METHOD FOR PRODUCING A STRUCTURED SURFACE

Abstract

A method for producing a decorative surface on a workpiece (1) is disclosed, the method comprising the following steps: feeding (S10) of the workpiece (1) coated with a liquid layer (2) to a digital printing station; application (S12) of an agent capable of at least partially absorbing electromagnetic radiation, at least on a partial area of the surface of the liquid layer (2), or which, in contact with the surface, produces a reaction product which is capable of at least partially absorbing electromagnetic radiation; 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, preferably less than 250 nm, particularly preferably less than 200 nm.

Furthermore, an apparatus (1) for carrying out this method is disclosed.

Claims

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) to a digital printing station; application (S12) of an agent capable of at least partially absorbing electromagnetic radiation, at least on a partial area of the surface of the liquid layer (2), or which, in contact with the surface, produces a reaction product which is capable of at least partially absorbing electromagnetic radiation; 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, preferably less than 250 nm, particularly preferably less than 200 nm.

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) in particular have a volume of 0.1 l to 1 l, preferably from 0.3 l to 0.8 l, especially preferably from 0.5 to 0.6 l, and/or the droplets (3) have a volume of 1 l to 80 l, preferably from 3 l to 12 l, especially preferably from 5 l to 10 l, and/or the chemical and/or physical properties of the agent are such that it absorbs at least 10%, preferably at least 30%, particularly preferably 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 introduce depressions, wherein the droplets (3) and/or the fine droplets (3a) are adapted in particular in volume and/or speed in order to influence the penetration depth and the displacement.

4. The method according to claim 1, characterized in that the formation of a microstructure or nanostructure is carried out by 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.

5. The method according to claim 1, characterized in that the liquid layer (2) consists of a polymerizable acrylate mixture, and/or the applied agent consists of a polymeriable 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%.

6. The method according to claim 1, characterized in that in a further step, curing (S16) of the layer (2) is carried out, preferably by irradiation with electromagnetic radiation, having 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 and/or by reaction curing, for example using a two-component system.

7. The method according to claim 1, 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%.

8. The method according to claim 1, characterized in that the applied agent, especially after irradiation (S14), is capable of evaporating within less than 3 minutes, preferably within less than 1 minute, especially preferably 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, particularly preferably within less than half a minute.

9. The method according to claim 1, 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 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.

10. The method according to claim 1, 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.

11. The method according to claim 1, 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 analog structuring method, in particular using an embossing roller, and/or is displaced by means of analog or digital methods by applying further structuring droplets, wherein depressions are introduced into the layer (2), and/or in a further step a decorative image is applied to the surface of the workpiece (1) and/or to the layer (2), in particular by digital printing, which surface is at least partially cured or which has a surface solidified by polymerization.

12. An apparatus (18) for carrying out the method according to claim 1, 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) 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); a radiation source (6) adapted to irradiate the surface of the liquid layer (2) with electromagnetic radiation (6a) having a wavelength of less than 300 nm, preferably less than 250 nm, particularly preferably less than 200 nm.

13. The apparatus (18) according to claim 12, comprising a curing station which includes: 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, wherein the radiation source is identical with the radiation source (6) and/or is a separate one, and/or a fluid source which is adapted to flow 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.

14. The apparatus (18) according to claim 12 further comprising the following elements: control means adapted to control the device in accordance with the method steps, and/or 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 expansion and the transport speed are matched 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 introduce a structure into 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 the workpiece (1).

15. The apparatus (18) according to claim 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 dispenser comprises at least one digital digital print head (4) or a digital nozzle bar adapted to dispense the agent, 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 part of the protective gas chamber (24).

Description

[0095] Furthermore, the description of concrete examples of the invention will be provided with the aid of the attached drawings.

[0096] FIG. 1 shows a workpiece coated with a liquid layer on which an agent in the form of droplets is applied;

[0097] FIG. 2 shows the workpiece in a protective gas chamber in which it is irradiated with electromagnetic radiation by means of a lamp;

[0098] FIG. 3 shows the workpiece with different mattnesses of the applied layer;

[0099] FIG. 4 shows the exposure of the liquid layer and the applied agent to electromagnetic radiation;

[0100] FIG. 5 shows another embodiment in which the agent was only applied to the surface of the liquid layer without changing its structure;

[0101] FIG. 6 shows an alternative workpiece as a sheet-like material.

[0102] FIG. 7 is a flowchart of a preferred embodiment of the method according to the invention;

[0103] FIG. 8 shows schematically an arrangement of a preferred embodiment of an apparatus according to the invention.

[0104] FIG. 1 shows a workpiece 1 with a liquid layer 2 applied to it and an agent sprayed onto layer 2 in the form of droplets 3 from digital print heads 4 arranged above. 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 in different areas on the liquid layer 2.

[0105] The agent is capable of absorbing electromagnetic radiation at least partially. Thus it can 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.

[0106] It can be seen that the droplets 3 produced depressions upon impact on the liquid layer 2, whereby the viscosity of the liquid layer 2 is such that these depressions do not immediately recede. Thus, by applying droplets 3, a structuring of the liquid layer 2 can be achieved for at least a certain period of less than 5 minutes, preferably less than 3 minutes, which can be permanently solidified by final curing.

[0107] In FIG. 2 this workpiece 1 with the liquid layer 2 is in an inert gas chamber 24, which predominantly has a nitrogen atmosphere in the inside 5 in order to keep oxygen atoms or oxygen molecules away from the surface of the layer 2 in order to inhibit unwanted chemical reactions with oxygen of the air.

[0108] The surface of layer 2 here has a structure created by droplets 3 as shown in FIG. 1. The droplets 3 are still in the depressions.

[0109] Furthermore, a radiation source 6 for electromagnetic radiation 6a is provided, under which the workpiece 1 is moved with the liquid layer 2, which is structured by the depressions. The radiation source 6 is adapted to emit electromagnetic radiation 6a onto the surface of the liquid layer 2. For example, the electromagnetic radiation 6a has a wavelength of less than 300 nm, preferably less than 250 nm, especially preferably less than 200 nm.

[0110] Instead of nitrogen, another inert gas atmosphere may also be formed in the inside 5 of the protective gas chamber 24, which is suitable for keeping oxygen atoms and/or oxygen molecules away from the surface of layer 2.

[0111] The protective gas chamber 24 can be adapted as a closed space or as a section through which a workpiece 1 is moved. This is particularly advantageous for sheet-like workpieces 1.

[0112] FIG. 3 shows the liquid layer 2 on workpiece 1 after irradiation with electromagnetic radiation 6a from radiation source 6. The surface of the liquid layer 2 is more or less strongly polymerized in different areas.

[0113] At areas 7, the electromagnetic radiation 6a could unhindered impact the surface of layer 2, whereby a stronger polymerization took place here. The surface has become rougher at this area, at least in the micro or nano range, since the molecules of the liquid layer 2 near the surface have become more strongly cross-linked due to the electromagnetic radiation 6a. Therefore, light falling on these areas 7 is now reflected in several directions, i.e. in a diffuse manner, which results in a higher degree of mattness of these areas 7.

[0114] In contrast, the electromagnetic radiation 6a could not directly reach areas 8 of the surface of the liquid layer 2, as these were covered with the agent in the form of droplets 3, as shown in FIGS. 1 and 2. The agent is now no longer present on the surface of the liquid layer 2, as it has evaporated, for example.

[0115] However, the agent has at least partially absorbed the electromagnetic radiation at lower areas 8, so that a polymerization of the surface of the liquid layer 2 could not take place here to the same extent as at the areas 7, resulting in the lower areas 8 being less rough, at least in the micro- or nano range, whereby a reflection of incident light is scattered less strongly. Areas 8 therefore appear shinier than areas 7.

[0116] FIG. 4 shows in the lower drawing a section, which is marked in the upper drawing by the two vertical dashed lines, of the layer 2 on the workpiece 1 and the agent sprayed on it in the form of droplets 3, which at least partially absorb the electromagnetic radiation 6a in the areas of the droplets 3.

[0117] It can be seen that in areas not covered by droplets 3, electromagnetic radiation 6a can impact unhindered on the surface of the liquid layer 2. 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.

[0118] In contrast, the intensity of the electromagnetic radiation 6a on the surface of the liquid layer 2 in areas 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.

[0119] FIG. 5 shows another embodiment in which the agent was only applied to the surface of the liquid layer without changing its structure.

[0120] The agent is applied here in the form of fine droplets 3a, which have been applied to the liquid layer in such a way that they do not sink into the surface of the liquid layer 2 or displace it and cause depressions. This can be achieved, for example, by adjusting the volume and/or impact speed of the fine droplets 3a in such a way that the surface of the liquid layer is not altered by them.

[0121] An impulse of the fine droplets 3a can be adjusted so that it is not sufficient to break the surface tension of the liquid layer 2, so that the fine droplets 3a do not sink into the liquid layer 2, and/or that it is not sufficient to overcome the viscosity forces of the liquid layer 2, so that no depressions are introduced into the liquid layer 2 due to the fine droplets 3a.

[0122] It can also be seen that the fine droplets 3a are sized to form a fine veil on at least part of the surface of the liquid layer.

[0123] In this way it is possible to apply electromagnetic radiation 6a onto the surface of the liquid layer 2 in different areas to a different extent, as it penetrates less strongly into the surface of the liquid layer in areas containing the agent. This is shown, comparable to FIG. 4, by the different arrow lengths of the electromagnetic radiation 6a. Thus, the surface in areas 7, which are not covered with the fine droplets 3a, is irradiated with higher intensity than areas 8, which were at least partially shielded from the electromagnetic radiation 6a by the agent in the form of fine droplets 3a or a veil thereof.

[0124] FIG. 6 shows an alternative workpiece 1 as sheet-like material, which is unwound from a roll 9 and also coated with a liquid layer 2. Workpiece 1 moves continuously to the right, where further processing steps (not shown) as described above follow.

[0125] The liquid layer 2 is applied in this embodiment after unrolling from the roll 9 using a rolling mill 10. The matting method can thus be applied not only to individual flat workpieces, such as boards made for example of wood, plastic or metal, but also to sheet-like workpieces 1.

[0126] FIG. 7 shows a flowchart of a preferred embodiment of the method according to the invention.

[0127] In a first processing step, application S20 of a liquid layer onto the surface of a workpiece takes place. This can be done, for example, in the manner shown in FIG. 6.

[0128] Then structuring S22 of the thus coated workpiece takes place, so that the liquid layer is provided with a structure after completion of this step. For example, the liquid layer can be structured by an analogous structuring method, in particular by mechanically embossing the surface of the liquid layer, for example by unrolling an embossing roller over the surface of the liquid layer.

[0129] Alternatively or additionally the structuring of the liquid layer can also be done digitally, whereby for example droplets are applied to the surface of the liquid layer with digital print heads, which droplets penetrate and/or displace the liquid layer. The droplets are advantageously made of the same material as the liquid layer in order to achieve a structuring effect. In a different embodiment, the droplets may consist of a material other than the liquid layer, whereby, for example, a chemical reaction between the liquid layer and droplets can be achieved, in particular by subsequent irradiation with electromagnetic radiation and/or electron beam and/or temperature increase. The chemical reaction is adapted in such a way that its reaction product has a structuring effect on the surface of the liquid layer, which changes it optically and/or haptically.

[0130] If there is a decorative image on the workpiece, which was covered by the application S20 of the liquid, in particular partially transparent layer, then during the structuring of the surface it is achieved that the structure is synchronous to the image visible through the liquid layer.

[0131] The thus prepared workpiece is then fed to a digital printing station (S10), for example via a continuous belt conveyor.

[0132] In a further step S12, the digital printing station enables the application of an agent, which is capable of at least partially absorbing electromagnetic radiation, onto the surface of the liquid layer.

[0133] The application S12 of the agent can be carried out in the form of droplets which, for example, are adjusted in speed and volume in such a way 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 agent can be applied S12 in the form of fine droplets, which are dimensioned in such a way that they do not change the surface of the liquid layer, but at least cover partial areas of it.

[0134] Subsequently, irradiation S14 of the surface of the liquid layer with high-energy electromagnetic radiation is performed as shown in FIGS. 2, 4 and 5, whereby partial areas of the liquid layer covered with the agent experience a reduced intensity of radiation compared to partial areas which are not covered by the agent and are directly exposed to radiation instead.

[0135] The irradiation S14 of the surface of the liquid layer leads to its polymerization to a certain penetration depth, for example 0.1 m, preferably less than 0.01 m, whereby the polymerization was stronger at the areas directly exposed to the radiation, as shown in FIG. 3. After completion of irradiation S14, these areas are therefore more matte than the areas covered with the agent.

[0136] Subsequently, the applied agent is evaporated in a further step S18. This can be done for example simply by heating the agent with an IR lamp, whereby the agent has advantageously a lower evaporation temperature than the liquid layer.

[0137] If, however, the agent has the property that it volatilizes after a certain time, the evaporation S18 can only consist of waiting until the agent has volatilized. This can be done, for example, by conveying the workpiece on a belt conveyor before the next method step is carried out, whereby this belt conveyor is configured in its length, transport speed and surrounding temperature in such a way that evaporation S18 is possible during transport.

[0138] Then, in a further step, curing S16 of the liquid and now at least partially matted layer takes place.

[0139] For this purpose, the workpiece, in particular the liquid layer, can again be irradiated with electromagnetic radiation from the same radiation source as that used in step S14. Alternatively, other radiation sources can be provided, or other types of curing, such as active or passive air drying, or irradiation with electrical radiation can be used.

[0140] FIG. 8 shows a schematic arrangement of a preferred embodiment of an apparatus 18 according to the invention.

[0141] A transport device 20, which is implemented as a belt transport, is shown, on which a workpiece 1 is transported in transport direction 28. A liquid layer 2 is applied to the top of workpiece 1.

[0142] During the following transport sequence, workpiece 1 is transported in transport direction 28 into a protective gas chamber 24. It contains a protective gas atmosphere, in particular an inert gas atmosphere, for example a nitrogen atmosphere, in its inside 5, whereby in particular oxygen can be kept away from the liquid layer 2, whereby unwanted chemical reactions are avoided.

[0143] Furthermore, digital print heads 4 are provided in the inside 5 of the protective gas chamber 24, which are adapted to apply to the liquid layer 2 an agent which is capable of at least partially absorbing electromagnetic radiation. In the shown illustration, this is done by applying droplets 3, whereby the digital print heads 4 are adapted to control the dispensing of droplets, in particular with regard to droplet speed, volume and impulse.

[0144] Alternatively or additionally, the agent can also be applied from the digital print heads 4 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 join together to form partial areas.

[0145] A radiation source 6 is arranged downstream of the digital print heads 4, which is adapted 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 liquid layer 2 in order to achieve the matting as described above.

[0146] Furthermore, a control means (not shown) is provided which is adapted to control the apparatus 18 and its elements in order to carry out the method according to the invention.

[0147] The embodiments shown here do not restrict the subject matter of the invention. Rather, other embodiments are conceivable. For example, the method described in FIG. 7 may also include further method steps, or individual method steps may be exchanged or omitted. In the following, further aspects of the invention are to be specified on the basis of further concrete examples.

EXAMPLE 1

[0148] An HDF board is coated with a white print primer. The thus coated board is fed to a digital printer (in an alternative embodiment also to a rotary printing machine with several colours) and printed decoratively with a wood decor, for example. In an alternative embodiment form, an intermediate layer of lacquer or primer, ideally one that is transparent, can be applied to the thus printed decorative layer. Then a liquid layer 2 with a layer thickness of 50-80 m is applied. This layer can be applied in a roller application machine or in an alternative embodiment also in a spraying machine. The layer consists of a UV-curing acrylate mixture. The thus coated HDF board 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.

[0149] In an alternative embodiment, the droplets can also consist of a solvent- or acrylate-based liquid.

[0150] The droplets change the surface of the still liquid layer at the areas where they impacted in such a way that they displace the still liquid layer 2 due to a high speed of 4-6 m/sec.

[0151] Then the workpiece with the thus modified liquid layer 2 is 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 reaches the underlying layer 2. The layer 2 begins to polymerize in its surface and thereby folds (cf. reference sign 7 in FIG. 3). In the deeper areas where the droplets 3 have at least partially absorbed the electromagnetic radiation, a lower polymerization and thus a lower folding occurs at the areas 8 in FIG. 3.

[0152] In this way, the desired product is obtained with different gloss levels or mattness in the pores or outside the pores. The workpiece is then fed to another UV radiation source with a wavelength >300 nm to completely cure the underlying, still liquid layer 2, in particular the acrylate layer.