Spot uv issue!!

Hi guys, it's been a while since I've posted but here's an issue that I hope someone somewhere can shed a little light on.

I've attached a pic of an issue that arose when we supplied printed sheets to an outside source for spot UV varnish onto our preprinted sheets.

The image shows what appears to be 'blobs' that turn out to be unkeyed areas of the spot UV. It is contained on one side of the sheet, and runs from grip to back edge.

We printed using our standard ink set + an overall seal water-based coating to both sides of the sheet. We've never had issues of this kind before using our current inks/ sealer combination and the supplier is our regular supplier.

There's only one sheet affected (it's a multipage brochure) and the 'blobs' come and go varying in intensity and location but always in that one 'track' ie the opposing side of the sheet is unaffected as is the reverse.

Any help would be appreciated.

ciao

Richard

 

Tough one, RichardK.

How much Time did the job sit from the printing of the first side to the second side. Or was it printed on a 10 c?

FSA

 

Printed on a Heidy CD 5 colour + anilox end of press coater. Air knives and IR.

It was a 3000 sheet on 170gm silk run so around 45mins …both sides aqueous coated and IR. Then around 48hrs before Spot UV.

Inks are conventional litho veg oil based both they and the coating are what we use all the time. There was a separate cover printed on slightly heavier silk 200gm, same amount of ink and spot UV coverage but as it was two up it was turned round (print wise) in half the time. No issue on that or the reverse of the affected sheets.

So yes … it's a head scratcher.

 

Update::

Just had the reprint back from the same supplier...same inks, same paper, same coating but this time no 'blobs'

 

What about powder on the stock before you sent it to be coated? if the uv coater picks up powder off the sheet it will stick on the rollers and cause problems such as this. also if the rollers are not set correctly on coater, it may cause similar problems.

 

Hi Richard,
It could be static electricity affect. Check the eliminator at Feeder. Circumferences conditions like humidity and temperature is important as well.
Good luck.

 

Looks a bit like the area affected has absorbed more IR because it is darker. The coating then dries on top of it but the IR energy in the sheet causes oils to leech through the coating interfering with the UV varnish which wont bond on oil. How much IR do you use when printing? If you are Aqueous coating it isn't any good to have the IR running on auto temp control because the coating artificially cools the sheet and forces the IR to put more energy in than is desirable.
Also your anilox needs to be putting down enough varnish to cover heavy inked areas, is it?
It may be this has happened now and you have just been caught out by circumstances on a particular day but it must be close to the edge to get it one day and not the next.
I'd look at how you run your IR whilst aquaeous coating, I have seen this before.

YG

 

Sounds like a reasoned assessment YG

However, there was 48hrs between print and Spot UV so I would have thought that would have been ample time for solvents/oils to disperse.
The Anilox roller has been replaced some weeks ago. No problems before or since with setoff - and no Spot UV problem with the other sections of the job that were printed on the same day. The area affected has dark and light zones, but again only one side and one 'track' affected. Head scratcher indeed.

 

It could be oil and solvent wont disperse in a pile, just sit in the coating. The areas in the photo affected are predominantly dark, any solvent /oil migration will spread to some degree.
Not saying I am right but there has to be a reason. There are many variables in our process trying to spoil a good job, maybe some conspired on that day to give this result.
Was this side printed first? Residual IR in the ink from the first pass then giving it another dose may have just tipped it. Management of IR/hot air is important on quality work like that.
Hope you get an answer some way because not knowing means it may come back and bite.

YG

P.S. We have met several times.

 

Residual heat...well I admit I didn't check stack temps...no need since we'd never had an issue before (or since...even on the reprint)

We've met? Quite possible...give me a clue. Yorkshire is a notorious hub for print and print engineers.

 

We both knew a DJ, suspect we're both glad we don't anymore.

YG

 

I wonder why only ever hear bad things about DJ

 

DJ actually helped me out of a deep, deep financial hole (actually, I'm not sure whether he got me into it in the first place ! - however, that's water under the bridge now, he did help me keep my home when we decided to close the business.

I'm sure bad things get said about many people, me included, eg two of my ex-staff members, whom I kept employed for over 10 years, decided that their one month's salary was worth more to them than my home.

I'm certain that my name has been ***** simply because I delayed the closure of the business in order to try to sell our press and so prevent the finance company repossessing it and our home.

Bitter? No, not really just sad that these two individuals bit the hand that fed them over the years.

 

May be what I said didn't come over in the way I meant, its not all bad.

YG

 

I'm sorry to hear all that, its always sad when people who have worked hard for a long time loose what the have worked for, beit a competitor, friend or complete enemy, it could happen to anyone and at then end of the day i think most of it is down luck

 

Thanks for the understanding.

It was a wrench but completely the right thing to do.

In hindsight (which is a lovely thing) I ought to have made one press crew redundant several years ago when the workload dropped ~ however, my heart ruled my head and we soldiered on in the hope that the recession would ease up. It didn't.

Anyway...moving on... I've just won a double sized run from the same client...I don't want to risk the same issue as happened on the first run so we're going to leave at least 48hrs between print and Spot UV, we're going to air the sheets after printing. But I've had a thought...would wax-free inks be the solution?

 

Yes definitely use wax free inks. It can only help.

YG

 

Hi!

Silicone treated powder could also be a problem.