LASER PRINTING PROCESS

Abstract

Printing process in which a substrate to be printed is disposed opposite an ink carrier having an ink layer, wherein the ink layer is regionally heated in such a way that bulges are formed in the ink layer, wherein the bulges contact the substrate and wherein ink splitting is brought about by relative movement between substrate and ink carrier.

Claims

1. A printing process in which comprising: disposing a substrate to be printed opposite an ink carrier including an ink layer, regionally heating the ink layer in such a way that a bulge is formed in the ink layer, wherein the bulge contacts the substrate, and moving the substrate relative to the ink carrier to thereby cause ink splitting onto the substrate.

2. The printing process according to claim 1, wherein the ink layer is regionally heated by a laser.

3. The printing process according to claim 1, wherein the ink carrier and the ink layer are moved parallel to one another.

4. The printing process according to claim 1, wherein the substrate and the ink carrier are moved relative to one another at a speed which corresponds at least to the printing speed.

5. The printing process according to claim 1, wherein when the bulge contacts the substrate, the substrate is guided past the ink layer at a distance of greater than 0.01 mm and/or less than 3 mm.

6. The printing process according to claim 1, wherein a printed ink layer applied to the substrate has a thickness of 1 to 100 m.

7. The printing process according to claim 1, wherein the ink layer is a wet ink layer disposed on the ink carrier and the ink carrier is laser-permeable.

8. The printing process according to claim 1, wherein the ink layer includes an ink comprising one or more of effect pigments, metal particles, and particles, the one or more of effect pigments, metal particles, and particles having a mean diameter of more than 1 m.

9. The printing process according to claim 1, the process further comprising one or more of baking a printed ink and applying two or more ink layers one above another.

10. (canceled)

11. The printing process according to claim 2, wherein the ink layer is regionally heated by a switched laser.

12. The printing process according to claim 4, wherein the substrate and the ink carrier are moved relative to one another at a speed which corresponds at least to double the printing speed.

13. The printing process according to claim 1, wherein when the bulge contacts the substrate, the substrate is guided past the ink layer at a distance of greater than 0.1 mm and/or less than 1 mm.

14. The printing process according to claim 1, wherein when the bulge contacts the substrate, the substrate is guided past the ink layer at a distance of greater than 0.1 mm and/or less than 0.5 mm.

15. The printing process according to claim 6, wherein a printed ink layer applied to the substrate has a thickness of 10 to 50 m.

16. The printing process according to claim 7, wherein the ink carrier comprises a polymeric film.

17. The printing process according to claim 16, wherein the polymeric film includes a polyimide film.

18. The printing process according to claim 1, wherein the ink carrier comprises a polymeric film.

19. The printing process according to claim 18, wherein the polymeric film includes a polyimide film.

20. The printing process according to claim 8, the one or more of effect pigments, metal particles, and particles having a mean diameter of more than 5 m.

21. A printing process comprising: opposing a substrate to an ink carrier including an ink layer to provide a gap between the substrate and the ink layer, heating the ink layer to form a bulge in the ink layer, the bulge spanning the gap, and providing relative movement between the substrate and the ink carrier and splitting at least a portion of the bulge from the ink layer onto the substrate.

22. A printing machine comprising: an ink carrier including an ink layer, and a laser scanner, the printing apparatus being configured to perform a process comprising: disposing the ink carrier opposite a substrate to be printed, regionally heating the ink layer with a laser emitted from the laser scanner to form a bulge in the ink layer, and splitting ink onto the substrate by permitting the bulge to contact the substrate and moving the substrate relative to the ink carrier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The subject matter of the invention is to be elucidated in more detail below by means of an exemplary embodiment with reference to the schematic drawings FIG. 1 to FIG. 7.

[0047] Represented schematically in the drawings, in each of FIG. 1 to FIG. 6, is the course of the process of the invention when applying a printed dot.

[0048] FIG. 7 shows schematically a printing machine of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0049] With reference to FIG. 1, the fundamental steps of the printing process of the invention will be elucidated.

[0050] In step (a), an ink (2) to be printed, which forms an ink layer (2), is located on an ink carrier (1). By means of a preferably switched laser bombardment with a writing laser (3) in step (b), a part of the ink (2), more particularly a solvent which the ink comprises, is heated, and so a bulge (4) is formed from the ink (2), as shown in step (c), this bulge, however, not leading, or leading only minimally, to detachment of ink. Since, as represented here in step (d), the bulge (4) is unable to attach by forces of adhesion to any substrate positioned beneath it, the bump retracts at least partly and there is little or no ink transfer. Printing therefore takes place, in accordance with the invention, only if a substrate is sited beneath the ink carrier (1) having the ink layer, in such a way that the bulge (4) makes contact with the substrate.

[0051] FIG. 2 shows fundamentally the same construction as in FIG. 1, there now being a substrate (6) to be printed located beneath the ink carrier (1) and the ink layer (2) (step a). As a result of laser bombardment (3), the ink layer (2) bulges in the direction of the substrate (6) to be printed (steps b-c). Contact occurs between the substrate (6) and the ink bulge (4) (step c). As a result of a difference in speed between the ink bulge (4) and the substrate (6), there is a necking (5) of the ink (step d). Lastly, ink splitting occurs, with at least part of the ink bump (4) transferring (e) onto the substrate (6) as a transferring ink dot (7).

[0052] FIG. 3 shows fundamentally the same construction as Fig.1 and FIG. 2. In contrast to FIG. 2, the substrate (6) here is moving not parallel to the ink carrier (1) and the ink layer (2), but instead in a perpendicular direction. Ink detachment owing to vertical changes in position between substrate (6) and the ink bulge (4) leads equally to a splitting of ink between ink bump (4), substrate (6) and ink layer (2).

[0053] A combination of mutually parallel and mutually perpendicular movement of substrate (6) and ink carrier (1), in other words a combination of the processes shown in FIG. 2 and FIG. 3, is also possible.

[0054] FIG. 4 shows the result if the ink carrier (1) comprising the ink layer (2) is moved more slowly relative to the substrate than the printing speed. The substrate is not shown in FIG. 4 (and also in FIG. 5 and FIG. 6).

[0055] As a result of the slower speed of the ink carrier (1) relative to the substrate, the writing laser (3) pulses repeatedly into the ink region (5) of the ink carrier (1) that has already emptied. The amount of ink transferring in the region of the bulge (4) here is smaller than the amount of ink of the preceding shot, because the writing laser (3) no longer encounters a fully filled ink region (2). As a result, the quality of the printed image deteriorates as the laser power goes down. The resulting printed image of unstable quality is, however, able to be used for the purpose, for example, of solid areas for transfer, or for digital ink spraying.

[0056] FIG. 5 shows the result if ink carrier (1) and ink layer (2) are moving at printing speed. In this case, the writing laser (3) always encounters a partly emptied ink region (5), and so it is no longer possible to print the same amount of ink as in the preceding laser shot. In this case, the quality of the printed image produced is again unstable as the laser power goes down, but the process can likewise be used for solid areas to be transferred, or for digital ink spraying.

[0057] FIG. 6 shows the printing procedure according to one preferred embodiment of the invention. In this case the ink carrier (1) comprising the ink layer (2) moves relative to the substrate faster than the printing speed. As a result, the writing laser (3) always encounters a fully filled ink region (2). Under these conditions, a stable and high-quality printed image can be produced with a higher laser power.

[0058] Described below are the results of the printing process of the invention in the context of various parameters.

[0059] The following typical system settings lead to the following print outcomes:

[0060] Settings 1 (as depicted in FIG. 5):

[0061] ink ribbon: continuous polymer ribbon,

[0062] laser: solid-state laser, especially 800-1800 nm,

[0063] laser power: 1-500 kW/mm.sup.2,

[0064] writing focus: 20-100 m,

[0065] thickness of ink layer on ink carrier: 20-50 m,

[0066] ink viscosity: 500-10 000 mPa s, preferably 1000-5000 mPa s,

[0067] speed of ink carrier: 0.9-1.1*printing speed,

[0068] distance of ink carrier to the substrate: approx. 0.5-2 mm,

[0069] printing speed: 1-10 m/min, and/or

[0070] printing width: 10-2000 mm

[0071] This produces a homogeneously printed surface with a wet ink film layer whose thickness corresponds approximately to the thickness of the ink layer on the ink carrier.

[0072] Settings 2 (as depicted in FIG. 6):

[0073] ink ribbon: continuous polymer ribbon,

[0074] laser: solid-state laser, especially 800-1800 nm,

[0075] laser power: 1-500 kW/mm2,

[0076] writing focus: 20-100 m,

[0077] thickness of ink layer on ink carrier: 20-50 m,

[0078] ink viscosity: 500-10 000 mPa s, preferably 1000-5000 mPa s,

[0079] speed of ink carrier: 2.5-3.5*printing speed,

[0080] distance of ink carrier to the substrate: approx. 0.1-0.5 mm,

[0081] printing speed: 1-10 m/min, and/or

[0082] printing width: 10-2000 mm

[0083] This produces a homogeneously printed surface and also a detailed pattern with a wet ink film layer whose thickness corresponds approximately to the thickness of the ink layer on the ink carrier.

[0084] The invention achieves ink separation between ink carrier and substrate by mechanical means. As a result, all that is needed additionally is the laser energy in order to achieve a partial positional change of the selected ink layer in the direction of the print substrate. The laser bombardment now brings about only a bulge of the ink in the direction of the substrate; the subsequent contact of the ink made to bulge by the laser, and the difference in speed between substrate and ink film, then lead to ink separation. For the mechanical ink separation, a difference in speed between ink ribbon and print substrate is not absolutely necessary; a positional change of ink ribbon relative to print substrate in terms of height produces the same effect.

[0085] If there is no contact between the ink bump and the substrate, ink transfer is very limited, or there is no ink transfer at all, owing to elastic contraction of the ink bump.

[0086] For the printing process of the invention, in general, relative to a conventional printing process in which drops of ink are shot out by means of the laser, only a fraction of the laser energy is required, with a simultaneous reduction in the scattering splashes. This leads to a considerable boost in quality of the printed image in conjunction with an increase in the printing speed.

[0087] When adjusting the difference in speed between ink ribbon and substrate, the ink ribbon speed ought not to be below the printing speed that is to be generated, if the printed image is to be stable. In this context it is immaterial whether the ink ribbon moves in the direction of the substrate or the ink to be printed is transported in the opposite direction. The decisive factor is the establishment of a difference in speed between ink ribbon and substrate.

[0088] The minimum ink ribbon speed is preferably the printing speed.

[0089] If ink ribbon speed is less than printing speed, then ink transfer is uncontrolled, since ink in that case is to be transferred from regions of the ink ribbon that are already being depleted of ink, thus leading to inhomogeneities.

[0090] If the ink ribbon speed is the same as the printing speed, then the laser power required is lower in principle; however, because of the uneven transfer of ink, the printed image is also uneven.

[0091] If the ink ribbon speed is greater than printing speed, then it is true that a greater laser power is needed in order to transfer the ink; however, the precision of printing becomes higher as the ribbon speed goes up. Optimum print precision can be achieved with an ink ribbon speed that is around 2-3 times the printing speed, with the direction of movement of the ink ribbon having no part to play.

[0092] FIG. 7 is a schematic view of an exemplary embodiment of a printing machine (14) of the invention.

[0093] The ink carrier (1) of the printing machine (14) is a circulating ink ribbon.

[0094] The ink ribbon is coated homogeneously and over its full area with ink (2) by the inking unit (8). The ink ribbon then moves in the direction of the arrow to the printing nip (10). Here, the ink carrier (1) is distanced from the substrate (6) to be printed, by means of a gap. The width of the gap is preferably adjustable and/or is regulated continuously. This can be done, for example, by means of adaptable distancing rolls (12).

[0095] In the printing nip (10), a laser beam (3) is focused by the ink carrier (1) into the ink (2) with a laser scanner. The local and targeted heating of parts of the ink (2) by means of the laser beam (3) causes explosive vaporization of a small region of the ink (2), and so a part of the printing ink (2) parts to some extent from the ink ribbon (1), and a bulge is formed and is subsequently transferred contactingly onto the opposite substrate (6). The printing nip (10) is therefore configured in such a way that a bulge in the ink spans the nip.

[0096] Subsequently, controlled by the distancing rolls (12) and the deflection rollers (11), the ink ribbon moves back in the direction of the inking unit (8). The contact between inking unit (8) and the ink ribbon replenishes the ink (2) that has been consumed. The excess ink (2) in the inking unit (8) is collected in the ink trough (9) at the bottom, and is added continuously and repeatedly to the printing operation.

[0097] As a result of the invention, success has been achieved in producing an improved printed image for a significant reduction in laser power.

LIST OF REFERENCE NUMERALS

[0098] 1. Ink carrier [0099] 2. Ink/ink layer/ink region [0100] 3. Writing laser/laser bombardment/laser beam [0101] 4. Bulge/ink bulge [0102] 5. Ink necking/emptied ink region [0103] 6. Substrate [0104] 7. Ink dot [0105] 8. Inking unit [0106] 9. Ink trough [0107] 10. Printing nip [0108] 11. Deflection roller [0109] 12. Distancing roll [0110] 13. Laser scanner [0111] 14. Printing machine