Silicone-treated polyester film

Rick Dzupina <rdzupina<-a t->interlog< . >com> writes

>I have been searching for information about silicone-treated mylar,
>specifically whether the silicone, when it is applied to the mylar,
>becomes cross-linked to the mylar substrate, or rests on the
>surface, to deteriorate at some time down the road.

I began an investigation into the physical characteristics of
silicone Mylar before beginning a large scale rehousing project for
our museum's collection of Beijing shadow puppets.  The puppets are
carved from skin, painted with dyes and coated with tung oil.  The
oil coating has remained tacky so a slick storage surface offered by
the silicone Mylar was desirable.

Much to our surprise, we found that the silicone coating on the
Mylar we had on hand in the lab was removed readily with a wide
range of solvents, an unacceptable quality when dealing with long
term storage as the possibility of the eventual loss of its
non-stick qualities when in contact with the soft oil seemed too
great.  We received our film from Archivart and I couldn't get any
technical info about the manufacture of this type from them.

I spoke with a number of technical reps from different coating
companies and found that there are basically three techniques used
in applying and polymerizing the silicone coating onto the Mylar
film including electron beam activation and UV and thermal curing
processes (I didn't get the sense that there was any crosslinking to
the Mylar substrate).  Within the curing modes are varying levels of
transfer and a wide range of release levels dependant upon the
polymerization method used.  Most of the reps agree that the UV
cured coatings will tend to transfer less than the heat cured
coatings, but you won't get the range of release levels with UV
cured films as you would with thermally cured ones.  The heat cured
coatings, however, are the ones used for making heat activated
adhesive films so you'd think that they are sufficiently polymerized
to withstand the high degree of solvents used in these processes.

After examining and testing a bunch of samples, I found that one
manufactured by a company called Douglas Hanson seems the most
stable concerning transfer and loss of non-stick qualities.  The
silicone coating on this sample has been polymerized through UV
activation.  Conservator's Products and Talas carry this type of
film.

I don't know if I've answered your questions.  Feel free to call
with comments or ideas.

Lisa Kronthal
Associate Conservator
American Museum of Natural History
Anthropology Department
Central Park West at 79th Street
New York, NY 10024
212-769-5446
Fax: 212-769-5334

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                  Conservation DistList Instance 11:13
                  Distributed: Friday, August 1, 1997
                       Message Id: cdl-11-13-003
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