ES2848179T3 - Digital printing with binder and powder - Google Patents

Abstract

A method of forming a digital impression (P) on a panel (1) comprising a surface (2), the surface being part of a building panel (1), such as a floor panel (1), wherein the method comprises: - moving the panel under a digital drop application head (30 '); - applying a liquid binder (11) with the digital drop application head (30 ') on the surface (2); - applying colorants (7) on the liquid binder (11) and the surface (2), where the colorants (7) are macro-colorant particles (64) larger than 20 microns; - joining a part of the colorants (7) to the surface (2) with the liquid binder (11); - removing unbound colorants (7) from the surface (2) so that a digital impression (P) is formed by the attached colorants (7); and - applying heat and pressure on the panel (1), the surface (2) and the colorants (7) joined so that the colorants (7) are permanently attached to the surface (2), where the colorants (7) they are pressed into the surface (2) when heat and pressure are applied to the panel (1).

Description

DESCRIPTION

Digital printing with binder and powder

Technical field

The description generally refers to the field of digitally created decorative surfaces for building panels, such as floor and wall panels. The description refers to a method and equipment for applying and bonding powder-based colorants so as to form a digital impression on said surfaces.

Scope

Embodiments of the present invention are especially suitable for use on floors, which are made up of floor panels comprising a core or a body, a decorative layer and preferably a transparent wear resistant structured layer on top of the decorative layer. Preferred embodiments are conventional laminate floors, powder-based floors, wooden floors, LVT-type plastic floors, and ceramic tiles. The following description of techniques, problems of known technology and objects and characteristics of the invention will focus above all, by way of non-limiting example, on this field of application and, in particular, on floor materials that are similar to floor materials. Conventional stratified floors or flooring materials with a resilient surface layer.

It should be noted that embodiments of the invention can be used to produce a digital image and / or digitally formed structure on any surface, but flat panels such as, for example, general building panels, wall panels, ceilings, are preferred. furniture components and similar products that generally have large surfaces with advanced decorative designs. The basic principles of the invention can be used to apply a print on paper, thin sheets, textiles, metals, solid wood, veneer, wood laminates, cork, linoleum, polymeric material, ceramics, wallpaper and similar surfaces.

Background

The following description is used to describe the background and products, materials and production methods that may comprise specific parts of preferred embodiments in the description of this invention.

a) Materials for laminate floors.

Most of all laminate floors are produced according to a production method generally called Direct Pressed Laminate (DPL). Said laminate floors have a 6-12 mm fiberboard core, an upper decorative laminate surface layer with a thickness of 0.2 mm and a lower balance layer with a thickness of 0.1-0.2 mm of laminate. , plastic, paper or a similar material.

The surface layer of a laminate floor is characterized in that the wear and decorative properties are generally obtained with two separate layers of paper, one on top of the other. The decorative layer is generally a printed paper and the wear layer is a clear coating paper, comprising small particles of aluminum oxide.

The decoration paper is the most fundamental of the lamination papers since it is the one that provides the visual aspect of the laminate. The weight of the decoration paper is generally in the range of 60-150 g / m2.

Cover paper is generally thinner with a weight of approximately 20 - 50 g / m2 and is made from pure cellulose, from delignified pulp. The cover paper becomes almost completely transparent after lamination and the appearance of the decoration paper is visible. Thicker cover papers with a considerable amount of aluminum oxide particles can provide high wear resistance. The disadvantage is that they are less transparent and the decorative pattern is covered by a gray layer that alters the printed pattern.

Decorative paper printing is very profitable. Rotogravure presses are used with printing rollers that can be 3 meters wide and can operate with a speed of up to 600 m / min. Printing rollers are generally produced by conventional mechanical engraving. Recently, digital laser engraving has been introduced, which enables faster decoration development and provides better decoration quality. Solventless inks with organic pigments are frequently used and excess ink is recycled.

The printed decorative paper and cover are impregnated with melamine-formaldehyde resins, generally referred to as melamine resins, and laminated onto an HDF core in large continuous or discontinuous laminating presses where the resin is heat-cured (approximately 170 ° C) and high pressure (40-60 bar) and the papers are laminated onto the core material. A stamped pressure plate or steel tape forms the surface structure. Sometimes a structured paper is used as a press matrix. On high-quality floors, the stamping is done in accordance with the design. The depth of the etching is limited to a distance of 0.1-0.2 mm (100-200 microns).

Laminate floors can also be produced with direct printing technology. An advantage is that the pressing operation can be avoided and that no printed papers are needed to provide a decorative surface. Hydroprint inks are used to print the decoration on a multi-color roller printing press on a pre-sealed core, and the print is covered with a protective transparent wear layer which can be a cover, a plastic foil or a lacquer. The production process is quite complicated and is only profitable for very large production volumes.

Direct printing technology can be replaced by 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 stage where the printing rollers are replaced by a non-contact digital printing process.

Digital printing can also be used to print on a sheet of paper that is used in the production of conventional laminates and heat and pressure laminates. Printing can be done before or after impregnation. Such printing before impregnation is complicated as the paper can expand and shrink during the printing and impregnation stage, and impregnation of small amounts is not profitable. Printing after impregnation on a melamine impregnated paper is very difficult as pigments applied on a melamine surface float during the pressing stage when the melamine resin is in a liquid state. These problems can be partially solved by a method where a raw paper, preferably comprising a base color, is applied and fixed to the core before printing and the impregnated paper or melamine powder is applied under and / or on the paper. raw so that the resins of the impregnated papers penetrate the raw paper during the pressing stage.

Laminate floors can also have a surface of paper sheets or plastic sheets and such sheet materials can also be digitally printed. A protective wear resistant clear coat which is usually a polyurethane lacquer is used to cover the printed decoration.

b) Powder-based floors (WFF)

New types of "paper-free" floors have recently been developed with solid surfaces comprising a substantially homogeneous powdery mixture of fibers, binders and wear resistant particles, which are hereinafter referred to as WFF (Wood Fiber Floor). wood fiber]).

The powdery mixture can comprise aluminum oxide particles, melamine-formaldehyde resins and wood fibers. In most applications, decorative particles such as, for example, color pigments are included in the mixture. In general, all of these materials are applied in dry form as a powder mixed in an HDF core and cured with heat and pressure to form a 0.1-1.0 mm solid layer. The powder, prior to pressing, is stabilized with humidity and IR lamps so that it forms a top layer of skin similar to a paper layer and this prevents the powder from being blown away during pressing. Melamine-formaldehyde powder and wood fibers can be replaced by thermoplastic particles.

Several advantages can be obtained over known technology and especially over conventional laminate flooring materials such as higher wear and impact resistance, deep stamping, higher production flexibility and lower costs. A stamping depth of 0.2-0.7mm can be easily achieved.

Powder technology is very suitable for producing a decorative surface layer, which is a copy of stone and ceramic. In the past it was more difficult to create designs such as, for example, wooden decorations. However, recently a digital powder printing has been developed and it is possible to create very advanced designs of any kind by injecting ink into the powder before pressing. Problems related to paper impregnation can be completely eliminated because impregnation is not required. The surface structure is produced in the same way as for laminate flooring materials by means of a structured pressure plate, a steel tape or a stamped matrix paper that is pressed against the dust. An advantage compared to other digital printing technologies is that the powder provides a base color and no protective layer is needed on top of the print as the ink can penetrate the powder. However, the penetration is quite limited since the ink drops will fixate to the first particle they encounter, mainly the fibers of wood. Increased wear resistance can be achieved by applying several layers of printed powder on each one or by using a dust cover as a protective layer applied over digital printing.

c) Melamine-formaldehyde resins.

A basic substance in laminate and WFF floors is melamine-formaldehyde thermosetting resin that is used as a binder. Melamine resin or melamine-formaldehyde resin (generally abbreviated to melamine) is a thermosetting hard plastic material made from melamine and formaldehyde by polymerization. Said resin, hereinafter referred to as melamine, comprises three basic stages. The stages, stage A, stage B, stage C, are described in Principles of Polymerization , George Odian, 3rd edition, p. eg, on pages 122 to 123. The first stage A without curing is obtained when melamine, formaldehyde and water are boiled to a liquid substance with a dry content of approximately 50%. The second semi-curing stage B is obtained when the liquid resin is used to impregnate, for example, a cover paper which, after the application of the liquid resin, is dried with heat. The molecules have started crosslinking, but it is still possible to cure the resin in a final stage if the drying of the resin is done for a fairly short time, for example one minute and with a heat of about 90-120 ° C.

Stage B can also be obtained by spraying the liquid resin over hot air so that the droplets dry and a dry semi-cured melamine-formaldehyde powder is obtained comprising small diameter spherical particles with a diameter of about 30-100 microns (0 , 03-0.10 mm).

The fully cured final stage C is obtained when, for example, melamine impregnated paper or WFF powder is heated to about 160 ° C under pressure for 10-20 seconds. The dried melamine formaldehyde resin softens, melts and cures to a fixed shape when the temperature increases during pressing. Curing is dependent on temperature and heating time. Curing can be obtained at lower temperatures for longer times or at a higher temperature for a shorter time. Spray dried melamine powder can also be cured at high temperature.

d) Wooden floors.

Wooden floors are produced in many different ways. Traditional solid wood floors have been developed to obtain raised floors with layers of wood applied over a core made of plywood, HDF or plywood. Most of these floors are supplied as pre-finished floors with a wooden surface that is coated with several clear coats at the factory. The coating can be made from UV-cured polyurethane, oil, or wax. Recently, wood flooring materials have also been produced with a digitally printed pattern that improves the design of the wood grain structure in wood species that do not have sufficient surface quality.

e) Ceramic tiles

Ceramic tiles are one of the main materials used as a material for flooring and wall coverings. The raw materials used to form tiles consist of clay minerals, feldspar, and chemical additives required for the forming process. A common method of producing ceramic tiles uses the following production steps. The raw materials are ground to a powder and mixed. Sometimes water is added and the ingredients are ground wet. The water is removed using a filter press followed by spray dehydration to obtain a powder. The resulting powder is dry compressed with a very high pressure (approximately 400 bar) to obtain a tile body with a thickness of 6-8 mm. The tile body is further dried to remove remaining moisture and to stabilize the tile body to a solid homogeneous material. Recently, large and thin panel dry pressing has been introduced. The coarse granular material is pressed with a very high pressure of up to 400 bar, and panels with a size of 1 * 2 m and larger, with thicknesses of only a few mm can be produced in an economical way. These panels can be used as wall panels and countertops. Production time has been reduced from several days to less than an hour. Such panels can be cut and shaped to production tolerances that are superior to traditional methods and can even be installed floating with mechanical fastening systems. One or more layers of glaze, which is a glass-like substance, are applied to the tile body by dry or wet methods. The thickness of the glaze is approximately 0.2 - 0.5 mm. Two glazes can be made on the tile, first a non-transparent glaze on the tile body and then a transparent glaze on the surface. The purpose of tile glazing is to protect the tile. Glaze is available in many different colors and designs. Some glazes can create different textures. After glazing, the tile is calcined in an oven or stove at very high temperatures (1300 ° C). During calcination, the glaze particles cure and fuse together and form a wear resistant layer. Mesh rollers are often used to create a decorative design. The rotary mesh-printing type of contact has many disadvantages, such as breakage and slow setting times. Therefore, several tile producers have recently replaced this conventional printing technology with digital ink jet printing technology which offers several advantages. Oil-based inks are generally used and the print is applied to the pressed tile body or to a base glaze that is applied smoothly. wet and dry before printing. A clear glaze layer can be applied over digital printing to improve wear resistance. Non-contact digital printing means there are no breaks and there is the possibility of using thinner tile bodies. Short set times, randomized printing without repeating effects, and the ability to print on surfaces of varying structures and on tiles with beveled edges are other major benefits. Other circumstances that have contributed to the introduction of digital printing technology in the tile industry are that ceramic tiles are quite small compared to, for example, laminate and powder-based floors that are produced as large pressed boards. about 2.1 * 2.7 m. Instead, small printers with a limited number of print heads can be used in the tile industry, and the initial investment is quite limited. Oil-based inks have a very long drying time and nozzle clogging can be avoided. Other advantages are related to the glaze that provides a base color. Generally, smaller amounts of pigments are required to form a tile pattern in a base color than to provide an advanced wood grain pattern on an HDF material or paper used in laminate flooring materials where impregnation and lamination create additional problems.

f) LVT flooring materials.

Luxury vinyl tiles, generally referred to as LVT flooring material, are constructed as a layered product. The name is somewhat misleading as most LVT floors are plank size with a wood pattern. The base coat is mainly made up of several individual base coats comprising different blends of PVC powder and chalk filler to reduce material costs. Generally, the individual base layers are about 1mm thick. The base layer has a high quality printed decorative PVC sheet on the top face. A clear vinyl wear layer with a thickness of 0.1-0.6mm is generally applied on the decorative sheet. Glass fibers are frequently used to improve thermal stability. The individual base layers, glass fibers, decorative sheet and clear layer are fused together with heat and pressure in continuous or batch presses. The clear coat can include a polyurethane coating, which provides additional wear and stain resistance. Some producers have replaced the clear vinyl layer with a polyurethane layer that is applied directly to the decorative sheet. Recently, new types of LVT floors have been developed with a base layer thickness of 3-6 mm and with edges comprising mechanical fixing systems that allow floating installations. LVT floors offer several advantages over, for example, laminate floors such as deep stability, flexibility, dimensional stability, resistance to moisture and lower noise.

LVT digital floor printing is only at an experimental stage, but if introduced it provides major advantages over conventional printing technology.

In summary, it can be mentioned that digital printing is used on various types of flooring to create a decoration. However, volumes are still very small, especially in laminate and wood flooring applications, mainly due to the high cost of ink and the high investment cost for industrial printers. The flexibility that digital printing technology provides is limited by stamping, which is fixed and cannot accommodate variations in digitally printed decoration. It would be a major advantage if the cost of ink could be reduced, that more cost-effective printing equipment could be used on an industrial scale, that higher wear resistance could be achieved without separate protective layers, and that variations in structures could be formed. stamped that correspond to variations in the digitally printed pattern.

Definition of some terms

In the following text, the visible surface of the installed floor panel is called the “front face ”, while the opposite face of the floor panel, facing the subfloor, is called the “rear face”.

By "up" is meant towards the front face and by "down" towards the rear face. By "vertically" is meant perpendicular to the surface and by "horizontally" parallel to the surface.

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

By "pigment ink" is meant an ink comprising pigments that are suspended or dispersed throughout a carrier fluid.

By "binder" is meant a substance that connects or helps to connect two particles or materials. A binder can be liquid, powdery type, a thermosetting or thermoplastic resin and the like. A binder can consist of two components that react when they come into contact one of the components can be liquid and the other dry.

By "matrix" also referred to as "mat" is meant a material that forms an embossed surface structure when the material is pressed against a surface.

By "Embossed In Register " or EIR it is meant that a printed decoration is in accordance with an embossed structure.

By "digital ink jet printing" is meant the digitally controlled droplet ejection of fluid comprising a colorant from a print head to a surface.

By "fingerprint" is meant a digitally controlled method of placing colorant on a surface.

By "colorant" is meant any material (colorant, organic or inorganic pigments, small colored particles, etc.) that can be used to provide a color on a surface preferably due to selective absorption or reflection of different wavelengths of light. .

By "panel" is meant a material in sheet form with a length and width that is greater than the thickness. This fairly broad definition includes, for example, laminate and wood flooring, tile, LVT, sheet-shaped wall coverings, and furniture components.

Known technique and problems with it

Generally known technologies that can be used to provide a digital impression and etched surface structure are described below. The methods may be used partially or fully in various combinations with preferred embodiments of the invention to create a digital print or a digital print in accordance with this description of the invention.

High definition digital inkjet printers use a non-impact digital printing process. The printer has print heads that "shoot" ink droplets from the print head to the surface in a very precise manner.

Multi-pass printing, also called sweep printing, is a printing method where the print head is moved across the surface many times to generate an image. Such printers are slow, but a small print head can produce a larger image.

Industrial printers are generally based on a single pass printing method, using fixed print heads, with a width corresponding to the width of the printed medium. The printed surface moves under the heads. These printers have a high capacity and are equipped with fixed print heads that are aligned one after the other in the feeding direction. In general, each head prints one color. These printers can be customized for each application.

Figure 1a shows a side view of a single pass digital inkjet printer 35 comprising five digital print heads 30a-e, which are connected with ink pipes 32 to ink containers 31 which are filled with ink from different colors. The ink heads are connected by digital data cables 33 to a digital control unit 34 that controls the application of the ink drops and the speed of the conveyor belt 21 which must be able to move the panel under the print heads with high precision. to ensure a high-quality image that comprises multiple colors.

Figure 1b shows a top view of a wood grain print P provided on a surface 2 of the panel. The surface of a floor panel is frequently stamped with a basic structure 17 which is the same for various basic decorations, as shown in Figure 1c. Advanced floors use so-called EIR stamping (matching stamping) 17 which is coordinated with the printed pattern P, as shown in Figure 1d.

A typical width of an industrial print head is approximately 6 cm and any length can be printed. Wide areas of 1 - 2 m can be printed with digital printers comprising several rows of print heads aligned side by side. 166 print heads may be required to provide 5-color printing of a 2m wide laminate flooring panel and the print can be destroyed if only a few nozzles on a print head are blocked by dry ink.

The number of dots per inch or DPI is used to define the resolution and print quality of a digital printer.

300 DPI is generally sufficient to, for example, print wood grain structures of the same quality as currently used in conventional laminate flooring material. Industrial printers can print patterns with a resolution of 300 - 600 DPI and even higher, and with a speed greater than 60 m / min.

The impression can be a "full impression". This means that the printed visual decoration is created primarily by the pixels of ink applied to the surface. The color of a powder coat or a base color of a paper generally has a limited effect on the visible pattern or decoration in such an embodiment.

The impression can also be a "partial impression". The color of another undercoat is one of the colors that are visible in the final decoration. The area covered by the printed pixels and the amount of ink that is used can be reduced and cost savings can be obtained from the lower ink usage and the higher printability compared to a full print layout. However a partial print is not as flexible as a full print as the base colors are more difficult to modify than when a full print is used.

Printing can be based on the CMYK color principle where white is provided by the surface. This is a 4-color configuration comprising cyan, magenta, yellow, and black. Mixing these colors together will provide a color / gamut space, which is relatively small. To increase the specific color, or the total gamut, patches of color must be added. A color spot can be any color. Colors are mixed and controlled by a combination of software and hardware (print engine / print heads). Flexibility can also be greatly increased when a white color is added to the printer.

CeraLoc Innovation BelgiumBVBA, a subsidiary of Valinge International AB, has developed a new technology that makes it possible to inject a liquid for digital printing into a layer of powder. This new type of "Digital Inkjet Printing" or DIP is obtained because the printing is done inside a powder that cures after printing. Ink and printing are included within the cured layer and are not applied over one layer as when using conventional printing methods. The print can be placed in various dimensions horizontally and vertically, at different depths. This can be used to create 3D effects when, for example, transparent and preferably bleached wood fibers are used. A two-layer impression can also be used to increase wear resistance. No protective layers are needed, eg cover, which alter the original design with shades of gray.

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

A suitable print head must be used to obtain high print quality and speed on powder-based layers and other layers as described above. A print head has several small nozzles that can launch and apply droplets of ink in a controlled manner.

Industrial ink jet systems are broadly classified between Digital Injection Print (Continuous Ink Jet - CIJ) systems or drop on demand (Drop on Demand - DOD) systems.

The CIJ continuously ejects the droplets from the print head. The drops pass through a set of electrodes that transmit a charge to each drop. The charged droplets then pass through a baffle plate that uses an electrostatic field to select which droplets to print and which to collect for reuse.

The DOD ejects the droplets from the print head only when required and all the droplets are applied to the surface.

The CIJ is used mainly in the coding and marking of products. DOD inkjet technology is currently used in most industrial inkjet applications when high quality decoration is required.

A typical ink droplet size is approximately 2-4 picoliters (= 1 * 10_12 liter or 0.000001 mm3). The size of each droplet can vary, depending on the type of ink and the type of head, usually between 1-40 picoliters and this corresponds to a droplet having a diameter of about 10-30 microns. The smaller droplets allow for high resolution images. Some print heads can fire different droplet sizes and can print a grayscale. Other heads can only fire a fixed droplet size. Print heads can be designed to fire larger droplets of up to 100 - 200 picoliters or more.

Various technologies can be used to fire the droplets from the nozzles.

Thermal print head technology is generally referred to as bubble jet printing, it uses print cartridges with a series of small chambers, each containing a heater. To eject a droplet from each chamber, a current pulse is passed through the heating element causing rapid vaporization of the ink in the chamber to form a bubble, which produces a large pressure rise, propelling an ink droplet to through the nozzle and to the surface. Most consumer inkjet printers use thermal print heads. Such thermal printers are generally designed for applying water-based inks with a viscosity of 2-5 centipoise (cps). Recently, Memjet has developed large-scale thermal print heads with a print width of 223 mm and a print speed of approximately 20 m / min or more. The print head contains 5 ink channels and two rows of nozzles per channel. Each individual nozzle structure is approximately 30 microns in section, allowing 800 dpi, where the second row of nozzles for each color is slightly offset from the first to provide 1600 dpi in combination. A Memjet printhead can continuously fire up to 750 million 2 picoliter droplets with a 14 micron droplet diameter per second. The cost of the thermal print head is less than 10% of the cost of conventional piezoelectric heads with similar capacity. Such thermal printers can apply water-based substances with a viscosity of 0.7-1.5 centipoise, which is similar to the viscosity of water (1 centipoise at 20 ° C). The Memjet print head comprises a self-cooling system with the heating element in the center of the ink chamber. As the drops are ejected, the new ink flows into the chamber and cools the heating element.

Thermal technology imposes the limitation that the ink must be resistant to heat, generally up to 300 ° C because the firing process is based on heat. This makes it very difficult to produce multi-color thermal heads for pigments. Memjet print heads are designed for dye-based ink and are therefore not used in the flooring industry and industrial applications where high-quality pigment-based inks are required.

Most commercial and industrial inkjet printers and some consumer printers use piezoelectric print head technology, which is the main technology used in the flooring industry. Instead of a heating element, a piezoelectric crystal material (generally referred to as Piezo) is used in an ink-filled chamber behind each nozzle. When a voltage is applied, the piezoelectric material changes shape, generating a pressure pulse in the fluid that forces an ink droplet from the nozzle. A piezoelectric print head configuration can use different basic warping principles to eject droplets from a nozzle. These principles are generally classified into compression, bend, push, and shear printhead technologies. A piezoelectric crystal can also be used to create acoustic waves as it vibrates and cause the ink to crumble into droplets at regular intervals. Piezo inkjet allows for a wider variety of inks and higher viscosity than thermal inkjet. The ink generally has a viscosity in the range of 2-12 centipoise and is well suited for applying pigment-based ink. In industrial applications, print heads that can handle high viscosity inks are often used, as the initial viscosity of the ink drops considerably during production when the temperature can rise to 40 or more and a low initial viscosity can be below the minimum level required for proper print head operation.

Figure 1e shows how the ink droplets 56 are ejected according to the bending mode of the piezoelectric material. A piezoelectric recording head 30 comprises arrays of very small orifices generally called jets 50 from which droplets 56 of ink 58, with pigments 12, are ejected onto a paper surface.

Ink 58 flows from an ink reservoir through an ink inlet 55 into an ink chamber 52. The electrical pulses flex a piezoelectric crystal 51 and a membrane 53. This deformation creates a pressure pulse that ejects a drop 56 of ink from the nozzle 54. Different sizes of drops can be shaped by varying the electrical charge. Typically, the nozzles are about 10 microns in diameter. Typical droplet volumes are in the range of 2-5 picoliters producing ink spot sizes 57 printed on a surface in the range of 10-20 microns. Each droplet can contain approximately 20% pigments. The remaining part is a liquid carrier and resins necessary to bond the pigments to the surface.

A digital image contains a grid of a fixed number of rows and columns of pixels, which are the smallest individual element in a digital image. The grid is called a raster. Pixels, which represent images like a computer file, are uniform in size and shape. They do not overlap and touch adjacent pixels on all sides. Raster images can be created by a variety of input devices, for example a digital camera. All known printers use a Raster Image Processing (RIP) computer program, and produce an analyzed output with a bitmap color profile that controls the print heads and provides the necessary data required to apply a ink drop on a surface in a predetermined raster pattern R1 - R4, as shown in Figure 1e.

A lot of ink types can be used. The main components are colorants that provide the color, a binder that binds the colorants to the surface, and a liquid carrier that transfers the colorant and binder from the print head in small, well-defined droplets to a surface in a non-contact application method. . The colorant is a dye or pigment or a combination of both. The carrier fluid can be water-based or solvent-based. The carrier fluid evaporates and leaves the colorant on the surface. UV curable inks are similar to solvent-based inks, but the carrier fluid cures when exposed to strong UV light.

A major problem with all types of inks and print heads is that when ink evaporates dry, it can dry out and clog the nozzles. Industrial printers can be provided with an ink circulation system that circulates the ink through the jets to increase the so-called "uncapping" time, which is the amount of time that a print head can be left uncapped and inactive. and keep shooting ink drops properly. Short uncapping or clogging time can result in permanent nozzle loss and unwanted lines can form across the entire surface when using single pass printers. Especially pigment-based inks comprising polymeric binder systems have a tendency to dry out and it would be an important advantage if uncapping time could be increased and nozzle clogging could be avoided.

A dye is a colorant that dissolves completely in the carrier fluid, and the ink is a true solution.

Pigments are a very fine powder of solid dye particles that are suspended or dispersed in a liquid carrier. Pigment-based inks are generally mixed individually using coloring pigments and various chemicals. The pigments used in digital ink are very small and have an average particle size of about 0.1 microns. The common nozzle size is about 10-20 microns, which means that the pigment particles have enough room to pass through the nozzle channels in the print head. The nozzles can still be blocked by the ink itself and by the pigments that form agglomerates of particles. High-quality pigment ink should keep the pigment suspended in the carrier fluid for a long period of time. This is difficult, especially for the rather low viscosities, which are required for good printhead operation. Pigments have a natural tendency to settle and settle in the liquid carrier. In high-quality pigment ink, pigment settling should not occur in the usual way. Advanced ink circulation systems are used to avoid these problems associated with high pigment ink.

Pigment inks are generally more stable to light, especially when exposed to UV light, and more resistant to fading than dye-based inks. Therefore, they are used in almost all applications for flooring material. Water-based digital inks that comprise color pigments are especially suitable for flooring applications and can provide a high-quality printing method on many different materials.

Pigments generally do not adhere to a smooth surface. They are similar to sand particles and can be easily removed from the driest and smoothest surfaces. Therefore, the water-based carrier fluid is generally mixed with small amounts of various different additives to provide an ink and special printing properties such as binders that provide adhesion of pigments to a surface, dot gain, pH level. , droplet formation, print head corrosion, fade resistance, etc. The inclusion of binder resins in the ink composition limits the possible amount of pigments, since both components increase the viscosity of the ink.

Color pigments as raw materials are quite competitive from an economic point of view, especially as particles larger than about one micrometer but the production of pigment-based inks comprising very small particles and other inks for digital printers is very complicated and expensive. , and this results in a very high cost of the ink which can normally be in the range of about 50-100 EUR / liter. Approximately 50 - 100 m2 of flooring material can be printed with one liter (20-10 g / m2) if a full high-quality print is applied, and this amounts to a printing cost of 1 - 2 EUR / m2. The cost of a conventional printed floor surface where printing rollers are used is only 10% of the cost for digitally printed floor surfaces. This means that conventional pigment-based liquid ink-based digital printing is only competitive in small series when very high production flexibility is required.

Digital ink jet printers use a non-contact method to apply ink to a surface. However, laser printing is based on a contact method in which a laser beam projects an image onto an electrically charged rotating drum, generally referred to as a conductive drum. The dried ink particles, generally referred to as toner, are then electrostatically captured by the charged areas of the drum. The ink comprises fine and very well defined spherical particles of dry plastic powder, such as, for example, styrene-acrylate copolymer or polyester resin that is mixed with coloring agents or carbon black. The particles are approximately 8-10 microns in diameter when 600 DPI print resolution is required. Some laser printers use even smaller particles with a diameter of about 5 microns. The thermosetting plastic material acts as a binder. The drum prints the image on a paper by direct contact and heat, which melts the ink with the paper, bonding the plastic powder to the paper. Color laser printers use the CMYK principle with colored dry ink, typically cyan, magenta, yellow, and black, which are mixed to provide a high-quality color image.

Impact laser technology is not used to print a flat panel surface, such as a floor panel surface.

3D printing is a well-known technology used to apply and connect various layers of liquid substance, powder, or metal sheets together to create advanced three-dimensional structures. The technology is used primarily in the production of small complex product prototypes. Several hundred layers can be applied one over another. Several principles are used to build layered structures. According to a basic principle, the powder layers are applied one on top of the other and some parts are joined by a UV-curing liquid substance applied by a digital print head on each powder layer. Unbound dust is removed when the complete structure of the product is formed. Another principle uses a small glue gun that applies several layers of hot plastic material in multiple layers. 3D printers have very low productivity, and the construction of even very small objects can take several hours. 3D printers are not used to create flat decoration on a surface where colorants are applied side by side and where unbound dust must be removed after each application of a coat. The structure of the layers applied one on top of the other is destroyed if pressure is used to cure the layers.

Dye-sublimation printers use a long roll of transparent cellophane film colored in red, blue, yellow and gray that are bonded together end to end. Included in this multi-sheet film bonded together are solid dyes corresponding to the four basic colors cyan, magenta, yellow, and black, with each sheet comprising only one color. The "print head" contains thousands of small heating elements that produce varying amounts of heat and the dye is transferred to a coated paper by "sublimation" meaning that the dye when heated turns into a gas without first converting. in liquid. These thermal print heads, hereinafter referred to as heated print heads to differentiate said thermal print heads from thermal print heads used in bubble jet printing, heat up as they pass over the film, causing the dyes vaporize before returning to their solid form on paper. This method eliminates the use of liquid ink and can provide high-quality photo-printing with tints that are transparent and blend to obtain a continuous-tone color. However, the method has many disadvantages. Each sheet must be the same size as the printed surface and the entire sheet is used even if a small part of the surface is printed with a specific color. To eliminate some of the disadvantages, dye-sublimation heat transfer printing printers have been developed, which use special inks that comprise sublimation particles. A conventional inkjet printer can be used to print an image with such sublimation ink on a special paper or sheet. After that, the image is transferred by pressure and heat to a polyester material or a surface that has a polymer coating.

Thermal printing with thermal print heads is also used to create digital prints directly on a heat-sensitive paper or indirectly with a thermal transfer printing method where heat is applied to a heat-sensitive transfer film. These printing methods are mainly used to apply a color to a paper and print, for example, labels. Heat print heads have several advantages. They are reliable since there is no risk derived from clogging by inks and the price is competitive. The main disadvantages relate to the high cost of the transfer paper or film and the color limitations, mainly one color. Heat print heads are available in widths up to 200mm and can provide up to 600 dpi resolution.

Digital printing is a very flexible method that can provide high-quality printing, but cannot be fully used in industrial applications and especially not on flooring materials due to the high cost of ink, problems related to drying and drying. nozzle clogging, especially when using pigment-based inks and the need for special protective layers that are expensive and not completely transparent. High ink costs are primarily due to the need to grind the color pigments to very small well-defined particles and disperse the particles throughout the carrier fluid. It would be a major advantage if digital images could be created with color pigments that could be larger, that would not be dispersed in a carrier fluid, and would not be applied as droplets by small nozzles. It would also be a critical advantage if digital images could be formed with higher wear resistance and without protective layers.

Most of all the floors described above and especially digitally printed floors have a patterned surface structure, especially when the decorative printed decoration is a wood pattern. In the past, the stamped structure was provided as a separate general structure that was used in many different types of decoration. Recently, most flooring producers have introduced the so-called Embossed In Register (EIR) method where the embossed surface structure is formed specifically for each type of wood species and the embossing is performed according to the printed decoration. This provides advanced designs that are difficult to differentiate from natural materials such as wood and stone. Stamping is obtained when the surface is pressed against a structured matrix which can be a steel plate, steel tape, metal roll, plastic foil or coated paper. The decoration must be placed with high precision against the pressing die. Generally, they are used digital cameras and mechanical devices that adjust the final position of the panel to match the decoration before pressing to obtain that location. A specific problem related to laminate flooring is the fact that printed paper swells and shrinks in an uncontrolled manner during impregnation and the size of the decoration can vary between different impregnated paper sheets.

The flexibility of digital printing is also limited when it comes to EIR surfaces, as the printed decoration must always be adapted to the stamping matrix. A common feature for all the floors described above is that all the surfaces in a production batch have the same basic structure and it is not possible to adjust and adapt any change in decoration. This repeating effect of the stamped structure provides a floor surface that is not similar to a wooden floor, where practically all the panels have different designs and structures due to the structure of the wood grains of the wood. You cannot produce copies of stones and other natural materials in a way that is a true copy of the natural material where the design and structure generally match perfectly and all the panels are different.

Digital inkjet technology is used primarily to gain benefits related to the ability to create a high-resolution image flexibly. However, the other aspects of the technology, mainly related to the possibility of applying a liquid substance with great precision in a method without impact, have not been fully used or developed, this is especially true in applications where a decoration is applied on a large size panel comprising a surface which, during production and especially after printing, receives its final shape and properties in production steps involving high pressure and heat.

It is known that the powder applied on a liquid substance could be used to create raised parts or an image on mainly a paper substrate and that the liquid substance can be applied digitally by means of an ink jet. 3D printing comprising several locally connected powder layers with a digital device such as an ink head and where excess unconnected powder particles are removed in a final stage, is a well-known technology that can be used to create a structure. stamped on a panel. It is also known that powder particles can be applied directly with a non-contact method on a surface comprising a binder or indirectly with a contact method where a transfer method is used. Combinations are even known where a non-contact transfer method is used, and the powder is removed from the transfer surface with heat or scraping.

Document US-3,083,116 describes an embossing printing powder and an embossing printing process that comprises dusting a powdered resin on a newly printed sheet, removing therefrom excess powder that does not adhere to the wet ink. , and applying heat to the retained powder on the sheet to fuse it so that the particles thereof flow together and adhere to the sheet. The powder can comprise a phenolic resin such as phenol, urea, and melamine.

US 3,440,076 describes a method for forming raised, hard printed characters on a sheet of paper. An ink composition is printed on the paper and then contacted with a dry material. One of the ink and dry material compositions contains a thermosetting resin and the other material is a blowing agent and a curing agent. The dry powder material that does not adhere to the ink is removed and the resin associated with the printed character is then heat cured at temperatures sufficient to melt the powder.

US 3,446,184 describes a method of forming a sticky image copy. The toner powder is applied in liquid form and a portion of the powder is retained by the liquid coating to form a visible image. The loose powder is removed and the sheet passes to a heating unit where the retained powder is fused to form a permanent image.

US-4,312,268 describes a method by which a water-based ink is digitally applied to a web and a single, single-color fusible powder is applied to the web and onto the ink. Some of the powdered material is bound to the liquid and the unbound powdered material is removed from the web prior to heating to dry the liquid and fuse the powdered material to the web by melting the powder. It has been mentioned that the powder material may have a particle size in the range of 5 to 1000 microns and may have a melting point or a melting temperature in the range of 50 to 300 ° C. The powdered material can be produced by dissolving or dispersing, respectively, a dye or a pigment in a resin or resin formulation, followed by grinding, spray cooling or the like to reduce the material to a fine powder. Powdered material can provide abrasion resistance qualities to ink that may contain phenolic resin. The liquid material, which is applied through the jets, can be transparent and colorless water.

GB-2 128 898 describes a method for forming raised decorative parts on a plastic tile. A decorative floor covering in the form of a tile has a design printed on its top surface. Particles such as inorganic sand particles are placed on the top surface of a plastic tile with at least part of the particles placed on the surface of the tile in accordance with the pattern printed on the surface of the tile. Excess sand particles are removed. A cured wear layer is superimposed on both the raised particles and the plastic base, so the surface of the wear layer in the areas containing particles and in the areas containing no particles will have different gloss characteristics. The process requires spattering of the particles onto an adhesive-coated surface to retain the particles in accordance with a pattern printed on the surface of the tile.

US-6,387,457 describes a method of using dry pigments for printing applications related to automotive paint, security printing, paint in general, and cosmetics. A binder material is applied to a surface of a substrate evenly or in a pattern. The binder is applied by inkjet, spraying, sieving, offset printing or rotogravure printing. The dried pigment is applied to the binder material in a pattern or uniform. The dry pigment material comprises flakes of non-metallic material having a particle size of less than about 100 microns. The flakes are aligned in a direction parallel to the surface of the substrate and a protective coating can be applied to the flakes.

EP-0403264 A2 describes a transfer method for forming a multi-color image on a drum that transfers the image to a paper. A fluid latent digital image is subsequently developed at a development station where a colored powder is applied to the fluid latent image and fixed to produce a permanent, visible image. Various digital print heads can be used that print with dye-free fluids comprising a mixture of water with polyhydric alcohols and their subsets of ethylene glycol, glycerol, diethylene glycol, and polyethylene glycol. During this development, a toner powder is applied to the entire surface of the paper and a tension is applied. The tension is then reversed to remove the toner from the background areas. Fixation is achieved by conventional copier fusing methods.

US-5,627,578 describes a method for producing raised letters and graphics in desktop printing applications using thermographic powder and an ink jet printer to apply a binder liquid. The method is similar to the previously described methods for producing raised text.

EP-0 657 309 A1 describes a multi-color transfer method using a transfer paper bearing a pattern formed by ink jet and powder similar to the methods described above. The transfer method is intended to decorate ceramics.

Patent WO 2007/096746 refers to systems and apparatus for transferring granulated material with a non-contact or contact method to a surface to be decorated, in particular to obtain decorations on ceramic tiles. A liquid digital pattern is provided by an ink jet on a transfer surface which can be a drum or a ribbon. The granulated material is applied and bonded to the transfer surface and only the bonded granulated material moves to a transfer zone where heat is applied over a specific part of the transfer surface in the transfer zone to separate the granulated material from the transfer surface and apply the granulated material on the receiving surface. The granules can also be scraped off. The important advantage of this method is that only the particles that form the final image are applied to the receiving surface. The main disadvantage is that the heating must be sudden and the particles must be released from the transfer zone and must fall on the receiving surface in a very controlled manner to obtain a high resolution image. High resolution can only be obtained with fairly heavy particles that fall by gravity onto the receiving surface. The granulated material used in the invention is of the type comprising non-porous granules, such as, for example, semolina of vitreous materials or sintered mixtures, sands, etc. in the various particle size ranges from 30 pm to 800 pm, preferably in the range from 50 pm to 150 pm. Transfer printing with a contact method is also described.

Documents WO 2011/107610 and EP-2 363 299 A1 describe a method of creating a relief or a pattern on a floor panel to avoid the use of expensive pressure plates. The method is the same as the known methods for creating a relief print. Describes a method of producing a decking by printing a curable substance to create a relief on the panel. Embossing can be applied in a basic decorative pattern that is directly printed or laminated onto the panel. The curable substance can comprise wear resistant particles. The curable substance can be digitally printed onto the panel by first printing a liquid with a predefined pattern and then providing an intermediate which can comprise a powder. The curable substance can be cured by UV radiation or it can be a varnish.

EP-2 213 476 A1 discloses that a predetermined pattern can be digitally printed on a carrier with curable liquid to form an embossed decoration pattern, which is pressed onto the cover. The curable liquid can be a plastic that becomes quite rigid after curing, for example an ink containing plastic. This method is not suitable for floor applications. The digital print head can only print a very thin layer with a thickness of about 10-20 microns. The thicknesses of at least 100-200 microns that are required to form a laminate stamp and 200-700 microns to match the requirement for powder-based floors cannot be produced economically.

Document WO 2012007230 describes a method for forming a 3D structure on a furniture or floor panel with a digitally controllable device. A decoration is applied with a flat three-dimensional structure of powder-based coating material comprising one or more layers that are locally solidified with a digitally controllable device under the action of light and / or thermal radiation. Excess non-solidified coating material is removed in a final production step. The three-dimensional structure can be digitally printed. A liquid coating material is applied on the 3D structure as a protective layer.

Most of the known methods are based on the direct application of powder on a surface comprising a binder pattern. They are primarily used to create relief text or three-dimensional decorations, which are cured and protected by means of a liquid coating. Such methods are not suitable for application to flooring material where colored powder must be incorporated into the surface to provide sufficient wear resistance. None of these direct application methods are combined with a pressing stage that compresses the applied powder and especially not with a pressing stage that cures the entire surface layer so that the powder particles fuse on the surface.

Some of the known methods are based on an indirect application of powder with a transfer method. Pressing is only used to transfer the powder from a support without performing pressing steps to cure the powder and the surface.

Known methods are not suitable for creating a high quality multi-color image on a building panel and especially not on a floor panel where UV light resistant pigments must be used and where the image must be incorporated into a resistant surface to wear. It is not known whether the principles described above can be used to create a digital image on a panel which, after the printing step, cures under elevated pressure and temperature and, especially, it is not stated how the known principles should be adapted for printing. laminate-like flooring surfaces and Wood Fiber Floors (WFF) where powder, ink and application methods must be tailored to specific thermosetting resins, wood fiber materials and pressure parameters, which are needed to cost-effectively form a high-quality multi-color wear, impact and stain resistant surface.

The known methods do not provide any solution to the main problem that is related to the bond between the powder and the liquid binder applied on a surface. To remove excess applied particles, generally strong air currents must be used and these air currents will remove even particles that should be bound by the binder.

The above description of various known aspects is the applicant's characterization thereof, and does not constitute an admission that the above description is prior art when the products, methods and equipment described are used partially or totally in various combinations.

Objectives and Summary

The primary objective of at least certain embodiments of the invention is to provide an improved and cost-effective printing method for applying colorants on a well-defined patterned surface, preferably a floor panel surface using digital ink heads that apply a liquid substance onto a panel surface.

A specific objective outside the scope of the present claims is to provide equipment for forming digital impressions according to the main objective.

The above objectives are illustrative, and embodiments of the invention may achieve different or additional embodiments.

Embodiments of the invention are based on a fundamental principle where conventional digital printing methods are divided into two independent stages comprising a separate application of a liquid binder and dry colorants. Colored particles are applied to a surface of the panel. Some particles are held together by a digitally formed pattern. The remaining unbound particles are removed and the remaining bound particles form a digital pattern. This two-stage process can be repeated and multiple colors can be applied so that an advanced multi-color high definition digital impression can be formed. The bonded colored particles and the surface of the panel are pressed together and a greater bond is obtained. Pressing is carried out at a higher temperature so that the colored particles and the surface are cured to obtain a wear resistant layer.

An advantage compared to conventional digital ink jet printing is that the colored particles are not dispersed in a liquid substance and are not applied by a digital print head onto a surface. According to embodiments of the invention, the print head is only used to apply an inexpensive and primarily water-based binder without pigments. Embodiments of the invention make it possible to combine a Lower cost of ink and digital print heads with higher productivity. Pigment-based colorants can be combined with very inexpensive print heads that can be thermal print heads. The colored particles can be wood fibers or pigmented mineral particles, and very realistic copies of wood and stone designs can be obtained with such decorative materials arranged in advanced high-quality patterns.

An advantage compared to known powder-based printing methods is that the colored particles are applied directly to a panel surface. Handling and transporting separate printed sheets that can cause dust to fall can be avoided. Placing separate surface layers such as sheets of paper on a panel can also be avoided, and digital printing can be positioned with high precision in relation to the panel. An advantage is that the composition of the material and the properties of the surface layer combined with heat and pressure are used to obtain a permanent bond of the colored particles to the surface and this bond can be obtained in the same pressing stage that is used for curing. and laminating the surface layer to the core of the panel. Bonding of particles with pressure and heat and using surface properties to provide bonding is superior to most other curing methods used in known powder-based printing methods. High bond strength can be obtained during application and dusting with the liquid binder that reacts with the resins that are included in the surface and in the powder.

A specific advantage is that the method is based on a liquid binder which is suitable for combining with heat and pressure and which can be a very simple substance comprising glycol which allows a long uncapping time. No UV curing chemicals or solvents are required, and this can provide a risk-free and cost-effective production method.

A first aspect of the invention is a method of forming a digital impression on a panel comprising a surface, the surface being part of a building panel, such as a floor panel, wherein the method comprises:

• move the panel under a digital drop application head;

• apply a liquid binder with the digital droplet application head on the surface;

• apply colorants on the liquid binder and the surface, where the colorants are macro-colorant particles larger than 20 microns;

• join a part of the colorants to the surface with the liquid binder;

• remove unbound colorants from the surface so that a digital impression is formed by the attached colorants; and

• apply heat and pressure to the panel, surface and bonded colorants so that the colorants are permanently bonded to the surface.

The colorants are pressed to the surface when heat and pressure is applied to the panel.

At least one of the surface and the colorants can be compressed by the step of applying heat and pressure to the panel, the surface, and the bonded colorants.

The liquid binder can comprise glycol or glycerin.

The surface may comprise a material that is heat and pressure curable.

The surface may comprise a material that is fusible with heat and pressure.

The surface can comprise wood fibers.

The surface may comprise a thermosetting resin that is cured by applying heat and pressure so that the colorants are permanently bonded to the surface with the cured thermosetting resin. The surface can be a part of a building panel.

The surface can be a part of a floor panel.

The surface can be a layer of paper or a sheet.

The surface may comprise a layer of powder.

The surface may comprise a color other than colorants.

The liquid binder can comprise water.

The applied liquid binder can be exposed to IR light or hot air.

The digital droplet application head can be a piezoelectric ink head.

The liquid binder can be applied as drops arranged in a grid and where the colorants are joined with several drops.

The liquid binder may comprise 10-70% water and 30-90% glycol and / or glycerin, by weight.

The surface may comprise a dry melamine-formaldehyde resin which melts when the liquid binder is applied and which bonds the colorants to the surface.

The colorants can comprise pigments mixed with a dry binder that interacts with the liquid binder.

The dry binder can comprise a thermosetting resin.

The colorants can each have a particle body comprising a wood fiber.

The method may comprise the further steps of applying new colorants with a different color to the first bonded colorants and on the surface, bonding a portion of the new colorants to the surface with a binder, and removing the new unbound colorants from the surface so a digital impression is formed with the primer and the new colorants placed side by side on the surface.

The colorants can be applied by dispersion.

Digital printing can comprise colorants arranged in a wood grain or stone pattern. The colorants can be applied in the liquid binder.

The surface with the attached colorants can be pressed with a pressure of approximately 40-60 bar and heated with heat to approximately 160 ° C.

The surface and the colorants can be pressed and cured to a hard surface with an etched structure so that a portion of the colorants is below the upper portions of the surface.

All known equipment intended for applying powder prints uses a flexible sheet, such as paper, as the application surface. There is no known cost-effective equipment that can be used to provide high-quality powder-based printing on a panel by applying colorants in a digitally formed binder design.

A second aspect is equipment for providing digital printing on a panel comprising a surface. The equipment comprises a conveyor, a digital droplet application head, a dry ink application station and a dry ink removal station,

wherein the conveyor is adapted to move the panel essentially horizontally under the digital droplet application head,

wherein the digital droplet application head is adapted to apply liquid white ink on the surface,

wherein the dry ink application station is adapted to apply dry ink comprising dry colorants in the blank ink, the liquid white ink being adapted to bond a part of the colorants to the surface, and wherein the removal station dry ink is adapted to remove unbound colorants from the surface after each application of white ink and dry ink.

The digital droplet application head may be adapted to apply liquid blank ink comprising glycol or glycerin to the surface.

The equipment may also comprise a press, wherein the press is adapted to apply heat and pressure to the panel, the surface and the bonded colorants, when the unbound colorants have been removed, so that at least one of the surface and the colorants are compressed and the surface and colorants are bonded together.

The digital drop application head can be digitally connected to a digital control unit that controls the application of the blank ink drops, the speed of the conveyor and the function of a dry ink application station.

The dry ink application station may comprise a roller.

The dry ink application station may comprise an etched, stamped, acid etched, shot peened or needle roller surface, which acts as a dispensing device which is adapted to move a predetermined amount of dry ink to the surface.

The dry ink removal station can be adapted to remove colorants using a stream of air.

The dry ink removal station can be adapted to remove colorants by air and vacuum currents that blow and suck the colorants.

The digital droplet application head can be a piezoelectric print head.

Multiple digital drop application heads can be positioned side by side so that virtually the entire width of the surface is covered by the heads.

The equipment may also comprise a stabilizer station adapted to provide humidity and heat to stabilize a powder surface comprising wood fibers and dry melamine resins, and wherein the stabilization is done prior to the application of the blank ink.

The digital droplet application head may be adapted to apply blank ink comprising water. The equipment may also comprise an IR lamp adapted to dry the blank ink after application. The dry ink application station and the dry ink removal station may be adapted to apply and remove dry ink particles from wood fibers.

Brief description of the drawings

The invention will now be described with reference to preferred embodiments and, in greater detail, to the accompanying illustrative drawings, wherein,

Figs. 1a-e illustrate known methods for producing a printed and embossed surface;

Figs. 2a-e illustrate a first principle of an embodiment of the invention;

Figs. 3a-d illustrate a second principle of an embodiment of the invention;

Figs. 4a-d illustrate a third principle of an embodiment;

Figs. 5a-h illustrate the digital application of pigments according to the first principle of an embodiment of the invention; Figs. 6a-d illustrate production methods based on the first principle of an embodiment of the invention and a panel with a decorative pattern formed according to one embodiment;

Figs. 7a-c illustrate the application of colorants on a surface;

Figs. 8a-h illustrate preferred embodiments of macro dyes;

Figs. 9a-e illustrate the application and pressing of macro dyes;

Figs. 10a-c illustrate the application and pressing of macrodyes;

Figs. 11a-c illustrate the application of various colors with a print head and the application and removal of colorants with an intermediate pre-pressing;

Figs. 12a-d illustrate transfer printing methods and panels with preferred surfaces;

Figs. 13a-d illustrate the application of colorants in patterns with methods where liquid white ink is not used to bond the colorants;

Figs. 14a-d illustrate press particle digital stamping; and

Figs. 15a-d illustrate digital stamping combined with digital transfer printing.

Detailed description

Figures 2a-2d schematically show an embodiment of the invention, which is based on a first principle where a binder pattern BP or image is digitally formed by an ink head that preferably only applies a binder 11 on a surface 2 as shown in figure 2a. The colorants 7, which may comprise small colored particles, for example pigments 12, are preferably randomly applied in dry form by a second device so that they are in contact with the binder pattern BP. Figure 2b shows a preferred embodiment where pigments 12 in dry form have been dispersed over the BP binder pattern. Figure 2c shows that binder 11 connects some pigments 12 that form the same pattern as binder 11 and an imprint P is formed on surface 2 when other unbound pigments 12 are removed from surface 2 by, for example, vacuum.

This three-stage process, hereinafter referred to as "print formation cycle" when the process refers to the application of a color, or "binder and powder printing," or BAP printing, when the process refers to to full printing, and where preferably a liquid binder 11, hereinafter referred to as "blank ink" and dry particles comprising colorants 7, hereinafter referred to as "dry ink" 15, are independently applied and binds together, and where unbonded particles are removed, it can provide digital P printing with the same and even superior quality than conventional digital printing technology.

The surface 2 can be a paper layer or a sheet or a powder layer.

The surface 2 can be a part of a building panel or a floor panel 1.

The binder may be blank ink 11 comprising a liquid substance which is preferably applied by means of a digital ink head.

The liquid substance can be water-based.

The surface 2 with the attached colorants 7 can be heated and pressed.

Surface 2 and colorants 7 can be pressed and cured against a hard surface with an embossed structure.

The colorants 7 can be macro-colorant particles larger than 20 microns and can be pressed into the surface 2.

The surface 2 can be a part of a panel 1 which can be a laminate or wooden floor, a powder-based floor, a tile or an LVT floor.

Liquid white ink can be replaced by a digital heating process, where heat from a heating digital print head or laser activates a binder included in the dry ink and / or on the surface.

Blank ink and dry ink can be applied in many alternative ways. The surface 2 can point up or down, and the white and / or dry ink can be applied from above or below. A surface 2 with white ink may, for example, point downward and may come into contact with a layer of dried ink. Unbound dry ink can be removed by gravity when the surface separates from the dried ink layer. To simplify the description, most of the preferred embodiments show an upward facing surface attached to a panel prior to printing. Separated surfaces 2 without a support panel 1 can be printed according to the principles of the invention.

The method is especially suitable in applications where considerable amounts of colorants, preferably pigments, are applied onto a large flat panel to form an advanced large decorative or printed pattern with preferably high resistance to wear, impact and UV light, and where the pattern is intended, preferably, to copy a wood or stone design. These designs are generally formed with a base color that, for example, gives the wood or stone the basic look and a few spots of color that are used to form the structure of the wood grains, knots, cracks and various defects. that are visible in the wood surface or cracks in glass structures and other defects in a stone design. The method is also very suitable for forming a pattern on a tile or for printing laminates and powder-based floors with a copy of, for example, a tile floor comprising tiles with different colors and grout lines between the tiles.

Contrary to known methods, the digital ink head, hereinafter referred to in the specification as "digital droplet application head 30 '", is not used to apply any type of conventional ink with pigments or dyes. This has the advantage that expensive inks comprising pigment dispersions and binder resins do not have to be handled by the digital droplet head 30 '. The blank ink is preferably a substantially transparent liquid substance which preferably essentially comprises water.

The blank ink, also called a liquid substance, preferably does not comprise pigments.

An impression provided by the white ink or liquid substance can be referred to as a liquid impression P. The liquid impression can be formed of drops of the white ink applied on the surface.

The colorants are preferably attached to the surface in two steps. The first bond is an application bond where the bonding of the colorants must be sufficient to keep the colorants connected to the binder pattern BP to allow removal of excess colorant that has been applied in areas outside of the binder pattern.

The second joint is a permanent joint intended to permanently connect the colorants of the application joint to the surface 2.

The first application bond and the second permanent bond may comprise an intermediate stabilization step where the structure of the bonded colorants is modified, for example, by heat and / or pressure, so that a new print formation cycle can be performed. . The intermediate stabilization step allows new unbound colorants that have been applied to the surface during a second print-forming cycle to be easily removed even on portions of the surface comprising colorants from the first print-forming cycle.

The first application bond is preferably obtained with a liquid substance, also called blank ink, which preferably comprises mainly distilled or deionized water. The adhesion of water can, in certain applications, especially when only one color is applied, connect the colorant to the surface with sufficient force to allow removal of unbound colorants. The production costs of such a liquid substance are extremely low and clogging of the nozzles when the binder dries can be avoided. Various chemicals can be added, eg glycol or glycerin, which are necessary to achieve the viscosity and surface tension of the liquid substance that may be necessary for proper print head operation. Water soluble polyethylene glycol (PEG), which is available in many different molecular weights, is especially suitable for modifying water so that a white ink with a suitable viscosity can be obtained that works, for example, with piezoelectric heads. Low molecular weight formulations, such as, for example, PEG 400 are especially suitable for use for blank ink and preferably in conjunction with dry ink or a surface comprising thermosetting resins, such as melamine. Water and PEG are compatible with melamine resins and allow quick and easy curing when heat is applied, and preferably pressure as well. A preferred non-drying solvent that is compatible with thermosetting resins should be miscible with water, have a boiling point greater than 100 ° C, and a melting point below the application temperature. Examples include, but are not limited to, ethylene glycol, propylene glycol, polyethylene glycol, diethylene glycol, butanediol, and glycerin. Combinations can also be used. In some applications other minor amounts of chemicals may be included in the blank ink, for example wetting agents and other chemicals necessary to prevent bleeding when the blank ink is applied to a surface. The blank ink may further comprise release agents, especially when the direct application of the colorants, hereinafter referred to in the specification as "direct BAP printing", as described above, is replaced by a transfer application, referred to as then in memory as "BAP transfer printing", where blank ink and colorants are applied, in a first step, onto a transfer surface, and then pressed against and bonded to the surface. Most of these additives are cost effective, and blank ink can cost a fraction of the cost of conventional pigment-based inks to produce.

Most piezoelectric print heads are designed to operate with a viscosity in the range of 2 to 12 centipoise (cps). The water-based blank ink can be easily adapted to meet all possible viscosity requirements.

A suitable blank ink that can preferably be used in a low-viscosity printhead designed to operate at a viscosity of about 5 cps, such as a Kyocera printhead, can be a water-based glycol solution comprising, for For example, about 75% by weight of ethylene glycol or 55% of diethylene glycol or 50% of propylene glycol or 38% of PEG 400 polyethylene glycol. You can also Use an aqueous based glycerin solution comprising about 40% glycerin. Deionized water can also be mixed with glycerin and glycol. A suitable blank ink for a low viscosity print head may comprise, for example, about 40% water, 50% glycerin, and 10% diethylene glycol.

A suitable blank ink that can preferably be used in a high-viscosity printhead designed to operate at a viscosity of about 10-12 cps, such as a Fuji printhead, can be a water-based glycol solution comprising , for example, about 95% (weight) ethylene glycol or 75% diethylene glycol or 70% propylene glycol or 50% polyethylene glycol PEG 400. A water-based glycerin solution comprising about 65% glycerin can also be used. Deionized water can also be mixed with glycerin and glycol. A suitable blank ink for a high viscosity print head may comprise, for example, about 30% water, 60% glycerin, and 10% diethylene glycol.

The water content of a blank ink adapted for high and low viscosity piezoelectric print heads can be further increased if high viscosity glycols are used; for example, polyethylene glycol with a molecular weight greater than PEG 400. A preferred blank ink that is preferably suitable for piezoelectric print heads may comprise 0-70% water and 30-100% glycol and / or glycerin. Even more preferred is a formulation comprising 10-70% water and 30-90% glycol and / or glycerin. A blank ink that is suitable for thermal bubble jet print heads that are designed for very low viscosities; eg 2-4 cps, may comprise more than 70% water.

All blank ink formulations can comprise small amounts, approximately 1%, of wetting agents such as BYK or Surfinol and chemicals such as Actidide that are intended to control bacteria and fungi.

The blank ink is preferably and essentially a non-curable liquid substance that is used to obtain the application bond and to bond the colorants until the final permanent bond occurs preferably with heat and pressure and with resins that are part of the substrate material. and / or dried ink particles. Such white ink will not bind the particles when it dries or when heat is applied.

The blank ink may comprise special curable binders, preferably water-based acrylic emulsions, which are compatible with water, glycol or glycerin. The binder content is preferable 5-20%. Acrylic emulsions will bond the particles when the water content evaporates and create a strong bond with high heat and pressure.

A high water content of at least 50% has the advantages that the cost of the material can be low. The uncovering time will be quite short, less than an hour, as the water evaporates. A low water content combined with a high glycol or glycerin content will greatly increase the uncapping time. White ink with a water content of less than 40% may have a decay time of several hours. A water content of less than 20% will provide a very long uncapping time that can exceed 6 hours. It is possible to use white ink that comprises more than 90% glycol and this can increase the uncapping time to several days. Blank ink can be made without water and high viscosity print heads can handle white ink comprising, for example, 100% ethylene glycol.

In industrial printers, an ink circulation system can be avoided when using blank ink that does not comprise any pigment dispersions or binders, and is primarily a water-based solution, as described above. This will decrease the cost of the printing equipment considerably.

Figure 2e shows the viscosity in cps of aqueous solutions of propylene glycol (PG) at temperatures of 20-30 ° C. W1 shows the viscosity of water. Pg1 comprises 50% PG and 50% water. Pg2 comprises 70% PG and 30% water. The viscosity of the blank ink adapted for a low viscosity recording head can be between 4-6 cps within the temperature range of 20-30 ° C. The viscosity of the blank ink adapted to high viscosity print heads can be between 8-14 cps and this may be outside the normal working conditions of the print head. This problem can be solved with printing equipment comprising a temperature control system that is preferably combined with a climate control system that controls humidity. The uncapping time for water-based blank ink can be increased if the relative humidity around the print heads is greater than 50%.

The binder that binds the colorants to the surface can comprise two components. The first binder component can be included in the blank ink. The second binder component can be included in the dry ink or on the surface and is activated by the blank ink. This makes it possible to use, for example, water to obtain the application bond, stabilization and permanent bond. Water can react with a binder that can be included in colorants or on the surface. Blank ink may comprise, for of course, a binder that can provide the same binding as the two components mentioned above.

The white ink can be applied on any surface 2, for example a non-transparent paper layer, an essentially transparent cover, a powder coat, a stabilized powder coat, a veneer or wood sheet, a glaze tile, a plastic sheet or a base color applied over a sheet-like material preferably comprising wood or polymeric material.

Applying surface 2 to a sheet material such as panel 1 provides several advantages. Handling and placing loose layers that can expand and shrink during application of liquid white ink can be avoided. The application bonding of the colorants 7 can be done with a very low bond strength, since the surface 2 is supported by the flat panel and can be moved horizontally on a conveyor belt directly to a press where permanent heat bonding takes place. and pressure. Stretching, cutting and stacking of paper and sheet surfaces can be avoided. Some surfaces such as uncured powder and tile glaze cannot be handled without a 1 panel support.

BAP printing on LVT floors can also be performed when, for example, individual base layers, preferably including a fiberglass layer, and a decorative plastic sheet with a base color are fused together to obtain a panel. A clear protective layer can be fused with heat and pressure onto the BAP print and the decorative plastic sheet in such a way that the dried ink particles are permanently bonded and fused to the surface. The blank ink can be tailored to prevent droplet floating on the smooth plastic sheet. This is an advantage if the blank ink has a high viscosity, preferably 10 cps and higher.

BAP printing on ceramic tiles is preferably performed when the powder is pressed to obtain a tile body that forms a panel. A glaze with preferably a base color is applied to the tile and a BAP print is applied to the dried glaze. The BAP impression and tile body are then pressed and a protective clear glaze is applied over the pressed impression. After glazing, the tile is calcined in a kiln or stove at very high temperatures such that the dried ink particles cure and melt within the body of the tile and the glaze.

The above-described embodiments are based on the fundamental principles that BAP printing is applied on a surface 2 which is part of a panel 1 and which also comprises a material composition such that when heat and pressure are applied, the panel, the surface and printing are permanently attached. Said surfaces may comprise thermosetting resins, preferably melamine-formaldehyde resins which are generally used in laminate floors of the WFF or paper type, curable and fusible mineral materials used in ceramic tiles or thermoplastic materials used in LVT floors.

Both direct and transfer BAP printing can also be used on textile surfaces. Dry ink and white ink can be specially adapted for various textile surfaces. Binders, dry ink viscosity, and colorant size can be tailored for proper colorant bonding and removal.

The application on some specific surfaces can be improved by what is called a corona treatment, sometimes also called air plasma. It is a surface modification technique that uses low temperature corona discharged plasma to convey changes to the properties of a surface. Corona plasma is generated by applying a high voltage to sharp electrode tips, which forms the plasma at the ends of the sharp tips. Materials such as plastic, glass, or paper can pass through the corona plasma curtain to change the surface energy of the material. The surface can also be treated with various types of mineral salts.

The surface may comprise a first base color, which can be used to create a greater portion of the visible colored surface. Powder-based surfaces, preferably comprising thermosetting resins, can be pre-pressed and preformed to a smooth surface that facilitates application and removal of colorants. Preferably, the pre-pressing is done with pressure and heat and during a pressing cycle time that ensures that the melamine resin is at a semi-cured level and at a B-stage as described in the introduction.

The colorant comprises, in a preferred embodiment, primarily color pigments 12 which are dispersed as a dry powder layer over the wet BP binder pattern, as shown in Figure 2b. The pigments can be mixed with other particles, for example melamine powder particles 13 which melt when in contact with the liquid BP binder pattern and which binds the pigments to the surface. Unbonded dry pigments and melamine powder 13 can be removed, for example, by a stream of air or by gravity and the remaining wet melamine 13 and color pigments 12 form an imprint P as shown in Figure 2c which is practically identical to the BP binder pattern created by the white ink. The dry ink can have the same material composition as surface layer 2 in a WFF type dust floor and can comprise a mixture of wood fibers, a dry melamine-formaldehyde resin powder, aluminum oxide particles and pigments. color.

Stabilization of the print can be partially or totally obtained by, for example, exposure to IR, hot air, UV light, microwave, pre-pressing or the like or combinations of such methods. The binder, which in this preferred embodiment is water or wet melamine, is preferably stabilized by pre-pressing which binds the color pigments to surface 2 by drying the wet melamine or melting the melamine particles. The pre-pressing compresses the surface of the printed pattern P. A second pattern with the white ink can be printed on the surface 2 and a second layer of pigments and melamine powder can be applied on the surface and on the first printing. This can be repeated and an advanced decoration can be created with various colors, so that the digital image comprises colorants with different colors placed horizontally displaced in the same plane.

The blank ink is preferably a substantially transparent liquid substance that does not discolour the bonded colorants. Blank ink with the same liquid substance can be used together with dry ink comprising many different colorants and this allows, for example, that a print head with the same blank ink can be used to apply different colors in various stages with an intermediate application of a digital pattern formed by the blank ink. This allows the number of print heads to be reduced considerably as a print head with an ink channel that applies the same blank ink can be used to apply a virtually unlimited amount of dry inks with different colors, particle sizes, structures , etc. The simple composition of the white ink makes it possible to use more cost-effective print heads as no color pigment will burn through the print head's small nozzles.

In some applications, the stabilization step may be sufficient to create the permanent bond. The final permanent bond can also take place when the surface is pressed and cured preferably under heat and pressure according to the methods that are used to cure a laminate or a powder-based surface comprising a thermosetting resin or a surface comprising a thermoplastic layer. . You can also use a UV-curable clear lacquer that is applied over the colorants and that after application is cured in a UV oven. This clear coat can be applied in liquid form by rollers or with digital piezoelectric heads and in one or more stages with intermediate UV curing. A thermoplastic resin or thermoplastic particles can also be used to obtain the first application bond or the second permanent bond. Paper or powder-based coverings comprising aluminum oxide and melamine resins can also be used as protective layers and as a permanent bond.

The low cost and simple chemical composition of the liquid substance applied by the droplet application head makes it possible to use the fairly simple technology of the digital print head to apply the liquid binder substance. CIJ (continuous inkjet) can be used as water is easy to recirculate and collected droplets can even be disposed of without any recycling. Cost effective thermal print heads can be used as water is easy to handle with bubble jet technology. Quite simple, high productivity piezoelectric heads can be used and DOD (drop on demand) systems can be used which have a long service life and need minimal maintenance due to the very favorable composition of the liquid substance that does not It will cause no production disruption as there are no pigments and preferably no quick-drying resins to be handled, which is the case when using conventional pigment-based inks.

The binder can comprise a wide variety of thermosetting and thermoplastic materials that can be used as particles or chemicals on the surface, in the dry ink, or as dispersions in the blank ink applied by the digital droplet application head. Most of these materials can be produced in dry powder form or as liquid dispersions. It is preferred that the chemical that provides the bond after drying is included in the surface or in the dried ink and that the blank ink is a simple liquid chemical without any resin or other chemicals that in dry form can clog the nozzles. .

As an alternative to thermosetting materials, such as melamine or thermoplastic materials, such as, for example, PVC powder, UV-cured polyurethane can be used, for example, in powder or dispersion form.

A UV curable polyurethane substance with a viscosity that is adapted to the digital droplet application head 30 'can be used. Water-based polyurethane dispersions are preferred as the liquid substance in the digital droplet application head, as they do not cure until exposed to UV light. Polyurethane dispersions are fully reacted polyurethane / polyureas of small, distinct polymeric particles and such particles can be produced in a size of approximately 0.01 - 5.0 microns and therefore can be manipulated on a digital print head. or other similar heads. Polyurethane dispersions can be combined with, for example, acrylic emulsions and other emulsions to reduce costs.

The digital droplet application head, which in some applications may preferably be a piezoelectric head, preferably has an ability to fire droplets with a droplet size of about 1-200 picoliters or greater. The size of the droplet and the intensity of the droplet can be varied and this can be used to vary the intensity of a color and to create what is called a "grayscale" with the same basic color. Larger drops will bond thicker layers of dry ink and smaller drops will bond thinner layers.

Water-based adhesives, such as soluble adhesives or water-dispersed adhesives, can also be used.

Other UV light cured materials such as epoxy acrylates, urethane, polyester, polyether, amine modified acrylic polyether, and various acrylate oligomers can be used as binders in powder form or as dispersions.

Blank ink can also be applied to a surface using spray nozzles or engraved rollers.

Figure 2d schematically shows a BAP printing station 40 of a binder printing equipment that can be used to create a digital impression P on a panel 1 comprising a surface 2, a core 3 and a support layer 4. A blank ink application station 36 comprising a digital droplet application head 30 ', which is preferably a piezoelectric head or a thermal print head, applies a binder pattern BP with blank ink 11. Multiple heads 30 'can be placed side by side to cover the width of the surface to be printed. The binder pattern is created digitally in the same way as in conventional digital printing. The colors are separated and each blank ink application station 36 applies primarily the same liquid ink or blank ink that is used to bond a specific color in each print formation cycle. The digital droplet application head is connected by a feed tube 32 to a container 31 with blank ink. The digital drop application heads 30 'are connected digitally with preferably data cables 33 or wirelessly to a digital control unit 34 that controls the application of the drops, the speed of the conveyor belt 21, the operation of a dry ink application unit 27, and the rest of the equipment used to bind and remove pigments.

The water-based droplets of the blank ink 11, which in this embodiment serve as an application binder, must remain moist until they pass through the dry ink application station 27 which, in this preferred embodiment, is a dispersion station. Dry ink 15, which in this preferred embodiment comprises color pigment dyes 12 mixed with a spray dried melamine powder 13 resin, is dispersed over liquid white ink 11.

The dispersing equipment comprises a hopper 45 containing dry ink 15, a scalpel 47 which together with a roller 46, preferably comprising an etched, stamped, etched or sandblasted surface 44, acts as a dispensing device that displaces a predetermined amount of dry ink 15 from hopper 45 to surface 2. Roller 46 may also have a roller surface 44 comprising small needles. Rotating and oscillating rollers can also be used. A material removal device that can be a rotating or oscillating brush 48 together with one or more rotating or oscillating meshes 49 that can oscillate or rotate in different directions can also be used in some applications.

The scalpel 47 can be rigid or flexible and can have an edge adapted to the structure of the surface of the roller. The oscillating or rotating meshes 49 can also be formed to disperse the dried ink 15 in a predefined manner and can be combined with one or more nets that can be used to screen the particles prior to application as a layer. The rotation of the roller, the position of the knife and the speed of the surface that is intended to be covered with the dried ink can be used to control the thickness of the layer.

The liquid white ink 11 and the pigment-dried ink 12 and the molten melamine particles 13, in this embodiment, are heated and stabilized while traveling preferably under a hot IR lamp 23, which is preferably located after the 30 'digital droplet application head in the feed direction.

A dry ink removal station 28, which in this embodiment is based on air currents and vacuum, removes pigments 12 and melamine particles 13 that are not wet and are not bound by the binder pattern BP and a print is provided. perfect color P. The dry ink removal station can be located after the IR lights 23 or between the IR lights and the dispersing station 27. This production step can be repeated and a second dispersion station 27 comprising another color can apply a second color in a binder pattern that can be applied by the same print head or a new print head used in a second cycle. printing formation. The dried pigments are removed and the melamine particles can pass through a sieve or filter and can be recirculated and reused again several times.

The panel 1 with the surface 2 preferably runs practically horizontally under the digital droplet application head 30 ', the dry ink application station 27 and the dry ink removal station 28 with one or more conveyor belts 21. It is evident that the digital droplet application head 30 ', the dry ink application station 27 and the dry ink removal station 28 can alternately move on a panel 1 during BAP printing.

The dried ink may also comprise, in addition to pigments and melamine particles, wear resistant particles, such as small aluminum oxide particles, and fibers, preferably wood fibers, which preferably may comprise or consist of bleached transparent or semi-transparent fibers. This dry ink can be used to create a solid print with pigments that are positioned vertically on top of each other with binders and wear resistant particles above and below the pigments. Small white ink droplets that may be due to capillarity and the combination of surface tension and adhesive forces penetrate the dry ink and bind larger amounts of dry ink than in a conventional ink application where the pigments are applied as small droplets on a surface.

A preferred embodiment of BAP printing is characterized in that the vertical extent of the colorants exceeds the vertical extent of the white ink droplets. Another preferred embodiment is characterized in that the digitally applied blank ink penetrates downward and upward from the surface after application. A highly wear resistant print can be obtained with a printing method comprising white ink and dry ink with wear resistant particles which are preferably incorporated into the dry ink.

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

Static electricity or ultrasound can be used to apply and / or remove unbound dust particles. The air currents and the vacuum that blow and / or suck the particles can preferably be combined with brushes. In general, all the wet and dry methods used to remove dust can be used separately or in various combinations to remove the unbonded parts of the dried ink. However, dry and non-contact methods are preferred.

Controlled complete or partial removal of unbound dry ink particles is essential for high quality printing with a pre-defined decorative image. Advanced removal systems can also be used that only remove colorants, for example colored pigments, while an essential part of the transparent melamine powder particles can remain on the treated surface. This can be achieved, for example, by a two-stage application where a first layer comprises only melamine resin or particles that have been applied to the surface before applying the blank ink with the colorants. Preferably, this first layer is stabilized. It can be sprayed with water and dried by eg IR or hot air. This independent binder layer which preferably comprises melamine can substitute, in some applications, for example prepreg paper, which in some application can be used as surface layer 2, and only non-impregnated paper with or without a base color can be used as surface 2 for the print application cycle.

The moisture content of the surface layer must be precisely controlled to facilitate removal of unbound dust particles. A moisture content below 8% or even more preferably not more than 6% is preferred. The surface layer 2 can be dried by, for example, IR lamps before the application of the white ink. A special chemical can be applied to seal the surface 2 or the top of the bonded colorants to create a seal layer or a release layer that can prevent the colorants from sticking to specific parts of the surface layer where it has not been applied ink on white.

The floor panel 1 generally comprises a lower balancing layer 4 of laminate, plastic sheets, coated paper or powder material. Said balancing layer can also be applied as a dry mix of melamine powder and wood fibers, which are stabilized by means of humidity and heat before pressing. Pigments can be included in the powder mix to provide a base color. The balancing layer can also comprise only melamine powder or a liquid melamine resin that is applied directly to the back face of the core 3, and no paper or wood fibers are needed to balance the surface layer. The melamine content in the surface layer is preferably higher than in the balancing layer. The rear face of the panel is very suitable to provide specific information to the installer or final consumer of the floor. Conventional digital printing or BAP printing can be used to create a digital pattern or text on the balance layer. Installation and maintenance instructions, logos or other types of instructions, pictures and information may be included and may replace generally applicable information on the packaging or in special instructions provided separately. Digital printing and especially BAP printing can be very cost effective since a single digitally applied color is generally sufficient in addition to a base color. The backing layer can also have a digital print that is only decorative.

Figures 3a-3d show an embodiment of the invention, which is based on a second principle where the dry ink 15, comprising colorants 7 and preferably also a binder that can be melamine 13, is applied in a first stage on a surface 2 After that, a digital impression is formed as a second stage, by the digital droplet application head which applies a BP pattern of white ink by means of the white ink on the dry ink. A main difference between the first and second principles is the sequence of application of the white ink and the dry ink. The white ink 15, according to the first principle, is applied in a first stage while, according to the second principle, the white ink 15 is applied in a second stage. The first principle is referred to below as "Binder Under Powder" printing and the second principle is referred to as "Binder On Powder" printing. BUP and BOP digital printing can be direct printing or transfer printing as described above.

These two principles, BUP and BOP, can provide different images with different color intensity. The white ink droplets 11, when applied according to the BUP principle, form ink spots when they strike the surface and said ink spots will cover an area much larger than the diameter of the droplets. Only part of the liquid substance in the ink stains will penetrate from the surface and into the dried ink. When the white ink droplets are applied according to the second BOP principle, they will first penetrate into the dry ink particles which will be bound together in small particle clusters and a smaller part of the liquid white ink droplets will arrive to surface 2 where the small clusters will be attached to the surface. Said application can be used to prevent bleeding in some application where the surface has an open structure that distributes a liquid substance. It should be mentioned that bleeding is not always a disadvantage as it can be used to create decorative effects. The application of dry ink must be precisely controlled when using the BOP principle, and the maximum thickness of the dry ink layer must be adapted to the size and intensity of the droplet so that the white ink penetrates through the layer of ink dry and to the surface. The thickness of the dry ink layer should preferably not exceed the maximum penetration level of the dry ink droplets.

The thickness of the dry ink layer can vary considerably when using the first BUP principle as excess unbound particles above the penetration level of the applied white ink droplets on the surface will be automatically removed, and the substance liquid on top of the dry ink particles can dry out. The thickness of the dry ink layer can be greater or less than the penetration level of the white ink droplets when using the BUP principle. This provides the ability to use combinations of white ink drop intensity and dry ink vertical spread to create color variations.

Both principles have advantages and disadvantages depending on the application.

The blank ink 11 may even comprise, in this embodiment, water which when applied melts, for example, the melamine particles 13 mixed with pigments 12 or melamine particles applied under the pigments. The binder connects some pigments that form the same pattern as the BP binder pattern while other unbound pigments are removed. Figure 3a shows the dry ink 15 comprising a mixture 13 of melamine powder and pigments 12 dispersed on a surface 2. Figure 3b shows a BP blank ink pattern applied digitally on the dried ink. Figure 3c shows that the unbound pigments and, in this preferred embodiment, also the melamine particles 13 have been removed. Figure 3d shows a BAP printing station 40 comprising a dispersing station 27, a blank ink application station 36, an IR oven 23, and a dry ink removal station 28 based on an air stream and vacuum. .

The first and second principles can be combined. The blank ink 11 can be applied before and after the application of the dry ink 15, and this can be used to bond a thicker layer of colorants and create a solid print with a large vertical spread and high wear resistance. The binder printing equipment may comprise binder printing stations applying dry and blank ink according to the first and second principles.

Figures 4a-4d show embodiments that are based on a third principle where the bonding of the dry ink 15 is carried out with digitally controlled heat that activates a thermosensitive resin and bonds the dry ink 15 to a surface 2 so as to form a digital impression P when unbound dry ink particles are removed. The dry ink 15 comprising colorants 7, preferably pigments 12, can be applied in a first step on a surface 2 as shown in Figure 4a. After that, a BP binder pattern or image is formed digitally by dry methods and after that, unbound dyes 7 are removed as shown in Figure 4c. Various methods can be used. Figure 4d shows a laser beam 29 that melts or cures a binder, for example, a thermosetting or thermoplastic resin 13 that can be mixed with the blank ink or be embedded in the surface 2. The dried ink can also be electrostatically connected to the ink. surface by means of the laser beam. A digitally created impression P is obtained when unbound or unconnected colorants are removed. The laser beam can be used to create a binder pattern with heat or electrostatically before and / or after the application of the colorants according to the first and second principles described above for the application of the blank ink.

Figure 4d illustrates a binder printing station 40 comprising a dry ink application station 27, a laser 29 and a dry ink removal station 28 based on a stream of air and vacuum. The laser 29 can be replaced by heating lamps that can be used to create images comprising, for example, fairly large areas of the same color as in some stone designs or base colors in wood grain designs.

Figure 4d also illustrates that a thermal bonding station 26 with heat print heads 80 comprising several small heating elements can be used to create high resolution prints by dry bonding methods. The heating recording head 80 can apply direct heat that bonds the dry ink particles 15, preferably comprising the pigments 12 and a heat-sensitive resin. The heating recording head 80 can also apply indirect heat by heating a heat transfer sheet 81 that can be in contact with the heating recording head 80 and dry ink particles 15. The heat transfer sheet 81 can be a copper or aluminum foil and may comprise small individual elements with high thermal conductivity, for example elements made of copper or aluminum, which are enclosed in a thermally insulating carrier that prevents heat from spreading between individual elements. The heat transfer sheet 81 can be used to increase printability. A thermal pulse from the print head by heating will heat a portion of the sheet and the heat will be maintained as the sheet follows the surface and transfers the heat to the dried ink particles.

Even a conventional laser system based on the impact method described above can be used to apply a digital impression partially or totally on a building panel or in conjunction with the binder printing methods described above.

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

Figures 5a-5h show schematic side views of the application of two different colors according to the first BUP principle. A first binder or a blank ink spot 11a, which in this embodiment essentially comprises water, is applied by a digital ink droplet application head on a surface 2 which may be a layer of stabilized powder or a paper as shown in Figure 5a. Head jets 50 apply blank ink drops 11 through nozzles 54 when heater 59 creates bubbles 60 in ink chamber 52 so that white ink drops 11 form liquid spots 11a when they strike surface 2. The digital droplet application head can also be a piezoelectric head and the water-based blank ink can also comprise a viscosity-increasing substance. The water-based blank ink may comprise glycol or glycerin.

A first dry ink layer comprising color pigments 12a and dry binder particles, in this preferred embodiment, the melamine particles 13a are applied on the surface 2 and on the liquid white ink spots 11a as shown in Figure 5b. The melamine particles 13a that are in contact with the water-based wet droplets will melt. A first IR lamp 23a can be used to dry the wet melamine and to bond the pigments to the surface as shown in Figure 5c and the unbound melamine and pigment particles are removed after that so that an image of pigment or decoration 12a corresponding to the applied binder pattern formed by the white ink droplets 11a as shown in Figure 5d. The figures. 5e-5h show that the same application can be repeated with a new application of dry ink comprising pigments 12b that have another color and mixed with particles 13b of melamine and a new pattern 11b of binder, so that an image with two types is obtained of color dyes or pigments 12a, 12b attached to two blank ink patterns 11a, 11b, as shown in Figure 5h.

Figure 6a shows an embodiment where the BAP digital printing equipment 40 comprises a station 36 for applying digital ink blank, a station 27 for applying dry ink, IR drying or curing 23 and a station 28 for vacuum removal. dry ink. In this preferred embodiment, the BAP printing equipment 40 is combined with a conventional ink jet printer 35. The BAP printing method can be used in this combination to create most of a digital print, while some parts of the final print can be created with a conventional inkjet printer. This can greatly reduce the cost of the ink as, for example, the cost-effective BAP method, where there are no pigments to handle by the digital droplet application head, can apply, for example, 90% of the pigments that are needed to create a fully printed digital pattern or decoration. Powder-based floors are especially suitable for this combined method. Powder coat 2a can provide a first base color. A second colored design can be applied with Ba P printing equipment and a third color can be applied with conventional digital printing equipment. No second color stabilization is required as additional dry colorants will not be applied or removed. This embodiment is characterized in that a tricolor image is formed by a base color, preferably included in a layer of powder or paper, dry colorants and liquid ink. The same type of print heads can be used to apply blank ink and conventional liquid ink.

A conventional digital printer can be used to apply blank ink that is used as a binder for dry ink and a conventional liquid ink comprising colorants. One or more ink channels can be filled with, for example, white ink having different drying and / or bonding properties than the rest of the channels comprising conventional pigment-based ink. The white ink droplets may become damp when the pigment-based droplets have dried. Blank ink can be used to apply colorants that make up the main parts of color in a digital print.

Figure 6b illustrates a binder and powder printing equipment 40 where the dry ink 15 comprising, for example, a mixture of pigments 12 and melamine powder 13, is applied by a dispersing station 27 which preferably comprises a roller etching 22 and preferably an oscillating brush 42. Unbound colorants, for example pigments and melamine particles are removed by a dry ink removal station 28 which recirculates the mixture 12, 13 or the blank ink to the dispersal station 27. A cloud of pigment / melamine powder can be created by air currents and only the pigment and melamine powder that come into contact with the wet binder 11 will be attached to the surface 2.

Figure 6c is a cross-section of a floor panel 1 and shows that the BAP printing method is especially suitable for applying a BAP digital print on a floor panel with a paper-like or powder-like surface 2 and with a system mechanical fastening device comprising a strip 6 with a fastening element 8 at one end that cooperates with a locking groove 14 on an adjacent edge of another panel for horizontal locking of adjacent edges and a tab 10 on one edge that cooperates with a tongue groove 9 on other edge for vertical locking of panels. Such floor panels generally have advanced stamped wood or stone decorations that require large amounts of different color pigments and a decoration that must be precisely positioned relative to the stamped structures and panel edges where the mechanical fastening system is formed. . Generally, the decoration must conform to the part of the edge of the surface part that is removed when the locking systems are formed. Figure 6c shows a wood grain pattern with a first S1 and a second S2 surface parts having different colors. The second surface part S2 which, in this embodiment extends mainly in the longitudinal direction L of the floor panel, is applied on a base layer 2 comprising the first surface part S1.

Figure 6d shows a dry ink removal station 28, which in this embodiment is based on air currents and vacuum that blows and sucks particles. One or more vacuum suction profiles 41 with openings covering the entire width of the applied dry ink layer can be used to remove virtually all unbound dry ink particles 11. One or more air blades 42 that also cover the entire width can apply air pressure on the remaining unbound particles so that they are released from the panel surface 2 and blown into the vacuum suction profile. The important advantage of this combined method is that high air pressure is more efficient and creates a stronger air stream than vacuum. This method can be used to remove virtually all visible dry ink particles from rough surfaces, such as a stabilized powder surface and rough paper surfaces. Even very small particles can be removed, for example small pigments or very small wood fibers. A two-stage process can be used to recirculate the dried ink. A first removal is performed with a dry ink removal station comprising only a vacuum suction device and removing all very loose particles, which may represent about 90% or more of the unbound dry ink particles. These particles are generally very clean and can be reused. A second formed dry ink removal station 28 based on vacuum and air pressure as shown in Figure 6d can be used to remove the remaining particles that may contain some particles from the powder-based surface 2 or from a precious application. of another color. These particles may not be suitable for recirculation.

All the methods described above can be partially or totally combined.

Figures 7a-7c describe the application and removal of colorants 64 having different sizes and how a solid print P can be formed by pressing dry ink particles 11 together.

The application and removal of colorants is, in some applications, important to obtain a high quality image. In some other applications this can be an advantage if some colorants are left on the surface as this can be used to create a more realistic copy of e.g. wood designs where the wood surface generally always comprises small flaws and spots of color that are randomly distributed. Small particles are also difficult to see and in many applications will not alter the overall impression of the decoration, especially if they are not applied in a raster pattern.

Figure 7a shows that very small particles 10-20 microns in size and smaller may show a tendency to adhere to a surface 2 which, for example, may be an uncoated paper surface comprising wood fibers 61 with a quite rough fiber structure. Figure 7a further shows a pressed part A and an unpressed part B of a panel surface 2. White ink drops are applied in a pattern raster R1-R4. The unpressed part B shows pigments 12a which after removal of the dry ink are bound to the white ink and other pigments 12b which are not bound by the white ink, but remain bound, for example, to the surface of the paper after removal due to friction or static electricity. Pressed part A shows pigments 12c that are permanently attached to surface 2 by pressure and heat. The pigments 12c which have been applied on top of each other are pressed to obtain a flat, solid print P with superimposed pigments. A BAP print provides the possibility to create a print corresponding to a practically undefined resolution using a rather low resolution, for example 300 DPI, when applying the ink 11 in white. Such a printed pattern can be practically identical to a wood grain structure on real wood or a stone pattern on real stone where the patterns are formed by different natural fibers or crystalline structures.

Figure 7b shows that the adhesion problem can be solved with dry ink comprising colorants 7 that are larger than, for example, conventional pigments 12. The colorants are preferably in the range of 30-100 microns. In some applications, colorants with a size of up to 300 microns or more can be used depending on the decoration. Such relatively large macrodye particles 64 can be formed in many different ways. Macrodyes 64 comprise, according to a preferred embodiment, pigments 12 attached to a body 66 of the particle. In this preferred embodiment, the particle body is a spray dried melamine particle 13. Such macrodye particles 64 with a size greater than 20 microns are much easier to disperse and remove than small pigments with a size of a few microns or less. An important advantage is that the pigments are attached to various parts of the particle body 66 - on the lower 66a and upper 66b parts - as shown in Figure 7c which is a side view of a macro dye 64 shown from above in Figure 7b. A spot 57 of a liquid white ink 11 binds a macrodye particle 64 comprising various pigments 12. The pigments 12 are placed vertically one on top of the other on opposite sides of a particle body 66 and such an embodiment can provide a deeper impression. with greater color intensity and wear resistance. Another advantage is that a small blank ink blot 57 can be used to bind large amounts of colorants or pigments since, in fact, they may have a mass or size that is greater than the mass or size of the ink blots in white applied as a drop from a 30 'digital drop application head. A large amount of pigment or colorants can be attached in this way with fairly small droplets of white ink. For example, one gram of blank ink can bind 1-5 grams of colorants. This is an important difference compared to conventional digital printing where the liquid ink generally only comprises 20% pigments and the ink drop always comprises a smaller amount of colorants than the ink drop itself. Generally, approximately 5 grams of conventional pigment ink must be applied to apply 1 gram of pigments on a surface.

Figures 8a-8h show preferred embodiments of macro dye particles 64. Said particles may comprise or consist of several individual colorant particles 69 which may be interconnected to other macro-colorant particles 64 having a specific color. Macrodye particles 64 can also be produced by a combination of various materials and chemicals having a particle body 66 and pigments included in the particle body 66 or attached to the surface of the particle body. Figure 8a shows an embodiment comprising a number of individual colorants 69, eg, pigments 12, which are interconnected with a binder and which form a macro-colorant particle 64. Such macro-colorants can be produced by mixing, for example, pigments 12 with a liquid thermosetting resin, for example melamine. The mixture is dried, ground and sieved to produce macro dyes comprising groups of pigments of a predetermined size.

Figure 8b shows a macrodye particle 64 having a particle body 66 of a thermosetting resin or spray dried thermoplastic resin comprising pigments 12a, 12b in the particle body 66 and on its surface. Pigments can be of different colors. The body colorant 66 can also be a dye. Mixing, for example, a liquid thermosetting resin, for example melamine, with pigments or dyes before spray drying can be used to produce such particles. Surface pigment can also adhere when mixing pigments with spray dried particles. The pigments will adhere to the surface of the spray dried particle body. The bond strength can be increased if the mixing is carried out with higher humidity or heat, especially when the body of the particle comprises melamine. The melamine-type particles can be heated in a final stage where the pigments will be firmly attached to the body. The level of cure of the melamine particles can be increased and this will prevent bleeding of the pigments during a final pressing and curing of the printed surface. The macrodye particles 64 preferably have a diameter of about 30-100 microns and the pigment content may be 10-50% of the total weight. The resin can be melamine or polyacrylate. A binder can also be added to the mixture to increase the bond between the pigments and the particle body.

Figure 8c shows a macrodye particle 64 comprising a thermosetting or thermoplastic particle body 66 with color pigment 12 in the particle body 66.

Figure 8d shows that, for example, macrodye particles 64 can be mineral particles comprising natural colors. Sand or stone powder or various types of minerals derived from, for example, oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium and glass powder can be used. A preferred material in some applications that seek to copy stone is sand, which is a naturally grainy material composed of finely divided mineral and rock particles. The composition and color of sand is highly variable, depending on local rock sources and conditions, but the most common types of sand comprise silica (silicon dioxide, or SiO ² ), usually in the form of quartz.

A preferred embodiment is aluminum oxide 63 which is well suited for bonding and coating with a melamine resin.

Mineral particles and especially colored glass particles comprising pigments, similar to the glaze powder used in the production of tiles, are well suited for BAP printing on tiles, although they can also be used in other BAP applications. A BAP print can be applied to the body of a tile comprising a base coat of glaze with a base color. Said basic glaze layer can be pressed or applied wet and dry. The BAP impression can melt, during the calcination of the tile, into the basic layer of glaze. A clear glaze layer can also be applied over the BAP print. A binder can be applied on the basic glaze layer, on the colored glass particles or on the dried ink, so that an application bond can be obtained by exposing the dry white ink to, for example, IR light or hot air.

Figure 8e shows that virtually all minerals, such as, for example, aluminum oxide particles 63, can be coated with a thermoplastic or thermosetting resin, for example melamine 13. The resin can be used to bond the color pigments 12 to the body 66 of the particle. These macro dyes 64 are very easy to apply to and remove from a surface and can provide a very wear resistant print with pigments applied on the tops and bottoms of the particle body 66. A preferred average size of mineral-based macrodyes is about 100 microns. This particle size can be used to create a wear resistant print with a particle depth of 100 microns. The binder content is preferably 10-30% and the pigment content is preferably 5 to 25% of the total weight of the macro dye particle.

Mineral particles comprising a pigment-coated aluminum oxide particle body 66 and a melamine resin are especially suitable for use as a dry ink when bonding with a heating recording head 80. Aluminum oxide particles have high thermal conductivity and melamine resin can be bonded with a heat of about 100 ° C.

Figure 8f shows that the macrodye particles 64 may comprise natural fibers, eg, wood fibers 61. Pigments are not needed as the fibers can have natural colors. Fibers from a batch of a different species of wood can be used, for example softwood such as pine and spruce and hardwood such as ash, beech, birch and oak. Colors can be modified by heat treatment. Even cork particles can be used. Such natural colorants may be coated with a binder, preferably a thermoplastic or thermosetting resin, for example melamine. The coating can be used to improve dispersion properties and / or as a binder to bond the macro dye to the surface and the binder pattern created by the blank ink.

Figures 8g and 8h show macro dye particles 64 comprising wood fibers 61 and wood chips 62 which have been coated with a resin and pigments 12.

Fiber-based macro stains can be used to create a nearly identical copy of wood. Different colored wood fibers form the wood grain pattern on a real wood plank. The BAP printing method allows the same principles to be used with different fibers that actually form the wood grain pattern and not small ink droplets arranged in a raster pattern. This is shown in Figure 6c. The panel 1 has a surface with a wood grain decoration comprising a first surface part S1 which is formed by a base layer 2 comprising wood fibers 61a having a first color. A second surface part S2 is formed of wood fibers 61b having a second color. The wood fibers that have the second color are applied and bonded to the base layer. The basic layer is preferably continuous. The second surface part S2 preferably covers a part of the first surface part S1. The base coat 2 can be a powder mixed with a thermosetting resin, a colored paper or a colored wood-based core. The fibers of the two surface parts S1, S2 preferably have different average sizes. The fibers of the second surface part S2 are preferably smaller than the fibers of the first surface part S1. The second surface parts S2 preferably comprise a pattern with a length L that exceeds the width W.

The resin coating can be used to bond pigments to the particle body and to bond the macrodye particle by the blank ink to the surface. The coating can be made in several stages with intermediate drying and curing of the resin. It is preferred that a first coating, drying and curing with a resin thermosetting, for example a melamine resin is performed at higher temperatures than the second cure. The first cure can be done so that the melamine resin cures in a practically C stage where the melamine will not float during the final pressing operation and this will eliminate pigment bleeding. The second coating is preferably cured in a B stage where it is possible to melt the melamine with the dried ink. Dry ink particles can be produced from wood fibers 61 which are mixed with pigments and melamine resin and thereafter pressed to a higher temperature for the melamine resin to cure. The pressed mix can be ground into small particles that are coated with liquid melamine resin and dried so that the outer melamine coating is in a B stage. A binder layer can be applied between the pigments and the body of the particle and on the pigments so that they are completely covered with a layer of binder. Several layers of pigments with different colors can be bonded to a particle body of a macro dye.

The dried ink can comprise a mixture of several different types of macro-colorant particles, for example, melamine / minerals, melamine / fibers, fibers / minerals, etc., and the structure and size of the macro-colorants can be used to create special decorations. .

The coating of the particle body 66 is preferably carried out in several stages where, for example, particles such as fibers or minerals from a first stage are mixed with a resin, preferably spray dried melamine and pigments. This mixture can be applied as a fairly thin layer, eg 1-3mm thick, on a conveyor belt. The mix is a third stage sprayed with water and dried with hot air or an IR lamp. The body of the particle, in this embodiment, the fibers or minerals, are coated and impregnated with the wet melamine and the pigments are attached to the body of the particle. The small thickness of the layer makes it possible to dry the layer for a short drying time, for example one minute, and the resin is still in a semi-cured B stage. The dry mix is removed from the conveyor belt by, for example, scraping and the dried flakes are ground and sieved to obtain predefined particle sizes. The spray-dried melamine particles and water can be replaced by a wet binder, for example, wet melamine that can be sprayed onto a mixture comprising pigments and particles that form the particle body 66.

Pigments can also be attached to particle body 66 with a binder comprising water-based acrylic emulsions.

Macro dyes can provide an impression that is very similar to an original wood or stone design, especially when fibers are used to copy a wood grain pattern and minerals to copy a stone design. Conventional rotogravure methods can be used with a printing cylinder to apply white ink to a surface. Dry ink comprising macrodye particles can be applied over the blank ink and the unbound particles can be removed according to the BAP printing principles described above. Such a printing method can be used to provide advanced printing comprising a design that cannot be created with conventional ink.

Macro stains can be used to create a pattern, preferably a wood or stone pattern on LVT floors. The BAP printing method can be used to apply a print on the core, on the foil or on the bottom or top side of the transparent protective layer. The colorants can melt into the layers during the pressing operation. Prints in different layers positioned vertically to each other can create a 3D effect. Printing on a clear coat can create an even more realistic 3D effect.

Figures 9a-9e show dry ink BAP printing comprising macro dyes 64 with a fiber-based particle body 66 61 coated with a melamine resin 13 and pigments 12. The jets 50 preferably from a thermal ink head apply droplets of ink 11 in white in a raster pattern R1 - R4 that form spots 57 of ink in white on the surface 2 which, in this embodiment, is a layer of previously pressed powder applied on a core 3, as shown in Figure 9a .

Figure 9b shows a dry ink layer 15 comprising fiber-based macrodyes 64 applied to the surface 2 and Figure 9c shows the dry ink layer when unbound macrodye particles have been removed. The white ink 11 penetrates into the dried ink layer 15 from the surface and upwards due to the wicking and binding properties, and various macro-colorants located vertically above each other can be joined by white ink spots 57. The horizontal extent1H2 of the individual colorants, preferably the macrodye particles 64, preferably exceeds the horizontal extent H1 of the ink spots 57 and the vertical extent V2 of the dry ink layer, after removal of the unbound particles, exceeds preferably the vertical extent VI of the blank ink spots 57. The vertical extent VI of the blank ink spots is generally about 10 microns or less. The vertical extent V2 of the applied and bonded blank ink layers, after removal of the unbound particles, can be at least 50 microns or even greater, preferably greater than 100 microns. This is a major difference compared to traditional inkjet printing, where the pigments are included in the ink droplets. BAP printing allows an impression that can be formed it comprises volumes of colorants greater than the volume of the blank ink applied by the digital droplet application head.

Figure 9d illustrates the BAP P print after a stabilization step which, in this embodiment, is a pre-press operation. The macro dyes 64 can be partially pressed into the powder-based surface 2.

Figure 9e shows the powder-based surface in a fully cured stage after the final pressing operation. The macro dyes 64 are pressed into the powder-based surface 2. The print P comprises pigments 12a, which are located in a first horizontal plane Hp1 at the top of the surface 2a and pigments 12b located in a second horizontal plane Hp2 below the body 66 of the particle and below the first horizontal plane Hp1. Macrodyes 64 comprise pigments 12a, 12b on the upper and lower face of particle body 66.

The macrodye particles are applied randomly, and preferably are offset relative to the raster pattern R1-R4 where each row and column represents a pixel and a spot 57 of dry ink. Print P can be a solid print with several macro dyes interconnected and / or superimposed on each other. The BAP printing in this preferred embodiment is characterized in that the blank ink 11 is applied in a raster pattern (R1-R4) and that the dry ink 15 is applied randomly with other colorants 7 or macro colorants 64. Preferably, the size of a macrodye particle 64 is such that it covers several pixels in a raster pattern.

The thickness (diameter) of the fibers 61 is preferably about 10-50 microns and the length can be 50-150 microns. In some applications the length may exceed 150 microns and realistic wood grain patterns can be formed with fibers having a length of approximately 100-300 microns.

Figures 10a-10c show a BAP impression with a very high wear resistance. Macrodyes 64a comprising a particle body 66 of pigment coated aluminum oxide particles 63 12a and a melamine resin 13 are applied to a surface which, in this embodiment, is a powder-based surface 2a comprising powder of melamine and pigments and preferably also wood fibers. The surface preferably includes a base color. A layer comprising macro-colorants that provide the panel with a basic color can also form the surface 2a and can be applied directly on a wood or plastic type core, a tile body or on a surface comprising powder, paper, a foil and the like. . Figure 10a shows macro dyes 64a attached to surface 2a by ink 11 in white. Figure 10b shows a second macro dye layer 64b comprising pigments 12b with a different color. Figure 10c shows the final cured surface with macro dyes that are pressed into the powder-based surface 2a and preferably covered with a clear coat, preferably a melamine coat 2b which can be applied after a pre-pressing operation but before the final pressing stage. The transparent melamine layer 2b may also comprise bleached transparent wood fibers. It can be a cover, a lacquer, a sheet or a glaze. High wear resistance can be achieved because a considerable part of the surface 2a, 2b, which includes the body 66 of the aluminum oxide particle 63 particle, must be worn away before all of the printing pigments 12a, 12b P go away. Aluminum oxide particles with or without pigments (not shown) are also preferably included in the powder-based surface layer 2a and / or in the transparent melamine layer 2b. The method can also be used to apply wear-resistant digital printing on many other surfaces such as paper, foil, tile, and other surface layers described in the present disclosure.

Figure 11a shows a BAP equipment comprising a number of BAP print stations 40a, 40b that are used in a print formation cycle applying a specific color. Each BAP station comprises a digital droplet application head 30'a, 30'b and a combined dry ink application and removal station 27a, 28a and 27b, 28b and pre-press units 37a, 37b that stabilize the dry ink 15 of so that a new layer of dried ink can be applied and removed according to the principles described above. One embodiment of unity can replace an IR lamp. One embodiment of the unit 37a preferably comprises a heating roller 38c and a cooling roller 38d, a belt 20 and a pre-press table 39. These parts can be replaced, in some applications, by a single roller. A liquid release agent 19 can be applied to the belt 20 by rollers 38a, 38b or brushes or similar devices. Preferably, the droplet application heads 30a ', 30b' use the same blank ink 11 to provide a multi-color print P. This is a significant advantage compared to conventional printing. The BAP printing method in fact allows the final printing ink to be mixed and produced in-line when the blank ink 11 and the colorants 7 of the dry ink 15 are bonded together on the surface 2.

Figure 11b shows schematically a compact BAP printing station 40 where, for example, a set of digital droplet application heads 30 'aligned in a row, each one comprising an ink channel, and a set of IR lamps 23 or pre-press units can be combined with various dry ink application stations 27a, 27b, 27c positioned in the feed direction after the head 30 'of digital drops app. A row of 30 'drop application heads can apply colorants with many different colors. The blank ink, which is preferably a substantially transparent liquid substance, preferably comprises a different color than a first and preferably also a second digital pattern formed by the digital droplet application head 30 '. This is a main difference compared to conventional digital printing where each print head applies a specific color and this color is always the same as the liquid substance applied by the print head. A surface layer 2 or a surface that is part of a floor panel 1 can move in two directions and each cycle can be used to apply a specific color with the same droplet application head. The bAp print station can comprise IR lamps or pre-press units and dry ink application stations on both sides of the digital droplet application head and different colors can be applied when the surface 2 moves under the head 30 'in each direction. This means, for example, that three colors can be applied by the same digital droplet head 30 'on a base color when a panel 1 moves under the head 30', again against its initial position and again under the head. The speed can vary between the various stages of application. This can be used to increase capacity. A wood grain pattern is generally made up of different amounts of specific colorants. The speed can be increased when the amount of a specific colorant is low since only a small amount of white ink has to be applied on the surface. A digital control system can be used to optimize capacity and adapt speed to the amount of blank ink 11 needed to form a specific digital pattern. Various alternatives can be used to combine a blank ink droplet application head with multiple dry ink application stations and removal stations. A panel can, after the first print formation cycle, be moved vertically or laterally towards a mechanical conveyor which takes it to an initial position. An intermediate stacking unit can also be used. Paper and roll sheet stock can be printed multiple times with the same droplet head and the same blank ink.

Figure 11c shows a pre-press unit 37 that can be used to pre-press a powder coat with a basic color prior to BAP printing. This pre-press unit can also be used to stabilize prints or to pre-press and connect a powder-based backing layer 4 on the back face of a core 3. When using melamine as a binder, a heating roller 38c and a pre-pressing table 39 can apply heat of, for example, 90-120 ° C and a chill roll 38d can cool the semi-cured layer 2 to a temperature preferably less than 80 ° C. For example, 5 bars or less, and the pressing time can be approximately 10 seconds or shorter. The melamine will be pre-pressed to a semi-cured stage B which can be further pressed and cured in a final pressing operation. A sheet material with a pre-pressed powder base surface and the backing layer can be produced and used as a pre-finished panel. Other binders, for example thermoplastic binders, can be pre-pressed at other temperatures specifically adapted to the properties of the binder.

Figure 12a shows that a BAP print station 40 and a pre-press unit 37 can be combined into a BAP transfer print station 41 and used together to create a digital BAP P transfer print on a surface 2. The ink 11 in White and dry ink comprising colorants 7, preferably pigments 12, are applied on a transfer surface 18 which may be, for example, a steel or plastic tape, or the like. The impression P is pressed onto a surface 2 by rollers 38c, 38d and preferably by a pre-press table 38. The BAP transfer printing unit may comprise a cleaning device 71, rollers 38a, 38b or brushes that apply a release agent 19 and preferably also an IR lamp 23 that dries the release agent before applying the blank ink 11 . The release agent can also be mixed with the dry ink 15.

The BAP transfer printing method provides the advantages that the dry, white ink can be applied on a predetermined transfer surface 18 which can be specially adapted for a high definition application of the white ink without any risk of bleeding and Easy application and removal of dried ink. This allows, for example, that a BAP print can be easily applied on rather rough surfaces such as, for example, textiles, carpets, various cardboard materials and the like. BAP transfer printing can be combined with the rest of the methods described, for example the method described in Figure 11b where a droplet application head 30 'is used to apply various colors.

Figure 12b shows a BAP transfer printing station 41 where the ribbon has been replaced by a roller 38 comprising a transfer surface 18. The roller preferably comprises heating 25a and cooling 25b zones. Unbound dried ink can be removed by gravity, which can be combined with ultrasound, vibrations, or drafts. This method can also be used to apply a direct BAP print on a flexible surface 2a which can be a paper, a sheet or the like. The application can be done in-line with a pressing operation or as a separate production stage.

Figure 12c shows a preferred embodiment of a floor panel 1. The panel 1 comprises a support layer 4 on the back face of the core 3 and a surface 2 on the upper part of the core comprising a sub-layer 2c, a paper or sheet 2b and a wear layer 2a on the paper. The support layer 4 and the sub-layer 2c can be applied as a dry melamine-formaldehyde powder and the wear layer can be applied as a dry melamine-formaldehyde powder comprising aluminum oxide particles. The paper may comprise a base color. A BAP print or conventional digital print can be applied on the paper. This dry process can be used to form a very profitable panel without any impregnation of a decorative paper or a protective covering. The spray dried melamine particles will melt during pressing and permeate the paper. It is clear that this dry method can be used to save costs even when using conventional decorative paper.

Figure 12d shows a method for forming a base layer on rough core materials 3 comprising cavities, cracks, folds or defects 3a, 3b. Said core material can be made of, for example, plywood or OSB. The problem is that a layer of powder is generally the same thickness in the cavities and in the upper parts of the core surface and there will not be enough powder to form a high-quality surface after pressing, since the density of the surface layer will be less in the parts of the surface with cavities. This problem can be solved with a first powder layer 2a which is applied as a filler and pressed by, for example, a roller or a ruler into the cavities so that a substantially flat powder-based surface layer 2a is formed. A second powder-based layer 2b can be applied over the first filler layer 2a. The two layers can be pre-pressed, as described above, and a base layer can be formed which, in a second step, can be printed with a preferably BAP print and thereafter cured with heat and pressure. The method can also be used without a print and only powder layers comprising fibers, binders and preferably pigments can be used. This embodiment is characterized in that the dust content above the cavities is greater than the dust content above the upper parts of the core. Dust content can be measured by measuring the weight of the powder above a cavity and above an upper part of the surface. The base layer comprising a first filler layer 2a and a second powder layer 2b can be covered by a conventional decorative paper and also preferably with a protective layer, for example a conventional coating or a clear lacquer.

Figure 13a shows that a conventional laser printing technology using electrical charges to attract and release dry ink particles can be adapted so that digital impressions can be provided on a core material 3 comprising a surface 2 preferably having a color base. The negatively charged dry ink particles 15, which may be conventional laser toner pigments, are applied by a developer roller 72 onto a photoconductive drum 70 which is in contact with a charge roller 71. A laser beam 29 projects an image onto the electrically charged photoconductive drum 70 and discharges the areas that are negatively charged and an electrostatic image is created. Dry ink particles are electrostatically captured by the discharged areas of the drum. The drum prints the print P on the surface 2 by direct contact. An electrical charge can be applied to the surface or the core so that the pigments are released from the drum and applied to the surface. A fusing roller 73 melts the dry ink particles onto the surface and binds the dry ink particles. A roller cleaning device 74 can be used to clean the photoconductive drum. The dried ink particles can comprise a thermoplastic or thermosetting resin that can be used to bond the particles to the surface with heat and pressure.

Figure 13b shows that laser printing technology can be used to apply a transfer print P onto a surface 2. The dried ink particles are applied onto a ribbon 20 comprising a transfer surface 18 and released from the photoconductive drum. 70 by an electrically applied roller 75 which applies an electrical charge to the ribbon 20. The dried ink particles are then fused by a pre-press table 39 which applies heat and pressure to the ribbon 20 and transfer surface 15. Heating 38c and cooling 38d rollers can be used. The ribbon can be replaced by a transfer roller, as shown in Figure 12b.

Figure 13c schematically shows several other preferred principles that can be used to apply particles in well-defined patterns on a surface 2 without a digital droplet application head applying a liquid binder of blank ink.

A first principle is a method of creating a base coat that comprises at least two different colors. A first layer 2a with a first base color is provided as a powder or colored paper. A second dry ink color 15 is dispersed over the first basic color. Some parts of the dry ink particles 15 are removed with a dry ink removal station 28 comprising several air nozzles 77a, 77b, which can remove the dry ink particles by, for example, vacuum before they reach the surface with base color 2a. The air nozzles 77a, 77b can be digitally controlled with preferably several valves and a dry ink pattern P can be formed. This can be repeated and various color patterns can be formed without any digital or blank ink droplet application head. This method is especially suitable for forming patterns that can be used partially or fully to copy wood or stone designs. This method can be combined with BAP digital printing or conventional digital printing. The method can also be used to create high resolution digital prints. The dry ink 15 may comprise high density particles, such as minerals, especially aluminum oxide particles or glass particles which, during dispersion, can fall in a predetermined direction essentially straight towards the surface 2 and precise partial vacuum removal can be performed when air is passed through the air nozzles 77a, 77b. The applied dry ink is preferably stabilized by spraying with water before or after application.

Dry ink particles can pass, according to a second principle, through a set of electrodes that transmit a charge to some particles. The charged particles can then pass through a baffle plate 79 which uses an electrostatic field to select the particles to be applied to the surface, and the particles to be collected and returned for reuse by the dry ink application system.

According to a third principle, a heating print head 80 comprising small heating elements producing varying amounts of heat similar to print heads used in dye-sublimation or thermal printing technologies can be used to bond colorants to a surface. Several heat print heads 80 may be joined in parallel so as to cover the entire width of a printed surface. Quite low temperatures of about 100 ° C can be used to obtain an application bond for the dry ink particles. The heat can also be quite high, for example 200 - 250 ° C, and such heat will not destroy the wood fibers in the paper or the powder-based layers. Various methods can be used to form a dry ink digital print where dry ink particles are attached to a surface in a digitally predetermined print. In contrast to known technology, such dry ink combination heating heads can be used to apply a wide range of different colors without any heat sensitive paper or transfer foils. A heat-sensitive binder, which can be a thermosetting or thermoplastic resin, wax, and the like with a low melting point, can be included in the surface layer or colorants of the dry ink. As the dry ink, a powder comprising dye-sublimation particles of different colors can be used. The heating recording head 80 can apply digitally controlled heat directly to well-defined parts of the dried ink after application, or to the surface layer before applying the dry ink. The heating ink head may comprise heating elements arranged on a substantially flat surface or on a cylinder that rotates when a surface with dry ink is moved under the recording head by heating. Alternatively, a heat transfer sheet 81, as shown in Figure 4d, may be applied between the dry ink and the print head 80 by heating and may slide against the heating elements and the ceramic substrate of the print head by heating. . Unbound colorants or non-vaporized dyes can be removed and reused.

Figure 12a shows that a heating recording head 80 can be used to provide heat on a transfer surface 18 that heats the dried ink 15. The transfer surface can be used as a heat transfer sheet 81. The heat recording head 80 may be positioned to provide heat across a transfer surface 18 or onto the dry ink 15 applied to the transfer surface 18. The heat recording head 80 can also heat portions of a surface prior to application of dry ink. The surface can be a board material, powder, paper, a sheet, a base coat, a transfer surface, and the other surface materials described in this description.

Figure 13d illustrates that the heat print heads 80 and dry ink 15 are especially suitable for use to form a digital print P on flexible thin surfaces 2 which, preferably, may be a paper, a sheet, a textile material and materials similar that generally have sufficient heat transfer capacity and heat resistance to function as a heat transfer sheet 81. A heat and powder printing equipment may comprise a dispersing station 27 which applies blank ink 12 on a surface, a heating print head 80 which joins a part of the blank ink 15 with heat to the surface 2 and a dry ink removal station 28 which removes unbound dry ink 15. In some applications, a pre-press unit 37 may be used, with vacuum applied to the underside of the surface or wobble to increase contact between the dry ink particles and the surface during thermal bonding. A separate thermal transfer sheet, as shown in Figure 4d, can be used to increase printability. The pre-press unit 37 can also comprise thermal print heads and heat can be applied from the top and / or bottom face.

The heat recording head 80, with or without a heat transfer sheet 81 can replace all of the digital droplet application heads 30 'in the embodiments of the present disclosure.

The embodiments of the three principles described above are based on the main method in which colorants are applied in dry powder form to a surface and bonded into a predetermined pattern that forms an impression. The surface can be a transfer surface 18 and all three principles can be used to provide transfer printing.

Figures 14a-14d illustrate a method of forming a digital stamp on a surface 2 preferably an EIR structure, hereinafter referred to as a BAP stamp. A digital droplet application head applies a blank ink pattern onto a carrier 68 as shown in Figure 14a.

Pressure particles 67 that are similar to the colorants shown in Figures 8d-8h can be applied onto carrier 68 which can be aluminum foil, plastic foil, paper, and the like. The Application can be the same as for BAP printing and all of the above-described methods can be used to apply the pressure particles 67 in a pattern onto a carrier 68. However, the pressure particles 67 do not have to be coated with pigments. They can be coated with a thermosetting 13 or thermoplastic resin. In some applications, the white ink is sufficient to provide an application bond. A heating print head can also be used to bond the pressure particles 67 to the carrier. Carrier 68 and / or blank ink may also comprise a binder. The particles are preferably hard minerals such as aluminum oxide, sand, stone dust, and the like. Such particles, which practically maintain their original shape during pressing and are not compressed during a pressing operation, are called hard pressure particles. The size of the particles must be adapted to the depth of the stamping. Particles with a diameter of about 0.2 mm can be used, for example, to create an emboss with a depth of at least 0.2 mm. The carrier 68 with the pressure particles 67 is positioned and coordinated with a printed pattern P which can be a conventional print or a BAP print applied on, for example, a powder or a paper surface 2. Figure 14b shows the pressing stage where the pressure particles 67 and the carrier 68 are pressed by the pressing table 24 into the surface 2. Figure 14c shows the stamped structure 17 when the carrier 68 with the particles 67 of Pressure is removed after pressing and a perfect digitally formed EIR surface is obtained that can be coordinated with any types of P digital impressions without any conventional press plate. A part of the surface structure, especially the microstructure 16 that provides the gloss level, can be formed by the carrier. The deep stamped structures 17 are formed by the pressure particles and the carrier 68.

BAP stamping provides the advantages that a deep stamp can be formed with only one or a few BAP application steps, since a considerable amount of pressure particles 68 can be applied with thin layers of blank ink 11. This method allows the embossing depth D to exceed the vertical extent V of the blank ink spots 57 connecting the pressure particles to the carrier.

Figure 14d shows a method of forming surface 2 of a BAP embossed panel. A blank ink application station 36 applied the blank ink 11 onto a carrier 68 which in this embodiment is preferably an aluminum foil or a coated adhesive liner. A dry ink application station 27 is used to apply the pressure particles 67 to the carrier. In some applications an IR lamp 23 may be used to create an application junction. The pressure particles are removed by a dry ink removal station 28 and the carrier with the pressure particles is again pressed against the substrate by a pressing table 24. The carrier and pressure particles are then removed, and a BAP stamped structure is formed.

The method can be used to form a conventional stamp or an EIR stamp.

The surface of the carrier 68 which is pressed against the embossed surface 2 can be coated so that different levels of gloss or microstructures can be obtained. Said coating is preferably performed digitally according to a method described in this description.

The pressure particles 67 can be attached to the carrier by all of the above-described methods. For example, heat print heads 80 and laser 29 can be used.

Figures 15a-15d show that the BAP transfer printing method can be combined with the BAP stamping method. Pressure particles 67 can be applied to one side of a carrier 68 and a BAP print can be applied to the opposite side of carrier 68 comprising a transfer surface 18 as shown in Figure 15a. Carrier 68 can be sheet, paper, and the like, as described above. BAP printing can also be replaced by conventional digital printing or even printing provided by conventional rollers. Preferably, the imprint P and the pattern of the pressure particles 67 are coordinated so that an EIR structure can be formed. Figure 15b shows that the carrier 68 and the pressure particles 67 together with the impression P are pressed against a surface 2. Figure 15c shows that the impression P is attached to the surface 2 and that the carrier 68 with the particles 67 of pressure forms a stamped structure 17 when removed after the pressing operation. The application of the pressure particles 67 and the dry ink printing can be done in line with the pressing operation, as shown in Figure 15d or as a separate operation where a pre-printed and pre-engraved carrier 68 is formed which is can be supplied as a single carrier, preferably as in sheet form. A combined BAP printing and embossing equipment may comprise blank ink application stations 36, dry ink application stations 27 and dry ink removal stations 28 which apply and remove the dry ink 15 and pressure particles 67 at the Opposite faces of a carrier 68.

The particles can also be attached to the carrier with a laser beam, thermal print heads, and the other methods described above.

The surface of the carrier 68 that is in contact with the surface 2 of the panel can be pre-pressed and different levels of gloss or microstructures can be formed. This pre-pressing can be done with conventional stamping cylinders or with a BAP stamping method. Various levels of gloss and microstructures by digital printing and a coating can be made according to any of the methods described in this description. The carrier 68 with the pressure particles 67 and preferably also with a transfer printing P can be supplied as a pressure die 78 and can be used to form an embossed structure on, for example, laminate, wood and wood-based floors. dust but also on LVT tiles and floors. The pressure die 78 can be used multiple times. The print P may be a conventional print, a digital ink jet print, a BAP digital print, or the like.

The method can also be used to form a more durable "mirror" pressure die which can be a sheet-shaped material where protrusions of the carrier 68 form cavities in the sheet-shaped press die. The support with the pressure particles can be pressed against an impregnated paper, preferably craft paper impregnated with phenol or powder comprising a thermosetting resin, and a structured laminated matrix can be formed which, in a second stage, can be used as a roll. pressing. Metal powder and glass fibers can be included to improve strength and heat transfer properties.

All of the methods described above can be combined partially or fully to create partially or completely a digital impression and / or a digital stamp.

The water-based blank ink in some applications can be combined or substituted by oil-based or solvent-based ink. The advantage of oil-based ink may be that it has a very long drying time and this can improve the performance of the digital droplet application head.

While illustrative embodiments of the invention have been described in the present description, the present invention is not limited to the various preferred embodiments described in the present description but includes each and every one of the embodiments having equivalent elements, modifications, omissions, combinations (eg, aspects throughout various embodiments), adaptations, and / or alterations as will be appreciated by those skilled in the art based on the present disclosure. The limitations of the claims should be broadly interpreted based on the language used in the claims and are not limited to the examples described in the present specification or during the process of granting the application, therefore such examples are to be construed as non-limiting.

Example 1 - Blank ink comprising water and glycol

A blank ink formulation was made for a Kyocera Piezo print head designed for inks with a viscosity of 5-6 cps. 60.8% deionized water was mixed with 38.0% polyethylene glycol PEG 400, 1.0% Surfynol wetting agent and 0.2% Actidide MBS for bacterial and fungal control.

Example 2 - Fiber-based dry ink

The dry ink powder was produced by mixing 20% (weight) of spray dried melamine-formaldehyde particles, 20% of dark brown pigments and 60% of pine wood fibers with an average length of about 0.2mm and a thickness of approximately 0.05 mm. The mixture was applied as a 1 mm thick layer by dispersing equipment on a steel tape. After that, the powder mixture was heated and moisture was applied by steam from deionized water. The mixture was dried with hot air, so that a hard stabilized powder-based surface layer was obtained with a semi-cured melamine binder. The dried layer was scraped off the tape and the dry wood particles coated with pigments and melamine resins were ground and sieved to obtain dry ink colorants with a size similar to the size of the individual wood fibers. A dry ink comprising dyes with a wood fiber body and with a surface covered with pigments bound to the fibers by the semi-cured melamine resin was obtained.

Example 3 - Digital printing with binder and powder

An 8mm HDF board was sprayed with small water droplets of deionized water and a 300 g / m2 powder mixture was applied comprising wood fibers, melamine particles, light brown pigments and aluminum oxide particles. by means of a dispersion equipment on the HDF core. The mixture was again sprayed with deionized water comprising a release agent and dried with IR light so as to obtain a partially stabilized, semi-cured hard powder-based surface bonded to the HDF core and having a basic light brown color. The panel with the stabilized powder surface was placed on a conveyor belt and moved under the Kyocera Piezo digital print head. The digital print head applied white ink droplets comprising mainly water and glycol, with a formulation as described in Example 1 above, onto the stabilized light brown powder-based surface and a grain pattern of liquid transparent wood on the surface with stabilized powder base. The wood grain pattern was placed at a predetermined distance from a long and short edge of the panel. The melamine on the surface under the applied transparent pattern melts when the digital piezoelectric coating head applies the water-based droplets onto the powder-based surface. The dried ink described in Example 2 above, which comprises a darker brown color than the light brown powder-based surface, in a second stage was dispersed over the entire powder-based surface with a transparent pattern from a dry ink application station comprising a hopper and a rotating and oscillating engraved roller with a diameter of 5 cm. A dry ink layer of approximately 30 g / m2 was applied on the surface of the panel. The melamine on the dry ink fibers that were in contact with the transparent white ink pattern melted, and the dry ink particles bonded to the stabilized powder surface. The panel with the transparent white ink pattern and the dried ink layer was displaced thereafter by a conveyor under IR lamps. The melamine in the clear pattern was re-dried and a stronger bond of the fibers to the pigments was obtained on top of the clear pattern. The panel was then moved with a conveyor under a dry ink removal station comprising a vacuum suction profile with an opening covering the entire width of the applied dry ink layer where essentially all the fibers not attached to the pigments were removed and an air knife that applied air pressure to the remaining unbound particles that had been released from the panel surface and blown into the vacuum suction profile so that essentially all ink particles were removed visible dry. A wood grain pattern was obtained comprising a base light brown color and a dark brown wood grain structure. A protective layer comprising a dry mixture of dried melamine and aluminum oxide particles was dispersed over the entire surface with the same type of dispersion station as described above for the blank ink. The protective layer was sprayed with small drops of water comprising a release agent and dried under IR lamps. After that, the panel with the printing and the protective layer was placed in a predetermined position relative to a long and short edge in a hydraulic press and pressed against a stamped steel plate for 20 seconds at a temperature of 170 ° C. and 40 bar pressure, and the powder-based surface with the wood grain pattern and the protective layer was cured to a hard wear-resistant surface with high-quality digital printing coordinated with the etched surface structure. The panel decoration was created using a basic color and a wood grain pattern comprising wood fibers and pigments. The obtained copy of a wooden design was very realistic as natural wood fibers were used to create the visible design.

Claims (14)

i. A method of forming a digital impression (P) on a panel (1) comprising a surface (2), the surface being part of a building panel (1), such as a floor panel (1), wherein the method comprises: • move the panel under a digital drop application head (30 '); • apply a liquid binder (11) with the digital drop application head (30 ') on the surface (2); • applying colorants (7) on the liquid binder (11) and the surface (2), where the colorants (7) are macro-colorant particles (64) larger than 20 microns; • join a part of the colorants (7) to the surface (2) with the liquid binder (11); • removing unbound colorants (7) from the surface (2) so that a digital impression (P) is formed by the attached colorants (7); and • apply heat and pressure on the panel (1), the surface (2) and the colorants (7) attached so that the colorants (7) are permanently attached to the surface (2), wherein the colorants (7) are pressed onto the surface (2) when heat and pressure are applied to the panel (1). The method according to claim 1, wherein at least one of the surface (2) and the colorants are compressed by the step of applying heat and pressure on the panel (1), the surface (2) and the colorants (7 ) United. The method according to claim 1 or 2, wherein the liquid binder (11) comprises glycol or glycerin. The method according to any one of the preceding claims, wherein the surface (2) comprises a material that is curable with heat and pressure. The method according to any one of claims 1-3, wherein the surface (2) comprises a material that is fusible with heat and pressure. The method according to any one of the preceding claims, wherein the surface (2) comprises a thermosetting resin (13) that cures with the step of applying heat and pressure so that the colorants (7) are permanently bonded to the surface (2) with the cured thermosetting resin. The method according to any one of the preceding claims, wherein the surface (2) comprises a layer of powder. 8. The method according to any one of the preceding claims, wherein the liquid binder (11) is applied as drops (56) arranged in a grid (R1-R4) and wherein the colorants (7) are joined with several drops. The method according to any one of claims 1-8, wherein the liquid binder comprises 10-70% water and 30-90% glycol and / or glycerin, by weight. The method according to any one of the preceding claims, wherein the surface (2) comprises a dry melamine-formaldehyde resin (13) that melts when the liquid binder (11) is applied and that binds the colorants (7) to the surface (2). The method according to any one of the preceding claims, wherein the macrodye particles (64) comprise pigments (12) attached to a particle body (66). The method according to any one of the preceding claims, wherein the colorants (7) each have a particle body (66) comprising a wood fiber (61). The method according to any one of the preceding claims, wherein the method comprises additional steps of applying new colorants (7, 12b) with a different color in the first attached colorants (7, 12a) and on the surface (2), bond a part of the new colorants (7, 12b) to the surface with a binder and remove the unbound new colorants (7, 12b) from the surface so that a fingerprint (P) is formed with the primer (12a) and the new colorants (12b) placed side by side on the surface (2). The method according to any one of the preceding claims, wherein the colorants (7) are applied in the liquid binder (11).