PAWTUCKET, RI, U.S.A., November 1, 2016: A new styrene block copolymer thermoplastic elastomer (TPE-S) for automotive interior parts such as cable ducts and grommets exhibits improved injection moldability compared with other elastomers while providing competitive physical properties and meeting stringent OEM requirements, it was announced today by Teknor Apex Company.
Sarlink® ML-2355B compound has been approved by VAG for cable ducts. Used to guide cables in their convoluted route through the spaces in pillars and other structures surrounding the passenger compartment, these ducts are complex parts with long flow paths and many undercuts, making them a challenge to mold and de-mold. Compared with other elastomers used for cable ducts, new Sarlink ML-2355B exhibits reduced viscosity for improved moldability, a wider processing window, and greater weld-line strength to facilitate air-assist de-molding. Unlike standard TPE-S compounds, it does not exhibit stress marks caused by deformation during mold release, and it avoids the de-molding difficulties posed by thermoplastic vulcanizates (TPVs) in parts with severe undercuts.
“The enhanced processability of Sarlink ML-2355B compound provides better surface quality than standard TPE-S materials and fewer sink marks, which exhibiting lower processing temperatures, faster cavity filling, and improved mold release,” said Jeffrey E. Dickerhoof, senior sales and marketing manager for the Thermoplastic Elastomer Division of Teknor Apex.
Sarlink ML-2355B TPE-S also provides numerous advantages over thermoset EPDM rubber, starting with a lower density that translates into 20% weight savings, plus the benefit—as a thermoplastic—of scrap recycling. “Processing improvements versus EPDM include shorter cycle times, easier processing of complex geometries, adhesion to polypropylene through two-component molding, and capability for robot-assisted de-molding, which is impossible with EDPM,” said Ger L. Vroomen, senior automotive market manager for Teknor Apex. “Sarlink ML-2355B compound also remains elastic over a broader temperature range and provides improved flex fatigue behavior.”
OEM part requirements for the VAG cable duct include an operational temperature range of -40 to 90°C; burning behavior meeting the TL-1010 flammability standard for passenger compartments; electrical insulation meeting specification PV 1015; a water-tight seal; and passage of natural weathering tests for one year in both hot and humid and desert-dry conditions. Minimum OEM material requirements for the application include odor and emissions, tensile strength and elongation, property retention after 90°C / 94 hrs. heat aging, and avoidance of cracks or surface changes after 150°C / 700 hrs. heat aging.
Sarlink ML-2355B TPE-S is a black 55 Shore A compound; other hardnesses are available. Teknor Apex can supply the compound worldwide.
Properties of the new compound in comparison with EPDM and TPV are shown below.
| TYPICAL PROPERTIES | TEST METHOD | EPDM RUBBER | HIGH-FLOW TPV | SARLINK® TPE ML-2355B |
|---|---|---|---|---|
| Hardness Shore A - Injection molded 1 in. | ISO 868 | 54 | 61 | 57 |
| Hardness Shore A - Injection molded 15 in. | ISO 868 | 51 | 57 | 52 |
| Density g/cc | ISO 1183 | 1.105 | 0.846 | 1.059 |
| Tensile strength (MPa) At break | ISO 37 | 12.0 | 4.0 | 5.3 |
| Tensile strength (MPa) at 500% elongation | ISO 37 | 1.0 | 2.0 | 1.7 |
| Elongation at break (%) | ISO 37 | 783 | 400 | 678 |
| Compression set (%) 22 hrs at 70°C | ISO 815 | 20 | 45 | 50 |
| Compression set (%) 70 hrs at 90°C | ISO 815 | 40 | 50 | 70 |
| Brittleness Point (°C) | ISO 812 | -52 (break) | <-60 (no break) | <-60 (no break) |
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