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Hi all I am having Gas Ghosting issues on my Heidelberg's Sm74,and 102Sp
Gas Ghosting is a chemical-activity influence that inks or varnishes have on each other during their drying phase. Possible ink incompatibility issue or too much ink. Dryer settings to high etc. Sometimes inexpensive papers can also have an influence on it.
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This can occur during the print process when solvents from ink drying on one side of a the sheet interact with the dry ink on the other creating a ghost image.
It can be prevented by using low VOC fount additives and/or faster drying inks or highly pigmented inks.
Increasing the level of IR (if you have one) can help...you need to be aiming for around 35º c in the stack.
We have had limited success in the past by passing the sheets through the press with just the IR on to force the solvents to be released.
As with all problems its better to prevent than try to cure the issue once it has arisen.
IMO you'd better look at your ink/fount combo and rethink it if you get this problem often.
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Ahh the old Gas ghosting--
I remember the day I printed a resonably long run for the car man AUDI,, job looked fantastic till the last side varnish went down gas ghosted the lot... had to reprint and followed the steps below = no gas hosting.
From the research I have done a lot of what richard said is right,, but some litreture points to the IR dryer having adverse effects. especicaly if you back the job up quickly,, basically the top layer of the ink is dryed by the IR and if its backed up quickly the gasses don't have a chance to escape.. Once the varnish is layed down the gas ghosting then appears.
A few good steps to lesson the issue... Given by Bob Peterson -Printplanet all simple steps that are outlined in any gas/gloss ghosting litriture
The IR driers and hot air knives only evaporate the moisture from the sheet this is the only role they play in speeding up drying. In most cases excessive heat is determental and will only exacerbate the problem.
I would recommend the following to reduce the chances of ghosting:
1. Print the heavy side first.
2. Dry the sheets in small lifts, 2-3 inches, keep them in strict sequence for backing up.
3. Allow maximum time (no less then 24-hours) before backing up the job.
4. Wind the sheets as soon as possible after backing up the job to get water and volatile gases out and fresh air in.
5. Varnish in-line when possible. Varnishing after drying often brings out or developes previously invisible ghosts.
6. Choose the correct ink for the paper. Some papers like Cast coated require higher solids ink.
7. Run as little foutain solution as possible. Just enough to keep it from drying up.
8. Keep delivery piles away from excessive heat or cold.
9. Have your ink company select an appropriate ink for the job and stick with it.
10. Do Not add any additional driers to the ink or fountain drying accelerators as this will only increase the odds of ghosting.
Following these rigorous guidelines should eliminate the problems you are encountering. Should you still have trouble your only other option would be to slip sheet the job as this will entirely prevent the ghosting.
veg oil based inks may help
I only experience this with flood varnish jobs, but as it dries the ghost will vanish.
all of lukes tips on preventing gas ghosting are good tips imho. the problem is that theres so many of them and if we were to apply all of them on every job then press production would be compromised.
i believe the trick is to be able to recognize a form that has the potential for gas ghosting and apply these tips only when we see the potential. after over 30 years experience in running multicolor presses ive learned to spot these high risk forms.
first of all as luke said jobs should be inline varnished whenever possible because its usually but not exclusively a problem that occurs when we offline varnish. i see the biggest potential for gas ghosting coming from forms that are run with very high total ink densities. graphic designers seem to always want to push the limits of total ink density. sure it really makes an image "POP" when you combine all 4 colors to produce these really high density super blacks but its risky.
the story unfolds something like this.....
1. we as pressman see a form with overly high total ink densities as we ready our plates to be hung.
2. after seeing these high total ink densities we opt to print the varnish offline so as to avoid the potential of offsetting the job.
3. we proceeed with the job saving the varnish to be done offline either on our press or worse yet to be handed off to the less experienced guy running the single color or 2 color press.
4. then the offline varnish happens and when that gas ghosting problem arises fingers are being pointed in the pressroom. cmon guys we all know how that one goes!!!
i say that we as pressroom supervisors or pressman need to educate the production people, customer service personnel, or pre press people as to how to avoid these high risk forms. this applies to all issues that may arrive in the pressroom not only just gas ghosting. i myself am sick and tired of being blamed for issues that arrive in the printing process that are caused by poor planning in the pre press dept.
there was a time when pre press personnel were experienced craftsman in their own right. now it seems that all it takes to become a pre press person is to complete a 6 month course. perhaps thats a bit of an exageration but you guys know what im talkin about.
i feel that the guy whos doing the prepress work for multicolor presses needs to be an employee of equal skill to the pressman thats running the multicolor press. and if hes not of equal skill then he should at the least be managed by someone of equal skill so as to guide him or her.
my experience in being able to recognize these high risk forms can not be summed up in words. there are no shortcuts to learning these things. trial and error are still the only way of avoiding these high risk situations. i can however say this.... always keep your eyes and minds open to the trends that cause these problems. when you see a problem like this arise pay close attention to all the details. and last but not least try to foster an enviroment in the company where theres an open line of communication between the pressroom and the rest of the company.
if your a pressroom supervisor and your not promoting this open communication then you are in my opinion failing!!! and if your upper management in a company thats not open to hearing from the pressroom supervisor you need to either hire someone you have more confidence in or find it in your hearts to open up to the suggestions of your pressroom supervisor. if your not doing this then you are doing your company a diservice!!!
I understand what your saying,, that those steps can't be followed on a multitute of jobs, simply put nothing would get done..
Our shop we had to varnish later as it was only a 4 col press and fortunatly for us we only had a small handfull of jobs that would be a gas ghosting risk. so each time they came through we ended up followed the steps.. but that might only be like 2 jobs per month,
When the gas ghosting first happened I got the blame "somthing you must of done - cause we've never seen that before" probably cause we never had a 4 col press befor I stated" informed them of what and why it was happening, found the relevent litriture on prevention methods and was laughed at with a " theres no way we can do that, the client wants it the next day blablabla... "
Once it happened again /again - they let us implement the steps.. wow look out no more gas ghosting, geezz I'm sure the client if they were informed of the problem would be happy to advance their order so we had sufficient turn around time to follow the steps.. And to then recieve a job free of ghosting.. And so thats what we did.. EDDUUMMAACCATTION
I agree totally with many of the previous Post on Gas Ghost Prevention Issues,I have had that problem in the past,as I'm sure any experienced Press Operator has,my only tip for prevention,if it hasn't already been mentioned,is to run the heavy side of the form 1st,Gloss Varnish off line and let this side dry before the 2nd side is run to seal the ink on the 1st side,then run the 2nd lighter copy side,doing it this way,I have never had a problem since with Gas Ghosting.."Seems there's never enough time to do the Job right the 1st time,but,there"s always enough time to re-run the Job" Pressman Pete
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