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 economical.

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, TPU film,

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 industry."

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 others.


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 PE

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 that title.

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.