Problems with wet trap and LED UV

[Alith7]

Morning all! Ready for another round of "what's wrong with the press that's they claim is prepress's fault"?? If you want to skip ahead to the question, jump down, I flagged it.

I have been running into some issues with wet trap causing color problems.
Basically, I've narrowed it down to with TAC being over 200% and heavy yellow, it's essentially impossible to get the color to print correctly.

What finally pegged the problem was a folder that we were printing today.
The original customer supplied files had a nasty 4-color breakdown of 88C - 62M - 55Y - 46K to make a dusky blueish green. No matter what we did on press, we could not come anywhere close to what the Epson / screen was showing.
I changed the art to 50C - 10M - 15Y - 82K, ran an Epson to check that it matched the original (it did), replated the job and hit the color in the first 100 sheets dead on.

In looking back at other jobs that I had problems hitting the target color, heavy ink densities (especially in the yellow) with a heavy wet trap seem to have the most problems.
another breakdown that was driving me nuts: 72C - 24M - 100Y - 8K
That one we ultimately switched back and printed conventional, which still gave me some problems, but we were able to hit the target.

I have proven that it's not my press profile well enough that they are at least not arguing about that for once! But I have no idea where to even start looking for what might be the problem / solution. I obviously can't recolor every job that goes through. sometimes that's not even an option.

-----> QUESTION
So my question is what could be causing problems with wet trap? Would substrate be an issue? Clay coating on the board stock? Too much / not enough water? Any help is much appreciated!

Thanks much for all your help!

 

[SteveSuffRIT]

Morning all! Ready for another round of "what's wrong with the press that's they claim is prepress's fault"?? If you want to skip ahead to the question, jump down, I flagged it.

I have been running into some issues with wet trap causing color problems.
Basically, I've narrowed it down to with TAC being over 200% and heavy yellow, it's essentially impossible to get the color to print correctly.

What finally pegged the problem was a folder that we were printing today.
The original customer supplied files had a nasty 4-color breakdown of 88C - 62M - 55Y - 46K to make a dusky blueish green. No matter what we did on press, we could not come anywhere close to what the Epson / screen was showing.
I changed the art to 50C - 10M - 15Y - 82K, ran an Epson to check that it matched the original (it did), replated the job and hit the color in the first 100 sheets dead on.

In looking back at other jobs that I had problems hitting the target color, heavy ink densities (especially in the yellow) with a heavy wet trap seem to have the most problems.
another breakdown that was driving me nuts: 72C - 24M - 100Y - 8K
That one we ultimately switched back and printed conventional, which still gave me some problems, but we were able to hit the target.

I have proven that it's not my press profile well enough that they are at least not arguing about that for once! But I have no idea where to even start looking for what might be the problem / solution. I obviously can't recolor every job that goes through. sometimes that's not even an option.

-----> QUESTION
So my question is what could be causing problems with wet trap? Would substrate be an issue? Clay coating on the board stock? Too much / not enough water? Any help is much appreciated!

Thanks much for all your help!

Please provide some basic information.
Where are UV LED lamps located? Between units, at delivery only?
What is you ink sequence/rotation/order? Note all units even if empty/blank.
Do you have a way of measuring UV output energy?

 

[Alith7]

Where are UV LED lamps located? Between units, at delivery only?
-- At delivery after all units & coater

What is you ink sequence/rotation/order? Note all units even if empty/blank.
-- K - C - M - Y - Empty - AQ Coater

Do you have a way of measuring UV output energy?
-- I don't think so, but I can ask if there's anything in the controls that they can check. what should I be looking for?

 

[Cornishpastythighs]

If your wet trapping lamp output is not a factor, that would be more about rub, scuff, setoff, blocking etc.
Things that can influence trap could be Ink Strength, Ink tack (tack sequence), Fountain solution (running too much or badly formulated), Stock absorbancy, running too much water in previous units, just to name a few issues that could effect how a wet ink wont stick to another wet ink

 

[gordo]

Piling on ;-)
If you were printing well before, has the pressroom made any changes (blankets, ink, etc) that they're not telling you about?
Do you have a golden benchmark sheet (when everything was running right) to compare your current trap to?
What are your RGB trap values?
What are your target SIDs? What are the SIDs of your problem presswork?

 

[Alith7]

so many questions!
not ignoring you, but juggling too much at once and sadly, this is one of the least important fires to put out. ugh!
I will get back to you with answers next week as my main pressman is out today.

Everyone have a happy and safe 4th of July (if you're in the US), otherwise have a great weekend!

 

[Alois Senefelder]

Hello Alith7

I'm posting 2 PDFs that I hope will help you. In my opinion many of the posts regarding problems you encounter, in the end, ALL relate to On Press Problems that the Press crew don't understand or unable to rectify, so passing the problem back to Pre-press.

1) I would also have you Ink Supplier conduct a "Press Audit"

2) Using UV and Conventional Inks - alternate is not a good combination on the same press.

Regards, Alois