CHIMEI (Chi Mei) ABS PA-758 is an acrylonitrile-butadiene-styrene injection moulding grade positioned for high-impact, high-gloss enclosures and structural components in which ductile failure behaviour is preferred over low-flow brittleness. Manufacturer technical literature identifies the material for medium-flow injection moulding where surface appearance and room-temperature impact resistance are specified together. Typical published datasheet values include a specific gravity of 1.04 g/cm³ and a melt mass-flow rate near 13 g/10 min when tested at 200 °C under 5 kg load in accordance with ASTM D1238 or ISO 1133-1:2022. Notched Izod impact values in manufacturer literature exceed 20 kJ/m² at 23 °C using ISO 180/1A test geometry. That combination separates PA-758 from high-flow general-purpose ABS grades, which typically exchange impact retention for longer spiral flow. Applications listed in manufacturer technical literature include vacuum cleaner housings, power tool casings, small appliance bodies, toys, office equipment enclosures, and automotive interior trim that does not require long-term unpainted outdoor weathering. No food-contact, medical, or flame-retardant status should be inferred without lot-specific regulatory documentation.

Material Data and Test Bench Conditions

The table below aggregates typical values from publicly available CHIMEI ABS PA-758 datasheets. Test specimens are injection moulded under ISO 294-1 and conditioned at 23 °C and 50 % relative humidity for 24 h before mechanical testing. The notched Izod impact values are geometry-dependent; ISO bars and ASTM flex bars are not directly interchangeable because of differences in notch radius, specimen width, and clamping configuration. The flexural modulus should be read as a low-strain secant modulus rather than a true elastic modulus, because ABS exhibits viscoelastic response even at room temperature. Tabulated values are typical lot averages, not guaranteed specification limits, and may shift with colour concentrate loading, mould surface finish, and barrel residence time.

Pre-drying of PA-758 pellets is required before melt processing. A dehumidifying closed-loop hopper dryer with a dew point at or below −30 °C should deliver 80 °C for 2–4 h when pellets have been stored in sealed packaging. Drying time is extended to 4–6 h when ambient relative humidity is above 60 % or when bags have been opened for more than 4 h. Residual moisture above 0.05 % is a process reject threshold because it generates splay, silver streaks, and visible loss of gloss on untextured surfaces. Regrind addition above 20–30 % by weight is not advisable for critical impact parts because repeated thermal history reduces the rubber-phase impact contribution and can shift the notched Izod response below specification. Hopper magnets and fines removal protect hot runner drops with gate diameters below 0.8 mm from contamination and tool damage.

What Distinguishes PA-758 from Lower-Impact ABS Grades?

Within the CHIMEI ABS portfolio, PA-758 occupies a mid-to-high impact position. PA-707-type grades concentrate on higher melt flow for thin-wall moulding and accept lower impact toughness. PA-757 balances high gloss with fast cycle economy. PA-758 shifts the balance toward notched impact retention while still providing sufficient flow for medium-section injection moulding. In production-scale comparisons on hydraulic injection moulding machines with clamp force between 100 and 180 tonnes, PA-758 fills snap-fit cantilevers and screw bosses with lower short-shot rates when the gate is kept within 0.8–1.5 mm land length, but injection pressure is commonly 5–15 % higher than PA-757 under identical screw speed because of lower melt mass-flow rate. The material is not a direct substitute for plating grades such as PA-747S, because electroplating adhesion depends on etch-resistant rubber-phase morphology and surface chemistry that are not optimised in PA-758. Where a part requires decorative chrome or bright metalisation, the plating grade should be retained. Published quantitative comparison data for all commercial CHIMEI grades under identical tool geometry is limited; grade substitution therefore requires tool-specific short-shot and impact validation.

PA-758 also differs from flame-retardant ABS grades. The published flame rating is HB under UL 94, so the material is not appropriate for enclosures requiring V-0, V-1, or 5VB performance. In electrical and electronic housing applications, the creep path and minimum wall thickness are governed by the end-product standard, not by the material alone. Designers should specify PA-758 only after confirming that the housing standard permits an HB-rated ABS and that the operating temperature does not approach the heat deflection temperature under load. For outdoor parts, unpainted PA-758 does not provide inherent UV stabilisation; black pigmentation with carbon black loadings of 2–3 % by weight may improve weathering resistance, but published data for this specific configuration is limited.

Injection Moulding Parameter Set and Screw Configuration

Processing of PA-758 on a standard single-screw injection moulding machine uses a general-purpose screw with L/D 20–22 and compression ratio 2.2–2.5. Barrel set-points follow a rising profile from the feed throat at 190 °C to the metering zone at 220–240 °C, with the nozzle held at or below 240 °C. A shut-off nozzle is preferred because the melt retains enough viscosity at low shear to drool from open nozzles. Mould temperature is maintained between 40 °C and 70 °C. The upper end of that range improves knit-line strength and gloss but extends cooling time. Table 2 summarises reference processing values commonly used for PA-758 in controlled production environments.

High-gloss mould filling requires injection speed sufficient to prevent premature freeze at the gate, but excessive shear can produce oriented rubber particles, visible flow lines, and surface haze. The practical shear-rate boundary for unfilled ABS in small gates is near 2.5 × 10⁴ s⁻¹; beyond this range, surface defects often appear in polished cavities. When moulding ribs and bosses, rib thickness should not exceed 0.6 of the adjacent wall thickness to reduce sink and cycle time. This is a mould-design constraint rather than a material limitation, but the impact-modified rubber phase in PA-758 can increase post-mould shrinkage when the cavity is overpacked. Short-shot studies should establish the transfer position before high-volume production, because the lower melt mass-flow rate can delay the fill-phase to holding-phase transition in hot runner tools.

When High-Gloss Surface Quality Is Required Without Painting

PA-758 is used where the mould texture itself must produce high-gloss surfaces without secondary coating. The mould surfaces are normally polished to SPI/SPE A1 or A2 finish, and peripheral venting is machined to 0.02–0.03 mm depth to prevent trapped gas from dulling the surface. Melt temperature is kept within the upper third of the recommended range, at approximately 230–240 °C, to improve gloss uniformity across large flat panels. Residence time above 8 min at 240 °C can produce yellowing in unpurged barrels and should be avoided. Gate land lengths of 0.8–1.5 mm and fan or tab gate designs reduce jetting on broad surfaces. A polished mould surface alone does not guarantee acceptable gloss; moisture, low melt temperature, or excessive regrind can produce haze and flow marks. For textured surfaces, draft angles should be at least 0.5–1.0°, with additional draft as texture depth increases. PA-758 is not a self-colouring grade, so colour concentrates should be evaluated for melt-flow shift after addition, because some pigment carriers can increase flow or reduce impact energy.

Unpainted PA-758 surfaces are not inherently scratch resistant, and surface hardness is typical for unfilled ABS. Rockwell hardness values in manufacturer literature are near 105 R scale, which is sufficient for appliance housings but lower than glass fibre–reinforced grades. If the application requires resistance to scuffing or repeated cleaning, the design should avoid high-gloss surfaces on horizontal loading areas. For applications involving cleaning chemicals, compatibility screening under ISO 22088-2 or a similar stress-cracking method is recommended before production. ABS grades, including PA-758, are susceptible to environmental stress cracking when in contact with aromatic hydrocarbons, ketones, esters, and some plasticisers under mechanical strain. Plasticised PVC gaskets or cables placed in direct contact with a stressed PA-758 housing can introduce plasticiser migration that initiates microcrazing. Published data for PA-758 under multi-axial stress with specific chemical exposure is limited; end-use testing is required for enclosures that must survive chemical wipe-down or industrial cleaning protocols.

Under Which Chemical Exposures Does PA-758 Require Compatibility Screening?

Silicone mould release agents can reduce subsequent adhesive wetting and cause painting defects. If painting or bonding is planned after moulding, release agent use should be restricted to low-residue grades and validated by adhesion testing. Solvent wiping with isopropanol may be acceptable for short contact times, but prolonged immersion in solvents can swell the ABS surface and reduce impact performance. The material should not be purged with acetal or PVC at high temperature, because decomposition products from those resins can contaminate the melt and affect surface quality. For toys and food-contact applications, relevant regional standards such as EN 71-3 or FDA 21 CFR must be reviewed for migration limits; PA-758 is not automatically certified for all jurisdictions. Regulatory declarations under RoHS 2011/65/EU and its amendments are typically available for CHIMEI ABS PA-758, but lot-specific documentation should be obtained from the supplier for compliance records. REACH SVHC status depends on the current candidate list and must be reconfirmed at the time of shipment.

Moulders shifting an existing tool from PA-757 to PA-758 should not assume identical processing. The lower melt mass-flow rate can increase peak injection pressure by 5–15 % at the same melt temperature. To hold the original fill time within 1.5–2.5 s, the screw speed may be reduced by 10–20 % or the nozzle temperature raised by 5–10 °C. Gate seal time should be revalidated because viscosity differences alter freeze-off behaviour at the gate. Dimensional validation under ISO 294-4 is recommended after any grade substitution to detect warpage and shrinkage changes in ribbed or boss-rich sections. Melt cushion stability should be recorded across shots; a variation above 0.5 mm indicates nonuniform plastication or check-ring leakage. The grade should not be run above 250 °C for extended periods, and barrel purging should be scheduled before and after colour changes. Production trial lots are needed to establish acceptable gloss, impact, and dimensional capability on the intended tool because published data for lot-to-lot variability under specific mould geometries is limited.