MATERIALS | THERMOPLASTIC ELASTOMERS
Right: Hexpol Dryflex HiF TPE skin and PP carrier back-foamed with PUR
says Global R&D Manager Klas Dannäs. “We continue to trial new and emerging raw material combinations.”
Sustainability also figures strongly in the story of
Kraton Corp’s development of its IMSS (Injection Moulded Soft-Skin) technology. A few months ago, it announced the first commercial application of IMSS in an automotive application – the instrument panel on the 2021 Buick GL6, built for the Chinese market by SAIC-GM, the Chinese joint venture between General Motors and SAIC Motor Corp. IMSS technology is based on ultra-high flow
hydrogenated styrenic block copolymers (HSBCs). Kraton says it allows injection moulding of large, thin-walled soft skin parts and also provides lower odour, fogging, VOCs, better aging, subsequently improved safety performance, and lower specific gravity than commonly used PVC soft skins. Kraton unveiled the technology a few years ago (see TPE feature in Injection World May 2018).
Below: Prototype instrument panel skin injection
moulded in a compound based on Kraton IMSS technology
Soft skin Kraton says the production of instrument panel soft skin with an injection moulding process can help automotive interior manufacturers avoid the high-cost, labour-intensive, and energy-consuming slush moulding process. Additionally, the injection moulding equipment offers higher efficiency, lower cost, and less energy consumption. The time needed for making an IMSS skin by injection moulding can be as low as one-fifth of that required for making a PVC soft skin of similar size by slush moulding. Injection moulding tools last longer than electroformed slush moulds, and Kraton claims development and manufacturing costs of IMSS skins are lower than PVC slush. The IMSS compound used to manufacture the Buick GL6 instrument panel soft skin was devel- oped and is supplied by Dawn New Materials in China. The company worked in close cooperation with Kraton as a technology transfer licensee of the IMSS technology. Kraton is also working on establishing technology licences with several
other compounders worldwide. One such compounder is Hexpol TPE. It recently launched the Dryflex HiF family of very high melt-flow and scratch resistant TPS-SEBS materials, incorporating Kraton IMSS technology. Hexpol says the grades open possibilities to produce large scale parts via injection moulding, including automotive interior surfaces, trims, and skins. Group product manager Dr. Thomas Köppl says:
“Until recently, TPEs have not been viable for large scale trim because these applications have much higher specifications regarding abrasion behaviour, processability and heat resistance. The new Dryflex HiF TPE grades fulfil these requirements and are injection mouldable, making them an interesting alternative to PUR coating, PVC slush moulding or TPO foil processes.” Hexpol has carried out a production trial in which 1.1 mm thin skins for the soft surface of a complete instrument panel were successfully injection moulded and back-foamed with PUR. According to Köppl, testing demonstrates that
Dryflex HiF TPEs pass the stringent lightfastness and heat resistance requirements for instrument panels (for example 120°C for 1,000 hours). “A low-gloss, matt surface with no visible weld lines is achievable as well as the moulding of different leather grains. Surface performance is confirmed by the testing of Erichsen scratch resistance and Crock abrasion. The lower density of Dryflex HiF TPEs (0.9 g/cm3
) can decrease part weight.”
Dryflex HiF TPEs can be used in multi-compo- nent applications with direct over-moulding to PP. Compared to existing TPU or PUR-RIM processes, which often use PC/ABS as the rigid component, the material’s ability to adhere to PP can deliver further cost and weight reduction in 2K processes, Köppl concludes. For automotive applications mostly under the
20 INJECTION WORLD | May 2021
www.injectionworld.com
IMAGE: KRATON CORP
IMAGE: HEXPOL TPE
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