What is Pick?
Most commonly picking of paper is defined as the damage of the paper surface during the printing operation. At the time the printing form is lifted off the paper, the ink exerts a force on the paper. When this force exceeds a certain value, the surface of the paper will be damaged. This test can be used to determine the delamination propensity of paperboard as well. The pick velocity is defined as the velocity at which picking starts in this test method (this is not the velocity on a printing press in practice); the pick resistance is characterized by the product of pick velocity at the start of pick and the viscosity of the pick test oil, devided by the viscosity of the pick test oil at 23°C.
This way it is possible, within limits, to eliminate differences in temperature. The determination of the pick velocity and the pick resistance is one of the most widely used tests performed on the IGT printability testers. The pick test with the aluminium roller is described in IGT information leaflet W31. This method is standardized internationally in e.g.
- ISO 3783
- Tappi 514
Using the multi-purpose printability tester “Amsterdam“, a print is made on a paper to be tested, with a pick test oil of your choice at an increasing speed with adjustable end-speed. After the print is made, it is scanned with a high resolution camera using a special illumination such that picking can be distinguished by an algorithm, developed by our team of software engineers. The pick resistance is shown on the screen. This value is calculated, based on the IGT Pick test oil selected by the user, the measured temperature and pick speed. Three parameters can be selected (entered or measured):
- IGT Pick test oil (4 different grades in viscosity)
- Temperature of the inked disc or environmental temperature
Just one value to indicate the picking resistance!
The automated multi-purpose printability tester
- Fully computer controlled, user friendly interface
- Accurate and fully automatic adjustable printing force as parameter of each test method
- Constant or increasing speed up to 4 m/s, so many paper types can be tested with the correct IGT Pick test oil (4 grades viscosity)
- Temperature controled by High Speed Inking Unit 4, or ambient temperature by means of a sensor for temperature and RH near the device.
- The deviation in temperature is calculated in the pick resistance.
- The high resolution camera with a powerful illumination creates grazing light in which the pick defects can be recognized as pick.
- The “Amsterdam” can also be used for an extensive set of other printability test methods.
- Reliable assessment of paper quality
- Operator independent
- No “Pick Start Viewer” needed for visual assessment
- Test only the property of the paper, not the eyes of the operator
- Based on years of experience and international CEPI test, the algorithm has been developed, fine-tuned and perfected based on thousands of IGT Pick test results
- All digital high resolution images are automatically stored on the internal memory of the computer and can be exported for further investigation
- Parts of the scan can also be magnified on the screen
- All data is saved in a file where all relevant parameters and results are available for further analysis