Transmission Efficiency of plastic Films Part 1

TRANSMISSION EFFICIENCY OF PLASTIC FILMS
used structural adhesives are based upon epoxy resins. An important property for a
structural adhesive is resistance to fracture (toughness). Thermoplastics, because
they are not cured, can deform under load and exhibit resistance to fracture. As a
class, thermosets are quite brittle, and thermoset adhesives are modified by
elastomers to increase their resistance to fracture.
Hot-melt adhesives are used for the manufacture of corrugated paper, in packaging,
in bookbinding, and in shoe manufacture. Pressure-sensitive adhesives are most
widely used in the form of coatings on tapes, such as electrical tape and surgical
tape. Structural adhesives are applied in the form of liquids, pastes, or 100%
adhesive films. Epoxy liquids and pastes are very widely used adhesive materials,
having application in many assembly operations ranging from general industrial to
automotive to aerospace vehicle construction. Solid-film structural adhesives are
used widely in aircraft construction. Acrylic adhesives are used in thread-locking
operations and in small-assembly operations such as electronics manufacture which
require rapid cure times. The largest-volume use of adhesives is in plywood and
other timber products manufacture. Adhesives for wood bonding range from the
natural products (such as blood or casein) to the very durable phenolic-based
adhesives.
There is a tendency among plastics technologists to look upon adhesives as oldfashioned
compared with ordinary heat sealing, let alone ultrasonic’s, infra-red and
high frequency welding. In addition, there is the complication that plastics such as
polyethylene and polypropylene have inert surfaces and are difficult to stick anyway.
The, adhesive sealing is still a very useful method of joining plastics, and can often
be very much quicker than other methods. Inert plastics can be pre-treated in the
same way as they are before printing, and a wide range of adhesives is now
available for use with plastics.
Adhesive seals, of course, provide yet another answer to the problem of unsupported
oriented films and are often used for polyester film. They are also useful where large
area seals are required such as in block-bottom sacks, or for attaching valves to
valved sacks. Finally, they are used for sealing plastics film and sheet to other
materials such as fiberboard (as in blister packaging). Adhesives can be applied to
plastics by similar methods those used for other materials, including direct roll
coating, detects roll kiss coating, reverse roll coating and air brush coating.
CHOICE OF METHOD
The choice of sealing method depends on many factors including the seal
characteristics required, production speed required the nature of the film to be sealed
and the cost/effectiveness of the energy source or sealant. The effectiveness of the
seal can be measured in a variety of ways, some of which are qualitative only but can
be useful for production testing.
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