Halo on plate Imaged on Screen PTR4100

[jotterpinky]

We recently had a tail clamp give up and the plate flapped a few times prior to someone hitting the off switch on our Platerite 4100. We got new clamps, reattached them everything seems to be working fine. However now we're getting a spot on the plate that looks a bit like a halo, where it's not imaged but should be. (see attached image) . Any idea what we should be looking for to get this fixed?

 

[ansoft]

Is it on one and the same place or on different places? Do you have a problem with the processor or the plates? If there is a problem with the focus, the spot will be blue, not white.

 

[mazengh]

When we've had this happen on our ptr-8000-II it's been a the punched circle sticking on the drum... try to clean your drum...

 

[jotterpinky]

Mazengh, I initially thought it might be something on the drum, I have not looked at it yet but I did look very carefully at the plate to make sure it wasn't bent or bowed out in the non-imaged area, it's perfectly flat and the plate looks flawless prior to imaging. I'll look closely at the drum and see if it has some sort of debris on it...why would this cause a non-image area just out of curiosity? One would think that it would simply be out of focus since it's closer to the laser by the thickness of the punch material.

Ansoft, this appears in exactly the same spot on each plate we do, we've imaged about 4 before we noticed the problem and several afterward to diagnos it. After we had the tail clamps go we imaged several good plates (at least so we thought since we noticed nothing wrong with them) so I'm not positive this had anything to do with it, maybe just coincidental. We also thought it was the plate but we reversed the next plate making sure to load it the opposite direction and it still shows in exactly the same spot even though the plate has been rotated 180 degrees which I believe rules out the plates themselves. These are Agfa Azura chem free plates so we only run them through a gumming unit that is next to new (maybe 100 plates through it so far). If you look closely prior to running them through the gumming unit but just after imaging you can see the missing spot so we don't believe it has anything to do with the processor.

 

[mazengh]

Mazengh, I initially thought it might be something on the drum, I have not looked at it yet but I did look very carefully at the plate to make sure it wasn't bent or bowed out in the non-imaged area, it's perfectly flat and the plate looks flawless prior to imaging. I'll look closely at the drum and see if it has some sort of debris on it...why would this cause a non-image area just out of curiosity? One would think that it would simply be out of focus since it's closer to the laser by the thickness of the punch material.

It usually happens when the punched circle sticks on the drum and it thickens that area under the plate.

 

[jotterpinky]

okay so after looking over the drum carefully it appears to pristine, no scratches, no foreign material of any consequence. However this morning I ran a test plate with a full image area and the spot is now in a different area of the plate so it must be moving around.

Any thoughts in light of this new information?

 

[heitechpro]

ptr4100

ptr4100

okay so after looking over the drum carefully it appears to pristine, no scratches, no foreign material of any consequence. However this morning I ran a test plate with a full image area and the spot is now in a different area of the plate so it must be moving around.

Any thoughts in light of this new information?

it is definitely dust on the drum. try cleaning the path, rollers and then the drum using little bit of IPA

 

[tomcatinc]

Bright halo on plate can happen only if you are doing negative working plates. If the area imaged is out of focus (like debris on drum that rises plate from ideal focus point or plate "punched" by a debris in transport path so some plate area is out of ideal focus point), laser can not deliver enough power to "glue" the inking layer to the substrate and it washes off. Cleaning should do the trick, as other mentioned it. A flashlite can greatly help in finding the debris on drum: put flashlight on one side of drum a light it to other side of trum. Anything that drops shadow makes your halo.