Method and application device for applying a transfer layer of a film to a substrate

Abstract

A method for applying a transfer ply of a foil to a substrate, with the steps of: a) regionally applying a radically curable adhesive to the transfer ply and/or the substrate by means of an inkjet printhead; b) precuring the adhesive by UV irradiation; c) applying the transfer ply to the substrate by means of a stamping apparatus; d) fully curing the adhesive by UV irradiation; e) peeling a carrier ply of the foil, to leave at least one first subregion of the transfer ply on an application region of the substrate, and at least one second subregion of the transfer ply on the carrier ply; f) winding up or recoiling the carrier ply with the remaining second subregion of the transfer ply; g) applying at least one further subregion of the transfer ply remaining on the carrier ply to the substrate by at least once repeating steps a) to f).

Claims

1. A method for applying a transfer ply of a foil to a substrate, comprising: a) transporting the foil to the substrate with a foil transport apparatus; b) regionally applying a radically curable adhesive to the transfer ply of the foil and/or the substrate by means of an inkjet printhead; c) precuring the adhesive by UV irradiation; d) applying the transfer ply to the substrate by means of a stamping apparatus; e) fully curing the adhesive by UV irradiation; f) peeling a carrier ply of the foil, to leave at least one first subregion of the transfer ply on an application region of the substrate, and at least one second subregion of the transfer ply on the carrier ply; g) winding up or recoiling the carrier ply with the remaining second subregion of the transfer ply; and h) applying at least one further subregion of the transfer ply remaining on the carrier ply to the substrate by at least once repeating steps a) to g), wherein the foil transport apparatus sets extension of the foil to a value of 1% to 6%, and wherein, to set a defined relative position between the foil and the substrate or between the foil and the inkjet printhead, the foil transport apparatus varies the extension of the foil on the basis of at least one positional data value.

2. The method as claimed in claim 1, wherein, by means of at least one first sensor, a positioning feature on the foil or the foil transport apparatus is detected and at least one first positional datum relating to the foil is generated.

3. The method as claimed in claim 2, further comprising transporting the substrate with a substrate transport apparatus, wherein, by means of at least one second sensor, a positioning feature on the substrate or the substrate transport apparatus is detected and at least one second positional datum relating to the substrate is generated.

4. The method as claimed in claim 3, wherein, the positioning feature on the substrate or the positioning feature on the foil is or comprises a registration mark provided during production of the substrate or a registration mark applied by means of the inkjet printhead or a design feature of the substrate or the foil or a sheet edge of the substrate or the foil.

5. The method as claimed in claim 3, wherein, by means of at least one third sensor, a positioning feature on the foil or the foil transport apparatus in the region of the inkjet printhead is detected and at least one third positional datum relating to the foil is generated.

6. The method as claimed in claim 3, wherein, at least one of the positional data is generated or corrected or verified on the basis of control commands transmitted beforehand to the substrate transport apparatus or the foil transport apparatus or the inkjet printhead.

7. The method as claimed in claim 3, wherein, the at least one subregion and/or the at least one further subregion are brought into a defined relative position to the inkjet printhead and/or to the application region of the substrate, as a function of at least one of the positional data.

8. The method as claimed in claim 7, wherein the foil transport apparatus is controlled or regulated as a function of the at least one second positional datum.

9. The method as claimed in claim 8, wherein the substrate transport apparatus or the inkjet printhead are controlled or regulated as a function of a control datum for the foil transport apparatus and of the first or third positional datum.

10. The method as claimed in claim 7, wherein the substrate transport apparatus is controlled or regulated as a function of the at least one first positional datum.

11. The method as claimed in claim 10, wherein the foil transport apparatus or the inkjet printhead are controlled or regulated as a function of a control datum for the substrate transport apparatus and of the second or third positional datum.

12. The method as claimed in claim 1, wherein the adhesive is applied using an inkjet printhead having a resolution of 300 to 1200 applicator nozzles per inch (npi).

13. The method as claimed in claim 1, wherein the adhesive is applied using an inkjet printhead having a nozzle diameter of 15 m to 25 m and/or a nozzle spacing of 30 m to 80 m.

14. The method as claimed in claim 1, wherein the adhesive is applied with a coat weight of 1.6 g/m.sup.2 to 7.8 g/m.sup.2 and/or with a layer thickness of 1.6 m to 7.8 m to the at least one subregion.

15. The method as claimed in claim 1, wherein the inkjet printhead provides drops of adhesive having a frequency of 6 kHz to 110 kHz.

16. The method as claimed in claim 1, wherein the inkjet printhead provides drops of adhesive having a volume of 2 pl to 50 pl with a tolerance of not more than 6%.

17. The method as claimed in claim 1, wherein the inkjet printhead provides drops of adhesive having a flight velocity of 5 m/s to 10 m/s with a tolerance of not more than 15%.

18. The method as claimed in claim 1, wherein the adhesive is applied with an application temperature of 40 C. to 45 C. and/or with a viscosity of 5 mPas to 20 mPas.

19. The method as claimed in claim 1, a spacing between inkjet printhead and substrate and/or foil during application of the adhesive does not exceed 1 mm.

20. The method as claimed in claim 1, wherein a relative velocity between inkjet printhead and substrate and/or transfer ply during application of the adhesive is 10 m/min to 100 m/min.

21. The method as claimed in claim 1, wherein an adhesive with the following volume composition is used: TABLE-US-00003 2-phenoxyethyl acrylate 10%-60%, 4-(1-oxo-2-propenyl)morpholine 5%-40%, exo-1,7,7-trimethylbicyclo[2.2.1]hept- 10%-40%, 2-yl acrylate 2,4,6-trimethylbenzoyldiphenyl 5%-35%, phosphine oxide dipropylene glycol diacrylate 1%-20%, urethane acrylate oligomer 1%-20%, carbon black pigment 0.01%-10%,

22. The method as claimed in claim 1, wherein an adhesive having a density of 1 g/ml to 1.5 g/ml, is used.

23. The method as claimed in claim 1, wherein the adhesive is precured 0.02 s to 0.25 s after the adhesive has been applied.

24. The method as claimed in claim 1, wherein the adhesive is precured with UV light, at least 90% of whose energy is irradiated in the wavelength range between 380 nm and 420 nm.

25. The method as claimed in claim 1, wherein the adhesive is precured with a gross irradiation power of 2 W/cm.sup.2 to 5 W/cm.sup.2 and/or with a net irradiation power of 0.7 W/cm.sup.2 to 2 W/cm.sup.2 and/or with an energy input into the adhesive of 8 mJ/cm.sup.2 to 112 mJ/cm.sup.2.

26. The method as claimed in claim 1, wherein the adhesive is precured with an exposure time of 0.02 s to 0.056 s.

27. The method as claimed in claim 1, wherein, when the adhesive is precured, its viscosity increases to 50 mPas to 200 mPas.

28. The method as claimed in claim 1, wherein the at least one subregion of the transfer ply provided with adhesive is applied to the substrate between a press roll and an impression roll.

29. The method as claimed in claim 1, wherein the at least one subregion of the transfer ply provided with adhesive is applied to the substrate with an applied pressure of 10 N to 80 N.

30. The method as claimed in claim 1, wherein the at least one subregion of the transfer ply provided with adhesive is applied to the substrate 0.2 s to 1.7 s after the precuring of the adhesive.

31. The method as claimed in claim 1, wherein the substrate, before the application of the at least one subregion of the transfer ply provided with adhesive, is pretreated, by a corona treatment, a plasma treatment or by flaming.

32. The method as claimed in claim 1, wherein the adhesive is fully cured 0.2 s to 1.7 s after the application of the transfer ply to the substrate.

33. The method as claimed in claim 1, wherein the adhesive is fully cured with UV light at least 90% of whose energy is irradiated in the wavelength range between 380 nm and 420 nm.

34. The method as claimed in claim 1, wherein the adhesive is fully cured with a gross irradiation power of 12 W/cm.sup.2 to 20 W/cm.sup.2 or with a net irradiation power of 4.8 W/cm.sup.2 to 8 W/cm.sup.2 or with an energy input into the adhesive of 200 mJ/cm.sup.2 to 900 mJ/cm.sup.2.

35. The method as claimed in claim 1, wherein the adhesive is fully cured with an exposure time of 0.04 s to 0.112 s.

36. The method as claimed in claim 1, wherein the carrier ply is detached 0.2 s to 1.7 s after the full curing of the adhesive.

37. The method as claimed in claim 1, wherein the inkjet printhead is driven by provision of a digital data set which defines those regions in which the adhesive is to be applied.

38. The method as claimed in claim 1, wherein the transfer ply is applied to the substrate by means of a thermoplastic toner at a temperature of 100 C. to 250 C., and at an applied pressure of 1 bar to 6 bar.

39. The method as claimed in claim 1, wherein the transfer ply is applied to the substrate by means of a thermoplastic toner in a roll arrangement having a press nip of 5 mm to 20 mm.

40. The method as claimed in claim 1, wherein the transfer ply is applied to a three-dimensional, domed, curved, cylindrical or flat substrate.

41. The method as claimed in claim 40, wherein the transfer ply is applied using a pressing apparatus which is transparent for a wavelength used for the precuring and/or full curing of the adhesive.

42. The method as claimed in claim 41, wherein the substrate, during the application of the transfer ply, is mounted rigidly or rotatably on a holding means which is transparent for a wavelength used for the precuring and/or full curing of the adhesive.

43. The method as claimed in claim 41, wherein the adhesive is precured or fully cured by irradiating it using a light source disposed within the pressing apparatus and or a light source disposed on the side of the pressing apparatus that faces away from the holding means.

44. The method as claimed in claim 42, wherein the pressing apparatus or the holding means has a pressing layer which is formed of one or more silicone plies and has a thickness in the range from 1 mm to 20 mm, and a hardness of 20 Shore A to 70 Shore A, and a surface roughness (mean roughness value) of below 0.5 m.

45. The method as claimed in claim 44, wherein the pressing layer has a surface structure, in the form of a pattern or decoration.

46. The method as claimed in claim 40, wherein the transfer ply is applied with an applied force of 1 N to 1000 N.

47. The method as claimed in claim 2, wherein the first positional datum comprises a position or extent of the transfer ply remaining on the carrier ply.

48. A method for applying a transfer ply of a foil to a substrate comprising: a) transporting the foil to the substrate with a foil transport apparatus; b) applying a thermoplastic toner to at least one subregion of the substrate and/or to at least one subregion of the transfer ply of the foil; c) applying the transfer ply to the substrate by means of a stamping apparatus; d) causing an applied pressure and heat to act on the transfer ply and/or the substrate; e) peeling a carrier ply of the foil, to leave at least one first subregion of the transfer ply on an application region of the substrate, and at least one second subregion of the transfer ply on the carrier ply; f) winding up or recoiling the carrier ply with the remaining second subregion of the transfer ply; and g) applying at least one further subregion of the transfer ply remaining on the carrier ply to the substrate by at least once repeating steps a) to f), wherein the foil transport apparatus sets extension of the foil to a value of 1% to 6%, and wherein, to set a defined relative position between the foil and the substrate or between the foil and the inkjet printhead, the foil transport apparatus varies the extension of the foil on the basis of at least one positional data value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now elucidated in more detail using exemplary embodiments. In the figures

(2) FIG. 1 shows a schematic representation of an application apparatus for applying a foil to a substrate, to illustrate the recognition of the relative position of foil and substrate;

(3) FIG. 2 shows a schematic representation of an application apparatus for applying a foil to a substrate, with sensors for recognizing the relative position of foil, substrate, and an inkjet printhead for adhesive application;

(4) FIG. 3 shows a schematic control circuit scheme for driving an application apparatus according to FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1 shows a schematic representation of an apparatus 1 for applying a foil 2, having a carrier ply and a transfer ply, to a substrate 3. In the representation, only the sensor technology for controlling foil advance and substrate advance is shown. Additional components of the apparatus 1 are illustrated schematically in FIG. 2.

(6) On both the foil 2 and the substrate 3 there are registration marks 21, 31, which can be detected by respective sensors 11, 12 of the apparatus 1. Foil advance and substrate advance can be controlled in dependence on the sensor data, and so foil 2 and substrate 3 are brought together in register in a roll arrangement 13 having a pinch roll 131 and an impression roll 132.

(7) As illustrated by FIG. 2, the foil 2 is guided by means of two traction mechanisms 14, 15 first to an inkjet printhead 16, which applies an adhesive to the transfer ply of the foil 2. In order to allow positionally accurate application of the adhesive, a registration mark 21 of the foil 2 is detected by means of a third sensor 17 upstream of the inkjet printhead 16. Following application of adhesive, the foil 2 is guided via a deflection roller 18 to the roll arrangement 13.

(8) The apparatus 1 may additionally comprise further components not shown in the figures. In particular, corresponding controllable traction mechanisms are provided for the substrate 3 as well. Furthermore, there may be UV lamps provided for the precuring and/or full curing of the adhesive. Additional roller arrangements serve to detach the carrier ply, with remaining, untransferred regions of the transfer ply, from the substrate 3, and to coil up the carrier ply detached.

(9) For the application of the transfer ply to the substrate 3 there are a number of possibilities. In the minimal variant described below, a bare continuous substrate 3 is assumed, which in particular also has no features that can serve as register mark 31. It is further assumed that no register mark on a component traveling along with the substrate 3 (roll, wheel) is employed either. Of course, such features may likewise be integrated into the control or regulation of the apparatus 1.

(10) In the application of the transfer ply, first of all a UV adhesive, as motif-providing layer, is applied to the substrate 3 or to the back of the foil 2. Application of this adhesive takes place in the form of the subsequent foil application or of the subsequent motif. The adhesive here may be printed on in the form of the motif or else, optionally, in the form of the motif and of an additional, separate register mark.

(11) [The foil 2 and the substrate 3 are subsequently brought together with the UV adhesive disposed between foil 2 and substrate 3. In the roll arrangement 13, the foil 2 is pressed against the substrate 3.

(12) Application of the foil 2 to the substrate 3 is followed by UV curing of the UV adhesive with the applied foil 2. After full curing, the carrier ply of the foil 2 is peeled from the substrate 3, together with untransferred regions of the transfer ply, and is wound up. Optionally there may also be recoiling of the foil 2 for the change of direction of the wound foil web. At this point, the first stamping pass is at an end.

(13) If the substrate 3 contains no register marks 31, it is barely possible to bring the stampings of the first pass in register (correct relative spacing) with the stampings of a second pass. This therefore entails a corresponding loss of inherently usable transfer ply between the two passes. With additional register marks 31 on the substrate 3, this problem can be avoided.

(14) At the start of the second stamping process, there is a roll change; in other words, the wound carrier ply with the remaining regions of the transfer ply is mounted on the unwind side.

(15) First of all it is now necessary to detect the regions of the foil 2 that have already been stamped, in other words the regions in which the transfer ply has already been transferred to the substrate 3.

(16) At the start of the second run, this detection may optionally also take place manually or by visual estimate. Preferably, however, it is accomplished by means of optical sensors.

(17) A useful region of the foil 2 thus recognized, in other words an as yet unstamped region of the transfer ply, must now be positioned relative to the printhead 16, if printing takes place onto the back of the foil 2. Otherwise, positioning takes place with respect to an adhesive motif printed on the substrate 3.

(18) At the start of the second run, this positioning may likewise be accomplished manually or by visual estimate. In the ongoing run, this takes place by means of optical sensors 11, 12, 17, the measurement values from which are employed for regulating foil traction by way of the traction mechanisms 14, 15.

(19) Then, with positioning correct, as also in the first stamping run, the foil 2 is brought together with the substrate 3, with the UV adhesive disposed between foil 2 and substrate 3; the film 2 is pressed against the substrate 3 in the roll arrangement 13; the UV adhesive is subsequently UV-cured with the applied transfer ply; and the foil 2, together with untransferred regions of the transfer ply, is peeled off and wound up.

(20) If there are still sufficiently large stampable regions of the transfer ply present on the foil 2, it is possible subsequently for a further stamping process to take place in the manner described.

(21) More precise control is possible if register marks 31 have been provided on the substrate 3 as well. With this variant, therefore, three elements must be positioned in register with one another, namely the substrate 3 with possibly motifs thereon, such as printed decorations, and/or a predetermined useful region of the substrate 3; the UV adhesive, as motif-providing layer for the foil 2 transfer ply to be applied; and also the transfer ply of the foil 2, optionally bearing motifs or a continuous design.

(22) In order to ensure in-register alignment between these elements, register marks 21, 31 are necessary. These may also be any embodiment of control marks, printing marks, raised portions of the foil 2, design features of foil 2 or substrate 3, sheet edges of foil 2 or substrate 3, or any other kind of guidance and/or control criteria.

(23) Such control criteria can be or must be present and/or generated on the substrate 3, the foil 2, and/or else on the printhead 16. It is also conceivable for registration to be able to be carried out by means of a control signal from the software for driving the substrate supply and/or the foil supply and/or the printhead driver.

(24) It is conceivable, furthermore, that the registration and/or a controlling-guiding signal or pulse, detected mechanically via the system, can be recorded. For example, on a transport roll for the substrate 3 and/or the foil 2, or on a corresponding co-rotating element (wheel, roller), a marking may be disposed which can be detected by means of optical sensors. In this way as well it is possible to detect length and/or time data relating to the position of foil 2, substrate 3 and/or printhead 16.

(25) The specific design of the register marks 21, 32 and also, where appropriate, of markings on co-travelling parts of the apparatus, is not subject to any specific rules, but must merely be adapted to the sensors 11, 12, 17.

(26) For these sensors 11, 12, 17, the use of optical systems is particularly preferred. This refers to all kinds of camera systems with or without their own evaluation unit. The signals generated can then be processed by corresponding software and therefore used as a guide criterion. It is also conceivable to have the optical systems likewise deliver a control pulse, which need not, but also can, be explicitly processed.

(27) It is possible, furthermore, to employ various sensor systems, especially reflected light sensors, color sensors, reflective light switches, light barriers (for recognizing sheet edges), ultrasonic sensors (for recognizing sheet edges), laser sensors, transmitted light sensors (for recognizing watermarks and the like) and/or sensors in optical waveguide technology.

(28) Such sensors 11, 12, 17 require an external signal amplifier, but are also available with internally integrated signal amplifiers. For signal processing it is immaterial whether the sensor, amplifier or a corresponding output signal in question is analog or digital.

(29) The signals from the sensors 11, 12, 17 and/or amplifiers may then be processed by corresponding software and hence used as a guide criterion. It is also conceivable for these signals from the sensors 11, 12, 17 and/or amplifiers to be used directly as a control pulse. Accordingly, external software and/or apparatus for signal processing is not explicitly required.

(30) In the text below, the pure positioning of the foil 2 relative to the substrate 3 is described in detail, initially without regard to the printhead 17. The sensor 12 is provided for this purpose and, as described above, may be optical, sensory and or mechanical, and is mounted in the region of the substrate feed. It should be borne in mind that the adhesive print may take place onto the substrate 3 or onto the foil 2. The particular embodiment selected, however, has no substantial influence on the principles of the control or regulation of the apparatus 1.

(31) The sensor 12 must be situated in front of the roll arrangement 13. It has emerged that a distance to roll arrangement 13 of 10 mm to 800 mm is particularly advantageous. Clean registration of motifs, etc., with one another can be accomplished only before the permanent joining, in other words before foil application to the substrate 3 in the roll arrangement 13, since after that it is no longer possible to exert any influence on this registration.

(32) It is, however, also possible to accomplish verification of the register accuracy after the roll arrangement 13, although in that case the subject under consideration is no longer the motif that has just been applied, but rather the subsequent motif. Here it is possible to determine deviation in the subregion of the transfer ply that has just been applied, and to generate corresponding correction instructions, where appropriate, to the traction mechanisms 14, 15. This mode is normally used for a control loop.

(33) The distance of the sensor 11 or 12 in front of the roll arrangement 13, of 10 mm to 800 mm, is made up of the distance of the roll arrangement 13 to the traction mechanism 15, the distance of the roll arrangement 13 to the printhead 16, the signal processing time for the printhead 16, the web speed of the substrate 3 and of the foil 2, and the signal processing of the sensors 11 and 12, respectively.

(34) Serving below as an example is the application scenario with a printhead 16. At a web speed of around 70 m/min, the software of the printhead 16 requires an initial travel section to the roll arrangement 13 (placing of the mark sensors 11 and 12 in front of the roll arrangement 13) of approximately 300 mm in order to process the signal. The sensor 12 for recognizing the substrate mark must therefore be positioned at least 300 mm in front of the roll arrangement 13.

(35) It is also necessary to take account of the distance from the printhead 16 to the roll arrangement 13, this distance being dictated by construction. This distance is therefore an offset value, since the foil position at which the printhead 16 prints is required to traverse this section to the roll arrangement 13, while the substrate 2 at the same time is also moving forward. It is therefore necessary for this distance to be added onto the distance between substrate mark sensor 12 and roll arrangement 13. In this example, this distance is about 350 mm. An overall initial-run section from the substrate sensor 12 to the roll arrangement 13 is therefore 300 mm+350 mm, in other words 650 mm.

(36) In the example just described, the register signal of the sensor 12 functions as a control signal, in other words as what is called a master, and hence as a guide signal for all subsequent regulation procedures.

(37) The foil supply unit consists of foil unwinders, traction mechanisms 14, 15, and foil rewinders. The traction mechanism 14, 15 may be equipped with stepper motor technology, sensor technology, etc. It is conceivable for the unit to consist in each case only of one component, of two or more components, or of a mixture of the abovementioned components. Additionally, this unit may be equipped with dancers, foil accumulators, etc.

(38) The apparatus 1 may also have two or more foil webs and/or foil tracks. In that case it is necessary for each foil web requiring registration to be equipped with a respective sensor 11.

(39) For registration of a single-image foil 2, it is necessary for a defined guide criterion to be installed in the foil. Here again, the form, as for example the geometric design, color, the design as diecut, stamp or watermark, the use of a mechanical component in the machine (co-travelling virtual mark on a roll or on a linear unit), etc., as guide criterion is not subject to any special rules.

(40) A continuous decoration may further be aligned by means of its stamping-out (i.e., the gap produced in the transfer ply) after the first stamping run, with the stamping-out then functioning as a guide criterion. Here as well, the design of the stamping-out used for guidance is freely selectable.

(41) The relative positioning of the foil 2 to the substrate 3 takes place preferably by way of the foil extension. This is explained in more detail below.

(42) As shown by FIG. 1, the read distance between substrate mark sensor 12 and roll arrangement 13 is X mm, and the distance of the foil mark sensor 11 to the roll arrangement 13 is Y mm. Since, in this specific case of cold foil stamping in permanent running, the foil 2 and the substrate 3 are in synchronism, the distance X must be greater than or equal to the distance Y for registration of the marks or images, or of foil 2 with respect to the substrate 3.

(43) The minimum difference, however, must not be too great. It has emerged that a minimum offset of 0 mm to 10 mm is acceptable.

(44) For the consideration of the registration process below, an offset of 0 mm is set as a precondition.

(45) The foil is generally conveyed with a basic extension of Z of 1 to 6, preferably 3, relative to the repeat length, in other words the spacing between successive marks 21, this conveying taking place constantly to the substrate 3. In normal operation, therefore, the foil 2 is always slightly pre-extended.

(46) In order to place the two control marks 21, 31 over one another, the foil mark sensor 11 is positioned in slave mode to the substrate 3 with its mark 31. This is accomplished via a slight change in foil extension, by the traction mechanism 14, 15 on the foil 2 braking the foil 2 to a greater or lesser degree, resulting in a reduced or increased foil extension ZM . Through this change in tension or extension it is possible for the guide criteria to be positioned relative to one another. For this reason it is also possible to realize the above-depicted minimum difference between X and Y, since a certain difference can be compensated by means of the foil extension. It is also possible to operate with a certain slight offset which is then likewise reflected in the foil extension.

(47) For in-register application of the transfer ply of the foil 2 onto the substrate 3, furthermore, a precise positioning of the UV adhesive print relative to the substrate 3 and/or to the foil 2 is necessary. For this variant of the method there are various sensor arrangements that can be employed.

(48) In a first variant there is only one sensor 12 for recognizing the substrate mark 31. This is suitable for foils 2 with continuous design, which are to be processed in only one stamping run. The sensor 12 for the substrate mark 31 in this case ensures the foil decoration at the intended site on the substrate 3.

(49) In a second variant there are two sensors 11, 12. This is suitable for foils 2 with individual-image design which are processed in only one stamping run. A sensor 12 for the substrate mark 31 and a sensor 11 for the foil mark 21 are sufficient here to ensure the positioning of the individual foil image at the intended site on substrate 3.

(50) The most accurate control is possible in an apparatus 1 having three sensors. With this it is possible to process a foil 2 with individual-image design in a plurality of stamping runs. Sensors 11, 12 for the substrate mark 31 and for the foil mark 21 ensure the desired relative position between foil 2 and substrate 3. For the positioning of the adhesive print on foil 2, in other words for the driving of the printhead 16, a further sensor 17 is provided. With this it is possible to control with accuracy not only the positioning of the individual foil image at the intended site on the substrate 3 but also the positioning of the adhesive print onto the foil 2.

(51) A complete system composed of substrate 3, foil positioning, and inkjet printhead 16 for implementing the latter method is described below with reference to FIG. 2.

(52) Overall, therefore, as described, a sensor 12 for the substrate 3, a sensor 11 for the registration of the foil 2 relative to the substrate 3, and a sensor 17 for the registration of the printhead 16 relative to the foil 2 are required. A foil traction mechanism 15 between the first traction mechanism 14 and the printhead 16 allows registration of the foil 2 between the two traction mechanisms 14 and 15 onto the master signal, generated by the sensor 12, with respect to the substrate 3. The two traction mechanisms 14, 15 displace the positioning of the foil 2 to the substrate 3 upstream in the foil course, in front of the printhead 16, by way of the foil extension. At the printhead 16, therefore, the foil 2 is already correctly positioned and need not subsequently be extended again. Consequently, the adhesive print provided on the foil 2 is also, advantageously, not co-extended as well, and so the printed image is not distorted.

(53) With regard to the driving of the apparatus 1, the signals of the sensors 11, 12, 17 must be considered as separate systems. Serving as master in the case described is the control mark 31 detected by the sensor 12 on the substrate 3. This is the so-called lead signal. Oriented on this signal are, firstly, the alignment and/or extension of the foil 2 by the traction mechanisms 14, 15 and/or, secondly, the positioning of the printhead 16, which is supported by the sensor 17 for re-reading the foil mark 21. As already described above, therefore, the foil 2 is positioned to the extent that the foil mark 21 is able to serve as a print start signal for the printhead 16.

(54) For the functioning it is necessary for the distance from the substrate mark 31 to the roll arrangement 13, referred to below as X, to be greater than or equal to the distance from the roll arrangement 13 to the printhead 16, hereinafter called M. A very largely equal distance is ideal, but if X>M, the time of printing can be adjusted accordingly via an offset value in the control (for example, a time delay or via a fixed foil path through non-driven print lines on the printhead 16). The start signal may be processed in the printhead control, or externally.

(55) In total, therefore, there are up to three input variablesi.e., the measured data from the sensors 11, 12, 17and three controlled variables, in particular the rate of advance and/or the extension of foil 2 and substrate 3, and also the positioning of the inkjet printhead 16, available for the control or regulation of the application apparatus 1. This results in a plurality of possibilities for implementing the control or regulation logic system.

(56) On the one hand it is possible for the traction mechanisms 14, 15 for the foil 2 to be controlled or regulated as a function of the substrate mark 31.

(57) In that case it is useful if the transport apparatus for the substrate 3 and/or the inkjet printhead 16 is controlled and/or regulated as a function of a control datum for the traction mechanisms 14, 15 and the foil mark 21.

(58) In this case, therefore, the datum concerning the substrate 3 serves as the master input variable, and control takes place in dependence on this variable. This control can in turn be implemented in a variety of ways.

(59) First of all it is possible to implement control with the print mark sensor 31 of the substrate 3, in other words with the sensor 11, in accordance with which the rate of advance of the foil 2 and also the inkjet printhead 16 are controlled.

(60) Alternatively, the print mark sensor 31 of the substrate 3 can be used for control, and, in dependence on this, there can be regulation of the foil 2 and subsequent regulation or driving of the inkjet printhead 16 by the foil mark 21, in other words the measurement values from the sensor 11 or 17, respectively.

(61) It is also possible to do without regulation of the transport of the foil 2. Here there is only regulation of the printing by the foil mark 21, in other words the sensor 11, or else by the print mark 31 of the substrate 3, in other words the sensor 12.

(62) Furthermore, control may be implemented with the print mark sensor 31 of the substrate 3, and also with regulation of the foil 2 on the basis of the data from the sensor 12, in which case it is possible to omit regulation of the print.

(63) Alternatively, the transport apparatus for the substrate 3 may also be controlled or regulated in dependence on the sensor 11, in other words on the foil mark 21.

(64) In that case it is useful if the traction mechanisms 14, 15 and/or the inkjet printhead 16 are controlled and/or regulated as a function of a control datum for the transport apparatus for the substrate 3 and as a function of the data from the sensors 12, 17.

(65) In this event, therefore, the datum relating to the foil 2 serves as the master input variable, and control takes place as a function of this variable. This control may likewise be implemented, in turn, in a variety of ways.

(66) Here as well it is possible to implement control with the print mark sensor 21 of the foil 2, in other words the sensor 11, according to which the rate of advance of the substrate 3 and also the inkjet printhead 16 are controlled.

(67) Alternatively, the print mark sensor 21 of the foil 2 can be used for control and, in dependence thereon, regulation of the substrate advance and subsequent regulation or driving of the inkjet printhead 16 may take place through the substrate mark 31, in other words the measurement values from the sensor 12.

(68) It is also possible to do without regulation of the transport of the substrate 3. In that case there is only regulation of the print by the substrate mark 31, in other words the sensor 12, or else by the registration mark 21 of the foil 2, in other words the sensor 11.

(69) Furthermore, control with the print mark sensor 11 of the foil 2 may also be implemented with regulation of the substrate 3 on the basis of the data from the sensor 11, in which case it is possible to do without regulation of the print.

(70) Regulation using the substrate mark 31 is preferred here as a master variable.

(71) An exemplary control circuit for this purpose is illustrated in FIG. 3. In a first step S1, the data from the sensors 11 and 12 are captured and a target/actual comparison is carried out. The data from the sensor 12, in other words the position of the substrate mark, serve as master signal. In the event of deviations from the relative target position between substrate mark and foil mark, the traction mechanism 14 is accelerated or braked accordingly.

(72) At the same time, in steps S2 and S3, the web speed of foil 2 and substrate 3 is monitored, and in step S4, likewise, a target/actual comparison is carried out. If the web speeds deviate from one another, particularly on account of an above-described change at the traction mechanism 14, then the traction mechanism 15 is driven correspondingly for the correction.

(73) In a further, parallel process to this, the printhead 16 is regulated as a function of the data from the sensor 17 and as a function of a fundamental control data set mandated by the pattern to be printed.

(74) Overall, therefore, all variables of the system are regulated as a function of the position of the substrate mark 31 as detected by means of the sensor 12.

(75) Below, additional elucidation is given of the other components of the apparatus 1, those not directly connected with the registration of adhesive printing, foil 2 and substrate 3, these components nevertheless being essential to the application of the transfer ply of the foil 2 onto the substrate.

(76) The inkjet printing takes place by way of a piezoelectric drop-on-demand printhead 16. For high-quality results, the printhead 16 must possess a particular physical resolution, droplet size, and nozzle spacing. These nozzles may be arranged in one or more rows. The physical resolution ought to be 300 npi to 1200 npi (nozzles per inch). A small nozzle spacing transverse to the printing direction ensures that the printed pixels likewise are close to one another transverse to the printing direction, or overlap, depending on quantity of adhesive.

(77) Generally speaking, the npi correspond to the dpi (dots per inch) on the print medium, in other words either on the substrate 3 or on the foil 2. When using the gray stage technology offered by certain printheads 16, gray stages are generated by different quantities of ink per printed pixel. The gray stages are generally produced by firing of a plurality of droplets of virtually identical size onto a printed pixel, these droplets combining while still in the flight phase to the substrate to form a larger drop of ink. The quantity of adhesive on the print medium behaves in analogy to the gray stages.

(78) The quantity of adhesive must be varied according to the absorbency of the substrate 3 or of the transfer ply of the foil 2, respectively. The quantity of adhesive on the foil 2 must be 1.6 to 7.8 g/m.sup.2 in order to ensure complete foil application to every substrate 3. The layer thicknesses of the applied adhesive are then 1.60 m to 7.80 m. For optimum wetting of the primer layer of the foil 2 with adhesive, this layer ought to have a surface tension of 38 to 46 mN/m, with the range from 41 to 43 mN/m in particular ensuring optimum ink acceptance.

(79) The nozzle spacing ought to be 30 to 80 m. In order to ensure high resolution in the printing direction, the piezoelectric actuator of the printhead 16 is required to fire off the droplets of adhesive with a frequency of 6 to 110 kHz, which for print-medium speeds of 10 m/min to 75 m/min produces a resolution on the print medium of 600 to 1200 dpi.

(80) The pressure within the nozzle chamber is preferably 10 mbar to 15 mbar and ought not to be exceeded, in order not to damage the piezoelectric actuator. The spacing of the nozzle plate of the printhead 16 relative to the foil 2, or to the substrate 3, respectively, ought not to exceed 1 mm, in order to minimize the effect of drafts of air in diverting the fine droplets of adhesive.

(81) The droplet volume ought to be 2 pl to 50 pl, with a tolerance of 6% of the droplet volume. In this way, for a given resolution, the necessary quantity of adhesive is applied uniformly to the print medium. The pixel size resulting from the droplet is dependent on the viscosity of the liquid.

(82) The droplet viscosity in flight ought to be 5 to 10 m/s with a tolerance of not more than 5%, so that all of the droplets of adhesive land very precisely alongside one another on the print medium. If the droplet velocity of the individual droplets deviates too greatly from one another, this is manifested in an uneven printed image.

(83) For optimum printability of the liquid, the viscosity of the liquid to be printed ought to be 5 to 20 mPas, typically 7 mPas to 9 mPas. In order to ensure consistent liquid viscosity, it is necessary for the printhead 16 or the adhesive supply system to be heated. For the corresponding viscosity, the adhesive temperature in operation ought to be 40 to 45 C. Droplet flight and impingement on the print medium cause an increase, as a result of cooling, in the viscosity of the droplet of adhesive, likely to 20 mPas to 50 mPas. An increase in the viscosity counteracts any running or spreading of the adhesive on the print medium.

(84) The adhesive employed is preferably a light gray UV-curing ink for use in piezoelectric drop-on-demand inkjet printheads 16. By energy input in the form of UV light, a radical chain reaction is triggered in the adhesive. In this reaction, polymers and monomers combine to form a solid network of molecules. The adhesive becomes hard or dry. The chain reaction is triggered by UV light in a wavelength range from 350 to 400 nm10 nm.

(85) The key difference between cationically curing adhesives and the radically curing system used here is that the cationic mechanism is substantially slower, i.e., through-curing takes longer. For foil application, however, a quick-curing system is needed, since otherwise it would not be possible to apply the foil 2 completely. In the course of UV irradiation of cationic adhesives, moreover, an acid is formed, and is responsible for the through-curing of the adhesive. Owing to this mechanism, print media must first be checked for compatibility for cationic systems, since alkaline or basic substances of some substrate surfaces may influence or prevent the through-curing of the adhesive. This is unnecessary here.

(86) The adhesive preferably has the composition as follows:

(87) TABLE-US-00002 2-phenoxyethyl acrylate 10% to 60%, preferably 25% to 50%; 4-(1-oxo-2-propenyl)morpholine 5% to 40%, preferably 10% to 25%; exo-1,7,7- 10% to 40%, preferably 20% to 25%; trimethylbicyclo[2.2.1]hept- 2-yl acrylate 2,4,6-trimethylbenzoyldiphenyl 5% to 35%, preferably 10% to 25%; phosphine oxide dipropylene glycol diacrylate 1% to 20%, preferably 3% to 10%; urethane acrylate oligomer 1% to 20%, preferably 1% to 10%; carbon black pigment 0.01%-10%, preferably 0.1% to 0.5%.

(88) With preference there is partial curing of the adhesive (also called UV pinning), spatially and temporally almost directly after the process of printing onto the foil 2. Only in this way is it possible to fix the defined, sharp motif on the foil 2. This fixing is brought about by an increase in viscosity of the adhesive, induced by partial triggering of the radical chain reaction.

(89) In terms of space, the partial curing takes place preferably 1 to 4 cm after the printing in machine direction, corresponding to a temporal spacing in machine direction of approximately 0.02 to 0.25 s (for a web speed of 10 to 30 m/min).

(90) The UV pinning unit ought to produce a gross UV irradiation power of 2 to 5 W/cm.sup.2 in order to bring the necessary and optimum energy input into the adhesive. 90% of the UV light delivered ought to be situated in the wavelength spectrum between 380 and 420 nm. This requirement can only be met by LED UV systems, since these systems deliver virtually monochromatic UV light, and the wavelength spectrum delivered is therefore much narrower than in the case of conventional medium-pressure mercury vapor lamps, for which the emitted spectrum encompasses a relatively large wavelength range. The window from which the radiation emerges ought to be approximately 10 mm to 30 mm in size in the machine direction, in order to allow the adhesive to be irradiated over its area.

(91) Depending on web velocity and foil velocity of around 10 m/min to 100 m/min, more particularly around 10 m/min to 75 m/min (or more), and through absorption and reflection of 50% to 60% of the UV light by the foil, the UV dose (mJ/cm.sup.2) penetrating to the adhesive is reduced. Additionally, the distance between the UV pinning lamp and the foil web lowers the irradiation power delivered, by approximately 10% in the case of an irradiation distance of 2 mm, for example. This dose can additionally be adapted via the web velocity, since to do so changes the irradiation time.

(92) As already described, the viscosity of the droplets of adhesive on the foil has already increased to likely 20 mPas to 50 mPas prior to the partial curing, as a result of cooling. The partial curing drives change in viscosity further forward. After the partial curing, the droplets have a viscosity of likely 50 mPas to 200 mPas, a figure which may vary according to the layer thickness of the adhesive. This fixes the adhesive reliably on the print medium. The motif on the foil 2, though fixed, is nevertheless still moist and can be printed onto the substrate 3 in the next step.

(93) At this point in the operation, the foil 2 with the adhesive, which is still wet and has the viscosity mentioned above, is pressed onto the substrate 3. The pressure, in the form of a linear pressing, is generated by a press roll 131 and an impression roll 132.

(94) The press roll 131 ought to consist of a solid plastic or rubber with a smooth surface, and ought to have a hardness of 70 to 90 Shore A. The impression roll 132 is preferably made of steel and has a hardness of 100 Shore A. The radius of the press roll 131 ought to be 1 cm to 20 cm, and that of the impression roll 132 ought to be 1 cm to 20 cm.

(95) In spatial terms, the roll arrangement is disposed approximately 10 cm to 30 cm after the partial curing of the adhesive in machine direction, corresponding to a temporal spacing of approximately 0.2 to 1.7 s (for a web speed of 10 m/min to 30 m/min). The linear pressing ought to take place with a force of between 10 N to 80 N, depending on the nature of the substrate.

(96) The wet adhesive with the foil 2 may be applied to various substrates 3. The foil 2 may be applied, for example, to paper substrates with a coated or uncoated surface, natural papers, plastics (PE, PP, PET), and label materials, and also to glass or ceramic. In the case of substrates made of plastic, glass or ceramic, a pretreatment may be useful in order to improve the adhesion of the adhesive to the substrate 3, such pretreatment taking place, for example, by corona, by plasma or by flaming). The application outcome is better in the case of smoother substrate surfaces.

(97) As a result of the partial curing and the associated change in viscosity of the adhesive, the application outcomes even on rough substrates 3, however, are improved significantly in comparison to the conventional method without change in viscosity. After the foil 2 has been pressed onto the substrate 3, the foil 2 with the adhesive, which is still wet, remains on the substrate 3 until the adhesive has undergone through-curing, and the carrier ply of the foil 2 is peeled off.

(98) Similar to the description given in reference to the precuring of the adhesive, application of the foil 2 to the substrate 3 is followed by the ultimate, full curing (postcuring) of the adhesive with the foil 2 on the substrate 3. In this step, the foil 2 bears very closely against the still-wet adhesive on the substrate 3 and by through-curing of the adhesive is able to enter into a firm and smooth bond with the substrate 3.

(99) Through-curing takes place with a strong LED UV lamp, which supplies a high irradiation power and ensures complete radical chain reaction within the adhesive. The reasons for the use of an LED UV system, and the factors for the irradiation power, have already been described with reference to the precuring and are valid for this operating step as well.

(100) In spatial terms, through-curing takes place approximately 10 to 30 cm after foil application in the machine direction, to a temporal distance of approximately 0.2 s to 1.7 s (at a web speed of 10 m/min to 30 m/min) after application. The distance between the lamp and the foil substrate web is preferably 1 mm to 10 mm, in order to achieve optimum through-curing but at the same time to prevent physical contact between the lamp and the substrate 3.

(101) The irradiation window of the lamp in machine direction ought to be 20 mm to 40 mm in size. The gross UV irradiation power ought to be between 12 W/cm.sup.2 and 20 W/cm.sup.2, so that the adhesive is completely through-cured with speeds of 10 m/min to 30 m/min (or higher) and with the other factors already mentioned above.

(102) It should be noted that these values are possible only theoretically (at 100% lamp power). At full power of the UV lamp, in the case of a 20 W/cm.sup.2 version, for example, and at a low web velocity, 10 m/min, for example, the foil substrate web becomes heated to such an extent that it can catch fire. After the through-curing, the foil 2 adheres completely to the adhesive and the adhesive adheres completely to the substrate 3. The carrier ply of the foil 2 can now be peeled off.

(103) In spatial terms, the detachment of the carrier ply takes place preferably approximately 10 cm to 30 cm after the through-curing in machine direction, corresponding to a temporal distance of approximately 0.2 s to 1.7 s (for a web speed of 10 m/min to 30 m/min). The carrier ply for detachment is preferably passed over a detachment edge, which allows contactless detachment of the carrier by means of an air cushion. The substrate 3 is now fully finished.

(104) The detached carrier ply, with the remaining, unstamped regions of the transfer ply, can now, as described, be rolled up, recoiled, and supplied for a further stamping pass.

LIST OF REFERENCE SYMBOLS

(105) 1 Apparatus 11 Sensor 12 Sensor 13 Roll arrangement 131 Pinch roll 132 Impression roll 14 Traction mechanism 15 Traction mechanism 16 Printhead 17 Sensor 18 Deflection roller 2 Foil 21 Registration mark (on foil) 3 Substrate 31 Registration mark (on substrate) S1 . . . S4 Method steps