Positive Ink Feed Simulation Test

[Alois Senefelder]

Star Target

Star Target

Messrs Al and Erik,


Still a "Sceptic" but in the interests of the Test, I suggest you make the addition of

a GATF Star Target on the test forme.

Al, being a "Dissenter" am I included with the Nay Sayers ???


Regards, Alois

 

[Al Ferrari]

Alois,

Not a bad suggestion. If there is a demand for it, I can add it. But I think we can learn a lot from the test as is without it. This is supposed to consume a modest effort on the part of participants.

A modest dose of skepticism can be a healthy thing. Will you be trying the test yourself, or are you a lithographer without a stone?

Al

 

[Alois Senefelder]

Alas !!!!!!

Alas !!!!!!

Al

Alas, no more "Smudging Ink on Paper " put the stones to good use as Memorial Stones !!!


Regards, Alois

 

[gordo]

Is there a reason that a 75% tone is not included? I would have thought that being able to measure any change in print contrast would be of value for this type of exercise.
Oh, and wouldn't it be good to also place a solid patch right beside the screened patch to make sure that measurements made reflect conditions in the same ink key zone?

best, gordon p

 

[Al Ferrari]

No, no reason at all Gordon. Just oversight. I threw that pdf together quickly for Erik per his description.

I'll take suggestions till mid day tomorrow, then as I find time on a day expected to be very busy, I'l throw the suggestions together. But don't wait up for me. Go ahead and make your own. It's a collective effort by all reading the thread.

But those with the access to a press should go ahead and perform the test with any less than optimal test image plate. We're going to learn something from the test no matter how fancy or simple the test image. It can be refined as we go along.

One idea that occurs to me is to make the test image like a short color bar with a star target, a solid patch, a 25% patch, a solid patch, a 50% patch, a solid patch, a 75% patch, a star target.

But again, let's not get hung up on designing the test image, and let's do the darn print test!

Al

 

[Deleted member 16349]

Is there a reason that a 75% tone is not included? I would have thought that being able to measure any change in print contrast would be of value for this type of exercise.
Oh, and wouldn't it be good to also place a solid patch right beside the screened patch to make sure that measurements made reflect conditions in the same ink key zone?

best, gordon p

Gordon, there are many opportunities to study these kind of print quality issues once positive ink feed become more accepted and established. I think there can be interesting studies done to look not only at dot gain but also wet trapping. It may be that the values of these process control parameters can be manipulated with variations in the application of water.

I thought having some kind of screen patches would be of interest but one could also argue that discussions of screen print quality are a distraction to the main purpose of the test. It might have been better to not have any screen patch on the test form at all for that reason.

Also the water levels in this test will be way out of the normal printing operating range so analysis of the quality of the printed screen is not so relevant to normal printing.

Because this is a simulation of positive ink feed for a low coverage print, the test can not run too long since the ink will be coming out of the system and resulting in a decreasing solid density situation. I am guessing that the run will only be between 5 to 10 minutes so I am looking at the main issue, which is the independence of print density relative to water setting.

Let's keep it simple and specific.

 

[gordo]

Gordon, there are many opportunities to study these kind of print quality issues once positive ink feed become more accepted and established. [snip]
I thought having some kind of screen patches would be of interest but one could also argue that discussions of screen print quality are a distraction to the main purpose of the test. It might have been better to not have any screen patch on the test form at all for that reason.

In the context of this test, print contrast is not a measurement of print quality it is an indicator of the effect of the change in water volumes.

But I'm probably out of my depth ;-)

best, gordon p

 

[Deleted member 16349]

In the context of this test, print contrast is not a measurement of print quality it is an indicator of the effect of the change in water volumes.

I am not sure what really would happen to the screen patch. As I said in an earlier post, during a test of positive ink feed, the engineers (at Drent Goebel), did not measure a higher dot gain when there was a higher level of water. In that case, it was not an indicator of the water volumes.

I don't know if that was just a fluke measurement but with such a short test as this simulation, I don't think one can say much conclusively about the affect of extra water on the screen.

Have I used the term "print quality" improperly when discussing these screens?

My thinking has been that if a screen normally prints at one dot percentage but then later prints at a different dot percentage, that to me is a print quality issue. Am I not using the right term to describe this?

 

[Bloodsaler]

From the introduction,I didn`t see any economy in positive ink feed simulation test.During the production run,it`s not easy to stop the ductor,and let the water level up and down as the test required,it will ruin the work.And for the test form is too small,so it can`t treated as a fingerprint.So to do the test is not as easy as the thread mentioned.
And the result only confirm water level doesn`t influence the solid density.It really helps in production run?
As i concern,its only a science research.
Maybe because english translation,i misunderstood something?

 

[Deleted member 16349]

From the introduction,I didn`t see any economy in positive ink feed simulation test.During the production run,it`s not easy to stop the ductor,and let the water level up and down as the test required,it will ruin the work.And for the test form is too small,so it can`t treated as a fingerprint.So to do the test is not as easy as the thread mentioned.
And the result only confirm water level doesn`t influence the solid density.It really helps in production run?
As i concern,its only a science research.
Maybe because english translation,i misunderstood something?

Bloodsaler,

The positive ink feed simulation test has not practical value for production. This is true. But positive ink feed does. The test is just to show the science behind positive ink feed because there are doubts, by experienced printers and experts in the industry, that density consistency, ink water balance are related to the consistency of the ink feed in presses.

If positive ink feed shows that density is mainly related to ink feed consistency and is not related to other variables, such as water, press speed and temperature, then it makes the process not only more consistent but also predictable.

This means that presetting the press and starting it and having it go directly to target densities, run consistently for the whole run, without any adjustments of the ink settings by an operator or by a closed loop colour control system, then becomes possible. This has a very practical potential.

 

[gordo]

I am not sure what really would happen to the screen patch. As I said in an earlier post, during a test of positive ink feed, the engineers (at Drent Goebel), did not measure a higher dot gain when there was a higher level of water. In that case, it was not an indicator of the water volumes.

I don't know if that was just a fluke measurement but with such a short test as this simulation, I don't think one can say much conclusively about the affect of extra water on the screen.

Have I used the term "print quality" improperly when discussing these screens?

My thinking has been that if a screen normally prints at one dot percentage but then later prints at a different dot percentage, that to me is a print quality issue. Am I not using the right term to describe this?

Print "quality" is a loaded descriptor - not a term that I would use in this context and is not what I was thinking about.

I'm just thinking about metrics that might give you data points to help understand what is happening when you run your test.

Dot gain at the 50% was one that you included. I would expect that given a constant SID but changing the water volume would not have much, if any effect on dot gain since the way that dot gain is calculated links them together. I.e. if SIDs change because they are being washed out by excess water then the dot gain reported by the instrument may not change - just because of how dot gain is calculated. Which is what seems to have happened at Drent Goebel. The same thing happens if you increase SIDs on press - dot gain as measured, may actually decrease. (That's a very complicated discussion though) Heck, it's even possible for a screened tone (e.g. 98% cyan) to measure as a higher SID than a solid (e.g. 100% cyan). (Another very complicated discussion though).

With print contrast (75% vs 100%) you are not really looking at dot gain, you are looking at the impact of water volume on the plate. So, given a constant SID, if you decrease the volume of water the SID may stay the same but the contrast will go down (as the screen fills in). Conversely, if you increase the volume of water and your theory proves out then the SID will be constant but the contrast may increase or decrease. If you increase the water and your theory fails, then the SID may shift and print contrast may also shift (higher or lower) and may help you to understand what happened.

So, theoretically, everything that is printed (solid patches or halftones) is printing solids - halftones are simply islands of solids surrounded by water. If you could measure the solid density of an isolated halftone dot it should be similar to the solid density of a large 100% patch. However, water volume potentially affects not only the density of the solid patch but the lack of ink film in the non printing areas. So, IMHO, it might be useful to have such a target in your test i.e. replace the 25% with a 75% tone.

That's why I thought adding a print contrast target might be useful.

best, gordon p

 

[Bloodsaler]

Bloodsaler,

The positive ink feed simulation test has not practical value for production. This is true. But positive ink feed does. The test is just to show the science behind positive ink feed because there are doubts, by experienced printers and experts in the industry, that density consistency, ink water balance are related to the consistency of the ink feed in presses.……

Yes,from your theory,the solid density go consistent,not related to water or other things.But you ignore the dot gain,this is influenced a lot by water,and also a important parameter to control the quality.Density up to the target,but the change of the dot area also can destroy the production.
So how you balance the density and the dot gain in this science?

 

[Deleted member 16349]

Y
So how you balance the density and the dot gain in this science?

This science is about controlling printed ink films. Controlling ink films is the foundation of the offset process and solid density is very much related to the printed ink film thickness. Dot gain is closely related to the ink film being printed.

This science is not specifically about controlling dot gain but dot gain should be more consistent and there is the possibility to influence the dot gain by limited adjustments of water. This is something for future investigation.

 

[Deleted member 16349]

Print "quality" is a loaded descriptor - not a term that I would use in this context and is not what I was thinking about.

I'm just thinking about metrics that might give you data points to help understand what is happening when you run your test.

Gordon,

I have to make a correction. The Drent Goebel engineers did not measure dot gain but were actually measuring the density of the screened patch. Since we had consistent SID that measurement is very much related to dot gain. That test was six years ago and thinking about it more, I remember that they just took a direct measurement of the screen density.

This is just what I did not want to have happen. Long discussion on something like dot gain which is not specifically related to what the test is about.

IMHO your view of what is physically happening with the dots and the calculations are in error and this leads you to incorrect conclusions. I will contact you off line to discuss this because I do not want to encourage more discussion of dot gain in this post.

I will also try not to respond to dot gain issues in these threads. It is interesting but it is a distraction.

 

[turbotom1052]

Eric your asking print proffesionals to test your theories and then in the next breath your telling them that they shouldnt interject their own personal observations or experiences into the mix. This is exactly what i meant when i suggested in an earlier post on this thread that you will not be satisfied with any conclusions or hypothesis anyone may come up with that is even remotely in conflict with your agenda.
If you turn to industry proffesionals, (and i believe there to be many here on the forum) you cant expect them to just follow you blindly without interjecting their own proffesional opinions. Give people the benefit of the doubt that they are capable of perhaps slight deviations in thinking from yours. Allow the pros to venture off into whatever discussions they see as applicable for the purpose of this thread. Your expecting that we all see the value of your work but it seems that your not as willing to see the value of ours. Perhaps this is the very reason you find yourself in conflict with the industries policy makers when it comes to adapting to alternate technologies. Id suggest looking at the possibility that there is some middle ground here. Some of your ideas i believe have some real merit but its my feeling that they will never make it to to Board rooms of the major manufacturers until such time that your able to allow people to have a little input with the path of developement.

 

[gordo]

Gordon,
[snip] Long discussion on something like dot gain which is not specifically related to what the test is about.
[snip]
I will also try not to respond to dot gain issues in these threads. It is interesting but it is a distraction.

OK - but for the record, I wasn't referring to dot gain - which I don't think will tell you much. I was referring to print contrast.

But since you brought up the subject of dot gain - the file that Al created for you and that you published here included a 50% patch to specifically measure dot gain which in your previous posting was something that you said you wanted to test: "I am curious to see how dot gain is affected on this simulation test." Now you're saying it's a distraction?

best, gordon p

 

[Green Printer]

At what point does one have to consider an inks inability to wet split transfer? This can have a huge effect on film transfer. I have seen an ink able to transfer at .05mils thickness on the rollers and others had to be a .5 mils. In many cases when the ink goes below a certain film thickness it becomes unstable and is in the realm of a semi-solid or partially polymerised state and will go back and forth between transfer and not transfer with water having a huge effect on this. This property mimics washout when it really is dried ink not transferring.
I would suggest using inks without driers so that this factor will be minimised.

Another factor entering the test is roller conditions. Any one doing the test should paste there roller firsts to eliminate any glazed rollers having an effect on this test.

 

[Deleted member 16349]

OK - but for the record, I wasn't referring to dot gain - which I don't think will tell you much. I was referring to print contrast.

But since you brought up the subject of dot gain - the file that Al created for you and that you published here included a 50% patch to specifically measure dot gain which in your previous posting was something that you said you wanted to test: "I am curious to see how dot gain is affected on this simulation test." Now you're saying it's a distraction?

best, gordon p

Yes, I am curious about dot gain but it is not the primary aim of the test. I don't have a densitometer and I was just going to visually look at the screens.

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.

 

[Deleted member 16349]

Another factor entering the test is roller conditions. Any one doing the test should paste there roller firsts to eliminate any glazed rollers having an effect on this test.

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.

 

[Deleted member 16349]

In many cases when the ink goes below a certain film thickness it becomes unstable and is in the realm of a semi-solid or partially polymerised state and will go back and forth between transfer and not transfer with water having a huge effect on this. This property mimics washout when it really is dried ink not transferring.
.

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.