Advise please - scumming

I need some advise please from members of the Forum.

We have recently run into a problem with scumming - dispite many anitiatives taken to overcome the problem, the problem still persists. Puzzeling is that the scumming only occurs on one side of the sheet and on turning the sheet the other way round, the problem follows. So irrespective on which way round the sheet is turned, it is specific to that side (T/S). Are there any recomendations or comments on what the possible causes could be?
many thanks

 

If I understand correctly - you say that the scumming is only on one side of the sheet.

This is strange, my first reaction would be to run a few sheets under impression without printing, maybe this could bump the top side of the sheet and it might take off what ever is causing the reaction. Put these same sheets through again, print and see if the probelm is still there.

Is it uncoated or coated stock? PH of the paper can play a part?? Difficult one???

 

Coated stock, running through a web heat set-offset press. Difficult indeed

 

This must be a paper problem if the scum follows from 'top to bottom' when the roll is unwound 'under' vs' 'over'.

 

I agree, if its on the other side when you flip the web it has to be the paper, sounds like you got a dud batch.
is it only doing it with that batch or on other stocks as well?