Spots developing on plates QM46

We have been having an issue where our plates come out fine, but develop spots as soon as we start running them. We currently run a DPM Pro 400 plate maker, which we got about 3 weeks ago, but we've had this problem for about 3 years (previous plate maker was a dpm 2508). We run 8mil MegaPro polyester plates. Our other press is a GTO, which uses the same plate material and imager, but doesn't have the same problem. We have been in contact with Presstek for over a year about the issue, with no solution. If we remake the plates, they usually work fine...

 

9 times out of 10 it's crap in the rollers. Dirt, dust, old ink chunks etc.....I have the same issue. I run a Hamada and Multi in a big old factory building and it dirty and nasty. Sometimes spots from the get go or if I stop a few mins. I use a deletion pen to remove them and continue on. Sometimes they go away (wear out) on their own. Never had this happen anywhere else with a clean press room. In your case the key is the GTO running the same plates without issue. Give the units the once over and cover them at night to keep dust and dirt out.

 

Appreciate the insight, but i just checked with the press operator, who told me that we've replaced every roller and the inside of the press is "spotless." Any other ideas? I definitely think it's operator error as opposed to the plate maker.

 

It could be a chemical issue however it's not very likely. Try running you fountain a little hot .

 

..I have seen this, and can not blame one specific cause, it is a combination of everything LOL... from chystals in older fountain soluiton, Cold plate material chemicals, to inks with no body so we are over inking to bring the colors up to match pms causing spots on the sheet. I have found that even if the DPM-2000 says it is up to temp...I wait 1hr before releasing plates. Also, how often do you check the exposure ??

 

Thanks swifty. The exposure is fine. I check it once a week. More if I think it might have an issue. The plate maker is actually a DPM Pro 400, which seems to be working really well. The plates seem to be fine when they output, and this issue happens on plates that have been output at various times of day, etc.

I'll check the fountain solution and ink type. I would guess the ink itself is not to blame though, since we use the same type on the GTO. Pretty sure they share fountain solution too.

I also just found out that the QM operator is using a parts washer, which my pressroom supervisor thinks may be causing the issue. I think he's using Pronto in it to clean many of the parts. No other operator I've worked with has used one, so I'm wondering if anyone else has any insight on that.

 

If you are using the same plates on 2 different machines with different results then it isn't the plates. So rule that put and move on. The fountain might not be strong enough to clean the plate while running and the spots keep coming back. This is why I suggested running the fountain a little hot (not temperature but adding more concentrate ). This might do two things either work or cause more issues. If it cause more issue then you know a good starting point on the problem .

 

He has tried changing the mix and type of fountain solution without significant result. The pressmen expressed that it seems like the plate is actually losing a layer where the spots are showing up. One of them thinks it may be too much tack actually pulling some of the plate or emulsion off the top. Does that sound plausible?

 

If the pressure to the plate is too great then yes or if a chemical other than ink and water is applied. So you're using pronto,is he wiping the blanket then starting on impression without the blanket drying? I assume you've check the pressures already. Is your pressman wiping the plate with anything or etching? If so see what the gto guy is doing and follow suit or stop following suit whichever it is.

 

I've seen an old beat up blanket cause issues like this also.

 

The blanket has been changed and is relatively new. The operator is using Pressman's Pride plate cleaner. He says that using it and letting it dry sometimes helps. Image attached

 

Can you post a picture of the spots? Are they in a row or random?

 

Random size and position. I'll post a pic next chance I get.

 

Have you checked the plate loading roller? There should be a small roller that rides on the plate as its loading to keep pressure on the cylinder. If it's funky or has too much pressure it might be scratching your plate as you load.

 

To second this ,if your operator is cleaning the roller in the parts washer the naphtha might be swelling it .

 

I still think it is the ink!! ink for a GTO is not ideal for a qm-46 !!!...quick test...when the spots happen...did you have problems bringing the ink up to color??.

 

Until you can pin point the exact issue why does he not just use a deletion pen to erase the spots? I'd get a few, stop delete and continue on fine. Poly plates are not made to use endless wipes of plate cleaner. On mine I can use true blue and water on a cotton pad to clean. I can also wipe the plates down and leave them on press overnight. Wipe them down in the am and go. They can be pretty durable but nothing like a metal plate. I'd also like to know why the guy is cleaning his rollers in the parts cleaner? Doesn't the press have a washup tray attachment? Seems like a pretty good waste of time to remove the rollers every time the press needs a washup. And the parts washer chemical concern as mr mark mentioned too. For the most part those parts washers do not filter the chemistry and added waste ink sits in the bottom of the tank. So it can be adding small particles of ink into the roller pores. Even though they "appear" clean.

 

I don't disagree with what ffr428 is saying however it sounds like the emulsion on the plate is coming off . This would be made worse by the deletion pen. This is also why I went away from ink and water chemical balance. It is a strange problem and the crap in the parts washer might be causing some issue as well.

 

So the ink is the same as has been used for many years before this issue on both presses. I doubt its that. The deletion pen will sometimes work to erase them and sometimes not. If it does, it seems that stopping and starting again usually comes with new dots appearing. It seems he's not actually using the parts washer for the rollers, just the washup tray. The solvent is petroleum distillates. I was misinformed on that. Here is a pic of the spots, you cant see all of them, but I've circled them. They appear in different places on each plate, but stay consistent once they're on the plate.

 

Ink is not the mixedwith same Way it used to be !!!!!!
today It is formulated for the larger presses!!!!!
How much ink does he have to dump on to bring the color up..
what is his water set at..