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W77 – Leaflet | Printing Smoothness

W77 - Printing Smoothness
AMSTERDAM - Multi-purpose printability tester
Version: 2023-06

Introduction

There are several methods to measure the roughness of paper. Many of them are based on air leakage. In the IGT Information leaflet W28 (IGT Roughness) a method is described which is based on filling irregularities of the surface of paper with roughness solution. The method described in this information leaflet W77 is based on printing the surface of the paper with a smooth printing form and a thin ink film under a low printing force. In this case only the tops of the paper surface are printed. Depending on the roughness of the paper there will be more or less white spots in the print: the rougher the paper the more white spots.
The method in this leaflet describes a print with 5 fields, every field printed with another printing force:

W77-1 - Printing smoothness at 500-400-300-200-100 N
W77-2 - Printing smoothness at 1000-800-600-400-200 N

Principle

The paper strip to be tested is printed with a standard ink using an IGT printability tester. The printing form is an aluminum disc. Only the tops of the surface of the paper are printed. The print is divided in 5 parts, each next part having a lower printing force. The rougher the paper the more white spots are visible in the print. The results are compared with a self-made reference or are compared with the results of other (standard) papers.

Printing smoothness, print

Method of operation

Materials

  • strips of paper to be tested, preferable 55 x 340 mm, 3 strips per sample
  • lint free rags
  • cleaning naphtha and ethanol
  • spectrophotometer if required

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 Smoothness 1: 500-400-300-200-100 N
  • Printing force Smoothness 2: 1000-800-600-400-200N
  • Ink film thickness 0,8 µm

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 and mark with top and/or bottom side, machine and/or cross direction and a code for the paper.
  2. Mount the packing on the sector of the Amsterdam printability tester.
  3. Select method Print Smoothness 500-100 N or Print Smoothness 1000-200 N.
  4. Fill the ink pipette with the ink to be used.
  5. Set the HSIU in Mode 2.
  6. Apply 0,03 ml of ink to a segment of the top roller and distribute the ink.
  7. Place the printing disc on the shaft of the HSIU and ink the printing disc.

NOTE: The amount of ink mentioned above is a guide line to reach an ink transfer of approximately 0,4 g/m². Depending on the type of paper, the type of ink and/or the desired ink film thickness this amount of ink must be changed.

Execution

Printing Smoothness, start position
  1. Mount a strip of paper or board to be tested on the sector.
  2. Place the printing disc on the 1st printing shaft.
  3. Touch the button [Print] en press both side buttons to make a print in 5 steps.
  4. If the camera was activated wait till the camera has scanned the print.
  5. Release side buttons when the display says DONE.
  6. If satisfied, save the results by entering your sample ID in the box [Batch].
  7. Take the printing disc from the shaft.
  8. Clean the printing disc.
  9. Remove the printed strip from the sector.
  10. Clean the rollers of the inking unit or use a clean segment for the next test.
  11. Touch [Back] and start up a new test. It is recommended to perform the test at least three times.

Store the printed strips in the standard atmosphere in a safe place for at least 24 hours to prevent damage.

Cleaning

  1. Clean the halftone printing 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 and ethanol.

Assessment

If a scan was made

The print is scanned and shown in the display.

Printing Smoothness, test result

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.

Scans are saved as black and white images, these are only to be used for illustrative reasons.

  1. Observe the printing result with a self-made reference or with other (standard) papers.
  2. 24 hours after printing, measure the printed strips with the spectrophotometer.
  3. Calculate the average of the measured results per field per type of paper.

NOTES

  1. Due to drying of the ink, it is not advised to add some ink to the same segment of the inking unit after a test. Clean the used segment first or choose the next segment of the top roller.
  2. The test inks have a shelf stock time: <3 years; open time: <1 year

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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