Evaluation of misregister on multiple coated fine papers in sheet fed offset printing

Abstract

Misregistration is one of the most common printing faults of wood free multiple coated fine papers in multicolor sheetfed offset printing. Misregister significantly reduces print quality and leads to complaints to the paper manufacturer. Unfortunately it is often difficult to identify the cause of a misregister problem, because apart from the potential paper impacts, several printing machine and printing ink parameters may also have an effect. It would therefore be an advantage – especially for the paper manufacturer – to be able to determine and influence the factors leading to this problem. In practice a qualitative evaluation of misregister is frequently carried out using a printer’s loupe, which is a quite subjective method and has the disadvantage of a rather low resolution. Evaluation of misregistrations using a light microscope allows higher resolution but is quite time consuming. Therefore, a new offline measuring device for fast and objective evaluation of misregistrations was developed in the R&D department of Sappi Gratkorn. First results using this device show the expected relationships between misregistration and ratio of machine/cross direction fiber orientation, influence of grain direction and filler content of the base paper. Furthermore, misregister was found to be dependent on the amount of fountain solution as well as on the smoothness of the rubber blankets.