Adhesive TPE bonds to ASA for auto exterior applications

Kraiburg TPE offers a broad range of thermoplastic elastomers (TPEs) for interior and exterior applications, as well as applications for engine compartments and power trains of motor vehicles. Gutsche Engineering – specialized in sophisticated vehicle components – also relies on the TPE manufacturer from Waldkraiburg, Germany, in producing its innovative roof rail cover. Gutsche Engineering has benefited from the cost-effective processing and above all from the outstanding weather resistance combined with cohesive adhesion to ASA (acrylonitrile-butadiene-styrene) resins in Kraiburg TPE’s Thermolast A compound for this application.

TPE compound adheres directly to ASA resin in overmolding process.

The component innovation from Gutsche Engineering provides a completely assembled cover with integrated seal for areas where the seal previously had to be mounted under the roof rail in a costly process. Simplifying the assembly process with the OEM is only one of the advantages that multi-component parts provide. The Thermolast A compound from Kraiburg TPE has enabled Gutsche Engineering to bond ASA and TPE in multi-component injection molding.

“We were looking for a TPE for the seal that can be molded directly onto the ASA hard component of the cover and ensure permanent and reliable adhesion to this copolymer,” explains Martin Gutsche, managing director of Gutsche Engineering. “Another decisive factor was the TPE’s viscosity, which makes it possible to implement the thin sealing lip geometry without imprints on the hard components by using the lowest mold cavity pressures possible. Along with tool technology and the molding concept, the TPE’s processing and product properties also played a significant role in achieving the required component quality.”

Due to successful collaboration on previous projects, Gutsche Engineering brought Kraiburg TPE into the development of the application at an early stage in order to identify the TPE that would be most suitable for the innovative application. “In order to determine the adhesion of the various material combinations depending on different processing parameters, we at Kraiburg TPE offer the service of performing specific tests to check peeling resistance in accordance with the specifications of the VDI 2019 standard,” says Matthias Michl, expert for window encapsulations, covers and frames at Kraiburg TPE in Waldkraiburg. “We know from past experience that including partners in projects at an early stage and the related preliminary tests can make a decisive contribution to minimizing development costs and advancing the product launch.”

In addition to established adhesion to polar thermoplastics, the chosen Thermolast A compound features high flowability, which allows filling molds for complex component geometries. The main requirements for the roof rail covers also included high weather resistance, as the covers are mounted at the highest point on the vehicles.

The Thermolast A compound used was not only able to meet the high OEM requirements involving two-year cycles of weathering in accordance with PV 3929 and PV 3930 standards in advance, by achieving > level 4 on the gray scale, but it also proved its value on the component during outdoor weathering. Thanks to its excellent weathering resistance and despite a thin seal lip geometry, the Thermolast A compound passed the outdoor weathering test without cracking.

The application implemented with Thermolast A has been in mass production as part of a roof rail system for a premium SUV since the first quarter of 2019.

“Exterior covers are applications that are becoming an increasingly important part of Kraiburg TPE’s business. Kraiburg TPE is further expanding its portfolio to meet the growing demand for high-quality surfaces combined with polar adhesion and high weather resistance. Kraiburg TPE is setting new standards in exterior applications with new compounds that above all provide a precise surface texture in combination with improved adhesion to PMMA and ASA,” Matthias Michl adds.

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