Ink-lift-off during offset printing: a novel mechanism behind ink–paper coating adhesion failure

Abstract

This paper reports on a special pilot coating and industrial printing trial designed to gain fundamental knowledge on ink adhesion failure on coated papers. We found that ink adhesion failure resulted in white spots without ink on the paper, referred to as uncovered areas and these spots gave print mottle problems. The white spots were due to two fundamentally different types of ink adhesion failure. One is the well-known ink rejection, which simply means that ink is not transferred to the surface. The other is a new type of ink adhesion failure, confirming a previous hypothesis suggested from laboratory observations. We refer to this as ink-lift-off adhesion failure, meaning that ink initially deposited on the paper surface becomes lifted off from the surface in a subsequent print unit. Adhesion failure by this mechanism was seen to occur more frequently than failure due to the well-known ink rejection.

Keywords:

• ink adhesion
• adhesion failure
• uncovered area
• offset
• GCC-based coating
• print mottle

Acknowledgement

This study was financially supported by OMYA International AG and Innventia AB, and their contributions are thankfully acknowledged. Norbert Gerteiser, Maurizio Sturzo and Oliver Grossmann amongst others are greatly thanked for the coordination of and the assistance during both the pilot coating trial and the printing trial. Joanna Hornatowska is sincerely thanked for her assistance with the SEM and EDS analyses.