Method and Device for Applying a Film

Abstract

A method for applying a transfer ply of a foil to a substrate, with the steps of: a) applying a radically curable adhesive to at least one subregion of the transfer ply by means of an inkjet printhead; b) pre-curing the adhesive by UV irradiation; c) applying the at least one subregion of the transfer ply provided with adhesive to the substrate; d) fully curing the adhesive by UV irradiation; e) peeling a carrier ply of the foil from the at least one subregion of the transfer ply.

An application apparatus and also printing apparatus for implementing such a method.

Claims

1. A method for applying a transfer ply of a foil to a substrate, the method comprising: a) applying a radically curable adhesive to at least one subregion of the transfer ply by means of an inkjet printhead; b) pre-curing the adhesive by UV irradiation; c) applying the at least one subregion of the transfer ply provided with adhesive to the substrate; d) fully curing the adhesive by UV irradiation; e) peeling a carrier ply of the foil from the at least one subregion of the transfer ply.

2. The method as claimed in claim 1, further comprising: applying a thermoplastic toner to at least one subregion of the substrate and/or to at least one subregion of a transfer ply of a further foil; applying the transfer ply to the substrate; causing an applied pressure, and heat, to act on the transfer ply and/or the substrate; peeling a carrier ply of the foil from the at least one subregion of the transfer ply.

3. A method for applying a transfer ply of a foil to a substrate, the method comprising: a) applying a thermoplastic toner to at least one subregion of the substrate and/or to at least one subregion of the transfer ply; b) applying the transfer ply to the substrate; c) causing an applied pressure, and heat, to act on the transfer ply and/or the substrate; d) peeling a carrier ply of the foil from the at least one subregion of the transfer ply.

4. The method as claimed in claim 3, further comprising: a) applying a radically curable adhesive to at least one subregion of the transfer ply by means of an inkjet printhead; b) pre-curing the adhesive by UV irradiation; c) applying the at least one subregion of a transfer ply provided with adhesive to the substrate; d) fully curing the adhesive by UV irradiation; e) peeling a carrier ply of the foil from the at least one subregion of the transfer ply.

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

6. 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 with a tolerance of not more than 5 m and/or with a nozzle spacing of 50 m to 150 m with a tolerance of not more than 5 m.

7. The method as claimed in claim 1, wherein the adhesive is applied with a weight per unit area of 0.5 g/m.sup.2 to 20 g/m.sup.2 and/or with a layer thickness of 0.5 m to 20 m, to the at least one subregion.

8. The method as claimed in claim 1, wherein the inkjet printhead provides droplets of adhesive with a frequency of 6 kHz to 110 kHz.

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

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

11. 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, to the transfer ply.

12. The method as claimed in claim 1, wherein a distance between inkjet printhead and substrate during application of the adhesive does not exceed 1 mm.

13. The method as claimed in claim 1, wherein a relative velocity between inkjet printhead and transfer ply during application of the adhesive is 10 m/min to 30 m/min.

14. The method as claimed in claim 1, wherein an adhesive of the following volume composition is used: TABLE-US-00006 2-phenoxyethyl acrylate 10%-60%, 4-(1-oxo-2-propenyl)morpholine 5%-40%, exo-1,7,7-trimethylbicyclo[2.2.1] hept-2-yl acrylate 10%-40%, 2,4,6-trimethylbenzoyldiphenyl phosphine oxide 5%-35%, dipropylene glycol diacrylate 1%-20%, urethane acrylate oligomer 1%-20%,

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

16. The method as claimed in claim 1, wherein the pre-curing of the adhesive takes place at 0.02 s to 0.025 s after the application of the adhesive.

17. The method as claimed in claim 1, wherein the pre-curing of the adhesive takes place with UV light at least 90% of whose energy is emitted in the wavelength range between 380 nm and 420 nm.

18. The method as claimed in claim 1, wherein the pre-curing of the adhesive takes place 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.

19. The method as claimed in claim 1, wherein the pre-curing of the adhesive takes place with an exposure time of 0.02 s to 0.056 s.

20. The method as claimed in claim 1, wherein the pre-curing of the adhesive is accompanied by an increase in its viscosity to 50 mPas to 200 mPas.

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

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

23. The method as claimed in claim 1, wherein the application of the at least one subregion of the transfer ply provided with adhesive to the substrate takes place 0.2 s to 1.7 s after the pre-curing of the adhesive.

24. 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.

25. The method as claimed in claim 1, wherein the full curing of the adhesive takes place at 0.2 s to 1.7 s after the application of the transfer ply to the substrate.

26. The method as claimed in claim 1, wherein the full curing of the adhesive takes place with UV light at least 90% of whose energy is emitted in the wavelength range between 380 nm and 420 nm.

27. The method as claimed in claim 1, wherein the full curing of the adhesive takes place with a gross irradiation power of 12 W/cm.sup.2 to 20 W/cm.sup.2 and/or with a net irradiation power of 4.8 W/cm.sup.2 to 8 W/cm.sup.2 and/or with an energy input into the adhesive of 200 mJ/cm.sup.2 to 900 mJ/cm.sup.2.

28. The method as claimed in claim 1, wherein the full curing of the adhesive takes place with an exposure time of 0.04 s to 0.112 s.

29. The method as claimed in claim 1, wherein the detachment of the carrier ply takes place 0.2 s to 1.7 s after the full curing of the adhesive.

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

31. The method as claimed in claim 1, wherein the application of the transfer ply to the substrate is carried out by means of a thermoplastic toner in a roll arrangement with a press nip of 5 mm to 20 mm.

32. The method as claimed in claim 1, wherein a foil is used which has a carrier ply of polyester, polyolefin, polyvinyl, polyimide, ABS, PET, PP, PE, PVC or PS with a layer thickness of 5 m to 50 m.

33. The method as claimed in claim 1, wherein a foil is used whose transfer ply has a detachment layer of an aqueous polyurethane copolymer, free from wax and/or silicone, with a layer thickness of 0.01 m to 2 m, which is disposed on a surfance of the carrier ply.

34. The method as claimed in claim 33, wherein a foil is used whose transfer ply has a varnish layer of nitrocellulose, polyacrylate and/or polyurethate copolymer with a layer thickness of 0.1 m to 5 m, which is disposed on a detachment layer surface facing away from the carrier ply.

35. The method as claimed in claim 34, wherein a foil is used whose transfer ply has a metal layer of aluminum and/or chromium and/or silver and/or gold and/or copper with a layer thickness of 10 nm to 200 nm, which is disposed on a varnish layer surface facing away from the carrier ply.

36. The method as claimed in claim 1, wherein a foil is used whose transfer ply has a primer layer of polyacrylates and/or vinyl aceto copolymers with a layer thickness of 0.1 m to 1.5 m, which forms a transfer ply surface facing away from the carrier ply.

37. The method as claimed in claim 36, wherein the primer layer is microporous.

38. The method as claimed in claim 36, wherein the primer layer has a surface tension of 38 mN/m to 46 mN/m.

39. The method as claimed in claim 36, wherein the primer layer has a pigmentation number of 0.5 cm.sup.3/g to 120 cm.sup.3/g.

40. The method as claimed in claim 36, wherein the primer layer has a melting point of 60 C. to 130 C.

41. The method as claimed in claim 1, wherein before and/or after the application of the transfer ply, a print layer is applied by means of a further inkjet printhead to the substrate and/or the transfer ply.

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

43. The method as claimed in claim 42, wherein the transfer ply is applied using a pressing apparatus which is transparent for a wavelength used for the pre-curing and/or full curing of the adhesive.

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

45. The method as claimed in claim 42, wherein the pre-curing and/or full curing of the adhesive is effected 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.

46. The method as claimed in claim 43, wherein the pressing means and/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/or a hardness of 20 Shore A to 70 Shore A, and/or a surface roughness (mean roughness value) of between 0.06 m and 0.5 m.

47. The method as claimed in claim 46, wherein the pressing layer has a surface structure, in the form of a pattern or decoration.

48. The method as claimed in claim 43, wherein the transfer ply is applied with an applied force of 1 N to 1000 N.

49. An application apparatus for applying a transfer ply of a foil to a substrate, by means of a method as claimed in claim 1, comprising: a supply roller for providing the foil; an inkjet printhead disposed downstream of the supply roller in the conveying direction of the foil, for applying a radically curable adhesive, and/or a printing apparatus for applying a thermoplastic toner to at least one subregion of the transfer ply; a first UV light source, disposed downstream of the inkjet printhead and/or of the printing apparatus in the conveying direction of the foil, for pre-curing the adhesive by UV irradiation; at least one roll arrangement, disposed downstream of the inkjet printhead and/or of the printing apparatus in the conveying direction of the foil, for applying the at least one subregion of the transfer ply provided with adhesive and/or toner to the substrate; a second UV light source, disposed downstream of the roll arrangement in the conveying direction of the foil, for fully curing the adhesive by UV irradiation; a peeling unit disposed downstream of the roll arrangement in the conveying direction of the foil, for peeling a carrier ply of the foil from the at least one subregion of the transfer ply.

50. An application apparatus for applying a transfer ply of a foil to a substrate, by means of a method as claimed in claim 1, comprising: a supply roller for providing the foil; an inkjet printhead disposed downstream of the supply roller in the conveying direction of the foil, for applying a radically curable adhesive, and/or a printing apparatus for applying a thermoplastic toner to at least one subregion of the transfer ply; at least one roll arrangement, disposed downstream of the inkjet printhead and/or of the printing apparatus in the conveying direction of the foil, for applying the at least one subregion of the transfer ply provided with adhesive and/or toner to the substrate; a peeling unit disposed downstream of the roll arrangement in the conveying direction of the foil, for peeling a carrier ply of the foil from the at least one subregion of the transfer ply.

51. The application apparatus as claimed in claim 50, additionally comprising a first UV light source, disposed downstream of the inkjet printhead and/or of the printing apparatus in the conveying direction of the foil, for pre-curing the adhesive by UV irradiation; a second UV light source, disposed downstream of the roll arrangement in the conveying direction of the foil, for fully curing the adhesive by UV irradiation.

52. The application apparatus as claimed in claim 49, wherein the inkjet printhead has a resolution of 300 to 1200 nozzles per inch (npi).

53. The application apparatus as claimed in claim 49, wherein the inkjet printhead has a nozzle diameter of 15 m to 25 m with a tolerance of not more than 5 m and/or a nozzle spacing of 50 m to 150 m with a tolerance of not more than 5 m.

54. The application apparatus as claimed in claim 49, wherein the first UV light source is an LED light source.

55. The application apparatus as claimed in claim 49, wherein the first UV light source in the conveying direction of the foil has a window width of 10 mm to 30 mm.

56. The application apparatus as claimed in claim 49, wherein the first UV light source in the conveying direction of the foil is disposed 1 cm to 4 cm downstream of the inkjet printhead.

57. The application apparatus as claimed in claim 49, wherein the roll arrangement comprises a press roll and a mechanical counterbearing, in particular an impression roll, a flat or a concave counterbearing.

58. The application apparatus as claimed in claim 57, wherein the press roll and/or the impression roll have a diameter of 1 cm to 3 cm.

59. The application apparatus as claimed in claim 57, wherein the press roll is formed from a plastic or rubber having a hardness of 70 Shore A to 90 Shore A.

60. The application apparatus as claimed in claim 57, wherein the counterbearing is formed of a material having a hardness of 60 Shore A to 95 Shore A, and/or having a degree of hardness of 450 HV 10 to 520 HV 10.

61. The application apparatus as claimed in claim 57, wherein the counterbearing is designed as a sonotrode of an ultrasonic bearing means.

62. The application apparatus as claimed in claim 57, wherein the roll arrangement comprises an infrared heater, an electrical heating element disposed within the press roll, or a heating-medium circuit disposed within the press roll.

63. The application apparatus as claimed in claim 49, wherein the roll arrangement is disposed at a distance of 10 cm to 30 cm from the first UV light source.

64. The application apparatus as claimed in claim 49, wherein the second UV light source is an LED light source.

65. The application apparatus as claimed in claim 49, wherein the second UV light source in the conveying direction of the foil has a window width of 20 mm to 40 mm.

66. The application apparatus as claimed in claim 49, wherein the second UV light source in the conveying direction of the foil is disposed 10 cm to 30 cm downstream of the roll arrangement.

67. The application apparatus as claimed in claim 49, wherein the peeling unit has a roll having a diameter of 0.5 cm to 2 cm over which the carrier ply can be peeled off.

68. The application apparatus as claimed in claim 49, wherein the peeling unit in the conveying direction of the foil is disposed 10 cm to 30 cm downstream of the second UV light source.

69. A printing apparatus having an inkjet printhead which is disposed movably in two orthogonal directions relative to a substrate to be printed, and also with an application apparatus as claimed in claim 49 which is disposed movably in two orthogonal directions relative to the substrate to be printed.

70. The printing apparatus as claimed in claim 69, wherein the printing apparatus has a support surface for the fixing of a substrate in sheet form.

71. The printing apparatus as claimed in claim 70, wherein the inkjet printhead and/or the application apparatus are disposed on a respective carriage which is movable in two orthogonal directions relative to the substrate to be printed.

72. The printing apparatus as claimed in claim 69, wherein the printing apparatus has a conveying apparatus for the relative moving of a substrate in sheet form or of a continuous substrate relative to the inkjet printhead and the application apparatus.

73. The printing apparatus as claimed in claim 72, wherein the inkjet printhead and/or the application apparatus are disposed on a respective carriage which is movable orthogonally to a conveying direction of the substrate to be printed.

74. The printing apparatus as claimed in claim 72, wherein the conveying apparatus is designed as a steel belt circulating around two rolls.

Description

[0141] The invention is now elucidated in more detail using exemplary embodiments. In the figures:

[0142] FIG. 1 shows a schematic representation of an exemplary embodiment of an application apparatus for applying a transfer ply of a foil to a substrate;

[0143] FIG. 2 shows a schematic representation of a flatbed printer according to the prior art;

[0144] FIG. 3 shows a schematic representation of an exemplary embodiment of a flatbed printer with an application apparatus according to FIG. 1;

[0145] FIG. 4 shows a schematic representation of a large-format printer for processing continuous substrates according to the prior art;

[0146] FIG. 5 shows a schematic representation of an exemplary embodiment of a large-format printer for processing continuous substrates with an application apparatus according to FIG. 1;

[0147] FIG. 6 shows a schematic sectional representation through the exemplary embodiment of a large-format printer according to FIG. 5;

[0148] FIG. 7 shows a schematic sectional representation through an exemplary embodiment of a foil following application thereof to a substrate;

[0149] FIG. 8 shows a schematic representation of an alternative exemplary embodiment of an application apparatus for applying a transfer ply of a foil to a substrate.

[0150] An application apparatus 1 for applying a transfer ply 21 of a foil 2 to a substrate 4 comprises a supply roller 11, on which the foil 2 is provided.

[0151] By way of guide rollers 12, the foil 2 is supplied to an inkjet printhead 13, by means of which droplets 3 of adhesive are applied to the transfer ply 21.

[0152] The droplets 3 of adhesive are then pre-cured by means of a first UV light source 14. The foil 2 is then supplied via a deflection roller 15 to a press roll 16, by means of which the adhesive-coated side of the transfer ply 21 is pressed onto a substrate 4. The opposing pressure here may be provided by an impression roll or else by a flat, solid base, something not explicitly shown here.

[0153] Following the application of the foil 2 to the substrate 4, foil 2 and substrate 4 are supplied to a second UV light source 17, which carries out full curing of the adhesive.

[0154] By way of a further roll 18 and/or of a detachment edge, not shown in any more detail here, lastly, a carrier ply 22 of the foil 2 is peeled off and wound up on a roller 19. Where the substrate 4 has been provided with the droplets 3 of adhesive, the transfer ply 21 remains on the substrate 4. The aforementioned detachment edge may be implemented by designing a bar-shaped hollow body on which an inlet for a compressed gas is arranged, and by designing at least one long edge of the detachment element in the form of a perforated detachment edge having outflow openings for the pressurized gas, in order to form a gas cushion between the carrier ply and the detachment edge. The angle of detachment in this case is dependent on the diameter of the roll 18 or, in the case of the detachment edge, on the orientation of the detachment edge.

[0155] By means of the application apparatus 1, therefore, an adhesive 3 is transferred by inkjet printing to a primer layer of the foil 2 and pre-cured, and is then pressed under pressure by the press roll 16 onto the substrate 4. The foil 2 with the adhesive 3 then bears against the substrate.

[0156] In the next step, the adhesive 3 between foil 2 and substrate 4 is through-cured by strong UV light. The adhesive 3 hardens under UV light. After curing has taken place, the carrier ply 22 can be peeled from the substrate 4. In this way the transfer ply 21 has been applied to the substrate.

[0157] An alternative exemplary embodiment of an application apparatus 1 is shown in FIG. 8. Here, the opposing pressure for the press roll 16 is provided not by a flat base, but instead by an impression roll 16.

[0158] The foil 2 is first conveyed past the inkjet printhead 13 and, as described, is coated with adhesive 3. After the foil web has been diverted over a deflection roller 15, the adhesive 3 undergoes pre-curing by the first UV light source 14.

[0159] The foil 2 with the pre-cured adhesive is now guided between the press roll 16 and the impression roll 16, where it is brought together with the substrate and applied thereto in the manner described.

[0160] Subsequently, in analogy to FIG. 1, full curing takes place by the second UV light source 17, and the carrier ply is detached by way of the roll 18. The coated substrate 4 is taken off via a further deflection roller 15, and can be further-processed directly or stored on a roller (not shown).

[0161] The foil consists preferably of at least five layers: carrier ply 22, detachment layer 23, varnish layer 24, metal layer 25, and primer 26 (tie layer).

[0162] A schematic cross-sectional representation of the foil 2 following application thereof to the substrate 4, but before detachment of the carrier ply, is shown in FIG. 7.

[0163] The carrier ply 22 consists preferably of polyester, polyolefin, polyvinyl, polyimide, ABS, PET, PC, PP, PE, PVC or PS with a layer thickness of 5 m to 50 m, preferably of 7 m to 23 m. The carrier ply 22 protects and stabilizes the transfer ply 21 during production, storage, and processing of the foil. If exposure of UV light is to take place from the side of the carrier ply 22 during the pre-curing or through-curing of the adhesive, then the selection of material is guided by the corresponding transparency of the carrier ply in the exposure wavelength range.

[0164] The detachment layer 23 is preferably made of acrylate copolymer, more particularly of an aqueous polyurethane copolymer, and is preferably free of wax and/or free of silicone, having a layer thickness of 0.01 m to 2 m, preferably of 0.1 m to 0.5 m, and is disposed on a surface of the carrier ply 22.

[0165] The detachment layer 23 permits simple and damage-free detachment of the carrier ply 22 from the transfer ply 21 after the application thereof to the substrate.

[0166] The varnish layer 24 consists preferably of nitrocellulose, polyacrylate, and polyurethane copolymer, with a layer thickness of 0.1 m to 5 m, preferably of 1 m to 2 m, and is disposed on a detachment layer 23 surface facing away from the carrier ply 22.

[0167] The metal layer 25 is preferably made of aluminum and/or chromium and/or silver and/or gold and/or copper, with a layer thickness of 10 nm to 200 nm, preferably of 10 nm to 50 nm, and is disposed on a varnish layer 24 surface facing away from the carrier ply 22.

[0168] Not only the varnish layer 24 but also the metal layer 25 generate the desired decorative effect of the transfer ply 21 following transfer thereof to the substrate 4. Through the combination of different varnish colors and metals it is possible to realize particularly appealing designs.

[0169] The primer layer 26 is preferably made of polyacrylates and/or vinyl acetate copolymers with a layer thickness of 0.1 m to 1.5 m, preferably of 0.5 m to 0.8 m, and forms a transfer ply 21 surface facing away from the carrier ply 22.

[0170] By inkjet printing onto the primer layer 26 of the foil 2, running of the adhesive is largely reduced. In comparison to substrate surfaces, the primer layer 26 of the foil 2 is slightly microporous or rough, thus ensuring sharper and defined adhesive pixels on the foil and, later, on the substrate.

[0171] The surface properties of the foil 2, especially its microporosity or its surface roughness, or else the surface energy, can be adjusted in a defined way through the appropriate choice of the primer layer 26 and/or the composition thereof and/or mode of application. This is not readily possible on the substrate 4, since the substrate 4 and hence its specific properties are in practice mandated and cannot be further modified.

[0172] In order to achieve further increase in the application quality, the gloss of the applied transfer ply 21 of the foil 2, and the adhesion, partial curing of the adhesive 3 is carried out after the adhesive 3 has been printed onto the primer layer, and before the foil 2 has been pressed against the substrate 4 by the press roll 16.

[0173] The resulting change in viscosity of the adhesive 3 on the primer layer affords not only the advantages just stated but also an increase in the size of the substrate spectrum that can be used. The change in viscosity results in the formation of a tough layer of adhesive on the primer layer, to which the metallized varnish layer of the transfer ply 21 adheres like a mirror following application and through-curing. Especially on rough natural papers as substrate 4, this affords an improvement in foil application. For all other substrates 4 as well, the quality and the durability of foil application are increased.

[0174] The inkjet printhead 13 is designed preferably as a piezoelectric drop-on-demand printhead. For high-quality results, the printhead 13 must possess a particular physical resolution, droplet size, and nozzle spacing.

[0175] These nozzles may be disposed 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. Generally speaking, the npi correspond to the dpi (dots per inch) on the printed foil.

[0176] The nozzle spacing ought preferably to be 50 m to 150 m, for a preferred nozzle diameter of 15 m to 25 m, in each case with a tolerance of 5 m, so as to produce consistent results.

[0177] When using the grey-stage technology, a plurality of grey stages can be generated on the same pixel. The grey stages are generally produced by firing off a plurality of droplets of equal size onto a printed pixel. The behavior of the quantity of adhesive on the foil 2 is analogous to that of the grey stages when applying printing inks.

[0178] The quantity of adhesive here must be varied according to the absorbency of the primer layer. The quantity of adhesive on the foil ought preferably to be 1.2 g/m.sup.2 to 12.6 g/m.sup.2, in order to ensure complete foil application to every substrate 4. The layer thicknesses of the applied adhesive are in that case 1.205 m to 12.655 m.

[0179] For optimum wetting of the primer layer of the foil 2 with adhesive 3, this layer ought to have a surface tension of 38 mN/m to 46 mN/m, with the range from 41 mN/m to 43 mN/m in particular ensuring optimum ink acceptance.

[0180] In order to ensure high resolution in the printing direction, the piezoelectric actuator of the inkjet printhead 13 must fire off the droplets 3 of adhesive with a frequency of 6 kHz to 110 kHz, thus producing a resolution on the foil 2 of 360 dpi to 1200 dpi for print-medium velocities (that is, conveying velocities of foil 2 and substrate 4) of 10 m/min to 30 m/min.

[0181] The pressure within the nozzle chamber of the inkjet printhead at the time of droplet delivery is preferably 1 bar to 1.5 bar and must not be exceeded, in order not to damage the piezoelectric actuator. For the remainder of the time, there is a slight underpressure of around 5 to 25 mbar prevailing at the nozzle openings, in order to prevent unwanted emergence of ink.

[0182] The distance between the nozzle plate of the inkjet printhead 13 and the foil 2 must not exceed 1 mm, in order to minimize the deflection of the fine droplets 3 of adhesive by air draft.

[0183] The droplet volume ought preferably to be 2 pl to 50 pl; the tolerance is 6% of the droplet volume. In this way, for a given resolution, the necessary, and a uniform, quantity of adhesive is achieved on the foil 2.

[0184] The droplet velocity in flight ought preferably to be 5 m/s to 10 m/s15%, so that all of the droplets 3 of adhesive land very precisely alongside one another on the foil 2. If the droplet velocity of the individual droplets deviates too greatly from one another, this is manifested in an uneven printed image.

[0185] The resulting pixel size is dependent on the viscosity of the adhesive 3. For optimum printability of the adhesive 3, its viscosity ought preferably to be 5 mPas to 20 mPas, more preferably 10 mPas to 15 mPas.

[0186] In order to ensure consistent viscosity of the adhesive 3, the inkjet printhead 13 or the adhesive supply system must be heated. For the stated viscosity, the adhesive temperature in operation must be 40 C. to 45 C.

[0187] Droplet flight and incidence on the foil 2 causes an increase, as a result of cooling, in the viscosity of the adhesive droplets 3, likely to 20 mPas to 50 mPas. An increase in viscosity of this kind counteracts any running or spreading of the adhesive 3 on the primer layer of the foil 2.

[0188] The adhesive 3 employed preferably is a UV-curing ink for use in piezoelectric drop-on-demand inkjet printheads, and in particular may be transparent or translucent or else transparently or translucently or opaquely colored, being colored grey or black, for example. By energy input in the form of UV light, a radical chain reaction is triggered in an adhesive 3 of this kind (or else varnish, glue). In this reaction, polymers and monomers combine to form a solid network of molecules. The adhesive 3 becomes hard or dry. This chain reaction is triggered by UV light in a wavelength range from 350 nm to 400 nm10 nm.

[0189] The key difference between the cationically curing adhesive from the prior art in comparison to radically curing systems of this kind is that the cationic mechanism is substantially slower; in other words, through-curing takes longer.

[0190] For foil application, however, a quick-curing system is needed, since otherwise it would not be possible to apply the foil completely.

[0191] In the course of the UV irradiation of cationic adhesives, moreover, an acid is formed which is responsible for the through-curing of the adhesive. Owing to this mechanism, foils and substrates must first, when using cationically curing adhesives, 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 3. Moreover, the acid could also have the disadvantageous effect of attacking a metal layer, particularly an aluminum layer in the foil.

[0192] Preference is given to using a transparent adhesive with a composition as follows:

TABLE-US-00005 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-trimethylbicyclo[2.2.1] hept-2-yl acrylate 10% to 40%, preferably 20% to 25%; 2,4,6-trimethylbenzoyldiphenyl phosphine oxide 5% to 35%, preferably 10% to 25%; dipropylene glycol diacrylate 1% to 20%, preferably 3% to 10%; urethane acrylate oligomer 1% to 20%, preferably 1% to 10%;

[0193] The subsequent partial curing of the adhesive 3 by means of the first UV light source 14 (also called UV pinning) takes place, in terms of time and space, almost directly after the printing operation onto the foil. Only in this way is it possible to fix the defined, sharp motif on the primer layer. Fixing is brought about by an increase in viscosity of the adhesive, induced by a partial triggering of the radical chain reaction.

[0194] In terms of space, the partial curing takes place preferably 1 cm to 4 cm after the printing in machine direction through the foil, corresponding to a time spacing in machine direction of approximately 0.02 s to 0.25 s.

[0195] The first UV light source 14 ought preferably to produce a gross UV irradiation power of 2 W/cm.sup.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 preferably to be in the wavelength spectrum between 380 nm and 420 nm.

[0196] This requirement can be met particularly well 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.

[0197] A window of the first UV light source 14, from which the radiation emerges, ought preferably to be about 10 mm to 30 mm in size in the machine direction, in order to allow two-dimensional irradiation of the adhesive 3.

[0198] Depending on web velocity and foil velocity of 10 m/min to 30 m/min (or higher), and through absorption and reflection of 50% to 60% of the UV light through the foil 2, the UV irradiation power is reduced. Additionally, the distance between the first UV light source 14 and the foil web reduces the irradiation power delivered, by about 10% for an irradiation distance of 2 mm, for example.

[0199] When these factors are taken into account, the adhesive 3 in the case of this method is irradiated with a net UV irradiation power of about 0.7 W/cm.sup.2 to 2 W/cm.sup.2. This corresponds to a net energy input (dose), for a preferred irradiation time of between 0.056 s (at 10 m/min web velocity with a 10 mm irradiation window) and 0.020 s (30 m/min; 10 mm), into the adhesive 3 of about 8 mJ/cm.sup.2 to 112 mJ/cm.sup.2, a figure which can be varied according to the partial curing required. This dose may additionally be adapted via the web velocity, since the irradiation time changes as a result.

[0200] As already described, the viscosity of the droplets 3 of adhesive on the foil 2 has already increased to likely 20 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, depending on layer thickness, the droplets have a viscosity of likely 50 mPas to 200 mPas, thereby fixing them reliably on the primer layer.

[0201] The motif defined by the adhesive 3 on the foil 2 is now fixed, yet is still moist and can be printed onto the substrate 4 in the next step.

[0202] At this point in the operation, the foil 2 with the adhesive 3, which is still wet, with the viscosity mentioned above, is pressed onto the substrate 4. The pressure, in the form of a linear pressing, is generated by a press roll 16 onto the foil 2 and the substrate 4.

[0203] The press roll 16 ought to consist of a solid plastic or rubber with a smooth surface, and ought preferably to have a hardness of 70-90 Shore A.

[0204] The opposing pressure is provided by an impression roll or else, as shown in FIG. 1, by a solid, flat base.

[0205] The impression roll or base is preferably made of a material which has a degree of hardness in the range from 60 Shore A to 95 Shore A, preferably in the range from 80 Shore A to 95 Shore A, and/or a degree of hardness in the range from 450 HV 10 (HV=Vickers hardness) to 520 HV 10, preferably in the range from 465 HV 10 to 500 HV 10. This material, for example, is plastic or silicone, or else a metal such as aluminum or steel. The radius of the press roll 16 and, where appropriate, of the impression roll ought to be 1 cm to 3 cm.

[0206] In spatial terms, the pressing of the foil 2 onto the substrate 4 takes place about 10 cm to 30 cm after the partial curing in machine direction, corresponding to a time spacing of around 0.2 s to 1.7 s.

[0207] The linear pressing exerted by the press roll 16 ought preferably to take place with a force of between 10 N to 80 N, a figure which may be adapted according to the nature of the substrate.

[0208] The foil 2 with the moist adhesive 3 may be applied to various substrates 4. The foil 2 is preferably applied to paper substrates with coated or uncoated surfaces, natural papers, plastics (PE, PP, PET, PS, PC, PVC), acetate laminations, and label materials.

[0209] In the case of plastics substrates, there may need to be a pretreatment in order to improve the adhesion of the adhesive 3 on the substrate 4 (e.g., by means of AC corona treatment (AC=Alternating Current), plasma treatment, flaming, or coating with varnishes and/or primers). The smoother the substrate surface, the better the application outcome.

[0210] As a result of the partial curing and the associated change in viscosity of the adhesive 3, the application outcomes on rough substrates 4 are significantly improved in comparison to the conventional method without change in viscosity.

[0211] After the foil 2 has been pressed onto the substrate 4, the foil 2 with the adhesive 3, which is still moist, remains on the substrate 4 until the adhesive 3 has undergone through-curing, and the carrier ply 22 is peeled off.

[0212] In the course of through-curing (post-curing) of the adhesive 3, after application of the foil 2, there is ultimate fixing of the adhesive 3 and hence of the foil 2 on the substrate 4. In this step, the foil 2 bears very closely against the adhesive 3, which is still moist, on the substrate 4, and through through-curing of the adhesive 3 is able to enter into a strong, smooth bond with the substrate 4.

[0213] Through-curing takes place under the second UV light source 17, which is preferably in the form of a strong LED UV lamp, which supplies a high irradiation power and ensures complete radical chain reaction within the adhesive 3. 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 pre-curing under the first UV light source 14, and are valid for this operating step as well.

[0214] In spatial terms, through-curing takes place about 10 cm to 30 cm after foil application in the machine direction, something which corresponds, depending on web velocity, to a time spacing of about 0.2 s to 1.7 s after application.

[0215] The distance between the second UV light source 17 and the foil substrate web is 1 mm to 2 mm, in order to achieve optimum through-curing, but at the same time to prevent physical contact between the second UV light source 17 and the substrate. The irradiation window of the second UV light source 17 in machine direction ought to be 20 mm to 40 mm in size.

[0216] The gross UV irradiation power ought to be preferably between 12 W/cm.sup.2 to 20 W/cm.sup.2, so that the adhesive 3 is fully through-cured at velocities of 10 m/min to 30 m/min (or higher) and with the other factors, already discussed with reference to the pre-curing.

[0217] Taking account of these factors, the adhesive 3 in this method is irradiated with a net UV irradiation power of preferably about 4.8 W/cm.sup.2 to 8.0 W/cm.sup.2. This corresponds to a net energy input (dose), for a preferred irradiation time of between 0.112 s (at 10 m/min web velocity with a 20 mm irradiation window) and 0.040 s (30 m/min; 20 mm), into the adhesive 3 of about 537 mJ/cm.sup.2 to 896 mJ/cm.sup.2, a figure which can be varied according to the required through-curing.

[0218] It should be noted that these values are possible only theoretically (at 100% lamp power). At full power of the second UV light source 17, in the case of the 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. The net energy input is therefore preferably between 200 mJ/cm.sup.2 and 400 mJ/cm.sup.2, according to web velocity.

[0219] After the through-curing, the foil 2 adheres completely to the adhesive 3, and the adhesive 3 adheres completely to the substrate 4. The carrier ply 22 can now be peeled off.

[0220] In spatial terms, the detachment of the carrier ply 22 takes place preferably about 10 cm to 30 cm after the through-curing in machine direction, corresponding to a time spacing of about 0.2-1.7 s, depending on web velocity. The carrier ply 22 for detachment is passed over a roll 18 having a radius of 0.5 cm to 2 cm and is detached radially via the roll 18. The detachment angle ought to be variably adjustable depending on the nature of the substrate. In the regions in which adhesive 3 was applied, the substrate 4 is now enhancedthat is, provided with the transfer ply 21.

[0221] Substrates 4 enhanced in this way can be overprinted, in a further operating step, by digital printing and probably also by conventional printing processes (e.g., offset printing, flexographic printing, gravure printing, letter press printing, screen printing). In order to permit in-register production, a register cross may be printed or applied as well. The enhanced substrate 4 is immediately ready for further operating steps or for further processing. The adhesive used attains its optimum through-curing about 24 h after curing by the post-curing UV lamp 17.

[0222] Combination with an inkjet and/or digital printing method is particularly useful. In that case the application apparatus 1 may be integrated directly into a flatbed or large-format printer.

[0223] An exemplary embodiment of a flatbed printer 5 according to the prior art is shown in FIG. 2. An inkjet printhead 51 of the flatbed printer 5 is mounted on a rail 52 and can be moved along this rail in the direction of the arrow 53. The rail 52 itself is movable orthogonally thereto in the direction of the arrow 54, and so the inkjet printhead 51 can be moved freely over a substrate support 55 for substrates 4 in sheet form.

[0224] As shown by FIG. 3, an application apparatus 1 can be integrated readily into a flatbed printer 5 of this kind. In that case, the application apparatus 1 is disposed on a further rail 56, on which it is movable likewise in the direction of the arrow 53. The rail 56 itself is movable orthogonal thereto, again in the direction of the arrow 54.

[0225] As is readily apparent, it is possible in this way for both the inkjet printhead 51 and the application apparatus 1 to pass over a sheet-like substrate 4, disposed on the substrate support 55, at any desired locations. It is therefore possible to combine black or colored inkjet printing with foil application, in which case the inkjet printing may take place both directly onto the substrate 4 and also onto the transfer ply 21 already applied.

[0226] As an alternative to this, an application apparatus 1 can also be integrated into a large-format printer for sheet-like or continuous substrates. An exemplary embodiment of such a printer 6 according to the prior art is shown in FIG. 4.

[0227] Here again, an inkjet printhead 61 is disposed on a rail 62 and is movable along said rail in the direction of the arrow 63. In contrast to a flatbed printer 5, the rail 62 in this case is fixed in its location. Instead, the substrate 4 is moved by suitable conveying means relative to the inkjet printhead 61 in the direction of the arrow 64 orthogonally to the direction of movement of the inkjet printhead 61.

[0228] For the integration of an application apparatus 1, this apparatus, as shown in FIG. 5, is disposed on a further rail 65, which extends parallel to the rail 62. The application apparatus 1 is therefore likewise movable in the direction of the arrow 63 parallel to the inkjet printhead 61. Combined with the substrate movement orthogonally thereto in the direction of the arrow 64, therefore, it is possible here as well for the entire substrate 4 to be passed over both by the inkjet printhead 61 and by the application apparatus 1, so that the printing and application effects already elucidated with reference to the flatbed printer 5 can be achieved. Alternatively, the rail 65 may also be integrated after the inkjet printhead 61, in which case overprinting of the applied transfer ply 21 is no longer possible.

[0229] In the schematic cross section, FIG. 6 shows how in this case it is possible, for example, for the substrate movement to be realized. The substrate 4 lies on a circulating steel belt 66, which can be moved backward and forward by two rollers 67. In this case, the steel belt 66 acts simultaneously as a counterpressure unit for the application of the foil with the press roll 16 of the application apparatus 1.

LIST OF REFERENCE NUMERALS

[0230] 1 Application apparatus

[0231] 11 Supply roller

[0232] 12 Guide roller

[0233] 13 Inkjet printhead

[0234] 14 First UV light source

[0235] 15 Deflection roller

[0236] 16 Press roll

[0237] 16 Impression roll

[0238] 17 Second UV light source

[0239] 18 Roller

[0240] 19 Roller

[0241] 2 Foil

[0242] 21 Transfer ply

[0243] 22 Carrier ply

[0244] 23 Detachment layer

[0245] 24 Varnish layer

[0246] 25 Metal layer

[0247] 26 Primer

[0248] 3 Adhesive

[0249] 4 Substrate

[0250] 5 Flatbed printer

[0251] 51 Inkjet printhead

[0252] 52 Rail

[0253] 53 Arrow

[0254] 54 Arrow

[0255] 55 Substrate support

[0256] 56 Rail

[0257] 6 Large format printer

[0258] 61 Inkjet printhead

[0259] 62 Rail

[0260] 63 Arrow

[0261] 64 Arrow

[0262] 65 Rail

[0263] 66 Steel belt

[0264] 67 Roller