Problem with plates fading

[Sjf]

Hi

For the last few weeks we've bee having problems with plate fading once they are on the plate, they can go as quickly as 5-10 pulls, also the problems seem to happen towards the bottom of the plate(where the plate is gripped in the imagesetter drum). The problem seems to be worse in the morning and as the day goes on it gets better.

Is this a problem with the imagesetters laser or the processors pre-heat?

This is what we're using

Cobra 2 ctp imagesetter(violet plates)
IGP Photopolyer(chemical based)

 

[DCurry]

It might be a problem with the chemistry used on press.

 

[PrePressTech]

Assuming metal plates:
Make sure developer temp, agitation is ok. No foaming in dev tank, pumps are working (replenish and circulation), rinse bar is working well (clean jets) and that the finisher is at the right level, and spraying properly. Machine is level, no kinked hoses, the list goes on. Also as mentioned the press chem (forgot the term) is generally important, this time of year evaporation problems are perhaps not a big issue.
Good luck.

 

[PrePressTech]

plate blinding at on edge.

plate blinding at on edge.

Try turning the plate 180 degrees through the processor to see if the problem stays the same (processor) or moves to the opposite side (CTP).

 

[KevinC@EFI]

Try turning the plate 180 degrees through the processor to see if the problem stays the same (processor) or moves to the opposite side (CTP).

Yes, that's always useful for isolating a processing issue from a plate/imaging/application issue. However, I'd normally recommend rotating the plate 90 degrees instead of 180 (if your processor is wide enough), or even sending it through your processor diagonally somewhat. (diagonally ensures that you can separate processing banding/artifacts from imaging artifacts - which are usually at right angles to the plate edges)

Kevin.

 

[hagar]

Hi

For the last few weeks we've bee having problems with plate fading once they are on the plate, they can go as quickly as 5-10 pulls, also the problems seem to happen towards the bottom of the plate(where the plate is gripped in the imagesetter drum). The problem seems to be worse in the morning and as the day goes on it gets better.

Is this a problem with the imagesetters laser or the processors pre-heat?

This is what we're using

Cobra 2 ctp imagesetter(violet plates)
IGP Photopolyer(chemical based)

When did the Cobra last have a PMV? The cobra has a spinner mirror which spins at 36rpm, like all systems which use spinners dust will cover the spinner which reduce the power which lands on the plate which in turn leads to plates fading on press.

If you want anymore info, PM me

 

[maxon]

Quite correct hagar, this is a typical underexposure symptom. Sjf, recalibrate your laser intensity and post your results. Make sure your plates are not expired or stored in very cold/humid conditions before exposing.

 

[Sjf]

Hi guys, thanks for the input, we had an engineer come in on friday and he showed us the mirror on the spinner and ye it was dusty as hell, he gave it and the other mirror a clean and it seems perfect now.