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Jan 1st, 2004                                Print this article

Thermosets refuse to buckle

By Matt Defosse

The jousting between metals, thermosets, and thermoplastics—primarily in the automotive, electrical/electronics, and consumer goods markets— continues apace.

In recent years, thermoplastics have won more of these fights than they've lost, but there is still plenty of scope for thermosets, and recent technology developments could lead to even broader interest in them (for a related article, see As I See It).

Officials at supplier Bakelite AG (Iserlohn, Germany) think they are near completion of more than a decade of work to cut curing times of thermoset compounds. Until recently, Bakelite's High Temperature Molding (HTM) system had not advanced beyond the R&D phase, but improvements in computer simulation of thermoset's in-mold behaviour led to a breakthrough. An experimental HTM tool running at the supplier demonstrates that a 25% curing time reduction is possible.

Other developments improving thermoset molders' lot include the gas evacuation technique—the first time gas-assist injection molding has been applied to thermosets—from compounder Bulk Molding Compounds Inc. (West Chicago, IL); this technology can reduce material required per part as well as cycle times (September 2003 MP/MPI). The Iserlohner Kunststoff-Technologie GmbH (Iserlohn, Germany) is developing processes for multimaterial molding of thermosets and functional elements made of thermoplastics, elastomers, or liquid silicone rubber.

Thermoset processors have seen recent success in automotive parts both large and small. On the small side, Christophery GmbH (Olsberg, Germany) replaced aluminum with a thermoset compound in the hydraulically driven pistons for an unidentified car's automatic drives. The increasing complexity of these parts has forced aluminum processors to add secondary steps during manufacturing, elevating part cost, whereas the thermoset parts leave the mold ready for use. Surface structure is well defined on the plastic parts, tolerances stay within .01 to .02 mm, and the plastic parts match the heat stability of the aluminum ones.

Larger are the first commercial all-plastics engine hoods for tractors, reaction injection molded by Wayand GmbH (Idar-Oberstein, Germany) for John Deere. The steel hoods formerly used required mounting of four separate parts. Wayand processes Metton LMR dicyclopentadiene, a two-component liquid system supplied by Metton Europe . (Düsseldorf, Germany), for the 16- and 20-kg parts. The RIM parts also met the OEM's impact resistance requirements.

Rare is recent reference to thermosets' use in packaging applications such as bottle closures. Thermosets were the first plastics to start nudging metals out of the market, thanks to their superior corrosion and chemical resistance. PP later pushed thermosets to the side. But according to officials at one of the world's largest package and closure processors, Owens-Illinois (Toledo, OH), the market is again proving fertile for thermosets.

These thermoset caps typically top-off high-end toiletry or cosmetic bottles, so closure cost is not the priority, but appearance is, notes David Waldock, thermoset business manager at Owens-Illinois. He notes the ease with which thermosets can be molded into different shapes and colors, enabling high-end cosmetic firms to use closures as part of their product differentiation strategy. Thermoset closures have more heft than thermoplastic ones, providing the upscale look and feel consumers desire, and they match well with the glass containers still dominant in the high-priced personal care market.

mdefosse@modplas.com

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