Gas Ghosting

[Lukew]

We are suffering from gas ghosting when we try and matt varnish both sides of a heavy coverage job on 135 -150 gsm stock,, most of these jobs have large coverage black with some reversed out panels,, one job was mainly solid black with an orange PMS colour as bars about 1/4 inch thick and out of the 7 bars on each side only one of them gas ghosted ??
Now I've read a fair bit about Gas Ghosting I know what causes it but don't know how to stop it happening but what ever I have tried at the moment hasv't helped.
Can it be the type of varnish being used, we are using a matt sealer as apposed to a matt varnish is there any difference?

Normally I would print the job and back it up in 15 - 20 min's then varnish it later that day.. This has resulted in gas ghosting sometimes you could print the same job 5 times and it may only gas ghost 1 out of 5 and you have changed nothing,

I have tried to
print the job then varnish one side the next day and then varnish the otherside the following day, this resulted in gas ghosting

I have tried printing one side and leaving it a lot longer before backing it up but still have the problem..

Yes I have the IR dryer on,
Would it help to print one side and varnish that side then the following day do the same on the other side..
I would of thought this would have traped the gasses in even more?

I have tried running it in stacks no higher then 500 sheets.. faned the sheets before backing it up
Has anyone tried the anti ghosting varnish from vanson ink's ?

Any suggestions would be great,, this is becoming a nightmare as its popping up out of the blue and when it happens the job is no good..
Luke..

 

[CKL]

I just spent 2 days with the Technical Director of Vanson. We talked about Gas Ghosting he never mentioned that varnish. Can you put an AQ on it. Even roller train AQ's will hide the ghost then dry trap the varnish to the AQ. We ran this way 10 years ago on some difficult pieces.

 

[nhprinter]

Gas Ghosting

Hi Luke,

There is no way to get rid of gas ghosting once you have it. You'll be told you can fan the sheets out to get rid of the gases that are causing the ghosting and wait a couple of days for it to dry, but I've never found that to work.

You should talk to your ink company. We had severe gas ghosting problems with one manufacturer so we changed to another and haven't seen it in years.

If you have to keep the same ink you'll have to run one side, varnish it, and then do the same to the other side. (as long as it's a full varnish which will "seal" the sheet) We did that for quite a while before we changed manufacturers.

BTW....without getting technical, the REAL problem is the paper. It's just that some ink manufacturers have compensated for it better than others.

Dave

 

[Bob Peterson]

Luke,

I will make the following recommendations:

1: Turn off your IR dryer. All the IR does is evaporate the fountain solution on the sheet,it does not speed up the drying of the inks.

2: Small lifts.

3: Immediately wind the lifts when the ink is set up enough and before backing up.

I have attached an informative artical by GATF pertaining to ghosting.

Best of luck.

Bob

 

[Lukew]

Thank you for all that info,,
so from now on I will make sure the job has a 24 hour period of drying before it is backed up, but I will try and varnish the side straight away after the first side is printed.. pitty we only have a 4 colour so inline varnishing isn't an option.

It has also been suggested to me to lay down a full solid of trans white on one side before printing comences and then to print first on that side, was told this seals the stock and doesn't allow the gasses to effect the other side...

 

[John A]

According to a recent technical paper I found by Googling "gas ghosting"

here's the link:

http://www.handschy.com/techdocs/Chemical Ghosting.pdf

Gas Ghosting isn't caused by ink gassing through the back of the sheet but rather ink gassing (up the lift) to the back of the sheet sitting on top of the newly printed sheet. The chemical deposit to the sheet above it caused the ink on the second pass through to react differently and show a ghost of the image from the sheet below it in the lift.

My point is, if that is true, (and I believe it is) laying down a solid under the (1st pass) printed image won't stop the problem.

The PDF I linked to above lays it out pretty simply, along with the limited options for helping to get rid of it.