11956Re: Photopolymer separating from polyester backer
- Aug 3, 2010This calls to mind something we were experiencing last year. We were using HX145 at the time, if I recall correctly. We were having some issues with certain plates coming out brittle, cracking, and separating from the backing. Other plates worked, but you could tell from a slight color variation that they were fragile. Still other plates worked fine. After some trial and observation, one of my cohorts felt it was the length of post exposure. I was under the impression (based on something I was taught about a different plate material) that you couldn't over post expose. However as we worked through the problem, I had to agree, that it was the length of time in post exposure.
To drive the point home, one weekend a plate was accidently left sitting out in a place where the afternoon sunlight would reach it. The plate had already been made and post exposed. When we returned, the whole thing had thousands of fissures.
I wonder if as you're compensating for the bulbs aging by increasing exposure, post exposure, or both, you're winding up with too much time in the direct uv light?
Painted Tongue Press
--- In PPLetterpress@yahoogroups.com, "idgradstudent" <glenwoodemorris@...> wrote:
> Thanks to Harold, Gerald, Peter, et al for the help and suggestions.
> I will have to do some testing at the edge of my exposure unit with my Stouffer scale and see if I am getting different results there, which seems likely.
> I have had intermittent problems with overexposure in certain areas as well, which has kept me from just increasing my exposure time. I am guessing this is the "hot spots" that some bulbs can develop over time?
> Is there any detrimental effect to new bulbs if you replace just the bulbs rather than swapping the bulbs and the ballasts?
> I will try exposing the back of the plate for 20 seconds to see if it might be a temporary workaround.
> Glenwood Morris
> Oslo Press Inc.
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