Transmission Efficiency of plastic Films Part 1

TRANSMISSION EFFICIENCY OF PLASTIC FILMS
for all properties, metalized films were found to be substantially better than unrealized
(transparent) films. A double sided metalized film was found to be substantially better
than a single sided metalized film. Potato crisps were chosen for study because they
are sensitive to oxygen, light and moisture and have a large surface area so that
changes in quality are easily detected.
In lamination, unsupported metalized films may well be most competitive as
alternatives to aluminum foil, which has to be paper-supported. Another plus point is
that metalized film may be printed before metalizing and the whole then sandwiched
in a laminate. On the other hand, if it is desired to print directly on to the metalized
surface then this presents no particular problems of ink adhesion or print quality other
than those normally associated with aluminum foil. When sandwich printing is the
method used, a depth and sparkle is added by viewing the print through the film.
Either opaque or translucent inks may be used to give a metallic colored effect.
A unique effect can be achieved by the vacuum metallization of expanded
polystyrene film. Instead of the bright metallic effects produced by other plastics films,
a frosted effect is obtained and this is combined with an attractive soft and silky feel.
The material may also be cold embossed, thus adding many other possibilities to its
decorative appeal.
The more rigid films, such as oriented polystyrene and PVC can be vacuum formed
to give a wide variety of finished products. Important factor when considering the use
of vacuum forming is that if the metalized coating is on the top surface it will reflect
some of the heat and so increase the heating cycle. Conversely, if the metalized
coating is on the underside of the film it will reflect the heat back through the film,
thus shortening the cycle.
A wide variety of plastics films are suitable for metalizing, including polyester,
polystyrene (both normal and expanded), and polypropylene, unplasticised PVC and
cellulose films. The first plastics film to be successfully vacuum metalized was
polyester and it was used for making Christmas trees and garlands. The market for
Christmas trees has now largely changed over to unplasticised PVC because of the
latter’s better non-flammable performance. The other main requirements of the
Christmas tree and garland applications are toughness and brilliance, with no
tendency towards limpness. Metalized polyester can also be laminated to PVC and
used in the manufacture of handbags, shoes and the decorative trim in cars, etc. One
interesting use of metalized polyester film is in the manufacture of ultra
lightweight mirrors. The metalized film is stretched over a framework attached to a
backing board in such a manner that the film is held clear of the backing board. In
addition to being very light in weight, the extremely low heat content of the film
means that condensation is greatly reduced because the film rapidly attains thermal
equilibrium with the atmosphere. These lightweight mirrors have been used in aircraft
wash rooms.
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