Dusseldorf. Germany — The latest Peugeot 308 has static window seals made from a TPV-S based on Kraton's SEBS material and polypropylene. The seals — including glass-run channels and belt-line seals — are made by Cooper-Standard. The material was developed by TPE compounder CTS based in Tiffauges, France.

According to Phillipe Durand, CTS executive in charge of the automotive market, the main benefit of the TPV-S seal is a consistent visual appearance among extrusions, corner mouldings and injection moulded components. The system also saves weight as it does not require metal inserts for rigidity. The absence of metal also allows the material to be more easily recycled, he said. Durand said the system cost was lower than more conventional EPDM seals, but insisted the main driving force had been improved appearance.

The main reason is not cost. The main reason is to improve the overall appearance and homogeneity and to gain an improvement in ageing resistance.'' He continued, "if it is only cost, then you cannot change. To have a different material you must have better properties and better performance, as well as lower cost." Durand added, "the cost per kilo [of the material] is higher, but the total system cost it is lower." He said that there are also savings in weight and benefits in terms of recyclability.

The seal is made from three different compounds. One for the main glass channel extrusions; another for the corner mouldings and a third more rigid material for the injection-moulded belt line seal. Alberto Fornaro. business manager for the compounding channel at Kraton said, "the tough nut was to get the same performance in terms of temperature and compression set. Now also this is achieved." He added, "This is a four-party cooperation" indicating the project was shared among the customer, processor, compounder and materials supplier.

Durand said, "the car makers or Cooper would not have pushed the solution if it were only about cost — there are drawbacks in terms of investment risk, homologation and other areas. The main advantage of SEBS is that you can modify the design."

Benoit Burel, business development manager at CTS said the company has been working on this kind of system for around 10 years.

 Burel said the company first put an SEBS seal on a Suzuki model  and the most recent project had been the Peugeot 1007, but these had been normal SEBS compounds. He added. "today on TPE seals, Peugeot is the leader to replace EPDM seals with TPE."

The Peugeot 308 seal is made from a TPV-S based on an interpenetrating network of polypropylene and SEBS (TPV-S). The development is significant, said Burel, because previous applications had been aimed primarily at the French domestic market and in relatively low-end vehicles. The Peugeot 308, he said will be sold into Germany and other demanding markets and is aimed at a higher market segment.

Durand said, "if you speak about compression set, it will of course be easy to show that thermoset rubber is better in that characteristic, but in this case, the shape of the seals has been adapted to work properly with the TPE." He added, "it is important to pass the specification, and not more." He said, "When TPE first came into the market, the rubber people said that it is not good enough in these properties, but that was not true. It worked in some applications. What is important is to be at the right level in the right application."

Durand added that the TPV-S is in some respects better than a pure EPDM profile. He said stress-relaxation is a better measure than compression set. People who focus on compression set sometimes overlook the ageing performance of EPDM, he said. While TPV-S looks worse than EPDM initially, it is better in the long run, as the TPV-S material does not age in the same way. With an EPDM profile. he said, the sealing performance drops off after 24 hours or a couple of days. With the TPV-S, the performance looks lower initially, but after a week, the performance is in fact better than the EPDM materials.

Durand added that the gloss and appearance of the seal also remain constant over the life of the car. "At the start with EPDM you have the same colour and gloss, but after time, the compounds used in the EPDM seal for the extrusions and the corner mouldings, they change at different rates." By contrast, said Durand, all three CTS materials age at the same rate, so the appearance remains consistent over the life of the vehicle.

Burel said the 308 uses around 3 - 4 kg of static seals per vehicle, and the car is being made at a rate of around 2000 units per day, which adds to a significant volume of material. He said CTS has built a new compounding line to serve this need. The €3.5 million line was justified purely on the Cooper/Peugeot contract, but it still has some spare capacity after the contract has been met.