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  • plate readings and tolerances

    Hello everyone,

    My question is: What are your tolerances for plate readings?

    We output a step wedge on all plates and measure every plate, charting the readings for reference. We have a Fuji Saber using the new LP-NV2 plates. Obviously some jobs are more critical than others, so we aren't critical on type only jobs or spot color jobs, but process jobs and repeat jobs we watch and keep within tolerance.

    Here is what is on our step wedge and our tolerances.
    2% +- .5%
    5% +- 1%
    10% +- 1%
    20% +- 1.5%
    30% +- 1.5%
    40% +- 2%
    50% +- 2%
    60% +- 2%
    70% +- 2%
    80% +- 2%
    90% +- 1.5%
    95% +- 1%
    97% +- 1%

    With the violet plates they seem to be consistent for a while then all of a sudden there is a shift. It could be chemistry, although we change the chemistry about every 300 plate, or it could be something else like humidity.

    Let me know what you think is acceptable.



  • #2
    Re: plate readings and tolerances

    We have a reflective densitometer with plate reading add-on, and we calibrate each time we use it. Our tolerance is +/- 2. We haven't had a problem with this setup for the years we've been using it, but we don't print to GRACoL2006_Coated1 yet, so I don't know if it would be affected by this tolerance or if we'd need a tighter tolerance then.



    • #3
      Re: plate readings and tolerances

      Mike, what halftone screen ruling are you using? (the finer the screen the greater the potential variation)

      thx, gordo


      • #4
        Re: plate readings and tolerances

        Normrally I Think there exist a Fogra tolerance of +- 1,5% on each patch and a difference of 1% on the same value over the whole plate.

        I can suggest to use a special platereader as the x-rite IC plate 2, to become reliable results.


        • #5
          Re: plate readings and tolerances

          We are using 175 line screen, and we are using the Xrite CCdot plate scanner to check the step wedge.


          • #6
            Re: plate readings and tolerances

            Fuji LHPJ plates.
            IC Plate II plate reader.
            +/- 1% almost every time.


            • #7
              Re: plate readings and tolerances

              Is the Fuji LHPJ plate a thermal plate? We're using the Fuji Saber which is not. Would a thermal device would be more stable?

              Fuji is talking about a processor-less violet plate coming out toward the end of next year, but who knows if that will be more stable.


              • #8
                Re: plate readings and tolerances

                > {quote:title=Whitaker wrote:}{quote}
                > Here is what is on our step wedge and our tolerances.
                > 2% +- .5%
                > 5% +- 1%
                > 10% +- 1%
                > 20% +- 1.5%
                > 30% +- 1.5%
                > 40% +- 2%
                > 50% +- 2%
                > 60% +- 2%
                > 70% +- 2%
                > 80% +- 2%
                > 90% +- 1.5%
                > 95% +- 1%
                > 97% +- 1%

                Wow! I wouldn't have thought that the reader could be demonstrated to be that repeatable.



                • #9
                  Re: plate readings and tolerances

                  I was hoping that the LP-NV2 plates would be more stable. We have been using LP-NV Plates for about 4 years, but I am expecting LP-NV2 to be here next week.

                  I have battled the dot shift problem since the Saber was first installed. We run 900-1500 plates between chemistry changes (4 to 6 weeks). We use a Beta Ultra Dottie 2 plate reader, which is very repeatable. There is ABSOLUTELY a dot shift that occurs, but after all this time I still can't pinpoint exactly why. We keep our Saber and processor very well maintained. I can produce the same dot shift at 150 LPI, 175 LPI, and 200 LPI (200 is our standard). I read the 1%, 2%, and 50% on every black plate (45 degree angle). I monitor temperature, pH, humidity, plate lot numbers, emulsion numbers, etc.

                  The dot shift we see here is across the whole scale almost like an exposure issue. The 1% dot sometimes disappears, (which is not too surprising), but sometimes it will be holding steady between 0.5% and 1.5% for a week or two or three, and then all of the sudden the 1% reads 2.5 or 3%. The rest of the scale follows (50% which is normally reading 56% with my plate curve applied is reading 58%)

                  I could explain this away if the lot number changed, or we did a chem change, or changed the scrub rollers or whatever. But more times than not, this will happen without much warning in a batch of plates with the same lot number that has been running perfectly for some time. Sometimes a new box of plates will be different, sometimes not. Sometimes the top 2 or 3 plates in a box will be different than the rest, sometimes not. It is very unpredictable, and very frustrating. Sometimes I will re-linearize to fix the issue only to have to re-linearize again in a few days when the dots mysteriously change back.

                  A couple of theories I have:

                  There is a neutral density filter wheel in the Saber that can get loose and shift, although I ask the tech to make sure it is ok at every PM call.
                  Transportation- I think temperature during shipping may have something to do with it.
                  Plate age- Plates that are too new seem to be more prone to shifting.
                  Developer Temperature fluctuations

                  Anybody else willing to speculate??

                  Dave Watson
                  Edwards Printing Co.



                  • #10
                    Re: plate readings and tolerances

                    Very impressive, all the care you have taken in studying the variations. I would suggest two possibilities, without much or any proof. Plate readings change with color, so there might be slight variations in the color of the emulsion. Another possibility is a change, even within a lot, of emulsion thickness. These emulsions are a couple of microns thick applied across a wide web of aluminum at fast pace, on a grain that also has some variation. I think the source of your variation can be found in these factors that are process variation, outside your control.
                    Just a thought.
                    John Lind
                    Cranberry Township, PA


                    • #11
                      Re: plate readings and tolerances

                      Rich Applo:
                      The CCDot scanner is rated to be +- .5% accurate, meaning if you read a patch and it says its 30%, you can believe that it is 30% +- .5%. BUT after using it for a couple years and taking multiple reading on the same patch it does seem to drift from one reading to the next, meaning if I read a 30% patch 4 times I might get a 29 1/2, then a 30, then a 29 1/2, then a 30 1/2. We don't get crazy taking multiple readings on all plates, we read, log it and move on.

                      David Watson:
                      Thank you for your response. You experience the same problems and frustration that I do. We change the chemistry more often, but currently I'm not monitoring pH. I just spoke with our dealer and he is getting me a measuring device for pH, but I'm not so sure that that is a factor here.

                      We had this problem yesterday. The first plate on a job was read and the 2% dot was a 4, the 5% was an 8 but the rest of the scale was in spec. I made an adjustment to the plate curve, made a new plate and the 2 was a 0! I removed the adjustment on the curve, made a new plate and all was well. Although this is a bit different than what you stated in your response I do see the same symptoms as you do with our Saber.

                      The LP-NV2s have not solved this problem. One issue I have with the new plate is that a 2% dot sent down with no curve comes out as a 0%. That doesn't seem right to me. Here are the readings I get with no curve applied to the plate:
                      2 = 0
                      5 = 3
                      10 = 8
                      20 = 20
                      30 = 31
                      40 = 43
                      50 = 57
                      60 = 66
                      70 = 76
                      80 = 85.5
                      90 = 93.5
                      97 = 98.5

                      The highlight is too light, quarter tones are linear, and the mid tones/shadows are too dark. Before we got these plates I was told they would be linear right out of the box. Not even close. Now, after our dealer has had some more experience with these plates, they are saying the readings that I am getting are similar to what other people are getting.

                      John Lind:
                      Thanks for the input, that may have something to do with this problem too.



                      • #12
                        Re: plate readings and tolerances

                        As a former Sabre user I feel your pain. However any rep that would tell you that your plates would be linear out of the box is on crack! The device needs to be linearized in order to get linear plates. The new high resolution violet plates from fuji are designed to give you better resolution so you can consistently hold 1%-99% on the plate as opposed to the old plates which fuji only guaranteed 2%-98%. I said I was a former Sabre user as I have dumped the sabre and went to a Screen Platerite 8800 thermal device and I have not looked back. It is CONSISTANT with a capital C. A 1% is a 1% and a 99% is a 99% and it perfect from 1-99.
                        It doesn't matter if it is the first plate using fresh chemistry or the 3000th plate it always reads the same as checked with an Xrite Platescope. The problem with violet plates is water quality and temp on the pre-wash and the age of the developer.


                        • #13
                          Re: plate readings and tolerances

                          > {quote:title=macphenom wrote:}{quote}
                          > The problem with violet plates is water quality and temp on the pre-wash and the age of the developer.

                          That's interesting. I know the pre-wash temp can be an issue. I try to control ours as best I can using a separate water panel for the pre-wash, but I did not consider the water QUALITY. I have considered a water softener, but only to ease the pain of cleaning the processor rollers that get a build-up of crap from all the minerals in the water here.

                          So who uses a water softener or R/O unit with violet plates? Has anyone made a transition from "bad" water to "good" water and noticed a difference besides the processor being easier to maintain and rollers lasting longer?

                          Dave Watson
                          Edwards Printing Co.



                          • #14
                            Re: plate readings and tolerances

                            I have been lurking for awhile, but this topic is one I've been working on. I too have been interested to see if the new LP-NV2's improved emulsion reacts more consistently with imaging, thus producing a more consistent dot.

                            I have two things that I've tried to get a better highlight dot... One was increasing the exposure energy beyond the typical 50 mJ called for on LP-NV's. The other was checking the laser focus. The latter did make some improvements, as did the former -- though with the latter the shadow dot was harder to manage (putting the problem on the other end of the curve).

                            The other problem is the approach visible light plates use... The combination of laser energy and chemistry crosslink the emulsion into what we end up with as an image on the plate. However, prior to the developer stage, the scrubber pressure, prewash temp, and preheat temp all play roles. Notably in my situation, the scrubber pressure as I use two gauges of plates. I need to adjust the pressure to be appropriate for my 12 gauge plates, but then that is a bit light on the 8 gaugers, etc. Bottom line is that there are a number of other variables beyond what has been mentioned in this thread so far.

                            Currently I am building a data acquisition system to monitor the process with much more scrutiny. This should be done within the next month or so. With that data, perhaps there will be much more to go on. If this proves effective, I'll seek other backup on this from those with Sabers, but for now I can only say that I plan on taking a very aggressive approach to develop a way to minimize the ongoing dot variance that the violet system appears to experience (backed up by all those who have posted here).

                            It'd be nice to go thermal, but that is not an option any time soon. Hopefully my data acq. will shed a lot of light on where the variability is...


                            • #15
                              Re: plate readings and tolerances

                              I have been using the LP-NV2 plates for about a month and a half now, and so far the dots seem a bit more stable, but still fluctuating. The pressroom seems to like them, they tell me that the plates print much sharper which helps with stability on press.

                              Jason: Have you switched to LP-NV2's yet? Any update to your last post??

                              Dave Watson
                              Edwards Printing Co.



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