PROCESSING | MULTI-LAYER PACKAGING
the scalability of micro- and nano-layering to industrially relevant production rates – including speeds of 200 ft/min and film geometries up to 36in widths, he said.
Fluff to film
As well as trying to ensure packaging recyclability, film extruders want to incorporate more recyclate into their products – preferably using the plastic waste from their own internal manufacturing processes. Steve De Spain, general manager of Reifen-
Above: Reifenhauser says its Evo Fusion can convert ‘fluff’ back into film
decreased haze and improved clarity – while COC’s presence raised heat resistance and boosted tensile yield strength. “COC can provide comple- mentary enhancements to PE which will enable recyclable all-polyolefin SUP films,” he said.
Layered approach One way to boost the properties of PE – and avoid having to use another material – is to use ‘layered co-extrusion’. Here, a single layer of PE is split into many micro- or nano-layers. Michael Ponting, chief science officer at Peak
Nano Systems, told delegates that this kind of layering can produce from 32 to more than 4,000 layers – helping to boost barrier properties and modulus. It is achieved using a feedblock that ‘multiplies’ the number of layers. “Microlayer coextrusion adds additional film
formulation freedom to rearrange polymer materi- als in unique combinations and very highly ordered structures,” he said. In addition, the technique can be applied to films made from recyclate. He reported both PP- and PE-based films that used nano layering and up to 50% recyclate. The nano layered PP films exhibited downgauging, improved film handling and higher mechanical properties (such as stress at break), while the nano layered LLDPE showed similar improvements. The technique has also been used to produce capacitor film – as an alternative to BOPP or BOPET. Benefits include: twice the dielectric constant; improved breakdown strength; and a 70°C increase in usage temperature. “Nano layering enabled a scalable product development path to high energy storage dielec- tric films – enabling capacitor device fabrication with up to 30% smaller volumes and increased temperature limits,” he said. Capacitor film development has demonstrated
16 FILM & SHEET EXTRUSION | September 2023
hauser in the US, told delegates that this can be done by converting either granules or ‘fluff’ back into film. He said that going through the re-pelletis- ing process can be energy- and cost-intensive – and that materials quality suffers. Instead, he said that scrap can be shredded and directly extruded back into film. “This reduces process steps and improves material quality,” he said. This can be achieved on the company’s Evo
Fusion twin-screw technology, he added. Skipping the re-pelletisation stage can save around 40% in energy, he said. He cited the example of PE/PET films, which have a scrap rate of around 15% – which typically cannot be used to create new films. However, using Evo Fusion, he says that the ‘fluff’ – comprising a PE/PET laminate – can be recovered and re-used. After being fed into the shredder, it can be used in the middle layer of new film – accounting for around 70% of film thickness. “This gives recycled PET/PE laminates a second life,” he said. Potential applications include packaging for diapers or detergents. A 20-micron, three-layer film incorporates: outer and inner layers (each 15%) using virgin resins; and a middle layer comprising 70% PET/PE ‘fluff’, plus some virgin resin and a compatibilizer. Other applications included a mailing bag, collation shrink film and trash bags.
Stretching properties Orientation can be a critical process in creating better packaging, according to Windmoller and Holscher. Mike Andrews, of technical sales and process support for extrusion at W&H in the US, said that machine direction orientation (MDO) can help to improve the sustainability performance of packaging film. MDO works by heating, stretching, annealing and cooling the film. This can be performed at high speed, leading to flat film with no creases and wrinkles, he said. A stretching unit fits neatly onto a blown film line.
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IMAGE: REIFENHAUSER
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