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W58 – Leaflet | Mottle: Print Index / Curve

Mottle: Print Index / Curve
AMSTERDAM - Multi-purpose printability tester
Version 2022-07

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

A paper is printed with IGT mottle test ink 4 times with the same printing form, that has been inked just once.
Method index: paper is printed 4 times with interval times of 10 s. After the last print the result is scanned and analysed.
Method curve: paper is printed 4 times with interval times of 15 s. After every print the result is scanned and analysed.

Mottle: Print Index / Curve, print

Method of operation

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: 625 N
  • Number of set-offs: 4
  • Interval times: 10 s (method index) or 15 s (method curve)
  • Ink film thickness 2,4 µm
  • 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: Print Index or Mottle: Print Curve.
  3. If desired, touch the checkbox Scan to scan and save (not applicable for Basic type Amsterdam).
  4. Fill the ink pipette with the IGT mottle test ink.
  5. Set the HSIU in Mode 2 (for changing settings and ink application, refer to your HSIU manual).
  6. Apply 0,10 ml of mottle test ink to the inking unit (4-segment top roller).
  7. Place the printing disc on the shaft of the HSIU and ink the printing disc.

Execution

  1. Mount a strip of paper or board to be tested on the sector of the Amsterdam.
  2. Place the printing disc with ink on the 1st printing shaft of the tester.
  3. Touch the button [Print] and press both side buttons: the sector and the 1st printing shaft 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. Keep side buttons pressed.
  2. At the near end of the interval time a warning signal is given. The second print is made.
  3. Repeat point 4 and 5 until all set cycles (standard preset: 4) are done.
  4. Keep side buttons pressed. The camera lowers to scan the print.
  5. Release side buttons when the display shows DONE.
  6. When press [SAVE] a pop-up keyboard appears to name and save both data and image.
  7. Remove the test strip from the sector.
  8. 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.
  9. 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.
  3. Before the interval time has elapsed a warning signal is given. Press the side buttons again. The second impression is made and the camera moves to its position to make a scan.
  4. Repeat point 5 and 6 until all set cycles (standard preset: 4) are done.
  5. After the last cycle, keep side buttons pressed to let the camera scan and release side buttons when the display shows DONE.
  6. The print is scanned and analysed and the camera moves upwards. Save or discard the results.
  7. When press [SAVE] a pop-up keyboard appears to name and save both data and image.
  8. Remove the test strip from the sector.
  9. 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.
  10. After finishing all tests, press [BACK]

Cleaning

  1. Clean the disc 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.

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.

Touch the textbox [Batch] on the left of the display, fill in the information and push [OK] save both data and image push [OK] again. 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
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