Pressing tool with colour effect and method for producing a pressing tool with colour effect

Abstract

The invention relates to a method for producing a pressing tool (4), wherein a pressing tool (4) is provided which has a pressing surface (5) designed for being brought into contact with a workpiece (6) and wherein in at least one defined structure region (A, B) of the pressing surface (5) periodic three-dimensional structures (11) with an average structure period (P) of P ≤ 1.5 µm and an average structure depth (T) of T ≤ 1 µm are produced by irradiating the defined structure region (A, B) by means of an ultrashort pulse laser which has a pulse duration of ≤ 10 ps.

Description

[0001] with color effect and process for one with color effect

[0002] The invention relates to a method for producing a pressing tool and to a pressing tool with a pressing surface for contacting a workpiece, wherein the pressing surface has a structured surface in at least one defined structural region, which can be transferred to a workpiece by pressing. Furthermore, the invention relates to the use of such a pressing tool and a workpiece comprising a wood-based material, in particular a coated wood-based material, or a plastic with a surface that comprises a structured surface in at least one defined structural region.

[0003] Generic workpieces that comprise a wood-based material, e.g., a coated wood-based material, or that comprise a plastic include laminate flooring or laminated material panels used in the furniture industry. It is known to structure the visible surface of such workpieces in order to imitate certain natural surfaces, for example. For example, a structured surface can be created that replicates the surface of concrete, stone, etc. Various methods are known for producing such structured surfaces, for example, laser ablation or etching processes.

[0004] EP 2 289 708 B1, for example, discloses a method for producing a surface structure of a metallic press sheet, endless belt or a cylindrical embossing roll using a laser.

[0005] In addition to imitating natural surfaces, it may also be desired that the visible surfaces of the workpieces exhibit varying degrees of gloss, from matte to glossy. This can also be achieved through targeted surface structuring.

[0006] DE 102007 055 053 A1, for example, discloses a pressing tool in the form of a press plate comprising a structured pressing surface with multiple gloss levels. The structured surface comprises a structure that exhibits a mountain-like surface with valleys and peaks. Material panels, e.g., laminates, can be produced using the press plate or its pressing surface, whereby the material panels have structured surfaces with multiple gloss levels that are associated with the pressing surface.

[0007] In addition, it may be desirable to impart a different color to the visible surfaces of the workpieces. Previously, color pigments (e.g., inks, varnishes, paints) were used for this purpose, for example, applied to the surface using a suitable printing process. However, such processes are relatively complex, especially when combined with the aforementioned surface structuring.

[0008] The object of the present invention was to overcome the disadvantages of the prior art and to provide an improved possibility of producing a colored surface on workpieces comprising a wood material or a plastic.

[0009] This object is achieved by the method mentioned at the outset in that the following steps are carried out: providing a pressing tool which has a pressing surface designed for contacting a workpiece, producing periodic three-dimensional structures with an average structural period of P < 1.5 pm and an average structural depth of T < 1 pm in at least one defined structural region of the pressing surface by irradiating the at least one defined structural region using an ultrashort pulse laser which has a pulse duration PD < 10 ps. This creates a surface which is structured in such a way that a colour effect can be achieved by diffraction of light. The periodic structures can be regarded physically as optical gratings. In this way, colour effects can be produced by laser structuring without the use of colour pigments.A desired coloration can be achieved by changing the mean structural period alone or in combination with the mean structural depth and / or the geometric shape of the three-dimensional structure.

[0010] It may be advantageous if the pressing surface is coated with a first coating with a layer thickness of at least 1 μm before irradiation, and the periodic three-dimensional structures are created on the first coating. This allows, for example, a protective layer to be applied to the

[0011] Press tool, e.g. to protect against wear, corrosion, etc.

[0012] It can be advantageous if the pressing tool used has a basic structure on the pressing surface to imitate a natural surface, which can be transferred to the workpiece, with the periodic three-dimensional structures being created on the basic structure. This allows an imitation of a natural surface to be created, which has areas with a specific coloring. The basic structure can be designed, for example, to imitate a wood or stone surface.

[0013] It can be advantageous for a position and / or a shape and / or a size and / or the average structural period and / or the average structural depth of the at least one defined structural region to be defined as a function of the basic structure of the pressing surface. Natural surfaces generally have a very individual appearance; in the case of wood, for example, individual grooves and knotholes. The periodic three-dimensional structures to be produced according to the invention can now be produced as a function of this individual appearance. As a result, the periodic three-dimensional structures can, for example, only be applied in the region of the basic structure which is designed to produce a knothole or an imitation of a knothole. The shape and size of the defined structural region as well as the position of the structural region on the pressing surface can, for example, correspond to the shape, size and position of the knothole to be imitated.The average structural period and / or the average structural depth can be selected, for example, depending on the desired color scheme.

[0014] The pressing tool can comprise a metallic material at least in the region of the at least one defined structural area of ​​the pressing surface, and / or the first coating can comprise a metallic material. A method for generating laser-induced periodic surface structures is used to create the periodic three-dimensional structure. This method can be used to generate so-called "laser-induced periodic surface structures" (LIPSS). The laser wavelength determines the period of the optical grating. The spacing of the individual LIPSS approximately corresponds to the wavelength of the laser used.

[0015] To achieve reliable coloring, the ultrashort pulse laser preferably has a wavelength A < 1064 nm.

[0016] For the ultrashort pulse laser, circularly polarized laser radiation or linearly polarized laser radiation is preferably used. Depending on the laser radiation used, structurally different LIPSS can be generated. For example, linearly polarized laser radiation results in linear or elongated LIPSS, while circularly polarized laser radiation results in essentially triangular LIPSS, both viewed from a top view of the surface. The different shapes of the LIPSS result in the respective color being recognizable from different viewing directions.

[0017] To ensure sufficient, but not excessive, material removal by the laser, the fluence of the ultrashort pulse laser is preferably equal to or greater than the ablation threshold of the metallic material. The ablation threshold depends on the respective material and can be assumed to be known.

[0018] According to a further advantageous embodiment of the invention, the pressing tool can comprise a metallic or ceramic material or a plastic, at least in the region of the at least one defined structural region of the pressing surface, and / or the first coating can comprise a metallic or ceramic material or a plastic, wherein a laser interference structuring method with at least two superimposed laser beams is used to produce the periodic three-dimensional structures. This allows the periodic structures to be produced using an alternative method. Compared to the above-mentioned method for producing laser-induced periodic surface structures, laser interference structuring has the advantage that it is independent of the material of the pressing tool or the first coating.While the process for creating laser-induced periodic surface structures requires a metallic surface, laser interference structuring can also be used on other materials. If three superimposed laser beams are used, more complex geometries can be created. While two superimposed laser beams can create essentially linear structures (in plan view), three laser beams can create essentially triangular structures (in plan view). The terms "essentially linear" and "essentially triangular" mean that the structures do not have to have a geometrically perfect "linear" or "triangular" shape, but that the shape can naturally exhibit certain deviations due to manufacturing reasons. A structure that is "linear" in plan view can, for example, be a type of elongated cuboid whose long side is much longer than its short side.A structure that appears “triangular” in plan view can, for example, be a pyramid or a truncated pyramid.

[0019] For reliable coloring, the ultrashort pulse laser preferably has a wavelength A < 1064 nm, with a wavelength A in the range of 1030 ± 5 nm to 1064 ± 5 ​​nm, or in the range of 515 ± 5 nm to 532 ± 5 nm, or in the range of 343 ± 5 nm to 355 ± 5 nm being particularly preferred. Similar to the LIPSS method above, the laser wavelength determines the structural period. The specified wavelength ranges refer to the infrared, green, and ultraviolet ranges.

[0020] The ultrashort pulse laser can have pulses with a repetition rate of < 2 MHz, preferably < 1 MHz. Alternatively or additionally, a seed laser of the ultrashort pulse laser can generate pulses with a frequency of > 40 MHz. This can increase the productivity of the structure manufacturing process.

[0021] It can be advantageous to define at least two structural areas on the pressing surface in which different periodic three-dimensional structures are created. This allows areas with different colors to be created.

[0022] At least some of the produced periodic three-dimensional structures can be coated with a preferably wear-resistant second coating, wherein a layer thickness of the second coating is determined such that the produced periodic three-dimensional structures are retained in the second coating. The layer thickness is therefore preferably less than the average structure depth T and is preferably < 1 pm. As a result, the structured surface can be coated, for example, with a wear-resistant layer. This can ensure that the structures are retained for longer, whereby the pressing tool can be used for longer. The second coating can be advantageous, for example, in the production of laminate flooring, since the pressing tool is subjected to considerable mechanical stress in this case.

[0023] The pressing tool is preferably a pressing plate, a pressing belt, or an embossing roller for use on workpieces comprising a wood-based material or a plastic, preferably laminate flooring or furniture workpieces, in particular cabinets, doors, worktops, and tables. This allows many common products to be provided with a color.

[0024] The task is further solved with the pressing tool mentioned above in that the structured surface comprises periodic three-dimensional structures with an average structure period P < 1.5 pm and with an average structure depth T < 1 pm.

[0025] Preferably, the periodic three-dimensional structures have a substantially linear shape in plan view or a substantially triangular shape and / or at least one of the following geometric shapes: cone, truncated cone, pyramid, truncated pyramid, wherein the pyramid and / or truncated pyramid preferably have a triangular base. This provides advantageous structures that allow color recognition from different viewing angles.

[0026] The pressing surface can be coated with a wear-resistant second coating at least in the region of the at least one structural region, wherein a layer thickness of the second coating is determined such that the periodic three-dimensional structures are retained in the second coating. The layer thickness is therefore preferably smaller than the average structural depth T of the periodic three-dimensional structures and is preferably < 1 pm. This allows the periodic three-dimensional structures to be protected from wear and the color to be retained for a long time. The pressing tool can have a basic structure on the pressing surface to imitate a natural surface, which can be transferred to the workpiece, wherein the periodic three-dimensional structures are formed on the basic structure. This makes it possible to create an imitation of a natural surface which has regions with a specific color.

[0027] The pressing tool is preferably used for machining a workpiece, wherein the pressing tool is pressed onto a workpiece surface of the workpiece, so that by means of the generated periodic three-dimensional structures an impression is created in the workpiece surface of the workpiece, which impression is substantially complementary to the periodic three-dimensional structures of the pressing tool, wherein a workpiece comprising a wood material or a plastic, for example a laminate flooring or a laminate material panel, is preferably used as the workpiece.

[0028] The object is further achieved with the workpiece mentioned at the outset in that the structured surface comprises periodic three-dimensional structures with an average structure period P < 1.5 pm and with an average structure depth T < 1 pm and that the periodic three-dimensional structures are produced by pressing on a pressing tool whose pressing surface essentially comprises complementary periodic three-dimensional structures.

[0029] It may be advantageous if at least some of the three-dimensional structures are coated with a preferably wear-resistant third coating, wherein the thickness of the third coating is determined such that the periodic three-dimensional structures are retained in the third coating. Alternatively or additionally, the third coating may be optically transparent. Since light can shine through the transparent coating onto the periodic three-dimensional structures, the thickness of the transparent coating may optionally also be greater than the average structure depth T of the periodic three-dimensional structures.

[0030] The workpiece can have a basic structure on its surface to imitate a natural surface, with the periodic three-dimensional structures formed on the basic structure. This allows an imitation of a natural surface to be created that has areas with a specific coloring.

[0031] For a better understanding of the invention, it is explained in more detail using the following figures.

[0032] They show in a highly simplified, schematic representation:

[0033] Fig. 1 shows a pressing device with a pressing tool and a workpiece;

[0034] Fig.2a a pressing tool with a first surface structure;

[0035] Fig.2b a pressing tool with a second surface structure;

[0036] Fig. 3 shows a pressing tool with two structural areas, each with a surface structure according to the invention;

[0037] Fig. 4 shows an exemplary device for carrying out the method according to the invention;

[0038] Fig. 5 shows a workpiece in an exemplary embodiment of the invention with several structural areas.

[0039] By way of introduction, it should be noted that in the variously described embodiments, identical parts are provided with identical reference symbols or component designations. The disclosures contained throughout the description can be applied analogously to identical parts with identical reference symbols or component designations. Furthermore, the positional information chosen in the description, such as top, bottom, side, etc., refers to the directly described and illustrated figure, and these positional information must be applied analogously to the new position in the event of a change in position.

[0040] Figure 1 shows a schematic and simplified representation of a pressing device 1. The pressing device 1 comprises a pressing ram 2 and a workpiece holder 3. A pressing tool 4 is arranged on a side of the pressing ram 2 facing the workpiece holder 3. The pressing tool 4 can, for example, be a press sheet made of a metallic material. On a surface facing the workpiece holder 3, the pressing tool 4 has a pressing surface 5 for contacting a workpiece 6. The workpiece 6 can be arranged on the workpiece holder 5 so that it is located between the pressing tool 4 and the workpiece holder 3.

[0041] A structured surface can be provided on the pressing surface 5, which can be embossed by the pressing ram 2 into a workpiece surface 7 of the workpiece 6 facing the pressing tool 4. This allows a structured surface to be created on the workpiece 6 that is essentially complementary to the structured surface of the pressing tool 4. In the example shown, the structured surface extends over the entire pressing surface 5. Of course, only a portion of the pressing surface 5 could also be structured.

[0042] The pressing device 1 can comprise a suitable guide device 9 for guiding the pressing ram 2. In addition, the pressing device 1 can comprise a suitable force-generating device 8 for actuating the pressing ram 2. The force-generating device 8 is preferably electrically controllable. To control the force-generating device 8, the pressing device 1 can comprise a control unit 10. The force-generating device 8 can, for example, comprise a suitable hydraulic, mechanical, or pneumatic actuator. The control unit 10 can control the force-generating device 8 in order to move the pressing ram 2 in the direction of the workpiece 6 and to press the pressing tool 4 onto the workpiece surface 7 with a sufficiently large pressing force F, as indicated by the arrow in Fig. 1. The pressing force F can vary depending on the material of the workpiece 6 and the surface structure of the pressing surface 5.

[0043] Figs. 2a and 2b show two different pressing tools 4, each with a top view of the pressing surface 5. Each pressing tool 4 has a pressing surface 5 with a basic structure designed to imitate a natural surface. For example, the pressing tool 4 shown in Fig. 2a has a pressing surface 5 with a basic structure designed to imitate wood. The pressing tool 4 shown in Fig. 2b, for example, has a pressing surface 5 with a basic structure designed to imitate stone.

[0044] The basic structure can, for example, be embossed into the workpiece surface 7 of a workpiece 6 using the pressing device 1 shown in Fig. 1. As mentioned above, alternatively or in addition to the illustrated basic structure, which is designed to imitate a natural surface, a surface structure can also be provided to achieve a specific degree of gloss. In addition to a basic structure imitating wood or stone, other structured surfaces can of course also be used to imitate other, preferably natural, surfaces.

[0045] Fig. 3 shows a pressing tool 4 in an exemplary embodiment of the invention, again in a plan view of the pressing surface 5. The pressing surface 5 has, on the one hand, a basic structure for imitating wood, which extends essentially over the entire pressing surface 5, as already shown in Fig. 2a. According to the invention, at least one defined structural region A, B with a structured surface is also provided on the pressing surface 5, which comprises periodic three-dimensional structures 11 with an average structural period P < 1.5 pm and with an average structural depth T < 1 pm. The structured surface of the defined structural region can be transferred onto a workpiece 6 by pressing, e.g. with the pressing device 1 shown in Fig. 1.

[0046] The periodic three-dimensional structures 11 of the specified dimension can be used to create an optical grating at which a color effect can be generated by diffraction of light. The defined structural area therefore appears colored to humans. The visible color depends essentially on the average structural period P. The physical effect of diffraction is known, which is why no further description is provided here.

[0047] In the example shown in Fig. 3, a first rectangular structural region A and a second rectangular structural region B spaced apart from it are provided on the pressing surface 5, the periodic three-dimensional structures 11 of which differ from one another. This allows different regions with different colors to be created. For better recognition, a detailed view A and detailed view B are shown for each of the structural regions A, B. Of course, the shape of the structural regions A, B is not limited to a rectangular shape, but a structural region could generally have any desired shape. In principle, however, the two structural regions A, B could also comprise identical periodic three-dimensional structures 11 in order to achieve the same color.

[0048] Of course, only a single structural area with a uniform structure could also be provided. For example, the structural area could extend over the entire pressing surface 5 of the pressing tool 4. If at least two structural areas A, B with different structures 11 are provided, these could also be directly adjacent to one another, for example.

[0049] Of course, more than two structural areas with identical or different periodic three-dimensional structures 11 could also be provided on the pressing surface 5. This can be advantageous, for example, to represent a text or a logo, e.g., to represent a trademark. For example, each letter of a text could be a separate structural area with a structuring according to the invention (see, for example, Fig. 5). The text can thus be represented in color.

[0050] In the context of the invention, the mean structural period P is understood to mean the mean distance between two consecutive three-dimensional structures 11, as shown in detail A and detail B. The periodic three-dimensional structures 11 of the first structural region A have a substantially triangular shape in plan view. The structural period P can be defined, for example, as the distance between the centers of two consecutive triangular structures. The triangular structures have the advantage that the coloring can be recognized from three viewing directions. The periodic three-dimensional structures 11 of the second structural region B have a substantially elongated or linear shape in plan view. The coloring can be recognized from two directions that are essentially aligned normal to the longitudinal direction of the linear structures.In addition to the triangular and linear structures shown, the periodic three-dimensional structures 11 could of course also have other shapes, for example, the following geometric shapes: cone, truncated cone, pyramid, truncated pyramid, with the pyramid and / or truncated pyramid preferably having a triangular base. However, this list is not exhaustive, and other shapes could also be considered.

[0051] Fig. 3 on the left shows a section through the pressing tool 4 according to the section line SS. In the sectional view it can be seen that the surface structure of the first structural area A differs from the remaining basic structure of the pressing surface 5. While the first structural area A is used for coloring, the remaining basic structure of the pressing surface 5 serves to imitate a wooden surface. However, the structural area A can also be superimposed on the surface structure to imitate a wooden surface, so that the coloring also serves to imitate the wooden surface. The average structural depth T of the three-dimensional structures 11 is also shown here. The average structural depth T is < 1 pm. The basic structure to imitate the wooden surface, on the other hand, can have a greater depth.In the context of the invention, the mean structure depth T is to be understood as the mean distance between the free ends of the periodic three-dimensional structures 11 facing away from the pressing surface 5 and their base connected to the pressing tool 4.

[0052] The periodic three-dimensional structures 11 can, for example, be created on the basic structure of the pressing surface 5, wherein a position and / or a shape and / or a size and / or the average structural period P and / or the average structural depth T of the at least one defined structural region is determined depending on the basic structure of the pressing surface 5. If the basic structure is designed, for example, to imitate wood, then the periodic three-dimensional structures 11 can, for example, only be applied in the area of ​​the basic structure that is designed to create an imitation of a knothole. A shape and size of the defined structural region as well as the position of the structural region on the pressing surface 5 can, for example, correspond to the shape, size and position of the knothole to be imitated. The average structural period P and / or the average structural depth T can, for example,depending on a desired color scheme that is to be transferred to the workpiece 6 in the area of ​​the knothole.

[0053] The pressing surface 5 of the pressing tool 4 can be coated with a wear-resistant second coating, at least in the region of the at least one structural area. A layer thickness is determined such that the periodic three-dimensional structures 11 are retained. The layer thickness is therefore preferably less than the average structural depth T and is preferably <1 μm. This increases the wear resistance of the pressing surface 5 and consequently the durability of the pressing tool 4, without the coloring effect being lost when the surface structure is transferred to a workpiece.

[0054] An exemplary embodiment of the method according to the invention for producing a pressing tool 4 is explained in more detail below with reference to Fig.4.

[0055] First, a pressing tool 4 is provided which has a pressing surface 5 designed for contacting a workpiece 6. An exemplary pressing tool 4 has already been described with reference to Fig. 1 and Fig. 2. Then, in at least one defined structural region of the pressing surface 5, preferably on the basic structure, the already described periodic three-dimensional structures 11 with an average structural period P < 1.5 pm and an average structural depth T < 1 pm are produced. Production takes place by irradiating the defined structural region using an ultrashort pulse laser which has a pulse duration of < 10 ps. Since the structural period P correlates with a wavelength A of the laser, the ultrashort pulse laser preferably has a wavelength A of A < 1064 nm.

[0056] Optionally, the pressing surface 5 could also be coated with a first coating having a layer thickness of at least 1 pm before irradiation and the periodic three-dimensional structures 11 could be generated in a defined structural area on the first coating.

[0057] Within the scope of the invention, two different methods can be used to produce the periodic three-dimensional structures 11. The first method is called laser interference structuring, and the second method is called the LIPSS method. Both methods are basically known in the prior art.

[0058] If the pressing tool 4 comprises a metallic or ceramic material or a plastic in the region of the at least one defined structural area of ​​the pressing surface 5 (or if the first coating comprises a metallic or ceramic material or a plastic), then, for example, the laser interference structuring method with at least two superimposed laser beams can be used to produce the periodic three-dimensional structures 11. An exemplary and schematic laser device 12 for performing laser interference structuring is shown in Fig. 4.

[0059] The laser device 12 can comprise a laser source 13 for generating a seed laser beam L1, a beam generating device 14 for generating suitable partial laser beams L2, L3 and a carrier 15 for arranging the part to be irradiated, here the pressing tool 4. The beam splitting device 14 can comprise, for example, a focus lens 16, a diffractive optical element 17 (abbreviated DOE), an aperture 18, a prism 19 and a deflecting mirror 20 for each partial laser beam L2, L3. In order to allow as many degrees of freedom as possible in the irradiation of the pressing tool 4, the beam generating device 14 can be movable, for example, in the vertical direction, here along the Z-axis, and the carrier 15 can be movable, for example, in the horizontal plane, here the XY plane, as indicated by the arrows in Fig. 4.

[0060] In addition, it can be advantageous if the focus lens 16 is movable relative to the aperture 17 in the vertical direction, here along the Z-axis. Furthermore, the deflecting mirrors 20 can be movable in the horizontal direction, here along the X-axis, and rotatable about a horizontal axis, here the Y-axis. The seed laser beam L1 can be split into two (or more) partial laser beams L2, L3 via the prism 19. The partial laser beams L1, L2 can be recombined via the deflecting mirrors 20 on the pressing surface 5 of the pressing tool 4 in order to interfere at the pressing surface 5. A close-up of the superposition of the two partial laser beams L1, L2 is shown in Fig. 4 Detail C.

[0061] By linearly displacing and simultaneously rotating the deflecting mirrors 19, different structural periods P can be generated on the pressing surface 5. The movement of the movable components can be achieved, for example, via suitable actuators, which could be controlled by a suitable control unit (not shown). Of course, the illustrated embodiment is only exemplary and not to be understood as limiting. For example, more than two superimposed (partial) laser beams L2, L3... Li could also be used to generate the periodic three-dimensional structures 11.

[0062] The wavelength A of the laser essentially determines the average structural period P of the periodic three-dimensional structures 11 to be produced. The wavelength A is therefore preferably A < 1064 nm. For example, a wavelength A in the range from 1030 ± 5 nm to 1064 ± 5 ​​nm (infrared range), in the range from 515 ± 5 nm to 532 ± 5 nm (green range), or in the range from 343 ± 5 nm to 355 ± 5 nm (ultraviolet range) can be used. In addition to the wavelength A, the angle of incidence a of the two partial laser beams L2, L3 can affect the resulting structural period P.

[0063] As shown in detail C in Fig. 4, the structures 11 generated on the pressing surface 5 result from the interference of at least two superimposed partial beams L2, L3. The wavelength A and the angle of incidence α are also shown here. The interference of the partial laser beams L2, L3 has interference maxima l_max and interference minima l_min in the region of the pressing surface 5, as indicated schematically. A fluence of the laser or the partial laser beams L2, L3 is preferably set such that the interference maxima l_max are at or slightly above the material-specific ablation threshold of the material of the pressing surface 5 in order to generate local material ablation, while the interference minima l_min are below the ablation threshold and thus do not lead to any material ablation.

[0064] The periodic three-dimensional structures 11 thus generated can, for example, have an average structural period P of 300-1500 nm. The average structural depth T can, for example, be 100-400 nm. The ratio between the structural depth T and the structural period P (the so-called aspect ratio) is preferably < 0.3. In interference structuring, the average structural period P can be influenced, alternatively or in addition to the selection of the wavelength A, by changing the angle of incidence α of the two partial laser beams L2, L3.

[0065] The ultrashort pulse laser used can, for example, have pulses with a repetition rate of < 2 MHz, preferably < 1 MHz. Alternatively or additionally, the seed laser L1 of the ultrashort pulse laser can generate pulses with a frequency of > 40 MHz.

[0066] If the pressing tool 4 comprises a metallic material at least in the region of the at least one defined structural region of the pressing surface 5 (or the optional first coating comprises a metallic material), then, as an alternative to laser interference structuring according to Fig. 4 for producing the periodic three-dimensional structures 11, a method for producing laser-induced periodic surface structures can be used. Laser-induced periodic surface structures are also known as "laser-induced periodic surface structures" (LIPSS). The method is therefore also called the LIPSS method. The physical principles of the LIPSS method are generally known in the prior art, which is why a detailed description is not provided here.

[0067] The irradiation of the surface is preferably carried out with an ultrashort pulse laser with a fluence which is at or just below the material-specific removal threshold of the metallic material of the pressing tool 4.

[0068] The spacing between individual LIPSS (the average structural period P) roughly corresponds to the wavelength A of the laser used. LIPSS can vary greatly in terms of their characteristics and geometric appearance. In the LIPSS process, the structural period P can be specifically influenced, for example, by changing the laser wavelength A (e.g. from 1030 nm to 515 nm). In addition to the laser wavelength A, the polarization of the laser is also a key influencing factor. For example, in the LIPSS process, circularly polarized laser radiation or linearly polarized laser radiation can be used for the ultrashort pulse laser. The linear or elongated LIPSS shown in Fig. 3 in detail B can be created, for example, by irradiation with linearly polarized laser radiation. If the polarization is changed to circular, triangular LIPSS can be created, as shown, for example, in detail A in Fig. 3.

[0069] The resulting LIPSS structure forms an optical grating for incoming light, against which it is diffracted. The diffracted light overlaps, creating colored interference fringes that together form a spectrum. When white light is used, a continuous spectrum is created, as with a prism, but is broken down into its wavelength components. If monochromatic light (light of one wavelength) hits the optical grating, the light is also diffracted and interferes, but it is not split. This effect can be used for security markings. Markings introduced in this way can only be read with a light source of a specific wavelength (matching the structural period P of the LIPSS). The LIPSS can therefore be viewed as a code, and the matching light source can be considered a key.

[0070] Due to the one-dimensional nature of linear LIPSS, the resulting color spectrum depends on the viewing angle or the angle of the incident light. Triangular LIPSS offer the advantage of being able to reproduce the color from three viewing directions. Thus, they can achieve a relatively constant color spectrum that is relatively independent of the viewing angle.

[0071] Fig. 5 shows an example of a workpiece 6. The workpiece 6 preferably comprises a wood-based material, such as solid wood, a wood fiber material or a wood chip material. Known wood fiber materials include, for example, medium-density fiberboard (MDF), high-density fiberboard (HDF), medium-hard fiberboard (HFM) or hard fiberboard (HFH). With wood chip materials, a distinction is made, for example, depending on the orientation and size of the chips, between long press chipboard (OSB), flat pressboard (P1 - P7) and extruded board (ES and ET). The workpiece 6 can, for example, comprise a coated wood-based material. The coating can comprise a paper impregnated with melamine resin. The coating can be pressed onto the wood-based material. The workpiece 6 can, for example, also comprise a suitable plastic. Suitable plastics include, for example, so-called luxury vinyl tiles (LVT).The workpiece 6 can be, for example, a laminate floor or a laminate material board or a piece of furniture or a part of a piece of furniture.

[0072] In the example shown, a third structural region C, a fourth structural region D, a fifth structural region E and a sixth structural region F are provided on the visible workpiece surface 7. The structural regions CF each have a structuring according to the invention with periodic three-dimensional structures 11 with an average structural period P of P < 1.5 pm and an average structural depth T of T < 1 pm. The structural regions CF can be produced by pressing on a suitable pressing tool 4, the pressing surface 5 of which comprises essentially complementary periodic three-dimensional structures 11.

[0073] As indicated in Fig. 5, in addition to the structural regions CF structured according to the invention, a suitable basic structure for imitating a specific natural surface can be provided, e.g., a stone surface, as indicated. The basic structure for imitating the natural surface can preferably be overlaid by the structural regions CF, so that the colored appearance is provided on the natural surface of the workpiece 6. As already described with reference to the pressing tool, a position, shape, and size of the structural regions CF can be determined, for example, as a function of the basic structure. In this way, a structural region can be adapted, for example, to the shape, size, and position of a feature of the surface to be imitated, e.g., to a knothole in a wooden surface.

[0074] The third structural region C here, for example, has an S-shape. The S-shape represents any desired shape. The third structural region C can, for example, have triangular periodic three-dimensional structures 11, as indicated by the dotted area. The fourth structural region D here has the shape of the letter "A," the fifth structural region E has the shape of the letter "B," and the sixth structural region F has the shape of the letter "C."

[0075] The letters represent any text. The fourth, fifth, and sixth structural regions DF can, for example, each have linear or elongated periodic three-dimensional structures 11, as indicated by the dashed areas. With identical structures, the letters appear in the same color. With different structures, especially with different structural periods P, the letters can also appear in different colors.

[0076] Analogous to the pressing tool 4, the periodic three-dimensional structures 11 produced on the workpiece 6 can also be coated with a third coating. The third coating can, for example, again be wear-resistant. A layer thickness of the third coating should be set such that the periodic three-dimensional structures 11 produced, in particular structure period P and structure depth T, are retained or are not changed or are changed only negligibly, so that the color is retained. A wear-resistant third coating can, for example, be advantageous for laminate flooring that is subject to high mechanical stress. This can improve the durability of the color. A layer thickness of the third coating is preferably < 1 pm.

[0077] Alternatively or additionally, the third coating can also be optically transparent. Since light can penetrate the transparent coating onto the periodic three-dimensional structures, the layer thickness of the transparent third coating can also be greater than the average structure depth T of the periodic three-dimensional structures. This means that the periodic three-dimensional structures do not necessarily have to be retained in the transparent third coating. This can, for example, achieve greater wear resistance.The embodiments show possible embodiment variants, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiment variants thereof, but rather various combinations of the individual embodiment variants with each other are also possible and this variation possibility lies within the skill of the person skilled in the art in this technical field due to the teaching of technical action by means of the objective invention.

[0078] The scope of protection is determined by the claims. However, the description and drawings are to be used to interpret the claims.

[0079] Individual features or combinations of features from the various embodiments shown and described may represent independent inventive solutions. The problem underlying the independent inventive solutions can be found in the description.

[0080] All information on value ranges in this description is to be understood as including any and all sub-ranges thereof, e.g. the information 1 to 10 is to be understood as including all sub-ranges, starting from the lower limit of 1 and the upper limit of 10, ie all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0081] For the sake of clarity, it should be noted that some elements have been shown not to scale and / or enlarged and / or reduced in size to improve understanding of the structure. Reference symbols l_max Interference maxima

[0082] 1 pressing device l_min interference minima

[0083] 2 press stamps

[0084] AF structural areas

[0085] 3 Workpiece recording a angle of incidence

[0086] 4 Press tool

[0087] A wavelength

[0088] 5 Pressing surface

[0089] 6 Workpiece

[0090] 7 Workpiece surface

[0091] 8 Power generation device

[0092] 9 Guide device

[0093] 10 Control unit

[0094] 11 Periodic three-dimensional structures

[0095] 12 Laser device

[0096] 13 Laser source

[0097] 14 Beam generating device

[0098] 15 carriers

[0099] 16 Focus lens

[0100] 17 diffractive optical element

[0101] 18 aperture

[0102] 19 Prism

[0103] 20 deflecting mirrors

[0104] L1 Seed laser beam

[0105] L2-L3 partial laser beams

Claims

Patent claims 1. A method for producing a pressing tool (4), characterized in that the following steps are carried out: - providing a pressing tool (4) having a pressing surface (5) designed to contact a workpiece (6), - producing periodic three-dimensional structures (11) with an average structure period (P) of P < 1.5 pm and an average structure depth (T) of T < 1 pm in at least one defined structure region (A, B) of the pressing surface (5) by irradiating the at least one defined structure region (A, B) by means of an ultrashort pulse laser having a pulse duration of < 10 ps.

2. Method according to claim 1, characterized in that the pressing surface (5) is coated with a first coating having a layer thickness of at least 1 pm before the irradiation and wherein the periodic three-dimensional structures (11) are produced on the first coating.

3. Method according to claim 1 or 2, characterized in that the pressing tool (4) has on the pressing surface (5) a basic structure for imitating a natural surface, which can be transferred to the workpiece (6), wherein the periodic three-dimensional structures (11) are produced on the basic structure.

4. Method according to claim 3, characterized in that a position and / or a shape and / or a size and / or the average structural period (P) and / or the average structural depth (T) of the at least one defined structural region (A, B) are determined as a function of the basic structure of the pressing surface (5).

5. Method according to one of claims 1 to 4, characterized in that the pressing tool (4) comprises a metallic material at least in the region of the at least one defined structural region (A, B) of the pressing surface (5) and / or the first coating comprises a metallic material and wherein to produce the periodic three-dimensional structures (11) a method for producing laser-induced periodic surface structures is used.

6. The method according to claim 5, characterized in that the ultrashort pulse laser has a wavelength A < 1064 nm.

7. The method according to claim 5 or 6, characterized in that circularly polarized laser radiation or linearly polarized laser radiation is used for the ultrashort pulse laser.

8. Method according to one of claims 5 to 7, characterized in that a fluence of the ultrashort pulse laser is equal to or greater than an ablation threshold of the metallic material.

9. Method according to claim 1 or 2, characterized in that the pressing tool (4) comprises a metallic or ceramic material or a plastic at least in the region of the at least one defined structural region (A, B) of the pressing surface (5) and / or wherein the first coating comprises a metallic or ceramic material or a plastic, wherein a method for laser interference structuring with at least two superimposed laser beams (L2, L3) is used to produce the periodic three-dimensional structures (11).

10. Method according to claim 9, characterized in that three superimposed laser beams are used to generate the periodic three-dimensional structures (11).

11. Method according to claim 9 or 10, characterized in that the ultrashort pulse laser has a wavelength A < 1064 nm, wherein preferably a wavelength A in the range from 1030 ± 5 nm to 1064 ± 5 ​​nm or in the range from 515 ± 5 nm to 532 ± 5 nm or in the range from 343 ± 5 nm to 355 ± 5 nm is used.

12. Method according to one of claims 1 to 11, characterized in that the ultrashort pulse laser has pulses with a repetition rate < 2 MHz, preferably < 1 MHz and / or wherein a seed laser of the ultrashort pulse laser generates pulses with a frequency of > 40 MHz.

13. Method according to one of claims 1 to 12, characterized in that at least two structural areas (A, B) are defined on the pressing surface (5), in which different periodic three-dimensional structures (11) are produced.

14. Method according to one of claims 1 to 13, characterized in that at least a part of the produced periodic three-dimensional structures (11) is coated with a preferably wear-resistant second coating, wherein a layer thickness of the second coating is determined such that the periodic three-dimensional structures (11) are retained, wherein the layer thickness of the second coating is preferably < 1 pm.

15. Method according to one of claims 1 to 14, characterized in that the pressing tool (4) is a pressing plate, a pressing belt or an embossing roller which is designed for use for a workpiece (6) which comprises a preferably coated wood material or a plastic, preferably laminate flooring, plastic flooring, in particular LVT, or furniture workpieces, in particular cabinets, doors, worktops, tables.

16. Pressing tool (4) with a pressing surface (5) for contacting a workpiece (6), wherein the pressing surface (5) has a structured surface in at least one defined structural area (A, B) which can be transferred to a workpiece by pressing, characterized in that the structured surface comprises periodic three-dimensional structures (11) with an average structural period (P) of P < 1.5 pm and with an average structural depth (T) of T < 1 pm.

17. Press tool (4) according to claim 16, characterized in that the periodic three-dimensional structures (11) comprise structures with a substantially linear shape in plan view and / or structures with a substantially triangular shape in plan view and / or at least one of the following geometric shapes include: cone, truncated cone, pyramid, truncated pyramid, wherein the pyramid and / or truncated pyramid preferably have a triangular base.

18. Press tool (4) according to claim 16 or 17, characterized in that at least two defined structural areas (A, B) are provided, the periodic three-dimensional structures (11) of which differ.

19. Press tool (4) according to one of claims 16 to 18, characterized in that the pressing surface (5) is coated at least in the region of the at least one structural region (11) with a preferably wear-resistant second coating, wherein a layer thickness of the second coating is determined such that the periodic three-dimensional structures (11) are retained, wherein the layer thickness of the second coating is preferably < 1 pm.

20. Press tool (4) according to one of claims 16 to 19, characterized in that the press tool (4) has on the pressing surface (5) a basic structure for imitating a natural surface, which can be transferred to the workpiece (6), wherein the periodic three-dimensional structures (11) are formed on the basic structure.

21. Use of a pressing tool (4) produced by a method according to one of claims 1 to 15 or of a pressing tool (4) according to one of claims 16 to 20 for machining a workpiece (6), characterized in that the pressing tool (4) is pressed onto a workpiece surface (7) of the workpiece (6), so that by means of the generated periodic three-dimensional structures (11) an impression is created in the workpiece surface (7) of the workpiece (6), which impression is substantially complementary to the periodic three-dimensional structures (11) of the pressing tool (4), wherein the workpiece (6) used is preferably a workpiece comprising a preferably coated wood material or a plastic, for example a laminate floor, plastic floor, especially LVT, or a laminate material board.

22. Workpiece (6) comprising a wood-based material, in particular a coated wood-based material, or a plastic, preferably laminate flooring, laminate material panel or furniture workpiece, with a workpiece surface (7) which comprises at least one defined structural region with a structured surface, characterized in that the structured surface comprises periodic three-dimensional structures (11) with an average structural period (P) of P < 1.5 pm and with an average structural depth (T) of T < 1 pm and that the periodic three-dimensional structures (11) are produced by pressing on a pressing tool (4) whose pressing surface (5) comprises essentially complementary periodic three-dimensional structures (11).

23. Workpiece (6) according to claim 22, characterized in that at least two structural regions (CF) are defined, the periodic three-dimensional structures (11) of which differ.

24. Workpiece (6) according to claim 22 or 23, characterized in that at least a part of the three-dimensional structures (11) is coated with a preferably wear-resistant third coating, wherein a layer thickness of the third coating is determined such that the periodic three-dimensional structures (11) are retained and / or wherein the third coating is optically transparent.

25. Workpiece (6) according to one of claims 22 to 24, characterized in that the workpiece (6) has a basic structure on the workpiece surface (7) for imitating a natural surface, wherein the periodic three-dimensional structures (11) are formed on the basic structure.

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