DE102015110236B4 - Method and device for producing a structure on a surface - Google Patents

Abstract

Method for producing a structure on a surface of a flat workpiece (1) with the following steps:
(A) applying a liquid base layer (2) to a surface of the workpiece (1);
(B) spraying a large number of droplets (3) into the still liquid base layer (2) in such a way that the layer thickness of the base layer (2) changes at the points where the droplets (3) are sprayed on, with the spraying the droplets (3) are introduced into the previously applied, liquid base layer (2) depressions;
(C) fixing the liquid base layer (2).

Description

The present invention relates to a method for producing a structure on a surface of a flat workpiece, as well as 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 a 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, in addition to a decorative coating, such as a wood replica or a tile replica for a stone-like laminate floor, also to have a structure in the surface.

According to the prior art, this is produced, for example, in a melamine coating process by means of an embossing die. In this case, for example, a 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, which is coated with a beech replica look. On the surface with the beech replica optics, the embossing plate then results in structures with a depth of usually 20 µm up to 150 µm or 200 µm.

These structures are either produced 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 high-quality products, a so-called synchronous pore is also used, in which the embossing plate has a structure that is used synchronously with the printed wood look. In this case, for example, a printed knothole is actually noticeably deeper than the remainder of the printed wood look standing next to it, which is slightly higher.

In addition to this so-called melamine pressing process, there are other processes for coating wood-based panels. In another known method, for example, a wood-based panel is painted, printed and then provided with a transparent topcoat. In order to obtain a corresponding surface structure here too, there is the option of applying a structure with a structured topcoat roller. Such a procedure is for example in the DE 10 2007 019 871 described.

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

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

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

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

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

For this purpose, the method according to the invention and the device according to the invention provide that, in a first step, a workpiece to be coated, e.g. a wood-based panel, a cement fiber panel or similar (flat workpiece), is coated with a liquid base layer. In a second step, a structure is then created in this still liquid base layer with the aid of sprayed-on liquid droplets. In a third step, the structure created in this way is fixed in that the liquid base layer and the sprayed-on liquid droplets are dried together.

Further advantageous refinements of the present invention are the subject matter of the subclaims.

Before or after fixing the liquid base layer, the sprayed-on droplets can be vaporized.

In an alternative embodiment variant, the sprayed-on 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 can preferably have a control unit or a control device. This can preferably take place on the basis of a digital template, which can be retrieved, for example, from a data memory belonging to the device. The control device can control the delivery of the droplets, for example the delivery volume and the speed of the droplets when they strike the base layer.

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

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

The sprayed-on droplets, which are sprayed on according to a digital template, can be 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, at least in partial areas of the surface, synchronously with the printed decorative image.

The sprayed-on droplets can consist of an acrylate-containing material and can preferably be applied to the workpiece according to a digital template.

After the step of fixing the liquid base layer and the sprayed-on 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 multiplicity of droplets can consist of at least two different materials, so that droplets with one material are applied at certain points and droplets with a different material composition are applied at certain points.

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-on droplets and the still liquid base layer, such that the reaction product between the base layer and the droplets visually and / or changed haptically.

• 1 Schnittansicht eines Werkstücks vor dem Tröpfchenauftrag;
• 2 Werkstück während des Tröpfchenauftrags;
• 3 Werkstück nach dem Tröpfchenauftrag und nach der Aushärtung;
• 4 Werkstück nach erfolgtem Tröpfchenauftrag in der Oberansicht;
• 5 Vorrichtung zur Erzeugung einer Struktur auf dem Werkstück

The invention is explained in more detail below with reference to the accompanying figures. They show:

• 1 Sectional view of a workpiece before the application of droplets;
• 2 Workpiece during droplet application;
• 3 Workpiece after application of droplets and after hardening;
• 4th Workpiece after application of the droplets in the top view;
• 5 Device for creating a structure on the workpiece

To do this shows 1 the workpiece to be provided with a structure 1 as well as the applied, liquid base layer 2 .

In 2 are also the sprayed droplets 3 to see which individual drops or several drops are shown lined up in different groups.

The result of the spray is in 3 shown in which the droplets 3 in the previously applied, liquid base layer 2 have made corresponding indentations and have deposited themselves at the end of the indentation. 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 lacquer of the liquid base layer.

In 4th is the workpiece 1 with the liquid base layer applied to it 2 seen from above. The corresponding structures of the sprayed-on droplets are indicated in sketches 3 have generated here.

Embodiment 1:

First, a chipboard with a thickness of 12 mm is fed to the device according to the invention. The device is used to generate a structure on a surface of the workpiece with a transport device for the delivery and / or removal of a workpiece provided with a liquid base layer in one transport direction, with one or more print heads and / or one or more nozzle bars for dispensing droplets and / or in the liquid base layer and with a fixing device, which is arranged downstream of the print head or heads in the transport direction and which heat and / or light to the The base layer of the workpiece radiates, the device having a control device. In this context, light is not only understood to mean light in the visible wavelength range, but in particular also UV light and infrared light.

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

Then the pre-coated plate is fed to a digital printing unit, in which an also acrylate-containing ink from digital print heads ( 4th ) into the still liquid acrylate-containing base layer ( 2 ) are sprayed on. 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 constituents. 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 in the still liquid base layer. The droplets are sprayed on 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. The droplets displace the liquid material at the point when they hit the 50 µm thick base layer. Depending on the size of the droplets and the speed of the droplets during spraying, the droplet material can penetrate into the liquid base layer, so that a depression, for example of 50% of the base layer, is created. In the application example presented here, a penetration depth of 25 µm. Alternatively, with a correspondingly changed droplet size and speed, the droplet can also penetrate less deeply and / or throw up displaced material to the side of the droplet, so that both a depression and adjacent elevations arise in the liquid base layer. After the droplets have been printed, the liquid base layer and the printed droplets are cured. In a particularly preferred embodiment, this curing is carried out within less than 5 seconds after printing with the aid of UV LEDs, which cure the acrylate material, which also contains appropriate UV photoinitiators, to such an extent that the surface solidifies and the liquid does not run any further more can happen.

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

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 this three-dimensional structure has been produced, with a depth of 2 μm-100 μm, particularly preferably 3 μm-50 μm, a decorative image is printed on the surface that has already been structured in accordance with the invention. In a preferred embodiment, the printing process is also carried out with the aid of an inkjet printer. The decorative image is matched to the three-dimensional structure in such a way that the decorative elements of the image are synchronous with the previously generated three-dimensional structure, at least in partial areas of the surface. Synchronous here means that the decorative imaging achieves a length-wise deviation from the three-dimensional structure underneath 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 knot hole and the correspondingly assigned structure, e.g. a round depression of the same size as the printed knot hole.

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 was printed, the material surface was given a suitable pressure-receiving layer as a coating, which in one embodiment consists of a white lacquer. The decorative image is then printed on this, preferably likewise using an inkjet process. Thereafter, in the method according to the invention, the coating is carried out with the liquid base layer, which in this case is transparent in order to recognize the decoratively printed image underneath. After the application of this liquid base layer, the structure according to the invention is then produced with the spraying on of the droplets, which structure is then fixed by the subsequent hardening of the liquid layer and the droplets. In this embodiment too, a synchronous structure is preferably generated between the image below and the structure applied. This synchronous structure is generated by comparing electronic image data, which are used both for printing the decorative image below and for spraying the droplets into the liquid base layer.

Embodiment 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 with a layer thickness of 40 μm by roller application. The aqueous acrylate varnish has a viscosity of 300 to 600 mPa s. The cement fiber board thus provided with the liquid base layer is then fed to a digital printer, where an aqueous ink with droplets with a volume of 10 - 40 pL is sprayed on. The structure created in this way is then pre-dried in an IR radiator and then finally dried in a nozzle channel in order to fix the surface structure created in this way.

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

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

In general, any combination of the various process steps, i.e. printing a decorative image, applying a liquid base layer, spraying droplets into the liquid base layer, fixing and curing the base layer, possibly printing a decorative image on an existing, previously created structure, as well as printing a structure according to the prior art already mentioned above according to the document DE 10 2009 044 802 possible. The best combination of these process steps depends on which structure depths and which structure edge sharpening are to be created. In any case, the composition of the liquid base layer depends on the selected combination of process steps. Thus, in one embodiment of the method according to the invention, the liquid base layer is made of a transparent material, preferably of an acrylate, which contains photoinitiators and cures 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 produced. Other colors, depending on the application for the liquid base layer, are also possible.

List of reference symbols

1

workpiece

2

base layer

3

droplet

4th

Digital print heads

5

UV emitter

6th

Belt transport

Claims (18)

Method for producing a structure on a surface of a flat workpiece (1) with the following steps: (A) applying a liquid base layer (2) to a surface of the workpiece (1); (B) spraying a large number of droplets (3) into the still liquid base layer (2) in such a way that the layer thickness of the base layer (2) changes at the points where the droplets (3) are sprayed on, with the spraying the droplets (3) are introduced into the previously applied, liquid base layer (2) depressions; (C) fixing the liquid base layer (2). Procedure according to Claim 1 , characterized in that the sprayed-on droplets (3) are vaporized before or after the fixing of the liquid base layer (2). The method according to any one of the preceding claims, characterized in that at Fixing the liquid base layer (2), the sprayed-on droplets (3) are also fixed. Method according to one of the preceding claims, characterized in that the droplets (3) are sprayed onto a surface according to a digital template from a digital print head and / or digital nozzle bar of a device for generating a structure. Method according to one of the preceding claims, characterized in that the liquid base layer (2) and / or the sprayed-on droplets (3) consist of a radiation-curing material. Method according to one of the preceding claims, characterized in that the fixing under step (C) is in the form of radiation curing by UV radiation or by electron beams and / or by IR radiation. Method according to one of the preceding claims, characterized in that the sprayed-on droplets (3) are sprayed on according to a digital template, which is coordinated with a decor image previously or subsequently printed on the surface in such a way that the resulting structure at least in partial areas of the surface synchronously the printed decor image is. Method according to one of the preceding claims, characterized in that the droplets (3) sprayed on according to a digital template consist of an acrylate-containing material. Method according to one of the preceding claims, characterized in that after step (C), fixing the liquid base layer (2), a further method step (D) is carried out, in which further droplets (3) are applied to the then fixed base layer (2) be sprayed on and then cured. 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, so that at certain points droplets with one material and at certain points droplets with a different material composition are applied will. Method according to one of the preceding claims, characterized in that after the large number of droplets (3) have been sprayed into the still liquid base layer (2), a chemical reaction occurs between the material of the sprayed droplets (3) and the still liquid base layer (2) , in such a way that the reaction product between the base layer (2) and the droplets (3) changes the structure at the point optically and / or haptically. Method according to one of the preceding claims, characterized in that the volume and / or the speed of the droplets (3) is varied during the spraying according to a digital template. Method according to one of the preceding claims, characterized in that the liquid base layer (2) and / or the sprayed-on droplets (3) consists of an aqueous paint system and / or a solvent-based paint system. Method according to one of the preceding claims, characterized in that the depression made in the liquid base layer (2) corresponds in particular to 50% of the thickness of the base layer (2). Method according to one of the preceding claims, characterized in that a three-dimensional structure with a depth of 2 µm to 100 µm, preferably 3 µm to 50 µm, is introduced by spraying the droplets (3) into the previously applied liquid base layer (2) . Method according to one of the preceding claims, characterized in that by varying parameters, such as in particular material, droplet speed and / or droplet volume, in addition to the introduced depressions, elevations are also formed by the displaced lacquer of the liquid base layer. Method according to one of the preceding claims, characterized in that the volume of the droplets (3) is 3 pl to 100 pl, preferably 6 pl to 60 pl, particularly preferably 10 pl to 40 pl. Device for generating a structure on a surface with a transport device (6) for the delivery and / or removal of a workpiece provided with a liquid base layer (2) in one transport direction, with one or more print heads (4) and / or one or more digital nozzle bars for dispensing droplets on and / or into the liquid base layer (2) and with a fixing device (5) which is arranged downstream of the print heads (2) and / or nozzle bars in the transport direction and which radiates heat and / or light onto the base layer of the workpiece and / or it dries for fixation by means of nozzles, the device having a control device which is designed to carry out the method according to one of the preceding claims.

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