IPC分类号：
D06N7/04 | B41J3/28 | B41J3/407 | B41J11/00 | B44C5/04 | G11B5/64 | B05D3/00 | B41F17/00 | B41J2/32 | B41M5/50 | B05D3/06 | B41J2/325 | B44C1/24 | C09D11/103
当前申请(专利权)人：
CERALOC INNOVATION AB
原始申请(专利权)人：
FLOOR IPTECH AB
当前申请(专利权)人地址：
PRÄSTAVÄGEN 513, 263 65 VIKEN, SWEDEN
发明人：
PERVAN, DARKO | PERVAN, TONY
代理机构：
BUCHANAN INGERSOLL & ROONEY P.C.
摘要：
Pigment based particles in powder form intended to be used as colorants (7) in a digital print formed by applying dry colorants (7) on a surface (2), bonding a part of the colorants (7) with a binder (11) and removing the non-bonded colorants (7) from the surface (2). A panel (1) with a surface (2) including a digitally formed print of macro colorants (64) including a particle body (66) and color pigments (12) attached to the surface of the particle body (66) is also described. The colorants (7) are arranged in patterns with pigments (12) on an upper and lower surface of the particle body (66).
技术问题语段：
The patent text describes two types of flooring products: laminate floors and powder based floors. Laminate floors are made by pressing a core with two layers of paper (a decorative layer and a balancing layer) and a layer of plastic, while powder based floors are made by applying a mixed powder of fibers, binders, and wear-resistant particles to a core and curing it under heat and pressure. The technical problem addressed in the patent text is to provide improved methods for producing laminate floors and powder based floors with better wear and impact resistance, increased production flexibility, and lower costs.
技术功效语段：
This patent is about a new and improved printing method that uses digital ink heads to apply colorants on surfaces, such as floor panels. The method uses dry pigment based particles that are coated with a resin that reacts with a liquid binder. These particles are applied to the surface using a print head and the binder helps to attach the particles firmly to the surface. This method makes it easier to apply and remove the colored particles, and provides better bonding and wear resistance compared to other methods. Additionally, the binder can be combined with heat and pressure, making the method more cost-efficient and environmentally friendly. Overall, this patent provides a more effective and cost-efficient way to print with colorants on surfaces.
权利要求：
1. A panel with a surface comprising a digitally formed print of macro colourants, the macro colourants comprising a particle body and colour pigments attached to an upper and lower surface of the particle body, wherein the macro colourants are arranged in patterns,
wherein the particle body comprises wood fibres.
2. A panel as claimed in claim 1, wherein the macro colourants have a length or diameter exceeding 20 microns.
3. A panel as claimed in claim 1, wherein the macro colourants form a solid print with overlapping macro colourants.
4. A panel as claimed in claim 1, wherein the panel is a laminate or wood floor, a powder based floor, a tile, or a LVT floor.
5. A panel as claimed in claim 1, wherein the panel surface comprises wood fibres and wherein the macro colourants are pressed into the surface.
6. A panel as claimed in claim 1, wherein the particle body is coated with a thermosetting resin.
7. A panel as claimed in claim 1, wherein the macro colourant particle is coated with a first layer that bonds the colour pigments to the particle body and a second layer comprising the dry resin and applied on the first layer.
8. A panel as claimed in claim 7, wherein the dry resin is a melamine formaldehyde resin.
技术领域：
[0002]The disclosure generally relates to the field of digitally created decorative surfaces for building panels such as floor and wall panels. The disclosure relates to a method and an equipment to apply and bond powder based colourants such that a digital print is formed on such surfaces.
FIELD OF APPLICATION
[0003]Embodiments of the present invention are particularly suitable for use in floors, which are formed of floor panels comprising a core or a body, a decorative layer and preferably a transparent wear resistant structured layer above the decorative layer. Preferred embodiments are conventional laminate floors, powder based floor, wood floors, plastic based LVT floors and ceramic tiles. The following description of techniques, problems of known technology and objects and features of the invention will therefore, as a non-restrictive example, be aimed above all at this field of application and in particular at floorings which are similar to conventional laminated floorings or floorings with a resilient surface layer.
[0004]It should be emphasized that embodiments of the invention may be used to produce a digital image and/or a digitally formed structure on any surface but flat panels such as, for example, building panels in general, wall panels, ceilings, furniture components and similar products that generally have large surfaces with advanced decorative patterns are preferred. The basic principles of the invention may be used to apply a print on paper, foils, textiles, metals, solid wood, wood veneer, wood based sheet materials, cork, linoleum, polymer material, ceramics, wall paper and similar surfaces.
背景技术：
[0005]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 disclosure of this invention.
a) Laminate Floorings.
[0006]The majority of all laminate floors are produced according to a production method generally referred to as Direct Pressed Laminate (DPL). Such laminated floors have a core of 6-12 mm fibreboard, a 0.2 mm thick upper decorative surface layer of laminate and a 0.1-0.2 mm thick lower balancing layer of laminate, plastic, paper or like materials.
[0007]The surface layer of a laminate floor is characterized in that the decorative and wear properties are generally obtained with two separate layers of paper, one above the other. The decorative layer is generally a printed paper and the wear layer is a transparent overlay paper, which comprises small aluminium oxide particles.
[0008]The decor paper is the most critical of the lamination papers as it gives the visual appearance of the laminate. The decor paper weight is generally in the range of 60-150 g/m2.
[0009]The overlay paper is generally thinner with a weight of about 20-50 g/m2 and is made of pure cellulose, which is based on delignified pulp. The overlay paper becomes almost completely transparent after lamination and the appearance of the decor paper is visible. Thicker overlay papers with a considerable amount of aluminium oxide particles may give a high wear resistance. The disadvantage is that they are less transparent and the decorative pattern is covered by a grey layer that disturbs the printed pattern.
[0010]Printing of decorative papers is very cost efficient. Rotogravure presses with printing cylinders that may have a width of 3 meters and that may run with a speed of up to 600 m/min are used. The printing cylinders are generally produced by conventional mechanical engraving. Recently digital laser engraving has been introduced which allows faster décor development and provides a better décor quality. Solvent-free inks with organic pigments are often used and excess ink is re-cycled.
[0011]The printed decorative paper and the overlay are impregnated with melamine formaldehyde resins, generally referred to as melamine resins, and laminated to a HDF core in large discontinuous or continuous laminate presses where the resin cures under high heat (about 170° C.) and pressure (40-60 bars) and the papers are laminated to the core material. An embossed press plate or steal belt forms the surface structure. Sometimes a structured paper is used as a press matrix. The embossing is in high quality floors made in register with the design. The embossing depth is limited to 0.1-0.2 mm (100-200 micron).
[0012]Laminated floors may also be produced with direct printing technology. One advantage is that the pressing operation may be avoided and that no printed papers are needed to provide a decorative surface. Hydro printing inks are used to print the décor by a multicolour printing press with rollers onto a pre-sealed core and the print is covered with a protective transparent wear layer that may be an overlay, a plastic foil or a lacquer. The production process is rather complicated and is only cost efficient in very large production volumes.
[0013]Direct printing technology may be replaced with digital printing technology that is much more flexible and small production volumes can be economically manufactured. The difference between these two methods is mainly the printing step where the printing rollers are replaced by a digital non-contact printing process.
[0014]Digital printing may also be used to print on a paper sheet that is used in conventional laminate production and laminated under heat and pressure. The printing may be made prior or after impregnation. Such printing prior to impregnation is complicated since paper may swell and shrink during the printing and impregnation step and small quantities are not cost efficient to impregnate. Printing after impregnation on a melamine impregnated paper is very difficult since pigments applied on a melamine surface float during the pressing step when the melamine resin is in a liquid state. Such problems may partly be solved with a method where a raw paper, preferably comprising a base colour, is applied and fixed to the core prior to printing and impregnated paper or melamine powder is applied under and/or over the raw paper such that the resins from the impregnated papers penetrate into the raw paper during the pressing step.
[0015]Laminate floors may also have a surface of paper foils or plastic foils and such foil materials may also be printed digitally. A protective wear resistant transparent layer that generally is a polyurethane lacquer is used to covers the printed décor.
b) Powder Based Floors (WFF)
[0016]Recently new “paper free” floor types have been developed with solid surfaces comprising a substantially homogenous powder mix of fibres, binders and wear resistant particles hereafter referred to as WFF (Wood Fibre Floor).
[0017]The powder mix may comprise aluminium oxide particles, melamine formaldehyde resins and wood fibres. In most applications decorative particles such as, for example, colour pigments are included in the mix. In general, all these materials are applied in dry form as a mixed powder on a HDF core and cured under heat and pressure to a 0.1-1.0 mm solid layer. The powder is, prior to pressing, stabilized with moisture and IR lamps such that it forms an upper skin layer similar to a paper layer and this prevents the powder from blowing away during pressing. Melamine formaldehyde powder and wood fibres may be replaced by thermoplastic particles.
[0018]Several advantages over known technology and especially over conventional laminate floorings may be obtained such as increased wear and impact resistance, deep embossing, increased production flexibility and lower costs. An embossing depth of 0.2-0.7 mm may easily be reached.
[0019]Powder technology is very suitable to produce a decorative surface layer, which is a copy of stone and ceramics. In the past it was more difficult to create designs such as, for example, wood decors. However, recently digital powder printing has been developed and it is possible to create very advanced designs of any type by injecting ink into the powder prior to pressing. Problems related to paper impregnation may be completely eliminated since no impregnation is required. The surface structure is made in the same way as for laminate flooring by a structured press plate, a steal belt or an embossed matrix paper that is pressed against the powder. A major advantage compared to the other digital printing technologies is that the powder provides a base colour and no protective layer is needed above the print since the ink may penetrate into the powder. The penetration is however rather limited since the ink drops will be bonded to the first particle that they hit, mainly the wood fibres. Increased wear resistance may be reached if several printed powder layers are applied on each other or if a powder overlay is used as a protective layer applied over the digital print.
c) Melamine Formaldehyde Resin.
[0020]A basic substance in Laminate and WFF floors is the thermosetting melamine formaldehyde resin that is used as a binder. Melamine resin or melamine formaldehyde resin (generally shortened to melamine) is a hard, thermosetting plastic material made from melamine and formaldehyde by polymerization. Such resin, hereafter referred to as melamine, comprises three basic stages. The stages, A-stage, B-stage, C-stage are described in Principles of Polymerization, George Odian, 3rd edition, which is hereby incorporated by reference, including particularly pages 122 to 123. The first uncured A-stage is obtained when melamine, formaldehyde and water is boiled to a liquid substance with a dry content of about 50%. The second semi-cured B-stage is obtained when the liquid resin is used to impregnate, for example, an overlay paper that after the application of the liquid resin is dried with heat. The molecules have started to cross link but the resin is still possible to cure in a final stage if the drying of the resin is made during a rather short time, for example, one minute and with a heat of about 90-120° C.
[0021]The B-stage may also be obtained by spraying the liquid resin over hot air such that the drops are dried and a dry semi-cured melamine formaldehyde powder is obtained that comprises small round spherical particles with a diameter of about 30-100 microns (0.03-0.10 mm).
[0022]The final completely cured C-stage is obtained when, for example, the melamine impregnated paper or the WFF powder is heated to about 160° C. under pressure during 10-20 seconds. The dry melamine formaldehyde resin becomes softer, melts and cures to a fixed form when the temperature increases during the pressing. The curing is dependent on temperature and heating time. Curing may be obtained at lower temperatures and longer time or at higher temperature during shorter time. Spray dried melamine powder may also be cured under high temperature.
d) Wood Floors.
[0023]Wood floors are produced in many different ways. Traditional solid wood floors have developed into engineered floors with wood layers applied on a core made of wood lamellas, HDF or plywood. The majority of such floors are delivered as pre-finished floors with a wood surface that is coated with several transparent layers in the factory. The coating may be made with UV cured polyurethane, oil or wax. Recently wood floorings 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 a sufficient surface quality.
e) Ceramic Tiles
[0024]Ceramic tiles are one of the major materials used for flooring and wall coverings. The raw materials used to form tiles consist of clay minerals, feldspar and chemical additives required for the shaping process. One common method to produce ceramic tiles uses the following production steps. The raw materials are milled into powder and mixed. Sometimes, water is then added and the ingredients are wet milled. The water is removed using filter pressing followed by spray drying into powder form. The resulting powder is then dry pressed under a very high pressure (about 400 bars) to 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 homogenous material. Recently dry pressing of large and thin panels have been introduced. Dry granular material is pressed with very high pressure up to 400 bars and panels with a size of 1*2 m and more and with thicknesses down to a few mm may be produced in a cost efficient way. Such panels may be used for wall panels and worktops. The production time has been reduced from several days to less than an hour. Such panels may be cut and shaped with production tolerances that are superior to the traditional methods and the may even be installed in a floating manner with mechanical locking systems. One or several layers of glaze, which is a glass like substance, are applied on the tile body by dry or wet methods. The thickness of the glazing is about 0.2-0.5 mm. There may be two glazes on the tile, first a non-transparent glaze on the tile body, then a transparent glaze on the surface. The purpose of tile glazing is to protect the tile. The glaze is available in many different colours and designs. Some glazes can create different textures. The tile is after glazing fired in a furnace or kiln at very high temperatures (1,300° C.). During firing, the glaze particles cures and melt into each other and form a wear resistant layer. Roller screens are often used to create a decorative pattern. The contact nature of the rotary screen-printing has many disadvantages such as breakages and long set-up times. Several tile producers have therefore recently replaced this conventional printing technology with digital ink jet printing technology that offers several advantages. Generally oil based inks are used and the print is applied on the pressed tile body or on a base glazing that is applied in wet form and dried prior to printing. A transparent glaze layer may be applied on the digital print in order to improve the wear resistance. Digital non-contact printing means no breakages and possibility to use thinner tile bodies. Short set-up times, randomized printing with no repetition effects and ability to print on surfaces of variable structures and on tiles with beveled edges are other major advantages.
[0025]Additional circumstances that have contributed to the introduction of the digital printing technology in the tile industry is the fact that ceramic tiles are rather small compared to, for example, laminate and powder based floors that are produced as large pressed boards of about 2.1*2.7 m. Rather small printers with limited number of print heads may be used in the tile industry and the initial investment is rather limited. Oil based inks have a very long drying time and clogging of nozzles may be avoided. Other advantages are related to the glazing that provides a base colour. Generally smaller amounts of pigments are required to form a tile pattern on a base colour than to provide an advanced wood grain design on a HDF or paper material used in laminate floorings where impregnation and lamination creates additional problems.
f) LVT Floorings.
[0026]Luxury Vinyl Tiles, generally referred to as LVT floorings, are constructed as a layered product. The name is somewhat misleading since a major part of LVT floors have a plank size with a wood pattern. The base layer is made primarily of several individual base layers comprising different mixtures of PVC powder and chalk filler in order to reduce material costs. The individual base layers are generally about 1 mm thick. The base layer has a thin high quality printed decorative PVC foil on the upper side. A transparent wear layer of vinyl with a thickness of 0.1-0.6 mm is generally applied on the decorative foil. Glass fibres are often used to improve thermal stability. The individual base layers, glass fibres, the decorative foil and the transparent layer are fused together with heat and pressure in continuous or discontinuous presses. The transparent layer may include a coating of polyurethane, which provides additional wear and stain resistance. Some producers have replaced the transparent vinyl layer with a polyurethane layer that is applied directly on the decorative foil. Recently new types of LVT floors have been developed with a base layer thickness of 3-6 mm and with edges comprising mechanical locking systems that allow floating installations. LVT floors offer several advantages over, for example, laminate floors such as deep embossing, flexibility, dimensional stability, moisture resistance and lower sound. Digital printing of LVT floors is only on an experimental stage but would, if introduced, provide major advantages over conventional printing technology.
[0027]As a summary it may be mentioned that digital printing is used in several floor types to create a décor. However the volumes are still very small, especially in wood and laminate flooring applications, mainly due to high cost of the ink and high investment cost for the industrial printers. The flexibility that the digital printing technology provides is limited by the embossing that is fixed and not possible to adapt to the variations of the digitally printed décor. It would be a major advantage if the ink cost could be reduced, if more cost efficient printing equipment could be used in an industrial scale, if a higher wear resistance could be reached without separate protective layers and if variations in the embossed structures may be formed that correspond to variations in the digitally printed pattern.
DEFINITION OF SOME TERMS
[0028]In the following text, the visible surface of the installed floor panel is called “front side”, while the opposite side of the floor panel, facing the sub floor, is called “rear side”.
[0029]By “up” is meant towards the front side and by “down” towards the rear side. By “vertically” is meant perpendicular to the surface and by “horizontally” parallel to the surface.
[0030]By “pigments” is meant a very fine powder of solid colorant particles.
[0031]By “pigment ink” is meant an ink comprising pigments that are suspended or dispersed throughout a carrier fluid.
[0032]By “binder” is meant a substance that connects or contributes to connect two particles or materials. A binder may be liquid, powder based, a thermosetting or thermoplastic resin and similar. A binder may consist of two components that react when in contact with each other. One of the components may be liquid and the other dry.
[0033]By “matrix” also called “mat” is meant a material that forms an embossed surface structure when the material is pressed against a surface.
[0034]By “Embossed In Register” or EIR means that a printed décor is in register with an embossed structure.
[0035]By “digital ink jet printing” is meant a digitally controlled ejection of drops of fluid comprising a colorant from a print head onto a surface.
[0036]By “digital print” is meant a digitally controlled method to position colorant onto a surface.
[0037]By “colourant” is meant any material (dye, organic or inorganic pigments, small coloured particles of any material etc.) that may be used to provide a colour on a surface preferably due to selective absorption or reflection of different wavelengths of light.
[0038]By “panel” is meant a sheet shaped material with a length and width that is larger than the thickness. This rather broad definition covers, for example, laminate and wood floors, tiles, LVT, sheet shaped wall coverings and furniture components.
Known Technique and Problems Thereof
[0039]The generally known technologies, which may be used to provide a digital print and an embossed surface structure, are described below. The methods may be used partly or completely in various combinations with preferred embodiments of the invention in order to create a digital print or a digital embossing according to this disclosure of the invention.
[0040]High definition digital ink jet printers use a non-impact digital printing process. The printer has print heads that “fire” drops of ink from the print head to the surface in a very precise manner.
[0041]Multipass Printing, also called scanning printing, is a printing method where the printer head moves transverse above the surface many times to generate an image. Such printers are slow but one small print head can generate a bigger image.
[0042]Industrial printers are generally based on a Single Pass Printing method, which uses fixed printer heads, with a width that corresponds to the width of the printed media. The printed surface moves under the heads. Such printers have a high capacity and they are equipped with fixed print heads that are aligned one after each other in the feeding direction. In general each head prints one colour. Such printers may be custom made for each application.
[0043]FIG. 1a, shows a side view of an industrial single pass digital ink jet printer 35 comprising five digital print heads 30a-e, which are connected with ink pipes 32 to ink containers 31 that are filled with ink of different colours. The ink heads are connected with digital data cables 33 to a digital control unit 34 that controls the application of the ink drops and the speed of the conveyor 21 that must be able to displace the panel under the print heads with high precision in order to guarantee a high quality image comprising several colours.
[0044]FIG. 1b shows a top view of a wood grain print P provided on a panel surface 2. The surface of a floor panel is often embossed with a basic structure 17 that is the same for several basic decors as shown in FIG. 1c. Advanced floors use a so-called EIR (Embossed In Register) embossing 17 that is coordinated with the printed pattern P as shown in FIG. 1d.
[0045]A normal width of an industrial print head is about 6 cm and any lengths may be printed. Wide areas of 1-2 m may be printed with digital printers comprising several rows of print heads aligned side by side. 166 print heads may be needed to provide a 5-colour print on a 2 m wide laminate floor panel and the print may be destroyed if only a few nozzles in one print head are blocked by dry ink.
[0046]Number of dots per inch or DPI is used to define the resolution and the printing quality of a digital printer. 300 DPI is generally sufficient to, for example, print wood grains structures of the same quality presently used in conventional laminate floorings. Industrial printers can print patterns with a resolution of 300-600 DPI and even more and with a speed exceeding 60 m/min.
[0047]The print may be a “full print.” This means that the visual printed décor is mainly created by the ink pixels applied on the surface. The colour of a powder layer or a base colour of a paper has in such an embodiment, in general, a limited effect on the visible pattern or déecor.
[0048]The print may also be a “part print”. The colour of another underlying layer is one of the colours that are visible in the final décor. The area covered by printed pixels and the amount of ink that is used may be reduced and cost savings may be obtained due to lower use of ink and increased printing capacity compared to a full print design. However a part print is not as flexible as a full print since the base colours are more difficult to change than when a full print is used.
[0049]The print may be based on the CMYK colour principle where the white colour is provided by the surface. This is a 4-color setup comprising cyan, magenta, yellow and black. Mixing these together will give a colour space/gamut, which is relatively small. To increase specific colour or the total gamut spot colours may be added. A spot colour may be any colour. The colours are mixed and controlled by a combination of software and hardware (print engine/print heads). The flexibility may also be increased considerably by adding a white colour to the printer.
[0050]New technology has been developed by CeraLoc Innovation Belgium BVBA, a subsidiary of Välinge International AB that makes it possible to inject a digital liquid print into a powder layer. This new type of “Digital Injection Print” or DIP is obtained due to the fact that printing is made into a powder that is cured after printing. The ink and the print are embedded into the cured layer and they are not applied on a layer as when conventional printing methods are used. The print may be positioned in several dimensions horizontally and vertically in different depths. This may be used to create 3D effects when, for example, transparent and preferably bleached wood fibres are used. A two-layer print may also be used to increase the wear resistance. No protective layers of, for example, overlay are needed that disturb the original design with grey shadings.
[0051]The DIP method may be used in all powder based materials, which may be cured after printing. However, the DIP method is especially suitable to be used when the powder comprises a mix of wood fibres, small hard wear resistant particles and a melamine resin. The surface layer may also comprise thermoplastic material, for example, vinyl particles, which are applied in powder form on a surface. This allows that the print may be injected in the vinyl powder particles. An improved design and increased wear resistance may be reached even in such materials.
[0052]A suitable printer head has to be used in order to obtain a high printing quality and speed in powder based layers and other layers as described above. A printer head has several small nozzles that can shoot and apply droplets of inks in a controlled way.
[0053]Industrial inkjet systems, are broadly classified as either continuous inkjet (CIJ) or drop on demand (DOD) systems.
[0054]CIJ ejects drops continuously from the print head. The drops pass through a set of electrodes, which impart a charge onto each drop. The charged drops then pass a deflection plate which uses an electrostatic field to select drops that are to be printed and drops to be collected and returned for re-use.
[0055]DOD ejects drops from the print head only when required and all drops are applied on the surface.
[0056]CIJ is primarily used for coding and marking of products. DOD inkjet technology is currently used in most existing industrial inkjet applications where a high quality décor is required.
[0057]A normal size of an ink droplet is about 2-4 picoliters (=1*10−12 liter or 0.000001 mm3). The size of each droplet may vary, dependent on ink type and head type, normally between 1-40 picoliters and this corresponds to a droplet that has a diameter of about 10-30 microns. Smaller droplets enable high-resolution images. Some printer heads can shoot different droplet sizes and they are able to print a grey scale. Other heads can only shoot one fixed droplet size. It is possible to design print heads that may fire bigger drops up to 100-200 picoliters or more.
[0058]Several technologies may be used to shoot the drops out of the nozzles.
[0059]Thermal print head technology generally referred to as bubble jet printing, use print cartridges with a series of tiny chambers each containing a heater. To eject a droplet from each chamber, a pulse of current is passed through the heating element causing a rapid vaporization of the ink in the chamber to form a bubble, which causes a large pressure increase, propelling a droplet of ink out through the nozzle and to the surface. Most consumer inkjet printers use thermal printer heads. Such thermal printers are generally designed to apply water based inks with a viscosity of 2-5 centipoise (cps)
[0060]Recently large-scale thermal print heads with a printable width of 223 mm and with a printing speed of about 20 m/min or more have been developed by Memjet. The print head contains 5 ink channels and two rows of nozzles per channel. Each individual nozzle structure is about 30-microns across, enabling 800 dpi, with the second row of nozzles for each colour slightly offset from the first to deliver 1600 dpi in combination. A Memjet print head can continuously fire up to 750 million 2 picoliters drops with a 14 micron drop diameter per second. The print head cost is less than 10% of the costs for conventional Piezo heads with similar capacity. Such thermal printers may apply water based substances with a viscosity of 0.7-1.5 centipoise which is similar to water viscosity (1 centipoise at 20° C.). The Memjet print head comprises a self-cooling system with the heating element in the middle of the ink chamber. As drops are ejected, new ink flows into the chamber and cools the heating element.
[0061]Thermal technology imposes the limitation that the ink must be heat-resistant, generally up to 300° C. because the firing process is heat-based. This makes it very difficult to produce pigment based multi colour thermal heads. The Memjet print heads are designed for dye based ink and are therefore not used in the flooring industry and in industrial applications where high quality pigment based inks are required.
[0062]Most commercial and industrial inkjet printers and some consumer printers use the piezoelectric printer head technology, which is the major technology used in the flooring industry. A piezoelectric crystal material (generally called Piezo) in an ink-filled chamber behind each nozzle is used instead of a heating element. When a voltage is applied, the piezoelectric material changes shape, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. A Piezo print head configuration may use different basic deformation principles to eject drops from a nozzle. These principles are generally classified in squeeze, bend, push and shear print head technologies. A piezoelectric crystal may also be used to create acoustic waves as it vibrates and to cause the ink to break into droplets at regular intervals. Piezo inkjet allows a wider variety of inks and higher viscosity than thermal inkjet. The ink has generally a viscosity in the range of 2-12 centipoise and is very suitable to apply pigment based ink. In industrial applications print heads that may handle high viscosity inks are often used since the initial viscosity of the ink decreases considerably during production when temperature may increase to 40° C. or more and a low initial viscosity may fall below the minimum level that is required for a proper functioning of the print head.
[0063]FIG. 1e shows how ink drops 56 are ejected according to the bend mode of piezoelectric material. A Piezo print head 30 comprises arrays of very small holes generally called jets 50 from which droplets 56 of ink 58, with pigments 12, are ejected on a paper surface.
[0064]The ink 58 flows from an ink container via an ink inlet 55 into an ink chamber 52. Electrical pulses bend a Piezo crystal 51 and a membrane 53. This deformation creates a pressure pulse that ejects an ink drop 56 from the nozzle 54. Different drop sizes may be formed by varying the electrical charge. The nozzles are typically about 10 microns in diameter. Typical drop volumes are in the range of 2-5 picoliters producing printed ink spot sizes 57 on a surface in the range of 10-20 microns. Each droplet may contain about 20% pigments. The remaining part is a liquid carrier and resins needed to connect the pigments to the surface.
[0065]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. The pixels, which represent images as a computer file, are of a uniform size and shape. They do not overlap and they 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) software, which takes an image file input and produces a colour profiled, screened, bitmap output that controls the print heads and provides the necessary data that is needed to apply an ink drop on a surface in a pre-determined raster pattern R1-R4 as shown in FIG. 1e.
[0066]A lot of ink types may be used. The main components are colourants that provide the colour, a binder that bonds the colourants to the surface and a liquid carrier that transfers the colorant and the binder from the print head in well-defined small drops to a surface with a non-contact application method. The colourant is either a dye or pigment or a combination of both. The carrier fluid may be water-based or solvent based. The carrier fluid evaporates and leaves the colourant on the surface. UV curable inks are similar to solvent based inks but the carrier fluid cures when exposed to strong UV light.
[0067]A main problem for all types of inks and print heads is that when ink dries by evaporation it may dry up and clog the nozzles. Industrial printers may be equipped with an ink circulation system that circulates the ink through the jets in order to increase the so called “decap” time which is the amount of time a print head can be left uncapped and idle and still fire ink drops properly. A short decap time or clogging may results in permanent nozzle loss and undesired lines may be formed over the whole surface when single pass printers are used. Especially pigment-based inks comprising polymer binders systems have a tendency to dry out and it would be a major advantage if the decap time could be increased and nozzle clogging could be avoided.
[0068]A dye is a colourant that is dissolved fully into the carrier fluid and the ink is a true solution. Pigments are very fine powder of solid colourant particles that are suspended or dispersed throughout a liquid carrier. Pigment based inks are generally individually mixed together by using colour pigments and several chemicals. Pigments used in digital ink are very small and have an average particle size of about 0.1 micron. The common size of the nozzles is about 10-20 microns, which means that the pigment particles have enough space to pass through the nozzle channels in the print head. The nozzles may still be blocked by the ink itself and pigments that form clusters of particles. High quality pigment ink should keep the pigment suspended in the carrier fluid for a long period of time. This is difficult particularly at the
发明内容：
[0099]The main objective of at least certain embodiments of the invention is to provide an improved and cost efficient printing method to apply colourants on a surface in well-defined patterns on preferably a floor panel surface by using digital ink heads that may apply a liquid substance on a panel surface.
[0100]A specific objective is to provide dry pigment based particles in powder form that may replace pigments in liquid ink and that may be used to create a high quality print.
[0101]The above objectives are exemplary, and the embodiments of the invention may accomplish different or additional embodiments.
[0102]Embodiments of the invention is based on a main principle where conventional digital printing methods are divided in two separate steps comprising a separate application of a liquid binder and of dry colourants. Coloured particles are applied on a panel surface. Some particles are bonded by a digitally formed pattern. Other non-bonded particles are removed and the remaining bonded particles form a digital pattern. This two-step process may be repeated and several colours may be applied such that an advanced multi colour high definition digital print may be formed. The bonded coloured particles and the panel surface are pressed together and an increased bonding is obtained. The pressing is made under increased temperature such that the coloured particles and the surface are cured to a hard wear resistant layer.
[0103]An advantage compared to conventional digital ink jet printing are that the coloured particles are not dispersed in a liquid substance and are not applied by a digital printing head on a surface. According to embodiments of the invention a print head is only used to apply a cost efficient and mainly water based binder without pigments. Embodiments of the invention makes it possible to combine lower costs for ink and digital print heads with improved productivity.
[0104]Pigment based colourants may be combined with very cost effective print heads that may be thermal print heads. The coloured particles may be pigment coated wood fibres or mineral particles and very realistic copies of wood and stone designs may be obtained with such decorative materials arranged in advanced high quality patterns.
[0105]An advantage compared to known powder based printing methods are that the coloured particles comprise a particle body that is coated with resin that reacts with the liquid binder. The coating is used to connect the pigments to the particle body but also to provide a binder when the resin is in contact with the liquid substance applied by a print head. The coloured particles have a material composition that provides an easy application and removal, appropriate bonding to the surface and a base for pigments that are firmly connected to a particle body such that floating of the small pigments may be avoided. The particles may have an appropriate size such that they may be pressed into a panel surface and this make it possible to apply pigments located on the lower side of a particle into the surface. Increased pigment bonding and wear resistance may be obtained compared to conventional methods where pigments are applied only on the upper surface parts.
[0106]A specific advantage is that the resin is adapted to a liquid binder that is suitable to combine with heat and pressure and that may be a very simple substance comprising for example water or glycol. No solvents or UV curing chemicals are required and this may provide a very environmental friendly and cost efficient production method.
[0107]A first aspect of the invention is a panel with a surface comprising a digitally formed print of macro colourants, the macro colourants comprising a particle body and colour pigments attached to an upper and lower surface of the particle body, wherein the macro colourants are arranged in patterns.
[0108]The particle body may comprise wood fibres.
[0109]The particle body may be a mineral particle.
[0110]The macro colourants may have a length or diameter exceeding 20 microns.
[0111]The macro colourants may form a solid print with overlapping macro colourants.
[0112]The panel may be a laminate or wood floor, a powder based floor, a tile, or a LVT floor.
[0113]The panel surface may comprise wood fibres and wherein the macro colourants are pressed into the surface.
[0114]A second aspect of the invention is dry ink comprising macro colourant particles for bonding to a liquid print applied on a surface by a digital drop application head, wherein the macro colourant particles each comprise:[0115]a particle body;[0116]a dry resin bonded to the particle body; and[0117]colour pigments bonded to the particle body,
wherein the dry resin is adapted to melt when the macro colourant is in contact with the liquid print and to bond the macro colourant to the surface.
[0118]The liquid print may comprises at least one of water, glycol, and glycerine.
[0119]The macro colourant particles may have a diameter or length larger than 20 microns.
[0120]The particle body may be a mineral particle or a fibre or a thermosetting resin.
[0121]The particle body may be an aluminium oxide particle.
[0122]The particle body may be a wood fibre.
[0123]The particle body may be coated with a thermosetting resin.
[0124]The dry resin may be a melamine formaldehyde resin.
[0125]The macro colourant particle may be coated with a first layer that bonds the colour pigments to the particle body and a second layer comprising the dry resin and applied on the first layer.
[0126]A third aspect of the invention is a method of bonding a dry ink to a surface, the method comprising bonding macro colourant particles to a liquid print applied on a surface by a digital drop application head, wherein the dry resin melts when the macro colourant contacts the liquid print to bond the macro colourant to the surface.
[0127]The liquid print may comprises at least one of water, glycol, and glycerine.
具体实施方式：
[0144]FIGS. 2a-2d show schematically an embodiment of the invention, which is based on a first principle where a binder pattern BP or image is formed digitally by an ink head that preferably only applies a binder 11 on a surface 2 as shown in FIG. 2a. Colourants 7, that may comprise small coloured particles, for example, pigments 12, are applied randomly preferably in dry form by a second device such that they are in contact with the binder pattern BP. FIG. 2b shows a preferred embodiment where pigments 12 in dry form are scattered over the binder pattern BP. FIG. 2c shows that the binder 11 connects some pigments 12 that form the same pattern as the binder 11 and a print P is formed on the surface 2 when other non-bonded pigments 12 are removed from the surface 2 by, for example, vacuum.
[0145]This three-step process, hereafter referred to as “print forming cycle”, when the process relates to a one colour application, or “Binder And Powder printing”, or BAP printing, when the process refers to the whole print and where preferably a liquid binder 11, hereafter referred to as “blank ink” and dry particles comprising colourants 7, hereafter referred to as “dry ink”15, are applied separately and bonded together and where non-bonded particles are removed, may provide a digital print P with the same or even superior quality as conventional digital printing technology.
[0146]The surface 2 may be a paper layer or a foil or a powder layer.
[0147]The surface 2 may be a part of a building panel or a floor panel 1.
[0148]The binder may be blank ink 11 comprising a liquid substance that is preferably applied by a digital ink head.
[0149]The liquid substance may be water based.
[0150]The surface 2 with the bonded colourants 7 may be heated and pressed.
[0151]The surface 2 and the colourants 7 may be pressed and cured to a hard surface with an embossed structure.
[0152]The colourants 7 may be macro colourant particles larger than 20 microns and they may be pressed into the surface 2.
[0153]The surface 2 may be a part of a panel 1 that may be a laminate or wood floor, a powder based floor, a tile or a LVT floor.
[0154]The liquid blank ink may be replaced with a digital heating process where heat from a digital heating print head or a laser activates a binder included in the dry ink and/or in the surface.
[0155]The blank ink and the dry ink may be applied in many alternative ways. The surface 2 may point upwards or downwards and the blank and/or the dry ink may be applied from above or from below. A surface 2 with blank ink may, for example, point downwards and may be brought into contact with a dry ink layer. Non-bonded dry ink may be removed by gravity when the surface is separated from the dry ink layer. In order to simplify the description, the majority of the preferred embodiments show a surface pointing upwards and attached to a panel prior to printing. Separate surfaces 2 without a supporting panel 1 may be printed according to the principles of the invention.
[0156]The method is particularly suitable in applications where considerable quantities of colourants, preferably pigments, are applied on a large flat panel in order to form an advanced large print or decorative pattern with preferably high wear, impact and UV resistance and where the pattern preferably is intended to copy a wood or stone design. Such designs are generally formed with one base colour that, for example, gives the wood or the stone the basic appearance and a few spot colours that are used to form the wood grain structure, knots, cracks and various defect which are visible in the wood surface or crystal structures cracks and other defects in a stone design. The method is also very suitable to form a pattern on a tile or to print laminate and powder based floors with a copy of, for example, a tile floor that comprises tiles with different colours and grout lines between the tiles.
[0157]Contrary to known methods, the digital ink head, hereafter referred to as “digital drop application head”30′, is not used to apply any type of conventional ink with colour pigments or dyes. This is an advantage since no expensive inks comprising pigment dispersions and binder resins have to be handled by the digital drop application head 30′. The blank ink is preferably an essentially transparent liquid substance that preferably mainly comprises water.
[0158]The blank ink, also called liquid substance, comprises preferably no pigments.
[0159]A print provided by the blank ink or liquid substance may be referred to as a liquid print P. The liquid print may be formed of drops of the blank ink applied on the surface.
[0160]The colourants are preferably bonded to the surface in two steps. The first bonding is an application bonding where the bonding of the colourants should be sufficient to keep the colourants connected to the binder pattern BP in order to allow the remaining excessive colourants that have been applied on areas outside the binder pattern, to be removed.
[0161]The second bonding is a permanent bonding intended to connect permanently the application-bonded colourants to the surface 2.
[0162]The first application bond and the second permanent bond may comprise an intermediate stabilization step where the structure of the bonded colourants are modified by, for example, heat and/or pressure such that a new print forming cycle may be made. The intermediate stabilization step allows that the new non-bonded colourants that are applied on the surface during a second print forming cycle may be easily removed even on surface parts that comprise colourants from the first print forming cycle.
[0163]The first application bonding is preferably obtained with a liquid substance, also referred to as blank ink, that preferably mainly comprises distilled or deionized water. The adhesion of water may in some application, especially when only one colour is applied, connect the colourant to the surface with a force that is sufficient to allow removal of the non-bonded colourants. The production costs for such a liquid substance are extremely low and clogging of the nozzles when a binder dries may be avoided. Some chemicals may be added, for example glycol or glycerine, that are needed to reach the viscosity and surface tension of the liquid substance that may be needed for a proper function of a print head. Water-soluble polyethylene glycol (PEG), that is available in many different molecular weights, is especially suitable to modify water such that a blank ink with an appropriate viscosity that works, for example, with Piezo heads may be obtained. Low monocular weight formulations such as, for example, PEG 400 are especially suitable to use in blank ink and preferably together with dry ink or a surface that comprises thermosetting resins such as melamine. Water and PEG are compatible with melamine resins and allows easy and fast curing when heat and preferably also pressure is applied. A preferred nondrying solvent that is compatible with thermosetting resins should be miscible with water, have a boiling point above 100° C. and a melting point lower than the application temperature.
[0164]Examples of such, but not restricted to, are ethylene glycol, propylene glycol, polyethylene glycol, diethylene glycol, butane diol and glycerine. Combinations can also be used. In some applications some other minor amounts of chemicals may be included in the blank ink, for example, wetting agents and other chemicals that are needed to prevent bleeding when the blank ink is applied on a surface. The blank ink may also comprise release agents, especially when a direct application of the colourants, hereafter referred to as “direct BAP printing” as described above is replaced by a transfer application hereafter referred to as “transfer BAP printing” where the blank ink and colourants are in a first step applied on a transfer surface and then pressed against and bonded to the surface. Most such additives are cost efficient and the blank ink may have a production cost which is a fraction of the costs for conventional pigment based inks.
[0165]Most Piezo print heads are designed to work with a viscosity in the range of 2 to 12 centipoise (cps). The water based blank ink may easily be adapted to meet all possible viscosity requirements.
[0166]A suitable blank ink that preferably may be used in a low viscosity print head designed to operate with a viscosity of about 5 cps such as a Kyocera print head may be a water based glycol solution comprising, for example, about 75% (weight) Ethylene Glycol or 55% Diethylene Glycol or 50% Propylene Glycol or 38% Polyethylene Glycol PEG 400. A water based glycerine solution comprising about 40% glycerine may also be used. De-ionized water may also be mixed with Glycerine and Glycol. A suitable blank ink for a low viscosity print head may, for example, comprise about 40% water, 50% Glycerine and 10% Diethylene Glycol.
[0167]A suitable blank ink that preferably may be used in a high viscosity print head designed to operate with a viscosity of about 10-12 cps such as a Fuji print head may 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 Glycerine solution comprising about 65% glycerine may also be used. De-ionized water may also be mixed with Glycerine and Glycol. A suitable blank ink for a high viscosity print head may, for example, comprise about 30% water, 60% Glycerine and 10% Diethylene Glycol.
[0168]The water content for blank ink adapted for low and high viscosity Piezo print heads may be increased further if high viscosity glycols are used; for example, Polyethylene Glycol with a higher molecular weight than PEG 400. A preferred blank ink that preferably is suitable for Piezo print heads may comprise 0-70% water and 30-100% Glycol and/or Glycerine. Even more preferred is a formulation comprising 10-70% water and 30-90% Glycol and/or Glycerine. Blank ink that is suitable for thermal bubble jet print heads that are designed for very low viscosities; for example, 2-4 cps may comprise more than 70% water.
[0169]All blank ink formulations may comprise small amounts, about 1%, of wetting agents such as BYK or Surfinol and chemicals such as Actidice intended for control of bacteria and fungi.
[0170]The blank ink is preferably essentially a non-curable liquid substance that is used to obtain the application bonding and to bond the colorants until the final permanent bonding takes place preferably with heat and pressure and with resins that are a part of the substrate material and/or the dry ink particles. Such blank ink will not bond particles when it dries or when heat is applied.
[0171]The blank ink may comprise special curable binders, preferably water based acrylic emulsions, which are compatible with water, glycol or glycerine. Preferable binder content is 5-20%. Acrylic emulsions will bond particles when the water content evaporates and they will create a strong bond under high heat and pressure.
[0172]A high water content of at least 50% gives the advantages that the material cost may be low. The decap time will be rather short, less than one hour, since water evaporates. A low water content combined with a high glycol or glycerine content will increase the decap time considerably. Blank ink with a water content below 40% may have a decap time of several hours. Water content below 20% will give a very long decap time that may exceed 6 hours. It is possible to use blank ink that comprises more than 90% glycol and this may increase the decap time to several days. Blank ink may be made without water and high viscosity print heads may handle blank ink that comprises, for example, 100% Ethylene Glycol.
[0173]An ink circulation system may be avoided in industrial printers when blank ink is used that does not comprise any pigment dispersions or binders and that is mainly a water based solution as described above. This will decrease the cost for the printing equipment considerably.
[0174]FIG. 2e shows viscosity in cps of aqueous Propylene Glycol (PG) solutions in temperatures 20-30° C. W1 shows viscosity of water. Pg1 comprises 50% PG and 50% water. Pg2 comprises 70% PG and 30% water. Viscosity of blank ink adapted for a low viscosity print head may vary between 4-6 cps within the temperature range of 20-30° C. The viscosity of blank ink adapted to high viscosity print heads may vary between 8-14 cps and this may be outside the normal working conditions of the print head. This problem may be solved with printing equipment that comprises a temperature control system that preferably is combined with a climate control system that controls the humidity. Decap time for water based blank ink may be increased if the relative humidity around the print heads is above 50%.
[0175]The binder that bonds the colourants to the surface may comprise two components. The first binder component may be included in the blank ink. The second binder component may be included in the dry ink or the surface and activated by the blank ink. This makes it possible to use, for example, water in order to obtain the application bonding, stabilization and permanent bonding. Water may react with a binder that may be included in the colourants or in the surface. The blank ink may of course comprise a binder that may provide the same bonding as the two components mentioned above.
[0176]The blank ink may be applied on any surface 2, for example, a non-transparent paper layer, an essentially transparent overlay, a powder layer, a stabilized powder layer, a wood veneer or wood sheet, a tile glazing, a plastic foil or a base colour applied on a sheet shaped material preferably comprising wood or polymer material.
[0177]The application of the surface 2 to a sheet shaped material such as a panel 1 gives several advantages. Handling and positioning of loose layers that may swell and shrink during the application of liquid blank ink may be avoided. The application bonding of the colourants 7 may be made with a very low bonding strength since the surface 2 is supported by the flat panel and may be displaced horizontally on a conveyor directly into a press where the permanent bonding with heat and pressure takes place. Rolling, cutting and stacking of paper and foil surfaces may be avoided. Some surfaces such as uncured powder and tile glazing cannot be handled without a support of a panel 1.
[0178]BAP printing on LVT floors may also be made when, for example, the individual base layers, preferably including a glass fibre layer, and a decorative plastic foil with a base colour are fused together to a panel. A transparent protective layer may be fused with heat and pressure on the BAP print and the decorative plastic foil such that the dry ink particles are permanently bonded and fused to the surface. The blank ink may be adapted such that floating of the drops on the smooth plastic foil is avoided. It is an advantage if the blank ink has a high viscosity, preferably 10 cps and higher.
[0179]BAP printing on ceramic tiles is preferably made when the powder is pressed to a tile body forming a panel. A glazing with a preferably base colour is applied on the tile and a BAP print is applied on the dry glazing. The BAP print and the tile body is thereafter pressed and a protective transparent glazing is applied on the pressed print. The tile is after glazing fired in a furnace or kiln at very high temperatures such that the dry ink particles cure and melt into the tile body and the glazing.
[0180]Embodiments described above are based on the main principles that the BAP print is applied on a surface 2 that forms a part of a panel 1 and that also comprises a material composition such that when heat and pressure is applied, the panel, the surface and the print will be permanently bonded together. Such surfaces may comprise thermosetting resins, preferably melamine formaldehyde resins which generally are used in WFF or paper based laminate floors, curable and fusible mineral materials used in ceramic tiles, or thermoplastic materials used in LVT floors.
[0181]Direct and transfer BAP printing may also be used on textile surfaces. Dry ink and blank ink may be specially adapted for various textile surfaces. Binders, dry ink viscosity and the size or the colourants may be adapted to provide an appropriate bonding and removal of the colourants.
[0182]Application on some specific surfaces may be improved by a so-called corona treatment, sometimes also referred to as air plasma. This is a surface modification technique that uses low temperature corona discharged plasma to impart changes in the properties of a surface. The corona plasma is generated by the application of high voltage to sharp electrode tips, which forms plasma at the ends of the sharp tips. Materials such as plastics, glass or paper may be passed through the corona plasma curtain in order to change the surface energy of the material. The surface may also be treated with various types mineral salts.
[0183]The surface may comprise a first base colour, which may be used to create a major part of the coloured visible surface. Powder based surfaces, preferably comprising thermosetting resins, may be pre-pressed and formed with a smooth surface that facilitates the application and removal of the colourants. The pre-pressing is preferably made with pressure and heat and during a press cycle time that ensures that the melamine resin is in a semi-cured level and in an B stage as described in the introduction.
[0184]The colourant comprises, in a preferred embodiment, mainly colour pigments 12 that are scattered as dry powder layer over the wet binder pattern BP as shown in FIG. 2b. The pigments may be mixed with other particles, for example, melamine powder particles 13 that melt when they are in contact with the liquid binder pattern BP and that bond the pigments to the surface. The dry non-bonded pigments and melamine powder 13 may be removed by, for example, an air stream or gravity and the remaining wet melamine 13 and colour pigments 12 form a print P as shown in FIG. 2c which is essentially identical to the binder pattern BP created by the blank ink. Dry ink may have the same material composition as the surface layer 2 in a powder based WFF floor and may comprise a mix of woof fibres, a dry melamine formaldehyde resin powder, aluminium oxide particles and colour pigments.
[0185]The stabilization of the print may be partly or completely obtained by, for example, exposure to IR, hot air, UV lights, microwaves, pre-pressing or similar or combinations of such methods. The binder, that in this preferred embodiment is water or wet melamine, is preferably stabilized by pre-pressing that bonds the colour pigments to the surface 2 by drying the wet melamine or by melting the melamine particles. The pre-pressing compresses the surface of the printed pattern P. A second pattern may be printed with the blank ink on the surface 2 and a second layer of pigments and melamine powder may be applied on the surface and over the first print. This may be repeated and an advanced décor may be created with several colours such that the digital image comprises colourants with different colours positioned horizontally offset in the same plane.
[0186]The blank ink is preferably an essentially transparent liquid substance that does not disturb the colour of the bonded colourants. Blank ink with the same liquid substance may be used together with dry ink comprising many different colourants and this allows that, for example, one print head with the same blank ink may be used to apply several different colours that may be applied in several steps with an intermediate application of a digital pattern formed by the blank ink. This allows that the number of print heads may be reduced considerably since one print head with one ink channel applying the same blank ink may be used to apply a practically unlimited number of dry inks with different colours, structures particle sizes etc. The simple composition of the blank ink makes it possible to use more cost efficient print heads since no colour pigments are fired through the small nozzles of the print head.
[0187]The stabilization step may in some applications be sufficient to create the permanent bonding. The final permanent bonding may also take place when the surface preferably is pressed and cured 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. An UV curing transparent lacquer that is applied over the colourants and that after application is cured in an UV oven may also be used. This transparent layer may be applied in liquid form by rollers or with digital Piezo heads and in one or several steps with intermediate UV curing. A thermoplastic resin or thermoplastic particles may also be used to obtain the first application bond or the second permanent bonding. Paper based or powder based overlay comprising aluminium oxide and melamine resins may also be used as protective layers and as permanent bonding.
[0188]The low cost and the simple chemical composition of the liquid substance applied by the drop application head makes it possible to use rather simple digital print head technology to apply the liquid binder substance. CIJ (continuous inkjet) may be used since water is easy to recycle and the collected drops may even be disposed without any recycling. Cost efficient thermal print heads may be used since water is easy to handle with bubble jet technology. Rather simple Piezo heads with high productivity and with DOD (drop on demand) systems may be used that may have a long life time and that require a minimum of maintenance due to the very favourable composition of the liquid substance that will not cause any production disturbance since there are no pigments and preferably no fast drying resins that must be handled, which is the case when conventional pigment based inks are used.
[0189]The binder may comprise a wide variety of thermosetting and thermoplastic materials that may be used as particles or chemicals in the surface, in the dry ink or as dispersions in the blank ink applied by the digital drop application head. The majority of such materials may be produced in dry powder form or as liquid dispersions. It is preferred that the chemical substance that provides the bonding after drying is included in the surface or in the dry ink and that the blank ink is a simple liquid chemical substance without any resins or other chemicals that in dry form may clog the nozzles.
[0190]As an alternative to thermosetting materials such as melamine or to thermoplastic materials such as, for example, PVC powder, UV cured polyurethane may, for example, be used in powder form or as dispersion.
[0191]UV curable polyurethane substance with a viscosity that is adapted to the digital drop application head 30′ may be used. Water-based polyurethane dispersions are preferred as a liquid substance in the digital drop application head since they do not cure until they are exposed to UV light. Polyurethane dispersions are fully reacted polyurethane/polyureas of small and discrete polymer particles and such particles may be produced with a size of about 0.01-5.0 microns and may therefore be handled in a digital print head or other similar heads. Polyurethane dispersions may be blended with, for example, acrylic emulsions and other emulsions in order to reduce costs.
[0192]The digital drop application head, that in some applications preferably may be a Piezo head, has preferably a capacity to fire drops with a drop size of about 1-200 picoliters or more. The drop size and drop intensity may be varied and this may be used to vary the intensity of a colour and to create a so-called “grey scale” with the same basic colour. Larger drops will bond thicker layers of dry ink and smaller drops will bond thinner layers.
[0193]Water based adhesives may also be used such as soluble adhesives or water dispersed adhesives.
[0194]Other UV cured materials such as acrylates of epoxy, urethane, polyester, polyether, amine modified polyether acrylic and miscellaneous acrylate oligomers may be used as binders in powder form or as dispersions.
[0195]The blank ink may also be applied on a surface by spray nozzles or by engraved rollers.
[0196]FIG. 2d shows schematically one BAP printing station 40 of a binder printing equipment that may be used to create a digital print P on a panel 1 comprising a surface 2, a core 3, and a backing layer 4. A blank ink application station 36 comprising a digital drop application head 30′, that preferably is a Piezo head or a thermal print head, applies a binder pattern BP with blank ink 11. Several heads 30′ may be positioned side by side in order to cover the width of the surface that is printed. The binder pattern is created digitally in the same way as in conventional digital printing. The colours are separated and each blank ink application station 36 applies mainly the same liquid substance or blank ink that is used to bond one specific colour in each print forming cycle. The digital drop application head is connected with a feeding pipe 32 to a container 31 with blank ink. The digital drop application heads 30′ are digitally connected with preferably data cables 33 or wireless to a digital control unit 34 that controls the application of the drops, the speed of the conveyor 21, the function of a dry ink application unit 27 and all other equipment that is used to bond and remove pigments.
[0197]The water based drops of the blank ink 11, which in this embodiment serve as an application binder, should be wet until they pass the dry ink application station 27 that in this preferred embodiment is a scattering station. Dry ink 15, that in this preferred embodiment comprises colourants of colour pigments 12 mixed with a resin of spray dried melamine powder 13, is scattered on the liquid blank ink 11.
[0198]The scattering equipment comprises a hopper 45 that contains dry ink 15, a doctor blade 47 that together with a roller 46, preferably comprising an engraved, embossed, etched or sand blasted roller surface 44, acts as a dispensing device that moves a pre-determined amount of dry ink 15 from the hopper 45 and to the surface 2. The roller 46 may also have a roller surface 44 that comprises small needles. Rotating and oscillating rollers may also be used. A material-removing device that may be an oscillating or rotating brush 48 may also be used in some applications together with one or several rotating or oscillating meshes 49 that may oscillate or rotate in different directions.
[0199]The doctor blade 47 may be rigid or flexible and may have an edge that is adapted to the structure of the roller surface. The oscillating or rotating meshes 49 may also be formed such that they spread the dry ink 15 in a pre-defined way and they may be combined with one of several nets that may be used to sieve the particles before they are applied as a layer. The rotation of the roller, the position of the doctor blade and the speed of the surface that is intended to be covered with the dry ink may be used to control the layer thickness.
[0200]The liquid blank ink 11 and the dry ink with pigments 12 and melted melamine particles 13 is in this embodiment heated and stabilized when it is displaced under preferably a hot IR lamp 23, which is located preferably after the digital drop application head 30′ in the feeding direction.
[0201]A dry ink removal station 28, that in this embodiment is based on air streams and vacuum, removes pigments 12 and melamine particles 13 that are not wet and not bonded by the binder pattern BP and a perfect colour print P is provided. The dry ink removal station may be located after the IR lights 23 or between the IR lights and the scattering station 27. This production step may be repeated and a second scattering station 27 that comprises another colour may apply a second colour on a binder pattern that may be applied by the same print head or a new print head that is used in a second print forming cycle. The removed dried pigments and melamine particles may pass through a sieve or a filter and they may be recycled and reused again several times.
[0202]The panel 1 with the surface 2 is preferably displaced essentially horizontally under the digital drop application head 30′, the dry ink application station 27 and the dry ink removal station 28 with one or several conveyors 21. It is obvious that the digital drop application head 30′, the dry ink application station 27 and the dry ink removal station 28 may alternatively be displaced over a panel 1 during the BAP printing.
[0203]The dry ink may in addition to pigments and melamine particles also comprise wear resistant particles, such as small aluminium oxide particles, and fibres, preferably wood fibres, that preferably may comprise or consist of bleached transparent or semi-transparent fibres. Such dry ink may be used to create a solid print with pigments that are positioned vertically above each other with binders and wear resistant particles above and below the pigments. Small drops of blank ink may due to capillarity and the combination of surface tension and adhesive forces penetrate into the dry ink and bond larger amounts of dry ink than an application with conventional ink where pigments are applied as small drops on a surface.
[0204]A preferred embodiment of BAP printing is characterized in that the vertical extension of the colourants exceeds the vertical extension of the blank ink drops. Another preferred embodiment is characterized in that the digitally applied blank ink drops penetrate downwards and upwards from the surface after application. A very wear resistant print may be obtained with a printing method comprising blank ink and dry ink with wear resistant particles preferably incorporated in the dry ink.
[0205]Several layers of prints may be position above each other and this may be used to increase the wear resistance further and to create 3D decorative effects.
[0206]Static electricity or ultrasound may be used to apply and/or to remove the non-bonded powder particles. Airstreams and vacuum that blows away and/or sucks up particles may preferably be combined with brushes. In general, all dry and wet methods that are used to remove dust may be used separately or in various combinations to remove the non-bonded parts of the dry ink. However, dry and non-contact methods are preferred.
[0207]A controlled complete or partial removal of the non-bonded dry ink particles is essential for a high quality print with a pre-defined decorative image. Advanced removal systems may also be used that only removes the colourants, for example, colour pigments while an essential part of the transparent melamine powder particles may remain on the surface. This may be accomplished by, for example, a two-step application where a first layer comprises only melamine resin or particles that are applied to the surface prior to the application of the blank ink with the colourants. This first layer is preferably stabilized. It may be sprayed with water and dried by, for example, IR or hot air. This separate binder layer that preferably comprises melamine may in some applications replace, for example, pre-impregnated paper, that in some application may be used as a surface layer 2, and only non-impregnated paper with or without a base colour may be used as a surface 2 for the print application cycle.
[0208]The moisture content of the surface layer should be accurately controlled in order to facilitate the removal of the non-bonded powder particles. Moisture content below 8% or even more preferably not exceeding 6% is preferred. The surface layer 2 may be dried by, for example, IR lamps prior to the application of the blank ink. Special chemical may be applied in order to seal the surface 2 or the upper part of the bonded colourants in order to create a sealing or a release layer that may prevent colourants to stick to specific parts of the surface layer where no blank ink is applied.
[0209]The floor panel 1 comprises generally a lower balancing layer 4 of laminate, plastic foils, coated paper or like material. Such balancing layer may also be applied as a dry mix of melamine powder and wood fibres, which are stabilized by moisture and heat prior to pressing. Pigments may be included in the powder mix to provide a base colour. The balancing layer may also comp