Blinding problem

[Hessel]

Hi i'm Hessel Roskam and new to this forum. I work at a newspaper printing company in the Netherlands and we have a major problem concerning blinding of the plates.
We have 2 presses, a Goss Universal 70 of 8 years old and a Goss FPS of 9 months old and the problem apears on both presses. We use AGFA Lap-V silver plates with 2 AGFA Polaris XTV imagers and AGFA LP82 developing machines. Our Ink supplier is Flint and we add solco chemicals to our water and our blancets are Reeves.

Normally on a superclean and fresh developing machine we can run max. 100.000 copies, wich should be around 200.000 acording to AGFA. When my machine has produced around 60m2 i can only run 50.000-60.000. Sometimes we already have blinding after 10.000 copies. There was one time already after 3000 copies several plates blinded.
We changed all the blancets, filling under the blancets, ink rollers, moist rollers.... etc etc. But the strange thing is we have it on a 8 year old press and a 9 month old press. We tried Sun ink but did not work. We tried draining all chemicals from the developing machine each morning but also did not work. Our water has been to a lab and there was no bacteria or some other problem in the water.
The major problem is that the moment we told AGFA we had a problem they went into defense mode instantly, they told us it is a mechanical wear of the press. But on a 9 month old press???
They also tell us we are the only company that has problems with the AGFA Lap-V silver plates but i know cases of the same problem in Belgium, Spain and also the Netherlands. And i'm sure there are more companies. Please if you know a company with the same problem or you had (have) the same problem please let me know.

Thanks

Kind regards

Hessel Roskam

 

[SteveAgfa]

Hessel:

<snip>

The major problem is that the moment we told AGFA we had a problem they went into defense mode instantly, they told us it is a mechanical wear of the press. But on a 9 month old press???

<snip>


I encourage you to continue to work closely with your local Agfa plate technical specialists. Mechanical wear is not a critique of the condition of your press, but rather a description of the effect seen on the plate, thereby aiding in finding the culprit situation and resolution. I have no idea of your specific situation, but I know of a case where one of my customers was over-diluting the fountain additive, reducing lubrication, and resulting in a polishing of the background - ie mechanical wear.

Again, please continue to work closely with your local Agfa specialists.

Regards,

 

[Hessel]

But there is no polishing effect at all it's only blinding of the image itself. We also tested when a plate started to blind we stopped the press and cleaned the plate and treat the plate with pure finisher concentrate and the image was back for about 5000 copies.
We don't know what to do anymore.

Kind regards

Hessel Roskam

 

[gordo]

Some things to consider that you may not have yet.
Blinding is a progressive loss of ink receptivity in the image or printing area while the background remains unaffected. It's usually a sign that the image has been attacked chemically.
A fountain solution which is too strong may bring about over emulsification (and as a possible consequence: plate blinding) due to the effect of surfactants or wetting agents. Has the source of the
fountain solution concentrate changed?
Check with the supplier whether it contains any different wetting agents, biocides, or preservatives.
Check pH/conductivity. Does fount solution contain too much gum or been contaminated with detergent?? Is the plate incompletely developed resulting in gum on image areas? Has a proprietary plate cleaner or abrasive scratch remover been used? Ensure that the plate has been thoroughly rinsed afterwards. Ensure that plate cleaner has not been allowed to dry on the plate. Check the dampeners. If they have recently been cleaned, ensure that no detergent has found its way into the dampening system. Covered dampeners must be thoroughly rinsed after being cleaned with detergent and before use on the press. Examine the incoming water supply, to see if the conductivity has changed. Harder water can be a source of minerals that can be deposited on the plate.
Blinding can also be caused by precipitation of calcium salts either from the ink, the paper or the fountain solution.
In this case, change the fountain solution. Sponge and bucket should be kept free from detergents and wash up solution should be kept from the plate. Clean and rinse dampener rollers/covers.
Mechanical blinding can be caused by too much ink deposited on the plate, plate-to-blanket pressure too high, durometer of rollers too hard, and abrasive particles contaminating fount solution. solvents, ink, etc.

best, gordo

my print blog here: Quality In Print

 

[VladCanada]

LP82 Developer Replenishment rate is VERY critical parameter!
Based on your explanation, after 60 square meters processing your run-length goes down dramatically.
IMHO exausted Developer is not refreshed properly.
Call AGFA for tech help. Serviceman has to check the real amount of repleniched chem and to recalibrate or fix the problem.
Even improper position of Dev spray pipe could case a foaming effect and the oxidation kills Dev sooner than normal.

 

[maxon]

VladCanada is perfectly right. If the image is weak (bad developer etc) you will gradually lose highlight dot area and that's mechanical wear, coating is too soft. Have you checked the dot percentage cross the plate on a worn plate ?

 

[Hessel]

When i measure a worn plate the dot is still there minus 1% maybe.
About the LP82 replenishment , i also have the problem after 100.000 copies when i do a big maintanance before i make the plates. So all chemicals are as fresh and clear as it can get. When i make an image of a developed plate on a techcon i see small holes in the solids and dots. They are tiny but they are there.

Gordo talked about a fountain solution but my technical english is not that good, can you discribe that to me? Is it something in the LP82 or is it a press isseu.

Hessel

 

[VladCanada]

fountain solution - a liquid for dampening system at the press

 

[Hessel]

Ah yes, well our press is connected to normal tapwater (if you know what i mean). With a chemical added ofcourse. But it has been like that for the last 8 years now. But the funny thing is another company in Netherlands, Belgium and Spain have it to. I had a look around some forums but i know there are more cases.
The only thing we have in common is all AGFA plates, developer, imager and ink.(Flint)

 

[VladCanada]

Another possible reason of blinding is - your Polaris.
The imaging process is NEGATIVE, and if the Laser exposure is higher then normal you will get a good image with sharp edges and Techcon reading shows good exposure calibration, but really the edges of printing elements have a hidden destructurisation. After a few tens of thousand (or even sooner) 2% dots gone, the real profile of printing elements becomes not flat but "round" a little bit... so an ink-accetpance will change as well.
Some AGFA Liap-V (O) Customers prefer Laser overexposure to avoid a toning effect at Alu background (non-printable part of image) and it works for short-run jobs, but if you need more prints.........

 

[Hessel]

We work with positive plates. I had overexposure, underexposure, elliptical dot, sublima (AM/FM) dot... But i know what you mean.
One thing i did not mention yet is that the 8 year old press the blinding starts in a corner on the tail of the plate and the 9 month old press has 1/2 inch wide lines every 1 1/2 inch.

 

[VladCanada]

So... clean the optics and get a proper exposure value (less than you've got now). I know that every Polaris user has an issue with the Exposure and only thing they do - increasing the laser exposure.
Do you clean the Spinner Prism facets regulary????????????????????

 

[VladCanada]

If you can see a dust contamination on every of 6 or 8 facets (one side is dirty than another) and if you see the blinding starts exactly on the end of scanning lines (one side of plate) - that's a sign to you, clean me ASAP!

Sure that's a Positive process, I'm sorry for the confusion (did not touch CTPs more than a year!)

 

[Hessel]

AGFA tells us that cleaning is not nescesairy on a Polaris XTV..... Should they clean it you think?

 

[VladCanada]

Does it mean the mirror is clean forewer because the top position of a Spinner? Khmmmm
It depends on the environment in Polaris room.
I have never work with the latest version XTV but the principle should be the same.

From LithoStar plates presentation file: Overexposure give shorter runs, underexposure - toning&scumming

 

[Hessel]

The new polaris XTV has less mirrors and the whole optical envirement is in a overpressure. So no dust can come in.

 

[Green Printer]

We have experienced the same effect a few times on sheetfed Komori and Sakurai. Every time the problem occurred it was ink related.

 

[Lukas Engqvist]

lines in the plate? Could be a deveoper issue. Have you checked that all pumps are working and that there is no build-up of chemicals making the feeding rollers jerky movements.
look for a roller/cogg with a circumfrence of 1 1/2 inches.

 

[Bret Hesler]

I had a similar experience with Fuji photopolymer plates. It turned out to be a press wash issue. Pressmen were using a water miscible press wash without mixing in water and without a thorough water rinse at the end of the washup. The Fuji tech brought a 2- step washup and Febo, after a few cleaning cycles alternating the products, the plates that blinded after 250 impressions ran beautifully.

Bret

 

[[email protected]]

We had this problem with these plates on sheetfed presses. AGFA rep said that the developer replenishment was critical. The development process is some sort of silver diffusion process and if the temp/time/activity of the developer is not optimal then we got blinding. The silver has to "go down" on the plate to use the reps words. We ended up cleaning and re-batching developer every week and our blinding problems went away.