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Spray powder effects on offline UV coating

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  • Spray powder effects on offline UV coating

    What kind of issues we can get in offline UV coating if a job printed with conventional inks and anti set-off powder was used?
    Asif Qazi

  • #2
    Here are a few I can think of if excess powder is used and I'm sure there are many others.

    Sheet will have a rough 'sandpaper' feel to it
    Uneven gloss with dull and glossy areas.
    Piling on the plate/blanket
    Spray residue in the equipment.
    Slip would be poor if you are putting product through other equipment like a folder/gluer

    I also believe that for UV coating to work well over Conventional ink you had to apply a Primer coating first
    Last edited by Cornishpastythighs; 02-02-2019, 01:08 PM.


    • #3

      When powder is used, it needs to be removed before UV coating. 2 ways to accomplish this, that I am aware of, running it back through the press with the Powdered side of the sheet touching the impression cylinder. The other is if the UV coater has a crusher unit installed.

      If there is powder on the sheet when coating you will not like the results, it will look just like Mr. Pasty Thighs said. I will add that there will be voids in the clear and it will not have that nice smooth finish.



      • #4
        Thank you all for your input.

        Another question, can coated or uncoated spray powder make any difference in UV coating or both types can cause similar issues?
        Asif Qazi


        • #5
          I used to work at a commercial shop where they had a small off-line UV coater in the bindery. It was made by Light-Tech, or something like that, I think it was 13" wide, and it was hand-fed. Also worth noting is that there was no blanket, it only had an applying roller. They would coat all sorts of jobs on it and we never had any special instructions in the press room as to how much powder to use on anything. We just did what we would always do, and there were never any issues that I was aware of, coming from the bindery.

          The powder units on the presses were Weko, and Oxy-Dry. If you're familiar with how these two brands work, I don't need to explain the differences. The same standard grain powder (fine) was used for everything, with high quality inks, so minimum powder could be used, and drying and set-off were never an issue. This was always preferable not because of any post-press considerations, but because of the obvious reasons related to on-press.

          I'm not saying that previous posts in this thread are wrong, mind you, because some of the possible issues mentioned may very well be accurate. I don't know. I'm just telling you about personal experience.


          • #6
            Aqazi81, If you are encountering an excess of anti setoff spray issue often we found these lamps helpful to detect too much offset spray on the sheet. We run 44" and 50" presses 6 colours plus coater and run high ink coverage jobs for packaging. Every now and then no matter how good your spray unit you could encounter a 'Spray Bomb' Good luck


            • #7
              Here in our country the offline coating units are mostly made of an old press and aftermarket UV driers. The UV coating is transferred through ink fountain to rollers, plate,blanket to substrate .
              ​​​​​​So as alibryan said, the roller coaters apply higher amount of coating layer to the substrate, this prevents issues related to powder. On the other hand the method that I'm referring to is always prone to these issues.
              The spray powder build up on blankets during coating and cause uneven coating and sand paper feel to the finished product.
              Asif Qazi


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