Focus on adhesives: New PBT offering outstanding adhesion with widely used silicone adhesive

Envalior is a new company, formed as a merger between industry leaders DSM Engineering Materials and Lanxess High Performance Materials. Here, experts from Envalior discuss its new offering, a silicone adhesive system that can bond individual, injection-moulded parts that are in high demand in the e-mobility automotive industry

E-mobility and the trend toward driving assistance and safety systems are leading to a sharp rise in demand in the automotive industry for thermoplastics for electronic equipment and modules. Typical applications include housings for radar sensors, control units and cameras. One common method of manufacturing these housings involves the bonding of individual, injection-moulded parts such as covers, side panels, bases and connectors. Silicone adhesive systems are commonly used here because of their efficiency and performance. The thermoplastic substrates often have to be adapted to suit these adhesives. One successful example of this is the new polyester Pocan® B3234HR S2 (PBT) from Envalior. This hydrolytically stabilised compound offers outstanding adhesion with a primer-free applied, thermally quick-hardening single-component silicone adhesive that is already widely used on the market.

Running change in series production

“Thanks to its outstanding bonding properties with this adhesive, our new compound has replaced a rival PBT product in the ongoing series production of electronics housings for driving stability systems. These safety-relevant systems are used in the electric and internal combustion engine vehicles manufactured by a number of international automotive manufacturers, including from China,” says Thomas Babl, who heads Envalior’s application development and technical customer service team at its site in Hong Kong. The driving stability systems are produced by TE Connectivity Corporation. The US technology company is one of the world’s leading providers of connection and sensor solutions for the transportation sector, as well as for a range of industrial, energy technology, medical technology and data communication applications.

Investing in standard adhesion test systems

Pocan® B3234HR S2 is based on Pocan® B3233HR. This PBT compound already offers excellent adhesion with numerous silicone adhesives and has proved itself over many years in the series production of in-vehicle electronic components, such as connectors and parking brake housings. “To optimise the material, we invested in two standard test systems for pull-off adhesion tests. We also developed our own manual peel test. Among other things, this allows us to quickly test the strength of adhesives and so instantly integrate our findings in ongoing development projects,” says Babl.

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Outstanding rating in the SAE/USCAR long-term hydrolysis test

The new Pocan® B3234HR S2 not only ensures high-strength adhesion with the single- component silicone adhesive but also offers outstanding hydrolysis resistance. In specimen tests based on the stringent long-term hydrolysis tests of the US Society of Automotive Engineers (SAE/USCAR-2 Rev. 7), it achieves “Class 4” – the second-best rating. This means that it has a similar level of hydrolytic stability to Pocan® B3233HR.“This ensures that the electronics housings for driving stability systems are resistant to hot and humid environments and can do their job without any issues,” says Dr. Claudia Schmid-Dähling, who is among those responsible at Envalior for Pocan® product development. The new structural material also exhibits similar mechanical properties to the tried-and-tested product Pocan® B3233HR. Especially impressive are the high tensile strength and elongation at break, which lend the material a high degree of resistance to burst pressure. Schmid-Dähling: “These mechanical properties are important because tests aimed at determining whether the housing stays tight even under high-humidity conditions are performed at high pressures.”

Laser marking capability at high speeds and frequencies

The new PBT compound is coloured black with “900867” from Envalior. One benefit of this highly versatile colour system is that the housings can be laser-marked at high speeds and frequencies and with a high level of contrast. “Information such as parts designations, batch numbers and QR codes is easily legible even when the lettering is really small,” says Schmid-Dähling. Another benefit of the colour system in PBT is that it ensures good absorption of the frequencies usually used in laser transmission welding, which helps to ensure high weld strength in this joining process.

Flame-retardant PBT with excellent silicone adhesion under development

Envalior will be putting the new test equipment to intensive use in the future with the aim of developing further specially tailored, application- and customer-specific thermoplastics for silicone adhesives. “We’re working, for example, on hydrolysis-resistant PBT compounds with good laser marking capability that not only offer firm adhesion with silicone adhesives but are also highly flame-resistant. They could potentially be used for housings located close to electric vehicle batteries,” says Babl.