Ink order for 4 colour process...

[Disappointed]

The setup - B3 Waterless Offset machine.

Can anyone tell me why I should not alter my ink order from K-C-M-Y to Y-M-C-K??

What are the possible side effects of doing so?

Is there a specific reason for running K-C-M-Y?


Many thanks


Dave

 

[Deleted member 16349]

The setup - B3 Waterless Offset machine.

Can anyone tell me why I should not alter my ink order from K-C-M-Y to Y-M-C-K??

What are the possible side effects of doing so?

Is there a specific reason for running K-C-M-Y?


Many thanks


Dave

The overprints will be affected and you would have to redo your colour management to account for the difference. As I understand it, it would not be compatible with existing standards.

 

[Disappointed]

Ok, thanks, just found this link too...

The Print Guide: Ink Sequence - 4/C process & beyond

 

[Disappointed]

Ok, moving on, what can cause this problem...

Purple job, high level of magenta & cyan, minimal yellow, no black.

Suffered serious yellow contamination resulting in wash up and fresh ink in duct after the run.

Any ideas?

 

[Deleted member 16349]

Ok, moving on, what can cause this problem...

Purple job, high level of magenta & cyan, minimal yellow, no black.

Suffered serious yellow contamination resulting in wash up and fresh ink in duct after the run.

Any ideas?

One question of interest would be whether you are backtrapping the m & c, coming up into the roller train via the yellow image areas or from the yellow non image areas of the plate.

 

[D Ink Man]

Ok, moving on, what can cause this problem...

Purple job, high level of magenta & cyan, minimal yellow, no black.

Suffered serious yellow contamination resulting in wash up and fresh ink in duct after the run.

Any ideas?

Yellow is TOO STRONG, definitely if running in a K-C-M-Y rotation. Is this the sequence sir?

D

 

[Disappointed]

One question of interest would be whether you are backtrapping the m & c, coming up into the roller train via the yellow image areas or from the yellow non image areas of the plate.

It will be the non image areas, small-format suffered badly at each end of the duct.

 

[Disappointed]

Yellow is TOO STRONG, definitely if running in a K-C-M-Y rotation. Is this the sequence sir?

D

Yes kcmy was the order, but it was doing it in the non-sheet area of the job - at each end of the duct on small format work.

 

[D Ink Man]

Add transparent white or overprint Varnish, at a ratio of 1:1. Rerun the same exact print form.

Then proceed to Print Planet and report the results. I promise, you will thank me someday. After the runs.

D Ink Man

 

[jason3791]

What is the ink film thickness on the fountain roller outside of the sheet (at the ends of the fountain), where I assume the keys are 100% closed? You mentioned that this is where the contamination is most present in the fountain.

 

[Disappointed]

Add transparent white or overprint Varnish, at a ratio of 1:1. Rerun the same exact print form.

Then proceed to Print Planet and report the results. I promise, you will thank me someday. After the runs.

D Ink Man

But a 50:50 mix would surely be nearly transparent? It would wreck our ISO ability and require a recalibration on that colour as well. I am not in a position to do a non-job test at present but will bear this idea in mind.

Could you elaborate your idea with a theory or reason please.

 

[Disappointed]

What is the ink film thickness on the fountain roller outside of the sheet (at the ends of the fountain), where I assume the keys are 100% closed? You mentioned that this is where the contamination is most present in the fountain.

The ink film would be nearly zero in the closed areas, we never run 100% closed as there is always a colour bar on the sheet and indeed the ducts can not be set to 100% closure.

 

[jason3791]

When I say closed I am speaking in terms of the console reading. Understanding that the zero set in the fountain is never physically closed what would the "zero set" film thickness on the fountain be? I agree with your thoughts on the 50:50 mix and the effects it would have on your current ISO ability. Increasing your film thickness by two fold would surely have drastic effect on your dot gain alone. This may however fix your problem.... but in my opinion possibly by doing the wrong thing. I believe this may have nothing to do with your ink. In fact I am almost positive if the notable contamination is appearing at the ends of the duct where there is no printable sheet. Think of reasons that your ink is travelling back up your rollers and ducting back to the fountain.

 

[Disappointed]

In fact I am almost positive if the notable contamination is appearing at the ends of the duct where there is no printable sheet. Think of reasons that your ink is travelling back up your rollers and ducting back to the fountain.

This is my main concern, where is the magenta and cyan ink coming from if there is no image on the plates and no paper in that area? There is a transport somewhere in the system but i can't figure out what yet. I can see that a high-tack yellow could drag back the magenta and cyan when running heavy coverage, but on a non-image job, the only thing that connects paper to ink rollers is the yellow plate so there must be a film coming back up on via the yellow plate non-image areas?

The console reading would be down at around 1.5 - 2 for a colour bar, normal print would be around 10-30, zero level is set with just a visible film on the duct roller, never scraping down to dry metal.

 

[jason3791]

So ask yourself this question again... what would cause ink to travel up the print unit back to the fountain? The continuous flow of ink down the unit relies on the constant removal of ink from the forms by the sheet. Input should be close to output, hence the ink flows down based on the laws of ink splitting. The ink cannot travel up the unit providing the film is thicker on the roller above it at all times. If you oscillate a heavier film of ink into the outer edges of the print unit there are two things happening. The first is that there is no output to a sheet because there is no sheet, so the ink has no where to exit. The second is that your ink film in this area all the way to the top of the unit is less than what is now sitting on the form roller through oscillation. At this point we have a roller above the form (non print area) that has less ink on it and where does the ink go? Based on the principles of ink splitting, right back up to the fountain (especially if you run closed keys or extremely small ink films outside of the sheet edge). Reducing the tack of the ink by adding trans white or whatever other magic component you choose will certainly help for reasons we all know about. It will certainly not stop the ink returning to the fountain, you just might not notice because it wont be a different colour. This is obviously more of an issue on a press that runs water because it is returning your "fountain solution" to the "fountain" as well. In fact on a brand new Komori you can close all the keys during a make-ready and purposely return ink to the fountain using this principle to achieve a lower density without using sheets! What colour is your yellow after doing this a few times?

Next time you run the job try opening the keys where there is only a colour bar (and possibly outside of the sheet area). If there is no image in this area, there is no need to worry if density on the colour bar is too high. Lock these keys out if you have closed loop colour control so they do not close back up. You will have to experiment..... you need just enough ink out there to stop the upward flow of ink.

Hope this makes sense. If not I can at least say I tried Good luck whichever options you try!

 

[Disappointed]

Thanks Jason,

But wouldn't opening the keys on non-image areas result in ink piling on the rollers and then when the keys shut for the next job, this ink would theoretically flood back to the duct?

Bear in mind that we never had this problem with our other ink set but we cannot use that one any more.

 

[Lukew]

I do not run with the outside image area/sheet size ink duct keys shut off anymore. Having them open reduces back tracking on the outer edge of the duct substantially.
Particular fountain solution & inks help reduce the issue also.

 

[Disappointed]

I do not run with the outside image area/sheet size ink duct keys shut off anymore. Having them open reduces back tracking on the outer edge of the duct substantially.
Particular fountain solution & inks help reduce the issue also.

What sort of opening volume would you use, this is a new idea to me, only been printing 30 years so i'm still a trainee

Are we saying that the ink does not keep building up on the roller ends (as i thought) but rather reaches a stable point that is simply higher than it would be with the duct closed down??

 

[BeauchampT]

My shop has a four colour MAN Lithoman...we have a few odd jobs that are two colour (don't ask....). Anyhow, we run black cyan, with magenta and yellow as dummy plates. For about a year, we were using a plate that was burnt as a non-image area plate 100% (all anodized aluminum showing). On a Lithoman, you can unclutch the ink train and just run the water form on plate. In theory, perfect....you apply water to entire plate, plate cools blanket, etc, etc.

Reality?? We had cyan ink coating our water forms in magenta and yellow by end of job (about 200,000 impresions). Reason: grain on the plate; we started using a plate that was bent back side out (the untreated aluminum is now our print surface). Problem never occured again. So, Disappointed, the basic problem is that your plate is picking up small amounts of ink from the emulsion applied to it and tracking it back over time. Running slightly higher levels of ink in the unit will help, but really the solution is a plate with a shallower grain....not ideal.

At least, that's what we've seen

 

[D Ink Man]

But a 50:50 mix would surely be nearly transparent? It would wreck our ISO ability and require a recalibration on that colour as well. I am not in a position to do a non-job test at present but will bear this idea in mind.

Could you elaborate your idea with a theory or reason please.

Not more transprent, it would be weaker. The idea is to increase replenishment in your yellow unit, due to the case of coverage, or lack thereof.

By enabling more ink to pass through through your train at a more normal rate, you shall minimize the problems you have encountered.

As far as G7 disturbance, don't fret it. Just key up and run to your target density. G7 is primarily goverened by ink shades, L*a*b* so your color values will not be disturbed by a decrease in ink color strength and increased passage of ink through the unit.

For a difficult light coverage form this is the most practical way to step out of the problem for a temporary condition (extremely light take off).

Hope that explains it and I hope it helps you.

D