Zhejiang Yima PC/ABS C is an unfilled polycarbonate/acrylonitrile-butadiene-styrene alloy supplied for injection moulding of dimensionally stable enclosures, structural brackets, and interior trim parts. The grade is produced as cylindrical pellets and is normally characterized by a density of 1.12–1.15 g/cm³ when tested to ISO 1183-1:2019. Melt volume rate for the general-purpose C designation typically falls within 15–25 cm³/10 min at 260 °C/5 kg when tested to ISO 1133-1:2022; exact lot-specific values must be taken from the supplier certificate of analysis because batch-to-batch variation in PC molecular weight and ABS rubber particle size affects both flow and impact. The material is not formulated with brominated flame retardants or halogenated synergists in the base grade. It carries internal lubricant and stabilizer packages but no filler or reinforcement. The C designation denotes a general-purpose balance of melt flow and impact resistance within the producer’s portfolio; it is not assigned to UV-stabilized or flame-retardant variants unless explicitly stated on the lot certificate.

What Separates PC/ABS C from Unblended PC, ABS, and Flame-Retardant PC/ABS?

Differentiation from unblended PC is primarily rheological and thermal. Unfilled PC exhibits a melt volume rate below 10 cm³/10 min at 300 °C/1.2 kg and a heat deflection temperature above 125 °C at 1.8 MPa, whereas the C grade flows at lower melt temperature and sacrifices roughly 15–25 °C of heat resistance. The ABS component lowers melt viscosity and notch sensitivity but also reduces resistance to aromatic hydrocarbons. Against unblended ABS, the C grade provides higher Vicat softening temperature and improved low-temperature impact retention, although ABS retains better flow in extremely thin sections below 1.0 mm. Against flame-retardant PC/ABS, the base C grade is not UL 94 V-0 at 1.6 mm and must not be substituted in enclosures carrying the UL 94 V-0 mark without requalification. Flame-retardant grades typically show notched Izod impact at 23 °C in the range of 20–40 kJ/m², lower than the general-purpose C envelope. PC/PBT grades are preferred where exposure to fuels or hot water exists; PC/ASA grades are specified for weatherable parts. The C grade is not the first choice for those service conditions unless the part is painted, metallized, or tested in the final assembly. Glass-fibre-reinforced PC/ABS grades offer higher flexural modulus above 3500 MPa but exhibit lower notched Izod impact and anisotropic shrinkage; the unfilled C grade avoids the anisotropic shrinkage associated with fibre reinforcement.

Injection Moulding Window and Moisture Control Requirements

Pre-drying is mandatory, not optional, for the PC phase. In a desiccant dryer with dew point ≤ -30 °C, pellets should be dried at 80–100 °C for 2–4 h to a residual moisture level below 0.02 % by weight. At relative humidity above 60 %, exposure of dried pellets to ambient air beyond 30 min can return enough surface moisture to produce splay. Melt temperature at the nozzle should be maintained between 250 °C and 280 °C, with barrel profiles typically set from 240 °C in the rear zone to 270 °C in the metering zone. Mould temperature should be controlled between 60 °C and 90 °C; thin-wall parts benefit from the upper end to improve wetting and knit-line strength. Screw design should use an L/D of 20:1 to 24:1 and a compression ratio of 2.0:1 to 2.5:1. Back pressure of 0.5–1.5 MPa is adequate for homogenization, and decompression after recovery should be limited to 2–4 mm to avoid air entrapment. Mould shrinkage according to ISO 294-4:2018 is anisotropic; parallel shrinkage of 0.4–0.7 % and transverse shrinkage of 0.5–0.8 % are typical for unfilled PC/ABS. Gate design must account for this differential, particularly in flat housings where cumulative shrinkage differences exceed 0.3 % across the part.

At production scale, three failure modes dominate when the C grade is processed outside these boundaries. Splay on the cavity surface typically indicates moisture or trapped volatiles, not a colour mismatch. Black specks and yellowing in hot-runner systems occur when melt residence time exceeds 8–10 min at 270 °C or when dead spots exist in the manifold. Weld lines in ribbed or multi-gated parts exhibit strength reductions of 20–40 % relative to bulk tensile strength because the PC phase freezes before the ABS phase can interdiffuse at the melt front; raising mould temperature to 85–90 °C and increasing injection velocity reduce the loss but do not eliminate it. Batch-to-batch variance in melt volume rate should be monitored against the supplier upper bound of 25 cm³/10 min; if the value shifts upward, lower molecular weight PC typically reduces notched Izod impact at 23 °C toward the low end of the 45–65 kJ/m² corridor. On a high-speed electric injection moulding machine with clamp force up to 1200 kN and screw diameter 30–35 mm, the grade is typically capable of filling a spiral flow length of 350–500 mm at 2.0 mm wall thickness with injection pressure above 80 MPa; published data for this specific configuration is limited, so a short-shot study on the production tool remains the only reliable method for establishing flow-length limits.

Regrind use from sprues and runners can be maintained at 20 % by weight if the regrind is dried to the same residual moisture level as virgin pellet. Higher regrind fractions increase the probability of black specks, reduce impact retention, and shift colour coordinates because the stabilizer package and ABS rubber particles are partially consumed during the first heat history.

Incoming inspection should record melt volume rate and moisture content, not rely solely on visual pellet appearance. A shift of ±3 cm³/10 min from the approved baseline often correlates with a measurable change in impact performance and requires revalidation. Capillary rheometry at 260 °C across shear rates of 100–1000 s⁻¹ can detect lot-to-lot differences that a single MVR point cannot; comparable unfilled PC/ABS grades display shear-thinning with apparent viscosity falling by 50–65 % between those shear rates. Moisture above 0.02 % may not be visible during purging but will reduce molecular weight at the melt temperature and can produce surface splay on textured tools.

Dimensional stability and flatness are influenced by gate geometry and packing. Direct edge gates or fan gates with land length of 0.5–1.0 mm and gate freeze time long enough to avoid sink marks but short enough to prevent overpacking at the gate are typical. Valve-gated hot-runner systems should use thermal gate tips with positive shut-off; open hot tips can drool at melt temperatures above 270 °C. Venting depth should be 0.02–0.04 mm for unfilled PC/ABS; insufficient venting causes burn marks at the end of fill and reduces weld-line strength. Holding pressure should be applied so that the gate seals after 2–4 s of pack; overly early gate freeze produces sink marks over ribs and bosses. In a flat housing with a 1.2 mm wall, a short packing time can produce central flatness deviation of 0.5–1.5 mm depending on part length; moving the gate from a short-side edge to a fan or diaphragm position can reduce warpage by orienting flow and balancing shrinkage ratio.

When Thin-Wall Housing Design Requires High Flow and Impact Retention

In thin-wall enclosures below 1.2 mm nominal wall stock, the melt-volume rate and documented impact retention of the C grade become selection criteria. Parts such as charger housings, remote-control bodies, and automotive interior switch panels use unfilled PC/ABS to balance stiffness, dimensional stability, and structural impact at a density of 1.12–1.15 g/cm³. Charpy notched impact for 4 mm specimens according to ISO 179-1/1eA:2010 is generally in the range of 40–60 kJ/m², while tensile elongation at break according to ISO 527-2/1A/50 is typically 40–80 %. In automotive interior trim, emissions performance is application-dependent and must be verified to OEM standards such as VDA 277 for volatile organic compounds or VDA 278 for fogging if required. Published data for the exact C grade on VDA 277 emission values is limited; validation on the final part is required before production release. The flow and impact balance makes the C grade suitable for snap-fit geometries if the snap arm is designed with generous radii. Sharp internal corners below 0.5 mm radius act as stress concentrators and can reduce impact retention in cold conditions below 0 °C; nucleated failure at the corner rather than bulk yielding is the limiting mode.

Stress-cracking resistance in service is governed by the PC phase. Aromatic and chlorinated solvents, ketones, esters, and strong alkaline cleaners can initiate environmental stress cracking in stressed PC/ABS parts. PVC gaskets and cables containing monomeric plasticizers such as DOP or DINP can cause migration-induced embrittlement when in direct contact with the C grade under pressure at elevated temperature. Amine-functional release agents, flame-retardant synergists, or sealants are generally incompatible with the polycarbonate phase and can cause surface haze or molecular weight reduction at processing temperatures. Continuous service temperature under mechanical load is typically limited to 70–80 °C for unfilled PC/ABS; higher excursions are acceptable only at low stress and must be validated on the part geometry. Environmental stress-crack screening should not rely on simple immersion tests alone; bent-strip testing under ISO 22088-3:2006 with target chemical contact provides more reproducible comparative data for lot release or material substitution.

Regulatory Compliance Is Contingent on Lot-Specific Certification and Downstream Validation

RoHS compliance for the base grade is typically verified against 2011/65/EU as amended by (EU) 2015/863, covering lead, cadmium, mercury, hexavalent chromium, PBB, PBDE, and the four phthalates. REACH SVHC declarations under Article 33 of (EC) No 1907/2006 require confirmation that no substance on the current candidate list exceeds 0.1 % w/w in the article. Food-contact status is not automatically available for PC/ABS C; end uses involving food contact require a separate 21 CFR 177.1580 clearance or EU 10/2011 migration validation. UL 94 classification for the base grade is typically HB at 1.6 mm; only the exact final colour, part thickness, and moulding lot can establish the compliance classification. Lot-level test data should be requested for density, melt volume rate, notched Izod impact at 23 °C, and heat deflection temperature because these four values provide a practical incoming quality-control dataset without requiring full mechanical characterisation on every batch.

Ultraviolet exposure and outdoor weathering are limiting factors. Unstabilised PC/ABS C will develop yellowing and gloss loss after extended UV exposure, and parts with a class-A surface should be painted, film-insulated, or converted to a PC/ASA grade if continuous exterior exposure is specified. Before substituting the C grade into an existing tool running a different PC/ABS, the lower impact or higher shrinkage of the replacement must be checked with prototype mouldings, not with datasheet comparisons alone.