roller probs

Hi, anyone out there can help, Lithrone 528 with coating unit. tried to print a full sra2 sheet 4 colour, best discribed as a light tan colour 20%k, 15%m, 5% c and 20%y. Load of roller marks length of sheet. All settings bang on, tried a host of random settings, tried moving the inking, changed all blankets (which helped a little). Took single colour pulls all of which were mark free but put them all together it looked really bad. Water checked and clean, tried diff stocks all with same results, couldn't do it as 5th colour as metalic spot on job, any ideas?

 

have u check your ICP film transfer cylinder? is it dirty? just guessing....

 

Any chance of taking a pic and uploading it so we can see the nature of the marks?

 

Do you mean across the width or from grip to backedge?

 

Yeah, it's the classic roller marks grip to tail edge. Looks worst say in aprox 3rd quarter.

 

What's your print sequence? We run KMCY 99% of the time on our L646.

Do you get the marks (horizontal or vertical relative to the grip? your post doesn't make it clear) when you drop 2 units only in pressure, say the black and magenta since they carry the most dot?

I't sounds more like a damp issue - what are dry solid pulls like?

What's in your fount?

 

Hi, Very much doubt it`s ICP or anti marking related. Could be a trapping issue. Which inks are you using on press? If all roller settings are spot on then have a quick look at packings(Heights/Condition). I believe you should be packing at around 0.85/0.90mm to get up to bearer heights.
Let me know if this helps & maybe I can suggest something else should these suggestions not work.

Good Luck.

PC

 

On the last print unit of all Komori sheetfed there's a legend plate which tells you the cylinder undercut, from this you get the packing heights to give correct print length as well as 'squeeze' between cylinders.

eg on our L626 it's 2.8mm undercut on the blanket cyl. and .2mm on the plate cyl. We run .3mm plates unpacked and top blanket is 1.95mm, underblanket is 1mm unpacked. Total squeeze = 0.25mm (All our cylinders are chromed)

 

i find backing impression pressure settings to absolute minimum also helps with tint solids, packings could be the answer if new blankets helped.

 

When you took single color pulls of the job, were all of the units in impression or just the unit that you were testing? Adding units into impression one by one may help you at least locate which unit the problem is in. If it's that sort of thing...

I'm supose theres no room to restrip/layout the job to avoid a take-off problem (just a workaround anyway...doesn't really solve the problem)

Good Luck

 

To be honest I think they were in presure, but all looked good on there own. I did put in the heavy copper roller that sits where the wash up tray goes and that helped a bit but still not good. I seem to remember something about replacing the underblanket with just the paper packing is that worth the effort?