RU2830892C2 - Slab and floor panel based on such slab - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: group of inventions relates to sheet material and a floor panel based on sheet material. Sheet material with at least two layers of material, besides, the first layer of material forms more than half of thickness of sheet material and consists of wood particles glued by means of the first binding substance and pressed. First binder is thermosetting. Second layer of material is present on the surface of the said sheet material and consists of dispersed particles glued by means of the second binder and compacted. Second binder is thermoplastic and is selected from polyvinyl butyral, wherein the dispersed particles are coated with a thermosetting binder before gluing and pressing.

EFFECT: improved sound insulation.

27 cl, 9 dwg

Description

The present invention relates to a sheet material and to a floor panel based on said sheet material.

More particularly, the invention relates to sheet materials that can be used to provide imitation floor panels. Floor panels of this type are known per se. For example, laminated floor panels with a core made from a wood fibre board, such as MDF or HDF (Medium or High Density Fibreboard), are known from WO 97/47834. Laminated floor panels of this type comprise a top layer based on one or more sheets of paper impregnated with melamine resin, including a sheet of paper with an imprint, which contains, for example, a printed image of a wooden floor panel. The imprint is protected by a transparent wear layer, which is also made from a sheet of paper impregnated with melamine, or a so-called overlay. It is well known that in the laminated floor panels of the prior art, during their use, unwanted sounds, such as sounds having a knocking character, can occur. Such sounds can be annoying and give away the fact that this is just an imitation of, for example, real wooden parquet, despite the fact that the appearance of such panels is hardly distinguishable from the latter. In addition, the use of melamine resin in the top layer can lead to the development of residual tensile stresses in the top layer. Therefore, strict requirements must be imposed on the base. For example, on the surface of a conventional MDF or HDF board, it is necessary to form a maximum density that can withstand high tensile stresses in the top layer. This maximum density can limit the risk of cracks in the top layer in the event of an impact.

It should be noted that in the standard production of MDF or HDF, the said maximum density near the surface occurs as a result of uneven heating of the pressed carpet of glued wood fibers. The fibers located near the heating elements, namely, on both surfaces of the pressed carpet of fibers, harden faster than the fibers that are in the center of the carpet of fibers. As a result, uneven compaction occurs. The present inventors currently believe that this maximum density in solid MDF or HDF material leads to the occurrence of sounds in the frequency range that is perceived as irritating.

It should be noted that the above-mentioned laminated panels are in practice usually produced by means of the so-called DPL process ("Direct Pressure Laminate"). Here, a stack is formed with a core and the required sheets of impregnated paper to form the top layer and an optional stabilizing layer on the underside of the panel. This stack is then fixed in a hot pressing operation using a short-cycle press and the resin present is cured. Optionally, a structure can be provided on the surface of the panel, if the press in question is equipped with a press structure element. The presence of the mentioned maximum density on the surface of the MDF or HDF core can lead to problems during pressing, in particular when it is necessary to form relatively deep structure elements, for example structure elements with a depth of 0.2 mm or more and/or a depth exceeding the thickness of the top layer, as is the case with WO 2006/066776.

In the meantime, there are currently alternatives to laminated floor panels on the market which, among other things, produce a more acceptable sound. Examples of this are floor panels with a thermoplastic top layer and/or a flexible plastic core, such as described in WO 2011/077311 or WO 2011/141849.

Also, for example, from WO 03/016655, possibilities are known for dampening sounds of a tapping nature with laminated floor panels to some extent by laminating an additional sound-damping layer in a position under the decorative layer having an imprint. This solution ensures the formation of a quieter sound, but the sound remains unnatural. In addition, the presented solution has reduced impact strength. The relatively fragile laminate layer can actually crack when, upon impact, it follows the deformation of the underlying softer sound-damping layer. The method for producing panels according to WO'655 is time-consuming, since the sound-damping layer must be glued to the base separately.

WO 2010/088769 discloses paper sheets for the production of laminated floor panels intended for impregnation with polyurethane, and WO 2010/006409 discloses a sheet material in which wood fibres are bonded by means of a binder based on isocyanate and polyol. The costs associated with the production of panels according to WO'769 or WO'409 are high, and the properties of the sheet material according to WO'409 may not be suitable for the production of a laminated floor covering for a floating floor.

In document EP 1 847 385 B1, in order to provide improved water resistance, a sheet material with three layers of material is presented, wherein the central layer of material consists of wood chips or wood fibres glued together by means of a first binder and pressed, and wherein on both sides of the sheet material there is a second or third layer of material, which consists of a so-called WPC, i.e. wood-plastic composite material. Said WPC comprises fibrous particles glued together by means of a second binder and pressed, wherein the second binder is an electrically conductive plastic, such as polyaniline or polypyrrole.

The present invention is primarily directed to the development of an alternative sheet material which, according to various preferred embodiments, provides a solution to one or more problems of the prior art sheet material, or floor panels which are based on said sheet material.

To this end, according to its first independent aspect, the invention relates to a sheet material with at least two layers of material, wherein the first layer of material forms more than half the thickness of the sheet material and consists essentially of wood particles glued together by means of a first binder and pressed, wherein the first binder is thermosetting, characterized in that the second layer of material is present on the surface of said sheet material and consists essentially of dispersed particles glued together by means of a second binder and pressed, wherein the second binder is thermoplastic and/or elastomeric or at least contains an essentially thermoplastic and/or elastomeric binder. The inventors believe that when using dispersed particles bonded by means of a thermoplastic and/or elastomeric binder on the surface of the sheet material, which are further bonded by means of heat curing, the sound having a tapping character generated by said sheet material is very similar to the sound of real wood. In addition, the second layer of material ensures the formation of a smooth structure on the surface in question and/or it may have some springback during its deformation in use. The sheet material of this type may additionally have a strength, expressed as IB ("Internal Bond", measured according to EN 319:1993), which is comparable or the same as that of the sheet materials of the prior art. The presence of the mentioned first layer of material is important for this.

Preferably, the thickness of said first layer of material is at least three times greater than the thickness of said second layer of material.

Preferably, said sheet material consists of said two layers of material. Then preferably, said first layer of material forms at least 75% of the thickness of the sheet material, and said second layer of material forms 25% or less of the thickness of the sheet material. According to this embodiment, the first layer of material provides sufficient mechanical strength, while the second layer of material can be provided to form the required sound and/or to simplify the formation of the structure. The inventors believe that the resulting asymmetrical structure of the sheet material does not necessarily lead to the formation of dimensional instability, such as warping. Despite the asymmetrical structure of the material, it is still possible to ensure a symmetrical density profile over the entire thickness of the sheet material.

Preferably, the dispersed particles of said second material layer are or comprise wood chips. Wood chips have internal vascular channels and thus provide a more flexible second material layer than in the case of using wood fibres in the second material layer. Of course, other dispersed particles or a mixture of dispersed particles of different materials can also be used. Thus, for example, ground, preferably hard, plastic and/or rubber can be used as dispersed particles, or ground waste from textiles or carpets can be used. The dispersed particles, in particular wood chips, of the second material layer can be impregnated with a synthetic material, such as glycerin. This is intended to improve the effectiveness of the second binder. The dispersed particles of said second material layer can also be or comprise wood fibres.

Preferably, the wood particles of said first layer of material are wood fibres.

Said first binder is preferably selected from the group comprising melamine formaldehyde, urea formaldehyde, melamine urea formaldehyde, phenol formaldehyde, phenol urea formaldehyde, MDI (methylene diphenyl diisocyanate), pMDI (polymeric methylene diphenyl diisocyanate), thermosetting acrylate resin and a binder obtained by reaction with dextrose, such as, for example, the binder described in EP 2 457 954.

Preferably, the first layer of material has a structure of a wood fibre board material, such as MDF or HDF, namely, in which the wood particles are wood fibres, and more preferably with a first binder selected from the group consisting of melamine formaldehyde (MF), urea formaldehyde (UF), melamine urea formaldehyde (MUF), MDI ("methylene diphenyl diisocyanate") and pMDI ("polymeric methylene diphenyl diisocyanate").

Another independent aspect of the invention relates to a sheet material. The sheet material comprises at least two layers of material, wherein the first layer of material forms more than half the thickness of the sheet material and essentially consists of a mineral sheet, and is characterized in that the second layer of material is present on the surface of said sheet material and essentially consists of dispersed particles glued together by means of a second binder and pressed, wherein the second binder is thermoplastic and/or elastomeric. The sheet material of this independent aspect has the same advantages as the sheet material of the first aspect of the invention. In the absence of incompatibility, the described embodiments of the first aspect of the invention can also be used in this other independent aspect of the invention.

In preferred embodiments of another independent aspect of the invention, the mineral sheet is or comprises magnesium oxide sheet, fibre cement sheet or gypsum board.

In preferred embodiments of another independent aspect of the invention, the mineral sheet comprises a filler, such as wood particles, wood chips or wood fibres.

Preferably, the dispersed particles of said second layer of material have a particle size of 500 μm or more, as expressed by the d50 value measured by laser diffraction granulometry, preferably according to ISO13320 (2009). Dispersed particles of this type provide a more compactible and elastic second layer of material, which has a good ability to absorb and dissipate vibration. Preferably, the particle size, expressed by said d50 value, is less than 3 mm. The d50 value of the dispersed particles is most preferably in the range of 1-2.4 mm.

Said second binder is preferably thermoplastic and is selected from the group comprising polyvinyl butyral (PVB), polyvinyl butyrate, polyvinyl chloride (PVC), polyvinylidene chloride (PVdC), polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), thermoplastic aliphatic polyester such as polylactic acid (PLA), thermoplastic olefin (TPO). The second binder is preferably halogen-free, for example preferably selected from the group comprising polyvinyl butyral (PVB), polyvinyl butyrate, polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET) and thermoplastic polyurethane (TPU). According to the variation, said second binder is elastomeric and is selected from the group comprising synthetic rubber (neoprene), optionally cross-linked polyvinyl butyral (PVB), silicone and natural rubber (polyisoprene).

According to a particular possibility, said second binder is obtained at least partially as a recycled material. For example, said polyvinyl butyral (PVB) can be obtained from glass recycling, more particularly from safety glass recycling.

Preferably, said second binder comprises or contains polyvinyl butyral, more preferably crosslinked polyvinyl butyral. Preferably, one or more of the group comprising epoxy resin, dialdehydes, phenolic resin and melamine resin are used as crosslinking agents.

Polyvinyl butyral (PVB), which can be cross-linked, is produced when, during the production of polyvinyl butyral, not all of the hydroxyl groups of the polyvinyl alcohol react with butyraldehyde. As a result, the polyvinyl butyral (PVB) still contains hydroxyl groups that can be cross-linked by reacting with cross-linkers, resulting in the formation of the elastomer, polyvinyl butyral (PVB).

Preferably, said second binder comprises or contains polyvinyl butyral, more preferably polyvinyl butyral contains plasticizers.

Preferably, the dispersed particles are coated with an adhesive with a thermosetting binder before gluing and pressing. More preferably, this gluing is carried out using melamine formaldehyde, urea formaldehyde, melamine urea formaldehyde, phenol formaldehyde, phenol urea formaldehyde, MDI (methylene diphenyl diisocyanate), pMDI (“polymeric methylene diphenyl diisocyanate”), a thermosetting acrylate resin, or a binder obtained by reaction with dextrose. More preferably, methylene diphenyl diisocyanate (MDI), which contains a polyol or polycaprolactam or other flexible chain extender; or polymeric methylene diisocyanate (pMDI), which contains a polyol or polycaprolactam or other flexible chain extender.

Coating dispersed particles with glue before gluing and pressing them has a number of advantages. The water resistance of the sheet material is improved. Also, the coating with glue prevents peeling during pressing. Thermal curing ensures the formation of internal bonds at the pressing stage, when the second binder becomes thermoplastic.

According to another preferred specific possibility, jointly or not jointly with the specific possibility mentioned, the second layer of material, in addition to the second binder and the dispersed particles, also contains an adhesive fraction, preferably a thermosetting adhesive and/or an adhesive selected from the group consisting of urea formaldehyde, melamine urea formaldehyde, (p) MDI, polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyurethane, an acrylate dispersion or a latex dispersion. If necessary, these thermosetting resins can be emulsified to improve processing. The addition of said adhesive can improve the formation of internal bonds and water resistance, as well as improve the ability of the second layer of material to maintain the pressed structure, for example in the case where the sheet material is used as a base in DPL pressing. As mentioned above, the dispersed particles, in particular wood chips, of the second layer of material can be impregnated with, for example, glycerol. Said impregnation improves the efficiency of the adhesive fraction, as a result of which an acceptable sound can be obtained together with an acceptable formation of internal bonds. Preferably, said second layer of material contains 0.5-5% by weight of such adhesive, more preferably 2-4% by weight.

Preferably, the first and second layers of material are fixed in the course of the same pressing operation and are bonded to each other, wherein, more preferably, the polycondensation moisture formed during the reaction of the first binder is absorbed into the wood fibres. Then, over the entire thickness of the sheet material, a density profile is preferably developed, which in this case has a maximum density near the surfaces. Preferably, one maximum is formed in the material of the first layer of material, whereas the second maximum is formed in the material of the second layer of material. Preferably, the maxima have the same height or almost the same height, for example, the maximum near one surface is no more than 10% higher than the maximum near the other surface. The density between said maxima preferably remains below the level of said maxima. In this way, a symmetrical or almost symmetrical density profile is formed in the new sheet material, similar to the density profile of the HDF sheet material of the prior art. According to the present invention, at least one of the maxima is located in said second layer of material. Since this maximum density is located in a softer material, a sound is formed that has a tapping character, which is very similar to the sound of real wood. The present inventors understand that they can use the non-uniform hardening and compaction that occurs during standard HDF production, with the difference that one of the maximum density is formed in the said second layer of material and, accordingly, produces a less irritating sound. Maintaining the maximum density in the first layer of material on the other surface of the sheet material is advantageous for the strength of the optional connecting means that can be located there. For example, in this high-density material, at least partially, the lower lip of the groove in the tooth and groove connection system can be formed, as a result of which an increased bond strength can be achieved.

According to an embodiment of the first independent aspect or another independent aspect, the sheet material comprises a third layer of material, wherein the first layer of material is located between the second layer of material and the third layer of material, wherein the third layer of material comprises the features of the second layer of material according to any of the embodiments of the first independent aspect of the invention. Such embodiments provide even more improved sound insulation, for example when using the sheet material as a floor covering, more particularly when using the sheet material as a floating floor covering.

According to an embodiment of the first independent aspect or another independent aspect, the surface of the first layer of material has a first color, and the surface of the second layer of material has a second color, wherein the surface of the first layer of material is visible on the surface of the sheet material near the surface of the second layer of material according to a regular or random pattern. According to these embodiments, for example, milling can be performed through the surface of the second sheet material, making a part of the surface of the first sheet material visible. The milling operation can, for example, form letters that make the surface of the first sheet material visible against the background of the second sheet material, or vice versa.

According to a specific independent aspect, the present invention relates to a sheet material with a density profile that has a maximum near both surfaces, and in which the density between said maxima remains below the level of said maxima, characterized in that the first of said maxima is located in a layer of material that contains a thermosetting binder, while the second of said maxima is located in a layer of material that contains a thermoplastic or elastomeric binder. It is obvious that the sheet material according to said specific aspect may additionally have the features of the first independent aspect of the invention and/or its preferred embodiments. Preferably, the density between said maxima remains above 80% of the average density of the sheet material. The average density of the sheet material is preferably at least 550 kg/m³, or more preferably at least 700 kg/m³ or at least 800 kg/m³.

According to the most preferred embodiment of the present invention, according to its first aspect, the sheet material consists of first and second layers of material, and it substantially does not contain additional layers of material. The binder of the first layer of material is melamine urea formaldehyde, and the wood particles in the first layer of material are wood fibers. The first binder constitutes 3-20% by weight of the first layer of material, preferably about 14% by weight. The first layer of material has a thickness that constitutes at least 70% of the thickness of the sheet material. The binder of the second layer of material is polyvinyl butyral (PVB), and the wood particles in the second layer of material are wood chips. The content of polyvinyl butyral (PVB) in the second layer of material is in the range of 10-60% by weight, preferably in the range of 25-50% by weight, or more preferably in the range of 35-50% by weight. The wood chip content in the second layer of material is in the range of 40-75% by weight, or more preferably in the range of 50-65% by weight. Preferably, the second layer of material additionally contains an adhesive fraction. This adhesive fraction can be provided by gluing the wood chips. The ratio of the adhesive content in the wood chips is preferably in the range of 2.5-7.5% by weight, and more preferably in the range of 4-6% by weight, and even more preferably in the range of 2-4% by weight. The adhesive can be, for example, MDI, UF, MUF, or polyurethane. The second layer of material has a thickness that is 30% or less of the thickness of the sheet material.

Based on the composition of the said most preferred embodiment, the inventors have developed a board with an internal bond strength lying in the range of 0.5-1.5 N/mm², and even in the range of 0.7-1.5 N/mm², measured according to EN 319:1993.

The material of the different layers of the plate material according to the first independent aspect is preferably provided in each case by several distribution operations. The method for producing the sheet material according to the first independent aspect itself forms a specific independent aspect of the invention and preferably comprises the following steps:

- optionally, a step of providing an adhesive on the dispersed particles of the second layer of material. For example, wood chips can be mixed and glued with an amount in the range of 2-7% by weight (and preferably 2-4% by weight) of a thermosetting adhesive such as phenol formaldehyde, urea formaldehyde, melamine urea formaldehyde, MDI (methylene diphenyl diisocyanate), polyurethane dispersion or acrylate dispersion;

- a step of providing particles based on a second binder. For example, particles made of polyvinyl butyral (PVB), such as recycled polyvinyl butyral (PVB), can be provided;

- optionally, a stage of mixing dispersed particles in particles of the second binder;

- a stage of applying wood particles of the first layer of material and the first binder to a transport device or a mold. Preferably, wood fibers are applied glued with melamine urea formaldehyde (MUF) or methylene diphenyl diisocyanate (MDI);

- optionally, a stage of compaction of the applied wood particles and the first binder;

- optionally, a step of wetting the already applied wood particles and the first binder, for example with water and/or glue; by means of this, the gluing or formation of internal bonds can be improved;

- a step of applying dispersed particles and particles of a binder of the second layer of material to the applied wood particles and the first binder. This step is preferably carried out on the basis of one or more distribution operations.

- optionally, a wetting step of all applied materials, for example with water and/or glue; by means of this, the adhesion or formation of internal bonds can be improved;

- a compaction and heating step for all applied materials. Preferably, compaction and heating takes place in a two-belt press, preferably only in one two-belt press. Preferably, the material of the first and second material layers is heated and compacted simultaneously. During this same treatment, adhesion between the two material layers is also preferably achieved.

Preferably, a bonded sheet material is obtained, which consists of two layers of material, namely, the said first layer of material and the said second layer of material. The inventors believe that the presence of a second binder of thermoplastic and/or elastomeric nature can ensure the formation of a flat surface during the compaction and heating step. The risk of possible through pressing or transfer of inhomogeneities in the applied layer to the surface of the second layer of material is limited. Compared to the MDF or HDF sheet material of the prior art, less or no sandblasting operations are required to achieve an easily laminated surface. The thermoplastic or elastomeric second binder flows between larger dispersed particles, in particular wood chips, and thus levels the resulting surface.

From the above it is clear that the sheet material according to the invention can be obtained in a single pressing operation, and that separate pressing operations or additional gluing operations are superfluous.

There are various specific embodiments for carrying out the step of applying the dispersed particles and the particles of the binder of the second layer of material to the applied wood particles and the binder of the first layer of material, some notable embodiments of which are listed below, without being an exhaustive list.

According to the first specific possibility, a mixture of glue-treated wood chips and polyvinyl butyral (PVB) particles is distributed through the same distribution operation.

According to the second specific possibility, two separate spreading operations are used. The glue-treated wood chips are spread in the first spreading operation, and the polyvinyl butyral (PVB) particles are spread in the second spreading operation.

According to the third specific possibility, the procedure is the same as in the second possibility, but a third separate spreading operation is added, during which the glue-treated wood chips are spread.

According to the fourth specific possibility, the procedure is the same as in the third possibility, but in the third separate spreading operation, untreated wood chips are spread.

According to the fifth specific possibility, a spreading operation is performed in which granules or a mixture of wood chips and polyvinyl butyral (PVB) are spread.

According to the sixth specific possibility, the procedure is the same as in the fifth possibility, but an additional second separate spreading operation is provided, during which the untreated wood chips are spread.

According to the seventh specific possibility, the procedure is the same as in the sixth possibility, in the second separate distribution operation, the glue-treated wood chips are distributed.

According to an eighth specific possibility, two or more dispensing operations are used, wherein granules or a mixture of wood chips and polyvinyl butyral (PVB) are distributed, wherein the mixtures in the different dispensing operations can optionally have a different composition. The difference in composition can also be expressed by different proportions in percentage by weight between the binder and the particles, and/or by different shapes and/or sizes of the particles of the binder and/or the particles in the different mixtures. According to a first important example of this, the composition of the mixture from the first dispensing operations can be advantageously adjusted to achieve sufficient adhesion to the material of the first layer of material, while the mixture, for example, from the second or subsequent dispensing operations can be adjusted to achieve a smooth surface with a limited risk of through pressing of uneven distribution from the underlying layers onto the surface of the sheet material. According to a second important example of this, the size of the wood chips or dispersed particles of the second layer of material is different, preferably in such a way that among two successive distribution operations, in the first distribution operation, larger wood chips or dispersed particles are applied than in the second distribution operation. According to a third important example of this, the melting temperature of the second binder is different, preferably in such a way that among two successive distribution operations, the first distribution operation has a binder with a lower melting temperature than the second distribution operation.

It should be noted that the combination of different sizes and shapes of mixtures/granules can provide improved sintering, resulting in a sheet material that is more cohesive, for example with internal bonds of 0.7 N/mm² or more. In addition, it should be noted that each of the distributed sublayers of the second layer of material can be produced separately with its own binder to particle ratio, adhesive proportion and particle size distribution.

Although the specific possibilities described above use wood chips as the dispersed particles and polyvinyl butyral (PVB) as the binder, they can, of course, be implemented, accordingly, with other dispersed particles and second binders.

Although the particulate polyvinyl butyral (PVB) or granules/blends have been discussed above, the polyvinyl butyral (PVB), or other second binder, may be prepared in various other ways. For example, the PVB may be finely ground, cut, cold cut, microextruded, micropelletized or granulated as mentioned earlier. Regardless of how the particulate polyvinyl butyral (PVB) is prepared, it preferably has a particle size, as expressed by the d50 value measured by laser diffraction granulometry (ISO13320(2009)), in the range of 0.1-2 mm. The lower end of the range is obtained, for example, by fine grinding, while particles at the upper end of the range may be obtained by extrusion.

In all the specific possibilities mentioned, one or more of the above-described spreading operations can be carried out, as mentioned above, by spraying the already applied material with water and/or glue. The glue can be, for example, MUF, UF, MF, MDI, PVA or PVAc. Water can improve the heat transfer during the compaction and heating stage, resulting in a more cohesive material, i.e. with stronger internal bonds according to EN 319:1993. A similar result can be obtained by spraying with glue.

For the same purpose as in the first independent aspect, according to a third independent aspect, the present invention further relates to a floor panel with a base obtained from a sheet material according to the first independent aspect and/or according to another independent aspect and/or according to said specific independent aspect and/or obtained by means of a method according to the second independent aspect and/or having the characteristic features of one or more preferred embodiments of each of these aspects. It is obvious that said floor panel can form an improved imitation of a real wooden floor panel, since the sound during use strongly resembles the sound of a wooden floor panel, and/or since said floor panel, regardless of the imitation it forms, produces a less annoying sound.

Preferably, the floor panel comprises a decorative top layer, which is applied to the surface of said sheet material, which is formed by said second layer of material. Obviously, in this case, the effect on the produced sound is most noticeable. In addition, this ensures the best way of using the possibility of structuring the second layer of material. Also, in the configuration according to the present preferred embodiment, the effect of reverse springback or the effect of reverse creep after an impact on this layer can be used in the best possible way.

Preferably, said decorative top layer comprises a sheet of paper with an imprint and a transparent or translucent layer applied thereto. Said transparent or translucent layer preferably comprises a synthetic material which is at least heat-curable. A texture and/or structure can be easily applied to said synthetic material, for example based on a heated structural mould or a press element. For said synthetic material, a thermosetting acrylate resin or an unsaturated polyester is preferably used. Said synthetic material is robust and the risk of rupture in the corresponding layer of synthetic material upon impact is limited. This risk is higher in itself than in the laminated floor panels of the prior art due to the presence of said second material layer. The use of said synthetic materials in the top layer allows the second material layer to be softer and/or more resilient than in the case of, for example, a melamine-based top layer. In addition, the second layer of material can have a restorative effect on any nicks formed as a result of an impact on the top layer. The inventors currently believe that any nicks on the surface of the top layer can be completely or partially eliminated by adding said second layer of material to the sheet material. This mainly occurs when the second layer of material contains polyvinyl butyral (PVB) as a second binder and wood chips as dispersed particles. The use of a top layer based on a thermosetting acrylate resin or unsaturated polyester generates much less residual tensile stress than in the case of, for example, a top layer based on melamine resin, as in the case of laminated floor panels of the prior art.

Preferably, said decorative top layer has a relief with structural features that have a depth greater than the thickness of the decorative top layer. Preferably, said structural features form lower edge regions at at least one or more edges of the floor panel, such as chamfered regions. In the case of lower edge regions, whether or not formed in the form of a chamfer, the decorative effect preferably extends to the corresponding upper edge. Preferably, the corresponding upper edge and/or the lower side of the decorative top layer, at the upper edge, is located at a horizontal level that extends below the level of said second material layer. In this way, the second material layer has a strong protection against influences, such as possible penetration of moisture through the joint between the upper edges of adjacent floor panels. The discussed structural features can be obtained at least on the basis of a hot pressing operation by means of a structural press element. During said pressing operation, the synthetic material of the upper layer can be hardened and, optionally, the binder of the second material layer is melted or at least made plastic, as a result of which the second material layer follows the imprinted structure of the upper layer. Also, in combination with the hot pressing operation, the sheet material can have a structure before it is transferred to the pressing operation, for example because the second material layer is locally pressed, for example by means of a mechanical processing operation, and/or because the second material layer is applied to the first material layer unevenly. For example, a technology such as is known per se for MDF or HDF bases from document WO 2017/072657 can be used.

It is obvious that the mentioned decorative top layer may also be of some other type, which does not include the top layer, which comprises a sheet of paper with an imprint and a transparent or translucent layer applied thereto. For example, the decorative top layer may comprise wood veneer, preferably a printed film of synthetic material, such as a printed PVC film with a PVC-based wear layer applied thereto, wherein the imprint is formed directly on the base with a transparent varnish coating applied thereto, such as an acrylic-based varnish coating, or the like.

In general, said decorative top layer may comprise a UV-curable or electron beam (EB)-curable transparent synthetic material, wherein said top layer may comprise a sheet of paper with an imprint or an imprint formed directly on the base.

It is obvious that where the above description refers to a print formed directly on a support, it is not excluded that, before printing it, the support is prepared by means of one or more ground coats or primers. Here, "a print formed directly on a support" means a print which is formed by applying ink or other coloring material in the form of a pattern to a support and, optionally, by applying ground coats and primer layers, preferably by means of a printing process such as rotogravure printing, screen printing or inkjet printing.

It should be noted that based on the present invention, according to one or more of its mentioned aspects, in the MDF or HDF production line of the prior art, an additional layer influencing the sound can be formed, namely the mentioned second layer of material, wherein this layer influencing the sound changes the frequencies of the surface sound, as a result of which the surface imitates the sound of real wood. At the same time, the compressibility of the sheet material is increased, as a result of which more complex and deep surface structures can be applied by means of a standard short-cycle press (single-plate press) and the structural elements of the press. In this way, the imitation of the appearance of a real wooden field can be performed even better. In addition, the inventors believe that the use of the second layer of material according to the invention improves the efficiency (e.g. scratch resistance and wear resistance) of the acrylic-based top layer compared to a top layer of this type applied to an MDF or HDF base. As mentioned above, this is preferably a thermosetting acrylic-based top layer, for example a top layer of the type described in the present applicant's unpublished application BE 2018/5787. Preferably, the top layer, for example a wear layer, which is applied over the printed decorative effect, comprises a thermosetting acrylate resin or a resin based on an unsaturated polyester. Said acrylate resin is preferably cured on the basis of a heat-initiated radical cross-linking reaction. Said curing preferably comprises at least one cross-linking of the double carbon bonds present in the acrylate resin. Said wear layer is preferably obtained on the basis of a mixture of an acrylate resin and a heat-initiating substance or, optionally, a mixture of a heat-initiating substance and a photo-initiating substance. Said thermal initiating substance is preferably an organic peroxide, preferably benzoyl peroxide, lauryl peroxide, ketone peroxide or diacyl peroxide or an initiating substance selected from the list comprising peroxyether, peroxyketal, hydroperoxide, peroxydicarbonate, peroxymonocarbonate and an azopolymer initiating substance. Said mixture preferably contains 0.1-5 parts of thermal initiating substance per 100 parts of acrylate resin, and preferably 0.5-2 parts of thermal initiating substance per 100 parts of acrylate resin. The wear layer can be cured uniformly or almost uniformly over its entire thickness. As mentioned above, heat curing preferably comprises chemical cross-linking, preferably of double carbon bonds present in the acrylate resin. Said decorative effect may comprise a carrier film provided with a synthetic material, such as a sheet of paper, wherein said synthetic material comprises double carbon bonds, for example selected from a list comprising polyurethane, a copolymer with urethane and acrylic groups, acrylate, latex, polyether and polyester, optionally in combination with a cross-linking agent. Alternatively or additionally, synthetic materials without double bonds may also be used, for example polyurethane dispersions.

In the case of a top layer that contains an acrylate resin, an aliphatic acrylate resin is preferably used, and/or the acrylate resin in question can be obtained at least on the basis of a multifunctional acrylate monomer and/or oligomer, such as a six-functional acrylate oligomer, and/or obtained at least on the basis of a monofunctional or difunctional acrylate monomer and/or oligomer, and/or obtained with at least a chemically modified acrylate, such as a fluoroacrylate.

The method for producing coated panels or floor panels with the features of the invention is preferably further characterised in that the panels comprise at least one base made on the basis of a sheet material according to the invention and have a top layer applied thereto, wherein said top layer comprises at least one decorative effect and a transparent or translucent wear layer, and the method comprises at least the following steps:

- a step of applying an acrylate resin containing a heat-initiating substance to said decorative effect; preferably being the acrylate resin described above; and

- a step of at least partially curing said acrylate resin by means of a hot pressing operation for forming at least one part of said wear layer. The pressing operation is preferably performed by means of a short-stroke press, and/or the pressing operation is performed at a temperature lying in the range of 120-220°C and/or under a pressure lying in the range of 10-80 bar. The pressing operation is preferably performed by means of a structural element of the press. Said pressing operation is preferably performed on a package that contains at least a base, a decorative effect and an acrylate resin. The step of applying the acrylate resin to said decorative effect is preferably performed when the decorative effect already forms part of the package that contains at least a base and a decorative effect. Preferably, said decorative effect comprises a carrier film, such as a sheet of paper, and the method further comprises at least the step of providing said carrier film with a synthetic material, such as at least applying a water-based synthetic material or a UV-curable water-based synthetic material to said carrier film. Optionally, the acrylate resin may already be applied to the paper with the decorative effect.

According to a variation of the present invention, the possible compositions of the second layer of material described above can also be used to form the entire thickness of the sheet material, or at least more than half the thickness of said sheet material. Then, according to a fourth independent aspect, the present invention also relates to a sheet material with at least one, and preferably only one, layer of material, wherein this layer of material mainly consists of dispersed particles glued with a binder and pressed, wherein the binder is thermoplastic and/or elastomeric. The inventors believe that a board of this type can be very flexible and can be used or provide a specific application and design freedom, for example, in the manufacture of furniture. Said sheet material can be obtained by means of thermal molding, and, in addition, the obtained sheet material can be easily recycled. The obtained sheet material can have a thickness in the range of 2-20 mm, preferably in the range of 6-15 mm. It is obvious that the material layer in question then preferably forms 50% or more of the thickness of the sheet material, preferably at least 75%, or even more preferably forms the entire thickness or almost the entire thickness of the sheet material.

Preferably, the sheet material according to the fourth aspect of the invention has a decorative top layer which is applied to the surface of the material layer.

According to another variation, the composition of said second layer of material can also be used as a base for a decorative coating material, such as a wrapping material. For this, according to an independent fifth aspect, the invention further relates to a decorative coating material with at least one decorative top layer, which is applied to the surface of the material layer, wherein this material layer mainly consists of dispersed particles glued together by means of a binder and pressed, wherein the binder is thermoplastic and/or elastomeric. In this way, a thin, flexible coating material is formed, for example having a thickness in the range of 1-5 mm, and more preferably in the range of 1.5-3 mm. Said coating material can be formed by means of thermal molding, can be completely waterproof and can be designed with the possibility of processing.

In the context of the fourth and/or fifth aspect, the binder used is preferably polyvinyl butyral (PVB).

Preferably, the dispersed particles used in the context of the fourth and/or fifth aspect are wood chips, preferably with dimensions expressed in d50 values, which are set out in the context of the first aspect. However, wood fibres can also be used as dispersed particles.

Preferably, the dispersed particles used in the context of the fourth and/or fifth aspect are coated with a thermosetting binder before gluing and pressing. More preferably, the adhesive coating is carried out using melamine formaldehyde, urea formaldehyde, melamine urea formaldehyde, phenol formaldehyde, phenol urea formaldehyde, MDI (methylene diphenyl diisocyanate), pMDI (“polymeric methylene diphenyl diisocyanate”), a thermosetting acrylate resin, or a binder obtained by reaction with dextrose. More preferable is the use of methylene diphenyl diisocyanate (MDI), which contains a polyol or polycaprolactam or other flexible chain extender; or the use of polymeric methylene diisocyanate (pMDI), which contains a polyol or polycaprolactam or other flexible chain extender.

According to an important example of the fourth and/or fifth aspect, 35-55% by weight of polyvinyl butyral (PVB) is used as a binder, and 45-65% by weight of wood chips is used as dispersed particles.

It should also be noted that when "internal bond" is mentioned above, the value is defined according to the definition based on EN 319:1993 for resistance to forces normal to the surface of the sheet material.

It should also be noted that the second layer of material mentioned in the previous independent aspects and their preferred embodiments may further comprise additives such as fire-retardant additives, water-resistant additives (e.g. wax, paraffin, etc.), adhesion promoters (e.g. silicic hydrogen-based additives), reinforcing materials (e.g. glass fiber, basalt fiber, etc.), odor imitation substances (e.g. to imitate the smell of natural wood), fillers (such as perlite, glass balls, CaCO3, etc.), coloring agents (e.g. to imitate the thickness of the top layer of veneer). The thickness of the second layer of material is preferably in the range of 0.3-3 mm.

If the sheet material according to the invention is used in a floor panel, for example as in the context of the third independent aspect, this floor panel is preferably provided at least at two opposite edges with a connecting means which ensures the connection of said floor panel at the edges in question with the same floor panel, wherein at the connected edges in question a mutual locking is formed both in the vertical direction perpendicular to the plane of the connected floor panels and in the horizontal direction perpendicular to the edges in question and lying in the plane of the connected floor panels. The connecting means in question is preferably formed essentially in said first layer of material. An optional contact near the upper edge can be formed on said second layer of material. Preferably, said connecting parts are formed essentially as a tooth and a groove which are provided with locking elements which prevent the tooth and the groove from moving away from each other in said horizontal direction. The said locking elements may comprise, for example, a recess limited by a projecting portion on one or both lips that limit the said groove, and a part of a tooth interacting with it. It is obvious that the said locking in the vertical direction is achieved by means of interaction between the tooth and the groove.

As stated in the introduction, the inventors believe that the presence of a density maximum near the surface of the MDF or HDF board is largely responsible for the formation of annoying noise.

Then, as a first alternative to the sheet material and floor panels according to the present invention, it is also possible to sandblast the MDF or HDF board to a level below the maximum density at least on the surface intended for walking on it. This sandblast operation is preferably carried out on both surfaces, as a result of which a stable board is again formed. It is therefore clear, according to the sixth independent aspect, that the present invention also relates to a method for producing floor panels, which method comprises at least the following steps:

- a step of producing a wood fibre board of the HDF type, namely having an average density of at least 800 kg/m³; preferably it refers to a wood fibre board based on wood fibres and UF, MF, MUF or pMDI resin;

- a stage of sandblasting one or both surfaces of the said wood fibre board to a depth of 0.3-1 mm, preferably 0.3-0.6 mm or about 0.4 mm;

- the stage of applying a decorative top layer to at least one of the sandblasted surfaces.

Preferably, the decorative top layer is a wood veneer, preferably printed, a film made of thermoplastic material, or a decorative top layer based on acrylic resin, preferably a thermosetting acrylic resin of the type described in more detail above, inter alia with reference to BE 2018/5787, or a resin based on unsaturated polyester.

Alternatives to acrylic resin include, for example, dual-curing aliphatic acrylate varnish (i.e., an aliphatic acrylate varnish that is cured by a combination of heat and UV curing), solvent-based urethane acrylate varnish, UV-curable or electron beam-curable acrylate varnishes.

Then, as a second alternative to the sheet material and floor panels according to the present invention, it is also possible to produce an MDF or HDF board with a more uniform density profile. This is possible, for example, by preheating the fibre mat before pressing it, for example by means of microwaves. It is therefore clear that, according to a seventh independent aspect, the present invention also relates to a method for producing floor panels, which method comprises at least the following steps:

- the step of providing a carpet of glued wood fibers, preferably glued by means of MF, MUF, UF, or pMDI;

- the stage of heating the said carpet, preferably by means of microwaves, before pressing it;

- a step of pressing said carpet into a fibreboard with an average density of at least 700 kg/m³ and more preferably at least 800 kg/m³;

- a step of applying a decorative top layer to at least one of the surfaces of said wood fibre board. Preferably, the decorative top layer is a wood veneer, preferably printed, a film made of thermoplastic material, or a decorative top layer based on acrylic resin, preferably a thermosetting acrylic resin of the type described in more detail above, inter alia with reference to BE 2018/5787, or a resin based on unsaturated polyester.

In the following, in order to better demonstrate the features of the invention, some preferred embodiments are described, by way of example and without limitation, with reference to the accompanying drawings, in which:

- Fig. 1 shows a floor panel with features of the invention;

- Fig. 2 shows a sectional view taken along line II-II in Fig. 1;

- Fig. 3 shows an enlarged view of the area F3 in Fig. 2, in the connected state of the two mentioned floor panels;

- Fig. 4 shows an enlarged view of the region F4 in Fig. 3;

- Fig. 5 schematically shows some stages of the method for producing sheet material with features of the invention;

- Fig. 6 schematically shows some stages of the method for manufacturing a floor panel with features of the invention;

- Fig. 7 shows an enlarged view of the region F7 in Fig. 5 according to the variation;

- Fig. 8 shows a graph of the density of the sheet material from Figs. 1-4 as a function of its thickness; and

- Fig. 9 shows a sectional view of a sheet material according to one embodiment of the invention.

Fig. 1 shows a decorative panel, more specifically a floor panel 1, according to the invention. The panel 1 is rectangular and oblong and comprises a pair of opposite short edges 2-3 and a pair of opposite long edges 4-5.

In Fig. 1-3 it can be seen that both pairs of opposite edges 2-3-4-5 are provided with a mechanical connecting means 6, which is mainly designed as a tooth 7 and a groove 8, limited by an upper lip 9 and a lower lip 10, wherein the tooth 7 and the groove 8 mainly provide locking in the vertical direction V1, and wherein the tooth 7 and the groove 8 are provided with additional locking elements 11-12, which mainly provide locking in the horizontal direction H1. Preferably, the locking elements comprise a projection 11 on the lower side of the tooth 7 and a recess 12 in the lower lip 10 of the groove, limited by a projecting part 13. The connecting means 6 shown in Fig. 1-3 provides at least a connection by means of a rotational movement W around the corresponding edges 2-3-4-5 and/or a connection by means of a substantially horizontal movement S of the edges 2-3-4-5 to be connected towards each other.

In Fig. 3 it is clearly visible that the decorative panel 1 comprises a base 14 on which a decorative top layer 15 is provided.

A specific feature of the floor panel 1 in Fig. 1-3 is, among other things, that the base 14 is obtained on the basis of a sheet material 16 according to the first aspect of the invention. For this purpose, the sheet material 16 comprises a first material layer 17, which forms more than half the thickness T of the sheet material 16 and consists essentially of wood particles glued by means of a first binder and pressed. In this case, the first material layer 17 has the structure of a conventional HDF board. It is precisely composed of wood fibers 18, glued by means of MUF and pressed.

In Fig. 4 it is clearly seen that the sheet material 16 additionally has a second layer 19 of material on the surface, wherein this second layer 19 of material essentially consists of dispersed particles 20 glued together by means of a second binder and pressed. The second binder in this case is a thermoplastic substance, more specifically polyvinyl butyral (PVB) obtained by processing glass. The dispersed particles 20 are wood chips with a particle size of 500 μm or more, as expressed by the d50 value measured by means of laser diffraction granulometry according to ISO13320 (2009). According to a specific example, the wood chips have the following particle size distribution.

Relative mass Size
(mm)
>3
2.5-3
2-2.5
1.4-2
1-1.4
<1 weight
(G)
21.5
48.5
29.5
189.5
63.5
162.5 Weight
(%)
4,174757
9,417476
5,728155
36,79612
12,3301
31,5534 515 100

The thickness T1 of said first layer 17 of material is at least three times greater than the thickness T2 of said second layer 19 of material.

The sheet material 16 consists of the said first layer 17 of material and the second layer 19 of material, and thus does not have any additional layers of material other than the said first and second layers 17-19 of material. The said decorative top layer 15 is applied to the surface of the sheet material 16, which is formed by the said second layer 19 of material.

Said decorative top layer 15 comprises a sheet of printed paper 21 and a transparent or translucent layer 22 applied thereto. In this case, the transparent or translucent layer comprises a synthetic material which is at least heat-curable, more specifically, here it refers to a thermosetting acrylate resin or an unsaturated polyester, preferably curable on the basis of at least a heat-initiated radical cross-linking reaction.

Fig. 4 shows a sheet of paper 21 with an imprint. Preferably, the core of this sheet of paper 21 is provided with a modified or unmodified melamine resin. On both surfaces of the sheet of paper 21 in this example, a synthetic material is provided that contains double carbon bonds, such as polyurethane. As an alternative to the mentioned polyurethane, for example, a water-based polyurethane dispersion can be used. In addition, as mentioned earlier, a transparent or translucent wear layer 22 is present. In the upper layer 15, in a position above the imprint 23, hard particles 24 are additionally applied, such as aluminum oxide particles, in order to achieve improved wear resistance.

In Fig. 2 and 3 it is clearly visible that the mentioned decorative top layer 14 has a relief with structural features which have a depth exceeding the thickness T3 of the decorative top layer 15. At the edges of at least two opposite sides, the floor panel has lower edge regions 25, in this case in the form of a chamfer. The imprint 23 or decorative effect extends to the corresponding upper edge 26. The lower side of the decorative top layer 15 is in the position of the upper edge 25 at a horizontal level L, which extends under the level of the second layer 19 of material.

Fig. 5 shows schematically a method for producing a sheet material 16 with the properties of the invention. This example relates to a method that is carried out on the basis of a production line 27, which essentially corresponds to a conventional production line for MDF or HDF. In this case, it starts with a mass 28 of material for said first layer of material 17, which in a preceding step S0 is assembled at least on the basis of said first binder and said wood particles. In this case, both components are fed simultaneously to a dispensing machine 29 in the form of wood particles, previously provided with a first binder, namely with a polycondensation adhesive, more particularly wood fibres 18, provided with a polycondensation adhesive, for example MUF.

The distributing machine 29 of said production line 27 may have any design. In this example, a distributing machine 29 is used, which is known per se from WO 03/053642. The distributing machine 29 in this example is provided with several mixing elements 30, which cause the glued wood fibres 18 to move in a distributing chamber 31. Based on the wood fibres 18, which exit the distributing chamber 31 on the lower side, a mass of material 28 is collected on a transport device or conveyor belt 32 located underneath it. For a further description of said distributing machine 29, see said international patent application. Of course, other types of distributing machines can also be used, such as, for example, the distributing machines described in international patent applications WO 99/36623 and WO 2005/044529.

When considered in order, after the distributing machine 29 comes the so-called scalpel shaft 33, which removes any excess wood fibers 18 from the mass 28 of material, after which the mass 28 of material with a flat or almost flat upper surface is obtained. It should be noted that the work with the mentioned scalpel shaft 33 is not essential.

In order, after the mentioned scalpel roller 33 there follows a compaction device or fore-press 34, in which the collected mass of material 28 is gradually compacted, before being fed into the actual hot pressing presses in step S2, to a state in which it can be transported more easily compared to an uncompacted collected mass of material 28. For this purpose, the collected mass of material 28 is transported in step S1, preferably, as shown here, between pressing belts 35, wherein these pressing belts 35 have a gradually decreasing clearance. During this preliminary compaction in the fore-press 34, heat is preferably not supplied and/or, preferably, the first binder present is not activated or only partially activated. In contrast, during the preliminary compaction, at least a partial removal of gases, such as air, present in the collected mass of material 28 is preferably ensured.

After said preliminary compaction has been carried out in step S1, granules 36 are applied to the material mass 28 of the first material layer 17. The granules 36 in question comprise said second binder and dispersed particles 20, in this case polyvinyl butyral (PVB) and wood chips, optionally supplemented with an adhesive fraction, for example pMDI. For this purpose, considered in order, after the distributing machine 29 there follows a device 37 for applying said granules 34 to the material mass 28. In this case, the device 37 carries out the distributing operation. For this purpose, a distributing device such as that known per se from GB 1,003,597 or GB 1,035,256 can be used. As can be seen in Fig. 5, said distributing device may comprise a receiver 38, which is connected to a metering shaft 39, which moves the granules 36 from the receiver 38. Said metering shaft 39 preferably has a structural design, whereby the granules 36 are then captured mainly by means of the lower structural parts of the metering shaft 39. Said distributing device preferably further comprises a device 40, which separates the granules 36 from said metering shaft 39. In this case, a brush device is used for this. Based on said distributing device, a sufficiently uniform distribution can be achieved.

After the compacting device or forepress 34 and the device 37, when viewed in the direction of flow, there is an actual press 41, in which the collected mass of material is pressed under the influence of heat. The temperature used can, for example, be in the range of 100°C - 150°C, and the pressure used can on average be, for example, in the range of 4-10 bar, although short-term maximum pressures of up to 40 bar are not excluded. Preferably, in this press 41, the binder present in the granules 36 is melted or at least heated above its glass transition temperature. Preferably, the activation of the first binder present on the wood fibers 18 also takes place here. In the case of a polycondensation adhesive, water or rather steam can be produced in this press 41.

The press 41 shown here is a continuous press, namely a press of the type in which the collected mass of material is transported and/or gradually pressed between pressing belts 42. When passing through said press 41, a change in pressure and/or temperature can be created. By means of this press 41, the density of the already partially compacted collected mass 16 of material can be at least doubled. It is obvious that the method according to the invention can also be carried out by means of other presses, for example by means of a steam press, by means of a multi-plate press or by means of a so-called short-cycle press. When using these other presses 41, the pressure and/or temperature used can be specified as a function of the time that the mass of material in question spends in the press 41.

From the above it is clear that Fig. 5 is an example of the fifth specific possibility described in the introduction for the stage of applying the dispersed particles 20 and the particles of the binder of the second layer 19 of material. It is obvious that in the production line 27 other specific possibilities presented there can be used by changing the content of the receiver 38 and/or the number of devices 37 according to the required possibility. Preferably, all devices 37 or distribution operations for the second layer 19 of material are located between the forepress 34 and the actual press 41.

Fig. 6 schematically shows some steps of the method for producing a floor panel 1 according to Figs. 1-4. In this example, it starts with a decorative top layer 15, which contains at least one sheet 21 of paper. The sheet of paper 21 is provided with an imprint 23. In a first step S3, the sheet of paper 21, more specifically the paper tape from which the sheet of paper 21 is later obtained by cutting, is provided with a synthetic material 43. For this purpose, the paper tape is unwound and the core is impregnated with a first synthetic material 43. The impregnation of the core can limit the risk of tearing of the sheet of paper 21 in the finished coated panel 1. In this example, this impregnation of the core takes place in two sub-steps, namely, a first sub-step S3A, in which the synthetic material 43 is applied by means of a roller 45, and a second sub-step S3B, in which the sheet of paper 21 is immersed in a bath 46 with a corresponding synthetic material 43. In this example, the synthetic material 43, which is applied in the first sub-step S3A and the second sub-step S3B, are one and the same. However, the synthetic materials applied in the first sub-step and in the second sub-step may also differ from each other, regardless of the actual application technology used. Between the first sub-step S3A and the second sub-step S3B, the paper sheet 21 follows a path 47 that ensures sufficient penetration of the first synthetic material 43 applied in the first sub-step S3A. As the first synthetic material 43, a modified or unmodified melamine-formaldehyde resin, a modified or unmodified urea-formaldehyde resin, or a modified or unmodified melamine-urea-formaldehyde resin may be used.

In Fig. 6 it is further seen that, after the said impregnation of the core, in a third sub-step S3C, aluminum oxide particles 24 can be applied, for example, as in this case, by means of a spreading operation. This is preferably followed by a fourth sub-step S3D of a drying operation in a drying oven 48. Optionally, in a fifth sub-step S3E, an interlamellar coating 44 can be applied to the side of the print 23 and/or to the side of the paper sheet 21 which is intended to face the wear layer 22, which improves the compatibility with the wear layer 22, formed from a thermosetting acrylate resin or an unsaturated polyester. This interlamellar coating 44 can, for example, consist of a water-based polyurethane coating, a water-based substance curable under the action of UV, and/or a carbodiimide. In the same step S3E, or in a separate step, a coating 44 can also be applied to the side of the paper sheet 21 intended to face the base 14. This coating 44 is intended to ensure better adhesion to the base 14. According to another possibility, said coating 44 can also be intended to ensure sound damping. In this case, it is preferable to use a polyurethane, for example an aromatic polyurethane or a thermoplastic polyurethane (TPU). After applying the interlamellar coating 44, as in this example, a drying operation similar to the drying operation in the fourth substep S3D can again be performed.

In the seventh sub-step S3F, the processed paper sheet 21 passes in this example along the cooling roller 49, and the paper web is separated into sheets.

In the second step S5, a package 50 is formed which at least contains a base 14 and a sheet of paper 21 with a print 23 obtained in step S3.

Preferably, the method according to the invention comprises at least a third step S5, namely the step of applying, on top of the print 23 or the decorative effect, an acrylate resin containing a heat-initiating substance, and a fourth step S6, namely the step of at least partially curing said acrylate resin during a hot-pressing operation. In the third step S5, the acrylate resin with the heat-initiating substance is also applied to the lower side 51 of the base 14 to form a stabilizing layer 52. It is obvious that in this case the third step S5, namely the step of applying the acrylate resin, is carried out when the sheet of paper 21 with the print 23 or the decorative effect already forms part of the package 50, which contains at least the base 14 and the decorative effect or the sheet of paper 21 with the print 23.

In the example shown, the pressing operation is carried out using a so-called short-stroke press 53, and more specifically using a structural element 54 of the press or pressing plate. The pressing operation is carried out on a stack 50, which contains a base 14, a sheet of paper 21 with an imprint 23, an acrylate resin of a wear layer 22 and a stabilizing layer 52. During the pressing operation, the structure 55 of the element 54 of the press is copied onto the surface of the wear layer 22.

In Fig. 7 a variation of the device 37 shown in Fig. 5 is shown. Here a device 56 is shown, which comprises one or more devices 37A-37B-37C or dispensing machines that apply dispersed particles, a first binder and/or granules to a transport device, in this case to a conveyor belt 57. The devices 37A-37B-37C shown here are the same as those described in the context of Fig. 5. The collected mass 58 of material for the second layer 19 of material, or a part thereof, is moved, in this case poured, through the conveyor belt 57 onto the mass 28 of material for the first layer 17 of material. It is obvious that using the device 57 shown here several specific possibilities can be implemented, as set out in the introduction for the step of applying the dispersed particles 20 and the particles 59 of the binder of the second layer 19 of material. Preferably, using at least one of the distribution devices, for example the distribution device 37B, wood chips are applied. Using one or more other distribution devices 37A-37C, particles 59 of the first binder can be applied to the conveyor belt 58. Preferably, as shown here, in the direction of passage, a layer of particles 59 of the binder is first applied, then a layer of wood chips and then again a layer of particles 59 of the binder.

It should be noted that the device 57, in which the second mass 58 of material is collected on the conveyor belt 58, can also be used for applying the discussed mass 58 of material onto a pre-formed base, which consists essentially only of the mentioned first layer 17 of material, instead of applying it onto the first mass 28 of material, which still has to be pressed.

Fig. 8 shows a graph with the density of the sheet material from Figs. 1-4 on the ordinate axis and the thickness on the abscissa axis, where the thickness is expressed in mm and the density in kg/m³. The thickness of 0 mm corresponds to the side of the sheet material which is formed by the first layer 17 of material, while the thickness of 8 mm is near the surface formed by the second layer 19 of material. The graph shows an average density of 830 kg/m³, a maximum density P1 near the surface of the first layer 17 of material of 1058 kg/m³ and a maximum density P2 near the surface of the second layer 19 of material of 1033 kg/m³. The graph clearly shows that the sheet material in question has the properties of the specific independent aspect set out in the introduction. Between the mentioned maximum densities P1-P2, the density remains below the level of these maxima, but remains above the level of 80% of the average density. The minimum density is 717 kg/m³ and is achieved at approximately half the thickness of the sheet material.

In Fig. 8 it is clearly seen that a density profile has been achieved which is very similar to the density profile of a standard HDF board, but in which one of the maximum densities P2 is formed in the said second layer 19 of material.

Fig. 9 shows a sectional view of a sheet material according to an embodiment of the invention. The sheet material comprises a base 16 and a decorative top layer 15. The base comprises a first layer of material 17, a second layer of material 19 and a third layer of material 61. The first layer of material 17 is located between the second layer of material 19 and the third layer of material 61. The first layer of material 17 can be made as described with respect to the first layer of material in any embodiment of the invention. The second layer of material 19 can be made as described with respect to the second layer of material in any embodiment of the invention. The third layer of material 61 comprises the features of the second layer of material as described in any of the embodiments of the second layer of material.

The present invention is in no way limited to the embodiments described above, and the said sheet material and floor panels can be made according to various variations without departing from the scope of the present invention.

Claims (27)

1. A sheet material with at least two layers (17-19) of material, wherein the first layer (17) of material forms more than half the thickness (T) of the sheet material (16) and consists of wood particles (18) glued together by means of a first binder and pressed, wherein the first binder is thermosetting, characterized in that the second layer (19) of material is present on the surface of said sheet material (16) and consists of dispersed particles (20) glued together by means of a second binder and pressed, wherein the second binder is thermoplastic and is polyvinyl butyral (PVB), wherein the dispersed particles (20) are coated with a thermosetting binder before gluing and pressing. 2. The sheet material according to claim 1, characterized in that the wood particles (18) of said first layer (17) of the material are wood fibers and preferably said first binder is selected from the group consisting of melamine formaldehyde, urea formaldehyde, melamine urea formaldehyde, phenol formaldehyde, phenol urea formaldehyde, MDI (methylene diphenyl diisocyanate), pMDI (polymeric methylene diphenyl diisocyanate), thermosetting acrylate resin and a binder obtained by reaction with dextrose. 3. A sheet material with at least two layers (17-19) of material, wherein the first layer (17) of material forms more than half the thickness (T) of the sheet material (16) and consists of a mineral sheet, characterized in that the second layer (19) of material is present on the surface of said sheet material (16) and consists of dispersed particles (20) glued together by means of a second binder and pressed, wherein the second binder is thermoplastic and is polyvinyl butyral (PVB), wherein the dispersed particles (20) are coated with a thermosetting binder before gluing and pressing. 4. The sheet material according to claim 3, wherein the mineral sheet is or comprises magnesium oxide sheet, fibre cement sheet or gypsum board. 5. A sheet material according to any one of claims 3, 4, wherein the mineral sheet contains a filler, such as wood particles, wood sawdust or wood fibres. 6. A sheet material according to any of the preceding claims, characterized in that the dispersed particles (20) of said second layer (19) of material are or contain wood chips or wood fibers. 7. A sheet material according to any one of the preceding claims, characterized in that the dispersed particles (20) of said second layer (19) of material have a particle size of 500 µm or more, as expressed by the d50 value measured by laser diffraction granulometry, preferably according to ISO13320 (2009). 8. A sheet material according to any of the preceding claims, characterized in that said second binder comprises or contains cross-linked polyvinyl butyral. 9. The sheet material according to claim 8, wherein the polyvinyl butyral contains plasticizers. 10. The sheet material according to claim 8 or 10, wherein the polyvinyl butyral is cross-linked by means of one or more cross-linking agents, preferably said one or more cross-linking agents comprising one or more from the group consisting of epoxy resin, dialdehydes, phenolic resin, melamine resin. 11. The sheet material according to claim 1, characterized in that the thermosetting binder with which the dispersed particles (20) are coated before gluing and pressing is or contains melamine formaldehyde, urea formaldehyde, melamine urea formaldehyde, phenol formaldehyde, phenol urea formaldehyde, MDI (methylene diphenyl diisocyanate), pMDI (polymeric methylene diphenyl diisocyanate), a thermosetting acrylate resin or a binder obtained by reaction with dextrose, preferably methylene diphenyl diisocyanate (MDI) or polymeric methylene diisocyanate (pMDI), which contains a polyol or polycaprolactam. 12. A sheet material according to any of the preceding claims, characterized in that the thickness (T1) of said first layer (17) of material is at least three times greater than the thickness (T2) of said second layer (19) of material. 13. Sheet material according to any of the preceding claims, characterized in that said sheet material (16) consists of said two layers (17-19) of material. 14. A sheet material according to any one of the preceding claims 1-12, wherein the sheet material comprises a third layer of material, wherein the first layer of material is located between the second layer of material and the third layer of material, and the third layer of material comprises the features of the second layer of material according to any one of claims 1-12. 15. A sheet material according to any one of the preceding claims, wherein the surface of the first layer of material has a first colour and the surface of the second layer of material has a second colour, wherein the surface of the first layer of material is visible on the surface of the sheet material near the surface of the second layer of material according to a regular or random pattern. 16. A floor panel with a base (14) obtained from sheet material (16) according to any of the preceding claims. 17. A floor panel according to claim 16, characterized in that the floor panel (1) comprises a decorative top layer (15) which is applied to the surface of said sheet material (16), which is formed by means of said second layer (19) of material. 18. A floor panel according to claim 17, characterized in that said decorative top layer (15) comprises a sheet (21) of paper with an imprint and a transparent or translucent layer (22) applied thereto. 19. A floor panel according to claim 18, characterized in that said transparent or translucent layer (22) comprises a synthetic material that is at least heat-curable. 20. A floor panel according to claim 19, characterized in that said thermosetting synthetic material is a thermosetting acrylate resin or an unsaturated polyester. 21. A floor panel according to claim 19, characterized in that said thermosetting synthetic material is or contains melamine-formaldehyde resin. 22. A floor panel according to any one of claims 17-21, characterized in that said decorative top layer (15) has a relief with structural elements that have a depth exceeding the thickness of the decorative top layer (15), wherein the relief preferably contains elements with a depth lying in the range of 200-2000 µm. 23. A floor panel according to claim 22, characterized in that said structural elements form lower edge regions (25) on at least one or more edges of the floor panel (1), such as chamfer-shaped regions. 24. A sheet material with at least one layer of material, wherein this layer (19) of material essentially consists of dispersed particles (20) which are glued together by means of a binder and pressed, wherein the binder is thermoplastic and/or elastomeric and said binder is polyvinyl butyral (PVB), wherein the dispersed particles (20) are coated with a thermosetting binder before gluing and pressing. 25. The sheet material according to claim 24, in which at least one decorative top layer (15) is located on the surface of the layer (19) of the material. 26. Sheet material according to any of paragraphs 24, 25, characterized in that the said dispersed particles (20) are wood chips or wood fibers. 27. The sheet material according to claim 24, characterized in that the thermosetting binder with which the dispersed particles (20) are coated before gluing and pressing is or contains melamine formaldehyde, urea formaldehyde, melamine urea formaldehyde, phenol formaldehyde, phenol urea formaldehyde, MDI (methylene diphenyl diisocyanate), pMDI (polymeric methylene diphenyl diisocyanate), a thermosetting acrylate resin or a binder obtained by reaction with dextrose, preferably methylene diphenyl diisocyanate (MDI) or polymeric methylene diisocyanate (pMDI), which contains a polyol or polycaprolactam.