EP3109056B2 - Method and device for producing a structure on a surface - Google Patents

Description

The present invention relates to a method for producing a structure on a surface of a flat workpiece, and a device for producing the structure.

A decoratively coated wood-based panel is state of the art and is used in a variety of applications, e.g. for the production of furniture, floor laminates and wall, ceiling or exterior panels. A typical example of these wood-based panels is chipboard, which is coated with a decoratively printed paper. Alternatively, there are also other types of fiberboard, e.g. MDF (medium density fiberboard) or HDF (high density fiberboard), as well as cement fiberboard and cement-bonded chipboard, which are used, for example, in thicknesses of approx. 3 to 50 mm for various applications.

In most of these applications, it is desirable to obtain a structure in the surface in addition to a decorative coating, such as a wood imitation or a tile imitation for a stone-like laminate floor.

According to the state of the art, this is produced, for example, in a melamine coating process using an embossing die. For example, paper printed with a wood look is impregnated with a melamine resin, dried and then pressed onto a chipboard in a heating press with an embossing plate. The result is a 12 mm thick chipboard that is coated with a beech imitation look. On the surface with the beech imitation optics, the embossing plate then creates structures with a depth of usually 20 µm up to 150 µm or 200 µm.

These structures are either manufactured in a wood-like manner, regardless of the type of wood actually printed, as a so-called “all-over” structure. In correspondingly more expensive processes with products that appear to be of higher quality, a so-called synchronous pore is also used, in which the embossing sheet has a structure that is applied synchronously with the printed wood look. In this case, for example, a printed knothole is actually noticeably deeper than the slightly higher rest of the printed wood look next to it.

In addition to this so-called melamine pressing process, there are other processes for coating wood-based panels. In another known process, for example, a wood-based panel is painted, printed and then provided with a transparent top coat. In order to obtain an appropriate surface structure here too, it is possible to apply a structure with a structured top coat roller. Such a procedure is, for example, in DE 10 2007 019 871 described.

All of these methods for structuring the surface have in common that they are relatively inflexible and that if a structure is changed, the respective tool (the roller or the press plate) has to be changed.

In order to avoid these disadvantages, there is a process for digitally applying a structure, which is in the DE 10 2009 044 802 is described.

However, this digital process also has disadvantages: a large amount of radiation-curing ink is used, which is very expensive. In addition, it is not always possible to achieve full surface coverage via the printed structure. Furthermore, the printed ink is less scratch-resistant and durable than is the case with other methods mentioned above.

The EP 1 902 849 A1 discloses an inkjet printing process in which a base layer is partially cured and then printed with ink, ink droplets being introduced into the base layer.

The WO 2015/078449 A1 discloses a method for inkjet or ink printing, wherein a liquid ink-receiving layer is applied to a substrate, liquid printing media is then applied thereto, and the ink-receiving layer is then solidified.

Against this background, the aim of the method according to the invention and the device according to the invention is to maintain the advantages of the flexibility of a digital structure and at the same time to exclude the disadvantages mentioned above.

This is achieved by the method according to the invention as defined in claim 1. For this purpose, in a first step, a workpiece to be coated, e.g. a wood-based panel, a cement fiber board or similar (flat workpiece) is coated on a surface of the workpiece with a liquid base layer. In a second step, a structure is then created in this still liquid base layer with the help of sprayed liquid droplets, with depressions being created by spraying the droplets into the previously applied liquid base layer. In a third step, this structure created in this way is fixed by fixing the liquid base layer. This is done, for example, by drying the liquid base layer and the sprayed-on liquid droplets together. The device according to the invention is defined in claim 13. Further advantageous embodiments of the present invention are the subject of the subclaims.

Before or after fixing the liquid base layer, the sprayed droplets can be evaporated.

In one embodiment variant, the sprayed droplets can also be fixed when the liquid base layer is fixed.

The droplets can be sprayed onto a surface of the workpiece according to a digital template from a digital print head or alternatively from a digital nozzle bar of a device for generating a structure. This device has a control unit or a control device. The control takes place according to a digital template, which can be retrieved, for example, from a data memory belonging to the device. The control device can appropriately control the delivery of the droplets, for example the delivery volume and the speed of the droplets when they hit the base layer.

In a preferred embodiment variant, the liquid base layer and/or the sprayed droplets can consist of a radiation-hardening material.

Fixing can take place in the form of radiation curing using UV radiation or electron beams. For this purpose, a corresponding device has appropriate UV lamps or electron beam-generating elements.

The sprayed droplets, which are sprayed on according to a or the digital template, are coordinated with a decorative image previously or subsequently printed on the surface in such a way that the resulting structure is applied to the workpiece synchronously with the printed decorative image at least in partial areas of the surface.

The sprayed droplets can consist of a material containing acrylate and are applied to the workpiece based on a digital template.

After the step of fixing the liquid base layer and the sprayed droplets, a further process step can be carried out in which further droplets are sprayed onto the then fixed base layer and then cured.

The large number of droplets can consist of at least two different materials, so that droplets with one material are applied to certain places and droplets with a different material composition are applied to certain places.

After and/or during the spraying of the large number of droplets into the still liquid base layer, a chemical reaction can take place between the material of the sprayed droplets and the still liquid base layer, such that the reaction product between the base layer and the droplets visually and/or the structure at that point. or haptically changed.

Fig. 1

Schnittansicht eines Werkstücks vor dem Tröpfchenauftrag;

Fig. 2

Werkstück während des Tröpfchenauftrags;

Fig. 3

Werkstück nach dem Tröpfchenauftrag und nach der Aushärtung;

Fig. 4

Werkstück nach erfolgtem Tröpfchenauftrag in der Oberansicht;

Fig. 5

Vorrichtung zur Erzeugung einer Struktur auf dem Werkstück

The invention is explained in more detail below using the attached figures. They show:

Fig. 1

Sectional view of a workpiece before droplet application;

Fig. 2

workpiece during droplet application;

Fig. 3

Workpiece after droplet application and after curing;

Fig. 4

Top view of workpiece after droplet application;

Fig. 5

Device for creating a structure on the workpiece

This shows Fig.1 the workpiece 1 to be provided with a structure and the applied, liquid base layer 2.

In Fig. 2 The sprayed droplets 3 can also be seen, which are shown in different groups, individual drops or several drops lined up next to each other.

The result of the spraying is in Fig. 3 shown, in which the droplets 3 have made corresponding depressions in the previously applied liquid base layer 2 and have settled at the end of the depression. Depending on the parameters used (material, droplet speed, droplet volume, etc.), in addition to the depression created by the droplet, elevations can also form due to the displaced paint of the liquid base layer.

In Fig. 4 the workpiece 1 with the liquid base layer 2 applied to it can be seen from above. The corresponding structures that the sprayed droplets 3 created here are sketched.

Example 1:

First, a chipboard with a thickness of 12 mm is fed to the device according to the invention. The device is used to create a structure on a surface of the workpiece with a transport device for transporting and / or removing a workpiece provided with a liquid base layer in a transport direction, with one or more print heads and / or one or more nozzle bars for dispensing droplets and/or into the liquid base layer and with a fixing device, which is arranged downstream of the print head(s) in the transport direction and which radiates heat and/or light onto the base layer of the workpiece, the device having a control device. Light is not just light to understand the visible wavelength range, but in particular also UV light and infrared light.

The device includes in the specific embodiment variant the Fig. 5 Digital print heads 4, a drying device 5, designed as a UV LED and a continuous transport 6, here designed as a belt transport. A dispensing device for applying the base layer 2 can also be provided. The chipboard can already be coated with a white primer. In an alternative embodiment, it is also possible for a decorative image, for example a wood imitation, a tile imitation or even a photorealistic image, to be printed on the already primed chipboard beforehand. The 12mm chipboard pretreated in this way is then coated with a liquid base layer in the form of an acrylate varnish, the layer thickness being between 5 µm and 200 µm, preferably between 10 µm and 60 µm. The acrylate varnish (“liquid base layer”) is in this exemplary embodiment a formulation with 30% by weight of a bi-acrylate HDDA, 40% by weight of a bi-acrylate DPGDA, 10% by weight of a cross-linker TM PTA, 3% by weight of an industry-standard photoinitiator and 17% by weight of other ingredients. The acrylate varnish has a viscosity of 80 - 500 mPa s, preferably 150 - 400 mPa s, measured at 25 ° C and normal pressure with a rheometer (eg the Kinexus model from Malvern).

The plate precoated in this way is then fed to a digital printing unit, in which an ink that also contains acrylate is sprayed from digital print heads (4) into the still liquid acrylate-containing base layer (2). The acrylate-containing ink contains 65% by weight of a methacrylate CTFA, 15% by weight of an N-vinyl caprolactam NFC, 8% by weight of a photoinitiator and 12% by weight of other components. The viscosity of the ink is 8 - 30 mPa s at a processing temperature of 20 - 45 °C (measured with the Kinexus rheometer from Malvern) and normal pressure. The surface tension is 22 - 38 mN/m, measured in a tensiometer, model K100 from Krüss at 20°C and normal pressure. In this exemplary embodiment, the droplets have a volume of 3 - 100 pl, particularly preferably 6 - 60 pl. The droplets are applied according to the digital printing template, so that the digital printing device can print a corresponding "image" as a variation of the layer thickness into the still liquid base layer. The droplets are sprayed at a distance of 0.5 mm to 10 mm from the liquid base layer; the distance is particularly preferably 0.5 mm to 4 mm. When the droplets hit the base layer, for example 50 µm thick, they displace the liquid material at that point. Depending on the droplet size and speed of the droplets when sprayed, the droplet material can penetrate into the liquid base layer, creating a depression, for example 50% of the base layer. In the application example presented here, the penetration depth is 25 µm. Alternatively, if the droplet size and speed are changed accordingly, the droplet can also penetrate less deeply and/or throw displaced material to the side of the droplet, so that both a depression and adjacent elevations are created in the liquid base layer. After the droplets are printed, the liquid base layer and the printed droplets are hardened. In a particularly preferred embodiment, this curing is carried out within less than 5 seconds after printing using UV LEDs, which harden the acrylate material, which also contains corresponding UV photoinitiators, to such an extent that the surface solidifies and the liquid no longer runs more can happen.

In a further step, the final hardening occurs through more intensive UV irradiation.

In an alternative embodiment of the method according to the invention, after the first application of the liquid base layer and the application of the droplets and the first curing, a second pass can take place, in which a further liquid base layer is applied and droplets are also sprayed on.

In a further alternative embodiment, after producing this three-dimensional structure with a depth of 2 µm - 100 µm, particularly preferably 3 µm - 50 µm, a decorative image is printed on the surface that was previously structured according to the invention. In a preferred embodiment, the printing process is also carried out using an inkjet printer. The decorative image is coordinated with the three-dimensional structure in such a way that the decorative elements of the image are synchronous with the previously created three-dimensional structure at least in partial areas of the surface. Synchronous means that the decorative imaging achieves a lengthwise deviation from the underlying three-dimensional structure of less than 5 mm, particularly preferably less than 1 mm. Deviations are measured here between parts of the image, e.g. a decoratively printed knothole, and the correspondingly assigned structure, e.g. a round depression of the same size as the printed knothole.

In an alternative embodiment, the decorative image is first printed on the workpiece, e.g. the wood-based panel, before the surface is structured. Before the image is printed, the material surface has a suitable print-receiving layer as a coating, which in one embodiment consists of a white lacquer. The decorative image is then printed onto this, preferably also using an inkjet process. In the method according to the invention, the coating is then carried out with the liquid base layer, which in this case is transparent in order to recognize the decoratively printed image underneath. After applying this liquid base layer, the structure according to the invention is then created by spraying on the droplets, which is then fixed by the subsequent hardening of the liquid layer and the droplets. In this embodiment, too, a synchronous structure is created between the underlying image and the applied structure. This synchronous structure is created by comparing electronic image data used both for printing the decorative underlying image and for spraying the droplets into the liquid base layer.

Example 2:

A cement fiber board with a thickness of 10 mm is transported to a roller application device, in which an aqueous acrylate varnish colored white with titanium dioxide is applied to the cement fiber board via roller application with a layer thickness of 40 µm. The aqueous acrylate paint has a viscosity of 300 to 600 mPa s. The cement fiber board with the liquid base layer is then fed to a digital printer in which an aqueous ink with droplets with a volume of 10 - 40 pL is sprayed on. The resulting structure is then pre-dried in an IR lamp and then finally dried in a nozzle channel in order to fix the resulting surface structure.

In an alternative embodiment, the liquid applied base layer can consist of an aqueous paint system or a solvent-based paint system. After the droplets have been sprayed on, this is then dried in a nozzle dryer, for example, and thus maintains the structure.

In an alternative embodiment, a solvent-based ink is first digitally printed onto a smooth workpiece, which reacts with the aqueous acrylate varnish applied in liquid form in a second step, such that the ink printed in the first step displaces the varnish in these areas. This displacement creates a structure at that point, which is then dried and fixed in the subsequent step by drying the aqueous acrylate varnish.

In general, any combination of the various process steps, ie printing a decorative image, applying a liquid base layer, spraying droplets into the liquid base layer, fixing and curing the base layer, if necessary printing a decorative image onto an existing, previously created structure and also printing a structure according to the state of the art already mentioned above in accordance with the document DE 10 2009 044 802 possible. The best combination of these process steps depends on which structure depths and which structure edge sharpness are to be created. In any case, the composition of the liquid base layer depends on the selected combination of process steps. In one embodiment of the method according to the invention, the liquid base layer is made of a transparent material, preferably an acrylate, which contains photoinitiators and hardens by UV radiation. In another alternative embodiment of the method according to the invention, the liquid base layer is colored white in order to print the optical image onto the structure created. Other colors, depending on the application for the liquid base layer, are also possible.

Reference symbols

1. 1 workpiece
2. 2 base layer
3. 3 droplets
4. 4 digital print heads
5. 5 UV lamps
6. 6 tape transport

Claims (13)

1. A method for producing a structure on a surface of a flat workpiece (1) with the following steps:

   (A) Application of a liquid base layer (2) on a surface of the workpiece (1);

   (B) Spraying of a plurality of droplets (3) into the still liquid base layer (2) in a manner, that the thickness of the base layer (2) changes on the positions, where the droplets (3) are spayed on, wherein indentations are formed in the liquid base layer (2) by the spraying of the droplets (3), wherein the sprayed droplets (3) are sprayed on according to a digital template, which is matched with a decor image that is printed on a surface beforehand or afterwards, in a manner, that the resulting structure is synchronous with the printed decor image for at least parts of the surface;

   (C) Fixation of the liquid base layer (2).
2. Method according to claim 1
   characterized in that
   the sprayed droplets (3) are evaporated, before or after the fixation of the liquid base layer (2).
3. Method according to claim 1
   characterized in that
   the sprayed droplets (3) are fixed through the fixation of the liquid base layer (2).
4. Method according to one of the preceding claims
   characterized in that
   a three-dimensional structure with a depth of 2 µm - 100 µm, preferably 3 µm - 50 µm, is formed by spraying the droplets (3) on the liquid base layer (2), which has been applied beforehand.
5. Method according to one of the preceding claims
   characterized in that
   the droplets (3) are sprayed on a surface by a digital print head and/or a digital nozzle beam of an apparatus for generating a structure on a surface according to a digital template.
6. Method according to one of the preceding claims
   characterized in that
   the liquid base layer (2) and/or the sprayed droplets (3) consist of a radiation-curing material.
7. Method according to the preceding claim characterized in that
   the fixation under step (C) is performed in a form of radiation-curing by means of UV radiation or by means of electron radiation.
8. Method according to one of the preceding claims
   characterized in that
   the droplets (3), which are sprayed on according to a digital template, consist of an acrylic material.
9. Method according to one of the preceding claims
   characterized in that
   after the step (C), fixation of the liquid base layer (2), a further method step (D) is carried out, in which additional droplets (3) are sprayed on the liquid base layer (2) and cured subsequently.
10. Method according to one of the preceding claims
    characterized in that
    during step (B), the plurality of droplets (3) consist of at least two different materials, in order that droplets with one material are applied on specific locations and droplets with a different material composition are applied on other specific locations.
11. Method according to one of the preceding claims
    characterized in that
    after the spraying of the plurality of droplets (3) into the still liquid base layer (2), a chemical reaction between the material of the sprayed droplets (3) and the still liquid base layer (2) occurs, wherein the reaction product between droplets (3) and base layer (2) changes the structure at this location optically and/or haptically.
12. Method according to one of the preceding claims
    characterized in that
    the volume of the droplet (3) varies according to a digital template during the spraying.
13. Device for the generation of a structure on a surface with a transportation device (6) for the supply and the removal of a workpiece provided with a liquid base layer (2) in a transport direction, with one or multiple print heads (4) and/or with one or multiple digital nozzle beams for the dispensing of droplets onto and/or into the liquid base layer (2) and with a fixation device (5), which is positioned subsequently to the print heads (2) and/or the nozzle beams in the transport direction and which radiates heat and/or light onto the base layer of the workpiece for fixing, wherein the device comprises a control device, which is configured for the execution of the method according to one of the claims 1 to 12.

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