The examples shown previously have all shown a Maxtone transition that fades out to 0%. This is generally how Maxtone is implemented in narrow-web applications. Narrow-web applications tend to use thinner plates, and impression can be more tightly controlled across the surface of the plate, because of the small size of the press and the common use of bearer bars. In these situations it is relatively easy to prevent over impression of the extreme highlights that would result in scum dot.
However, in wide-web applications for flexible packaging, or for direct-print corrugated, there are two factors which can make it difficult to have transitions fade completely to 0%, even when Maxtone is being used.
The first problem is that these applications tend to use thicker plates and lower line screen frequencies. In the case of direct-print corrugated, very thick plates and very low line screens make it very difficult for the smallest dots to develop on a plate and rise to full relief height. The lower the line frequency, the further the individual dots are separated from each other. Maxtone dots can be quite separated from their nearest neighbors, and the lower overall amounts of UV energy in highlight areas and lack of shoulder linking of dots makes it difficult to get these dots to develop to the point where they will print properly without producing scum dot.
For this reason, for wide web and direct-print corrugated applications, you should only apply Maxtone so that a maximum of 50% of the dots are removed at the extreme highlight. This sounds complicated, but you could consider it in this way: if the minimum exposure value on a corrugated plate is determined to be 12%, you would apply Maxtone at this size, but set a bump curve at 6%, and set the Minimum Dot Size setting to clip out all tones below 6%.
1%–12% step wedge output, showing Maxtone set for 85-line direct-print corrugated, based on a 12% minimum dot, with no bump curve or minimum dot cut-off value set
Note: This is not recommended, because dots below approximately 6% will reproduce as scum dot. (Note that this setup may be fine if using thin plates on a narrow-web press.)
Sample run with same Maxtone settings, but with the addition of a bump curve that bumps the 1% to 6%
Note: Maxtone is removing approximately 50% of the dots at 6%, which means that Maxtone at the minimum value will be well-supported when printing on a corrugated press.
Harmony bump curve further modified
Note: The bump remains the same, but the 3% value has also been pushed up to approximately 12%. This compresses Maxtone to only the first three steps in the gradient to minimize visual impact.
A bump curve is used in this application, but with Maxtone a minimum tonal value of half that is possible when using full AM. This use of Maxtone can open up 50% more highlight tones than were previously available and still ensure that there is enough support to prevent the lightest highlight tones from over-impressing and printing as scum dot. Again, you can consider using a compression curve to limit Maxtone to only the first few steps of the tonal scale. In the example above, you could consider bumping the 1% value to 6%, and bumping the 3% value up to 13%, which will effectively limit Maxtone to the nominal 1%, 2%, and 3% steps, producing a subtle feathering.
At this point, you can consider the Maxtone screen settings optimized. However, in order to achieve the best results on plate, you must understand how HyperFlex works in conjunction with Maxtone. HyperFlex is an enabling technology for Maxtone that allows you to achieve superior results over competitive hybrid flexo screening.