Low dot gain & poor trap values?

[tmiller_iluvprinting]

Our presses are G7 calibrated. Our CtP plate setter is calibrated and our plates are measured on a regular basis to confirm calibration. R/O system is in place for our incoming water supply. We run Komori and Heidelberg presses, which use a different series fount from the same manufacturer. We use the same ink series from the same manufacturer on all presses. Presses are correctly packed & one of our presses uses a blanket from a different manufacturer. We have been experiencing low dot gain on all presses and poor cyan/magenta trap in blue overprints(58-62%, sometimes lower.) Our dot gains are sometimes 8-10% lower than the dot gains that we documented during our G7 calibration/verification runs. The problem can be intermittent, because at times we do not have issues, and our press-proof match is good. I have measured plates before and after runs and the plates are holding well. We have been battling these issues for almost a year and we are stumped. Since the one common denominator is the ink we use, are we safe to assume that the issue may be ink related?
Best regards,
Todd

 

[QualityPrint]

I have seen this happen from substrate to substrate as well. You can rule out the ink idea by taking a can of any color and put about a pound in the fountain. Record that dotgain and put the rest of the can on the shelf marked "batch sample" or something. When you see the gains shift washup the unit and dig out the ink in the fountain and grab your batch sample and put in into the cleaned fountain. If the gains go back to normal then you know it is the ink. The cyan/magenta trap is the hardest to maintain because the inks are so close together. We have profiled using many different papers and have seen that trap shift dramatically from paper to paper.

So in this case I would focus on ink and paper at first.

 

[Lukas Engqvist]

The trap values can have nothing to do with Ctp. The problem is on the press (or possibly paper as QualityPrint suggests). Have you done a fount ink drop test? (since you also mention the dot gain)

 

[tmiller_iluvprinting]

Lukas,
Please explain the 'fount ink drop' test. Thank you.
-Todd

 

[gordo]

I wasn't going to comment, but....

The original post has virtually no relevant information that is useful in addressing the described problem.
There is a listing of components of the print production process, however there is no information reflecting the most important factor in printing success - manufacturing process control, or more specifically statistical process control.

gordo

 

[tmiller_iluvprinting]

Gordo,
You are correct, the light just turned on! Thank you.
Regards,
Todd

 

[bbtommyd]

Over simplification perhaps, but I would check blanket packing first. If you have records (SPC) from previous jobs that didn't have the issue, look there first.