AILU 08, Daresbury Laboratory, June 2008

Guido Hennig, Karl - Heinz Selbmann, Stephan Brüning, Silke Pfinninger, Johannes Brendel

Large Scale Laser Microstructuring of Gravure Printforms

TopicsLasers in the printing industry

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

Overview #11. Print processes with laser fabrication of the print form

European Printing Market

Offset Printing 42% Screen Printing 2%

Others: Plateless, Inkjet 17%

Gravure Printing 16%

Steel Roller + Cu/Cr or Zn/Cr surface Layer

Gravure Cylinder

Ink

Doctor blade

Substrate

Impression roller

Flexography 23%

105 < # Runs < 8x106

European Printing Market

Offset Printing 42% Screen Printing 2%

Others: Plateless, Inkjet 17%

Gravure Printing 16%

Steel Roller + Cu/Cr or Zn/Cr surface Layer

1. Printprocesses using laser microfabrication Overview #2

Flexography 23%

103< # Runs <105 10 < # Runs <104102 < # Runs < 106

(Nassofset)Al(oxide) Offset Plate, Silicon rubber coated

Flexography sleeve, plate

Metallic or textile web,plate,sleeve

Electro-plated Sleeve

Examples: Cups, Textiles, T-shirt, electronic prints

overview2. Gravure - Fabrication of the printform

Methods of gravure cylinder imaging

- Film based: Film - Exposition of a photosensitivemask, developing and chemical etching(analog process)

- Electromechanical: Digital Imaging by Engraving with a diamond tip @ 8 kHz.

- Laser based: 1. Digital Mask Ablation by Laser followed by etching

2. Direct Digital Laser Ablation of metallic surface material

Binary (on / off- modulated) Ablation of Masks

Cu, electroplated

Nd:Yag,Fiberlaser, TEM008 - 200W10 - 20µm

etching

Steel

mask

4 - 650

[µm]Ablated areas

Etched cells

2.1 Digital Mask ablation2. Gravure - Fabrication of the printform

- Simultaneously 4 – 6 beams are generated from a single laser source

- Splitting and position control by Multifrequency AOM – Soundfields

Digilas 4 - Beam

Laser AOM Lens

Roller surface

2. Gravure - Fabrication of the printform 2.1 Digital Mask ablation

2. Gravure - Fabrication of the printform 2.1 Digital Mask ablation

Multiple 4 beams

Lasertraces

Ablated areas of the mask

Print roller

Etchingresults

Multifrequency AOM – Soundfields

1. Screen adjustment 2. Position and power for each shot of a pulse string

are programmable within modulator rise time

binary on / off modulated

BILD!!

Process steps

Mask Ablation with laser

Spray Coating

Spray Etching

Immersion Ring Coating

Printing

2.1 Digital Mask ablation

Deplating of used Cr, Cu

Cu plating, Finishing

Chromium-Plating

Cleaning

Laser process

Coating

Etching

2. Gravure - Fabrication of the printform

Testpattern for printed electronics:

FET structures

Substrate: polymer foil or glas

Conducting ink (silver particles) (SIGPA)

2.1 Gravure - digital mask ablation 2.1.1 Printed electronics

2.2 Direct Laser Ablation

Q-switch Nd-Yag70kHz,

Fiber Optics

Focusing Optics

Cylinder

Laser AOM

Image Data

2x 35 kHz

DIRECT ENGRAVING OF METALLIC SURFACES

Melting and vaporisation

500 W

2. Gravure - Fabrication of the printform

1 pulse 1 cell

2.2 Direct Laser Ablation

Direct laser engraving of metallic print rollers

Cell Proportions:

Depth: 0 - 45 µmDiameter: 25 - 150 µm

Screen: 70 - 300 l/cm

Options for different cell shapes

2. Gravure - Fabrication of the printform

The power scaling of a fixed beam profile defines a specific inherent aspect ratio AR for each % tone value.

3.1 Cell shapes and power modulation

depth variable

100%

50 %

5%

power

Depth and diameter variable, coupled

Tone

shape: conventional halfautotypicalprofile: top hat Gauss

3. Flexible cell shaping

Conditions for optimised ink transfer 0.1 < AR < 0.5 for low quality substrates

0.05 < AR < 0.5 for high quality substrates

AR = depth/diameter

3.2 Ink transfer and AR

Independent control of depth and diameter

3. Flexible cell shaping

AR > 0,5 AR < 0.05

- ink dries before substrate contact

- unstable ink transfer- missing dots- doughnut print

- no ink transferbecause ofcapillary forces

30 µm

2 µm

3.4 Beam profile modulation #1

Fiber Optics

Focusing Optics

Cylinder

Laser AOM

Image Data

2x 35 kHz

Intensity profile

modulation

Power modulation

3. Flexible cell shaping

a1 (%,t)

In (x,y)an (%,t)

a2 (%,t) I2 (x,y)

I1 (x,y)

Control unit

constant intensityprofile

highly dynamicalintensity profile

Image % - values

modulation Optics for intensity profile shaping (lenses, phaseplates, apertures, DOE)

I(x,y,%,t)

3. Flexible cell shaping 3.4 Beam profile modulation #2

3. Flexible cell shaping 3.4 Beam profile modulation #3

3.8 Printing with SHC: Benefit

• Cell profile can be adjusted individually for each tone value

• Optimum matching to various printing substrates and printing conditions

HalfautotypicalSC-A paper, 40 %

Super HalfautotypicalSC-A paper, 40 %

SHC Laser profile modulation: strongly area and depth variable

Ink transfer on low grade paper

3. Flexible cell shaping

Overview4. Parameters and Features

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

4.1 Treatment of large surfaces4. Parameters

High Power Multimode Laser:

2x Nd:YAG 1064 nm, 400 W 35 kHz Q – switch, 10 mJ

Engraving Head:

Power 500 WPulse Frequency 70.000 cells /s

single shotEngraving @ 70l/cm: 11.6 Min / m2

Engraving Time / m2

050

100150200250300350400

0 100 200 300 400 500

screen [L/cm]

min

high resolution screens

low resolution

EM Laser

Printing CharacteristicSmoother Print with DLS cylinders

Direct Laser@ 120 l/cm

Much smoother print due to finer dots/ higher resolution

Stylus Engraving@ 70 l/cm

4. Parameters

Same stability for Zn and Cu after chromium plating

Lower energy input for Zn Higher ablation efficiency , lower threshold precisely response of the material (small residuals) better fine control of tone values

4.2 Material

Cu Zn

Absorption of light @ 1064nm: < 6 % 50 %

Melting point: 1356 K 693 K

Vaporisation point: 2835 K 1180 K

ZnCu

[W/K x m]

Cu Zn Cr Al

Cu Zn Cr Al

Why Zinc ?

Laser Alternatives

Zn(Relative) Low

Intensity

Cu , Cr, CeramicsHigh Intensity

Fiberlaser, Disklaser,

Slab lasercw, gated

Q – switch (MOPA)

Short Pulse (ps) Laser,multipleshots(> 103 /cell)

MDC Laser (pulsed)

time

power

time

power

time

power

5. New Engraving Concepts 5.1 Laser Sources

Track width

One Shot - One Cell

Screen 70 l/cm Screen 140 l/cm

Track width

1 2 31 2

Single Pulse1 pulse 1 cell / SHC applicable

1 10 20 40

Image Setter Technique

Screen 70 l/cm Screen 140 l/cm

Track width

30

Cw gatedImage Setter Technique

5.2 Screen algorithms5. New Engraving Concepts

5. New Engraving Concepts

Engraving of metals, cw – Fiber laser @ 600 W, M 2 = 1.2

Cu

Zn

Image Setter Technique: Resolution 1000 l/cm

5.2 Screen algorithms: cw – fiberlaser # 1

100 µm

100 µm

5.2 Screen algorithms: cw – fiberlaser # 25. New Engraving Concepts

Engraving of Ceramics (cw Fiberlaser 600 W)

1000 µm150 µm

Glue tranfer in carpet production Glue transfer to car glas foils

Depth 90 µm

Cell diameter 150 µmDepth 400 µm

Cell diameter 1 mm

Spot size 15 – 20 µm

Resolution 1000 Lines/cm

Engraving of Embossingtoolswith cw – Fiberlaser 200 W, M2 = 1.1, Multilayer technique

5. New Engraving Concepts 5.2 Screen algorithms: cw – fiberlaser # 3

Cubic and prismatic tools from EPDM for surface structuring of optical design functions

Embossing cylinder for ingrain wallpaper

300 µm 300 µm

Summary Lasers gravure industry: - LPSSL, DPSSL, fiber lasers

Advantages of direct laser engraving - efficiency, resolution, precisionvs. EM

The flexible beam profile modulation - optimisation of the cell shape - optimised ink transfer - economical printing.

OutlookFiberlasers 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)

5. Outlook

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 from the press

Cylinder ready to print

Cylinder Workflow # 1Appendix

Cleaning and Finishing after engraving

Cr polishing

Cr plating

Appendix Cylinder Workflow #2

bdk – Laserline, CologneAppendix

Saueressig - production line, GermanyAppendix.

Thank you for your attention!

MDC MAX DAETWYLER

Dayton, USA

Meet the author:

Dr. Guido Hennig

g.hennig@ daetwyler-graphics.ch

Headquarter Bleienbach, Switzerland