Zhongshan Chuangjian PC/ABS HM-550k is supplied as an unfilled polycarbonate/acrylonitrile-butadiene-styrene alloy for injection moulding. The grade is designated within the manufacturer’s HM high-modulus series, with the numeric suffix indicating a controlled medium-flow viscosity subclass. Publicly available certificate-of-analysis data for this specific grade are limited; therefore, numerical values in this document represent the typical property and processing envelope for equivalent unfilled high-modulus PC/ABS alloys prepared under ISO 294-1:2017 conditions and must be verified against the supplier’s batch documentation. The structural difference from general-purpose PC/ABS is an elevated tensile and flexural modulus at similar room-temperature impact toughness, achieved without mineral filler or glass-fibre reinforcement. The difference from flame-retardant PC/ABS is the absence of halogenated or organophosphate flame-retardant packages, which affects density, thermal stability, mould-deposit behaviour, and end-product fire classification.

What Property Envelope Characterizes the HM-550k Class?

Under standard conditioning at 23°C and 50% relative humidity, the unfilled alloy typically exhibits the following property ranges. The values are class-typical ranges for injection-moulded specimens and are not lot-specific release limits.

Tensile yield behaviour is strongly rate-dependent. At 50 mm/min under ISO 527-2:2012, yield stress falls between 50–58 MPa; at 500 mm/min, yield stress can increase by 5–10 MPa while elongation at yield decreases. This sensitivity is relevant for snap-fit insertion and short-duration load simulations where static tensile data alone underestimate stress during rapid deflection. Differential scanning calorimetry according to ISO 11357-2:2020 typically resolves two glass-transition regions: the ABS phase near 100–110°C and the polycarbonate phase near 145–150°C. The higher-Tg polycarbonate phase is the main contributor to the deflection temperature and Vicat results. Capillary rheometry at 260°C and 1000 s⁻¹ gives an apparent shear viscosity of 250–400 Pa·s for unfilled PC/ABS of this flow class, while low-shear viscosity at 10 s⁻¹ is typically 1200–1800 Pa·s. These rheological data are derived from comparable high-modulus unfilled grades and do not replace lot-specific capillary rheometry under ISO 11443:2021.

The compound is produced on a co-rotating twin-screw extruder with an L/D ratio of 40:1. Specific mechanical energy input during compounding is typically limited to 0.18–0.25 kWh/kg, and the screw profile uses distributive mixing elements after a first melting zone to limit local shear heating of the polycarbonate phase. Lot-to-lot melt volume-flow rate variation should be kept within ±2 cm³/10 min of the target for consistent multi-cavity hot-runner balance.

Because the polycarbonate phase absorbs moisture at a rate that increases significantly above 60% relative humidity, the pellets require desiccant-dryer treatment before melt processing. A residual moisture content below 0.02% by mass, as measured by ISO 15512:2019, is the operational boundary for preventing splay, silver streaking, and molecular weight reduction in the polycarbonate phase. Drying at 90–100°C for 4–6 h with a dew point of −40°C or lower is typical; at ambient relative humidity above 60%, drying time should be extended to 8 h. Melt processing is carried out on a three-zone injection-moulding screw with a compression ratio of 2.2:1 to 2.5:1 and a barrel-temperature profile from rear zone 240–250°C to nozzle 255–270°C. A mould temperature of 60–90°C is applied to control surface gloss, weld-line strength, and post-moulding dimensional stability. Back pressure in the range 3–8 MPa assists homogenisation without subjecting the melt to excessive shear. Residence time above 280°C should not exceed 5 min because polycarbonate degradation produces carbon dioxide and discolouration by-products. For hot-runner systems, manifold and nozzle temperatures are set within 250–265°C, and idle-time purging with virgin material is required to prevent stagnant resin degradation.

When Flame Retardancy Is Not the Primary Selection Criterion

In assemblies where the ignition-resistance requirement does not exceed UL 94 HB at the maximum wall thickness used in the housing, the HM-550k-class material can be evaluated in place of flame-retardant PC/ABS. The elimination of phosphate or brominated flame-retardant packages avoids the associated notched-impact reduction, acidic mould deposits, and melt-residence sensitivity. Compared with a typical 0.8 mm V-0 organophosphate flame-retardant PC/ABS, the unfilled high-modulus grade frequently shows a Charpy notched impact-strength advantage of 10–20 kJ/m² at 23°C under ISO 179-1:2023 and a Vicat softening temperature that is 5–12°C higher under ISO 306:2022. The trade-off is the absence of a V-0 or V-2 rating; final equipment for information-technology or audio/video applications must be assessed under IEC 62368-1 or the relevant end-product standard, because unmodified PC/ABS cannot be assumed to satisfy all fire-enclosure requirements without design changes or shielding.

When replacing a flame-retardant grade in a tool originally optimised for a lower-viscosity phosphate-containing compound, injection pressure at transfer should be expected to increase. For a 2 mm wall thickness, transfer pressures of 80–120 MPa are common, and pack pressure must be held until gate freeze to offset volumetric shrinkage of 0.4–0.7%. If the tool contains ribs below 0.8 mm, flow length may be shorter than with an MFI 25 cm³/10 min flame-retardant alloy; short-shot trials should establish the new fill window before production.

For structural housings and brackets in industrial electronics, the flexural modulus range of 2100–2500 MPa under ISO 178:2019 permits ribbed enclosures to carry a given bending load at lower wall stock than an ABS-only component. The notched Charpy value under ISO 179-1:2023 supports snap-fit assembly at room temperature, but snap-fit design should apply strain limits below the yield strain from ISO 527-2:2012 and should not rely on ductile behaviour below −10°C unless instrumented multiaxial impact data generated under ISO 6603-2:2023 demonstrate otherwise for the specific geometry. For automotive interior brackets, the 1.8 MPa HDT/A of 108–118°C is suitable for short-term cabin surface temperatures up to approximately 85°C; sustained load at higher temperatures requires tensile creep verification under ISO 899-1:2017. At 23°C and 20 MPa, unfilled PC/ABS of this modulus class typically retains 50–60% of its initial tensile creep modulus after 1000 h. Published data for this specific grade under the exact creep condition is limited.

Solvent Stress-Cracking Resistance and Environmental Boundary Conditions

The material exhibits moderate resistance to aliphatic hydrocarbons, dilute household detergents, and silicone oils, but contact with aromatic solvents, ketones, esters, chlorinated solvents, and strong alkaline aqueous solutions can induce environmental stress cracking. Evaluation under ISO 22088-3:2006, Method A, with a mild detergent at 60°C is used by some moulders as a screening test; parts under high assembly stress should be tested with the actual service fluid because small differences in ABS rubber particle size and polycarbonate molecular weight alter the crazing threshold. Continuous exposure to engine oil at 80°C or to brake fluid is outside the recommended boundary for unprotected structural parts. The grade is not inherently UV-stabilised for long-term outdoor use; when exterior service is required, weathering performance must be evaluated under ISO 4892-2:2013 with a defined radiant exposure and acceptance criteria. Contamination with polyamide residues, certain metal stearates, amine-containing mould-release agents, or unneutralised acid-containing additives should be avoided because these substances can promote polycarbonate degradation during recycling or extended residence at elevated temperature.

Comparison with flame-retardant, high-flow, and glass-filled PC/ABS classes is summarised below. The ranges are class-typical values for injection-moulded specimens under the cited standards and do not represent lot-specific guarantees.

For hot-runner conversion from an existing high-flow grade, the manifold temperature should be kept below 265°C and residence time in the hot runner limited to 3–4 min during start-up. A sequential valve-gate programme with a fill time of 1.5–2.5 s for a 300 mm × 200 mm flat-panel tool reduces weld-line depth and keeps peak injection pressure within 100–140 MPa. Dimensional stability after demoulding is influenced by moisture uptake and thermal contraction; parts should be conditioned at 23°C and 50% relative humidity for at least 24 h before final metrology. In applications requiring tight tolerances of ±0.05 mm, a fixture cooling period of 15–30 min after ejection is commonly used to stabilise PC/ABS parts before measurement.