Emulsification rate of sheet-fed offset ink and its effect on printed quality

This thesis is a study of Surland\u27s Emulsification Method, and is intended to demonstrate the effect of change in emulsification rate curve with different types of fountain solution whose surface tension was varied. The surface tension of a fountain solution can be changed by the addition of isopropyl alcohol. Two inks were modified to produce the same tack reading but a different emulsification capacity. Using the Surland method the two inks and two fountain solutions generate four different emulsification rate curves and these four curves are tested for their effect on printed quality. The printing performance of an ink is judged by the ease with which an ink can obtain ink-water balance as well as the degree of freedom from printing problems such as catching up and plate scumming. The printed sheets are sampled and the data is analyzed statistically using solid ink density and dot gain as response variables. The RIT Symmetrical Scale was included in the printing form design to facilitate solid ink density measurement and dot gain calculation. Solid ink density and dot gain variations are calculated within each printing run. The addition of isopropul alcohol to a dampening solution not only reduces its surface tension and increase its wettability but it also suppresses an ink\u27s continuous emulsification tendency. Ink and water balance is easily controlled when a printing ink is able to reach a state of equilibrim with dampening solution. On the basis of observation during the on press printing run it was found that a high percentage of isopropyl alcohol in a dampening solution can dissolve the blue toner from the black ink and requires an increase of ink feed to obtain the desired optical density. This study indicates the tendency of plate catching up can be associated with emulsification rate curves. The Pb type of emulsification rate curve can be so modified that press run will encounter fewer problems. Density variation within a press run is then more easily controlled