Gawain wrote:
> My understanding of dry down is that it is only a function of paper
> shrinkage-- as the paper shrinks, the image particles come closer together,
> resulting in higher density (both physically and visually). Sizing would
> presumably influence degree of paper expansion and contraction, so the
> influence of sizing would be predicted by this explanation. Are there other
> factors or better explanations than this?
Not only contraction during drying -- sizing also influences how deeply the
sensitizer penetrates into the paper, thus how much of the paper
contraction involves image particles. If the sensitizer were all in a
miniscule layer right on top -- as with printing on glass, glazed ceramic,
or enameled steel plates -- contraction of the substrate would be
essentially irrelevant to the image thickness and therefore density. Even
if you had nothing but a dried pool of sensitizer (imagine dried saltwater
on glass) and -- counterfactually -- could keep it there during development
(or rinsing in the case of POP processes), the image grains themselves
would likely compact some while drying, so even in principle there will
probably always be some drydown. Since the only ways I have found to coat
non-permeable substrates involve the use of subbing with a finite
thickness, in practice even on those materials one gets a bit more drydown
than a dried layer of sensitizer alone would give.
Best regards,
etienne
Received on 07/20/06-10:05:32 PM Z
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