Unravel all the wiring from a typical luxury car, and it would stretch more than a mile and half. Just about every inch of that wire would be covered with coatings that haven’t changed much in three decades. The dominant coating material, PVC, has the distinction of being both cheap and effective in about 60 percent of automotive wiring applications. And for those wires that can’t use PVC, mostly those that see high heats in the engine compartment, crosslinked polyethylene works just fine. “There hasn’t been much innovation in wire coatings since the 70’s,” admits Lynn Long, specialty wiring manager for Delphi Packard Electric, one of the world’s biggest suppliers of automotive wiring systems.
Yet PVC and crosslinked polyethylene each have environmental drawbacks that have now opened the door for a new kind of wire insulation from Delphi and GE Advanced Materials. Based on an alloy of GE’s polyphenylene oxide (PPO) and an olefin, this new Flexible Noryl wire coating lacks the halogens and potential for dioxin release that have given PVC a bad name. And unlike crosslinked polyethylene, PPO lends itself to recycling. “Automotive OEMs have been asking us not just for a material that is halogen-free but also one that is recyclable,” says Ed Monroe, a cable program manager at Delphi. “PPO fits the bill on both scores.”If saving the environment was all the PPO wire coating could do, it probably wouldn’t get past the starting line in the automotive business. As Monroe points out, the push to eliminate halogenated compounds from cars and to recycle automotive wiring comes down to largely voluntary efforts taking place in Europe and Japan. “Regulations have been discussed, but nothing is on the horizon,” he says. PPO, however, has some design, performance, and potential installed cost advantages that will likely make it attractive regardless of its environmental impact.Design Strengths
Monroe sums up these design advantages in just three words: thinner, lighter, and stronger. With a specific gravity a few percent lower than PVC, the PPO coating has an inherent weight advantage when the two materials are used on an equal basis. But far bigger savings come from the ability to use less PPO to match or even beat the performance of PVC. For example, on wires up to 1.5 mm2, Delphi would typically use a 0.4-mm-thick PVC coating to meet its customers’ requirements. The corresponding PPO thickness, by contrast, would be just 0.2 mm.
The thinner the PPO coating also reduces wire diameter by roughly 25 percent with an even larger reduction in wire bundle sizes. The cross-sectional area of a typical bundle passing through an instrument panel could be reduced by roughly 40 percent because “thinner wires nest better,” Monroe explains. The resulting weight savings from the thinner wire coatings would conservatively come to ten percent, which can save ten lbs or more per vehicle now that cars routinely carry 100 lbs or more of wire.
PPO owes its weight and size reduction capabilities to what Monroe calls a “unique balance” of those mechanical and physical properties that really matter to wire and cable suppliers. One of them is toughness. Delphi’s test results show that the PPO offers 7 to 10 times more pinch and abrasion resistance than an equal thickness of PVC. Even at PPO’s reduced wall thickness it offers two to four times greater pinch and abrasion performance, Monroe reports. “Because Noryl is so much tougher, we can push it into thinner walls,” he says.
And the material’s thermal performance contributes to thinner walls too--by allowing less material to meet a given set of temperature requirements. Monroe points out that the PPO, which has a glass transition temperature of 212 C, has already passed the industry’s 110 C thermal tests for Class B wire. And he’s confident that the material will soon pass 125 C tests as well. “There’s no question we’ll get there,” he says.
And this kind of thermal performance already beats PVC. With the exception of some specialty high heat grades, PVC compounds will only pass an 85 C test, he adds.In some applications--those needing short protection rather than continuous use--Monroe says the higher heat resistance of PPO will even permit reductions in copper cross sections.As for cost, PPO won’t compete against PVC on the basis of raw material prices. But Monroe believes PPO’s design advantages can produce a substantial reduction in installed and lifecycle costs--from solving packaging problems at the design stage to easing assembly to reducing weight in the finished vehicle. “The real key to this material is the opportunity to reduce wire size,” he says. Environmental Edge
Miles of wire. Today’s luxury cars carry more than a mile and half of wire--much of it coated with PVC.
Relative to crosslinked polyethylene (XLPE), which is both tough and heat resistant, the thermal and abrasion advantages of PPO may be less compelling. Monroe believes that XLPE will persist in the highest-heat applications, such as wiring on the engine. It’s not that PPO can’t meet the high heat application requirements, “but XLPE may be more stable and offer a bigger safety factor,” Monroe says. He adds that Delphi and GE are looking into ways to crosslink PPO to boost its already-outstanding heat resistance.
Still, for all but the highest heat applications under the hood, PPO may still compete against XLPE for three reasons. One is the installed cost. Long says the PPO coating will likely cost “something between PVC and XLPE.”The other is PPO’s environmental edge. XLPE starts off as a thermoplastic, but the crosslinking turns the end into a thermoset, which can’t be melt-processed a second time. PPO, by contrast, can be reclaimed, reground, and turned into other plastic products. Keith DuPont, GE Advanced Materials program director, notes that reclaimed Flexible Noryl won’t go back into the wire a second time--because the plastic could pick up copper that would interfere with its electrical and mechanical properties. Reclaimed PPO can, however, be injection molded into a variety of products, including ones used to tie wire bundles together. Manufacturing comes into play here too. Delphi runs some of the world’s most productive wire-coating lines. “We have some of the fastest extruders around,” says Monroe. The company routinely extrudes wire coatings at more than 40 mph and resists any technology that will slow its extrusion lines down. With PPO, Delphi been able to maintain its fastest fast line speeds. Delphi has already signed up one automaker to try its the new wire insulation. Monroe won’t say which one yet, but he says the technology will appear on a 2006 vehicle. The company has also converted one of its high-speed lines to the PPO and can run both ISO and SAE wire configurations. In the latter sizes, the company has extruded the PPO over wire as small as 26 gauge.Web Resources
General information on GE Advanced Materials can be found at www.geadvancedmaterials.com.