Dirty Screens

[vaugh6288]

Hi there,

I have posted a few topics on similar issues but I wanted to reach out again with some more details.

We have been having issues on both our Heidelberg 5 color presses where when we print gradients or certain color builds and even in photographs we get "dirty" results. What I mean by that is there seems to be artifacts that affect the overall look of the printed image. Gradients are grainy instead of smooth. Specs appear in highlights in random places, etc. We've experimented with different papers (example: from matte to gloss same brand, from matte to matte different brands) to see if that eliminated any of the anomalies and that did not affect any real change. We've even experimented with FM screening but we still seem to be getting these results.

We use 175-200 line screen AM round dot screening using Prinergy using a standard screen angle: Cyan - 165, Magenta - 105, Yellow - 0, Black - 45. We use Heidelberg Perfect Plus blankets.

Has anyone else had these issues in some what similar circumstances? I'd certainly appreciate any input. We're always trying to improve!!

 

[gordo]

Hi there,

I have posted a few topics on similar issues but I wanted to reach out again with some more details.

We have been having issues on both our Heidelberg 5 color presses where when we print gradients or certain color builds and even in photographs we get "dirty" results. What I mean by that is there seems to be artifacts that affect the overall look of the printed image. Gradients are grainy instead of smooth. Specs appear in highlights in random places, etc. We've experimented with different papers (example: from matte to gloss same brand, from matte to matte different brands) to see if that eliminated any of the anomalies and that did not affect any real change. We've even experimented with FM screening but we still seem to be getting these results.

We use 175-200 line screen AM round dot screening using Prinergy using a standard screen angle: Cyan - 165, Magenta - 105, Yellow - 0, Black - 45. We use Heidelberg Perfect Plus blankets.

Has anyone else had these issues in some what similar circumstances? I'd certainly appreciate any input. We're always trying to improve!!

Are there specs in the non-print areas? Are they on the plates?
Do you have a (cheap) USB microscope like this:

That you can use to check the integrity of dots and ink lay down?

BTW Your Magenta should be at 115° not 105° (probably a typo)

The screen angles are standard, round dot is preferred for CtP, 175-200 is fine for AM so all's good there.
FM screening wouldn't make any difference - and it didn't.
Paper is unlikely to cause specs or graininess unless it's sandpaper.

Right now I'd speculate that it's either the plates not cleaning out completely in the processor (so some specs of coating remain in the grain and pick up ink and print) or it's an ink issue (poor ink transfer, poor ink pigment grind/dispersion).

Another less likely cause is loose dust/spray powder particles on the paper surface adhering to the blanket, take on ink and print as dark specks, or show up as voids in print. Dust deposits can occur during sheeting or trimming operations. Your microscope would show if that's the issue.

 

[vaugh6288]

Gordo,

I have also suspected it's something going on with the plate(s). But I wanted to confirm that my Prinergy settings do have Magenta @ 105 degrees (see attached).

We do not see specs or artifacts in the non-printed that I am aware of. I have a microscope but not a USB camera (going to be buying one of those tomorrow).

How do we measure or tell if the plates aren't fully cleaning out?

Thanks!!

 

[vaugh6288]

No Title

Sorry - photo attached

 

[gordo]

Gordo,

I have also suspected it's something going on with the plate(s). But I wanted to confirm that my Prinergy settings do have Magenta @ 105 degrees (see attached).

We do not see specs or artifacts in the non-printed that I am aware of. I have a microscope but not a USB camera (going to be buying one of those tomorrow).

How do we measure or tell if the plates aren't fully cleaning out?

Thanks!!

Magenta at 105° is very, very, odd. Typically Cyan occupies the 115° angle and Magenta the 75°. These are sometimes swapped. But 105° - weird. I would try and find out why Magenta was set there. In any case that would have no effect on speckles - moiré yes, speckles no.

The USB microscope is cheap and a great way to share images of dot formation for analysis.

if the plates aren't fully cleaning out you need to see if a speck in the presswork is also at a corresponding location on the plate.