SML’s latest generation of MDO (machine-direction orientation) film-stretching units features rollers on two frames that can be adjusted on the fly for efficiency and reduction of waste, the company said.
The distance between the two frames precisely defines the length of the stretching gap. This allows the MDO process to be adapted to the type of polymer and to the relevant production line speed.
“Essentially, it gives you the option to change the film properties by changing the stretch gap on the run,” said Mark Jones, SML’s director of support services in North America. “If you’re a manufacturer a nd you have a particular type of product that you want to run, you don’t have to run the product and then see what it looks like and then shut down the machine, make adjustments, and then start up again. You can change the physical properties on the run by adjusting the gap.”
The adjustments are made through a computer control system, so it is much quicker and easier to fine-tune MDO stretched film production to meet requirements.
“The old process, whereby you had to stop and make mechanical adjustments with a spanner, slowed down development a lot,” Jones said. “It made it impractical for certain types of applications.”
The dual-frame design also makes it much easier to clean the MDO unit because the rollers are more accessible, Jones said.
Overall, the dual-frame design contributes to higher production speeds, significantly shorter downtimes and a boost in overall line efficiency, the company said.
The unit is not limited to processing polyolefins but also is suited to PET applications like film for candy wrapping, adhesive tapes and shrink labels for bottles.
One of the most popular applications is films for stand-up pouches, the company said. Usually, films for stand-up pouches have a thickness range from 25 to 80 microns and are made from combinations of polyolefins that frequently are not compatible with recycling.
SML’s MDO units can manufacture thinner films from mono-axially oriented PE (MOPE), which can replace biaxially oriented PET (BOPET) or biaxially oriented PP (BOPP) film on the outside of the pouches. In this way, pouches with a single-material structure can be produced. These thinner, mono-material pouches are easy to recycle. At the same time, the raw material costs, and the general carbon footprint, are reduced.
“The additional stiffness of MDO stretched polyethylenes allows production of lightweight standup pouches without using a difficult-to-recycle material combination,” Jones said. “Plus, the orientation improves film barrier properties. So, you produce this lightweight, easy-to-recycle pouch, and the improved barrier helps keep flavors in the pouch and any external aromas out.”
“Loss of aromas through the packaging is known as ‘flavor scalping,’” Jones said. “PET is better than MOPE at preventing this, but depending on several factors – expected storage time, flavor compound types etc. – MOPE may still be good enough for some applications.”
SML’s MDO units are sold as part of new film extrusion lines, or they can be retrofitted for use on existing lines.
Bruce Geiselman, senior staff reporter
Contact:
SML North America Service Inc., Gloucester, Mass., 978-281-0560, www.sml.at
About the Author
Bruce Geiselman
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.