12875Re: [PPLetterpress] Laser Engraved Photopolymer Plates
- Oct 23 11:13 AMThese 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:
> Maybe a picture or two is worth a thousand words:
> These are microscopic views of the surface of a halftone image. This
> why photopolymer can provide such exquisite detail. The relief depth
> between imaging of close proximity decreases with exposure and
> On 10/23/11 10:00 AM, Scott Rubel wrote:
>> 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
>> 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.
>> On Oct 22, 2011, at 10:57 PM, Gerald Lange wrote:
>>> 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
>>> --- 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
>>>> 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
>>>> 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
>>>> 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.
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