We don’t see this defined parabolic shape in the set of data from 800RPM because the ink doesn’t get worked enough to reach it’s peak adhesiveness therefore has not time to decline. If we had let the machine run for longer than the specified 10minutes, the ink’s tack would have, at some point, began to decline.
Web offset inks usually start off at a low tack since the ink film is thicker and contains more oil from the solvent. As the film gets worked, the rollers will even out the thickness and the solvent evaporates. As the ink film is getting thinned and oil evaporates the tack will continue to rise until it reaches a maximum. After this point the ink tack begins to gradually decrease.
Printablity:
Controlling ink tack on press is a key quality control measure in most press shops. If ink tack is not meeting the requirements that are needed for a specific job, then this will directly skew the image reproduction quality. Not only does ink tack affect the surface of the paper, but in order for inks to adhere to each other, inks must be printed in specified order (high to low tack).
Runnability:
Ink tack has to be controlled and maintained at specific levels in order for the ink to adhere properly not only to each other but to the paper as well. If tack is too low, misting will occur (ink becomes airbourne, spewing off the rollers) , and if too high then picking will occur (fibers from the paper are pulled off the substrate and get lodged in the press and on rollers).
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