Polymers target metal at NPE

Wilmington, DE -The polymer scientists at DuPont Engineering Polymers have been busy getting ready for the upcoming National Plastics Exposition, which will take place this June in Chicago. The company's technology vice president, William Hsu, recently offered a glimpse of the new materials-including ones for metal replacement, one-material EMI shielding, connectors, gears, automotive fuel components, and other targeted uses. Here's a look at them:

Zytel HTN, DuPont's line of high-temperature nylons, will grow with the introduction of two new grades, HTN 53G and HTN 54G. Both are intended as metal replacements in a variety of structural parts-particularly in automotive powertrain, chassis, and interior uses. According to Hsu, both materials reconcile the contradictory goals of strength, stiffness, and toughness at high temperatures. "The 54G series is particularly good in this respect," he says. "Its tensile module of 11.5 Gigapascals at 100C indicates useful levels of strength, and the elongation values at about 3% mean that it's a really tough material." The 53G resin is even stronger and stiffer, though it loses more of these properties at temperatures over 100C, Hsu adds.

For EMI/RFI shielding of electronic devices, DuPont will roll out a series of Zytel DMX nylon 66 grades modified with carbon fibers, particles, or a combination of the two. In addition, the materials contain tougheners to offset the property losses due to high levels of carbon. Hsu says the company has formulated grades with shielding values from 25 to 75 dB and has tested attenuation at frequencies up to 4 GHz. "Those levels of performance meet the shielding requirements of most electronic devices, including computers, hard drives, and cell phones," he says. Best of all, the materials meet these requirements without any need for metal shields or conductive coatings.

Another less conductive grade, Zytel FE5495, will be available for dissipating overflow charges in high-voltage transformers and other electrical equipment without the use of conductive paint. It offers a volume resistivity of less than 1,000 V cm, says Hsu. And still more conductive materials will serve as antistatics for automotive fuel system parts. These materials include a toughened, conductive Zytel grade (FE8209) for parts such as tank caps or fuel line fasteners; a stiff, strong Delrin acetal for parts subject to fuel exposure; and a toughened Delrin acetal for parts such as fuel modules or gas-tank filler pockets.

To outdo PPS in connector applications, DuPont will introduce a new grade of liquid crystal polymer (LCP), Zenite 6244, whose shrinkage rate closely matches PPS, potentially enabling a switch from PPS to LCP without the need for new molds. But why switch? "To save money of course," Hsu says, explaining that LCP overcomes a price disadvantage by increasing productivity through cycle-time reductions and flashless molding. As an example, Hsu points to the experience of an unnamed connector manufacturer that tripled its production rate on a high-volume line of large connectors (up to 16 inches long) by adopting the new LCP.

DuPont will also roll out new mineral-filled LCP grades formulated to reduce warp. Zenite 3224 contains 20% mineral filling and no glass. Zenite 3226 has a 30% mineral and 10% glass filling.

A new flame-retardant (FR) nylon, Zytel FR 50 HF, targets molding productivity with a melt viscosity about 40% less than DuPont's comparable FR grades. "The bottom line is that it can fill molds for thinner parts, and it can fill them faster than standard flame retardant nylons," Hsu says.

DuPont will introduce several new grades of its Delrin acetal. Hsu says all the grades "tweak" or add to acetal's established properties-mechanical performance, dimensional stability, low wear, and low friction. For printer gears, one new Delrin bumps up the dimensional stability for better molding in humid conditions of Southeast Asia. Another grade targets high-load gears. Hsu notes that it handles operating temperatures up to 10C higher than general purpose Delrin. And another upcoming Delrin will offer resistance to diesel fuel. "Our goal is to open up more applications in diesel fuel by meeting European test requirements for defined levels of property retention after 2,000 hours in diesel fuel at 90C," Hsu says. Lastly, the company will bring out a new grade of general-purpose Delrin that strikes a new balance between strength and melt-viscosity. Hsu explains that "it flows better than our 100 Series resins, but its impact strength is higher than lower-viscosity 500 series resins."