Highlight dot dropoff poly

[Polyprintgirl]

Hi, wondering if anyone has any ideas how to prevent highlight dot "dropoff". We are running 1.5 mil polyethylene with .067" photopolymer plates w/.020" backing tape, with 120L screens.

One jpg shows the dropoff on the printed poly, the other file shows the dgc applied to the job. We'd bumped the highlights initially because they had been dropping out on press, but now we're wondering if we need to run a separate dgc for gradations.

Thanks in advance for any comments.

 

[WI-Flexo]

Actually for 120LS the print looks pretty good. Are you trying to let the gradient go to 0% with a smoother transition? Depending on what you are trying to achieve your best options are probably to carry the gradient at your minimum dot through the entire area or look into a samba style dot (AM screen with FM highlight). May be able to offer more ideas based on what you want to see.

 

[dgerharter]

In my limited experience, you can't totally eliminate highlight drop off - but you can minimize the effects. First you should talk with your plate and tape vendors and run a few tests to see which plate and tape combination (there are many choices of each) give you the best compromise between resistance to dot gain and highlight hold, while keeping the ability to print decent solids. Generally speaking, to print higher ruling process color you would choose a harder plate and a softer tape - while solids usually require a softer plate and firmer tape.
Once you have settled on a plate/tape combination, run some gradient tests (uncompensated) at different screen rulings to see which ruling(s) give the best overall tone range. Then you can calibrate your cutback/bump curve to give you the dot gain you want. Then you can determine where your highlights drop off and use a Samba or other hybrid screen technology. These screen sets change the min dot to what you can actually print, and convert tones lighter than that to either an FM pattern or selectively removes dots from the AM pattern to reduce the tone.
David

 

[Polyprintgirl]

Thanks Wi-Flexo and dgerharter for your comments. We did want to try to achieve a smoother transition in the gradient if we could. We don't have the Samba option, yet. Sometimes we'll run the screens separately from the solids just so we can hold the screens open, and we use different tape combinations in certain ways to help runs solids or screens better. We're still working on calibrating the press at this time, the cutback curve was applied based on our initial dot gain numbers. Maybe we will make a gradient dgc that has the highlight bump removed. Thanks again.