mottle problem

[mlarmour]

Hi all,

I am having a problem with mottle in my process printing. It's occuring in a dark blue colour. I'm printing 175lpi, and have tried both KCMY and KMCY sequences.

Any ideas on what is going on or suggestions on how to track down the problem appreciated!

Matthew Larmour

 

[Paultheprinter]

Re: mottle problem

Hi matthew,

My guess is paper, if you changed the sequence and it stayed the same then i would not blame the inks but check ink viscosity and if possible raise chiller temp rollers two degrees to aid ink flow and lay down. If no luck check plate to blanket preassure with ink strip or packing guage. Then next thing to check is blankets, what is there surface type are they cast or ground and what is there shaw hardness. The harder the blanket the more probable a mottle will be smoothed out. Fount could play a important role to as too much water on the first unit could cause the paper on the second and third to not lay down ink as well, check conductivity and mix controlled mix in a one litre jug and compare I have had issues when i run to much IPA i get mottle. Last to check is taking the units after the CM off impression to rule out any back trap mottle on later units. If problems still persist try different a gloss sheet to see how that looks.

Paul.

Edited by: Paul Green on Feb 8, 2008 6:27 AM

 

[Anita]

Re: mottle problem

Thats a wonderful checklist ! covering almost all the points...
Also, you could try keeping Black unit's impression off, if then it prints fine.. it colud be water-interference mottling. To avoid water-interference mottling, low supply of fount and low IPA percentage is recommended.

 

[Paultheprinter]

Re: mottle problem

Thanks anita,



Had mottle problems before and had to dig deep to find any answers, another point which gets missed is fountain solution temperature. We all know how important conductivity and ph are but im finding more and more that the temp is critical. My technotrans unit reads 7 degrees c at the moment but in the bowl its only 10.5, but by the time its reached the 5 unit its more like 14 degrees. This leads to over supply and all of the problems associated with this, and we never question readouts as much as we should, if i put my hand in it feels cold enough but in reality im starting to edge out of a reasonable operating window.



Cheers paul