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.
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.
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.
