EP3666525B1 - Method and device for producing a structured surface - Google Patents

Description

The present invention relates to a method and a device for producing a decorative surface, in particular on a workpiece.

The aim of all decorative surfaces or decoratively coated surfaces is to look as true to nature as possible. In order to achieve this, for example, chipboard, MDF boards, HDF boards, plastic panels or external facades, e.g. metal sheets or plastic sandwich structures and similar panels with a replica of a natural material, e.g. wood, stone, are used according to the status of The technology then provides the surface with a three-dimensional embossed structure (haptics).

This feel is often applied synchronously with the underlying decorative image. This means that in the case of a wood imitation, e.g. a printed knothole is covered with a depression in the embossed structure above it, while higher areas of the wood look do not have an embossed depression.

Such a structure is also called a synchronous pore. This synchronous pore can be done in an analogous way using an embossing die tailored to a decorative image, which is in a press, for example in a cycle press or a continuous double belt press (cf. DE 103 16 695 B4 ) is placed in the exact decor.

The disclosure document EP 3 109 056 A1 shows a process in which such a synchronous structure can be applied very flexibly to a lacquer layer based on a digital template.

With all of these processes, it is very desirable to not only be able to feel the decorative and printed image as well as the structure (haptics), but also to recognize it visually. This means that during three-dimensional structuring, a difference in gloss level should be achieved between the deeper areas (pores) and the higher areas. The level of gloss is determined below according to the method according to DIN EN ISO 2813:2015-02. Gloss measurement measures an amount of light that a surface reflects relative to a reference standard of polished glass. The unit of measurement used is GU (Gloss Units). The amount of light reflected on the surface depends on the angle of incidence and the properties of the surface. When measuring gloss, different angles of incidence (20°, 60° and 85°) can be used to record the degree of reflectance, with measurements preferably being taken at the angle of incidence of 60°. Alternatively, the average value of measurements at the three angles of incidence can also be used. The reflectance compares the percentage of light energy emitted and received by a glossmeter at a specific angle of incidence.

Any surface or section of surface that, according to the standard, achieves less than 20 units of gloss when measured with a gloss meter is defined as "matt", and any surface or section of surface that achieves more than 60 units of gloss is defined as "glossy". designated. One of the two lacquer layers can be matt and the other glossy.

In order to achieve such a difference in the gloss points from the shiny areas to the less glossy areas of, for example, a difference of 20 points of gloss, preferably less than 10 points of gloss, using the digital method, it is known to use different digitally applied varnishes and thereby produce different degrees of gloss work. However, this process is very complex because different paints have to be used.

Furthermore, the change in the degree of gloss of an at least not completely solidified, in particular liquid, layer is known from the prior art not yet polymerized plastic, which is stimulated to polymerize by irradiation with high-energy electromagnetic radiation with a wavelength of less than 300 nm, preferably less than 250 nm. Due to the polymerization only in the upper layer of this liquid layer, which was applied, for example, with a layer thickness of 50 μm (polymerization, for example, only takes place in a layer of less than 0.1 μm, preferably less than 0.01 μm), results Through the polymerization of this thin layer, a “skin” forms on the still liquid layer underneath. As a result, this skin has wrinkling in the micro range or in the nano range, which ultimately causes the matting of this surface because, compared to an untreated layer, it increasingly scatters incident light in several spatial directions.

This process is known, for example, from the product area of “Innovative Surface Technologies GmbH”.

With this matting process, however, the resulting surface is evenly matted and has the same degree of gloss or mattness in all lower and higher areas. Especially in the case of wood reproductions with a very low level of gloss (very deep matt) of, for example, less than 5, preferably less than 3, gloss points, the structural depths of e.g. 10 to 50 µm previously applied using the known processes can be achieved with a height difference between the deeper pores and the higher areas can no longer be visually recognized.

Furthermore, from the US 2013 / 0 341 532 A1 a system and a method for drying ink are known.

The EP 2 418 019 A1 shows a process for the partial matting of UV lacquer layers.

From the EP 2 857 221 A1 a panel with a super matt surface is known.

Finally, it shows DE 10 2016 120 878 A1 a method for creating surface effects in a coating using high-energy particle radiation.

It is therefore the object of the present invention to demonstrate a method and a device with which a decorative surface can be produced very flexibly without involving the disadvantages of the various paints required.

This task is solved by the independent claims. Advantageous further training is the subject of the subclaims.

• Zuführen des Werkstückes, das mit einer flüssigen Schicht beschichtet ist, zu einer digitalen Druckstation;
• Aufbringen eines Mittels, das dazu ausgebildet ist, elektromagnetische Strahlung zumindest teilweise zu absorbieren, zumindest auf eine Teilfläche der Oberfläche der flüssigen Schicht, oder welches in Kontakt mit der Oberfläche ein Reaktionsprodukt entstehen lässt, das derart beschaffen ist, dass es elektromagnetische Strahlung zumindest teilweise zu absorbieren vermag;
• Bestrahlen der Oberfläche der flüssigen Schicht und des Mittels mit elektromagnetischer Strahlung mit einer Wellenlänge von weniger als 300 nm, bevorzugt weniger als 250 nm, besonders bevorzugt weniger als 200 nm;

In order to be able to produce these differences in gloss and at the same time influence the level of gloss by means of the microfolding described above using high-energy, electromagnetic radiation with a wavelength of less than 200 nm, the method according to the invention suggests the following procedure:
According to the invention, a method for producing a decorative surface on a workpiece according to claim 1 is provided. The procedure includes the following steps:

• feeding the workpiece coated with a liquid layer to a digital printing station;
• Applying an agent which is designed to at least partially absorb electromagnetic radiation, at least to a partial area of the surface of the liquid layer, or which, in contact with the surface, creates a reaction product which is such that it at least partially absorbs electromagnetic radiation able to absorb;
• irradiating the surface of the liquid layer and the agent with electromagnetic radiation with a wavelength of less than 300 nm, preferably less than 250 nm, particularly preferably less than 200 nm;

In order to make the method flexible, electromagnetic radiation with different wavelengths in different time sequences is preferably used. Preferably, a wavelength of less than 200 nm is used first, then a wavelength of less than 250 nm and finally a wavelength of less than 300 nm.

Preferably, the agent is sprayed onto the liquid layer in the form of fine droplets and/or applied in the form of droplets, in particular by means of a digital print head or a digital nozzle bar.

Preferably, the chemical and/or physical properties of the agent are designed to absorb at least 10%, preferably at least 30%, particularly preferably at least 50% of incident electromagnetic radiation.

The higher the absorption property of the agent, the less of it must be applied to the liquid layer to achieve the same absorption effect. Good absorption properties therefore enable the process to be operated economically.

In this application, the fine droplets preferably form a uniform layer on the surface of the liquid layer when they are applied, and are particularly suitable for application over larger areas.

The fine droplets in particular have a volume of 0.1 μl to 1 μl, preferably from 0.3 μl to 0.8 μl, particularly preferably from 0.5 to 0.6 μl.

The droplets in particular have a volume of 1 μl to 80 μl, preferably from 3 μl to 12 μl, particularly preferably from 5 μl to 10 μl.

The speed of the droplets and/or the fine droplets is in particular between 0.5 m/s and 12 m/s, preferably between 3 m/s and 7 m/s, particularly preferably between 5 m/s and 6 m/s.

In one embodiment, the surface of a liquid layer on a workpiece is sprayed with droplets of an agent in the form of a liquid before the still liquid paint layer is irradiated with high-energy electromagnetic radiation with a wavelength of less than 200 nm, which is designed to: to at least partially absorb the high-energy electromagnetic radiation. This ensures that the polymerization in the surface of the underlying layer and droplets does not polymerize or polymerizes much less at the points where the surface was sprayed with the droplets and the degree of mattness is therefore different, preferably lower, than at those that did not pass through the droplets sprayed surfaces.

Preferably, the droplets and/or the fine droplets are released in such a way that when they hit the surface of the liquid layer, they at least penetrate into it partially penetrate, and/or come to rest on it and/or displace it and create depressions, the droplets being adjusted in particular in volume and/or speed in order to influence the penetration depth and displacement.

The release of the fine droplets is preferably controlled in such a way that their momentum when striking the surface of the liquid layer is not sufficient to at least partially overcome the surface tension and/or the viscosity forces of the liquid layer, so that the fine droplets preferably rest on the surface of the liquid layer come to rest in a liquid layer.

The release of the droplets is preferably controlled in such a way that their impulse when striking the surface of the liquid layer is sufficient to at least partially overcome the surface tension and/or the viscosity forces of the liquid layer, so that the droplets displace the liquid layer, whereby a structure with a height difference of 10 to 50 µm can be introduced into the liquid layer.

By irradiating the surface of the liquid layer with the electromagnetic radiation, with a wavelength of less than 300 nm, preferably less than 250 nm, particularly preferably less than 200 nm, a microstructure or a nanostructure is preferably formed in the surface of the uppermost partial area The liquid layer is formed by micro-folding, which scatters the reflection of incident light and thus creates an optically matter impression. The microfolding of the uppermost surface of the liquid layer is caused by polymerization of the same, as described in the introduction.

In order to enable this process to be carried out, the liquid layer preferably consists of a polymerizable acrylate mixture. It also preferably has radiation-curing properties.

In a specific exemplary embodiment, the liquid layer consists of an acrylate lacquer 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 industrially standard photoinitiator and 17 % by weight of other components. The acrylate varnish has a viscosity of 80-500 mPas, preferably 150-400 mPas, measured at 25 ° C and normal pressure with a rheometer.

Furthermore, the applied agent preferably consists of a polymerizable acrylate mixture and/or of a solvent-containing liquid and/or of an aqueous mixture, in particular with a water content of more than 30%, preferably more than 50%.

The layer is preferably hardened by irradiation with electromagnetic radiation, with a wavelength preferably greater than 250 nm, particularly preferably greater than 300 nm, and/or by irradiation with electron radiation and/or by active and/or passive drying.

Active drying is understood to mean any type of drying in which the liquid layer is dried by creating special conditions. The liquid layer can be dried in particular by flowing with a fluid, in particular with air, and/or by supplying heat, in particular by means of IR radiation or by using a heater.

Passive drying, on the other hand, is preferably characterized by the fact that the liquid layer hardens alone and without further processing. This can be done, for example, by transporting the workpiece on a free section of a belt transport and/or by placing the workpiece down.

Curing is preferably carried out by means of reaction curing using, for example, a two-component system which cures by chemical reaction between the components within less than 30 minutes, preferably less than 5 minutes.

• einen Stoff aus der Gruppe der gehinderte Amine in einer Konzentration von 0 - 20%
• einen Stoff aus der Gruppe der N,N'-Diphenyleoxamide in einer Konzentration von 0 - 20%.

The applied agent preferably consists only of water, or in addition to water with a total proportion of 10 - 99%, it has at least one of the following ingredients in the stated concentration (vol%):

• a substance from the group of hindered amines in a concentration of 0 - 20%
• a substance from the group of N,N'-diphenyleoxamides in a concentration of 0 - 20%.

• einen Stoff aus der Gruppe der gehinderte Amine in einer Konzentration von 0 - 20%
• einen Stoff aus der Gruppe der N,N'-Diphenyleoxamide in einer Konzentration von 0 - 20%.

In addition to an alcohol and/or a glycol with a total proportion (alcohol and/or glycol) of 10 - 99%, the applied agent preferably has at least one of the following ingredients in the stated concentration (vol%):

• a substance from the group of hindered amines in a concentration of 0 - 20%
• a substance from the group of N,N'-diphenyleoxamides in a concentration of 0 - 20%.

• einen Stoff aus der Gruppe der Benzophenone in einer Konzentration von 0 - 15%
• einen Stoff aus der Gruppe der Benzotrialzole in einer Konzentration von 0 - 15%.

In addition to a polymer content of 10-99%, the applied agent preferably has at least one of the following ingredients in the stated concentration (vol%):

• a substance from the group of benzophenones in a concentration of 0 - 15%
• a substance from the group of benzotrialzoles in a concentration of 0 - 15%.

Furthermore, the applied agent is preferably such that it is particularly preferred, in particular after irradiation with electromagnetic radiation, in particular of less than 300 nm, preferably of less than 250 nm of less than 200 nm, within less than 3 minutes, preferably within less than 1 minute, particularly preferably within less than half a minute.

The faster the agent evaporates from the surface of the liquid layer after its application or after the above-mentioned irradiation, the faster it is possible to switch to the next processing step, which brings advantages in terms of cycle time and production speed.

A further step in the execution of the process is particularly preferably provided, in which the evaporation of the agent is carried out within less than 3 minutes, preferably within less than 1 minute, particularly preferably within less than half a minute.

Such an evaporation step can in particular be designed in such a way that the workpiece with the agent applied to the liquid layer is transported through a correspondingly designed route section which has special evaporation conditions for the agent.

The evaporation of the agent can in particular be carried out actively, with the agent being evaporated by creating special conditions. The agent can be evaporated in particular by means of a fluid flow, in particular air, and/or by supplying heat, in particular by means of IR radiation or by using a heater.

Alternatively or additionally, the agent can also evaporate alone and without further processing. This can be done, for example, by transporting the workpiece on a free section of a belt transport, and/or by storing the workpiece, with further processing taking place after evaporation.

When the agent hits the surface or comes into contact with the surface of the liquid layer, it preferably undergoes a chemical reaction in this way that there is an optical and/or haptic change to the surface at these points.

This can preferably be done by polymerizing the surface of the liquid layer together with the agent, which is triggered and/or enhanced in particular by irradiation with electromagnetic radiation. The polymer formation changes, for example, the reflection properties of the surface of the liquid layer and/or its roughness.

Particularly preferably, a chemical reaction step is provided which is designed in such a way that the chemical reaction between the agent and the layer is given sufficient time for this chemical reaction to take place at least partially.

Such a chemical reaction step can in particular be designed in such a way that the workpiece with the agent applied to the liquid layer is transported through a correspondingly designed route section which has special reaction conditions for the agent and the liquid layer.

This can be achieved, for example, by supplying heat, in particular by means of IR radiation or by using a heater.

The chemical reaction is preferably designed in such a way that upon impact or further contact between the agent and the liquid layer, a reaction product is formed which has an absorption property towards electromagnetic radiation.

When it hits the layer, the applied agent preferably enters into a chemical reaction in such a way that the reaction product at this point is irradiated with electromagnetic radiation with a wavelength of less than 300 nm, preferably less than 250 nm, particularly preferably of less than 200 nm, no or less microstructure formation is achieved than on the areas where no agent was applied to the surface.

Preferably, a further step is also provided in which the liquid layer is applied to a surface of the workpiece.

This can be done, for example, by roller application, in which the surface of the workpiece is coated with the liquid layer over the entire surface or over partial areas that are to be structured. Alternatively, the application can also be carried out using a spray head, which applies the liquid layer to the surface of the workpiece using nozzles.

Preferably, a further step, carried out at the same time as the application of the agent, is part of the process in which the liquid layer is structured using an analog or digital structuring process, whereby in particular a structure of the liquid layer with a height difference of 10 to 50 μm is achieved.

A further step is preferably also provided in which the liquid layer is structured by means of an analog structuring process, in particular with an embossing roller or an embossing plate, and/or is displaced by structuring droplets by means of analog or digital application, in particular by means of a digital print head, whereby the structuring depressions are introduced into the layer.

The structuring droplets in particular have a volume of 1 μl to 80 μl, preferably from 3 μl to 12 μl, particularly preferably from 5 μl to 10 μl.

The speed of the structuring droplets is in particular between 1 m/s and 12 m/s, preferably between 3 m/s and 7 m/s, particularly preferably between 5 m/s and 6 m/s.

The structuring droplets preferably consist of the same material as the liquid layer, so that when they hit the liquid layer, only a physically caused displacement for structuring the liquid layer occurs.

Alternatively or additionally, structuring droplets can also be applied that differ in their composition, in particular in their density, from the liquid layer. It is also conceivable to design these structuring droplets in such a way that they react chemically with the surface of the liquid layer in order to achieve an optical and/or haptic change to this surface.

Furthermore, it is conceivable that the structuring of the liquid layer is carried out in such a way that this structure is formed as synchronously as possible (i.e. with a maximum deviation of 2 mm, preferably 1 mm) to a decorative image applied to the workpiece under the liquid layer. i.e. If a wood grain is depicted on the workpiece, the structuring also reproduces a wood grain that corresponds to the grain of the decorative image. The layer is then preferably at least partially transparent after curing at the latest, so that the decorative image becomes correspondingly visible.

Preferably, a further step can also be provided in which, for example, a decorative image is applied to the workpiece using digital printing. Alternatively, a decorative image can also be applied to a structured layer that is at least partially hardened or which has a surface solidified by polymerization. This decorative image can be designed in one or more colors.

The method steps described here are not to be seen as limiting the subject matter of the method according to the invention. Rather, further methods can be obtained by exchanging, repeating or omitting individual steps, as long as the steps essential to the invention are retained. For example, after the first coating with a liquid layer, a further coating with a liquid layer can also be carried out, which is also matted in order to achieve special optical effects.

• eine Transportvorrichtung mit einer Haupttransportrichtung, wobei die Transportvorrichtung dazu ausgebildet ist, ein Werkstück, das mit einer flüssigen Schicht beschichtet ist, zu weiteren Elementen der Vorrichtung zu transportieren,
• eine Abgabevorrichtung, die dazu ausgebildet ist, ein Mittel zumindest auf eine Teilfläche der Oberfläche der flüssigen Schicht aufzubringen;
• eine Strahlenquelle, die dazu ausgebildet ist, die Oberfläche der flüssigen Schicht mit elektromagnetischer Strahlung mit einer Wellenlänge von weniger als 300 nm, vorzugsweise weniger als 250 nm, besonders bevorzugt weniger als 200 nm, zu bestrahlen.

According to the invention, a device according to claim 10 is also provided, which is suitable for carrying out the method according to the invention. The device is provided with the following elements:

• a transport device with a main transport direction, the transport device being designed to transport a workpiece that is coated with a liquid layer to further elements of the device,
• a dispensing device configured to apply an agent to at least a portion of the surface of the liquid layer;
• a radiation source which is designed to irradiate the surface of the liquid layer with electromagnetic radiation with a wavelength of less than 300 nm, preferably less than 250 nm, particularly preferably less than 200 nm.

The device preferably has a curing station, which can be designed differently in order to achieve curing of the at least partially liquid layer.

For this purpose, a radiation source can preferably be provided which is designed to irradiate the liquid layer and/or the applied agent with electromagnetic radiation of variable wavelength, in particular with IR radiation, at least until it is partially hardened.

The radiation source is preferably designed separately and/or identical to the radiation source which emits the electromagnetic radiation with a wavelength of less than 300 nm, preferably less than 250 nm, particularly preferably less than 200 nm.

Alternatively or additionally, the radiation source can emit electron radiation of variable wavelength.

Furthermore, the curing station preferably has a fluid source which is designed to flow around the layer, in particular with air, whereby the fluid can be influenced in particular in the parameters of flow velocity and/or temperature and/or humidity.

Furthermore, the curing station preferably has an electron beam source which is designed to irradiate the liquid layer and/or the applied agent with electron radiation at least until they are partially hardened.

Furthermore, the curing station preferably has a drying station which is designed to accommodate the workpiece until the layer has at least partially hardened and, in particular, to provide a predetermined drying temperature by means of a heat source to which the workpiece with the layer can be exposed.

The device preferably also has a control means which is designed to control the device in accordance with the method steps. This can be, for example, an electronically controlled control unit, in particular a control device, which is designed to transmit electronic control signals to the other elements of the device and preferably to receive signals from the other elements of the device. For example, feedback about the amount of droplets currently released or their speed and other information relating to the method can be transmitted to the control means, whereby it receives information about the current implementation of the method and can provide appropriately adapted control signals.

Preferably, the device further has a reaction area which is designed to enable evaporation and/or a chemical reaction, the reaction area being designed in particular as an area through which the transport device transports the workpiece, and its extent and the transport speed are related to each other are coordinated so that evaporation and/or a reaction are at least partially enabled. For example, this can be a chamber through which the workpiece, which can also be web-shaped, is transported.

The device preferably also has a protective gas chamber which is designed to at least contain the workpiece and/or the layer and/or the agent to surround a part of the route during transport with a protective gas, in particular an inert gas, preferably nitrogen. This makes it possible to create an atmosphere that does not influence a chemical reaction of the layer with the agent or polymerization by electromagnetic radiation.

The device preferably also has an application device which is designed to apply the liquid layer to the workpiece. This application device in particular has a rolling mill which is designed to coat the workpiece with a liquid layer. Alternatively or additionally, a spray head can also be provided, which applies the liquid layer to the surface of the workpiece using nozzles.

The device preferably also has a structuring element which is designed to introduce a structure into the liquid layer. This can preferably be an analogous embossing roller or an embossing plate, on which a structure is provided by means of elevations, which can be transferred to the liquid layer by pressing it into it. Alternatively or additionally, the structuring element has at least one digital print head, which is designed to apply structuring droplets to the liquid layer. The digital print head is preferably able to adapt the pulse and/or volume and/or speed of the structuring droplets in such a way that the structuring droplets achieve a structuring effect by striking the liquid layer, in particular by displacing the liquid layer.

The device preferably also has an application device for applying a decorative image, with at least one digital print head which is designed to apply color to the surface of the layer and/or the workpiece. This makes it possible to provide the surface of the workpiece and/or the layer with a decorative image.

Preferably, the transport device has a conveyor belt, with the above-described elements of the device one after the other in the main transport direction are arranged. In particular, a processing sequence of the process steps can be specified via the arrangement order.

The dispensing device preferably has at least one digital print head which is designed to dispense the agent. The digital print head is preferably designed so that it can optionally release the agent in the form of fine droplets or droplets onto the surface of the liquid layer. Preferably, it is further designed to meter in particular the volume, speed and/or momentum of the fine pots and/or droplets in accordance with a specification, for example from the control means. The reaction region preferably has special boundary conditions that are necessary to trigger evaporation and/or a chemical reaction. The reaction region preferably extends over at least part of the protective gas chamber. This advantageously ensures that the reaction takes place at least partially under protective gas, so that the influence of undesirable chemical components, in particular the ambient air, is minimized.

The device elements described here are not to be seen as limiting the subject matter of the device according to the invention. Rather, further devices can be obtained by exchanging, multiplying or omitting individual elements, as long as the elements essential to the invention are retained in accordance with the claim.

For example, after the first coating and matting with a liquid layer, a further coating with a liquid layer can also be carried out, which is also matted in order to achieve special optical effects.

Figur 1

ein Werkstück das mit einer flüssigen Schicht beschichtet ist und auf das ein Mittel in Form von Tröpfchen aufgetragen wird;

Figur 2

das Werkstück in einer Schutzgaskammer, in der es mittels einer Lampe mit elektromagnetischer Strahlung bestrahlt wird;

Figur 3

das Werkstück mit unterschiedlichen Mattierungsgraden der aufgetragenen Schicht;

Figur 4

die Einwirkung der elektromagnetischen Strahlung auf die flüssige Schicht und auf das aufgetragene Mittel;

Figur 5

eine weitere Ausführungsform, in der das Mittel lediglich auf die Oberfläche der flüssigen Schicht aufgetragen wurde, ohne diese in ihrer Struktur zu verändern;

Figur 6

ein alternatives Werkstück als Bahnware

Figur 7

ein Ablaufdiagramm einer bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens;

Figur 8

einen schematischen Aufbau einer bevorzugten Ausführungsform einer erfindungsgemäßen Vorrichtung.

Concrete exemplary embodiments of the invention are described below with the aid of the accompanying drawings. Show it:

Figure 1

a workpiece that is coated with a liquid layer and to which an agent is applied in the form of droplets;

Figure 2

the workpiece in a protective gas chamber in which it is irradiated with electromagnetic radiation using a lamp;

Figure 3

the workpiece with different degrees of matting of the applied layer;

Figure 4

the effect of electromagnetic radiation on the liquid layer and on the applied agent;

Figure 5

a further embodiment in which the agent was only applied to the surface of the liquid layer without changing its structure;

Figure 6

an alternative workpiece as rail goods

Figure 7

a flowchart of a preferred embodiment of the method according to the invention;

Figure 8

a schematic structure of a preferred embodiment of a device according to the invention.

In Figure 1 is a workpiece 1, shown with a liquid layer 2 applied thereon and an agent that was sprayed onto the layer 2 in the form of droplets 3 from digital print heads 4 arranged above it. The workpiece 1 is moved from right to left in a transport direction under the print heads 4, so that the print heads 4 can apply the droplets 3 to different locations on the liquid layer 2.

The means is designed to at least partially absorb electromagnetic radiation. It can thus be achieved that parts of the surface of the liquid layer 2, which are covered with the agent, can be at least partially shielded from the direct influence of electromagnetic radiation.

It can be seen that the droplets 3 have created depressions when they hit the liquid layer 2, the liquid layer 2 having such a viscosity that these depressions do not immediately disappear. Thus, by applying the droplets 3, a structuring of the liquid layer 2 can be achieved at least over a certain period of time of less than 5 minutes, preferably less than 3 minutes, which can be permanently solidified by final curing.

In Figure 2 This workpiece 1 with the liquid layer 2 is located in a protective gas chamber 24, which predominantly has a nitrogen atmosphere inside 5 in order to keep oxygen atoms or oxygen molecules away from the surface of the layer 2 in order to make undesirable chemical reactions with oxygen in the air more difficult.

The surface of layer 2 here has a structure which is formed by the droplets 3, as in Figure 1 represented, was generated. The droplets 3 are still in the depressions.

Furthermore, a radiation source 6 for electromagnetic radiation 6a is provided, under which the workpiece 1 with the liquid layer 2 structured by the depressions is moved through. The radiation source 6 is designed so that it emits the electromagnetic radiation 6a onto the surface of the liquid layer 2. The electromagnetic radiation 6a has, for example, a wavelength of less than 300 nm, preferably less than 250 nm, particularly preferably less than 200 nm.

Instead of nitrogen, another inert gas atmosphere can also be formed in the interior 5 of the protective gas chamber 24, which is suitable for keeping oxygen atoms and/or molecules away from the surface of the layer 2 in particular.

The protective gas chamber 24 can be designed as a closed space, or as an area through which a workpiece 1 is moved. This is particularly advantageous for web-shaped workpieces 1,

Figure 3 shows the liquid layer 2 on the workpiece 1 after irradiation with electromagnetic radiation 6a from the radiation source 6. The surface of the liquid layer 2 is polymerized to a greater or lesser extent at various points.

At points 7, the electromagnetic radiation 6a was able to hit the surface of layer 2 unhindered, as a result of which stronger polymerization took place here. The surface has become rougher at this point, at least in the micro or nano range, since the molecules of the liquid layer 2 near the surface have become more strongly networked due to the electromagnetic radiation 6a. Therefore, light that falls on these points 7 is now diffusely reflected in several directions, whereby a higher degree of dullness of these points 7 is achieved.

In contrast, the electromagnetic radiation 6a could not directly reach the points 8 of the surface of the liquid layer 2, as this, as in the Figures 1 and 2 shown, with the agent in the form of droplets 3 were covered. The agent is now no longer present on the surface of the liquid layer 2 because, for example, it has evaporated.

However, the agent has at least partially absorbed the electromagnetic radiation in the lower locations 8, so that polymerization of the surface of the liquid layer 2 could not take place here to the same extent as in the locations 7. As a result, the lower locations 8 are therefore less rough , at least in the micro or nano range, whereby a reflection of incident light is scattered less strongly. Spots 8 therefore appear shinier compared to spots 7.

Figure 4 shows in the lower illustration a section, which is marked in the upper illustration by the two vertical dashed lines, from the layer 2 on the workpiece 1 and the agent sprayed thereon in the form of droplets 3, which contain the electromagnetic radiation 6a at the points of At least partially absorb droplets 3.

It can be seen that in places that are not covered with the droplets 3, the electromagnetic radiation 6a can hit the surface of the liquid layer 2 unhindered. This is illustrated by the length of the arrows of the electromagnetic radiation 6a, which describe the intensity with which the surface of the liquid layer 2 is irradiated.

In contrast, the intensity of the electromagnetic radiation 6a on the surface of the liquid layer 2 at locations that are covered with droplets 3 is significantly lower, as can be seen from the comparatively short arrows of the electromagnetic radiation 6a below the droplets 3.

Figure 5 shows a further embodiment in which the agent was only applied to the surface of the liquid layer without changing its structure.

The agent is applied here in the form of fine droplets 3a, which were applied to the liquid layer in such a way that they do not sink into the surface of the liquid layer 2 or do not displace it and create depressions. This can be achieved, for example, by adjusting the volume and/or impact speed of the fine droplets 3a so that the surface of the liquid layer is not changed by them.

In this case, a pulse of the fine droplets 3a can be adjusted such that it is not sufficient to break the surface tension of the liquid layer 2, as a result of which the fine droplets 3a do not sink into the liquid layer 2, and/or that it is not sufficient to to overcome the viscosity forces of the liquid layer 2, whereby no depressions are introduced into the liquid layer 2 due to the fine droplets 3a.

It can also be seen that the fine droplets 3a are dimensioned such that they form a fine veil on the surface of the liquid layer, at least on partial areas thereof.

In this way, it is possible to introduce electromagnetic radiation 6a to the surface of the liquid layer 2 at different levels at different points, since it penetrates the surface of the liquid layer to a lesser extent at points that have the agent. This is comparable to Figure 4 , represented by the different arrow lengths of the electromagnetic radiation 6a. Thus, the surface at points 7 that are not covered with the fine droplets 3a is irradiated with higher intensity than points 8 that were at least partially shielded from the electromagnetic radiation 6a by the agent in the form of fine droplets 3a or a veil thereof .

Figure 6 shows an alternative workpiece 1 as web material, which is unwound from a roll 9 and is also coated with a liquid layer 2. The workpiece 1 moves continuously to the right, where further processing steps described above (not shown) follow.

In this embodiment, the liquid layer 2 is applied by means of a rolling mill 10 after unrolling from the roll 9. The matting process can therefore be applied not only to individual flat workpieces, such as panels, for example made of wood, plastic or metal, but also to web-shaped workpieces 1,

Figure 7 shows a flowchart of a preferred embodiment of the method according to the invention.

In a first processing step, a liquid layer S20 is applied to the surface of a workpiece. This can be done, for example, in Figure 6 done in the manner shown.

The workpiece coated in this way is then structured S22, so that the liquid layer is provided with a structure after this step has been carried out. The liquid layer can be structured, for example, by an analogous structuring process, in particular mechanical Embossing the surface of the liquid layer, for example by rolling an embossing roller on the surface of the liquid layer.

Alternatively or additionally, the structuring of the liquid layer can also be done digitally, for example using digital print heads to apply droplets to the surface of the liquid layer, which penetrate into it and/or displace it. The droplets are advantageously made of the same material as the liquid layer in order to simply achieve a structuring effect. In another embodiment, the droplets can consist of a different material than the liquid layer, whereby, for example, a chemical reaction between the liquid layer and the droplets can be achieved, in particular by later irradiation with electromagnetic radiation and/or electron radiation and/or increasing the temperature. The chemical reaction is designed in such a way that its reaction product has a structuring effect on the surface of the liquid layer, whereby it is changed optically and/or haptically.

If there is a decorative image on the workpiece, which was covered by the application S20 of the liquid, in particular partially transparent layer, the structuring of the surface ensures that the structure is synchronous with the image visible through the liquid layer.

The workpiece prepared in this way is then fed to a digital printing station, for example via a continuous belt transport (S10).

In a further step S12, the digital printing station enables the application of an agent designed to at least partially absorb electromagnetic radiation to the surface of the liquid layer.

The application S12 of the agent can take place in the form of droplets, which, for example, are coordinated in speed and volume so that they can overcome the surface tension and / or the viscosity forces of the liquid layer in order to structure it. Alternatively or additionally, the application of S12 of the agent in the form of fine droplets, which are dimensioned so that they do not change the surface of the liquid layer, but only cover it at least on partial areas.

This is followed by irradiation S14 of the surface of the liquid layer with high-energy electromagnetic radiation, as in Figures 2 , 4 and 5 shown, wherein portions of the liquid layer that are covered with the agent experience radiation influence with reduced intensity compared to portions that are not covered with the agent and are instead directly exposed to the radiation.

The irradiation S14 of the surface of the liquid layer leads to its polymerization to a certain penetration depth, for example 0.1 μm, preferably less than 0.01 μm, which, as in Figure 3 shown, occurred more strongly in the areas that were directly exposed to the radiation. After the irradiation S14 has been completed, these areas are duller than the areas that were covered with the agent.

The applied agent is then evaporated in a further step S18. This can be done, for example, simply by heating the agent with an IR lamp, for example, the agent advantageously having a lower evaporation temperature than the liquid layer.

However, if the agent has the property that it evaporates after a certain time, evaporation S18 can simply consist of waiting until the agent has evaporated. This can be done, for example, by transporting the workpiece on a belt transport before carrying out the next method step, this belt transport being designed in terms of its length, transport speed and ambient temperature in such a way that evaporation S18 is made possible during transport.

Then, in a further step, the liquid and now at least partially matted layer is hardened S16.

For this purpose, the workpiece, in particular the liquid layer, can be irradiated again with electromagnetic radiation which comes from the same radiation source as was used in step S14. Alternatively, other radiation sources can also be provided, or other types of curing can take place, such as active or passive air drying, or irradiation with electron beams.

Figure 8 shows a schematic structure of a preferred embodiment of a device 18 according to the invention.

A transport device 20 is shown, which is designed as a belt transport, on which a workpiece 1 is transported in the transport direction 28. A liquid layer 2 is applied to the top of the workpiece 1.

The workpiece 1 is transported into a protective gas chamber 24 in the transport direction 28 as the transport progresses. This has a protective gas atmosphere, in particular an inert gas atmosphere, for example a nitrogen atmosphere, in its interior 5, whereby oxygen in particular can be kept away from the liquid layer 2, thereby avoiding undesirable chemical reactions.

Furthermore, digital print heads 4 are provided in the interior 5 of the protective gas chamber 24, which are designed to apply an agent which is designed to at least partially absorb electromagnetic radiation to the liquid layer 2. In the illustration shown, this is done by applying droplets 3, with the digital print heads 4 being designed to control the droplet delivery, particularly with regard to droplet speed, volume and momentum.

Alternatively or additionally, the application of the agent from the digital print heads 4 can also take place in the form of fine droplets 3a, which are distributed as evenly as possible on the surface of the liquid layer 2 and in particular combine to form partial areas.

The digital print heads 4 are followed by a radiation source 6, which is designed to emit electromagnetic radiation 6a with a wavelength of in particular less than 300 nm, preferably less than 250 nm, particularly preferably less than 200 nm, onto the surface of the liquid layer 2 to achieve the matting described above.

Furthermore, a control means (not shown) is provided, which is designed to control the device 18 and its elements in order to carry out the method according to the invention.

The embodiments presented here do not limit the subject matter of the invention. Rather, further embodiments are conceivable. This is how it can be done Figure 7 The methods described also have further process steps, or individual process steps can be swapped or omitted. Further aspects of the invention will be specified below using further concrete exemplary embodiments.

Example 1:
An HDF board is coated with a white printing base. The plate coated in this way is fed to a digital printer (in an alternative embodiment also a rotary printing machine with several colors) and decoratively printed with, for example, a wooden decor. In an alternative embodiment, an intermediate layer of varnish or primer, ideally transparent, can be applied to this decorative layer printed in this way. A liquid layer 2 with a layer thickness of 50-80 µm is then applied. This layer can be applied in a roller application machine or, in an alternative embodiment, in a spray machine. The layer consists of a UV-curing acrylate mixture. The HDF plate coated in this way is fed to another printing station in which droplets 3 are sprayed onto parts of the surface from digital print heads. In the embodiment shown here, these droplets consist of an aqueous mixture, containing in particular the following components

In an alternative embodiment, the droplets can also consist of a solvent-based or acrylate-based liquid.

At the points where they hit, the droplets change the surface of the still liquid layer in such a way that they move at high speeds of 4-6 m/sec. displace the still liquid layer 2.

The workpiece with the liquid layer 2 modified in this way is then fed to a radiation source 6, which emits electromagnetic radiation 6a with a wavelength of <250 nm onto the surface. This electromagnetic radiation is at least partially absorbed by the droplets 3 and hits the underlying layer 2. This layer 2 begins to polymerize on its surface and thereby fold (cf. reference number 7 Fig. 3 . In the deeper locations where the droplets 3 have at least partially absorbed the electromagnetic radiation, there is less polymerization and thus less folding at the locations 8 in Fig. 3 .

This results in the desired product with different levels of gloss or mattness in the pores or outside the pores. The workpiece is then fed to another UV radiation source with a wavelength > 300 nm in order to completely harden the underlying, still liquid layer 2, in particular the acrylate layer.

Claims (13)

1. A method for producing a decorative surface on a workpiece (1), comprising the following steps:

   - feeding (S10) of the workpiece (1) coated with a liquid layer (2) which is polymerizable by electromagnetic radiation to a digital printing station;

   - application (S12) of an agent at least on a partial area of the surface of the liquid layer (2) by the digital printing station, wherein the agent is adapted to at least partially absorbing electromagnetic radiation to reduce the intensity of electromagnetic radiation on the surface of the liquid layer (2), or which, in contact with the surface, produces a reaction product which is adapted to at least partially absorbing electromagnetic radiation to reduce the intensity of electromagnetic radiation on the surface of the liquid layer (2);

   irradiation (S14) of the surface of the liquid layer (2) and of the agent with electromagnetic radiation having a wavelength of less than 300 nm, wherein

   the formation of a microstructure or nanostructure is carried out by the irradiation (S14) of the surface of the liquid layer (2) with the electromagnetic radiation in the surface of the uppermost partial area of the liquid layer (2), which in the later use of the workpiece (1) scatters light reflection and thus results in an optically more matte impression, wherein

   areas (7) of the liquid layer (2), which were not covered by the agent are polymerized more strongly as areas (8), which were covered by the agent,

   irradiation of the surface of the liquid layer (2) and of the agent with electromagnetic radiation having a variable wavelength for curing (S16) of the layer (2) with electromagnetic radiation.
2. The method according to claim 1, characterized in that

   the agent is sprayed onto the liquid layer (2), in particular by means of a digital print head (4) or a digital nozzle bar, in the form of fine droplets (3a) and/or applied in the form of droplets (3), wherein the fine droplets (3a) have a volume of 0,1 pl to 1 pl, preferably from 0.3 pl to 0.8 pl, especially preferred from 0.5 to 0.6 pl, and/or the droplets (3) have a volume of 1 pl to 80 pl, preferably from 3 pl to 12 pl, especially preferred from 5 pl to 10 pl, and/or

   the chemical and/or physical properties of the agent are such that it absorbs at least 10%, preferably at least 30%, particularly preferred at least 50%, of incident electromagnetic radiation.
3. The method according to claim 2, characterized in that
   the droplets (3) and/or the fine droplets (3a) are dispensed in such a way that upon impact on the surface of the liquid layer (2) they at least partially penetrate it and/or come to rest on it and/or displace it and form depressions, wherein the droplets (3) and/or the fine droplets (3a) are adapted in volume and/or speed in order to influence the penetration depth and the displacement.
4. The method according to one of the preceding claims, characterized in that

   the liquid layer (2) consists of a polymerizable acrylate mixture, and/or

   the applied agent consists of a polymerizable acrylate mixture and/or of a solvent-containing liquid or of an aqueous mixture, in particular with a water content of more than 30%, preferably more than 50%.
5. The method according to one of the preceding claims, characterized in that

   the applied agent consists only of water or, in addition to water having a total content of 10 - 99%, contains at least one of the following ingredients in the indicated concentration (vol%):

   - a substance from the group of hindered amines in a concentration of 0-20%

   - a substance from the group of N,N'-diphenyleoxamides in a concentration of 0 - 20% and/or

   the applied agent comprises, in addition to an alcohol and/or a glycol having a total content (alcohol and/or glycol) of 10 - 99%, at least one of the following ingredients in the indicated concentration (vol%):

   - a substance from the group of hindered amines in a concentration of 0-20%

   - a substance from the group of N,N'-diphenyleoxamides in a concentration of 0 - 20%, and/or

   the applied agent comprises, in addition to a polymer content of 10-99%, at least one of the following ingredients in the indicated concentration (vol%):

   - a substance from the group of benzophenones in a concentration of 0 - 15%

   - a substance from the group of benzotrialzoles in a concentration of 0 - 15%.
6. The method according to one of the preceding claims, characterized in that

   the applied agent, especially after irradiation (S14), is adapted to evaporate within less than 3 minutes, preferably within less than 1 minute, especially preferred within less than half a minute, and/or

   in that a further step (S18) is provided in which the evaporation of the agent is carried out within less than 3 minutes, preferably within less than 1 minute, especially preferred within less than half a minute.
7. The method according to one of the preceding claims, characterized in that

   upon impact on the surface of the layer (2), the agent undergoes a chemical reaction with the layer (2) in such a way that an optical and/or haptic change of the surface occurs at the respective areas, and/or

   that a chemical reaction step is provided which is adapted so that the chemical reaction between the applied agent and the layer (2) is given sufficient time for the chemical reaction to at least partially take place.
8. The method according to one of the preceding claims, characterized in that
   upon impact on the layer (2), the applied agent undergoes a chemical reaction with the layer (2) such that the reaction product achieves by the irradiation (S14) at this area no or less micro- or nanostructure formation than on the areas on which no agent has been applied to the surface.
9. The method according to one of the preceding claims, characterized in that

   in a further step (S20) the liquid layer (2) is applied to a surface of the workpiece (1), and/or

   in a further step (S22) carried out in particular simultaneously with step (S12), the layer (2) is structured by means of an analogous structuring method, in particular using an embossing roller, and/or is displaced by means of analogous or digital methods by applying further structuring droplets, wherein depressions are formed in the layer (2), and/or

   in a further step a decorative image is applied, in particular by digital printing, to the surface of the workpiece (1) and/or to the layer (2) which is at least partially cured or which has a surface solidified by polymerization.
10. Apparatus (18) for carrying out the method according to one of the claims 1 to 9, comprising the following elements:

    - a transport device (20) having a transport direction (28), the transport device (20) being adapted to transport a workpiece (1) coated with a liquid layer (2) which is polymerizable by electromagnetic radiation to further elements of the apparatus,

    - a dispenser adapted to apply an agent to at least a partial area of the surface of the liquid layer (2), wherein the dispenser has at least one digital digital print head (4) or a digital nozzle bar adapted to dispense the agent;

    - a curing station comprising a radiation source which is adapted to irradiate the liquid layer (2) and/or the applied agent with electromagnetic radiation of variable wavelength, in particular with IR radiation, and/or electron radiation of variable wavelength at least until its partial curing

    - a control means adapted to control the apparatus in accordance with the method steps,

    - a radiation source (6), which is adapted to irradiate the surface of the liquid layer (2) with electromagnetic irradiation (6a) having a wavelength of less than 300 nm, wherein the radiation source is identical with the radiation source (6) and/or is a separate one.
11. The apparatus (18) according to claim 10, wherein
    the curing station comprises:

    - a fluid source which is adapted to stream in particular air around the layer (2), wherein the fluid can be influenced in particular in the parameters flow speed and/or temperature and/or humidity, and/or

    - an electron beam source which is adapted to irradiate the liquid layer (2) and/or the applied agent with electron radiation at least until its partial curing, and/or

    - a drying station adapted to receive the workpiece (1) until at least partial curing of the layer (2) and to provide, in particular by means of a heating source, a predetermined drying temperature to which the workpiece (1) with the layer (2) can be exposed.
12. The apparatus (18) according to claim 10 or 11 further comprising the following elements:

    - a reaction zone adapted to allow evaporation and/or a chemical reaction, wherein the reaction zone is adapted in particular as a zone through which the transport device transports the workpiece (1), and its extension and the transport speed are coordinated to one another such that evaporation and/or reaction are at least partially possible, and/or

    - a protective gas chamber (24) which is adapted to surround the workpiece (1) and/or the layer (2) and/or the agent with a protective gas, in particular an inert gas, preferably nitrogen, at least on a partial section during transport, and/or

    - an application device (10) adapted to apply the liquid layer (2) to the workpiece (1), and/or

    - a structuring element, in particular an embossing roller and/or a digital print head, which is adapted to form a structure in the liquid layer (2), and/or

    - an application device for applying a decorative image, comprising at least one digital print head adapted to apply paint to the surface of the layer (2) and/or of to the workpiece (1).
13. The apparatus (18) according to one of the claims 10 to 12, wherein

    the transport device (20) comprises a conveyor belt and the elements are arranged one after the other in the transport direction (28), and/or

    the reaction zone has special boundary conditions necessary to trigger evaporation and/or a chemical reaction, and/or

    the reaction zone extends over at least a part of the protective gas chamber (24).

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