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12876Re: Laser Engraved Photopolymer Plates

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  • Gerald Lange
    Oct 23 11:28 AM
      Scott

      Hmmm, I guess a picture isn't worth a thousand words.

      No, these are not laser cut, these are film exposed. Obviously, there would be a difference in the relief structure between the two processes. That was the point. Film based photopolymer has varied relief, that is why it works, and, ahem, why this should be a consideration in presswork.

      Gerald
      http://BielerPress.blogspot.com



      --- In PPLetterpress@yahoogroups.com, Scott Rubel <scott@...> wrote:
      >
      > 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?
      >
      > --Scott
      >
      > 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
      > >>>>
      > >>>>
      > >
      > >
      > >
      > > ------------------------------------
      > >
      > > Yahoo! Groups Links
      > >
      > >
      > >
      >
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