Kumho Petrochemical ABS 770 is an acrylonitrile-butadiene-styrene copolymer injection-moulding grade supplied in natural and pre-coloured pellet form. The grade is positioned in the manufacturer’s general-purpose ABS series with a flow/impact balance intended for medium-flow industrial moulding. In the dispersed-phase morphology, an emulsion-polymerised polybutadiene rubber phase provides low-temperature ductility, while the continuous styrene-acrylonitrile matrix governs modulus, thermal resistance, and solvent susceptibility. Representative manufacturer-published values include specific gravity of 1.05 under ASTM D792-20, melt flow rate of 20 g/10 min at 220°C/10.0 kg under ASTM D1238-20, tensile yield strength of 43 MPa under ASTM D638-14, elongation at break of 20% under ASTM D638-14, flexural modulus of 2.3 GPa under ASTM D790-17, notched Izod impact of 22 kJ/m² at 23°C under ISO 180/1A, and heat deflection temperature of 89°C at 1.82 MPa under ASTM D648-18. The standard grade carries UL 94 HB classification at 1.5 mm nominal thickness. These values are typical lot averages, not lot-release minima; published data for this specific configuration is limited where flame-retardant or colour concentrates are pre-compounded by downstream users.

On production-scale reciprocating-screw injection-moulding machines with clamp force between 80 t and 150 t, screw diameter from 30 mm to 50 mm, and L/D ratio of 20–22, the melt temperature measured at the nozzle is commonly held at 220°C to 240°C for natural resin. A barrel profile from hopper to nozzle of 200°C, 210°C, 220°C, 220°C avoids excessive frictional heat. At melt temperatures above 260°C or after barrel residence time longer than 15 min, oxidative degradation of the polybutadiene phase becomes visible as yellowing and is accompanied by a measurable decline in notched Izod impact under ISO 180/1A. Batches conditioned overnight in open silos above 60% RH require desiccant drying at 80°C for 3–4 h to a dew point of -20°C or lower; residual moisture above 0.05 wt% produces splay on the part surface when melt temperature exceeds 220°C and becomes more severe at thin-wall projections below 1.2 mm.

Published data for this specific configuration is limited for oscillatory shear rheometry, but unfilled ABS of comparable melt flow rate exhibits pronounced shear-thinning behaviour. Capillary rheometry at 220°C is used to characterise the flow curve; moulders often observe that raising melt temperature from 220°C to 240°C reduces apparent viscosity and improves fill in wall sections below 1.2 mm, but it narrows the thermal degradation margin in hot-runner systems. The practical consequence is that fast-fill segments should be followed by a controlled packing phase to prevent over-shearing at the gate and to maintain impact retention at knit lines.

During incoming-lot release, resin lots are typically tested under ISO 1133-1:2022 for melt mass-flow rate and ISO 1183-1:2019 for density. If a lot is received with a melt flow rate more than ±10% from the target value, the moulder should adjust screw speed and back pressure rather than melt temperature. A back pressure of 5–10 MPa and screw speed of 60–100 rpm on a 40 mm screw provide a stable melt cushion; higher back pressure above 15 MPa increases residence time and reduces notched impact. These adjustments are standard in injection-moulding production rather than grade-specific limitations.

What Separates ABS 770 from Higher-Flow and Higher-Impact Grades in the Same Series?

Within the Kumho Petrochemical ABS portfolio, the grade occupies a deliberate position between high-flow and high-impact injection-moulding grades. Relative to a high-flow grade such as ABS 780, ABS 770 retains higher notched Izod impact at 23°C under ISO 180/1A but exhibits lower melt flow under ASTM D1238-20; this trade becomes relevant when a tool is converted from a fast-filling thin-wall resin to a more ductile specification. Relative to a high-impact grade such as ABS 710, ABS 770 offers a reduction in injection pressure and shorter fill time, but it cannot replace the higher-impact material in applications requiring retained impact at -30°C unless ISO 6603-2 puncture-impact testing confirms otherwise. The representative datasheet envelope below is compiled from public supplier literature and may vary by manufacturing site and colour package.

Typical injection-moulded applications include electronic housings, appliance control panels, office-automation covers, vacuum-cleaner bodies, and automotive interior trim. For automotive interior trim, fogging resistance is normally evaluated under ISO 6452 and odour under VDA 270; the grade is not pre-qualified for every OEM specification. For external electrical housings, comparative tracking index and glow-wire requirements are not satisfied by the standard unfilled HB grade; grades with flame-retardant additives are required where IEC 60695-2-11 testing is part of the approval package.

Chemical compatibility of the styrene-acrylonitrile matrix is more restrictive than that of the polybutadiene impact modifier. Continuous contact with short-chain ketones, esters, chlorinated solvents, or aromatic hydrocarbons under moulded-in stress can produce environmental stress cracking; ASTM D543-21 immersion testing at 23°C and 1% strain is required for any external plasticiser exposure from PVC gaskets or labels. Strong oxidising acids, including concentrated nitric acid, are not compatible. Aliphatic hydrocarbons, weak aqueous acids, and alkaline detergents are generally tolerated under intermittent contact, but validation under ISO 22088-2:2016 is recommended before production release. The standard grade is not formulated for direct food-contact or drinking-water applications; no EU Regulation 10/2011 positive-list or FDA 21 CFR 175.300 compliance is implied for the unfilled natural formulation. Regulatory records supplied with the grade typically confirm EU RoHS Directive 2011/65/EU Annex II restrictions and EU REACH Regulation (EC) No 1907/2006 SVHC candidate-list status at the ship date.

When Regrind Ratios Exceed 20% and Residence Time Drifts

In closed-loop moulding, regrind addition above 20 wt% in natural ABS 770 changes the melt flow rate and notched impact envelope. On a 120 t injection-moulding machine with a 40 mm screw and 180 g shot weight, batch-to-batch variation of melt flow rate in natural lots is typically controlled within ±10% relative; pre-coloured compounds can exceed this range because pigment concentrates and wax-based colour carriers reduce melt viscosity. Granulated sprue and runner scrap should be dried at 80°C for 2 h and blended through a gravimetric feeder with virgin material to avoid screw-slip feeding instabilities. If hot-runner manifold temperatures exceed 230°C or if the material remains in the hot runner for more than 10 min during interruption, surface blush and black specks may appear; purging with a rigid styrene-based purge compound at 240°C is then needed before re-start. Jetting failures are observed when the nozzle melt temperature falls below 220°C and injection velocity exceeds 120 mm/s, particularly on parts with gate land lengths below 0.5 mm.

Moulded shrinkage of ABS 770 is typically 0.4% to 0.7% in the flow direction and 0.5% to 0.8% perpendicular to flow, as determined in a 3 mm plaque under ASTM D955-21. Shrinkage anisotropy is lower than glass-filled grades, but corner warpage occurs when cooling is differential across wall sections; mould temperature should be held between 40°C and 80°C using turbulent flow in conformal cooling channels with a Reynolds number above 10,000. Gate diameter of 1.0 mm to 1.5 mm and land length of 0.5 mm to 1.0 mm are common for electronic housings with nominal wall thickness 2.0 mm. Multi-stage injection profiles with a short fast-fill segment followed by controlled packing at 50–70 MPa hydraulic pressure reduce sink marks in ribbed sections.

For colour masterbatch dilution on a co-rotating twin-screw extruder with L/D 32:1 and screw speed 300 rpm, melt temperature at the die plate should not exceed 230°C; a barrel profile of 190°C to 220°C avoids premature degradation of the masterbatch carrier while maintaining dispersive mixing. Underwater pelletising water temperature of 40°C to 50°C is used to control pellet shape and reduce surface moisture pickup. The compounder should inert the feed throat with nitrogen when moisture content of incoming pellets exceeds 0.10 wt%.

Since the standard grade is not pre-qualified for every OEM specification, end-use validation remains necessary. Flow-length-to-wall-thickness ratios above 150:1 should be verified by short-shot studies under ISO 294-1 before production. Splay, delamination, or unexplained loss of impact at cold temperatures below -20°C indicate moisture carryover or excessive regrind degradation rather than a generic formulation limit. For load-bearing continuous-use applications in air, the long-term service temperature of unfilled ABS should not exceed 70°C; the heat deflection temperature is a short-term deflection index, not a continuous-use rating. Published data for this specific configuration is limited for long-term creep and fatigue under customer-specific loading; ISO 899-1:2017 tensile creep and ISO 179-1:2010 Charpy impact testing are required before substituting ABS 770 into structural parts.