Transmission Efficiency of plastic Films Part 1

TRANSMISSION EFFICIENCY OF PLASTIC FILMS
In the case of a simple sealed sachet, the exertion of hand pressure will show up any
leakage by an escape of air. Another simple test is to insert a dyestuff on the inside
of the seal and observe any leakage. A visual check under polarised light is also
useful.
6.2 ADHESIVE LAMINATION
Adhesive lamination is adaptable to short as well as long runs and is well-suited to
the one-step production of laminates having more than two components. Laminating
processes can be divided into two major categories, namely, wet bonding and dry
bonding.
WET BONDING
Wet bonding uses solvent or aqueous-based adhesives and can only be used when
one or more of the webs are permeable to the water or other solvent used in the
adhesive formulation. In general, wet bonding is not usually successful with plastics
films even when laminating them to paper.
However, wet bonding using organic solvent-based adhesives, has been carried out
in some instances, and even aqueous based adhesive lamination can be carried out
for films such as cellulose acetate when bonded to paper. The cellulose acetate is
fairly permeable to water vapor and so aids drying out of the water after laminating. In
any case, the finished laminate must be run through a drying oven to speed up the
drying process, whereas when laminating fiber board to fiber board the water is
usually absorbed into the two webs and additional drying is unnecessary.
DRY BONDING
The dry bonding process incorporates either, (1) the use of an aqueous or solventbased
adhesive film that is dried prior to laminating or, (2) a hot melt adhesive, based
on wax or on one of a range of polymers.
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