Advances in die manufacturing that have allowed the production of film with numerous layers are helping manufacturers to churn out lighter-weight products.
Today, it’s not uncommon for extrusion lines to produce 15- or 16-layer films, even as many as 50 layers, said Mark Jones, director of support services for extrusion equipment manufacturer SML North America Service Inc. “That allows you to reduce the thickness of the film because you put special polymers in very, very thin layers, but you put them in there, and it helps to keep the physical properties.”
Older machines might have produced just three or four different layers, he said.
To accommodate thinner films, equipment manufacturers have increased the speed of their winders. When manufacturers reduce film thickness, the associated decrease in weight causes profits to drop. However, they can maintain their profits by boosting line speed to produce the same weight of film in the same time period as before.
“What machinery manufacturers have been doing is they produce new winding equipment because the limit on most of the legacy lines is not the extrusion side of producing the melt or the die side, it’s how fast you can wind this film,” Jones said. “What you’re seeing now from a lot of the machinery suppliers is that they will offer retrofit winders … that will allow the speed of the line to go up.”
As cast films have gotten thinner, manufacturers had to make changes to film rollers.
“If you’re running very thin films, obviously, they are a lot more delicate,” Jones said. “When you’re running these through a big, heavy line, you can’t have a lot of drag on the rollers. You’ve got to make sure everything runs very freely. You can’t put a lot of tension on the film.”
As a result, today’s rollers are very lightweight have bearings that spin with less resistance, he said.
A problem with thin stretch film is it tends to rip at the edges when used to wrap loads.
“There is a growing move on stretch wrap to fold the edges over,” Jones said. “If you imagine this film with a very thin, fragile edge, you fold it over so now it’s twice as thick and it’s a lot tougher.”
The problem is the film, once folded, is twice as thick at the edges.
“To still make a nice roll out of that, you then have to change the winder in a way that moves the film from side to side to avoid the thick edges from building up into a lump,” Jones said. “SML has a patented system for folding the edges over especially on thin films and then winding in such a way the package still looks good.”
The result is a roll of film that is slightly wider than the original film, but that avoids having the thick edges wound on top of each other.
Making a thin product even thinner is a big ask, but, as Jones pointed out, the innovations have paid dividends.
“If you can reduce the weight of the film that you’re producing, it means that your transport costs go down, because, obviously, wherever you’re going to make this stuff, you have to transport it to the user,” he said.
SML North America Service Inc., Gloucester, Mass., 978-281-0560, www.sml.at
Bruce Geiselman | Senior Staff Reporter
Senior Staff Reporter Bruce Geiselman covers extrusion, blow molding, additive manufacturing, automation and end markets including automotive and packaging. He also writes features, including In Other Words and Problem Solved, for Plastics Machinery & Manufacturing, Plastics Recycling and The Journal of Blow Molding. He has extensive experience in daily and magazine journalism.
