Ink Density Uniformity on Circumferential Direction

[DeltaE]

Hello everybody,


I have a question about the solid ink density in circumferential direction, the uniformity of density in sheetfed offset machine (ex: Heidelberg CD102, Rapida 106, Man Roland 700, Komori,...)
How can I improve the uniformity of ink density on the circumferential direction?

I knew that we can try somethings below to get good uniformity ink density in circumferential direction.
- Adjust the timing of oscillating roller
- Tighten blanket correctly
- Use minimum amount of dampening solution

Could you please share your point about this?

Thanks in advance!
Regards,
DeltaE

 

[cementary]

Could you tell us what uniniformity on press sheet tail to head you're trying to achieve? In my experience 0.08-0.10 D is fine for ManRoland 700 and 0.05-0.08 D is fine for ManRoland 900.
in any case you should probably add to your checklist rollers condition both ink and dampening

 

[DeltaE]

cementary Thank you! The condition of inking and dampening rollers is very important to uniformity!

Last week, when we made a G7 colorspace, I had the density deviation from front to tail:
- Black: +/- 0.05
- Cyan: +/- 0.04
- Magenta: +/- 0.04
- Yellow: +/- 0.03

It was fine for us to get a good enough data when measuring, but I am really want to improve the uniformity. That's reason of my question here.
BTW, why the density deviation of your ManRoland 900 is narrower than 700's? Bigger size should have larger deviation, shouldnt it?

 

[cementary]

I think that smaller deviation for ManRoland 900 is due to bigger ink train and maybe better oscillators.
Larger deviation for our 700 is due to not-the-best roller condition

Regarding your data — IMHO, normal density variation during run is 0.08 D across the sheet
You won't see difference with your eyes, but G7 measurements will.
Our target densities +/- 0.08 - 0.10 D stays within 3.5 dE76 from target CIE Lab, so we "dance" from that data.

IMHO, one can not achieve density variation smaller than 0.04 D in production (not test runs) only by manipulating measured data.

 

[SteveSuffRIT]

I think the circumferential density variation tolerance used by GATF/PIA for press testing is a range <=0.06.
What is your density variation across the sheet? In theory it should be less because you have more control over that with ink keys.
Rearranging the target orientation (rotate portrait or landscape) may help?
Steve Suffoietto

 

[DeltaE]

Erik Nikkanen Thank you for great input!

 

[Alois Senefelder]

Gentlemen,


Ink Density and Roller Train Designs.


While Erik's posit contains some valid comments, again he fails to mention some Fundamentals!


1) Flexo Anilox Inking systems and Gravure Printing - USE fluid ink, whereas Lithographic Inks are - Non-Newtonian and combine with a Newtonian Fluid (F.S- Water)

2) Disturbances in IFT caused by the Plate Cylinder Gap.


Regards, Alois

 

[Alois Senefelder]

Gentlemen and Mr. Erik Nikkanen.


Ink transportation in Anilox Offset Printing - Fundamentals

I hope of interest and value


Regards, Alois.

View attachment Anilox Offset Printing # 1059.pdf

 

[turbotom1052]

Let me try to make a case for why small deviations in circumferential density can have unacceptable results. So here's the scenario... An identical image is printed in 4color process 2 up from front to back on a sheet. The magenta unit has front to back variation in density of the "ACCEPTABLE" 10 points as mentioned by a previous poster, with the heavy magenta falling on the tail image. The cyan has the same "ACCEPTABLE" tolerance but the heavy cyan favors the gripper image. Now that "ACCEPTABLE" 10 point tolerance, because its on 2 separate units, in effect becomes 20 densitometer points!!!

 

[DeltaE]

Let me try to make a case for why small deviations in circumferential density can have unacceptable results. So here's the scenario... An identical image is printed in 4color process 2 up from front to back on a sheet. The magenta unit has front to back variation in density of the "ACCEPTABLE" 10 points as mentioned by a previous poster, with the heavy magenta falling on the tail image. The cyan has the same "ACCEPTABLE" tolerance but the heavy cyan favors the gripper image. Now that "ACCEPTABLE" 10 point tolerance, because its on 2 separate units, in effect becomes 20 densitometer points!!!

It is nightmare of printer! ha ha ha