Abrasion-resistant wood-based panel.

Abstract

The present invention relates to a method for the production of an abrasion-resistant wood-based plate having an upper and a lower side, with at least one decorative layer arranged on top, in particular having a structure synchronous with the decoration. At least six layers of resin are applied over the decorative layer. Abrasion-resistant particles are sprinkled onto the first, moist resin layer, after which the second resin layer is applied without intermediate drying of the first resin layer. Each of the other resin layers is applied after the previous resin layer has dried. Here, the third, fourth, and fifth resin layers each contain glass spheres.

Description

[0001] The present invention relates to an abrasion-resistant wood-based panel provided with a decorative layer, in particular a wood-based panel provided with a structure synchronous to the decor. Description

[0002] A wide variety of products and product surfaces subject to wear and tear from mechanical stress must be protected from premature damage or destruction by applying wear-resistant coatings. These products can include, for example, furniture, interior panels, flooring, and so on. Depending on the frequency and intensity of the stress, different protective measures must be applied to guarantee the longest possible service life for the user.

[0003] Many of the products mentioned above have decorative surfaces that quickly become unsightly and / or impossible to clean due to wear and tear from intensive use. These decorative surfaces very often consist of papers impregnated with thermosetting resins, which are pressed onto the wood-based substrates using short-cycle presses. Melamine-formaldehyde resin is very commonly used as the thermosetting resin.

[0004] One approach to improving the wear resistance of decorative surfaces involves applying or incorporating abrasion-resistant particles into the resin layers near the surface. This can be achieved, for example, by applying a liquid resin containing abrasion-resistant particles to the relevant surfaces, with corundum particles typically used as abrasion-resistant particles in the case of decorative wood-based panels.

[0005] To avoid the sedimentation of the corundum particles in the liquid resin, into which the corundum is often introduced for application, and the associated problems, the abrasion-resistant particles can also be sprinkled on using a suitable device.

[0006] Another problem caused by corundum-containing formulations in the further process step of pressing is the sheet metal wear of the structured press plate in the short-cycle press, which is higher the more corundum in g per square meter is applied, the larger the grain size and the worse this corundum is covered by corundum-free resin layers.

[0007] In the past, to reduce sheet metal wear, the corundum-containing layer was sealed off from the pressed sheet metal by subsequent resin layers. For this purpose, glass beads can be incorporated into the liquid layer structure along with the resin layers, with the glass beads acting as spacers between the abrasion-resistant particles and the pressed sheet metal. This was able to reduce sheet metal wear, at least to some extent. Such approaches are described, among others, in the published EP 3 480 030 A1 and EP 3246175 A1. In particular, EP 3246175 A1 discloses an abrasion-resistant wood-based panel with the following layer structure (viewed from bottom to top): Countercoat consisting of four resin layers, wood-based panel, primer layer, printed decorative layer, first resin layer, layer of abrasion-resistant particles, second resin layer, third resin layer with glass beads, fourth resin layer with glass beads.

[0008] However, to produce wood-based panels with high abrasion resistance, particularly in abrasion classes AC4 to AC6, while simultaneously minimizing press plate wear, it is necessary to increase the quantity of abrasion-resistant particles. As already mentioned, this also means increased wear on the press plates, which cannot be adequately reduced with current approaches.

[0009] The present invention is therefore based on the technical objective of ensuring low press sheet wear while reliably achieving high abrasion resistance values, particularly abrasion classes AC4 to AC6. This should be achieved primarily for coated and printed wood-based panels processed in a single process in a wide variety of formats. Where possible, process simplification and at least cost neutrality should be achieved. The disadvantages already discussed should, if possible, be eliminated by the new process. This new process should also enable effective quality control that provides timely information about the current process.

[0010] The problem stated is solved according to the invention by wood-based panels with the features of claim 1.

[0011] The wood-based panels according to the invention are provided in a process for producing an abrasion-resistant wood-based panel with a top and a bottom, with at least one decorative layer arranged on the top, in particular with a structure synchronous to the decor, wherein the process comprises the following steps: Applying at least one first resin layer containing cellulose fibers to the protective layer arranged on the decorative layer on the top surface of the wood-based panel, wherein the first resin layer has a solids content between 60 and 80 wt%, preferably 65 and 70 wt%, and particularly preferably between 65 and 67 wt%; uniformly sprinkling abrasion-resistant particles onto the first resin layer on the top surface of the wood-based panel; wherein the first resin layer on the top surface of the wood-based panel, provided with the abrasion-resistant particles, is not dried after application; applying at least one second resin layer onto the first, moist resin layer on the top surface of the wood-based panel, provided with the abrasion-resistant particles, wherein the second resin layer has a solids content between 60 and 80 wt%, preferably 65 and 70 wt%, and particularly preferably between 65 and 67 wt%;Subsequent drying of the assembly consisting of a first resin layer and a second resin layer in at least one drying device; application of at least one third resin layer, wherein the third resin layer has a solids content between 60 and 80 wt%, preferably 65 and 70 wt%, particularly preferably between 65 and 67 wt%, and contains glass beads; subsequent drying of the applied third resin layer in at least one further drying device; application of at least one fourth resin layer, wherein the fourth resin layer has a solids content between 50 and 70 wt%, preferably 55 and 65 wt%, particularly preferably between 58 and 62 wt%, and contains glass beads; subsequent drying of the applied fourth resin layer in at least one further drying device;Applying at least one fifth resin layer, wherein the fifth resin layer has a solids content between 50 and 70 wt%, preferably 55 and 65 wt%, particularly preferably between 58 and 62 wt%, and contains glass beads; subsequent drying of the applied fifth resin layer in at least one further drying device; applying at least one sixth resin layer, wherein the sixth resin layer has a solids content between 50 and 70 wt%, preferably 55 and 65 wt%, particularly preferably between 58 and 62 wt%, and does not contain glass beads; subsequent drying of the applied sixth resin layer in at least one further drying device; and pressing the layered structure in a short-cycle press.

[0012] The process thus enables the cost-effective production of wood-based panels with a decorative layer, the decorative layer having a structure synchronized with the decor, in various formats with high wear resistance. According to the present process, a first resin layer, in particular a first thermosetting resin layer with a high solids content, such as a melamine-formaldehyde resin layer, is applied to the decorative layer (pretreated or untreated) of the wood-based panel. The first resin layer is not initially dried or partially dried; instead, the abrasion-resistant particles are evenly sprinkled onto the wet or still liquid first resin layer on the surface of the wood-based panel using a suitable spreading device.Since the first layer of resin is still liquid when sprinkled on, the abrasion-resistant particles can sink into the resin layer. Due to the high solids content of the resin and the resulting increased viscosity, the abrasion-resistant particles are also well embedded in the resin layer.

[0013] Subsequently (i.e., without intermediate drying of the first resin layer with the abrasion-resistant particles sprinkled onto it), a second resin layer with a higher solids content is applied to the still-moist first resin layer. This is achieved by installing an applicator unit downstream of the spreading machine (i.e., between the first dryer and the spreading machine) in the processing direction. The additional applicator unit, with its roller application, picks up the abrasion-resistant particles that are not adhered to or have not penetrated the first resin layer and transports them back to the resin application unit. There, an equilibrium concentration is reached, and the removed abrasion-resistant particles are evenly distributed by the roller onto the subsequent surfaces. This results in an accumulation of abrasion-resistant particles in the second application unit up to a maximum abrasion-resistant particle content of 10%.This prevents loose particles from being blown away or picked up in the dryer.

[0014] This is followed by a third resin layer with increased solids content and glass beads, then a fourth and fifth resin layer with normal solids content (approx. 55-60 wt%) and glass beads, and a sixth resin layer with normal solids content without glass beads.

[0015] The layered structure of resin layers with increased solids content and conventional, normal solids content, cellulose fibers, and glass beads covers the abrasion-resistant particles, preventing them from protruding from the coated surface. This reduces or even largely eliminates the adverse effects of corundum particles protruding from the coated surface, for example, on a subsequent press plate.

[0016] This process increases the service life of the press plates in the downstream pressing process for laminate formation. Overall, process costs are reduced due to lower material and maintenance costs. Furthermore, no new equipment or fixtures need to be installed in the production line.

[0017] The present layer structure also enables the embossing of structures synchronized with the decor using deeply structured press plates. This is made possible by the overall layer thickness, which can only be achieved through the specific resin composition with layers of resins with varying solids contents. Thus, improvements of between 25 and 50% can be observed with this process, based on the recorded sheet service life.

[0018] In a preferred embodiment of the present method, the wood-based panel coated with the decorative layer is not heated in a dryer, such as an IR dryer, before the first resin layer is applied. This can be achieved by switching off an IR dryer provided in the production line, or by not having an IR dryer in the production line at all. By avoiding heating the wood-based panel coated with a decorative layer, electrostatic charging of the panel surface is prevented, and the coating pattern when the corundum is applied is homogeneous. The thermal buoyancy resulting from the heat emitted by the panel surface is also reduced.

[0019] The omission of heating the printed wood-based panel in an IR dryer is not obvious to a person skilled in the art, since a protective layer of a not yet fully cured resin is applied to the decorative layers created by direct printing. This protective layer can be a formaldehyde-containing resin, in particular a melamine-formaldehyde resin, urea-formaldehyde resin, or melamine-urea-formaldehyde resin, and may contain glass beads (50–150 µm in size) as spacers for the intermediate storage of the panels. This protective layer serves as temporary protection for the decorative layer during storage prior to further finishing. The protective layer on the decorative layer is not yet fully cured, but rather contains a certain residual moisture content of approximately 10%, preferably approximately 6%, and is still capable of further cross-linking. Such protective layers are described, for example, in WO 2010 / 112125 A1 or EP 2 774 770 B1.

[0020] The typically used step of heating decorative layers provided with such a (thermoset) protective layer serves to dry the protective layer and adjust the residual moisture level, thus ensuring the stickiness of the protective layer and the adhesion of subsequent resin layers.

[0021] However, it has been shown that heating the protective layer has a negative effect on the distribution pattern of the abrasion-resistant particles. Omitting the heating step of the printed wood-based panel coated with a protective layer results in a homogenized distribution pattern and thus a uniform distribution of the abrasion-resistant particles on the panel surface.

[0022] The resin layers used in the present process are preferably based on aqueous formaldehyde-containing resins, in particular melamine-formaldehyde resin, urea-formaldehyde resin or melamine-urea-formaldehyde resin.

[0023] The resins used preferably contain additives such as hardeners, wetting agents (surfactants or mixtures thereof), defoamers, release agents, and / or other components. The wetting agent is used in each resin layer in an amount of 0.1–1% by weight. Release agents and smoothing agents are preferably added to the fifth and sixth resin layers in amounts between 0.5–1.5% by weight.

[0024] A latent hardener, such as alkanolamine salts of acids, e.g., an alkanolamine salt of a sulfonic acid (see DeuroCure from Deurowood), is preferably used as the hardener. The latent hardener is preferably added to the resin immediately before the coating unit to prevent premature hardening of the resin and thus losses. Accordingly, the hardener is preferably not added centrally, but rather the variable amount of hardener is added only at the corresponding coating units. This has the advantage that, in the event of a system malfunction, the resin can remain in the lines longer without the hardener. Only the coating units containing resin hardener need to be specifically adjusted to the system's pot life. This significantly reduces losses due to the need to pump out resin hardener during downtime or malfunctions.

[0025] The proportion of hardener in the individual resin layers varies and can range from 0.5 to 1.5 wt%, preferably 0.7 to 1.3 wt%. It is particularly preferred that the proportion of hardener per resin application decreases in the production direction; i.e., the hardener content is higher in the lower resin layers than in the upper resin layers. By reducing the amount of hardener from the lower to the upper resin layers, uniform curing of the individual resin layers in the KT press can be achieved.

[0026] In one variant of the process, the first resin layer is applied in an amount between 10 and 100 g / m², preferably 40 to 80 g / m², and particularly preferably 45 to 60 g / m². The first resin layer is applied, for example, using a grooved application roller in a first application unit.

[0027] The first resin layer contains cellulose fibers.

[0028] The addition of cellulose fibers allows the viscosity of the resin to be applied to be adjusted and the application rate of the first topcoat to the wood-based panel to be increased. The amount of cellulose fibers applied with the first resin layer can be between 0.1 and 1 wt%, preferably between 0.5 and 0.8 wt% (based on the amount of resin to be applied), or between 0.1–0.5 g / m², preferably 0.2–0.4 g / m², and particularly preferably 0.25 g / m². The cellulose fibers preferably used are white and in the form of a fine or granular, slightly hygroscopic powder.

[0029] In another embodiment, particles made of corundum (aluminum oxides), boron carbides, silicon dioxides, or silicon carbides are used as abrasion-resistant components. Corundum particles are particularly preferred. These are preferably high-quality (white) corundum with high transparency, so that the optical effect of the underlying decoration is affected as little as possible. Corundum has an irregular shape.

[0030] The amount of abrasion-resistant particles applied is 10 to 50 g / m², preferably 10 to 30 g / m², and particularly preferably 15 to 25 g / m². The amount of abrasion-resistant particles applied depends on the desired abrasion class and the particle size. For example, the amount of abrasion-resistant particles for abrasion class AC3 is in the range of 10 to 15 g / m², for abrasion class AC4 it is in the range of 15 to 20 g / m², and for abrasion class AC5 it is in the range of 20 to 25 g / m² when using F200 grain size. In the present case, the finished panels preferably have abrasion class AC4.

[0031] Abrasion-resistant particles with grain sizes in classes F180 to F240, preferably F200, are used. The grain size of class F180 covers a range of 53–90 µm, F220 45–75 µm, F230 34–82 µm, and F240 28–70 µm (FEPA standard). In one variant, white corundum particles F180 to F240, preferably with a main grain size range of 53–90 µm, are used as the abrasion-resistant particles. In a particularly preferred embodiment, corundum particles of class F200 are used, wherein F200 is a mixture between F180 and F220 and has a diameter between 53 and 75 µm.

[0032] The abrasion-resistant particles must not be too fine (risk of dust formation) but also not too coarse. The size of the abrasion-resistant particles therefore represents a compromise. In a further embodiment, silanized corundum particles can be used. Typical silanizing agents are aminosilanes.

[0033] In a further embodiment of the method, the second resin layer to be applied to the top surface of the wood-based panel is applied in an amount between 10 and 50 g / m², preferably 20 to 30 g / m², and particularly preferably 20 to 25 g / m². The total amount of the second resin layer is less than the amount of the first resin layer. In a preferred embodiment, the second resin layer to be applied to the top surface of the wood-based panel does not contain glass beads.

[0034] The total amount of first and second resin layers is between 50-100 g / m², preferably 60-80 g / m², and particularly preferably 70 g / m². In one variant, the amount of the first resin layer is 50 g / m² and the amount of the second resin layer is 25 g / m².

[0035] As mentioned above, the abrasion-resistant particles in the second resin layer are enriched by the inclusion of loose particles during the second application process. This can result in an abrasion-resistant particle content of 5 to 15 wt%, preferably 10 wt%, in the resin applied as the second layer.

[0036] As explained above, subsequent layers of resin, a third, fourth, fifth and sixth layer of resin, are applied to the second layer and dried after each application.

[0037] The amount of the third resin layer applied to the top surface of the wood-based panel can be between 10-50 g / m², preferably 20-30 g / m², and particularly preferably 25 g / m².

[0038] As described above, the third resin layer contains glass beads that act as spacers. The glass beads preferably used have a diameter of 90–150 µm. The glass beads can be applied together with the third resin layer or sprinkled separately onto the third resin layer. The amount of glass beads is 10 to 50 g / m², preferably 10 to 30 g / m², and particularly preferably 15 to 25 g / m². The batch preferably consists of approximately 40 kg of liquid resin plus glass beads and additives. The glass beads can also be in silanized form. Silanizing the glass beads improves their embedding in the resin matrix.

[0039] The amount of the fourth resin layer applied to the top surface of the wood-based panel (which also contains glass beads) can be between 10-40 g / m², preferably 15-30 g / m², and particularly preferably 20 g / m².

[0040] As explained above, the solids content of the fourth resin layer (as well as the fifth and sixth resin layers) is lower compared to the first to third resin layers. The varying solids content of the resin layers allows for a greater overall layer thickness due to the higher solids content in the first to third layers, while the reduced solids content in the fourth to sixth resin layers ensures that the drying and pressing time is sufficient for the entire structure.

[0041] The amount of the fifth resin layer applied to the top surface of the wood-based panel can be between 10 and 40 g / m², preferably 15 to 30 g / m². As described above, the fifth resin layer also contains glass beads. The glass beads can be applied together with the third resin layer or sprinkled separately onto the third resin layer.

[0042] The sixth resin layer, applied after drying on top of the fifth resin layer, contains no glass beads. Omitting glass beads from the sixth resin layer ensures that the underlying resin layers, which have already dried, are not damaged and that the surface of the resin structure does not appear cracked.

[0043] The total thickness of the applied resin layers on the wood-based panel is between 120 and 200 µm, preferably between 150 and 200 µm. This total layer thickness is therefore significantly greater than that achieved by previous methods, which typically achieve layer thicknesses of up to 50 µm.

[0044] In addition, a layer of resin is applied to the underside of the wood-based panel together with the second, third, fourth, fifth and sixth layers of resin to be applied to the top side of the wood-based panel.

[0045] Parallel to the application of the second resin layer to the top surface of the wood-based panel, a resin layer is also applied to the underside of the panel. The amount of resin applied to the underside of the panel can be between 50 and 100 g / m², preferably 60 to 80 g / m², and particularly preferably 60 g / m². Preferably, the lower resin layer is colored (e.g., brownish) to simulate a counter-cure. The second resin layer is preferably applied simultaneously to the top and underside of the wood-based panel using at least one double application unit (roller application unit). After application of the second resin layer, the assembly consisting of the first and second resin layers is dried (air-dried) in a first drying unit.

[0046] In the same way, a third, fourth, fifth and sixth layer of resin are applied to the underside parallel to the top side of the carrier plate in double application systems and dried after each application.

[0047] The resin layer(s) applied to the underside act as a counter-tension. By applying approximately the same amount of resin to both the top and bottom of the wood-based panels, it is ensured that the tensile forces generated by the applied layers during pressing cancel each other out. The counter-tension applied to the underside corresponds approximately in layer structure and thickness to the layer sequence applied to the top side, but without the addition of glass beads.

[0048] The resin layers are dried at dryer temperatures between 150 and 220°C, preferably between 180 and 210°C, particularly in a convection dryer. The temperature is adjusted to the respective resin layers and can vary in the individual convection dryers; for example, the temperature in the second, third, and fourth convection dryers can be 205°C, and in the fifth and sixth convection dryers, 198°C. However, other dryers can also be used instead of convection dryers.

[0049] In the pressing step following the final drying step, the layer structure is compressed under pressure and temperature in a short-cycle press at temperatures between 150 and 250°C, preferably between 180 and 230°C, particularly preferably at 200°C, and at a pressure between 30 and 60 kg / cm², particularly preferably between 40 and 50 kg / cm². The pressing time is between 5 and 15 seconds, preferably between 7 and 10 seconds. By comparison, a pressure of 50–60 kg / cm² is applied for 16 seconds for decorative papers.

[0050] Preferably, the coated wood-based panel is aligned in the short-cycle press with a structured press plate located in the short-cycle press, using markings on the wood-based panel, so that a perfect match is achieved between the decor on the wood-based panel and the structure to be embossed on the press plate. This enables the production of a decor-synchronous structure. During pressing, the melamine resin layers melt and a laminate is formed through a condensation reaction, including the components corundum / glass / fibers.

[0051] In another embodiment, the at least one wood-based panel is a medium-density fiberboard (MDF), high-density fiberboard (HDF), particleboard, oriented strand board (OSB), plywood panel, and / or a wood-plastic composite panel.

[0052] In one embodiment, an unsanded wood fiberboard, in particular MDF or HDF, is used, which is still provided with a pressed skin (rotation layer) on its top surface. Aqueous melamine resin is applied to the top surface to fill the pressed skin. The melamine resin is subsequently melted in the short-cycle press and thus acts as a tempering agent in the area of ​​this layer; i.e., it counteracts delamination.

[0053] The decorative layer mentioned above can be applied by direct printing. In the case of direct printing, a water-based, pigmented printing ink is applied using gravure or digital printing processes, whereby the water-based pigmented printing ink can be applied in more than one layer, e.g., in the form of two to ten layers, preferably three to eight layers.

[0054] In the case of direct printing, the application of at least one decorative layer is carried out, as mentioned, using an analog gravure and / or a digital printing process. Gravure printing is a printing technique in which the elements to be reproduced are recesses in a printing plate, which is inked before printing. The ink is primarily located in the recesses and is transferred to the substrate, such as a fiberboard, due to the pressure of the printing plate and adhesive forces. In contrast, with digital printing, the image is transferred directly from a computer to a printing press, such as a laser printer or inkjet printer. This eliminates the need for a static printing plate. Both processes allow the use of water-based inks or UV-based colorants. It is also conceivable to combine the aforementioned gravure and digital printing techniques.A suitable combination of printing techniques can be achieved either directly on the substrate or the layer to be printed, or before printing by adapting the electronic data sets used.

[0055] Along with the decoration, the markings required for alignment in the press are also printed on the surface.

[0056] According to the invention, at least one primer layer is arranged between the wood-based panel or carrier panel and the at least one decorative layer.

[0057] The primer layer is applied before printing.

[0058] The primer layer preferably used comprises a composition of casein or soy protein as a binder and inorganic pigments, in particular inorganic color pigments. White pigments such as titanium dioxide or other color pigments, such as calcium carbonate, barium sulfate, or barium carbonate, can be used as color pigments in the primer layer. In addition to the color pigments and the casein or soy protein, the primer may also contain water as a solvent. It is also preferred if the applied pigmented primer layer consists of at least one, preferably at least two, and particularly preferably at least four successively applied layers or coatings, wherein the amount applied between the layers or coatings may be the same or different.

[0059] The method described above thus enables the production of the wood-based panel according to the invention with the following layer structure (viewed from bottom to top): Backing layer consisting of five resin layers - wood-based panel - primer layer - printed decorative layer - protective layer, in particular a protective layer made of a resin that is not yet fully cured - first resin layer with cellulose fibers - layer of abrasion-resistant particles - second resin layer - third resin layer with glass beads - fourth resin layer with glass beads - fifth resin layer with glass beads - sixth resin layer (without glass beads).

[0060] The protective layer serves to cover and protect the decor during intermediate storage (stacking, storage, transport). The additional resin layers on the top surface together form an overlay that protects the finished laminate against abrasion and enables a decor-synchronized texturing.

[0061] The production line for carrying out the above-described process includes the following elements: at least one first application device for applying a first resin layer, which may contain fibers, to the top surface of the wood-based panel; at least one device arranged downstream of the first application device in the processing direction for sprinkling a predetermined quantity of abrasion-resistant particles; at least one second application device arranged downstream of the first application device and sprinkling device in the processing direction for applying a second resin layer to the top surface of the wood-based panel; at least one drying device arranged downstream of the second application device in the processing direction for drying the layer structure of the first and second resin layers;at least one third application device arranged downstream of the drying device in the processing direction for applying a third resin layer containing glass beads to the top surface and / or a resin layer parallel to the underside of the carrier plate; at least one further drying device arranged downstream of the third application device in the processing direction for drying the third upper and / or corresponding lower resin layer; at least one fourth application device arranged downstream of the further drying device for applying a fourth resin layer containing glass beads to the top surface and / or a resin layer parallel to the underside of the carrier plate (without glass beads); at least one drying device arranged downstream of the fourth application device in the processing direction for drying the fourth upper and / or corresponding lower resin layer; at least one fifth application device arranged downstream of the drying device in the processing direction for applying a fifth resin layer containing glass beads to the top and / or a resin layer parallel to the underside of the substrate (without glass beads); at least one drying device arranged downstream of the fifth application device in the processing direction for drying the fifth upper and / or corresponding lower resin layer; at least one sixth application device arranged downstream of the drying device in the processing direction for applying a sixth resin layer to the top and / or a resin layer parallel to the underside of the substrate;at least one drying device arranged downstream of the sixth application device in the processing direction for drying the sixth upper and / or corresponding lower resin layer; and at least one short-cycle press arranged downstream of the last drying device in the processing direction.

[0062] In a preferred embodiment of the present production line, no drying device is provided upstream of the first order processing device, or if a drying device is installed as part of the production line, this drying device is not in operation, i.e., not active.

[0063] Furthermore, no drying device is provided between the spreading device and the second application device. Instead, the still-damp plate is fed directly into the second application device after leaving the spreading device.

[0064] In one embodiment, the production line comprises a simple, single-sided coating unit for applying the first resin layer to the top surface of the printed wood-based panel and five double coating units for applying five further resin layers to the top and bottom surfaces of the wood-based panel, wherein at least one drying device for drying the top and / or bottom resin layer is provided behind each double coating unit.

[0065] The spreading device for the abrasion-resistant particles, integrated into the production line, is suitable for spreading powders, granules, and fibers, and comprises an oscillating brush system. The spreading device essentially consists of a feed hopper, a rotating, textured roller, and a scraper. The amount of abrasion-resistant material applied is determined by the rotational speed of the roller. The spreading device preferably includes a spiked roller.

[0066] In one embodiment of the production line, the at least one spreading device is surrounded by, or located within, at least one cabin equipped with at least one means for removing dust generated within the cabin. The dust removal means can be in the form of an extraction device or an air blowing device. Air blowing can be achieved via nozzles installed at the plate inlet and outlet, which blow air into the cabin. These nozzles can also prevent the formation of an inhomogeneous curtain of dust on the abrasion-resistant material due to air movement.

[0067] Removing dust from abrasion-resistant materials from the vicinity of the spreading device is advantageous because, in addition to the obvious health risks for workers on the production line, the fine dust from abrasion-resistant particles also settles on other parts of the production line, leading to increased wear and tear. Therefore, housing the spreading device in a cabin not only reduces the health risks associated with dust in the area surrounding the production line but also prevents premature wear.

[0068] The spreading device is preferably controlled by a light barrier, the light barrier being arranged in the processing direction in front of the roller (spreading roller) located below the spreading device. Controlling the spreading device with a light barrier is advantageous because there are gaps of varying sizes between the individual wood-based panels. The control system starts the spreading process as soon as a panel is positioned in front of the spreading roller.

[0069] In one embodiment of the spreading device, at least one funnel is provided in front of the spreading roller for collecting excess abrasion-resistant particles (i.e., abrasion-resistant particles that are not scattered on the at least one wood-based panel, but rather fall in front of the spreading roller before the wood-based panel is moved under it by means of the transport device).

[0070] In a further development, the hopper is coupled to at least one conveying device and a screening device, whereby the excess abrasion-resistant material collected in the hopper is transported via the conveying device to the screening device. The mesh size of the screening device corresponds to the largest particle size of the abrasion-resistant material used (i.e., approximately 80–100 µm). In the screening device, dirt particles and clumped material (such as lumpy resin or clumped abrasion-resistant material) are separated from the collected abrasion-resistant material, and the screened abrasion-resistant material can be returned to the spreading device (recycled).

[0071] As explained above, it is also planned to add the hardener to the liquid resin at the corresponding application units or devices for the various resin layers. In one embodiment of the present production line, at least one metering system is provided for adding the hardener to each application unit. The hardener is pumped from the at least one metering system into the resin reservoir and mixed with the resin in the reservoir, for example, by means of a suitable agitator.

[0072] The invention is explained in more detail below with reference to the figures in the drawings, using an exemplary embodiment as an example. The figures show: Figure 1 is a schematic representation of a production line for a wood-based panel.

[0073] The one in Figure 1The schematically depicted production line includes an IR dryer 1a, which is switched off. Removing the IR dryer 1a from the production line prevents the electrostatic charging of the plate surface that would otherwise occur in the IR dryer, thus enabling the formation of a homogeneous scattering curtain of corundum.

[0074] The production line further includes a single-sided coating unit 1 (grooved roller), and five double coating units 2, 3, 4, 5, 6 for the simultaneous application of the respective resin layer to the top and bottom of the individual printed material sheets, e.g., printed HDF sheets, as well as four convection dryers 2a, 3a, 4a, 5a, 6a arranged behind the coating units in the processing direction.

[0075] Following the first application roller 1, a first spreading device 20 is provided for the uniform distribution of the abrasion-resistant material, such as corundum, onto the first resin layer on the top surface of the HDF board. Corundum F200, which measures approximately 53–75 µm in diameter according to the FEPA standard, is used as the abrasion-resistant material. The spreading device 20 essentially consists of a feed hopper, a rotating, textured spiked roller, and a scraper. The application rate of the material is determined by the rotational speed of the spreading roller. Depending on the required abrasion class of the product, between 12 and 25 g / m² of corundum is spread onto the resin-coated board (AC4 (according to EN 13329) = 20 g / m²). The corundum falls from the spiked roller onto the melamine-coated board at a distance of 5 cm. Since the first layer of resin is still liquid at the time of application, the abrasion-resistant particles can sink into the resin layer.Under the present spreading device, at least one funnel (not shown) is provided in front of the spreading roller for collecting excess abrasion-resistant particles (i.e., abrasion-resistant particles that are not spread on the at least one wood-based panel, but rather fall in front of the spreading roller before the wood-based panel is moved under it by means of the transport device).

[0076] In the double-sided coating unit 2, the board coated with melamine-formaldehyde resin and corundum is coated with a further layer of melamine-formaldehyde resin (approximately 20 g / m²). Simultaneously, small amounts of the unbonded corundum are removed and accumulate in the melamine resin bath until saturation (approximately 10 wt%). This lost portion of the corundum is then continuously reapplied to the board by the roller coating unit 1-1. This second application covers the corundum grains with liquid resin and incorporates them into the overlay layer. This prevents the corundum from being removed in the convection dryer due to the high air turbulence.

[0077] The structure consisting of the first and second resin layers is dried in convection dryer 2a.

[0078] The third double application unit 3 for applying the third resin layer can be followed by a further spreading device 20 for applying glass beads to the third resin layer, followed by a third convection dryer 3a for drying the third resin layer. The spreading device 20 for the glass beads is optional. The glass beads can also be applied together with the third resin layer.

[0079] After applying the fourth to sixth resin layers in a fourth to sixth double coating unit 4, 5, 6 and drying in a convection dryer 4a, 5a, 6a, the layer structure is cured in a short-cycle press 7 at a pressing temperature of 180–220 °C and a pressing time of 8 to 10 seconds under a specific pressure of < 40 kg / cm². The pressed panels are cooled and stored.

Claims

1. Wood-based panel with at least one decorative layer arranged on the upper side, in particular with a structure synchronous with the decor, and with the following layer structure viewed from bottom to top: - Wood-based panel , - primer layer, - print decor layer, - protective layer, - first resin layer with cellulose fibers, - layer of abrasion-resistant particles, - second resin layer, - third resin layer with glass beads - fourth resin layer with glass beads - Fifth resin layer with glass beads - sixth resin layer without glass beads, wherein a backing layer is provided on the underside of the wood-based panel, the backing layer consisting of five resin layers, each of which corresponds to the second to sixth resin layers provided on the upper side of the wood-based panel, but does not contain any glass beads, wherein the multilayer resin structure on the upper side of the wood-based panel containing abrasion-resistant particles, cellulose fibers and glass beads has a total layer thickness of between 120 and 200 µm, preferably between 150 and 200 µm.

2. Wood-based panel according to claim 1, characterized by markings in the decorative layer for aligning the wood-based panel in a press, in particular to a structured press plate located in a short-cycle press.

3. Wood-based panel according to one of the preceding claims, characterized in that the protective layer consists of a melamine-formaldehyde resin, urea-formaldehyde resin or melamine-urea-formaldehyde resin containing glass beads.

4. Wood-based panel according to one of the preceding claims, characterized in that the resin layers are based on aqueous formaldehyde-containing resins, in particular melamine-formaldehyde resin, urea-formaldehyde resin or melamine-urea-formaldehyde resin.

5. Wood-based panel according to one of the preceding claims, characterized in that the abrasion-resistant particles are corundum particles.

6. Wood-based panel according to one of the preceding claims, characterized in that the amount of abrasion-resistant particles is 10 to 50 g / m2, preferably 10 to 30 g / m2, more preferably 15 to 25 g / m2.

7. Wood-based panel according to one of the preceding claims, characterized in that the glass beads have a diameter of 90 to 150 µm.

8. Wood-based panel according to one of the preceding claims, characterized in that the amount of glass beads in the third resin layer is 10 to 50 g / m2, preferably 10 to 30 g / m2, more preferably 15 to 25 g / m2.

9. Wood-based panel according to one of the preceding claims, characterized by an abrasion value in the abrasion classes AC4 to AC6.

10. Wood-based panel according to one of the preceding claims, characterized in that the amount of cellulose fibers in the first resin layer is between 0.1-0.5 g / m2, preferably 0.2-0.4 g / m2, more preferably 0.25 g / m2.

11. Wood-based panel according to one of the preceding claims, characterized in that the wood-based panel is a medium-density fibre (MDF), high-density fibre (HDF) or chipboard or coarse chipboard (OSB) or plywood panel and / or a wood-plastic panel.