Tepex: An Ideal Flame Retardant Material

Thanks to its special semi-finished structure, the continuous fiber-reinforced thermoplastic composite material Tepex also shows good fire-resistant performance even if it does not contain flame retardant additives.

Dr. Stefan Seidel, Head of Research and Development at Bond-Laminates, said: “The test also shows that our composite materials are very suitable for the structure and housing parts of high-voltage batteries for electric vehicles. For safety reasons, these parts need to have excellent flame retardant properties. This type of material is a lightweight alternative to aluminum and can provide a cost-effective component solution. This is due to the hybrid molding method that can bring various functions together and thereby reduce costs. The processing method is simple, needing no rework.”

The major test purpose in United States Federal Motor Vehicle Safety Standard FMVSS 302 (Federal Motor Vehicle Safety Standard) is to define the combustion characteristics of materials in automotive interiors, such as burning speed. In the test, the non-flame retardant Tepex performed well. The material was indeed ignited, but within the preset test time, the flame hardly spread outward.

At the same time, according to the provisions of UN 180,6.2.4, a brazier test is performed on the non-flame retardant Tepex. Place the test sample flat on the burning fuel, directly expose it to the fire for 70 seconds, and indirectly expose it to the fire for 60 seconds. This test truly simulates the fire conditions that Tepex may face in typical applications, such as underbody paneling components.

As Seidel said: “In these two tests, there were no holes in the composite material, and the fibers were not burned.” The plastic did not show any drip burning, and the test piece itself went out. “The reason for the flame retardant properties is that the content of flame retardant continuous fibers is high and the proportion of flammable plastics is relatively low.

In addition, the UL 94 test conducted did not provide any reliable basis to explain the actual fire behavior of Tepex. The reason is that the vertically fixed specimen is exposed to the flame from the edge. Seidel said: “This method is not consistent with the typical Tepex installation. Usually, our composite material undergoes overmolding and reinjection processes, which can prevent the flame from entering the fiber end.”

Bond-Laminates provides halogen-free flame retardant Tepex materials based on polyamide, polycarbonate and polyphenylene sulfide for applications requiring mandatory V-0 classification. For example, the polycarbonate product types are listed as V-0 on the UL yellow card, and the sample thickness is between 0.4-2.2mm.

In the electric vehicle power system, the potential application ability of Tepex material is great. Bond-Laminates comprehensively studies the combustion behavior of the Tepex material based on second-injected polyamide 6 through its own testing device. The “HiAnt carrier” used in the test is a U-shaped profile made of Tepex, the inside of which is reinforced by various transverse ribs made of polyamide 6, with or without flame retardant packaging. The actual test sample was exposed to 6 positions in a flame at 900°C for 30 seconds to 5 minutes, for example, on a polyamide rib or where it has not been repeatedly molded.

In this test, the non-flame retardant Tepex material once again confirmed its excellent fire performance. After five minutes of flame treatment, only the part without a special flame retardant of the molded rib material got burned. In contrast, if ribs and second-moulded areas made of tested flame-retardant polyamide are used, the flame in the flame treatment area will not spread, but will extinguish when the burner is removed. Seidel said: “For the design of flame-retardant components, combining non-flame-retardant Tepex with flame-retardant injection molding materials can provide a very large safety factor. We have seen the great potential of this material combination for high-voltage battery components such as housings and partitions, can also be applied to the floor of induction battery charging systems.”