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Polyester
film encapsulation
A method of single-sheet paper support that has won
favor in recent years because of its total reversibility
is polyester
film encapsulation.
In this method, the damaged sheet is sandwiched between
two sheets of polyester film (Mylar type D or Melinex
type 516). The film should not contain plasticizers
or surface coating, or be a plastic other than polyester.
The film is sealed around the edge using either double-sided
adhesive
tape, heat welding, sewing, or ultra-sonic
welding. Encapsulation relies on the electrostatic nature
of the polyester to support the document, but this property
can be detrimental to text and images created with unstable
media, such as pencil or charcoal, as it can release
the image from the paper. Because the deterioration
of acidic materials is accelerated by complete enclosure,
the document should be de-acidified prior to encapsulation.
Alternatively, if the text or image is only on one side
of the document, a single sheet of alkaline paper should
be cut to size and placed in the encapsulation with
the document to create an alkaline environment. Documents
should be clean and dry before encapsulation. For some
documents, complete encapsulation may not be necessary,
and polyester sleeves can be purchased and used. For
large, single-sheet documents such as maps or posters,
encapsulation is an excellent solution providing flat
storage is available.
To encapsulate a document, two pieces of 3 or 4 mil
polyester
film are cut roughly 7 centimeters larger than the width
and length of the document. The document is centered
on one of the polyester sheets and weighted down. If
double-sided adhesive
tape is used, it should be applied to
the polyester sheet approximately 3 millimeters away
from the edge of the document. The weight is then carefully
removed from the document, the top polyester sheet is
placed on top of the document, and the weight is put
back on. The top protective layer of the tape is removed
along one edge by lifting the edge of the top polyester
sheet. The film is pressed down to adhere to the tape,
then the protective tape layer on the other edges is
removed and the film smoothed down with a soft cloth
or squeegee to squeeze out the air. Excess film is trimmed
away roughly 3 millimeters from the outer tape edge.
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Polyester
welding equipment is either heat (radio welding)
or ultrasonic. The radio welder uses a heat bar
that effectively seals and cuts the polyester.
Radio welding, though cheaper than ultrasonic,
thickens a sheet's edge, which is problematic
when several sheets must lie on top of each other.
The ultrasonic machine welds the polyester with
a head that moves across it at a regulated speed.
The advantage of ultrasound is that a weld may
be placed at any point on the polyester—not
just the edge—and it doesn't cause thickening.
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Next: Cleaning soiled
paper
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