Method for producing a structure on a surface

Abstract

A method for manufacturing a structure on a surface of a workpiece (1) is disclosed, the method having the following steps: applying a liquid base layer (2) onto the surface of the workpiece (1); spraying on at least one droplet (3) into the not yet congealed base layer (2), wherein the at least one droplet (3) at least partially, preferably completely, penetrates into the base layer (2); fixing the base layer (2); and at least partially removing the at least one droplet (3). Further, a second method having the following steps is disclosed: spraying on at least one droplet (3) onto the surface of the workpiece (1); applying a liquid base layer (2) onto the surface of the workpiece (1), wherein the base layer (2) flows around the at least one droplet (3) and preferably at least partially covers the at least one droplet (3); fixing the base layer (2); at least partially removing the at least one droplet (3). Finally, a device for performing the methods is disclosed.

Claims

1. A method for producing a structure on a surface of a workpiece, the method haying the following steps: applying a liquid base layer onto the surface of the workpiece; spraying on at least one droplet into the not yet congealed base laver, wherein the at least one droplet penetrates at least partially into the base layer, fixing the base layer; and at least partially removing the at least one droplet; wherein the method further haying the following steps: spraying at least one another droplet onto the surface of the workpiece before applying the liquid base layer onto the surface of the workpiece, wherein the base layer flows around the at least one droplet and at least partially covers the at least one another droplet, at least partially removing the at least one another droplet.

2. The method according to claim 1, wherein by the spraying on the at least one droplet into the not yet congealed base layer, at least one recess is brought in, wherein the at least one recess is filled by the at least one droplet, and/or wherein the layer thickness of the base layer at the place where the at least one droplet has been sprayed on changes.

3. The method according to claim 1, wherein before the spraying on of the least one droplet, a further processing step in which a solidification of the base layer takes place insofar as the base layer comprises a higher viscosity than upon its application onto the workpiece, however, it is not yet congealed, takes place.

4. The method according to claim 1, wherein the at least one droplet is sprayed on at a temperature of >40° C. and the liquid base layer and/or the workpiece has a temperature of <40° C.

5. The method according to claim 1, wherein the at least partially removing of the at least one droplet takes place by means of mechanical and/or chemical and/or physical procedures, wherein, optionally, also material of the base layer is removed.

6. The method according to claim 1, wherein the at least one droplet consists of a material which cannot be stimulated to cure by UV radiation.

7. The method according to claim 1, wherein the liquid base layer encompasses the at least one droplet in such a manner that an orifice having a smaller area then a vertically upward projection of the at least one droplets remains in the base layer or that the liquid base layer completely encompasses the at least one droplet.

8. The method according to claim 1, wherein the base layer is fixed in such a manner that, after the fixation of the base layer, the surface of the fixed base layer has no unevenness larger than maximum 20 μm by the at least one droplet remaining in the base layer.

9. The method according to claim 1, wherein the base layer is fixed in such a manner that an area comprising the at least one droplet has a different hardness grade, preferably of at least a factor 2, with respect to an area without applied droplets.

10. The method according to claim 1, wherein the at least one droplet has another gloss grade than the fixed base layer after curing or fixation in the base layer.

11. The method according to claim 1, wherein at least two droplets are placed one above the other at the same spatial place in the liquid base layer and/or on the workpiece so that, before the applying and/or before the fixing of the base layer, a compound droplet results.

12. The method according to claim 1, wherein the at least one droplet is sprayed on at a temperature of >40° C. and the liquid base layer and/or the workpiece has a temperature of <40° C.

13. The method according to claim 1, wherein the at least partially removing of the at least one droplet takes place by means of mechanical and/or chemical and/or physical procedures, wherein, optionally, also material of the base layer is removed.

14. The method according to claim 1, wherein the at least one droplet consists of a material which cannot be stimulated to cure by UV radiation.

15. The method according to claim 1, wherein the liquid base layer encompasses the at least one droplet in such a manner that an orifice having a smaller area then a vertically upward projection of the at least one another droplet remains in the base layer or that the liquid base layer completely encompasses the at least one droplet.

16. The method according to claim 1, wherein the base layer is fixed in such a manner that, after the fixation of the base layer, the surface of the fixed base layer has no unevenness larger than maximum 20 μm by the at least one droplet remaining in the base layer.

17. The method according to claim 1, wherein the base layer is fixed in such a manner that an area comprising the at least one droplet has a different hardness grade, preferably of at least a factor 2, with respect to an area without applied droplets.

18. The method according to claim 1, wherein the at least one droplet has another gloss grade than the fixed base layer after curing or fixation in the base layer.

19. The method according to claim 1, wherein the at least one droplet congeals when contacting the workpiece and/or the base layer or imbibes a solid aggregate state, and/or wherein the at least one droplet is fixed in a separate step or together with the base layer.

20. The method according to claim 19, wherein that congealing of at least one droplet takes place when contacting the base layer and/or the workpiece within less than 8 seconds.

21. The method according to claim 19, wherein the at least one droplet is re-liquefied by means of a solvent after the fixation of the base layer.

22. The method according to claim 19, wherein the at least one droplet is at least partially liquefied before and/or during the at least partially removing by reheating, and is removed out of or from the base layer in this way.

23. The method according to claim 19, wherein the at least partially removing of the at least one droplet is performed by a first mechanical removal of the cured base layer, optionally followed by a mechanical brushing out of the at least one droplet and/or by a thermic heating and sucking of the then re-liquefied at least one droplet.

24. The method according to claim 10, wherein the at least one droplet is more elastic or softer compared to the fixed base layer.

25. The method according to claim 10, wherein the at least one droplet undergoes a reduction of volume during congealing or fixing.

26. The method according to claim 1, wherein the at least one droplet congeals when contacting the workpiece and/or the base layer or imbibes a solid aggregate state, and/or wherein the at least one another droplet is fixed in a separate step or together with the base layer.

27. The method according to claim 26, wherein the at least one droplet is re-liquefied by means of a solvent after the fixation of the base layer.

28. The method according to claim 26, wherein the at least partially removing of the at least one droplet is performed by a first mechanical removal of the cured base layer, optionally followed by a mechanical brushing out of the at least one droplet and/or by a thermic heating and sucking of the then re-liquefied at least one droplet.

29. The method according to claim 26, wherein that congealing of at least one droplet takes place when contacting the base layer and/or the workpiece within less than 8 seconds.

30. The method according to claim 26, wherein the at least one droplet is at least partially liquefied before and/or during the at least partially removing by reheating, and is removed out of or from the base layer in this way.

31. The method according to claim 26, wherein the at least one droplet is more elastic or softer compared to the base layer.

32. The method according to claim 26, wherein the at least one droplet undergoes a reduction of volume during congealing or fixing.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS Below, the invention is elucidated by means of preferred embodiments by means of the attached drawings.

(1) In particular:

(2) FIG. 1 shows a workpiece with a liquid base layer into which liquid droplets have been sprayed;

(3) FIG. 2 shows a possibility to remove again the sprayed droplets;

(4) FIG. 3a shows a workpiece with a liquid base layer into which liquid droplets have been sprayed, wherein the liquid base layer at least partially encompasses the droplets;

(5) FIG. 3b shows the same workpiece as in FIG. 3a after a further processing step;

(6) FIG. 4 shows a device according to the invention for performing the method;

(7) FIG. 5 shows a workpiece with a liquid base layer into which liquid droplets have been sprayed, wherein several droplets have been sprayed on at the same place; and

(8) FIG. 6 shows a spraying of droplet onto a workpiece before the application of the liquid base layer and a possibility for applying a liquid base layer onto a workpiece.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

(9) FIG. 1 shows a workpiece 1 with a liquid base layer 2 onto which liquid droplets 3 have been sprayed. These droplets 3 locally displaced the liquid base layer 2, whereby recesses arise. The droplets 3 partially fill out the recesses arisen by the spraying on, for example up to 50% of the height or of the volume of the recess, or up 100% of the height or of the volume of the recess so that a basically smooth surface results after the spraying on of the droplets 3 and before the curing of the liquid base layer 2.

(10) FIG. 2 shows, in the view I on the left side, a workpiece 1 according to FIG. 1 with the sprayed on droplets 3 and with an already cured liquid base layer 2. This workpiece 1 is conveyed to a heat source 402 in the form of an infrared lamp which is illustrated in view II above the workpiece 1. Below this heat source 402, the surface of the workpiece 1, in particular, the base layer 2 and the droplets 3 are reheated by the infrared radiation. By the heating, the droplets 3 are re-liquefied, whereby the base layer 2 cured in the meantime remains solid. Subsequently, the workpiece 1 with the liquid droplets 3 is conveyed to a suction device 403, shown in view III on the right side, where the again liquid droplets 3 are sucked up. In this way, the droplets 3 can be completely or also only partially removed from the base layer 2. Upon partially removing, attention should be paid to not to liquefy the entire droplet 3.

(11) Such an arrangement of heat source 402 and suction device 403 can, for example, be provided in a device as shown in FIG. 4 for performing the method according to the invention.

(12) FIG. 3a shows a workpiece 1 with a liquid base layer 2 into which liquid droplets 3 have been sprayed. In contrast to the configuration in FIG. 1, the liquid base layer 2 has shut again at least partially above the droplets 3 before the fixation. While the two droplets 3 on the right side are completely enclosed by the base layer 2, no complete closing of the surface of the base layer 2 can be recognized above the left droplet 3. Here, above the droplet 3, an orifice, the area of which in a vertical upward direction is however smaller than an area of a vertically upward projection of the droplet 3, remained.

(13) FIG. 3b shows the workpiece 1 from FIG. 3a after a mechanical machining performed, for example, by a grinding machine, following to the fixation of the base layer 2. By this machining, a determined amount of material of the base layer 2 has been removed so that the penetrated droplets 3 have been exposed again.

(14) The exposure of the droplets 3 can, thereby, take place such that only so much material of the base layer 2 is removed that the droplets 3 are admittedly visible, however, they have not been exposed across their entire cross-sectional area. This result is shown in FIG. 3b. Thereby, it can be clearly recognized that the recesses of the base layer 2 form undercuts filled by the droplets 3. If the droplets 3 are removed from the base layer 2 subsequently, as, for example, shown in FIG. 2, the undercut remains in the base layer 2 which can achieve a decorated effect.

(15) Alternatively thereto or in other areas of the base layer 2, also so much material can be removed that the droplets 3 are exposed with their entire upwardly projected cross-sectional area. Then, no undercut remains in the recess. Instead, an edge sharply slanting into the recess is generated. In this manner, a sharp contour, for example of a woodgrain, can be depicted.

(16) FIG. 4 shows a device according to the invention for performing the method according to the invention.

(17) The device is formed as a production line comprising individual units 100, 200, 300, 400, 450 configured to perform the individual method steps. Alternatively or additionally, the device can also comprise the units 410 and 420.

(18) The device further comprises a transport unit 500 configured to convey a workpiece 1 to the individual units 100, 200, 300, 400, 450.

(19) Further, the device comprises a control unit 600 configured to control the individual units 100, 200, 300, 400, 450, 500 for performing the corresponding method steps or for initiating the performing of the method according to the invention in the device.

(20) In the shown illustration of the device, the transport unit 500 comprises a conveyor belt extending from the left to the right and being configured to convey workpieces 1 to this individual units 100, 200, 300, 400, 450 from the left to the right in a conveying direction.

(21) In the conveying direction, first, an application unit 100 configured to apply the base layer 2 in a liquid form onto the workpiece 1 is shown. In the illustrated embodiment, the application unit 100 comprises a rotating application roller 101 by which the base layer 2 is applied onto the upwardly pointing surface of the workpiece 1 as well as a counter pressure roller 102. Thereto, the application roller 101 unrolls on the surface of the workpiece 1. However, in an alternative embodiment, alternatively or additionally, the application unit 100 can also comprise other elements configured for application of the base layer 2. In particular, digital print units, as a digital print head or a digital nozzle beam, which apply the base layer 2 onto the workpiece 1 instead of the application roller 101 or additionally to it can be provided. Alternatively, the application unit 100 can also be formed as a casting machine in which the workpiece 1 is moved through a lacquer curtain.

(22) Thereby, in a preferred embodiment, parameters of the base layer 2, in particular, the amount of material or the thickness of the layer or the temperature of the base layer 2 when being applied onto the workpiece 1 can be influenced by the application unit 100.

(23) In the conveying direction, a dispensing unit 200 configured for dispensing the droplets 3 into the not yet congealed base layer 2 follows on the application unit 100. For dispensing the droplets 3, the dispensing unit 200 comprises one or several digital print head or print heads and/or, as the case may be, arranged one after another in the conveying direction, one or several digital nozzle beams with several digital print heads which can dispense or spray on the droplets 3 onto the base layer 2, the digital print heads extending across the width of the workpiece. Thereby, the dispensing unit 200 is configured such that the droplets 3 penetrate into the not yet congealed base layer 2 such that they displace the base layer 2 and form recesses therein, the recesses being at least partially filled by the droplets 3. The dispensing unit 200 (or digital print station) can further be configured such that the droplets 3 penetrate into the not yet congealed base layer 2 such that they are at least partially enclosed by the base layer 2.

(24) In a preferred embodiment, thereby, parameters of the droplets 3, in particular, the volume of the droplets or the mass of the droplets or the dispensing or impingement speed onto the base layer 2 can be influenced by the dispensing unit 200. The volumes of the droplets can preferably be controlled within a range of 3 to 200 pL (Picoliter), the impingement speed is preferably in the region of 2 to 10 m/s, especially preferred in the region of 3 to 5 m/s.

(25) In the conveying direction, a fixation unit 300 configured to fix the base layer 2 follows on the dispensing unit 200. For fixing the base layer 2, the fixation unit 300 comprises at least one UV light source 301, as, e.g., a LED UV radiator. Thereby, the at least one UV light source 301 radiates UV light onto the base layer 2 and initiates curing or polymerization procedures therein, whereby the base layer 2 which at least has not been congealed before the radiation by UV light solidifies and cures now or by which the base layer 2 is fixed. Alternatively or additionally, also a heat source and/or a flow source can be provided. The heat source, for example, an infrared light source or a heater is configured to emit heat to the workpiece 1, the base layer 2 and/or the droplets 3. The flow source, for example, a blower, is configured to let flow air or another gas or medium for drying over the base layer 2 and/or the droplets 3 in order to achieve drying or also a fixation by means of drying of the base layer 2 and/or of the droplets 3.

(26) In an especially preferred embodiment, thereby, the parameters with which the fixation unit 300 is operated, in particular, the energy or wavelength of the emitted UV radiation of the at least one UV light source 301, the emitted energy of the heat source, the mass flow or the flow speed or the temperature of the flowing medium of the flow source, can be influenced by the fixation unit 300. Usually, the wavelength of the UV radiation lies in the UV-A and, as the case make be, in the UV-B region, i.e., 280 nm to 400 nm. The power of the UV radiators for a production velocity of 20 m/min is at about 2× to 5×200W/cm working width, i.e., upon a width of a workpiece of 135 cm, a requested power of the UV radiators of about 50 to 125 kW results.

(27) In a preferred embodiment, the fixation unit 300 is configured to fix, except the base layer 2, also the droplets 3.

(28) In the conveying direction, a processing unit configured to rework the workpiece 1 with the located thereon fixed base layer 2 and droplets 3 follows on the fixation unit 300.

(29) Thereby, a reworking step is the at least partial removing of the droplets 3 from the base layer 2. Thereto, the processing unit comprises various elements. In the here shown embodiment, the unit 400 is formed as a nozzle channel having a heat gun in order to reheat and liquefy the congealed droplets 3 after the fixation of the base layer 2. In the downstream unit 450, the such liquefied droplets 3 are sucked up again. This takes place by a suction device 403 already mentioned in FIG. 2.

(30) In an alternative embodiment, a processing unit can also comprise the units 410, 420. These can also be provided additionally to the units 400, 450. The unit 410 is thereby formed as a grinding device (grinding machine). Thereby, the unit 410 comprises a circulating abrasive belt 411 which runs synchronously or in counter direction to the workpiece 1 guided on the transport device 500. In this way, material can be removed from the base layer 2, whereby the droplets 3 and the base layer 2 can be at least partially exposed.

(31) The unit 420 comprises a brush 421, here, formed as a rotating brush roller. The brush 421 is configured such that it can remove the droplets 3 from the fixed or congealed base layer 2 by means of mechanical cooperation of bristles with the droplets 3. Thereby, the droplets 3 are preferably congealed in the base layer 2 so that the bristles of the brush 401 can easily engage the droplets 3.

(32) However, the suction device 403 of the unit 450 can also be configured to suck the droplets 3 in solid form out of the base layer 2. This requires that the droplets 3 are configured such that they do not coalesce during the solidification.

(33) Alternatively or additionally, the unit 410 can also comprise such a grinding device configured to at least remove a part of the congealed base layer 2 by grinding. Thereby, the removal of the base layer 2 preferably takes place in layers so that material of the base layer 2 is removed from above by grinding. Thereby, the grinding device can also be configured to remove, except the congealed base layer 2, also material of the droplets 3.

(34) The grinding device is preferably configured to at least partially expose the droplets 3 if they have been at least partially encompassed by the base layer 2 before. Subsequently, the exposed droplets can then be completely or partly removed by means of a unit 420 by means of the rotating brush 421.

(35) Alternatively or additionally, the processing unit also comprises a dispensing unit configured to dispense a substance onto the fixed base layer 2 and/or the droplets 3, wherein the substance is configured to undergo a chemical reaction with the base layer 2 and/or with the droplets 3. Alternatively, the substance can also be a solvent in order to bring the droplets 3 into solution and to subsequently suck them up by a unit 450. In this manner, the base layer 2 and/or the droplets 3 can at least partially be removed. However, alternatively or additionally, an optical and/or haptic modification of the base layer 2 and/or of the droplets 3 can be achieved.

(36) In a preferred embodiment, the processing unit is configured to influence the amount of material removed from the base layer 2 and/or from the droplets 3.

(37) The control unit 600, for example, comprises a control means, as, for example, here, an electronic control device in which a program code is present which, upon its execution, causes the control unit 600 to perform the method according to the invention.

(38) In a not shown embodiment, the device can also be formed such that the application unit 100 is arranged only after the dispensing unit 200. In this way, the application of droplets 3 onto the workpiece 1 followed by an application of a liquid base layer 2 is possible. Also, an arrangement of dispensing unit 200, application unit 100 and a further dispensing unit 200 in the conveying direction can be possible in order to enable an application of droplets 3 onto the workpiece 1 and also onto the base layer 2.

(39) The processing unit can comprise all above mentioned units 400, 410, 420, 450 in arbitrary order in the conveying direction or only a selection of these units 400, 410, 420, 450, wherein also a repetition of units 400, 410, 420, 450 in the conveying direction is conceivable.

(40) FIG. 5 shows a workpiece 1 for a case of implementation in which several droplets 3 have been dispensed at the same spatial place and remain in the liquid base layer 2 on top of each other (left and right arrangement of the droplets 3). Here can clearly be seen that the droplets 3 have been stapled on top of one another so that a clearly deeper recess or a clearly deeper structure is generated in the base layer 2. In the left arrangement of the droplets 3, the recess also extends as deep as the surface of the workpiece 1.

(41) FIG. 6 shows in the illustration on top spraying of droplets 3 onto a workpiece 1 before the application of a liquid base layer. Below, first, the application of a liquid base layer 2 onto a workpiece 1 by means of an application roller 101 is shown. The bottommost illustration shows a possibility to apply a liquid base layer 2 onto a workpiece 1 by means of a casting machine 103.

(42) In the illustration on top, the workpiece 1 is fed to a digital print head 201 dispensing droplets 3 onto the surface of the workpiece 1. As illustrated, these can also be brought together to larger droplets or to more complex shapes.

(43) The intermediate illustration shows an application of a liquid base layer 2 onto this workpiece 1. Thereby, the droplets 3 located on the surface of the workpiece 1 are accordingly flowed around by the liquid base layer 2. Thereby, the liquid base layer is applied onto the workpiece 1 by means of an application roller 101. As already elucidated above, the application roller thereby corresponds with a counter pressure roller 102. So, an application of the liquid base layer 2 takes place, wherein the application roller 101 unrolls on the surface of the workpiece 1, wherein the workpiece 1 moves through from the left to the right under the application roller 101.

(44) In the bottommost illustration, the liquid base layer 2 is applied by means of a casting machine 103, wherein the casting machine 103 generates a curtain of the material of the liquid base layer 2, wherein the workpiece 1 is than moved through under the curtain from the left to the right.

(45) Finally, the further description of the invention takes place by means of five specific embodiments.

Embodiment 1

(46) A workpiece 1 in the form of a chipboard with a thickness of 12 mm is fed to a paint station. In the paint station, the chipboard is provided with a white basecoat on at least the surface. This basecoat is cured by means of a UV module. Subsequently, the so white-primed chipboard is digitally printed by a wood decor, for example oak or pine decor, in the digital printing procedure.

(47) Subsequently, the workpiece 1 printed in this way is fed to a further paint station in which the liquid base layer 2 is applied onto the workpiece 1, namely, in the form of a UV curing acrylate lacquer according to the state of the art. As application amount, a value of more than 30 g/m.sup.2 at a layer thickness of more than 30 μm, especially preferred more than 120 μm layer thickness, is chosen.

(48) Subsequently, the workpiece 1 is fed to a digital print station including print heads with a liquid (ink) heated to 85° C. As ink, for example this one of the company Sunjet with the brand name Sunjet Crystal HEP9520 is chosen. From this print station, subsequently, a plurality of droplets 3 of the ink are dispensed according to a digital printing template onto the workpiece 1 with the liquid base layer 2, wherein, thereby, recesses of 30 to 120 μm are brought in into the still liquid base layer 2. The droplets 3 are applied at a temperature of more than 80° C. and congeal when impinging onto the liquid base layer having a temperature of 20 to 30° C. by cooling within less than 0.5 seconds in the recesses brought in by themselves.

(49) Thereafter, the workpiece 1 is fed to a UV curing in which three UV lamps having a power of respectively 200 W/cm.sup.2 cure the base layer.

(50) Subsequently, the workpiece 1 with the cured base layer 2 is heated to more than 100° C. surface temperature in an IR station with infrared radiation so that the droplets 3 become liquid again. These liquid droplets 3 are then removed from the base layer 2 in a suction station.

(51) Alternatively or additionally, the droplets 3 are removed by means of mechanical means, as, for example, a rotating brush.

(52) In a further development of this embodiment, after the removal of the droplets 3, the workpiece 1 is fed to a grinding machine or a combined grinding/brush machine in order to generate grinding striae which make the structure produced according to the method of invention look more naturally.

Embodiment 2

(53) The workpiece 1 in the form of a plastic board of a PVC mixture having a thickness of 5 mm and a surface imprinted before in a decorative manner is fed to a coating station.

(54) Here, a liquid base layer 2 of a UV curing acrylate material according to the state of the art is applied, namely with a layer thickness of 40 to 300 μm, preferred with 90 to 120 μm.

(55) The workpiece 1 coated in this way is subsequently conveyed to a digital print station where the liquid base layer 2 is structured according to a digital template by means of thereon emitted ink in the form of droplets 3. Thereby, the dispensed droplets 3 having a volume between 6 pL and 400 pL penetrate into the liquid base layer 2 such that the base layer 2 shuts again above them after the penetration of the droplets 3.

(56) The droplets 3 are made of a material which consists of acrylate as an essential base. However, the droplets 3 do not include means for initiating a UV curing as this is the case upon the material of the liquid base layer 2.

(57) In the subsequent UV station, therefore, the liquid base layer 2 is cured by means of UV LED radiators, whereas the enclosed droplets 3 remind liquid.

(58) Subsequently, by means of a mechanical procedure using a grinding machine, the surface of the cured base layer 2 is grinded so far as the still liquid droplets 3 underneath are just exposed. In a further method step, the still liquid droplets 3 are brushed out by means of a brush.

(59) In an alternative embodiment, the still liquid droplets 3 are removed by the application of a solvent and a subsequent sucking of the solvent.

Embodiment 3

(60) A workpiece 1 in the form of a plastic board of a filled PP mixture (e.g., polypropylene with chalk) having a thickness of 4.2 mm, a length of 2.800 mm, a width of 1.350 mm and a surface painted in a uncolored manner is fed to a coating station. On and under the uncolored surface, further lacquer and/or primer layers can be applied.

(61) In the coating station, a liquid base layer 2 of an UV-curing acrylate material according to the state of the art is applied, namely having a layer thickness of 100 to 150 μm. After the below described fixation by means of UV radiation, this material has a melting point of >300° C. The viscosity of this layer is at about 11 mPa s at a temperature of 85° C.

(62) The workpiece 1 coated in this way is subsequently conveyed to a digital print station where the liquid base layer 2 is structured by means of ink dispensed thereon in the form of droplets 3 according to a digital template. The droplets consist in a ratio of 20-40% of Isophorone diamine and have a melting point of 88° C. They are available in the print station at a temperature of 95° C. and are dispensed out of digital print heads onto the liquid base layer 2 at this temperature. The distance of the print heads to the liquid base layer 2 is 1 mm to 10 mm, preferred 1.5 mm to 3 mm. The speed of the droplets 3 before the penetration into the liquid base layer 2 is 3 to 10 m/s, preferred 4 to 5 m/s. The dispensed droplets 3 have a volume between 6 pL and 400 pL, preferred 10 to 30 pL.

(63) The digital print heads in the print station are configured such that the can dispense from one print head several droplets 3 on top of one another to one spatial place. Thereby, in the liquid base layer 2, a kind of “tower” out of droplets 3 lying one above another is formed, the height h of the tower is determined from
h=n×D,

(64) whereby n: number of the droplets dispensed one above another at one place, and D: diameter of the droplets. In the preferred embodiment, for n=3 droplets having a respective volume of 80 pL and a diameter of 40 μm, a height h=120 μm results.

(65) The digital print station is designed such that the print heads extend in one or several rows across the entire width of transport. In an embodiment according to the invention, the print heads of the company Xaar (type Xaar 1003) which have an effective printing width of 68 mm are used. Therefore, per row, 20 print heads are used in order to achieve a minimum printing width of more than the width of the workpiece of 1.350 mm.

(66) In an alternative embodiment, three rows respectively having 20 print heads Xaar 1003 are used in the succession in the passage direction. Thereby, at a feeding speed of the workpiece 1 of 25 m/min, the print station can dispense respectively one droplet per place from the three print head rows at the same spatial place, wherein the droplets penetrate into the liquid base layer as described above, cure one above the other and achieve a total height of 3×D (diameter per droplet).

(67) In all above mentioned embodiments, the workpiece 1 is conveyed through the printing station (cf. FIG. 4) at the above mentioned speed of 25 m/min. Thereby, at least one droplet 3 at one spatial place—or, as above alternatively shown, a quantity n of droplets 3 one above the other at one spatial place—is dispensed into the liquid base layer 2. By the continuous feeding speed and the continuously working print heads across the entire width of the workpiece, a “structure image” on the workpiece 1 created according to a digital template can be generated. That is, that, for example, at several places in the feeding direction linearly in succession, respectively three droplets 3 are placed one above the other and, thus, a straight “stroke” as a recess having a depth h=3×D arises. Alternatively, all structures which have been created in a digital template are possible.

(68) In the subsequent UV station, therefore, the liquid base layer 2 is cured by means of UV LED radiators, whereas the droplets 3 have already been congealed before.

(69) In a further method step, the congealed droplets 3 are brushed out by means of a brush.

(70) In an alternative embodiment, the congealed droplets are liquefied again in a hot air channel having a nozzle temperature of 125° C. and are sucked up thereafter.

(71) In a further alternative embodiment, the congealed droplets 3 are solvated again by the application of a solvent and removed by a subsequent suctioning of the solvent. In an especially preferred embodiment, the droplets 3 are of a water-soluble material so that, in particular, water is deployed as solvent.

Embodiment 4

(72) In an alternative embodiment, the constitution of the droplets 3 can be selected as follows: Paraffin/wax: 19% EVA: 10% polyamide resin: 29% low molecular alcohol: 39% additives (for degasifying): 3%

(73) In this embodiment, the droplets 3 are removed by means of mechanical means after the congealing and fixing of the liquid base layer 2, or, alternatively, they are re-liquefied by the heating in the hot air oven and, thereafter, removed by mechanical means and/or suction from the base layer 2.

Embodiment 5

(74) In this embodiment, the droplets 3 are applied before the application of the liquid base layer 2.

(75) A workpiece 1 in the form of an HDF board having a density of 850 kg/m.sup.3 in the dimensions of 8 mm thickness, 2450 mm length and 1550 mm width is fed to a digital print station. In advance, the HDF board is prepared by one or several paint or primer steps and, subsequently, digitally printed with a decorative image of a wood replication (for example, beechwood parquet three-rod). Alternatively, after this imprinting, an intermediate lacquer layer can also be applied.

(76) In the digital print station, a plurality of droplets 3 having a volume between 12 pL and 40 pL are printed onto the decoratively printed surface in advance, namely according to a digital template. Thereby, between at least 100 up to 10,000 droplets per cm.sup.2 area are applied. These droplets 3 consist of a paraffin mixture which is imprinted at a temperature of 80° C. and which congeals when contacting the surface within less than 3 seconds, preferred, less than 1 second.

(77) In an alternative embodiment, the droplets 3 are applied according to a digital template which has been created from the digital image of the decorative surface printed by means of digital processing methods in advance. Thereby, it can be achieved that the droplets 3 are, for example, printed exactly there where the decorative image of the beechwood parquet has a knothole so that the structures generated later by the method according to the invention are synchronous to the underlying decorative image. Several droplets 3 at one spatial place can also be arranged one above the other so that the entire difference in height between the surface of the workpiece 1 and the highest point of the applied droplets achieves h=n×D, with h: difference in height, n: number of droplets one above another, and D=diameter of one droplet 3.

(78) In an exemplary embodiment, for n =5 droplets 3 and a diameter per droplets of D=25 μm, a height h=125 μm results. A plurality of these such generated “towers” of droplets 3 lying one above the other are arranged side-by-side, longitudinally or across the feeding direction so that a structure of a plurality of a droplet chains and individual droplet agglomerations result on the workpiece 1. Thereby, the height of the individual “towers” can be different, namely by variation of the quantity of the droplets 3 one above the other and also by variation of the volume of the droplets and, therefore, of the diameter D of the droplets.

(79) Subsequently, a liquid base layer 2 of a UV curing acrylate material according to the state of the art is applied, namely having a layer thickness of 120 μm. The liquid base layer 2 is applied by means of a casting machine in which a liquid curtain is generated by a dip roller and a casting lip (cf. 103 in FIG. 6). The thickness of the layer can be influenced and controlled by the viscosity of the material of the liquid base layer (here, UV curing acrylate lacquer according to the state of the art), by the numbers of revolution of the dip roller of the casting machine and by the feeding speed of the workpiece 1 (here HDF board).

(80) In the subsequent UV station, the liquid base layer 2 is cured by means of UV LED radiators.

(81) After the curing and the fixation of the liquid base layer, the droplets 3 are removed by mechanical means or, alternatively, are re-liquefied by the heating in an hot air oven and, subsequently, removed by mechanical means and/or section.

(82) In an alternative embodiment, the still liquid droplets 3 are removed by the application of a solvent and subsequent suction of the solvent.

(83) In a further alternative embodiment, the material of the droplets 3 is selected such that it starts shrinking upon radiation by UV radiation. Thereby, after the fixation of the liquid base layer 2, the droplets 3 lose contact with it and can be sucked up by simple means.

LIST OF REFERENCE SIGNS

(84) 1 workpiece

(85) 2 base layer

(86) 3 droplet

(87) 100 application unit

(88) 101 application roller

(89) 102 counter pressure roller

(90) 103 casting machine

(91) 200 dispensing unit

(92) 201 digital print head

(93) 300 fixation unit

(94) 301 UV light source

(95) 400 unit

(96) 401 brush

(97) 402 heat source

(98) 403 suction device

(99) 410 unit

(100) 411 abrasive belt

(101) 420 unit

(102) 421 brush

(103) 450 unit

(104) 500 transport unit

(105) 600 control unit