The compound identified as API Megol AM SEBS-Comp. DP2217/90PBT belongs to the hydrogenated styrenic block copolymer class described by ISO 18064:2022 as TPS. The manufacturer’s suffix 90PBT is a coding convention rather than a published numerical specification. It is read in current API product literature as a nominal hardness target of 90 Shore A and a formulated adhesion package directed toward polybutylene terephthalate substrates. The AM designation separates the grade from non-functionalised SEBS compounds requiring primer, plasma, or corona treatment before overmolding onto semi-crystalline polyesters.

The material is supplied as a compounded SEBS system rather than a neat block copolymer. Compounding elements for this class typically include hydrogenated styrenic block copolymer, paraffinic or naphthenic process oil, polyolefin viscosity modifiers, functionalized compatibilizer, hindered phenolic antioxidant, phosphite process stabilizer, and light stabilizer. The saturated midblock structure reduces backbone unsaturation relative to SBS and SIS thermoplastic elastomers, supporting better thermo-oxidative stability at melt processing temperatures up to approximately 210 °C for short residence intervals. Grade-specific formulation percentages are not published; lot-level composition is controlled by the manufacturer’s internal production standard.

Compared with a standard SEBS-Comp. grade without the AM designation, DP2217/90PBT is not optimized for generic polypropylene bonding. The adhesion package shifts the melt surface energy and may reduce peel strength on polypropylene compared with a standard SEBS when processed in the same tool. Operators should not treat the grade as a universal overmolding thermoplastic elastomer; it is directed at PBT and possibly PBT-rich blends only after first-article validation.

What DP2217/90PBT specifies in the TPS compound portfolio

The numeric segment DP2217/90 is a development formulation identifier. It does not by itself communicate melt flow rate, tensile strength, or tear strength. It is differentiated from harder or softer equivalents within the same family primarily by the Shore hardness target and the related tensile modulus. Hardness is commonly reported under ISO 7619-1:2010 or ASTM D2240, with a nominal value of 90 Shore A inferred from the suffix. Shore hardness alone does not predict adhesion; the PBT suffix is therefore operationally significant because it indicates that the compatibilizer package is selected to wet and bond to PBT rather than to polyamide, polycarbonate, or acrylonitrile-butadiene-styrene.

Mechanical properties for adhesion-modified 90 Shore A TPS compounds in this class commonly fall within a reference envelope of density 0.95–1.05 g/cm³ when measured under ISO 1183-1:2019, tensile strength 8–12 MPa under ISO 37:2017, elongation at break 400–600% under ISO 37:2017, and tear strength 25–40 N/mm under ISO 34-1:2015. These ranges are class-typical and must not be treated as lot-specific certificate values for the API grade; the current datasheet for this specific configuration should be obtained from API’s controlled document system.

Adhesion to PBT is the primary differentiator. The AM chemistry commonly includes maleic anhydride-functionalized polyolefin or acrylic acid-functionalized compatibilizer species that interact with hydroxyl and carboxyl end groups generated on the exposed PBT surface. The bond mechanism is not solely mechanical interlocking. Interfacial chemical coupling contributes to peel strength retention after thermal cycling. Release values are normally determined by a 90-degree peel test analogous to ISO 813:2019 or by an internal overmold adhesion method using plaque inserts and defined gate positions.

On production-scale injection molding machines with general-purpose screws of 20:1 to 25:1 L/D and compression ratios of 2.0:1 to 2.5:1, the TPS compound is generally processed with a flat or slightly rising barrel profile from 170 °C in the feed zone to 210 °C at the nozzle. First-stage injection speed is set to fill the cavity within 1.5 to 2.5 seconds for thin-wall sections without exceeding 100 MPa peak hydraulic pressure. Because TPS melt viscosity is shear-rate dependent, runner and gate dimensions should be selected to maintain a shear rate below 50,000 s⁻¹. Higher shear rates can cause visual streaking and may reduce adhesion at the melt front. The specific melt flow index for DP2217/90PBT is not embedded in the code and must be read from the certificate of analysis.

Mold temperature is a critical process variable. PBT substrates should be preheated to at least 80 °C and maintained above the PBT cold-crystallization threshold during second-shot transfer. A mold temperature of 30–60 °C for the TPS portion is common, but the substrate insert must retain sufficient thermal energy to soften the interfacial layer. Excessively low substrate temperature below 80 °C produces a quenched PBT skin with low free volume and poor molecular interdiffusion. Excessively high melt temperature above 230 °C may degrade the functionalized compatibilizer and generate oxidative by-products at the bond interface.

Adhesion testing at first-article approval establishes the lower release limit

At first-article approval, overmolded test plaques with a PBT substrate of 2 mm to 3 mm thickness are produced on the intended production tool and tested after 24 h conditioning at 23 °C and 50% relative humidity. The lower release limit is typically not derived from a datasheet value; it is set from production capability and adhesion retention after 7-day heat aging at 85 °C. A common boundary condition is the observation of cohesive failure within the TPS layer rather than adhesive failure at the interface. Test methods include ISO 813:2019 for 90° peel and internal overmold tensile separation methods based on ISO 527-1:2012 specimen geometry.

Validation should include thermal shock cycling from −40 °C to 85 °C because interfacial stresses develop from differences in coefficient of linear thermal expansion between PBT and the TPS overmold. A PBT substrate with 30% glass fiber reinforcement has a lower expansion coefficient than unfilled PBT and may produce lower peel strength retention after cycling because the interfacial stress concentrates at the edge of the overmolded feature.

When PBT substrates replace mechanical fastening in handheld power tool housings

When PBT substrates replace mechanical fastening in handheld power tool housings, a TPE-U or TPE-E alternative is often evaluated against a TPS compound on the basis of chemical resistance, service temperature, and bond durability. In such applications, DP2217/90PBT is relevant where a soft-touch grip or sealing gasket must be molded directly onto a glass-fiber-reinforced PBT shell without a primer. The maximum long-term service temperature for a TPS SEBS grade is generally lower than that of a TPE-E copolyester; continuous exposure above 120 °C will be outside the reliable envelope unless confirmed by the supplier. The saturated midblock, however, provides better hydrolysis resistance than polyester-based TPE-E and better low-temperature flexibility than many TPE-U grades.

For dynamic flex applications such as trigger seals or vibration-isolating grommets, flex fatigue performance should be evaluated under ISO 132:2017 or an internal cyclic deformation method. TPS compounds may exhibit lower tensile set resistance than high-performance TPE-E grades, but their lower density and reduced moisture uptake often reduce shot-to-shot mass variation in multi-cavity tools.

Comparative property ranges across TPS, TPE-U, and TPE-E overmolding grades

Selection comparisons should be based on material class data rather than hardness alone. The following table summarizes typical reference ranges used in overmolding grade screening. Values are not lot-specific and do not replace the supplier datasheet for DP2217/90PBT.

One recurring production failure in TPS-to-PBT overmolding is the presence of mold release agent carried over from the PBT substrate operation. Silicone-based external release sprays reduce the surface energy of PBT below the wetting threshold and produce adhesive delamination. The same effect is observed with hydrocarbon waxes. Automated cleaning with cold plasma or low-pressure air ionization shortly before the second shot is used on some multi-component lines, but the cleanest process path is the elimination of external release agents on the PBT tool.

Valve-gate hot-runner systems require careful gate temperature control. A gate temperature above 220 °C may cause TPS drool and stringing at the gate, while a gate temperature below 170 °C may produce high shear stress and localized viscosity rise. Cold-runner systems with edge gates are preferred for overmolded sealing components because the sprue and runner remain attached to the TPS shot and do not require separate degating that can introduce stress concentrations at the bond line.

Pre-drying is required when packaging integrity has been breached or when the material has been exposed to ambient relative humidity above 60% for more than 8 h. A desiccant dryer set to 70–80 °C with a dew point of −30 °C and residence time of 2–3 h is a standard starting point, although SEBS is not highly hygroscopic. Avoid blending with amine-containing antistatic additives, certain benzotriazole UV absorbers at elevated levels, or unsaturated rubber masterbatches that can alter adhesion and melt stability. The material should not be processed at melt temperatures above 240 °C or held in the barrel for more than 10 minutes at the upper processing limit; oxidative gel particles may form and plug hot-runner gates.

Differences from other products in the same portfolio include the substrate-specific chemistry. A standard SEBS overmolding grade may provide lower cost and broader polypropylene adhesion but generally fails in primerless PBT bonding. TPE-U grades offer higher tensile strength and abrasion resistance but can absorb moisture, leading to hydrolysis during processing if drying is inadequate. TPE-E grades provide higher upper service temperatures but are more sensitive to wet processing and can be more difficult to bond to PBT without surface activation. DP2217/90PBT occupies the intermediate position for PBT-specific applications where hydrolysis resistance, lower density, and direct adhesion are valued simultaneously.

For multicomponent tools with rotating cores, the set time is controlled by the recrystallization of the PBT substrate and the melt strength of the TPS layer. Opening the mold before the TPS layer has cooled below its solidification point can create gate pull-out and local interfacial shear. The cooling time for a 2 mm overmold section is generally short, but the limiting factor is usually the PBT core temperature rather than the TPS skin. Published data for this specific configuration is limited to API’s commercial technical data sheet and certificate of analysis; therefore lot-specific values for melt flow rate, volatile content, and peel strength on PBT should be requested prior to tool construction.