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Toughened PPA meets auto connector needs

The plastics used for the latest generation of automotive connectors don't have it easy. High reflow temperatures in surface-mount applications call for materials with a high heat deflection temperature, while terminal insertion and the need for snap-fit features call for a reinforced material with good elongation and strength properties. Motorola's Automotive Industrial Electronics Group recently picked a new polyphthalamide (PPA) with the right collection of properties when it developed a header connector for an automotive control module, according to Vince Guarna, the group's director of technology and engineering. Called AT-6115, this Amodel PPA offers an HDT of 568F at 66 psi, a tensile elongation of 4%, and a tensile strength of 16.5 kpsi. Other key mechanical properties include a flexural modulus of 625 kpsi and a charpy impact of 6.0 ft-lb/in2.

BP Amoco Chemicals

New nylons

RTP Co. has added nylon 4/6 to its lineup of engineering thermoplastics. These 200 G Series nylons can be modified for strength, wear, conductivity, and flame retardance.

Colored grades are also available.

RTP Co.

A clear winner for light guides

A cyclic olefin copolymer (COC) emerged as the clear winner when Stewart Connector Systems (Glen Rock, PA) needed a material that could serve as a light guide on a magnetic telecom connector. The company adds these light guides-which measure 0.12x0.5 inches and attach to the connector body with a press fit-to some of the single-port connectors in its MagJack line. By carrying a color-coded indicator light from an LED at the back of connector to the connector's face, the light guide lets users know whether all the MagJack's components are working properly. According to Stewart vice-president Chuck Wingate, Topas COC (from Ticona) not only has the clarity needed to carry the light, but it also held the tight dimensional tolerances (0.003 inches) during an infrared reflow soldering process that sends temperatures up to 464F for 10 seconds. "Topas gave us the ability to maintain the dimensional integrity of the light guide during soldering while providing the clarity to transmit light at the brightness levels we need," he says.

Ticona

Microcellular nylons yield production benefits

While glass-reinforced nylon has long delivered strength and stiffness in structural applications, the right processing method can help it achieve its mechanical properties more cost effectively. Arburg Inc., a maker of injection molding machines, learned that lesson recently when it applied microcellular molding technology (MuCell from Trexel) to a nylon pipe-isolation-mount housing. Measuring 72x72x25 mm, the housings hold a vibration-damping part that isolates pipes in a molding machine's hydraulic-fluid reservoir from pump vibrations. In the past, the company made these rugged housings from solid molded nylon. By imparting a microcellular structure to a 33% glass-filled nylon (Zytel from DuPont), Arburg realized production advantages that engineering manager John Adamowicz sums up as "less warp, faster cycle, and less material." Adamowicz reports the microcellular parts exhibit 75% less warpage than solid parts, not only increasing yields but also producing a flatter seal against the steel wall of the reservoir. The microcellular parts also cool faster and are less dense-for 25% savings in molding cycle time and a 27% reduction in weight. Best of all, the production gains didn't come at the expense of mechanical performance; Adamowicz notes that the housing remained every bit as strong and stiff as its solid predecessor.

Plastics take the heat

The portfolio of thermally conductive polymers from Cool Polymers Inc., some of which offer heat transfer capabilities as high as 100 W/mK, continues to grow into new resin families. According to business development director Jim Miller, the company has now developed injection-moldable liquid crystal polymers (LCP) with thermal conductivities between 15-20 W /mK. LCPs in the Cool Poly D Series are electrically insulative, while those in the Cool Poly E Series are electrically conductive. The company has also developed elastomeric materials for use in a variety of conformal thermal interfaces. TPO, TPV and urethane varieties offer thermal conductivity up to 20 W /m K and are available in a wide durometer range.

Cool Polymers Inc.

Cool Poly LCP properties
Cool Poly E2 Cool Poly D2

Thermal conductivity, W/mK

20

15

Volume resistivity, ohm-cm

0.1

1014

CLTE, ppm/ degrees C

Parallel

7

4

Normal

20

10

Heat deflection temperature, degrees C

@1.8 Mpa

260

260

@0.45 Mpa

270

270

Tensile Strength, MPa

120

40

Flexural Modulus, MPa

35,000

n/a

Impact Strength, kJ/m 2

Charpy unnotched

5

3

Charpy notched

2

1

UL Flammability (UL 94) @ 1mm

V0

V0

Density, g/cc

1.7

1.8


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