Machine Design

Vulcanized TPE seals the deal

Hong Yang Sealings in China, has developed its own coextrusion process for applying colorful weather-resistant topcoats on automotive door seals.

The decorative topcoat on this door seal from Hong Yang Sealings is visible in the interior of Mazda 323 vehicles built for the Chinese market by Haima Motor. The topcoat a NexPrene 9075A vulcanized thermoplastic elastomer (TPV) from Solvay Engineered Polymers, Inc. The TPV material is applied to a thermoset EPDM profile that incorporates a foamed bulb seal and solid backbone.

The conventional way to make these seals includes three primary features. A foamed thermoset rubber bulb that touches the door and provides the functional seal. It sits on a backbone of solid thermoset rubber, extruded over a metal structure that clamps onto the cars doorframe. A wing with a colored topcoat is visible in the interior and covers the edges of headliners, pillars, and carpeting.

Hong Yang's proprietary technique lets technicians coextrude seal bodies and foamed bulbs from EPDM thermoset rubber. The seals are then topcoated with a vulcanized thermoplastic elastomer (TPV) called NexPrene 9075A from Solvay Engineered Polymers, Inc., Auburn Hills, Mich. The combination is said to significantly improve both the quality and weatherability of automotive door seals while letting designers closely match topcoats to any color palette the OEM desires. This includes "champagne" and "light stone" as well as other light hues that historically were hard to match and weathered poorly with conventional thermoset-based topcoats.

"Thermoset EPDM also needs sulfur-based curing agents that limits color choice to darker shades," explains Kevin Cai, product development manager at Solvay Egineered Polymers. "And regardless of titanium dioxide or pigment concentrations, it doesn't weather well. Conventional phenolic-cured TPVs may be easier to color than thermoset EPDMs, but natural grades of these TPVs exhibit unacceptable levels of color variation, and dont weather well when colored in light hues."

In contrast, says Hui Wang, deputy general manager at Hong Yang, the UV stabilized NexPrene 9075A comes in natural, easily colors during production with color concentrates, and wont show noticeable color change even after many years of use, based on extensive heat-aging and accelerated weathering tests.

Additionally, the proprietary coextrusion process reportedly creates stronger bonds between the color layer and the thermoset backbone than that of other commonly used methods. NexPrene 9075A also provides a deeper and more distinct grain than thermoset rubber or conventional thermoplastic elastomer materials. The top-coated profiles are cut to length to fit door openings and corner moldings join to the profiles by overmolding.

More Information:
Solvay Engineered Polymers Inc.

This article appeared in the December issue of the Materials Monthly e-mail newsletter. If you enjoyed this article and would like to read similar articles sign up today for our free e-mail newsletters!
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