Digital binder printing

Abstract

A method and equipment to form a digital image on a surface by applying a powder layer including colour pigments on the surfaces, bonding a part of the powder and removing the non-bonded powder from the surface.

Claims

1. Equipment to provide a digital image on a building panel, wherein the equipment comprises a digital coating head, a powder scattering unit, a curing oven and a powder removal system wherein: the digital coating head is adapted to apply a liquid substance on the panel, the powder scattering unit is adapted to apply a powder layer comprising colour pigments on the panel, wherein the liquid substance is adapted to bond a part of the powder to the panel, the curing oven is adapted to cure the liquid substance and the powder removal system is adapted to remove the non-bonded powder from the panel, and wherein the powder removal system is based on an air stream and optionally a vacuum.

2. A method of forming a digitally printed image with colour pigments on a surface of a building panel, the method comprising forming at least two layers of digital prints, each layer being formed by: scattering colour pigments on the surface; bonding a part of the colour pigments to the surface; and removing the non-bonded colour pigments from the surface such that a layer of a digital print is formed by the bonded colour pigments.

3. The method as claimed in claim 2, wherein the colour pigments are bonded to a binder.

4. The method as claimed in claim 3, wherein the binder is separately applied on the surface of the building panel.

5. The method as claimed in claim 3, wherein the binder is a liquid substance.

6. The method as claimed in claim 5, wherein the liquid substance is water-based.

7. The method as claimed in claim 5, wherein the liquid substance is UV curable and wherein the method further comprises exposing the liquid substance to UV light.

8. The method as claimed in claim 3, wherein the binder is a powder.

9. The method as claimed in claim 3, wherein the binder comprises a thermosetting resin or a thermoplastic resin.

10. The method as claimed in claim 2, wherein the colour pigments are mixed with a binder.

11. The method as claimed in claim 2, wherein said at least two layers are positioned above each other.

12. The method as claimed in claim 2, wherein said at least two layers are positioned next to each other.

13. The method as claimed in claim 2, wherein said at least two layers comprises a first layer and a second layer, a color of the second layer being different that a color of the first layer.

14. The method as claimed in claim 2, wherein said at least two layers comprises a first layer and a second layer, the non-bonded colour pigments of the first layer being removed before forming the second layer.

15. The method as claimed in claim 2, wherein the surface of the building panel comprises a thermosetting resin.

16. The method as claimed in claim 2, wherein the surface of the building panel is a paper layer or a foil, or wherein the surface of the building panel comprises a powder layer or a stabilized powder layer.

17. The method as claimed in claim 2, wherein the building panel is a floor panel, a wall panel, or a furniture component.

18. The method as claimed in claim 2, wherein the building panel is a floor panel comprising a mechanical locking system for vertical and horizontal locking.

19. The method as claimed in claim 2, wherein the step of bonding said part of the colour pigments to the surface comprises applying a liquid substance by a digital coating head.

20. The method as claimed in claim 2, further comprising applying heat and pressure to the surface of the building panel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIGS. 1a-d illustrate know methods to produce a printed and embossed surface;

(3) FIGS. 2a-d illustrate a first aspect of the invention;

(4) FIGS. 3a-d illustrate a second aspect of the invention;

(5) FIGS. 4a-d illustrate a third aspect of the invention;

(6) FIGS. 5a-h illustrate digital application of pigments according to the first aspect of the invention;

(7) FIGS. 6a-c illustrate embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

(8) FIGS. 2a-2d show an embodiment of the invention, which is based on a first principle where a binder pattern BP or image is formed digitally by a digital coating head that applies a binder 11 in the form of a liquid substance. A digital print head or digital ink head that is mainly used to apply a liquid substance without any colorants, and which is not intended to print a coloured image is hereafter referred to as a “digital coating head”. Pigments 12 are scattered randomly by a second device over the binder pattern BP. The binder connects some pigments to form the same pattern as the binder while other non-bonded pigments are removed.

(9) This two-step process, where the pigments and a liquid binder are applied separately, may provide an image with the same quality as conventional digital printing technology. The method is particularly suitable in applications where considerable quantities of pigments have to be applied on a large flat panel 1 in order to form an advanced large image or decorative pattern. Contrary to known methods, the digital coating head, is typically not used to apply any type of conventional ink with colour pigments. This is a major advantage since no expensive inks comprising pigment dispersions have to be handled by the digital coating head.

(10) FIG. 2a shows that a binder pattern BP is formed on a surface 2 of a building panel 1 by a digital coating head 30 as shown in FIG. 2d. The surface 2 may, for example, be a paper layer, a stabilized powder layer, a foil or a base colour applied on a material, preferably a wood or plastic based core material. The binder 11 is in this preferred embodiment water based and comprises preferably mainly water, such as at least 50% water. The binder 11 may further comprise additives such as release agents, surface tension agents, wetting agents, viscosity increasing agents, etc. A pigment layer 12 is applied, for example, by scattering as dry powder over the wet binder pattern BP as shown in FIG. 2b. The pigment layer may comprise, for example, melamine formaldehyde powder particles that melt when they are in contact with the water-based pattern BP. The dry pigments and melamine formaldehyde powder that do not contact the water-based pattern BP are removed by, for example, an air stream and the remaining colour pigments 12 form a print P as shown in FIG. 2c, which is essentially identical to the binder pattern BP.

(11) The print P may be dried and stabilized by, for example, exposure to IR or UV lights that heat up the wet melamine formaldehyde resin and bond the colour pigments to the surface 2 by drying the wet melamine formaldehyde resin. A second bonded pattern may be coated on the surface 2 and a second layer of pigments and melamine formaldehyde powder may be applied on the surface and over and/or adjacent to the first print. An advanced décor may be created with several colours.

(12) The binder in this embodiment may comprise wet melamine formaldehyde and may be applied in two steps, first as a liquid substance, such as water, from the digital coating head 30, and second as powder from a scattering unit 27. The powder may be mixed with the dry colour pigments. This simplifies the function of the digital coating head that only has to apply water drops without any, or with limited amounts of, binders and colour pigments.

(13) The binder may be included in dry form in the powder and activated by the liquid substance applied by the coating head as described above or it may only be included in the liquid substance applied by the digital coating head.

(14) This method wherein the liquid substance and the powder are applied directly on a panel is suitable to form a digital image on a building panel. A method comprising the following steps is especially suitable for forming an image on a floor surface having high impact and wear resistance. A liquid substance compatible with thermosetting resins is applied and the substance must have specific chemical properties such that no defects are caused during curing of the thermosetting resins. This may be accomplished with a liquid substance that for example comprises water and/or glycols. The substance should be applied on a surface of a building panel in order to eliminate problems related to positioning of the print on the panel. Thermosetting resins such a melamine formaldehyde resins are preferably included in a surface layer of a panel and/or in the powder applied on the panel and they may react with the liquid substance and bond the powder to the panel surface such that non-bonded powder may be removed. The powder comprises preferably UV stable colour pigments. The advantages are that such combination of materials may be pressed and cured with high pressure, exceeding 40 bars, and heated to a temperature exceeding 160 degrees Celsius. The surface and the digitally formed image may be cured to a hard wear resistant surface without so called bleeding of the pigments during the pressing and heating step and the pigments may be incorporated into the cured surface such that they may create a UV stable wear resistant image similar to the images of conventional laminate floors.

(15) A wide variety of thermosetting and thermoplastic materials may be used as particles in the scattered powder or as dispersions or liquid substances in the binder applied by the digital coating head. The majority of such materials may be produced in dry powder form or as liquid dispersions.

(16) As an alternative to thermosetting materials, such as melamine formaldehyde, or to thermoplastic materials, such as, for example, PVC powder, UV curable polyurethane may, for example, be used in powder form or as dispersion.

(17) UV curable polyurethane substance with a viscosity that is adapted to the digital coating head 30 may be used. Water-based polyurethane dispersions are preferred as a liquid substance in the digital coating head since they do not cure until they are exposed to UV light. Polyurethane dispersions are fully reacted polyurethane/polyureas of small and discrete polymer particles and such particles may be produced with a size of about 0.01-5.0 microns and may therefore be handled in a digital print head or other similar heads. They may have 20-70% solid content. Polyurethane dispersions may be blended with, for example, acrylic emulsions and other emulsions in order to reduce costs.

(18) The digital coating head 30 that preferably is a Piezo head has preferably a capacity to fire drops with a drop size of about 1-200 picolitres or more. The drop size may be varied and this may be used to vary the intensity of a colour and to create a grey scale with the same basic colour.

(19) Water based adhesives may also be used such as soluble adhesives or water dispersed adhesives.

(20) Other UV curable materials such as acrylates of epoxy, urethane, polyester, polyether, amine modified polyether acrylic and miscellaneous acrylate oligomers may be used in powder for or as dispersions.

(21) FIG. 2d shows one “binder printing” station of a binder printing equipment that may be used to create a digital print with the digital “binder print” method. A digital coating head 30, that may be a Piezo head, applies a binder pattern BP. Several coating heads 30 may be positioned side by side in order to cover the width of the surface that is printed. The binder pattern is created digitally in the same way as in conventional digital printing. The colours are separated and each coating unit 36 applies mainly the same substance that is used to bond one specific colour in each coating step. The digital coating head is connected with a feeding pipe 32 to a container 31 that comprises a binder or a one component of a binder, preferably a water based substance, which in this embodiment may be mainly distilled or deionized water. The digital coating heads are connected with digital data cables 33 to a digital control unit 34 that controls the application of the drops, the speed of the conveyor 21, the function of a powder application unit and all other equipment that is used to bond and remove pigments.

(22) The water drops that serve as a binder 11 should be wet until they pass a scattering station 27 that applies a powder mix that in this preferred embodiment comprises colour pigments 12 and melamine formaldehyde powder 13. The melamine formaldehyde particles in the powder mix that are in contact with the wet water based binder pattern BP melts and the water/melamine formaldehyde solution acts as a binder that connects a part of the pigment/melamine formaldehyde mix to the surface 2 of the panel 1. When the powder mix is displaced under a preferably hot UV curing oven 23 with ultra violet light, which is located preferably after the digital coating unit 36 in the feeding direction, a practically instant bonding or curing within a few seconds may take place.

(23) A powder removal system 28 that in this embodiment is based on an air stream and vacuum removes pigments and melamine formaldehyde particles that are not bonded by the binder pattern BP and a perfect colour print P is provided. This production step may be repeated and another colour may be applied by a second scattering unit 27 that comprises another colour. The removed dried pigments and melamine formaldehyde particles may pass through a sieve or a filter and they may be recycled and reused again several times.

(24) Melamine formaldehyde or other binders may also be included in the surface layer 2 as a dry layer when, for example, a melamine formaldehyde impregnated paper layer or a stabilized powder layer is used as a basic surface. The water based bonding pattern will melt a part of this melamine formaldehyde layer and only pigments may be applied as powder by the scattering unit 27 and recycled. This method may also be used when a complete binder substance is included in the liquid substance applied by the digital coating head.

(25) The powder mix may, in addition to pigments and melamine formaldehyde particles, also comprise wear resistant particles such as small aluminium oxide particles and fibres, preferably wood fibres that preferably comprise bleached transparent or semi-transparent fibres. Such a mix may be used to create a solid print with pigments that are positioned vertically above each other with binders and wear resistant particles above and below the pigments. A water-based substance without any pigments may penetrate deeper into the powder mix than pigments applied as dispersion in a conventional digital printing and a very wear resistant print may be obtained.

(26) Several layers of prints may be position above each other and this may be used to increase the wear resistance further and to create 3D decorative effects.

(27) Static electricity may be used to apply and/or to remove the non-bonded powder particles. Airstreams and vacuum that blows away and/or sucks up particles may be combined with brushes. In general all dry and wet methods that are used to remove dust may be used separately or in various combinations to remove the pigments and the non-bonded parts of the scattered powder mix. However, dry and non-impact methods are preferred.

(28) A controlled complete or partial removal of the non-bonded pigments is essential for a high quality print with a pre-defined decorative image. Advanced removal systems may also be used that only removes the colour pigments while the essential part of the transparent melamine formaldehyde powder particles may remain on the surface. This may be accomplished by, for example, a two-step scattering where a first layer comprises only melamine formaldehyde particles that are connected to the surface prior to the application of the binder, sprayed with water and dried with IR, hot air, UV and similar methods. This separate melamine formaldehyde layer may in some applications replace, for example, pre-impregnated paper and only non-impregnated paper with or without a base colour may be used as a surface layer 2.

(29) The moisture content of the surface layer should be accurately controlled in order to facilitate the removal of the non-bonded powder particles. Moisture content below 6% is preferred. The surface layer 2 may be dried by, for example, IR or UV lamps or hot air prior to the application of the pigments. Water and special chemicals, such as release agents, may be applied in order to seal the surface 2 or the upper part of the bonded colour pigments in order to create a sealing or a release layer that may prevent colour pigments to stick to specific parts of the surface layer where no binder is applied.

(30) The print may be covered with transparent protective layers of, for example, a paper based or powder based overlay comprising aluminium oxide and melamine formaldehyde resins or a UV curing coating that may be applied by rollers or digitally with, for example, Piezo coating heads.

(31) FIGS. 3a-3d show an embodiment of the invention, which is based on a second principle where the pigments 12 in a first step are scattered on a surface 2 and a pattern or image is thereafter formed digitally by a digital coating head that only applies a binder pattern BP on the scattered mix. The digitally applied binder may comprise water that melts, for example, melamine formaldehyde particles 13 mixed with pigments 12 or applied under the pigments. The binder connects some pigments to form the same pattern as the binder pattern BP while other non-bonded pigments are removed. FIG. 3a shows a substantially homogenous mix of melamine formaldehyde powder 13 and pigments 12 scattered on a surface 2. FIG. 3b shows a digitally applied binder pattern BP applied on the mix. FIG. 3c shows that all non-bonded pigments, and in this embodiment also melamine formaldehyde particles 13, have been removed. FIG. 3d shows a binder printing station comprising a scattering unit 27, a digital coating unit 36, a UV oven 23 and a powder removal system based 28 on an air stream and vacuum.

(32) The first and the second principles may be combined. A binder pattern may be applied prior and after the application of the pigment mix and this may be used to create a solid print with a larger vertical extension and higher wear resistance.

(33) FIGS. 4a-4c show an embodiment of the invention, which is based on a third principle where the pigments 12 in a first step are scattered on a surface 2 and a binder pattern BP or image is thereafter formed digitally by a laser beam 29 that melts or cures a binder that may be mixed with the pigments 12 or included in the surface 2. A digitally created print P is obtained when the non-bonded pigments are removed.

(34) FIG. 4d shows a binder printing station comprising a scattering unit 27, a laser 29, and a powder removal system 28 based on an air stream and vacuum. The laser may be replaced with heating lamps that may be used to create images that comprise rather large areas of the same colour as in some stone designs. Even a conventional laser system based on the above described impact method may be used to apply an digital print partly or completely on a floor panel or in combination with the above described binder printing methods.

(35) All the above-described principles may be partly or completely combined and a production line may comprise several digital binder printing station according to the first, second or third principles.

(36) FIGS. 5a-5h show application of two different colours according to the first principle. A first binder 11a that in this embodiment is essentially water is applied by a digital Piezo head on a surface 2 that may be a stabilized powder layer or a paper as shown in FIG. 5a. A first powder layer comprising colour pigments 12a and melamine formaldehyde particles 13a is applied on the surface 2 and on the binder 11a. Melamine formaldehyde particles 13a that are in contact with the wet water drops will melt. A first UV oven 23a dries the wet melamine formaldehyde and bonds the pigments to the surface as shown in FIG. 5c and the non-bonded melamine formaldehyde and pigment particles are removed such that a pigment image 12a that corresponds to the applied binder 11a is obtained. FIGS. 5e-5h show that the same application may be repeated with another pigment colour 12b mixed with melamine formaldehyde particles 13b and a new binder 11b such that a two colour image is obtained with two types of colour pigments 12a, 12b as shown in FIG. 5h.

(37) FIG. 6a shows an embodiment where the digital binder printing equipment comprising a digital coating unit 36, a scattering unit 27, UV curing unit 23, and a powder removal vacuum system 28, is combined with conventional ink jet printer 35. The binder printing method may use this combination to create the major part of a digital image while some parts of the final print may be created by the ink jet printer. This may reduce the ink cost considerably since, for example, the cost effective binder printing method, where no pigments have to be handled by the digital coating head, may apply, for example, 90% of the pigments which are needed to create a fully printed décor or pattern.

(38) FIG. 6b shows a binder printing equipment where pigments 12 and melamine formaldehyde powder 13 are applied by a scattering unit 27 comprising preferably an embossed roller 22 and an oscillating brush 42. The non-bonded pigments and melamine formaldehyde particles are removed by a powder removal system 28 that recycles the mix 12, 13 into the scattering unit 27. A pigment/melamine formaldehyde dust cloud may be created by airstreams and only the pigments and melamine formaldehyde powder that come into contact with the wet binder 11 will be bonded to the surface 2.

(39) FIG. 6c shows that the method is especially suited to apply a digital binder print on a floor panel 1 with a paper based or powder based surface 2, a core 3, a balancing layer 4, and with a mechanical locking system comprising a strip 6, with a locking element 8 in one edge that cooperates with a locking groove 14 in an adjacent edge of another panel for horizontal locking of the adjacent edges and a tongue 10 in one edge that cooperated with a tongue groove 9 in another edge for vertical locking of the panels. Such floor panels have generally advanced wood or stone decors that require large amounts of different colour pigments and a decor that has to be positioned accurately in relation to embossed structures and the panel edges with the mechanical locking system.

(40) In all embodiments, the surface of the building panel may comprise a thermosetting resin, for example, melamine formaldehyde resin. The building panel may be formed by applying heat and pressure, preferably after the digitally created image is formed by the bonded colour pigments. In one embodiment, the binder mixed with the dry colour pigments is cured simultaneously as the binder in the surface of the building panel, preferably by applying heat and pressure.

(41) All the above-described methods may be partly or completely combined.

EXAMPLE

(42) A powder mix of 300 g/m2 comprising wood fibres, melamine formaldehyde particles, brown colour pigments and aluminium oxide particles such as corundum was applied by scattering equipment on an 8 mm HDF core. The mix was sprayed with deionized water and dried by an UV oven such that a hard stabilized powder based surface with a brown basic colour was obtained. The panel with the stabilized powder surface was put on a conveyer and displaced under a digital Piezo coating head that applied drops of water on the stabilized surface and that printed a transparent wood grain pattern on the surface. The melamine formaldehyde under the transparent pattern melted when the digital coating Piezo head applied the water drops. Black pigments were in a second step scattered over the whole surface and the transparent pattern. The panel was thereafter displaced by a conveyor under an UV oven. The melamine formaldehyde in the transparent pattern was dried again and the pigments above the transparent pattern were bonded to the surface. The panel was thereafter displaced under a vacuum-sucking pipe where all non-bonded pigments and melamine formaldehyde particles were removed. A wood grain pattern comprising a brown base colour and a black wood grains structure was obtained. A protective layer comprising melamine formaldehyde and aluminium oxide particles was scattered over the entire surface. The layer was sprayed with water and dried under an UV oven. The panel with the print and the protective layer was thereafter pressed during 20 seconds under a temperature of 170 degrees C. in a 40 bars press and the powder-based surface with the grain structure and the protective layer was cured to a hard wear resistant surface with a high quality print.

Embodiments

(43) 1. A method of forming a digitally printed image (P) with colour pigments (12) on a surface (2) of a building panel (1), comprising the steps of: scattering dry colour pigments (12) on the surface (2), bonding a part of the dry colour pigments to the surface (2), and removing the non-bonded dry colour pigments from the surface such that a digitally created image (P) is formed by the bonded colour pigments (12).

(44) 2. The method as in embodiment 1, wherein the dry colour pigments (12) are bonded to a binder, the binder being separately applied on the surface (2) of the building panel (1).

(45) 3. The method as in embodiment 1, wherein the dry colour pigments (12) are mixed with a binder.

(46) 4. The method as in embodiment 2 or 3, wherein the binder comprises a thermosetting resin.

(47) 5. The method as in embodiment 2 or 3, wherein the binder comprises a thermoplastic resin.

(48) 6. The method as in any one of embodiments 2-5, wherein the binder is a powder.

(49) 7. The method as in any one of the preceding embodiments, wherein the surface (2) of the building panel (1) comprises a thermosetting resin, preferably melamine formaldehyde resin.

(50) 8. The method as in any one of the preceding embodiments, wherein the surface (2) of the building panel (1) is a paper layer or a foil.

(51) 9. The method as in any one of embodiments 1-7, wherein the surface (2) of the building panel (1) comprises a powder layer.

(52) 10. The method as in any one of the preceding embodiments, wherein the building panel is a floor panel (1).

(53) 11. The method as in embodiment 10, wherein the floor panel (1) comprises a mechanical locking system (6, 8, 9, 10, 14) for vertical and horizontal locking.

(54) 12. The method as in any one of the preceding embodiments, wherein the building panel is a wall panel or a furniture component (1).

(55) 13. The method as in any one of the preceding embodiments, wherein the non-bonded dry colour pigments (12) are removed by an airstream.

(56) 14. The method as in any one of the preceding embodiments, wherein the step of bonding said part of the dry colour pigments to the surface (2) comprises applying a liquid substance (11) by a digital coating head (30).

(57) 15. The method as in embodiment 14, wherein the liquid substance (11) is water based.

(58) 16. The method as in embodiment 14 or 15, the method further comprising exposing the liquid substance to UV light (23).

(59) 17. The method as in embodiment 16, wherein the liquid substance (11) is water based UV curable polyurethane.

(60) 18. The method as in any one of embodiments 14-15, wherein the liquid substance (11) comprises a thermosetting binder.

(61) 19. The method as in any one of the preceding embodiments 14-18, wherein the liquid substance is applied with a Piezo ink head.

(62) 20. The method as in any one of the preceding embodiments, wherein the step of bonding said part of the dry colour pigments to the surface (2) comprises applying a laser beam (29).

(63) 21. The method as in any one of the preceding embodiments, further comprising applying heat and pressure to the surface (2) of the building panel (1).

(64) 22. An equipment to provide a digital image (P) on a building panel (1), wherein the equipment comprises a digital coating head (30), a powder scattering unit (27), and a powder removal system (28) wherein: the digital coating head (30) is adapted to apply a liquid substance (11) on the panel, the powder scattering unit (27) is adapted to apply a powder layer comprising colour pigments (12) on the panel, wherein the liquid substance (11) is adapted to bond a part of the powder to the panel, and the powder removal unit (28) is adapted to remove the non-bonded powder from the panel (1).

(65) 23. An equipment as in embodiment 22, wherein the powder comprises a thermosetting resin.

(66) 24. An equipment as in embodiments 22 or 23, wherein the liquid substance (11) is water based.

(67) 25. An equipment as in any one of embodiments 22-24, wherein the liquid substance (11) is exposed to UV light.

(68) 26. An equipment as in any one of embodiments 22-25, wherein a surface layer (2) of the building panel (1) comprises a thermosetting resin, preferably melamine formaldehyde resin.

(69) 27. An equipment as in any one of embodiments 22-26, further comprising a pressing unit adapted to apply heat and pressure to the panel (1).