Plastics companies are developing some very unique injection-molding resins that conduct electricity. These manufacturers often utilize nanotechnology to produce tiny metal fibers and strands that are incorporated into the matrix of the polymer. Both the metal’s conductive and physical properties impact the performance of the composite material, so the function of the product or part must be perfectly understood at the beginning of the project.
A wide variety of resins can be “doped” with conductive metal—the most popular resins are polycarbonate (PC), polypropylene, ABS, polyamide 6/6, and PC/ABS. Conductive fillers are typically stainless steel fiber and nickel-plated carbon fiber. Nickel is conductive, magnetic, and corrosion resistant. All these composite materials can be injection-molded (including complex shapes), producing parts that are as hard and durable and conductive as the metallic parts they replace—as well as lighter in weight.
Resins are doped with a specific concentration of micro-sized or nano-sized metallic materials and then pelletized. These particles are then homogenized throughout the material during injection molding. The shape of the metallic particles are also important—they can range from nickel-coated fibers that act as major conductors and ground planes to three-dimensional branched or looped nanostrands that also provide specific mechanical properties and electromagnetic shielding.
Applications for conductive composites abound, including electronics, lighting circuitry, medical devices, cable connectors, antennas, shielding, switch actuators, and thermal equipment.
ElectriPlast Corporation in Bellingham, Washington makes electrically conductive hybrid plastics for industrial, commercial and consumer products and services. Its core product line, ElectriPlast™, is a family of non-corrosive, electrically-conductive resin-based materials whose properties allow it to be molded into multiple shapes and sizes associated with plastics and rubbers—but which is as electrically conductive as if it were metal. By replacing traditional metal parts component weight may be reduced by 40 to 70 percent.
In February the company announced an agreement with Korean firm Hanwha L&C, a global supplier of interior and exterior automotive components made from lightweight materials such as glass fiber mat-reinforced thermoplastic, lightweight reinforced thermoplastic (LWRT), and expandable polypropylene (EPP).
Hanwha L&C conducted extensive independent testing of conductivity, shielding (both electric and electro-magnetic), and mechanical strength; the results met or exceeded all the company’s requirements.
“We see the conductive plastics market as a tremendous growth opportunity and the ElectriPlast technology as a leader in this young industry” says Won S. Choe, Hanwha L&C’s vice president of business development. “We have many potential uses for ElectriPlast in our different lines of business, including our automotive division.”
Because of more stringent federal fuel-efficiency expectations, the automotive industry has been looking for ways to reduce the weight of cars to reduce fuel consumption. One of the solutions is proving to be plastic composites that are just as strong as the metal they replace—and significantly lighter. Both thermoplastic and thermosetting composites are being engineered to replace steel and aluminum without compromising performance. Making these parts from plastic composites can also increase innovation in the design phase, giving manufacturers more opportunities to reduce overall production costs.
Reinforcing plastics with short glass fibers improves strength, stiffness, and heat deflection temperatures. Glass fiber-reinforced thermoplastics and polypropylenes are being used more in the automotive industry to replace metal parts (as well as plastic parts that don’t last as long as glass-reinforced plastics). Glass-reinforced polyamide and polyphthalamide are becoming popular replacements for metal in cylinder heads and other engine cooling components in vehicles. Glass-fiber content can be 50 percent or more, creating a very high modulus. These short glass-reinforced plastics can be ideal materials for parts and products in other industries where superior strength, heat-resistance, and lighter weight are required.
There are also long fiber-reinforced thermoplastics and polypropylene (LGFPP)—although these are more expensive, they are higher performance, especially in high-temperature applications. Because of its strength, LGFPP is an ideal material for manufacturing parts with thinner walls—which also reduces weight and material costs. LGFPP also has a lower specific gravity than other resins such as PA or PC/ABS, another cost reducer.
Carbon fiber-reinforced plastic (CFRP) is another family of lightweight materials that provide superior strength and has high interest among automobile manufacturers, especially for larger body parts such as side panels, which could reduce the weight of a car by 50 percent or more.
To further this research, Ford Motor Company has partnered with Dow Chemical Company to investigate ways to bring carbon fiber into high-volume auto production—with the goal of reducing the average car’s weight by 750 pounds. Key research considerations include material cost, faster processing of carbon fiber molding, and discovering new ways to join composites to metal. Carbon fiber is already in production in limited volumes for specialty cars, most notably Germany’s BMW, but the process is slow and expensive.
Not to be outdone, General Motors Company just signed a deal with Japanese firm Teijin Ltd. to build a $7.9-million composites development center in the Detroit suburb of Auburn Hills. The center will develop large-volume carbon fiber production for the auto industry using a proprietary process that can mold carbon fiber reinforced thermoplastic within cycle times of one minute.