25% Dot Gain on Press Sheet

[jsnkiefer]

Hello all,
I've output the magenta plate and the 40% patch reads 38.7% (close enough).
The same patch on the press sheet reads 65%. I know a 100# gloss sheet
should not have 25% press gain, but the pressman insist they're running the correct density and it IS NOT THEM (big suprise, right?).

Any ideas on what is going on is GREATLY appreciated.

You out there Gordo?

 

[Lukas Engqvist]

25% on gloss? What process are you talking about? and what screening? I think it should be more like 13% @40%

 

[jsnkiefer]

he is running 4/C process on a Heidelberg SM 74 @ 150 line screen.
Thanks, Lukas.

 

[Ti7]

Only the magenta unit is gaining? Are the other colors within tolerance?

 

[Bob Peterson]

Take a look at the dots on the color bar. Is there any doubling or slurring? This will cause excessive dot gain.

 

[jsnkiefer]

Only the magenta unit is gaining? Are the other colors within tolerance?

Sorry Ti7, ALL colors are gaining C+17, M+25, Y+25, K+15.

 

[jsnkiefer]

Take a look at the dots on the color bar. Is there any doubling or slurring? This will cause excessive dot gain.

Not that I can notice, they look pretty clean.

 

[Ti7]

Are the blankets loose? Are they over packed? Is the stock distorted (wavy) or not square on the gripper edge? try increasing the gripper bite by maxing out the head stops to the most foward position to gain more grip.

 

[Lukas Engqvist]

Do you have slurr marks on yourtest stripp? (Concentric circles and/or parallell lines horisontally and vertically)

 

[Bob Peterson]

Has the pressman added tack reducer to the ink? If so, he may have over done it.

 

[jsnkiefer]

Are the blankets loose? Are they over packed? Is the stock distorted (wavy) or not square on the gripper edge? try increasing the gripper bite by maxing out the head stops to the most foward position to gain more grip.

They tell me the blankets aren't loose and the packing is correct. Stock appears okay.

I'll ask the pressmen to make sure it's square and increase gripper bite and recheck (I'm in prepress).

 

[jsnkiefer]

Do you have slurr marks on yourtest stripp? (Concentric circles and/or parallell lines horisontally and vertically)

I don't see any, Lukas.

 

[Kramer68]

Is there a zone control cooler for the units, is it running too hot.

 

[Lukas Engqvist]

slurr markes are control marks that you place there, for similar reason as registration marks.

 

[jsnkiefer]

slurr markes are control marks that you place there, for similar reason as registration marks.

sorry, I meant that I didn't see any slurring (the marks are there).

 

[gordo]

sorry, I meant that I didn't see any slurring (the marks are there).

You don't actually need a specific target in the color bar to check for doubling or slur - every printed element on the sheet will show if there's a problem.
What would help is if you had a microscope that can take pictures. They cost much less than a $100 and can help you as well as people on the forum identify if there's a problem with doubling, slur, ink transfer, etc. Here's an example of doubling in the black printer which would show up as excessive dot gain:

The only things I could add to the great suggestions posted so far: are your temperature controls working correctly? Is it possible that the wrong press curve got applied?

You seem to have the same problem with the Yellow.

Is this a live production job? Do you have a press sheet from the same press from a previous run that you can compare, by measuring and examining under a loupe, with the sheet that you're running now? To see what might have changed.

best, gordo

 

[David Milisock]

Hello all,
I've output the magenta plate and the 40% patch reads 38.7% (close enough).
The same patch on the press sheet reads 65%. I know a 100# gloss sheet
should not have 25% press gain, but the pressman insist they're running the correct density and it IS NOT THEM (big suprise, right?).

Any ideas on what is going on is GREATLY appreciated.

You out there Gordo?

Is the ink density being run to the ink manufacturers specification?

Are all other press specifications within tolerance?

 

[SilvaJr]

Is the plate really flat (uncalibrated), or are you applying a curve in your plateroom for some unknown reason?

 

[Bondi_dan]

I humbly suggest that it is your roller nip settings.

Probably both ink and fountain are not at manufacturer's specs.

Regards,

 

[jsnkiefer]

You don't actually need a specific target in the color bar to check for doubling or slur - every printed element on the sheet will show if there's a problem.
What would help is if you had a microscope that can take pictures. They cost much less than a $100 and can help you as well as people on the forum identify if there's a problem with doubling, slur, ink transfer, etc. Here's an example of doubling in the black printer which would show up as excessive dot gain:

The only things I could add to the great suggestions posted so far: are your temperature controls working correctly? Is it possible that the wrong press curve got applied?

You seem to have the same problem with the Yellow.

Is this a live production job? Do you have a press sheet from the same press from a previous run that you can compare, by measuring and examining under a loupe, with the sheet that you're running now? To see what might have changed.

best, gordo

No this isn't a production job. They're running a color calibration chart for me to
create color profiles. The plates have been output without a press curve applied
and I've checked the color bar on the plate to make sure the patches were true
before they started running. They're running to the ink manufacturer's densities,
but when I saw the sheet there was an obvious red push. I then checked the color
bars on the printed sheet and read C57%,M65%,Y65%,K55% on the 40%patches.