Bada AG BADAFLEX® SEBS-Comp. TPE-S 50A 1659 2K is a thermoplastic elastomer compound based on a styrene-ethylene/butylene-styrene triblock architecture. The hydrogenation of the butadiene-derived midblock distinguishes SEBS from unhydrogenated SBS and reduces the concentration of unsaturated double bonds that otherwise accelerate oxidative chain scission and UV degradation. The grade designation 50A nominally corresponds to 50 Shore A hardness evaluated according to ISO 48-4:2018 or ASTM D2240-15, typically within a ±5 Shore A production tolerance. The suffix 1659 2K identifies a two-component injection moulding variant, indicating that the compound is formulated for overmoulding onto polyolefin substrates, most commonly polypropylene. Published data for this specific configuration is limited; performance values in this document are therefore class-representative for Shore A 50 SEBS-based TPE-S two-component compounds unless a Bada AG certificate of analysis is cited.

Why Does Hardness Alone Fail to Define a Two-Component SEBS Compound?

Hardness is a frequently quoted property, but it does not provide a sufficient basis for selecting a two-component SEBS compound. Shore A values can be obtained from different formulation routes—paraffinic oil loading, styrenic block content, molecular weight distribution, and filler type—each of which affects tensile behaviour, tear resistance, compression set, rheology, and adhesion to polypropylene. In a SEBS network, the styrenic end-blocks form microphase-separated domains that act as physical crosslinks below the styrene glass transition temperature. The ethylene/butylene midblock provides elastomeric recovery above its glass transition. A Shore A 50 compound may therefore exhibit different adhesive behaviour depending on whether the hardness is generated by plastication, by higher styrene content, or by filler. For overmoulding applications, the relevant properties include melt flow index, tensile stress at 100 percent elongation, compression set under service temperature, and 90 degree peel adhesion to the substrate, none of which are captured by the hardness value alone.

The ranges in the table are not a substitute for the current Bada AG release data sheet. Lot-to-lot variance in SEBS compounds produced on twin-screw extruders with 40:1 L/D can shift tensile strength by ±1 MPa and elongation by ±50 %; therefore, incoming quality control should include rheological and mechanical testing after drying. For two-component production, the most sensitive parameters are interfacial adhesion and the viscosity match between first and second shot materials, because a viscosity mismatch beyond 20 % may cause flow marks, knit lines, or substrate deformation.

Pre-drying is required when pellets have been exposed to ambient humidity above 60% RH or when packaging has been open for more than 4 h. A desiccant dryer set to 60–80 °C for 2–4 h with a dew point of -20 °C or lower prevents surface splay, hydrolysis of adhesion modifiers, and inconsistent shot-to-shot viscosity. Barrel temperature profiles of 180–230 °C from feed throat to nozzle are class-representative for SEBS TPE-S compounds of this hardness; the nozzle and hot-runner manifold should be held toward the lower end to avoid thermal degradation of the hydrogenated midblock and additive migration. Mold temperatures of 20–50 °C are common, but the substrate-facing cavity wall may require higher heat input to promote adhesion. Back pressure of 0.5–2.0 MPa and screw rotation speed of 60–120 min⁻¹ are typical starting points; specific machine conditions must be developed on a production-scale injection moulding machine with a shut-off nozzle and a two-shot barrel arrangement.

Processing Envelope, Rheology and Two-Component Bonding

SEBS TPE-S melts exhibit pronounced shear thinning. Capillary rheometry according to ISO 11443:2021 on class-representative Shore A 50 SEBS compounds reveals apparent viscosity decreasing from roughly 250–500 Pa·s at 100 s⁻¹ to 50–120 Pa·s at 1000 s⁻¹ at 230 °C. Published data for the 1659 2K variant is limited; the range is therefore not a specification. For filling thin-wall sections below 1.5 mm, high shear rates occur at the gate, and shear heating can produce local temperatures 10–20 °C above set values. Hot-runner systems should use heated sprue bushings rather than unheated torpedoes, and gate diameters below 0.8 mm are generally avoided to limit excessive shear and surface streaking.

Injection moulding machines used for two-component SEBS overmoulding are typically equipped with a rotary platen, core-back tooling, or transfer tooling. The clamp force requirement is commonly estimated at 0.5–1.0 kN/cm² of projected part area for class-representative SEBS TPE-S compounds, although mould complexity, wall thickness, and flow length change the pressure integral. Transfer from the first shot to the second shot should be kept short to minimise substrate cooling; PP substrates below 80 °C at the interface often show reduced peel adhesion because limited interdiffusion and recrystallisation occur before wetting is complete. Conversely, substrate surface temperatures above 120 °C can soften thin PP walls and cause sink marks or weld line separation.

Adhesion in two-component SEBS/PP systems is generally attributed to interdiffusion of the amorphous EB midblock with the PP melt and mechanical interlocking in the semi-crystalline surface. The 2K designation indicates that the compound may include a compatibilizing additive or tailored molecular weight distribution; however, the manufacturer does not disclose the formulation. Contamination by mould release agents, fingerprint oils, or condensation disrupts the interface. In production, robotic end-of-arm tooling, flame treatment of the substrate, or plasma treatment is sometimes used, but Bada AG application data should be consulted for the 1659 2K grade.

Production-scale failure modes observed in class-representative SEBS TPE-S two-component moulding include delamination at the gate perimeter when PP substrate temperature drops below 80 °C, gloss variation caused by local shear heating above 230 °C, and splay caused by moisture above 0.05% by weight. Mould release agents that contain silicone or fluoropolymer can reduce peel adhesion below 1 N/mm; aluminium tools with high thermal diffusivity may need mould insulation or cartridge heaters to maintain substrate interface temperature. These observations are not unique to Bada AG BADAFLEX® SEBS-Comp. TPE-S 50A 1659 2K but apply broadly to two-component SEBS/PP systems.

Compared with an SBS-based TPE-S of equal Shore A 50, BADAFLEX® SEBS-Comp. TPE-S 50A 1659 2K offers improved resistance to thermo-oxidative breakdown because the hydrogenated midblock lacks the 1,4-butadiene double bond. This difference is measurable as lower gel formation during prolonged melt residence and better retention of elongation after outdoor exposure; the relevant accelerated weathering standard is ISO 4892-2:2013 for xenon-arc exposure. Compared with TPU of comparable hardness, the SEBS compound has lower density, lower abrasion resistance, better hydrolytic stability, and generally lower adhesion to polar substrates; TPU is selected when abrasion or oil resistance is required, but it often requires more intensive drying at 80–110 °C. Compared with TPV, the SEBS compound offers easier flow at low shear, softer feel, and lower compression set at room temperature but typically lower hot-oil resistance and lower service temperature; TPV is preferred for continuous service above 135 °C in air, while SEBS grades are generally not recommended above 105–120 °C in continuous load. Compared with silicone elastomer, SEBS TPE provides recyclability, lower raw material cost, and better colour consistency, but it does not match low-temperature flexibility below -60 °C or high-temperature resistance above 150 °C. These comparisons are class-level and should not be read as specifications for the 1659 2K variant.

When the Melt Contacts PP Substrates During Overmoulding

Interfacial bonding is not instantaneous. The melt must wet the substrate, swell the amorphous PP surface, and penetrate the crystallite boundary regions before cooling freezes the interface. If the second-shot melt temperature is below 200 °C or the substrate surface temperature is below 80 °C, peel strength to PP often falls into the low end of the 1–4 N/mm range typical for class-representative SEBS compounds; with interfacial temperatures above 110 °C and sufficient hold pressure, values can exceed 5 N/mm in 90 degree peel tests. Published data for this specific product is limited, so these values are process-design estimates and not release limits. The moulding sequence should avoid injecting the SEBS melt against a PP surface that has already been ejected and reinserted, because oxidative ageing and surface hydrocarbon contamination reduce reproducible bonding.

Thin PP substrates require balancing the melt temperature and the substrate thermal mass. If the substrate is below 1.5 mm, the second-shot heat may deform it; reducing melt temperature to the lower end of the barrel profile can preserve dimensional stability but may reduce bond strength. In such cases, substrate pre-heating is used rather than raising the SEBS melt temperature. Plasticizer oil migration in SEBS compounds can also alter adhesion and surface feel. Low-molecular-weight paraffinic oil can migrate to the interface and create a weak boundary layer; therefore, the adhesion-modified 1659 2K grade is likely formulated with controlled oil loading or a higher-molecular-weight midblock. The exact formulation is not disclosed. Haze, tack, and paintability are influenced by oil type; for unpainted soft-touch parts, surface smoothness should be monitored.

Compliance testing for this grade must be obtained from Bada AG because regulatory status depends on the specific pigments, stabilization package, and feedstock lot. The following checklist is a structural framework, not a declaration of conformity.

Stabilizers and pigments can alter compliance status; therefore, the specific 1659 2K colour batch must be confirmed by the supplier for the intended use. Hydrogenated styrenic block copolymers are not considered biodegradable; disposal should follow local industrial waste regulations.

Production-scale experience on two-shot rotary injection machines has shown that interruption of the second-shot injection for more than 10 min can require purging because the melt in the hot runner becomes increasingly viscous; this behaviour is common for SEBS compounds with high oil content. Gate freeze time for two-component SEBS TPE-S is often short, and hold pressure must be transferred before gate solidification. For Bada AG BADAFLEX® SEBS-Comp. TPE-S 50A 1659 2K, specific gate dimensions, hot runner temperature, and substrate pre-heating should be fixed by a processing window study using the current production lot.