MATERIALS | THERMOPLASTIC ELASTOMERS


Right: Components in car HVAC vent systems are a target for Hexpol Dryflex grades


other TPEs for interior applications on the market, Hexpol says. They display low odour with results 2.0 to 3.0 in standards such as VDA 270. According to gravimetric fogging standard ISO 6452, conden- sate levels are under 1.0 mg, while VOCs measured in the VDA 278 thermodesorption test are between 60 and 120 µg/g; fog is from 200 to 600 µg/g. Dryflex Interior TPEs have passed additional interior tests for lightfastness, flammability and mechanical performance, the company notes. Good flow properties make possible finely struc- tured surfaces and complex geometries in part designs. Available in customer specific colours as well as black and natural, they are currently offered in hardnesses between 25 and 85 Shore A. Thomas Köppl, Group Product Manager at


Hexpol TPE, says that for seals in HVAC systems, soft TPEs in the range of 25 to 60 Shore A are often used. This low hardness is necessary to ensure a reliable seal and to avoid rattling noises (a growing requirement with the move to EVs, he notes). The materials and components need to withstand high mechanical and thermal loads, and mechanical properties must not change appreciably, even after 1,000 hours at 90°C. The finished components must also function properly at both high and very low temperatures. This includes noiseless opening and closing of the vents, as very soft materials could produce noises as a result of sticking to the hard component. Hence the need for materials that do not become tacky, regardless of the temperature. Additional mechanical properties include low


compression set (typically <50% after 22 hours at 70°C) and tensile properties such as high flexibility, tensile strength and tear resistance. Components must withstand long-term cyclical loads, with no cracking after frequent loading and unloading. Lubrizol Engineered Polymers says it is working on a novel technology to obtain thermo- plastic polyurethanes (TPUs) with low volatiles. It cites a new 85 Shore A material which is designed to achieve extreme low emissions in accordance with VDA 278 (see table below). Lubrizol says the material offers an adequate hardness, as well as excellent mechanical proper-


Gravimetric Fogging (ISO 6452), mg


Standard TPE Low VOC TPE


Low VOC 85 Shore A TPU


1.0-2.0 0.3-0.7 0.5


*VDA 278 requirements: VOC ≤ 100 µg/g; FOG ≤ 250 µg/g. Source: Lubrizol Engineered Polymers


20 INJECTION WORLD | May 2019 www.injectionworld.com


ties (36 MPa tensile strength, 593% elongation at break) and flow. A similar grade from the same Pearlthane series is being used in rolling shutters in centre consoles in automotive. The TPU is over- moulded on top of ABS. Its fast processing proper- ties are essential in this case, the company says. Away from automotive, Teknor Apex late last


year introduced a new series of styrenic TPEs that provide the surface appearance and haptics of silicone rubber, which exhibit lower compression set than standard TPS compounds, withstand temperatures in excess of 100°C, and provide chemical resistance for food-grade, cosmetics, and other regulated applications. Monprene RG-15100 Series TPEs meet US and


EU regulations for single- and repeated-use applications with dry, acidic, aqueous, and alco- holic food types. Shore A hardnesses range from 30 to 80, and all grades are translucent. The compounds are suitable for injection moulding and extrusion applications such as: utensil grips; kitchen appliance seals, gaskets, and tubing; food-saver container seals; dropper bulbs; and cosmetics applications. These TPEs can be used with containers that must be microwave- and dishwasher-safe. They may be two-component moulded with polyolefins. “Pre-compliance with regulations accelerates our customers’ speed to market with new prod- ucts,” says Christopher Smith, senior market manager for the Thermoplastic Elastomer Division


VDA 278 VOC, µg/g *


120-400 60-120 100


VDA 278 FOG, µg/g *


2000-3000 200-2000 153


PHOTO: HEXPOL TPE


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