W32 | W66 – Leaflet | Wet Pick – Wet Repellence
Wet Pick - Wet Repellence
AMSTERDAM - Multi-purpose printability tester
Version: 2022-11
Introduction
In the offset printing technique paper is dampened with fountain solution, which means that the surface strength will decrease. For that reason, it can be of interest to carry out the IGT pick test after dampening the paper. This leaflet describes this method.
W32 Leaflet Wet pick - Wet Repellence describes a method with a rubber printing disc of 85 Shore A.
W66 Leaflet Wet pick - Wet Repellence describes the method with a rubber printing disc of 65 Shore A.
Principle
Paper is dampened with water or fountain solution at a constant speed and subsequently printed with a pick test oil also at constant speed.
A part of the sample is damped and another part is not. Both areas can be compared with the help of reference paper.
Method of operation
Materials
- [402.354.002] Damping disc 0,25 µm or
- [402.354.005] Damping disc 0,50 µm or
- [402.354.010] Damping disc 1,00 µm
- [435.031.412] Doctor blade holder
- [180.431.710.001] Doctor blade
- [404.001.005] Paper packing 55 mm
- [402.634.412] Printing Disc black rubber 85 Shore A
- [402.678.412] Printing Disc black rubber 65 Shore A
- [404.800.001] IGT Pick test ink low tack or
- [404.800.002] IGT Pick test ink medium tack or
- [404.800.003] IGT Pick test ink high tack
- [404.009.029] Reference paper, C2846, 55 mm
- [466.000.710] IGT High Speed Inking Unit (HSIU)
- [466.003.003] Top roller – 4 segments – conventional inks
- [408.000.200] IGT ink pipette 0,01 ml resolution
- 3 strips of substrate to be tested, dimensions 55 x 340 mm
- 3 strips of reference paper, dimensions 55 x 340 mm
- dampening fluid
- cotton pads
- lint free rags
- cleaning naphtha and ethanol
Testing conditions
Standard test atmosphere according to ISO 187 (23,0 ± 1,0 °C and 50 ± 2% RH)
When using the software analysis license, the actual temperature and RH% need to be entered in the fields [°C] and [RH%] to enable correct calculation of Pick Resistance. These data are also saved with each test performed.
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, at choice (though with interval time: ≤1 m/s, without: ≤3 m/s)
- Printing force: 650N
- Interval time: at choice
- Ink film thickness: 3,2 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: 23,0 °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
- 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.
- Select method Wet pick – Wet Repellence.
- If desired, touch the checkbox Scan to Scan and save (not applicable for Basic type Amsterdam).
- Mount the paper packing on the sector.
- Fill the ink pipette with the desired IGT pick test ink.
- Set the HSIU in Mode 2 (for changing settings and ink application, refer to your HSIU manual).
- Apply 0,14 ml of ink on a segment of the top roller.
- Place the printing disc on a shaft of the HSIU and ink the printing disc.
NOTE: Due to the drying properties of the ink it is not advised to add some ink after a test.
Execution
- Mount a strip of paper or board to be tested on the sector of the Amsterdam.
- Place a clean dampening disc on shaft 1 and mount the blade holder onto the two pins of the accessory holder with the blade pointing to the right and downward.
- Place a small strip of cotton pad (5 x 50 mm) just left of the doctor blade on the dampening disc.
- Place the printing disc with ink on the 2nd printing shaft of the tester.
- Touch the button [Print] and press both side buttons to rotate the sector, both shafts into the start position and to lower the blade.
- Release side buttons and apply dampening fluid onto the cotton pad. When done press both side buttons again.
- Keep both side buttons pressed to meter the dampening disc, moisten the paper on the sector and make the first print.
- Take the sample from the sector.
- Mount the second sample on the sector and press both side buttons again to make a second print.
- Keep side buttons pressed till a scan has been made and the display says DONE.
- Before starting a new test, clean the disc and the used segment of the inking unit (or use the next segment) and start inking the disc again.
- Add dampening fluid on the cotton pad if necessary.
- It is recommended to perform the test at least three times per sample.
If the camera was activated
The print is scanned and the camera moves upward.
Save or discard the results.
Start from point 1 for a next test. After finishing all tests, press [Back] and clean and store all parts.
Cleaning
- Clean the printing disc with lint-free rags and naphtha.
- Clean all rollers of the inking unit, including the metal ones with lint-free rags and naphtha.
- Make sure the Amsterdam is clean and if necessary dry with some ethanol or cleaning naphtha on a lint free rag.
Assessment
If a scan was made
The picture of both prints is saved.
Wet repellence in the first print shows as a non-printed area. In the second print the areas C and D have accepted less respectively more ink than areas A and B. In between the two fields of the print, a transition may show as partly dampened and partly printed only.
Scans are saved as black and white images, these are only to be used for illustrative reasons.
If no scan was made
The assessment may be done visually or with a densitometer.
Visually (d = density)
- No wet pick / no wet repellence: d A = d B and d C = d D. No paper particles are left behind on the printing disc after the first print.
- Wet repellence: d A > d B and d C < d D. No paper particles are left behind on the printing disc after the first print.
- Wet pick: d A > d B and d C > d D. There are paper particles left behind on the printing disc after the first print.
Densitometrically (d = density)
After the ink has dried measure the density of the areas A, B, C and D. The drying time of the IGT ink is about 30 minutes. Calculate the wet pick and wet repellence with the following formulas:
- Wet pick + wet repellence: [(d A – d B) / d A] x 100% = (a)
- Wet pick: [(d C – d D) / d C] x 100% = (b)
- Wet repellence: (a) – (b) = (c)
Meaning of the calculations above:
- No wet pick / no wet repellence: (a) = 0
- Wet Pick: (b) > 0. The higher (b) the more wet pick.
- Wet repellence: (c) > 0. The higher (c) the more wet repellence.
NOTES
- Pick test inks have a shelf stock time <3 years, open time <1 year.
- This test does also exists for 4 fields instead of 2: Wet pick – Wet Repellence 4 F.
Randstad 22 - 02
1316 BX Almere
The Netherlands
P.O.box 22022
1302 CA Almere
The Netherlands
