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Technology tackles material and energy costs in film extrusion 21687

October 1, 2006

15 Min Read
Technology tackles material and energy costs in film extrusion

Ask film processors what’s tying up their money, and they’ll likely rattle off a laundry list of capital equipment they’re paying down. Ask Gary Oliver, of feedblock and flat-die manufacturer Cloeren (Orange, TX), and he’ll tell you otherwise—and no, he isn’t angling for a sale.

You know I joke with these guys, and they say, ‘You make machinery, that’s way you say that,’” Oliver says, “but really; machinery is cheap. Capital machinery is cheap. Resin is expensive.”

Oliver specifically recalls a medical film processor running barrier products with a nylon/EVOH/polyethylene structure. Overcompensating with pricy resins to achieve a permeability standard it had long since surpassed, Oliver offered the processor some back-of-the-envelope calculations and told them a new $125,000 die that more effectively controlled thickness could be paid off in under a year. The company bought in, purchased a die, and saw its return on investment in only three months.

David Nunes, president of blown-film extruder, die, and auxiliary manufacturer Hosokawa Alpine (Natick, MA) has been giving his customers a similar pitch. “The actual cost of the machine is really minimal compared to if you’re getting the best equipment to properly, efficiently process your most important commodity, which is your resin,” Nunes says.

At a time when resin and energy costs are at all-time highs, film processors are reclaiming control over business variables they still influence, and when materials and utilities bills are high, a simple remedy is to use less. This fact hasn’t been lost on the industry suppliers, who see opportunity in processors’ newfound conservation.

Crunching the numbers

For Oliver, the arithmetic is fairly elementary. If a line consumes 3000 lb/hr of resin with a composite cost of $2.00/lb, it’s burning through $6000 of material every 60 minutes. In a 10-hour day, that’s $60,000. A new die costs roughly twice that much, and if it cuts 10% off your resin costs, the payback is in months not years.

For Cloeren (Orange, TX), whose dies and feedblocks target the cast-film industry, the key to reducing material waste is truly flat films. In blown film, the tube shape can hide discrepancies by distributing them throughout the film’s surface. In a cast line however, even a 1 micron fault, once it’s rolled on top of itself 1000 times, grows to a sizable flaw. Processors adopted oscillating rollers to randomize thickness variations, but the trade off is a rough edge that must be trimmed, often 3.5 inches or more per side. Sometimes the material can be reclaimed, but in higher-tech barrier products, which are more expensive to begin with, scrap is usually scrap.

Working with undisclosed gauging companies, Cloeren introduced a flat-film technology with width variations down to ±0.8%, cutting oscillation to roughly 0.75 inch and greatly reducing scrap. In addition, Cloeren’s edge-encapsulation technology keeps more expensive resins used in multilayer structures away from edge where they’d be trimmed and discarded. The technology also stabilizes the edge by putting high-melt-strength materials in that location.

Oliver points out that using less material paradoxically means creating films with more layers, where cheaper materials are used for thicker sections, and more expensive resins go into thinner areas. Multilayer structures can achieve the same mechanical properties as thicker films, but in a downgauged version.

Even glass, if sliced thin enough, becomes flexible, and the same is true of highly crystalline, rigid barrier materials like nylon. In addition, new material developments are creating hybrid resins with the potential for even higher numbers of layers and greater downgauging.

Oliver points out one in particular: Dow’s Shuttle catalyst system that makes block olefin copolymers, which combine soft and hard resin in the same polymer chain, with tremendous potential for unique packaging structures.

Hosokawa’s Nunes, and all machinery manufacturers, keep a close eye on such polymer developments and their prices, saying material runs from 60% to two-thirds of film extruders’ costs, forcing his company to create more efficient equipment.

To that end, the company introduced the X-Series die, which it says eliminates port flow by using sophisticated machining for a spiral geometry. Patent-pending, the design allows for better material gauging. Hosokawa, which uses grooved-feed extruders, has also created a crammer feeding system where trim can be ground and returned in fluff form directly back to the line. The patented technology is viable for the 500-plus grooved feed lines Hosokawa has placed in North America, by its estimate, allowing the reclaim of scrap that hadn’t been possible before.

Film takes a bath

Brampton Engineering (BE; Brampton, ON) is encouraging film extruders interested in saving materials and energy to take the plunge. Five years ago at K 2001, the company introduced its AquaFrost downward-blown film extrusion concept, which uses chilled water as a heat-transfer medium instead of air.

Since then, commercial acceptance has increased, with eight lines now in place in North America, Europe, and Asia, but the company is most excited about the newest customer, which is only minutes away.

Packall Packaging, which will have a system installed in December (September 2006 MPW), has maintained a close working relationship with long-time supplier BE and will allow the company to use the system as a lab line and showcase for potential customers. The other seven clients running the technology have confidentiality agreements, barring photographs or other publicity, which might otherwise help potential customers grasp the technology.

Peter Bicak, BE’s engineering group manager who helped spearhead AquaFrost’s development and commercialization, said the technology’s genesis lies in clients’ request for high-end barrier films with less haze and greater flexibility for processes like deep-draw thermoforming. BE, which has traditionally focused on five- to nine-layer or more multilayer films using nylon or EVOH for barrier, says using water quenching, which accelerates cooling and lessens crystallization, creates amorphous films with better optics, lower haze, better gloss, and processing friendly mechanical properties.

Where a traditional blown-film system, using internal bubble cooling (IBC) and an external air ring, might leave you with 6-8% haze in a 150-micron film, AquaFrost is around 2%, which Bicak says is competitive with cast film. Bicak also says the more effective cooling allows production improvements of 1.5 to 2 times conventional lines.

To meet haze requirements, some processors used nylon 6/6/6, sometimes called copolymer nylon, or an amorphous nylon blended 15% by weight with nylon 6. This can lift resin costs 20-30%. AquaFrost lets processors run standard nylon 6 barrier films, where that material makes up one-third of the total cost structure, so that in Canadian dollars, if a shop processed 550 kg/hr for 22 hr/day and paid $3.20/kg instead of $3.40, it would save $2420/day or $72,000/month.

In addition to the ability to use cheaper materials, Bicak points out that the AquaFrost water-quenching design eliminates layflat issues, saying there is no variation, “period.” On a conventional line, depending on the effectiveness of the outer air ring and IBC cooling, Bicak says processors set blades to trim 3/8-inch or more from their rolls. In cast-film lines using a distributing block for multilayer structures, 12-15% can be scrapped. True layflat also means there’s no need to worry about edge feed of pricier materials. Of the commercial installations he can discuss, Bicak says one customer is removing less than 5 mm per side due to edge buildup since its winder doesn’t oscillate, but two other lines, including one that just started up in China, run trimless.

In Canadian dollars, if a processor normally trimmed 25 mm off an 1130-mm layflat film, or 3%, scrap costs would equal $1234/day (550 kg/hr for 22 hr/day at $3.40 kg), and $37,000/month.

In terms of energy savings, a conventional blown-film line’s external air ring and IBC both use blowers to cycle air through chillers and process exhaust, often with three 40-hp blowers for the air ring and two 20-hp units for the IBC. For the AquaFrost, there is only a 5-hp pump to cycle water cooled by the plant’s chiller unit to the top of the tower where downward blowing starts. BE estimates a conventional 600 kg/hr line uses 80.6 kw/hr while the same output on an AquaFrost line would use 8 kw/hr.

Taking control

As Hosokawa’s Nunes points out, “scrap nowadays is like gold,” and to a large extent, is something that can be controlled, according to Cloeren’s Oliver. “[Processors] can watch their energy consumption and labor rates. Resin costs they can’t control, so they’re always coming back to, ‘How can I make this thinner, cheaper,’ and so on, to try to control the item that gives them the most difficulty from a pricing standpoint.”

Tony Deligio | [email protected]

Contact information

Brampton Engineering www.be-ca.com

Cloeren Inc. www.cloeren.com

Dow Chemical Co. www.dow.com

Extrusion Dies Industries LLC www.extrusiondies.com

Hosokawa Alpine American www.hosokawamicron.com

Kiefel www.kiefel-extrusion.com

Macro Engineering www.macro-eng.com

Cast film market anything but flat

According to the latest study from The Freedonia Group (Cleveland, OH), U.S. plastics film demand will grow by 4.5%/yr through 2010, driven by cost/performance and source reduction advantages.

Much of this growth in North America and elsewhere will be in cast film extrusion. The issues facing cast film extruders according Tim Callahan, president/CEO of flat die producer Extrusion Dies Industries (EDI, Chippewa Falls, WI) include demand for smaller lots to avoid storage, faster production changes meaning longer stints between major maintenance, and quicker cleaning. Competitor Gary Oliver, senior corporate scientist at Cloeren (Orange, TX) says film flatness, up-time, and edge trim are the issues moving processors today. It all comes down to saving money. (See adjacent story.)

“Take film flatness. Thin cast films have to be oscillated so non-uniform gauge is not wrapped one spot over itself over and over causing a hard band. To prevent this, film is moved back and forth as much as 100 mm to keep these hard bands from forming,” Oliver says. “That 100 mm translates to over wide film and a lot of edge trim. We have customers that have reduced oscillation down to 17 mm because of the flatness we can achieve. That means less edge trim and big saving in expensive films, some of which cannot be recycled.”

Although Oliver says the elimination of scrap generation rather than reprocessing it is the ultimate goal, David Finnemore, director of European sales and service, Battenfeld Gloucester Engineering (BGE; Gloucester, MA) says in the low-end manual stretch-wrap business a high percentage of scrap is typically inserted into the core layers of multi-layer structures to cut costs. Nicola Lombardini, R&D director at equipment maker Gruppo Colines (Nibba, Italy) says for processors of cast polypropylene (CPP) and polyethylene stretch film a maximum of 40% of the total gross throughput can be reprocessed edge trim, but no more due to the inconsistency of the MFI that fillers cause.

“Customers typically add an anti-oxidant masterbatch to the recyclate layer in order to reduce gels and die lip build-up,” says BGE’s Finnemore. “High levels of pre-processed materials typically give melting issues in the screws, causing machine direction pumping that results in pressure instabilities in the die and has an effect on final film thickness.”

Fillers cause problems

Because of increased fillers, additives, and scrap levels resulting in viscosity level differences from virgin, Stephan van Dun, general manager of flat die producer Verbruggen (Temse, Belgium) says surface treatment of flow pipes and the die is becoming more critical. Although filler tends not to be abrasive, it can have high adhesion and stick to surfaces causing die buildup or melt imperfections.

Van Dun says new coatings developments such as physical vapor deposition (PVD) of chrome-nitrate to improve tool steel hardness are coming to the forefront because they allow better layer tolerance control. “These coatings are much thinner (5-7 µm) than conventional chrome plating (generally 30 µm). You have to remember that the coating will not generally be a uniform 30 µm over the entire surface so you lose layer exactness and get a wave effect,” he says. “With thinner coatings, one has a better chance of layer control.”

Heinz Groß, owner of Dr.-Ing. H. Gross Kunststoff-Verfahrenstechnik (Rossdorf, Germany) sees diamond-like carbon (DLC) coatings for flow channel surfaces as having great potential.

Higher output, thinner coextruded films (12-15 µm), faster extrusion, and wider lines are continuing demands seen on the cast film market today. Verbruggen’s Van Dun says CPP processors are moving from 3m wide to 4.2m lines and he expects this to increase in the future. Thomas Langer, managing director at Brückner Formtec (Siegsdoef, Germany) says wider CPP lines mean reduced edge trim problems.

Langer also believes film widths will level off between 3.5-6m for CPP since the key components such as winders, rolls, and dies beyond 6m are exorbitantly expensive. He says the trend in cast PET film extrusion is not in terms of width but in film thickness (getting thinner) and inline lamination.

Disagreement among producers

Deckling and encapsulation remain topics of concern although Mauro Andreoli, sales/marketing at machinery maker Macchi (Venegono Inferiore, Italy) says “both ... are not to be considered universal solutions to common problems. A skin-deep evaluation may prompt the proverbial Eureka! but one must always consider the polymer behavior, relevant chemistry in order to ensure a stable extrudate curtain with no neck-in weaving, and without melt splitting at the interface of the encapsulation layer.”

Verbruggen doesn’t sell dies without deckling or at least the provision to add deckling later. Van Dun says customers generally opt for internal deckling even with nonadjustable fixed inserts since they are cheaper and afford easier maintenance and cleaning. Colines’ Lombardini says external deckling among his barrier film customers is no longer requested. Cloeren produces most of its dies with some form of internal deckling which allows the die slot opening to be refined to the absolute minimum to make a product that saves edge trim and therefore money.

Not so says Helmut Meyer, head of engineering, cast film lines at equipment maker Reifenhäuser (Troisdrof, Germany). The company equips 90% of its sold lines with inhouse developed cast dies, most include external deckling for multilayer films of five-layers or more. He says external deckling allows even melt flow with fewer chances of particles catching along channels or die to burn and cause black specks or gels. He feels internal deckling also results in more leak problems as the die ages.

Encapsulation is only a hot topic with barrier films where processors want to reduce their edge waste. Cloeren’s Oliver says previously processors needed encapsulation when producing linear low-density PE stretch film to increase output speed and ensure the film’s edges remained stable. But the introduction of specialized LLDPE grades have allowed processors to better control edge stability without the expense of encapsulation.

The number of layers of cast film is another point on which die and equipment makers can’t fully agree. EDI licensed a Dow Chemical (Midland, MI) technology announced just before NPE that is said to allow up to 80 layers in a 50-µm film. This microlayer technology is nothing new, says Cloeren’s Oliver, who says his company patented a micro-layer technology in 2003 for 74 layers. Applications so far are for iridescent decorative films.

Yet EDI’s Callahan says what his company licensed is a third generation development going beyond such limited applications. He sees demand for so many layers in packaging to extend shelf life and for standup pouches.

“Barrier materials [EVOH and nylon] are tough to get good barrier performance whenever you have square corners or areas where the material can bend or break,” Callahan says. “The extra layers, although thinner, will provide more barrier protection and the chance to use less material for thinner layers, thereby lowering costs.”

The process should cover pinholes and black specks better than fewer layers and could allow processors of coextruded cast PET films to save money by using high-priced grades only in specific layers. “This should be a Godsend for operators of biaxially oriented films where line breaks due to gels or pin holes can be limited by encapsulating the defects in more layers, thereby keeping the line up and running longer,” he says.

BGE’s Finnemore agrees and says microlayer technology “could be the next big step forward in barrier-film production.” Others are more skeptical, believing the idea is an example of over-engineering, or that the demand for so many layers is not yet there.

Power savings seen

Energy savings remains an issue that penetrates every customer discussion before a cast line sale, says Reifenhäuser’s Meyer, especially with customers faced with high power bills such as in Italy. His company’s latest cast development involves use of its REItorque extruders powered by linear motors (June 2003 MP, p. 61; MPI, p. 57) said to offer a 20% saving on energy. The company is also testing copper shell casting rolls to improve cooling compared to steel rolls, he says.

Brückner’s twin screw PET cast line claims to save up to 30% on energy cost by eliminating resin predrying. At a recent open house of Macchi’s 2000 cast-film line for stretch film, visitors witnessed gearless drives on the complete web path and winding to save energy. Only on the coextrusion section does the line include standard AC driven, water cooled motors because Andreoli says suitable torque motors are still unavailable.

Membrane feedblocks, according to Heinz Gross, offer a means to best optimize melt outflow. Gross points to a new three-layer pilot film and sheet line at Bayer MaterialScience’s Leverkusen, Germany lab that includes a membrane feedblock to optimize thickness distribution of the A- and B-layers with the help of 12 adjustable screws across the 50-mm-wide flow channel.

Robert Colvin | [email protected]

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