Ink Scratching off

Discussion in 'UV' started by jd34tab, Oct 21, 2010.

  1. jd34tab

    jd34tab Member

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    Does anyone have trouble printing a black solid and coating it, and the black scratches off ? This is on a UV press. And it is printed on styrene. If you have had this problem before and solved it, can you help me with this? Thank you!
     
  2. Data

    Data Senior Member

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    I take it the material is relatively new, ie. under 6 months old? And you are using inks specifically for plastic?
     
  3. jd34tab

    jd34tab Member

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    Yes the ink is for plastic and now we have found putting a gray color, which we use a lot, under the black helps it stick better. To me this should not have to be done when the other colors are ok.
     
  4. Data

    Data Senior Member

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    One for the ink techs maybe cos now your black isnt on the plastic its on the grey.

    Although we have the same if we run to heavier black film for inmould.

    Another one to watch (same issues) is if you use Uv that will later be in contact with water.
     
  5. topper

    topper Member

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    There are two possibilities with this black. One is that the wave length of your lamps does not reach all the way through the black ink film so you are not getting a full bottom cure. This is somewhat evident in the fact you can cure a grey and the black will hold "better." Primarily because the partially cured film will hold on better to a like material rather than the plastic. Secondly it could be that the black formula isn't biting the plastic well and the inherent shrinking of the cured coating is causing a form of delamination of the black film.
    Remember that opaque white and black are the two most difficult colors to cure for primarily the same reason, penetration of light. One reflects the light too readily and the other consumes the light too readily. Both causing the same issue of under-cure. You may need a more agressive black formula or an increase of Photo initiator for bottom cure. Also check the age of your lamps, they degrade over time and emmit less intense light which can cause an issue as well.
     
  6. steveo

    steveo Senior Member

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    "You may need a more agressive black formula or an increase of Photo initiator for bottom cure."
    true , you can add more and also running slower speeds can help cure ink better , I just ran a double hit of a dark brown on foil and had to slow the press down to cure better......
     
  7. jonprintz

    jonprintz Member

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    The scratch resistant properties of black (with no undercolor) on styrene are always less than on other stocks...even when the ink is fully cured. As already stated, make sure your lamps / reflectors are in optimum condition. The main problem is just the styrene. It is preferable to coat or varnish styrene jobs that have heavy black images on styrene.
     
  8. turbotom1052

    turbotom1052 Senior Member

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    Have you had the styrene dyne tested, and did it receive a recent corona treatment?
     
  9. peheidelberg

    peheidelberg Member

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    check your lamps as Topper has said but also the refectors as they also get dull and cause problems as I have had this before in the past
     
  10. jhesch

    jhesch New Member

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    It is important to test Dyne level and corona treat. If you have an open unit put down a litho primer.
    Are you putting on a gloss UV coating or a water based?
    i have heard some have had success with the poor mans corona treatment, open first unit with a hit of water and ~20% alcohol..never tested and not sure i would recommend.
    it is also possible to overcure, but that usually causes the coating to scratch off not the black.
    My best advice is to prime the sheet. Several companies make a good one.
     
  11. Jon1909

    Jon1909 Member

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    What type of ink is being used? I've had the same problem before with a different bond and we had to use straight UV inks instead of hybrids.
     
  12. Drew812

    Drew812 Member

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    I dont believe its a plastic issue if its just the black. To make black solids look good with UV ink we usually have to lay down a heavy ink film and you know what that means, lots of water. Are we using too much alcohol sub in the mix? And do you use interdecks between every unit? Running black last? All these come in to play, yes we know the black itself is hard to cure due to the UV wavelength. And if it is a plastic issue due to being an old batch try hitting it with a light before any printing if you have an extra unit (another poor mans corona treatment). I dont mind helping fellow pressmen, let us know your configuration.
     
  13. Rasheed khan

    Rasheed khan New Member

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    Respected All:
    we print UV ink on MPET laminated with board(box board) but received complaint of scuffing/rubbing from our customer.
    surface tension of MPET was 42 and in-line UV coating was also applied after printing moreover all the dryer and UV lamp working properly.
    please advice?
     

  14. rchamness19

    rchamness19 Member

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    I have found that the Toka VP series works best on styrene
     
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