Dot gain problem with Man Roland 505 (need help)

[Alois Senefelder]

Hello Hannes and fellow Lithographers,

Cause: Variation of Dwell Time in the Plate/Blanket/Impression Nips, as the cylinders rotate through the - Forces of Pressure

PDFs - I hope you will find of interest and value.


Regards, Alois

[Alois Senefelder]

Hello fellow Lithographers,

To continue ---

PDFs - "The effect of printing blankets on the rolling condition of printing cylinders"



Regards, Alois

[Hannes]

Thank you for the answer. At the moment, we haven't found solution. All I know is that when you print with the lowest densities then the dot gain is 15% to 20%. If you print normal densities or a little higher then the dot gain is 20% +

We will start compensating dot gain by decreasing dot on the printing plate.

[frank67]

Which fountain are you use from Fuji?

[Hannes]

Acedin D1991 - works everywhere else and I think it very good fount.
Before Fuji there was Hostmann's Combifix

[bikozak]

This is a good one Hannes. If you really did check all the things mentioned by Gordo above, then to me it sounds like your ink is not stable at the densities you are running. I say this because you see variation from job to job and color to color. I would be interested to know if the dot gain fluctuations coincide with heavy or light coverage between colors and jobs.

[Kaoticor]

I really haven't paid attention to it. That's a good idea. Could you please explain how the dot gain changed with different speeds?

Best regards,
Hannes

Sorry for the delay in responding, forgot about this thread. Here at our shop we notice shifts in dot gain in press speed. Some of the pdf's mentioned on here touch on a few of the contributing factors. One thing you can look out for (in addition to what the other posts mentioned) is press temperature and running speed.

Example - You are running the press at a slow speed and it has not heated up yet, and then you make your calibration curve on your plate. Later, you get in to a heavy production run and speed the press up and more heat is generated, affecting various conditions inside the press. Variables like dot gain can look completely different. We had to start making curves only after normal conditions were reached.

[BeauchampT]

Sorry for the delay in responding, forgot about this thread. Here at our shop we notice shifts in dot gain in press speed. Some of the pdf's mentioned on here touch on a few of the contributing factors. One thing you can look out for (in addition to what the other posts mentioned) is press temperature and running speed.

Example - You are running the press at a slow speed and it has not heated up yet, and then you make your calibration curve on your plate. Later, you get in to a heavy production run and speed the press up and more heat is generated, affecting various conditions inside the press. Variables like dot gain can look completely different. We had to start making curves only after normal conditions were reached.

A great deal of what Kaoticor mentions here relates to the effect of press conditions on ink properties. Differences in speed and temperature affect the viscosity, tack, rheology, etc. of the ink.

One question regarding the densities that you run on press - you say you run coated paper, so those densities don't sound totally out there to me, but...what sort of densitometer are you using (Status E, T, etc...)? Those values may not be an issue at all.

[PSchw]

You may have a registration issue on your press. Have the press checked with a special test form. I have a computer ssytem what measures you exact registration. You can contact me at any time via email peter@ot-ec.com.