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Excessive dot gain (or other) - please give me the advice!

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  • #16
    Originally posted by DeltaE View Post

    The non-printing area is not kept clean as in the ref. In my opinion, I think there is something wrong with the combination of ink and dampening solution.
    What do you think?

    Thank you!
    Regards,
    DeltaE
    Something is different but I don't know for sure what it is. It might just be more water in one ink film than in the other for some reason. Hopefully others can suggest a more specific description of this problem.

    On the issue of dot area, I think you have the wrong formula. For dot area, you need to use the Murray Davies equation. Sorry, I could not properly copy and paste a text of that formula. If you look it up, you will see it is a bit more complicated than the one you suggested.



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    • #17
      Originally posted by gordo View Post

      Assuming your measuring device is correct, your K SID/ink film thickness is too high by about 20 points. Your M is to low by about 10 points - your ref by 20.



      That's not the formula for dot gain.




      Dot gain is not the result of something wrong. It is inherent to the process. It is a process control metric not a target. Tone reproduction is the target.



      An AM halftone has an inherent ink/water balance conflict. It needs minimum water in the highlights to avoid washing out the dots but maximum water in the shadows to keep them from filling in.
      gordo
      Thank you! I have just received a basic lesson!
      I mean excessive dot gain when 80% in the plate becomes 97-98% in the printout.
      Yes, your point shows me an idea that I should check the dampening solution again; it seemed to be able to clean the hafttone area but not able to clean the shadow.

      Erik Nikkanen
      Thank you for your support!

      Comment


      • #18
        Originally posted by Alois Senefelder View Post
        A first fundamental MUST DO -- GO and LOOK ............ A good indication of Ink/Water Balance is a "thin scum line" unbroken 1- 2 mm wide that forms
        on the bend at the grip edge of the plate and extends the width of the plate.
        Regards, Alois
        Alois, from my experience "scum line" has nothing to do with the dot distortion due to lithography troubles. We've always seen this scum line on plates. Our printmen cannot add that much water to prevent it appearing (:

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        • #19
          Originally posted by DeltaE View Post
          I had measured the SID of black and magenta again with function relative ink density (status T) then get the result:
          Black: ref = 1.99, sample = 2.01
          Magenta: ref = 1.25, sample = 1.32
          Funny, but we have same SID target for black (Status E, but it doesn't matter for black). gordo mentioned that it is too high, but for our ink we can't go that low, 'cause at 1.8 we'll see Lab 21 0 0.
          This lead me to another thought — was ink takeoff the same over printsheet in both runs?
          With our ink we have noticed long time ago that when we have a little actual ink area coverage over the sheet — we have pluggy shadows and distorted dot. Especially with longer runs, closer to the middle of the run.
          On the contrary, with high area coverage we have clean shadows and less distorted dot.

          So i wonder — were measurements the same with first 500-1000 sheets?

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          • #20
            Cementary,


            I did not claim that the "Scum Line" had anything to do with "Dot Distortion" it is merely the first step in eliminating a variable input, put simply for you - "A very good first visual indication of Ink/Water Balance"

            Regards, Alois

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            • #21
              DeltaE,

              You did not answer my questions about the Plates!


              Make and type of plate ? also I would look at the Chemistry of your F.S


              Regards, Alois
              Last edited by Alois Senefelder; 01-05-2018, 06:25 AM. Reason: ***************

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              • #22
                DeltaE,


                Also check the Shore Hardness of the Plate Dampeners and Metering Rollers


                Regards, Alois

                Comment


                • #23
                  Originally posted by cementary View Post

                  Funny, but we have same SID target for black (Status E, but it doesn't matter for black). gordo mentioned that it is too high, but for our ink we can't go that low, 'cause at 1.8 we'll see Lab 21 0 0.
                  The specification is, AFAIK, that at K 1.70 (dry, non-polarized) you should have L 15, a 0, b 0

                  If you're not getting that then that suggests that:
                  A: your polarized instrument is affecting the reading
                  B: your instrument's calibration may be off

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                  • #24
                    Originally posted by DeltaE View Post

                    gordo
                    Thank you! I have just received a basic lesson!
                    I mean excessive dot gain when 80% in the plate becomes 97-98% in the printout.
                    Yes, your point shows me an idea that I should check the dampening solution again; it seemed to be able to clean the halfttone area but not able to clean the shadow.
                    Your dot gain compensation curve may be wrong in the shadows or you're "in the noise" of the instrument - i.e. it's not giving you accurate readings at that tone value.

                    I thought someone would mention it, but the problem might be revealed in the photo of the black.

                    image_7241.jpg

                    I didn't understand it so I was hoping someone smarter than me would explain it. Then I could take credit for knowing it all along ;-)

                    What are those lines between the dots?

                    Note there are many more of them in the "After" pic. They would result in a higher dot gain reading.

                    Normally if you have slinging/misting the ink threads would be in line with the direction of the paper through the press. But in this case they are in line with the angle of the halftone dots - which should be at 45°. This makes no sense.

                    As far as I can see from these photos, you have good ink lay down, no over emulsification, no ink/water issues, etc.

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                    • #25
                      Originally posted by gordo View Post

                      The specification is, AFAIK, that at K 1.70 (dry, non-polarized) you should have L 15, a 0, b 0

                      If you're not getting that then that suggests that:
                      A: your polarized instrument is affecting the reading
                      B: your instrument's calibration may be off
                      Gordo, it's not one instrument. We have 5 scanning densitometers, 2 scanning spectrodensitometers, one i1pro2, one exact advanced, one densitometer from techkon and all shows same density.
                      most of them show polarized density but do you honestly believe that polarization can affect reading by .30 D?

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                      • #26
                        Gentlemen,


                        I have already said in my first Post - The Black 40% image is "Showing" signs of low dampening level, WHY because the growth patterns of INK GRAINS forming between the dots.

                        A) Low Dampening Level B) Plates poorly "Desensitzed" C) Chemistry of the F.S.


                        Regards, Alois

                        Comment


                        • #27
                          Originally posted by cementary View Post

                          Gordo, it's not one instrument. We have 5 scanning densitometers, 2 scanning spectrodensitometers, one i1pro2, one exact advanced, one densitometer from techkon and all shows same density.
                          most of them show polarized density but do you honestly believe that polarization can affect reading by .30 D?
                          No, I,’m just WAGging.

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                          • #28
                            Originally posted by gordo View Post

                            No, I,’m just WAGging.
                            as we're all I suppose (:

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                            • #29
                              Originally posted by Alois Senefelder View Post
                              Gentlemen,


                              I have already said in my first Post - The Black 40% image is "Showing" signs of low dampening level, WHY because the growth patterns of INK GRAINS forming between the dots.

                              A) Low Dampening Level B) Plates poorly "Desensitzed" C) Chemistry of the F.S.


                              Regards, Alois
                              if delta experience smth we do, then increase in dampening levels won't help neither cheking and recheking plates desensitization.
                              As for fs chemistry - I would suggest checking doser system. Technotranse for example can be weird sometimes

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                              • #30
                                Originally posted by cementary View Post

                                as we're all I suppose (:
                                [QUOTE=cementary;n272039]


                                Methinks we're suffering from SDPSS (Single Data Point Speculation Syndrome) - like these guys:

                                tumblr_m59kgnTbUJ1qfvq9bo2_r1_12801.jpg

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