Test set to execute Scumming tests in combination with an IGT printability tester.
Scumming of the lithographic plate in offset printing may be caused by the printed paper. During offset printing the paper is moistened by the rubber blanket. Depending on the number of times the moistening takes place (multi-colour offset printing) and the resistance of the coating against water, certain components of the coating will be dissolved and deposited on the blanket, from which they are transferred to the plate. This may lead to discoloration in the non-image areas of the print. This phenomenon may be of a dual nature: tinting and scumming. Tinting occurs when the paper components are decreasing the surface tension between ink and water in such a way that an ink/water emulsion is formed. The scumming is the result of a decrease in the water sensitivity of the offset plate, so that non-image areas accept ink. This is more serious, as it may ruin the plate during the press run. The scumming test is a rapid and simple method to assess the tendency of offset papers to scumming.
Can be used in combination with the following IGT Printability testers:
For more information look at the test method information W21 Scumming