It all started with a teapot.
In 1994, a British appliance maker came to LNP Engineering Plastics Inc. (Exton, PA) with a request: Help us design an electric teapot that won't melt when it runs out of water. The company's current teapots used wires inside of plastic heating coils. The design worked well as long as the teapot was full, since the water acted like a heat sink, and soon boiled.
But with the British penchant for tea, many people left their teapots plugged in all day. And when a teapot boiled off its water, the plastic heating coil grew so hot that it would deform and melt. So LNP's engineers spent two years mixing different recipes of resins and fillers, searching for a combination that would create the heat and then conduct it, not absorb it, says George E. Niznik, LNP's vice president and director of R&D and technology.
They had nearly solved the puzzle when the British company cancelled its order, abandoning its plan to build a better teapot.
Other companies might have written off the experience, and moved on to other products. But LNP kept tinkering with its new mixture, Niznik says. In 1996, a U.S. home-appliance company came to LNP for help in designing a hot water heater with plastic heating coils. LNP pulled out the teapot project and tweaked the design, designing a plastic that would conduct heat without conducting electricity. But again, the customer backed out before creating a product.
Yet the engineering work behind this new plastic lived on. In February, 1999, LNP decided it was good enough to put in its catalog, and gave it a name--Konduit(TM) Thermally Conductive Thermoplastic Compounds. Since then, several companies have used it in their designs, and Design News readers voted it the Best Product of 1999.
Today there are two families of Konduit, and dozens of specific mixtures. LNP engineers can tailor the recipe to achieve specific levels of conductivity, brittleness, flexibility, thermal expansion, lubricity, structural strength, and more.
LNP delivers the tailored Konduit compound in pellet form, so companies can feed it into their own injection molding hoppers, flow it into molds, and make any shape they want. Applications range from automotive solenoids to computer chips to heated toilet seats. Since it can be molded to any shape, Konduit can also be used in metal replacement and thermal management, says Mark G. Kaptur, LNP product marketing manager.
A computer made with Konduit components could dissipate heat from chips through its own structure, instead of using an electric fan and aluminum heatsink. Lighting fixtures and microwave ovens could encapsulate their voltage transformers in Konduit, to radiate heat more cheaply, with fewer copper coils and steel laminations.
The two-tier product line includes a low-cost group, which uses a ceramic additive to impart thermal and/or electrical conductivity at heat transfer levels of 2 W/m degrees K (Watts per meters-degrees Kelvin). And a high-performance group uses a carbon-fiber filler to achieve thermal conductivity of 10 W/m degrees K. They are available in nearly any resin, but LNP will focus on crystalline instead of amorphous resins to achieve better flow rates for injection molding.
LNP's engineers must perform a constant balancing act to mix Konduit for prime performance in every new application, says James M. Finan, senior product development chemist. In the low-cost product, the ceramic particles must be touching, or nearly touching, to conduct heat. So a typical Konduit recipe may include just 30% resin and 70% ceramic, by weight.
At these levels, Konduit's thermal and electrical conductivity rises, and its thermal expansion is very low, but it also becomes more brittle, more stiff, and less viscous. So LNP engineers must juggle the various demands:
For use in a hamburger grill, the Konduit mix had to withstand high temperatures, resist animal fat, have a high coefficient of friction, be FDA-compliant, and still be injection moldable. That meant the mixture required less ceramic and more resin.
For use in covering a solenoid under the hood of a drag racing car, the Konduit had to conduct heat, allowing the manufacturer to use less expensive wire. But the mix also had to have a low coefficient of thermal expansion, so the Konduit would not expand at high temperatures and break the watertight seal around the sensitive electronics. That meant the mixture required a slightly different ratio of ceramic and resin.
In both cases, LNP engineers found the right mix of additives and ingredients. After all, they were used to creating different mixtures throughout the product's long development history.
For example, during the design of the hot water heater, LNP's engineers kept running into new challenges. They had to fix the dimensional stability, so the plastic wouldn't change shape as it heated, and break sensitive seals. They had to cure voids in the plastic molds, which would cause arcing under electric current.
Confronted with those early hurdles, Niznik didn't get discouraged. "The first 90% is always easy," he says. "It's the last 10% that's the hardest. That's how I knew we were getting close. We're the kind of company that gets plastics to do things they're not supposed to do."
So the engineers tried dozens of mixtures before they found the right one, says Gunther G. Graber, principal engineer.
"It took about two years before we had something workable," he says. "The seed was there. It just needed a little water to grow."
LNP is an international producer of thermoplastic compounds, with headquarters in Exton, PA, and U.S. manufacturing in Thorndale, PA (where Konduit is currently made); Columbus, IN; and Santa Ana, CA. It has international plants in the UK, Netherlands, France, and Malaysia. For more details, see the company's web site at www.lnp.com.