In general it is very difficult to carry out small-scale gravure printing tests. It is difficult to keep the ink with its volatile solvents constant during a test and this is also valid for water based inks. For laboratory trials there is a need for a system that uses only little ink and paper. A good solution is the Global Standard Tester with the gravure attachment. With this system it is possible to make gravure prints under different testing conditions with different types of printing forms. The prints can be used for testing properties of ink and paper as e.g.: colour, adhesion, light fastness, smoothness, and so on. Instead of paper one may read substrate as many other materials such as boards, plastic films, foils, and so on. There are 2 testing methods for the dry properties of the ink and the smoothness of the substrate:
• Method “gravure 180°”. In this method the printing form is inked only one time and directly after inking the print is made (IGT information leaflet W67 for smoothness and W82 for colour)
• Method “gravure 360°”. In this method the printing form is inked twice and directly after each inking a print is made, so 2 prints are made after each other (IGT information leaflet W73 for smoothness and W83 for colour).
There can be a difference in the ink transfer and printing quality between these two methods. This is also dependent to the combination of ink, substrate and the testing conditions.
Principle
The gravure attachment consists of an engraved printing form (disc), a doctoring system and an impression cylinder. Some drops of the ink are put on the printing disc, the surplus of ink is wiped off and a print is made on the substrate, which has been attached to the impression cylinder. The standard printing form has 11 fields of 70 l/cm (175 l/inch) and depth from 11 to 33 µm . Other engravings are available. The print can be used for examining the colour of gravure ink and to test other dry properties.
Method of operation
• It is recommended to execute the test in the standard atmosphere; to most standards it is 23.0 ± 1.0 °C (73.4 ± 1.8 °F) and 50 ± 2% rh.
• For the operation of the Global Standard Tester follow the instructions of the manual, IGT information leaflet W100 and the display accurately.
• Handle the samples carefully.
Assessment
1. For colour measurement: Check the colour visually in comparison with the original sample or measure the colour with a spectrophotometer at the desired location of the print.
2. For dry properties: Check the desired dry properties according to the testing method at the desired location of the print
3. Calculate the average and if required the standard deviation. In some cases it may be useful to mention the highest and lowest value as well.
