IGT Testing Systems
Menu
  • Print
  • PDF

W92 – Leaflet | Mottle: Ink Trap Index / Curve | Amsterdam 5/6

W92 - Mottle: Ink Trap Index / Curve
AMSTERDAM 5/6 - Multi-purpose printability tester
Version 2022-09

Introduction

Mottling is an unwanted variation in optical properties of the (mostly solid) print, appearing as small dark and light areas at the surface of paper (board) caused by ink, paper or press (circumstances). Mottle is affected by type of ink, colour sequence, construction of the printing press, printing speed, rubber blanket, damping fluid and, most important, the paper composition. Variations in the surface characteristics as absorption, smoothness and formation play an important role in mottle and are caused by the production process and the components in the paper.

In the following W-leaflets several mottle methods are described:
W57: Back Trap Mottle
In back trap mottle paper is printed and the ink of the printed strip is set off 4 times to 4 clean printing discs with interval times.

W58: Print Mottle
A paper strip is printed 4 times with the same printing disc.

W59: Water Interference Mottle
Water interference mottle is the uneven printing result, caused by insufficient and uneven water absorption of the paper, followed by uneven ink absorption.

W92: Ink Trap Mottle
Ink trap mottle is the uneven printing result caused by a trapping in tack and/or viscosity of the ink in wet-on-wet printing and is also influenced by an uneven absorption of the ink in the paper.

These tests can all be done in two method settings:
1. Method Index: the result is scanned and saved after the last print.
2. Method Curve: the result is scanned and saved after each print.

Principle

Paper is printed wet-on-wet with two offset inks in two colours. Subsequently this print is brought into contact 4 times with clean printing forms (rubber blanket).

Mottle: Ink Trap, print

Method of operation

A print is made with two offset inks at choice.

Method index: the printed strip is brought into contact 3 times with clean printing forms (rubber blanket) with interval times of 10 s. After the last pass, the test result is scanned and analysed.

Method curve: the printed strip is brought into contact 3 times with clean printing forms (rubber blanket) with interval times of 15 s. After each pass, the test result is scanned and analysed.

Materials

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, 0,2 m/s
  • Printing force: 500 N
  • Number of set-offs: 3
  • Interval times: 10 s (method index) or 15 s (method curve)
  • Ink film thickness 2,4 µm (two segments for two colours)
  • Camera lamp high (not applicable for Amsterdam Basic type)
  • Checkbox Scan activated (not applicable for Amsterdam Basic type)

IGT High Speed Inking Unit 4 (HSIU)

  • Water bath: 23 °C (73,4 °F)
  • Mode 2:
    • Start-up time [10 s]
    • Distribution time 1 [20 s] | Distribution speed 1 [0,5 m/s]
    • Inking time discs [15 s]

Preparation

  1. Cut paper strips of 55 x 340 mm and mark with top and/or bottom side, machine and/or cross direction and a code for the paper.
  2. Select either method Mottle: Ink Trap Index or Mottle: Ink Trap Curve.
  3. If desired, touch the checkbox Scan to scan and save (not applicable for Basic type Amsterdam).
  4. Fill the ink pipettes with offset inks to be tested.
  5. Set the HSIU in Mode 2 (for changing settings refer to your HSIU manual).
  6. Apply 0,1 ml of ink to the inking unit (4-segment top roller).
  7. Place the printing discs on the shafts of the HSIU and ink the printing discs.

Execution

  1. Mount a strip of paper or board to be tested on the sector of the Amsterdam.
  2. Place the printing discs with ink on the printing shafts 1 and 2 of the tester. Place the clean discs on the other shafts.
  3. Touch the button [Print].
  4. Press both side buttons: the sector and the printing shafts rotate into the start position and the print is made.

For method index:

  1. After making the initial print, the first interval time of 10 s is entered. At this moment you may release the side buttons and immediately replace the disc on printing shaft 1 with a clean one (only for Amsterdam 5).
  2. At the near end of the interval time a warning signal is given. Press both side buttons to bring the clean disc into contact with the print on the sector. The first set-off from the print is made with the clean printing disc.
  3. The second interval time of 10 s starts. Release both side buttons again.
  4. When the warning signal is given press both side buttons again and repeat points 6 and 7 until all cycles (standard preset: 3) are done.
  5. Keep side buttons pressed. The camera lowers to scan the print.
  6. Release side buttons when the display shows DONE.
  7. The print is scanned and analysed and the camera moves upwards. Save or discard the results.
  8. When press [SAVE] a pop-up keyboard appears to name and save both data and image.
  9. Remove the test strip from the sector.
  10. Before starting a new test, clean the disc and use a new segment of the inking unit, apply ink and start inking the disc again.
  11. After finishing all tests, press [BACK].

For method curve:

  1. After making the initial print, the camera lowers to make a scan.
  2. The first interval time of 15 s is entered. At this moment you may release the side buttons and immediately replace the disc on printing shaft 1 with a clean one (only for Amsterdam 5).
  3. Before the interval time has elapsed a warning signal is given. Press the side buttons again. The first set-off from the print is made with the clean printing disc.
  4. The camera lowers to make a scan.
  5. The second interval time of 15 s starts. Release side buttons again.
  6. Repeat point 7, 8 and 9 until all set cycles (standard preset: 3) are done.
  7. After the last cycle, keep side buttons pressed to let the camera scan and release side buttons when the display shows DONE.
  8. The print is scanned and analysed and the camera moves upwards. Save or discard the results.
  9. When press [SAVE] a pop-up keyboard appears to name and save both data and image.
  10. Remove the test strip from the sector.
  11. Before starting a new test, clean the disc and use a new segment of the inking unit, apply ink and start inking the disc again.
  12. After finishing all tests, press [BACK].

Cleaning

  1. Clean the discs with lint-free rags and cleaning naphtha.
  2. Clean all rollers of the inking unit, including the metal ones with lint-free rags and cleaning naphtha.
  3. Make sure the Amsterdam is clean and if necessary clean with some ethanol or cleaning naphtha on a lint free rag.

Assessment

The results are automatically analysed and shown in the display; the mottle is recorded in 3 values: contrast, cloudiness and orientation.

Test result

For the method curve, data are given for each scan. The first scan is the initial print, the subsequent scans are mottled.
For the method index, only one scan is made at the end. Magnification of the scan via touch screen is possible.

Afterwards the data and images can be transferred to a USB stick. For the correct procedure please refer to the manual of the Amsterdam.
Data are saved in a CSV format that can be loaded into Excel. Images are saved as PNG files. The data will relate the results to a specific image to enable you to combine both.

NOTES

  1. Shelf life Mottle ink: 3 years, period after opening: 1 year.
  2. Be aware that due to aging or intensive use the life time of the discs is limited.

Randstad 22 - 02

1316 BX Almere

The Netherlands

P.O.box 22022

1302 CA Almere

The Netherlands

+31 20 40 99 300 +31 20 40 99 339 info@igt.nl
  • Print
  • PDF
Print Friendly, PDF & Email