API Megol AM SEBS-Comp. SV/PS is an SEBS-based thermoplastic elastomer compound supplied under the Megol brand. The SV/PS suffix designates a low-gloss tactile surface variant with a polystyrene adhesion package; public documentation for this specific configuration is limited, and the suffix decode should be confirmed against the release datasheet. Published data for SEBS compounds with comparable styrenic block architecture place density between 0.89 g/cm³ and 0.91 g/cm³ per ISO 1183-1, hardness between 40 Shore A and 70 Shore A per ISO 868, and tensile strength from 3 MPa to 8 MPa per ISO 37. The material is supplied as a pelletised injection-moulding and overmoulding compound intended for bonding to amorphous polystyrene. Because the grade is a compounded TPE-S rather than a reactor TPE, its hardness, flow, and adhesion properties are adjusted by blending styrenic block copolymer with process oil, polystyrene, or polypropylene modifiers. Production engineering is therefore constrained by processing boundaries, adhesion mechanics, and comparative property data.

Why Does the SV/PS Designation Alter Substrate Fusion Layer Behaviour?

The PS suffix indicates an adhesion-modified SEBS compound formulated to bond to polystyrene substrates without an external primer. In overmoulding, a fusion layer forms when the SEBS melt at the interface is maintained above the glass transition temperature of the PS insert, typically 95–105 °C for general-purpose polystyrene. The melt front must retain enough thermal energy for chain interdiffusion across the interface. At a nozzle temperature of 200 °C and a mould cavity steel temperature of 35–45 °C, peel strength values for comparable SEBS/PS pairs are reported between 8 N/mm and 12 N/mm under ISO 813. Below the PS glass transition, adhesion is dominated by mechanical anchoring rather than diffusion and is significantly lower. The SV surface attribute is associated with reduced 60° gloss, typically below 2.0 GU measured per ISO 2813, and with a dry static coefficient of friction of 0.6 to 1.0 per DIN EN ISO 8295. These values are drawn from general styrenic TPE literature and should not replace datasheet verification for release-lot material.

Twin-screw compounding of SEBS soft-touch grades typically uses co-rotating extruders with L/D ratios of 40:1 to 52:1. The SEBS polymer is fed into the first barrel section, process oil is injected downstream, and mineral fillers or polypropylene are added through side feeders. Shear heating in kneading blocks may raise melt temperature by 8–15 °C above the barrel setpoint when screw speed exceeds 400 min⁻¹. This thermal history affects the styrenic domains: excessive temperature degrades the polystyrene end blocks and lowers tensile strength, while insufficient temperature leaves oil poorly dispersed and creates surface streaks. Production experience shows that purging with polypropylene or low-density polyethylene at 200 °C prevents cross-contamination. PVC or acetal residues should be removed before running SEBS because acidic decomposition products from these polymers can destabilise the hydrogenated midblock.

When Polystyrene Substrate Melt Tracks Exceed 15 mm in Overmoulding

Overmoulding PS inserts with SEBS compounds is sensitive to flow length because the melt cools rapidly against the lower-temperature insert. In a thin-wall section of 2.0 mm, the practical flow path for a 50 Shore A SEBS compound is generally 80–120 mm at an injection velocity of 40–80 mm/s and a melt pressure of 10–20 MPa. When the melt track exceeds 15 mm in a gate-detached area, packing pressure decays and the characteristic velvet texture may become non-uniform. Injection-moulding work should follow ISO 294-1:2017 for specimen preparation and process stability. Clamp force for SEBS soft-touch moulding is normally calculated at 0.4–0.6 tonnes per square centimetre of projected area. For a projected area of 100 cm², the required clamp force is 40–60 t. Holding pressure is kept at 50–70% of peak injection pressure to avoid sink marks without overpacking the soft material. Gate dimensions for TPE-S grades are larger than those for rigid PS; a tab gate thickness of 0.8–1.5 mm is typical for soft-touch applications.

Values in the table are representative published ranges for comparable soft-touch grades, not OEM release specifications for this compound. Lot-specific certificates remain the authoritative source for production validation.

Regulatory status for SEBS-based soft-touch compounds is application-dependent. EU single-market placement requires REACH registration for all constituent substances; electrical and electronic applications are evaluated under RoHS Directive 2011/65/EU including the delegated directive (EU) 2015/863 phthalate restrictions. Food-contact uses may be supported by FDA 21 CFR 177.2600 when the specific grade and colourants are approved for repeated contact with aqueous and fatty foods. Skin-contact applications require biocompatibility data according to ISO 10993-5 for cytotoxicity and ISO 10993-10 for irritation and sensitisation. These references describe the general compliance framework for SEBS compounds; a certificate of compliance for the SV/PS grade remains mandatory before production release.

Rheology, Hardness, and Overmolding Window Boundaries

Melt mass-flow rate for SEBS injection-moulding grades measured under 230 °C and 2.16 kg piston load per ISO 1133-1:2022 is generally 1–10 g/10 min. Apparent viscosity at 1000 s⁻¹ and 200 °C falls between 50 Pa·s and 150 Pa·s for many soft-touch grades. Barrel temperature settings below 180 °C are not recommended because the styrenic domains do not fully soften and surface roughness remains high. Above 240 °C, thermo-oxidative degradation becomes time-dependent, and melt residence is limited to 4–6 min. Mould temperature is set at 20–50 °C; higher mould temperatures above 45 °C improve molecular contact with the PS insert but can raise gloss beyond the SV surface specification. Pre-drying at 80 °C for 2 h is recommended when moisture content exceeds 0.05% by weight per ISO 15512 or when storage relative humidity has exceeded 60%. The narrow processing window for soft-touch adhesion is therefore controlled by a combination of barrel profile, injection speed, and mould steel temperature.

Thermal Stability Falls Off Above 240 °C Melt Residence

Thermal degradation of SEBS compounds under injection moulding is not linear. At melt temperatures above 240 °C, the stabiliser package is consumed and oxidative chain scission accelerates. Yellowness index, measured by ASTM E313, may increase by 2–4 units after 8 min at 245 °C. This is accompanied by a drop in apparent viscosity and a loss of tensile strength of 10–20%. Moulders should therefore maintain shot size between 30% and 80% of barrel capacity, use back pressure no higher than 10 bar, and reduce screw rotation speed to 80–120 min⁻¹ during recovery. If a line stoppage exceeds 5 min, the barrel should be set back to 160 °C or purged with polypropylene. These limits are standard for SEBS soft-touch grades; a validated thermal stability study on the SV/PS compound is required for critical applications.

Compared with olefinic thermoplastic vulcanisates, SEBS compounds do not require vulcanization and can be reground. TPVs generally show lower compression set at 100 °C, often 25–40% per ISO 815-1, while SEBS soft-touch grades may exceed 50%. SEBS offers lower density and no cure-system odour. Compared with aliphatic TPU, SEBS has lower abrasion resistance and lower tear strength but provides better hydrolysis resistance and lower hardness without plasticiser migration. Compared with silicone-based elastomers, SEBS cycles faster in injection moulding but has lower continuous-use temperature. Within the Megol SEBS range, the SV/PS variant is distinguished by its adhesion package for untreated PS substrates; general-purpose Megol SEBS grades may require a primer or a different insert material for equivalent peel strength. The choice should be validated by peel testing on the actual insert geometry under production conditions.

Mould design for SV/PS overmoulding requires gates positioned away from visible surfaces to reduce flow marks. Vent depths for SEBS compounds are typically 0.02–0.05 mm for soft-touch surfaces; deeper vents cause flash. Ejection systems require large-diameter pins and stripper plates because soft-touch compounds deform at ejection temperatures. Mould release agents should be avoided because they reduce bond strength to PS. If a release agent is used, isopropyl alcohol cleaning of the PS insert is required before overmoulding. Shrinkage for SEBS compounds is anisotropic and depends on flow direction; values from 1.2% to 1.8% are typical, measured per ISO 294-4. Warpage in PS overmoulded parts arises when unequal shrinkage between the hard substrate and the soft layer exceeds 0.5% differential. These design constraints apply to SEBS-based soft-touch grades and are relevant to SV/PS processing.

The compound should not be blended with high-styrene-content rigid PS scrap above 10% because this raises hardness and reduces bond flexibility. Avoid addition of free aromatic phosphate flame retardants above supplier limits because they may migrate to the PS interface and reduce adhesion. Halogenated flame retardants that generate acidic degradation products are incompatible with the hydrogenated midblock. Pigments containing zinc stearate can alter surface gloss and may require revalidation of the SV surface effect. These incompatibility boundaries come from general SEBS compounding practice and should be checked against the supplier’s formulation constraints for the specific grade.

Batch-to-batch variation in SEBS soft-touch compounds is observed when process oil is not fully absorbed. In production, oil migration to the surface produces a sticky feel and reduces the coefficient of friction. This is typically caused by oil addition rates above 30 phr or by screw residence time below 20 s. Melt-feeding problems in twin-screw compounding also arise when the SEBS crumb is not pre-blended with powdered additives. On injection moulding lines, colour streaking can occur when the screw L/D is below 20:1 because the colour concentrate is not sufficiently distributed. These are field observations from SEBS soft-touch processing and may affect SV surface quality specifically because low-gloss, velvet textures expose streak defects more visibly than high-gloss surfaces.

Adhesion failure in PS overmoulding is classified as adhesive if separation occurs at the SEBS–PS interface or cohesive if fracture occurs within the SEBS layer. Peel tests according to ISO 813 are used to distinguish the modes. When cohesive failure is observed, the bond is considered adequate and design changes focus on soft-layer tear resistance. When adhesive failure occurs, the usual corrective sequence is to raise melt temperature by 5–10 °C, increase mould temperature, reduce injection velocity to avoid shear heating, or clean the PS insert to remove mould release. If the PS insert contains a high level of external lubricant, surface wiping with isopropyl alcohol increases surface energy. These adjustments are made within the narrow processing window described above.

SEBS compounds have good ozone and weathering resistance due to the saturated aliphatic midblock. Accelerated weathering per ISO 4892-2 can be used to evaluate colour shift and surface changes; published data for this specific configuration under outdoor weathering is limited. For outdoor applications, UV stabilisers are necessary because polystyrene end blocks can yellow under prolonged UV exposure. The grade should not be used for implantable medical devices without dedicated testing.