A Guide to Shrink Wrap Materials by iupon13

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									?This article will address shrink wrap materials as they relate to the packaging of
individual rather than collation packs.It is valid to consider that shrink wrapping for
transit and shrink wrapping of large loads fall into separate categories. As a
consequence, these would need to be addressed in their own right. The wrapping of
individual packs falls under the category of display packaging.

It is realistic to dispose of polyethylene relatively early on in this consideration since
this material is not particularly suited to display. Its failures lie in a lack of strength
that can only be compensated by appropriate thickness, poor clarity inherent in its
chemical composition and a very soft surface which offers little or no sparkle or gloss,
which at the same time scuffs and attracts dust. As a consequence, polyethylene is an
unlikely candidate for display packaging although it would be wrong to assume that it
is never used. From time to time, there are applications where the above
disadvantages are not particularly significant in the context of the end use and as a
consequence, it can be used. However, for the greatest part, display packaging
involves the use of either PVC or polyolefin shrink film.

PVC - plasticised polyvinylchloride - has seen declining volumes over recent years as
polyolefin films have been able to overcome machineability issues that make them, as
a consequence, more likely candidates for use. PVC films are, without question, the
easiest to seal and shrink in production but they continue to suffer from a number of
issues that may be regarded by any end user as having greater or less significance. On
sealing, PVC films degrade and small quantities of hydrogen chloride - HCL - are
given off; these combine with any moisture to produce hydrochloric acid. This causes
degradation of equipment and also acts as an irritant to any operator. Although there is
no toxicity issue as such, there is an issue with regard to providing satisfactory
working conditions and appropriate ventilation together with operator training and
screening is necessary. Carbon deposits are also created on sealing and these require
regular cleaning. Seal and shrink results are otherwise excellent although PVC seals
are weak by comparison with those of polyolefin.

As PVC is plasticised, so it is necessary to store this film both before and after use in
such a way as to avoid extremes of temperature. Although exceptionally high
temperature is not particularly relevant to a wrapped pack, it is particularly relevant to
PVC film on the reel before use. The material must be held at a temperature around
20 degrees centigrade or alternatively it is likely to suffer shrink damage, which will
render it unusable.

In respect of extreme cold, the reverse applies. PVC film on the reel will not suffer
from exposure to cold since provided the material is returned to room temperature it
will be usable. However, wrapped packs will be prone to damage if they become
particularly cold as the plasticiser will harden and the film will tend to shatter.

Last but not least, PVC has suffered from constant criticism by virtue of its chlorine
atom, which is seen as environmentally unfriendly. Historically, there have also been
other concerns raised with regard to vinyl chloride monomer and the type of
plasticiser and stabiliser used although none of these have particular currency at this
time.

PVC shrink film continues to occupy some of the market for display and continues to
offer excellent machineability, which should not be ignored. It is generally not used in
food shrink applications. It finds specialised application on over wrap equipment
where a more rigid form is used - the wrapped pack can be shrunk to offer a
particularly high quality finish. The plasticiser content of standard PVC shrink film
can be varied to allow the production of slightly softer or slightly harder material. The
softness imparts better strength whilst hardness provides a more rigid feel to the
finished pack, which can be preferred on a given application.

Polyolefin films have continued to be developed to offer the best attributes of PVC -
the ease of sealing and shrinking - without its demerits - the issues noted above with
regard to use and storage. It must be noted that polyolefin shrink films also produce
fumes on sealing and it is no less relevant to deal with these through appropriate
ventilation. Polyolefin films now offer easy sealing such that specific grades will seal
as readily as PVC. The shrink window with polyolefin is not quite as flat as with PVC
and hence, equipment generally needs to be of quite a good standard to offer a good
result. Nevertheless, polyolefin will offer stronger seals by comparison with PVC and
good quality shrink down which is generally close to that offered by PVC - the latter
will continue to offer better shrink results. However, there are no real issues with pre
or post production storage. Overall, polyolefin represents a better mix of the best
attributes and it is as a consequence of this that its market share has grown.

Environmental concerns are yet again another issue. Polyolefin materials are
produced only from oil-based feed stocks - they use only non- renewable resources. In
production or post-production, material cannot be recycled save into a lower form of
plastic. In comparison, PVC's principal constituent is common salt available from
seawater whilst any scrap can be readily recycled back into PVC film. There are
numerous formulations of polyolefin shrink film designed to offer attributes
appropriate to the end use.

Films are invariably offered as multi-layer complexes. These layers comprise
polyethylene and polypropylene in various forms. At the premium end of the market,
irradiation is used to alter the molecular structure of polyethylene films and this gives
the material particularly strong seal and puncture and tear resistance characteristics.
However, irradiation militates against easy sealing and a consequence, due allowance
must be given to this.

Polyolefin films are also formulated to offer low shrink force whilst they have also
been extended into food use where both anti fog and barrier grades are available.
Further enhancements include printing as well as pre-perforation which offers
valuable benefits in manufacture. Advice should always be sought so that any end
user ensures that the correct selection of material is made with attributes chosen
appropriately at every point as well as costs being minimised.
About the author: Richard Jankel - http://www.kempner.co.uk - Shrink wrap expert at
Kempner, the UK's largest distributor of display shrink wrap film machinery and
materials. If you plan to reproduce this article, please include the above link.

								
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