TPE allows for easier adhesion of roof rail covers using multi-component injection moulding

In a joint development project, German TPE supplier Kraiburg worked with vehicle components maker Gutsche Engineering to produce its roof rail cover.

Gutsche Engineering says it has benefited from the cost-effective processing and above all from the outstanding weather resistance combined with cohesive ASA adhesion in Kraiburg’s Thermolast A compound for this application.

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 has enabled Gutsche to bond ASA and TPE in multi-component injection moulding.

“We were looking for a TPE for the seal that can be moulded directly onto the ASA hard component of the cover and will 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 mould cavity pressures possible. Along with tool technology and the moulding

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 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 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 in Waldkraiburg, Germany. “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 minimising development costs and advancing the product launch.”

In addition to established adhesion to polar thermoplastics, the chosen compound features high flowability, which allows filling moulds for complex component geometries, says the material maker. 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.

Kraiburg also says the 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 grey 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 compound passed the outdoor weathering test without cracking, says Kraiburg.

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

Michl adds that exterior covers are applications that are becoming an increasingly important part of the company’s business. “Kraiburg 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,” he concludes.