Weird scumming problems

[robbg439]

Hi all,
I'm having some strange scumming issues. It look like dust particles or something. I say strange because I've never had this problem before, and I haven't changed a thing with my chemistry, ink, plate, or anything. The only thing I've done recently is deglaze all my rollers and blankets, but that seems like it should alleviate problems, not cause them. At first I though maybe I didn't get all the deglazer rinsed off, but I've rinsed everything so many times at this point that it seems impossible. I've adjusted all my pressures, cleaned everything up really good, and no dice. The scumming is more or less all over the print, though heavier in some spots. It persists in the same pattern on each impression, though its different if I make a new plate and start over.

I'm working with polyester laserplates imaged on a hp 5100, printing with a hamada duplicator. Any ideas as to what could be causing this and how I could fix it?

[adub]

I had almost the exact same problem recently, I'm pretty sure it was a bad batch of plates, try a fresh box see if that helps. The weird thing with ours was that those dots (look like cotton fibers) would pop up really bad on some jobs not at all on others. Go figure...

[robbg439]

Well i've been working on the last 10 plates in a box, so maybe thats the problem. Old plates? Who knows. I'm picking up a fresh box tomorrow so maybe that will help.

[Cornishpastythighs]

I would focus in on the last things you mentioned you did Rollers/Blankets, were you having this issue before you did the deglazing or did you just do the deglazing as a good maintenance printing practice? Did you see the issue after the work you did on the rollers and blankets. I'm not familiar at all with your press but we dont usually deglaze blankets we replace them with new ones. Maybe remove the ink form rollers and dampener form and give them a quick look over maybe its time to replace them.

[robbg439]

Yeah the deglazing was a maintenance thing, didn't have this problem before. Pardon my ignorance, but what would be a visual indication that the rollers need replacing? They look normal to me. I've kind of ruled out this being a blanket issue, it seems like the plate is picking up ink where it shouldn't, and it can't do that from the blanket.

[Cornishpastythighs]

Did you remove the rollers to deglaze(scrub) or run a bunch chemicals on them and wash up. Could be your rollers were so bad the chemicals you used put them over the edge. I would remove my form rollers and inspect them for wear,pinholes, durometer I would then inspect the other rollers in the roller train to see if they are wearing out. It may sound stupid but whenever I have seen scumming like this in the past its been due to a miss fed sheet or small piece of a sheet wrapped around a roller inside the press that I couldnt readily see.

[robbg439]

the fresh box of plates did the trick. Thanks for the tips! I was about to lose my mind.

[Cornishpastythighs]

good work robbg439, its refreshing to actually get some feedback from someone as to how a problem was corrected. Too many times it seems people post for help and they get loads of suggestions and possible corrective actions from this group and you never hear back whether anything worked.
Many thanks, Cornish

[Big Dave]

Cornish, It's not just this forum, but many other forums have similar issues with people posting for help and not posting the solution to their problem...

[Raymond Ramirez]

Cornish.
Thank you for saying something about posting. I know for a fact that post are seen by thousands of people and the answers are a great help.

Rob
understand one thing. You have changed a batch of plates and it seems like it is solved. the batch of plates that where used doesn't necessarily mean that that they are out of manufacturers specification. There might be something that has caused that run number of plate's to fail. you might get into 3 or 4 different batches and then it will show up again.

Without knowing the particulars of your shop (plate manufacture, processing, plate-setter..etc) We can not say if it will not show up again.

The plate is the most obvious because its the only thing we can see.

example:

Positive plate, low laser power, dirty optics, old developer chemistry, storage, etc..

The laser clears the background and the developer clear's what the laser hit's. If the plate is a newer batch The speed of exposure may react different than an older batch of plates.

Manufactures have tolerances that they try to meet or exceed. I know Agfa, Kodak and Fuji do there best to make sure that the difference is minimal but the other variable's I listed may exacerbate the issue making it seem like a plate issue.

I am by no means saying that the plate was not the issue. If no one else is experiencing the problem and they are on the same plate I would say it may show up again. Of course when you least expect it or when you are down to your last box of plates and have a very critical job in house. (you know how that never happens).

Questions to ask,

When was the last time your optics where cleaned?

Chemical change?

If you use sock material in the processor when was that changed?

when was the gum changed not replenished but changed?

Is the gum flowing correct or is it contaminated with small partials?

is the developer exit rollers contaminated with hard sediment?

I have seen when the exit rollers actually rubber stamp the plate with emulation and embed it so it looks like is doesn't clear correctly but in fact it did.

There maybe other factors unseen that has caused the plate to fail.

nonetheless
you get the jist of what is going on. and I am just carrying on

Cheers