The conventional ink does not get thoroughly dried when the sheets arrive at the delivery pile in sheet-fed offset printing. Avoidance of smearing, offsetting (transferring ink onto sheet), and blocking in the pile (sheets piled upon each other sticking to each other) yet remain the main requisites in sheet-fed offset printing.
Using powder ink than conventional ink solves the immediate problems but entails a variety of other problems, such as, soiling of the press, defects related to quality in the printing area i.e. reduced gloss, and problems with finishing.
Since there is a layer of powder in between the sheets, there is no contact of wet ink surface with the following sheet. The delivered powder is actually a small proportion of what amount was sent to the sheet. If the press is running fast, then more powdered ink does not reach the sheet and the remaining of the powder gets piled up in the delivery area i.e. called Soiling of ink. If the offset print is long, for example an eight-color press for perfecting and straight printing, then the ink has to be fresh for longer time so that it does not start to build-up on the impressions cylinders, and it aggravates the soiling in the delivery area. As a consequence, powdering has to be really intense on long, fast-running sheet-fed press. There are powder extraction systems in the delivery area which actually remove most of the soiling but yet there remains some residue, this makes it important to clean the work area, though less often.