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Pls help troubleshooting - Inline aqueous coating in sheetfed machine

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  • Pls help troubleshooting - Inline aqueous coating in sheetfed machine

    Hello everyone,

    I have a problem with inline aqueous coating in sheetfed machine:
    - Heidelberg CD102
    - Coating unit with tresu chambered blade
    - Anilox 60 lpcm
    - underlay thickness = 1.3 mm
    - blanket thichness = 1.95 mm
    - blanket tighten with torque wrench 45
    - some area does not need to be coated therefore I have to remove the rubber layer of blanket in those areas.

    There is a mark on the rear edge of each uncoated area. (Please see the pictures for more detail)
    I had tried:
    - to deal with underlay thickness (packing sheet) - increase or descrease
    - to make kiss-pressure between anilox roller and blanket cylinder
    - to deal with printing pressure between blanket cylinder and impression cylinder

    But it still remains. Please help me or leave your idea about this! I am very appreciated!

    Regards,
    DeltaE
    The mark in arrow direction The mark in arrow direction

  • #2
    The blanket cutting looks rough. The blanket surface may have lifted slightly away from the blanket backing creating a little bump which could cause application roller to lift causing a void. When you strip away the blanket surface delamination can occur for multiple reasons. Not cutting all the way through and you pull too hard. Not using a good blanket for cutting knock outs. Over packing. Over torquing.etc.

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    • #3
      This is speculation.
      It’s a form of starvation ghosting. Because of the cutout on the blanket the coating builds up in that area of the blanket. Then it gets dumped on the trailing edge making it thicker there. That in turn changes the thickness of the coating immediately after the cut out. That reduces the amount of coating there ceating a thinner patch of coating until the coating film thickness has a chance to recover.
      Take off bars might help.
      Last edited by gordo; 09-14-2018, 01:12 PM.

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      • #4
        I'm going to go along with both suggestions. The blanket cut looks rough. Even at best it's a tough thing to pull off. And as Gord says, you're getting an excess buildup over the non print area. I think all you can try is very, very minimal pressure. I think the best thing would be to spot varnish off one of your print units.

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        • #5
          This coating 'bump' can sometimes happen when the application roller is running at a slightly different speed than the blanket.

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          • #6
            Originally posted by Cornishpastythighs View Post
            This coating 'bump' can sometimes happen when the application roller is running at a slightly different speed than the blanket.
            This!!!

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            • #7
              Originally posted by turbotom1052 View Post

              This!!!
              Agreed. Thank you very much!

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