Large Scale Laser Microstructuring of Gravure Printforms. Guido Hennig, Karl - Heinz Selbmann, Stephan Brüning, Silke Pfinninger, Johannes Brendel

Transcription

1 Large Scale Laser Microstructuring of Gravure Printforms Guido Hennig, Karl - Heinz Selbmann, Stephan Brüning, Silke Pfinninger, Johannes Brendel AILU 08, Daresbury Laboratory, June 2008

2 Lasers in the printing industry Topics 1. Introduction to Gravure printing 2. Gravure print form fabrication at MDC Max Daetwyler Group - Mask Ablation - Direct Laser Engraving 3. Flexible cell shape / benefits - Adaptable Beam Profile for different print media (different print substrates, magazines, packaging, embossing) 4. Requirements for the gravure process, determining laser parameters and material - Processing Time - Precision (Zn vs. Cu) 5. New methods - New Laser Sources and Engraving concepts 6. Outlook - Laser in Print applications the Future

3 1. Print processes with laser fabrication of the print form Overview #1 European Printing Market Others: Plateless, Inkjet 17% Gravure Printing 16% Steel Roller + Cu/Cr or Zn/Cr surface Layer Flexography 23% Offset Printing 42% Screen Printing 2% Substrate Doctor blade Impression roller Gravure Cylinder Ink

4 1. Printprocesses using laser microfabrication Overview #2 European Printing Market Others: Plateless, Inkjet 17% Gravure Printing 16% Flexography 23% Offset Printing 42% Screen Printing 2% Steel Roller + Cu/Cr or Zn/Cr surface Layer Flexography sleeve, plate Al(oxide) Offset (Nassofset) Plate, Silicon rubber coated Metallic or textile web,plate,sleeve Electro-plated Sleeve 10 5 < # Runs < 8x < # Runs < < # Runs < < # Runs <10 4 Examples: Cups, Textiles, T-shirt, electronic prints

5 2. Gravure - Fabrication of the printform overview Methods of gravure cylinder imaging - Film based: Film - Exposition of a photosensitive mask, developing and chemical etching (analog process) - Electromechanical: Digital Imaging by Engraving with a diamond 8 khz. - Laser based: 1. Digital Mask Ablation by Laser followed by etching 2. Direct Digital Laser Ablation of metallic surface material

6 2. Gravure - Fabrication of the printform 2.1 Digital Mask ablation Binary (on / off- modulated) Ablation of Masks mask Nd:Yag, Fiberlaser, TEM W 10-20µm Cu, electroplated etching [µm] Ablated areas Steel Etched cells

7 2. Gravure - Fabrication of the printform 2.1 Digital Mask ablation Digilas 4 - Beam Laser AOM Lens Roller surface - Simultaneously 4 6 beams are generated from a single laser source - Splitting and position control by Multifrequency AOM Soundfields

8 2. Gravure - Fabrication of the printform 2.1 Digital Mask ablation Multiple 4 beams binary on / off modulated Print roller Lasertraces Etchingresults BILD!! Multifrequency AOM Soundfields Ablated areas of the mask 1. Screen adjustment 2. Position and power for each shot of a pulse string are programmable within modulator rise time

9 2. Gravure - Fabrication of the printform 2.1 Digital Mask ablation Deplating of used Cr, Cu Process steps Spray Coating Cu plating, Finishing Coating Immersion Ring Coating Laser process Etching Cleaning Chromium- Plating Printing Mask Ablation with laser Spray Etching

10 2.1 Gravure - digital mask ablation Printed electronics Testpattern for printed electronics: FET structures Substrate: polymer foil or glas Conducting ink (silver particles) (SIGPA)

11 2. Gravure - Fabrication of the printform 2.2 Direct Laser Ablation DIRECT ENGRAVING OF METALLIC SURFACES Laser 2x 35 khz AOM Q-switch Nd-Yag 70kHz, 500 W Fiber Optics Image Data Melting and vaporisation 1 pulse 1 cell Focusing Optics Cylinder

12 2. Gravure - Fabrication of the printform 2.2 Direct Laser Ablation Direct laser engraving of metallic print rollers Cell Proportions: Depth: 0-45 µm Diameter: µm Screen: l/cm Options for different cell shapes

13 3. Flexible cell shaping 3.1 Cell shapes and power modulation 100% Tone power 50 % 5% shape: conventional halfautotypical profile: top hat Gauss depth variable Depth and diameter variable, coupled The power scaling of a fixed beam profile defines a specific inherent aspect ratio AR for each % tone value.

14 3. Flexible cell shaping 3.2 Ink transfer and AR AR = depth/diameter AR < 0.05 AR > 0,5 2 µm - ink dries before substrate contact - unstable ink transfer - missing dots - doughnut print Conditions for optimised ink transfer 0.1 < AR < 0.5 for low quality substrates 30 µm - no ink transfer because of capillary forces Independent control of depth and diameter 0.05 < AR < 0.5 for high quality substrates

15 3. Flexible cell shaping 3.4 Beam profile modulation #1 Laser 2x 35 khz Power modulation AOM Fiber Optics Image Data Intensity profile modulation Focusing Optics Cylinder

16 3. Flexible cell shaping 3.4 Beam profile modulation #2 constant intensity profile Image % - values Control unit a 1 (%,t) I 1 (x,y) a 2 (%,t) I 2 (x,y) a n (%,t) modulation I n (x,y) Optics for intensity profile shaping (lenses, phaseplates, apertures, DOE) I(x,y,%,t) highly dynamical intensity profile

17 3. Flexible cell shaping 3.4 Beam profile modulation #3

18 3. Flexible cell shaping 3.8 Printing with SHC: Benefit Ink transfer on low grade paper SHC Laser profile modulation: strongly area and depth variable Halfautotypical SC-A paper, 40 % Super Halfautotypical SC-A paper, 40 % Cell profile can be adjusted individually for each tone value Optimum matching to various printing substrates and printing conditions

19 4. Parameters and Features Overview Specific requirements for the gravure process, defining the laser parameters treatment of large surfaces in short time, one shot one cell, laser diameter matches cell diameter high power, Multimode laser ablation with micrometer precision Zn best response beam pointing stability Fiber coupling different printmedia (magazine, packaging embossing, different print substrates, paper) adaptable cell shape (aspect ratio) for best ink transfer beam intensity profile modulation definition of standards and calibrations precise power control, pulse to pulse stability, definition of a gradation tool

20 4. Parameters 4.1 Treatment of large surfaces High Power Multimode Laser: 2x Nd:YAG 1064 nm, 400 W 35 khz Q switch, 10 mj Engraving Head: Power 500 W Pulse Frequency cells /s single shot 70l/cm: 11.6 Min / m 2 min low resolution EM Engraving Time / m 2 Laser screen [L/cm] high resolution screens

21 Smoother Print with DLS cylinders Printing Characteristic Direct 120 l/cm Much smoother print due to finer dots/ higher resolution Stylus 70 l/cm

22 4. Parameters 4.2 Material Why Zinc? [W/K x m] Cu Zn Absorption of 1064nm: < 6 % 50 % Melting point: 1356 K 693 K Vaporisation point: 2835 K 1180 K Cu Zn Cr Al Lower energy input for Zn Higher ablation efficiency, lower threshold precisely response of the material (small residuals) better fine control of tone values Same stability for Zn and Cu after chromium plating Cu Zn Cu Zn Cr Al

23 5. New Engraving Concepts 5.1 Laser Sources MDC Laser (pulsed) Laser Alternatives power time Fiberlaser, Disklaser, Slab laser cw, gated Q switch (MOPA) power time power Short Pulse (ps) Laser, multiple shots (> 10 3 /cell) Zn (Relative) Low Intensity Cu, Cr, Ceramics High Intensity time

24 5. New Engraving Concepts 5.2 Screen algorithms Single Pulse 1 pulse One 1 cell Shot / SHC - One applicable Cell Cw gated Image Setter Technique Screen 70 l/cm 1 2 Screen 140 l/cm Screen 70 l/cm Screen 140 l/cm Track width Track width Track width

25 5. New Engraving Concepts 5.2 Screen algorithms: cw fiberlaser # 1 Engraving of metals, cw Fiber 600 W, M 2 = 1.2 Image Setter Technique: Resolution 1000 l/cm Zn 100 µm Cu 100 µm

26 5. New Engraving Concepts 5.2 Screen algorithms: cw fiberlaser # 2 Engraving of Ceramics (cw Fiberlaser 600 W) 1000 µm 150 µm Glue tranfer in carpet production Glue transfer to car glas foils Depth 400 µm Cell diameter 1 mm Spot size µm Resolution 1000 Lines/cm Depth 90 µm Cell diameter 150 µm

27 5. New Engraving Concepts 5.2 Screen algorithms: cw fiberlaser # 3 Engraving of Embossingtools with cw Fiberlaser 200 W, M 2 = 1.1, Multilayer technique 300 µm 300 µm Cubic and prismatic tools from EPDM for surface structuring of optical design functions Embossing cylinder for ingrain wallpaper

28 5. Outlook Lasers gravure industry: Advantages of direct laser engraving vs. EM The flexible beam profile modulation Summary Outlook - LPSSL, DPSSL, fiber lasers - efficiency, resolution, precision - optimisation of the cell shape - optimised ink transfer - economical printing. Fiberlasers are already common for mask ablation and started to enter the direct ablation processes and Laser Systems in Gravure and Embossing. (cw - and MOPA Systems) Ultrashort pulse Systems are options for the future, if the power matches the requirements for efficiency and the costs are drastically reduced. The ability for big ink volumes enables new applications with special pigments and special materials (for example printing of RFID, electronic circuits or displays)

29 Appendix Cylinder Workflow # 1 Cylinder from the press Deplating of chromium and Zinc Degreasing and polishing Zinc plating 60 µm Surface fine polishing Laser engraving Cleaning and polishing Chrome plating Chrome polishing Cylinder ready to print

30 Appendix Cylinder Workflow #2 Cr polishing Cr plating Cleaning and Finishing after engraving

31 Appendix bdk Laserline, Cologne

32 Appendix. Saueressig - production line, Germany

33 Thank you for your attention!

34 MDC MAX DAETWYLER Headquarter Bleienbach, Switzerland Meet the author: Dr. Guido Hennig daetwyler-graphics.ch Dayton, USA