LG Chem ABS ER-870 is an acrylonitrile-butadiene-styrene extrusion resin supplied as pelletized feedstock for monolayer sheet, profile, and formed appliance components. The material is formulated for a balance of melt strength in thick-gauge sheet and low-temperature ductility in the formed part. Producer literature reports a melt flow rate of 4.0–6.0 g/10 min at 220 °C under 10 kg load according to ISO 1133-1:2022. Density is 1.04 g/cm³ per ISO 1183-1:2019. Representative lot-release values include tensile yield stress of 43–46 MPa at 50 mm/min per ASTM D638-14, flexural modulus of 2.10–2.30 GPa per ISO 178:2019, notched Izod impact at 23 °C of 320–360 J/m per ASTM D256-10, and Vicat softening temperature of 96–99 °C under 50 N loading per ISO 306:2022 method B50. These are typical datasheet values, not lot-specific guarantees; the shipment certificate should be consulted before process windows are fixed.

In ambient relative humidity above 60%, the resin should be pre-dried in a desiccant dryer at 80 °C for 2–4 h to reduce residual moisture below 0.02 wt% as determined by ISO 15512:2019. Wet pellets produce splay and surface bubbles in sheet above 0.5 mm. Because ABS is hygroscopic, silos and transfer lines should be sealed and, where possible, blanketed with dried air at a dew point of –20 °C or lower. Unnecessary pellet exposure to ambient air during hopper loading should be avoided, particularly in high-humidity production halls without climate control.

What Limits Process Stability in Sheet Extrusion of ER-870?

Single-screw extruders with 30:1 L/D barrier screws are commonly used for ER-870 sheet production. A typical barrel profile from feed throat to die is 180 °C, 200 °C, 215 °C, 225 °C, 230 °C, and 230 °C at the die. Melt temperature measured by an immersion probe at the die adapter should remain between 210 °C and 240 °C. A melt gear pump between the screw tip and die reduces pressure fluctuation to approximately ±0.15 MPa and permits gauge tolerance on polished rolls of ±0.03 mm on 2.0 mm sheet. Screen packs of 100/60/20 mesh remove contamination but increase melt residence time; pressure build-up above 10 MPa before the screen changer indicates gel accumulation or excessive fines.

At melt temperatures above 250 °C, the polybutadiene phase undergoes thermal oxidative crosslinking. Ambering increases, and notched Izod impact retention after thermoforming falls. The condition is visible as yellowing in unpigmented sheet and as black specks after regrind. If a production line stops for more than 15 min, the screw should be purged with an ABS purging compound or general-purpose polystyrene. PVC residue should not be introduced into the same barrel because residual hydrogen chloride can cause surface blush and accelerate corrosion on polished die lips. Processors have also observed die-lip deposit formation when high-shear mixing sections generate local melt temperatures above the recommended upper limit.

In industrial refrigerator-liner production, pre-dried ER-870 sheet is heated to a surface temperature of 140–170 °C before vacuum or plug-assist forming. The lower portion of this range reduces sag but increases spring-back in deep-draw corners; the upper portion improves detail replication but raises the risk of blushing and wall-thickness variation. Mold temperature is typically maintained at 60–80 °C to reduce frozen-in strain. Edge trim regrind may be incorporated at 20–30 wt% when the sheet is unpigmented and when the regrind is dried to the same moisture specification as virgin pellets. Higher regrind levels generally reduce low-temperature impact retention because the rubber phase has already been through one thermal history.

Published comparative data for ER-870 in coextruded capstock structures with PMMA or ASA is limited; tooling trials are recommended to establish layer adhesion and thermal expansion differences. For monolayer applications, the material is more suited to opaque or lightly pigmented sheet than to high-transparency packaging because ABS is inherently translucent to opaque.

When High-Gloss Capstock Is Not Required

ER-870 is frequently specified where a high-gloss outer surface is not the primary requirement, such as refrigerator door liners, inner cases, and utility panels that are hidden from direct view after assembly. The grade is generally easier to calender into matte or embossed sheet than high-gloss injection-molding grades because its lower melt flow rate preserves roll pattern transfer. Part design should avoid sharp undercuts below 1.0 mm radius when post-forming trimming is manual, because notched Izod impact retention can be reduced by surface scratches introduced during trimming.

Comparative Typical Property Ranges for ER-870 and Other ABS Families

The following table summarizes representative datasheet values for ER-870 in relation to broad commodity ABS families. The comparative columns are given as typical ranges and are not a substitute for grade-specific certificates.

The main difference between ER-870 and high-heat ABS families is the Vicat softening temperature. ER-870 is not intended for continuous exposure to hot-fill or automotive heat-sink environments where the local air temperature can exceed 85 °C. Compared with general-purpose extrusion ABS, ER-870 typically retains a higher notched Izod impact value at 23 °C after a given thermal history, but this advantage narrows if melt temperature control is poor or if regrind content is excessive.

Extended Melt Residence Alters Rubber-Phase Crosslink Density

At screw residence times over 8 min and melt temperature above 245 °C, the polybutadiene rubber particles undergo gelation. The melt becomes increasingly shear-thinning, and die swell may decrease. Formed parts can show a reduction in notched Izod impact at –30 °C by 20–30% relative to virgin pellets. The degradation is not always detected by melt flow rate alone because chain scission in the styrene-acrylonitrile phase can increase melt flow while crosslinking in the rubber phase simultaneously reduces impact. For this reason, melt flow rate and notched Izod impact should be measured together when qualifying regrind or when evaluating a new extruder screw design. If a screw has a high compression ratio above 3.2:1, the added shear heating may require a lower barrel set point near the vent to avoid melt temperatures above 240 °C.

ER-870 is often selected for applications that do not require continuous exposure to hot water above 70 °C. The grade’s resistance to aqueous acidic cleaning solutions is acceptable for intermittent contact, but alkaline cleaners above pH 10 at elevated temperature may induce environmental stress cracking in formed parts with high frozen-in strain. Unpigmented or food-contact formulations require supplier documentation for the specific coloration package; migration testing may be required under the relevant regional regulation. The grade is not recommended for continuous hot-water contact above 70 °C without part-specific validation.