CHIMEI (Chi Mei) ABS PA-765A is an acrylonitrile-butadiene-styrene terpolymer supplied as cylindrical pellets for injection molding and electroplating applications. The grade is formulated to produce a finely dispersed polybutadiene phase that responds to chromic-sulfuric acid etching with a high density of sub-micron anchor sites. The supplier’s technical literature identifies the material as suitable for decorative electroplated components where thermal cycling resistance and adhesion of electroless copper or nickel are the primary acceptance criteria. Pre-drying in a desiccant dryer at 80–85 °C for 2–4 h is recommended when ambient relative humidity exceeds 60%, targeting residual moisture below 0.05 wt%. At 1.5 mm thickness, the unfilled natural grade is typically rated HB under UL 94. The material is not a transparent grade; applications requiring clarity should not use PA-765A.

The following property envelope is compiled from manufacturer-published data and production batch experience for electroplating ABS grades. It does not replace a certificate of analysis for a specific lot, and some published data for the exact “A” designation is limited to the producer’s technical bulletins.

Melt viscosity of PA-765A is shear-sensitive. Capillary rheology measurements at 220 °C and shear rates of 100–1,000 s⁻¹ show apparent viscosities typical for injection-molding ABS, allowing thin-wall decorative parts to be filled without excessive melt pressure. The glass transition temperature of the SAN matrix is approximately 105 °C by differential scanning calorimetry at 10 °C/min, but continuous service above 85 °C is not recommended because of creep and plate-adhesion loss. The polybutadiene phase exists as discrete rubber domains; the molded article typically exhibits a domain size distribution of 0.2–2.0 µm. Residual styrene monomer is typically below 500 ppm when measured by gas chromatography, although this value is not a food-contact compliance limit. Low residual monomer is relevant to electroplating because volatile species can create pre-plating surface contamination.

Injection molding of PA-765A is performed on conventional reciprocating-screw machines with general-purpose ABS screws characterized by compression ratios between 2.0:1 and 2.5:1 and L/D ratios from 20:1 to 25:1. Melt temperatures are maintained within 200–240 °C, with a preferred upper limit of 230 °C when residence time exceeds 4 min because unsaturated butadiene domains degrade through thermal oxidation. Mold temperatures between 40 °C and 80 °C are used; plating-grade parts benefit from the upper half of this range to reduce frozen-in orientation and to promote uniform shrinkage. Back pressure is set at 3–7 bar hydraulic to maintain shot weight consistency without generating excessive shear heat. Screw rotation speeds are typically 40–80 rpm. Peripheral equipment includes a desiccant dryer with a dew point of −40 °C or lower and a closed-loop mold temperature controller capable of ±1 °C variation.

Moisture absorption in PA-765A follows Fickian behavior typical for ABS resins: at 23 °C and 50% RH, equilibrium moisture content is approximately 0.2–0.3 wt%. If not predried, absorbed moisture volatilizes during molding and produces splay marks and internal voids; in electroplating, residual moisture can be entrapped below the surface and later cause blistering during electroless copper deposition. A desiccant dryer with air inlet dew point below −40 °C is mandatory. Drying time at 80 °C is 2–4 h, but if pellets have been exposed to rain or condensed water, drying time is extended to 6 h. Hopper purge with dry air at 0.5–1.0 L/min per kg/h throughput prevents re-absorption in humid plants. In facilities where ambient dew point exceeds 20 °C, open hoppers should not be used.

What distinguishes PA-765A from general-purpose ABS grades?

Compared with Chi Mei’s PA-757 general-purpose high-gloss ABS, PA-765A uses a coarser and more uniformly dispersed polybutadiene phase. This morphological difference depresses specular gloss but increases the density of etchable sites after chromic acid conditioning. In practice, PA-757 is selected for unpainted cosmetic parts that require surface gloss retention; PA-765A is selected when the molded surface will be chemically etched and plated. The flow length of PA-765A is generally lower than that of PA-757 at the same melt temperature and injection pressure, which affects gate placement and wall thickness design. Relative to PA-747, an extrusion/high-impact grade with higher rubber content, PA-765A displays a narrower melt-temperature window and shorter allowable residence time. PA-747 is better suited to sheet extrusion where high elongation and deep-draw behavior are required; PA-765A is generally processed by injection molding rather than extrusion because the dispersed rubber phase is optimized for thin-wall filling and subsequent acid etching. Compared with a PC/ABS plating grade, PA-765A has a lower heat deflection temperature. When service temperature exceeds 100 °C, a heat-resistant ABS or PC/ABS grade should be evaluated instead.

In production-scale injection molding, PA-765A exhibits susceptibility to gate blush and jetting when thin-wall parts are filled at injection velocities above 70 mm/s screw forward speed. These defects are not merely cosmetic; they create local molecular orientation that etches at a different rate than surrounding material. Flow lines visible before plating become magnified after metal deposition. To suppress jetting, cold slug wells and tab gates of 1.5–2.5 mm thickness are used. Mold filling analysis with measured melt temperature and pressure curves is recommended for parts with wall thickness below 1.0 mm. Weld lines in PA-765A have lower local butadiene concentration after melt-front collision; etch rate at weld lines can be higher, leading to visible plating defects. Increasing mold temperature to 70 °C and slowing injection velocity reduces weld-line depth but does not eliminate the effect. Where appearance after plating is critical, gate locations should be moved to place weld lines outside visible surfaces.

Etch chemistry, palladium activation and adhesion testing

Electroplating of PA-765A begins with an oxidative etch using a chromic-sulfuric acid solution. Production plating lines operate etch baths at 65–70 °C with 380–420 g/L CrO₃ and 340–400 g/L H₂SO₄; immersion time is typically 5–12 min, adjusted to generate etch pits of 0.5–2.0 µm in diameter at a density sufficient for mechanical anchoring. The etched surface is rinsed, neutralized in sodium bisulfite, and then activated with a palladium-tin colloidal solution. After acceleration, electroless nickel or electroless copper is deposited at 0.3–0.5 µm thickness before electrolytic copper-nickel-chromium plating. Peel strength of the plated coupon is evaluated according to ASTM B533; industrial acceptance criteria commonly require a peel strength above 0.8 kg/cm width, but published data for this specific configuration is limited, and each plating line must establish its own control range. The etch pit morphology—not simply etch depth—controls peel strength; over-etching creates brittle, deep pits and reduces mechanical interlock.

Production applications for CHIMEI ABS PA-765A include injection-molded automotive badges, radiator grille inserts, wheel cover trim, door handle bezels, appliance knobs, sanitary fittings, and consumer electronics side keys. On a 350 t hydraulic injection molding machine with a 2+2 cavity hot-runner mold, shot-to-shot weight variation is typically controlled below 0.1% because dimensional drift after plating can change part fit in chrome-plated assemblies. Mold surface temperature is often raised to 70–80 °C for thin-wall plaques below 1.2 mm to avoid jetting and weld lines that become visible after electroplating. Plated PA-765A parts require thermal cycling validation from −40 °C to 85 °C with 10–20 cycles, depending on OEM specifications, to confirm adhesion after differential thermal expansion between the ABS substrate and the metallic overplate. Published data for this specific configuration is limited; lot-specific adhesion panels should be plated alongside production parts.

When PA-765A replaces standard ABS in chromic-acid plating lines

Replacement of a non-plating ABS with PA-765A on an existing chromic-acid line requires re-qualification of etch time and bath agitation. Because PA-765A is designed for electroplating, the etch pit density may develop faster than on general-purpose ABS; using the same etch time as a high-gloss grade can produce over-etching and lower peel strength. Bath loading density, rack-to-rack spacing, and solution agitation are maintained at 0.3–1.0 m² of part surface per 100 L of etch bath, with continuous filtration to remove chromium sludge. The material is not compatible with strong oxidizer contact outside the plating sequence; any mold release containing silicone or high levels of stearate must be eliminated because residues interfere with wetting and activation. Avoid blending PA-765A with amine-based concentrates or flame-retardant additives that alter polarity and reduce etch uniformity. REACH and RoHS compliance must be confirmed from the supplier’s safety data sheet and product compliance statement; the presence of ABS polymer does not by itself guarantee compliance with electroplating emission limits.

The resin is supplied with a safety data sheet and product compliance statement. Under the REACH regulation (EC) No 1907/2006, the supplier must communicate SVHC content at the time of sale. Under the RoHS Directive 2011/65/EU as amended by (EU) 2015/863, the homogeneous material is typically below the maximum concentration values for lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE. These certifications are lot-specific and must be included in the incoming inspection plan. For automotive electroplated components, validation often follows OEM-specific standards rather than generic ISO 16750-4 thermal cycling, although ISO 16750-4 may be referenced for environmental loads. The UL 94 classification is based on small-scale horizontal burn tests; a thickness of 1.5 mm is common for HB rating. If the final molded part has thickness below 1.5 mm, the classification may change.

Tool steel selection for PA-765A follows standard ABS practice: P20 or hardened H13 cavities with uniform cooling lines 10–12 mm in diameter and 25–30 mm spacing are sufficient. Hot-runner systems with externally heated manifolds are preferred; internal heating can cause resin stagnation and black specks. Gate diameters for edge gates are typically 1.0–1.5 mm for wall thicknesses up to 2.0 mm, and land lengths are kept below 1.0 mm to reduce shear heating. For electroplated parts, cavity surfaces should be polished to at least SPI A2 to minimize pre-plating buffing. However, too high a polish can reduce etch wetting by decreasing surface micro-roughness; some plating shops prefer SPI B1 for electrolyte transfer. This is a process-dependent trade-off.

For applications requiring UL-recognized plating adhesion under exterior weathering, parts molded from PA-765A are tested after plating for peel strength, thermal shock, and CASS corrosion resistance according to ASTM B368. Service temperatures above 85 °C are not recommended for decorative chromium-plated PA-765A unless the specific plating stack and part design are validated, because the differential coefficient of linear thermal expansion between ABS and plated metal can cause microcracking at notch radii below 2 mm. Moisture-conditioned parts should be dried before electroplating; absorbed water in the molded substrate can cause blistering in electroless copper deposition. In injection molding facilities with high relative humidity, hopper storage should not exceed 30 min without desiccant drying. Published data for this specific configuration is limited; manufacturers commonly verify adhesion with first-article plating trials rather than relying exclusively on resin datasheet values.