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12877Re: [PPLetterpress] Laser Engraved Photopolymer Plates

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  • Scott Rubel
    Oct 23, 2011
      Well, it was worth a thousand words to someone asking about the
      structure of a plate exposed with a negative.

      I was just relating my own limited experience with lasers and assumed
      this would produce straight sides which, like metal type, are more
      forgiving with imperfect rollers and adjustments, thus one less thing
      I have to teach an employee.

      Always looking for the easy way.

      --Scott

      On Oct 23, 2011, at 11:28 AM, Gerald Lange wrote:

      > 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
      >>>>>>
      >>>>>>
      >>>
      >>>
      >>>
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      >>
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