CHIMEI (Chi Mei) ABS PA-765 is a high-impact acrylonitrile-butadiene-styrene injection-molding grade supplied as natural or precolored pellets. Within the Chi Mei ABS portfolio, PA-765 is positioned as a rubber-modified grade with a higher dispersed polybutadiene phase content than general-purpose PA-757 and with a melt-viscosity balance intended for large, thin-walled, or complex tools in reciprocating-screw injection machines. Density is normally reported under ISO 1183-1:2019 and falls in the unfilled-ABS band of 1.03–1.06 g/cm³. Melt mass-flow rate should be stated under ASTM D1238-20 at 220 °C/10 kg because different loading conditions alter the ranking of high-impact ABS grades. Specimen conditioning for mechanical testing typically follows ISO 291 at 23 ± 2 °C and 50 ± 5 % RH. Flammability is normally reported as UL 94 HB at a stated minimum thickness, but the classification is color- and thickness-dependent. No single property value should be transferred into an engineering calculation without the current grade-specific certificate of analysis, because rubber-phase architecture may shift within the supplier’s release window.

The material is not a direct drop-in for PA-757 when dimensional stability, tensile yield stress, or high-gloss surface appearance dominate the specification. Conversely, when PA-765 replaces PA-747 or another high-impact ABS in a tool with thin hinge bosses or snap-fit features, it may offer better filling behavior at equivalent clamp force. The molder must verify gate freeze time and weld-line strength because higher rubber content reduces thermal diffusivity and can prolong cooling time relative to lower-impact ABS grades.

How Does the Rubber-Phase Architecture Govern Impact–Flow Balance?

The impact performance of PA-765 is governed by polybutadiene-rich core particles and the grafted styrene-acrylonitrile shell. High-impact ABS derives toughness from cavitation and craze multiplication; the rubber particles act as stress concentrators that release triaxial tension at notch tips. Under ASTM D256-10e1, the notched Izod test registers the energy consumed by crack initiation and limited propagation. For high-impact ABS with rubber-phase content similar to PA-765, low-temperature impact retention is controlled by the glass transition temperature of the polybutadiene phase and the particle-size distribution. If rubber-phase gel content is too low, particles coalesce during compounding and molding, and the product loses mechanical performance after multiple heat histories. If gel content is too high, the grafted SAN shell cannot maintain interfacial adhesion, and material fails by particle pull-out rather than cavitation.

In processing terms, the rubber phase increases low-shear viscosity and makes the melt more shear-thinning than general-purpose ABS. Capillary rheometry under ISO 11443 typically shows a power-law index below 0.30 between 100 s⁻¹ and 1000 s⁻¹ for high-impact ABS. This means injection-speed changes produce non-linear pressure responses: raising volumetric flow rate by 20% may reduce melt pressure less than predicted from a Newtonian assumption but may increase shear heating at the gate. For PA-765, gate land lengths and runner diameters should therefore be designed from the grade’s viscosity curve, not copied from a lower-toughness ABS tool.

The mechanical tradeoff is measurable. Compared with PA-757, PA-765 shifts the balance toward higher notched Izod impact energy under ASTM D256-10e1 and lower tensile yield stress under ASTM D638-14. Flexural modulus under ASTM D790-17 may be reduced by approximately 10–20% relative to medium-impact ABS, while notched Izod impact may increase by roughly 50–100% depending on specimen thickness, gate location, and conditioning temperature. These are class-level ranges for high-impact ABS rather than product-specification limits; the current PA-765 datasheet should be consulted for final design values.

Production-scale molding of PA-765 is typically performed on a hydraulic or electric reciprocating-screw machine with an ABS screw of 20:1 to 25:1 L/D and compression ratio of 2.2:1 to 2.8:1. A non-return valve with free-flow area of at least 70% of the screw cross-section reduces stagnation and black speck defects. Clamp force is calculated from projected area; high-impact ABS commonly requires 2.5–4.0 tonnes/cm² of projected area, although thin-wall parts with flow-length-to-thickness ratios above 150:1 may exceed 120 MPa injection pressure and require closed-loop injection velocity control.

A common production-line failure mode is feed-throat bridging when dry, angular regrind particles entangle with pellets. This is observed when regrind concentration exceeds 20 wt% and the hopper is fed from a single-compartment loader without material-level control. The defect appears as intermittent screw-starved cycles and injection-weight variation, not as a moisture defect. Adding a vertical hopper magnet and reducing regrind fines below 2 wt% usually stabilizes shot weight to within ±0.2% on a 250-ton machine running a 6-cavity tool.

Gate design for PA-765 should account for higher rubber-phase viscosity. Edge gates and fan gates are preferred over pinpoint gates for thicker sections because high shear at small gates can locally degrade rubber particles and produce jetting. Gate land length should be kept below 1.0 mm for wall thickness below 2.0 mm, and the gate cross-section should be sized for a shear rate below 10⁴ s⁻¹. Vent depths from 0.02 mm to 0.03 mm are standard for ABS; insufficient venting produces burn marks and weak weld lines. In polished molds, mold temperature near the upper band of 80 °C is often required because higher rubber content reduces melt front transparency and can otherwise produce a matte ring around the gate.

These values are a representative ABS high-impact molding envelope and must be adjusted for actual wall thickness, hot-runner configuration, pigment loading, and regrind content. Nozzle temperature should be held near the front-zone setting, not above 240 °C, because localized overheating in the nozzle body can generate gel particles.

When Melt Residence and Shear Work Exceed the Degradation Threshold

Thermal degradation in PA-765 follows oxidative attack on the polybutadiene phase and chain scission or crosslinking in the styrene-acrylonitrile matrix. Above 240 °C, surface defects associated with degraded rubber particles may appear before a substantial drop in tensile properties. Yellowness index measured under ASTM E313-10 can increase by 2–5 YI units after 10 min of residence at upper melt temperature; 60° gloss measured under ASTM D523-14 may fall by more than 10 gloss units. These are not fixed product limits because screw size, heater band uniformity, and hot-runner residence time distribution affect local temperature. Production-scale failure modes include intermittent black specks, splay-like defects near the gate, and loss of notched Izod impact at the weld line. When a 50-mm screw machine is interrupted for longer than 10 min at 240 °C, purging with a low-viscosity ABS or a commercial purging compound is standard. Purging with rigid PVC, polyacetal, or halogenated compounds is incompatible because decomposition gases corrode mold steel and can contaminate PA-765 surfaces.

Hot-runner systems should not use oversized manifolds for PA-765. Melt stagnation at valve-gate actuators and unheated nozzle tips broadens residence time distribution and causes periodic burn streaks. The preferred practice is to match manifold flow-channel diameter to shot weight and to avoid hot-runner temperature above 240 °C, irrespective of barrel setpoint. If black specks appear only after color change, the likely source is carbonized ABS retained in a dead zone rather than incoming pellet contamination.

Moisture Uptake, Regrind Management, and Feed-Throat Stability

Moisture control is process-critical when ambient relative humidity exceeds 60%. A desiccant dryer with a closed-loop air supply is mandatory; hot-air hopper dryers are not adequate for PA-765 when tight surface gloss and impact retention are required. Pellet moisture above 0.05 wt% is typically expressed as splay, particularly on flat decorative surfaces. Regrind levels up to 20 wt% of the same unpigmented resin are common, but high regrind reduces low-temperature impact and shifts mold shrinkage. For UL-listed end products, the Recognized Component directory may limit regrind to 0 wt% unless specifically tested.

Regrind particle-size control prevents feed-throat segregation. Granulator screens above 8 mm produce coarse flakes that bridge in the hopper and cause screw-starved cycles; screens below 4 mm increase fines and dust, which can bake onto the screw root. The target fraction is typically 4–8 mm with fines below 2 wt% through a 1 mm sieve.

Within the Chi Mei ABS portfolio, PA-765 differs from PA-757 primarily in rubber-phase volume and resulting mechanical balance. PA-757 is a general-purpose grade with higher tensile yield stress and flexural modulus under ASTM D638-14 and ASTM D790-17, but lower notched Izod impact under ASTM D256-10e1. PA-747 is a high-impact grade with similar toughness to PA-765 but may exhibit lower melt flow rate under ASTM D1238-20, which makes PA-765 preferable for tools with long flow paths at moderate clamp force. When PA-765 is substituted into existing tooling designed for PA-747, venting and gate freeze time should be verified at wall thickness below 2.0 mm. When substituted for PA-757, tooling may require an increase in mold temperature to maintain surface gloss and a reduction in holding pressure to avoid overpacking because the higher rubber phase lowers modulus and increases melt compressibility.

Application selection for PA-765 is documented in tools such as vacuum-cleaner housings, power-tool clamshells, household appliance shrouds, and industrial guards. These components commonly have wall thickness between 2.0 mm and 3.5 mm, snap-fit closures, and bosses for self-tapping screws. The material’s high-impact performance is evaluated at 23 °C and at low temperatures such as -30 °C using notched Izod specimens cut from standardized plaques or the production tool; weld-line specimens should be tested separately because weld-line impact retention in high-impact ABS is lower than bulk values. Environmental stress-cracking resistance should be evaluated under ISO 22088-2 for any chemical contact, because ABS is sensitive to ketones, esters, aromatic hydrocarbons, and certain plasticizers. For outdoor or UV-exposed parts, unpigmented ABS is not suitable without UV stabilization or opaque capstock; accelerated weathering under ISO 4892-2 or ASTM G154 should be used to establish color shift and impact retention.

When replacing PA-747 or PA-757 in existing tooling, the molder should document melt temperature at the nozzle, cooling time, cushion, and gate freeze time across a production run. Tooling issues that are hidden with general-purpose ABS, such as sharp transitions at the gate land, undersized vents, or unbalanced runner systems, often appear with PA-765 because its higher rubber-phase viscosity and lower modulus alter pressure distribution in the cavity. Published data for PA-765-specific end-product performance in proprietary assemblies is limited; therefore, application suitability should be confirmed by first-article inspection and mechanical testing rather than by similarity alone.