From all outward appearances, waterless print production looks just like conventional wet offset—the press is the same, and the inks look identical and come in similar packaging and all the same colors. It would be hard to tell the difference between a running wet-offset press and a running waterless press if you were standing, say, 10 feet away.
To understand the differences between the two print processes, it's helpful to think of waterless as a different operating system for the press. Just as you would use different commands for a Mac- or PC-based operating system, waterless operates differently and has different controls than wet offset.
Wet offset’s two-fluid system
In wet-offset printing, the press uses two different fluid-delivery systems—one for ink and one for water or fountain mix. The wet-offset process requires that the plate be wetted with fountain mix in order to properly resist ink. Because of this, much of the press operator's focus is on achieving and maintaining the proper balance between fountain mix delivered to the plate and ink volume delivered to the plate.
Wet offset delivers optimal print quality when ink and water are properly balanced. Too much water and halftones will print weak or mottled; solids can appear streaky. Too little water and the plate will eventually fail to resist ink in the background, and scumming or tinting will occur. In short, the fountain mix controls how efficiently the ink transfers to the plate.
Single fluid printing with waterless
In waterless printing, the ink-resistant property is built into the plate. This means there is only one fluid to work with—just ink. This makes waterless simpler to control than wet offset. There is, however, one very important control that requires the press operator's attention in waterless—the temperature of the press rollers and cylinders.
Similar to the function of proper ink/water balance in wet offset, press temperature controls the transfer of ink. If temperature is too cold, ink will become stiff, with lower flow and transfer properties. Reduced ink transfer will appear as mottled or grainy solids. If the ink becomes too stiff, some picking or piling may also appear.
As temperatures increases, the ink will become more fluid, transferring more readily—too hot and the ink will become too fluid, eventually reaching a point where the ink-resistant properties of the plate can no longer hold the ink off. The result looks very similar to scumming or toning—ink will appear in the background as a fine tint in some or all colors.
Maintaining press temperature
Press temperature control systems are normally thermostatically controlled. They can be set to maintain the press within an upper and lower limit for temperature. Most waterless inks have an operating window of roughly 75°F–95°F (24°C–35°C), and press temperature control systems can easily maintain within this range.
So, the most important key in getting top results with waterless is learning to think differently about how the operating system works. With waterless, it is all about managing the flow of ink by keeping the press in the proper temperature range.