Uncoated papers can produce unique effects thanks to their high volume, weight, and opacity. Printing them successfully, however, requires some special attention to detail. For best results in image modulation, Heidelberg recommends using compressible blankets with hard packing and setting a higher contact pressure than with coated papers.
Uncoated papers printed with inks that dry oxidatively should have a pH value of about 5.5, since acidic stocks can lengthen drying times—as much as four times longer than in jobs with coated papers. With this in mind, avoid stacking uncoated sheets so high that they begin to take deposits from darker motifs or larger ink surfaces on the next page. Because of dust accumulation, the press (including inking units and blankets) should be cleaned regularly.
Heidelberg presses offer a multitude of solutions to meet the challenge of running with uncoated papers. For example, a suction brush inserted before the first printing unit frees the paper from lint to the greatest extent possible. Highly automated suction heads transport even high-volume and heavy uncoated papers safely through the press. Special inking and dampening units, UV and infrared drying systems, and many other features help ensure excellent results with uncoated papers.