Silicone-treated polyester film

Sara Moy <moy.sara [at] gmail__com> writes

>Does anyone know if silicon coated polyester (Mylar) has a shelf
>life?  I have recently encountered some that appears to be degraded.
>It has a milky, streaky appearance and grimy and tacky feeling.   A
>1997 DistList posting expressed some concern regarding the
>cross-linking to the Mylar substrate. I have attempted to contact
>manufacturers of silicon polyester to obtain more information on the
>chemistry and method of manufacture, however with no avail.  I
>believe that the polyester can be coated using solvents or by means
>of thermal or UV curing.

Silicone release polyester is manufactured by 'converters' who coat
the polyester film with silicone release agent. Exactly how, I do
not know. But I can tell you that beginning about 10-15 years ago it
started becoming more difficult to find release films that were
slick and clear, as they seemed always to be in the 1970's and 80's.
Beginning in the mid-90's, I think, we started getting release film
that was cloudy/milky in appearance. On some occasions, the release
agent felt tacky rather than slick. We were informed by the
resellers that this was OK. And, with the exception of slickness,
the materials do seem to have normal release properties. But I have
never been happy with either the milkiness or the tackiness. So I
hope this thread will result in some new sources for this very
useful material.

It is my assumption that the polyester is essentially inert, and not
subject to deterioration that would explain what you are seeing. I
also think, and hopefully others can confirm, that the silicone
release agent is vulcanized on the polyester film and should also be
very stable, if it is fully cured. So I wonder if the material you
are evaluating has altered with time or arrived in the state you now
observe?

Steven Prins
Conservator of Paintings
Steven Prins and Company
1570 Pacheco, Suite D-4
Santa Fe, NM 87505
505-983-2528


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                  Conservation DistList Instance 20:28
                 Distributed: Monday, November 27, 2006
                       Message Id: cdl-20-28-010
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