Fading\blinding in first unit only
We're experiencing a problem in our first unit only that we haven't seen before. KCMY sequence, gloss coated 100# text, longer runs than we normally do, these are 125,000 sheets. First day on press, no problems, runs all day 30,000+, second day within 1 hour of startup, K plate starts losing dots, gain drops about 15-20% at 50, make new plate, start back up everything ok the rest of that day. Start back up the next day and same thing happens.
This is only happening in this first unit, so looked to find anything particular to that unit, checked roller settings, wiped down paper, all units cleaned same, same result each day, they tried not cleaning the plate off at night just letting the ink sit on it so it wasn't touched with cleaner and same result the next day. They tried cleaning the plate really good with Nova to get it back with no success.
We are using Fuji LHPJ plates which have been totally bulletproof for us for 2.5 years now.
My thoughts were blinding, this is a new paper to us but still a good gloss coated sheet, was going to check fountain solution but discovered that our pH and conductivity meter isn't working and hasn't for a while but they are checking pH with strips? The other thing I've wondered about is they say when cleaning the blankets and plates at night the last thing they do is put the waters on to rinse the plate and so it gets some gum, could this be a source of chemical blinding if small amounts of blanket wash getting in solution? or contaminated fountain solution drying up on the plates over night? Either way, they do the same to all 6 units so why only this problem in the first?
Also, we are using light tack ink in first unit and medium tack for CMY units to try and help with picking or piling? Our ink people tell us no one is using medium tack inks much anymore so they don't stock them, that most everyone is using light tack, does that sound right? We are running 20 micron FM and used medium tack for several years in the interest of sharper print.
Any ideas or thoughts on what to do next in the process of elimination?
Last edited by Prepper; 08-27-2012 at 07:36 AM.
When was the last time the entire dampening system on this press was completely flushed? Get a good dampening system cleaner, from your fountain solution supplier, and flush the whole system. The goal is to get all of the calcium out of the system. If this doesn't eliminate the problem, it could be the ink. I have attached a Prisco Tech Talk that touches on the subject (I don't work for Prisco).
If the above doesn't resolve the problem try this:
As a test. Either try a different batch of black or change the black to last down. If you still have the problem with a different batch of black or with cyan in the first unit, there may be a problem with the batch of black you encountered the problems with.
They haven't changed the solution in a few weeks. They say that adding some as its used up replenishes it so they've completely changed it out over time, this doesn't add up for me but that's what they do. Topping off your car with oil is not the same as changing it, and I suspect this isn't the case with fountain solution either, as diluting contaminants doesn't clean it, it only dilutes it.
Anyway, we haven't experienced any sensitivity, just blinding\fading. They did do a calcium washup, which they said hadn't been done in a couple of months, but we had the same thing the next day also.
They don't believe in last down blacks either, say you don't get same result, from tests we did I saw very little difference. We run 2 types of jobs here, 4-color jobs where they run KCMY in units 2-5 (leave unit 1 open with pressure on to clean paper) and 6-color jobs which are KCMY+2 spots. I proposed running CMY in units 2-4 always and just changing K from unit 1 to unit 5 as needed thus eliminating the longer, thorough cleanups because of moving the colors around in the units but the pressman thought the last down black was too different to do that.
This was a new paper to us so I suggested running on a different paper for a day and then see what happens the next morning. I think I would have cleaned out the fountain solution and if it still happened changed paper and see if it went away then. One thing at a time.
So let me get this straight.
Same ink as you always run.
Same plate as you always run.
Same ink sequence as you always run.
Longer run than you usually run so plates are being left on the press overnight.
Different stock than you normally run.
Of course you should go ahead and implement a rigid Fountain solution checking/cleaning regime as that is best practice anyway for good printing.
Maybe your plate needs to be baked for the longer runs.
Maybe your plate/blanket squeeze is out of whack.
Could be your rollers have hardened enough that they are not so good on an unbaked plate on the longer runs.
Have your pressman gum the plates in correctly and not the lazy way (the black anyway)
Find out from the stock supplier if anyone else is having the same issue.
Yes to checking/cleaning regime, but that isn't happening now and probably won't in the future. How do you convince people that don't think it necessary?
On squeeze, they've checked everything out.
On baking plates, this is happening after only 30k, these are 300k plates, and only in unit 1, and only on 2nd day within an hour of starting up, dots start fading off.
Roller Durometers in unit 1? I guess people who dont believe in fountain solution care and maintenance wouldnt be interested in durometer guages either
Have you physically examined the plates after this problem? Are you really getting a sharpened dot on the plate itself from wear? Really important to know if the dots have physically worn or not, or if something else is giving you the gain loss.
Yes, they do appear lighter under a glass but I only measure about a 5% difference between the old and a new plate. The press was showing about a 16% loss.
We run to G7 and the 50% K patch was reading .41 at that point where it should have been .50+paper=.58 in this case. I know that's density and not related, just stating how much lighter it was. We then started changing the plates before it got that far.
They are running the same paper today but from a different shipment, they said it's much cleaner and the plate is running okay today so far, and that was after sitting since last Thursday night. Go figure?
Are we talking about Plate Image Wear ? - Image Blinding is a different problem
My first thought is this is a Paper Problem, my next is have the 1st unit Blanket Tension been checked ?
had same thing happen on 60# offset (new paper) extra large quantities(200,000+) calcium deposits were blinding 1st down black plate on the perfector press we were running on first unit but no trouble with black 5th unit looked at 1st unit rollers end play etc etc cleaned and changed fountain solution pressmax 270A seemed to help also went to low tac black (superior AE 1777) seemed to carry more water which helped plate resist blinding also looked at the expose time on plates was fine on avg runs but needed to step up a little all these things i mentioned plate expose ,better carry water black ink and fountain solution with a good running unit roller set no end play etc etc got us to get better mileage on our plates 250,000-325,000imps hope this helps good luck ...steve