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Plate Blinding on Press

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  • Plate Blinding on Press

    Hello all, I hope someone can shed some light on this major processor problem i had this week. It started on Tuesday, the litho department was printing a job with 3 layouts, 2 sets of plates were made about a 2 weeks ago and the plates for the third form were made Monday. When they tried to print the plates from Monday they were getting major blinding on all colors across the sheet something i had never seen before in this trade, i made another set of plates, same result, i asked them to put on plates from a different job that were made Monday, same result. I called Agfa and explained everything and they said i needed roller bearings replaced for about 12 rollers between the wash and finishing tanks because residue from the wash tank was entering the finishing tank and probably contaminating the plates, so we had them changed and did a full maintenance , back to press, same results. Then they inspected all the rollers and decided that the developer rollers needed better cleaning so they did that and same result. Then more inspection of the processor reveals that the developer rollers closest to the wash tank might not be turning properly because some structure parts seemed warped and might not be turning properly so they did a band aid fix until replacement parts arrived. We are now at Thursday evening, made some new plates for a job being printed that night and all seemed well, everything printed properly, Friday morning i made new plates for the next job on all ok, i made 2 other sets of plates that went on later that day all ok, no more blinding. My biggest concern now is everything really fixed because even the 2 Agfa tech's were scratching their heads for almost 3 days about this. Without a definite and exact explanation from Agfa about why we had this problem it still leaves me a bit on edge. If anyone has any thoughts on what really caused me this problem i would really appreciate your input.

    Note: We tried plates from 3 different batch numbers, developer and finisher from 2 different batch numbers. Also we burned plates for new jobs and had them developed in another processor at another plant and printed fine.

  • #2
    Re: Plate Blinding on Press

    "We tried plates from 3 different batch numbers, developer and finisher from 2 different batch numbers. Also we burned plates for new jobs and had them developed in another processor at another plant and printed fine."

    I'ts important to isolate all your raw materials when troubleshooting. One that people often forget is the water used to mix developers and finishers and sometimes used for rinsing.

    A problem that just "goes away" after extended fiddling with the process is the hardest to troubleshoot. The cause for these problems is most often is an uncontrolled variable. What in your process are you controlling well? What are you aware of but not controlling? (Maybe just monitoring)

    It sounds like the Agfa techs were seeing evidence of mechanical abrasion or fluid shear on the plate. This is usually a result of poor roller maintenance in a developer. Ask the techs to describe, very accurately, each maintenance task performed and the results of those tasks. If you were involved, you may have this information already.

    Finally, don't assume that there is one "silver bullet" that will explain any given process issue. More often than not, in an uncontrolled process, there are many factors that contribute.

    Good luck!

    Edited by: QualityGuy on Feb 11, 2008 7:53 AM - Spelling


    • #3
      Re: Plate Blinding on Press

      If you have a G+J processor, make sure you are not getting water in your finisher (pre-bake solution)
      These processors seem to have a nasty habit of the solenoid dor the water shut off sticking in the on position and allowing water to get in the finisher. Take a look at the finisher jug. It should have a dark color to it if it is OK. If it is a lighter color, then there is contamination from water at some point, and it should be changed with a fresh jug. We have the guys mark a line with a red Sharpie on the jug to indicate the level at the beginning of the shift. The next shift looks to make sure that the level is decreasing instead of increasing, and, if it is decreased, they put a new line and write the time on it. If it has INCREASED, they know that it is contaminated, and change the jug, and call AGFA tech.

      We disconnected the power to the solenoid, and manually open the valve. This seems to work, but does not correct the "problem" with the solenoid, but keeps the jug from getting contaminated.

      Also, if you have one of those "chemistry treating" units that conditions the chemistry's PH before flushing down the drain, make sure it is able to handle the amount of developer and is not allowing any back flow back to the processor. We had a problem with that once and it caused a similar problem.

      good luck!


      • #4
        Re: Plate Blinding on Press

        Thanks for the input guys, blinding seems to be gone, but i am still a little edgy about it, we'll see how the week goes.


        • #5
          Re: Plate Blinding on Press

          Sorry to sound ignorant. What is blinding? (I am a graphic designer, not a press operator.)


          • #6
            Re: Plate Blinding on Press

            Hi there,

            It is common practice to talk about blinding when the image area of the plate no longer accepts ink or repels water. The result is a weak area of image on the blanket/substrate. This can be due to mechanical or chemical wear on the hydro-phobic area of the plate.



            • #7
              Re: Plate Blinding on Press

              Just went through blinding myself and it was mold in the wash water tank. We couldnt see it and we clean out the tank on an every other day cycle but it was still there. We did a rinse using some bleach then refilled and it seems to be working fine. Also put in a dehumidifer in our prepress room hoping that helps.


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