EN 45545-2:2020.

[0072] The product complies with the test T02 requirement R1 for HL1, HL2 and HL3 of standard EN 45545-2:2020.

[0073] The product complies with the test T03.01 requirements R1 for HL1 and HL2 of standard EN 45545-2:2020.

[0074] The product was assigned for low VOC emissions, i.e. the A+ category in accordance with the French Regulation of 19 / 04 / 2011 , relating to the labeling of construction products, wall coverings, floors, paints and varnishes, doors and windows.

[0075] As opposed to products according to the present invention, a product according to Example 1 of US 2023 / 107134 A1 fails testing according to EN 45545-2:2020.

[0076] The product of the present invention outperforms a comparative product using flexible PVC in fire testing according to UNI EN 13501-1:2009.

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 an adhesive layer onto a top surface of the plane metal substrate;- laminating a layered laminate comprising a PVC film and a PVF film onto the top surface of the plane metal substrate, the PVC film contacting the adhesive layer, thereby forming a laminated assembly with a PVF top surface, wherein the layered laminate further comprises a laminate adhesive layer for bonding the PVC film to the PVF film, and an optional ink layer between the PVC and the laminate adhesive layer, wherein the laminate adhesive layer comprises an acrylic adhesive, and wherein the PVC is rigid PVC.

2. Method according to claim 1, wherein the adhesive layer comprises a polyester based adhesive.

3. Method according to any one of the preceding claims, wherein the PVC film comprises one or more pigments.

4. Method according to any one of the preceding claims, wherein the PVC film has a thickness of between 70 and 250 pm, preferably of between 90 and 180 pm, most preferably of between 100 and 135 pm.

5. Method according to any one of the preceding claims, wherein the PVF film comprises an embossed pattern on the PVF top surface.

6. Method according to any one of the preceding claims, wherein the PVF film has a thickness of 6 - 50 pm, preferably of 8 - 32 pm, more preferably of 10 - 20 pm.

7. Method according to any one of the preceding claims, wherein the laminate adhesive layer has a thickness of between 2 - 10 pm, preferably between 3 - 8 pm, more preferably between 4 - 6 pm.

8. Method according to any one of the preceding claims, further comprising applying a strippable film covering the PVF top surface.

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

10. Method according to any one of the preceding claims, further comprising rewinding the laminated assembly resulting in a laminate coil.11 . Method according to any one of the preceding claims, further comprising cutting the laminated assembly to produce slit coils.

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

13. Laminated assembly obtainable by the method of any one of claims 1 - 12.

14. Product comprising a laminated assembly according to claim 13.

15. Product according to claim 14, which is an interior decorative surface panel.

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