Gas Ghosting

Discussion in '4-Color Offset Presses +' started by gazman, Mar 12, 2010.

  1. gazman

    gazman Senior Member

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    We have recently been experiencing a problem with gas (chemical) ghosting appearing on jobs that we print with a matt aquueos coating. The problem has happened on 3 occasions with 3 different paper types. We have not changed coating type or supplier.
    Any ideas on the cause and ways to prenent would be appreciated.
    Cheers Gazman:confused:
     
    Last edited: Mar 12, 2010
  2. steveo

    steveo Senior Member

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    This happens occationally and its frustrating...matt varnish and coating are more prone to gas ghosting or fuming ....did you try printing one side and letting it dry and winding up the sheets? even after its printed winding it several times doesnt alway get rid of the gas ghosting. Did you get together with your ink manufacturer?
    Ive seen jobs where recoating has helped to an extent but not a guaranteed fix.....how is the humidity in your press room? temp?
    try a slower setting ink and wind the job several times before backing up , see if this doesnt help.....also printing the heavier coverage side 1st will help if thats how the job is laid out....
    good luck

    Steve

    Steve
     
  3. gazman

    gazman Senior Member

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    Thanx for the reply Steve . We r meeting with our ink and coting rep to discuss the issue.
    The weird thing is that we have been running the same ink and coating combo for years without a single gas ghosting problem something must of changed just cant figure out what it is...
     
  4. steveo

    steveo Senior Member

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    No problem , sometimes you just dont know when this is going to occur but theres steps to take to ensure preventing it or mimimizing the ghost and/ or saving the job, it may be worth it when you have a job with dul l/ matt varnish or coating on dull stock to take a lift of the first side before completing the job and flipping it over after winding it and giving it a reasonable amount of time to set-up. Then see if you get the fuming....heres a link with some tips >>>http://www.heidelberg-news.com/www/html/en/content/articles/tips_and_tricks/hn_263_avoiding_ghosting
    like I said it happens and sometime you can save the job but Ive seen it so bad other times that you just cant do anything , repeated winding and climate control and sometime recoating may help....let me know what you find out....

    Steve
     
  5. Loupeyeyed

    Loupeyeyed Senior Member

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    The only true cure to gas ghosting that I've learned is plenty of dry-time. The problem usually only happens on dull stocks or covers with spot varnishes. Usually a lot of ink ganged in to a tight photograph and then varnished. My way around this problem with Van Son, Wikoff, Superior, Kohl Madden, and Zipset is to print all of the process or inks first. Even if a job is not laid out sheetwise. Let the job sit on the floor at least one full day and even better over the weekend. Varnish your original first side of the job with an dryer additive in the varnish such as Van Son's Speedy Dry. Run your varnish light! Then yank the job. At least a day later, flip the job and varnish the other side. I worked for a company who could not realize that gas ghosting was very likely to happen on these dull stocks and they always laid everything they could out work and turn. I tried to tell them to go sheetwise with them because of this problem but it never sunk in. I got it down to a pat by doing what I stated earlier. I would at least get all of the printing done minus varnish, then have the nightshift guy put a hit of light hit of varnish on my downside at the end of his shift. First thing in the morning, I could flip the job with the varnish plate still hung and print the second side. Has worked for me so far. One instance that it didn't, involved a large metallic solid backed up by small spot varnished photos. We actually had to reprint this particular job and were successful by letting the metallic dry over the weekend.
     
  6. adcellprinter

    adcellprinter Member

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    i thought it was a stock issue? we had trouble on a couple of jobs where there was huge ink coverage with reverse text, but it was always the same brand of paper, sometimes gloss or matt/silk. i did an 85000 run w/turn (solid with reverse text both sides) job on gloss 150g which involved two batches of the same stock. one batch of stock gas ghosted and the other didn't. you could tell the ones that weren't right even after doing one side, they just didn't look right - (technical explanation). because it was a solid black job we used about 80kg of black ink and there was different batches of ink in the job as well. the stock that did it felt like it still had moisture in it and it didn't print as cleanly and was curled, whereas the stock that didn't do it felt dry and crisp and flat.
    our press engineer said it has to do with the paper not curing properly after being made and then releasing gas when being printed because of a reaction to the ink/fount.
    i'd never ever seen it until i started using this other brand of paper, still use it too, coz its cheap. bit hard to convince them to use a different stock when the company has used it for so long as their house stock!
     
  7. adcellprinter

    adcellprinter Member

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    the worst gas ghosting i've seen was when i tried to varnish a digital job off the copier (not my idea!) i don't think varnish and toner go well together!
     

  8. madjock

    madjock Member

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    Well here is my opinion for what it's worth, but it is based on a lot of experience and investigation.
    First of all I have never had a job with in-line aqueous coating ghost, conventional wisdom says that coating almost always eliminates ghosting so this must be a pretty rare occurence.
    In my experience I have found that it doesn't matter how dry the first side is, it will still ghost, and has done on many occasions for me, what I have found is that the gloss of and ink is affected by the rate at which the ink dries, the faster it dries the better the gloss, if the ink can dry at a uniform rate you get an even gloss, which it will if the sheet above has no ink on it, as the ink gets some of the oxygen required for drying from the paper itself, however if there is ink on the above sheet then the ink will not dry at a uniform rate, the ink in contact with the already printed ink wil dry slower giving less gloss and this is what causes ghosting, you can test it out by rubbing some bronzing powder on the sheet before it is completely dry, and you will see that it adheres in a pattern that corresponds to the printed image on the reverse of the sheet above.
    I have had jobs ghost on all kinds of paper, jobs that have been aired repeatedly and to all intents and purposes are bone dry, yet frustatingly, they still ghost.
    The best way to prevent it is to look carefully at each job and try and anticipate forms likely to ghost, and print them in a sequence that will minimise or prevent ghosting, obviously some forms will be very difficult to deal with, for those I would run in small lifts and get them aired up as soon as you can...and good luck!
     
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