- Created: 13-12-21
- Last Login: 13-12-21
Machinery makers are being challenged to address the
increasing demands of cast stretch film — getting film thinner
and thinner while improving strength and flexibility. New
technologies introduced at K 2013 have improved even more.
In general, cast film markets
worldwide are healthy, and the cast stretch film market is
particularly strong and growing. It's solid in North
America, growing at nearly 3 percent annually, while growth is
even higher in many emerging economies around the world. Despite
the slowdown that's taken place in many of those economies,
as well as in many economically mature regions, globalization of
manufacturing means that a lot of shipping is going on.
These days much of that shipping takes the form of pallets
stacked with cartons or other shapes of packaging traveling by
ship, train and truck. Shippers believe all that merchandise
should arrive at its destination perfectly intact. Yet recent
studies estimate that annual losses due to products damaged in
handling and transport cost shippers about $2.6 billion.
That is precisely the problem that rolls of stretch film have
been relieving for decades. Everyone involved with goods
transport for any length of time has seen the percentage of
pallets securely wrapped in transparent film steadily increase.
It is still increasing, as is the strength of the film — even
as it has gotten thinner and, as a result, more sustainable and
Naturally, it took a parade of significant materials, machinery
and processing innovations to make stretch film stronger,
thinner, lighter and more sustainable and economical. And just
as naturally, with stretch film usage rising, along with market
demands for improved performance and lower cost, the development
of technology innovations is holding its fast pace.
Clear evidence of that is the variety of technological
innovations coming from machine line makers — often in concert
with resin suppliers — that are now offering stretch film
processors options and tools to improve their products that, as
recently as 10 years ago, were unthinkable. Examples: A leading
supplier of cast stretch film lines is moving what was a major
off-line process to in-line; another longtime maker of cast film
lines has developed a totally new, stretch-film-specific winder
to spearhead a major push into that market.
Steve Post, VP of cast film at extrusion and converting system
supplier Davis-Standard LLC, Pawcatuck, Conn., says about 80
percent of the total cast film machine market consists of stretch
wrap, hygiene film (diaper back sheets, hospital gowns and bed
sheets, etc.) and cast polypropylene. Stretch is by far the
biggest part, hygiene film is growing and so is cast PP,
PE film, though almost
all in Asia.
Suppliers of stretch film in North America are bullish about a
market that's growing at close to a 3 percent annual clip,
says Post. And, he points out, it's growing from a
relatively large base. Suppliers feel resin prices will drop as
natural gas supplies increase. Shipping film made in the U.S. to
Europe is well within the realm of possibility.
Post says one familiar trend is continuing in the stretch film
market — downgauging. A few decades ago film that was 25 to 30
microns, or around 1 mil thick, was considered thin. Post says
his company's lines are now making stretch film as thin as 6
microns in the conventional process and the pre-stretch process,
where the film is stretched in-line to make it stiffer and
thinner. That's thin for sure, but the real breakthrough
here is that the pre-stretching is being done in-line, on a
station just before the winder.
Pre-stretch began in Europe about 10 years ago and began to take
off about three years ago in North America, where currently
it's growing at a rate of more than 15 percent a year. But
as Post points out, no one is doing pre-stretching in-line now.
It is being done off-line using rewinders. Aiming to change
that, Davis-Standard launched its new dsX s-tretch pre-stretch
cast film extrusion line at the K 2013 show in Düsseldorf,
Germany, and made pre-stretch film in-line on a working line at
its German facility.
Fast forward to now, when Post says Davis-Standard has perfected
the process of doing pre-stretch in-line. Its first installation
takes place this month in Southeast Asia.
We only had run at a limited speed," he says of last
year's K show display. "Now we're running near
1,000 meters per minute. We've run at speeds faster than the
The dsX s-tretch line is 2 meters wide so it has a lower
footprint but allows for growth. Because it uses pre-engineered
technology, it can be available in as little as six months in
five- and seven-layer options. In the future, the line will be
offered with environmentally friendly coreless technology so
both material and disposable costs will be reduced.
Some benefits of making pre-stretched stretch film in-line vs.
off-line are obvious: no production floor space taken by
rewinders, less movement of rolls across the production floor,
reduced labor and a lot of time saved. Fans of lean
manufacturing will love it.
But Post says there's another benefit that trumps all the
Most cast film processes are limited by line speed: how fast you
can cool the film, or pin the web to the chill roll out of the
die. As film keeps getting thinner with machines like
film machine, TPU film machine,
EVA film machine, etc., if line speed doesn't increase
the net output of the line drops. Most cast stretch film, both
hand and machine rolls, is sold by the pound. Lower machine
output is a problem for the processor. Post says that with in-
line pre-stretch, the processor can make film from the die at a
slower speed — conventional process limits are 1,600 to 1,800
feet per minute — but if the film is stretched three times in-
line the result can be an effective line speed greater than
3,000 feet per minute.
One additional benefit of pre-stretching worth mentioning: It
results in a stiffer film, and that means better load retention
and much lower load movement on stretch-wrapped pallets. Since
the pallets and their contents are better supported during the
transportation cycle, there should be less waste caused by
damaged goods and more smiling shippers.
Though most stretch wrap film is made of 2-4 melt index linear
low density polyethylene, some metallocene-catalyst materials
may be used to increase puncture resistance or to give better
properties to the tack layer. Polypropylene may be used to make
the film stiffer overall. But when any of these are used in a
film structure they are 5 to 10 percent of the content, at most.
Linear low is still the go-to material, and there is one
technological development in cast film that may help it keep
Regarding another trend in cast film technology: Post says that
though most cast stretch film uses five- or seven-layer
structures, there has been a lot of discussion recently about
microlayer and nanolayer structures. Extrusion die makers
Nordson Extrusion Dies Industries LLC (EDI) and Cloeren Inc.
both supply feed blocks that can make film structures in the 20-
to 35-layer range.