Panel with sealed joints

Abstract

The present disclosure relates to a method of producing a panel (1), preferably a floor panel. The method comprises providing a fiber board having an edge (5); applying a curable liquid onto the edge (5) of the fiber board (1); and subjecting the edge of the fiber board to a high frequency field for curing the curable liquid. The present disclosure further relates to a corresponding system for producing a panel.

Description

[0001] Panel with sealed joints

[0002] Technical field

[0003] The present disclosure relates to a method of producing panel, preferably a floor panel. The present disclosure further relates to a system for producing a panel, preferably a floor panel.

[0004] Background art

[0005] Laminate panels for structural and decorative use are widely known in the prior art for a wide range of applications. Notably, laminate floor panels have proved to be a suitable alternative to natural wood floor panels. Laminate panels have enhanced uniformity, durability, and appearance while facilitating installation and maintenance. Further, laminate panels have an improved C02 footprint.

[0006] When producing a laminate panel, a HDF (high density fiber) board may be laminated with impregnated papers. On one side of the HDF panel, a decor paper and a functional paper may be provided. On the rear side of the HDF board, for balancing purposes, a backing paper may be provided. Afterwards, the HDF board may be cut, and joining profiles maybe milled into the edges of the board. The joining profiles allow for interconnecting several laminate panels in a glue-free manner.

[0007] When the edges of laminate panels with such milled joining profiles come into contact with water, the water may penetrate the panel and cause an undesired swelling of the panel.

[0008] In the recent years, water-resistant (floor) panels have been developed, which further enhances the usability of laminate panels. Such panels may for example be placed in environments in which it is likely that the panels come into contact with water, for example in kitchen areas or in a bathroom. In order to avoid a swelling of the panels when in contact with water, the boards are produced with reduced swelling properties. Such boards present a suitable and eco-friendly alternative to other floor coverings commonly used in a kitchen or bathroom. In particular, ceramic tiles or PVC floor coverings have a significantly worse C02 balance than HDF-based laminate panels.

[0009] In order to produce a laminate panel with reduced swelling properties, paraffines are commonly used with increasing amount to reduce the swelling properties. Further, common HDF boards with reduced swelling properties often have a large amount of resin, wherein the resin is typically containing a large amount of melamine resin. In addition, the wood fibers can be modified such during the pulping process that the produced (HDF) board has reduced swelling properties. Alternatively, to the use of melamine reinformed urea glue, Polymeric diphenylmethane diisocyanate (PMDI) is used in the art to reduce swelling properties.

[0010] The methods of the prior art to produce laminate panels with reduced swelling properties require enhanced material costs and large energy consumption. Producing laminate panels with reduced swelling properties thus impairs the eco-friendliness and economic advantages of laminate panels. Also affected is the potential recycling properties of the flooring. It has been shown that recycling properties of HDF improve when less amount of glue and no PMDI are used.

[0011] It is known in the prior art to seal the only the joining edges of laminate panels. Fluoropolymer-based agents, which have a strong hydrophobic effect, can be applied on the joining edges. Alternatively, oils or paraffins can be used to for hydrophobization of the joining edges. These techniques, however, do not provide for a complete sealing of the joining edges. Parts not covered by a hydrop hobizing agent are a weak point of the panel, in which water may penetrate the panel and cause swelling of the panel. Further, the usage of fluoropolymers will be strongly limited by law.

[0012] Further, is known to apply acetic anhydride onto the wood fibers at the joining edges. Such an acetylation may provide for a local reduction of swelling properties. Water, however, may then penetrate further into the panel causing swelling in areas not acetylized. It is thus an object of the present invention to produce a panel having reduced swelling properties while overcoming the above deficiencies of the prior art at least partially. In particular, the present invention aims at producing a panel having reduced swelling properties in an eco-friendly and cost-efficient way.

[0013] A solution is provided according to the subject matter of the independent claims.

[0014] Summary of the invention

[0015] An aspect of the present disclosure relates to a method of producing a panel, preferably a floor panel. The panel maybe produced from a fiber board, for example from a HDF board. The board may comprise one or more paper layers, such as e.g. a decor layer and a backing paper, which may be laminated to the board. The produced panel may be a laminated panel as will be appreciated by the person skilled in the art.

[0016] The method comprises providing a fiber board having an edge. The board may be cut from a larger board, with the cut edges defining the edges of the board. The board may have a rectangular shape with four edges.

[0017] The method further comprises applying a curable liquid onto the edge of the fiber board. The curable liquid may be applied onto each edge of the fiber board, for example on all four edges of a rectangular board. The curable liquid is applied such that the edge(s) are fully covered by the curable liquid.

[0018] The method further comprises subjecting the edge of the fiber board to a high frequency field for curing the curable liquid. Accordingly, the edge(s) with applied curable liquid are subjected to the high frequency field such that the curable liquid is cured. The entire fiber board may be subjected to the high frequency field, for example in a high frequency diyer.

[0019] The inventor has found that by curing the curable liquid in a high frequency field, the swelling properties of the resulting panel can be significantly reduced. After having applied the curable liquid onto the edge of the board, the curable liquid may penetrate into the board. The penetration depth may depend on the characteristics of the board, the viscosity of the liquid and the amount of applied liquid, among others, as will be appreciated by the person skilled in the art. By curing the curable liquid by means of the high frequency field, a good barrier against water is created.

[0020] The high frequency field provides for such energy that a fast, preferably prompt or instant hardening and cross-linking of the curable liquid takes place on the entire edge of the board covered with the curable liquid. The use of the high frequency field provides for a uniform polymerization along the entire edge.

[0021] It is elementary that the required energy for curing the curable liquid is simultaneously provided along the entire edge. This is achieved by making use of the high frequency field. A curing by heating, with the heat being created by means of convection or radiation, cannot provide for such uniform curing and strong water barrier. With heating, outer layers of the edge coating being closer to the heat source cure faster than subjacent layers. Thus, with curing by heating, the outer layers may already have hardened while the subjacent layers may still be in the liquid phase. Free intrinsic water within the board may vaporize and leak through the few hardened layers, thereby creating pores in the edge seal through which water may later penetrate the panel.

[0022] With the application of the high frequency curing, the curable liquid hardens instantly such that a uniform and gapless seal is provided along the edge, without leaving any pores through which water could penetrate into the panel. The curable liquid is not cured with a curing gradient, but rather instantly along its entire depth, and along the entire edge. Water vaporizing during the curing process cannot leak through this instantly formed seal, such that no pores are created as with heat curing. Accordingly, the created edge seal is homogenous, uniform, complete and gapless, providing for a strong barrier against water. As a result, the produced panel is characterized by reduced swelling properties.

[0023] The resulting panel comprises only a small amount of binding agents and hydrophobizing agents. Accordingly, the panel produced in an eco-friendly and costefficient manner. Further, after its lifecycle, the panel can be recycled with reduced efforts. In a preferred embodiment, applying the curable liquid onto the edge of the fiber board comprises spraying the curable liquid onto the edge of the fiber board. The spraying maybe performed by means of a common suitable apparatus, e.g. a Vacumat® sprayer apparatus. By spraying the curable liquid onto the edge, a homogeneous and gapless coating on the edge can be achieved, enabling a strong water barrier after curing of the curable liquid. Preferably, the curable liquid is sprayed such that the curable liquid is not sprayed onto the top surface of the fiber board. The spraying apparatus may thus be configured and arranged accordingly. Having the curable liquid on the top surface may result in unaesthetic residues. Such residues are to be avoided on the top surface of the board, particularly if the top side is the visible side of the later placed (floor) panel.

[0024] Preferably, the curable liquid is applied only onto the edge of the fiber board. Thuy, only the edge may be coated with the curable liquid, while the top and bottom surface of the fiber board are free of the curable liquid when applying the high frequency field to cure the curable liquid. By this, unaesthetic residues on the surfaces of the fiber board are avoided.

[0025] Preferably, when subjecting the edge of the fiber board to the high frequency field, the top surface of the board is free of the curable liquid. The curable liquid may not have been applied to the top surface at all, or may have been removed therefrom prior to curing the curable liquid by means of the high frequency field. By this, the risk of unaesthetic residues on the top surface of the fiber board is reduced.

[0026] Preferably, the method further comprises, prior to subjecting the edge of the fiber board to the high frequency field, the step of providing a protection layer onto the top surface of the fiber board, wherein the protection layer preferably comprises silicon oil. For example, the protection layer may comprise polydimethylsiloxane. Preferably, dodecamethylcyclohexasiloxane may be used, dissolved in water in very low concentrations (between o.i - 1%). With this, the top surface of the fiber board can be protected from unaesthetic residues which maybe formed when parts of the curable liquid on the top surface are being cured. The protection layer maybe provided immediately before application of the curable liquid. Preferably, the curable liquid comprises curable oligomers or curable monomers. These oligomers or monomers may be polymerized by means of the high frequency field in order to cross-link and form the barrier against water.

[0027] Preferably, the curable liquid comprises an isocyanate, an amino resin, an acrylate, a phenol resin, a lignin-based resin, and / or a curable oil. Components with high crosslinking potential and possibly suitable spraying characteristics are preferred, such that they can easily be applied onto the edge of the board in a liquid phase and can be hardened by means of the high frequency field. Particularly preferred, the curable liquid comprises or is a polymeric diphenylmethane diisocyanate (PMDI). In the high frequency field, and due to the free water being present in the fiber board, the PMDI cross-links well and fast. Further, the PMDI penetrates well into the edge of the board.

[0028] Preferably, the fiber board is subjected to the high frequency field at least i second after the curable liquid is applied onto the edge of the fiber board, further preferred at least 5 seconds, further preferred at least 10 seconds after the curable liquid is applied onto the edge of the fiber board. This provides for sufficient time for the curable liquid to penetrate into the board. Preferably, the curable liquid penetrates into the board up to a depth of several millimeters before curing the curable liquid by means of the high frequency field.

[0029] Preferably, the panel has a swelling potential of at most 10 %, preferably of at most 5 %. The resulting panel may thus have reduced swelling potential, allowing for versatile usage of the panel, for example in a kitchen or bathroom. The swelling potential may be characterized by a measurement according to ISO 24336.

[0030] Preferably, the frequency of the high frequency field is at least 10 kHz. Such frequencies allow for a fast hardening of the curable liquid to produce a homogeneous and gapless water barrier at the edge of the board. Depending on the composition of the curable liquid, even frequencies in the microwave regime maybe used, i.e. of 300 MHz to 300 GHz. For example, the frequency may be in the range of 5 MHz to 5 GHz. Preferably, the frequency of the high frequency field is in the range of between 30 kHz and 300 GHz. Preferably, the method further comprises, prior to applying the curable liquid onto the edge of the fiber board, the step of milling a joining profile into the edge of the fiber board. The joining profile maybe milled in a conventional manner, in order to allow for joining several panels with each other. The joining profile may have a sophisticated shape, defined by elements such as grooves and protrusions. After milling the joining profile into the edge of the board, the curable liquid may be applied to cover the entire edge with the entire joining profile, such that a homogeneous and gapless water barrier is produced.

[0031] Preferably, the fiber board is a HDF board. It may have a density of at least 500 kg / m3. HDF-board based panels may be used for a variety of purposes, for example in construction, flooring, furniture, home appliances, automobiles. HDF boards maybe made out of exploded wood fibers that have been highly compressed, and are known to swell (thickness increases) when exposed to water. By providing papers on its surfaces and sealing its edges in the manner as described herein, this risk is reduced.

[0032] Another aspect of the present disclosure relates to a system for producing a panel, preferably a floor panel. The system comprises means for providing a fiber board having an edge; means for applying a curable liquid onto the edge of the fiber board; and means for subjecting the edge of the fiber board to a high frequency field for curing the curable liquid. Preferably, the means for subjecting the edge of the fiber board to a high frequency field comprises a high frequency diyer.

[0033] Description of preferred embodiments

[0034] In the following, the invention is described with reference to the enclosed figures.

[0035] Fig. 1 schematically illustrates a panel according to an embodiment of the present disclosure; and

[0036] Fig. 2 illustrates a flowchart of a method of producing a panel according to an embodiment of the present disclosure.

[0037] Fig. 3 illustrates a system for producing a board according to an embodiment of the present disclosure. Figure i schematically illustrates a panel i according to an embodiment of the present disclosure. The panel 1 comprises a HDF board 2 which forms the core of the panel 1. On the top surface of the HDF board 2, a melamine impregnated paper is provided as a decor paper 3. On the rear side of the HDF board 2, for balancing purposes, a backing paper 4 is provided. The decor paper 3 and the backing paper 4 provide for a water barrier, thus sealing the main surface of the HDF board 2 against water.

[0038] A joining profile is milled into the edge 5 of the HDF board 2. By means of this joining profile, the panel 1 may be joined with or connected to another panel with a corresponding edge profile.

[0039] The surface 6 of the joining profile on the edge 5 is sealed such that water cannot enter the HDF board via its edge 5. For providing this sealing effect, a curable liquid, in this example being polymeric diphenylmethane diisocyanate (PMDI), is sprayed on the surface of the joining profile. After allowing for the PMDI to penetrate the surface 6 of the joining profile, the edge 5 is subjected to a high frequency field in order to cure the PMDI. In the high frequency field, the PMDI hardens and cross-links instantly, such that a homogeneous and gapless water barrier is eventually provided on the edge 5.

[0040] Figure 2 illustrates a flowchart of a method 10 of producing a panel, for example of producing a panel as illustrated in Figure 1. In step 11, a HDF board is provided. The HDF board may have a swelling potential of 15% (according to ISO 24336). In step 12, a joining profile is milled into the edge of the HDF board. In step 13, a curable liquid, for example PMDI, is sprayed onto the edge of the HDF board such that the joining profile is fully covered by the liquid. In step 14, the liquid is given time to penetrate the surface of the edge of the HDF board, for example between 1 second and 15 seconds. In step 15, the edge is subjected to a high frequency field. For this purpose, the HDF board may be inserted into a high frequency dryer. The resulting panel has a reduced swelling potential, e.g. of at most 10%.

[0041] The skilled person understands that the production method may comprise further production steps, for example to provide a decor paper and / or a backing paper on the board. As will be appreciated by the skilled person, the curable liquid is designed such that it penetrates the HDF board at its edges, and cures or hardens homogeneously and (almost) instantly in the high frequency field. The curable liquid may comprise a mixture of different substances, in order to provide for enhanced characteristics. For example, the curable liquid may comprise oils or cross-linkable ways, which may provide for additional hydrophobic properties of the resulting panel. The curable liquid may further comprise substances which reduce creaking sounds which may occur at the interface of joined panels, when the panel is used as a floor panel.

[0042] The curable liquid may comprise or consist of PMDI. Alternatively, the curable liquid may comprise or consist of an acrylate, a melamine formaldehyde, a phenol formaldehyde resin, epoxies, polyesters. The use of drying or cross-linking oils is also conceivable, as well as the use of linseed oil, walnut oil, soybean oil, sunflower oil, tall oils, oils with a high proportion of unsaturated fatty acid residues.

[0043] Preferably, after subjecting the edge of the fiber board to the high frequency field, the board may be further sealed, for example its surfaces, by applying a suitable sealing substance which may be based on a silicon material. With this, potential weak spots on the surfaces of the board may be eliminated. This particularly applies if the papers applied to the board (e.g. decor paper) are featuring gaps or pores, thus not providing a sufficient water barrier.

[0044] The production of the panel may be performed in an inline production system, in which the boards are transported (automatically) through the production line. The boards maybe transported with speeds of up to 200 m / min. As will be appreciated by the skilled person, a fast production cycle requires a high penetration potential of the curable liquid, such that it is able to penetrate the edge of the board sufficiently before the board is entering the high frequency field.

[0045] Figure 3 illustrates a system 20 for producing a panel, for example of producing a panel as illustrated in Figure 1. The system is designed as an inline production line, in which an HDF board may be transported automatically from one processing station to the next. At milling station 21, a joining profile is milled into the edge of the HDF board. The board is then transported to a coating station 22, in which the top and bottom surface of the board is coated with dodecamethylcyclohexasiloxane. The board is then transported to a spraying station 23, in which PMDI is sprayed onto the edges of the board. The board is then transported to a curing station 24 in which the PMDI is cured in a high frequency field.

[0046] The skilled person understands that the production line may comprise further production stations, for example to provide a decor paper and / or a backing paper on the board.

Claims

Claims1. Method of producing a panel, preferably a floor panel, the method comprising: providing a fiber board having an edge; applying a curable liquid onto the edge of the fiber board; subjecting the edge of the fiber board to a high frequency field for curing the curable liquid.

2. The method of claim i, wherein applying the curable liquid onto the edge of the fiber board comprises spraying the curable liquid onto the edge of the fiber board.

3. The method of any one of claim 2, wherein the curable liquid is sprayed such that the curable liquid is not sprayed onto a top surface of the fiber board.

4. The method of any one of claims 1-3, wherein the curable liquid is applied only onto the edge of the fiber board.

5. The method of any one of claims 1-4, wherein, when subjecting the edge of the fiber board to the high frequency field, a top surface of the board is free of the curable liquid.

6. The method of any one of claims 1-5, further comprising, prior to subjecting the edge of the fiber board to the high frequency field: providing a protection layer onto a top surface of the fiber board, wherein the protection layer preferably comprises silicon oil.

7. The method of any one of claims 1-6, wherein the curable liquid comprises curable oligomers or curable monomers.

8. The method of any one of claims 1-7, wherein the curable liquid comprises an isocyanate, an amino resin, an acrylate, a phenol resin, a lignin-based resin, and / or a curable oil.

9. The method of any one of claims 1-8, wherein the fiber board is subjected to the high frequency field at least i second after the curable liquid is applied onto the edge of the fiber board, preferably at least 5 seconds, further preferred at least 10 seconds.

10. The method of any one of claims 1-9, wherein the panel has a swelling potential of at most 10 %, preferably of at most 5 %.

11. The method of any one of claims 1-10, wherein the frequency of the high frequency field is at least 10 kHz, preferably in the range of between 30 kHz and 300 GHz.

12. The method of any one of claims 1-11, further comprising, prior to applying the curable liquid onto the edge of the fiber board: milling a joining profile into the edge of the fiber board.

13. The method of any one of claims 1-12, wherein the fiber board is a HDF board.

14. System for producing a panel, preferably a floor panel, the system comprising: means for providing a fiber board having an edge; means for applying a curable liquid onto the edge of the fiber board; means for subjecting the edge of the fiber board to a high frequency field for curing the curable liquid.

15. The system of claim 14, wherein the means for subjecting the edge of the fiber board to a high frequency field comprises a high frequency diyer.

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