Delta e changing by 0.40 if density increases 0.05

Discussion in 'Ink' started by Apolloeagle, Feb 11, 2024.

  1. Apolloeagle

    Apolloeagle Member

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    Hi we are struggling to keep a consistent Delta e of under 2.0 ! Customer will reject anything above ‍. The delta e will change by 0.40 with only an increase of 0.05 in density . Almost impossible to control .Colour is Cool Grey 11 any advise as the rejected stuff is beyond a joke ?
     
    Last edited: Feb 11, 2024
  2. mantman

    mantman Senior Member

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    You could alter recipe with higher trans white so you can go heavier on ink. Dunno just a thought.
     
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  3. Apolloeagle

    Apolloeagle Member

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    Hi we’re trying this option . The image control system struggles more than the human eye . When you’ve got 22 cartons on a sheet and with all the other checks it’s a complete nightmare . We use an x rite spectro to measure the delta e it can jump 0.50 across a carton , they are only 40 mm by 30 mm squares. The surface of the board is poor think this has a lot to do with it . Then dry back ……‍♂️‍♂️‍♂️‍♂️‍♂️
     
  4. alibryan

    alibryan Senior Member

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    Add a certain amount of Opaque White (for less transparency) into the CG11 formula to help hold more consistent color, and tighten up your tolerances on your scanner to less than 0.05 on your densities. Also, change the degree of your ink charge oscillator to alter the points of ink density variance across the sheet.
     
  5. Apolloeagle

    Apolloeagle Member

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    Thanks for the advice. We’ve done that and get fairly good results front to back .I’m on a KBA 105 and the image control doesn’t seem up to the job, as it measures the Control Strip no matter how close we get to a flatline on the scanner as soon as we switch to the camera it tends to close most keys down and open up the odd one ? We need more patches for the camera to see when I mention this as usual I hit a brick wall !
     
  6. alibryan

    alibryan Senior Member

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    If what I think you’re saying is what you are saying, that sounds like split-key info. When it happens with the density scanner it’s because the density patches aren’t in the center of the ink zone so the scanner is sometimes getting partial density from the zone right next to a patch. It then tells the press to close down one ink key and open the one next to it (splitting the keys), trying to compensate for it. It’s a machine so it doesn’t think and even though the auto-adjust settings will work fine most of the time, they don’t always, and sometimes you have to override them and adjust the keys manually.
     
    Last edited: Feb 12, 2024
  7. Apolloeagle

    Apolloeagle Member

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    Yes what I thought , the delta e tolerance is just too tight when it’s jumping so much with such a minor increase in density. Thanks again for the reply .
     
  8. alibryan

    alibryan Senior Member

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    The ink key scanner data from the sheet is a separate issue from your Delta E variance. I don’t know if your CG11 is mixed in house, bought from a vendor, what formula you’re using, etc., but your oscillation charge adjustment should help stabilize any variance you’re getting if it’s across the sheet. If it’s overall ink variance control from sheet to sheet throughout the run that makes no sense either as once a press run is settled in you should be able to hold (any) color to within a couple of points in density (and under 2 on your Delta E).
     

  9. Apolloeagle

    Apolloeagle Member

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    Hi the Delta E reading is jumping all over the place even measuring the same patch , its those couple of points of density that make it jump . Black density of 1.07 we get a Delta E of 0.30 ...great , have a density of 1.12 Delta E jumps to 2.50 . CRAZY :)
     
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