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Article | February 28, 1998
Woodland Poly casts for western film business
Cast and blown film-making equipment, using metallocene resins, enable Woodland Poly to produce rugged stretch-wrap film in thin gauges for its customers in the west.
Three-layer coextrusions Besides producing thinner films the Battenfeld equipment also enables Woodland Poly to manufacture multilayer coextrusions. Both the blown and cast systems are equipped with three extruders which the film maker uses to produce three- five- and seven-layer coextrusions. "By using a three-layer structure" Chen explains "we can vary the amount of materials in each of the layers to provide specific properties to meet application needs or to minimize costs." He cites a film's cling properties as an example. "Look at a lot of warehouses around here and see how many pallets they wrap on a daily basis" he says. "These are loaded tightly onto a truck. If you're using a monolayer film like many manufacturers produce polyisobutylene [PIB] is added as a tackifying agent throughout the film. When a customer unloads a truck film blocking can cause loads to stick together and create a mess. "With three-layer coextrusion capability we can produce a film with cling characteristics only on the inside layer that contacts the load. Meanwhile the outer layer will not have cling and you won't have blocking when two wrapped pallets make contact." Customer advantages While metallocene stretch film sells at "about a five-percent upcharge" compared to conventional film Chen believes it pays off for customers. One such customer is Yosemite Wholesalers Merced CA. "We've used Woodland Poly as our sole stretch film supplier for a little over a year now" explains Steve Fells assistant director of the Yosemite distribution center. He indicates that Yosemite wasn't especially pleased with cost and quality issues concerning previous stretch film suppliers. "We've gone to a 60-gauge film from a 70-gauge that we used previously and we've discovered that it does a good job protecting our pallet loads that we ship to Save Mart" says Fells. He explains that Yosemite distributes pallet loads of dry and refrigerated packaged foods to nearly 100 Save Mart Supermarkets stores. At the stores operators use new stretch film to wrap pallet loads of spoiled produce that's packed in boxes and shipped back to Yosemite for composting. Both Yosemite and Save Mart outlets hand-wrap these pallet loads. Fells estimates that Yosemite orders 360 cases of wrap (with each case holding four 12" dia rolls) every eight weeks. Sophisticated processes Woodland Poly's primary product mix includes wicketed bags produce bags bulk converter rolls and bag and can liners. By adding the cast and blown film lines the company was able to enter the stretch film business. Chen acknowledges that being competitive in this market won't be easy but the Battenfeld equipment gives them a running start. The cast film line was added last February. Chen estimates that it accounted for 80% of the company's 1997 film output. The cast system's footprint is roughly 20' W x 60' L. Its primary components include three extruders supported by vacuum loading feeding and blending systems; casting and cooling units; and winding and slitting systems. Resin and additives are drawn by vacuum from silos to the blending system. A microprocessor controls the blending functions. From the blender the resin flows to a gravimetric feed hopper then to an extruder. Each of the three extruders says Chen comes equipped with four hoppers located on a second mezzanine that allow blending of various resins and additives into the center core layer and two outer "skin" layers. This is done to deliver specific properties to the film such as puncture resistance cling clarity etc. The core layer usually about 80% of the finished film structure is extruded through the primary 6" 30:1 extruder. (Through multiplication the 30:1 length/diameter ratio indicates a barrel length of 180"). The skin layers are extruded via two 31/2" 30:1 satellite extruders. Through compression and heat the material is mixed into a homogenized liquid melt. On each of the three extruders the melt passes through a screen changer filtering system and into a multi-layer feedblock where the materials are delivered through a die and onto a roller. An edge pinning system helps deliver the material to the two outer edges of the roller. An air knife and vacuum system draw the material against the chill roll to help quench (cool and set) the material on the roll. The film continues to quench as it passes over two additional chill rolls towards the winding station. Film is monitored for gauge variations and speed from the point it meets the roll to the winding section. A motor-driven oscillating system gently oscillates the entire film web back and forth between 1/4" and 1/2" so that if there is an uneven spot in the film it will be distributed randomly throughout the width of the film thereby preventing lumps or shallow spots when the film is wound. Once wound the 103"-wide film is slit into individual rolls of varying widths by pneumatically actuated razor slitters which are also part of the Battenfeld system. The shaft containing the rolls of wound film is cantilevered to swing outward allowing easy access to the rolls where employees take them off the shaft and place them onto a pallet for eventual shipment to customers. To produce individual rolls with slightly wider cores for easy handling the slitter knives cut a 1" channel of film between each roll. This film called "bleed trim" by Chen is drawn away by vacuum hoses and is reprocessed with edge trim.Battenfeld supplied a repelletizing line to Woodland. Blown film blossoms Chen praises the cast film system's computer controls for helping to maintain film consistency. And he's pleased with the 3 lb/hr output Woodland Poly produces on the cast side. He's also considering adding a second Battenfeld cast line if market demand merits such a purchase. By no means however does he underestimate the value of the Battenfeld blown film line which was up and running by November '96. "We run the line so that it produces about 1 pounds per hour" he says. "Of course blown film is much stronger than cast because it's biaxially oriented." The Battenfeld blown film system he says "enables us to produce film very economically. That's important because the market is extremely competitive. I expect this line will account for about sixty percent of our stretch film output this year." Like its cast film counterpart the blown film system includes three extruders and microprocessor controls. The primary smooth-bore extruder screw is 6" 24:1. The two additional grooved screws are 80 mm (approximately 31/16") 24:1. The blown film manufacturing process is similar to cast up until the resin melt reaches a circular die where air blows the material upwards inside a 35' tower. The material bubble is quenched by air then collapsed at the top. A nip roll produces a flat sheet that's slit and wound at two stations.
Overcapacity and price pressures in the marketplace don't bode well for the profitability of stretch film manufacturers. Especially for a newcomer like Woodland Poly founded just three years ago by an investor group that purchased a film-making plant in Woodland CA. But by retaining a core of competent workers already in the plant and adding new cast and blown film machinery Woodland Poly has positioned itself to prosper regardless of market conditions. "Overcapacity [of stretch film] is estimated at twenty to twenty five percent" says company president and CEO Dan Chen. "And a lot of that relates to the use of old film-making technology. By that I mean a lot of machinery used today is unable to produce thinner films in gauges of seventy sixty even fifty that the market now demands." Chen counts on two newer film manufacturing lines from Battenfeld Gloucester Engineering (Gloucester MA) to produce filmsfrom 50 gauge to 1.2 mils. Both a cast and a blown film line were installed within the past 18 months at the 240 sq' Woodland facility. Last year the two lines produced about 8 million lb of polyethylene stretch film both low-density and linear-low varieties. Chen expects the lines to make 18 million lb this year; combined capacity for the two machines is 30 million lb/yr. About half of Woodland Poly's film output incorporates metallocene resins that are known for providing strength and puncture resistance. Those characteristics make it possible for Woodland Poly to manufacture thinner gauges of film with characteristics comparable to thicker films from conventional resins. The metallocene LDPE is supplied by Exxon Chemical (Houston TX). Exxon and Mobil Chemical (Edison NJ) are Woodland's two primary LDPE/linear LDPE resin suppliers.
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