A new high-tech weave gives the convertible top on the 2012 BMW 6 Series cabriolet a stylized look.
The Haartz Corp.-supplied soft top is comprised of an acrylic/polyester (PET) weave outer fabric, a rubber inner layer, and a polyester lining fabric. Achieving the outer weave's new optional black/silver high-tech appearance involves using a contrasting color yarn with the filament PET.
"The difference in luster and silver color in comparison to the black acrylic yarn gives the material an optical effect that changes based upon lighting conditions," Matthew Williams, Haartz Corp.'s Director of Business Development, told AEI.
Versions of the high-tech weave are also available on the BMW 1 Series cabriolet as well as the Mini Cooper and the Rolls-Royce Phantom cabriolets, according to Bill Malavich, Haartz's R&D Manager for Automotive Exteriors and the launch manager for the second-generation 650i soft top.
An extrusion coating process applies a rubber film to the textiles at Haartz's Acton, MA, facility, while a knife-coating process applies the rubber film to the textiles at Haartz's plant in Germany. After the textiles have been coated, the rubber film is vulcanized by hot air.
"The combination of these manufacturing processes is critical in the case of the 6 Series convertible because it minimizes the appearance of fold-marks in areas of the top cover that are tightly compressed in the down-stack position," said Malavich.
A reaction injection molding (RIM) polyurethane-foam layer, customized to BMW's specific shape and acoustic targets, further enhances an acoustical-grade fabric laminate.
Noted Malavich, "The tightly controlled elongation and recovery properties of the Haartz topping material ensure that sound is not transmitted through the soft top into the vehicle cabin due to turbulent wind buffeting."
Since the electronically powered convertible top can be exposed to snow, sun, rain, and other weather variables throughout the year, specially developed polymers in the fabric coating help protect the roof material from harsh environmental conditions.
For example, sun fade is addressed through application-specific acrylic fibers with optimized pigment systems while waterproof protection is provided by a Haartz-formulated rubber inner layer designed to withstand cracking over years of usage.
"Our rubber layer formulations allow for consistent tensile and flexural modulus values in hot and cold temperature extremes, so the convertible top has the same closing force in all environments," said Malavich.
A customized flex/fatigue test ensures that the fabrics will not delaminate from the rubber layer after repeated convertible-top open and close cycles.
Haartz's R&D activities are focused on developing a next-generation soft top with improved soiling resistance and fabric cleanup (especially for light color options) as well as customized weave designs and noise suppression.
"When the soft top is closed, the consumer expects the vehicle to be as quiet as a coupe. Which is why at Haartz, we strive to continuously improve the acoustical performance of the convertible top," said Malavich.