Development of a method for pre-damping in laboratory offset printing units

At the Iggesund mill there are several methods and equipments in laboratory scale that simulate the offset printing process in order to evaluate mottle tendency or ink tack for instance. However, it is not possible to study the effect of pre-damping prior to printing on these properties, which mostly is the case in industrial printing. The purpose of this work was therefore to develop a method for pre-damp application used prior to laboratory offset printing in order to learn more about the ink/fountain solution/substrate interaction. This method was used to study the effect of pre-damp on ink tack measurements and on water interference mottle tendency in laboratory scale.

The initial trials were focused on ink tack measurements without pre-damp in order to achieve knowledge about this type of measurement. The effect of different parameters used within the ink tack measurements was also investigated. The ink tack measurements were rather sensitive to the method of ink distribution procedure, the positioning of the tack disc and the fastening of the paperboard sample. Additionally, the printing speed, the printing pressure and the hold time affected the measurements. However, measurements in the cross direction and the machine direction of the paperboard were compared, and did not show a significant difference. Different levels of tackiness of the ink were also tested. For instance, an ink that previously had caused delamination failure in industrial offset printing showed a relatively high ink tack.

Author: Backstrom, Margareta

Source: Lulea University of Technology

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