CLEANING APPARATUS AND METHOD FOR LASER CLEANING OF A PRINTING PLATE

Abstract

Aspects of the present disclosure are directed to a cleaning apparatus for cleaning printing plates. In some embodiments, the cleaning apparatus may comprise a laser arrangement including a pulsed laser for generating laser pulses with pulse duration in the picosecond range. The cleaning apparatus may further comprise laser guidance means for guiding the laser pulses onto a path on a printing plate. Other aspects of the present disclosure are directed to a method including the steps of generating laser pulses with pulse duration in the picosecond range and guiding the laser pulses onto a path on the printing plate.

Claims

1. A method of laser cleaning a printing plate in a cleaning apparatus, the method including the steps of: generating picosecond laser pulses with a pulse duration between 1-250 picoseconds at a laser; and guiding the laser pulses onto a path on the printing plate.

2. The method according to claim 1, wherein the step of generating the picosecond laser pulses has a pulse duration between 1-100 picoseconds.

3. The method according to claim 1, wherein the step of generating the picosecond laser pulses has a pulse duration between 25-100 picoseconds.

4. The method according to claim 1, wherein the laser pulses have a pulse wavelength between 800-1200 nanometers.

5. The method according to claim 1, wherein the step of generating the picosecond laser pulses has a pulse duration about 10 picoseconds and a pulse wavelength of 1064 nanometers.

6. The method (100) according to claim 1, wherein the steps of: generating the picosecond laser pulses have a repetition rate between 1-180 kilohertz (kHz), 10-180 kHz, 20-120 kHz, 40-80 kHz or 40-60 kHz; guiding the laser pulses with a path speed of 5-5000 millimeter/second (mm/s), 50-4000 mm/s, 500-3000 mm/s, 1000-2500 mm/s or 2000 mm/s; and further including the steps of: adjusting the laser pulses to an average intensity between 500-3600 Watts per square meter (W/m.sup.2) on the printing plate; and rotating the printing plate.

7. The method according to claim 1, wherein the path passes each surface area of the printing plate two or more times.

8. A cleaning apparatus for cleaning printing plates, the cleaning apparatus comprising a laser arrangement including a pulsed laser configured and arranged for generating picosecond laser pulses having a pulse duration between 1-250 picoseconds (ps), and laser guidance means configured and arranged for guiding the laser pulses onto a path on a printing plate (80).

9. The cleaning apparatus according to claim 8, wherein the laser pulses have a pulse duration between 1-100 ps.

10. The cleaning apparatus according to claim 8, wherein the laser pulses have a pulse duration between 25-100 ps.

11. The cleaning apparatus according to claim 8, wherein the pulsed laser is further configured and arranged to generate laser pulses having a wavelength of 800-1200 nanometers.

12. The cleaning apparatus according to claim 8, wherein the laser pulses have a pulse duration about 10 ps and a pulse wavelength of 1064 nanometers.

13. The cleaning apparatus according to claim 8, wherein the laser guidance means is further configured and arranged to guide the laser pulses with a path speed between 5-5000 millimeter/second (mm/s), 50-4000 mm/s, 500-3000 mm/s, 1000-2500 mm/s or 2000 mm/s.

14. A cleaning apparatus according to claim 8, wherein the cleaning apparatus further includes a shaft extending substantially horizontal about an axis, the shaft configured for receiving and supporting a printing plate during operation, and wherein the shaft is rotatably supported at a support end and connected to a drive configured and arranged to rotate the shaft about the axis in a rotational direction, the shaft further including an opposite end that is free and configured and arranged to receive a printing plate along the axis.

15. The cleaning apparatus according to claim 8, wherein the cleaning apparatus further includes a controller configured and arranged to generate picosecond laser pulses with a pulse duration between 1-250 picoseconds at the pulsed laser, and guide the laser pulses onto a path on the printing plate.

16. A computer program comprising instructions to cause the cleaning apparatus according to claim 8 to execute the following acts: generate picosecond laser pulses with a pulse duration between 1-250 picoseconds at a laser, and guide the laser pulses onto a path on the printing plate.

17. A computer-readable medium having stored thereon the computer program of claim 16.

18. (canceled)

Description

DESCRIPTION OF THE DRAWING

[0136] FIG. 1 illustrates a cleaning apparatus;

[0137] FIG. 2 illustrates a second embodiment cleaning apparatus;

[0138] FIG. 3 illustrates a third embodiment of a cleaning apparatus;

[0139] FIG. 4 illustrates SEM images of an anilox roller with no ink and an anilox roller with black inkunprocessed;

[0140] FIG. 5 illustrates SEM images of an anilox roller with no ink and an anilox roller with black ink cleaned with nanosecond laser pulsesnanoseconds single pass;

[0141] FIG. 6 illustrates SEM images of an anilox roller with no ink and an anilox roller with black ink cleaned with nanosecond laser pulsesnanoseconds 10 passes;

[0142] FIG. 7 illustrates SEM images of an anilox roller with no ink and an anilox roller with black ink cleaned with picosecond laser pulsepicoseconds 100 passes;

[0143] FIG. 8 illustrates SEM images of an anilox roller with no ink and an anilox roller with black ink subjected to a single pass of picosecond laser pulsespicoseconds single pass: and

[0144] FIG. 9 illustrates the method of of laser cleaning a printing plate.

ITEMS

[0145]

TABLE-US-00001 Cleaning apparatus 10 Shaft 20 Support end 22 Movable arrangement 28 Drive 30 Laser arrangement 40 Laser 42 Laser guidance means 44 Laser pulses/Laser beam 46 Path 48 Axis 70 Rotational direction 72 Printing plate 80 Method 100 Rotating 110 Generating 120 Guiding 130 Adjusting 140

DETAILED DESCRIPTION OF THE INVENTION

[0146] FIG. 1 illustrates a schematic of a cleaning apparatus 10. The cleaning apparatus 10 comprises a shaft 20, which extends substantially horizontal about an axis 70. The shaft is configured for receiving and supporting a printing plate 80 during operation.

[0147] The shaft 20 is rotatably supported at a support end 22 and connected to a drive 30 for a rotation about the axis 70 in a rotational direction 72. The shaft 20 has an opposite end 24 that is free for receiving a printing plate 80 along the axis 70.

[0148] The cleaning apparatus 10 further comprises a laser arrangement 40, which comprises a laser 42 arranged with laser guidance means 44 for guiding a laser beam 46 onto a path 48 on the printing plate 80 during operation.

[0149] The shown path 48 is the point on which the laser beam hits the printing plate 80 along the axis 70. The shaft 20 and printing plate 80 rotates as one body and thereby the laser beam 46 may cover the entire printing plate 80 at each point along the path 48.

[0150] FIG. 2 illustrates a schematic of another cleaning apparatus 10. The cleaning apparatus 10 comprises a shaft 20, which extends substantially horizontal about an axis 70. The shaft is configured for receiving and supporting a printing plate 80 during operation. The shaft 20 is rotatably supported at a support end 22 and connected to a drive 30 for a rotation about the axis 70 in a rotational direction 72. The shaft 20 has an opposite end 24 that is free for receiving a printing plate 80 along the axis 70.

[0151] The cleaning apparatus 10 further comprises a laser arrangement 40, which comprises a laser 42 arranged with laser guidance means 44 for guiding a laser beam 46 onto a path 48 on the printing plate 80 during operation.

[0152] The shown path 48 is the point on which the laser beam hits the printing plate 80 along the axis 70. The shaft 20 and printing plate 80 rotates as one body and thereby the laser beam 46 may cover the entire printing plate 80 at each point along the path 48.

[0153] The path 48 may move back and for the along the axis, such that the printing plate 80 has time to cool or such that the ablated material can diffuse away from the printing plate 80.

[0154] FIG. 3 illustrates a third embodiment of a cleaning apparatus 10. The cleaning apparatus 10 comprises two rotatable cylinders on which a printing plate 80 is arranged. The rotatable cylinders rotate the printing plate 80. This particular setup is well known to the person skilled in the art.

[0155] The cleaning apparatus 10 further comprises a laser arrangement 40, which comprises a laser 42 arranged with laser guidance means 44 for guiding a laser beam 46 onto a path 48 on the printing plate 80 during operation.

[0156] The shown path 48 is the point on which the laser beam hits the printing plate 80 along the axis 70. The shaft 20 and printing plate 80 rotates as one body and thereby the laser beam 46 may cover the entire printing plate 80 at each point along the path 48.

[0157] The path 48 may move back and for the along the axis, such that the printing plate 80 has time to cool or such that the ablated material can diffuse away from the printing plate 80.

[0158] FIG. 4 illustrates SEM images of an unprocessed (i.e. not cleaned) anilox roller with no ink and an anilox roller with black ink.

[0159] The figure shows the anilox roller with no ink and the anilox roller with black ink using two different SEM detectors.

[0160] Column A shows images using Inlens, which is used for topographic information.

[0161] Column B shows images using secondary electron (SE2) which show morphology of the area.

[0162] I and III is a 500 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0163] II and IV is a 1000 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0164] Cracks are visible in the no ink sample presumably from the re-solidification of the material after being machined or due to mechanical stress during the lifetime of the roller.

[0165] FIG. 5 (nanoseconds single pass) illustrates SEM images of an anilox roller with no ink and an anilox roller with black ink cleaned with nanosecond laser pulses. The SEM images are taking of surface areas which have been subjected to a single (i.e. 1) pass.

[0166] Experiments of nanosecond pulse were made using: 200 ns, 75 ns, 50 ns and 25 ns pulse duration. Scanning speeds of 1,500, 1,000, 500 and 100 mm s1. Power of 1, 5 and 10 W; the only fixed parameter for the trial was a repetition rate being 25 kHz.

[0167] In example the best results were found for the following settings. The laser system used for cleaning the anilox rollers generated pulses with pulse duration of 50 ns and scanned the surface at a speed of 500 mm s.sup.1 and the power was 1 W and the repetition rate was 25 kHz.

[0168] The figure shows the anilox roller with no ink and the anilox roller with black ink using two different SEM detectors.

[0169] Column A shows images using Inlens, which is used for topographic information.

[0170] Column B shows images using secondary electron (SE2) which show morphology of the area.

[0171] I and III is a 500 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0172] II and IV is a 1000 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0173] Samples BI and BII shows cracks (see arrows).

[0174] Samples BIV show melted surfaces (see arrows) as compared to FIG. 4 BII.

[0175] Thus even for a single pass of a nanosecond (50 ns) laser pulse there are noticeable changes in the surface of the anilox roller.

[0176] FIG. 6 (nanoseconds 10 passes) illustrates SEM images of an anilox roller with no ink and an anilox roller with black ink cleaned with nanosecond laser pulses. The SEM images are taking of surface areas which have been subjected to ten passes.

[0177] The laser system used for cleaning the anilox rollers generated pulses with pulse duration of 50 ns and scanned the surface at a speed of 500 mm s.sup.1 and the power was 1 W and the repetition rate was 25 kHz.

[0178] The figure shows the anilox roller with no ink (I,II) after laser treatment and the anilox roller with black ink (II, IV) after laser treatment using two different SEM detectors,

[0179] Column A shows images using Inlens, which is used for topographic information.

[0180] Column B shows images using secondary electron (SE2) which show morphology of the area.

[0181] I and III is a 500 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0182] II and IV is a 1000 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0183] Surface modification is visible in all cases, more so in black ink samples, resulting in change of geometry of the pockets.

[0184] The anilox roller with no ink, i.e. I, II, shows clear signs of cracks as indicated by arrows. Inspection of the images shows many more cracks than indicated by the arrows.

[0185] The black ink sample, i.e. III, IV, shows a smoother surface (see arrows) after ten passes negatively affecting the performance of ink delivery. The increased smoothing of the surface is probably due to a higher absorption of the beam with the black ink.

[0186] No mechanical tests were performed of the two anilox rollers, but there is an indication of heat affected zones i.e. melting, re-solidification and cracks. It is clear the black ink had a high absorption as there is significant melting present, which changes the geometry of the pockets.

[0187] FIG. 7 (picosecond 100 passes) illustrates SEM images of an anilox roller with no ink and an anilox roller with black ink cleaned with picosecond laser pulse.

[0188] All the images presented are shown with the left part being an untreated area and the right-hand side showing the cleaning process after 100 passes. The cleaning process is more evident in the black sample as the ink has been completely removed and there is no damage in the substrate.

[0189] The SEM images are taking of surface areas which have been subjected to 100 passes.

[0190] Column A shows images using Inlens, which is used for topographic information.

[0191] Column B shows images using secondary electron (SE2) which show morphology of the area.

[0192] I and III is a 500 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0193] II and IV is a 1000 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0194] The SEM images show an increase in dimples, which increases the transfer volume, at the bottom of the structures and there is no damage or melting visible.

[0195] Comparing the untreated area (the left sides) with laser treated area show no induction of cracks.

[0196] The surface of the anilox rollers where examined with SEM after one single pass. The SEM images are shown in FIG. 8, where the black ink anilox roller showed a change in morphology of the ink and the surface looks rougher as the laser-ink interaction takes place.

[0197] This showed that the picosecond laser pulses for ink removal are selective compared to the nanosecond laser pulses, where after a single pass the anilox material started to melt.

[0198] Multiple passes 10, 20, 100 were made and no visible damage could be detected on the substrate. FIG. 6 shows the anilox roller surface after 100 passes and shows no visible damage.

[0199] Thus, successful laser cleaning was achieved with the picosecond laser with no evidence of damage from multiple laser passes.

[0200] FIG. 8 (picosecond one pass) illustrates SEM images of an anilox roller with no ink and an anilox roller with black ink subjected to a single pass of picosecond laser pulses.

[0201] The SEM images are taking of surface areas which have been subjected to 1 pass.

[0202] Column A shows images using Inlens, which is used for topographic information.

[0203] Column B shows images using secondary electron (SE2) which show morphology of the area.

[0204] I and III is a 500 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0205] II and IV is a 1000 magnification of the anilox roller with no ink and the anilox roller with black ink, respectively.

[0206] The surface of the anilox rollers where examined with SEM after one single pass. The SEM images show that the black ink anilox roller, i.e. III, IV, had a change in morphology of the ink and the surface looks rougher as the laser-ink interaction takes place.

[0207] The underlying anilox roller was not visible after a single pass.

[0208] This shows that the picosecond laser pulses for ink removal, i.e. III, IV, are selective compared to the nanosecond laser pulses, see FIGS. 5 and 6, where after a single pass the anilox material started to melt.

[0209] The same applies for the no ink samples, i.e. I, II, showing no signs of induced cracks or melting.

[0210] FIG. 9 illustrates a method 100 of of laser cleaning a printing plate 80.

[0211] The method 100 comprises one or more acts of generating 120 picosecond laser pulses 46. There is an act of guiding 130 the laser pulses 46 onto a path 48 on the printing plate 80. There is an act of generating 120 the laser pulses 46 with a repetition rate between 1-180 kHz, 10-180 kHz, 20-120 kHz, 40-80 kHz or 40-60 kHz. There is an act of guiding 130 the laser pulses 46 with a path speed of 5-5000 mm/s, 50-4000 mm/s, 500-3000 mm/s, 1000-2500 mm/s or 2000 mm/s. There is an act of adjusting 140 the laser pulses 46 to an average intensity between 500-3600 W/m.sup.2 on the printing plate 80. There is an act of rotating 110 the printing plate 80.

[0212] The laser pulses 46 may have a pulse wavelength between 800-1200 nm.

[0213] The path 48 may pass each surface area of the printing plate 80 two or more times.