Metallocenes make their mark

With a new breed of cast stretch wrap films made from metallocene resins offering greater puncture resistance, high elongation and low noise compared to conventional cast films, many packagers are beginning to take a closer look. Office furniture giant Steelcase, Inc., Grand Rapids, MI, is one of the first users of one of these films, Max Plus I, a linear low-density polyethylene film. It's part of the MaxTech(TM) series of metallocene cast films recently unveiled by Pactiv Inc. (Pittsford, NY), which the supplier claims is one of the first such breeds on the market. (Editor's note: Pactiv purchased the Mobilrap stretch film business from Mobil Chemical in November '95.) Steelcase's Athens, AL, plant uses the film to overwrap individual panels that are used in the construction of office cubicles. The panels are wrapped on two Lan-ringer® horizontal stretch wrapping systems from Lantech (Louisville, KY) after being fitted with corrugated end caps from Menasha's Sus-Rap Packaging Div. (Danville, VA). According to Phil Dortch, a Steelcase packaging engineer who was involved in the switch, it represented an opportunity to move from a LLDPE blown film, which the plant had been using, to a cast film. There are two benefits to this. First, cast films are generally quieter during wrapping than blown films, according to Greg Hardin of Dillard Packaging Systems (Greensboro, NC), which sold Steelcase the stretch wrapping equipment and distributes the film. Blown films require additives to create the cling that's inherent in cast films. Two stretch wrappers running simultaneously with blown film-especially the very high-end film Steelcase had been using-made a tremendous amount of noise in an otherwise quiet manufacturing environment, according to Dortch. The second benefit of switching from blown to cast film, according to Dillard's Hardin, is economics. Cast films are typically less expensive than blown films. But prior to metallocene cast films, no cast film would have been able to handle the Steelcase application, requiring the performance (and the expense) of a high-end blown film. Indeed, the metallocene film was so tough that it enabled Steelcase to downgauge from a 100-ga blown film to an 80-ga cast film, representing a slight savings for Steelcase. That's not to say that metallocene films are inexpensive. "[The metallocene cast film] is among the most expensive cast films," Hardin admits. But a traditional cast film wouldn't have been able to handle the requirements of this application, he says. Metallocene-based cast films have begun to blur the distinction between blown and cast films, both in performance and economics. According to Tenneco, this film is made from metallocene resins designed specifically for stretch film manufacturing. During the polymerization process, the resin manufacturer, Exxon Chemical Co. (Houston, TX), adds a catalyst based on a combination of metallic and organic compounds. This metallocene catalyst allows Exxon to incorporate the desired stretch film properties into the resin. Pactiv then uses a cast film manufacturing process it developed specifically for metallocene resins to produce the cast films. Stretch wrap vs. boxes For the Athens, AL, plant, the stretch wrapping solution itself is fairly new. Up until September '95, the large panels were first inserted into polyethylene bags, fitted with expanded polystyrene corner caps and placed in corrugated boxes. Today, the packaging process starts out as panels convey toward the stretch machines. The stretch machine operators fold and place foam-lined corrugated end caps around the panels. The end caps consist of three layers of A-flute single-face with a fourth layer nested into the open single-face. A 1/16" layer of expanded polypropylene foam is laminated to one side, which is applied against the product. The corrugated is perforated so that it can be broken in half. The two pieces are each folded to create separate end caps. The panels are then wrapped as the film carriage moves around the horizontal panels, wrapping from above and below. The panels are gripped at the leading and trailing edges to provide clear access to the full front and back of the panels during wrapping. The stretch wrap, in addition to securing the corner caps, provides a protective, puncture-resistant barrier around the panel. The film is also strong enough to wrap around the sharp edges of the metal base of the panels without tearing, according to Dortch. Though one of the benefits of the metallocene film is a higher elongation factor, Steelcase uses the same 150% prestretch factor it used for the heavier film. After stretch wrapping, another operator removes the panels from the packaging line. Other benefits Along with the source reduction in the film, the new process requires three workers. Previously, five workers were needed to operate the plant's box packaging line, which consisted of fairly custom equipment tailored to the product. Though it was fast enough for Steelcase's needs, it was more labor intensive than the stretch wrapping solution. The equipment payback was just over six months, according to Dortch; most of that was material savings, and the rest was labor and warehouse space. "We used to have to stock separate boxes for 40 different sized panels," explains Dortch. "Now we just store rolls of stretch wrap and one end cap design." Throughput is virtually the same. The stretch film also generates a few side benefits. One is that the packages are easier to hold and handle. Also, since the film is clear, it's possible to quickly and easily check the order for shipping damage without having to open a box. The panel's color and material can also be verified. Interestingly, delivery truck unloading time increased. Reason: workers that unload the panels are more careful since they can now see the contents. Finally, Steelcase's dealers also have less material to dispose of, saving them labor and disposal fees. According to Dortch, the success of this solution is prompting other Steelcase plants to adopt it. One in California was the next to see the benefits. "They've already purchased a machine, installed it, and are now in the process of debugging it," he says.