PetroChina Jilin ABS HF681 is an injection-moulding grade of acrylonitrile-butadiene-styrene terpolymer. The material is composed of a continuous styrene-acrylonitrile copolymer phase and a dispersed polybutadiene rubber phase grafted with SAN; the graft shell controls rubber particle adhesion and energy absorption during impact, while the free SAN matrix governs melt-flow behaviour and rigidity. The designation places HF681 in the high-flow segment of the producer’s ABS portfolio. In published product literature the melt mass-flow rate is commonly reported at 220 °C with a 10 kg load using ISO 1133-1:2022; high-flow grades of this type typically show values between 15 g/10 min and 25 g/10 min, with lot-specific results issued on the certificate of analysis. Density is measured by ISO 1183-1:2019 and falls within 1.04 g/cm³ to 1.06 g/cm³ for unfilled ABS. The product is supplied as cylindrical pellets for injection moulding of thin-wall components in appliances, consumer electronics, and automotive interior trim. The material is not intended for applications exceeding 80 °C under continuous mechanical load, nor for repeated low-temperature impact below −20 °C unless the end-user has validated part performance under ISO 179-1/1eA or ISO 180/1A. Because the grade’s high-flow architecture is achieved through control of molecular mass and rubber morphology, the impact resistance is typically lower than that of general-purpose or high-impact ABS grades from the same production family. Moisture uptake during storage should be controlled; residual moisture above 0.10 % by weight before melt processing is a known cause of surface splay and reduced weld-line strength.

What Injection-Moulding Parameters Are Required for Thin-Wall ABS Components?

Processing HF681 on a reciprocating-screw injection-moulding machine requires independent control of melt temperature, screw recovery, backpressure, and mould surface temperature. The melt temperature measured at the nozzle should be kept between 220 °C and 250 °C; the lower half of that range is preferred to limit polybutadiene degradation, while the upper half may be required for hot-runner systems with long flow channels and restricted gates. Barrel temperature settings are commonly arranged as a reverse profile from rear zone to nozzle: 200–210 °C in the rear, 220–230 °C in the centre, and 230–240 °C at the front and nozzle. Mould temperature should be controlled at 30–70 °C; higher mould temperatures improve knit-line fusion and surface gloss but increase cooling time and part-ejection friction. Screw geometry with a L/D ratio of 20:1–24:1 and compression ratio of 2.0:1–2.5:1 is appropriate for standard ABS; when a high-shear mixing screw is used, melt temperature should be monitored because shear heating in high-flow ABS can raise actual melt temperature by more than 10 °C above barrel setpoint. The material should be dried in a desiccant-bed dryer at 80 ± 5 °C for 2–4 h, with dryer dew point below −30 °C, to reach residual moisture below 0.10 %; drying times must be shortened or temperatures reduced if pellet discoloration is observed. Injection velocity should be set high enough to fill the cavity before freeze-off, particularly for wall sections below 1.2 mm, where fill times below 1.0 s are often required. Holding pressure is typically maintained between 40 MPa and 70 MPa, with an adequate residual melt cushion of 2–4 mm; a cushion below 1.5 mm can produce pressure loss at the screw tip and dimensional variation. Backpressure during screw recovery should be limited to 0.5–1.0 MPa. A shut-off nozzle or needle-valve gate is recommended to prevent drool and maintain stable melt density.

In cavity-pressure-controlled injection moulding of electronic enclosures and appliance fascia, the benefit of HF681 appears as reduced peak injection pressure and longer flow paths at equivalent wall thickness. On a moulding machine with a clamp force of 1,200 kN producing flat panels with 1.5 mm nominal wall, the observed fill ratio and gate-freeze behaviour are determined less by the material’s nominal melt-flow rate than by gate geometry, venting, and melt-front velocity. Pin gates below 0.8 mm diameter are generally unsuitable for thin-wall ABS at melt temperatures below 230 °C because shear heating at the gate can cause material degradation and visible gate blush. Edge gates with land lengths between 0.5 mm and 1.0 mm are preferred. Vent grooves should be cut to a depth of 0.02–0.03 mm to permit gas escape; insufficient venting produces burn marks and weld-line weakening. The grade is used in thin-wall enclosures for routers, set-top boxes, power strips, and domestic appliance control panels. These applications typically require mould shrinkage between 0.4 % and 0.7 % in the flow direction after 24 h at 23 °C and 50 % relative humidity per ISO 294-4:2018. Weld-line strength in such parts is lower than bulk strength; if the part is subjected to snap-fit assembly, bosses and weld lines should be placed away from high-tensile zones. Published data for the exact flow-length performance of HF681 in spiral-flow tooling is limited; processor-specific mould-filling trials are required to establish maximum flow length at a given wall thickness and injection speed.

Property Profile and Comparative Positioning Against General-Purpose ABS

HF681 differs from general-purpose ABS such as the producer’s standard injection grades primarily through an upward shift in melt-flow rate and a corresponding reduction in notched impact strength. The table below summarises the analytical dimensions that differentiate the high-flow grade from general-purpose ABS using standard ISO test methods.

The higher melt-flow range of HF681 reduces viscosity under standard conditions and improves thin-wall filling at lower injection pressure. The trade-off appears most clearly in the notched Izod impact range, which is shifted downward relative to general-purpose grades because the molecular architecture that increases flowability also reduces energy absorption in the rubber phase. The Vicat softening temperature of HF681 remains in the range of standard ABS, meaning the grade should not be substituted for heat-resistant ABS grades in components exposed to local hot spots above 90 °C. Where the application requires both thin-wall filling and high impact toughness, a high-flow-high-impact grade or a polycarbonate/ABS blend may be more appropriate; the selection should be confirmed by notched impact testing at the lowest service temperature and by instrumented falling-dart testing under ISO 6603-2:2023.

Incompatibilities with process auxiliaries and certain additives should be treated as material boundaries. The grade is based on an ABS matrix and should not be purged with PVC, acetal, or polycarbonate residues; PVC decomposes at ABS processing temperatures and carbonizes in the barrel, while acetal depolymerization can produce formaldehyde and temperature-control loss. Purge material should be an ABS-compatible acrylic or SAN-based purge. Colour masterbatches must use a SAN carrier; polyethylene or wax-based masterbatches may phase-separate and produce surface delamination. Flame-retardant packages containing halogenated additives or antimony trioxide can alter melt viscosity and mould deposit formation; if flame retardance is required, the processor should select a pre-compounded FR ABS rather than adding powders at the press. Regrind use should be limited to 20 wt% for appearance-critical parts and 50 wt% for non-appearance parts, provided the regrind is dried to below 0.15 % moisture and is free of metal or silicone contamination. Repeated regrind cycles above 250 °C increase yellowness and reduce impact due to polybutadiene crosslinking; melt-flow stability tests after 5 remoulding cycles should be used to establish allowable regrind levels for critical production.

When Backpressure and Residence Time Are Not Controlled

In high-volume production of thin-wall parts, the most common failure modes associated with high-flow ABS are not short shots but discoloration, surface splay, and screw recovery inconsistency caused by improper backpressure and residence time. If barrel residence time exceeds 6–8 min at melt temperatures above 240 °C, visible yellowing and a shift in melt-flow rate can occur before mechanical properties fall outside specification. The non-return valve should prevent melt leakage; screw recovery time should be shorter than cooling time to avoid idle melt standing in the barrel. Backpressure above 2.0 MPa on a closed-loop injection unit can over-shear the material and raise actual melt temperature beyond the setpoint. This is observed as brown streaks first appearing at the gate and near hot-runner tips, not as uniform part failure. When surface splay occurs despite adequate drying, check feed-throat humidity, resin conveying air dew point, and hopper loader seals. Ambient relative humidity above 60 % increases re-absorption of moisture in dried pellets during transfer; a closed-loop drying and conveying system with dry-air purge is required under such conditions. The melt cushion should remain between 2 mm and 4 mm; cushion loss below 1.5 mm is associated with shot-weight instability and local shrinkage variation. Screw speed during plasticising should be set to achieve recovery without exceeding 100 rpm on general-purpose injection screws, unless the screw manufacturer’s shear-rate limits specify otherwise. These operational limits are independent of lot-to-lot variation in virgin pellets but become more restrictive with high percentages of regrind or with masterbatch containing mineral fillers.

Specification compliance for HF681 is application-dependent and must be obtained from the producer’s declaration or a qualified testing laboratory. The following matrix lists the regulatory and standard frames most often reviewed for injection-moulded ABS components.

Food-contact status under FDA 21 CFR or EU 10/2011 is not automatically granted for HF681; a separate compliant grade or positive migration testing must be used. Likewise, automotive interior applications with odour and fogging limits require validation against the manufacturer’s test standards and lot-specific volatile organic compound measurements. No generic product summary replaces the producer’s certificate of analysis, raw material safety data sheet, or current regulatory declaration.