Recoatable decorative laminate panels

Abstract

The invention relates to a decorative laminate panel manufactured with a unicolour or printed decor paper as well as a manufacturing process for the laminated panels. To avoid the hot pressing the decor paper is saturated with a clear or transluscent alkali metal silicate and the surface of the decorative panel is; a. Coated with a clear protective layer, or b. Coated with a clear protective layer containing a photocatalyst, or c. Coated with a clear protective layer to provide a gloss or matte finish

Description

[0001] The invention relates to a decorative laminate panel manufactured with a unicolour or printed décor paper as well as a manufacturing process for the laminate panels.Background

[0002] Decorative panels based on décor papers, also known as saturating base paper, are in wide ranging use, being processed to provide a decorative colour or printed decorative surface in many objects, not least in furniture, cabinetry, flooring and wall panelling. A major application is as a low pressure laminate (LPM) whereby the décor paper is saturated with thermosetting amino formaldehyde resin or resins, partially cured (b-stage), and later the b-stage impregnated film is pressed at an elevated temperature between pressplates to provide the decorative surface on a woodpanel such as particleboard or fibreboard, for example medium density fibreboard (MDF) or high density fibreboard (HDF). The decorative surface of the LPM panel based on thermosetting amino formaldehyde resin is inert, resistant to staining and not designed for changes to the surface after the hot pressing step.

[0003] This is a mature industry which uses well known processes to complete the conversion of décor paper into LPM panels. Décor paper is also used to manufacture high pressure laminates (HPL) and compact laminates. Décor paper is manufactured within parameters such as colour, opacity, porosity (Gurley), wet strength and pH. When stored in appropriate conditions décor paper has a virtually unlimited shelf life until it is impregnated with thermosetting amino-formaldehyde resins. A worldwide industry, leading décor paper manufacturers are located in Europe, Asia and North America; Munksjo, Technocell, Koehler & Kingdecor to name a few. In broad terms décor paper grammages range from about 50g / m 2< to 150g / m 2< and the ash content 25% to 40% primarily using TiO2 as the opacifying agent.

[0004] Woodpanels are an economical and environmentally friendly choice as a substrate for décor papers, where in a positive climate action the wood sequesters CO 2 during the growth of the tree. While oriented strand board (OSB) is a widely manufactured woodpanel it currently is not an alternative to particleboard and MDF woodpanel substrates for hot press lamination of amino formaldehyde impregnated décor paper, due in one example to the variations in density across the surface from the inhomogeneous strand structure. Several producers offer OSB that does not use a formaldehyde based binder and are presented as 'no added formaldehyde" (NAF) or "zero added formaldehyde" (ZAF). Particleboard and fibreboard offer a flat uniform surface and the amino resin impregnated décor papers at b-stage allow the resin to flow in a controlled manner into the woodpanel surface and are fully cured in-situ.

[0005] Proposed changes to the traditional decorative panel which avoid using an amino formaldehyde impregnated décor paper have been presented in AU2020281056 and EP3896043 which are incorporated in their entirety. EP3896043 is the manufacture of a high opacity laminate surface whereby a nonwoven glass fleece is impregnated with a mixture of melamine, cyanuric acid and styrene maleic anhydride amic acid. The impregnation mixture avoids using TiO 2 to provide opacity and does not utilise a formaldehyde based resin. AU2020281056 is directed to painting a mineral silicate material as a coating onto the surface of a substrate or a substrate with an intermediate layer. A build-up of the mineral silicate surface coating may be achieved by painting more than one mineral silicate coating onto the substrate or intermediate layer.

[0006] As the manufacture of décor papers is a well-established and economical means to provide colour and or a printed motif, it would be advantageous to make use décor papers in the manufacture of a decorative laminate where there is no hot pressing step, avoiding the use of thermosetting amino formaldehyde resin, and where the choice of substrate could be expanded to include OSB and other materials which may be inhomogeneous or fragile and not suitable for hot pressing b-staged amino formaldehyde impregnated décor paper.

[0007] Furthermore, to first use the original decorative aspect of the colour or printed décor paper and then later to be able re-use the decorative panel with a different colour or print without causing damage to the substrate would be advantageous in both economic and environmental terms.

[0008] For the aforementioned reasons, the object of the present application is to demonstrate a decorative laminate panel which can be produced without hot pressing.

[0009] To solve the problem according to the invention for a decorative laminate panel, it is provided that the decorative paper is saturated with a clear or translucent alkali metal silicate and that the surface of the decorative panel is: a. Coated with a clear protective layer, or b. Coated with a clear protective layer containing a photocatalyst, or c. Coated with a clear protective layer to provide a gloss or matte finish, wherein the clear protective layer is a mineral silicate paint.

[0010] An advantageous embodiment of the laminate plate as well as a process can be taken from the sub-claims.

[0011] An objective of the invention is achieved by avoiding the use of thermosetting formaldehyde based saturation resins and no hot pressing, instead the décor paper is saturated with a substantially clear alkali metal silicate solution, preferably a sodium silicate solution. The clear sodium silicate solution saturates the décor paper without affecting the colour or the printed motif. There are no VOCs emanating from the sodium silicate material.

[0012] Instead of a heated short cycle press pressing the amino-formaldehyde impregnated décor paper onto the substrate, the adhesion of the décor paper to the substrate may be done by applying a glue to the substrate and applying the unsaturated décor paper to the glued substrate, alternatively the glue may be applied to both the substrate and to the reverse side of the décor paper and the substrate and décor paper brought together. Preferably a light pressure is applied to the décor paper and maintained for a short time to enhance the bonding between the substrate and the décor paper.

[0013] The decor paper glued to the substrate is saturated with a sodium silicate solution. The application of the sodium silicate solution is by roller coating, spraying or any other appropriate means. Preferably the sodium silicate is not in excess and any excess may be removed by a doctor blade.

[0014] Furthermore, in an alternative means of saturation, the decor paper may be saturated with the sodium silicate solution and partially cured before being glued to the substrate material. To maximise productivity, this saturation step and gluing to a substrate may be an in-line process.

[0015] The sodium silicate material can be cured by removal of water and or by chemical reaction. Care has to be taken when removing the water so as not to trap water below the surface which may causing blistering. Using NIR electromagnetic radiation enables the quick removal of water without overheating the surface. Chemical reactions with the sodium silicate material reduce surface permeability and increase water resistance, for example by reacting the sodium silicate with a salt of aluminium, magnesium, sodium or zinc oxide or calcium carbonate preferably precipitated calcium carbonate. However, using precipitated calcium carbonate in the sodium silicate solution will have an effect on the colour of the décor paper and or the printed motif. Therefore, the precipitated calcium carbonate is included as part of the filler during the manufacture of the décor paper and the chemical reaction to cure the sodium silicate takes place when the sodium silicate solution saturates the décor paper. A chemical reaction to cure the sodium silicate provides an improved heat and water resistant surface. Nevertheless, the surface of the sodium saturated décor paper is prone to water damage, or efflorescence, therefore a coating compatible with the sodium silicate and affording a hard wearing characteristic and low permeability of water would be beneficial. Fig.1 depicts the detrimental efflorescence effect shown as a white surface blemish.

[0016] Mineral silicate paints are compatible with sodium silicate allowing the décor paper saturated with sodium silicate to be painted with a clear mineral silicate paint, for example a clear potassium silicate paint. Advantageously, the mineral silicate paint can be applied to the sodium silicate saturated décor paper before the complete curing of the sodium silicate.

[0017] Mineral silicate paints are water borne, odourless and contain no VOCs and are non-film forming. According to literature available from CEFIC, soluble silicates have no significant environmental impact and do not possess a chemical oxygen demand (COD) or a biological oxygen demand (BOD). The alkaline nature of sodium silicate and mineral silicate paints provide resistance to microbial attack.

[0018] Commonly known as "water-glass", soluble sodium silicates are a colourless inorganic material where the main use has been as a thin film bonding agent for porous substrates such as paper and cardboard processed at high machine speeds where the thin film and fast setting characteristics are advantageous. Other applications utilising sodium silicate can be found in US8888904 - Heat generating graphite sodium silicate coating agent, wherein sodium silicate is a fire resisting agent; US4973506 / EP0314625 B1 - "Verbundplatte für Verkleidungen von Oberflächen von Bauwerken" wherein the sodium silicate forms part of a non-decorative intumescent protective panel; Gebrauchmuster DE29908316 U1 "Dämmelement oder Dekorplatte für Wände und Decken" wherein sodium silicate may be used to bond mica (in German = Glitter) to the surface of a insulation panel (Dämmelement). There is no available literature known to the inventors where sodium silicate is used to saturate a décor paper where the décor paper is used as the decorative aspect of a decorative laminate.

[0019] By varying the SiO 2 to Na 2 O ratio and the solids content different properties can be targeted. The SiO 2 to Na 2 O ratio generally varies from 1.6 to 3.3 and the solids content of sodium silicate solution is generally in the 25% to 65% range. The sodium silicate solution may be modified with the addition of small amounts of a surfactant, or a flexibilising agent such as glycerine or other polyhydric alcohols. In contrast to thin film gluing applications, for example WO87 / 02936 nominates a range between 4-10 lbs / 1000ft2, saturating a decor paper with a sodium silicate solution uses significantly more sodium silicate, without being a limiting example in excess of 200g / m2 of liquid sodium silicate can be achieved with a 200g / m2 décor paper. This volume of sodium silicate enhances the fire resistance of the decorative laminate surface.

[0020] The substrate for a decorative panel with a sodium silicate saturated décor paper may be chosen from materials such as plasterboard, solid wood panels such as CLT, wood based panels such as plywood, particleboard, fibreboard, or OSB, or a combination of materials, for example a combination of thin MDF and OSB. Other materials such as plastic and metal may also be covered with a sodium silicate saturated décor paper layer and a clear protective layer. Depending on the desired effect there may be an intermediate layer between the décor paper layer and the substrate, for example a layer to minimise the show-through of OSB strands, or to cover the edges of the panel. The intermediate layer and or the decorative paper layer may extend further to cover all or part of the edge and or the reverse side of the panel. Some examples of extending the decorative layer or intermediate layer are depicted in <a href='javascript:;' class="see-img-anchor" img-id="IMGF0002" img-title="Fig.2, 2', 2" and 2'">Fig.2, 2', 2" and 2'".

[0021] The use of a décor paper with low ash content and high bulk would be advantageous to avoid uneven expansion and wrinkles occurring, for example a décor paper of 200g / m 2< with about 20% ash content has proven to be less susceptible to uneven expansion and wrinkles in comparison to a 105g / m 2< 30% ash décor paper.

[0022] The décor paper provides a decorative surface having a colour or printed design common to décor papers used for traditional decorative laminates. However, unlike traditional decorative laminates where the décor paper is impregnated with a formaldehyde based resin, the basis of this invention is to saturate the décor paper with a metal alkali silicate, preferably a sodium silicate solution. Furthermore, the sodium silicate solution is not pigmented so as not to impact the decorative aspect of the original décor paper. While it is standard practise to print the décor paper before impregnation, it is also practical to print the decorative surface after the decorative layer has been saturated with sodium silicate and the sodium silicate set or partially cured. The set or partially cured surface of the sodium silicate saturated décor paper may have a primer applied before for printing, preferably inkjet printing.

[0023] The set or partially cured surface of the sodium silicate saturated décor paper, whether printed or not printed, may be coated with one or more applications of a mineral silicate paint, in which case the mineral silicate paint may contain a photocatalyst, for example Ecosil-ME (Keimfarben GmbH, Diedorf Germany). Preferably the photocatalyst is in the outermost mineral silicate paint coating. Providing the photocatalyst in an inorganic material allows the photocatalyst to perform its designed function without also destroying the carrier material it is bound in. Mineral silicate paint is an inorganic material which does not form a film, therefore the air borne VOCs are able to contact the photocatalyst much more readily than if the photocatalyst is encapsulated in a film forming coating. According to literature to be optimally effective the photocatalyst needs light and air, as well as direct contact with the pollutant (Effective Cleaning with Light, Feb 1, 2011 Dr Stephan Blöss, Kronos International Inc.).

[0024] If a photocatalyst is not included in the mineral silicate paint, then a clear protective coating may be applied to the mineral silicate paint and in addition to surface protection, the clear protective coating may provide a desired gloss or matte finish. Crommelin ®< Diamond Coat Sealer in Gloss or Satin finish proved effective, see Fig.3.

[0025] Traditional decorative laminates, with the exception of some white grades, use a clear amino formaldehyde resin for both core and surface. The surface layer of melamine formaldehyde is a thermoset resin and once fully cured in a hot press the surface texture and gloss level cannot be changed. With the invention based on a décor paper saturated with sodium silicate and applying a mineral silicate paint to the sodium silicate saturated décor paper, it is practical to at a later date change the gloss level, or to re-use the panel with a new colour or to apply a new printed motif to the surface, see Fig.4a / 4b. Small imperfections in the surface can be removed and the surface repainted with a clear mineral silicate paint.

[0026] When a unicolour or printed motif is presented using a sodium silicate saturated décor paper it is logical that the coating of the sodium silicate saturated décor paper will be with a clear as possible material. Besides using a clear mineral silicate paint, the clear protective coating may be used to provide a different effect to the surface, for example Crommelin ®< DiamondCoat anti-slip or Chugoku Fluorex (CMP Japan) for weather resistance.

[0027] The decorative aspect of the decorative panel surface may be created by using a unicolour décor paper, or printed décor paper. The décor paper surface layer should have the capacity to absorb the sodium silicate solution in quantities that enhance fire resistance, for example a 200g / m 2< décor paper with 20% ash content will readily absorb 200g / m 2< of liquid sodium silicate (~40% solids). The weight of the paper and ash content is not limited to 200g / m 2< or 20% ash content. The sodium silicate solution has a tacky aspect, therefore it is preferable to avoid an excess of the sodium silicate solution outside the décor paper, however small excesses can be tolerated and covered by a mineral silicate paint. The mineral silicate paint can be applied before the sodium silicate is completely cured and dry.

[0028] Typically to cure the sodium silicate requires application of heat to remove the water from the saturated decorative surface material, and or a chemical reaction. The décor paper may contain a filler material which will catalyse the sodium silicate solution, for example but not limited to aluminium sulphate, magnesium sulphate or precipitated calcium carbonate. The catalyst filler may comprise 100% of the filler in the décor paper, alternatively the catalyst filler may be one component of the filler material used in the manufacture of the décor paper.

[0029] A significant process advantage to boost productivity is that before the sodium silicate material has been fully cured it is possible to coat the surface of the sodium silicate saturated décor paper with a mineral silicate paint. The mineral silicate paint is not film forming and allows the evaporation of water from the sodium silicate to complete the curing process. This is described in Example 1.

[0030] There may be a substantially clear protective coating applied to the sodium silicate saturated decorative surface layer. The substantially clear protective layer may include additives to provide properties such as an antimicrobial or antibacterial, furthermore a photocatalyst may be incorporated to destroy VOCs from the surrounding environment when air contacts the decorative panel surface. The photocatalyst can be chosen to perform its function of destroying airborne VOCs by being reactive in sunlight and / or indoor lighting, for example KRONOClean 7000 (Kronos Titan GmbH, Leverkusen Germany).

[0031] The surface of the decorative panel surface may be smooth or structured. As a decorative effect, the surface wood strands of an OSB panel may be allowed to telegraph through the decorative surface layer by wetting of the OSB surface, either before or during the adhesion of the decorative layer and or the intermediate layer which creates the opportunity for the wood strands to expand, see Fig.5. A 200g / m2 décor paper with 20% ash has more bulk than a standard 80g / m2 décor paper and a structured roller can be used to provide a structured surface effect when applied before the sodium silicate saturated décor paper has fully cured. A structured effect may be created in the décor paper during the manufacture of the décor paper.

[0032] The reverse side of the decorative panel surface may have a sodium silicate saturated décor paper, or may be coated with a substance or material to prevent ingress of water or to provide insulation or another means of fire protection. The edges of the decorative panel may be treated to prevent ingress of moisture, which may be a wax coating, or a surface layer may extend beyond the edge of the panel and be forced on to the edge section, or even extending further to cover part or all of the rear of the panel.Examples

[0033] (1) A 200g yellow décor paper (Munksjo France reference 77777) was glued to a 6mm OSB panel (Egger OSB'race) previously laminated with a 70g / m2 nonwoven glass fleece (Ahlstrom Finland) as the interlayer. The glue used was Selleys ®< AllFix Big Jobs Multipurpose adhesive. The format of the panel was 290mm x 210mm and the laminated panel (OSB + nonwoven glass fleece + décor paper + glue) weighed 346.6g (5.69 kg / m2). After impregnation with a liquid sodium silicate (Type NC203, Northcote Pottery Supplies / SDS from REDOX P / L dated 19 / 03 / 2015) the weight increased to 358.4g ( = 11.8g liquid sodium silicate) and allowed to dry in ambient conditions. The weight decreased over 4 hours to 353.9g at which point a clear potassium mineral silicate paint (20% solids) was applied to the décor surface and the weight increased to 359.2g (= 5.3g liquid potassium mineral silicate paint). Left to dry at ambient conditions after 2 hours the weight decreased to 355.01g and was stored in an unheated room overnight. The following morning the weight was measured as 350.7gms. (2) A 200g / m2 blue décor paper (20% ash content) was glued to one side of a 6mm OSB substrate. The glue (Selleys ®< AllFix Big Jobs Multipurpose adhesive) is coated onto the OSB substrate and onto the reverse side of the décor paper, then the substrate and décor paper are combined. A smooth weight is applied to the surface of the décor paper to ensure a tight contact between the OSB and the décor paper. Applied by hand using a broad blade spatula, the amount of glue is approximately 300g / m 2< on the OSB and approximately 200g / m 2< on the back of the décor paper. Subsequently, the décor paper surface was impregnated with approximately 300g / m 2< of clear sodium silicate solution (Type NC203, Northcote Pottery Supplies / SDS from REDOX P / L dated 19 / 03 / 2015) and left to dry under atmospheric conditions. The décor paper saturated with sodium silicate was coated with a clear matt potassium silicate paint (ca. 20% solids) (Murobond, Sydney AU). The amount of liquid clear matt potassium silicate paint was approximately 67g / m 2< . (3) A 70g / m 2< nonwoven glass fleece (Ahlstrom, Finland) was glued to a 6mm OSB substrate using Selleys ®< AllFix multipurpose adhesive. Subsequently, a glue (Selleys ®< AllFix) is coated onto the glass fleece and onto the reverse side of a 200g / m2 yellow décor paper, then the OSB+glass fleece and décor paper are combined and kept under a slight pressure. Later a clear solution of sodium silicate is impregnated into the surface of the yellow décor paper and allowed to dry. The distinctive pattern of wood strands can be seen, Fig 5. Subsequently, a clear liquid potassium silicate paint was applied to the surface of the sodium silicate impregnated décor surface. (4) A 200g / m2 black décor paper (Munksjo France ref. 99536) was glued directly to a MDF substrate. The black décor paper was saturated with a solution of sodium silicate and allowed to dry. The sodium silicate saturated surface was allow to dry under ambient conditions and subsequently a clear potassium silicate paint was applied to the surface. Later the mineral silicate surface was lightly sanded with a 80grit sandpaper to remove surface impurities (glue), followed by another light sanding with a 400grit sandpaper, see Fig. 6a. The surface was again coated with clear potassium mineral silicate paint and a homogenous black surface created, see Fig. 6b. To compare gloss or matt finishes, a black décor surface was subsequently coated with Crommelin ®< DiamondCoat Gloss sealer, see Fig.3. (5) A 105g beige décor paper was glued directly to a MDF substrate and later saturated with a sodium silicate solution. The surface appearance was not uniform due to irregular expansion of the décor paper when in contact with the glue before the sodium silicate was used to saturate the décor paper. Subsequently the decorative surface was sanded with a P400 grit sandpaper and then a mineral silicate primer applied. Later the surface was painted with a pigmented potassium silicate paint (Murobond colour ref. Alfalfa), see Fig 4. Figure 1: depicts the deleterious efflorescent affect on an uncoated sodium silicate surface of a decorative panel Figure 2: depicts the decorative layer (2B) covering the edge of the panel (2A). The protective layer shown as 2C. Figure 2': depicts an intermediate layer (2D) covering the edge and reverse of the panel Figure 2": depicts an intermediate layer covering the upper edges of the panels, extending over part of the groove (2E) (double groove construction) Figure 2‴: depicts an intermediate layer covering the upper edges of the panels, extending to the tongue (2F), and over part of the groove (2E) (tongue & groove construction) Figure 3: depicts a gloss or matte protective layer on the surface of the decorative laminate panel Figure 4a: depicts a decorative laminate panel with a protective layer applied to the surface Figure 4b: depicts a partial recoating of the decorative laminate panel (Fig. 4a) Figure 5: depicts the inhomogeneous strand construction of an OSB panel allowed to telegraph through the decorative surface Figure 6a: depicts the surface of a black decorative surface that has been sanded to remove soke surface impurities Figure 6b: depicts the surface of a sanded black decorative surface (Fig 6a) recoated with a clear potassium silicate mineral paint

Claims

1. A decorative laminate panel manufactured with a unicolour or printed décor paper, characterised in that the décor paper is saturated with a clear or translucent alkali metal silicate and that the surface of the decorative panel is; a. coated with a clear protective layer, or b. coated with a clear protective layer containing a photocatalyst, or c. coated with a clear protective layer to provide a gloss or matte finish, wherein the clear protective layer is a mineral silicate paint.

2. A decorative laminate panel according to claim 1, wherein the alkali metal silicate is sodium silicate.

3. A decorative laminate panel according to claim 1 or 2, wherein the mineral silicate paint is a potassium mineral silicate paint and contains a photocatalyst.

4. A decorative laminate panel according to one of the claims 1 - 3, wherein the photocatalyst is functional in both sunlight and indoor lighting.

5. A decorative laminate panel according to one of claims 1-4, wherein the décor paper ash content contains in part a filler material which is provided to catalyse the sodium silicate material.

6. A decorative laminate panel according to claim 5, wherein the filler in the décor paper is precipitated calcium carbonate.

7. A decorative laminate panel according to any preceding claim, wherein a printed motif is applied to the sodium silicate saturated panel surface, preferably by inkjet printing.

8. A decorative laminate panel according to any preceding claim, wherein one or more surface layers extend beyond the decorative surface and covers the edges and or part or all of the reverse side of the decorative panel.

9. A process whereby a décor paper is saturated with a solution of an alkali metal silicate and subsequently coated with a clear mineral silicate paint.

10. A process according to claim 9, wherein the clear mineral silicate paint is applied to the sodium silicate saturated décor paper surface before the sodium silicate material is fully cured.

11. A process according to claim 9 or 10, wherein the original decorative surface of the sodium silicate saturated décor paper is re-purposed with a new surface colour or printed motif.

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