Coated wood products and method of producing coated wood products

Abstract

A coated wood product, comprising a barrier layer and a photocatalytic layer and a method for producing such a coated wood product.

Claims

1. A method of manufacturing a photocatalytic lacquered wood product, wherein the method comprises: lacquering an underlying wood product to obtain a base coat comprising at least one lacquer layer; coating said base coat with a barrier coating fluid comprising barrier particles, to obtain a transparent barrier layer; spraying said transparent barrier layer with a photocatalytic coating fluid comprising photocatalytic nanoparticles to obtain a transparent photocatalytic layer disposed on said transparent barrier layer, said photocatalytic nanoparticles being embedded and homogenously distributed in said transparent photocatalytic layer; and then curing said wood product such that at least the base coat is cured.

2. The method as claimed in claim 1, wherein the method comprises semi-curing said base coat, prior to coating with the barrier coating fluid.

3. The method as claimed in claim 1, wherein the photocatalytic nanoparticles comprise TiO.sub.2.

4. The method as claimed in claim 1, wherein a thickness of said barrier layer is up to about 1 μm.

5. The method as claimed in claim 1, wherein a thickness of said photocatalytic layer is up to about 1 μm.

6. A building panel produced according to the method in claim 1.

7. The method as claimed in claim 1, further comprising curing the barrier layer.

8. The method as claimed in claim 1, further comprising curing the photocatalytic layer.

9. The method as claimed in claim 1, further comprising curing the barrier layer and the photocatalytic layer.

10. The method as claimed in claim 1, wherein the base coat comprises a base lacquer, a middle lacquer and a top lacquer.

11. The method as claimed in claim 1, wherein the barrier particles in the transparent barrier layer prevent the photocatalytic nanoparticles from reacting with the base coat.

12. The method as claimed in claim 1, wherein a size of a droplet of the photocatalytic coating fluids is up to about 200 μm.

13. The method as claimed in claim 1, wherein the method comprises drying said barrier coating fluid, prior to spraying with said photocatalytic coating fluid.

14. The method as claimed in claim 13, wherein the barrier coating fluid is a waterborne fluid.

15. The method as claimed in claim 13, wherein the barrier coating fluid is applied by spraying.

16. The method as claimed in claim 15, wherein a size of a droplet of said barrier coating fluid is up to about 200 μm.

17. The method as claimed in claim 1, further comprising drying said photocatalytic coating fluid after spraying said transparent barrier layer with said photocatalytic coating fluid and before said curing.

18. The method as claimed in claim 1, wherein the photocatalytic coating fluid comprises the photocatalytic nanoparticles in a concentration of up to about 30 wt %.

19. The method as claimed in claim 17, wherein an amount of at least one of said barrier or photocatalytic coating fluid(s) is up to about 15 ml/m.sup.2.

20. The method as claimed in claim 17, wherein the photocatalytic coating fluid is a waterborne fluid.

21. The method as claimed in claim 1, wherein the barrier particles comprise a silicon containing compound.

22. The method as claimed in claim 21, wherein the silicon containing compound is selected from 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will in the following be described in connection to exemplary embodiments and in greater detail with reference to the appended exemplary drawings, wherein:

(2) FIG. 1 Illustrates a wood product according to an embodiment of the invention;

(3) FIG. 2 Illustrates a wood product according to an embodiment of the invention;

(4) FIG. 3 Illustrates a method for producing a coated wood product;

DETAILED DESCRIPTION

(5) In FIG. 1 an embodiment of a wood product 1, e.g. a photocatalytic lacquered board, is disclosed comprising a board 2 with a surface of wood, e.g. plywood, solid wood or a HDF/MDF board with a veneer or linoleum, a base coat 3 and a topcoat 5, 6. The topcoat comprises a barrier layer 5, comprising embedded barrier particles, and a second layer 6, comprising embedded photocatalytic nanoparticles. An area of mixed barrier and photocatalytic nanoparticles may be arranged between the barrier layer 5 and the second layer 6.

(6) In an alternative embodiment, which is shown in FIG. 2, the topcoat 7 comprises barrier particles and photocatalytic nanoparticles. The topcoat 7 comprises a lower part with high concentration of the barrier particles and an upper part with a high concentration of the nanoparticles and a mixed area there between comprising both barrier particles and nanoparticles.

(7) In one embodiment there is a second coat 4 above the base coat and under the topcoat. The second coat may be an additional lacquer layer. Also the base coat and the topcoat may comprise more than one layer in all embodiments.

(8) In all embodiments, the base coat 3 may be at least one lacquer layer. By lacquer layer is also meant any varnish layer. The base coat 3 may be transparent. The base coat may for example be a UV curable lacquer or an oxidation lacquer (drying). The base coat is not part of a paper layer, as in a paper laminate. For example, the base layer may be a separate layer, independently applied to a topmost surface of a board.

(9) Furthermore, in all embodiments, the topcoat 5, 6, 7 may be transparent. The topcoat may be a water-based coating or a solvent based coating. In an embodiment wherein the topcoat comprises a barrier layer 5 and a second layer 6 comprising the photocatalytic nanoparticles, both the barrier layer 5 and the second layer 6 may be transparent. The barrier layer is not part of a paper layer, as in a wear resistant layer in a paper laminate. For example, the barrier layer is a separate layer, independently applied to a base coat.

(10) In all embodiments, the barrier particles are preferably SiO2, or a silicium containing compound such as SiO2, colloidal SiO2, functional nanoscaled SiO2, silicone resin, organofunctional silanes, and/or colloidal silicic acid silane and/or a combination of said compounds. The barrier particles protect the base coat from being damaged or impacted by the photocatalytic activity of the photocatalytic nanoparticles. The barrier particles prevent the base coat from being degraded by the photocatalytic activity of the photocatalytic nanoparticles.

(11) The photocatalytic nanoparticles may be transparent. The photocatalytic nanoparticles may have a size of less than 35 nanometres, preferably about 20 nanometres.

(12) FIG. 3 discloses a production line for manufacturing a photocatalytic lacquered wood product comprising transparent photocatalytic nanoparticles, the method comprising the steps of: applying a base coat by lacquering on an underlying wood product to obtain at least one overlaying lacquer (step 31); coating said overlaying lacquer(s) with a barrier coating fluid, preferably comprising a Si-containing compound, to obtain a transparent barrier layer (step 33); coating said transparent barrier layer with a photocatalytic coating fluid, preferably comprising TiO2, to obtain a transparent photocatalytic layer (step 35); and curing said overlaying lacquer(s), barrier layer and photocatalytic layer (step 37).

(13) The production line may comprise one or more of the additional step(s): Curing or semi-curing said overlaying lacquer, prior to coating with a barrier coating fluid (step 32); drying said transparent barrier layer composition (step 34); and/or drying said photocatalytic coating composition (step 36).

(14) The coating is preferably performed by spraying.

(15) Any step may be multiplied such as applying several layers of barrier/photocatalytic to obtain multi-layered products with longer service life.

(16) The base coat may comprise more than one overlaying lacquer, for example a base lacquer, a middle lacquer and a top lacquer. The overlaying lacquer(s) may be for example be a UV curable lacquer or an oxidation lacquer (drying). The overlaying lacquer(s) may be transparent.

Example 1

Applying a Photocatalytic Top Layer Composition by Spray Application on Wet Top Lacquer—Air Mixed Nozzles

(17) A 8×30 cm wooden floor board was lacquered with a base lacquer, a middle lacquer and a top lacquer forming overlying lacquers. The wet top lacquered wooden floor board entered the application of the photocatalytic composition coating with a velocity of 30 m/min. The wet lacquered wooden floor board was coated according to: 1) 5 ml/m2 of a 5.6 wt % SiO2 in water fluid was applied. 2) IR drying of the excess amount of water by a 3 kW IR lamp and by applying heated dry air. 3) 5 ml/m2 of a 5.0 wt % TiO2 in water fluid was applied. 4) IR drying of the excess amount of water by a 3 kW IR lamp and by applying heated dry air. 5) Curing of the wooden composite sample with UV light.

(18) Ad 1) The barrier layer coating fluid (1) used was a stable nanoparticle dispersion based on a 5.6 wt % water based dispersion of colloidal SiO2 surface modified with epoxy silane mixed with 0.5 wt % BYK 348 or similar as wetting agent. The average particle size was 7 nm. The barrier layer coating fluid was applied with air atomized nozzles (5 mL/m.sup.2 corresponding to 34 ml/min) given a droplet size of <50 micron meter average droplet size.

(19) Ad 2) The barrier layer coated sample was IR dried with a 3 kW IR heating unit theoretically capable of evaporating 3-5 g/m2 of water.

(20) Ad 3) The photocatalytic coating fluid (3) used was a stable TiO2 nanoparticle dispersion based on a 5.0 wt % water based dispersion of doped TiO2 capable of absorbing visible light (380-500 nm) mixed with 0.5 wt % BYK 348 as wetting agent. The average particle size was 18 nm. The photocatalytic coating fluid was applied with air atomized nozzles (5 mL/m.sup.2 corresponding to 34 ml/min) given a droplet size of <50 micron meter average droplet size.

(21) Ad 4) The photocatalytic coated sample was IR dried with a 3 kW IR heating unit theoretically capable of evaporating 3-5 g/m2 of water.

(22) Ad 5) The photocatalytic lacquered wooden sample was UV cured.

Example 1a

Applying a Photocatalytic Top Layer Composition by Spray Application on Wet Top Lacquer—Rotation Atomizer

(23) Same as Example 1; however, the application of barrier layer (1) and the application of TiO2 (3) is made with a high speed rotating atomizer nozzle yielding a very fine mist of droplets making a very uniform coating.

Example 2

Photocatalytic Activity by EtOH Degradation

(24) The photocatalytic activity of a sample prepared according to Example 1 was evaluated against degradation of EtOH by monitoring the CO.sub.2 release. The CO.sub.2 release test resulting from degradation of EtOH is a fast model experiment which is used to estimate the air quality improvement. The samples are placed in a 6 l sealed box with a 500 ppm ethanol atmosphere inside and the CO.sub.2 concentration is followed over time. The EtOH is degraded to CO.sub.2 due to the photocatalytic particles in the lacquered wood. The sample was irradiated with a light source yielding UV=1.250 mW/cm.sup.2.

(25) TABLE-US-00001 TABLE 1 Activity of background substrated lacquered sample. Photocatalytic Lacquer Sample Rate [ppm CO2/hr] 25

Example 3

Improved Washability by Contact Angle Measurement

(26) The contact angle with water was measured for a reference (no light) and for a photocatalytic coated sample as described in Example 1 applying the PGX from FIBRO System AB (see Table 2). These measurements were repeated 5 times at random positions on the board. Upon light exposure (0.68 W/m2/nm at 340 nm) the coated part of the lacquered board had become hydrophilic, as evidenced by the low contact angle. Importantly the photocatalytic topcoating was transparent making it invisible on the lacquered board. Furthermore, no chalking or other damaging effects of the lacquer were seen.

(27) TABLE-US-00002 TABLE 2 Contact angle measurements. Photocatalytic Lacquer Reference  0 hr 81.0 ± 3.0 79.8 ± 3.2 12 hr 65.2 ± 5.4 81.7 ± 0.8 61 hr 45.3 ± 3.6 76.7 ± 1.1 95 hr 48.5 ± 3.1 73.6 ± 1.0

Example 4

Applying a Photocatalytic Top Layer Composition by Spray Application on Wet Top Lacquer—Air Mixed Nozzles

(28) A wooden floor board was lacquered with a base lacquer, a middle lacquer and a top UV curable lacquer forming overlying lacquers. The wet top lacquered wooden floor board entered the application of the photocatalytic composition coating with a velocity of 10 m/min. The wet lacquered wooden floor board was coated according to: 1) 5 ml/m2 of an appr. 3.5 wt % aqueous solution of colloidal silicic acid silane fluid was applied. 2) IR drying of the excess amount of water by 3 kW IR lamp and by applying forced heated dry air. 3) 5 ml/m2 of a 1.0 wt % TiO2 in water fluid was applied. 4) IR drying of the excess amount of water by 3 kW IR lamp and by applying forced heated dry air. 5) Curing of the wooden composite sample with UV light.

(29) Ad 1) The barrier layer coating fluid (1) used was an appr. 3.5 wt % aqueous solution of colloidal silicic acid silane fluid mixed with 0.5 wt % wetting agent. The barrier layer coating fluid was applied with air atomized nozzles (5 mL/m.sup.2 corresponding to 12.5 ml/min) given a droplet size of <50 micron meter average droplet size.

(30) Ad 2) The barrier layer coated sample was IR dried with a 3 kW IR heating unit capable of evaporating 5 g/m2 of water.

(31) Ad 3) The photocatalytic coating fluid (3) used was a stable TiO2 nanoparticle dispersion based on a 1.0 wt % water based dispersion of doped TiO2 capable of absorbing visible light (380-500 nm) mixed with 0.5 wt % wetting agent. The average particle size was 18 nm. The photocatalytic coating fluid was applied with air atomized nozzles (5 mL/m.sup.2 corresponding to 12.5 ml/min) given a droplet size of <50 micron meter average droplet size.

(32) Ad 4) The photocatalytic coated sample was IR dried with a 3 kW IR heating unit capable of evaporating 3-5 g/m2 of water.

(33) Ad 5) The photocatalytic lacquered wooden sample was UV cured.

Example 5

Visual Appearance and Gloss Level

(34) The gloss level for a reference (no barrier layer and no photocatalytic particles) and for a photocatalytic coated sample as described in Example 4 were measured at an angle of 60°. These measurements were repeated 3 times at random positions on the board. Visual inspection of the photocatalytic coating showed a transparent coating on the lacquered board.

(35) TABLE-US-00003 TABLE 3 Gloss measurements. Photocatalytic Board Reference Board 42.7 ± 1.1 38.8 ± 0.4