Panel and method for manufacturing panels

Abstract

 Panel comprising a substrate (2) having two major surfaces (3-4), wherein a facing layer (5) is provided at at least one of said major surfaces (3-4), wherein said substrate (2) comprises glued and pressed particles and/or one or more layers of wood, characterized in that the substrate (2) at at least one of said major surfaces (3-4) comprises a plurality of portions (6) recessed with respect to an edge portion (7) of the respective major surface (3-4).

Description

[0001] The present invention relates to a panel, in particular a furniture panel. The invention also relates to methods for manufacturing such panels.

[0002] More specifically, the invention relates to such panels that comprise a substrate having two major surfaces and wherein a facing layer is provided at at least one of said major surfaces. Such panels are known per se and can be used for manufacturing furniture or any component thereof, such as kitchen cabinets, cupboards, worktops, tabletops, shelves, doors, panels, side pieces and so one.

[0003] It is known to use substrates that comprise glued and pressed particles in such panels, and/or to use facing layers that create a decoration effect at the surface of such panel.

[0004] As a substrate wood particleboard or wood fiberboard can be used, for example medium or high density fiberboard (MDF or HDF). It is known how to manufacture such wood based panels. The lignocellulose material is reduced to particles, in the case of particleboard or oriented strand board (OSB) of different size and shape or reduced to fiber particles, in the case of MDF or HDF, by means of suitable particle generation equipment. This lignocellulose material is then treated by a sequence of operations, for example including drying, coating and/or mixing with binding agents, such as resins and/or glues, and forming a material mass or mat. The material mass is then pressed, possibly including a pre-pressing stage for degassing, and heated in order to form a plate shaped material, by means of suitable pressing equipment, such as by means of a continuous or discontinuous press. In the latter case a single opening or multi opening press could be used.

[0005] As a facing layer a plurality of materials can be used, such as veneer, foils, paper sheets, laminate material such as DPL (Direct Pressure Laminate) or HPL (High Pressure Laminate). Specific examples of such facing layers include melamine impregnated papers, finish foils, thermoplastic foils, such as foils on the basis of PVC or PET), lacquers, facing layers comprising a print performed directly on the substrate material, such as a print performed by inkjet or rotogravure. All these facing layers aim at providing a final panel surface with a desired surface décor and/or texture. Such known panels are rather heavy and give ergonomic problems when trying to package all panels of a furniture item in one or a limited number of packs, such as is normally done for ready to assemble furniture or "flatpack" furniture. The weight of such panels is particularly unwanted when shelves are considered. Such shelves can already bend under their own weight and give rise to a permanent distortion. Heavy panels are also undesirable for application as a door or worktop. The excessive weight of panels can lead to expensive and cumbersome transportation, to heavy and expensive fastening and/or connection means for assembly of several panels into a furniture unit, or for connection of the panel to a wall, such as may be the case for a door (hinges) or shelve.

[0006] Recently several proposals for solving the weight problem with furniture panels have emerged.

[0007] A first proposal for a light product is the so-called "sandwich panel" or "hollow core panel". Several examples of such panels are disclosed in patent documents WO 2006/100295 and WO 2007/131904. These light weight building panels comprise a honeycomb material as a substrate. Such honeycomb material is commonly made out of cardboard and necessitates the use of separate laths or profiles for forming a frame at the edges of the furniture panels. This frame adds to the strength of the panel and allows that possible, e.g. decorative, edging material can adhere to these laths or profiles and/or that possible furniture fittings can be fixed thereto. A further disadvantage of such honeycomb material is that it has to be made to measure for the desired panel and does hence not allow for flexible or smooth manufacturing. These "hollow core" panels can generally be produced by attaching surface panels of small thickness on a frame of wood, or built of beams or profiles made of wood based panel material, wherein this frame is preferably available at the edges of the final panel. Typically, the hollow space between the surface panels and delimited by the frame is filled with a material having a honeycomb structure or similar, as is the case in said patent documents. This "hollow" material and its manufacturing process, including preparing the frame, inserting the filling material, such as the honeycomb, and adhering the surface panels requires several manufacturing steps in the manufacturing process. Final costs are much higher than the conventional wood based panels as above defined. A still further disadvantage of such honeycomb material as disclosed in said patent documents is the absence of any screw holding material in the centre of the panel's substrate. "Hollow panels" in general have critical issues when it comes to assembling several furniture parts. Problems arise with drilling holes and inserting screws, except where the frame is underneath the surface panels. According to the state of the art this critical issue is solved by adding frame parts where drilling a hole, inserting a screw or in general fixing a part is expected or needed.

[0008] A second proposal for a light product is disclosed in WO 2009/017451. This document discloses a wood-based furniture component that comprises chipboard substrate material, wherein this chipboard material at one major surface thereof is provided with projecting chip segments. These projecting chip segments have been created by means of a structured pressing belt or plate, that forms the material mass, consisting of particles and binding agent, in the production of the particle board. The said projecting chip segments project with respect to an edge portion of the obtained substrate material. Such board also necessitates the use of laths or profiles for forming the edges of the final furniture panels, leading to similar disadvantages as stated above with respect to honeycomb material. Using strongly structured pressing belts or plates in the manufacture of particleboard is very troublesome and could lead to undesired variations in obtained board quality. The non-uniform pressure distribution in the press, used in the manufacture of such board, leads to all sorts of negative side-effects that put a burden on reliable production. The production technique shows few flexibility, since the position of the projecting areas of the chipboard substrate must be predetermined during the pressing. A change in this position requires the use of an adapted pressing belt. The production technique also inevitably leads to density variations in the plane of the produced chipboard material, that might lead to dimensional distortions, such as bending.

[0009] A third proposal for a light product consists of a furniture panel comprising a low density wood based panel as a substrate. Uniformly decreasing the density leads to poor mechanical properties and to bad surface properties. A too low density can lead to excessive absorption of glue, melamine, lacquer, paint, ink and so one. Moreover if a too low density might again lead to problems with screw holding and/or application of edging material.

[0010] US 2003/183057 discloses a method for punching holes in a particleboard. The holes extend from one major surface through the other throughout the thickness of the particleboard. The particleboard carries a veneer or laminate facing layer on at least one of its major surfaces and the punched holes extend through the facing layer as well. The said holes are wire openings that allow the passage of wires and cables through the panel. Only one such hole is provided in the panel.

[0011] With the objective of attaining sound attenuation in a room, by means of wall or ceiling panels WO 2008/068298 discloses a wall or ceiling panel made of a wood-based composite material, such as MDF, wherein the panel comprises an external surface provided with grooves communicating with through holes. The panel also comprises thermal conditioning means associated to one of its external surfaces. As the holes have the particular function of sound-deadening, they are inherently considerably small and do not result in a significant weight reduction of the entirety of the panel.

[0012] With the same objective EP 0 504 629 discloses a panel having a first core element with through holes made up of recessed portions formed at both major surfaces, wherein these recessed portions meet in the depth of the first core element to form said through holes. At one major surface of said first core element a sound-absorbing material in the form of a rock wool or glass wool pad is applied, which might in its turn be covered by a chipboard or gypsum board. Said sound-absorbing material forms a second core element. At the other major surface of the first core element the holes are left open towards the room in order to let sound enter the through holes. The weight reduction attained by the through holes is minimal, since the first core element forms only a limited part of the panel.

[0013] The present invention firstly aims at an alternative furniture panel that can be of light weight. According to several preferred embodiments the present invention can also offer a solution for one or more of the problems associated with the state of the art. A specific objective of the invention according to such preferred embodiment is a wood based panel for furniture use having an average density lower than products like particleboard, fiberboard, MDF, HDF, OSB, i.e. lower than 500 kilograms per cubic meter. Such panel or board could be used in a wall covering, a ceiling use, a flooring or in any application where wood based panels are in use, according to the state of the art.

[0014] Therefore the present invention concerns a panel comprising a substrate having two major surfaces, wherein a facing layer is provided at at least one of said major surfaces, wherein said substrate comprises glued and pressed particles and/or one or more layers of wood, characterized in that the substrate at at least one of said major surfaces comprises a plurality of portions recessed with respect to an edge portion of the respective major surface. Preferably said recessed portions make up for at least 10 percent of the total volume of the panel, i.e. of the substrate and the one or more facing layers. It is clear that such facing layers, when present, define the outside surface of the panel of the invention and that the substrate can comprise any core element or a plurality thereof, that is underneath or in between said one or more facing layers. Preferably said recessed portions are obtained by removing material from one or more of said major surfaces.

[0015] The presence of two or more recessed portions, according to the invention, allows minimizing the weight of the final panel. Preferably at least 25 percent of said major surface is recessed, and even better at least 30 or 45 percent of that surface. Preferably the volume of the substrate material and/or the panel is reduced by at least 10 percent, preferably leading to an equivalent weight reduction of the substrate and/or panel. Even better the volume of the substrate material and/or the panel is reduced by at least 25 or 30 percent.

[0016] Due to the fact that the portions are recessed with respect to an edge portion of the major surface into which these portions are provided, it is obtained that the edges of the substrate remain relatively solid, such that edging materials can be more easily provided. The portions are preferably recessed with respect to a substantial edge portion of the major surface, i.e. at least 50 percent, but even better 80 or 90 percent of the edge contour, and still better with respect to the whole edge contour of the substrate. Preferably the major surface into which said recessed portions are provided is substantially flat and preferably at the same level as said edge portion. Preferably the panel of the invention is free from profiles or laths at the side edges of the substrate material.

[0017] In general, it is preferred to avoid the presence of recessed portions and/or through holes at the edge of the substrate material or panel, such that the recessed portions do not or only minimally interfere with fixing means or edging material. Similarly, recessed portions and/or through holes might be undesired in some internal part of the panel in order to increase the local panel strength and/or screw holding ability.

[0018] Preferably the said substrate material, with the exception of said recessed portions, consists of a substantially homogeneous material. Preferably the homogeneity is expressed by a variation of density in the plane of the substrate material that is lower than 20 percent, and even better lower than 10 percent. Due to the production of substrates comprising pressed and glued particles a density variation exceeding those levels can be present in the thickness direction of the substrate material, though not necessarily. As stated above, the recessed portions preferably consist of removed material portions, rather than of pressed in lowered regions, such that said homogeneity can be obtained in a straightforward manner. The fact that the substrate material is homogeneous leads to advantageous with respect to minimizing the risk of obtaining bend panels. Indeed with a homogenous substrate it can be expected that the tendency that dimensional distortions originate is minimized.

[0019] Preferably the said substrate material comprises wood particles, such as chips or fibers. These materials are preferred because of their economic and ecologic properties. Wood particles in the form of chips or fibers allow for a straightforward forming of said recessed portions and/or for the creation of smooth surfaces, for example by punching. Examples of such materials include wood chipboard, preferably having a central layer of coarse chips, faced with surface layers composed of fine chips. Other examples include wood fiberboard, such as wood fiberboard made according to the dry process, such as LDF, MDF or HDF (Low, Medium or High Density Fiberboard). Preferably such wood based material comprises a binding agent in an amount of less than 20 weight percent.

[0020] Preferably for the substrate use of made of a material having a mean density between 300 and 650 kilograms per cubic meter. This range of density allows for reducing weight while maintaining sufficient strength, considering the recessed portions. This material can either be wood based or based on another organic material such as flax, hemp, miscanthus, and so on. Preferably use is made of LDF having a mean density of about 500 kilograms per cubic meter, i.e. a density between 450 and 600 kilograms per cubic meter, wherein 550kg/m² is an ideal value. A density lower than 300 kilograms per cubic meter can lead to undesired surface properties.

[0021] Preferably said substrate, comprising said two or more recessed portions, is made in one piece in the same material. It is not excluded that, in addition to this substrate material, one or more other substrate portions and/or materials are available in the panel, whether or not provided with recessed portions. Preferably said substrate extends from one to the other of a pair of opposite edges of said panel. Still better said panel is rectangular and said substrate extends from one to the other of both pairs of opposite edges.

[0022] Preferably said edge portion of said substrate material is available at the edge of the panel, whether or not provided with additional edging material. Even better the edge contour of the panel is substantially formed by the edge of said substrate material, whether or not provided with additional edging material.

[0023] Preferably said substrate material, at least at said edge portion, has a thickness amounting to at least 70 percent of the total panel thickness, and preferably at least 80 percent of the total panel thickness.

[0024] The panel of the invention preferably has a total thickness ranging from 15 to 50 millimeter. In this range the invention allows attaining a significant weight reduction, especially when the panel has a total thickness of more than 25 or 30 millimeter.

[0025] Preferably said facing layer is provided at least at said major surface that comprises the recessed portions, wherein said facing layer preferably extends over a plurality of said portions. In this case it is obtained that the recessed portions are, at least partially hidden for the user. Still better the surface layer extends uninterruptedly over the entirety of the recessed portions. According to the most preferred embodiment the facing layer substantially covers said major surface, i.e. for at least 50, but even better for at least 85 or 95 percent thereof, or wholly. Preferably said facing layer extends over the major surface at least up to and over said edge portion of the substrate.

[0026] Preferably said facing layer is composed of a basic, preferably structural layer and a separate decoration. With a "structural layer" is meant a layer that provides increased dimensional stability to said separate decoration. Said structural layer preferably has a bending stiffness that is at least twice as high as the bending stiffness of said separate decoration alone. Such structural layer preferably has a bending stiffness allowing it to cross the largest internal distance of a recessed portion without it being subject to visible deformation in normal furniture load conditions.

[0027] According to a first example said facing layer is at least composed of a basic layer that comprises a 1 to 4 millimeter thick sheet, preferably wood based sheet or panel, and possibly a separate decoration. Tests have shown that such layer is ideally fit to reduce visible deformation of the facing layer in normal furniture load conditions. According to a preferred embodiment said layer is a layer of HDF, preferably having a mean density of over 1000 kilograms per cubic meter. A layer of 1,5 to 3 mm thick can suffice for attaining the desired dimensional stability. According to this first example, said 1 to 4 millimeter thick sheet may form the final surface of the panel, or be upgraded with a separate decoration. Said facing layer may consist of one single layer, structural or not, that forms the final surface. Preferably such single layer consists of a wood or wood-based sheet or panel, e.g. a veneer sheet, such as a wood sheet of 1 to 4 millimeter thickness. According to another example such single layer, structural or not, consists of a stone or ceramic sheet or panel, preferably having a thickness of 1 to 4 millimeter, e.g. so-called "Laminam". The inventor has found that it is feasible to use ceramic compounds, ceramic panels or other ceramic based materials, such as the one that is available with the tradename "Laminam", as a facing layer or part thereof.

[0028] According to a second example said facing layer comprises a layer, structural or not, that consists of a plurality of material sheets bounded together. Preferably said material sheets, such as paper sheets, are provided with thermosetting resin providing for said bound. Preferably said sheets are so-called kraft papers, namely paper sheets having a weight ranging from 150 to 400 grams per square meter. According to this second example said facing layer is preferably formed as a laminate plate consisting essentially of paper sheets and resin, or so-called HPL (High Pressure Laminate) or CPL (Continuous Pressure Laminate).

[0029] It is noted that the above said separate decoration preferably comprises a print or a coloration. This print or coloration can be provided on a material sheet such as a paper sheet or a synthetic foil, e.g. PVC foil, or can be provided directly on the basic layer of said facing layer, which possibly comprises said structural layer or wood based sheet. In the case of a print or coloration provided on a material sheet, such sheet can form part of the abovementioned laminate plate, or be provided on an underlying basic material layer of said facing layer, which possibly comprises said structural layer or wood based sheet. In the latter case in which the material sheet is provided on an underlying basic material layer, said material sheet may comprise a paper décor, such as a resin impregnated décor paper, a finish foil, a thermoplastic foil like PVC or PET foil, a HPL or a CPL. In the case of a print or coloration provided directly on the basic layer, the surface of the basic layer may be upgraded by operations like sanding, lacquering and/or coloring. Thereafter a décor is applied by direct printing by means of one or more of several printing techniques, including but not limited to digital printing and/or rotogravure printing.

[0030] It is further noted that the basic layer of such facing layer can comprise any material, in particular wood-based material, such as particleboard, OSB, MDF, HDF, a solid wood layer, veneer, plywood, LVL (laminated veneer lumber) and similar.

[0031] According to a preferred embodiment of the invention, said facing layer provides for a panel surface with special technical and/or aesthetic properties, such as the property of thermal insulation or radio-frequent shielding. Such facing layers may comprise aluminium, steel, copper and/or alloys of several materials.

[0032] It is clear that said facing layer may comprise one or more layer that fully or partially consist of synthetic material, such as of thermoplastic material for example chosen from the group of polycarbonate, PVC and/or PET, or of laminated multilayer materials, acrylic material. Such material are convenient to give the surface functional and/or aesthetic properties.

[0033] It is noted that said separate decoration can be applied to said basic layer of the facing layer before, after or while the basic layer is attached to the respective major surface of the substrate material. As an example, in the case of a print or coloration provided directly on the basic layer, a base coat can be prepared on the basic layer while it is still separate from the substrate material, while e.g. the print and/or final top coating can be applied on a sandwich comprising at least said substrate material and said basic layer. This might for example be the case when the top coating is applied at least partially by the method of spray coating.

[0034] Preferably said recessed portions comprise holes that extend through the complete thickness of said substrate. Such through holes offer the most convenient way of minimizing total panel weight and/or are more convenient for realizing. Such through holes can for example be realized by any cutting technique, such as sawing e.g. by means of a hole saw, laser cutting, water jet or other jet cutting technique. The most preferred technique for realizing said recessed portions in the form of through holes is a punching technique. Another possibility includes drilling, milling, grinding and/or broaching. Of course such techniques are best performed before applying any facing layer or part thereof. It is clear that techniques such as drilling, milling, grinding and/or broaching can also be used for realizing recessed portions having a depth smaller than the substrate thickness.

[0035] Preferably the facing layer is applied to the respective major surface using an adhesive, preferably a hotmelt glue, such as an adhesive on the basis of polyurethane. In general any adhesive or bonding agent can be used for creating a connection or joint between layers of the same or different material. The adhesive or bonding agent can be applied to one or both surfaces to be joint, for example by means of spray guns, spreading bars, curtain coating and/or rollers, such as by means of one or more flat rollers, grooved rollers, "stork" rollers and/or "rill" rollers. The adhesive or bonding agent can be thermoplastic, as mentioned above, or chemically activated using multiple interacting components and/or hardening additives, or hardened by evaporation of solvents including water, or physically activated by heat, light or other sources of energy. In case the adhesive or bonding agent is based on a multicomponent hardening mechanism, one or some of the components, but not all, could be applied on one surface and the other components on the opposite surface to be joint. It is clear that joining the layers producing the final panel product can be done in several steps, one by one, or several or all at the same time.

[0036] Preferably a facing layer is applied on both major surfaces of said panel. Preferably, said substrate material substantially defines the distance between said two facing layers. In the case where said facing layer is applied to the respective major surface by means of an adhesive connection, it is clear that the thickness of such adhesive connection can be very limited, i.e. less than 1 millimeter, such that indeed the substrate material defines the distance between said two facing layers.

[0037] Preferably the edges of the panel are provided with a separate edging material, such as a PVC or ABS edging material. PVC and ABS edging material is a quite rigid edging material. The panel of the present invention can also be finished at the edges with a laminate edging material that is glued on, preferably on the edge of the substrate material.

[0038] According to an interesting preferred embodiment, one or more of the edges of the panel can be finished by an extension of the facing layer or part thereof, e.g. an extension of at least the possible separate decoration of such facing layer. In the case such facing layer comprises a printed or colored PVC foil, such foil can be vacuum pressed on the respective major surface and one or more edges of the panel. In the case such facing layer comprises a printed or colored paper sheet, e.g. provided with resin, an extension of such sheet can be formed around and upon the edge, after having applied said sheet to the major surface, for example by means of a so-called postforming technique. By way of example of postforming techniques in general reference is made to FR 2629387 and FR 2595622. Of course such postforming techniques could also be applied in the case of PVC or other thermoplastic foils. In the case such facing layer comprises a print or coloration provided directly on the basic material of the facing layer, the print or coloration may extend on the edge of the panel, e.g. on the edge of the substrate material available at said edge of the panel, thereby forming a decorative edging material. According to this interesting preferred embodiment, two opposite edges of the panel can be finished by such extension, preferably extending from one one piece separate decoration that also covers one of the major surfaces of the panel or part thereof.

[0039] According to still a further interesting preferred embodiment a one piece separate decoration could be used on both major surfaces of the panel, as well as preferably on at least one or two side edges of the panel, thereby forming the edging material on these side edges. In the case of finish foil, thermoplastic foils or other foils or flexible material webs such as papers, such is possible by wrapping techniques, also defined as all-round coating techniques. It is not excluded that all six surfaces of the panel, namely the two major surfaces and the four side edges, are provided with only one one piece separate decoration material, that at the same time forms the edging material.

[0040] The present invention also aims at manufacturing techniques for panels having reduced weight. The inventive techniques relate to methods for manufacturing a panel, wherein it is started from a material mass containing at least particles and binding agent, wherein said material mass is pressed to form a continuous or discontinuous plate shaped substrate. The particularity of the method of the invention lays in one or a combination of two or more of the following characteristics:

• the characteristic that material is removed from at least one major surface of said plate shaped substrate in order to form recessed portions in said major surface and that the removed material is recovered for forming the material mass of similar panels, hereinafter called the first possible characteristic;
• the characteristic that material is removed from at least one major surface of said plate shaped substrate in order to form recessed portions in said major surface and that said material removal is at least executed by punching holes extending through the total thickness of said substrate, hereinafter called the second possible characteristic;
• the characteristic that material is removed from at least one major surface of said plate shaped substrate in order to form recessed portions in said major surface and that said material removal is performed subsequent to, but in line with said pressing, hereinafter called the third possible characteristic.

[0041] According to a variant the particularity of the method of the invention lays in the characteristic that material is removed from said material mass preceding a pressing stage in order for said plate-shaped substrate to have recessed portions in at least one of its major surfaces and that the removed material is recovered for forming the material mass of similar panels. Preferably said pressing stage at least leads to a doubling of the density of said material mass.

[0042] It is known that in a manufacturing method for plate shaped substrates material comprising particles and binding agent, such particles can be gained from larger resources, such as wood logs or other wood parts, by breaking, grounding and/or refining such resources to the desired dimension of the final particle, e.g. to the dimension of a fiber. After reaching the desired dimension glue is added to the particle and a material mass of glued particles, to be pressed, is formed It is clear that glue could be added before, while or after said material mass is composed, but preferably before any pressing has been performed. As a glue preferably a melamine and/or ureum containing glue is used such as melamineformaldehyde (MF), ureumformaldehyde (UF) or melamineureumformaldehyde (MUF). According to a variant a glue on the basis of isocyanate can be used, such as methyleendiphenyldiisocyanate (MDI).

[0043] According to the first preferred characteristic or said variant, the removed material can be reintroduced in the manufacturing method for forming the plate shaped substrate, by reintroducing it into the particle generation equipment, such as into the breaker, grounding equipment and/or refiner. Preferably it is reintroduced into the breaker, such that the obtained particles are provided with an additional amount of glue.

[0044] According to the third preferred characteristic removal of the material is performed in line with said pressing. Such set-up leads to a very flexible manufacturing method, that minimizes logistic costs for possibly reintroducing the removed material into the breaker, grounding equipment and/or refiner, such as is possible with a method conforming to said first preferred characteristic.

[0045] It is clear that the punching technique, according to said second preferred characteristics, is very interesting for the reasons already mentioned.

[0046] Preferably the plate shaped substrate, after it has been pressed, and before said material is removed has a substantially flat major surface. It is possible that operations are performed on the plate shaped substrate material after pressing, but before the material of the recessed portions is removed, such as one or more grounding operations, e.g. using abrasive paper belts.

[0047] Preferably the pressed plate shaped substrate comprises the substrate material of a plurality of panels, such that a dividing operation is needed for obtaining the final panels. Such dividing operation can for example be performed by using one or more sawing operations. Preferably the formation of the recessed portions takes place on the plate shaped substrate before it is being divided into the substrate material of the final panels.

[0048] Preferably the material of the recessed portions is removed by means of a digitally steered process. Preferably such process allows realizing the recessed portions according to a predetermined pattern. Such pattern can for example be determined by an order of a plurality of panels, wherein the substrate material of these panels is obtained from the same plate shaped substrate. Such pattern can further be determined such that none or only a minor number of the recessed portions are present at the edge of the substrate material. Preferably said pattern is determined such that the recessed portions are only formed internally in a plurality or all of the final panels to be obtained from the same plate shaped substrate.

[0049] Preferably use is made of so-called two dimensional nesting algorithms for calculating the position of all panel's substrate material on a larger plate shaped substrate such that the plate shaped substrate is optimally used. Any unused material of the plate shaped substrate can, comparably to the removed material of the recessed portions, be reintroduced into the particle generation equipment.

[0050] In the case a facing layer is present on the final panel, such facing layer or part thereof can either be applied to the substrate material, while this material forms still part of a larger plate shaped substrate, or be applied thereto, while the substrate material has about or exactly its final dimensions.

[0051] It is clear that the recessed portions and/or through holes as abovementioned with respect to the first and/or second aspect of the invention can be of any shape. They can have a constant cross-section, as would be the case with cylindrical portions, or changing cross-section, as would be the case with pyramidal portions. In general the cross-section of the recessed portions and/or through holes can define any area, ranging from circular, polygonal, such as triangular, square, rectangular, hexagonal, to irregular shape. The recessed portions and/or through holes can either be all of the same size and/or shape or either have one or more different shapes and/or sizes. The shape and/or size of the recessed portions and/or through holes can be altered in order to obtain an optimal weight reduction, while maintaining strength and/or screw holding capacity, where desired The recessed portions and/or through holes can have different layouts, either regular or irregular. They may be arranged in arrays, aligned on rows and/or columns, alternated or in any regular or irregular configuration.

[0052] It is further clear that the recessed portions and/or through holes as abovementioned with respect to the first and/or second aspect of the invention can be produced on one or both major surfaces of the substrate material, either in a single operation or in a sequence of operations. Through holes can be produced in a single operation, e.g. by removing material starting from one major surface all through the thickness of the substrate, or in several operations, e.g. by removing material at both major surfaces until the thus formed recessed portions meet in the depth of the substrate material. In this latter case the recessed portions at both major surfaces do not necessarily need to have the same shape and/or position, as long as they cooperate to form a through hole at least over a portion of their cross-section. It is noted that said recessed portions and/or through holes can be realized before, after or during the attachment of said facing layer to the respective major surface.

[0053] It is noted that according to preferred embodiments of the invention according to its first and/or second aspect it is possible to obtain a sandwich panel, where the thickness of the panel is defined by a composition of more than one layer of wood based panel and possible adhesive connections, wherein the substrate material is a wood based material with reduced average density, wherein said density reduction is obtained by removing material to form said recessed portions. The substrate material in itself may or may not be composed of several of said wood based panel layers. Preferably at least the facing layer comprises such wood-based panel layer. Preferably said facing layer further comprises a separate decoration layer.

[0054] It is clear that the invention primarily is meant for panels having a substrate material comprising glued and pressed wood particles, such as chipboard, OSB, MDF, HDF or LDF. According to variants of the invention according to its first aspect, the invention, instead of being applied to a panel the substrate material of which comprises glued and pressed particles, is applied to a panel the substrate material of which comprises one or more layers of wood, such as a panel having a substrate material consisting of solid wood, glued and pressed layers of wood, plywood, LVL (Laminated Veneer Lumber) or similar. It is clear that several preferred embodiments of the first aspect of the invention can be applied, mutatis mutandis, to panels having a substrate material comprising one or more layers of wood.

[0055] With the intention of better showing the characteristics of the invention, in the following, as an example without any limitative character, several preferred forms of embodiment are described, with reference to the accompanying drawings, wherein:

• figure 1 gives a perspective view of a panel according to the invention;
• figure 2 represents a cross-section according to the line II-II as represented in figure 1
• figures 3 and 4 are views similar to that of figure 2, but illustrating variants;
• figure 5 represents a cross-section according to the line V-V as represented in figure 2;
• figures 6 to 12 are views similar to that of figure 5, but illustrating variants;
• figure 13 represents a cross-section according to the line XIII-XIII as represented in figure 12;
• figure 14 is a view similar to that of figure 5, but illustrating a variant;
• figure 15 represents a cross-section according to the line XV-XV as represented in figure 14;
• figures 16 and 17 are view similar to that of figure 2, but illustrating variants;
• figure 18 schematically illustrates a method according to the invention;
• figure 19 gives an enlarged view on the area indicated as F19 on figure 18.

[0056] Figure 1 shows a panel 1, that could be used as a furniture panel.

[0057] As illustrated in figure 2 the panel 1 comprises a substrate 2 having two major surfaces 3-4, wherein a facing layer 5 is provided at at least one of said major surfaces 3-4. In this case the facing layer 5 has been applied on both major surfaces 3-4 of the substrate 2. The substrate 2 comprises glued and pressed wood particles, in this case glued and pressed wood fibers that form a Low Density Fiberboard (LDF). The substrate 2 comprises a plurality of portions 6 recessed with respect to an edge portion 7. It is clear that the recessed portions 6 make up for a substantial part of the volume of the panel 1, in this case at least 10 percent of the total volume of the panel 1. It is remarked that said substrate material 2 is made in one piece of the same material, namely said LDF board material.

[0058] In the example the recessed portions 6 comprise holes that extend through the complete thickness T1 of the substrate material 2. The major surfaces 3-4 of the substrate material 2 are substantially flat and at the same level as an essential edge portion 7, in this case at the same level as the entire edge 7, with the exception of said recessed portions 6 of the substrate material 2.

[0059] The presence of recessed portions 6 or through holes at the edge 7 of the substrate material 6 is avoided in the embodiment of figure 2. The edge portion 7 of the substrate material 2 is available at the edge 8 of the panel 1 to substantially form the edge contour of the panel 1. Said edge 8 of the substrate material 2 has been provided with an additional edging material 9, in this case a so-called ABS edging material 9. From the drawings it is clear that said substrate material 2, at said edge portion 7, has a thickness T1 amounting to at least 70 percent of the total panel thickness T. Said edging material 9 covers the entire thickness T1 of the substrate material 2, and, in this case, also the thickness T2 of both facing layers 5. It is possible to make the facing layer 5, or the separate decoration 10, extend over the edging material 9. In any case, said edging material 9 preferably extends over the side edge 8 of the panel 1 at least for the majority of the thickness T of the panel 1.

[0060] In the example a facing layer 5 has been applied at both major surfaces 3-4 of the substrate material 2. In this case similar facing layers 5 have been applied at both major surfaces 3-4 of the substrate material 2. It is clear that this is not necessarily the case. In this case, both facing layers 5 comprise a basic layer 11 that has been provided with a separate decoration 10. The basic layer 11 consists of a 1 to 4 millimeter thick HDF board material and the separate decoration 10 comprises a melamine impregnated décor paper. The facing layers 5 extend over some, in this case over all, recessed portions 6, such that the relevant recessed portions 6 are hidden to the user.

[0061] Figure 3 shows an example where the recessed portions 6 are formed as excavations, i.e. not extending through the complete thickness T1 of the substrate material 2. Figure 3 further illustrates that in such case, the non-recessed major surface 4 of the substrate material 2 makes a basic structural layer of the facing layer 5 adhered thereto superfluous.

[0062] Figure 4 gives an example where the separate decoration 10 of the facing layer 5 in one piece extends over at least one of the side edges 8 of the panel 1, thereby also forming the additional edging material 9 that extends over the edge contour of the substrate material 2. In such an embodiment a finish foil, or thermoplastic foil can conveniently be used. For example a PVC foil applied using a vacuum press allows for adherence around rounded edges of such panel 1, such as over the rounded edge 12 illustrated here.

[0063] The examples make clear that special embodiments of the invention can be defined as sandwich panels having one single substrate layer 2 and two surface layers 11 applied on opposite major surfaces 3-4 of the substrate layer 2, wherein these surface layers 11 are part of or form the facing layers 5. It is clear that such sandwich panels 1 could be formed according to several variants, such as by using a substrate layer 2 produced by combining several core layers and/or by using one or more surface layers 11 produced by combining several layers.

[0064] Figure 5 illustrates an embodiment where the recessed portions 6 have a circular cross-section. It is clear that such recessed portions 6 could extend through the entire thickness T1 of the substrate material 2 or not. In this example all recessed portions 6 have the same cross-section and are arranged in an array.

[0065] Figure 6 illustrates an embodiment wherein the recessed portions 6 have an arrangement wherein the position of recessed portions 6 in adjacent rows is offset. This arrangement allows for a larger material and weight consumption.

[0066] Figure 7 shows a variant wherein the arrangement comprises at least two recessed portions 6 with different cross-sections. In this case a large and small circular cross-section. This arrangement allows for a still larger material and weight consumption.

[0067] Figure 8 shows an embodiment wherein the recessed portions 6 have a polygon cross-section, in this case a square cross-section.

[0068] Figure 9 shows an embodiment wherein the recessed portions 6 have a triangular cross-section.

[0069] Figure 10 shows an embodiment wherein the recessed portions 6 have a rectangular cross-section.

[0070] Figure 11 shows an embodiment wherein the recessed portions 6 have an elongated cross-section. In this case the longitudinal direction L1 of the elongated cross-section is aligned with a main direction of the panel 1 or substrate material 2, in this case with the longitudinal direction of the panel 1 or substrate material 2.

[0071] It is clear that the arrangements and/or shapes of the recessed portions 6 illustrated in the preceding drawings could be used either for holes extending through the entire thickness T1 of the substrate material 2 or for excavations having a depth smaller than the thickness T1 of the substrate material 2.

[0072] Figure 12 shows an embodiment where recessed portions 6 have been formed starting from both major surfaces 3-4 of the substrate material 2. The recessed portions 6 at both major surfaces 3-4 comprise portions 6 with an elongated cross-section. The longitudinal direction L1 of said portions 6 at one major surface 3 are oriented at an angle, in this case perpendicularly, with the longitudinal direction L2 of said portions 6 at the other major surface 4.

[0073] Figure 13 shows that the respective recessed portions 6 meet in the depth of the substrate material 2 to form a through hole over a portion of their cross-section.

[0074] Figure 14 shows an embodiment where the recessed portions 6 conveniently have been realized by several saw cuts 13. Figure 15 shows the same recessed portions 6 in a cross-section.

[0075] Figure 16 shows an embodiment where the recessed portions 6 have a cross-section that changes in the depth of the substrate material 2. In this case the cross-section diminishes as depth increases.

[0076] Figure 17 gives another example where the recessed portions 6 have a changing cross-section. In this case the recessed portions 6 are formed by two cylindrical portions formed at opposite major surfaces 3-4, that meet in the depth of the substrate material 2.

[0077] It is clear that also figure 12 and 13 formed an illustration of recessed portions 6 having such changing cross-section.

[0078] Figure 18 illustrates a method according to the invention. In the example, this relates to a method which is performed by means of a production line 14, which substantially corresponds to a typical LDF, MDF or HDF production line. Herein, it is started from a material mass 15, which, in a preceding step S0, has been composed at least by means of two components. In this case, both components together are supplied to a strewing machine 16, in the form of wood particles previously provided with binding agent, more particularly wood fibers 17 provided with polycondensation glue. The wood particles have been obtained using particle generation equipment 18, such as breakers, grounders and/or refiners. It is clear that such particle generation equipment 18 is illustrated here in a purely schematic way.

[0079] The strewing machine 16 of such production line 14 may be constructed in any manner. In the example, a strewing machine 16 is applied such as the one known from WO 03/053642. The strewing machine 16 of the example is provided with a plurality of agitating elements 19, which put the wood fibers 17, which are provided with glue, in motion in the strewing chamber 20. By means of the fibers 17 exiting the strewing chamber 20 at the bottom, the material mass 15 to be pressed is composed on the transport conveyor 21 situated there below. For a further description of such strewing machine, reference is made to the aforementioned international patent application. Of course, other types of strewing machines are also suitable, such as, for example, the strewing machines described in the international patent applications WO 99/36623 and WO 2005/044529.

[0080] Seen in flow direction, a so-called scalpel roller 22 is situated after the strewing machine 16, which roller 22 removes possible excess wood fibers 17 from the composed material mass 15, after which then a material mass 15 having a flat or virtually flat upper surface is obtained. It is noted that it is not mandatory to work with such scalpel roller 22.

[0081] The material mass 15 obtained by strewing may have a thickness T3 which is up to 50 times or more larger than the thickness T1 of the finally to be obtained board or substrate material 2, as it is pressed, in one or more densifying steps S1-S2, until this required thickness T1 of the board or substrate material 2 is achieved. During these densifying steps S1-S2, the material mass preferably experiences at least a doubling of its density. These further densifying steps S1-S2 are also represented schematically here.

[0082] In flow direction after said scalpel roller 22, there is a densifying device or pre-press 23, in which the material mass 15, prior to the actual hot pressing in step S2, gradually is densified to a condition in which it can be transported in a simpler manner compared to the un-densified material mass. To this aim, the material mass 15 during step S1 preferably, as represented here, is transported between pressing conveyors 24, wherein these pressing conveyors 24 show an intermediate distance which decreases in flow direction. In this pre-densification in the pre-press 23, preferably no heat is supplied and/or, preferably, the present binding agent is not yet or only partially activated. Mainly, the pre-densification preferably aims at an at least partial removal of the gasses, such as air, present in the material mass 15.

[0083] After the densifying device or pre-press 23, seen in flow direction, the actual press device 25 is situated, in which the material mass 15, whether or not already pre-densified, is pressed under the influence of heat. The applied temperature may be situated, for example, between 100°C and 150°C, and the applied pressure may be situated on average between 4 and 10 bar; however, short peak pressures up to 40 bar are not excluded herein. Preferably, the activation of the binding agent present substantially is performed in this press device 25. In the case of a polycondensation glue, water or rather steam may be created in this press device 25.

[0084] The press device 25 illustrated here is of the continuous type, namely, of the type in which the material mass 15 is transported and/or gradually pressed between pressing conveyors 26. In flow direction of such press device, a pressure and/or temperature course can be set. By means of this press device 25, the density of the already partially densified material mass 15 may at least be doubled. It is clear that the method of the invention can be performed by other press devices 25, too, such as, for example, by a steam pressure device, by a multi-stage press or by a so called short-cycle press. In these other press devices, the applied pressure and/or temperature can be set in function of the time that the respective material mass will remain in the press device.

[0085] In the example a continuous plate shaped substrate 27 is formed. Subsequent to and in line with said pressing S1-S2, material 28 is removed from at least one major surface 3-4 of said plate shaped substrate 27 in order to form recessed portions 6, in this case holes extending through the complete thickness T1 of the plate shaped substrate 27. The removed material 28 is recovered and introduced in the particle generation equipment 18. The recovered particles from the removed material 28 is used to form the material mass 15 of similar plate-shaped substrates 27.

[0086] According to the present example embodiment of the invention the material removal is executed by punching holes through the total thickness T1 of the plate shaped substrate 27.

[0087] Figure 19 illustrates that such through holes can be punched by a mechanical operation of perforation. Such mechanical operation is known per se in other technical fields, such as in the field of metal working. The perforation tool 29 comprises a punch 30, a stripper 31 and a die 32. The substrate material 2 is sheared by pressing the punch 30 through the substrate 2 into the die 32, and the substrate 2 is punctured. The stripper 31 contacts the substrate 2 while it is being punched, to hold it, and/or to limit the motion of the substrate 2 when the punch 20 is retracted from the die 32. The removed material 28 is scrap, and as illustrated in figure 18, can be reintroduced into the particle generation equipment 18. The punch 30 and die 32 work together to obtain a hole with a good surface quality and with the desired shape. Preferably a clearance is available between the punch 30 and the die 32, to ensure a clean cut.

[0088] Punching tools 30, if several are available, can be controlled one by one, in groups or simultaneously for all of the perforation tools 29. Stripper devices 31, if several are available, can be controlled one by one, in groups or simultaneously for all of the perforation tools 29.

[0089] Punching operation has the advantage of being very fast and reliable, compared e.g. to drilling. Punching operations can be operated in sequences or as a single operation. Some examples of possible operations and sequences are given here below.

[0090] As a first example the holes desired in the substrate material of one panel can be realized one by one. Hereby it is meant that the material removal is at least performed by a tool that operates in sequence on different areas of the plate-shaped substrate. The tool is moved across the substrate from one position to another, where a hole is to be formed. Of course it is also possible to move the substrate instead of the tool, or in combination with the tool movement.

[0091] As a second example the holes desired in the substrate material of one panel can be realized in groups. Hereby it is meant that the material removal for the holes is at least performed by two or more tools that operate in line on one axis, or in groups with various configurations, and by moving in sequence the plate-shaped substrate or the two or more tools together or both the substrate and the tools from one position to another, where a series or group of holes is to be formed. This second example preferably allows to use or not use some of the tools out of said two or more tools, one by one, to avoid producing holes in some part of the plate-shaped substrate, e.g. to increase local strength of the final product.

[0092] As a third example the holes desired in the substrate material of one panel can be realized all at once. Hereby it is meant that the material removal for the holes is performed by operating in the same step all of the tools to form all holes in the plate-shaped substrate material. Preferably, in such case, a generic tool array is used that allows selectively operating the tools, such that holes formed in some parts of the substrate material can be avoided upon desire.

[0093] As illustrated in figure 18 the material removal for the recessed portions 6 is preferably performed while the plate-shaped substrate 27 is still in the form of a continuous stretch of material. It is not excluded that some or all recessed portions 6 are realized, after the continuous stretch of plate-shaped substrate material 27 has been divided into plates. It is noted that in the former case, it could be desirable to have the material removal tools move at the same speed or similar speed as the continuous stretch of material, for example in the case of perforation tools 29. It is further noted that in the latter case the plates of substrate material 2 can be at standstill while the material removal for creation of the recessed portions 6 is performed.

[0094] It is clear that, according to the invention, it is not excluded that one or more of said recessed portions 6 or through holes are filled with a material that is lighter than the original board material, for example with a foamed material. Preferably, however, a weight reduction of at least 10 percent of the panel is still attained. It is further clear that, according to preferred embodiments of the invention, said recessed portions 6 are voids, that are filled with air only.

[0095] It is further clear that a method according to the variant named in the introduction could be attained by removing from the material mass 15 before the material mass 15 enters the densifying device or pre-press 23, and/or after the material mass 15 has exited the densifying device but before entering the actual press device. In any case preferably a doubling of the density of the material mass 15 is still performed after the removal of the relevant material. It is noted that such embodiment offers the advantage that the binding agent in the removed material 28 has not cured completely, such that the particles recovered from the removed material 28 retain their original binding activity to a substantial degree. This is for example important when the binding agent undergoes an irreversible curing reaction, such as is the case with thermosetting binding agents. According to this variant the material is preferably removed after the scalpel roller 22, if such is available. Starting from a flat composed material mass 15 is beneficial for the quality of material removal.

[0096] According to a further variant instead of removing material from the material mass 15, said material mass 15 can be composed to have recessed portions or holes. Such can be obtained for example by using a structured transport conveyor 21 or other core parts that, preferably temporarily, fill and/or form voids at least while the material mass 15 is being composed. Such method is not illustrated here, but does belong to the scope of the invention.

[0097] The present invention is in no way limited to the above described embodiments, but such panels and methods could be performed according to several variants without leaving the scope of the present invention.

Claims

1. Panel comprising a substrate (2) having two major surfaces (3-4), wherein a facing layer (5) is provided at at least one of said major surfaces (3-4), wherein said substrate (2) comprises glued and pressed particles, characterized in that the substrate (2) at at least one of said major surfaces (3-4) comprises a plurality of portions (6) recessed with respect to an edge portion (7) of the respective major surface (3-4), and in that the recessed portions (6) make up for at least 10 percent of the total volume of the panel (1).

2. Panel according to claim 1, characterized in that said facing layer (5) is provided at least at said major surface (3-4) that comprises the recessed portions (6).

3. Panel according to claim 1 or 2, characterized in that said particles are wood particles.

4. Panel according to claim 3, characterized in that said substrate (2) comprises wood fiberboard having a mean density lower than 600 kilograms per cubic metre.

5. Panel according to any of the preceding claims, characterized in that said facing layer (5) extends over a plurality of said portions (6).

6. Panel according to any of the preceding claims, characterized in that said facing layer (5) is composed of a basic, preferably structural layer (11) and a separate decoration (10).

7. Panel according to claim 6, characterized in that said basic layer (11) comprises a 1 to 4 millimeter thick wood-based sheet.

8. Panel according to claim 6 or 7, characterized in that said basic layer (11) comprises a plurality of material sheets bounded together.

9. Panel according to any of claims 6 to 8, characterized in that said separate decoration (10) is a printed or colored material sheet.

10. Panel according to any of the preceding claims, characterized in that said recessed portions (6) comprise holes that extend through the complete thickness (T1) of said substrate (2).

11. Panel according to any of the preceding claims, characterized in that a facing layer (5) is applied on both major surfaces (3-4) of said substrate (2).

12. Panel according to any of the preceding claims, characterized in that said substrate (2) is made in one piece in the same material.

13. Method for manufacturing a panel, wherein it is started from a material mass (15) containing at least particles and binding agent, wherein said material mass (15) is pressed to form a continuous or discontinuous plate shaped substrate (27), characterized in that material is removed from at least one major surface (3-4) of said plate shaped substrate (27) and/or from said material mass (15) in order to form recessed portions (6) in said major surface (3-4) and that the removed material (28) is recovered for forming the material mass (15) of similar panels (1).

14. Method for manufacturing a panel, wherein it is started from a material mass (15) containing at least particles and binding agent, wherein said material mass (15) is pressed to form a continuous or discontinuous plate shaped substrate (27), characterized in that material is removed from at least one major surface (3-4) of said plate shaped substrate (27) in order to form recessed portions (6) in said major surface (3-4) and that said material removal is at least executed by punching holes extending through the total thickness (T1) of said substrate (2).

15. Method for manufacturing a panel, wherein it is started from a material mass (15) containing at least particles and binding agent, wherein said material mass (15) is pressed to form a continuous or discontinuous plate shaped substrate (27), characterized in that material is removed from at least one major surface (3-4) of said plate shaped substrate (27) in order to form recessed portions (6) in said major surface (3-4) and that said material removal is performed subsequent to, but in line with said pressing (S1-S2).

Drawing