Portland, Ore. - A new type of conductive polymer created at Integral Technologies Inc. promises to offer a plastic material that can be used as a substitute for metal.
While today's conductive polymers are more flexible and weigh less than metal, their higher impedance has made them suitable only for low-voltage, low-current applications. When polymers are doped enough to support high-current ac, for instance, they become too brittle. Now Integral Technologies (Bellingham, Wash.) claims to have melded polymers with micron-sized metal filaments to create a material with properties that are the best of both worlds, to form anything from copper wires to flexible interconnects to antennas.
"Ours is the world's only highly conductive polymer," claimed Thomas Aisenbrey, inventor of the material and general manager and vice president of product development at Integral. "It's conductive enough that you can run heavy current through it, either ac or dc."
Called ElectriPlast, the approach is derived from a material called Plastenna that Aisenbrey engineered to make moldable antennas for wireless telephone handsets. The company embedded metal filaments in the handsets' case to gather RF signals. Then it broadened the recipe for the material, so that now its process can be used to make nearly any currently available polymer conductive.
"ElectriPlast is a proprietary recipe creating a vast family of highly conductive polymers that can be molded into virtually any shape or dimension that any other plastic, rubber or other polymer can be molded into," said Aisenbrey.
In addition to becoming conductive, the structural characteristics of any polymer base (called a resin) for ElectriPlast will be reinforced, making the material stronger. Because of this, almost anything made from metal today can now be molded from ElectriPlast, according to the company.
"Many of our recipes are stronger than metal but 40 percent lighter than aluminum," said Aisenbrey. "Imagine how many pounds we can take out of an airplane or a car. The energy that will be saved alone makes it worth it."
The recipe is highly flexible. "ElectriPlast can mimic just about any metal with different formulations," said Aisenbrey. "We use a variety of doping agents-many different kinds of micron filaments-to create a microstructure within the polymer matrix. We can mimic aluminum, copper, even superconductors."
The company said it can use more than 15,000 different commercially available resins, from rubber to hard plastic. A customer chooses a polymer resin that is strong enough structurally for an application, then directs Integral Technologies to build an ElectriPlast version so that it has the characteristics of the metal needed for the application.
"We can go from a very flexible material to very stiff," said Aisenbrey. "If you want a really strong polycarbon, we have Lexan compounded, or if you want a high-temperature or long-lived material, we have those compounded."
The compounded material delivered from Integral Technologies can be molded using the same processes as normal Lexan, except that now the plastic material will also conduct electricity. "The secret is the recipe with which we compound the conductive elements with the plastic," said Aisenbrey. "It homogenizes the particles very conformally so that you have a really good conductor throughout the material."
Another key feature of ElectriPlast is the shape of the embedded filaments. Instead of using spherical nanoparticles, Integral Technologies micron-long filaments. Thus the electrons flowing in the material are virtually assured of finding a path from one end to the other. "The problem with nanoparticles is that there are only 12 possible points of contact that the electrons can travel on-your aspect ratio is not very good," said Aisenbrey. "But with the way we dope with micron-sized filaments, there are 675 possible points of contact, making our throughput much better."
For antennas, the Plastenna material embeds millions of tiny filaments that can each act independently as microantennas, even though they are merely compounded into the shell of the phone.
"Plastennas respond to RF signals regardless of their polarization, rather than just in two dimensions, like a piece of metal," said Aisenbrey. "A piece of metal is never going to react as well, because it doesn't have all the different angles of the [polymer] matrix to work with."
The company also claims that Plastenna is indifferent to the proximity of other objects. Consequently, its resonant frequency remains locked on.
"Because the micromatrix has a reduced-impedance load [compared with a metal antenna that takes the signal directly to ground], it hardly shifts off frequency when your body is next to it, which is another feature," said Aisenbrey.
ElectriPlast materials exhibit the high thermal conductivity of a metal, making them candidates for heat removal. For instance, a ElectriPlast heat sink could be molded with very densely packed fins to dissipate heat.
Materials formed with the recipe can also be magnetized, making it possible to mold parts for applications where magnetism enables a control function. "We can mold cable heads that shield like metal but are lighter, stronger and can be formed in one step," said Aisenbrey. "We have also demonstrated a braking system that uses a magnetic field to slow things down."
Integral Technologies is licensing ElectriPlast to major corporations. Although over 40 companies are molding test parts with ElectriPlast recipes today, no commercial products have incorporated the material to date. Aisenbrey expects to announce the first products using ElectriPlast next year.