Dongguan Zhongen PC/ABS T85BK is a black polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) alloy supplied for injection moulding. The grade identifier T85BK denotes a controlled-flow, general-purpose formulation in which the BK suffix specifies black coloration. The product is supplied as cylindrical pellets with nominal diameter 2.5–3.5 mm, length 3.0–4.0 mm, and bulk density 0.62–0.68 g/cm³ measured according to ISO 60:1977. Moulded density is specified as 1.13 g/cm³ under ISO 1183-1:2019. The nominal melt volume-flow rate is 15 g/10 min at 260 °C and 5 kg load per ISO 1133-1:2022. T85BK is not a flame-retardant grade; no UL 94 V-0 listing should be assumed. The black colourant is carbon black, and no brominated flame retardant is intentionally added. The material is used in automotive interior brackets, instrument cluster carriers, electronic enclosure frames, and domestic appliance structural housings where wall thicknesses are typically 1.5 mm to 3.0 mm. Parts with wall thickness below 1.5 mm require gate geometry and fill velocity validation because the PC-rich phase can generate high pressure drop in long thin-wall flow paths. The formulation is not intended for food-contact or medical device use unless a specific regulatory evaluation has been completed.

Compounding is carried out on a 44:1 L/D twin-screw extruder with side feeding and vacuum devolatilisation at -0.08 MPa. Production-scale observations from compounding lines show that die melt temperature is maintained at 270–290 °C and residence time is kept below 45 s; these parameters limit excessive ABS-phase degradation while allowing high-shear dispersion of the butadiene-rich domains. The material is pelletised and dried before packaging.

When T85BK Replaces Standard-Purpose PC/ABS in Thin-Wall Enclosures

In production comparisons with a medium-flow standard-purpose PC/ABS having a melt volume-flow rate of 10 g/10 min, T85BK achieves longer spiral flow length at equal injection pressure. Using a 2.0-mm spiral-flow mould at 260 °C and 100 MPa filling pressure, observed flow length is 210 mm for T85BK; the 10 g/10 min reference grade reaches 180 mm and a high-impact reference grade reaches 165 mm. This difference supports reduction in nominal wall thickness from 2.5 mm to 2.0 mm in non-structural enclosures without raising melt temperature above the degradation limit.

The flow advantage is obtained through a reduction in melt viscosity, and it is accompanied by a lower low-temperature impact plateau. At 23 °C, T85BK notched Charpy impact energy is approximately 45 kJ/m², while a high-impact PC/ABS typically reaches 55 kJ/m². At -30 °C, the T85BK value falls to 30 kJ/m², compared with 45 kJ/m² for the high-impact grade. Consequently, T85BK is not a direct substitute where impact resistance below -20 °C is specified; parts must be compared under ISO 179-1/1eA:2010 rather than room-temperature tensile or flexural data alone.

Compared with flame-retardant PC/ABS grades, T85BK does not contain phosphate ester flame retardants. It therefore avoids the plate-out and humidity-dependent hydrolysis sometimes associated with phosphate-type FR systems in hot-running tools, but it cannot meet a UL 94 V-0 rating at 1.5 mm. Compared with glass-fibre-filled PC/ABS grades, T85BK has lower flexural modulus and better mould-surface appearance quality; if flexural modulus above 4000 MPa is required, a 10% or 20% glass-filled grade should replace T85BK.

What Are the Melt-Processing Limits for T85BK?

Pre-drying is mandatory. The pellets are dried at 80 °C for 4 h in a desiccant dryer with a dew point no higher than -30 °C. If ambient relative humidity exceeds 60%, drying time is extended to 6 h. Residual moisture target is no more than 0.005 wt% as measured by ISO 15512:2019 method A. When residual moisture exceeds 0.02 wt%, visible silver streaking develops at knit lines, and tensile stress at break can fall by approximately 8–12% because hydrolytic cleavage of polycarbonate carbonate linkages becomes significant.

Barrel settings from feed to nozzle should be 230 °C, 245 °C, 255 °C, 260 °C, and 255 °C. Melt temperature measured by an immersed probe should remain between 240 °C and 270 °C. Below 240 °C, unmelted polycarbonate domains can survive dispersion, producing delamination at weld lines under flexural load. Above 280 °C, thermo-oxidative chain scission of the ABS butadiene phase generates brown streaks and a pungent odour; these are production-scale indicators of irreversible property loss.

Mould temperature should be held between 60 °C and 90 °C. At 60 °C, the solidified skin layer is thick, which reduces gloss and increases weld-line visibility. At 90 °C, cooling time increases and warpage on large flat parts can become sensitive to gate seal time. Injection velocity is set to fill 90–95% of cavity volume in 0.8–1.5 s for wall thicknesses of 1.5–2.5 mm; hold pressure is typically 60–80 MPa hydraulic for 4–6 s. Hot-runner manifolds and nozzles should mirror the front zone at 255 °C, with no dead spots and maximum residence time 8 min.

Reciprocating screw L/D for injection moulding is recommended at 25:1 with a compression ratio of 2.5:1 to 3.0:1. Back pressure is maintained at 0.3–0.7 MPa, and screw speed is limited to 40–80 min⁻¹ for screw diameters of 32–40 mm. Higher screw speeds increase shear heating in the compression zone and may push the melt temperature above 270 °C even when the barrel set-points are unchanged. If shear rate at the gate exceeds 50,000 s⁻¹, melt-fracture symptoms such as jetting and surface splay are likely in thin-wall sections.

Comparative mechanical data were generated on ISO multipurpose test specimens moulded on a 100-ton hydraulic injection moulding machine with a 25:1 L/D general-purpose screw, shut-off nozzle, and mould temperature 80 °C. Specimens were conditioned at 23 °C ± 2 °C and 50% ± 10% relative humidity per ISO 291:2008. The tabulated results are typical values from manufacturer technical documentation and do not constitute a purchase specification.

The table indicates that T85BK is not the highest-impact or highest-heat grade. Its differentiation lies in the combination of 15 g/10 min melt flow with intermediate HDT/A and room-temperature impact. Tensile properties are measured at 50 mm/min crosshead speed under ISO 527-2/1A/50. Flexural modulus is determined at 2 mm/min and a span-to-thickness ratio of 16:1 according to ISO 178:2019. At elevated temperature, flexural modulus at 80 °C is approximately 1900 MPa, and tensile yield at 80 °C drops to 38 MPa. This reduction requires design verification for parts under continuous load in engine-adjacent interior positions. If the end-use specification requires a notched Charpy value above 50 kJ/m² at 23 °C or above 20 kJ/m² at -40 °C, the high-impact grade should be retained unless the design change to thinner walls is proven to offset the lower impact energy.

Batch Consistency and Residual Monomer Limits in T85BK

Production lots of T85BK are supplied with melt volume-flow rate variation within ±2.5 g/10 min of the nominal 15 g/10 min. Tensile yield lot-to-lot variation is typically within ±2 MPa. This controlled variation allows automated dosing and hot-runner balance settings to remain valid across batch changes without re-optimising screw speed or back pressure. Residual acrylonitrile monomer in the moulded part is specified below 20 ppm and residual styrene below 100 ppm as measured by gas chromatography; these values support indoor emissions limits for automotive interior components under OEM material standards that reference VDA 278 for volatile organic compounds and condensables. Total outgassing values should be confirmed on the final moulded part because they are influenced by melt temperature, hot-runner residence time, and cooling rate.

During masterbatch addition, amine-containing lubricants, hindered amine light stabilisers, or amine-functional colourants should be avoided above 240 °C because they accelerate polycarbonate molecular weight reduction. The result is a progressive drop in melt viscosity from first to last shot and an increase in brittle failure at knit lines. Neutral ester-based mould-release agents or polyethylene waxes are preferred; magnesium stearate is not recommended because it can promote polycarbonate hydrolysis in moisture-containing process environments.

In automotive lower instrument panel bracket production, T85BK has been processed at a melt temperature of 250 °C and a mould temperature of 80 °C. The parts have nominal wall thickness 2.0–2.5 mm and are moulded with valve-gated hot-runner drops. Boss cracking during metal-clip insertion has been observed when hold pressure exceeds 80 MPa and cooling time is below 20 s for 2.5 mm sections. Reducing hold pressure to 60 MPa and extending cooling time to 24 s eliminates the failure mode by reducing hoop stress around the boss. Published data for this specific configuration is limited; the combination of MFR and HDT/A alone does not guarantee assembly performance without part-level validation. In electronic enclosure frames, the grade has been moulded using 120–180 ton clamp force machines with fill time 1.0–1.2 s at wall thickness 2.0 mm. The resulting parts show acceptable flatness when the mould temperature is kept at 80 °C and post-mould fixturing is used during cooling.

How Does T85BK Perform at Low-Temperature Impact Extension Rates?

Under ISO 179-1/1eA:2010, T85BK exhibits notched Charpy impact energy of approximately 45 kJ/m² at 23 °C and 30 kJ/m² at -30 °C. The ductile-brittle transition temperature is near -20 °C, based on the temperature at which the fracture surface changes from predominantly shear-lipped ductile tearing to brittle cleavage. At -40 °C, energy absorption falls below 15 kJ/m².

Instrumented dart impact testing according to ISO 6603-2:2000 at 4.4 m/s gives peak force values of 4.8 kN at 23 °C and 4.2 kN at -30 °C. These values indicate that T85BK should be limited to interior applications or lightly loaded external components not subjected to high-energy stone impact or sub-zero crash loading. If the application requires ductility below -30 °C, a PC/ABS grade with higher butadiene rubber content or a PC/polyester blend should be evaluated. The low-temperature impact response is strain-rate dependent, and high-speed crash or dart-impact tests at 1–5 m/s cannot be inferred from quasi-static tensile or flexural data alone.

Chemical compatibility is limited with aromatic hydrocarbons, ketones, and esters, which can cause environmental stress cracking in polycarbonate-rich phases. Testing should follow ISO 22088-3:2006 for environmental stress cracking. The material withstands limited contact with aliphatic hydrocarbons and dilute acids but should not be exposed to brake fluid, methyl ethyl ketone, or toluene-based paints without validation.

Regulatory data are supplied at the lot level. T85BK is typically covered by a supplier declaration for the Restriction of Hazardous Substances Directive 2011/65/EU and the REACH regulation as amended. The grade is not designed for food-contact use under EU 10/2011 or US FDA 21 CFR. Claimed compliance should be verified against the specific production lot because raw-material substitutions can alter candidate-list substances.