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Ink Density Uniformity on Circumferential Direction

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  • Ink Density Uniformity on Circumferential Direction

    Hello everybody,


    I have a question about the solid ink density in circumferential direction, the uniformity of density in sheetfed offset machine (ex: Heidelberg CD102, Rapida 106, Man Roland 700, Komori,...)
    How can I improve the uniformity of ink density on the circumferential direction?

    I knew that we can try somethings below to get good uniformity ink density in circumferential direction.
    - Adjust the timing of oscillating roller
    - Tighten blanket correctly
    - Use minimum amount of dampening solution

    Could you please share your point about this?

    Thanks in advance!
    Regards,
    DeltaE


  • #2
    Could you tell us what uniniformity on press sheet tail to head you're trying to achieve? In my experience 0.08-0.10 D is fine for ManRoland 700 and 0.05-0.08 D is fine for ManRoland 900.
    in any case you should probably add to your checklist rollers condition both ink and dampening

    Comment


    • #3
      cementary Thank you! The condition of inking and dampening rollers is very important to uniformity!

      Last week, when we made a G7 colorspace, I had the density deviation from front to tail:
      - Black: +/- 0.05
      - Cyan: +/- 0.04
      - Magenta: +/- 0.04
      - Yellow: +/- 0.03

      It was fine for us to get a good enough data when measuring, but I am really want to improve the uniformity. That's reason of my question here.
      BTW, why the density deviation of your ManRoland 900 is narrower than 700's? Bigger size should have larger deviation, shouldnt it?

      Comment


      • #4
        I think that smaller deviation for ManRoland 900 is due to bigger ink train and maybe better oscillators.
        Larger deviation for our 700 is due to not-the-best roller condition

        Regarding your data — IMHO, normal density variation during run is 0.08 D across the sheet
        You won't see difference with your eyes, but G7 measurements will.
        Our target densities +/- 0.08 - 0.10 D stays within 3.5 dE76 from target CIE Lab, so we "dance" from that data.

        IMHO, one can not achieve density variation smaller than 0.04 D in production (not test runs) only by manipulating measured data.
        Last edited by cementary; 04-16-2019, 03:26 AM.

        Comment


        • #5
          I think the circumferential density variation tolerance used by GATF/PIA for press testing is a range <=0.06.
          What is your density variation across the sheet? In theory it should be less because you have more control over that with ink keys.
          Rearranging the target orientation (rotate portrait or landscape) may help?
          Steve Suffoietto

          Comment


          • #6
            The variances you listed from head to tail are perfectly fine, and about as good as it gets. In fact, I would say that even with a press that's perfectly dialed in, your tolerances are still going to vary slightly from those measurements, even from sheet to sheet.

            Comment


            • #7
              Originally posted by DeltaE View Post
              Hello everybody,


              I have a question about the solid ink density in circumferential direction, the uniformity of density in sheetfed offset machine (ex: Heidelberg CD102, Rapida 106, Man Roland 700, Komori,...)
              How can I improve the uniformity of ink density on the circumferential direction?

              I knew that we can try somethings below to get good uniformity ink density in circumferential direction.
              - Adjust the timing of oscillating roller
              - Tighten blanket correctly
              - Use minimum amount of dampening solution

              Could you please share your point about this?

              Thanks in advance!
              Regards,
              DeltaE
              This is a great and important topic but it is also a complicated one. Even for modern offset, it is related to press design and to the actual image being printed.

              Basically it is a problem of how the ink films are managed on the form rollers.

              Just looking at the circumferential problem.

              If one thinks of the most basic roller train design, where there is only one form roller contacting the plate and only one roller in the roller train supplying fresh ink to the form roller, then one can more easily see the problem and what is needed to improve it.

              Ideally with this arrangement, one would want a uniform ink film on the form roller to obtain a uniform print ink film.

              So when the image areas of the plate takes ink off the form roller, that leaves patterns of thinner ink film on the form roller. Those patterns of thin ink film need to be filled in before the next rotation of the form roller as it contacts the plate. Also the non patterned portions of the form roller should not get extra ink from the roller supplying ink from the roller train.

              The way to break up these patterns on the form roller is with nips. So the more rollers, not in the ink supply chain of rollers, that one can have contacting the form roller, the more even the ink film will be. These rollers would also act as a reservoir of ink to modulate the over all storage of ink available to the form roller.

              This is the basic problem and it is also true for multiple form rollers. One wants the removal of patterns form any form roller.

              Other issues can affect variation in local ink films, such as the timing of the ductor, the oscillation, water application etc. but it is the job of the design of the press to minimize these.

              Other press designs do not have these issues. The Anicolor press print evenly around the circumference and so do flexo and gravure presses. A more conventional lithographic offset press can be made to improve this issue but there is no interest from the press manufacturers to address this.

              IMO a density variation of 0.05 is not small. Too often there are excuses made for the poor performance of offset and statements that it is acceptable in practice.

              Variations in how the press prints around the circumference means that the press does not actually have a specific profile. This causes problems in prepress.

              The aim of press design should be that the press can inherently print consistently and predictably in all locations of the print, across and circumferentially. And do this independently of the image it is printing. This is a realistic goal.

              Comment


              • #8
                Erik Nikkanen Thank you for great input!

                Comment


                • #9
                  Gentlemen,


                  Ink Density and Roller Train Designs.


                  While Erik's posit contains some valid comments, again he fails to mention some Fundamentals!


                  1) Flexo Anilox Inking systems and Gravure Printing - USE fluid ink, whereas Lithographic Inks are - Non-Newtonian and combine with a Newtonian Fluid (F.S- Water)

                  2) Disturbances in IFT caused by the Plate Cylinder Gap.


                  Regards, Alois

                  Comment


                  • #10
                    Originally posted by Alois Senefelder View Post
                    Gentlemen,


                    Ink Density and Roller Train Designs.


                    While Erik's posit contains some valid comments, again he fails to mention some Fundamentals!


                    1) Flexo Anilox Inking systems and Gravure Printing - USE fluid ink, whereas Lithographic Inks are - Non-Newtonian and combine with a Newtonian Fluid (F.S- Water)

                    2) Disturbances in IFT caused by the Plate Cylinder Gap.


                    Regards, Alois
                    I fail on a lot of things but you never fail to miss the point of my comments. :-)

                    My main point was that if one can design a roller train so it manages the ink films on the form roller properly, then one can get improved consistency of the print in the circumferential direction. Yes, a lot of things need to be considered.

                    The Anicolor press is a press that has non-newtonial inks, has a dampening system and a gap but since the design of the press manages ink films on the blanketed form roller consistently, it prints consistently around the circumference.

                    Comment


                    • #11
                      Gentlemen and Mr. Erik Nikkanen.


                      Ink transportation in Anilox Offset Printing - Fundamentals

                      I hope of interest and value


                      Regards, Alois.

                      Anilox Offset Printing # 1059.pdf





                      Comment


                      • #12
                        Originally posted by Alois Senefelder View Post
                        Gentlemen and Mr. Erik Nikkanen.


                        Ink transportation in Anilox Offset Printing - Fundamentals

                        I hope of interest and value


                        Regards, Alois.

                        [ATTACH]n284545[/ATTACH]




                        I don't think the use of anilox for offset is a good future direction. I also think it is not the best for use with flexo either. Just my view.

                        Comment


                        • #13
                          Let me try to make a case for why small deviations in circumferential density can have unacceptable results. So here's the scenario... An identical image is printed in 4color process 2 up from front to back on a sheet. The magenta unit has front to back variation in density of the "ACCEPTABLE" 10 points as mentioned by a previous poster, with the heavy magenta falling on the tail image. The cyan has the same "ACCEPTABLE" tolerance but the heavy cyan favors the gripper image. Now that "ACCEPTABLE" 10 point tolerance, because its on 2 separate units, in effect becomes 20 densitometer points!!!

                          Comment


                          • #14
                            Originally posted by turbotom1052 View Post
                            Let me try to make a case for why small deviations in circumferential density can have unacceptable results. So here's the scenario... An identical image is printed in 4color process 2 up from front to back on a sheet. The magenta unit has front to back variation in density of the "ACCEPTABLE" 10 points as mentioned by a previous poster, with the heavy magenta falling on the tail image. The cyan has the same "ACCEPTABLE" tolerance but the heavy cyan favors the gripper image. Now that "ACCEPTABLE" 10 point tolerance, because its on 2 separate units, in effect becomes 20 densitometer points!!!
                            It is nightmare of printer! ha ha ha

                            Comment

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