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W99- Leaflet | PICK: IGT PRE-WET

PICK: IGT PRE-WET
AMSTERDAM - Multi-purpose printability tester
Version 2021-12

INTRODUCTION

Most commonly picking of paper or paper board is defined as the damage of the paper surface during the printing operation. Delamination of paperboard can be described as the splitting between for example the liner and the next layer or between inner layers during the printing process.

At the time the printing form is lifted off the paper or paperboard the ink is exerting a certain force on the surface. This force is increasing with an increase in the viscosity and tack of the ink and the printing speed. When this force exceeds a certain value, the surface of the paper will be damaged or a delamination between layers of the paper board will occur.

In the offset printing technique paper is dampened, 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. The method without dampening the paper is Pick IGT-ISO 3783 and described in leaflet W31.

The pick or delamination resistance is defined as the velocity at which picking, or delamination starts at a pick test oil temperature of 23°C. In older publications the pick or delamination resistance is described as the Viscosity Velocity Product (VVP). As the VVP is a constant value for a certain type of paper or paper board the pick or delamination resistance (velocity at 23°C) can be calculated from this VVP. Also, it is possible to compare the test results of papers and paperboards obtained with different grades of pick test oil using this VVP.

PRINCIPLE

Paper is dampened with water or fount at a constant speed and subsequently printed with a pick test oil at an increasing speed. The picking result is observed and measured as the first point of damaging in the print.

METHOD OF OPERATION

Pick: IGT pre-wet

STANDARDS

This test method is derivative from the standard  ISO 3783:2006, Tappi 514 and in many countries as well. In the Netherlands in NEN 3095:1990 nl.

MATERIALS

 

  • [402.354.002] Dampening disc 0,25 µm  or
  • [402.354.005] Dampening disc 0,50 µm or
  • [402.354.010] Dampening disc 1,00 µm
  • [435.031.412] Doctor blade holder
  • [180.431.710.001] Doctor blades
  • [402.301.441.720] Printing disc, 10 mm, black aluminium, scale (pick and delamination)
  • [402.301.720] Printing disc, 10 mm aluminium (for delamination only)
  • [404.004.010] Pick test oil low viscosity
  • [404.004.020] Pick test oil medium viscosity
  • [404.004.030] Pick test oil high viscosity
  • [404.004.070] Pick test oil extra high viscosity
  • [404.001.005] Paper packing 55 mm
  • [404.000.220] Pick Start Viewer  or
  • [441.000.040.090] Delamination viewer V shape for board or
  • [441.000.040.180] Delamination viewer  U shape for paper
  • [466.000.710] IGT High Speed Inking Unit 4 (HSIU)
  • [466.003.003] Top roller 4 segments for conventional inks
  • [408.000.200] IGT ink pipette

  • 5 strips of substrate to be tested, dimensions 55*340 mm
  • Ruler
  • Lint free rags
  • Ethanol or cleaning naphtha

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

Condition the paper to be tested and other items in the standard atmosphere for at least 2 hours.

STANDARD SETTINGS

AMSTERDAM – MULTI-PURPOSE PRINTABILITY TESTER

  • Printing speed: increasing, end speed at choice
  • Printing force: 350 N
  • Pick test oil film thickness 8 µm (= volume 0,28 ml)
  • Camera lamp low (Not applicable for Amsterdam Basic type)
  • Checkbox Scan activated (Not applicable for Amsterdam Basic type)

SETTINGS HIGH SPEED INKING UNIT 4: MODE 3

  • Waterbath : 23°C-73,4°F
  • Start-up time  [5s]
  • Distribution time 1 [30s] | Distribution speed 1 [0,5 m/s]
  • Distribution time 2 [10s] | Distribution speed 2 [0,2 m/s]
  • Inking time discs [0,2 m/s]

PREPARATION

  1. Cut paper strips of 55*340 and mark with top and/or bottom side, machine and/or cross direction and a code for the paper.
  2. Select method Pick: IGT Pre-wet.
  3. If desired, touch the checkbox Scan to scan and save (not applicable for Amsterdam Basic type)
  4. Mount the paper packing on the sector.
  5. Fill the ink pipette with the desired IGT pick test oil.
  6. Set the HSIU in Mode 3
  7. Apply 0,28 ml of oil on a segment of the top roller.
  8. Place the printing disc on the shaft of the HSIU.

EXECUTION

Pick pre wet position doctorblade

FOLLOW THE INSTRUCTIONS ON THE DISPLAY.

  1. Mount a strip of paper or board to be tested on the sector of the Amsterdam.
  2. 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:
  3. Place a small strip of cotton pad (5×50 mm) just left of the doctor blade on the dampening disc
  4. Place the printing disc with oil on the 2nd printing shaft of the tester.
  5. Touch the button [Print] and press both side buttons to rotate the sector and both shafts into the start position and to lower the blade.
  6. Release side buttons and apply dampening fluid onto the cotton pad. When done press both side buttons again.
  7. Keep both side buttons pressed to meter the excess dampening fluid, moisten the paper on the sector and make the print and – if applicable – scan.
  8. Release side buttons when the display says DONE .
  9. Bevel

    Take the sample from the sector and immediately check with the pick start or delamination viewer and mark the first visible damage of the surface. More detailed information is described in the section Assessment.

  10. If the black disc with scale was used: assess the disc on the first point of picking and make a record. (See section Assessment.)
  11. Before starting a new test, clean the printing disc and the used segment of the inking unit (or use the next segment) and start inking the printing disc again.
  12. Add dampening fluid on the cotton pad if necessary.
  13. 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.
  14. It is recommended to perform the test at least five times per sample.

 

CLEANING

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

ASSESSMENT

IF A SCAN WAS MADE:

the results are automatically analysed and shown in the display: pick distance in mm, pick velocity and resistance in m/s.
The image has a ruler to refer to and may look like:

When you move your finger along the image of the stain, this part will be enlarged in the box where the data are visible. The data will be shown again as soon as you release your finger from the image.

NOTE 1: the camera scans picking. In case the software should also calculate delamination, proceed as follows:

  • Before saving, remove the print from the sector.
  • Assess the start of delamination in mm with the help of the delamination viewer and a ruler.
  • Select the button [Delamination] on the screen of the Amsterdam and enter the distance manually.
  • Then save.

Take the sample from the sector immediately after printing and check with the pick start viewer and/or delamination viewer. Mark the first visible damage of the surface.

If satisfied, touch the textbox <BATCH> on the left of the display to save both data and image with the help of the pop-up keyboard that automatically appears. 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.

 

Pick Staart Viewer

IF NO SCAN WAS MADE

To view the result of delamination, place the test strip in the delamination viewer and by carefully moving the test strip along the U-profile or V-profile check where delamination starts and mark this point.

Measure the pick distance between the starting point of the print (= the centre of the initial print contact line) and the point where picking or delamination begins at the test strip.  Make a record in mm.


If desired derive the pick velocity in m/s from the velocity table or with the formula:
For picking: Vp = 0,005 * Ve * dp
For delamination: Vd = 0,005 * Ve * dd

Herein is:

  • Vp = velocity at point d (in m/s)
  • Vd = delamination at point d (in m/s)
  • Ve = set end speed (in m/s)
  • dp = distance from beginning of the print to beginning of picking (in mm)
  • dd = distance from beginning of the print to beginning of delamination (in mm)

Velocity table

If desired, calculate the pick or delamination resistance from the Velocity Viscosity Product (VVP) in N/m with the formula:
For picking: P23 = Vp * ɳ t / ɳ23
For delamination: D23 = Vd * ɳ t / ɳ23

Herein is:

  • P23 = Pick resistance at 23 °C in m/s
  • D23 = Delamination resistance at 23 °C in m/s
  • Vp = Pick velocity in m/s (velocity at the point where picking begins) at the measured temperature
  • Vd = Delamination velocity in m/s (velocity at the point where picking begins) at the measured temperature
  • ɳt = Viscosity in Pa.s at the measured temperature (see table 1)
  • ɳ23 = Viscosity in Pa.s at 23 °C (see table in section “Notes”)

NOTES

  1. Viscosity table: viscosity of pick test oils in Pa.s

    A single damaging at >20 mm before the point where picking begins, is NOT the first point of picking or delamination.

  2. If picking or delamination occurs at <20 mm from the starting point of the print, the test must be repeated at a lower speed. In case the lowest speed has been applied already a change to a lower grade of the pick test oil is necessary.
  3. If no picking occurs or the picking occurs at >180 mm from the starting point of the print, the test must be repeated at a higher speed. In case the highest speed has been applied already a change to a higher grade of the pick test oil is necessary.
  4. The black aluminium printing disc with ruler, is specially used for paper of which the beginning of picking can be difficult to detect. For other papers it can give additional information. For example: loosened fibres or coating particles may be picked up by the oil before the actual overall damaging of the paper surface takes place. These particles are visible on the disc also.
  5. The viscosity of the pick test oils is temperature dependent. The Velocity Viscosity Product (VVP) may be used to compensate these differences. See Viscosity table.

 

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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