Panel coating

Abstract

A method for coating of a floor panel and a floor panel produced by the method. A method for producing a laminated product, for example a building panel, preferably a floor panel. The method includes applying a paper on one side of a wood fiber based core, e.g., an HDF panel, creating a décor on the paper by a digital printing process, applying a resin, preferably a melamine formaldehyde resin, on the paper, heating the décor and the paper with the resin, preferably by using an IR lamp; and applying heat and pressure in order to cure the resin and thereby obtain a laminated product. Also, alternative methods for producing a laminated product, and such a laminated product.

Claims

1. A floor panel comprising: a core, a balancing layer on a rear side of said core, a surface layer on a front side of said core, said surface layer comprising a decorative paper, a protective transparent paper, a first powder-based sublayer arranged under the decorative paper, and a second powder-based sublayer arranged between the decorative paper and the protective transparent paper, wherein the first sublayer comprises fibers having an average length which is smaller than the average length of the fibers in the decorative and protective transparent papers.

2. A floor panel according to claim 1, wherein the second sublayer comprises fibers having an average length which is smaller than the average length of the fibers in the decorative and protective transparent papers.

3. A floor panel according to claim 2, wherein the fibers in the first sublayer and/or the fibers in the second sublayer have an average length of about less than 1 mm.

4. A floor panel according to claim 1, wherein the balancing layer is a powder-based balancing layer comprising wood fibers.

5. A floor panel according to claim 1, wherein the decorative paper is impregnated with resins from the second powder-based sublayer.

6. A floor panel according to claim 1, wherein the protective transparent paper has a weight of 20-30 g/m.sup.2.

7. A floor panel according to claim 1, wherein the second powder-based sublayer comprises a thermosetting resin and wear-resistant particles.

8. A floor panel according to claim 1, wherein the second powder-based sublayer comprises a melamine formaldehyde resin and aluminum oxide particles.

9. A floor panel according to claim 1, wherein the second powder-based sublayer comprises bleached transparent wood fibers.

10. A floor panel according to claim 9, wherein the wood fibers are provided in powder form.

11. A floor panel according to claim 1, wherein the protective transparent paper is an impregnated overlay with or without aluminum oxide particles.

12. A floor panel according to claim 1, wherein a digital print is applied on the decorative paper.

13. A floor panel according to claim 1, wherein the core is a wood fiber-based core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1a-1d illustrate known laminated floor panels.

(2) FIGS. 2a-2d illustrate a first embodiment of the invention.

(3) FIGS. 3a-d illustrate a second embodiment of the invention.

(4) FIGS. 4a-4d illustrate a third embodiment of the invention.

(5) FIGS. 5a-5c illustrate forming of the surface layer.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(6) The disclosure will in the following be described in connection to exemplary embodiments.

(7) FIGS. 2a-2d show a first embodiment of the invention.

(8) FIG. 2a shows a panel P comprising a core 3, preferably a HDF core and a balancing layer 4 on the rear side of the core 3. The balancing layer 4 may be a conventional kraft paper impregnated with a thermosetting resin, preferably a melamine formaldehyde resin, or a powder backing comprising wood fibers and a thermosetting resin, preferably a melamine formaldehyde resin. The application of a powder backing is made by a scattering unit 10 in the same way as shown in FIG. 4a. The spraying 11 and the drying device 7 will stabilize the powder and create a balancing layer 4 that may be connected to the core 3 such that the panel P may be turned with the rear side pointing downwards prior to the application of the surface layers 1, 2, 12. A resin 5, preferably a liquid thermosetting resin that preferably is a melamine formaldehyde resin, is applied on the upper side of the core 3, preferably with a roller 6 or by spraying. The resin is heated and dried by using a drying device 7 such as for example an IR lamp, hot air, microwaves and similar.

(9) FIG. 2b shows a paper layer 2 that is applied on the dried resin. The paper is preferably a raw paper. The paper may comprise a basic color or may be partly printed. It is not necessary to align the paper precisely since there is no final printed pattern on the paper 2.

(10) FIG. 2c shows a digital print 8 that is printed on the paper 2 by a digital printing device 9. Digital printing is a non-contact process where a digital print head, preferably a Piezo head, fires drops of a liquid substance on a substrate and creates a pattern. The liquid substance may comprise color pigments and may be water based. Alternatively the pigments may be applied separately in dry powder form and the digital print head may essentially only apply a liquid substance that may be transparent and that may comprise a substance that acts as a binder and connects the pigments to the substrate. Non-bonded pigments may be removed by for example an air stream or gravity. Such a two-step digital binder and powder (BAP) printing is very cost efficient especially when large amounts of pigments are used to create a pattern. BAP allows that substantial amounts of pigmented powder may be applied for example more than 20 g/m.sup.2 preferably about 20-50 g/m.sup.2.

(11) FIG. 2d shows that the paper 2 is coated with a liquid thermosetting resin, preferably a melamine formaldehyde resin, in order to create a protective layer 1 similar to a conventional overlay. The coating is preferably made in the same way as shown and described in FIG. 2a. The liquid resin comprises preferably aluminum oxide particles and/or cellulose fibers preferably alpha cellulose fibers.

(12) A coating of the paper with a base color may also be made prior to the digital printing.

(13) The first embodiment of the method comprises the step of: coating of a wood fiber based core 3, preferably an HDF panel, with a liquid melamine formaldehyde resin; drying the liquid resin; attaching a paper 2 to the core 3; providing a décor 8 on the paper 2 by a digital printing process; coating the paper 2 with the decor with a liquid melamine resin, preferably comprising aluminum oxide particles and/or cellulose fibers preferably alpha cellulose fibers; drying the coating; and applying heat and pressure to cure the resins and thereby obtain a laminated product.

(14) An advantage is that it is possible to use an unprinted paper, which reduces the warehouse costs and improves the process flexibility. By printing the paper after the paper is attached to the core the accuracy of the décor position is improved.

(15) The coating of the paper may be replaced or combined with a conventional overlay that is applied over the digitally printed paper.

(16) FIGS. 3a-3d show a second embodiment of the invention. The forming of the balancing layer 4, the coating of the core 3 and the digital printing of the paper as shown in FIGS. 3a-3c are the same as in the first embodiment. However, the protective layer 1 has been replaced with a powder overlay that is scattered by a scattering unit 10 in dry form over the paper 2 with the digital print 8 as shown in FIG. 3d. Said powder overlay preferably comprising fibers, preferably processed wood fibers, a resin, preferably a melamine formaldehyde resin, and wear resistant particles, preferably aluminum oxide. A liquid substance preferably comprising water may be sprayed on the powder overlay by a spraying device 11 and dried by a drying device 7 in order to stabilize the powder prior to the pressing operation.

(17) The second embodiment of the first aspect of the method comprises the step of: coating of a wood fiber based core 3, preferably an HDF panel, with a liquid melamine formaldehyde resin; drying the liquid resin; attaching a paper 2 to the core 3; providing a décor 8 on the paper 2 by a digital printing process; applying a powder overlay 1 on the printed décor paper 2, said overlay 1 preferably comprising fibers, a resin, preferably a melamine formaldehyde resin, and wear resistant particles, preferably aluminum oxide, applying moisture on the powder overlay 1; drying the powder overlay 1; and applying heat and pressure to cure the resins and thereby obtain a laminated product.

(18) A further advantage with the second embodiment is that the impact resistance is improved due to the substantial amounts of fibers in the resin matrix, obtained from the powder overlay.

(19) FIGS. 4a-4d show a third embodiment of the invention. FIG. 4a shows that a powder sublayer 12 comprising a wood fibers and a thermosetting resin, preferably a melamine formaldehyde resin or a melamine/urea resin is applied on the upper side of the core 3.

(20) The balancing layer 4 may be a paper or a powder backing as described above. The sublayer 12 may be applied in the same way as the powder overlay with a scattering unit 10. Preferably a spraying device 11 that applies moisture on the powder and a drying device 7 may also be used to stabilize the powder in order to facilitate the application of the paper 2 over the powder sub layer 12. FIGS. 4c and 4d show that the paper 2 is provided with a digital print 8 by a digital printing device 9 and preferably with a powder overlay 1 or a conventional paper overlay 1 as described above. The powder overlay 1 may be applied by a scattering unit 10, sprayed with water by a spraying device 11 and dried by a drying device 7.

(21) The third embodiment of the method comprises the step of: applying a powder based sublayer 12 on a core 3, preferably an HDF panel, and preferably applying moisture on the sublayer and thereafter drying the sublayer; attaching a paper 2 on the sublayer 12; providing a décor 8 on the paper 2 by a digital printing process; applying a powder overlay 1 on the printed décor paper 2, said overlay preferably comprising fibers, a resin, preferably a melamine formaldehyde resin, and wear resistant particles, preferably aluminum oxide, applying moisture on the powder overlay 1; drying the powder overlay 1; and applying heat and pressure to cure the resins and thereby obtain a laminated product.

(22) A further advantage with the third embodiment is that the demand for drying is decreased since no wet resins are applied. The sub layer 12 gives an increased impact resistance and possibility to form a surface with deep embossing. The sub layer 12 is a cost efficient way to provide a sufficient amount of binders that may penetrate into the paper 2 during pressing

(23) The surface weight of the powder overlay is preferably about 200 g/m.sup.2 but may be as low as 50 g/m.sup.2 or exceed 400 g/m.sup.2. The weight of the sub layer is preferably 100-500 g/m.sup.2.

(24) The invention makes it possible to reduce the weight of the décor paper since no impregnation is needed and there is no need for a high “wet strength”. The weight of the raw paper may be lower than 60 g/m.sup.2 preferably about 40 to 50 g/m.sup.2. The press parameters in the three embodiments above are preferably about 40 bar and the temperature in the range of about 160-200° C., preferably about 180° C., with a pressing time of about 10-30 seconds depending on the layer thickness.

(25) FIG. 5a shows the surface layer prior to pressing according to the third aspect of the invention. The sub layer 12 comprises, in this embodiment, wood fibers 14, dry thermosetting resin particles 15, and preferably also color pigments 13 that give the sub layer a basic color and prevents that the core surface is visible through the thin paper. This reduces the requirement on the digital print 8 and the print may be made with lower ink content, preferably with an ink content of less than 10 g/m.sup.2. The powder overlay 1, which is applied over the paper 2 with the digital print 8, comprises aluminum oxide particles 16, wood fibers 14 and resin particles 15. FIG. 5b shows the surface layer after pressing. The powder has been compressed and the pressed surface layer has in this embodiment preferably a thickness T2 that is less than about 80% and even more preferably less than about 50% of the surface thickness T1 prior to the pressing. The compression of the powder under heat and pressure, when the powder resin 15 becomes fluid, impregnates the paper 2 from above and from below and connects the surface layers to the core 3.

(26) The basic principles of the invention to use a powder sub layer 12 to impregnate a raw paper 2 during pressing may also be used even without the digital printing to produce a surface with a conventional raw decorative printed paper and preferably also with conventional overlay and/or a conventional balancing paper.

(27) A preferred embodiment is a panel P comprising a powder based balancing layer 4, a powder based sub layer 12 on the upper part of the core 3, a raw decorative paper 2 applied on the powder based sub layer 12 and a protective overlay 1 on the raw decorative paper.

(28) The powder based balancing layer 4 gives an improved balancing of the panel P since the fiber properties and orientation in the balancing layer 4 and the sub layer 12 may be similar and may result in the same shrinking after pressing and in different climate conditions. The protective overlay 1 may be a powder or paper based protective layer as described in the embodiments above.

(29) FIG. 5c shows a surface layer comprising a powder overlay 1a and a paper overlay 1b applied on the powder overlay. Preferably the paper overlay 1b is a raw paper which during pressing is impregnated with resins from the powder overlay 1a under the paper overlay 1b. The advantage is that the paper overlay 1b protects the press plates from the wear caused by the aluminum oxide particles. Very thin overlay papers may be used with a weight of 20-30 g/m.sup.2.

(30) The surface layer according to this embodiment comprises a first powder based sub layer 12 under a decorative paper 2 and a second powder based sub layer 1a under a transparent paper located above the decorative paper 2.

(31) A powder based layer is characterized in the mechanically processed fibers have an average length of about less than 1 mm. Fibers used in an HDF core or in paper are longer and have an average length of several mm. The surface of the panel P is characterized in that the fibers in first 12 and second 1a sub layers are smaller than the fibers in the decorative paper the paper overlay.

(32) Several alternatives are possible. The powder overlay 1a may only comprise melamine formaldehyde resins and aluminum oxide particles. It may also comprise bleached transparent wood fibers. The paper overlay may be a conventional impregnated overlay with or without aluminum oxide particles.

(33) The second sublayer 1a will improve the wear and impact resistance even in the case when a conventional overlay is used.

(34) A raw and essentially transparent paper overlay may also be used as a print carrier. A digital print 8 is applied on the print carrier. The print may be applied prior to or after the application of the raw overlay on the core. The raw overlay is preferably applied on a powder based sub layer 12 comprising fibers 14, a thermosetting resin 15, and color pigments 13. A powder overlay or a second conventional overlay may be applied on the raw overlay as a protective layer 1. The raw overlay is during pressing impregnated from the resins in the sub layer 12 and in the protective layer 1.

EXAMPLE

(35) In example 1 below the powder mix formulation for the balancing layer 4 and the first sub layer 12 used comprising 50 weight-% recycled MDF fibers (Valinge Innovation Sweden), 50 weight-% Melamine Formaldehyde resin (Preferably 4865, Dynea). The powder formulation for the second sub layer 1a used comprises processed bleached wood fibers of about 25 wt %, 65 wt % of melamine formaldehyde resin and 10 wt % of aluminum oxide particles

Example 1: Powder Based Panel Obtained Through Heat and Pressure

(36) A balancing layer 4 and a first sub layer 12 was formed by scattering 300 g/m.sup.2 of powder on the rear side and the front side of a 9.7 mm HDF core.

(37) A raw decorative paper 2 with a weight of 60 g/m.sup.2 was applied on the first sub layer 12 and a second sub layer 1a was applied on the decorative paper by scattering 200 g/m.sup.2 of powder.

(38) A 25 g/m.sup.2 raw overlay was applied on the second sub layer 1a.

(39) The core with the surface and balancing layers was pressed in a press with a pressure of 40 kg/cm.sup.2, during 20 seconds. The upper press table applied a heat of 170° C. on the surface layer and the lower press table applied a heat of 175° C. on balancing layer. The surface was pressed against a press plate with an embossing depth of 0.3 mm.

(40) A panel with an embossed decorative structure and a small pre tension backwards and a slightly convex surface was obtained. All raw papers were impregnated and cured during the pressing operation.

EMBODIMENTS

(41) 1. Method for producing a laminated product, for example a building panel, preferably a floor panel (P), wherein the method comprising the steps of: applying a paper (2) on one side of a wood fiber based core (3), e.g., an HDF panel, creating a décor (8) on the paper (2) by a digital printing process, applying a resin (5), preferably a melamine formaldehyde resin, on the paper (2); heating the décor (8) and the paper (2) with the resin (5), preferably by using an IR lamp (7); and applying heat and pressure in order to cure the resin and thereby obtain a laminated product.

(42) 2. The method as in embodiment 1, wherein the method further comprises the step of applying a powder based sub layer (12) on the core (3), said powder based sub layer (12) comprising wood fibers and a powder resin, preferably a melamine formaldehyde resin, before the paper (2) is applied on the core (3).

(43) 3. The method as in embodiment 2, wherein the method further comprises the step of applying moisture on the powder based sub layer (12) and thereafter applying heat in order to dry the powder based sub layer (12).

(44) 4. The method as in embodiment 1, wherein the method further comprises the steps of: applying a liquid resin (5), preferably a melamine formaldehyde resin, on the core (3); and drying the liquid resin (5), preferably by using an IR lamp (7), before the paper (2) is applied on the core (3).

(45) 5. The method as in any one of the preceding embodiments, wherein the resin (5) applied on the paper (2) is in powder form.

(46) 6. The method as in embodiment 5, wherein the method further comprises the step of applying moisture on the resin (5) in powder form.

(47) 7. The method as in any one of the preceding embodiments, wherein the method further comprises the step of applying wear resistant particles (16), preferably aluminum oxide particles, on the paper (2) before heating the décor (8).

(48) 8. The method as in any one of the preceding embodiments, wherein the method further comprises the step of applying cellulose fibers, preferably alpha cellulose fibers, on the paper, before heating the décor (8).

(49) 9. The method as in any one of the preceding embodiments, wherein the method further comprises the step of applying a balancing layer (4) on the other side of the core (3), before applying heat and pressure, to obtain a balancing layer.

(50) 10. The method as in embodiment 9, wherein the balancing layer (4) is a powder layer comprising wood fibers and a resin or a paper.

(51) 11. The method as in embodiments 2 or 3, wherein the paper (2) is a thin raw paper with a weight of about 40-60 g/m.sup.2.

(52) 12. The method as in embodiment 2 or 3, wherein the paper (2) is a thin raw paper with a weight of about 40-50 g/m.sup.2.

(53) 13. The method as in any one of the preceding embodiments, wherein a digital non-contact process is used comprising a Piezo print head that applies water based drops.

(54) 14. The method as in embodiment 13, wherein color pigments (13) are applied in a separate step in dry form and bonded by the water based drops.

(55) 15. The method as in any one of the preceding embodiments, wherein the step of creating the décor (8) by the digital printing process is performed after the paper (2) is applied to the core (3).

(56) 16. Method for producing a laminated product, for example a building panel, preferably a floor panel (P), wherein the method comprising the steps of: applying a powder based sub layer (12) comprising wood fibers and a thermosetting resin on a wood fiber based core (3), e.g., an HDF panel, applying a raw paper (2) on the powder based sub layer (12), applying a protective powder based or paper based overlay (1) comprising a melamine formaldehyde resin and aluminum oxide on said raw paper (2); applying heat and pressure in order to impregnate the raw paper (2), to cure the resin and thereby obtain a laminated product.

(57) 17. The method as in embodiment 16, wherein a powder based balancing layer (4) comprising wood fibers and a thermosetting resin is applied on a rear side of the core (3).

(58) 18. The method as in embodiment 16 or 17, wherein said overlay (1) is a powder based overlay (1a), and wherein a paper overlay (1b) is applied on the powder based overlay (1a).

(59) 19. A floor panel (P) comprising:

(60) a core (3), preferably a wood fiber based core,

(61) a balancing layer (4) on a rear side of said core (3), and

(62) a surface layer on a front side of said core (3), said surface layer comprising a decorative paper (2), a protective transparent paper (1b), a first powder based sub layer (12) arranged under the decorative paper (2), and a second powder based sub layer (1a) arranged between the decorative paper (2) and the protective transparent paper (1b),

(63) wherein the first and the second sub layers (12, 1a) comprise fibers having an average length which is smaller than the average length of the fibers in the decorative and overlay papers (2, 1b).