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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.

  • Created: 13-12-21
  • Last Login: 13-12-21

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