Colour variation in the real world...

[Disappointed]

Hi all, I'm looking for information from printers 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,
Dave

 

[Cornishpastythighs]

A couple of points, you say your press is temperature controled but have you actually tracked the temperature changes of rollers and ink during the runs with an IR Thermometer.
Make sure your press operators are not 'over controlling' the process, anyone who has ever observed a press operator will see that they pull a sheet and make an adjustment, pull a sheet make another adjustment and so on.
We can exclude dampening as you have said it's waterless

 

[Disappointed]

Yes, we have tracked the temps and while they do vary, plate and blanket cylinders especially, the TVI will change on a fresh start up, its like every single job is slightly different.

I'm pretty confident that our operator won't bother doing anything more than absolutely neccessary

Dave

 

[gebalazs]

Same experience here

Same experience here

Hi!

It's good to know that I'm not alone with this issue. I have the same experience but to be honest the papers I measured were not exactly the same - only very similar. Hence I was surprised about the dot gain differences. The operators swore that the printing pressure is set correctly (according to paper thickness) and they haven't changed the blanket tension and everything is super good. And still the difference is there. I couldn't figure out yet what the hell is it then.
We're using Heidelberg SM with 8 units.

By the way ...
Do you see the TVI difference at the same density values?

Balázs

 

[Disappointed]

Hi!

By the way ...
Do you see the TVI difference at the same density values?

Balázs

Yes, it just seems to vary all the time. We can usually nail the SID's to within +/- 0.1d or better but still the TVI varies, i have been told that our control of SID is very tight, it does give the operator a headache sometimes!

Maybe technology and analysis is outstripping offset printing's ability to perform and this is all just normal????


Dave

 

[Deleted member 16349]

Yes, it just seems to vary all the time. We can usually nail the SID's to within +/- 0.1d or better but still the TVI varies, i have been told that our control of SID is very tight, it does give the operator a headache sometimes!

Maybe technology and analysis is outstripping offset printing's ability to perform and this is all just normal????


Dave

An SID variation of +/- 0.1 is not tight at all. It is a big variation in ink film thickness which can lead to variations in TVI. A variation of +/- 0.01 would be very tight.

 

[Disappointed]

An SID variation of +/- 0.1 is not tight at all. It is a big variation in ink film thickness which can lead to variations in TVI. A variation of +/- 0.01 would be very tight.

Sorry, my fault, after checking through my reams of notes here it turns out we are running to +/-0.05 which i feel is pretty tight. Yes 0.1d is pretty slack.
The press default setting is 0.1d variation.

Dave

 

[gebalazs]

Hi again,

Are the printing plates correct? I mean if you image a linear plate is 5% really 5% in every case?

I know it's imaged inside the press so I don't know if there's a possibility to check it.

Br,
Balázs

 

[Disappointed]

Hi, we cant actually measure the plate as it needs special equipment.

We can get the press to a linear state and this is part of the setup procedure so it 'can' do 5% = 5% for at least that set of plates. From then on the only readings we can get are from the finished jobs which should reflect the ISO/fogra39 curve data for TVI gains. This is the point where we are seeing the variations.

We cant therefore tell if the plates are varying or the press is varying im afraid. Its a downside of the DI process in my opinion.

Dave

 

[rich apollo]

I hear that waterless is EXTREMELY temperature sensitive.

 

[Disappointed]

I hear that waterless is EXTREMELY temperature sensitive.

It certainly is but the rollers are controlled and the room is fully airconditioned, its all we can do.

 

[Lukas Engqvist]

DI press and waterless? What plates are you using? We don't have a DI press but thinking abou the process makes me wonder, is it thermal plates? If you have no chemistry/low chemistry you will need to wash away non-printing areas? It is hard to know if it is the "imaging" or "developing" or "printing" phase that is unstable (or all three)
Have you mapped a curve to see how dot gain varies with density? Some target densities are more stable than others (within the ISO bracket ofcourse).
Paper of same brand can sill vary, even variations between sida a and b are not uncommon.
On some papers we may get a freak dotgain and then the printer will just lower the density for an over all balance… this is why we need intelegent printer and not "blind" printing by SID numbers. The standard is to give us a target so that we can get consistent output, it is the output that is important rather than the numbers.

 

[Disappointed]

The plates are from the m/c manufacturer and it is chemical free. Developing is mechanical - the image areas are rubbed away and the waste is vacuumed off then auto-wiped with a moist cloth device. Personally i feel that the plate is the weak spot in this system.

It would work ok if used manually by a very competent operator by varying the SID all day but this is not what ISO is about. The ISO framework relies on all figures being within a certain range to give a matched output - this is where we need to be. It does work and has done in the past. If both proof and press sheet pass the test blind, when introduced to each other the output WILL match, regardless of machine or system.

Its a great idea as it means that any printer anywhere in the world will be able to match your proof just by passing the SID/TVI criteria required by the ISO system.

The trouble we have is that the press is unstable somewhere and we cant get a fix on TVI values for more than a few jobs.