Thin lines appearing on plates

Hello everybody,
Sample.jpg


I am using Fuji LH-PJ positive plates and we are seeing that after around some 20,000 prints thin dotted lines start to appear and if left unattended they tend to "grow" into full lines. It has happened on all units. We have also noticed that the lines appear in the same position, once we change jobs.

We think there is an issue with the press since we had tried different plates with the same lines showing up, only difference is the time it takes for the them to show. Haven't been able to pinpoint the problem, any recommendations?
 

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Magnus59

Well-known member
We have seen similar lines coming from the plate autoloader on the press, the O rings on the wheels tend to get a build up of ink when un-mounting the plates, this then transfers to the next set of plates. It could also be a problem with the processor. Unlikely to be an imaging problem , because I would expect the lines to be there from the start and not increase in intensity.
 

maxon

Well-known member
Has nothing to do with the plate itself, these appear to be scratches down to bare aluminium and holding ink during printing. Look for whatever can cause such mechanical abrasion during plate mounting or press run. Does it come up on all colour units if several ? In same place ? I agree with Magnus59 can be an APC issue. Carefully mount the plate by hand, check plate surface in strong light before starting run then stop and inspect again every few thousand sheets.
 
Clarification: Lines are darker or lighter? Show in image or non-image area?
Lines are lighter and appear all along the area, most noticeable on non image areas but if the job is mostly light colors and the line appears on the black unit it will show all across
 
Has nothing to do with the plate itself, these appear to be scratches down to bare aluminium and holding ink during printing. Look for whatever can cause such mechanical abrasion during plate mounting or press run. Does it come up on all colour units if several ? In same place ? I agree with Magnus59 can be an APC issue. Carefully mount the plate by hand, check plate surface in strong light before starting run then stop and inspect again every few thousand sheets.
All units and same place. I'll check a new plate and againg after. Thanks
 

Tmax

Member
Agree with the others, something is scratching the plate and removing emulsion to bare metal. Does it go all the way down the plate? Are the scratches lead edge to tail edge?
 
Agree with the others, something is scratching the plate and removing emulsion to bare metal. Does it go all the way down the plate? Are the scratches lead edge to tail edge?
They go around almost all the way. Starting at where the plate meets the ink, but haven't look at the tail edge.
Line ends.jpg
 

schenkadere

Well-known member
We are suddenly experiencing the same thing with Fuji LH-PL plates. Oddly for us, it is occurring at more random position on the sheet but only on the operator side, and only happening on one press. Also initially it was isolated to one unit, but no longer.

They have carefully looked the press over and cannot find anything.

My next thought is try a different lot# of plates, but of course all the plates of that size in shop are the same lot #.

I'm going to try to get a tech rep here to hopefully rule out the plates.
 
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maxon

Well-known member
I would put a USB microscope on the plate. What offset machine do you use ? Who checked the machine ... the pressmen themselves ?
I say Alois is right, leave the affected plate(s) on the cylinder and check the blankets for damage or metal flecks possibly embedded into rubber using a magnifier at positions matching the lines on plate/sheet. Make sure fountain solution is clean and filtered, printing units carefully cleaned overall especially clamp area looking for aluminium dust. Run at lower speed to see if lines change.
 
Bouncing ideas off our master operator we narrow it down to the markings we make to identify operator, date etc. We use a knife for this purpose and a small speck or swarf is generated as in the picture. We will use some other marking method hoping this does the trick.

Everybody's input has been very helpful. I would like to thank y'all!
 

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I would put a USB microscope on the plate. What offset machine do you use ? Who checked the machine ... the pressmen themselves ?
I say Alois is right, leave the affected plate(s) on the cylinder and check the blankets for damage or metal flecks possibly embedded into rubber using a magnifier at positions matching the lines on plate/sheet. Make sure fountain solution is clean and filtered, printing units carefully cleaned overall especially clamp area looking for aluminium dust. Run at lower speed to see if lines change.
Roland 900. Maintenance checked the machine as well, but now that we are after flecks I am waiting for the next line to appear to check with a microscope.

I just posted a sample picture with a marking where a small roll of aluminium forms at the end. And I just realized that on the first pictured posted you can see large dots at the end of the marking. I guess if lucky the fleck stays there, if not it falls and ends up on the blanket.
 

schenkadere

Well-known member
I don't understand. This was a practice your plant has always done and it just became an issue now?
I'm very curious to see if this does truly solve your issue. Please post back after some time.

I have a Fuji tech rep coming to our plant today for our line issue.
 
I don't understand. This was a practice your plant has always done and it just became an issue now?
I'm very curious to see if this does truly solve your issue. Please post back after some time.

I have a Fuji tech rep coming to our plant today for our line issue.
It wasn't a standard practice until new customer asked for it and we decided to do it for everything. We had lines before but it does seem they showed up more often after this.
 

schenkadere

Well-known member
It wasn't a standard practice until new customer asked for it and we decided to do it for everything. We had lines before but it does seem they showed up more often after this.
As suspected, the Fuji tech said it's not the plates...good for me...bad for the pressroom.
 

Magnus59

Well-known member
As suspected, the Fuji tech said it's not the plates...good for me...bad for the pressroom.
We're fortunate in having a Kodak rep who takes ownership of problems like this. We recently had an issue with spots on a big job, long run and many plates, as usual, finger were pointed at Prepress before looking into anything else, I called in the Kodak rep, who organised a free pack of plates from another batch, the problem persisted. He cam back with a microscope to look at the spots and suggested they were coming from the press. He then opened a palette of the stock we were using and went through it sheet by sheet. It turned out there was random foreign matter in the stock which was transferring to the blankets, then onto the plates, resulting in the rogue spots.
 

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