Colour variation in the real world...

Hi all, I’m looking for information from people running to ISO12647 standards on machines like Heidelberg SM’s etc with full integration of colour control and so on.

We are running an inplant print room with a waterless DI press, and using PressSign by Bodoni software to check & verify a match to the ISO standard. The proofing is also fully ISO compatible.

I am seeing wide variations in TVI beween jobs and also during a longer run. The standards call for a +/- 4% TVI variation and it goes outside this region regularly.

What i am trying to ascertain is, is this behaviour typical of printing in general or a fault on our press/system?? Although we have been brinting for over 20 years now, it is only recently that we have been able to gain this much insight into the process due to advances in press technology and measurement systems.

How close do other printers attempt to match a proof?

We need to repeatedly hit the same output as we maintain a vast library of printed matter and colour control is vital. This was our main reason for going to a DI press & ISO as ISO is a good system to obtain this goal. We have found that a +/- 2% TVI variation is noiticeable to the human eye so the swings we are seeing are very apparent when comparing to a proof.

We only ever use one inkset and very few papertypes so variations are minimalised here. Press speed does not vary from one job to another either. Once set, the SID levels are not altered from one job to the next. The press is temperature controlled and also running in a controlled environment. Run lengths vary from 500 to 20,000, short runs are run at 6000/hr and longer runs at 8000/hr

Are we trying to achieve the impossible or can this be done in the real world?

Thanks in advance,

No takers???

Assuming you don’t print in a controlled climate I’d say that if you are like us I’d suggest the biggest factor in contributing to variation in dot gain would probably be temperature and humidity. Also you need to stay on top of your CTP and ensure that you are always applying your correction curves to linearised plates.