Aqueous Coating Cracks

Discussion in 'Heidelberg Printing Presses' started by aqazi81, May 27, 2017.

  1. aqazi81

    aqazi81 Senior Member

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    Hi All,
    We are facing issue with coating cracks on heavier coverage areas. Low coverage areas have no issue or very little visible.
    Please view the attached images of the issue. IMG_20170527_134409 (1).jpg IMG_20170527_134409.jpg IMG_20170527_134514.jpg IMG_20170527_135553.jpg
     
  2. turbotom1052

    turbotom1052 Senior Member

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    Aqazi,
    my first thought would be to say that its happening as a result of the cure. I would suggest adjusting the cure to arrive at pile temps of no more than 105 degrees F. by mostly your hot air knives, as opposed to infared lamps. If you can not get that temp using mostly the air knives id be looking at why not!!!. Also it would be advised to make sure that you have good extraction of all the solvent rich gases from the entire delivery. This extraction of the delivery gases will seem counterintuitive as along with the gases you will be pulling heat, thus making it more difficult to arrive at the desired temps. But the moisture rich gasses must be removed to make for a good cure. Your air knives will need to work harder to keep temps up but I think you will find drying will be without the "pucker" that I believe is causing your cracking issue in thick coverage areas.
     
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  3. aqazi81

    aqazi81 Senior Member

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    Thank you Turbotom for your reply, We have tried with different temps already and even without IR or Hot Air but no use.
     
  4. glenn lamarche

    glenn lamarche Member

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    Ontario Canada
    Hello We have also had cracking in the past but never really figured it out . we will turn up the fan pulling the gases and moist air thanks for the info

    Glenn
     

  5. Jeff Sullivan

    Jeff Sullivan New Member

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    Location:
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    It looks to me like you are getting what's known as mudcracking. It's caused by the coating drying to fast for the ink. The heavy coverage ink areas dry slower than light coverage. That is why it is not happening over the light coverage. Your inks may be taking on too much water. You could also try applying more coating and reducing air knives to slow down coating dry time. Be careful not to block piles!
     
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