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12875Re: [PPLetterpress] Laser Engraved Photopolymer Plates

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  • Scott Rubel
    Oct 23 11:13 AM
      These are very clear pictures, but are these laser cut? Is there no
      difference between the structure of plate exposed to a negative and
      one from a laser?


      On Oct 23, 2011, at 10:21 AM, Gerald Lange wrote:

      > Scott
      > Maybe a picture or two is worth a thousand words:
      > http://www.flickr.com/photos/bielerpress/6272724517/in/photostream/#/
      > photos/bielerpress/6272724517/in/photostream/lightbox/
      > http://www.flickr.com/photos/bielerpress/6273250924/in/photostream/#/
      > photos/bielerpress/6273250924/in/photostream/lightbox/
      > These are microscopic views of the surface of a halftone image. This
      > is
      > why photopolymer can provide such exquisite detail. The relief depth
      > between imaging of close proximity decreases with exposure and
      > provides
      > structure.
      > Gerald
      > http://BielerPress.blogspot.com
      > On 10/23/11 10:00 AM, Scott Rubel wrote:
      >> Gerald,
      >> Good thinking about all this. I certainly would want it to be a
      >> minimum of 2400, for one thing, but I have not known how to think
      >> about the other disadvantages.
      >> The thing that I hope for when I think about the potential of laser
      >> is
      >> straight sides to the raised type. I don't I understand why there
      >> would be a limit to the depth in a counter as opposed to any other
      >> part. My knowledge of lasers is based on mostly half- or 3/4-witted
      >> speculation mixed with fantasy, which is why I do not understand your
      >> last paragraph, but I trust your assessment.
      >> --Scott
      >> On Oct 22, 2011, at 10:57 PM, Gerald Lange wrote:
      >>> Scott
      >>> I suspect that if cut just short of the floor of the plate rather
      >>> than down to the backing there would be no problem with the steel
      >>> reflecting. A more significant concern would be cutting through the
      >>> pre-exposed floor as plate stability would be sacrificed. Actually,
      >>> with this technique, the thinner the plate the better. All that
      >>> I assume the identity of the plates themselves and the correct
      >>> timing for the exposure is a minor problem. 1200 dpi is still not
      >>> good enough, basically high-end laser printer quality. Imagesetter
      >>> quality at a minimum of 2400 dpi would be needed to match current
      >>> film based exposure.
      >>> A major concern would be maintaining relative reverse relief depth,
      >>> which is fairly uniform when exposing photopolymer plates specified
      >>> for letterpress applications, no matter what the thickness of plate.
      >>> For instance, the relief depth of the counter of a small point size
      >>> lowercase e or o is not going to be open to the depth of the floor
      >>> of the plate. It is halted with maximum exposure at a specific
      >>> range, about .30 mm; relief depth is not uniform [which is actually
      >>> the best technical argument refuting the practice of extreme
      >>> impression]. I don't see how this could be controlled with a laser
      >>> cutter.
      >>> Gerald
      >>> http://BielerPress.blogspot.com
      >>> --- In PPLetterpress@yahoogroups.com, Scott Rubel<scott@...> wrote:
      >>>> The website days it goes to 1200 dpi. If the coordinate tracking is
      >>>> accurate as it cuts, that should render pretty good six point type.
      >>>> It is hard to tell the quality of the laser, but I think I will ask
      >>>> them for a sample of steel backed polymer. I wonder how that works
      >>>> without the steel acting like a mirror.
      >>>> These laser beams can be unbelievable thin, if they are high
      >>>> quality.
      >>>> I work at a place where we make giant cameras for giant telescopes,
      >>>> and we order custom "slit masks" which are large sheets of aluminum
      >>>> with thousands of precision placed cuts in them. The cuts aren't
      >>>> much
      >>>> thicker than a hair, and you would think the laser is just moving
      >>>> along a path and cutting the slit, but in reality it cuts out the
      >>>> shape of the slit and almost microscopic blanks fall out of the
      >>>> metal
      >>>> every time a slit is cut. So if this Epilog Legend 36EXT machine is
      >>>> high quality, I would think six point type should work fine.
      >>>> --Scott
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