NZ615297B2 - A powder mix and a method for producing a building panel - Google Patents

Abstract

Dislcosed herein is a method for producing a building panel comprising the steps of: - applying a powder mix layer (2) on a substrate (1), the powder mix layer comprising wood fibres and a binder; - adjusting a weight loss on cure of the powder mix layer by a step of applying a stabilisation fluid (at 4), or a step of drying (5), or a combination thereof such that the powder mix layer obtains the weight loss on cure in a range of about 2 to about 7 wt-%; and - applying heat and pressure (6) to the powder mix layer when arranged on the substrate and curing the powder mix layer having the weight loss on cure in the range of about 2 to about 7 wt-%, and thereby obtaining a layer of the building panel formed by the powder mix layer. (at 4), or a step of drying (5), or a combination thereof such that the powder mix layer obtains the weight loss on cure in a range of about 2 to about 7 wt-%; and - applying heat and pressure (6) to the powder mix layer when arranged on the substrate and curing the powder mix layer having the weight loss on cure in the range of about 2 to about 7 wt-%, and thereby obtaining a layer of the building panel formed by the powder mix layer.

Description

A POWDER MIX AND A METHOD FOR PRODUCING A BUILDING PANEL Technical fieId The disclosure generally relates to the field of fibre-based panels with a wear resistant decorative surface layer, ularly building panels and more particularly floor panels. The disclosure relates to a building panel with such wear ance decorative surface and to production methods for such panels and a mixed/prefab layer for such methods and panels.

Known Technigues Recently new “paper free” Wood Fibre Floor (WFF) types have been developed with solid surfaces comprising a substantially homogenous mix of fibres, binders and wear resistant particles. Such a new type of panel called Wood Fibre Floor (WFF) is sed in /065769, which shows both products and methods to produce such a product.

The wear resistant particles are preferably aluminium oxide particles, the binders are preferably thermosetting resins such as amino resins and the fibres are preferably wood based. Other suitable wear resistant materials are for example silica or silicon carbide. In most applications decorative les such as for example colour pigments are included in the homogenous mix. In general all these materials are preferably applied in dry form as a mixed powder on a HDF core and cured under heat and pressure to a 0.1 - 1.0 mm solid layer.

Powder technology is very suitable to produce solid decorative surface layer, which are much thicker than conventional laminate surface layers. Such solid powder based layers create a much higher tension on the panel when they swell or shrink and balancing is a problem. It is ore ult to produce a panel with a thick and a high quality surface, which is also stable and flat in variable moisture conditions. rmore, pores may be formed in the surface layer resulting in weak stain resistance.

Summary of the ion An objective of certain embodiments of the invention is to improve the known Wood Fibre Floor (WFF) panels. A r object is to provide a product preferably having a width cupping of —O.15% to +0.20% under test conditions according to ISO 24339:2006(E), and/or a water vapour permeability of less than 3 g/m2*24 hours according to EN 12572 and/or a e staining of 5(5) according to EN438 based on test using a ent marker. The foregoing objects should be read disjunctively with the object of at least ing the public with a useful alternative.

This may be achieved by a powder mix layer for the tive surface layer of a WFF- panel with a controlled loss on cure and a method of producing a building panel.

By loss on cure is in this application meant the weight loss, calculated as weight percentage of the original weight, occurring when heating the powder at 160°C for 5 minutes. The weight loss corresponds to re released from the powder. Under these conditions the released moisture consists 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 at 160°C and the resin cross-links via a condensation reaction, i.e. water is released by the condensation reaction.

By moisture content is meant the weight loss, when the powder is dried under milder conditions at ambient atures and only the free water in the powder is released, without curing the resin.

If the loss on cure is too low the powder mix layer will not be completely impregnated by the binder when the binder is in the fluid state during the pressing. An inferior impregnation of the powder mix layer results in discolouration of the tive surface of the WFF panel, due to pores close to the surface.

If the loss on cure on the other hand is too high, a high amount of pores in the WFF layer are created during the pressing. The pores give a poor resistance of surface staining and increased water/vapour permeability. Increased water/vapour permeability can result in increased cupping of the panels under test conditions according to lSO 24339:2006(E).

The loss on cure depends on the amount of binder in the powder mix layer, the moisture content in the powder mix layer when entering the WFF production line and the amount of powder stabilization fluid d in the WFF production line. The loss on cure before pressing may be controlled by an in-Iine or off—line drying process in which the powder layer is dried. The drying may be carried out by heating, e.g., lR heating, preferably in-line, drying in a chamber, preferably in-line, or drying in a controlled climate, preferably off-line.

The drying process stabilizes the powder in the powder mix layer and applying a powder ization fluid may not be necessary.

If the drying process es heating, the binder in the powder mix layer may be melted and the powder is stabilized by the melted binder. Thereby, the drying process may make the stabilization fluid redundant.

According to a first aspect of the invention a powder mix layer for producing a building panel with a loss on cure in the range of about 2.5 to about 7 wt-%, preferably about 3 to about 6 wt-% is provided.

A powder mix layer having a loss on cure in the above described range overcomes the above described disadvantages and exhibits improved stain resistance, water/vapour ance and binder impregnation as described above.

The powder mix layer may have a loss on cure in the range of about 2 to about 7 wt—%, preferably in the range of about 4 to about 6 wt-%, preferably about 5 wt-%.

The powder mix is a substantially homogenous mix, which comprises in one embodiment wood fibres, preferably of HDF, a binder, preferably a melamine resin, and wear resistant particles, ably a powder of silica, more preferably essentially of aluminium oxide. A more preferred loss on cure is about 3.5 wt-%, to 5.5 wt-%.

According to a second aspect of the invention, a method of producing a building panel is provided. The method comprises the steps of: - applying a powder mix layer on a ate, the powder mix layer sing wood fibres and a ; - adjusting a weight loss on cure of the powder mix layer by a step of applying a stabilisation fluid, or a step of drying, or a combination thereof such that the powder mix layer obtains the weight loss on cure in a range of about 2 to about 7 wt—%; and - applying heat and pressure to the powder mix layer when arranged on the ate and curing the powder mix layer having the weight loss on cure in the range of about 2 to about 7 wt-%, and thereby obtaining a layer of the building panel formed by the powder mix layer.

Preferred weight loss on cure ranges are about 4 to about 6 wt—%, about 5 wt—% and about 2.5 wt—% to about 7 wt-%.

A powder mix layer produced according to the ive method wherein the powder mix layer has a loss on cure in the above described range overcomes the above described disadvantages and exhibits improved stain resistance, water/vapour resistance and binder impregnation as described above.

In one embodiment, a powder mix is chosen such that the powder mix already has a loss on cure in the above defined ranged. As an alternative, the loss on cure of WC 2012/141646 the powder mix layer may be adjusted by for e applying a stabilisation fluid or by drying in order to change the moisture content of the powder mix. The relevant time for determining the loss on cure of the powder mix layer is the moment before applying heat and pressure.

By adjusting the binder content and the re content in the powder mix, and the amount of any added ization fluid, a desired loss on cure of the powder mix layer may be obtained. Furthermore, the loss on cure may be controlled by drying the mix, thereby adjusting the moisture content.

The curing performed by applying heat and pressure may be performed at high line speed and the powder layer withstands high acceleration and retardation forces created, at short press cycles of about 20 seconds.

The powder mix in the second aspect may be the same as the embodiments of the first aspect. ingly, the powder mix layer may comprise a substantially homogenous mix of wood fibres and a binder, preferably a thermosetting resin, more preferably melamine. The powder mix layer may further comprise wear ant particles, preferably of aluminium oxide or of a silica powder.

The loss on cure is measured using a gravimetric method comprising heating the powder mix layer at 160°C for five s.

The powder mix layer may be heated before pressing, preferably by lR heating, and preferably with an effect of about 15-25 kW/m. A preferred g speed in the range of about 1-4 m/min, most preferably about 3m/min at an effect of about 20kw.

Preferably, the substantially homogenous mix is ioned before being applied in order to obtain the desired loss on cure of the powder mix layer.

In the curing step, the pressure applied may be in the range of about 20 kg/cm2 to about 60 kg/cmz, preferably about 40 kg/cmz, and the temperature of the press plate may be in the range of about 160 to about 200°C, preferably about 180°C, The heat and pressure may be applied in the range of about 10 to about 200 seconds, preferably in the range of about 10—60 seconds, and as an example in about 40 seconds.

The powder mix layer may comprise wood fibres and a binder, preferably a thermosetting resin. 2012/050384 The method may comprise the further step of applying a stabilisation fluid, preferably water, on the powder mix.

The method may comprise the further step of drying the powder mix layer, preferably by applying heat with an effect of about 15-25 kW/m and a g speed in the range of about 1—4 m/min, preferably about 3 m/min.

The method may comprise the further steps of fixing the powder mix layer to the ate, preferably by applying stabilisation fluid and drying with an effect of about —25 kW/m and a feeding speed in the range of about 1-4 m/min, preferably about 3 m/min.

The method may comprise the further step of adjusting the loss on cure of the powder mix layer by the step of applying the stabilisation fluid, or the step of drying, or a combination thereof such that the powder mix layer obtains the loss on cure in said range. Thereby, the loss on cure of the powder mix layer can be adjusted such that a loss on cure in the desired range can be obtained, even if the powder mix originally has a loss on cure outside the desired range.

The powder mix layer may be applied by scattering. The powder mix may be applied by an applying unit, preferably a scattering unit, which forms the powder mix layer.

The powder mix layer may be applied as a continuous powder mix sheet.

Consequently, it is possible to produce a separate layer such as a uous powder mix sheet. In this embodiment, the substrate may be a press belt, a release foil etc. The components of the powder mix is connected er but essentially uncured, in a te process and in a separate production line. The separate layer may be based on carrier, e.g. a paper or a metal or plastic foil, but the powder mix may also only be bonded together by it self achieved by e.g. g with a fluid, preferably water and drying. The powder mix sheet may be stored and later applied on the core as a powder mix layer.

The substrate may be a core, preferably a wood-based core, more preferably a HDF or MDF board.

The layer may form a decorative surface layer arranged on the core.

A third aspect of the invention is a production line comprising an ng unit for applying a powder mix layer on a substrate, a pressing unit for applying heat and W0 2012/141646 pressure on the powder mix layer and a conveyor that comprises conveyor units preferably with separately controllable feeding speed of the substrate. The tion line may also se stabilisation units and/or drying units. The conveyor preferably ses separate or units at each of the production units. The separate conveyor units provide an enhanced control of the loss on cure, since the feeding speed at each production unit (the applying unit, stabilisation unit and/or drying unit) can be controlled and thereby it will be easier to control the amount of applied powder or stabilisation unit or degree of drying. Furthermore the separate or units prevent moisture/water from being transported between the production units by the conveyor .

In all s the wood fibres may be both virgin, refined and/or processed, sing lignin and without lignin, e.g. or-cellulose fibres or holocellulose. A mixture of refined and unrefined fibres may also be used. It is also contemplated that vegetable fibres asjute, linen, flax, , hemp, bamboo, bagasse and sisal may be used. Also mineral fibres and carbon fibres may be used.

The applying unit is preferably a scattering device. The substrate is preferably an HDF or MDF board, which is preferably provided with a balancing layer .

Brief Description of the Drawings The invention will in the following be described in connection to preferred embodiments and in greater detail with reference to the appended ary drawings, wherein Fig 1 illustrates a production line ing to an embodiment of the invention; Fig 2 illustrates a panel with a decorative layer according to an embodiment of the invention; Fig 3 illustrate the relationship between moisture content and loss on cure for the formulation in e 1-4 Detailed Description of Embodiments A panel 7, which is described with reference to fig 1 and 2, comprises according to one embodiment of the invention a wood fibre based core 1, an essentially homogenous decorative surface layer (transparent or non-transparent) 2 and preferably a balancing layer 8. The panel 7 is in one embodiment integrally formed in a production line (see fig 1) where the surface layer 2, the core 7 and the balancing layer 8 are formed in the same pressing operation 6.

Figure 2 shows the decorative surface layer and the core in more detail. The surface layer ses a substantially homogenous mixture of fibres 14, small hard wear resistant particles 12, 12’ and a binder 19. The fibres 14 are ably wood fibres. The binder 19 is preferably a binder that cross-links by a condensation on. The binder is preferably a thermosetting resin such as amino-resins or phenolic resin. In one embodiment, the binder is melamine formaldehyde. The wear resistant particles 12,12’ are preferably aluminium oxide particles. The surface layer preferably may also comprise pigment 15.

The e layer may comprise colour pigments 15 , optionally, other decorative materials or chemicals. tive materials include, for example, materials that may affect design aspect(s) the surface layer. Exemplary design materials include materials effecting texture, reflectivity, shine, luminescence, transparency, etc.

In methods according to embodiments of the invention preferably the same scattering 3 and pressing units 6 as disclosed in or WO 2009/124704 are used, ably together with a structured press plate in the method. Each of and are hereby incorporated 2O by reference in its entirety.

Fig 1 discloses a production line according to an embodiment of the invention. The production line comprises an applying unit 3, preferably a scattering unit for applying/scattering a powder mix 2 on the core 1, e.g. an HDF/MDF board, which is ably already provided with a balancing layer 8. A stabilisation unit 4 for applying a stabilization fluid and a drying unit 5 for drying the powder mix layer are provided. A pressing unit 6 finally s heat and re on the powder mix layer, the core and the balancing layer in order to cure the binder and thereby obtaining the finished building panel 7 with a decorative surface layer. The production line further comprises a conveyor (not shown) preferably sing separate conveyor units such that the speed of the core 1 through the production line can be varied at the ent units e.g. at the applying unit 3, the stabilisation unit 4 or at the drying unit 5. A suitable conveyor is a belt or roller conveyor.

A powder formulation can for example se an essentially homogenous W0 41646 2012/050384 powder mixture comprising 187.5 g/m2 recycled HDF fibre with a moisture content of 5.2 %, 62.5 g/m2 Aluminium Oxide (ZWSK-180 ST, Treibacher Schleifmittel AG), 265,625 g/m2 Melamine Formaldehyde resin (Prefere 4865, Dynea), 62.5 g/m2 Titanium dioxide (Kronos 2190, Kronos) and 46,875 g/m2 pigment (Heucosin G10512, Heubach).

The core of an HDF board preferably has a moisture content of 0-6 %.

The ring unit has the 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 length wise the board. The amount of stabilization fluid may vary between 0 up to 200 g/m2.

The scattering unit comprises a needle belt and a scattering roller. The scattering roller is provided with needles in the range of about , preferably about 50- 100, and most preferably about 70—90 needles per cmz. The needle length is about 0.5-2.5 mm, preferably about 1—2 mm and most ably about 1.5 mm. Several ring units machines to even out differences in the applied powder mixture.

Furthermore, the scattering device may be provided with a needle belt with s 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 The stabilization unit may stabilize using steam, nozzle spray coating, ultra sonic spray coating, a stabilization sheet comprising a sheet based material with inherent stabilizing properties or a surface coverage providing the stabilizing properties.

Stabilization fluid may comprise solvents such as non-polar solvents, polar aprotic solvents and polar protic solvents or es thereof. red solvents are polar protic solvents such as isopropanol, ethanol and water. Most preferred is water.

The stabilization fluid can further comprise additives such as wetting agents, ers, release agents, anti-slip agents, anti-abrasives and catalysts. tive effects can also be added in the form of inks, dyes and effect pigments. ln examples 1-4 below the powder formulation was used comprising 34 weight-% recycled HDF fibre (valinge innovation ), 10 weight—% Aluminium oxide (ZWSK 180-ST, cher Schleifmittel AG), 50 weight—% Melamine Formaldehyde resin (Prefere 4865, Dynea), 2 weight-% Titanium dioxide (Kronos WO 41646 2190, Kronos) and 4 weight—% pigment (G 6555 N, Heubach GmbH).

The relation between Weight Loss on Cure and the free moisture content, that is excluding the water released in the curing of the melamine resin, in the powders used in the examples, is shown in fig 3.

Depending on the loss cure of the powder mix applied to the substrate, a stabilization fluid may be applied and/or drying may be performed. if the loss on cure of the powder mix applied to the substrate is within the above described range, no stabilization fluid is to be added and no drying is to be performed. If the loss on cure of the powder mix applied to the ate is outside the above described range, a ization fluid is to be added, or drying is to be performed, depending if the loss on cure is too low or too high, in order to obtain a powder mix having the desired loss on cure before applying heat and pressure.

Even if the loss on cure of the powder mix d is within the above described range, it may be desired to apply a stabilization fluid in order to stabilize the powder layer. In order to adjust the loss on cure of the powder mix layer, subsequent drying may be required.

Alternatively, the binder content of the powder may also be adjusted in order to obtain the desired loss on cure of the powder mix layer.

Example 1: Powder based product obtained through heat compression of an incorrectly treated powder, ative example; no drying and a stabilization fluid of water (ZOg/mz) A powder based product comprising an HDF core with a thickness of 9.7 mm, a balancing paper 550 g/m2 of a scattered powder layer and 20 g/m2 isation fluid, giving an a loss on cure of 8 wt-%, was pressed in a short cycle press using a force of 40 kg/cm2 for 37 seconds at a surface temperature on the upper press plate of 184 °C and a surface temperature on the lower press plate of 180 °C. The press plate was a granite structure plate.

The resulting product was: o a building panel with a solid surface having a width cupping outside -O.15 % to +02% led board according to lSO 24339:2006(E). Typical values obtained are -O.26 % to +0.29%. . staining of 3(5) according to EN438 based on test using a permanent marker . water vapour permeability in excess of 5.3 g/m2*24 hours according to EN 12572 Example 2: Powder based product obtained through heat ssion of a treated , preferred example, drying and a stabilization fluid of water (20g/m2) A powder based product comprising a HDF core with a thickness of 9.7 mm, a balancing paper and 550 g/m2 of a scattered powder layer and 20 g/m2 of isation fluid was pressed in a short cycle press using a force of 40 kg/cm2 for 37 seconds at a surface ature on the upper press plate of 184 °C and a surface temperature on the lower press plate of 180 °C. The press plate had a granite structure. Prior to pressing the powder was treated by an IR drying with an effect of 19 kW/m and a g speed of 27 m/min in order to obtain a loss on cure of 4.6 wt-% as measured using a gravimetric method comprising heating the treated powder at 160 °C for five minutes.

The ing product was: 0 a solid surface having a width cupping within -0.15 % to +02 % installed board according to ISO 24339:2006(E), typical values obtained are -0.07 % to +0.17 %. . staining of 5(5) according to EN438 based on test using a permanent marker . water vapour permeability lower than 1.1 g/m2*24 hours according to EN 12572.

Example 3: Powder based product obtained h heat compression of an incorrectly treated powder, comparative example, stabilization fluid and over drying.

A powder based product comprising a HDF core with a thickness of 9.7 mm, a balancing paper and 550 g/m2 of a scattered powder layer with 20 g/m2 of stabilisation fluid, was pressed in a short cycle press using a force of 40 kg/cm2 for 37 seconds at a surface temperature on the upper press plate of 184°C and a surface temperature on the lower press plate of 180°C. The press plate had a granite structure. Prior to ng the powder was treated by an lR drying process with an effect of 19 kW/m and a feeding speed of 1.5 m/min in order to obtain a loss on cure of 2.5 wt-% as measured using a gravimetric method comprising heating the treated powder at 160°C for five s.

The resulting product was: W0 2012/141646 . a building panel with a solid surface having a width cupping inside -O.15 % to +0.2 % on installed board according to ISO 2433912006(E) o staining of 3(5) according to EN438 based on test using a permanent marker 0 water vapour permeability of 2.5 g/m2*24 hours according to EN 12572 . Discoloured decorative surface, due pores close to surface.

Example 4: Powder based product obtained through heat compression of a treated powder, red example, drying and without stabilization fluid of water.

A powder based product sing a HDF core with a thickness of 9.7 mm, a balancing paper and 550 g/m2 of a red powder layer, with a loss on cure of 5.3 % before drying, was pressed in a short cycle press using a force of 40 kg/cm2 for 37 seconds at a e temperature on the upper press plate of 184 °C and a surface temperature on the lower press plate of 180 °C. The press plate had a granite structure. Prior to pressing the powder was treated by an IR drying with an effect of 19 kW/m and a feeding speed of 2.7 m/min in order to obtain a loss on cure of 3.7 wt-% as measured using a etric method comprising heating the treated at 160 °C for five minutes.

The resulting product was: . A solid surface having a width cupping within —O.15 % to +0.2 % on the installed board ing to ISO 24339:2OOG(E), typical values obtained are -0.05 % to +020 %. o staining of 5(5) according to EN438 based on test using a permanent marker . water vapour permeability lower than 1.9 g/m2*24 hours according to EN 12572.

Claims (17)

What is claimed 1. is:

1. A method of producing a building panel comprising the steps of: - applying a powder mix layer on a substrate, the powder mix layer comprising wood fibres and a binder; - adjusting a weight loss on cure of the powder mix layer by a step of applying a stabilisation fluid, or a step of drying, or a combination thereof such that the powder mix layer obtains the weight loss on cure in a range of about 2 to about 7 wt-%; and 10 - applying heat and pressure to the powder mix layer when arranged on the substrate and curing the powder mix layer having the weight loss on cure in the range of about 2 to about 7 wt—%, and thereby obtaining a layer of the building panel formed by the powder mix layer. 15

2. The method according to claim 1, wherein the weight loss on cure is in the range of about 4 to about 6 wt—%.

3. The method according to claim 1 or 2, n the weight loss on cure is about 5 wt-%.

4. The method ing to any one of claims 1—3, wherein the binder is a setting resin. 25

5. The method according to any one of claims 1-4, wherein the stabilisation fluid is water.

6. The method according to any one of claims 1-5, wherein the step of 30 drying comprises applying heat with an effect of about 15-25 kW/m and a feeding speed in the range of about 1—4 m/min.

7. The method ing to any one of claims 1-6, comprising the further steps of fixing the powder mix layer to the substrate.

8. The method according to claim 7, wherein the step of fixing comprises applying stabilisation fluid and drying with an effect of about 15—25 kW/m and a feeding speed in the range of about 1-4 m/min.

9. The method according to claim 6 or 8, wherein the feeding speed is about 3 m/min.

10. The method according to any one of claims 1-9, wherein the powder mix layer is applied by scattering.

11. The method according to any one of claims 1-10, wherein the powder mix layer is applied as a continuous powder mix sheet.

12. The method according to any one of claims 1-11, wherein the substrate is a core.

13. The method according to claim 12, n the core is a wood-based 15 core.

14. The method according to claim 12 or 13, wherein the core is a HDF or MDF board. 20

15. The method according to any one of claims 12-14, wherein the layer forms a decorative surface layer arranged on the core.

16. A building panel ed by the method according to any one of claims 1-15.

17. The method according to claim 1, substantially as herein bed with reference to any one of the Examples and/or