Transmission Efficiency of plastic Films Part 1

NYLONS:
TRANSMISSION EFFICIENCY OF PLASTIC FILMS
Nylon films have been used for the vacuum packing of foodstuffs, in particular
cheese slices, because of their low gas permeabilities. Their high softening points
have led to their use for boil-in-the-bag packs, another valuable property, here, being
their low odour transmission. A similar use is for the packaging of surgical equipment
for steam sterilization.
Because of the grease resistance of nylon films they are used for the packaging of
engineering components which have been protected with a film of grease. A
nylon/polyethylene laminate is used for the packaging of putty and certain fish packs
such as frozen prawns, the nylon being present to give oil and grease resistance and
as an oxygen barrier.
The biaxial orientation of nylon films gives improved flex crack resistance, barrier
properties and mechanical properties, and these have been utilized in the packaging
of processed and natural cheeses, fresh and cooked meats and frozen foods.
Package forms include pouches and bag-in-box.
POLYSTYRENE:
1. BI-AXIALLY ORIENTED FILM
In thin gauges, below about 75µm oriented polystyrene film is used for window
cartons. In addition to its transparency it has excellent dimensional stability. Such
films are also used for the over wrapping of lettuces and other fresh produce where a
‘breathable’ film is required. Because it has been stretched during manufacture, the
film is also suitable for use in shrink wrapping.
In thicker gauges, oriented polystyrene has been used for blister packaging as well
as for the thermoforming of clear vending cups and other types of rigid tubs. Such
tubs have been used for desserts, preserves and automatic vending of complete
meals and have been suggested for many other food packaging applications.
In the U.S.A., a large market has been building up for the manufacture of transparent
trays for the pre-packaging of fresh meat. The oriented polystyrene trays have made
inroads, into the meat tray market because the housewife has expressed a
preference for see through trays where both sides of the cut of meat can be seen,
2. TOUGHENED POLYSTYRENE
The incorporation of synthetic rubbers to increase the flexibility and impact strength
of polystyrene affects the clarity, and even in gauges down to about 100 µm thick it is
no more than translucent. It is thermoformed into a wide variety of tubs, trays,
vending cups and other types of packaging. Tubs are used for dairy products such as
cream, yoghurt, cheese, butter and ice-cream as well as for the ready diluted orange
squashes sold in cinemas and railway buffets. Tough need polystyrene trays are also
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