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Discoloration on side of press sheet.

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  • #16
    Hello lantz,


    Lost in Translation !!!!!!


    Hard Line ?? ---- do you mean the area of "Back Ground Scum " on the Lefthand side in the " non image areas" ?????

    You need to learn the Nomenclature of Lithographic Printing Terms.

    Also, as suggested look at you Plate Imaging Process - USE proper Litho Plates !!

    Last edited by Alois Senefelder; 11-14-2017, 02:13 PM. Reason: ******

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    • #17
      Hey Alois, I'm not sure what you mean. I know the nomenclature, and I'm using the same poly plates that I always use and that others always use. Did you see the photo in my original post? The job is a 6x9 vertical postcard on 100# uncoated cover stock. The sheet is being fed portrait, but the card is rotated counterclockwise so that it's horizontal. The issue I'm having isn't scumming, it's that the left edge of the card (when viewed vertically) is significantly darker to the point of creating a literal hard line, that is different from the rest of the image area. It's about 3/4" thick. Because the image is horizontal, that means that the problem area is closer to the tail edge of the sheet. Hopefully I'm making sense, but if you haven't looked at the photo in the original post, please do, as it may provide a bit more context.

      At this point I've switched to a brand new blanket, imaged a new plate, adjusted form-to-oscillator pressures, adjusted form-to-plate pressures (they always get a little off when it gets cold, so no surprise there), tried different amounts of impression pressure - nothing works. The one last thing I have to try is to run the job on the other head, to eliminate the possibility of ghosting from the second unit blanket. But if that doesn't work, I'm at a loss. I have no idea what else it could be..

      Thanks,
      - Lantz

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      • #18
        I think its a file issue. Incorrect layering on a digital device will produce prints like this. If they created the bleed by drawing a box and filling it with the background color it would be hard to see on the plate. Do you have the full pro version of acrobat where you can click on the image and see if a box coincides with the darker area. An update to acrobat could cause this to be different than a previous version handled it. I've seen rotating the image before processing take care of this.

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        • #19
          Thanks for your input, Bill. I wondered originally if it was a file issue, but I've seen the same issue pop up fairly recently with some cards we designed in-house to promote a book we're publishing, and I know for sure that we set it all up properly. Although now that I'm looking at some samples of those cards, it doesn't seem to be nearly as drastic. In any case, the file they sent us was a .TIFF with just one layer. Do you think there's some sort of weird transparency thing happening that I would only see with a file that has its layers?

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          • #20
            Hello Lantz,

            I'm getting lost now !! all I can see is a Diagonal View of a printed sheet - just " indicate the area" of concern ?

            Regards, Alois

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            • #21
              Alois, look at the words "Save the Date" and then let your eye follow left to where the top left crop marks are. Do you see how that side of the sheet is significantly darker than the rest of the sheet? It goes all the way down the image. But it doesn't have anything to do with the ink keys because the image is horizontal, so running on the long edge. But the edge opposite the problem area doesn't look like that. Does that clarify things?

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              • #22
                Its such a sharp line I still think that its an imaging problem especially now that you say it was done on a laser printer . . what line screen are you using, what resolution is the laser printer set on, what kind of laser is it . . . we use a laser printer for our quick print type of work but not for screens or halftones . . .
                "If you think you are too small to be effective
                you have never been in the dark with a mosquito."

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                • #23
                  It's a Xerox C75 digital press burning the plates at 1200dpi. It works fine for everything else, including bigger solids than this one. *shrug* There's no other platemaking solution available to us at the moment, unfortunately. The digital press really does a good job with the plates, though.

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                  • #24
                    It's not a solid, well in fact it is a solid but you keep saying that its not supposed to be . . . the transition from step to step can be very sharp in the imaging you might try looking at Gordos blog at

                    http://the-print-guide.blogspot.com

                    or this thread which addresses the issue here on print planet

                    https://printplanet.com/forum/prepre...nd-line-screen

                    I'm guessing here since you didn't say what screen ruling you are using but if you are using 100 lpi screening you will only be able to achieve 145 gray levels so you are losing 111 of the possible 256 gray levels.

                    It's been a long time since I was using a 1200 dpi device now we are using a 2540 plate setter but as I recall the less difference between starting % and ending % makes banding much more likely which I think might be your problem, without seeing the file thats the best guess I could make at this time . . .
                    "If you think you are too small to be effective
                    you have never been in the dark with a mosquito."

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                    • #25
                      Yeah, I mean that particular image is not a 100% "solid" but rather a big screen. One side of it looks fine, the other side of it doesn't. The line screen is 85lpi. But again, we've done smaller solids (actual solids) where the issue popped up and larger solids (11x17 posters with huge blocks of color) where there was no issue, all with the same platemaking workflow. A lot of folks who run poly plates are still using the HP5500 and these plates look a million times better than I ever got off that machine. So I'm hesitant to think it's a platemaking issue, although it's certainly in the realm of possibility. I'll take a look at these links tomorrow.

                      Thanks for the help and will send an update tomorrow.

                      - Lantz

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                      • #26
                        running an 85 line screen will give you more grey values but . . . . solids is easy gradations are hard . . . specially in the 1 to 5 % areas they tend to plug . . .
                        "If you think you are too small to be effective
                        you have never been in the dark with a mosquito."

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                        • #27
                          Platemaking and/or file issue should be easy to ruleout by simply turning the image 180 degrees. After that, if you move the image up or down 'on the plate' and the problem still appears in the same area 'on the press' as before, that will at least tell you that it's a mechanical issue and it's happening on press.

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                          • #28
                            If the gripper edge is where I think it is - I was confused by the posters description of this as well - then the job is being run 'portrait' and I'll throw my hat into the 'not enough ink/rollers to carry the solid' position on the matter. See attached for where I think grip is.
                            Don't know if this has been suggested already but you could try burning the plate with the image the other way around. That should give you an answer. If it is the size of the solid, try thinning the ink. gripper.pdf

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                            • #29
                              PS/ being a 'Save The Date' I suspect this is a wedding announcement and anything to do with a wedding announcement is ALWAYS going to be a pain in the ass. I suggest you send the customer to a printer in town that you hate.

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                              • #30
                                Hello Lantz,

                                I see the problem now !!!!! you have a - Imaged Bar "Area" of high SID - many of the replys suggest you look at the

                                Plate Imaging, I agree

                                Regards, Alois


                                PS - The use of Polyester Plates should be - Banned!!

                                Think of the Planet, you can recycle Metal Plates NOT Polyester Plates made Using Toners

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