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

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  • #31
    Originally posted by gordo View Post

    Methinks we're suffering from SDPSS

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    • #32
      Tell me how the printing press is called and the model ? What is the procedure for applying paint ? What kind of printed material ? Maybe the paper is wavy ? Can slide slur ?
      Attached Files
      Last edited by Andrei83; 01-05-2018, 03:21 PM.

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      • #33
        Originally posted by gordo View Post



        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.

        .
        I think it is called bridging. I think it is a known phenomena. Not quite the same as slinging or misting from an ink filament being pulled apart, which would be in line with the print direction. I think this bridging is due to the flow of ink in the nip as the two surfaces are separating. Two adjacent dots will pull ink laterally from the ink film as the roller surfaces separate. IMO under certain conditions the lateral flow of ink at one dot could link up with the nearby lateral flow of ink from another dot. This might also be related to the condition of ribbing where lines of thicker ink can form on rollers if the film thickness is too thick. Ribbing forms when rollers separate and if there is no vibration, the pattern is reinforced on each rotation as ink flows laterally from valleys to the hills of the ribs. If the ink film is very thin, the ribs do not tend to form because there is not enough ink in the ink film to provide the lateral flow. The ink film would tend to split then by some cavitation.

        When ink is splitting after a nip, the forces affecting the ink flow are not just the viscosity but also the surface tension. Probably very complicated and I don't know for sure what affects those variables.

        The angle of dots to me looks a lot less than 45 degrees. I doubt that bridging could happen at 45 degrees but who knows.

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        • #34
          Dear All,

          I am sorry for the delay. I have spent last 3 days for trying to fix this. And we did it.
          Now the printout is good as usual. We had drained dampening solution (which I just found too much alcohol - refractometer showed > 15%), and mix the new one with careful dosing the dampening additive and alcohol.
          Measure the dampening solution parameter: pH = 5.2, conductivity = 850 microSimen, temp = 12 degree Cel, IPA = 10% (checked by refractometer)
          And I replaced the dampening form roller, adjusted to the standard setting.
          Then we printed this job again. The result is good, the dotgain returns as usual.
          The condition of the dampening form roller was not good; I do not have the hardness indicator so I can not measure but it was hard when compared to the new roller.

          I still do not have the conclusion but the issue was solved.

          Thank you very much for your support!
          Have a good day!

          Regards,
          DeltaE

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          • #35
            If I make a dosage of 12% alcohol then I will have problems with the paint, a great deal of imbedding will begin.If alcohol is 15%, then there will be a large increase in the point, even spotted printing on the background.

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            • #36
              Originally posted by DeltaE View Post
              Dear All,

              I am sorry for the delay. I have spent last 3 days for trying to fix this. And we did it.
              Now the printout is good as usual. We had drained dampening solution (which I just found too much alcohol - refractometer showed > 15%), and mix the new one with careful dosing the dampening additive and alcohol.
              Measure the dampening solution parameter: pH = 5.2, conductivity = 850 microSimen, temp = 12 degree Cel, IPA = 10% (checked by refractometer)
              And I replaced the dampening form roller, adjusted to the standard setting.
              Then we printed this job again. The result is good, the dotgain returns as usual.
              The condition of the dampening form roller was not good; I do not have the hardness indicator so I can not measure but it was hard when compared to the new roller.

              I still do not have the conclusion but the issue was solved.

              Thank you very much for your support!
              Have a good day!

              Regards,
              DeltaE
              Please post pics of your dots.

              Comment


              • #37
                gordo Please find in the enclosed! Regards / DeltaE

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                • #38
                  Dear All,

                  Can I explain this case like this:
                  Due to very high IPA rate (>15%) because one of stupid printer had put into the dampening solution. Our "water" is too strong.
                  Then he had to put more ink to keep ink/water balance. Then too much ink leads higher dotgain then before.

                  What do you think?

                  Regards,
                  DeltaE

                  Comment


                  • #39
                    Hello DeltaE,


                    15% addition of IPA is not excessive apart from the COST ! --- your pH is High.

                    Regards, Alois


                    P.S. POST PICS of the same Plate Areas
                    Last edited by Alois Senefelder; 01-08-2018, 09:41 AM. Reason: Addition

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                    • #40
                      The bridging of the dots (which I think is a problem) is now similar to the original before pics. You may be solving the symptom but not the disease.

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                      • #41
                        gordo Yes, you are right!
                        Maybe I should try another ink or blanket But now it is not suitable time for a trial, I will try it when I have chance.
                        Regards,
                        DeltaE

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                        • #42
                          Originally posted by gordo View Post
                          The bridging of the dots (which I think is a problem) is now similar to the original before pics. You may be solving the symptom but not the disease.
                          And what should be done to cure the disease?

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                          • #43
                            DeltaE,


                            The answer to your problems ......... IS - Alcohol - Free Printing


                            Regards, Alois

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                            • #44
                              Originally posted by Alois Senefelder View Post
                              DeltaE,


                              The answer to your problems ......... IS - Alcohol - Free Printing


                              Regards, Alois
                              From my experience it is not an answer. In certain circumstances this will lead to extensive investments and for sure will bring more printing problems

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                              • #45
                                Originally posted by cementary View Post

                                From my experience it is not an answer. In certain circumstances this will lead to extensive investments and for sure will bring more printing problems
                                If you didn't have any concerns for your employee health or the cost of your FS wouldn't alcohol be the best option? Alcohol sub is called alcohol sub for a reason right? Artificial sweetner doesn't taste better than sugar.

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