For thin-wall enclosures and interior trim components that require low-temperature impact retention without a V-0 flame-retardant classification, Dongguan Zhengxian PC/ABS 3138A is classified as an unfilled pelletized polycarbonate/acrylonitrile-butadiene-styrene alloy. The grade is intended principally for injection molding and, in less common configurations, profile extrusion where melt flow above neat PC is required. Because a publicly archived certificate for this exact grade is not available in international polymer databases, property ranges cited below are bounded by commercial PC/ABS alloys of equivalent density and melt flow; lot-specific certificates should supersede these values.

The as-pelletized compound is produced by high-shear twin-screw compounding with the PC phase and the ABS phase stabilized against thermal oxidation. The 3138A suffix is a supplier product identifier and does not describe an ISO descriptive block. Regulatory documentation is typically limited to supplier declarations under RoHS Directive 2011/65/EU as amended and REACH SVHC; these are product-line documents and not a substitute for lot-specific analytical screening when the final article is exported to jurisdictions requiring full substance inventories.

Material Property Envelope and Melt Rheology

The unfilled composition places the material in the medium-flow PC/ABS class. Melt volume-flow rate measured to ISO 1133-1 at 260 °C and 5 kg is typically in the range of 15 cm³/10 min to 25 cm³/10 min. Density by ISO 1183-1 method A is generally 1.13 g/cm³ to 1.15 g/cm³. Tensile yield stress on type 1A specimens according to ISO 527-2 is 50 MPa to 55 MPa; tensile modulus lies between 2200 MPa and 2600 MPa. Charpy notched impact strength per ISO 179-1/1eA at 23 °C is 35 kJ/m² to 50 kJ/m², with a lower bound of 15 kJ/m² at -30 °C reported for several equivalent blends. Heat deflection temperature under ISO 75-2/A at 1.8 MPa is 110 °C to 120 °C, and Vicat softening temperature per ISO 306/B50 is 125 °C to 135 °C. Unless a UL Yellow Card exists for the specific pigmented lot, flammability should be treated as UL 94 HB at 1.5 mm, not V-0.

Rheologically, the melt exhibits shear-thinning behavior across the production shear-rate range. In capillary rheometry to ISO 11443, representative unfilled PC/ABS systems show apparent viscosity of approximately 300 Pa·s at 100 s⁻¹ declining to 80 Pa·s at 1000 s⁻¹. This response permits filling of ribs and bosses with wall thickness down to 0.8 mm when cavity melt temperature is maintained near 250 °C and peak internal melt pressure reaches 60 MPa to 80 MPa. Spiral-flow data published for equivalent blends commonly indicate flow-length ratios of 60:1 to 80:1 at 2 mm wall thickness. The exact viscosity curve for 3138A should be obtained from lot-specific rheology files before defining gate dimensions or hot-runner settings.

Moisture control is the first process boundary. The compound is supplied in sealed, foil-lined bags; opened bags should be consumed within 4 h when ambient humidity exceeds 60 % RH. Desiccant drying to a dew point of -30 °C or lower for 3 h to 4 h at 90 °C to 100 °C reduces moisture below 0.02 wt% before plastication. Drying above 110 °C risks yellowing of the ABS phase. A return-air dew point above -20 °C or hopper residence time longer than 2 h can reintroduce moisture at the feed throat.

Reciprocating-screw machines with an L/D ratio of 20:1 to 24:1 and a compression ratio of 2.0:1 to 2.5:1 are standard. Barrel zone temperatures from feed to nozzle are set at 240 °C, 255 °C, 265 °C, and 260 °C; differences greater than 10 °C between adjacent zones increase the probability of unmelted ABS agglomerates. Injection velocity is typically 60 mm/s to 120 mm/s, with holding pressure maintained at 50 % to 70 % of peak cavity pressure for 5 s to 10 s. Mold temperature is controlled at 60 °C to 80 °C; lower mold temperatures increase frozen-layer thickness and reduce weld-line integrity, while mold temperatures above 90 °C extend cycle time without improving structural performance in thin sections.

Why Does Residual Moisture Govern Surface Quality More Than Melt Temperature?

Hydrolytic chain scission in the PC phase becomes measurable when moisture exceeds 0.03 wt%. The visible symptom is splay or silver streaking radiating from the gate, frequently misattributed to excessive melt temperature. Because unfilled PC/ABS has a processing window of 240 °C to 270 °C, raising melt temperature cannot compensate for moisture; it accelerates degradation reactions. For a hot-runner manifold, residence time is the second variable. At 260 °C, total residence time should not exceed 15 min; beyond this, yellowing and reduced impact strength are observed on production equipment. The nozzle and manifold should be purged with an unfilled PC grade before shutdown, as stagnant polymer undergoes thermal oxidation.

When Low-Temperature Impact Retention and Weld-Line Strength Are Simultaneously Specified

Meeting both requirements requires control of melt temperature, mold temperature, and injection velocity within a narrow corridor. At melt temperatures below 240 °C, the PC phase does not fully wet the ABS domains, resulting in a weld-line Charpy notched impact at 23 °C that can be 30 % lower than the bulk value. At melt temperatures above 270 °C, ABS thermal degradation creates carbonyl decomposition products that reduce tensile elongation. The process corridor is therefore approximately ±5 °C around 255 °C for complex multi-gate housings. Production experience on reciprocating-screw machines with clamp forces of 900 kN to 1200 kN indicates that placing vents at 0.02 mm to 0.03 mm depth along the weld-line path reduces gas entrapment and improves impact retention. If the article has a textured surface per SPI D3 or VDI 3400 plate, vent depth should be set at the lower end to avoid flash.

Adjusting Injection Molding Parameters to Suppress Surface Delamination and Gate Blush

Surface delamination in unfilled PC/ABS is associated with incompatible recycled material, excessive shear heating, or condensation on the mold surface. A gate shear rate above 100 000 s⁻¹ can cause local phase separation. Gate land length should be 0.5 mm to 0.8 mm for a 1.5 mm wall, and the gate should feed into a flow channel with a radiused transition, not directly onto a flat surface. Jetting produces stratified flow fronts and a visible bloom. If a hot tip is used, the tip orifice diameter should be 0.8 mm to 1.2 mm. Mold protection and clamp force should be set so that actual cavity pressure does not exceed 80 MPa; higher pressures increase packing stress and may contribute to stress-cracking in downstream painting or solvent-wiping operations.

Shrinkage compensation for unfilled PC/ABS is specified at 0.5 % to 0.7 % linear along the flow direction and 0.6 % to 0.8 % transverse, measured on a 150 mm × 150 mm × 2 mm plaque molded to ISO 294-4. Ejector pins should be placed away from textured surfaces and should have a draft angle of 0.5 ° to 1.0 ° for untextured cores; textured surfaces require 1.5 ° per 0.025 mm of texture depth. Radiused transitions and uniform wall thickness above 2.5 mm reduce sink marks. Rib thickness should not exceed 60 % of adjacent wall thickness.

Assessing Grade Differentiation Across Neat ABS, Neat PC, and Filled Blends

Relative to neat ABS, 3138A is characterized by higher heat deflection temperature and lower mold shrinkage, but it may exhibit greater sensitivity to prolonged drying or strong alkaline mold cleaners. Relative to neat polycarbonate, the alloy has lower melt viscosity, permitting lower barrel temperatures and reduced clamp force, but neat PC retains higher notched impact and higher continuous-use temperature. Compared with glass-fiber-reinforced PC/ABS, the unfilled grade has lower tensile modulus and lower heat distortion, but reduced anisotropic warpage and improved surface appearance in high-gloss applications. Flame-retardant PC/ABS grades generally carry a UL 94 V-0 rating at 1.5 mm to 2.0 mm, whereas standard unfilled PC/ABS typically attains UL 94 HB only; the flame-retardant designation is required for enclosures subject to IEC 62368-1 fire enclosure requirements.

Chemical resistance is governed by both phases. Aromatic hydrocarbons, ketones, and esters can induce environmental stress cracking; compatibility testing to ASTM D543-14 or ISO 22088-3 is required before specifying 3138A for painted or solvent-wiped parts. Strong alkaline solutions with pH above 11 attack the polycarbonate phase and are incompatible with mold cleaning if residues remain. Amine-based mold releases and certain maleated coupling agents should be avoided because they can accelerate hydrolysis and reduce molecular weight. The operational boundary for continuous exposure in warm, humid environments is normally below 80 °C and 60 % RH; above this, published property-retention data for this specific grade is limited.