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Problem with PP crop marks

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  • nuftus
    Hello, Long time reader, first time poster here. Have much appreciated the knowledge and professionalism. I have been processing my own photopolymer plates
    Message 1 of 5 , Jun 13 8:48 PM
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      Hello,

      Long time reader, first time poster here. Have much appreciated the knowledge and professionalism.

      I have been processing my own photopolymer plates without a problem until recently. I was hoping for some tips and guidance to help troubleshoot.

      During the drying process, our crop marks are curling upwards. It is as though they no longer want to be part of the bottom of the polymer.

      Here is a photo of the problem:
      http://www.ewebs.com/cropprob.jpg

      The circumstances:
      - Crop marks are 0.5pt.
      - We have had no problems with 0.5pt crop marks in the past
      - While artwork is finely detailed, the rest of the plate will expose and dry fine.
      - Usually we: Expose for 2 mins. Wash-out for 3-4mins. Dry for 8-10mins. Re-expose for 4 mins.
      - We have tried first exposing for 3 mins, but it makes little difference
      - I have tried exposing using a different polymer sheet, but it makes no difference
      - We notice the crops start curling up after 4 mins drying
      - Polymer is "Mavelon DF3-94B"
      - It has been raining recently, and room temperate dropped to approx 20 degrees celcius

      Any tips to help troubleshoot would be appreciated.

      Thankyou
    • bielerpr
      Hi Nuftus I am not familiar with these plates and thus can t comment on the various timings but generally this would indicate you need more exposure time and
      Message 2 of 5 , Jun 13 9:17 PM
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        Hi Nuftus

        I am not familiar with these plates and thus can't comment on the various timings but "generally" this would indicate you need more exposure time and maybe less washout. (The pic is very useful by the way). Beyond that, temperature could be a consideration, bulb problems, plate age or formulation, and on and on. Try to modify the exposure and washout to a point where it seems to be improving, and that might give you a clue. If not, you have some of the "on and on" problems. Maybe also put a space heater in the room to boost the temp a bit.

        Gerald
        http://BielerPress.blogspot.com

        --- In PPLetterpress@yahoogroups.com, "nuftus" <noftus@...> wrote:
        >
        > Hello,
        >
        > Long time reader, first time poster here. Have much appreciated the knowledge and professionalism.
        >
        > I have been processing my own photopolymer plates without a problem until recently. I was hoping for some tips and guidance to help troubleshoot.
        >
        > During the drying process, our crop marks are curling upwards. It is as though they no longer want to be part of the bottom of the polymer.
        >
        > Here is a photo of the problem:
        > http://www.ewebs.com/cropprob.jpg
        >
        > The circumstances:
        > - Crop marks are 0.5pt.
        > - We have had no problems with 0.5pt crop marks in the past
        > - While artwork is finely detailed, the rest of the plate will expose and dry fine.
        > - Usually we: Expose for 2 mins. Wash-out for 3-4mins. Dry for 8-10mins. Re-expose for 4 mins.
        > - We have tried first exposing for 3 mins, but it makes little difference
        > - I have tried exposing using a different polymer sheet, but it makes no difference
        > - We notice the crops start curling up after 4 mins drying
        > - Polymer is "Mavelon DF3-94B"
        > - It has been raining recently, and room temperate dropped to approx 20 degrees celcius
        >
        > Any tips to help troubleshoot would be appreciated.
        >
        > Thankyou
        >
      • Jessica Hosgood
        Hello, I ran into the same issue when I first started exposing plates (3 mins). Exposing for a longer time (6 or even 8 mins) solved the problem. The rest of
        Message 3 of 5 , Jun 14 12:22 AM
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          Hello,

          I ran into the same issue when I first started exposing plates (3 mins). Exposing for a longer time (6 or even 8 mins) solved the problem. The rest of the plate was usually fine, I guess because elements were "stuck" to each other, whereas crop marks are isolated.
          If you didn't have this problem before it could be, as Gerald says, that the bulbs in your exposure unit are getting old and need to be changed.

          Jessica


          --- In PPLetterpress@yahoogroups.com, "nuftus" <noftus@...> wrote:
          >
          > Hello,
          >
          > Long time reader, first time poster here. Have much appreciated the knowledge and professionalism.
          >
          > I have been processing my own photopolymer plates without a problem until recently. I was hoping for some tips and guidance to help troubleshoot.
          >
          > During the drying process, our crop marks are curling upwards. It is as though they no longer want to be part of the bottom of the polymer.
          >
          > Here is a photo of the problem:
          > http://www.ewebs.com/cropprob.jpg
          >
          > The circumstances:
          > - Crop marks are 0.5pt.
          > - We have had no problems with 0.5pt crop marks in the past
          > - While artwork is finely detailed, the rest of the plate will expose and dry fine.
          > - Usually we: Expose for 2 mins. Wash-out for 3-4mins. Dry for 8-10mins. Re-expose for 4 mins.
          > - We have tried first exposing for 3 mins, but it makes little difference
          > - I have tried exposing using a different polymer sheet, but it makes no difference
          > - We notice the crops start curling up after 4 mins drying
          > - Polymer is "Mavelon DF3-94B"
          > - It has been raining recently, and room temperate dropped to approx 20 degrees celcius
          >
          > Any tips to help troubleshoot would be appreciated.
          >
          > Thankyou
          >
        • KalleP
          Hi, ... Not having done any plates personally I still have thoughts on your problem. Assuming most of the other variables are similar this looks like the
          Message 4 of 5 , Jun 15 3:07 AM
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            Hi,

            > During the drying process, our crop marks are curling upwards. It is as though they no longer want to be part of the bottom of the polymer.

            Not having done any plates personally I still have thoughts on your problem.

            Assuming most of the other variables are similar this looks like the polymer does not have a chance to expose all the way to the base to 'attach' the printing face to the plate. The thin crop mark has to expose all the way down through the narrow slit in the negative without help from adjacent text to raise the floor.

            Two fixes suggest themselves, as others have mentioned increase the exposure time, and secondly to add a bit of back exposure across the whole plate or even only around the crop masks with a cardboard or paper mask. Photopolymer has a factory exposure from the back to bond it to the film and this can be safely added-to at the expense of the plate relief depth. Metal backed plates will not work with this work around.

            The thought was that your light output is less than usual and bulb age and temperature are suspected. I have read in many scanner manuals that they take 3 minutes to stabilise in light intensity before they reach the specified even level if they use fluorecent illumination. I also know that old tubes may fail to light up in very cold weather so temperature is certainly implicated here if you have had a cold spell. To fix it, warm up your exposure unit with a heater or run a 5 or 10 minute dummy exposure cycle just before you do the plate to bring the tubes up to temperature.

            It may be an indication of ageing tubes but increasing the exposure is a safe fix usually if the level of illumination is still even across all the tubes.

            Regards

            Kalle
            --
            Idyllic Press - Johannesburg, South Africa
          • Gerald Lange
            Kalle Yes, for the most part this is correct re: exposure and temperature. There is a certain latitude available in regard to exposure. Increase it and you
            Message 5 of 5 , Jun 15 3:48 AM
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              Kalle

              Yes, for the most part this is correct re: exposure and temperature.

              There is a certain latitude available in regard to exposure. Increase it
              and you will likely have better results. Especially since there is a
              given wane to bulbs over time. Increasing exposure should probably be
              your first attempt at correction...

              As you point out, sheet photopolymer plates are already back-exposed. It
              will likely not help to add to this though, if you even can, re your
              term "safely" (since it has already been done at the manufacturer),
              though I have read it proffered for "deep relief" polyester-backed
              plates as a fix (but only from one source). Not sure how valid this is,
              these plates are not formulated for letterpress in the first place. Hard
              to make a silk purse out of a pig's ear.

              Gerald
              http://BielerPress.blogspot.com


              On 6/15/11 3:07 AM, KalleP wrote:
              > Hi,
              >> During the drying process, our crop marks are curling upwards. It is as though they no longer want to be part of the bottom of the polymer.
              > Not having done any plates personally I still have thoughts on your problem.
              >
              > Assuming most of the other variables are similar this looks like the polymer does not have a chance to expose all the way to the base to 'attach' the printing face to the plate. The thin crop mark has to expose all the way down through the narrow slit in the negative without help from adjacent text to raise the floor.
              >
              > Two fixes suggest themselves, as others have mentioned increase the exposure time, and secondly to add a bit of back exposure across the whole plate or even only around the crop masks with a cardboard or paper mask. Photopolymer has a factory exposure from the back to bond it to the film and this can be safely added-to at the expense of the plate relief depth. Metal backed plates will not work with this work around.
              >
              > The thought was that your light output is less than usual and bulb age and temperature are suspected. I have read in many scanner manuals that they take 3 minutes to stabilise in light intensity before they reach the specified even level if they use fluorecent illumination. I also know that old tubes may fail to light up in very cold weather so temperature is certainly implicated here if you have had a cold spell. To fix it, warm up your exposure unit with a heater or run a 5 or 10 minute dummy exposure cycle just before you do the plate to bring the tubes up to temperature.
              >
              > It may be an indication of ageing tubes but increasing the exposure is a safe fix usually if the level of illumination is still even across all the tubes.
              >
              > Regards
              >
              > Kalle
              > --
              > Idyllic Press - Johannesburg, South Africa
              >
              >
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