Transmission Efficiency of plastic Films Part 1

TRANSMISSION EFFICIENCY OF PLASTIC FILMS
treats as an adhering surfaces and improves the bond strength. The most commonly
used reactive gas for this process is ozone formed by an electrical discharge
mechanism. This method is particularly valuable where unlike materials, such as
nylon and polyethylene, have to be combined. Co extrusion generally is an important
addition to the various techniques used for producing composite-films.
The main advantages of coextruded films over conventionally produced laminates
are lower cost, a lower tendency towards delaminating and a greater flexibility in
obtaining a wide range of properties. The possibilities of cost savings may not be
immediately obvious. After all the equipment needed is bound to be more expensive
than that necessary to produce the separate films. Extrusion speeds will probably be
lower although developments in equipment design may well alter this. The first
possibility of cost savings lies in the fact that in multi-layer extrusion the finished
laminate is produced in one operation. In normal laminating procedures of course,
the respective single films have first to be extruded followed by reeling-up and
storage. Later on, these reels have to be un-reeled and run through the laminating
process and this obviously adds to labor costs. Cost savings on material are also
possible. The minimum thickness of any particular ply in a conventional laminate is
often dictated by its handling characteristics on laminating equipment rather than by
the barrier or other properties required. However, very thin plies indeed can be
produced by co extrusion so that the optimum thickness can be chosen for the job. In
this connection it is interesting to note that three layer films have been produced with
a thickness of less than 25 µm overall.
Apart from cost savings in the production of the laminated film, there are also
possible savings in bag making. Multi-layer lay-flat film can be produced by coaxial
extrusion. It is then possible to make a bag of laminated construction merely by
making one cross- seal. Coaxial extrusion then provides the only method of
producing a bag of laminated construction with out side or centre seams.
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