CHIMEI (Chi Mei) ABS PA-764 is a plating-grade acrylonitrile-butadiene-styrene terpolymer supplied by Chi Mei Corporation under the Polylac trade designation. It is specified for injection-moulded components that require electroplating with copper-nickel-chromium layers without an intermediate lacquer or adhesion promoter. Published manufacturer data for the grade, when reported according to standard methods, place melt volume-flow rate between 20 cm³/10 min and 30 cm³/10 min at 220 °C under a 10.0 kg load in ISO 1133-1:2022. Density is declared in the range of 1.04 g/cm³ to 1.06 g/cm³ by ISO 1183-1:2019. Tensile stress at yield, measured on type 1A specimens according to ISO 527-2:2012, is typically 37 MPa to 42 MPa, and notched Izod impact strength at 23 °C on 4.0 mm bars tested to ISO 180/A is reported between 15 kJ/m² and 25 kJ/m². Flexural modulus, determined by ISO 178:2019, is typically in the range of 2.0 GPa to 2.4 GPa. The grade’s lower rubber-phase content relative to high-impact extrusion grades such as PA-747 is deliberate: it reduces deep elastomer extraction during chromic acid etching and produces finer micro-roughness for metal interlocking.

At the molecular level, the resin consists of a styrene-acrylonitrile continuous phase and a grafted polybutadiene disperse phase. Public datasheets do not disclose the full monomer ratio, but typical plating ABS resins of this class maintain butadiene between 10 wt% and 20 wt%, acrylonitrile between 18 wt% and 25 wt%, and styrene as the balance. The rubber-phase particle size distribution is the principal differentiating factor in PA-764. Laser diffraction analysis of extracted gel shows a median particle diameter below 1.0 µm, with coarse fractions above 3.0 µm minimized. Coarse rubber particles create crater-like etch features and reduce the uniformity of palladium-tin nucleation. The molecular design therefore shifts the product away from the high-impact domain of PA-747 and toward more consistent plateability in short-cycle injection moulding.

Capillary rheometry on ABS of this flow class at 220 °C typically shows an apparent viscosity of 150 Pa·s to 300 Pa·s at 100 s⁻¹, falling to 30 Pa·s to 60 Pa·s at 1000 s⁻¹. The power-law index ranges from 0.30 to 0.40. This shear-thinning response means that small changes in injection speed produce larger pressure-drop changes in PA-764 than in lower-flow ABS grades such as PA-747. It also explains why the grade fills thin-wall sections but requires careful gate design to prevent jetting and local melt-temperature spikes.

What Limits Plating Adhesion in High-Flow ABS Grades?

High flow in ABS is often achieved by reducing molar mass or increasing lubricant content, both of which can depress plating adhesion. PA-764 addresses this by controlling polybutadiene crosslink density and graft ratio rather than by uncontrolled molecular-weight reduction. The etch process in a chromium trioxide-sulfuric acid bath selectively oxidizes the polybutadiene phase, leaving sub-micron cavities that mechanically lock the subsequent electroless nickel or copper layer. If the rubber phase is over-stabilized with hindered phenolic antioxidants, the etch rate drops below the removal threshold and leaves glossy non-adherent islands. If the rubber phase is under-crosslinked, the etch can enlarge cavities beyond 1.0 µm and weaken the surface region. Either condition results in blistering or peel failure after thermal cycling.

Adhesion is typically quantified as peel strength of an electrolytic copper strip plated to a specified thickness and pulled at 90° according to ASTM B533. On PA-764 mouldings, flat-plaque peel values at 23 °C are commonly accepted in the range of 0.6 N/mm to 1.2 N/mm. Values below 0.4 N/mm after thermal shock from −40 °C to 85 °C are usually associated with insufficient etch micro-roughness or excessive moulded-in stress. Variability across a 100 mm × 100 mm plaque should be less than 15%; larger scatter frequently indicates non-uniform cavity surface temperature or hesitation flow marks. In one production environment, replacing a 3.0 mm cold runner with a heated valve-gate hot runner of 0.8 mm gate diameter reduced post-etch surface mottling and lowered reject rates from 4.5% to 1.1% on a 120-tonne clamping-force machine.

Processors should not infer that high flow alone guarantees plateability. At the injection moulding stage, excessively high melt temperature above 250 °C accelerates oxidative degradation of butadiene and produces yellow-streak defects after etching. Barrel residence time longer than 7 min at 245 °C can reduce notched Izod impact strength below 10 kJ/m². These properties do not recover by lowering the temperature later in the run.

PA-764 requires predrying in a desiccant-hopper dryer before melt processing. A residual moisture target below 0.05% is standard; at ambient relative humidity above 60%, pellets can pick up surface moisture within 30 min if left in an open hopper. Drying at 80 °C for 3 h to 4 h with inlet air dew point of −30 °C or lower is sufficient for most storage histories. Regrind from plated reject parts should remain below 20 wt% because residual chromium and palladium contamination can produce black specks and flow instability. Extruder barrel settings are usually a flat-to-reverse profile from 210 °C at the feed throat to 230 °C at the nozzle; the melt stream measured by immersion thermocouple should not exceed 245 °C.

Mould temperature is more sensitive than melt temperature for downstream plateability. A cavity-wall surface temperature of 40 °C to 60 °C, measured with a contact pyrometer, produces a skin morphology that etches uniformly. Raising mould surface temperature beyond 80 °C increases surface gloss but lowers exposed butadiene at the surface and may reduce etch depth. Mould temperature below 30 °C induces high orientation and stress, which appear as flow lines and etch pits after 15 min in the chromium trioxide bath. These effects are batch-to-batch stable only if mould-temperature control circuits are balanced; differences exceeding 5 °C across the cavity can produce measurable adhesion scatter.

Batch-to-batch variation in PA-764 is typically expressed through melt-flow index and notched Izod impact values on the certificate of analysis. A lot-to-lot MFR shift from 24 cm³/10 min to 28 cm³/10 min under ISO 1133-1:2022 may require a 5 °C to 10 °C reduction in melt temperature to maintain the same flow length. Similarly, a drop in notched Izod impact from 22 kJ/m² to 18 kJ/m² does not necessarily indicate out-of-specification material if the part design safety factor is adequate, but it should trigger a review of drying and residence time before plating. Converters with high scrap rates on plating lines should archive inlet hopper moisture, melt temperature at the nozzle, and lot number for each shift; these three variables explain most PA-764 adhesion deviations.

Thermal Deflection, Moisture Uptake, and Pre-Drying Boundaries

Heat deflection temperature of PA-764 under 1.80 MPa flexural stress, tested according to ISO 75-2/Ae on annealed 80 mm × 10 mm × 4 mm specimens, is typically reported between 86 °C and 92 °C. Vicat softening temperature using ISO 306/B50 is in the range of 96 °C to 102 °C. These values are adequate for electroplated interior components and many exterior trim parts, but they place a service ceiling near 85 °C for continuous exposure. The linear coefficient of thermal expansion of ABS, 70 × 10⁻⁶ K⁻¹ to 90 × 10⁻⁶ K⁻¹, is significantly higher than that of electrolytic chromium at approximately 7.0 × 10⁻⁶ K⁻¹, so thermal cycling imposes biaxial stress at the metal-polymer interface. Parts requiring continuous service above 100 °C are typically moved to heat-resistant ABS or polycarbonate/ABS alloys; PA-764 is not the appropriate selection for those operating conditions.

Water absorption at saturation in 23 °C water, tested under ISO 62, is generally 0.6% to 0.8% for unplated resin. The effect is not usually the primary dimensional driver in fully plated components, but it becomes significant when only one side is plated and the reverse side remains exposed to humid air. Differential water uptake across a 2.5 mm wall can produce curvature of 0.3 mm to 1.0 mm over a 150 mm length after 500 h at 40 °C and 90% RH. Pre-drying must therefore be coupled with controlled storage; components awaiting plating should be sealed in moisture-barrier packaging or processed within 24 h to avoid re-adsorption above 0.10% moisture.

Compared with PA-757, a general-purpose injection-moulding ABS, PA-764 is not simply a coloured variant. PA-764 is designed with a more controlled rubber gel fraction and a narrower butadiene agglomerate size distribution. On a 2.0 mm spiral-flow mould at 230 °C and 60 °C mould temperature, PA-764 typically fills 20% to 30% farther than PA-757 under identical injection pressure. This longer flow length reduces the temptation to raise melt temperature during filling, but it also demands re-optimization of the holding-pressure profile because gate freeze time is shorter. Compared with PA-747, a high-impact ABS, PA-764 exhibits lower notched Izod impact strength but lower etched-surface variance. The high-impact PA-747 often gives deeper, less uniform etch pits because the larger rubber domains dissolve out more aggressively; this can increase adhesion scatter and blistering in plated applications. Compared with PA-765, a flame-retardant ABS, PA-764 does not carry that grade’s flame-retardant package and is not rated UL 94 V-0; it avoids surface bloom and plate-to-plastic adhesion loss sometimes associated with flame-retardant migration.

Regulatory documentation for PA-764 generally supports compliance with RoHS 2011/65/EU and the candidate list under REACH. Food-contact suitability must be confirmed separately against FDA 21 CFR 177.1020 and applicable national measures, because electroplating process chemicals and the final plated surface are not automatically food-contact approved. Material safety data and certification documents should be requested from the manufacturer for each production lot.

When PA-764 Replaces PA-757 on a 120-Tonne Injection Line

Direct substitution of PA-764 into an existing PA-757 process is rarely neutral. Because PA-764 has a higher melt-flow index and lower apparent viscosity at 230 °C, screw recovery time often decreases by 10% to 18% on a 22:1 L/D three-zone screw. The injection velocity profile should be re-qualified: injection rates above 80 mm/s at the screw front can create jetting and shear heating, producing surface streaks that appear only after etching. Holding pressure should be re-established by gate-seal studies rather than transferred from PA-757. The lower melt elasticity of PA-764 shortens gate freeze time and increases sink-mark sensitivity to holding-pressure decay. A melt cushion of 3 mm to 5 mm and hydraulic back pressure of 0.5 MPa to 1.0 MPa are typical starting points.

On the plating line, mouldings from PA-764 are annealed at 65 °C to 75 °C for 30 min to 60 min to relax frozen orientation before degreasing. Skipping annealing is associated with increased edge delamination after the first electrolytic copper layer. Etching is carried out in a chromium trioxide-sulfuric acid bath at 60 °C to 68 °C for 5 min to 12 min; the line must titrate hexavalent chromium and sulfate concentrations within vendor-specified limits, because excursions outside the approved envelope produce non-uniform etching at knit lines and gate regions. Published data for etch rate of this specific PA-764 configuration is limited, so each plating line establishes its own operating window on test plaques before production lots are processed.

External mould-release agents containing silicone must not be used on PA-764 components intended for electroplating. Silicone migration decreases surface energy below 32 mN/m and interferes with palladium-tin nucleation, producing skip plating. Colour concentrates should use an ABS-compatible carrier; ethylene-vinyl acetate carrier levels above 1.5 wt% can soften the surface layer and lead to local over-etching. Contamination with polyamide or acetal residues must be avoided, because these immiscible domains are attacked differently by the chromic acid etch and create crater defects. Storage of unopened bags is typically accepted for 24 months from the date of manufacture when kept below 30 °C and protected from direct sunlight. Pellets should not be stored near open containers of chlorine-based disinfectants or aggressive solvents, because absorbed vapours may produce surface voids and brown specks during injection moulding.

If moisture regain is suspected, a two-stage drying sequence of 70 °C for 6 h followed by 80 °C for 2 h is applied before feeding the hopper. Blending of dried and undried pellets in the same hopper is not recommended because the moisture gradient across the shot leads to visible splay and inconsistent etch appearance. Where production scheduling requires material changes on the same injection machine, a purging compound with styrenic compatibility should be run until the melt stream is clear; residual incompatible resin on the screw or check ring is a common cause of black-spec contamination and adhesion failure on PA-764 parts.