spotting on plate

Jeremy

Active member
I'm having a problem with spots appearing on my plate during make-ready or a run. I can't figure it out. I thought it might be a bad batch of chemicals or plates, but they've all been changed and I'm still having this issue. I have a DPM2340 from Presstek. It's about four years old but very well maintained. I only use their chemicals and plates (8mil poly). My exposure is correct according to the output plate. You do not see the spots on the plate when it is made and you can remove them with deletion fluid after they appear, but obviously that's not always an option depending on where they show up. It almost seems like it's powder or paper dust as it sometimes happens to both plates in the same place. The spots are various sizes and don't appear in the same place every time. It's completely random. I thought about recalibrating it but my densitometer doesn't read in screen percentages and I don't know the math to convert it.
 

rich apollo

Well-known member
Had something like that with a completely different system - turned out to be chunks/flakes of emulsion floating around in the developer and then being re-deposited on the plates.
 

Brian G

Active member
Jeremy: are the spots always in the non-image area?
If they show up during make ready, do they go away during the run?
If they show up in the run, do they go away after a while?
Our press operator (who's been running poly for 10 years) said, if he's just going off the details you provided, it sounds like a press issue.
However, years back we were running poly plates to imprint on preprinted "shells" that carried powder from the first preprint run. The powder caused an issue similar to the one you described.
What your describing doesn't sound like toning. We attack our toning issues by checking the exposure and the life of the activator.

We had an issue last year in which white spots were randomly showing up in the image area. Our processor is generally in great shape but we had not been giving our activator rollers a deep scrubbing at each cleaning. The rollers actually had a layer of silver on them where the plates always traveled! That affected the image area on the plate and showed up as white spots in the image area on the paper.

If things haven't changed recently, I understand that all poly material is manufactured by Agfa or Mitsubishi.
Since you mentioned Presstek, I'm guessing that your using the Mega Plate or whatever they call it. I'm pretty sure that's a Mitsubishi plate. If you can get a hold of Mitsubishi, they have excellent tech support.

brian
 

Jeremy

Active member
Yes, the spots are in the non-image area.
No, they do not go away during the run. They do not go away unless I use deletion fluid. I tried just cleaning the plate and blanket and they still remain.

I thought it may have been floaties in my activator, but I etch my plates before they go on press.

I'm not sure what it could possibly be as far as a press issue. I'm not second guessing your pressman or his experience, it just doesn't make sense to me. What did you when you had this problem with preprinted shells?
 

Brian G

Active member
I'm not sure what it could possibly be as far as a press issue. I'm not second guessing your pressman or his experience, it just doesn't make sense to me. What did you when you had this problem with preprinted shells?
I'll have to make a correction. We were having issues with powder on the preprinted shells even with metal plates. (This was/is for a GTO two-color and a GTO four color). So far the only satisfactory solution has been to print the shells 1-up (to avoid having to cut down multiples) and with no powder applied at all. (That takes more time, of course).
bg
 

RGPW17100

Well-known member
I have seen this with silvermaster type plates. Over the years silver deposits build up in the activator tank. These particals will release from the rollers, transfers or compartments and re lodge back on the plate. When we had this we noticed we went from Four weeks to every two weeks doing chemistry changes finally we went to CTP metal. I hope I am wrong here. Good Luck
 

Jeandavid1972

New member
Spots on plates

Spots on plates

Hi, Jeremy. you know I'm just having the exactly same problem I'm working on a QM46 2 color and every time I tried to print something with poly plates it's a mess. Tomorrow I'm just gonna tried a new different plates. I will let you know if i have good results on this, on the meantime please keep me post if you have any solution.
Thanks a lot.
 

BeauchampT

Well-known member
That sounds like contamination. I have seen the same issue. Try running different stock or a jb without powder on it already.
 

Jeandavid1972

New member
spots on Polyplates

spots on Polyplates

hi, I really appreciatte your attention. I'm gonna explain a little more extensive this problem. Everything was ok and suddenly one day I just started to have this spots on the plates when I'm printing. The weird thing is that in the beggining before mounting the plates, you won't see any spots on it. but, after you mount the plate and start running, this spots starts to emerge on the plates. the spots are always of the color that I'm using and once you see the spots on the printing paper you can check the plates again and you will see the spots on the plates. So what i do is to clean the plates with an spot remover and after that the spots disappears. but, sometimes you keep running and the spots will appear somewhere else on different places. I've been controlling this spots with the remover spots but every single job is the same problem. If somebody can help me with this I will really aprecciate it.
 

Lukew

Well-known member
This is a frequent problem. Some blame the plate maker others the press. Both are to blame. We get these dots when we used nikken founts and bmm 2in1 fount. We changed founts problem went away. Switching back to either two founts problem arised again. My guess is overly aggressive founts combined with poor desensitising properties is showing up an issue with these plates.. I know it used to drive me insain. Stop to adjust plates durring makeready would see all 4 plates with various dots. Only to be removed with deletion pen or sometimes plate cleaner. Glad I dont have the issue any more.
 

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