Manroland 205E make-ready (2006) (CIP3+Techkon RS400)

[majklcze]

Hello guys,

I´m sending quick update.
We have improved our process with dot gain calibration according to new Fogra51/52 color standard.
Now we are using Printflow DIPS to load CIP3 data, that we have corrected a lot, we are also more conservative with close-loop corrections. We run about 100+ archs before measuring again.

So now we have multiple CIP3 curves for almost all materials we use.
We have three hot-folders on our CTP with basic material types, dot gain corrected - Coated, Uncoated and stock.
all theese steps was necessary to get better color density results...

I hope we will need lower amount of paper in future, now we are doing on 400+ B2 sheets to get to this: (I have also increased tolerances because our machine is 13 years old...)

 

[Deleted member 16349]

Hello guys,

I´m sending quick update.
We have improved our process with dot gain calibration according to new Fogra51/52 color standard.
Now we are using Printflow DIPS to load CIP3 data, that we have corrected a lot, we are also more conservative with close-loop corrections. We run about 100+ archs before measuring again.

So now we have multiple CIP3 curves for almost all materials we use.
We have three hot-folders on our CTP with basic material types, dot gain corrected - Coated, Uncoated and stock.
all theese steps was necessary to get better color density results...

I hope we will need lower amount of paper in future, now we are doing on 400+ B2 sheets to get to this: (I have also increased tolerances because our machine is 13 years old...)

I am glad you feel you have improved your situation.

It has been almost two years since your first post and I would say that you might be managing your problems a bit better, but they are still there. This is typical of how the industry deals with problems. They don't really solve them, they just try to manage them.


Increasing tolerances is also a handy way the industry avoids solving variation problems. Just curious. What tolerance values do you have now?

 

[majklcze]

I am glad you feel you have improved your situation.

It has been almost two years since your first post and I would say that you might be managing your problems a bit better, but they are still there. This is typical of how the industry deals with problems. They don't really solve them, they just try to manage them.


Increasing tolerances is also a handy way the industry avoids solving variation problems. Just curious. What tolerance values do you have now?

Thanks for reply. Now we have 8% tolerance. I will return to 5% soon..

Yes it took so long, but we are small family company. I came into industry and I needed to learn everything by myself. Im doing my best, and now I can see light at the end of the tunel

 

[Deleted member 16349]

Thanks for reply. Now we have 8% tolerance. I will return to 5% soon..

I can see light at the end of the tunel

That light might be the oncoming train.

What do you mean by 8% and 5%? Is this related to dot gain variation or is it supposed to be related to solid density variation?

Can you give an example just to clarify it. Thanks.

 

[majklcze]

That light might be the oncoming train.

What do you mean by 8% and 5%? Is this related to dot gain variation or is it supposed to be related to solid density variation?

Can you give an example just to clarify it. Thanks.

8% in solid density variation on stock paper and carton. 5% on gloss coated premium paper.

 

[Deleted member 16349]

8% in solid density variation on stock paper and carton. 5% on gloss coated premium paper.

Thanks for your clarification.

It might be used often but I think it is wrong to use percentage change values with respect to density values. The units for density are density points. So a tolerance of +/- 0.05 points would be more correct IMO.

Density is logarithmic and not linear. It is also from optical reflection measurements and it is not directly related to the amount of ink.

A change in density of 0.05 points could be a change of the amount of ink printed from 6% to 8% or even more for newspaper inks. The strength of the ink is a factor of how much the printed density will change for a given increase in printed ink film. The substrate will also affect the density value. Coated substrate will have a higher density for the same amount of ink printed on it than if it was printed on uncoated substrate, due to optical effects that the substrate and ink combination will have.

In the case of solid density for printing, one can see that the printing process is not a highly precise process. Your new tolerance of +/- 0.08 density points is maybe about +/- 12% of ink variation. That is a total range of about 24% of ink variation that you are trying to hit. That is a pretty big "barn door" target. The fact that these kinds of variations exist demonstrates that the process has poor control of the ink feed and ink film management on form rollers, inking the plate.

Changes in the amount of fountain solution feed into the press and existing in the roller train, probably has the biggest affect on changes in ink feed and therefore in printed density. This is true for existing presses with conventional ductor or continuous ductor presses. Not for modified presses with positive ink feed, done properly.

You might want to stress to your operators to be very careful with changes to the dampening system or look at the conditions the might evaporate water from the roller train at different rates when running the press.

Good luck with your continued efforts.

 

[majklcze]

Thanks for your clarification.

It might be used often but I think it is wrong to use percentage change values with respect to density values. The units for density are density points. So a tolerance of +/- 0.05 points would be more correct IMO.

Density is logarithmic and not linear. It is also from optical reflection measurements and it is not directly related to the amount of ink.

A change in density of 0.05 points could be a change of the amount of ink printed from 6% to 8% or even more for newspaper inks. The strength of the ink is a factor of how much the printed density will change for a given increase in printed ink film. The substrate will also affect the density value. Coated substrate will have a higher density for the same amount of ink printed on it than if it was printed on uncoated substrate, due to optical effects that the substrate and ink combination will have.

In the case of solid density for printing, one can see that the printing process is not a highly precise process. Your new tolerance of +/- 0.08 density points is maybe about +/- 12% of ink variation. That is a total range of about 24% of ink variation that you are trying to hit. That is a pretty big "barn door" target. The fact that these kinds of variations exist demonstrates that the process has poor control of the ink feed and ink film management on form rollers, inking the plate.

Changes in the amount of fountain solution feed into the press and existing in the roller train, probably has the biggest affect on changes in ink feed and therefore in printed density. This is true for existing presses with conventional ductor or continuous ductor presses. Not for modified presses with positive ink feed, done properly.

You might want to stress to your operators to be very careful with changes to the dampening system or look at the conditions the might evaporate water from the roller train at different rates when running the press.

Good luck with your continued efforts.

Thanks for your message, you are right with tolerances, my idea was to start with wider tolerances and getting them as tight as possible.

Now we are facing next problem, as you said the stability of fountain solution etc... But we still have problem with low ink coverage areas/press runs. It seems that it is much harder to get low coverage colors to desired density, and we end over-inked very fast... Do you have any recomandation how to maintain this?

Thanks for tips

 

[Deleted member 16349]

Thanks for your message, you are right with tolerances, my idea was to start with wider tolerances and getting them as tight as possible.

Now we are facing next problem, as you said the stability of fountain solution etc... But we still have problem with low ink coverage areas/press runs. It seems that it is much harder to get low coverage colors to desired density, and we end over-inked very fast... Do you have any recomandation how to maintain this?

Thanks for tips

Low ink coverage control is one of the more interesting problems in offset and is also very solvable if there was a real interest in solving it but there isn't. That is too bad for everyone.

First I will comment of the some of the main issues with controlling low coverage and then I will suggest some practical things you might try. I am not a press operator. I view it from an engineering point of view. An experienced press operator should have tricks that they can do to help control but I will comment on what might be tried based on analysis.

1. Even though the setting of an ink key would be mechanically precise and predictable, the actual amount of ink being fed into the press roller train is not precise or predictable. The variation of ink feed mostly happens at the ductor as conditions in the roller train change.

2. Zero set point can not be set accurately on a press with a conventional ductor. Zero set point is the point where ink should just start to be fed into the roller train. It is the zero datum point for the preset values of the ink keys. It is not the fully shut position of the ink key.

For high coverage, say 60%, and error in the zero set point of +/- 2% is not too much but when you are at low coverage, the relative error becomes very large. A 5% setting could actually be 7% or as low as 3%. That would be +20% or -40% error. That is huge.

3. Sensitivity to moves of the ink key position is much higher with low coverage. If you have an ink key setting of 50% and you move it to 55%, the increase is 10%. If you have an ink key setting of 5% and you move it only 1% to 6%, that in an increase of 20%. That is a big increase. What if you actually needed a value of something in between the 5% and the 6% setting. That can be a problem.

4. Response time is much longer for low coverage. At steady state conditions, it is true that the average amount of ink being printed equals the average amount of ink being fed into the roller train and the ink stored on the roller train is basically constant. But when you want to go from one density level to another you have to go through a transient.

What happens during this transient? First one must understand that one prints ink onto a substrate based on the amount of ink stored in the ink films on the roller train and not directly from the amount of ink being fed into the roller train. So a higher print density requires a higher storage of ink on the rollers.

With higher coverage, which requires more ink feed, the change in the storage of the ink on the rollers happens much more quickly when one increased the ink feed rate. But with low coverage, it take much more impressions to get to the point where the roller train has obtained the right amount of ink storage which will result in the increase in stable density. So with low coverage, the operator must me more patient had wait to see where the resulting density will settle to. He can cause problems if he makes his changes to soon.

5. Presetting algorithms do not calculate accurately the presetting values for the ink keys. Ink consumption for each ink key zone is not directly related to area coverage of the image on the plate, in line with the ink key. Press design factors and printing factors affect the calculations. If one only considers image area, the errors can be as high as 40%. Not good.

6. Oscillation in the press moves ink laterally on the roller train relatively more for low coverage than for high coverage. When so little ink is printed out of the press, this gives more time for the oscillating roller to move ink laterally. This also depends on how accurate the ink feed is in the areas adjacent to the low coverage areas. It is complicated.


As one can see, there are many issues but as I have said earlier, they all can be solved with press design changes if there would have been an interest. It is not so difficult a situation.

OK, but that is no help to you since you have to work with what you have. So here are some suggestions.

There is no way to obtain an accurate starting condition for very low coverage on your press. Sure a closed loop control would help deal with that starting condition but if you don't have that, then the operators need to be aware of how sensitive it is at low coverage. Make very small moves with the ink keys and wait for it to settle.

If you have a high coverage print very close to the low coverage print, you might be able to control the low coverage by making small adjustments to the high coverage ink key setting and allow the oscillation to feed the change of ink feed laterally to the low coverage region.

If you have a wide area of low coverage, say more than 4 ink key widths, maybe only use one of the ink keys to control the whole wide area by allowing the oscillation to feed ink laterally.

Add take off bars to use up more ink.

I hope this helps. Good luck again.

 

[Cornishpastythighs]

For low coverage try reducing the ink strength a little bit to allow yourself to carry a bit more ink