Method for impregnating a sheet of paper

Abstract

The method for impregnating a sheet of paper comprises the steps of providing a sheet of paper, providing an impregnation compound, and impregnating the sheet of paper with the impregnation compound. The impregnation compound comprises acrylate oligomers and acrylate reactive diluents. The acrylate oligomers have a molar mass equal to or higher than 800 g / mol and preferably lower than 10000 g / mol. The acrylate reactive diluents have a molar mass lower than 800 g / mol.

Description

[0001] Method for impregnating a sheet of paper

[0002] The invention relates to a method for impregnating a sheet of paper, e.g. a printed sheet of paper. The invention relates to a method for impregnating a printed sheet of paper for use as decorative layer in a decorative panel.

[0003] WO20 13 / 050910A2 discloses a floor panel comprising a core, a print and a wear resistant layer. The core is assembled at least from a plurality of paper sheets impregnated with a thermosetting resin. The thermosetting resins can be chosen from the list consisting of melamine formaldehyde, urea formaldehyde, melamine urea formaldehyde, and lignosulfonate.

[0004] US2008 / 0057276A1 discloses decorative panels comprising a decorative layer and a carrier layer. In an example, a surface layer of 90 g / m2of a transparent resin (35% HDD A diluted polyurethane acrylate) was applied to an 80 g / m2paper printed with a decorative wood decor by rotary screen printing. The paper is partially impregnated by the surface layer, and the surface layer is radiation-cured with an electron beam. A second 25 g / m2paper impregnated with 245% melamine resin was placed between the aforesaid, partially impregnated printed paper and a stack of 30 papers impregnated with a phenol- based resin. This assembly of papers was placed in a press and compressed at a temperature of 160° C. and a pressure of 70 bar for 30 minutes.

[0005] It is an objective of the invention to provide methods for impregnating sheets of paper, e.g. for use in the production of decorative panels, that solve one or more problems of the prior art.

[0006] The first aspect of the invention is a method for impregnating a sheet of paper. The method comprises the steps of providing a sheet of paper; providing an impregnation compound; and impregnating the sheet of paper with the impregnation compound. The impregnation compound comprises acrylate oligomers and acrylate reactive diluents. The acrylate oligomers have a molar mass equal to or higher than 800 g / mol and preferably lower than 10000 g / mol, and more preferably lower than 7000 g / mol. The acrylate reactive diluents have a molar mass lower than 800 g / mol, and preferably lower than 600 g / mol.

[0007] It is a benefit of the invention that an impregnated paper sheet is obtained that has after curing of the impregnation compound excellent resistance to tearing and slitting of the paper, as well as excellent water resistance. The small molecules of the impregnation compound allow that the pores of the sheet of paper are easily and fully filled wit the impregnation compound, resulting in the beneficial performance properties of the impregnated sheet of paper after curing the impregnation compound.

[0008] The impregnated sheet of paper can be used in the production of decorative panels, e.g. as decorative layer.

[0009] With “acrylate oligomers” is meant oligomers comprising reactive acrylate groups, preferred acrylate oligomers for use in the impregnation compound have acrylate functionality higher than 1.

[0010] As used in this document, the molar mass of a compound is the calculated molar mass. The calculated molar mass is obtained by adding the atomic masses of all atoms present in the structural formula of a compound. When the exact structural formula of a compound is not known, the molar mass of the compound is the number average molecular weight determined using Triple Detection Size Exclusion Chromatography using tetra hydrofuran THF as eluent.

[0011] In the context of this document, the acrylate functionality of a compound is the combined number of acrylate and methacrylate groups per molecule of the compound. The acrylate functionality of a compound comprising different types of molecules not necessarily having the same acrylate functionality is determined as the molar based weighed average.

[0012] A preferred impregnation compound is characterized in that it comprises acrylate reactive diluents having acrylate functionality at least 2, preferably at least 2.5, more preferably at least 2.8. Such acrylate reactive diluents ensure excellent crosslinking after full cure.

[0013] When “oligomers” is used, preferred are oligomers having molar mass equal to or higher than 800 g / mol and more preferably lower than 10000 g / mol, and even more preferably lower than 7000 g / mol.

[0014] The ratio of the amount by weight in the impregnation compound of the acrylate reactive diluents to the acrylate oligomers preferably ranges between 1.2 and 1.85, more preferably between 1.4 and 1.6.

[0015] It is a benefit of such embodiments that the impregnation compound penetrates very well in the sheet of paper.

[0016] Preferably, the viscosity of the impregnation compound is less than 1500 mPa.s, measured at 25 °C.

[0017] A preferred method is characterized in that the acrylate oligomers and / or the acrylate reactive diluents comprise one or more than one hydroxyl reactive groups. With hydroxyl reactive groups is meant reactive groups that can react with hydroxyl groups present in the sheet of paper.

[0018] The hydroxyl reactive groups can bond to hydroxyl groups of the sheet of paper, contributing to an improved performance of the cured impregnated sheet of paper, e.g. in terms of resistance to splitting and water resistance, e.g. when the impregnated sheet of paper is integrated in a decorative panel.

[0019] The hydroxyl reactive groups can be selected from isocyanate groups, melamine groups, carboxyl groups or amine groups; or combinations thereof. Preferred amine groups are primary amine groups and secondary amine groups. Melamine acrylate oligomers can be used in the invention. The melamine group of melamine acrylate oligomers provides hydroxyl reactive groups to the impregnation compound. The use of melamine acrylate oligomers is of further interest, as such impregnated paper sheet can be laminated more easily to wood-based board, e.g. to a wood fiber board or to a wood chip board. The melamine can react with the wood of the board in the lamination process.

[0020] A preferred method is characterized in that the impregnation compound comprises acrylate oligomers (preferably having a molar mass equal to or higher than 800 g / mol and more preferably lower than 10000 g / mol, and even more preferably lower than 7000 g / mol) that comprise one ore more than one hydroxyl groups, and / or that the impregnation compound comprises acrylate reactive diluents (preferably having a molar mass lower than 800 g / mol, and more preferably lower than 600 g / mol) that comprises hydroxyl groups. It is a benefit that these hydroxyl groups can react with the hydroxyl reactive groups to form strong covalent bonds in the impregnated sheet of paper, thereby improving the properties of the impregnated sheet of paper after curing the impregnation compound.

[0021] A preferred method is characterized in that all acrylate reactive diluents comprise at least one hydroxyl reactive group or at least one hydroxyl group; or both.

[0022] Such embodiments are preferred as it is ensured that in a process step in which the temperature of the impregnated sheet of paper is increased, substantially all acrylate reactive diluents will react through their hydroxyl reactive group or through their hydroxyl group, thereby being integrated in a larger molecule. This way, substantially no more unbonded acrylate reactive diluent is present, which is beneficial for obtaining a non-tacky state of the impregnated sheet of paper which can be processed in a future production step to a fully cured state via addition reaction of the acrylate double bonds in the non-tacky impregnated sheet of paper. The non-tacky state allows that the sheet of paper can be rolled or stacked during a long time without risk of release problems. The impregnation compound preferably comprises a crosslinker. The presence of the crosslinker facilitates the partial curing of the impregnated sheet of paper to produce an intermediate product; and improves the mechanical properties of the impregnated sheet of paper after its full curing.

[0023] Suitable crosslinkers for use in the inventions can be selected from formaldehyde, melamine, isocyanate, aziridine, carbodiimide, polyol; and combinations thereof. Suitable polyols are diols, e.g. polyethylene glycol.

[0024] A preferred impregnation compound does not comprise non-reactive solvent. It is a benefit that no process step is required to volatize non-reactive solvent.

[0025] A preferred impregnation compound comprises non-reactive solvent, preferably in an amount less than 20 wt% of the impregnation compound. The use of a non-reactive solvent allows to reduce the viscosity of the impregnation compound, in order to facilitate the impregnation of the sheet of paper with the impregnation compound.

[0026] The impregnation compound can comprise a photo-initiator. It is a benefit of such embodiment that after impregnating the sheet of paper with the impregnation compound, the impregnation compound can be partially cured, in which addition reaction of the acrylate groups is initiated by UV-radiation dissociating the photo-initiator. In this way, the impregnation compound can e.g. be cured to non-tacky state.

[0027] A preferred embodiment of method of the invention is characterized in that the impregnation compound does not comprise photo-initiators. Especially when the impregnation compound comprises hydroxyl reactive groups, and preferably also hydroxyl groups, the impregnated sheet of paper can be brought to partially cured state by increasing the temperature in which the reactive groups create covalent bonds.

[0028] The impregnation compound can comprise antistatic additives, such as carbon particles or quaternary ammonium salts, or combinations thereof. The acrylate oligomers can consist of or comprise urethane acrylate oligomers. Particularly preferred urethane acrylate oligomers for use in the impregnation compound comprise isocyanate groups. The isocyanate groups can react with hydroxyl groups of the paper, and - if present - with hydroxyl groups of acrylate oligomers and / or of acrylate reactive diluents of the impregnation compound. This way, it is easy to bring the impregnated sheet of paper to partially cured - and even to non-tacky - state. Such embodiments also result in impregnated sheets of paper with excellent properties after fully curing the impregnation compound.

[0029] The acrylate oligomers are preferably selected from urethane acrylate oligomers, polyester acrylate oligomers, polyether acrylate oligomers, epoxy acrylate oligomers; and combinations thereof.

[0030] The impregnation compound preferably comprises a catalyst.

[0031] A preferred embodiment is characterized in that a catalyst is applied to the impregnated sheet of paper before of after the step of impregnating the sheet of paper with the impregnation compound.

[0032] The catalyst can catalyze a reaction - e.g. a reaction between hydroxyl reaction groups of the impregnation compound and hydroxyl groups of the paper and / or of the impregnation compound - in the impregnation compound in order to partially cure the impregnated sheet of paper. The use of the catalyst is preferred in order to ensure that all hydroxyl reactive groups - e.g. all isocyanate groups - have reacted in a process of partially curing the impregnated sheet of paper by means of increasing the temperature. This way, when storing the partially cured impregnated sheet of paper, it is avoided that reaction of isocyanate groups occurs, as all isocyanate groups have already reacted. Reaction of isocyanate groups when the sheet of paper is stored in roll form would create a memory to the sheet of paper: when unrolling the sheet of paper, it would not be flat, but remain curved which would make further processing of the sheet of paper more cumbersome. Reaction of isocyanate groups when the partially cured sheet of paper is stored could also create tackiness issues. Preferred catalysts for use in the invention are metal soaps. More preferred are sodium soaps, calcium soaps, bismuth soaps and zinc soaps (e.g. zinc neodecanate); or combinations thereof.

[0033] Preferred catalysts are unsaturated metal soap, more preferably unsaturated sodium soaps, unsaturated calcium soaps, unsaturated bismuth soaps or unsaturated zinc soaps.

[0034] The use of metal soaps is beneficial as the inventors have realized that in impregnation compounds comprising a peroxide thermo-initiator, the presence of the metal soap prevents the thermo-initiator from initiating the addition reaction of acrylate groups at room temperature.

[0035] Preferred catalysts for use in the invention are alkaline catalysts.

[0036] A preferred method is characterized in that the step of impregnating the sheet of paper with the impregnation compound is followed by the step of increasing the temperature of the impregnated paper sheet.

[0037] This way, the impregnated sheet of paper can be partially cured, e.g. to non-tacky state. The increase of temperature can initiate the chemical reaction of hydroxyl reactive groups (e.g. isocyanate groups) with hydroxyl groups in the paper or in the impregnation compound.

[0038] A preferred method is characterized in that in the step of increasing the temperature of the impregnated paper sheet substantially all hydroxyl reactive groups of the impregnation compound have reacted.

[0039] Hydroxyl reactive groups (e.g. isocyanate groups) in the impregnation compound could be present in the acrylate oligomers, in acrylate reactive diluents or in crosslinkers. Ensuring that substantially all hydroxyl reactive groups of the impregnation compound have reacted when increasing the temperature of the impregnated sheet of paper has the positive effect that when storing the partially cured impregnated sheet of paper, it is avoided that reaction of hydroxyl reactive groups (e.g. isocyanate groups) occurs. Reaction of hydroxyl reactive groups (e.g. isocyanate groups) when the sheet of paper is stored in roll form would create a memory to the sheet of paper: when unrolling the sheet of paper, it would not be flat, but remain curved. Reaction of hydroxyl reactive groups (e.g. isocyanate groups) when the partially cured sheet of paper is stored could also create tackiness issues.

[0040] It is preferred that in the step of increasing the temperature of the impregnated paper sheet substantially all acrylate reactive diluents have reacted. Such embodiments facilitate obtaining a non-tacky state of the impregnated sheet of paper as the acrylate reactive diluents - which are liquid and have a small size - have reacted to a larger molecular size, preventing their migration.

[0041] A preferred embodiment is characterized in that the impregnation compound comprises a first thermo-initiator; wherein in the step of increasing the temperature of the impregnated paper sheet, the temperature of the impregnated paper sheet stays below the 60 seconds half-life temperature of the first thermo-initiator. It is a benefit of such embodiments that after increasing the temperature of the impregnated sheet of paper the impregnation compound with which the sheet of paper is impregnated is brought to partially cured state (and more preferably to non-tacky state) while maintaining the ability to in a later production process curing the impregnation compound - e.g. in a thermal pressing step - via addition reaction of the acrylate groups initiated by thermally activating the first thermo-initiator.

[0042] More preferably, the first thermo-initiator provides between 0.2 and 1 wt% of the impregnation compound.

[0043] The impregnation compound preferably comprises a second thermo-initiator; wherein in the step of increasing the temperature of the impregnated paper sheet, the impregnated paper sheet reaches a temperature higher than the 60 seconds half-life temperature of the second thermo-initiator. This way, the second thermo-initiator can initiate addition reactions of the acrylate double bonds for obtaining a partially cured state - and preferably a non-tacky state - of the impregnated sheet of paper.

[0044] The terms “first thermo-initiator” and “second thermo-initiator” do not indicate an order of any way, but indicate that it relates to different thermo-initiators.

[0045] More preferably, the second thermo-initiator is provided in the impregnation compound in an amount to convert between 40 and 50% of the acrylate reactive bonds of the impregnation compound.

[0046] More preferably, the second thermo-initiator is provided in the impregnation compound in an amount insufficient to initiate all acrylate reactive groups present in the impregnation compound.

[0047] Preferably, the second thermo-initiator is present in the impregnation compound in an amount of 0.075 to 0.15 wt%.

[0048] A preferred method is characterized in that the acrylate oligomers provide at least 30 wt% of the impregnation compound, wherein the acrylate reactive diluents provide at least 50 wt% of the impregnation compound. Such recipes for the impregnation compound provide impregnation compounds with sufficiently low viscosity to allow efficient and effective impregnation of the sheet of paper, and which provide excellent properties after fully curing the impregnation compound.

[0049] Preferably, the percentage by weight of the acrylate reactive diluents in the impregnation compound is at least double the percentage by weight of the acrylate oligomers in the impregnation compound.

[0050] A preferred method is characterized in that the step of impregnating the sheet of paper with the impregnation compound comprises the step of guiding the sheet of paper through a bath comprising the impregnation compound, preferably followed by the step of removing excess impregnation compound taken up by the sheet of paper from the bath, e.g. by means of guiding the impregnated sheet of paper through a set of rollers, or by means of one or more than one knife.

[0051] Such methods allow efficient and effective impregnation of the sheet of paper with the impregnation compound.

[0052] Preferably, between 25 and 45 gram per square meter dry weight of impregnation compound is applied to the sheet of paper.

[0053] A preferred method is characterized in that the step of impregnating the sheet of paper with the impregnation compound is preceded or succeeded by the steps of impregnating or coating the sheet of paper with a water-based aminoplast compound, and the step of drying the aminoplast compound applied to the sheet of paper, wherein the aminoplast compound is selected from a urea formaldehyde compound, a melamine formaldehyde compound or a melamine urea formaldehyde compound.

[0054] Such embodiments have the benefit that the mechanical properties of the impregnated sheet of paper after fully curing the impregnated sheet of paper are improved, e.g. improved resistance to splitting when milling coupling parts at the edges of a decorative panel comprising one or a plurality of the fully cured impregnated sheet of paper.

[0055] Such embodiments have the further benefit that the use of the aminoplast compound facilitates laminating the impregnated sheet of paper to a wood-based board, e.g. to a wood fiber board or to a wood chip board, e.g. in a thermal press lamination operation, without the need of an additional adhesion layer.

[0056] A preferred method is characterized in that the step of impregnating the sheet of paper with the impregnation compound is preceded or succeeded by the steps of impregnating or coating the sheet of paper with a water based styrene-butadiene copolymer and the step of drying the styrene-butadiene copolymer applied to the sheet of paper. Such embodiments provide a more flexible impregnated sheet of paper. The higher flexibility is of interest for the process efficiency in applying an acrylate lacquer to the impregnated sheet of paper. Furthermore, such embodiments provide improved water resistance of the impregnated sheet of paper after fully curing it.

[0057] A preferred method is characterized in that a polyurethane dispersion is applied to one or to both sides of the paper sheet impregnated with the impregnation compound.

[0058] The polyurethane dispersion will provide improved adhesion when laminating the impregnated sheet of paper to a board: the polyurethane layer will act as a tie layer between the impregnated sheet of paper and the board.

[0059] A polyurethane layer - e.g. applied via a polyurethane dispersion - can be beneficial when an acrylate lacquer is to be applied on the impregnated sheet of paper. The acrylate lacquer can be applied on the side of the impregnated sheet of paper comprising a polyurethane layer. The polyurethane layer prevents air bubble from escaping from the impregnated sheet of paper into the acrylate lacquer. The polyurethane layer acts as a seal for air bubbles. Air bubbles in the acrylate lacquer layer would create a visual defect and a reduction of the properties of the lacquer layer.

[0060] The polyurethane layer at the side of the impregnated paper sheet onto which an acrylate lacquer layer will be applied is particularly beneficial in situations wherein the other side of the impregnated paper sheet is also provided with a polyurethane layer, as this latter polyurethane layer also acts as a seal for air bubbles when applying the acrylate lacquer layer to the impregnated sheet of paper.

[0061] The second aspect of the invention relates to a method as in any embodiment of the first aspect of the invention, characterized in that an acrylate lacquer is applied onto the impregnated sheet of paper, preferably wherein between 30 - 400 gram per square meter of dry weight acrylate lacquer is applied. More preferably more than 50 gram per square meter of dry weight acrylate lacquer is applied, even more preferably, more than 100 gram per square meter of dry weight acrylate lacquer is applied.

[0062] Such embodiments provide the possibility of embossing the acrylate lacquer in a thermal pressing operation in which the acrylate lacquer is cured. The embossment allows to provide a realistic imitation of a wood decor when a wood decor has been printed to the sheet of paper.

[0063] The applied acrylate lacquer can be cured to non-tacky state, preferably by means of UV- radiation (e.g. using a UV lamp or using UV-LED radiation) or EB (electron beam) radiation. In a later processing operation, the acrylate lacquer can be embossed and cured together with the impregnation compound in a thermal pressing operation. This can be achieved by activating thermo-initiators to initiate addition reactions of the acrylate double bonds.

[0064] A preferred method according to the second aspect of the invention is characterized in that the acrylate lacquer comprises

[0065] - one or more acrylate and / or methacrylate oligomers, preferably wherein said oligomers have a molar mass equal to or higher than 800 g / mol, and preferably lower than 10000 g / mol, and more preferably lower than 7000 g / mol;

[0066] - one or more acrylate reactive diluent and / or methacrylate reactive diluent and / or (meth)acrylamide reactive diluents; wherein said reactive diluents have a molar mass lower than 800 g / mol, and preferably lower than 500 g / mol;

[0067] - optionally one or more photo-initiators; and

[0068] - one or more thermo-initiators.

[0069] Such embodiments allow curing to partially cured (and preferably non-tacky state), and future (meaning in a future processing operation) full cure, by means of radical induced addition reactions of the acrylate double bonds in the acrylate lacquer. The radical induced addition reactions can be initiated by the thermo-initiator(s) present in the acrylate lacquer, e.g. in a final thermal pressing operation. The presence of photo-initiators in the acrylate lacquer is optional. Presence of photoinitiators can allow partically curing (e.g. to non-tacky state) of the acrylate lacquer layer by means of UV-radiation (e.g. using a UV lamp or using UV-LED radiation) or EB (electron beam) radiation.

[0070] It is also possible that the acrylate lacquer does not comprise a photo-initiator.

[0071] With acrylate oligomers in the acrylate lacquer is meant oligomers comprising at least one acrylate reactive group. With methacrylate oligomers in the acrylate lacquer is meant oligomers comprising at least one methacrylate reactive group.

[0072] The acrylate lacquer can comprise molecules having reactive groups such as hydroxyl and / or isocyanate groups that can react when increasing the temperature of the acrylate lacquer after its application to partially cure the acrylate lacquer, preferably to non-tacky state. The acrylate double bonds can be cured later on, e.g. in a thermal pressing operation that can be combined with a lamination operation.

[0073] The ratio of the amount by weight in the acrylate lacquer between on the one hand the one or more acrylate reactive diluent, the methacrylate reactive diluent and the (meth)acrylamide reactive diluents; and on the other hand the one or more acrylate and / or methacrylate oligomers preferably ranges between 1.2 and 1.85, more preferably between 1.4 and 1.6.

[0074] It is a benefit of this embodiment that high reactivity of the acrylate lacquer is obtained, for excellent adhesion with the impregnated sheet of paper.

[0075] A preferred method according to the second aspect of the invention is characterized in that the acrylate lacquer comprises a product having isocyanate functionality, preferably having isocyanate functionality at least 1.2, more preferably at least 2. Such embodiments provide better adhesion between the acrylate lacquer and the sheet of paper impregnated with the impregnation compound. The product having isocyanate functionality can be selected from an acrylate oligomer (e.g. an urethane acrylate oligomer) having isocyanate functionality, a polyurethane having isocyanate functionality, a di-isocyanate (e.g. a difenyl di-isocyanate and / or a polymeric isocyanate such as polymeric difenyl di -isocyanate), or combinations thereof.

[0076] A preferred method of the second aspect of the invention is characterized in that the acrylate lacquer layer comprises one or more photo-initiators, wherein the acrylate lacquer comprises photo-initiators in a combined amount less than 1 wt% of the combination of the one or more acrylate and / or methacrylate oligomers and the one or more acrylate and / or methacrylate and / or (meth)acrylamide reactive diluents.

[0077] Such embodiments allow the acrylate lacquer to be partially cured by means of activating the photo-initiators by means of radiation energy, but avoids overcuring the acrylate lacquer in the step of its partial curing. The intention is to be able to emboss the partially cured acrylate lacquer layer in a later thermal pressing operation, in which the acrylate lacquer is fully cured by activating thermo-initiator(s) present in the acrylate lacquer.

[0078] A preferred acrylate lacquer comprises one or more photo-initiators, wherein the one or more photo-initiators of the acrylate lacquer comprise or consist of Norrish type I photoinitiators. Such photo-initiators provide good performance for the partial curing of the acrylate lacquer layer.

[0079] The one or more thermo-initiators of the acrylate lacquer preferably comprise a first thermo-initiator and a second thermo-initiator, wherein the 60 seconds half-life temperature of the second thermo-initiator is at least 8°C higher than the 60 seconds halflife temperature of the first thermo-initiator.

[0080] Such embodiment is beneficial, as it allows that in the (final) thermal curing of the acrylate lacquer - e.g. by means of a thermal pressing operation in which the acrylate lacquer layer is provided with a texture - the acrylate lacquer layer is gradually cured, resulting in an acrylate lacquer layer having better properties, e.g. mechanical properties such as wear resistance. Especially the formation of cracks in the coating layer is prevented.

[0081] The one or more thermo-initiators of the acrylate lacquer can comprise a third thermoinitiator, wherein the 60 seconds half-life temperature of the third thermo-initiator is at least 8°C higher than the 60 seconds half-life temperature of the second thermo-initiator.

[0082] Such embodiment is beneficial, as it allows that in the (final) thermal curing of the acrylate lacquer - e.g. by means of a thermal pressing operation in which the acrylate lacquer layer is provided with a texture - the acrylate lacquer layer is gradually cured, resulting in an acrylate lacquer layer having better properties, e.g. mechanical properties such as wear resistance. Especially the formation of cracks in the coating layer is prevented.

[0083] The one or more thermo-initiators of the acrylate lacquer can comprise a fourth thermoinitiator, wherein the 60 seconds half-life temperature of the fourth thermo-initiator is at least 8°C higher than the 60 seconds half-life temperature of the third thermo-initiator.

[0084] Such embodiment is beneficial, as it allows that in the (final) thermal curing of the acrylate lacquer - e.g. by means of a thermal pressing operation in which the acrylate lacquer layer is provided with a texture - the acrylate lacquer layer is gradually cured, resulting in an acrylate lacquer layer having better properties, e.g. mechanical properties such as wear resistance. Especially the formation of cracks in the coating layer is prevented.

[0085] Providing a second thermo-initiator, and optionally a third thermo-initiator, and optionally also a fourth thermo-initiator, has the benefit that deeper embossments can be made in a thermal pressing operation.

[0086] The acrylate lacquer can comprise silica (SiCE), preferably in an amount more than 0.05 wt% of the acrylate lacquer, and preferably less than 3 wt% of the acrylate lacquer. Such embodiments are favored as in the process of partially curing the acrylate lacquer layer to non-tacky condition using excimer radiation or LED-radiation, a partially cured coating layer is obtained that results in more homogeneous coating surface when thermally pressing the acrylate lacquer layer in which the acrylate lacquer layer is provided with a relief by copying the texture of a structured press element and in which the acrylate lacquer layer is thermally cured.

[0087] The acrylate lacquer may comprises AI2O3, preferably with average particle size less than 30 micrometer, preferably in an amount more than 0.05 wt of the acrylate lacquer, and preferably less than 7 wt% of the acrylate lacquer.

[0088] Such embodiment is favored as after final curing of the acrylate lacquer layer, better scratch resistance is obtained.

[0089] The acrylate lacquer can comprise wear resistant particles, e.g. corundum, silicon carbide, diamond or nanosilica.

[0090] The acrylate lacquer may comprise wear resistant particles, e.g. corundum or silicon carbide, wherein the wear resistant particles have an average particle size between 40 and 100 micrometer.

[0091] The method of the second aspect of the invention preferably comprises the steps of

[0092] - optionally applying a first UV-radiation step to the impregnated sheet of paper onto which the acrylate lacquer has been applied;

[0093] - applying a second UV-radiation step by passing the impregnated sheet of paper onto which the acrylate lacquer has been applied under an excimer-type monochromatic radiation lamp; and

[0094] - applying a third UV-radiation step to the impregnated sheet of paper onto which the acrylate lacquer has been applied; wherein in the method the acrylate lacquer provided by partial curing to B-stage; and wherein the surface of the acrylate lacquer is not tacky; preferably wherein the surface of the acrylate lacquer obtained is wrinkled and / or comprises micro folds. This way, the acrylate lacquer layer can be brought into partially cured non-tacky condition.

[0095] A preferred method of the second aspect of the invention is characterized in that the step of applying an acrylate lacquer onto the impregnated sheet of paper, comprises the step of applying a first acrylate lacquer onto the impregnated sheet of paper and the step of applying a second acrylate lacquer on the first acrylate lacquer, preferably wherein the second acrylate lacquer provides on the impregnated sheet of paper less than 40 wt% - and preferably less than 30 wt% - of the combination of the first acrylate lacquer and the second acrylate lacquer. Thus, the acrylate lacquer is applied in such embodiment by at least applying the first acrylate lacquer and the second acrylate lacquer.

[0096] It is a benefit of such embodiments that the first acrylate lacquer can be a cheap lacquer of which preferably a thicker layer is applied than the layer thickness of the more expensive second acrylate lacquer. The second, more expensive, acrylate lacquer can be applied to provide improved process or product performance.

[0097] It is possible to include wear resistant particles (e.g. corundum particles) in the second acrylate lacquer whereas none are included in the first acrylate lacquer layer.

[0098] Alternatively, it is possible to include wear resistant particles (e.g. corundum particles) in the first acrylate lacquer layer and in the second acrylate lacquer layer, wherein the wear resistant particles in the second acrylate lacquer are finer than in the first acrylate lacquer. This way, a lacquer layer with improved scratch resistance can be obtained.

[0099] Preferably, the first acrylate lacquer as well as the acrylate lacquer comprise (meth)acrylate oligomers and (meth)acrylate reactive diluents.

[0100] An adhesion layer can be applied to the paper sheet, before or after the step of applying the acrylate lacquer onto the impregnated sheet of paper. The adhesion layer can be applied at the side opposite to the side comprising the acrylate lacquer, or opposite to the side onto which the acrylate lacquer will be applied. This way, lamination of the sheet of paper is facilitated, e.g. in a thermal pressing operation in which the sheet of paper is laminated to a board and in which the lacquer layer is embossed and thermally cured.

[0101] The adhesion layer can preferably be a polyurethane adhesion layer, more preferably applied as a polyurethane dispersion; or can be a melamine adhesion layer or a urea based adhesion layer or combinations thereof

[0102] A preferred method of the first aspect or of the second aspect of the invention is characterized in that the impregnated sheet of paper is wound on a roll. Such embodiments are favored, as further processing of the impregnated sheet of paper is facilitated by unwinding the impregnated sheet of paper from the roll.

[0103] A preferred method of the first aspect or of the second aspect of the invention is characterized in that the sheet of paper comprises a printed decor.

[0104] A preferred method of the first aspect or of the second aspect of the invention is characterized in that the sheet of paper is a Kraft paper sheet.

[0105] Such impregnated sheets of Kraft paper can be used in the production of a High Pressure Laminates (HPL) in which a number of (e.g. three) impregnated sheets of Kraft paper are stacked, with a resin impregnated printed sheet of paper on that stack, and are cured together in a thermal pressing operation. The High Pressure Laminate can be laminated, preferably using an adhesive, to a board in order to provide the board with a decorative top layer.

[0106] Such impregnated sheets of Kraft paper can also be used for producing a board, wherein a number of such sheets is stacked and thermally pressed together. The impregnation compound of the impregnated sheets of Kraft paper cures in the thermal pressing operation, thereby laminating the sheets of Kraft paper together to form a board. The boards obtained in such process can replace the well known compact boards, in which sheets of Kraft paper impregnated with phenol formaldehyde resin are laminated together.

[0107] The third aspect of the invention is an impregnated sheet of paper, characterized in that the sheet of paper is obtained via a method as in any embodiment of the first aspect or as in any embodiment of the second aspect of the invention.

[0108] The impregnated sheet of paper of the third aspect of the invention preferably comprises partially cured acrylate lacquer. Both surfaces of the impregnated sheet of paper are in non-tacky state.

[0109] The fourth aspect of the invention is an impregnated sheet of paper, characterized in that the impregnated sheet of paper comprises a sheet of paper impregnated with a partially cured acrylate impregnation compound as well as a partially cured acrylate lacquer applied on a side of the impregnated paper sheet. Both surfaces of the impregnated sheet of paper are in non-tacky state. The partially cured acrylate impregnation compound comprises a first thermo-initiator. The partially cured acrylate lacquer comprises a first thermo-initiator.

[0110] The impregnated sheet of paper of the fourth aspect of the invention can be stored. The impregnated sheet of paper can be processed in a thermal pressing operation in which the acrylate impregnation compound as well as the acrylate lacquer are fully cured by a thermally initiated - thanks to the presence of the thermo-initiators - addition reaction of acrylate double bonds present in the partially cured acrylate impregnation compound and in the partially cured acrylate lacquer. The thermal pressing operation can involve embossing the acrylate lacquer and / or laminating the impregnated sheet of paper to a substrate, e.g. to a board.

[0111] The first thermo-initiator of the partially cured acrylate impregnation compound can be the same as the first thermo-initiator of the partially cured acrylate lacquer. However, the first thermo-initiator of the partially cured acrylate impregnation compound can differ from the first thermo-initiator of the partially cured acrylate lacquer. The impregnated sheet of paper of the fourth aspect of the invention can be obtained via a method according to the second aspect of the invention. The impregnated sheet of paper of the fourth aspect of the invention can have features as described in the embodiments of the second aspect of the invention.

[0112] A preferred impregnated sheet of paper of the fourth aspect of the invention is characterized in that the impregnated sheet of paper is provided as a roll of paper.

[0113] The impregnated sheet of paper of the fourth aspect of the invention can be an impregnated sheet of paper as in the third aspect of the invention.

[0114] A preferred impregnated sheet of paper of the third aspect or of the fourth aspect of the invention is characterized in that the impregnated sheet is provided for use as a top layer in a decorative panel.

[0115] A preferred impregnated sheet of paper of the third aspect or of the fourth aspect of the invention is characterized in that the impregnated sheet of paper is provided for use as a carrier sheet in a High Pressure Laminate.

[0116] A preferred impregnated sheet of paper of the third aspect or of the fourth aspect of the invention is characterized in that the impregnated sheet of paper is provided for use as multiple layers in a core of a decorative panel, wherein in the decorative panel the multiple layers are bonded by curing the impregnation compound of the multiple layers of the impregnated papers sheet.

[0117] A preferred impregnated sheet of paper of the third aspect or of the fourth aspect of the invention is characterized in that the impregnated sheet of paper has a moisture content less than 8 wt%, preferably less than 6 wt%, more preferably less than 5 wt%. It is a benefit of such embodiments that problems with moisture are prevented in a thermal pressing operation in which the impregnation compound and the acrylate lacquer are cured via thermal activation. The fifth aspect of the invention is a decorative panel. The decorative panel comprises a core and a decorative top layer. The decorative top layer comprises an impregnated sheet of paper obtained from a method as in any embodiment of the second aspect of the invention, or an impregnated sheet of paper as in any embodiment of the third aspect or of the fourth aspect of the invention. The decorative core layer is adhered to the core. The impregnation compound has been cured, preferably by means of thermal curing, more preferably by a thermal pressing operation.

[0118] The decorative top layer can be embossed. The decorative top layer can have been embossed in a thermal pressing operation in which the impregnation compound is cured.

[0119] The core can be selected from the list consisting of a wood-based board (e.g. a wood fiber board, a wood chip board or a plywood board), a mineral based board (e.g. a gypsum board, a magnesium oxide (MgO) based board or a cement board) or a - whether or not filled - polymer board.

[0120] The impregnated sheet of paper of the decorative panel of the fifth aspect can be an impregnated sheet of paper obtained from a method as in any embodiment of the second aspect of the invention, or can be an impregnated sheet of paper as in the fourth aspect of the invention. The impregnation compound is cured by a thermal pressing operation, wherein in the thermal pressing operation the acrylate lacquer is thermally cured.

[0121] Preferably, at least the acrylate lacquer is provided with a texture in the thermal pressing operation.

[0122] The sixth aspect of the invention relates to a laminate, characterized in that the laminate comprises a number of impregnated sheets of paper obtained in a method as in any embodiment of the first aspect of the invention, or a number of impregnated sheets of paper as in the third aspect of the invention, stacked onto each other. The laminate optionally comprises a decorative top layer. In the stack the number of impregnated sheets of paper are bonded together by curing the impregnation compound. The laminate of the sixth aspect of the invention can be used in a subsequent process in the same way as a High Pressure Laminate (HPL) is used: it can be laminated to a board using an adhesive.

[0123] The decorative top layer can be provided by an impregnated sheet of paper obtained in according to any embodiment of the second aspect of the invention, or an impregnated sheet of paper as in the fourth aspect of the invention. Such decorative top layer can be bonded by means of curing the impregnation compound of the impregnated sheet of paper of the decorative top layer.

[0124] Preferably, in embodiments according to the sixth aspect of the invention, the number of impregnated sheets of paper obtained in a method as in any embodiment of the first aspect of the invention, or a number of impregnated sheets of paper as in the third aspect of the invention, that are stacked onto each other is less than five, e.g. three.

[0125] The seventh aspect of the invention relates to a decorative panel, characterized in that the decorative panel comprises a number of impregnated sheets of paper obtained in a method as in any embodiment of the first aspect of the invention, or a number of impregnated sheets of paper as in the third aspect of the invention, stacked onto each other. The decorative panel optionally comprises a decorative top layer. In the stack the impregnated sheets of paper are bonded together by curing the impregnation compound.

[0126] The decorative panel of the seventh aspect of the invention provides an alternative for the so-called compact boards, in which a board is provided by laminating together Kraft paper sheets impregnated with phenol formaldehyde resin.

[0127] A preferred decorative panel according to the seventh aspect of the invention is characterized in that the decorative top layer comprises an impregnated sheet of paper obtained from a method according to the second aspect of the invention, or an impregnated sheet of paper according to the fourth aspect of the invention. Preferably, the cured impregnation compound of the impregnated sheet of paper of the decorative paper layer provides adhesion with the stack, more preferably via a thermal lamination step.

[0128] A preferred embodiment of the decorative panel of the seventh aspect is characterized in that at least the decorative top layer is embossed, preferably in a thermal pressing operation in which the impregnation compound is cured.

[0129] Preferably, the decorative panel of the seventh aspect of the invention is characterized in that at least ten impregnated sheets of paper obtained in a method as in any embodiment of the first aspect of the invention, or as in the third aspect of the invention, are stacked onto each other.

[0130] With the intention of better showing the characteristics of the invention, hereafter, as an example without any limitative character, several preferred embodiments are described, with reference to the accompanying drawings, wherein: figure 1 illustrates a method according to the invention, figure 2 shows a method according to the invention, figure 3 shows a thermal pressing operation as can be used in the invention, figure 4 shows a decorative panel according to an aspect of the invention, figure 5 shows a laminate according to the invention, and figure 6 shows a decorative panel according to an aspect of the invention.

[0131] An example of an impregnation compound for use in the invention is provided by recipe 1 :

[0132] 15 parts by weight of glyceryl propoxy triacrylate (GPTA),

[0133] 15 parts by weight of dipropylene glycol diacrylate (DPGDA),

[0134] 30 parts by weight of pentaerythritol triacrylate (PETIA),

[0135] 20 parts by weight of an isocyanate functionalized urethane acrylate oligomer, having acrylate functionality 3.4 and isocyanate functionality 1.4,

[0136] 20 parts by weight of a urethane oligomer having isocyanate functionality 2, 0.08 parts by weight of tert.butylperoxyneodecanoate (TBPND), a thermoinitiator,

[0137] 0.25 parts of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator, Optionally 0.1 parts by weight of a photo-initiator

[0138] GPTA, DPGDA and PETIA are reactive diluents. PETIA is a reactive diluent comprising a primary hydroxyl group.

[0139] TBPND has a self-accelerating decomposition temperature of 15°C - 20°C and a half life of 1 minute at 100°C. TBEC has a half life of 1 minute at 175°C.

[0140] In the exemplary impregnation compound of recipe 1, the 20 parts by weight of a urethane oligomer having isocyanate functionality 2 can be replaced by an additional 20 parts by weight of the isocyanate functionalized urethane acrylate oligomer, having acrylate functionality 3.4 and isocyanate functionality 1.4.

[0141] The impregnation compound of recipe 1 can optionally comprise a catalyst, e.g. a metal soap.

[0142] Another example of an impregnation compound for use in the invention is provided by recipe 2:

[0143] 10 parts by weight of a polymeric dimethyl difenyl di -isocyanate based isocyanate,

[0144] 10 parts by weight of dipropylene glycol diacrylate (DPGDA),

[0145] 45 parts by weight of pentaerythritol triacrylate (PETIA),

[0146] 35 parts by weight of an isocyanate functionalized urethane acrylate oligomer, having acrylate functionality 3.4 and isocyanate functionality 1.4,

[0147] 0.25 parts of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator.

[0148] Another example of an impregnation compound for use in the invention is provided by recipe 3 :

[0149] 20 parts by weight of poly-isocyanate, 15 parts by weight of dipropylene glycol diacrylate (DPGDA),

[0150] 30 parts by weight of pentaerythritol triacrylate (PETIA),

[0151] 35 parts by weight of hydroxyl functionalized urethane acrylate oligomer, having acrylate functionality 3.4,

[0152] 0.25 parts of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator, Optionally 0.04 parts by weight of a photo-initiator.

[0153] Another example of an impregnation compound for use in the invention is provided by recipe 4:

[0154] 20 parts by weight of poly-isocyanate,

[0155] 15 parts by weight of glyceryl propoxy triacrylate (GPTA),

[0156] 30 parts by weight of pentaerythritol triacrylate (PETIA),

[0157] 15 parts by weight of isocyanate functionalized urethane acrylate oligomer, having acrylate functionality 3.4 and isocyanate functionality 1.4,

[0158] 20 parts by weight of hydroxyl functionalized urethane acrylate oligomer, having acrylate functionality 3,

[0159] 0.25 parts of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator, Optionally 0.04 parts by weight of a photo-initiator.

[0160] Another example of an impregnation compound for use in the invention is provided by recipe 5 :

[0161] 10 parts by weight of poly-isocyanate,

[0162] 50 parts by weight of pentaerythritol triacrylate (PETIA),

[0163] 30 parts by weight of isocyanate functionalized urethane acrylate oligomer, having acrylate functionality 3.4 and isocyanate functionality 1.4,

[0164] 10 parts by weight of hydroxyl functionalized polyester acrylate oligomer, having acrylate functionality 3,

[0165] 0.25 parts of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator.

[0166] Another example of an impregnation compound for use in the invention is provided by recipe 6:

[0167] 10 parts by weight of poly-isocyanate, 50 parts by weight of pentaerythritol triacrylate (PETIA),

[0168] 10 parts by weight of dipropylene glycol diacrylate (DPGDA),

[0169] 30 parts by weight of isocyanate functionalized urethane acrylate oligomer, having acrylate functionality 1 and isocyanate functionality 2.2,

[0170] 10 parts by weight of hydroxyl functionalized polyester acrylate oligomer, having acrylate functionality 3,

[0171] 0.05 parts by weight of tert.butylperoxyneodecanoate (TBPND), a thermoinitiator,

[0172] 0.30 parts of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator.

[0173] Another example of an impregnation compound for use in the invention is provided by recipe 7 :

[0174] 25 parts by weight of glyceryl propoxy triacrylate (GPTA),

[0175] 25 parts by weight of pentaerythritol triacrylate (PETIA),

[0176] 30 parts by weight of isocyanate functionalized urethane acrylate oligomer, having acrylate functionality 1 and isocyanate functionality 2.2,

[0177] 10 parts by weight of hydroxyl functionalized polyester acrylate oligomer, having acrylate functionality 3,

[0178] 0.05 parts by weight of tert.butylperoxyneodecanoate (TBPND), a thermoinitiator,

[0179] 0.3 parts of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator,

[0180] Optionally 0.04 parts by weight of a photo-initiator.

[0181] Another example of an impregnation compound for use in the invention is provided by recipe 8:

[0182] 29 parts by weight of glyceryl propoxy triacrylate (GPTA),

[0183] 35 parts by weight of pentaerythritol triacrylate (PETIA),

[0184] 35 parts by weight of isocyanate functionalized urethane acrylate oligomer, having acrylate functionality 1 and isocyanate functionality 2.2,

[0185] 1 part of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator,

[0186] Optionally 0.07 parts by weight of a photo-initiator. The impregnation compounds of recipe 2, 3, 4, 5, 6, 7 and 8 can optionally comprise a catalyst, e.g. a metal soap.

[0187] An example of an acrylate lacquer for use in the invention is provided by recipe 9: 35 parts by weight of glyceryl propoxy triacrylate (GPTA), 15 parts by weight of tripropyleneglycol diacrylate (TPGDA), 10 parts by weight of isocyanate trifunctional urethane, 30 parts by weight of a trifunctional urethane, 10 parts by weight of a tetrafunctional polyester acrylate oligomer, 0.2 parts of tert-butylperoxy 2-ethylhexyl carbonate (TBEC), a thermo-initiator 0.2 parts by weight of OO-(t-amyl) 0-(2-ethylhexyl) monoperoxycarbonate (TAEC), a thermo-initiator,

[0188] 0.1 parts by weight of a photo-initiator.

[0189] GPTA and TPGDA are reactive diluents comprising acrylate groups.

[0190] Figure 1 shows a method according to the invention. In the first process step, a printed sheet of paper 1 having a weight of 70 grams per meter is unrolled from a roll and impregnated in a bath 2 with the impregnation compound 3 of recipe 1. The sheet of paper impregnated with the impregnation compound 3 is squeezed between two rollers 4, to set the amount of impregnation compound 3 with which the sheet of paper 1 is impregnated, e.g. 40 grams per square meter. The sheet of paper impregnated with the impregnation compound 3 passes through an oven. The residence time of the sheet of paper in the oven is 1 minute at 120 °C oven temperature. This oven passage results in a non-tacky surface of the impregnated sheet of paper. The impregnated printed sheet of paper is wound on a roll 6.

[0191] In the oven 5, a chemical reaction occurs between the isocyanate groups in the impregnation compound and with hydroxyl groups in the sheet of paper as well as with hydroxyl groups in the impregnation compound. One of the two thermo-initiators, more particularly TBPND, is activated in the oven, while the other thermo-initiator, more particularly TBEC, is not activated in the oven. The thermo-initiator activated during the passage through the oven 5 initiates addition reactions between acrylate groups in the oligomers and the reactive diluents. However, the amount of this thermo-initiator is such that only part of the acrylate groups react. The result of the oven passage is that the impregnated printed sheet of paper 7 has non-tacky surfaces.

[0192] In a second process step, the roll of paper 6 obtained in the first process step is unwound. The sheet of paper 7, impregnated in the first process step with the impregnation compound, is coated in the coating applicator 8 with an acrylate lacquer 9, e.g. the acrylate lacquer of recipe 9. For decorative floor panel applications, 150 - 240 gram per square meter of the acrylate lacquer can be applied. For furniture panel applications it can be sufficient to apply 40 - 180 gram per square meter of the acrylate lacquer. The acrylate lacquer layer obtained is partially cured in one or more UV-radiation steps 10 - which can include an excimer radiation step - to non-tacky state. The non-tacky sheet of paper 11 impregnated with the impregnation compound and coated with the acrylate lacquer layer is wound on a roll 12.

[0193] In between the first process step and the second process step, the side of the impregnated sheet of paper opposite to the side receiving the acrylate lacquer in the second process step can be provided with an adhesion layer, e.g. by coating a water-based polyurethane dispersion followed by a drying step, preferably at a temperature not higher than the oven temperature of the first process step. The adhesion layer can be beneficial to improve the adhesion of the impregnated sheet of paper to a board in a thermal lamination step.

[0194] It is also possible however to apply an adhesion layer at the side opposite to the side of the impregnated sheet of paper comprising the acrylate lacquer layer after applying and partially curing the acrylate lacquer layer. As an example, an adhesion layer can be applied by coating a water-based polyurethane dispersion followed by a drying step, preferably at a temperature not higher than the oven temperature of the first process step. The adhesion layer can be beneficial to improve the adhesion of the impregnated sheet of paper to a board in a thermal lamination step. Figure 2 shows a method according to the invention. The reference figures in figure 2 have the same meaning as in figure 1. The difference between figures 1 and 2 is that in figure 2 the two steps of the method shown in figure 1 are performed in line and continuously.

[0195] Figure 3 shows a thermal pressing operation as can be used in the invention. A stack comprising from top to bottom a printed sheet of paper 24 impregnated with an impregnation compound (e.g. with the impregnation compound of recipe 1) and comprising an acrylate lacquer layer (e.g. with the acrylate lacquer of recipe 9), a board 26 and optionally a balance layer 28 being a sheet of paper impregnated with a thermoset resin, e.g. impregnated with a partially cured acrylate impregnation compound is positioned in a single daylight press 20 having a structured press element 22. The printed sheet of paper 24 impregnated with an impregnation compound and comprising an acrylate lacquer layer can be provided - at the opposite side of the side comprising the acrylate lacquer layer - with an adhesion layer. The printed sheet of paper 24 impregnated with an impregnation compound and comprising an acrylate lacquer layer can be as produced in the methods shown in figures 1 or 2.

[0196] The single daylight press 20 is closed. Using temperature, e.g between 180 and 210 °C, and pressure, e.g. 5 - 100 kg / cm2during 12 - 30 seconds, the thermo-initiators of the impregnation compound (which is in the example of recipe 1 TBEC) and of the acrylate lacquer (which is in the example of receipt 9 TBEC and TAEC) are activated resulting in addition reactions of acrylate groups of the impregnation compound and of the acrylate lacquer. The use of the structured press element 22 results in an embossed, cured surface of the decorative panel made in the thermal pressing operation. At the same time, the printed sheet of paper 24 impregnated with an impregnation compound and comprising an acrylate lacquer layer is laminated to the board 26. The optional balance layer 28 is also laminated to the board in the thermal pressing operation.

[0197] In the same way as recipe 1, recipes 2, 3, 4, 5 , 6, 7 and 8 can be used to impregnate the printed sheet of paper. Figure 4 shows a decorative panel 30 according to an aspect of the invention. The decorative panel can be made in the thermal pressing operation shown in figure 3. The decorative panel comprises a board 26, optionally a balance layer 26 at the bottom of the board, and a decorative top layer provided by the printed sheet of paper 24 having been impregnated with an impregnation compound (e.g. with the impregnation compound of recipe 1) and comprising an acrylate lacquer layer (e.g. obtained with the acrylate lacquer of recipe 9). The impregnation compound and the acrylate lacquer layer are substantially fully cured. The decorative top layer is provided with an embossed structure in the thermal pressing operation.

[0198] Figure 5 shows a laminate 40 according to the invention. The laminate 40 is shown in exploded view, showing the layers of the laminate 40 prior to the layers being laminated to each other in a thermal pressing operation similar to the one shown in figure 3 for the production of a decorative panel.

[0199] The laminate comprises a number (e.g. three as shown in figure 5) sheets of paper 41 impregnated with a partially cured impregnation compound (e.g. with the impregnation compound of recipe 1), e.g. sheets as obtained in the first step of the method shown in figure 1.

[0200] The laminate comprises a decorative top layer 42 comprising a printed sheet of paper 43 impregnated with a partially cured impregnation compound (e.g. with the impregnation compound of recipe 1) and provided with a partially cured acrylate lacquer layer 44 (e.g. obtained with the acrylate lacquer of recipe 9). The decorative layer 42 can be a sheet of paper obtained in the second process step of figure 1.

[0201] The stacked layers 41, 42 can be laminated in a thermal pressing operation, in which the acrylate lacquer layer 44 can be embossed. The operation is similar to the operation to manufacture a decorative panel using a board as carrier for the decorative top layer as explained in figure 3. The laminate 40 can be glued onto a board in order to serve as a wear resistant decorative top layer, e.g. for use as furniture panel.

[0202] Figure 6 shows in exploded view a decorative panel 60 according to an aspect of the invention. The reference numerals in figure 6 have the same meaning as in figure 5. The decorative panel 60 is built up in a similar way as the laminate of figure 5. However, the number of sheets of paper 41 impregnated with a partially cured impregnation compound (e.g. with the impregnation compound of recipe 1) is much bigger, such that after the thermal pressing operation a decorative panel 60 is obtained instead of a laminate sheet obtained in figure 5.

[0203] The present invention is in no way limited to the embodiments described as an example and represented in the figures, on the contrary it can be realized in various forms and dimensions, without leaving the scope of the invention.

Claims

Claims1 Method for impregnating a sheet of paper, comprising the steps of- providing a sheet of paper;- providing an impregnation compound; and- impregnating the sheet of paper with the impregnation compound; wherein the impregnation compound comprises acrylate oligomers and acrylate reactive diluents; wherein the acrylate oligomers have a molar mass equal to or higher than 800 g / mol and preferably lower than 10000 g / mol, and preferably lower than 7000 g / mol; wherein the acrylate reactive diluents have a molar mass lower than 800 g / mol, and preferably lower than 600 g / mol.2.- Method as in any of the preceding claims, characterized in that the acrylate oligomers and / or the acrylate reactive diluents comprise one or more than one hydroxyl reactive groups, e.g. selected from isocyanate groups, melamine groups, carboxyl groups or amine groups (preferably primary amine groups or secondary amine groups); or combinations thereof.3.- Method as in any of the preceding claims, characterized in that the impregnation compound comprises acrylate oligomers that comprise one or more than one hydroxyl groups, and / or that the impregnation compound comprises acrylate reactive diluents that comprise one or more than one hydroxyl groups.4.- Method as in any of the preceding claims, characterized in that all acrylate reactive diluents comprise at least one hydroxyl reactive group or at least one hydroxyl group; or both.5.- Method as in any of the preceding claims, characterized in that the impregnation compound comprises a crosslinker, preferably selected from formaldehyde, melamine,isocyanate, aziridine, carbodiimide, polyol (e.g. a diol, e.g. polyethylene glycol) or combinations thereof.6.- Method as in any of the preceding claims 1 - 5, characterized in that the impregnation compound does not comprise non-reactive solvent.7.- Method as in any of the preceding claims 1 - 5, characterized in that the impregnation compound comprises non-reactive solvent, preferably in an amount less than 20 wt% of the impregnation compound.8.- Method as in any of the preceding claims, characterized in that the ratio of the amount by weight in the impregnation compound of the acrylate reactive diluents to the acrylate oligomers ranges between 1.2 and 1.85, preferably between 1.4 and 1.6.9.- Method as in any of the preceding claims 1 - 8, characterized in that the impregnation compound comprises a photo-initiator.10.- Method as in any of the preceding claims 1 - 8, characterized in that the impregnation compound does not comprise photo-initiators.11.- Method as in any of the preceding claims, characterized in that the impregnation compound comprises antistatic additives, such as carbon particles or quaternary ammonium salts, or combinations thereof.12.- Method as in any of the preceding claims, characterized in that the acrylate oligomers consist or comprise urethane acrylate oligomers; preferably urethane acrylate oligomers comprising isocyanate groups.13.- Method as in any of the preceding claims, characterized in that the acrylate oligomers are selected from urethane acrylate oligomers, polyester acrylate oligomers, polyether acrylate oligomers and epoxy acrylate oligomers, and combinations thereof.14.- Method as in any of the preceding claims, characterized in that the impregnation compound comprises a catalyst, or that a catalyst is applied to the impregnated sheet of paper before of after the step of impregnating the sheet of paper with the impregnation compound.15.- Method as in claim 14, characterized in that the catalyst is a metal soap, preferably a sodium soap, a calcium soap, a bismuth soap or a zinc soap (e.g. zinc neodecanate), or combinations thereof; and / or preferably an unsaturated metal soap, preferably an unsaturated sodium soap, an unsaturated calcium soap, an unsaturated bismuth soap or an unsaturated zinc soap.16.- Method as in any of the preceding claims 14 - 15, characterized in that the catalyst is an alkaline catalyst.17.- Method as in any of the preceding claims, characterized in that the step of impregnating the sheet of paper with the impregnation compound is followed by the step of increasing the temperature of the impregnated paper sheet.18.- Method as in claim 17, characterized in that in the step of increasing the temperature of the impregnated paper sheet substantially all hydroxyl reactive groups of the impregnation compound have reacted.19.- Method as in any of the preceding claims 17 - 18, characterized in that in the step of increasing the temperature of the impregnated paper sheet substantially all acrylate reactive diluents have reacted.20.- Method as in any of the preceding claims 17 - 19, characterized in that the impregnation compound comprises a first thermo-initiator; wherein in the step of increasing the temperature of the impregnated paper sheet, the temperature of the impregnated paper sheet stays below the 60 seconds half-life temperature of the first thermo-initiator, preferably wherein the first thermo-initiator provides between 0.2 and 1 wt% of the impregnation compound.21.- Method as in any of the preceding claims 17 - 20, characterized in that the impregnation compound comprises a second thermo-initiator; wherein in the step of increasing the temperature of the impregnated paper sheet, the impregnated paper sheet reaches a temperature higher than the 60 seconds half-life temperature of the second thermo-initiator.22.- Method as in claim 21, characterized in that the second thermo-initiator is provided in the impregnation compound in an amount insufficient to initiate all acrylate reactive groups present in the impregnation compound.23.- Method as in claim 21, characterized in the second thermo-initiator is provided in the impregnation compound in an amount to convert between 40 and 50% of the acrylate reactive bonds of the impregnation compound.24.- Method as in any of the preceding claims 21 - 23, characterized in that the second thermo-initiator is present in the impregnation compound in an amount of 0.075 to 0.15 wt%.25.- Method as in any of the preceding claims, characterized in that the acrylate oligomers provide at least 30 wt% of the impregnation compound, wherein the acrylate reactive diluents provide at least 50 wt% of the impregnation compound, preferably wherein the percentage by weight of the acrylate reactive diluents in the impregnation compound is at least double the percentage by weight of the acrylate oligomers in the impregnation compound.26.- Method as in any of the preceding claims, characterized in that the step of impregnating the sheet of paper with the impregnation compound comprises the step of guiding the sheet of paper through a bath comprising the impregnation compound, preferably followed by the step of removing excess impregnation compound taken up by the sheet of paper from the bath, e.g. by means of guiding the impregnated sheet of paper through a set of rollers, or by means of one or more than one knife.27.- Method as in any of the preceding claims, characterized in that between 25 and 45 gram per square meter dry weight of impregnation compound is applied to the sheet of paper.28.- Method as in any of the preceding claims, characterized in that the step of impregnating the sheet of paper with the impregnation compound is preceded or succeeded by the steps of impregnating or coating the sheet of paper with a water-based aminoplast compound, and the step of drying the aminoplast compound applied to the sheet of paper, wherein the aminoplast compound is selected from a urea formaldehyde compound, a melamine formaldehyde compound or a melamine urea formaldehyde compound.29.- Method as in any of the preceding claims, characterized in that the step of impregnating the sheet of paper with the impregnation compound is preceded or succeeded by the steps of impregnating or coating the sheet of paper with a water based styrene-butadiene copolymer and the step of drying the styrene-butadiene copolymer applied to the sheet of paper.30.- Method as in any of the preceding claims, characterized in that a polyurethane dispersion is applied to one or to both sides of the paper sheet impregnated with the impregnation compound.31.- Method as in any of the preceding claims, characterized in that an acrylate lacquer is applied onto the impregnated sheet of paper, preferably wherein between 30 - 400 gram per square meter of dry weight acrylate lacquer is applied.32.- Method as in claim 31, characterized in that the applied acrylate lacquer is cured to non-tacky state, preferably by means of UV-radiation (e.g. using a UV lamp or using UV-LED radiation) or EB (electron beam) radiation.33 Method as in any of the preceding claims 31 - 32, characterized in that the acrylate lacquer comprises- one or more acrylate and / or methacrylate oligomers, preferably wherein said oligomers have a molar mass equal to or higher than 800 g / mol;- one or more acrylate reactive diluent and / or methacrylate reactive diluent and / or (meth)acrylamide reactive diluents; wherein said reactive diluents have a molar mass lower than 800 g / mol, and preferably lower than 500 g / mol;- optionally one or more photo-initiators; and- one or more thermo-initiators; preferably.34.- Method as in claim 33, characterized in that the acrylate lacquer comprises a product having isocyanate functionality, preferably having isocyanate functionality at least 1.2, more preferably at least 2.35.- Method as in claim 34, characterized in that the product having isocyanate functionality is selected from an acrylate oligomer (e.g. a urethane acrylate oligomer) having isocyanate functionality, a polyurethane having isocyanate functionality, a diisocyanate (e.g. a difenyl di-isocyanate and / or a polymeric isocyanate), or combinations thereof.36.- Method as in any of the preceding claims 33 - 35, characterized in that the ratio of the amount by weight in the acrylate lacquer between on the one hand the one or more acrylate reactive diluent, the methacrylate reactive diluent and the (meth)acrylamide reactive diluents; and on the other hand the one or more acrylate and / or methacrylate oligomers ranges between 1.2 and 1.85, preferably between 1.4 and 1.6.37.- Method as in any of the preceding claims 33 - 36, characterized in that the acrylate lacquer layer comprises one or more photo-initiators, wherein the acrylate lacquer comprises photo-initiators in a combined amount less than 1 wt% of the combination of the one or more acrylate and / or methacrylate oligomers and the one or more acrylate and / or methacrylate and / or (meth)acrylamide reactive diluents.38.- Method as in nay of the preceding claims 33 - 37, characterized in that the acrylate lacquer layer comprises one or more photo-initiators, wherein the one or more photoinitiators of the acrylate lacquer comprise or consist of Norrish type I photo-initiators.39.- Method as in any of the preceding claims 33 - 38, characterized in that the one or more thermo-initiators of the acrylate lacquer comprise a first thermo-initiator and a second thermo-initiator, wherein the 60 seconds half-life temperature of the second thermo-initiator is at least 8°C higher than the 60 seconds half-life temperature of the first thermo-initiator.40.- Method as in claim 39, characterized in that the one or more thermo-initiators of the acrylate lacquer comprise a third thermo-initiator, wherein the 60 seconds half-life temperature of the third thermo-initiator is at least 8°C higher than the 60 seconds halflife temperature of the second thermo-initiator.41.- Method as in claim 39, characterized in that the one or more thermo-initiators of the acrylate lacquer comprise a fourth thermo-initiator, wherein the 60 seconds half-life temperature of the fourth thermo-initiator is at least 8°C higher than the 60 seconds halflife temperature of the third thermo-initiator.42.- Method as in any of the preceding claims 33 - 41, characterized in that the acrylate lacquer comprises silica (SiCh), preferably in an amount more than 0.05 wt of the acrylate lacquer, and preferably less than 3 wt% of the acrylate lacquer.43.- Method as in any of the preceding claims 33 - 42, characterized in that the acrylate lacquer comprises AI2O3, preferably with average particle size less than 30 micrometer, preferably in an amount more than 0.05 wt of the acrylate lacquer, and preferably less than 7 wt% of the acrylate lacquer.44.- Method as in any of the preceding claims 33 - 43, characterized in that the acrylate lacquer comprises wear resistant particles, e.g. corundum, silicon carbide, diamond or nanosilica.45.- Method as in any of the preceding claims 33 - 44, characterized in that the acrylate lacquer comprises wear resistant particles, e.g. corundum or silicon carbide, wherein the wear resistant particles have an average particle size between 40 and 100 micrometer.46.- Method as in any of the preceding claims 33 - 45, characterized in that the method comprises the steps of- optionally applying a first UV-radiation step to the impregnated sheet of paper onto which the acrylate lacquer has been applied;- applying a second UV-radiation step by passing the impregnated sheet of paper onto which the acrylate lacquer has been applied under an excimer-type monochromatic radiation lamp; and- applying a third UV-radiation step to the impregnated sheet of paper onto which the acrylate lacquer has been applied; wherein in the method the acrylate lacquer provided by partial curing to B-stage; and wherein the surface of the acrylate lacquer is not tacky.47.- Method as in claim 46, characterized in that the surface of the acrylate lacquer obtained is wrinkled and / or comprises micro folds.48.- Method as in any of the preceding claims 43 - 47, characterized in that the step of applying an acrylate lacquer onto the impregnated sheet of paper, comprises the step of applying a first acrylate lacquer onto the impregnated sheet of paper and the step of applying a second acrylate lacquer on the first acrylate lacquer, preferably wherein the second acrylate lacquer provides on the impregnated sheet of paper less than 40 wt% - and preferably less than 30 wt% - of the combination of the first acrylate lacquer and the second acrylate lacquer; preferably wherein the first acrylate lacquer as well as the second acrylate lacquer comprise (meth)acrylate oligomers and (meth)acrylate reactive diluents.49.- Method as in any of the preceding claims 33 - 48, characterized in that the method comprises the step of applying an adhesion layer to the paper sheet, before or after the step of applying the acrylate lacquer onto the impregnated sheet of paper, wherein the adhesion layer is applied at the side opposite to the side comprising the acrylate lacquer or opposite to the side onto which the acrylate lacquer will be applied.50.- Method as in any of the preceding claims 49, characterized in that the adhesion layer is a polyurethane adhesion layer, preferably applied as a polyurethane dispersion; or is a melamine adhesion layer or a urea based adhesion layer or combinations thereof51.- Method as in any of the preceding claims, characterized in that the impregnated sheet of paper is wound on a roll.52.- Method as in any of the preceding claims 1 - 51, characterized in that the sheet of paper comprises a printed decor.53.- Method as in any of the preceding claims 1 - 51, characterized in that the sheet of paper is a Kraft paper sheet.54.- Impregnated sheet of paper, characterized in that the sheet of paper is obtained via a method as in any of the preceding claims.55.- Impregnated sheet of paper as in claim 54, characterized in that the impregnated sheet of paper comprises a partially cured acrylate lacquer, wherein both surfaces of the impregnated sheet of paper are in non-tacky state.56.- Impregnated sheet of paper, preferably as in any of the preceding claims 54 - 55, characterized in that the impregnated sheet of paper comprises a sheet of paper impregnated with a partially cured acrylate impregnation compound as well as a partially cured acrylate lacquer applied on a side of the impregnated paper sheet; wherein both surfaces of the impregnated sheet of paper are in non-tacky state;wherein the partially cured impregnation compound comprises a first thermo-initiator; and wherein the partially cured acrylate lacquer comprises a first thermo-initiator.57.- Impregnated sheet of paper as in any of the preceding claims 54 - 56, characterized in that the impregnated sheet of paper is provided as a roll of paper.58.- Impregnated sheet of paper as in any of the preceding claims 54 - 57, characterized in that the impregnated sheet is provided for use as a top layer in a decorative panel.59.- Impregnated sheet of paper as in any of the preceding claims 54 - 57, characterized in that the impregnated sheet of paper is provided for use as a carrier sheet in a High Pressure Laminate.60.- Impregnated sheet of paper as in any of the preceding claims 54 - 57, characterized in that the impregnated sheet of paper is provided for use as multiple layers in a core of a decorative panel, wherein in the decorative panel the multiple layers are bonded by curing the impregnation compound of the multiple layers of the impregnated papers sheet.61.- Impregnated sheet of paper as in any of the preceding claims 54 - 60, characterized in that the impregnated sheet of paper has a moisture content less than 8 wt%, preferably less than 6 wt%, more preferably less than 5 wt%.62.- Decorative panel, characterized in that the decorative panel comprises a core and a decorative top layer; wherein the decorative top layer comprises an impregnated sheet of paper obtained from a method as in any of the preceding claims 1 - 53 or as in any of the preceding claims 54 - 61; wherein the decorative core layer is adhered to the core, and wherein the impregnation compound has been cured, preferably by means of thermal curing, more preferably by a thermal pressing operation.63.- Decorative panel as in claim 62, characterized in that at least the decorative top layer is embossed, preferably in a thermal pressing operation in which the impregnation compound is cured.64.- Decorative panel as in any of the preceding claims 62 - 63, characterized in that the core is selected from the list consisting of a wood-based board (e.g. a wood fiber board, a wood chip board or a plywood board), a mineral based board (e.g. a gypsum board, an MgO based board or a cement board) or a - whether or not filled - polymer board.65.- Decorative panel as in any of the preceding claims 62 - 64, characterized in that the impregnated sheet of paper is an impregnated sheet of paper obtained from a method as in any of the preceding claims 33 - 52, wherein the impregnation compound is cured by a thermal pressing operation, wherein in the thermal pressing operation the acrylate lacquer is thermally cured, preferably wherein in the thermal pressing operation at least the acrylate lacquer is provided with a texture.66.- Laminate, characterized in that the laminate comprises a number of impregnated sheets of paper obtained in a method as in any of the preceding claims 1 - 53 stacked onto each other and optionally a decorative top layer, wherein in the stack the multiple number of impregnated sheets of paper are bonded together by curing the impregnation compound.67.- Decorative panel, characterized in that the decorative panel comprises a number of impregnated sheets of paper obtained in a method as in any of the preceding claims 1 - 54 stacked onto each other and a decorative top layer, wherein in the stack the impregnated sheets of paper are bonded together by curing the impregnation compound of the impregnated sheets of paper.68.- Decorative panel as in claim 67, characterized in that the decorative top layer comprises an impregnated sheet of paper obtained from a method as in any of the preceding claims 33 - 52.69.- Decorative panel as in claim 68, characterized in that the cured impregnation compound of the impregnated sheet of paper of the decorative paper layer provides adhesion with the stack, preferably via a thermal lamination step.70.- Decorative panel as in any of the preceding claims 68 - 79, characterized in that at least the decorative top layer is embossed, preferably in a thermal pressing operation in which the impregnation compound is cured.

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