Kumho Petrochemical ABS 750 is an acrylonitrile-butadiene-styrene injection moulding grade supplied as a general-purpose material for appliance housings, automotive interior trim, electrical enclosures, and consumer housings. The commercial designation identifies a high-flow, general-purpose ABS within the Kumho Petrochemical range. The grade is normally reported with a melt mass-flow rate of 35 g/10 min under 220°C and 10 kg load in accordance with ISO 1133-1:2022. Density is cited at 1.04 g/cm³ by ISO 1183-1:2019. Notched Charpy impact at 23°C is approximately 24 kJ/m² by ISO 179-1/1eA. Tensile yield stress is reported near 47 MPa by ISO 527-2. Flexural modulus is near 2400 MPa by ISO 178. These are representative lot-average values, not specification limits. The certificate of analysis for the specific production lot remains the controlling document, and the current manufacturer technical data sheet supersedes any secondary compilation.

Within the Kumho Petrochemical ABS line, the 750 designation does not cover electroplating grades, high-heat grades, or flame-retardant extrusion grades. The material is intended for injection moulding; it is not assigned for extruded sheet or profile use. Colour-dependent specimens may differ from natural values because pigments alter melt viscosity, notched impact, and heat deflection temperature. Black ABS 750 may show slight reductions in notched impact at 0°C compared with unpigmented resin. These shifts are determined on a lot-specific basis rather than by a fixed rule.

How does ABS 750 respond to predrying and high-shear injection moulding?

Predrying is mandatory when pellet moisture exceeds 0.05 wt%. A desiccant dryer with a dew point below -20°C is held at 80°C for 2 h to 4 h. If ambient relative humidity exceeds 60% RH, open storage time should be kept below 30 min before drying. Hopper dryers alone are not adequate under those conditions. Drying above 90°C or beyond 6 h can discolour pellets because the polybutadiene phase is thermally sensitive. The moisture limit is critical because residual moisture hydrolyses the styrene-acrylonitrile phase only weakly, but it turns to steam in the barrel and appears as silver streaking on the moulded surface.

On production-scale injection moulding machines from 80 tonnes to 250 tonnes clamp force, using general-purpose screws with L/D ratios of 20:1 to 22:1 and compression ratios of 2.2:1 to 2.6:1, barrel temperature is set between 200°C and 230°C. The rear zone is kept at 180°C to 200°C, the middle zone at 200°C to 220°C, and the front zone at 210°C to 230°C. Nozzle temperature is offset 5°C to 10°C below the front-zone setpoint to reduce drool. Melt residence time should not exceed 6 min at 230°C; beyond 8 min, visual yellowing and styrene odour become detectable. Mould temperature is controlled at 40°C to 70°C. The lower limit shortens cycle time but freezes the surface before full packing; the upper limit improves knit-line strength and surface gloss but increases cooling time and can cause sticking on textured surfaces.

Back pressure is set between 0.5 MPa and 2 MPa to control melt density and colour dispersion. Screw recovery speed is limited to 30 min⁻¹ to 70 min⁻¹ to avoid excessive shear heating. Injection velocity is profiled rather than fixed: in thin-wall sections below 1.2 mm, peak injection speed is normally above 100 mm/s. Switch-over from velocity to pressure control occurs by screw position, typically 2 mm to 3 mm before full fill, not by hydraulic time. Cavity pressure during packing is held at 35 MPa to 50 MPa for general parts, but published data for this specific configuration is limited and must be validated with pressure sensors in the mould.

Clamp force is calculated from projected area. ABS 750 generally requires 3.0 kN/cm² to 5.0 kN/cm² of projected area at a nominal wall of 2.5 mm. Thinner walls and longer flow paths raise the required cavity pressure; insufficient clamp force opens the parting line and produces flash. The non-return valve should be checked for clearance because high-flow ABS leaks backward through worn valves more readily than lower-MFR materials, reducing shot-to-shot consistency.

If natural ABS 750 is coloured at the press, masterbatch addition is normally 1 wt% to 2 wt%. The melt temperature should be kept below 230°C to avoid thermal degradation of organic pigments. Inconsistent metering produces MFR shifts because the carrier resin in the masterbatch may have a different viscosity. Gravimetric metering is preferred over volumetric dosing when shot weight is below 50 g.

Tooling for ABS 750 uses cold runners with circular or trapezoidal cross-sections. Gate land length is maintained between 0.5 mm and 1.0 mm, and gate thickness is limited to 60% of the local wall section. The high MFR permits filling of ribs as thin as 0.8 mm without switching to a special high-flow grade. Weld-line impact in those ribs may fall below the bulk notched Charpy value because molecular entanglements across opposing flow fronts are less developed. Gates are positioned to move weld lines away from boss roots, snap-fit root radii, and screw-boss side walls. Published data for this specific configuration is limited; prototype moulding with instrumented falling-dart impact or notched impact specimens cut from weld locations is required before release. Mould release is achieved with conventional draft angles of 0.5° to 1° on textured surfaces and 0.25° to 0.5° on polished cores. Ejector pins should be placed opposite thick sections to reduce stress whitening during ejection.

For decorative parts, ABS 750 can be painted after surface treatment, but the high flow does not inherently provide better paint adhesion than lower-flow grades. Adhesion is controlled by surface polarity, mould release selection, and solvent aggressiveness. Silicone-based mould releases reduce paint adhesion and should be avoided on visible surfaces. When hot-stamping or in-mould labelling is used, the processing window is narrower than for lower-flow grades because higher melt temperature can wash out foil or film edges. The moulder should run temperature trials at the lower end of the melt range first and increase only as needed to fill.

ABS 750 is not an electroplating-grade ABS. Electroplating grades in the Kumho Petrochemical range use a higher butadiene content and a narrower melt-processing window to produce selective etching sites for electroless nickel or copper deposition. If ABS 750 is exposed to a chrome plating line, the adhesion may be lower because the etch rate of the matrix differs. The difference is process-relevant when a housing design specifies plated ABS; ABS 750 should not be substituted without plate-adhesion testing by thermal cycling and peel evaluation.

When Kumho Petrochemical ABS 750 displaces lower-flow general-purpose grades in thin-wall enclosures

The principal distinction is the melt-flow position. A lower-flow general-purpose ABS is typically reported at 10 g/10 min to 15 g/10 min under 220°C and 10 kg. ABS 750 at 35 g/10 min improves thin-wall fill and shortens injection time but trades away some low-temperature impact and edge-gate blush resistance. This is not a lower-quality shift; it is a molecular-weight and butadiene population difference. Processors sometimes raise melt temperature to force a lower-flow grade into thin sections, but that degrades the polybutadiene phase and reduces notched Izod at 0°C. The 750 grade is selected when geometry and cycle time, not cold-temperature impact, are the controlling variables.

Compared with a high-impact ABS, ABS 750 shows lower notched Charpy and lower ductility in thick sections. High-impact grades are often reported at 8 g/10 min to 10 g/10 min MFR and 35 kJ/m² to 45 kJ/m² notched Charpy at 23°C. The higher MFR of ABS 750 is achieved partly through lower molecular weight of the styrene-acrylonitrile phase, which lowers melt viscosity but also lowers threshold strain for craze initiation under certain loading rates. Therefore ABS 750 should not replace a high-impact grade when a part must pass a drop test at -20°C or when thick bosses create multi-axial tensile stress. Table 1 summarises the type of property shift across three ABS categories. The values are representative and are not grade-to-grade specifications.

The data demonstrate that flow increases are accompanied by reductions in impact, and impact increases are accompanied by reductions in flow. ABS 750 sits in the high-flow general-purpose region, with sufficient room-temperature impact for many appliance and enclosure applications but with measurable boundary conditions at low temperature and high strain rate. The notched Charpy value of 24 kJ/m² at 23°C should not be extrapolated to sub-zero service because the ductile-to-brittle transition in high-flow ABS moves upward relative to high-impact grades.

The grade difference also appears in gate freeze time. Because ABS 750 has higher MFR and lower molecular weight, the gate seal time may be slightly shorter than that of lower-flow grades. Packing must therefore be adjusted earlier to avoid overpacking or sink marks. In hot-runner moulds, lower molecular weight reduces shear heating in the nozzle; setpoint adjustments are required when switching from a high-impact grade.

Post-moulding shrinkage for ABS 750 is normally forecast at 0.4% to 0.7% in the flow direction and 0.5% to 0.8% in the transverse direction after 1 h at 23°C. Long-term dimensional stability is evaluated by ISO 294-4. Parts are allowed to stabilise for at least 24 h before critical dimensional inspection. Annealing at 70°C for 2 h reduces residual stress but may alter surface gloss on textured surfaces and can cause slight dimensional relaxation. Moisture absorption at equilibrium is low; dry-as-moulded parts can still move several micrometres per millimetre when exposed to humid air, which is normal for an amorphous styrenic resin.

Chemical resistance of ABS 750 is adequate for dilute aqueous acids, alkalis, and many aliphatic hydrocarbons. The material is not recommended for continuous immersion in ketones, esters, aromatic solvents, or chlorinated solvents because these attack the styrene-acrylonitrile matrix. Stress cracking can occur when a moulded part under tensile load contacts plasticised PVC or certain hydrocarbon-based greases; evaluation should follow ISO 22088-2 or an equivalent constant-strain method. The butadiene phase is also sensitive to ozone and to strong oxidising environments; unprotected exterior use is therefore limited unless a UV-stabilised grade is used.

Compliance checks and chemical resistance boundaries

ABS 750 carries an UL 94 HB classification at 1.6 mm thickness. It is not V-0, V-1, or V-2 rated and must not be selected for applications requiring an ignition-resistance rating. Incorporation of halogen-free flame-retardant masterbatches into ABS 750 is not recommended without full re-qualification because the additives shift melt viscosity, reduce notched impact, and can generate mould deposits. For electrical enclosures requiring glow-wire performance, the part design and wall thickness control the result, but the base resin alone does not provide a self-extinguishing behaviour.

Regulatory declarations apply to the homogeneous material. Table 2 lists the main compliance boundaries for specification review. It is not an exhaustive regulatory certification.

For food-contact and potable-water applications, lot-specific confirmation under 21 CFR 181.32 is required because not all production campaigns are cleared or tested for migration limits. REACH and RoHS declarations apply to the homogeneous material at the concentration thresholds shown in Table 2; they do not cover post-added colourants, regrind, or mould-release agents. ABS 750 should not be blended with polycarbonate or styrene-acrylonitrile regrind streams without verification of MFR, thermal stability, and notched impact under ISO 179-1/1eA. Regrind addition is normally limited to 20 wt%; higher fractions increase lot-to-lot variation, silver streaking, and delamination risk. The material is not suitable for continuous load-bearing applications at temperatures above the heat deflection limit; creep data should be generated under the specific stress and temperature rather than inferred from short-term tensile values. Moulders should also avoid mould releases containing silicone on visible surfaces if painting or plating is planned, because residues reduce adhesion.

Incompatibilities include prolonged contact with ketone-based purge compounds, which can swell the surface and cause microcracking, and use with certain amine-based additives in downstream coating systems, which can interact with residual monomers but published data for this specific configuration is limited. The resin should be processed in a well-ventilated area because thermal decomposition at melt temperatures above 260°C releases styrene and other volatile decomposition products.