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W76-2 – Leaflet | Flexo Set-off

Flexo Set-off
AMSTERDAM - Multi-purpose printability tester
Version 2022-02

INTRODUCTION

Flexographic printing is a printing technique that uses a flexible relief printing plate. This plate, mounted on a plate cylinder, is used as the image carrier being inked by the anilox roller which transfers an amount of ink to the printing plate. The inked printing plate prints the ink on the substrate.

Set off is a defect characterized by the transfer of wet ink to the reverse side of the printing side. Ink set off can be prevented by ensuring that the combination of ink and paper are compatible enough to promote rapid ink vehicle penetration or surface drying.
How fast the ink penetrates into paper after printing has to do with absorption. A slow absorption or a high amount of ink printed may result in smearing. A fast absorption may cause changes of the dry ink properties.
The set off test is usually carried out as a comparative test. The chosen set off time intervals may differ per type of ink and/or substrate.

PRINCIPLE

A strip of the substrate to be tested is printed with a flexo ink. After specific times the strip is brought into contact with a blank strip of a set-off reference paper. Part of the ink, which is still present at the surface of the printed strip, will set-off on the counter paper. The more ink is absorbed into the printed strip, the less ink will transfer to the counter strip. The amount of the transferred ink is a value for the set-off.

METHOD OF OPERATION

Flexo Set-off

 

 

MATERIALS

360° sector for flexo for AMSTERDAM

  • [402.331.412] Printing disc aluminium, pin, 50 mm (1x)
  • [402.226.412] Anilox disc, 4 engravings *)
  • [364.000.166] 360° sector for flexo for AMSTERDAM
  • [435.031.412] Doctor blade holder
  • [180.431.710.001] Doctor blade flexo
  • [403.010.001] Printing form photopolymer, 1,7 mm *)
  • [403.011.001] Compressible mounting foam tape
  • [404.009.029] IGT C2846 reference paper
  • Flexo ink

*) other types are available


  • strips of substrate to be tested, dimensions 55 x 200 mm
  • (disposable) ink pipettes
  • lint free rags
  • velvet
  • cleaning solvent for ink
  • ethanol

TESTING CONDITIONS

Standard test atmosphere according to ISO 187 (23,0 ± 1,0 °C and 50 ± 2% RH)

SAMPLE CONDITIONING

Be aware of the fact that a different way of conditioning of the samples can have influence on the results.

 

STANDARD SETTINGS

AMSTERDAM – MULTI-PURPOSE PRINTABILITY TESTER

  • Printing speed: constant, 0,7 m/s
  • Printing force: 100 /150 N
  • Inking revolutions of anilox roller: 3
  • Interval times between print and set-offs: 2 s

 

PREPARATION

  1. Cut paper strips of 55 x 200 mm and mark with top and/or bottom side, machine and/or cross direction and a code for the paper.
  2. Select the method Flexo Set-off.
  3. Set the printing speed, anilox force, printing force, interval time and the number of revolutions to the desired values.
  4. MOUNT THE 360° SECTOR (especially for Flexo Set-off).
  5. Mount the photopolymer with double-sided foam tape. Position the sector on the AMSTERDAM: press both side buttons to rotate the sector into the start position. Then release the buttons. Observe the position of the seam of the photopolymer: in start position it should be direct under the 2nd printing shaft.
  6. Mount a test strip on the impression cylinder with a piece of tape at the beginning and the end of the strip. The beginning of the strip must be at the location of the disc that is of about 90° before the pin.
  7. Mount a strip of the set-off paper C2846 (reference paper) on the 2nd half of the sector with a piece of tape at the beginning and the end of the strip.
  8. Mount the doctor blade into the blade holder.
  9. Place the blade holder onto the two pins of the accessory holder.
  10. Place the anilox roller on the 1st printing disc shaft of the tester.
  11. Place the impression cylinder with the test strip on the 2nd printing disc shaft of the tester.

EXECUTION

  1. Touch the button [PRINT].
  2. Press both side buttons to rotate the sector into the start position, to lower the doctor blade on the anilox disc and to rotate the disc on the 2nd shaft to the start position.
  3. Apply a few drops of flexo ink on the anilox disc just left of the blade with the help of the (disposable) pipette.
  4. Press both side buttons to preink the anilox disc, to ink the photopolymer and to print the substrate. The anilox will be lifted off during the test. The reference paper strip must be taped direct after the part of the photopolymer that is inked in.
  5. Release the side buttons.
  6. Take the printed sample and the aluminium printing disc from the tester and let it dry conform type of ink. Take the counter printed sample from the sector.
  7. Clean all parts.
  8. Repeat the points 1 through 7 for every strip until the last part has been set-off.
  9. It is recommended to execute the test at least three times per combination of ink and substrate.

 

CLEANING

  1. Clean the discs with lint-free rags with cleaning solvent for the ink and after that with ethanol.
  2. Clean the photopolymer.
  3. Clean the doctor blade.

NOTE: Follow the instructions in the manual for deep-cleaning of the anilox.

ASSESSMENT

Let the printed samples dry and observe the amount of ink in the set off areas on the reference paper.

Record accurately the conditions and the results of the test and refer to this testing method.

Flexo Set-off: print and counter print

IGT Testing Systems
Randstad 22 - 02
1316 BX Almere, The Netherlands
P.O.box 22022
1302 CA Almere, The Netherlands
Telephone: +31 20 40 99 300
E-mail: info@igt.nl
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