Technical field

The present invention relates to a method of manufacturing a building panel comprising a core, a decorative layer and a balancing layer. Technical background

Floor panels, such as laminate floor panels or wood fibre floor (WFF) panels, are usually provided with a balancing layer on a rear side of the panel. The balancing layer may also be called a backing layer or

counteracting layer. On the opposite side of the core, a decorative surface layer is arranged. The decorative layer may comprise a resin impregnated decor paper and a resin impregnated overlay paper. The decorative layer may also be a surface layer formed from a mix comprising wood fibres and a thermosetting binder as described in WO2009/065769. Such floor panels are marketed under the trademark NADURA ^® .

When the thermosetting binder in the decorative surface layer, for example, melamine formaldehyde resin, is cured, shrinking of the melamine formaldehyde resin leads to tension in the decorative surface layer. The internal stress formed in the decorative surface layer may cause warping of the panel. The tension at the front side of the panel should be compensated by a counteractive tension at the rear side of the panel. Therefore, a balancing layer is arranged on a rear side of the core opposite the decorative surface layer. The balancing layer is adapted to counteract and balance tension formed during curing of the decorative surface layer. The balancing layer may be a resin impregnated paper or a formed of a mix comprising wood fibres and a thermosetting binder of the type described in

WO2012/141647.

An article by Le Fur et al. ("Recycling melamine-impregnated paper waste as board adhesive", Holz als Roh- und Werkstoff, Vol. 62, 2004, pp. 419-423, ISSN 0018-3768) discloses use of melamine impregnated paper offcuts and waste. In one approach, the melamine impregnated waste paper is used as a binder for forming a particleboard. The melamine waste paper was applied to wood particles, and no other binder was added in order to form the particleboard. In a second approach, melamine impregnated paper is used as a melamine substitute during the formulation of and preparation of liquid melamine-urea-formaldehyde (MUF) resins. The resin is centrifuged to separate the resin from the cellulose fibre originating from the melamine waste paper. The resin including the melamine part of the waste material was applied to wood particles for forming a particleboard.

It is a general desire of floor producers to decrease the cost for producing the floor panels. The balancing layer is one area where

improvements relating to cost reduction is desirable.

Summary

It is an object of at least embodiments of the present invention to provide an improvement over the above described techniques and known art.

A further object of at least embodiments of the present invention is to provide a balancing layer produced at lower cost than a conventional balancing layer.

A further object of at least embodiments of the present invention is to use production waste resulting from manufacture of building panels, or from manufacture of components of building panels.

At least some of these and other objects and advantages that will be apparent from the description have been achieved by a method of

manufacturing a building panel comprising a core, a decorative layer and a balancing layer, comprising applying a first mix comprising a binder and particles formed from production waste comprising resin impregnated paper on a first surface of a core, applying a decorative layer on a second surface of the core, and curing the first mix to form the balancing layer of the building panel.

The method may further comprise mixing the thermosetting binder and the particles formed from production waste comprising resin impregnated paper to form the first mix.

The binder is preferably a thermosetting binder. If it is not required to counteract forces formed by the surface layer by means of the balancing layer, the binder may be a thermoplastic binder and a protective layer is formed. A mixture of a thermosetting binder and a thermoplastic binder is also contemplated.

By production waste is meant both residues from production and left- overs, such as unconsumed material, intended for use in production. The production may be paper impregnation processes, lamination processes, pressing processes, etc. The first mix is preferably a dry powder mix.

The thermosetting binder may be a separate binder. For example, the thermosetting binder is preferably not a resin separated from the production waste. The thermosetting binder may be separate from any resin in or obtained from the production waste. The thermosetting binder may be added in addition to the production waste and any resin therein. The thermosetting binder may be a fresh thermosetting binder. By fresh is meant not recycled. Preferably, the thermosetting binder has its reactivity maintained.

An advantage of embodiments of the present invention is that production waste can be used for forming the balancing layer instead of going to waste. By replacing a part of the material of the balancing layer with production waste, the cost for producing the balancing layer can be reduced. Additionally, instead of paying for disposal of left-overs, such as unused material, for example, resin impregnated decor papers, backing papers and overlays, such material can be used for forming the balancing layer. Thereby, the amount of waste material can be reduced, and consequently also the cost for disposal of the waste material. Since the papers are impregnated with a binder, disposal of the waste material must follow current regulations due to the resin content, thus resulting in a higher cost for disposal compared to unimpregnated paper. Thereby, the cost can be reduced both by replacing material and reducing the cost that would otherwise have arisen for disposal of material.

A further advantage is that the processed production waste can improve the flowing properties of the first mix, thereby facilitating scattering the first mix for forming the balancing layer. Furthermore, if the production waste comprises substantially uncured binder, the substantially uncured binder in the processed production waste can be used as binder for the balancing layer and the amount of the thermosetting binder added to the first mix can be reduced. By substantially uncured is meant that the thermosetting binder being primary in its B-state, for example, at least 90 wt% of the thermosetting binder may be in the B-state. Thermosetting binders may be classified as A-, B-, and C-stage according to their extent of reaction compared to the extent of reaction at gelation. In an A-stage thermosetting binder, the extent of reaction is less than the extent of reaction at gelation, i.e. uncured. A B-stage thermosetting binder is close to the gel point. A C-stage thermosetting binder is well past the gel point. The A-stage thermosetting binder is soluble and fusible. The B-stage thermosetting resin is still fusible but is barely soluble. The C-stage thermosetting binder is highly crosslinked and both infusible insoluble. (Principles of Polymerization, George Odian, 3 ^rd edition).

The production waste may comprise resin impregnated paper, such as resin impregnated decor paper, resin impregnated backing paper or resin impregnated overlay paper. The resin impregnated paper may be left-overs, such as decor papers having decors no longer used, or decor papers, backing papers and/or overlay papers which are old, e.g., which have been stored for a longer time than recommended. The resin impregnated papers may also be residues from manufacture. The residues may result from edge cutting, performed when cutting the edges of the paper after impregnation. The residues may result from edge trimming, performed after pressing when trimming the edges of the paper to the edge of the board.

The particles formed from production waste may comprise

lignocellulosic material or cellulosic material, or a combination thereof.

Consequently, the first mix may comprise lignocellulosic or cellulosic material originating from the resin impregnated papers of the production waste.

Lignocellulosic or cellulosic material is preferably not removed from the production waste. Lignocelulisic or cellulosic material is preferably not separated from the resin of the production waste.

The first mix may be a powder mix, preferably a dry powder mix. The dry mix may have a moisture content of 2.5 - 9 wt%.

The thermosetting binder may be applied on the core in dry powder form.

The thermosetting binder may be in powder form, preferably in dry powder form, when mixed with the particles formed from production waste.

The particles formed from production waste may be formed by mechanically processing, preferably by grinding, production waste comprising resin impregnated paper. The step of mechanically processing the production waste comprising the resin impregnated paper into particles may be performed separately from the step of applying the first mix comprising the particles.

The step of mechanically processing the production waste may comprise grinding the resin impregnated paper.

The resin impregnated paper may be a resin impregnated decor paper, a resin impregnated backing paper or a resin impregnated overlay paper. By backing paper is also meant balancing paper, counteracting paper, etc. The resin content of the total weight of the resin impregnated paper may be 25-85 wt%.

The resin impregnated paper may comprise a substantially uncured thermosetting binder. By substantially uncured is meant that the

thermosetting binder being primary in its B-state, for example, at least 90 wt% of the thermosetting binder may be in the B-state. For example, the

production waste may comprise substantially uncured resin impregnated paper. The thermosetting binder may be an amino resin, for example, melamine formaldehyde resin, urea formaldehyde, phenol formaldehyde, or a combination thereof.

The resin impregnated paper may comprise a substantially cured thermosetting binder. By substantially cured is meant that the thermosetting binder being primary in its C-state, for example, at least 90 wt% of the thermosetting binder may be in the C-state. For example, the production waste may comprise substantially cured resin impregnated paper. The thermosetting binder may be an amino resin, for example, melamine formaldehyde resin, urea formaldehyde, phenol formaldehyde, or a

combination thereof.

The particles formed from production waste may comprise wear resistant particles, such as aluminium oxide (corundum). The production waste may, for example, originating from overlay papers comprising wear resistant particles.

The method may further comprise applying a stabilization fluid on the first mix, turning the core having the first mix applied thereto, such that the first mix is directed downwards from a surface of the core before applying the decorative layer.

The method may further comprise drying the first mix before turning the core.

The first mix may further comprise lignocellulosic or cellulosic particles separate from the particles formed from production waste. The cellulosic particles may at least partially bleached. By the lignocellulosic or cellulosic particles are meant particles being different from any the lignocellulosic material or cellulosic material originating from the production waste. The lignocellulosic or cellulosic particles are added to the particles formed from production waste. The first mix may be formed by adding said particles formed from production waste to a mix comprising the thermosetting binder and said lignocellulosic or cellulosic particles.

The first mix may comprise 1 -50 % by weight of said particles formed from production waste, preferably 1 -25 % by weight, more preferably 1 -10 % by weight. The first mix may comprise additives, such as wetting agents, release agents, catalyst, etc. The first mix may further comprise pigments and/or hard particles, additives, etc.

The ration of the particles formed from production waste to the thermosetting binder of the first mix may be in the range of 1 :20 to 1 :5, such as about 1 : 10.

The decorative layer may comprise a resin impregnated decor paper. A resin impregnated overlay paper comprising wear resistant particles may be arranged on the decor paper.

The decorative layer may comprise a second mix comprising lignocellulosic or cellulosic particles and a thermosetting binder. The second mix may further comprise wear resistant particles. The second mix is preferably a powder mix.

The core may be a wood based board, such as Medium Density Board (MDF),High Density Board (HDF), particleboard, Oriented Strand Board

(OSB), or plywood. The core may be a WPC (Wood Plastic Composite) or a thermoplastic core.

The decorative layer may comprise wear resistant particles.

According to a second aspect of the invention, a building panel is provided. The building panel may comprise a core having a first and a second surface, a balancing layer arranged on the first surface of the core, and a decorative layer arranged on the second surface of the core, wherein the balancing layer comprises a binder and particles formed from production waste comprising resin impregnated paper.

The building panel may be a floor panel. The floor panel may be provided with a mechanical locking system.

The binder is preferably a thermosetting binder. If it is not required to counteract forces formed by the surface layer by means of the balancing layer, the binder may be a thermoplastic binder and a protective layer is formed. A mixture of a thermosetting binder and a thermoplastic binder is also contemplated. The thermosetting binder may be a separate binder. For example, the thermosetting binder is preferably not a resin separated from the production waste. The thermosetting binder may be separate from any resin in or obtained from the production waste. The thermosetting binder may be added in addition to the production waste and any resin therein. The thermosetting binder may be a fresh thermosetting binder. By fresh is meant not recycled. Preferably, the thermosetting binder has its reactivity maintained.

The particles formed from production waste may comprise

lignocellulosic or cellulosic material. Thereby, the balancing layer may further comprise lignocellulosic or cellulosic particles. Consequently, the balancing layer may comprise lignocellulosic or cellulosic material originating from the resin impregnated papers of the production waste. The lignocellulosic material or cellulosic material of the production waste may originate from the resin impregnated paper.

The balancing layer may further comprise lignocellulosic or cellulosic particles, or a combination thereof. By the lignocellulosic or cellulosic particles are meant particles being different from any lignocellulosic material or cellulosic material originating from the production waste.

The second aspect of the invention incorporates all the advantage previously described relating to the inventive method.

According to another aspect of the invention, a method of

manufacturing a building panel comprising a core, a decorative layer and a balancing layer is provided. The method may comprise applying particles formed from production waste comprising resin impregnated paper on a first surface of a core, applying a decorative layer on a second surface of the core, and curing the first mix to a balancing layer of the building panel.

Preferably, the resin impregnated paper may comprise uncured resin. The uncured resin in the resin impregnated paper may create the

counteracting forces of the balancing layer such that a balancing layer comprising no additional thermosetting binder can be obtained.

Brief description of the drawings

The present invention will by way of example be described in more detail with reference to the appended schematic drawings, which show embodiments of the present invention.

Figs. 1 a-e illustrate a method to form a balancing layer.

Figs. 2a-d Illustrate a method to form a balancing layer. Fig. 3 illustrates a building panel wherein the decorative layer is laminate.

Detailed description

Figs. 1 a-e illustrate a method of forming a building panel. The building panel may be a floor panel, a wall panel, a ceiling panel, a furniture

component, a worktop, etc. The method comprises arranging a core 2 on a conveyor belt. The core 2 may be a board, such as a wood based board. The wood based board may, for example, be a HDF, MDF, particleboard, OSB, plywood, etc., or a WPC (Wood Plastic Composite). The core 2 may also be a thermoplastic core.

The method further comprises applying a first mix 3 on a first surface of the core 2. The first mix 3 comprises particles formed from production waste comprising resin impregnated paper and separate particles of thermosetting binder. The first mix 3 is applied as a powder.

By production waste is meant both residues from production and leftovers, such as unconsumed material intended for use in production.

Production of building panels, for example, floor panels, results in a certain amount of production waste. The production waste may, for example, be unconsumed material, such as decor papers, backing papers and overlay papers used for laminate flooring production. Decor papers may be printed resin impregnated papers. Overlay papers may also be resin impregnated and comprise wear resistant particles. The printed decor of decor papers may be outdated and therefore can no longer be used. Both overlay papers, backing papers and decor papers may have a limited storing time due to the resin included in the paper, which may start to cure. Unconsumed material may therefore be overlay papers, backing paper, and decor papers, which have been stored for a longer time than recommended.

The production waste may also be residues from production. Residues may originate from the production of the laminate papers, e.g., resin impregnated papers for use as decor papers, backing papers or overlay papers. When impregnating the papers, the edges of the papers are cut, in order to obtain a straight edge, in an edge cutting operation, resulting in production waste comprising substantially uncured binder. Residues may also originate from pressing of the resin impregnated papers to a core for forming a building panel having a laminate surface layer. After pressing, the edge of the resin impregnated papers extending beyond the edge of the core are trimmed, resulting in production waste comprising substantially cured binder.

Consequently, the production waste may comprise both substantially uncured and substantially cured binder, depending on the origin of the residues. If cured particles are included in the residues, the cured particles may function as hard particles facilitating scattering of the first mix 3.

The production waste may comprise both lignocellulosic material and/or cellulosic material, or a combination thereof. The lignocellulosic or cellulosic material originates from the resin impregnated paper of the production waste.

The production waste comprising resin impregnated paper is mechanically processed into particles. The production waste is preferably grinded. After grinding, the production waste is preferably sieved. The maximum particle size may be less than 1 mm, preferably less than 0.5 mm, preferably less than 0.3 mm.

The processed production waste, preferably grinded into particles, is mixed with a binder in a mixing station. The resulting first mix 3 is preferably stored in a container. The first mix 3 is preferably a homogenous mix. The binder is preferably a thermosetting binder, such as an amino resin, for example, melamine formaldehyde resin, urea formaldehyde, phenol formaldehyde, or a combination thereof. The thermosetting binder is preferably in powder form, and preferably mixed with the production waste in powder form. The thermosetting binder added to the production waste is separate from the resin impregnated paper of the production waste. For example, the thermosetting binder is preferably not a resin separated from the production waste. The thermosetting binder may be separate from any resin in or obtained from the production waste. The thermosetting binder may be added in addition to the production waste and any resin therein. The thermosetting binder is not a recycled binder. The thermosetting binder is newly produced. Preferably, the thermosetting binder has its reactivity maintained.

In one embodiment, wherein it is not required that the balancing layer counteracts the decorative layer, the binder may be a thermoplastic binder. In this embodiment, the balancing layer is a protective layer.

In one embodiment, the binder may comprise a mix of a thermosetting binder of the type described above and a thermoplastic binder. In addition to the particles formed from processed production waste and the binder, the first mix 3 may also comprise lignocellulosic or cellulosic particles separate from any lignocellulosic or cellulosic material from, or obtained from, the resin impregnated paper of the production waste. The lignocellulosic or cellulosic particles are added to the first mix 3. The lignocellulosic or cellulosic particles may have maximum size of less than 1 mm, preferably less than 0.5 mm, preferably less than 0.3 mm. It is also contemplated that vegetable fibres as jute, linen, flax, cotton, hemp, bamboo, bagasse and sisal may be used. Also mineral fibres and carbon fibres may be used.

The first mix 3 may be formed by adding particles formed from the production waste to a powder mix comprising the thermosetting binder and the lignocellulosic or cellulosic particles. The particles may be mixed with the thermosetting binder and the lignocellulosic or cellulosic particles in a mixing station. The thermosetting binder content of the powder mix comprising the thermosetting binder may be 30-70 % by, preferably 40-65 % by weight, more preferably 50-60 % by. The amount of thermosetting binder added depends on the concentration of uncured resin in the production waste used in the mix.

If needed, the mix formulation can be modified, such that thermoplastic particles, pigments, hard particles, release agents, wetting agents and similar materials are included into the mix. The thermoplastic particles may be mixed at random into the mix or applied as a separate thin layer and may be used to provide a sealing against moisture penetration into the core.

The first mix 3 may further comprise additives, such as wetting agents, release agents, catalysts, etc. The first mix 3 may also comprise pigments.

The first mix 3 is applied on a first surface of the core 2, preferably by scattering as shown in fig. 1 a. The first mix 3 is applied as a powder. The binder of the first mix 3 is applied as a powder. The first mix 3 is applied as a dry mix. The first mix 3 may be applied by a scattering device 1 1 , for example, comprising a hopper, a roller 12 and optionally one or more nets. A first layer is thereby formed on the first surface of the core 2. The first layer is adapted to form a balancing layer 13.

The scattering device 1 1 may have capacity of scattering of 100-1000 g/m2 with a tolerance of +/- 5% as measured using a calibration cup with an area of 100x100 mm cross- and lengthwise the board.

The scattering device 1 1 may comprise a needle belt and a scattering roller 12. The scattering roller 12 may be provided with needles in the range of about 30-120, preferably about 50-100, and most preferably about 70-90 needles per cm2. The needle length may be about 0.5-2.5 mm, preferably about 1 -2 mm and most preferably about 1 .5 mm. Several scattering devices 1 1 may be used to even out differences in the applied powder mixture.

Furthermore, the scattering device 1 1 may be provided with a needle belt with needles with a preferred length of about 15-20 mm, a preferred frequency in the range of about 500-1000 rpm preferably about 1000 rpm, and a stroke length of about +/- 3 mm.

Figure 1 b shows that the first mix 3 applied on the core 2 is thereafter pre-stabilized by a stabilization fluid 7, preferably comprising water, which is applied by a stabilizing device 9. The amount of stabilization fluid may vary from 0 up to 200 g/m2, and for example from 5 to 100 g/m2.

The stabilization device 9 may apply the stabilization fluid by using steam, nozzle spray coating or ultra-sonic spray coating.

The stabilization fluid 7 may comprise solvents, such as non-polar solvents, polar aprotic solvents and polar protic solvents or mixtures thereof. Preferred solvents are polar protic solvents, such as isopropanol, ethanol and water. Most preferred is water.

The stabilization fluid 7 can further comprise additives, such as wetting agents, defoamers, release agents, anti-slip agents and catalysts.

The first layer 3 is thereafter preferably dried, as shown in fig. 1 b. Such drying can be performed off-line in a controlled environment or in-line by applying heat 8 with a heating device 10 on the first mix 3. The heating device 10 may comprise infrared light (IR).

The stabilization 7 and the following drying 8, attaches the first layer 3 to the core 2, to such an extent that the core 2 with the first layer 3 can be turned 180° to bring the first layer 3 downwards, as shown in figure 1 c, such that it may be transported further along the production line or be stacked on a pallet for intermediate storage before further production takes place.

In figure 1 d, a second mix 1 is applied to a second surface of the core

2 for forming a decorative layer 12. The second mix 1 may comprise lignocellulosic or cellulosic particles, a binder, preferably a thermosetting binder, and optionally wear resistant particles. The second mix 1 may further comprise pigments. A print 4 may be printed into the second mix, preferably by means of digital printing. The second mix 1 is preferably applied as a powder. The second mix 1 is preferably applied by scattering the second mix in powder form. The second mix 1 may be applied as one or several layers to form a second layer.

As an alternative to applying the second mix 1 for forming the decorative layer 12, the decorative layer 12 may be a laminate, as shown in fig. 3. In this embodiment, a decor paper 21 is arranged on the second side of the core 2. An overlay paper 22 may be arranged on the decor paper 21 . The overlay paper 22 may comprise wear resistant particles. The decor paper 21 and/or the overlay paper may be impregnated with a binder, such as a thermosetting binder, or may be unimpregnated. If using unimpregnated papers, a binder may be applied between the core and the decor paper, and/or between the decor paper and the overlay paper, and/or on the overlay paper.

As further alternatives, the decorative layer 12 may be a veneer layer, a wooden layer, a layer of thermoplastic material, etc. Any such layer may be combined with a powder based layer.

The core 2 with the decorative layer 12 and the first mix 3 adapted to form the balancing layer 13 is thereafter fed into a press where the layers are cured under heat and pressure. Thereby, a building panel 6 is formed, comprising a balancing layer 13 arranged on a first surface of the core 2, as shown in fig. 1 e.

Figs. 2a-d shows an alternative method of manufacturing a building panel. In fig. 2a, a first mix 3 of the type described above with reference to figs. 1 a-e is applied on a carrier 1 1. The first mix 3 comprises particles formed from production waste comprising resin impregnated paper as described above. The first mix 3 further comprises a thermosetting binder of the above described type. The first mix 3 may further comprise lignocellulosic or cellulosic particles, additives, etc. as described above with reference to figs. 1 a-e. The components are preferably mixed into a first mix as described above, preferably in powder form.

The first mix 3 is preferably scattered on the carrier 1 1 , for example, by means of a scattering device 1 1 of the type described above, for example, comprising a hopper, a roller 12 and optionally one or more nets. The carrier 1 1 may be a conveyor belt. The carrier 1 1 may also be a paper sheet or a non-woven.

By scattering the first mix 3 on the carrier 1 1 , a first layer is formed, adapted to form a balancing layer 13. A stabilization fluid 7, preferably comprising water, may be applied to the first mix 3. The stabilization fluid 7 may be applied by a stabilizing device 9. The stabilization fluid 7 may further comprise additives, such as wetting agents, release agents, catalysts, etc. The first layer is thereafter preferably dried. Such drying can be performed off-line in a controlled environment or inline by applying heat 8 with a heating device 10 on the mix 3. The heating device 10 may comprise infrared light (IR).

The first mix 3 may be dried to a loss on cure of 1 .5 - 15 wt%. By "loss on cure" is meant the weight loss, calculated as weight percentage of the original weight, occurring when heating the impregnated paper at 160°C for 5 minutes. The weight loss corresponds to moisture released from the impregnated paper. Under these conditions the released moisture is of two parts. The first part is the free moisture formed from water and/or other substances having a boiling point below 160°C being trapped in the powder and the second part origins from the cross linking of the binder. Melamine formaldehyde resin cures during the heating up to 160°C and the resin crosslinks via a condensation reaction, i.e., water is released by the condensation reaction.

As an alternative or complement, the stabilization fluid 7 may be applied on the carrier 1 1 before applying the first mix 3.

In one embodiment, the first layer 3 is formed into a pre-preg as disclosed in US patent application no. 13/445,379, which hereby is

incorporated by reference in its entirety, for example by pre-pressing. The pre-preg can be handled separately and be stored.

In fig. 2b, a core 2 is arranged on the first layer 3. The core 2 may be of the type described above with reference figs. 1 a-e. A first surface of the core 2 is abutting the first layer 3.

In fig. 2c, a second mix 1 is applied on a second surface of the core 2 for forming a decorative layer 12. The second mix 1 may be scattered on the second surface of the core 2. The second mix 1 may comprise lignocellulosic or cellulosic particles, a binder, preferably a thermosetting binder, and optionally wear resistant particles. The second mix may further comprise pigments. A print 4 may be printed into the second mix 1 , preferably by means of digital printing. The second mix 1 may be applied as one or several layers to form a second layer.

As an alternative or complement to applying a second mix 1 , the decorative layer 12 may be a laminate, as shown in fig. 3. In this embodiment, a decor paper 21 is arranged on the second side of the core 2. An overlay paper 22 may be arranged on the decor paper 21. The overlay paper 22 may comprise wear resistant particles. The decor paper 21 and/or the overlay paper 22 may be impregnated with a binder, such as a thermosetting binder, or may be unimpregnated. If using unimpregnated papers, a binder may be applied between the core and the decor paper, and/or between the decor paper and the overlay paper, and/or on the overlay paper.

As further alternatives, the decorative layer 12 may be a veneer layer, a wooden layer, a layer of thermoplastic material, etc. Any such layer may be combined with a powder based layer.

The core 2 with the decorative layer 12 and the first layer 3 adapted to form a balancing layer 13 is thereafter fed into a press where the layers are cured under heat and pressure. Thereby, a building panel 6 having a balancing layer 13 is formed, as shown in fig. 2d.

Fig. 3 shows a building panel 6 having a core 2, a decorative layer 12 and a balancing layer 13. The core 2 may be a board, such as a wood based board. The wood based board may, for example, be a HDF, MDF, particle board, OSB, plywood, etc., or a WPC (Wood Plastic Composite). The core may also be a thermoplastic core.

The balancing layer 13 is arranged on a first surface of the core 2, adapted to face the subfloor when the building panel installed as a floor panel. The balancing layer 13 is formed of a first mix 3 of the type described above, comprising particles formed from production waste and a

thermosetting binder.

The decorative layer 12 is arranged on a second surface of the core 2, adapted to face the interior of a room when the building panel is installed as floor panel. The decorative layer 12 comprises a decor paper 21 and an overlay paper 22. The decor paper 21 comprises a print. The decor paper 21 and the overlay paper 22 are preferably resin impregnated. The overlay paper 22 preferably comprises wear resistant particles, such as corundum.

In an alternative embodiment, the particles formed from production waste of the above described type and the binder of the above described type is applied to the core separately, and are not mixed prior to being applied to the core.

In the above description, balancing layer is used as equivalent to any protective layer. It is contemplated that there are numerous modifications of the embodiments described herein, which are still within the scope of the invention as defined by the appended claims.

It is contemplated that no additional thermosetting binder is added to the particles formed from production waste comprising resin impregnated paper. Thereby, particles formed from processed production waste

comprising resin impregnated paper forms the balancing layer. Substantially uncured resin in the production waste formed from resin impregnated paper may create the counteracting forces of the balancing layer such that no separate binder has to be added to the particles formed from production waste.

EXAMPLES

In the examples, production waste from the following resin impregnated papers were used:

Backing paper having a paper weight of 140 g/m2 impregnated with 170 g/m2 melamine formaldehyde resin, which has been stored approximately one year.

Decor paper having a paper weight of 80 g/m2 impregnated with 80 g/m2 melamine formaldehyde resin, which has been stored approximately one year.

Overlay paper having a paper weight of 25 g/m2 impregnated with 75 g/m2 melamine formaldehyde resin, which has been stored over one year.

The papers were divided into coarse particles and then milled in a hammer mill to a powder having a particle size of less than 1000 pm.

A powder backing mix was prepared comprising 56 wt% of spray-dried melamine formaldehyde resin (MF), 1 wt% AI2O3, 3 wt% pigments and 40 wt% of cellulosic or lignocellulosic particles.

Eight different mixes were prepared, wherein the powder backing mix was mixed with a varying amount of particles formed from production waste comprising resin impregnated paper according to the following. Production waste from Powder backing resin impregnated papers mix

Example 1 0 wt% 100 wt%

Example 2 5 wt% 95 wt%

Example 3 10 wt % 90 wt%

Example 4 25 wt% 75 wt%

Example 5 50 wt% 50 wt%

Example 6 75 wt% 25 wt%

Example 7 90 wt% 10 wt%

Example 8 100 wt% 0 wt%

450 g/m2 of each mix was applied on a HDF board having a thickness of 9.7 mm for forming a balancing layer. Water was applied on the mix in an amount of approximately 20 g/m2. The board having the mix applied thereon was pressed at 40 bar during 35 seconds at a temperature of 160°C.

All resulting boards having a balancing layer formed by any one of the eight examples created a counteracting force, resulting in a board having a convex shape. All eight examples resulted in counteracting forces of comparable strength to a conventional backing paper or a powder backing layer of the type disclosed in WO2012/141647, which hereby is incorporated by reference in its entirety.