Ink where it shouldn't be, plate blinding?

Sample.jpg
Hello folks, i've been having this issue with mostly magenta and reds, after a short run (2,000-5,000) we get ink in areas where there should be none and also in small text areas. Is this plate blinding or what is this called? We think it might be conductivity and/or pH related. Any feedback is greatly appreciated!
 

Magnus59

Well-known member
Plate blinding causes image areas to become none receptive, usually due to excess gumming, not something we see often with CTP plates
This looks like simple catchup (scumming) due to incorrect ink/water balance.
 

SteveSuffRIT

Well-known member
Without knowing the true root cause, the only term I would use to describe this is the nonimage area or background is printing dirty.
There are technical differences between catchup or dryup (not enough water), tinting and toning (too much water, look for wash/flood marks and over emulsified ink) and scumming (quality of water). If plate, then its called sensitivity.
Catchup/dryup almost always first shows at gripper edge on sheetfed press.
If you erase a small area of this dirty area, regum, and print again, what happens?
If it stays dirty, its tint/tone. If it is now clean, its scum.
Can't rule out roller setting either until stripes are checked.
As mentioned earlier by Magnus above, blinding is the image area not taking ink.
 

gordo

Well-known member
Looks like scumming.
Scumming is the sensitization of the non-printing areas of the plate which results in the adhesion of ink to these areas.
"Catch up" looks similar to scumming, however, it can be readily differentiated from scumming since catch up is a direct consequence of insufficient dampening. If scumming continues after simply increasing dampening levels, you could try cleaning the plate with fountain concentrate or, (with caution), plate developer. If clean printing is the result then a check into the plate room is warranted.
Check that the developer bath has been correctly replenished, and is not contaminated. Brushes and rollers in the plate processor should also be thoroughly cleaned and checked.
Another area to investigate is the strength of the fountain solution. Weak fountain solution will not keep the plate running cleanly, at normal levels of dampening, and may be unable to keep the plate clean.
The proper fountain solution strength can be evaluated by measuring conductivity to ensure that the conductivity of the solution is within the recommended range provided by the
manufacturer.
Poorly maintained rollers in both the inking and dampening systems may also contribute to uncontrolled scumming so checking roller durometer is a good idea.
 

Pommyding

New member
View attachment 291393 Hello folks, i've been having this issue with mostly magenta and reds, after a short run (2,000-5,000) we get ink in areas where there should be none and also in small text areas. Is this plate blinding or what is this called? We think it might be conductivity and/or pH related. Any feedback is greatly appreciated!
Had a same problem with our ryobi 3304 turned out our fount solution was out of date … and the ink was too runny replaced the solution and an h changed to best one inks
 

turbotom1052

Well-known member
If a plate is allowed to run for too long with insufficient dampening, so as to run with an inked non image area, it is common for that area to become sensitized and continue to take ink even after damp feed is increased.
 

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