RU2636516C2 - Method for applying coating on construction panel by method of digital printing or digital coating - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: in method for applying a coating on a construction panel (1) having a decorative wooden surface (5), a UV-curable coating layer is applied by a digital printing head (30) to the decorative wooden surface (5) of the construction panel (1) by means of applying the UV-curable coating drops with the digital printing head (30). The drops are arranged so that they overlap each other. The UV-curable coating layer is then cured by UV radiation (23), thereby forming a transparent protective surface layer (L1, L2, L3). The decorative surface (5) is visible through said transparent protective surface layer (L1, L2, L3). The floor panel (1) has a core (3), a surface layer (2) comprising a surface (5) of a wood material, a print (P), and transparent layers (L1, L2, L3). The lower transparent layer (L1) is under the print (P). The upper transparent layer (L3) is above the print (P). The lower transparent layer (L1) is a UV-curable polyurethane. A part of the wood material surface (5) and the print (P) form a part of the visible surface layer (2), and the print is at least partially synchronized with the visible design and/or the structure of an individual floor panel. In the method for forming the decor on the construction panel (1), by means of a digital control system (39) of technical vision, providing the digital input to the digital printing head (30), a digital image of the surface (2) of the construction panel (1) is created by means of the digital control system (39) of technical vision. In addition, the digital control system of technical vision is used to provide the digital input to the digital printing head (30) based on said digital image. Thereafter, digital printing is performed on at least a part of said surface (2) of the construction panel (1) by means of the digital printing head and by means of a print. The print is at least partially adapted to the digital image of said surface (2) of the construction panel (1).

EFFECT: improving the surface quality and improving the design of wooden building panels.

21 cl, 11 dwg

Description

Technical field

The invention relates, in general, to the field of panels with a decorative wear-resistant surface, preferably floor and wall panels. The invention relates to building panels with such decorative surfaces and to manufacturing methods for the manufacture of such panels.

Application area

Embodiments of the present invention are particularly suitable for use in floors that can be formed from floor panels comprising a core, a decorative layer and a transparent wear-resistant layer on top of the decorative layer. Therefore, the following description of the known method, the problems of known systems, as well as the objectives and features of the invention, will be given as a non-limiting example, oriented to this field of application, and in particular to decks similar to ordinary decks from wood and laminate.

It should be emphasized that embodiments of this invention can be used to manufacture the surface layer in any type of panel, for example, building panels, such as wall panels, ceilings, as well as furniture components and similar components.

BACKGROUND OF THE INVENTION

Most of all laminate floors are made in accordance with a manufacturing method, commonly referred to as a direct pressure laminate (DPL) manufacturing method. The floors made in this way contain a core of a fiberboard 6-12 mm thick, an upper decorative surface layer with a thickness of 0.2 mm laminate and a lower balancing layer with a thickness of 0.1-0.2 mm laminate, plastic, paper or similar material.

The surface layer of laminate flooring is characterized in that its decorative and wear properties are generally obtained using two separate layers of paper stacked one on top of the other. The decorative layer is generally printed paper, and the wear layer is transparent overlay paper that contains small particles of aluminum oxide.

The printed decorative paper and overlay are impregnated with melamine resins and layered on a wood fiber core in large-sized presses for forming laminated plastics, where the resin is cured by strong heat and high pressure, and the said papers are layered on the core material.

The floor of laminate is made in the form of floor plates, in the general case, with a size of 2.1 × 2.7 m, and after pressing, they are divided into several separate floor panels, in the general case, with a size of about 1.3 × 0.2 m The edges are subsequently machined and equipped with mechanical locking systems.

Laminate floors can also be made using printing technology. One advantage is that the pressing operation can be avoided and that printed papers are not required to provide a decorative, wear-resistant surface.

Floor panels with a direct print laminate surface comprise a core of high density wood fiber board (HDF) of the same type as SPD. Decor is printed directly on the core. The manufacturing process is quite complicated and cost-effective only with very large volumes of production.

In a first step, a combination of water-based painted primers and sealants is applied to the core to provide core adhesion and basic color. Such a coating is referred to as an adhesive coating in the following text.

To print the decor using a multi-color printing machine with rollers that print directly onto a pre-compacted core, water-based inks are used. The layer with the printed decor must be protected from wear. In some cases, a paper-based overlay is used, and the plate is pressed in a traditional press to form laminate. The most common way to achieve high abrasion resistance is to use anti-abrasive UV sealants, which are then applied to the print with rollers and cured by ultraviolet radiation. You can also get structured and synchronized surfaces through embossed rollers. A few layers are applied to the print. To increase the thickness of the protective layer, soil coatings are used, and coating coatings are used to ensure the resistance of the final structure to contact mechanical damage. The embossed structures may be formed by embossed rollers, which may also have a structure comprising a circumferential register of the printing cylinders.

Direct printing technology can be replaced by digital printing technology, which is much faster to change, so that it can be used to make cost-effective production in small volumes. The difference between these two methods lies mainly in the printing phase, where the printing rollers are replaced by a contactless digital printing process and where the desired image is applied directly to the core, previously subjected to finishing processing. In conclusion, a transparent coating is applied that protects the digital image, and structured surfaces are usually the same type as those used in direct printing. You can create printed images of any type, but the surface structure is always limited by the shape of the embossed rollers or structured films that are pressed to the surface.

Digital printing can also be used to print on a sheet of paper, which is used in conventional laminate manufacturing. The digital fingerprint can be applied on the upper side of the decorative paper, which has a basic color, or on the lower side of the overlay, and this can be done before or after impregnation. The print can also be done on raw paper, with or without a base color, and the paper can be impregnated directly during pressing - with resin from a powder, a layer of liquid or an impregnating paper applied above and below the paper for digital printing. Raw paper can be connected to the core before the digital printing step, and this allows the use of thinner raw paper, and positioning problems can be mitigated.

Recently developed floors of a new type - “paperless” - with hard surfaces containing an essentially homogeneous mixture of fibers, binders and wear-resistant particles. This floor is called fiberboard (wood fiber floor, WFF).

The wear resistant particles are preferably alumina particles, the binders are preferably thermosetting resins such as amino resins, and the fibers are preferably wood-based fibers. In most applications, a homogeneous mixture includes decorative particles, such as color pigments, for example. In the general case, it is preferable to apply all of these materials in a dry form — as a mixed powder — onto the core of the fiberboard and cure by heating and applying pressure to obtain a continuous layer 0.1-1.0 mm thick.

You can get several advantages over the well-known technology, especially over traditional laminate flooring:

- the wear-resistant surface layer, which is a homogeneous mixture, can be made thicker and achieve wear resistance, which is much higher;

- you can get new and very promising decorative effects with deep embossing and through decorative materials that can be embedded in a homogeneous surface layer and coordinated with embossing;

- using a homogeneous surface layer, which is thicker and has a higher density, it is possible to achieve increased resistance to shock;

- a homogeneous surface layer may contain particles that have a positive effect on the acoustic and wetting properties;

- since it is possible to use cheap and even reusable materials, and several stages of manufacturing can be eliminated, it is possible to reduce production costs.

Powder technology is very suitable for producing a decorative surface layer, which is a copy of stone and ceramics. However, it is difficult to create designs, such as, for example, wood surroundings. However, recently developed digital powder printing, and now it is possible to create very promising designs of any type by introducing a digital fingerprint into the powder before pressing.

Wood flooring is obtained in many different ways. Traditional wooden floors have been developed, which are built-in floors with wood layers applied to a core made of wooden plates, fiberboard or plywood. Most of these floors come in the form of pre-finished floors with a wood surface, which is covered with several transparent layers at the manufacturer. Wood flooring is one of the largest applications of the coating process using rollers and curing using ultraviolet radiation (UV curing), which involves the application of multilayer coatings to seal and protect the surface of a tree. Typically, for transparent backing layers, an environmentally friendly, UV-curable, water-based polyurethane is used (water-based, UV-curable, polyurethane). This application process usually involves the application of several types of transparent coatings - UV cured primers, fillers, sealants and topcoats (UV primers, UV fillers, UV sealants and UV coatings). Each coating layer has its own function. Surface characteristics like abrasion resistance, hardness, resistance to contact mechanical damage, etc., can be adjusted to suit different quality requirements. All such layers are applied by roller coating devices, and each individual layer is UV cured. A high-quality wooden floor may contain a transparent protective layer with a mass of about 60-120 g / m ² , and about 5-10 layers or more can be applied by means of rollers in stages with intermediate UV curing.

As a first step, an adhesive coating is rolled to form a bond between the wood and the subsequent finishing coatings. Depending on the type of wood used in the floor and the desired final appearance, the next step can take place at a filler station where a UV curable filler (UV filler) can be applied, and the UV oven cures this filler in one or several steps. At the next stages, priming is carried out, which provides the main thickness of the transparent surface, and in conclusion, a final finishing is carried out, involving the application of several coating coatings using roller coating devices. The number of coatings used depends on the manufacturer, but each coating is followed by a passage through the UV curing oven.

Nearly all manufacturers of high-quality wood flooring use wear-resistant particles, such as alumina particles in some or more layers, to increase the wear resistance of a transparent surface. Transparent coating coatings that resist contact mechanical damage contain nanoparticles that provide high levels of resistance to contact mechanical damage.

Recently, some laminate floors have been produced with transparent coatings based on UV-curable substances over resin-impregnated surfaces, for example over decorative paper or melamine-formaldehyde resin impregnated paper or overlay, to provide a smoother surface that resembles a wood surface . Smooth floors with a foil surface or a polyvinyl chloride (PVC) surface - the so-called luxury vinyl flooring (VCL) (LVT) - use a transparent polyurethane coating as a covering to increase the deformation resistance and wear resistance of vinyl floors.

The transparent protective layers applied and structured by the roller are very important parts of the floor surface technology and would constitute their main advantage if such applications could be implemented in a more cost-effective and fast-moving manner and with improved properties, mainly in the context of design and quality .

Definition of some terms

In the following text, the visible surface of the installed floor panel is referred to as the “front side”, and the opposite surface of the floor panel facing the raised floor is called the “back side”. By “surface layer” are meant all layers that give the panel its decorative properties and its wear resistance and which are applied to the core closest to its front side, preferably covering the entire front side of the floor plate.

By “coating” is meant a layer of a substance sprayed on top of a surface for protection or decoration.

By “imprint” is meant a decor or an image. By “adhesive coating” is meant the application of layers or primers that are used to improve the bonding between the core material and other layers applied to the core. Under the "primer coating" refers to layers that are used to increase the thickness of the transparent protective layers. “Topcoat” refers to topcoats applied to a primer to give resistance to contact mechanical damage and final gloss levels.

The word “up” refers to the direction to the front side, and the word “down” refers to the direction to the back side.

By “pigments for printing ink for digital printing” is meant a material that changes the color of reflected or transmitted light as a result of absorption with selectivity along the wavelength.

By “dye-based paint” is meant a colored substance having an affinity for the substrate on which it is applied. In general, the dye is applied in an aqueous solution, which may also contain a binder, and may require etching to improve the dye's resistance to fiber. Unlike pigments, which are some insoluble particles, the dye is completely soluble in water like sugar.

By “water-based or water-based printing ink” is meant a printing ink in which water is used as a liquid substance. Water-based fluid is a carrier of pigments. Some binder is also present in the system to bond the pigments to the substrate.

By “solvent based printing ink” is meant a printing ink that generally contains three main constituents, such as a fluid carrier, pigments and resins. Technically, “solvent based ink” is a term referring only to an oil-based ink carrier portion that carries other components in liquid form and evaporates immediately after being sprayed onto the surface.

By “UV-curable printing ink or coating” is meant a printing ink or coating that is or which, after application, is cured by exposure to UV radiation in a UV oven.

Well-known method and its attendant problems

A common feature of all such floors, as described above, which contain a transparent protective layer over the decorative layer, is that such transparent layers are applied by rollers. The problems associated with applying transparent layers will be described below with reference to wood flooring.

In FIG. 1a shows the coating of the rollers on a panel 1, which is transported under the rollers and UV-cured on the conveyor 21. The transparent layers LI, L2, L3 are applied by the rollers 22a-c and cured by the UV ovens 23a-c in several steps.

In FIG. 1b shows the coating by rollers on a floor panel 1 with wooden surfaces 2 and a mechanical locking system comprising a tongue 10 and a tongue groove 9 for vertically locking the edges and a strip 6 with a locking element 8 that interacts with the locking groove 14 in the adjacent edge for horizontal locking of the edges . Roller coating is complicated when the coating is applied to a surface that is not completely flat. It is difficult to avoid marks at the short edges of the floor panel where the roller 22 meets the edge 15a and leaves the edge 15b. Such problems are especially associated with those floor panels that are coated as separate panels, i.e. not as large plates that are divided into several separate floor panels after coating, and as separate floor panels that are provided with a mechanical locking system before coating the surface and which contain an edge that is not fully supported vertically by the lower edge 16. It is also difficult apply the bevels 15a, b on the long and short edges, and flowing over the edges can change the blocking geometry. Coating on individual floor panels may be applied before forming the blocking system and / or bevels. This method gives very sharp edges, which may contain small cracks, and it is necessary to apply the coating to the bevels in a separate operation, where the overflow of the coating material can create undesirable visual edge effects.

Coating production lines equipped with stations with rollers and UV curing furnaces are usually very long and can be 50-100 m long. Rubberized rollers have a limited service life and must be cleaned when new coatings are applied. Structured rollers are expensive and able to form only a predetermined embossed pattern, which cannot be changed during manufacture until the structured roller is replaced with another embossed roller. If it was possible to apply the coating in a non-contact manner with increased accuracy and quick readjustment, this would be a significant advantage.

The following describes the general technology used in the industry to provide digital printing. The methods described below can be used individually or in combination, creating a digital fingerprint or providing digital application of a substance in the embodiments of this invention.

High-resolution digital printers use bumpless printing processes. The printing device has printheads that very accurately “shoot” ink droplets from the printheads onto the substrate.

Multipass printing, also called scanning printing, is a printing method when the head of the printing device transversely moves over the substrate many times to generate an image. Such printers are slow, but one small printhead can generate a larger image.

Industrial printing devices are generally based on a single pass printing method involving the use of stationary heads of a printing device with a width that corresponds to the width of the print media. Under the heads moves the substrate for printed information. Such printing devices have a large capacity and are equipped with stationary printing heads that are aligned one after the other in the feed direction. Each head prints in one color. Such printing devices can be made to order for each application.

In FIG. 1c shows a one-pass printing apparatus 35 comprising five digital printheads 30a-e, which are connected by ink tubes 32 to ink containers 31 filled with inks of different colors. The printing ink heads are connected by digital data cables 33 to a digital control unit 34 that controls the supply of ink droplets and the speed of the conveyor 21, which must be able to move the panel under the print heads with high accuracy to guarantee a high-quality image containing several colors. In order to avoid clogging of nozzles, ink is generally circulated through the print head, ink tubes and the ink container.

The typical width of an industrial printhead is approximately 6 cm, and segments of any length can be printed. Using digital printers containing several rows of print heads aligned side by side, you can print wide areas of 1-2 m in size.

Recently, printheads have been developed that can apply 5 different colors and can have a width of about 20-30 cm. Digital printers are capable of printing images with high resolution at speeds exceeding 60 m / min. Significant improvements are continually being made in the context of speed, resolution, investment and printing costs.

The DPI setting is used to characterize print quality through a digital printing device. It describes the resolution of dots per inch in a digital fingerprint.

The relatively low resolution is typically below 100 DPI. This provides high printing speed and low ink content. 200 DPI is generally sufficient to provide prints that can be used in decking applications. 300 DPI is generally sufficient, for example, to print structures of wood fibers of the same quality as that used in conventional laminate flooring.

Industrial printers can print drawings with a resolution of 300-1000 DPI and even more.

Ink may be spot color inks. In such an embodiment, the printing ink is specially prepared and adapted to a specific color suitable for a particular image. Instead of creating color by mixing the pixels of the CMYK colors, the ink that produces the spot pixel has a specific, predetermined color.

The fingerprint may be a “full fingerprint”. This means that visible print decor is created primarily through pixels of printing inks applied to the powder or applied to the surface of the paper. The color of the powder layer or the base color in such an embodiment has, generally speaking, a limited effect on the visible pattern or decor.

A fingerprint may also be a “partial fingerprint”. The color of the other - underlying - layer is one of the colors that are visible in the finished decor. The area covered by the printed pixels and the amount of printing ink used can be reduced, and due to less use of printing ink and a larger print volume compared to a full printed image, a reduction in costs can be obtained.

The print can be based on the CMYK color principle. This is a 4-color system, which includes cyan, magenta, yellow and black. Mixing them together gives a color space that is relatively small, or a color palette that is relatively small. To increase this space or this palette, you can add a specific color or spot colors of the entire spectrum. Spot color can be any color. You can use additional colors, such as orange, green, blue, red, light gray, as well as light shades of purple and cyan or white. These colors can be used individually or in combination. Color mixing and control is carried out using a combination of software and hardware (print processors and / or printheads).

Valinge Innovation AB has developed a new technology that enables the incorporation of a digital fingerprint into a powder layer. A high-resolution print in a powder layer requires a special software program and its implementation in relation to a specific printing ink, to a specific printing method, to the distance from the print head to the powder layer and to the powder used. To control the print speed, the position of the ink droplets, the volume and shape of the ink droplets, use the Digital Powder Processing Process of Raster Images or DP-RIP.

Processes such as DP-RIP can be developed that provide a print or decor that can be positioned in several dimensions, for example, in powder-based surfaces, horizontally and vertically at different depths. This can be used to create bulk effects when transparent fibers are used, and to increase wear resistance. A particular advantage is that the print extends from the top of the surface layer downward. This provides a situation in which part of the print will always be at the surface, even when part of the surface is worn out. Protective layers that distort the original image are not needed.

This new type of “digital input fingerprint” or DIP is obtained by printing into a powder that is cured after printing. The print is embedded in the cured layer, and not applied to the layer, as in the case when conventional printing methods are used.

The DIP method can be used in all powder-based materials, for example, molding materials and similar plastic materials that can be cured after printing. However, the DIP method is particularly suitable for use when the powder contains a mixture of wood fibers and, optionally, for example, small hard particles and a binder such as melamine formaldehyde resin. The surface layer may also contain a thermoplastic material, for example, vinyl particles, which are applied to the substrate in the form of a powder. This ensures that a print is introduced into the particles of the vinyl powder. Even in such materials an improved design and increased wear resistance can be achieved.

To obtain high print quality and high speed printing in layers based on powders and other layers described above, it is necessary to use a suitable head of the printing device. The head of the printing device has several small nozzles that can controllably “shoot” drops of printing inks (“drop on demand” - DOD - inkjet printing technology with inconsistent dropping). The volume of each drop can be changed depending on the type of printing ink and type of printhead, usually in the range from 1 to 100 picoliters. You can design printheads that can "shoot" with droplets of a larger volume - up to over 200 picoliters. Some heads of printing devices can “shoot” drops of different volumes and are capable of printing within the grayscale scale. Other heads can “shoot” only drops of one - fixed - volume.

To "shoot" drops from the nozzle, you can use different technologies.

The technology of heads of thermal printing devices involves the use of cartridges for printing with a number of miniature cameras, each of which contains a heater, all of which are created by photolithography. In order for the droplet to eject from each chamber, a current pulse is passed through the heating element, causing a rapid evaporation of the printing ink in the chamber with the formation of a bubble, which leads to a large increase in pressure, pushing a drop of printing ink through the nozzle to the substrate. Most consumer inkjet printers from companies like Canon, Hewlett-Packard, and Lexmark use thermal print heads.

Most commercial and industrial inkjet printheads and some consumer printheads, such as those made by Epson, use piezoelectric printhead head technology. Instead of a heating element, a piezoelectric material is used in the ink-filled chamber behind each nozzle. When voltage is applied, the piezoelectric material measures the shape, which leads to the generation of a pressure pulse in the fluid, pushing a drop of ink from the nozzle. Piezoelectric printing (also called piezo printing) allows the use of a wider range of printing inks than inkjet thermal printing, since there is no requirement for a volatile component and the question of coagulation does not arise. Many types of inks can be used, such as dye-based inks, solvent-based inks, latex inks, or UV-curable inks.

Printing inks for flooring applications are generally individually mixed with each other through the use of UV stabilized color pigments (UV stable color pigments) and several chemicals. Particularly suitable are water-based inks containing colored pigments, and they can provide a cost-effective way to print with high quality in many different materials.

The foregoing description of the various known aspects represents their characterization by the applicant, and not the assumption that any information from the foregoing description is related to the prior art. Some of the above technologies are known and used individually, but not in all of the above combinations and not in all of the above methods.

Most floorings obtained by digital printing, with the exception of floors where an input print is used in powder, must have a transparent protective layer, which is applied by rollers. To obtain the advantages associated with the ability to quickly adapt to creating high-resolution images, mainly digital application technology is used. However, other aspects of this technology are not fully utilized or developed, mainly related to the possibility of a very accurate deposition of a substance in a non-contact way, in particular, not in combination with substances that are not intended to create an image and which are intended to be applied in significant quantities to protect the image, decor or surface structure, so that these substances can be used for applications related to flooring, or other applications where similar e properties.

It would also be an advantage if it were possible to combine digital prints and digital prints with the decorative properties and structures of a panel, for example a panel with a wood surface, which may have a decor and structure that can be improved by a partial print and / or print. This can cost-effectively provide higher surface quality.

EP 2108524 (Flooring Industries Ltd) describes a method for manufacturing a coated panel with a surface comprising protrusions formed by two or more digital fingerprints provided on top of each other.

WO 2011/064075 A2 (Theodor Hymmen Holding Gmbh) describes a method for creating a three-dimensional structure on a surface. A panel with a printed decorative surface is coated with a transparent varnish cured by radiation, which is applied by inkjet printing to create a structured layer. The structure is formed through the use of drops of different volumes and several layers of prints. This structure can be synchronized with a printed decorative pattern, providing for the formation of different levels of gloss through transparent printing ink. The printed decorative surface may be on paper, foil or a coated plate. A digital fingerprint can be applied to a structure created digitally, and the fingerprint can be coated with a transparent protective layer, which is applied by conventional rollers.

US 2011/0171412 (Döhring) describes a direct print digital fingerprint printed on a fiberboard. The optical characteristics of this plate are at least partially visible and are embedded in the decor layer design. The decor is covered using a roller with a transparent protective layer.

JP 2008-265229 describes a method for coating and patterning a base material. Base materials, such as wood material or film material, are coated with a flexible resin layer. The decorative pattern is formed by a solid protective layer, which is applied by ink jet coating on a flexible resin layer.

These methods are unsuitable for use, for example, in wood flooring, where the protective layers are applied on separate panels and cannot be used to provide a digital fingerprint or digital impression that forms part of the final decor or surface structure and which has to be adapted to the basic designs and structures of each separate panel.

SUMMARY OF THE INVENTION

The general objective of certain embodiments of the invention is to develop a building panel, preferably a floor panel, and a method for manufacturing such panels with a transparent protective surface that has better and / or different structural properties or a better and / or different cost structure than known building panels.

The specific task of at least certain embodiments is to improve the surface quality and improve the design of wooden building panels, especially wooden floor panels, which generally cover as separate panels, each panel providing significant design changes and surface defects .

Another specific objective of at least certain embodiments is to develop an improved method for coating individual wooden building panels, such as wooden floor panels, especially individual panels already provided with a mechanical locking system at their edges and / or bevels.

The above objectives are possible, and embodiments of the invention may provide for the solution of other or additional tasks.

The first aspect of the invention is a method for coating a building panel having a decorative wood surface, comprising the steps of:

- apply a layer of UV-curable coating using a printhead for digital printing on the decorative surface of the wood of the building panel; and

- curing the UV curable coating layer by means of UV radiation, thereby forming a transparent protective surface layer, wherein said decorative surface is visible through said transparent protective surface layer.

A building panel may be a floor panel.

Digital coating is a non-contact method that provides major advantages over the conventional roller coating method.

A building panel, such as a floor panel, may be a separate panel having a size that is substantially the same as a finished building panel containing machined edges.

A building panel, such as a floor panel, may include a mechanical locking system at two opposite edges.

A building panel may contain a bevel on the edge.

The UV curable coating layer may be a liquid polyurethane substance.

The UV curable coating layer may be a water based UV curable polyurethane.

The curable coating layer may be a radiation curable coating layer. The radiation curable coating layer may be UV curable, thermal radiation, electron beam, etc.

A curable coating layer, such as a UV curable coating layer, may contain an acrylate or methacrylate monomer, or an acrylate or methacrylate oligomer. The radiation curable coating layer may comprise an acrylic resin. The acrylate or methacrylate monomer, or the acrylate or methacrylate oligomer, can be an epoxy acrylate, epoxymethacrylate, urethane acrylate, urethane methacrylate, polyester acrylate, polyester methacrylate, polyether acryl acrylate acrylate, acryl acrylate acrylate, acryl acrylate acrylate, acryl acrylate acrylate, acryl acrylate acrylate, acryl acryl acrylate The above examples are examples of monomer or oligomers polymerized by a reaction involving free radicals.

The aforementioned monomers or oligomers can form a component of a radiation curable coating layer.

Decorative surfaces may contain a print, preferably a digital print.

The print head for digital printing may be a piezo print head.

The print head for digital printing can be configured to supply droplets, preferably a volume of about 60-200 picoliters.

The UV curable coating layer may contain particles that are wear resistant and / or resistant to contact mechanical damage.

The UV curable coating layer may comprise a structured surface with depressions and protrusions.

The structured surface may include a register of the decorative surface.

A second aspect of the invention is a floor panel having a core, a surface layer comprising wood material, an imprint and transparent layers. The lower transparent layer may be below the print, and the upper transparent layer may be above the print, the lower transparent layer may be UV-curable polyurethane, and part of the surface of the wood material and the print form part of the visible surface layer. The fingerprint may be at least partially synchronized with the visible design and / or structure of a separate floor panel.

Such wood floors can have a very attractive design, even when low quality wood is used as the core. The print that is applied by the print head for digital printing can be adapted to each individual floor panel, and you can use the print to form an image and / or print, which improves the basic design or structure of the floor panel.

The top transparent layer may contain water-based polyurethane.

The top clear cover layer may be embossed.

The upper transparent layer can be embossed with a register of the print.

A third aspect of the invention is a method of forming decor on a building panel using a digital vision control system that provides digital input to a print head for digital printing, including the steps of:

- create a digital image of the surface of the building panel through a digital control system of technical vision;

- use the digital control system of technical vision to provide digital input into the print head for digital printing based on the digital image;

- digital printing is carried out on at least part of said surface of the building panel using a printhead for digital printing and using a print that is at least partially adapted to the digital image of said surface of the building panel.

The main advantage is that you can use a digital vision system to analyze each individual panel, and a computer program can direct printheads that print on areas of the surface that need an improved design or improved structure.

A building panel may be a floor panel.

The print may contain color pigments.

The surface of the panel may contain a transparent substance that is UV curable and which, after curing, forms an embossed structure.

The building panel and manufacturing method in accordance with embodiments of the invention makes it possible to cost-effectively manufacture highly improved patterns with high wear and shock resistance using a digital non-contact coating method. With this digital coating method, even non-oriented structured surfaces having a register print can be formed.

Embodiments and details of various aspects may be combined with embodiments and details of other aspects.

A fourth aspect of the invention is a proposed method for coating a building panel, comprising the steps of:

- form a transparent protective surface layer by applying a layer of UV-curable coating using a digital head for coating on the decorative surface of the building panel;

- cure the coating layer using UV radiation.

A building panel may be a floor panel. The decorative surface may be wood fiber.

Brief Description of the Drawings

The invention will be described in more detail below in connection with options for implementation and with reference to the accompanying possible drawings, while:

in FIG. 1a-c show a known roller coating and digital printing method;

in FIG. 2a-b depict a digital coating method;

in FIG. 3a-c depict digital inkjet printing in transparent layers;

in FIG. 4a-c illustrate digital printing and embossing.

Detailed Description of Embodiments

In FIG. 2a shows a floor panel 1 comprising a solid wood core 3 and a decorative surface 5, which is the upper part of a solid wood core. The floor panel 1 may comprise bevels 15a, 15b at the edges of the floor panel 1. Several transparent layers of adhesive coating L1, primer L2 and topcoat L3 are applied on the wood surfaces. The adhesive coating and primer are applied by rollers and are UV curable. A coating coating in this embodiment is digitally applied.

In FIG. 2b shows the basic principles and equipment for a digital coating method. As a digital coating head, a digital coating unit 36 is used comprising a print head 30 for digital printing. The print head 30 for digital printing is preferably stationary. The print head 30 for digital printing applies a transparent coating layer L3, preferably on a primer coating L2. Digital application can be done without any contact between the panel and the print head 30 for digital printing, and the coating is applied in the form of droplets that “shoot” from the print head 30 for digital printing to a decorative surface that may contain an adhesive coating L1 under the primer .

The ultraviolet UV curing oven 23 is preferably located after the digital coating unit 36 in the feed direction and can provide almost instantaneous curing of the coating within a few seconds, especially if a UV curable polyurethane coating with a suitable photopolymerization initiator is used. The digital print head 30, which is preferably a piezo head, preferably has some capacity for “shooting” droplets with a droplet volume of about 50-200 picoliters or more. Drops can have a diameter of 30-100 microns or more and can create a drop spot on the surface that exceeds 100 microns. The drops are preferably arranged so that they overlap each other. This overlap can be obtained by combining the volume of the drop and the position of the drop. Several printheads, one after the other in the feed direction, can also be used to create a continuous layer even when individual drops are applied as a raster image.

The UV curable coating is preferably a water based UV curable polyurethane substance having a viscosity that is adapted to the print head 30 for digital printing. As a coating used in a print head for digital printing, water-based polyurethane dispersions are preferred. They can be environmentally friendly and technically superior to similar solvent based coatings. They may not contain, for example, isocyanate and may have zero or very low levels of volatile organic substances. They have acceptable properties in the context of hardness, extraneous stains and abrasion resistance, impact strength and flexibility at certain temperatures.

Polyurethane dispersions are fully reacted polyurethane polyureas from small and discrete polymer particles, and such particles can be obtained with a size of about 0.01-5.0 microns, as a result of which they can be manipulated in a piezo printing head for digital printing or other similar heads. They can have a solids content of 20-70%, and using the digital coating method you can get a wide range of layers with different hardness. Polyurethane dispersions can be mixed, for example, with acrylic emulsions to reduce costs in some applications. They may also contain particles with low wear resistance and low resistance to contact mechanical damage, for example, aluminum oxide particles that can be manipulated using a piezo head. Such particles should be fairly small, since the nozzle opening in most digital printheads is about 10 microns in size. The wear resistant particles are preferably less than 5 microns, and in an even more preferred embodiment, the wear resistant particles have a size of about 1 micron or less.

The wear resistant particles can preferably be applied by dispersing the particles in the form of a dry powder, for example, on a primer coating, which is preferably in a liquid state and has not yet been cured. A second primer coating or topcoat can be applied to the wear resistant layer. The advantage is that large particles that can clog nozzles are not fed by the print head for digital printing. Separate dispersion provides the ability to supply particles with a size of 10-100 microns.

The coating is stored in liquid form in the coating container 31, which is connected to the print head 30 for digital printing by the coating supply pipe 33. A digital control unit 34 connected to the print head and the conveyor using data cables 33 or wireless means controls the droplet volume and speed of the conveyor 21, which moves the panel 1 relative to the print head 30 for digital printing.

Such a digital coating unit is much more cost-effective than a conventional digital printing device, since it is possible to “shoot” much larger droplets, and this gives an increased printing speed and less problems with the channels in the head, which can be blocked by a larger particle present in the printing ink when the printer is working with high resolution and small drops. Each digital coating head, made in the form of a digital print head, can be given a design that allows only one layer to be applied, without the need to coordinate the application of droplets with such different print heads, as with conventional multi-color digital printing, in the process which drops, aligned side by side in the form of a raster image, create a digital image.

You can design special printheads for digital printing, which ensures the supply of very large droplets in the range of 200-400 picoliters or more, and the nozzle opening can exceed 20 microns. Such digital printheads are generally unsuitable for use as conventional printheads for the purpose of creating high-resolution images. Their design can provide a cost-effective supply of large overlapping drops in significant quantities. Each printhead, which is used primarily as a digital head for coating, can be given a design that provides the supply of coating weighing 10-20 g / m ² or more in one step through.

The coating line can be very compact, and the UV curing oven can be placed close to the digital coating unit. The coating can be very accurate, and the non-contact method provides better opportunities than roller coating when applying UV curable coating on the edges, on bevels 15a, 15b formed on the edges, and on surfaces that are not completely flat, for example such as brushed wood surfaces or scraped wood surfaces, or a multilayer paper or powder based floor. UV curable protective layers can be digitally applied to virtually all types of floors to improve surface properties or designs. Therefore, in accordance with an embodiment of the invention, some parts of the surface can be formed by known methods, obtaining the basic strength of the designs or structures, and the final layers can be applied digitally by coating. To improve surface properties, flooring with surfaces containing paper, powder, cork, vinyl and even stone and ceramic tiles, as well as similar materials, can be digitally applied.

The UV curable liquid coating provides the advantage that the coating is liquid until it is exposed to UV radiation. This improves digital coating performance and avoids many of the problems associated with, for example, solvent based inks.

Of course, digital coating equipment may have multiple printheads. Digitally, it is possible to coat individual panels or to a large sheet, which after coating is divided into several panels.

The above principles can preferably be used for applying a primer coating L2 and / or an adhesive coating L1. You can apply all the transparent layers that are used to protect the surface of the wood or printed image. The digital coating method can be used to apply transparent layers with a film thickness that corresponds to a mass of 5-10 g / m ² . You can even get thicker layers, for example, corresponding to a mass of 10-20 g / m ² , and using 5-10 coating stations, you can achieve the total thickness corresponding to a mass of about 100-120 g / m ² . You can also pass the panel through the coating station several times.

In FIG. 3a shows that a digital fingerprint P1 can be applied to a transparent layer, and such a fingerprint is characterized in that one transparent layer L2 is below the fingerprint, and another transparent layer L3 may be located above the fingerprint P1. The surface of the panel, preferably being the top of the wood material 5, can be visible and can, together with the print P, form part of the final decor of the surface and decorative surface 2. The floor panel 1 can be provided with bevels 15a, 15b at its edges. A digital coating method is applied to at least the upper transparent layer. The P2 fingerprint can also be incorporated into a wet, transparent coating before UV curing.

Such methods, where the P1 fingerprint is applied to the transparent layer or when the P2 fingerprint is introduced into the transparent layer, can be used to obtain improved design properties, since several images with transparent layers between the prints can be placed on top of each other, and this can provide three-dimensional images similar to stone surface with transparent or translucent crystals. Such three-dimensional images can be partially or fully formed by conventional roller coating methods, which can be combined with digital printing or digital coating.

In FIG. 3b shows a first process step of a combined production line for digital printing and digital coating. The digital fingerprint P1, P2 is applied to the cured layer or to a wet transparent layer. The print can be cured by means of a UV oven 23, if the print is introduced, for example, into a wet layer of polyurethane.

In FIG. 3c shows a digital coating unit 36 that can apply a clear primer or topcoat to a digital fingerprint. This coating is UV curable in a UV oven 23. Digitally, a transparent or translucent adhesive coating can be applied under the print.

If the digital coating unit 36 is connected — wirelessly or via a data cable — to the digital printing unit 35, as shown in FIG. 3c, so that it is possible to control the digital fingerprint and the digital coating method and adapt them to specific designs that are based on a combination of patch and coating, this is an advantage. It is also possible to digitally connect the vision system 39, and the digital coating method and / or digital printing can be adapted to specific surface structures and designs. The vision system can be used, for example, in concert with the steps of printing and coating, creating a digital image of the surface of the panel, which preferably comprises a wood-based surface 2. The panel may be a separate floor panel, which may be a solid wood panel or a panel containing a core coated with a layer of wood, for example 0.3-3 mm. Using the vision system 39, it is possible to detect and analyze surface defects such as extreme color deviations, cracks, knots, repetitive effects, etc., preferably by analyzing a digital image of the panel surface and comparing this image with images already stored in memory system of technical vision. This system can be “intelligent,” and new images and correction commands can increase efficiency. Special software can be developed for different types of wood. It is possible to at least partially digitally print on the visible surfaces of the panel based on such digital image analysis that defects are hidden or corrected with a digital fingerprint, or that some areas of the surface are printed to create an attractive wood design, for example, to create an improved structure of wood fibers after finishing. As an alternative or complement to digital printing, a transparent coating can be applied based on digital image analysis. For example, you can change the degree of gloss of the surface of the panel and you can apply a larger amount of liquid substance, concealing cracks or depressions in the surface of the wood. This surface can be exposed to different types of light when a digital camera takes a picture, and this can expand the ability to detect specific defects.

The above-described digital printing method controlled by a vision system (VCDP method) can also be used on a different floor than wood floors. The printed surfaces of the paper and foil provide for repeated effects transferred from the printing cylinders. Such effects can be partially eliminated by digital printing under the control of a vision system. This method is preferably combined with a process step in which the overprinted substrate is connected to the core prior to the final digital printing step. The main advantage is that it is not necessary to accurately position the already printed substrate on the panel, because the vision system 39 can detect the exact position and / or specific design, and the digital printing device can use the complementary design with high accuracy. If paper is used, it may be advantageous if such paper is raw paper without any tar. The necessary thermosetting resin can be injected from the soil layer under the substrate and / or from the coating layer on a printed surface. The coating layer may be a powder layer containing abrasion resistant particles and a thermosetting resin or a conventional overlay, and the resin may be cured by applying heat and pressure. The digital coating described above can also be used as a coating layer.

The VCDP method can also be used to create decor in the floor of a fiberboard with a powder-based surface. A powder having one or more colors can be dispersed on the stove and a basic design can be created. The vision system and computer system can analyze the basic design and provide the necessary digital input to a digital printing device, which in the second step can adjust or improve the basic design. The advantage is that the basic design can provide the bulk of the pigments, and the amount of printing ink supplied by the digital printing device can be significantly reduced, preferably by a few grams per square meter, for example, 1-5 g / m ² . In some applications, a printing ink content of 3 g / m ² or less may be sufficient. This method can also be used to create surface designs on ceramic tiles.

The VCDP method is very suitable for combining with a binder and powder printing method (BAP method), in which digital drawing or image formation is possible by means of an inkjet head, which applies only a liquid binder to the surface without any pigments. The binder may be a water-based substance containing glycerin, which provides a suitable viscosity. The second device randomly scatters the pigments over the liquid-formed pattern. A binder binds several pigments that form the same pattern as the binder, and other non-bonded pigments are removed. This two-step process, in which the pigments and the liquid binder are applied separately, can provide an image with the same quality as conventional digital printing technology, and it is a very cost-effective way to create a basic design that is adjusted or improved at the final stage of digital printing providing for the application of printing ink based on a pigment, preferably water-based printing inks. The powder may be a transparent substance, for example, bleached wood fibers, and the BAP method can be used to create an embossed transparent surface.

In FIG. 4a shows how a digital fingerprint P can be applied to or inserted into a coating layer L3 and / or a primer coating L2. The decorative surface 5 may be a layer of wood, for example, whole-wood, a sheet of wood or wood veneer, which can be glued to the core 3, for example, a core of plates, fiberboard or plywood. To improve the design of the decorative surface using a digital fingerprint.

In FIG. 4b shows that digital coating can be used to provide a digitally embossed surface, hereinafter referred to as DSP. You can provide the first - covering - layer L3a-L3d with a continuous cross-section, which simulates, for example, the structure of wood fibers. This layer is applied in the form of a transparent image having a vertical extension. The wet three-dimensional structure may be UV-curable, and in the preferred embodiment, a second or third coating may be applied with an intermittent structured cross section on the first layer. Intermittent layers can be used to build a vertically extending structured surface with the same or different gloss levels. Embossed structures can be formed, for example, with a depth of about 0.1 mm or more with any profiles.

This method can be used to very quickly adapt the formation of improved structures, and prints can be precisely coordinated with imprinted surfaces, preferably with a digital fingerprint, as shown in FIG. 4c. The print P is coordinated with the structure L3a-c, and the individual parts of the digital image can be provided with clearly defined surface structures in which, for example, a specific roughness is printed on a part of the surface, which causes the formation of small depressions 37, and other parts of the image can be formed in the surface, which contains small protrusions 38. Such a surface with a digital print with register, referred to below in the context of DERIS technology, makes it possible to create separate panels that are unique They are nonsense and do not provide for any repetition effect associated with the design or structures. Since embossed cylinders or matrix films are not required, as in conventional technology, it becomes possible to quickly re-adaptable and cost-effective to obtain a wide range of practically unlimited structured designs.

DERIS is preferably used together with an image obtained by digital printing. Such an image can be printed on paper, foil, on a plate material or injected into a powder based surface. The digital printing apparatus 35 and the coating unit 36, which forms the coating layers L3, are preferably digitally connected to a computer that coordinates the surface design and the surface structure.

DERIS technology can even be used to coordinate the coverage of a single structured surface with separate wood panels that have different designs, or with any other panels where a surface design or structure has already been formed. This is an advantage, especially in an application where digital printing is used to improve wood surface design. By digital printing, as described above, the design can be improved in the case of lower quality wood species. For example, by means of a technical vision control system comprising a digital camera or scanner, it is possible to take a digital picture of a wood surface of a panel. This is preferably done in conjunction with the application of a transparent coating that provides a finished surface with digital embossing. The control system of technical vision can be used together with a computer program that can analyze a digital image and can adjust the digital coating so that it is coordinated with the structure of the wood fibers and the design of each individual panel.

Such digital embossing methods under control of a vision system (VCDE methods) are not used in decking applications. The VCDP and VCDE methods can be combined and thereby very cost-effective, improved decors and structures can be formed.

The VCDE method is particularly suitable for forming embossed structures on panels where parts of the decor are not digitally formed in accordance with the previous printing step. Even so, productivity and workmanship can be improved, since there is no need to use high-quality transportation units that accurately move the panel between the various stages of printing, coating and feeding, which must all be coordinated to give a high quality finished surface. A vision system, which can preferably also be combined with a positioning system between the various process steps, can be very cost-effective compared to known methods.

All described embodiments may be combined, and all transparent layers may contain color pigments.

The digital coating method can also be used to apply other chemicals to the panel, such as glue, preferably water-based glue.

The digital UV curable polyurethane coating method used to produce three-dimensional structures can also be used for another application, and not just for building panels, as described above. A digital printer and a UV oven can be used to vertically apply and cure many layers of UV curable polymers of various types to create complex structures and patterns with a vertical length of 1-10 mm and even more. The first layer can be applied to the substrate, which moves forward and backward in the UV oven after applying a new layer. You can also arrange two heads for digital piezo printing, for example, so that there is a UV oven between them, and the substrate can be moved from the first printhead through the UV oven to the second printhead and vice versa. This sequence can be repeated many times, and the thickness of each layer can be 0.1-0.3 mm or even more, depending on the viscosity of the liquid polymer, which can be, for example, polyurethane. In general, additional substances are not required to cure the polyurethane, and the same type of UV curable liquid polyurethane can be used on both heads of the printing devices. In both printing devices, it is also possible to use different substances, which can be used to reduce the curing time. This manufacturing method can be combined with a technical vision system, and partially concrete three-dimensional structures can be formed on specific clearly defined sections of various objects that may contain different materials. Three-dimensional structures can have different colors that are digitally applied to UV curable polyurethane.

Such digital methods for creating three-dimensional structures can be used to provide a matrix that can be used as a structure sheet when strips based on laminate and powder are pressed in a press to cure the surface.

It is assumed that there are numerous modifications of the embodiments described herein that are also within the scope of the claims described by the appended claims.

For example, it is contemplated that curing the curable coating layer with UV radiation can be replaced by a curing method with other radiation. It is also contemplated that the present invention can be used for other types of layers of radiation curable coatings.

As is obvious from the description, using a printhead for digital printing, the coating layer can be applied directly to the surface of the building panel forming the decorative layer, or it can be applied to the intermediate layer located on the surface of the building panel.

In the above information, it is assumed that the term "transparent" means essentially transparency in the same sense as this concept is usually used in the description of coatings for traditional wooden floors. The transparent protective surface layer is transparent to such an extent that the decorative wood surface below it is visible through this transparent protective surface layer.

Examples

Example 1

Put a digital image on the panel, which is a fiberboard. The image was created using a single-pass printing device containing 5 stationary printing piezo heads. Ink was water-based inks and contained color pigments.

To apply a transparent layer of UV-curable water-based polyurethane, which corresponds to a film with a mass of 10 g / m ² , a printing piehead with a drop volume of 50 picoliters was used. The above material was cured in a UV oven and a digital image was obtained with a transparent layer deposited digitally.

Example 2

Put a digital image on the panel, which is a fiberboard. The image was created using a single-pass printing device containing 5 stationary printing piezo heads. Ink was water-based inks and contained color pigments.

To apply a transparent layer of UV-curable water-based polyurethane, which corresponds to a film with a mass of 10 g / m ² , a printing piehead with a drop volume of 50 picoliters was used. The above material was cured in a UV oven.

Using a printing piezo head with a droplet volume of 50 picoliters, a second - similar - transparent layer was applied with a mass of 5 g / m ² . This layer was applied as a transparent image coordinated with a digital image.

The above material was cured in a UV oven and a wood fiber design was obtained with a wood fiber structure including a register of wood fiber design.

The digital coating method can also be used to seal the edges and / or the locking system 9, 10 to prevent moisture penetration, eliminate the squeaking sound or change the frictional properties of the active surfaces in the locking system. The main advantage is that the liquid substance can be applied with high accuracy and, for example, undesirable sagging on the surface can be avoided. The print head is usually used for vertical application of a liquid substance from a distance of several millimeters to the surface. The printheads can be used for applying liquid substances from a distance of up to 10 mm or more, and it can be applied at various angles to the surface, for example, 0-10, 10-20, 20-45 degrees, or even more than 45 degrees, from above or from below . This makes it possible to use interlocking systems with improved geometries along with a combination of several printheads located at several angles. The liquid substance may be liquid wax, which after cooling to room temperature becomes a soft layer.

Claims (28)

1. The method of coating a building panel (1) having a decorative surface (5) made of wood, including the steps in which: - apply a layer of UV-curable coating using a printhead (30) for digital printing on a decorative surface (5) of wood of a building panel (1) by applying drops of UV-curable coating using a printhead (30) for digital printing; while the drops are arranged so that they overlap each other; and - curing the UV curable coating layer with UV radiation (23), thereby forming a transparent protective surface layer (L1, L2, L3), while said decorative surface (5) is visible through said transparent protective surface layer (L1, L2, L3). 2. The method according to claim 1, wherein the building panel (1) is a floor panel. 3. The method according to p. 1 or 2, in which the building panel (1) is a separate panel having a size that is essentially the same as that of a finished building panel containing machined edges. 4. The method according to p. 1 or 2, in which the building panel (1) contains a system (9, 10, 6, 8, 14) of mechanical locking on two opposite edges. 5. The method according to claim 1 or 2, in which the building panel (1) comprises a bevel (15a, 15b) at the edge. 6. The method of claim 1 or 2, wherein the UV curable coating layer is a liquid polyurethane substance. 7. The method according to claim 1 or 2, in which the layer of UV-curable coating is a UV-curable water-based polyurethane. 8. The method according to p. 1 or 2, in which the decorative surface (5) contains a print (P). 9. The method according to p. 1 or 2, in which the print head (30) for digital printing is a print piezo head. 10. The method according to p. 1 or 2, in which the above drops have a volume of approximately 60-200 picoliters. 11. The method according to claim 1 or 2, in which the layer (L2, L3) of the UV-curable coating contains particles that are wear-resistant and / or resistant to contact mechanical damage. 12. The method according to claim 1 or 2, in which the layer (L2, L3) of the UV-curable coating contains a structured surface with depressions (37) and protrusions (38). 13. The method according to p. 12, in which the structured surface provides a register of the decorative surface (5). 14. The floor panel (1) having a core (3), a surface layer (2) comprising a wood material surface (5), an imprint (P) and transparent layers (L1, L2, L3), characterized in that the lower transparent layer (L1) is below the print (P), and the upper transparent layer (L3) is above the print (P), and the lower transparent layer (L1) is a UV-curable polyurethane, while part of the surface (5) of the wood material and the print (P) form part of the visible surface layer (2), and the print is at least partially synchronized with the visible design and / or structure of a separate floor panel. 15. The floor panel according to claim 14, characterized in that the upper transparent layer (L3) contains water-based polyurethane. 16. The floor panel according to claim 14 or 15, characterized in that the upper transparent layer (L3) is embossed. 17. The floor panel according to claim 14 or 15, characterized in that the upper transparent layer (L3) is embossed with a register of print (P). 18. A method of forming decor on a building panel (1) using a digital control system (39) for technical vision, which provides digital input into the print head (30) for digital printing, which includes the steps in which: - create a digital image of the surface (2) of the building panel (1) through a digital control system (39) technical vision; - use the digital control system of the technical vision for providing digital input to the print head (30) for digital printing based on said digital image; - digitally print at least a portion of said surface (2) of the building panel (1) using a print head for digital printing and using a print that is at least partially adapted to the digital image of said surface (2) of the building panel (1) . 19. The method of claim 18, wherein the building panel is a floor panel. 20. The method according to p. 18 or 19, in which the imprint (P) contains colored pigments. 21. The method according to p. 18 or 19, in which the surface (2) of the panel (1) contains a transparent substance that is UV-curable and which, after curing, forms an embossed structure.

Images