UV Printing — Horse of a Different Color
As for the UV learning curve, it's ongoing, reports Marrs. "We have to recalibrate our plate- setter to accommodate the different curves for UV, and cut plate curves back to allow for UV dot gain. On-press, we use a different fountain solution, different washup solution, different blankets. Blankets often can be reused, but the ink-water balance is critical; you don't have much latitude."
Look Before You Leap
Can any Tom, Dick or Harriet set up a UV press and begin printing money? Not quite. In fact, while the printers with whom we spoke were united in their enthusiasm for the UV process, they also mentioned a variety of special considerations involved in the decision to "go UV." Forewarned is forearmed:
o PREPRESS. Good communication between the prepress department and the pressroom is essential. Not only must screening curves be adjusted to account for the additional dot gain that occurs with UV inks, but jobs also must be proofed on the actual substrates on which they will be printed.
o ON-PRESS. UV presses typically operate within much tighter tolerances with respect to ink-water balance and exposure to UV radiation. Press blankets can become embossed, shortening their useful lives. Roller settings must be precise. Heat that is a byproduct of exposing substrates to ultraviolet energy is a continual source of concern. Too-high temperatures will produce distortion in paper and plastic that can cause a job to go off-register.
To avoid these problems, practitioners suggest acquiring a press that is capable of putting all of the colors down at once. And that's not all. Undercure a job, and it won't dry properly. Overcure it, and the substrate becomes brittle. Some plastic substrates can become discolored when exposed to excessive heat. If the surface tension of a plastic substrate is lower than the surface tension of the ink, the ink won't stick.