Make Every Pellet Count: Extrusion technology opens door to save that scrap

Encapsulation technology to reduce waste during cast-film processing appears to be in strong demand today for both coextruded barrier films and to some extent for stretch film lines, says Sam Iuliano, product manager at die builder Extrusion Dies Industries (EDI; Chippewa Falls, WI).

Yet competitor Peter Cloeren, president and owner of flat die manufacturer Cloeren (Orange, TX), says there remains too little understanding of the practical application of this technology. ’If one looks at new global film extrusion installations, I would estimate that less than 30% utilize encapsulation,” Cloeren says. ’There is room for growth and proliferation within this technology.”

David Finnemore, VP product and process technology, Gloucester Engineering (Gloucester, MA), says only the largest processors of stretch film, who have fast/wide lines, see the benefit of the technology in terms of better speed and yield. Robert Moeller, technical director extrusion at Davis-Standard Converting Systems (Pawcatuck, CT), says processors can also expect, in many cases, quicker changeover times and less downtime during width changes.

’Most stretch films today are composed of narrow branched linear polymers such as LLDPE. Such resins are subject to relatively high neck-in characteristics, which are typically a speed-limiting and yield-burden factor,” says Cloeren. On a typical 3m-wide stretch line, he says die width can be reduced approximately 6% when encapsulation is used, with a 12% increase in speed, ’resulting in an additional production output of 4.3 tonnes/24 hours on a 16-µm (60-gauge) film.”

But the technology is finding most interest among processors of multilayer films. Barrier resins—such as EVOH, PVdC, or nylon—trimmed from the sides of extruded cast film and mixed with existing layer scrap, generally polyolefin-based, will form globules, which can lead to surface defects, and layer delamination if these globules start to migrate toward the outside layers during extrusion, Iuliano says. Therefore processors see encapsulating barrier films using a polymer, generally a polyolefin that can be trimmed and re-fed as fluff or repelletized directly back during processing, as a way of reducing material costs. Cloeren, however, warns that processors need to evaluate on a case-by-case basis the chemical and rheological issues of the film structure to determine if encapsulation is justified.

Paul Bullock, sales manager cast film at equipment producer Reifenhäuser Extrusion (Troisdorf, Germany), says using a cheaper resin to encapsulate, such as a C4 polyethylene, is a possibility, yet ’the benefits are outweighed by using one of the main layer polymers so that at least the primary edge trims can be directly recycled in-line” He also says that considering that with cast film ’net output ratio to gross output is around 92%, end users look to save by using as wide a line as possible to reduce the percentage of scrap in kg/hr and by feeding in as much scrap as practical.”

Markus Stumpf, cast film technical sales manager at film equipment manufacturer Windmöller & Hölscher (Lengerich, Germany), which delivers encapsulation as standard on all Filmex multilayer cast lines, believes that encapsulation can offer savings of more than $550,000 on resin costs/yr. This is calculated on a standard 9-layer barrier web line churning out 2200 lb/hr with an average trim waste rate of 200 lb/hr, at least 50% of edge trim is directly re-fed back into the process at a film cost of $0.80/lb.

Italian equipment maker Colines (Nibbia) points to even more surprising data it presented at last year’s Plastivision plastics show in India, with Colines customer B-Pack Holding (S. Pietro Mosezzo, Italy) supplying the data. This processor was able to reduce barrier film scrap from 25% to less than 5% with encapsulation, resulting in a savings of €1 million/yr, says marketing manager Francesco Peccetti.

Gloucester Engineering’s Finnemore says in barrier applications, encapsulation is designed to take up the neck-in region of the die, leaving the barrier materials to be integrally extruded through the die. ’The target here is to reduce the barrier-layer scrap level to less than 2%, a significant saving,” he notes.

Reifenhäuser’s Bullock mentions equipment his company offers where a primary edge trim, between 50-75 mm/side depending on line speed, gauge, and resin type due to neck-in, is taken from behind the chill roll. This is followed by a narrower (generally less than 2 cm) secondary trim that includes ’mixed” layers, resulting in actual waste. The primary edge trim is reusable and, according to him, generally lands in re-feed hoppers placed directly on the main extruder throat for processing into one of the layers of the film. This method, he says, avoids the extra processing step and cost factor to repelletize, and reduces the effect of an additional thermal history on the polymer.

Davis-Standard’s Moeller believes it can be less expensive for a processor to add a small 35-50-mm extruder to each end of the die to feed the encapsulation layers as opposed to the cost of complex feed pipes in a single extruder design. Bullock from Reifenhäuser says using a separate extruder to feed an encapsulating polymer to the edges of the die distribution channel of a coat hanger die is generally easier to manage than complex feed pipes to a feedblock.