Method of applying a photocatalytic dispersion

Abstract

A method of applying a photocatalytic dispersion (10) on a paper (2), including impregnating a paper (2) with a thermosetting resin, drying the resin impregnated paper (2), applying a photocatalytic dispersion (10) comprising photocatalytic nanoparticles on the dried, resin impregnated paper (2), and drying the resin impregnated paper (2) having the photocatalytic dispersion applied thereon. Also, to such a photocatalytic dispersion.

Claims

1. Method of applying a photocatalytic dispersion on a paper, the method comprising impregnating a paper with a thermosetting resin, drying the resin impregnated paper, applying a photocatalytic dispersion comprising photocatalytic nanoparticles on the dried, resin impregnated paper, and drying the resin impregnated paper having the photocatalytic dispersion applied thereon, wherein the photocatalytic dispersion further comprises scratch resistant particles.

2. Method according to claim 1, wherein the photocatalytic dispersion further comprises an anti-photogreying additive.

3. Method according to claim 2, wherein the anti-photogreying additive is a surfactant.

4. Method according to claim 3, wherein the surfactant is a polyether modified siloxanes.

5. Method according to claim 2, wherein the anti-photogreying additive is present in the photocatalytic dispersion in a concentration higher than 0.1 wt. %.

6. Method according to claim 2, wherein the anti-photogreying additive is present in the photocatalytic dispersion in a range of 1-35 wt. %.

7. Method according to claim 1, wherein the scratch resistant particles are nanosized silica particles.

8. Method according to claim 7, wherein the scratch resistant particles are or comprise aluminium oxide.

9. Method according to claim 1, wherein the scratch resistant particles are disc shaped particles having a width/thickness ratio being equal or exceeding 3:1.

10. Method according to claim 1, wherein the photocatalytic nanoparticles are photocatalytic titanium dioxide.

11. Method according to claim 1, wherein photocatalytic nanoparticles have primary particle size of less than 50 nm.

12. Method according to claim 1, wherein the photocatalytic dispersion is waterborne.

13. Method according to claim 1, wherein the photocatalytic dispersion is applied by at least one roller.

14. Method according to claim 1, wherein the paper is a continuous paper web.

15. The method according to claim 1, wherein a loss on cure of the resin impregnated paper after the drying is less than 20%.

16. A method of applying a photocatalytic dispersion on a paper, the method comprising: impregnating a paper with a thermosetting resin, drying the resin impregnated paper, applying a photocatalytic dispersion comprising photocatalytic nanoparticles and scratch resistant particles on the dried, resin impregnated paper, and drying the resin impregnated paper having the photocatalytic dispersion applied thereon, wherein a ratio of the amount of photocatalytic nanoparticles to the amount of scratch resistant particles is between 1:4 and 1:1.

17. A method of applying a photocatalytic dispersion on a paper, the method comprising: impregnating a paper with a thermosetting resin, drying the resin impregnated paper, applying a photocatalytic dispersion on the dried, resin impregnated paper, the photocatalytic dispersion comprising photocatalytic nanoparticles, scratch resistant particles, and an anti-photogreying additive, and drying the resin impregnated paper having the photocatalytic dispersion applied thereon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will by way of example be described in more detail with reference to the appended schematic drawings, which show embodiments of the disclosure.

(2) FIG. 1 shows a photocatalytic process of titanium dioxide.

(3) FIG. 2 shows an embodiment of a method of applying a photocatalytic dispersion.

(4) FIGS. 3a-b show an embodiment of a method of applying a photocatalytic dispersion.

(5) FIG. 4 shows an embodiment of a method of manufacturing a panel.

(6) FIG. 5 shows a panel having a photocatalytic dispersion applied thereon.

(7) FIG. 6 shows an embodiment of a method of manufacturing a panel.

DETAILED DESCRIPTION

(8) A method of applying a photocatalytic dispersion will now be described with reference to FIG. 2. FIG. 2 shows an impregnating line 1 for impregnating a paper 2 with a thermosetting resin. The paper is preferably a continuous paper web. The paper comprises preferably cellulosic material.

(9) In a first step, the paper 2 is impregnated with a thermosetting resin 4 in an impregnation station 3. The thermosetting resin 4 is preferably an amino resin such as melamine formaldehyde resin, phenol formaldehyde resin, urea formaldehyde resin, or a combination thereof. Preferably, the resin is melamine formaldehyde resin.

(10) The paper 2 is impregnated with the thermosetting resin 4 in any conventional way. For example, the paper 2 may pass a container 5 with the resin 4. The paper 2 may also pass between rollers 6, pressing the resin 4 into the paper 2. The resin 4 is preferably pressed into the paper 2 from both sides of the paper 2. By thermosetting resin is also meant a composition comprising a thermosetting resin.

(11) In one embodiment, wear resistant particles 7 are applied on an upper side of the resin impregnated paper 2. When later arranged on a substrate, this side will be facing downwards, towards the substrate. The wear resistant particles 7 are provided for obtaining wear resistant properties of the paper. The wear resistant particles 7 may be aluminium oxide (Al.sub.2O.sub.3), for example corundum. The wear resistant particles 7 may have an average particle size of 5-100 m. The wear resistant particles 7 may be scattered on the upper side of the paper 2.

(12) The resin-impregnated paper 2 is thereafter dried. Preferably, the paper 2 is guided into a first drying station 8. The paper 2 is preferably dried by means of heated air. The temperature in the first drying station 8 may be 100-150 C. As an example, the temperature may be about 100-110 C. at the entrance of the first drying station 8, and may be 140-150 C. at the end of the first drying station 8. It is also contemplated that the paper 2 may be dried by means of, for example, IR.

(13) The paper is preferably dried to such an extent that the loss on cure of the paper after drying is less than 20%, preferably less than 15%. The loss on cure of the paper after drying may be 9-20%, such as 10-13%.

(14) When the paper 2 has been impregnated with the thermosetting resin 4 and dried, a photocatalytic dispersion 10 is thereafter applied on the paper 2 in a subsequent step in an application station 9.

(15) The photocatalytic dispersion 10 is applied by one or more rollers 11 onto the paper. The photocatalytic dispersion 10 may be filled into a container in which the paper 2 passes. The photocatalytic dispersion 10 may be circulated.

(16) The photocatalytic dispersion 10 is applied on at least one side of the paper 2. The photocatalytic dispersion 10 may be applied on a side of the paper 2 facing downwards when passing the impregnation line 1. When later arranged on a substrate, this side will be facing upwards, forming an upper surface.

(17) The photocatalytic dispersion 10 may be applied on the paper 2 in an amount of 10-50 g/m.sup.2, more preferably 20-40 g/m.sup.2 such as about 30 g/m.sup.2 such as about 20 g/m.sup.2. In one embodiment, the photocatalytic dispersion is applied in an amount of 1-10 g/m.sup.2.

(18) As an alternative or complement, the photocatalytic dispersion may be applied by any other means, such as by spraying, brushing, digital printing etc.

(19) The photocatalytic dispersion 10 comprises photocatalytic nanoparticles. The photocatalytic nanoparticles may be photocatalytic titanium dioxide (TiO.sub.2). The photocatalytic titanium dioxide particles are preferably in anatase form.

(20) The photocatalytic composition may comprise photocatalytic TiO.sub.2 particles in dispersion. The photocatalytic TiO.sub.2 are preferably in anatase phase. The photocatalytic dispersion may be dispersed in a solvent, preferably water. The concentration of photocatalytic TiO.sub.2 particles in the dispersion is preferably in the range 0.3 wt. % to 40 wt. %, more preferably in the range 1.0 wt. % to 30 wt. % such as in the range 5 wt. % to 25 wt. %. The photocatalytic TiO.sub.2 particles are preferably applied on the paper 2 in an amount of 0.5-12.5 g/m.sup.2, more preferably 1-10 g/m.sup.2 such as less than 10 g/m.sup.2 such as less than 5 g/m.sup.2.

(21) In an embodiment, the photocatalytic particles may be doped with non-metals and/or metals. The TiO.sub.2 particles may be doped with non-metals and/or elements such as but not limited to the list of C, N, F, S, Mo, V, W, Cu, Ag, Au, Pt, Pd, Fe, Co, La, Eu, WO.sub.2, and PdO or a combination thereof.

(22) The photocatalytic particles may be nanosized TiO.sub.2 particles. The TiO.sub.2 particles may have a size in the range from 5-250 nm, preferably in the range 5-100 nm, more preferably in the range 5-50 nm, most preferably in the range of 5-30 nm.

(23) The photocatalytic dispersion 10 may be stabilized by pH and/or a dispersant agent. The photocatalytic dispersion 10 may be stabilized at pH>9 by preferably, but not limited to, amines, for example triethylenamine. The photocatalytic dispersion may also be stabilized at pH<4 by preferably, but not limited to, a strong acid like HCl. The photocatalytic dispersion may further be stabilized by a dispersion agent to keep the particles in suspension and from re-agglomerating. The dispersion may be stabilized by, but not limited to, propylene glycol. In an embodiment, binders are added to the photocatalytic composition to enable and to improve the adhesion of the TiO.sub.2 particles to the substrate on which the composition is applied. Preferably these binders are non-photocatalytically degradable in the group of preferably, but not limited to, silanes, siloxanes, silicones, SiO.sub.2, surface modified SiO.sub.2, amorphous TiO.sub.2, alkoxides, Ti-alkoxides, Si-alkoxides, UV curable binders and heat curable binders.

(24) In an embodiment, the photocatalytic composition 10 is a stable nanosized TiO.sub.2 dispersion in water with a size in suspension of said photocatalytic particles of less than 50 nm in concentration of said TiO.sub.2 particles up to 40 wt. %. Additives may be added to the photocatalytic composition in order to, for example, enhance the coating and film formation properties and to improve the colourfastness upon light exposure. Additives may be added to the photocatalytic composition as to improve the coating and/or application properties of the photocatalytic composition. Examples of such additives are humectants. Furthermore, wetting agents may be added to the photocatalytic composition to enhance the wetting of the photocatalytic composition on a substrate. An example of such wetting agent may be, but not limited to, the group of polyether modified siloxanes silicone surfactant such as polyether modified siloxanes.

(25) The photocatalytic dispersion 10 may further comprise scratch resistant particles. The scratch resistant particles provide the paper with scratch resistant properties.

(26) In one embodiment, the scratch resistant particles comprise nanosized silica particles. The silica particles may be fused nanosized silica particles. The silica particles may comprise a silicium containing compound such as SiO.sub.2, colloidal SiO.sub.2, functional nanoscaled SiO.sub.2, silicone resin, organofunctional silanes, and/or colloidal silicic acid silane and/or a combination of said compounds.

(27) The nanosized silica may have a primary particles size of less than 50 nm, preferably less than 30 nm, more preferably less than 20 nm. As an example, the nanosized silica may be of the type DeuroGuard NS marked by Deurowood.

(28) The ratio between the amount of photocatalytic nanoparticles such as TiO.sub.2 and the amount of nanosized silica may be 1:4, such as 1:3, such as 1:2 such as 1:1.

(29) In other embodiments, the scratch resistant particles comprise aluminium oxide (Al.sub.2O.sub.3), zirconia (ZrO.sub.2), or a combination comprising silica, aluminium oxide, and/or zirconia.

(30) In one embodiment, the scratch resistant particles may comprise disc shaped particles. The disc shaped particles may have an average particle size of 1-100 m, for example 1-30 m. The width/thickness ratio may equal or be exceeding 3:1, preferably equal or exceeding 5:1.

(31) The disc shaped scratch resistant particles may be or comprise aluminium oxide (Al.sub.2O.sub.3). As an example, the scratch resistant particles may be of the type Microgrit WCA S marketed by Micro Abrasives Corporation.

(32) In one embodiment, the photocatalytic dispersion 10 comprises different types of scratch resistant particles, such as both nanosized silica and disc-shaped particles.

(33) The photocatalytic dispersion may further comprise an anti-photogreying additive. The anti-photogreying additive may be a surfactant. The surfactant may be a non-ionic surfactant. The surfactant may be a silicone surfactant, preferably a non-ionic silicone surfactant. More preferably, the surfactant may be a polyether modified siloxanes. More preferably, the surfactant may be a polyether modified polysiloxanes. More preferably, the surfactant may be a polyether modified polymethyl siloxane. As an alternative, the surfactant may be polydimethylsiloxane co-polymer.

(34) In a further embodiment, the anti-photogreying additive may be a polyglycol, preferably poly(ethylene glycol) methyl ether.

(35) In a further embodiment, the anti-photogreying additive may be a polyoxyethylene sorbitan, preferably polyoxyethylene sorbitan. Preferably, the anti-photogreying additive may be a polyoxyethylene sorbitan monooleate.

(36) In a further embodiment, the anti-photogreying additive may be polyvinyl alcohol (PVA) and/or polyvinyl pyrolidon (PVP), and/or poly(ethylene glycol) methyl ether, preferably combined with a wetting agent.

(37) The photocatalytic dispersion may comprise at least 0.1 wt. % of the anti-photogreying additive such as the surfactant, preferably at least 1 wt. % of the anti-photogreying additive such as the surfactant, more preferably at least 10 wt. % of the anti-photogreying additive such as the surfactant. The anti-photogreying additive such as the surfactant may be present in the photocatalytic dispersion in the range of 1-35 wt. %, preferably 1-15 wt. %, more preferably 5-12 wt. %.

(38) The anti-photogreying additive such as the surfactant may reduce photogreying while maintaining the photocatalytic activity of the photocatalytic nanoparticles. The photocatalytic activity is preferably maintained to a level of at least 90% of the level achieved without the photogreying additive. The photogreying index of the photocatalytic dispersion may be less than 6, preferably less than 5, more preferably less than 4, most preferably less than 3 such as less than 2.

(39) After the paper 2 has been coated with the photocatalytic dispersion 10, the paper is dried. Preferably, the paper 2 is preferably guided into a second drying station 12. The paper 2 is preferably dried by means of heated air. The temperature in the second drying station 12 may be 120-100 C. As an example, the temperature may be about 120 C. at the entrance of the second drying station 12, and may be about 110 C. at the end of the second drying station 12. It is also contemplated that the paper may be dried by means of, for example, IR.

(40) The dried paper 2 may be cut into sheets, or may be wound, for example on a roller, as shown in FIG. 2, depending on the subsequent process.

(41) The impregnated paper 2 may be stored after impregnation, or may directly be used in a lamination process.

(42) The impregnated paper 2 may be an overlay paper 21. The impregnated paper may be a dcor paper. If the impregnated paper 2 is a dcor paper, the dcor paper is arranged such that the dcor faces downwards in the impregnation line and such that the photocatalytic dispersion 10 is applied on the dcor.

(43) In one embodiment, which is shown in FIGS. 3a-b, the paper is first impregnated in an impregnation process, which is shown in FIG. 3a, and thereafter the photocatalytic dispersion 10 is applied, which is shown in FIG. 3b.

(44) In a first step, corresponding to the first part of the impregnation line shown in FIG. 2, the paper 2 is impregnated with a thermosetting resin 4 in an impregnation station 3, which is shown in FIG. 3a. The thermosetting resin 4 is preferably an amino resin such as melamine formaldehyde resin, phenol formaldehyde resin, urea formaldehyde resin, or a combination thereof. Preferably, the resin is melamine formaldehyde resin.

(45) The paper 2 is impregnated with the thermosetting resin 4 in any conventional way. For example, the paper 2 may pass a container 5 with the resin 4. The paper 2 may also pass between rollers 6, pressing the resin 4 into the paper 2. The resin 4 is preferably pressed into the paper 2 from both sides of the paper 2. By thermosetting resin is also meant a composition comprising a thermosetting resin.

(46) In one embodiment, wear resistant particles 7 are applied on an upper side of the resin impregnated paper 2. When later arranged on a substrate, this side will be facing downwards, towards the substrate. The wear resistant particles 7 are provided for obtaining wear resistant properties of the paper. The wear resistant particles 7 may be aluminium oxide (Al.sub.2O.sub.3), for example corundum. The wear resistant particles 7 may have an average particle size of 5-100 m. The wear resistant particles 7 may be scattered on the upper side of the paper 2.

(47) The resin-impregnated paper 2 is thereafter dried. Preferably, the paper 2 is guided into a first drying station 8. The paper 2 is preferably dried by means of heated air. The temperature in the first drying station 8 may be 100-150 C. As an example, the temperature may be about 100-110 C. at the entrance of the first drying station 8, and may be 140-150 C. at the end of the first drying station 8. It is also contemplated that the paper 2 may be dried by means of for example IR.

(48) The paper is preferably dried to such an extent that the loss on cure of the paper after drying is less than 10%. The loss on cure of the paper after drying may be 5-9%.

(49) The dried, resin impregnated paper 2 is thereafter wound on a roller as shown in FIG. 3a, or cut into sheets (not shown).

(50) In a second step, which may be separate and/or offline from the impregnation process described with reference to FIG. 3a, the photocatalytic dispersion 10 is applied to the dried, resin impregnated paper 2, which is shown in FIG. 3b.

(51) The photocatalytic dispersion 10 is applied to the dried, resin impregnated paper 2. The photocatalytic dispersion 10 is of the same type as described above with reference to FIG. 2. The paper 2 may be in form of a continuous paper web as shown in FIG. 3b, or have been cut into sheet (not shown).

(52) Independent of the paper 2 being a continuous web or cut into sheets, the photocatalytic dispersion 10 is applied on the dried, resin impregnated paper 2. The photocatalytic dispersion 10 is of the type described above with reference to FIG. 2. The photocatalytic dispersion 10 may comprises an anti-photogreying additive of the type described above with reference to FIG. 2, scratch and/or wear resistant particles of the type described above with reference to FIG. 2, and additives of the type described above with reference to FIG. 2. The photocatalytic dispersion 10 is preferably applied by means of spraying. FIG. 3b shows spraying of the photocatalytic dispersion 10 by a spraying device 30. The size of the droplets may be in the range of 1-200 m, and may be up to about 200 m, 150 m, 100 m, 50 m, 25 m or 10 m. The photocatalytic dispersion 10 may be applied on the paper 2 in an amount of 10-50 g/m.sup.2, more preferably 20-40 g/m.sup.2 such as about 30 g/m.sup.2 such as about 20 g/m.sup.2. In one embodiment, the photocatalytic dispersion is applied in an amount of 1-10 g/m.sup.2. The concentration of photocatalytic TiO.sub.2 particles in the dispersion is preferably in the range 0.3 wt. % to 40 wt. %, more preferably in the range 1.0 wt. % to 30 wt. % such as in the range 5 wt. % to 25 wt. %. The photocatalytic TiO.sub.2 particles are preferably applied on the paper 2 in an amount of 0.5-12.5 g/m.sup.2, more preferably 1-10 g/m.sup.2 such as less than 10 g/m.sup.2 such as less than 5 g/m.sup.2.

(53) Alternatively, or as complement, the photocatalytic dispersion is applied by roller coating, brushing, digital printing, etc.

(54) The paper 2 having the photocatalytic dispersion applied thereon is thereafter dried, preferably by a drying device 31. Preferably, the paper 2 is dried by means of IR or NIR. It is also contemplated that the paper may be dried by means of for example heated air, for example as described with reference to FIG. 2.

(55) The dried paper 2 may be cut into sheets, or may be wound, for example on a roller, as shown in FIG. 3b, depending on the subsequent process.

(56) The impregnated paper 2 may be stored after impregnation, or may directly be used in a lamination process.

(57) The impregnated paper 2 may be an overlay paper 21. The impregnated paper may be a dcor paper. If the impregnated paper 2 is a dcor paper, the dcor paper is arranged such that the dcor faces downwards in the impregnation line and such that the photocatalytic dispersion 10 is applied on the dcor. The impregnated paper 2 having the photocatalytic dispersion applied thereon may be arranged on a substrate 13. The substrate 13 may be wood based substrate such as HDF, MDF, particle board, OSB, WPC (wood plastic composite). The impregnated paper 2, such an overlay paper 21, may also be arranged on a dcor paper 14 arranged on the substrate 13, as shown in FIG. 4.

(58) The impregnated paper 2 is arranged on the substrate 13 or on the underlying dcor paper 14 such that the side of the paper on which the photocatalytic dispersion 10 is applied is facing upwards away from the substrate 13 or underlying paper 14. If wear resistant particles 7 have been applied on the other side of the paper, this side of the paper is facing the substrate 13 or the underlying dcor paper 14.

(59) By applying heat and pressure, the thermosetting resin of the impregnated paper 2 is cured and the impregnated paper 2 is laminated to the substrate 13 or underlying paper 14. In FIG. 4, the substrate 13, the dcor paper 14 and the impregnated paper 2 forming the overlay paper 21 is conveyed through a continuous press 15, wherein the substrate 13, dcor paper 14 and the overlay paper 2 are attached to each other. Thereby, a panel 20 comprising a photocatalytic surface having scratch resistant properties is obtained, as shown in FIG. 5. As an alternative to a continuous press, a static press may also be used.

(60) The photonic efficiency of the paper 2 having photocatalytic properties may be exceeding 0.025%, preferably exceeding 0.05%, more preferably exceeding 0.1%. The paper 2, 21 on which the photocatalytic dispersion has been applied obtains hydrophilic properties. The contact angle with water may be less than 40 under indoor lightning conditions, preferably less than 30, more preferably less than 25 such less than 20.

(61) As shown in FIG. 5, the panel 20 comprising a substrate 13 of the above described type, a dcor paper 14 arranged on the substrate and the impregnated paper 2 forming the overlay paper 21, impregnated and applied with a photocatalytic dispersion 10 according the above described method.

(62) The overlay paper 21 comprises in the embodiment shown in FIG. 5 wear resistant particles 7 on the side of the overlay paper 21 facing downwards, i.e. facing the dcor paper 14. The wear resistant particles 7 may have an irregular shape. The overlay paper 21 further comprises photocatalytic nanoparticles 16 on the side of the overlay paper 21 facing upwards, i.e. facing away from the dcor paper 14. The overlay paper 21 further comprises scratch resistant particles. The scratch resistant particles may be nanosized silica 17. The scratch resistant particles may also be disc-shaped particles 18 of for example aluminium oxide. The disc-shaped particles 18 are orientated such along the surface of the overlay paper 21.

(63) In one embodiment, the photocatalytic dispersion is applied in connection with manufacturing a panel 20, which is shown in FIG. 6.

(64) A balancing layer 19 is arranged on a conveyor belt 33. The balancing layer 19 may be a backing paper. The backing paper is preferably a resin impregnated paper. A substrate 13 is arranged on the balancing layer. The substrate 13 may be a wood-based board such as MDF, HDF, particle board, OSB, WPC (Wood Plastic Composite), etc. The substrate 13 may be formed of several resin impregnated papers. As an alternative to a backing paper, the substrate 13 may be provided with a powder based balancing layer on one side of the substrate 13. The powder based balancing layer may comprise a thermosetting binder and lignocellulosic and/or cellulosic particles.

(65) A decorative layer 14 may be arranged on a surface of the substrate 13 opposite the balancing layer 19. The decorative layer 14 may be a printed paper or foil of any type as shown in FIG. 6. The decorative layer 14 may also be formed of a print printed on the substrate 13.

(66) An overlying layer 21 is arranged on the decorative layer 14, as shown in FIG. 6. The overlying layer 21 may also be arranged on the substrate if no separate decorative layer is provided. The overlying layer 21, on which the photocatalytic dispersion is to be applied, forms an outermost surface layer of the panel 20.

(67) The overlying layer 21 is in the embodiment shown in FIG. 6 provided in form of a dried, resin impregnated paper 2. The impregnated paper 2 may be an overlay paper. The overlay paper may comprise wear and/or scratch resistant particles of the above described type. The overlay paper is impregnated with a thermosetting binder. The thermosetting resin is preferably an amino resin such as melamine formaldehyde resin, phenol formaldehyde resin, urea formaldehyde resin, or a combination thereof.

(68) Preferably, the resin is melamine formaldehyde resin. The paper is preferably dried to such an extent that the loss on cure of the paper is less than 10%. The loss on cure of the paper may be 5-9%. The paper has been impregnated and dried is a separate process from the process of forming the panel.
The photocatalytic dispersion 10 is applied on the overlying layer 21. The photocatalytic dispersion 10 is of the type described above with reference to FIG. 2. The photocatalytic dispersion 10 may comprises an anti-photogreying additive of the type described above with reference to FIG. 2, scratch and/or wear resistant particles of the type described above with reference to FIG. 2, and additives of the type described above with reference to FIG. 2. The photocatalytic dispersion is preferably applied by means of spraying. In FIG. 6, the photocatalytic dispersion 10 is applied by a spraying device 30. The size of the droplets may be up to about 200 m, 150 m, 100 m, 50 m, 25 m or 10 m. The photocatalytic dispersion 10 may be applied on the paper 2 in an amount of 10-50 g/m.sup.2, more preferably 20-40 g/m.sup.2 such as about 30 g/m.sup.2 such as about 20 g/m.sup.2. In one embodiment, the photocatalytic dispersion is applied in an amount of 1-10 g/m.sup.2. The concentration of photocatalytic TiO.sub.2 particles in the dispersion is preferably in the range 0.3 wt. % to 40 wt. %, more preferably in the range 1.0 wt. % to 30 wt. % such as in the range 5 wt. % to 25 wt. %. The photocatalytic TiO.sub.2 particles are preferably applied on the paper 2 in an amount of 0.5-12.5 g/m.sup.2, more preferably 1-10 g/m.sup.2 such as less than 10 g/m.sup.2 such as less than 5 g/m.sup.2.

(69) Alternatively, or as complement, the photocatalytic dispersion 10 is applied by roller coating, brushing, digital printing, etc.

(70) The paper 2 having the photocatalytic dispersion applied thereon is thereafter dried by means of a drying device 31. Preferably, the paper 2 is dried by means of IR or NIR. It is also contemplated that the paper may be dried by means of for example heated air, for example as described with reference to FIG. 2.

(71) As an alternative, the photocatalytic dispersion 10 may be applied before the dried, resin impregnated paper 2 is arranged on the substrate 13.

(72) The layers are thereafter pressed together to form a panel 20 by applying heat and pressure. Thereby, a panel 20 having outermost layer 21 having photocatalytic properties is obtained. The photonic efficiency of the outermost layer 21 such as an overlay paper having photocatalytic properties may be exceeding 0.025%, preferably exceeding 0.05%, more preferably exceeding 0.1%. The paper 2, 21 on which the photocatalytic dispersion has been applied obtains hydrophilic properties. The contact angle with water may be less than 40 under indoor lightning conditions, preferably less than 30, more preferably less than 25 such less than 20.

(73) In the embodiment disclosed in FIG. 6, the different layers are provided as sheets. However, the different layers may as an alternative be provided as continuous webs of material. For example, the dried, resin impregnated paper may be provided in form of sheets, which may be stacked, as shown in FIG. 6. Alternatively, the dried, resin impregnated paper may be provided as a continuous web (not shown). It is contemplated that there are numerous modifications of the embodiments described herein, which are still within the scope of the disclosure as defined by the appended claims.

(74) It is for example contemplated that the photocatalytic dispersion is applied in more than one step. The photocatalytic dispersion may be applied twice, or more, to the dried, resin impregnated paper. The photocatalytic dispersion may comprise different scratch resistant particles in the different application steps.

(75) It is also contemplated that embodiments of the method may be used to impregnate and apply a photocatalytic dispersion on any other types of sheets and substrates than a paper, such as a web of glass fibres or a non-woven, or a sheet of any other type.

EXAMPLES

Example 1

(76) A melamine formaldehyde resin impregnated AC 3 overlay paper was coated with a 1:1 formulation containing appr. 30 wt. % nanosized photocatalytic anatase TiO.sub.2 and appr. 30 wt. % nano silica formulation. The composition was applied on the AC3 overlay paper with a wire rod and ambient dried. The melamine impregnated and TiO.sub.2 and SiO.sub.2 coated overlay paper was pressed together with a dcor, a core and backing paper to a laminate structure. The pressed laminate was visually checked for photogreying after UV exposure and the photocatalytic activity was tested regarding the degradation of ethanol.

Example 2

(77) A melamine formaldehyde resin impregnated AC 3 overlay paper was coated with a 1:1 formulation containing appr. 30 wt. % nanosized photocatalytic anatase TiO.sub.2 composition containing 9 wt. % polyether modified polysiloxanes as anti-photogreying agent and appr. 30 wt. % nano silica formulation. The composition was applied on the AC3 overlay paper with a wire rod and ambient dried. The melamine impregnated and TiO.sub.2 and SiO.sub.2 coated overlay paper was pressed together with a dcor, a core and backing paper to a laminate structure. The pressed laminate was visually checked for photogreying after UV exposure and the photocatalytic activity was tested regarding the degradation of ethanol.

(78) The ethanol test is performed by monitoring the CO.sub.2 release from the photocatalytic degradation of ethanol under UVA irradiation. The CO.sub.2 is measured with a CO.sub.2 detector mounted in an air tight box of approximately 6 L. The sample and 50 L 10% EtOH solution is added to the box. The activity of the tested sample is expressed as the release of CO.sub.2 per hour per area of tested sample. The release of CO.sub.2 is expressed as the slope of the logged CO.sub.2 graph.

(79) TABLE-US-00001 Photogreying Photocatalytic Activity Example 1 Yes Example 2 No 1546 ppm/hr/m.sup.2

Example 3

(80) A melamine formaldehyde resin impregnated AC 3 overlay paper was coated with a 1:1 formulation containing appr. 30 wt. % nanosized photocatalytic anatase TiO.sub.2 composition containing 9 wt. % polyether modified polysiloxanes as anti-photogreying agent and appr. 30 wt. % nano silica formulation. The composition was applied on the AC3 overlay paper with a RDS4 wire rod yielding approximately 30 g of wet formulation per m2 of overlay paper. The coated overlay paper was ambient dried. The melamine impregnated and TiO.sub.2 and SiO.sub.2 coated overlay paper was pressed together with a dcor, a core and backing paper to a laminate structure. The pressed laminate was visually checked for Photogreying after UV exposure and the photocatalytic activity was tested regarding the degradation of ethanol as in example 1.

(81) TABLE-US-00002 Photogreying Photocatalytic Activity Example 3 No 5198 ppm/hr/m.sup.2