Weak Black Plate Burning

Discussion in 'DI Presses' started by impressed, Feb 13, 2012.

  1. impressed

    impressed Member

    Joined:
    Jul 2011
    Messages:
    47
    Location:
    ONTARIO CANADA
    I'm consistently having problems printing solid blacks on my QMDI. Small black fonts and pictures are fine, but once it gets to coverage 1/16” wide and up it won’t fill the image solidly, it’s speckled and light even if we push the ink up. I suspect it’s a plate burning or cleaning issue, as after a burn I can see that the plate itself in the heavy coverage areas is weak. Wiping the plate with alcohol helps somewhat to get started, but even with that the plate image isn’t strong like on the other 3 units. Again, it's only the black unit (one) that has this problem.

    We’ve tried a different ink, with no success. I haven't tried running black on a different unit, planning on giving that a whirl tomorrow.

    Anyone have an idea of what problem/fix might be or a similar experience?
     
  2. Marc Bremer

    Marc Bremer Senior Member

    Joined:
    Jan 2010
    Messages:
    239
    Location:
    Netherlands
    I always add CMY to larger area's of black.
     
  3. Paul Cavanaugh

    Paul Cavanaugh Senior Member

    Joined:
    Dec 2009
    Messages:
    630
    Location:
    Kennesaw, GA
    Solid blacks need to be built with CMY as mentioned above. Otherwise they will look mottled and light. I have heard multiple explanations as to why although there are two which seem to make sense.

    1. The pigment in the waterless inks are not as strong as conventional inks in the fact they have to have more body, body takes more filler whihc leaves less room for pigment, hence a slightly lighter color. Magenta is supposed to be the one that suffers the most from this explanation given to me by and ink representative.

    2. Where the ink is carried on the waterless plate is different than on a conventional plate. On a conventional plate the ink sits on top of the area of the plate that accepts ink and it is pressed onto the blanket. On waterless plate the area that accepts ink is a valley etched by the laser. As a result solids have to be pulled from the low spot in the plate by the blanket leaving a mottled look to the solid.

    If you build your black solid with CMY you will alleviate the issue.
     
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