This invention relates to a method for manufacturing panels, as well as to panels which can be obtained by such method.

More particularly, the method relates to methods for manufacturing panels of the type which is at least composed of a substrate and, provided on said substrate, a top layer with a printed decor. Herein, this may relate, for example, to furniture panels, ceiling panels, floor panels or the like, which substantially consist of an MDF or HDF (Medium or High Density Fiberboard) basic panel or substrate and a top layer provided hereon. In particular, it relates to a method wherein one or more material layers are provided on the substrate, wherein at least one of these material layers is provided by means of a print which is performed directly on the substrate, wherein this print then forms at least a portion of said printed decor.

Such panels are known as such, for example, from document US 1 ,971 ,067 or document DE 195 32 819 A1. From said documents, it is also known that said material layers can comprise one or more basic layers, wherein these basic layers substantially extend underneath said print, and/or can comprise one or more finishing layers, which substantially extend above said print. Such finishing layers may comprise, for example, transparent or translucent synthetic material layers which form a protective layer above the printed decor and, for example, can comprise wear-resistant particles, such as aluminum oxide. It is not excluded that this protective layer comprises a material sheet, such as a paper sheet.

The state of the art in respect to panels which are provided with a print which is performed directly on the substrate further becomes clear from documents WO 01/48333, WO 02/00449, WO 2004/042168, EP 1 454 763, DE 197 25 829 C1 and DE 10 2004 009 160 A1.

It is known, amongst others, from document WO 01/48333, that either lacquers or synthetic resins can be applied for realizing said material layers. In the case of synthetic resins, these are applied via a carrier sheet which in advance has been provided with such synthetic resin and is provided on the substrate by means of a heated press. In the case of lacquers, for example, UV-hardening lacquers can be applied.

It is known, amongst others, from documents DE 197 25 829 C1 , WO 2011/045690 or EP 1 454 763, that one or more synthetic resins applied in liquid form can be used for realizing said material layers. After these resin layers have dried, they are hardened in a heated press. By means of such method, paper-free top layers can be realized.

Floor panels which are realized according to methods of the state of the art may show the disadvantage that the surface is insufficiently waterproof. In particular, such panels are subjected to degradation by exposure to steam of boiling water.

The present invention primarily aims at offering an alternative method of the above-mentioned type, which, according to various preferred embodiments thereof, can offer a solution for one or more of the problems with the panels obtained by the methods of the prior art.

To this aim, the invention relates to a method for manufacturing panels of the type which is at least composed of a substrate and, provided on said substrate, a top layer with a printed decor, wherein the top layer comprises at least two material layers, namely at least a first material layer forming a basic layer for a second material layer provided thereon in the form of a print, wherein the method consists at least of applying said two material layers, wherein said print or second material layer is performed directly on the substrate material and this print forms at least a portion of. said printed decor, with the characteristic that, for applying said first material layer or basic layer, it is started from a water-based two-component lacquer, hereinafter also 2K lacquer or 2K primer or 2K basic layer. It is clear that by "directly" herein is not excluded that already one or more material layers can have been provided on the substrate before the print is performed. Namely, by "directly" is meant that the printing operation takes place on the substrate and, for example, not on a separate carrier sheet which afterwards is provided on the substrate.

The use of a water-based two-component lacquer enhances the adherence between substrate and print. Preferably, as a first component said water-based two-component lacquer comprises a dispersion of amine-, hydroxy- or carboxy- functional acrylate copolymer or a polyester polyol or a vinyl polymer. As the second component, said water-based two-component lacquer preferably comprises a hardening agent, such as an isocyanate and/or an aziridine component which is added to the lacquer, preferably in a concentration of 2 to 15%, or still better between 4 and 9%, wherein 6% is a good value. In the case that the second component is an isocyanate, preferably an aliphatic isocyanate is used, for example, HDI (Hexamethylene Di-lsocyanate). Chemically seen, the isocyanate or aziridine component will react with polyol or hydroxy, carboxy or amine functionalities which are present in the lacquer itself, namely in said first component and/or in the thermo-hardening resin, preferably in the melamine formaldehyde resin of a possible transparent or translucent synthetic material layer, by which urethane compounds are formed. The urethane compounds provide for an increased waterproofness and a good adherence between the substrate and the print and with the thermo-hardening resin or the possible transparent or translucent layer.

Isocyanate and aziridine show the feature that they react with water. This feature is particularly useful when such basic layer is combined with further water-containing material layers, such as with a print by means of water-based inks, or with a transparent or translucent synthetic material layer on the basis of a thermo- hardening resin. Thermo-hardening resins, such as melamine formaldehyde resin, mostly are water-based and also chemically produce water when polycondensating or hardening. An excess of water in the top layer to be hardened may lead to undesired effects, such as a deficient adherence among the layers of the top layer and/or the substrate, either locally in the form of porous spots, or rather global in the form of blisters. The presence of the isocyanate and/or aziridine can offer a certain remedy for such undesired effects. When melamine formaldehyde resin or another thermo-hardening resin comprising hydroxy and/or amine functional groups is used, the risk of the occurrence of such defects is reduced to a major extent.

Preferably, in total 20 to 250 grams per square meter of dry weight of a layer on the basis of said two-component lacquer are applied. Preferably, this is performed in a plurality of partial layers, wherein at least two partial layers with an application of 10 grams per square meter or more are applied and preferably at least three such partial layers are performed. Preferably, said water-based two-component lacquer comprises at least 2 and preferably at least 5 percent by weight of the component on the basis of isocyanate and/or aziridine. In the case of isocyanate, preferably aliphatic isocyanate is concerned, for example, HDI. Said percentages are calculated on the total system of water and the aforementioned two components.

According to the most preferred embodiment, said water-based two-component lacquer is composed as follows:

- A water-based lacquer, consisting of a dispersion with 40 to 80 percent by weight of dry matter and still better 50 to 75 percent by weight of dry matter, wherein this dry matter preferably is of an amine, hydroxy or carboxy functional copolymer or of a polyester polyol;

- 30 to 60 percent by weight of a pigment, such as titanium oxide, in said dispersion;

- an addition of 2 to 15 percent by weight, preferably approximately 6 percent by weight, to the total system of said dispersion of an isocyanate, such as HDI. As aforementioned, the method preferably is applied when water-based pigmented inks are employed as a starting point for said print. However, the invention is also useful when other pigmented inks are applied, such as UV inks.

Preferably, the applied quantity of ink is limited to less than 15 grams per square meter, dry weight. Limiting the quantity of applied ink also means limiting the moisture present in the top layer, which moisture finally will have to be removed.

Said two-component lacquer can be made pigmented. For example, a white lacquer can be applied, or a yellow or beige lacquer. The use of a basic color can induce a limiting of the total quantity of ink to be applied for preparing a well- defined printed decor.

According to the most preferred embodiment, the method also comprises at least the step of providing a transparent or translucent synthetic material layer above said print. Preferably, for providing said transparent or translucent layer, one starts from a thermo-hardening resin, such as melamine. The 2K basic layer of the invention in particular offers a solution for problems occurring with the finishing with such melamine or melamine formaldehyde resins. These resins are water- based and also chemically produce water as a byproduct of their polycondensation.

Preferably, said transparent or translucent layer comprises hard particles, preferably between 10 and 40 grams per square meter. Herein, this preferably relates to aluminum oxide particles. The inventor has found that, by means of the 2K primer and such amount of hard particles in the thermo-hardening resin of the transparent or translucent layer, it is possible to achieve a quantity AC4 according to EN13329-Annex E.

Preferably, for said transparent or translucent layer, it is started from a paper sheet provided with thermo-hardening resin, or a so-called overlay. Such paper sheet, without resin, preferably has a dry weight situated between 10 and 30 grams per square meter. Preferably, a quantity of resin is applied which corresponds to one and a half to five times this dry paper weight, wherein this quantity of resin is measured in a condition in which the resin has a residual moisture content of 7% or less.

According to the most preferred embodiment, the substrate, the first and the second material layer and said transparent or translucent layer are pressed together in a press device, wherein the thermo-hardening resin of said transparent or translucent layer is hardened. In this press treatment now the presence of moisture in the top layer is critical. Namely, the temperature applied in the press is higher than 100°C, for example, between 150°C and 250°C, and inherently leads to boiling of the water which is present. This moisture or this vapor must be able to disappear approximately completely from the composition. The 2K primer contributes to that. Preferably, a press device is applied of the short-cycle press (In German: Kurztaktpresse) type. The applied pressures may vary from 3 to 60 kg/cm ² . Preferably, a pressure situated between 25 and 50 kg/cm ² will be applied.

Preferably, during said hardening a relief is realized, the recesses and/or protrusions of which extend at least in the transparent or translucent layer.

Preferably, the residual moisture content of said water-based two-component lacquer and/or the print and/or the remaining layers of the top layer is less than 11% and still better less than 9% when the pressing is started, in other words, at the moment when the stack of at least the substrate, the first and second material layers and said transparent or translucent layer enter the press device. To this aim, prior to the press treatment said stack can be dried by hot air and/or by means of infrared heating elements.

The combination of a print layer on the basis of pigmented inks and a melamine- based finishing layer is of particular interest, as in this manner a stable print, in particular under the influence of sunlight, can be achieved in combination with a hard surface layer. Moreover, it is possible to provide fine structures or relief in a thermo-hardening layer, such as in a melamine layer, by means of a press treatment, such as with heated molds or pressing plates. Preferably, to this aim a discontinuous press device, such as a so-called short-cycle press, is applied. The inventors have found that applying pressures situated between 30 and 60 bar and temperatures between 120 and 230°C does not lead to problems for a print on the basis of water-based pigmented inks and may imply a good hardening of the top layer. Possibly, catalysts or hardening agents can be used for restricting the temperature for hardening the thermally hardening finishing layer. Preferably, the thermally hardening material of the finishing layer has already been subjected to a partial drying treatment before the press treatment is performed, wherein the final hardening then largely or entirely is obtained in the press device. It is clear that according to this practical example also another polycondensation resin can be applied than the melamine resin mentioned herein. Further, it is clear that instead of working with a finishing layer which comprises a carrier sheet, such as a paper sheet, also a finishing layer can be used which is applied in liquid form, which finishing layer, for example, is partially hardened by means of a drying oven before the final hardening largely or entirely is achieved in the press device. Preferably, the finishing layer of this second practical example is provided with hard particles, such as aluminum oxide, preferably having an average grain size situated between 30 and 100 micrometers. The amount of aluminum oxide particles preferably is between 20 and 35 grams per square meter.

Examples of thermo-hardening resins are urea formaldehyde, melamine, melamine formaldehyde, methane diphenyl diisocyanate, phenol formaldehyde, resorcinol formaldehyde and resorcin phenol formaldehyde. Preferably, the print is performed by means of a digital printing technique, such as by means of one or more inkjet print heads. Herein, a so-called single-pass printing device as well as a so-called multi-pass printing device can be chosen.

Preferably, said basic layer is free from carrier sheets, such as free from paper sheets. Preferably, the entire obtained top layer of the panels is free from such carrier sheets or paper sheets. However, it is not excluded that the 2K primer of the invention would be applied on a paper sheet already present on the substrate. In such case, this preferably relates to a colorless water-based lacquer, thus, without a pigment. So, for example, the water-based lacquer of the invention can be provided on a paper sheet which beforehand has been glued to the substrate by means of a thermo-hardening glue, such as urea formaldehyde or phenol formaldehyde glue.

Preferably, the method of the invention provides for one or more basic layers, which are situated underneath the print, and for one or more transparent or translucent finishing layers, which are situated above the print. Of course, the basic layer of the invention, which comprises the water-based 2K lacquer, can consist of a plurality of material layers, wherein then at least one thereof comprises said water-based 2K lacquer.

Providing a plurality of said basic layers, print and/or finishing layers can be performed with one or more intermediate drying treatments, grinding treatments or brushing treatments.

It is clear that said transparent or translucent synthetic material layer as such can be composed of a plurality of finishing layers. According to the method of the invention, embedding hard particles in the finishing layers, namely in the transparent or translucent synthetic material layer, can be performed in various manners. So, for example, they can be blended into the material of the respective finishing layer before the latter is provided on the substrate. According to another example, they are provided, by means of, for example, a strewing device, on and/or in the finishing layer concerned, which has already been provided on the panel and which preferably still is moist. In a similar manner, other components, too, can be embedded into the basic layers and/or finishing layers, such as, for example, cellulose fibers or pigments of any type.

It is clear that for applying the water-based 2K lacquer or the components thereof, all techniques known as such can be used, such as application techniques making use of rollers, sprinkling devices, spraying devices, strewing devices, spreading devices and so on.

It is clear that the invention further also relates to panels which are obtained by means of the method of the invention.

Preferably, the print relates to a print provided by means of a digital printing device, such as an inkjet printer. Due to the fact that the print is digital and is performed directly on the substrate, the motif is controllable and is not or practically not subjected to extension or shrinkage after being provided.

Preferably, water-based pigmented inks are applied for performing the print. In such case, the drying of the inks preferably is performed by means of infrared radiation. Preferably, inks of at least four different colors are used, such as the basic colors cyan, magenta, yellow and black. Preferably, the applied printing device comprises at least one inkjet print head per color. Possibly, the number of colors can be extended to more than four. Preferably, a maximum limit of ten different colors is applied. Ideally, 6 or 8 different colors are applied. The inkjet print heads concerned can be of the single-pass type or of the multiple-pass type. Further, it is clear that it is not excluded that the applied inks may be UV inks. With UV inks, there will also be problems with moisture in the finishing layers when these are composed of thermo-hardening resin, such as on the basis of melamine or melamine formaldehyde resin. With the intention of better showing the characteristics of the invention, hereafter, as an example without any limitative character, some preferred embodiments are described, with reference to the accompanying drawings, wherein:

Figure 1 schematically represents some steps of a method with the characteristics of, amongst others, the first aspect of the invention;

Figure 2, in cross-section and at a larger scale, represents a view according to the line ll-ll represented in figure 1 ;

Figure 3 represents a panel, more particularly a floor panel, having the characteristics of the invention; and

Figure 4, in cross-section and at a larger scale, represents a view according to the line IV-IV represented in figure 3.

Figure 1 represents some steps S1-S7 of a method for manufacturing panels or boards 1 with the characteristics of the present invention. Herein, this relates to a method for manufacturing panels or boards 1 of the type which is at least composed of a substrate 2 and, provided on said substrate 2, a top layer 3 with a printed decor 4. In the example of figure 1 , specifically a method is illustrated for manufacturing floor panels 5 with a wood-based substrate 2, such as with a substrate 2 on the basis of MDF or HDF. To those skilled in the art, it is clear how a similar method for manufacturing other panels, such as ceiling panels or furniture panels, can be obtained.

For manufacture, it is started from larger boards 1 , of which in a dividing step, not represented here, a plurality of said panels 5 can be formed. Preferably, the larger board 1 consists of MDF or HDF with a ground surface. The larger board preferably has been ground at least with a grain P180. Preferably, the larger board is successively ground with grain P150, P180 and P220. The grinding operation is applied for adjusting the thickness of the board and for obtaining a smooth surface. In the example of the method of figure 1 , on the surface of the larger board 1 in a first step S1 a material layer 6 with a water-based primer 7 is provided. This step is optional. Herein, the amount of applied primer 7 may vary between 5 and 20 grams per square meter, wherein 10 grams per square meter is an appropriate value. In the example, the primer is provided over the entire surface to be printed of the board 1 by means of a roller 8. In the example, in a second step S2 at least a second material layer 9 is provided on the surface of the larger board 1. Herein, this relates to a basic layer 9 of a substantially uniform color, which is applied by means of at least one roller 10. It is this layer which according to the invention comprises a water-based two- component lacquer. In this case, this relates to a water-based two-component lacquer which comprises an amine-, hydroxy- or carboxy-functional acrylate copolymer as the first component and comprises an aliphatic isocyanate, namely HDI, as the second component.

It is clear that in the example of figure 1 the aforementioned first material layer 6 as well as the aforementioned second material layer 9 are applied in liquid form. They can also be applied in a plurality of partial layers, the latter either being dried and/or ground in between or not.

Of course, the material layers 6-9 of the first step S1 and the second step S2 can be applied in any manner. Preferably, they are applied by means of one or more rollers. The water-based two-component lacquer of the invention can be applied, for example, by means of a roller device with a single roller, wherein this roller preferably rotates concurrently with the substrate, or by means of a roller device with two rollers with mutually opposed sense of rotation, wherein the second roller in feeding direction then preferably will rotate in opposite sense to the moving direction of the substrate. By means of this last-mentioned roller device, also known as a spreader device, particularly smooth surfaces and finally a better printing quality can be obtained.

Preferably, the applied second material layer 9 is dried, preferably with hot air having a temperature of 40° to 90°, preferably during 15 to 120 seconds.

Preferably, said second material layer 9 is applied in successive partial layers, wherein the following scheme may serve as an example:

- providing 25 grams per square meter of a white- or yellow-pig mented water-based two-component lacquer;

- drying the applied partial layer by means of hot air having a temperature of 60°C during 25 to 50 seconds;

- twice repeating the preceding two steps, such that in total a lacquer application of 75 grams per square meter is obtained;

- optionally providing a transparent water-based two-component layer and/or providing 2 to 20 grams per square meter of an inkjet coating.

In a third treatment step S3, a material layer 1 is applied in form of a print 12 which is performed directly on the substrate material 2. This print 12 forms at least a portion of the printed decor 4 of the final panels 5. Prior to the print 12 of treatment step S3, possibly a heating of the lacquered larger board 1 can be performed, preferably by means of one or more infrared heating elements. The represented print 12 relates to a print with a wood pattern. As represented, it is possible that said basic layer 9 contributes to the appearance of the panel 5 or the board 1. In the example, the print 12 is performed by means of a digital printing device 13, such as by means of an inkjet printing device. In the example, the printing device 13 comprises at least four inkjet print heads. Here, each of the four represented inkjet print heads 14 is responsible for applying ink of a specific color, whereby a multi-color print can be achieved. Preferably, the inkjet printing device 13 is of the so-called multi-pass principle, wherein a certain print head 14 moves a plurality of times over the surface to be printed of the board 1. During such pass, the respective substrate 2 or the respective board 1 preferably is held still. In between two passes, the print heads 14 and/or the substrate 2 or the board 1 can be moved with the aim of printing another portion of the surface of the board 1 in a subsequent pass. This movement can be similar to, equal to or smaller than the distance between two points of the printing portion provided in a previous pass. In this manner, it can be obtained that the printing points of the printing portion still to be performed are provided in the subsequent pass in between the printing points of the printing portion of one or more preceding passes. Of course, it is not excluded that stationary print heads and/or the so-called single-pass principle may be used, in which latter a respective substrate 2 or a respective board 1 is provided with a print 12 in a single movement. For a more detailed description of the single-pass principle, reference is made to EP 1 872 959. It is noted that in a printing device of the single-pass type the board may lie still, for example, on a vacuum table, whereas a shuttle with print heads moves over the board and prints it in a single movement, or reverse, namely that the print heads stand still and that the board moves in a single movement below the print heads and is printed.

In the represented example, the print 12 is performed by means of water-based pigmented inks, which in this case, in a separate step S4, are at least partially dried and/or hardened by means of one or more infrared heating elements 15. Possibly, such light source can be integrated in the printing device 13 or on one or more of the print heads 14. By means of such embodiment, the step S4 can be performed approximately simultaneously with the step S3. According to the invention, it is, of course, not excluded that UV inks are used, wherein any drying treatment then preferably is performed by means of a UV radiation source.

In a fifth treatment step S5, a translucent or transparent synthetic material layer 16 is applied, which, in the final floor panel 5, shall be situated above the material layer 11 which is provided by means of a print 12. In the example, the respective synthetic material layer 16 consists of two separately deposited material layers 16A-16B, both substantially consisting of melamine-based thermo-hardening resin. In the example, the application itself is performed by means of rollers 10. Of course, other application techniques are not excluded. As represented in dashed line 17, possibly a drying operation or a hardening operation can be applied to this first material layer 16A. A hardening of melamine can be performed, for instance, by blending in or applying an appropriate hardening agent. According to a not-represented variant, the translucent or transparent synthetic material layer 16 may substantially consist of a carrier sheet provided with a thermo-hardening resin, preferably a paper sheet impregnated with this resin, which sheet is provided on the printed substrate 2. Other techniques for depositing the material layers 6-9-16 of the first, second and/or fifth step are, for example, techniques making use of sprinkling or spraying devices, or application techniques making use of negative pressure.

In a sixth treatment step S6, in the example hard particles 18 are provided on the still moist or wet synthetic material layer 16, in this case by means of a strewing device 19. Such strewing devices 19 are known as such, for example, from document GB 1 ,003,597 or GB 1 ,035,256. Herein, the hard particles 19 are put from a recipient 20 onto a roller 10, such as an anilox roller, from where they then are removed again by means of a brush 21. In this case, a rotating brush is represented; however, use can also be made of a to- and fro-moving brush. For the hard particles 18, use can be made of aluminum oxide particles having an average particle size of less than 200 μηι.

It is possible that after said sixth treatment step S6, partial step S5B and possibly the sixth step S6 are repeated one or more times, whether or not with intermediate drying operations. In such case, it is possible that the average particle size of the hard particles 18 is chosen smaller as they are provided in a layer situated closer to the final surface.

It is clear that such separate sixth step S6 is optional. Namely, the hard particles 18 may be omitted, or techniques may be used wherein the hard particles 18 are blended into the material which is applied in the partial steps S5A and/or S5B. In the case that in step S5 use is made of a carrier sheet, the hard particles 18 can also be provided on or in this carrier sheet prior to depositing the latter on the substrate.

It is possible that one or more of the above-mentioned layers and/or other layers are provided on the bottom side 22 of the substrate 2 or the board 1. Preferably, at least one material layer 23 is provided, which realizes a water- and/or vapor- sealing effect on the underside 22 of the board 1 or the panels 5 obtained therefrom.

In a seventh treatment step S7, the substrate 2 provided with the material layers 6- 9-11-16-23 is brought into a heated press device 24, where it is pressed between press elements 26. In this case, schematically a short-cycle press is represented. However, use can also be made of a continuous press device, wherein belt- shaped press elements are applied instead of plate-shaped press elements 25, as represented here. During the press treatment S7 the hardening of the thermally hardening resin is performed at least partially. In the polycondensation of such resin, water is produced as a byproduct. Preferably, a pressing temperature of 160 to 220°C is applied during 15 to 45 seconds, and a pressure of 25 to 50 kg per square centimeter (25 to 50 bar). A good value determined by the inventor is a temperature of 180°C-195°C during 30 to 45 seconds at a pressure of 40 bar.

Preferably, the residual moisture content of said water-based two-component lacquer 9 and/or the print 12 and/or the remaining layers 16-23 of the top layer 3 is less than 11 % and still better less than 9% at the start of the treatment step S7, in other words, at that moment when the stack of at least the substrate 2, the first and second material layers 9-11 and said transparent or translucent layer 16 enter the press device 24. To this aim, said stack can be dried prior to the press treatment by means of hot air and/or by means of infrared heating elements, however, this is not represented here. Figure 2 represents the result of such press treatment S6. It is shown clearly that in the surface of the board 1 , more particularly in the material layers 6-9-11-16 provided thereon, a relief 26 can be realized. This may be, for example, as one or both press elements 25 from figure 1 are provided with a structure and will press this structure during the press treatment S6 into the surface of the board 1 or the material layers 6-9-11-16 provided there. Preferably, this relates to a relief 26 with recesses and/or protrusions which correspond to the print 12. As represented, the impressions 27 realized by means of the press element may manifest themselves in one or more of the material layers 6-9-11-16 provided on the board 1. Preferably, the substrate 2 itself is not deformed, although this is not excluded. Of course, it is also not excluded that at least the print 12 remains undeformed and that the impressions 27 thus manifest themselves exclusively or substantially in one or more of the material layers 16, or finishing layers, which are provided above the print 12.

It is clear that it is not necessary for the method of the invention that all steps S1- S7 represented in figure 1 are applied. The essential feature of the method of the invention namely consists in that in at least one material layer 9 underneath the print 12 a water-based two-component lacquer is applied.

It is also clear that also other layers than those illustrated by means of figure 1 can be applied and that other techniques can also be applied for providing the various material layers 6-9-11-16-23.

As aforementioned, in a further not represented dividing step the larger boards 1 can be subdivided into a plurality of smaller panels 5, which approximately show the dimensions of the final panels 15. This may take place, for example, by means of a multirip saw.

Figure 3 shows that the obtained rectangular panels 5, at least on two opposite edges 28-29 and in this case on both pairs of opposite edges 28-29-30-31 , possibly can be provided with profiled edge regions 32, which comprise, for example, coupling means 33 with which two of such panels 5 can be coupled to each other. The treatment step in which the possible profiled edge regions 32 are realized is not represented here. Such treatment step may take place at any time after performing said dividing step. The invention is of particular importance with such panels. As the adherence of the top layer now is improved, the risk of damaging the top layer when realizing the coupling means 33 is minimized.

Figure 4 represents an example of such coupling means 33. For further examples, reference is made to document WO 97/47834.

It is also noted that the thickness of the layers 6-9-11-16A-16B-16 in the figures is represented only schematically and has to be considered non-limiting.

The present invention is in no way limited to the herein above-described embodiments; on the contrary, such methods and panels can be realized according to various variants, without leaving the scope of the present invention.