BR112015001612B1 - method of forming a digitally printed image with colored pigments on a building panel surface - Google Patents

Abstract

DIGITAL BINDING PRINTING. The disclosure relates to a method and apparatus for forming a digital image on a surface by applying a layer of powder comprising colored pigments onto the surfaces, binding a part of the powder and removing unbound powder from the surface.

Description

TECHNICAL FIELD

[0001] The disclosure generally refers to the field of digitally created decorative surfaces preferably constructing panels such as floor and wall panels. The disclosure relates to methods and equipment for producing such decorative surfaces.

APPLICATION FIELD

[0002] The embodiments of the present invention are particularly suitable for use on floors, which may be formed from floor panels comprising a core, a decorative layer and a transparent, wear-resistant structured layer. The following description of technique, known technology problems and objectives and aspects of the embodiments of the invention should therefore as a non-restrictive example be considered above all in this field of application and in particular in floors that are similar to conventional laminate floors or floors with a resilient surface layer.

[0003] It should be emphasized that embodiments of the invention can be used to produce a digital image on any surface, but flat panels such as, for example, general building panels, wall panels, ceilings, furniture components and the like that they usually have large surfaces, with advanced decorative patterns preferred. The method can also be used to apply a print on any surface that may be flat, curved, structured or the like, on papers, metallic sheets, textiles, metal, wood veneer, cork, polymeric material and similar surfaces.

BACKGROUND

[0004] The majority of all laminate flooring is produced according to a production method commonly referred to as Direct Compressed Laminate (DPL). Such laminate flooring comprises a core of 6-12 mm fiber board, a 0.2 mm thick decorative surface layer of laminate upper decorative surface layer and a 0.1-0 lower balance layer. 2mm thick of laminate, plastic, paper or similar material.

[0005] The surface layer of a laminate floor is characterized in that the decorative and wear properties are usually obtained with two separate layers of paper, one above the other. The decorative layer is usually a printed paper and a wear layer is a transparent overlay paper, which comprises small aluminum oxide particles.

[0006] The printed decorative paper and overlay are impregnated with melamine formaldehyde resins and laminated to an HDF core in large batch or continuous laminated presses where the resin cures under high heat and pressure and the papers are laminated to the material of core. A press plate in the form of relief or steel belt forms the surface structure. Sometimes a structured paper is used as a press die.

[0007] Laminate floors can also be produced with printing technology. One advantage is that the pressing operation can be avoided and that no printed paper is needed to provide a wear-resistant decorative surface.

[0008] Floor panels with a Direct Printed Laminated Surface comprise the same HDF core type as DPL. The decoration is printed directly onto the core. The production process is quite complicated and is only cost effective in very large production volumes. Hydroprint inks are used to print the decoration by a multi-color printing press with rollers that print directly onto the pre-sealed core.

[0009] Direct printing technology can be replaced with Digital Printing Technology which is much more flexible and small production volumes can be manufactured economically. The difference between these two methods is mainly the printing step where printing rollers are replaced by a digital non-contact printing process and where the desired image is directly applied onto the pre-finished core.

[0010] Digital printing can also be used to print onto a sheet of paper which is used in the production of conventional laminates and be used to print onto a sheet of paper which is used in the production of conventional laminates and laminated under heat and pressure. Printing can be done before or after impregnation.

[0011] Sheets of paper and plastic are also used as surface layers in flooring and such materials can also be digitally printed.

[0012] Recently new "paper-free" floor types are developed with solid surfaces comprising a substantially homogeneous powder mixture of fibers, binders and wear resistant particles.

[0013] The powder mixture may comprise aluminum oxide particles, melamine formaldehyde resins and wood fibers. In most decorative particle applications such as, for example, colored pigments are included in the mix. In general all these materials are applied in dry form as a powder mixed into an HDF core and cured under 0.1 - 1.0 mm solid layer heat and pressure. The powder is stabilized before pressing with moisture and UV lamps so that it forms an upper skin layer similar to a paper layer and this prevents the powder from blowing away during pressing. Melamine formaldehyde resin and wood fibers can be replaced by thermoplastic particles.

[0014] Several advantages over known technology and especially over conventional laminate flooring can be obtained such as increased wear and impact resistance, deep embossing, increased production flexibility and lower costs.

[0015] Powder technology is very suitable for producing a decorative surface layer, which is a copy of stone and ceramic. However, it is more difficult to create projects such as, for example, wooden decorations. However, recently digital powder printing is developed and it is possible to create very advanced designs of any kind by injecting ink into the powder and creating a digital press on the powder before printing. The surface structure is made in the same way as for laminate flooring by a structured printing plate, steel belt or an embossed matrix paper which is pressed against the powder.

[0016] Floors with a wooden surface are produced in very different ways. Traditional solid hardwood floors are engineered into engineered floors with layers of wood applied over a core made of wood sipes, HDF or plywood. Most such floors are released as pre-finished floors with a wooden surface that is coated with several transparent layers at the factory. Recently wood floors are also produced with a digitally printed pattern that improves the wood grain structure design on wood species that do not have sufficient surface quality.

[0017] Digital printing is used on different floor types to create a decoration. However, volumes are very small mainly due to the high cost of ink and the investment cost act for industrial printers. It can be a greater advantage if the cost of ink can be reduced and if more cost effective equipment can be used on an industrial scale.

DEFINITION OF SOME TERMS

[0018] In the following text, the visible surface of the installed floor panel is called "front side", while the opposite side of the floor panel, facing the subfloor of the floor panel, facing the subfloor, is called "rear side" . By "surface layer" is meant all layers that are given to the panel its decorative properties and its wear resistance.

[0019] By "print" is meant a decoration or image. By "up" is meant towards the front side and by "down" towards the rear side. By "vertically" is meant perpendicular to the surface and by "horizontally" parallel to the surface.

[0020] By "pigments" is meant a very fine powder of solid coloring particles.

[0021] By "Pigment ink" is meant an ink comprising pigments that are suspended or dispersed throughout a transport fluid.

[0022] By "dry ink" is meant a colored substance which is completely dissolved within the transport fluid and the resulting ink is a true solution completely soluble as sugar in water.

[0023] By "aqueous or water-based ink" is meant an ink where water is used as a liquid substance in the ink. The water-based liquid transports pigments.

[0024] By "solvent-based ink" is meant ink that generally contains three main parts such as fluid transport, pigments and resins. Technically, solvent paint generally refers only to the oil-based transport portion of the paint that keeps the other components in liquid form and once applied to a surface through blasting evaporates.

[0025] By "UV curable inks or coating" is meant an ink or coating which after application is cured by exposure to strong UV light in a UV oven.

[0026] By "binder" is meant a substance that connects or contributes to connect two particles or materials. A binder may be liquid, powder-based, a thermosetting or thermoplastic resin, and the like.

[0027] The general technology, which is used by the industry to provide a digital print, is described below. The methods described below can be used to, separately or in combination, create a fingerprint or a digital application of a substance in the embodiments of this disclosure.

[0028] High definition digital presses use non-impact printing processes. The printer has printheads that "fire" the ink drop from the printheads onto the substrate in a very precise way.

[0029] Multi-pass printing, also called raster printing, is a printing method where the print head moves transversely above the substrate many times to generate an image. Such printers are slow, but a slow printhead can produce a larger image.

[0030] Industrial printers are generally based on a Single Pass printing method, which uses fixed printer heads, with a width that matches the width of the printed medium. The printed substrate moves under the heads. Such printers have a high capacity and are equipped with fixed printheads that have realigned one after the other in the feed direction. Each printhead prints one color. Such printers can be customized for each application.

[0031] Figure 1a shows a single pass printer 35 comprising five digital print heads 30a-e, which are connected with ink tubes 32 to ink containers 31 which are filled with ink of different colors. The printheads are connected with digital data cables 33 to a digital control unit 34 which controls the application of ink drops and the speed of the conveyor 21 which moves the panel under printheads with high precision to ensure an image High quality comprising various colors. Figure 1b shows a wood grain print P provided on a panel surface 2. The surface of a floor panel is often in relief form with a pattern structure 17 which is the same for various basic decorations as shown in figure 1c . Advanced floors use an embossing 17 which is in register with the printed pattern P as shown in figure 1d.

[0032] A typical width of an industrial printhead is about 6 cm and any lengths can be printed. 1-2m wide areas can be printed with digital printers comprising several rows of misaligned side by side.

[0033] Number of dots per inch or DPI is used to define the resolution and print quality of a digital press. 300 DPI is generally sufficient so, for example, printing wood grain structures of the same quality presently used in conventional laminate flooring industrial printers can print patterns with a resolution of 300 - 600 DPI and even more with a speed exceeding 60 m/ min.

[0034] The impression can be a "total impression." This means that the visible printed decoration is mainly created by the ink pixels applied to the surface. The color of a layer of powder or a base color of a paper has in such a modality, in general, a limited effect on the visible pattern or decoration.

[0035] The print can also be a "part print". The color of another underlying layer is one of the colors that are visual in the final decoration. The area covered by printed pixels and the amount of ink that is used can be reduced and cost savings can be achieved due to lower ink usage due to lower ink usage and increased printability compared to a project of full print. However, a part print is not as flexible as a full print as the base colors are more difficult to change when a full print is used.

[0036] Printing can be based on the principle of CMYK colors. That is, a 4-color montage comprising cyan, magenta, yellow and black. Mixing these together will give a color space/gamma, which is relatively small. To enhance specific color or full gamut stain colors can be added. The spot color can be any color. Colors are mixed and controlled by a combination of software and hardware (print engineering/printheads).

[0037] New technology is being developed by Valinge Innovation AB that makes it possible to inject a fingerprint into a layer of powder. This new type of "Digital Injection Printing" or DIP is achieved due to the fact that printing is done on a powder which is cured after printing. The print is embedded in the cured layer and is not applied over a layer as when conventional printing methods are used. The print can be positioned in various dimensions horizontally and vertically at different depths. This can be used for 3D effects when transparent fibers are used and to increase wear resistance No protective layers are required to disturb the original design.

[0038] The DIP method can be used on all powder-based materials that can be cured after printing. However, the DIP method is especially suitable to be used when the powder comprises a mixture of wood fibers, small hard wear resistant particles and a melamine formaldehyde resin. The surface layer can also comprise thermoplastic material, for example vinyl particles, which are applied in powder form onto a substrate. This allows the print to be injected into the vinyl powder particles. Improved design and increased wear resistance can be achieved even in such materials.

[0039] A suitable printer head has to be used in order to obtain a high print quality and speed in the powder based layers and other layers as described above. A printer head in several small nozzles that can fire ink droplets in a controlled mode (Drop On Demand - DOD). The size of each droplet may vary depending on ink type and head type, typically between 1-100 picoliters. It is possible to design printheads that can fire larger drops of up to 200 picoliters. Some printer heads can fire different droplet sizes and they are capable of printing a grayscale; Other heads can only fire a fixed droplet size.

[0040] Different technologies can be used to fire asdrops out of the nozzle.

[0041] Thermal printhead technologies use print cartridges with a series of tiny chambers each containing a heater, all of which are constructed by photolithography. To eject a droplet from each chamber, a pulse of current is passed through the heating element to form a bubble, which causes a large increase in pressure, propelling an ink droplet out through the nozzle to the substrate. Most consumer inkjet printers from companies including Canon, Hewlett-Packard, and Lexmark use thermal printer heads.

[0042] Most commercial and industrial inkjet printer heads and some consumer printers such as those produced by Epson use piezoelectric printer head technology. A piezoelectric material in a paint-filled chamber behind each nozzle is used instead of a heating element. When a voltage is applied, the piezoelectric material changes shape, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. Piezoelectric inkjet (also called Piezo) also allows for a wider variety of inks than thermal inkjet, as there is no requirement for a volatile component, and no issue with kogation. Many types of ink can be used such as dye inks, solvent based inks, latex inks or UV curable inks.

[0043] Pigment-based inks are often individually mixed together using color pigments and various chemicals. A pigment is a very fine powder of solid coloring particles that are suspended or dispersed throughout a liquid carrier. Pigments used in digital ink have an average particle size of about 0.1 micron. The common size of nozzles is about 20 microns which means the pigment particle has enough space to pass through the nozzle channels in the printhead. The nozzles can also be blocked by the ink itself and the pigments that form clusters of particles. A high quality pigment ink should keep the pigment suspended in the transport fluid for a long period of time. This is particularly difficult at the low viscosities that are required for good printhead operation. Pigments have a natural tendency to settle out and fall down into the liquid carrier. In high quality pigment ink, no settling out of the pigment should normally occur.

[0044] Water-based inks comprising colored pigments are especially suitable and can provide a high quality printing method on very different materials. Pigment inks are generally more fixed in color and more fade resistant than dye-based inks.

[0045] Pigments do not adhere to a surface. They are similar to sand particles and are easily removed from most dry surfaces. The water-based transport fluid is therefore generally mixed with small amounts of various other additives to provide special ink and printing properties, such as binders which provide pigment adhesion to a surface, dot gain, pH level , drop formation, printhead corrosion, fade resistance, etc.

[0046] As such, color pigments are quite cost-competitive, but the production of pigment-based inks and other inks for digital printers is very complicated and expensive and this results in a very high cost for ink that can normally be in the range of around 100 EUR/litre. About 100 m2 of floor can be printed with a liter if a full quality print is applied and this gives a cost of 1 EUR/m2. The costs for conventional printed floor surfaces where printing cylinders are used are only 10% of the cost for digitally printed floor surfaces.

[0047] Digital inkjet printers use a non-contact method to apply ink onto a surface. Laser printing, however, is based on a contact method where a laser beam projects an image onto an electrically charged rotating drum. Dry ink particles, often called toner, are then electrostatically collected by the charged areas of the drum. The paint comprises fine particles of dry plastic powder mixed with carbon black or coloring agents. The thermoset plastic material acts as a binder. The drum prints the image onto a paper by direct contact and heat, which fuses the ink into the paper binding the plastic powder to laser printers to the paper. Color laser printers use the principle of CMYK with color dry ink, typically cyan, magenta, yellow, and black that are mixed together in order to provide a high quality color image.

[0048] Impact method laser technology is not used for printing flat panel surfaces such as floor panel surfaces.

[0049] The above description of various known aspects is the applicants' characterization, and is not an admission that any of the above description is prior art. Several of the technologies described above are known and used individually, but not in all combinations and modes as described above.

[0050] As a summary it can be mentioned that digital printing is a very flexible method, but it cannot be fully utilized due to the high cost for the ink. Costs are primarily caused by the need to grind the colored pigments to very small, well-defined particles and disperse the particles throughout the transport fluid. There could be a greater advantage if digital images could be created with ink that does not contain colored pigments or colored substances.

[0051] Digital application technology is only used to obtain advantages related to the possibility to create a high resolution image in a flexible mode. However, the other aspects of the technology, mainly related to the possibility of applying a liquid substance very precisely with a non-impact method, are not fully utilized or developed.

[0052] It is known that powder applied onto a liquid substance can be used to create enlarged portions or an image on primarily a paper substrate and that the liquid substance can be digitally applied by inkjet.

[0053] US 3,083,116 describes augmented printing powder and an augmented printing process comprising sprinkling a powdered resin onto a freshly printed sheet, removing excess powder that does not adhere to the wet ink therefrom, and applying heat to the powder retained on it. the sheet to fuse the same so that the particles of it will fuse together and adhere to the sheet. The powder may comprise a phenolic resin.

[0054] US 3,446,184 describes a method for forming a sticky image copy. Toner powder is applied in a liquid formation and a portion of the powder is retained by the liquid coating, forming a visible image. Loose powder is removed and the sheet passes through a heating unit where trapped powder is removed and the sheet passes through a heating unit where trapped powder is fused to form a permanent image. Stray dust is removed and the sheet passes a heating unit where trapped dust is melted to form a permanent image.

[0055] US 4,312,268 describes a method whereby a water-based ink is digitally applied to a continuous web and single colored meltable powder material is applied to the web and over the ink. Some of the powder material is bonded to the liquid, and unbound powder material is removed from the web before heating the web to dry the liquid and melt the powder material to the web by melting the powder. It is mentioned that the powder material can have a particle size in the range of 5 to 1000 microns and can have a melting point or melting point in the range of 50 to 300 degrees centigrade. The powder material can be produced by dissolving or dispersing, respectively, a dye or pigment in a resin or resin formulation, followed by grinding, spray cooling, or the like to reduce the material to a fine powder. The powder material can provide abrasion resistant qualities to paint which may contain phenolic resin. The liquid material, which is applied by jets, can be clear or colorless water.

[0056] US 6,387,457 describes a method of printing using dry pigments. A binder material is applied to a surface of a substrate evenly or in a pattern. Dry pigment is applied to the binder material in a pattern or evenly. The dry pigment material comprises flakes of non-metallic material having a particle size less than about 100 microns. The flakes are aligned in a parallel direction with the substrate surface.

[0057] EP 0 403 264 A2 describes a transfer method for forming a multicolored image on a drum which transfers the image onto a paper. A digital fluid latent image is subsequently developed at a developing station where colored powder is applied to the fluent latent image and fixed to produce a visible, permanent image. Various digital printheads can be used that print with dyeless fluids comprising a mixture of water and polyhydric alcohols and their subsets of ethylene glycol, glycerol, diethylene glycol and polyethylene glycol. A powdered toner is applied across the surface of the paper and a voltage is applied during this development. Voltage is then reversed to remove toner from the background areas. Fixation is achieved through conventional copier fusing methods.

[0058] EP 0 657 309 A1 describes a multiple color transfer method using a transfer paper carrying a pattern formed by ink jet and powder similar to the methods described above. The transfer method is intended for decorative ceramics.

[0059] WO 2011/107610 describes a method for creating an elevation or embossing on a floor panel in order to avoid the use of expensive press plates. The method is the same as the known methods for creating an augmented impression. It describes a method for producing a floorboard by pressing a curable substance to create a rise on the panel. Elevation can be applied over a basic decorative pattern that is directly printed or laminated onto the panel. The curable substance can be digitally printed onto the panel by first printing a liquid in a predefined pattern and then providing an intermediate substance which can comprise a powder. The curable substance can be cured by UV radiation or it can be a varnish.

[0060] Known methods are not suitable for creating a high quality multicolor image on a building panel, and especially not on a floor panel where UV resistant pigments are to be used and where the image is to be embedded in a floor panel where UV resistant pigments should be used and where the image should be embedded in a wear resistant surface. It is not known that known principles can be used to create an image on a floor surface that is pressed and especially not how the principles should be adapted for printing similar floor surfaces to laminate and Wood Fiber Floors (WFF) where the powder, ink and application methods must be adapted to the specific resins, materials and printing parameters that are needed to form a resistant high quality multicolored surface that are needed to form an impact resistant high quality multicolored surface and stain in a cost effective way.

OBJECTIVES AND SUMMARY

[0061] The purpose of at least certain embodiments of the invention is to provide a method and equipment for producing a digitally printed building panel, preferably a floor panel, which can be produced more cost effectively without ink comprising a colored substance, by for example, no color pigments that are cumbersome to manipulate in a digital printhead.

[0062] The above objectives are exemplary and the modalities of the invention may carry out different or additional modalities.

[0063] A first aspect of the invention is a method of forming a digitally printed image with colored pigments on a surface of a building panel, comprising the steps of:

[0064] sprinkle a powdered resin dispersing dry colored pigments on the surface,

[0065] bind a part of the dry colored pigments to the surface, and

[0066] remove the unbound dry colored pigments from the surface so that a digitally created image is formed by the bound colored pigments.

[0067] According to a principle of the first aspect, a pattern or image can be digitally formed by a digital coating head or the image can be formed by a digital coating head which applies only a binder onto a surface. Pigments are randomly diffused by a second device over the pattern. The binder binds some pigments to form the same pattern as the binder while other unbound pigments are removed.

[0068] This two-step process, where pigments and a liquid binder are applied separately, can provide an image with a quality comparable to conventional digital printing technology, eg comparable to at least 300 DPI.

[0069] According to a second principle of the first aspect pigments can be diffused onto a surface in a first step and a digital coating head which only applies a binder onto the diffused mixture after which it forms a pattern or image digitally. The digitally applied binder may comprise water which melts, for example melamine formaldehyde particles which may be mixed with pigments, less thoroughly mixed with the pigments. The binder binds some pigments that form the same pattern as the binder while other unbound pigments are removed.

[0070] According to a third principle of the first aspect, pigments can be diffused onto a surface in a first step and a binder pattern or image is then digitally formed by a laser beam that binds some pigments to the surface by melting or curing a binder which can be mixed with the pigments or embedded in the surface under the pigments A digitally created impression is obtained when unbound pigments are removed.

[0071] Dry colored pigments can be bonded to a binder on the surface of the building panel. The binder can be applied separately to the surface of the building panel.

[0072] Dry colored pigments can be mixed with a binder.

[0073] The binder may be a powder, preferably a dry powder, or a liquid substance.

[0074] The binder may comprise a thermosetting resin or a thermoplastic resin. The surface of the building panel may comprise a thermosetting resin, preferably melamine formaldehyde resin.

[0075] The surface can be a paper layer, a sheet, a wood or wood-based layer, or a dust layer. The powder layer may comprise a mixture comprising lignocellulosic or cellulosic particles, a binder and optionally wear resistant particles, for example aluminum oxide. The binder is preferably a thermosetting binder such as melamine formaldehyde resin.

[0076] The building panel may have a surface of a paper impregnated with resin, thermoplastic film or sheet, a powder layer comprising lignocellulosic or cellulosic particles and a binder. The building panel can be formed by applying heat and pressure.

[0077] The building panel can be a floor panel. The surface can be a part of a floor panel.

[0078] The floor panel can comprise a mechanical locking system for vertical and horizontal locking.

[0079] The building panel can be a wall panel or a furniture component. The surface can be a part of a wall panel or a furniture component. Pigments can be removed by a current of air.

[0080] The step of attaching said part of the dry colored pigments to the surface may comprise applying a liquid substance by a digital coating head. The liquid substance can be applied to the surface before the dry color pigments are applied to the surface, or it can be applied to the surface after the dry color pigments have been applied to the surface.

[0081] The liquid substance can be water based.

[0082] The liquid substance can be exposed to UV light.

[0083] The liquid substance may be water-based UV-curable polyurethane.

The liquid substance may comprise a binder such as a thermosetting or thermoplastic binder.

[0085] The liquid substance can be applied with a Piezo ink head.

[0086] The step of binding said part of the dry colored pigments to the surface may comprise applying a laser beam to bind the dry colored pigments to the surface.

[0087] The method may further comprise applying heat and pressure to the surface of the building panel. The surface of the building panel can be pressed after the digitally created image has been formed by the bonded colored pigments. Final bonding of the dry colored pigments to the surface of the building panel can occur by applying heat and pressure to the surface of the building panel. For example, the binder binding the dry colored pigments to the surface of the building panel can be cured by applying heat and pressure to the surface of the building panel. The binder, for example a thermosetting resin such as melamine formaldehyde resin, binding the dry colored pigments to the surface of the building panel can be cured simultaneously as the binder, for example a thermosetting resin such as melamine formaldehyde resin, of the surface of the construction panel. Curing can occur by applying heat and pressure to the surface of the building panel.

[0088] The second aspect of the invention is to provide equipment for forming a digital image on a building panel, wherein the equipment comprises a digital coating head, a powder diffusion unit and a system for applying a liquid substance on a surface of the building panel or on a layer of powder comprising colored pigment and/or binder on a surface of the building panel. The powder diffusion unit is configured to apply a layer of powder comprising colored pigments onto the surface of the building panel. The liquid substance is configured to bond a part of the dust to the surface of the building panel, and the dust removal units configured to remove unbound dust from the surface of the building panel. A digital image is thus formed by the bonded colored pigments.

[0089] The powder may comprise a thermosetting resin.

[0090] The liquid substance can be water based. The liquid substance can be exposed to UV light.

[0091] A surface of the building panel comprises a thermosetting resin, preferably melamine formaldehyde resin.

[0092] The equipment may further comprise a pressing unit adapted to apply heat and pressure to the surface of the building panel. The surface of the building panel can be pressed after the digital image has been formed by the bonded colored pigments.

[0093] The production method and equipment according to the modalities of the invention make it possible to produce very advanced decorative patterns in a flexible and very cost effective way since the digital equipment is only used to create a pattern with a binder that does not have any colored pigments.

[0094] Modalities and details of various aspects can be combined with modalities and details of other aspects. Mixing of colored pigments in the liquid binder is not excluded and thus it can be used, for example, to apply smaller amounts of pigment with the digital coating head than may be necessary for a specific color combination.

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] The invention will be described below in connection with exemplary embodiments and in greater detail with reference to the attached exemplary drawings, in which:

[0096] figures 1a-d illustrate known methods to produce a printed surface and in relief form;

[0097] figures 2a-d illustrate a first aspect of the invention;

[0098] figures 3a-d illustrate a second aspect of the invention;

[0099] figures 4a-d illustrate a third aspect of the invention;

[0100] figures 5a-h illustrate the digital application of pigments according to the first aspect of the invention;

[0101] figures 6a-c illustrate embodiments of the invention.

DETAILED DESCRIPTION OF MODALITIES

[0102] Figures 2a-2d show an embodiment of the invention that is based on a first principle where a BP binder pattern or image is digitally formed by a digital coating head that applies a binder 11 in the form of a liquid substance. A digital printhead or digital inkhead which is primarily used to apply a liquid substance without any colorants, and which is not intended to print a color image is hereinafter referred to as a "digital coating head". Pigments 12 are randomly diffused by a second device over the BP binder pattern The binder binds some pigments to form the same pattern as the binder while other unbound pigments are removed.

[0103] This two-step process, where pigments and a liquid binder are applied separately, can provide an image with the same quality as conventional digital printing technology. The method is particularly suitable in applications where considerable amounts of pigment have to be applied over 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 colored pigments. This is the biggest advantage since no expensive inks comprising pigment dispersions have to be handled by the digital coating head.

[0104] Figure 2a shows that a BP binder pattern is formed on a surface 2 of a building panel 1 by a digital coating head 30 as shown in figure 2d. The surface 2 can, for example, be a paper layer, a stabilized powder layer, a metallic foil or a base color applied over a material preferably over a core material based on wood or plastic. Binder 11 is in this preferred embodiment water based and preferably comprises 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 layer of pigment 12 is applied, for example, by diffusing as a dry powder onto the BP binder pattern as shown in figure 2b. The pigment layer may comprise, for example, melamine formaldehyde powder particles which melt when in contact with the water-based BP standard. The dry pigments and melamine formaldehyde powder that do not contact the water-based BP pattern are removed, for example, by a current of air and the remaining 12 color pigments form a print P as shown in figure 2c, which is identical to standard BP binder.

[0105] Print P can be dried and stabilized, for example, by exposure to IR or UV light which heats the wet melamine formaldehyde resin and binds the colored pigments to surface 2 by drying the wet melamine formaldehyde resin. A second bonded pattern can be coated onto surface 2 and a second layer of pigments and melamine formaldehyde powder can be applied over the surface and over and/or adjacent to the first print. Advanced decor can be created with multiple colors.

[0106] The binder in this modality can comprise wet formaldehyde melamine and can be applied in two steps, first as a liquid substance, such as water, from the digital coating head 30, and second as a powder from a diffusion unit 27. Powder can be mixed with dry colored pigments. This simplifies the function of the digital coating head which only has to apply water drops without any or limited amounts of binders and color pigments.

[0107] The binder can be included in dry form in the powder and activated by the liquid substance applied by the coating head as described above or it can only be included in the liquid substance applied by the digital coating head.

[0108] This method in which the liquid substance and powder are applied directly onto a panel is suitable for forming 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 so that no defects are caused during curing of the thermosetting resins. This can be done with the liquid substance which, for example, comprises water and/or glycols. The substance should be applied to a surface of a building panel in order to eliminate problems related to the placement of the print on the panel. Thermoset resins such as melamine formaldehyde resins are preferably included in a surface layer of a panel and/or in the powder applied on the panel and can react with the liquid substance and bind the powder to the surface of the panel so that unalloyed powder can be removed. The powder preferably comprises UV stable colored pigments. The advantages are that such a combination of materials can be pressed and cured at high pressure, exceeding 4 MPa (40 bar), and heated to a temperature exceeding 160 degrees Celsius. The digitally formed surface and image can be cured to a hard wear resistant surface without the so-called overflow of pigments during the pressing and heating step and the pigments can be incorporated into the cured surface so that they can create an image UV stable wear resistant similar to conventional laminate flooring images.

[0109] A wide variety of thermosetting and thermoplastic materials can be used as particles in the diffused powder or as dispersions or liquid substances in the binder applied by the digital coating head. Most such materials can be produced in dry powder form or as liquid dispersions.

[0110] As alternative materials for thermosetting materials such as melamine formaldehyde, orthothermoplastic materials such as, for example, PVC powder, UV curable polyurethane can, for example, be used in powder form or as a dispersion.

[0111] UV-curable polyurethane substance with a viscosity that is adapted to the digital coating head 30 can be used. Water-based polyurethane dispersions are preferred as a liquid substance in the digital coating head as they do not cure until exposed to UV light. Polyurethane dispersions are fully reacted polyurethane/polyureas of small, discrete polymeric particles and such particles can be produced with a size of about 0.01-5.0 microns and can therefore be manipulated in a fingerprint or other print head similar heads. They can be 20 -70% solid content. Polyurethane dispersions can be blended with, for example, acrylic and other emulsions in order to reduce costs.

[0112] The digital coating head 30 which is preferably a Piezo head preferably has an ability to fire droplets with a drop size of about 1 - 200 picoliters or more. The droplet size can vary and this can be used to vary the intensity of a color and create a grayscale with the same basic color.

[0113] Water-based adhesives can also be used such as soluble adhesives or water-dispersed adhesives.

[0114] Other UV curable materials such as deepoxy acrylates, urethane, polyester, mixed acrylate oligomers and amine modified acrylic polyether can be used in powder form or as dispersions.

[0115] Figure 2d shows a "bond printing" station of a bonding printing equipment that can be used to create a fingerprint with the "bonding printing" method. .A 30 digital coating head which can be a Piezo head applies a BP binder pattern. Several coating heads 30 can be positioned side by side in order to cover the width of the surface being printed. The binder pattern is digitally created in the same way as in conventional digital printing. The colors are separated and each coating unit 36 mainly applies the same substance that is used to bind a specific color in each coating step. The digital coating head is connected with a feed tube 32 to a container 31 comprising a binder or a 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 which controls drop application, conveyor speed 21, the function of a powder application unit and all other equipment that is used for turn on and remove pigments.

[0116] The water droplets serving as a binder 11 must be wet until they pass the diffusion station 27 which applies a powder mixture which in this preferred embodiment comprises colored pigments 12 and melamine formaldehyde powder 13. Melamine formaldehyde particles in the powder mixture, which are in contact with the BP standard water-based binder melts and the water/melamine formaldehyde solution acts as a binder that binds a part of the pigment/melamine formaldehyde mixture to the surface 2 of the panel 1. When the powder mixture is displaced under a preferably hot UV curing oven 23 with ultraviolet light, which is preferably located after the digital coating unit 36 in the feed direction, a practically instantaneous cure or bond within a few seconds can occur.

[0117] A dust removal system 28 which in this embodiment is based on a stream of air and vacuum removes pigments and melamine formaldehyde particles that are not bound by the BP binder pattern and a color perfect P print is provided. This production step can be repeated and another color can be applied by a second diffusion unit 27 comprising another color. The removed dried melamine formaldehyde pigments and particles can pass through a sieve or filter and can be recycled and reused over and over again.

[0118] Melamine formaldehyde or other binders can also be included in surface layer 2 as a dry layer when, for example, a paper layer impregnated with melamine formaldehyde or a stabilized powder layer is used as a base surface. The water based bonding pattern will melt a part of this melamine formaldehyde layer and only pigments can be applied as powder by the diffusion unit 27 and recycled. This method can also be used when a full binding substance is included in the liquid substance applied by the digital coating head.

[0119] The powder mixture may, in addition to pigments and melamine formaldehyde particles, also comprise wear-resistant particles such as small aluminum oxide particles and fibers, preferably wood fibers which preferably comprise transparent or semi-transparent bleached fibers. Such a mixture can 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 can penetrate deeper into the powder mixture than pigments applied as a dispersion in a conventional digital print and a very wear resistant print can be obtained.

[0120] Multiple layers of prints can be positioned on top of each other and this can be used to further increase wear resistance and create 3D decorative effects.

[0121] Static electricity can be used to apply and/or remove unbound dust particles. Air and vacuum currents that blow away and/or suck in particles can be combined as brushes. In general all wet and dry methods that are used to remove dust can be used separately or in various combinations to remove pigments and unbound parts from the diffused dust mixture. However, dry and non-impact methods are preferred.

[0122] Controlled total or partial removal of unbound pigments is essential for high quality printing with a predefined decorative image. Advanced removal systems can also be used that remove only the colored pigments while the essential part of the clear melamine formaldehyde powder particles can remain on the surface. This can be done, for example, in a two-step diffusion where a first layer comprises only melamine formaldehyde particles that are attached to the surface before application of the binder, sprayed with water and dried with IR, hot air, UV and methods similar. This separated melamine formaldehyde layer can, in some applications, replace, for example, prepreg paper and only prepreg paper with or without a base color can be used as a surface layer 2.

[0123] The moisture content of the surface layer can be precisely controlled in order to facilitate the removal of unbound dust particles. Moisture content below 6% is preferred. The surface layer 2 can be dried, for example, by IR or UV lamps or hot air before applying the pigments. Water and special chemicals such as release agents can be applied in order to seal the surface 2 or the top of bonded color pigments in order to create a seal or release layer that can prevent colored pigments from adhering to parts specific to the surface layer where no binder is applied.

[0124] The print can be covered with transparent protective layers of, for example, a paper-based or water-based overlay comprising aluminum oxide and melamine formaldehyde resins or a UV-curing coating that can be applied by rollers or digitally with, for example, Piezo coating heads.

[0125] Figures 3a - 3d show an embodiment of the invention, which is based on a second principle where pigments 12 in a first step are diffused onto a surface 2 and a pattern or image is then digitally formed by a digital coating head which only applies a standard BP binder to the diffused mixture. The digitally applied binder may comprise water which melts, for example, melamine formaldehyde particles 13 mixed with pigments 12 or applied under the pigments. The binder binds some pigments to form the same pattern as the BP binder pattern while other unbound pigments are removed. Figure 3a shows a substantially homogeneous mixture of melamine formaldehyde powder 13 and pigments 12 diffused over surface 2. Figure 3b shows a digitally applied binder BP pattern applied to the mixture. Figure 3c shows that all unbound pigments and in this embodiment also melamine formaldehyde 13 particles have been removed. Figure 3d shows a binder printing station comprising a diffusion unit 27, a digital coating unit 36 and a UV oven 23 and a dust removal system 28 based on an air stream and vacuum.

[0126] The first and second principles can be combined. A binder pattern can be applied before and after the application of the pigment mixture and this can be used to create a solid impression with a greater vertical extension and more wear resistance. high.

[0127] Figures 4a - 4c show an embodiment of the invention, which is based on a third principle where pigments 12 in a first step are diffused onto a surface 2 and a binder or image BP pattern is then digitally formed by a beam laser 29 which fuses or cures a binder that can be mixed with pigments 12 or included in surface 2. A digitally created impression P is obtained when unbound pigments are removed.

[0128] Figure 4d shows a bonding printing station comprising a diffusion unit 27, a laser 29, and a dust removal system 28 based on a stream of air and vacuum. The laser can be replaced with heat lamps that can be used to create images that comprise fairly large areas of the same color as in some stone designs. Even a conventional laser system based on the impact method described above can be used to apply a digital print partially or completely onto a floor panel or in combination with the bonding print methods described above.

[0129] All the principles described above can be partially or completely combined and a production line can comprise several binder printing stations according to the first, second or third principles.

[0130] Figures 5a - 5h show the application of two different colors according to the first principle. A first binder 11a which in this embodiment is essentially water is applied by a Piezo digital head onto a surface 2 which can be a stabilized powder layer or a paper as shown in figure 5a. A first layer of powder comprising colored pigments 12a and melamine formaldehyde particles 13a is applied onto surface 2 and onto binder 11a. Melamine formaldehyde 13a particles that are in contact with wet water droplets will fuse. A first UV oven 23a dries the wet melamine formaldehyde and binds the pigments to the surface as shown in figure 5c and melamine formaldehyde and unbound pigment particles are removed so that an image of pigment 12a corresponding to the applied binder 11a is obtained. . Figures 5e - 5h show that the same application can be repeated with another color pigment 12b shown with melamine formaldehyde 13b particles and a new binder 11b so that a two color image is obtained with two types of color pigments 12a, 12b as shown in figure 5h.

[0131] Figure 6a shows an embodiment where the digital binder printing equipment comprising a digital coating unit 36, a diffusion unit 27, a UV curing unit 23, and a vacuum dust removal system 28 is combined with conventional inkjet printer 35. Binder printing method can use this combination to create a larger part of a digital image while some parts of the final print can be created by the inkjet printer. This can reduce the ink cost considerably since, for example, the cost effective binder printing method, where no pigment has to be handled by the digital coating head, can apply, for example, 90% of the pigments that are needed to create a fully printed pattern or decoration.

[0132] Figure 6b shows a binder printing equipment where pigments 12 and melamine formaldehyde powder 13 are applied by a diffusion unit 27 preferably comprising a relief roller 22 and an oscillating brush 42. The pigments and particles of unbound melamine formaldehyde are removed by a dust removal system 28 which recycles the mixture 12, 13 within the diffusion unit 27. A pigment/ melamine formaldehyde dust cloud can be created by air currents and only the pigments and dust of melamine formaldehyde that come into contact with the wet binder 11 will be bonded to the surface 2.

[0133] Figure 6c shows that the method is especially suitable for applying 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 on one edge that cooperates with a locking groove 14 on an adjacent edge of another panel for horizontal locking of adjacent edges, and a tongue 10 on an edge that cooperated with a tongue groove 9 on another edge for vertical locking of panels. Such floor panels are usually advanced wood or stone decorations that require large amounts of different colored pigments and a decoration that has to be positioned precisely in relation to the relief structures and panel edges with the mechanical locking system.

[0134] In all embodiments, the surface of the building panel can comprise a thermosetting resin, for example melamine formaldehyde resin. The building panel can be formed by applying heat and pressure, preferably after the digitally believed image is formed by the bonded colored pigments. In one embodiment, the binder mixed with the dry colored pigments is simultaneously cured as the binder on the surface of the building panel, preferably by applying heat and pressure.

[0135] All of the methods described above can be partially or fully combined.

EXAMPLE

[0136] A 300 g/m2 powder mixture comprising wood fibers, melamine formaldehyde particles, brown colored pigments and aluminum oxide particles such as corundum was applied by the diffusion equipment onto an 8 mm core. The mixture was sprayed with deionized water and dried by a UV oven so that a hard stabilized powder-based surface with a brown base color was obtained. The panel with the stabilized powder surface was placed on a conveyor and moved under a Piezo digital coating head which applied water drops onto the stabilized surface and which printed a clear wood grain pattern on the surface. The melamine formaldehyde under the clear pattern melted when the Piezo digital coating head applied the water drops. Black pigments were in a second stage diffused over the total surface and the transparent pattern. The panel was then moved by a conveyor under a UV oven. The melamine formaldehyde in the clear pattern was dried again and the pigments above the clear pattern were bonded to the surface. The panel was then moved under a vacuum suction tube where all unbound pigments and melamine formaldehyde particles were removed. A wood grain pattern comprising a brown base color and black wood grain structure was obtained. A protective layer comprising melamine formaldehyde and aluminum oxide particles was diffused over the entire surface. The layer was sprayed with water and dried under a UV oven. The panel with the printing and protective layer was then pressed for 20 s at a temperature of 170 degrees C in a 4 MPa (40 bar) press and the powder-based surface with the grain structure and protective layer was Cured to a hard wear-resistant surface with a high quality print.

Claims (12)

1. Method of forming a digitally printed image (P) with colored pigments (12) on a surface (2) of a building panel (1), characterized by comprising the steps of:• diffusing dry colored pigments (12) onto the surface (2),• bond a part of the dry color pigments to the surface (2),• remove the unbound dry color pigments from the surface so that digitally created image (P) is formed by the dry color pigments by the bonded color pigments (12), and• applying pressure and heat to the surface (2) of the building panel (1), the step of bonding said part of the dry colored pigments to the surface (2) comprising applying a liquid substance (11) by a digital coating head (30). 2. Method according to claim 1, characterized in that the dry colored pigments (12) are bonded to a binder on the surface (2) of the building panel (1). 3. Method according to claim 1, characterized in that the dry colored pigments (12) are mixed with a binder. 4. Method according to claim 2 or 3, characterized in that the binder comprises a thermosetting resin. 5. Method according to claim 2 or 3, characterized in that the binder comprises a thermoplastic resin. 6. Method according to any one of claims 2 to 5, characterized in that the binder is a powder. 7. Method according to any one of the preceding claims, characterized in that the surface (2) of the building panel (1) comprises a thermosetting resin, preferably melamine formaldehyde resin. 8. Method according to any one of claims 1 to 7, characterized in that the surface (2) of the building panel (1) comprises a layer of dust. 9. Method according to any of the preceding claims, characterized in that the building panel is a floor panel (1). 10. Method according to any of the preceding claims, characterized in that the building panel is a wall panel or a furniture component (1). 11. Method according to any of the preceding claims, characterized in that the dry colored pigments (12) are removed by a current of air. 12. Method according to any of the preceding claims, characterized in that the liquid substance (11) is based on water.

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