Details:
Summary:
In conventional offset lithographic printing, it has been well established that the existence of a continuous layer of fountain solution (FS) on the surface of the non-image area is an essential condition to ensure correct operation of lithography. However, the mechanistic function of FS in preventing the ink from being transferred onto the non-image area has not been fully understood. Several major mechanistic interpretations can be found in the literature, which are based either on comparing of static works of adhesion and cohesion of ink and FS, or on the splitting of the "weaker" FS layer. Although the latter becomes more accepted, direct experimental evidence is difficult to find in the literature. On the other hand, confusing information found in the literature showed that the ink transfer (or non-transfer) observations reported in many case studies correlate well with simple comparisons of works of adhesion, cohesion and spreading data of ink/FS, ink/plate and FS/plate obtained under the static condition. These results therefore imply that, in explaining the function of FS in preventing ink transfer to the non-image area, the ink/FS interfacial adhesion failure would be the dominant mechanism.
This study presents results obtained from some novel experiments using Teflon or ice as a substrate, the work of adhesion and cohesion were not able to predict ink transfer in some cases. Instead, the adhesion force and ink tack force may be more useful for the prediction of ink transfer to onto a substrate. This work also provided direct experimental evidence which shows that the splitting of the FS layer was involved in the prevention of ink-transfer to the non-image areas and the thickness of the FS layer is critical in allowing the splitting to occur.