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W38- Leaflet | Picking Westvaco | Amsterdam

PICKING: WESTVACO METHOD
AMSTERDAM - Multi-purpose printability tester
Version: 2021-11

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.

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. The determination of the pick velocity and the pick resistance is one of the most widely used tests performed on the IGT printability testers.

This W38-leaflet describes a pick test with a steel, grooved printing disc, known as pick Westvaco. This method is most commonly used in the USA and can be performed on any Amsterdam printability tester, using an external inking device.

PRINCIPLE

With inking device the groove of the Westvaco printing disc is filled with pick test oil. A print is made on the paper or paperboard to be tested, at an increasing speed. The first point of damage to the surface is observed and measured. The pick and/or delamination resistance is calculated.

MATERIALS

 

  • [402.320.015.412] Printing disc, 20 mm, groove: depth 15 µm, width 10 mm or
  • [402.320.030.412] Printing disc, 20 mm, groove: depth 30 µm, width 10 mm or
  • [402.320.060.412] Printing disc, 20 mm, groove: depth 60 µm, width 10 mm
  • [413.012] Rod Westvaco
  • [404.004.010] Pick test oil low viscosity or
  • [404.004.020] Pick test oil medium viscosity or
  • [404.004.030] Pick test oil high viscosity or
  • [404.004.070] Pick test oil extra high viscosity
  • [404.001.005] Paper packing 55 mm
  • [441.000] Pick Start Viewer  or
  • [441.000.040.090] Delamination viewer for board (V shape)
  • [441.000.040.180] Delamination viewer for paper (U shape)
  • [413.060.710] Westvaco Inker (optional)
  • [110.031.100] On-line analysis Software IGT Pick (Optional)

  • 5 strips of substrate to be tested, dimensions 55*340 mm
  • 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 licence, the actual temperature and RH need to be entered into the Amsterdam to enable correct calculation of Pick Resistance.
  • Condition the paper to be tested and other items in the standard atmosphere for at least 2 hours.

STANDARD SETTINGS

  • Printing speed: increasing, end speed at choice.
  • Printing force: 700 N.
  • Camera lamp low (Not applicable for Amsterdam Basic type)
  • Checkbox Scan activated (Not applicable for Amsterdam Basic type)

PREPARATION

  1. Cut the paper strips and mark them with top and/or bottom side, machine and/or cross direction and a code for the type of paper.
  2. Select method Pick Westvaco.
  3. If desired, touch the checkbox Scan to scan and save (not applicable for Basic type Amsterdam)
  4. Mount the paper packing on the sector.
  5. Fill the ink pipette with the desired IGT pick test oil.

EXECUTION

  1. Mount a strip of paper or board to be tested on the sector of the Amsterdam.
  2. Place the printing disc on the Westvaco inking device, using the adaptor.
  3. Apply a small amount of pick test oil on top of the Westvaco printing disc.
  4. Move the rod upwards towards the disc by moving the lever.
  5. Place the swing over the pin inside the adaptor and rotate clockwise to distribute the oil.
  6. Place the disc on the first printing shaft of the Amsterdam printability tester.
  7. Touch the button [Print] and press both side buttons to rotate the sector and the printing shaft into the start position.
  8. Keep both side buttons pressed to make the print.
  9. Wait till the camera has scanned the print and release side buttons when the display says DONE.
  10. Before saving, remove the print from the sector
  11. Assess the start of delamination in mm with the help of the delamination viewer and a ruler.
  12. Select the button [Delamination] on the screen of the Amsterdam and enter the distance manually.
  13. If satisfied, save the results by entering your sample ID in the box <Batch>
  14. Take the sample from the sector.
  15. Before starting a next test, clean the disc and the rod.
  16. It is recommended to perform the test at least five times per sample.

Screen shot DelaminationIF THE CAMERA WAS ACTIVATED

The print is scanned and analysed. After that 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

IF NO SCAN WAS MADE

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

CLEANING

Clean the Printing disc with lint-free rags and cleaning naphtha.

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.

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.

If no scan was made:

Pick Start Viewer

to view the result of picking, place the test strip under the opening of the pick start viewer. Looking from above into the viewer assess the test strip and mark the point where picking begins.

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 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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