Bada AG BADAFLEX® SEBS-Comp. TPE-S 65A 1938 EX is a thermoplastic elastomer compound based on a hydrogenated styrene-ethylene/butylene-styrene block copolymer. Under ISO 18064, the designation TPE-S identifies a styrenic block copolymer thermoplastic elastomer; the hydrogenated midblock separates SEBS from unsaturated SBS grades and provides improved resistance to oxidative, ozone, and ultraviolet degradation. The nominal hardness is 65 Shore A when measured according to ISO 48-4 or ASTM D2240 using a standard test plaque and dwell time. The EX suffix identifies an extrusion-oriented melt-viscosity envelope within the BADAFLEX TPE-S range, with flow characteristics adjusted for profile, tube, sheet, and cable jacket die stability rather than thin-wall injection moulding. The designation 1938 refers to the Bada AG internal formulation code and should be cross-referenced against the manufacturer’s technical datasheet and batch certificate of analysis. Published data for this specific configuration is limited; therefore, the following statements summarise the general behaviour of SEBS-based TPE-S compounds at this hardness and the processing constraints relevant to extrusion-grade conversion.

What distinguishes the 65 Shore A extrusion grade within the BADAFLEX TPE-S series?

Compared with injection-moulding-oriented TPE-S grades at similar hardness, the 1938 EX variant is formulated for higher melt strength and lower die-swell fluctuation during continuous extrusion. Thermomechanical behaviour is controlled by phase-separated morphology: styrenic endblocks with a glass-transition temperature of approximately 95 °C form physical crosslinks, while the ethylene/butylene midblock with a glass transition below −50 °C supplies elastomeric recovery. In profile and annular dies, this morphology produces shear-thinning behaviour that reduces pressure drop at high wall shear rates but retains enough extensional viscosity to resist sagging immediately after the die lip. Consistent melt pressure before the breaker plate is more decisive than absolute viscosity. A screen pack of 60/100/60 mesh can reveal gel agglomerates, unmelts, or filler accumulation through pressure-rise rate; pressure drift of 0.5 MPa to 1.0 MPa across a clean screen pack is often considered normal during start-up, while larger excursions indicate poor homogenisation. The EX grade is not interchangeable with standard injection-moulding SEBS grades if the application requires tight weld-line aesthetics or high-flow thin-wall filling, because extrusion-optimised molecular weight distribution typically favours higher die swell and lower spiral flow.

Melt Filtration, Predrying, and Extrusion Screw Design

Industrial processing of the 1938 EX grade on single-screw extruders with an L/D ratio of 25:1 to 30:1 and a barrier or Maddock mixing section is appropriate for most profile and tubing operations. Barrel profiles commonly begin at 150 °C to 170 °C in the feed zone and rise to 180 °C to 210 °C at the die; exact set points are dependent on screw speed, die resistance, melt pressure, and downstream pull ratio. SEBS compounds are not hygroscopic in the manner of TPU or polyamide, but surface moisture on pellets stored in cold or high-humidity conditions can generate splay, surface roughness, and dimensional instability in extruded profiles. Predrying at 60 °C to 80 °C for 2 h to 4 h is advisable when pellet packaging has been opened for extended periods or when vacuum venting is unavailable. Extruders without venting can tolerate lower moisture only if pellets remain sealed until use and hopper temperature is maintained below the dew point of the surrounding air. Melt temperatures above 230 °C can shift the styrenic endblock network and cause viscosity loss, while temperatures below 160 °C may produce surface melt fracture in high-drawdown profiles. Die swell should be controlled through melt-temperature adjustment rather than increased screw speed alone, because shear heating in the metering zone can create a non-uniform melt stream even when the die pressure appears stable.

Vacuum venting at −0.08 MPa to −0.09 MPa gauge is often used to remove low-level volatiles and processing oil decomposition products. If the compound is run on a twin-screw compounding line for masterbatch addition, specific energy input must be controlled to avoid excessive chain scission. Production-scale experience with SEBS extrusion grades indicates that repeated reprocessing of regrind above 20 wt% can reduce melt strength and alter die swell even when hardness and tensile values remain within specification. Regrind should be introduced as a uniform melt stream with controlled particle size, and closed-loop dosing is preferred over manual addition to avoid surging.

Application Envelopes in Sealing, Grip, and Flexible Connection Parts

The material is intended for continuous profiles, flexible connectors, gaskets, edge protection strips, cable jackets, soft-touch grips, and anti-slip surfaces that require elastic recovery, colourability, and low-gloss finish. In sealing applications, compression set measured under ISO 815-1 or ASTM D395 is a deciding parameter. SEBS compounds at 65 Shore A typically exhibit compression set at 70 °C for 22 h in the range of 25% to 45% depending on oil type, endblock content, and filler package; published data for this specific configuration is limited and should be established on the finished gasket geometry. Styrenic endblock content governs the upper service temperature and set resistance. Lower endblock content improves elastic recovery but reduces tensile strength, while higher endblock content raises hardness and service temperature. In grip applications, the coefficient of friction is dominated by surface topography and secondary finishing; no single coefficient is specified for the unfilled 1938 EX compound because final texture and mould release residues control tactile behaviour. The compound is generally colourable, and low-volatile formulations may be evaluated for automotive interior components under VDA 278 or VDA 270 on the fabricated part. For food-contact uses, conformity to European EU 10/2011 and US FDA 21 CFR 177.1810 is formulation-dependent and must be declared by Bada AG in writing; the base SEBS polymer class is recognised in those frameworks, but processing oils and additives determine the migration profile. In cable jacket applications, low-temperature flexibility below −40 °C and torsional recovery are usually more relevant than tensile strength, and dynamic cable fatigue testing under the intended bend radius should accompany any material substitution.

For overmoulding on polypropylene or polyethylene substrates, mechanical interlocking or melt bonding is generally favoured over adhesive bonding. The processing window depends on the substrate surface temperature and the time available for interfacial diffusion. Overmoulding onto polar substrates such as PC/ABS or polyamide normally requires independent bonding validation because SEBS does not develop intrinsic polar adhesion. In insert moulded grips, venting and uniform melt arrival are more critical than high hold pressure; the low viscosity of SEBS at melt temperature can lead to flashing if tool maintenance tolerances are poor.

When hot-runner or high-shear moulding conditions are imposed

Although the EX designation identifies extrusion, the grade may be converted by injection moulding only after evaluating shear heating at the gate and hot-runner manifold. SEBS compounds exhibit pseudoplastic flow, and shear rates in a hot runner can exceed 10 000 s⁻¹, producing melt-temperature overshoot of 10 °C to 20 °C above the barrel setting. The resulting viscosity reduction assists filling but can degrade melt strength and produce jetting or gate blush. Clamp-force calculation should be based on projected cavity area and a cavity pressure of 0.35 MPa to 0.70 MPa at the gate, not on injection pressure at the barrel. Hot-runner systems must avoid dead spots that can generate black specks from over-residence. Open nozzles with positive shut-off are preferable, hold pressure is often set at 50% to 80% of fill pressure, and decompression distance should prevent drool without sucking air into the melt. Part ejection may require a draft angle of 1° to 3° and a release system selected from polyolefin or fluorinated mould releases to reduce surface tack. In comparison with SBS compounds, the hydrogenated SEBS midblock allows longer hot-runner residence without extensive cross-linking or odour, but maximum residence time should still be validated by colour drift and melt-pressure stability. When the material is run as an extruded profile that is later injection overmoulded, the interface temperature must exceed the styrenic endblock softening point long enough to form a cohesive bond; line speed and post-mould cooling should be controlled to prevent interfacial stress whitening.

Comparative Test Methods and Alternative TPE Chemistries

Under tensile testing according to ISO 37 or ASTM D412, SEBS grades at 65 Shore A often show anisotropic behaviour after orientation in a die; extrusion direction can display higher tensile strength than transverse direction. In contrast, TPVs at similar hardness usually show better compression set but narrower processing windows and may require higher melt temperatures. TPU offers higher tensile and abrasion resistance but introduces moisture sensitivity, higher density, and greater processing complexity. Silicone offers superior high-temperature properties but cannot be reprocessed by conventional thermoplastic extrusion. SBS may be lower in cost but is less resistant to ozone and oxidative embrittlement over time. Flexible PVC can be substitution-prone because of phthalate and volatile concerns, but SEBS differs in surface energy, weldability, and flame behaviour. The table below identifies the standard-test framework used for incoming inspection and material substitution evaluation.

Substitution from cross-linked TPV to SEBS often improves weld-line strength and regrind recovery but may reduce resistance to hot oil and hydrocarbon fluids. When replacing flexible PVC, the SEBS compound offers phthalate-free softness and lower weight, but the conversion requires re-validation of print adhesion, solvent bonding, and flame behaviour. In comparison with SBS, the hydrogenated midblock in SEBS reduces ozone-induced chain scission and preserves elongation after prolonged UV exposure; nevertheless, SBS may be adequate for indoor grip applications where oxidative stability is not critical. No single hardness value should be used to infer performance. Tensile modulus at 100% elongation under ISO 37 should be compared because the shape of the stress-strain curve controls handle feel and recovery in the final part.

Operational Boundaries and Incompatibilities

The grade should not be exposed continuously to aromatic solvents, chlorinated hydrocarbons, or strong oxidizing acids; swell and extractable loss can occur. Adhesion to rigid substrates is often achieved by mechanical interlocking, insert moulding, or polyolefin tie layers rather than conventional solvent welding. Although SEBS offers good hydrolysis resistance compared with TPU, prolonged immersion in hot water above 60 °C can extract process oils and increase hardness. The working life of extruded profiles exposed to cyclic compression should be established by dynamic mechanical fatigue testing at the expected strain amplitude; static tensile data under ISO 37 do not predict crack initiation rates under repeated flexing. Avoid combination with amine-based additives or aggressive peroxide initiators because radical processes can destabilize the endblock network and produce odour or melt-index drift. Processing with high levels of polyolefin regrind can reduce clarity, increase surface haze, and alter elastic recovery in a hardness-dependent manner. For outdoor applications, stabiliser content should be confirmed through accelerated weathering under ISO 4892-2 or ASTM G155 on the actual profile, because colour pigments can mask early surface cracking.

Batch release for the 1938 EX grade is based on melt-viscosity curve superposition, Shore A hardness, tensile strength, elongation at break, density, and ash content. Incoming inspection should compare the supplier’s certificate of analysis against a retained reference compound because oil and filler batch variations can alter die swell even when hardness and tensile values remain within specification. Processing records from compounding are typically controlled within a defined specific energy input; excessive shear during pelletizing can shift the effective viscosity envelope and produce inconsistent drawdown in downstream extrusion. Published data for this specific configuration is limited, and site-specific machine trials remain necessary for new die geometries, high-line-speed cable jacketing, or closed-loop regrind incorporation above 20 wt%.