Positive Ink Feed Simulation Test

[gordo]

Yes, it has turned out to be a distraction because the discussions are about dot gain. You brought up the subject of print contrast and suggested a 75% screen. Someone else could bring up some other test patch. Hey let's cover the whole plate with test patches and see what happens. More data the better.

Ouch! it appears that turbotom1052 is right.

gordon p

 

[Green Printer]

I have seen this phenomena with Dry Offset (not waterless).

In the context of positive ink feed, this phenomena is in a way is self correcting.

With positive ink feed. If you run and things are stable but then suddenly ink transfer to the plate or substrate drops due to this thin ink film issue, which can be due to some disturbance. When the ink transfer rate drops but ink is still being fed into the rollers in a positive and consistent manner, the ink film will increase on the roller train and this will restore the ink transfer to the plate or substrate.

Small changes in ink transfer in the print will be adjusted by changes in the ink film storage on the rollers. This would bounce around the average ink transfer rate which must be the same as the ink feed rate.

If someone is doing the test I was trying to point how that they could have false readings on the ink drying up and not transferring.

 

[Deleted member 16349]

If someone is doing the test I was trying to point how that they could have false readings on the ink drying up and not transferring.

I guess that could happen on the simulation test if the ink started up too thin on the rollers. It would confuse the results. Test are always very tricky.

 

[turbotom1052]

Another factor that needs to be considered when doing the test is the press itself.

This morning I attempted to do a test at a printer. The manager, Chet Keenan and the printer Frank Gonsalves at a The Print House shop here in Toronto were very helpful.

In our initial discussions, Frank said that such a small coverage does not tend to wash out easily. This brought up the problem that if this is true, then any simulation test of small coverage is not valid.

So I said that I would need to do a test of the normal running conditions for that small coverage and see if increasing the water greatly would wash it out. So we did that test first. Frank started the print run at a reasonable density. He increased the water setting to maximum and there was little difference in the print density. This was interesting.

Part of the problem was that the highest water setting on this Heidelberg QM 46-2 was not enough to greatly wet the polyester plate. The plate was still quite dry. This might have been related to other settings but I was not going to ask them to change their set up for this test.

Since water levels could not be increased greatly on this press, there was no point in doing the simulation test.

So my point is here, don't attempt to do the test unless you can set the water levels so high on your press that it does soak the plate.

the problems with trying to do this test with a form containing heavier coverage is that you could not hold off the ink feed into the roller train for very long before the ink film on the rollers diminishes to a point where all you will have in the rollers is water. Im not denying the fact that a printed image can continue to look saleable at sky high water levels,but its the effects of a high water level over time that will tend to catch up and show itself in print quality. Now if your standard job is a run of 100 sheets, and your running sky high water with a very light coverage form, then i say you very well may be able to print 100 saleable sheets. But up that run to 1000 sheets and im certain that print quality will suffer. It also needs to be considered that a smaller press like a Heidelberg QM46 has much less storage capacity in the ink train. A total of a couple of square inches of coverage would strip the rollers of ink pretty quick. Step up to a Speedmaster 102 or an xl 105 and that same image will be able to print longer without starvation based on that presses higher ink storage capacity.
So it would appear that for the purposes of this test it would be required to set a standard to which all testers must run. Clearly determine press type, then clearly determine amount of impressions with the inker held off. After all that is done then you need to arrive at a way of determining exactly what is considered overdampening. Good luck with bringing that variable under control!!! The biggest problem with all of this is the need to simulate laboratory conditions in a commercial printing enviroment. eric perhaps you should consider enlisting PIA or some other printing lab to test your theories under some strictly controlled conditions, instead of getting all of us here on the forum to fund your research.

 

[Deleted member 16349]

the problems with trying to do this test with a form containing heavier coverage is that you could not hold off the ink feed into the roller train for very long before the ink film on the rollers diminishes to a point where all you will have in the rollers is water. Im not denying the fact that a printed image can continue to look saleable at sky high water levels but its the effects of a high water level over time that will tend to catch up and show itself in print quality. Now if your standard job is a run of 100 sheets and your running sky high water with a very light coverage form then i say you very well may be able to print 100 saleable sheets. But up that run to 1000 sheets and im certain that print quality will suffer.

It was never suggested to run high water levels for production. That would not be good.

The test press today was set up so it did not provide high levels of water. This limitation is good for their production but unfortunately not so good for my test.

Yes, high coverage would not be good for this test.

Right now I am worried about the validity of the test for very low coverage. Frank, the pressman said that low coverage does not tend to washout easily but high coverage does. If this is true even at very high water levels then the simulation test is not useful. But also if it is true, it implies that water is not inhabiting the ink transfer to the plate for low coverage. The washout effect of the high coverage can then be explained by loss of ink supply into the press.

I need to do another test on a press that can supply lots of water to help sort out these issues.

 

[Alois Senefelder]

Polyester Plate - Ugh

Polyester Plate - Ugh

Hello Mr. Erik Nikkanen also fellow Lithographers also Turbotom,

IMHO this test would be more valid using a Presensitized Plate than a Polyester one.

Salient Point - Inking Unit Area

One way of judging the size of an inking unit is to compare the largest printing size with the area of the inking unit. This area comprises the surface area of all the rollers and distributors, from the ductor to the inking rollers. A good inking unit should, one one hand, have a large storage capacity, but on the other hand, should also react as fast as possible to corrections. On some Heidelberg presses, the inking unit area is 7.1 times larger than the printing area.


Regards, Alois

 

[Deleted member 16349]

This morning I attempted to do a test at a printer. The manager, Chet Keenan and the printer Frank Gonsalves at a The Print House shop here in Toronto were very helpful.

In our initial discussions, Frank said that such a small coverage does not tend to wash out easily. This brought up the problem that if this is true, then any simulation test of small coverage is not valid.

So I said that I would need to do a test of the normal running conditions for that small coverage and see if increasing the water greatly would wash it out. So we did that test first. Frank started the print run at a reasonable density. He increased the water setting to maximum and there was little difference in the print density. This was interesting.

Press test no. 2

Today, a second press test was done at another printer. The manager Tom Fotinakopoulos and the pressman Gary Crisp at a local KwikKopy here in Toronto were also very helpful.

This test was not the positive ink feed simulation test but just a low coverage test to see if their press would wash out the print. This was similar to the test done at The Print House last Wednesday where the low coverage plate was run in the normal conditions with the ductor in operation.

Gary also commented that low coverage does not wash out quickly. Then we started the press, let it stabilize and then turned the water up to maximum. More water seemed to go to the plate on this press. Gary said that at this water level, high coverage would get washed out quite quickly. The test result showed that low coverage did not seem to change much at all. No immediate washout. Maybe with time it would. Frank said that on Wednesday’s test, that if you print longer the density would drop off when you print such low coverage.

The press was an ABDick duplicator and the plates where polyester plates.

Conclusion.

There is no point running the Positive Ink Feed Simulation test because it would provide basically the same result and therefore would not have any usefulness as a test.

This testing had a result that I was not expecting but it was worth it for me to go through the expense. The proposed test is not useful as a simulation of positive ink feed but it clearly shows that large changes in water does not affect ink transfer in the roller train and to the print.

Both pressmen have said that high coverage would have been washed out at those elevated water levels but the low coverage would not be washed out immediately. They said that low coverage would drop in density only after a long time. This implies to me that washout is more related to ink supply than to water interfering with ink transfer to the plate. High coverage requires a high rate of ink feed without interruption, while low coverage can get some of its ink from the roller train over a short period of time.


Of course there will be arguments for and against this conclusion but let’s also do a Mind Experiment. Hopefully it will help shape some of the opinions.

Let’s say we have a press.

On the left side of the sheet we will print a high coverage bar or solid block.
On the right side of the sheet, we will print a very low coverage solid bar.

So we print and get to steady state conditions where both the high coverage block on the left prints at the same density as the low coverage bar on the right side.

Now we increase the water significantly and what do we get.

The left side high coverage block starts to wash out but the right side bar continues to print at basically the same density. This seems to be supported by experience of the two pressmen and by testing of low coverage.

So what is happening?

We can look at this from the perspective of a person experienced in the process and who does not accept the idea that variations in ink feed is the fundamental cause of ink water balance problems.

Some will argue that it is over emulsification. Let’s talk about this. We can even use Alois’ emulsification lab test chart for this.

Emulsification. Which side should emulsify first?

On the left side, we have high coverage and this implies we have a lot of fresh ink moving quickly through the roller train. On the right side, we have low coverage and this implies that we have very little ink moving through the roller train but have the same ink sitting on the roller for a long time.

Both sides get a large amount of water applied. If we are to think in terms of the emulsification chart provided by Alois, then I think the right side would become more emulsified because one has the same ink on the rollers being subjected to high levels of water over a longer period of time than the high ink usage rate on the left side. But the right side does not wash out. This implies that high levels of emulsification do not cause washout. High levels of emulsification do not prevent ink transfer.

Ink Transfer

The right side does not washout for a long time and it is reasonable to think that it gets its ink from the rollers even if the ink feed would stop.

The high coverage side washes out quickly. The print gets lighter and lighter with less ink being printed. So where has that ink gone that was being fed into the press? If a high rate of ink feed goes into the press but does not come out on the paper, it can not magically disappear. How do the experienced process people explain this?

End of the Mind Experiment.

Wrap Up.

So it turned out that the Positive Ink Feed Simulation test was not useful as a simulation of positive ink feed but this whole effort did show that high levels of water and emulsification are not the cause of a lack of ink transfer and washout.

What is also interesting and something I was not so aware of was the change in print density from high coverage to low coverage. The implication here is that if there are changes in the water application on press, the density across the sheet will not change uniformly but will change depending on the coverage. That is also a new detail for me.

In the end, I got something out of these tests. I learned some things that were new but the intention of the tests was not for me to understand that positive ink feed will eliminate density variation and ink water balance. I have already tested that before. The test was for the benefit of others to help them think in a new direction.

I am guessing that this discussion will also not help that effort and once this thread is finished, which will be shortly for me, I think I will not discuss positive ink feed on the forum for quite some time. It’s not the right place. At least not for me.

 

[turbotom1052]

Its my feeling that even though the offset lithography process is theoretically the same regardless of press manufacturer, and of press size you need to have an understanding of as follows....
Although im not at all experienced with running smaller duplicator style presses like the AB dick you mentioned, i have worked around them, and spoken with the pressman that run them often enough to echo their words. Ive been told that a very common addition to these duplicator style presses is either a kompac, or a crestline style continuous flow dampening system. Ive heard from numerous guys over the year that these dampening sytems require the very minimum, if any operator intervention in order to achieve saleable printing results. This is often the very reason that these presses are equipped with these type of dampening systems.
That being said i think it needs to be taken into consideration the skill levels of the Pressman that run these presses. Now Eric i dont know if your testing has been limited to the above mentioned presses or pressman but if so id say that the conclusions drawn as a result of these tests would be questionable at best.
Its not my intention to degrade the process or the personel at this level but if your ultimate goal is to sell your technology to larger press manufacturers or to comapnies more involved with "color printing" then id say your testing needs to be more focused towards a higher level of relevancy. If your goal is to sell a product with a much broader appeal then id say that you need to narrow your focus a bit.
Different dynamics come into play when you step up in press size and print quality standards. Just as an example ill site the need on larger presses for either a crowned metering roller or an adjustment for skew. On a smaller press theres no need for such and adjustment because the width of the rollers are not sufficient to require such an adjustment. Running a water system with a metering roller thats parallel to the pan roller and with no skew adjustment would be pretty difficult to achieve on say a 40 inch or larger machine. The level of engineering required to manufacture this into a press is higher. The level of pressmanship required to understand these same principals are also higher.

 

[inkinveins]

I did not perform the test as originally outlined, but in my attempt through other R and D, I stumbled upon the fact that wash out occurs at the ductor, ( Believe me, to my disbelief ). This is compatible with what Eric find in a previous post
A brief synopsis of my findings goes as such :
Testing a 4 color job approx. 10% coverage on drive side of form and approx. 60 % coverage on operator side of form. Upon extreme introduction of dampening solution in a continous state ( Via the metering roller, even water film ). The density reduction on the drive side was 22%, and the density reduction on the operator side was 55%. The most offensive change was the side with the heaviest ink key opening, leading me to believe with an even introduction of water, the ink train became less able to receive ink off the ball than the lighter coverage side. This was proven multiple times on the same form. Not only did this alter the unit I affected change on, it also affected change on the succeeding unit. On the operator side where density difference was the most affected, It also affected density in a negative manner in the following unit. As if the substrate carried water to the succeeding unit and wetted the blanket, in turn causing poor transfer from the plate. Interesting
P.S. This test was done on paper, not on plastic, on a conventional press after a steady state running condition was established with no other variables introduced