Thought I'd add my usual two-cents worth to this thread. Not sure what
kind of machines, devices, contraptions, etc you are all using but
given just about everything else involved with photopolymer processing
the vacuum frame is where I have encountered most problems.
I use a mid-size A&V and it has a kreene sheet that rolls out on a
steel bar. Back end of it is duct-taped down. First time I saw this
was on a BASF and I thought they were kidding. My A&V came new with
the same engineering marvel. After a few blown negs and an extremely
frustrating time getting the tape back down so that it didn't throw
the kreene off I just decided to get rid of the steel bar and the duct
tape. Now I just leave a piece of properly sized kreene on the table,
folding it back to insert the plate, and then readjusting it. Works
If I have a consistent wrinkle sucking air at the edge of the kreene I
put a strip of magnetic rubber sheeting down. I suspect strips of
leading would work as well, if not better.
I use a photographer's squeegee to run the kreene down smooth against
the neg. Anything will do. A static free cloth will work. But a lot of
pressure (push-down) should not be used here, however, as raw polymer
reacts adversely to pressure. Same care should be used when cutting
raw material. Proper handling, prior to exposure, is quite important.
I no longer cut negs sized beyond the plate's edge. Preferring to cut
clean the plate edges later rather than risk blowing the plate. And I
no longer gang plates. Same reason. I blow out all dust, hair, etc,
with compressed air (negs/plates/kreene/vacuum table).
These are simply practices I've gotten into because I've found there
is less risk of blowing a plate. Its one thing to blow a plate when
you are doing your own work, its another thing altogether when you are
supplying plates for a client.
So going back to Yehuda's query I'd say vacuum leakage might be the
usual suspect but a similar result could occur because of structural
reaction by the raw polymer (mishandling) or as I suggested in the
prior post, by aging past its shelf-life. I suspect erratic washout
could also contribute to this.
Very early on I put a link to Polyfibron's website in PPL's Bookmarks.
They have a very useful set of technical notes there that greatly help
in problem solving, both in processing and when printing.