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  • Discoloration on side of press sheet.


    Hi folks,

    I'm running an Itek 3985 with Crestlines, and right now I'm doing a save the date postcard for a client, just one color on Mohawk 100# Eggshell cover stock. I'm having this issue where the sides of the printed image are a lot different in color, thus creating what seems to be a hard line. In the below image, I'm running a 6x9 postcard landscape, so the gripper/ink keys are along edge. What's confusing is that it seems like the keys are open enough because the edges of the sheets are pretty even all the way across. The below image is a little weird because there *is* a gradation in their file, so even though it looks like the middle just doesn't have enough ink, it does look that way in their file.

    Anyway, anyone know what do about it? I've had the issue before with other, more straightforward solids where the edges always seem to be either darker or lighter than the rest of the solid and that creates a line. There's no line in the plate (which I print off our Xerox C75 digital press) and there's an appropriate amount of plate-to-blanket pressure. I tried changing blankets but still had the same issue on both. What am I missing?

    Thanks,
    - Lantz


  • #2
    If you're gripping the 'left' (6") side of the stock (where approximately 1" of the image is darker), you're actually running this job in portrait format. And what I think you're seeing is sometimes referred to as mechanical ghosting. It's usually caused by the roller configuration not being able to handle that much ink lay down, but can also be caused by certain other machine pressures. In either case and if there's room, I would try turning the job to grip it along the 9" edge of the sheet, (landscape format) or, stay in portrait and lower the image on the plate so it lands beyond the dark area, to eliminate the ghost.

    Comment


    • #3
      Alibryan, the gripper is the 9" side. So, like I said... it's running landscape. I'm running it one-up landscape on a 9.5" x 13" sheet because we're using the other half of the sheet to duplex afterwards. Do you think that the mechanical ghosting is still a possibility? Another variable is that I typically use plate cleaner to prep plates - kind of a holdover from when I used to image plates on an HP5000, but I'm wondering if the plate cleaner is breaking down some of the information in the solid and giving me issues. I'll try a fresh plate tomorrow, but I'm interested in this mechanical ghosting. What is it about the configuration of the rollers that it "can't handle" laying down enough ink to print a solid? And how would I fix that?

      Thanks,
      - Lantz

      Comment


      • #4
        Okay, I didn't understand the actual sheet size but Landscape and Portrait have to do with where you are gripping the sheet, not which way the images appear on it. So if as you say; you're gripping the narrow side of the sheet - then it's actually Portrait format.

        That said; with the line being perfectly straight, (I could be wrong, but) I don't think you're causing it with plate cleaner. I rather think it's a ghosting issue and it has to do with either machine pressures, or roller train capacity. I think it's the latter and probably has more to do with the rollers on your press not being able to 'paint the sheet'. It's a duplicator to begin with and they're not really designed to do that anyway, so I don't know if you can really fix it. But either way, you should be able to hide the problem by moving the image out of that area. Good Luck.

        Comment


        • #5
          Sorry for any confusion. The press sheet is portrait but the image is horizontal. The gripper is at the short edge of the sheet but the long edge of the image on the plate.

          The Itek 3985/Ryobi 3302 is perfectly capable of running big solids. I frequently run 11x17 posters on it with large solids that bleed with no issue. I've seen incredible work come off of it. I don't think the issue has anything to do with its capability. It's no Heidelberg, but three form rollers have a lot of capacity. I'll try moving the image on the sheet to see if that helps, though I can't understand right now why that would matter.

          Any other thoughts on this would be appreciated.

          Thanks all.

          - Lantz

          Comment


          • #6
            move the sheet out of center to the plate either direction does the heavy area shrink or enlarge or stay consistent to the rest of the image? If it stays consistent look at a new plate. if it moves look at pressure or your ink is contaminated.

            Comment


            • #7
              Hey Bill, I'm not sure I understand. The issue goes across the sheet laterally, so moving the sheet position won't do anything. Do you mean I should move the image on the blanket, either up or down, to see if the problem area changes or stays consistent? And when you say look at pressure, which pressure are you referring to? Form to plate? Form to oscillator? etc.

              Thanks,
              - Lantz

              Comment


              • #8
                Sorry miss understood feed direction too, yes move the image on the blanket, what was that effect? you checked blanket pressure so yes roller pressures, weird things happen. I would also try running the stock the other direction grain for some stocks cause strange effects.

                Comment


                • #9
                  After moving the image down on the blanket, the issue moves with the image. I really am thinking that it could be roller pressures but I'm still not clear on which pressures to check. Anyone have any suggestions? Is it the pressure of the forms as they ink the place or something else?

                  - Lantz

                  Comment


                  • #10
                    Hello lantz,


                    What you are seeing - IS Mottle, not discoloration .

                    1) DO not change anything, Print a a Gloss paper, same gsm and Uncoated paper and see the printed result .

                    2) IF possible use a Metal Imaged Plate.

                    A quick of the Cylinder Pressures - 1) Roll up the Plate - SOLID with Ink - NO Damp
                    2) Put press on Impression - while stationary, and then check the INK STRIPE on Blanket Cylinder, next Ink up the Blanket Solid and check Impression Cylinder Stripe
                    3) The INK stripes should be about 2mm EVEN WIDTH across the wiidth of the cylinders.

                    Regards, Alois
                    Last edited by Alois Senefelder; 11-14-2017, 11:21 AM. Reason: *******

                    Comment


                    • #11
                      Hi Alois. Thanks for your comments. I ran some glossy stock and had the same issue. Form to plate stripes are a little off, so I made a couple of adjustments and will get back to it after lunch. I'm hoping to not have to go to the form to oscillator stripes, which involves taking out all the rollers. How would I go about adjusting the impression cylinder stripe? Is that just with the impression knob, to adjust the blanket to impression pressure? If I back off the impression too much, the image gets a little spotty. I don't generally set it very heavy but I'm not sure how much less I can run.

                      Comment


                      • #12
                        Hello lantz.

                        Set ALL the rollers ___ Correct !!!!!!!!!!!!!!!!!!

                        Just try my suggestions with your present Press Settings and see what the result is first.

                        Also these areas of "Cloudy Print" could be areas of emulsified ink and could be mistaken for "Mottle"


                        Regards, Alois

                        Comment


                        • #13
                          I know it looks weird, but that really is how their file is and is what they want. I'm just trying to figure out why there's that hard line on the left side of the card (i.e. the tail edge of the image as it appears on the plate). I guess I'll go into the form-to-osc and start there... thanks.

                          Comment


                          • #14
                            It might be how the plate is imaged . . . I'd take a close look at the plate and see how the gradation goes from the middle to the edge . . . could you post a press ready pdf for us to look at?
                            "If you think you are too small to be effective
                            you have never been in the dark with a mosquito."

                            Comment


                            • #15
                              It won't let me post a PDF here, only an image file. I took a pretty close look at the plate and, I mean sure, it's being made on a laser printer, so it's not smooth like it would be if it were made on an imagesetter for a metal plate. But I don't see any obvious hard line or any sharp turn in the gradation. (Incidentally, I originally thought the line came from having the edges be darker than in the middle, but it's only on that one side and it's quite a difference, so I ruled it out.)

                              I went through and made some fine-tune adjustments to my form-to-osc pressures and saw no change...

                              - Lantz

                              Comment

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