The characteristics of flexo plate media often make it impossible to develop the smallest AM highlight dots on plate. The effective minimum dot value that can be achieved will vary, depending on media type, thickness, line frequency, UV exposures, and plate washout process. It is impossible to properly reproduce tones below the minimum dot value. The point at which this loss of tone reproduction occurs is often called the flexo break.
Left: What flexo printers would like to print, full dynamic range; right: How AM flexo actually prints, with flexo break
The traditional strategy for dealing with the flexo break was to use a calibration (bump) curve to move the 1% value up to the break point. Strategies for creating bump curves, and specifics on how to create bump curves for use in Prinergy and Prinergy Evo, are described in Creating bump curves and tone reproduction curves.
After the bump curve is applied, images will be reproduced without a flexo break. However, they will suffer from a loss of dynamic range, and a lot of detail carried in the highlight regions will not be reproduced. The other problem with using a bump curve is that it is impossible to reproduce a lightly-feathered gradient edge. With the heavy gain characteristic of flexo, a minimum dot will commonly reproduce at 10–12% or darker. This means that at a gradient, measured tone values will go directly from 0% (substrate) to 10–12% on the printed piece, which gives a very hard edge to any gradient.
You may want to be able to print drop shadows and gradients that fade off imperceptibly to 0%, so that there is no tone jump visible at the edge. Maxtone can make this possible. Often, with thin plates on a narrow-web press, it is possible to use Maxtone to fade down to 0%, with print areas measuring as little as 1% after printing. With wide-web applications, or thick plate applications like direct-print corrugated, Maxtone may be able to reduce the printed highlight values to half of the previous AM minimum dot value. How far Maxtone is able to improve the situation will be determined through fingerprinting.