Cabot CABELEC® CA4676 is a carbon-black-modified low-density polyethylene compound supplied as pelletized feedstock for direct processing in injection moulding, sheet extrusion, blown-film extrusion, blow moulding, profile extrusion, and cable semiconductive layer extrusion. The material is not a masterbatch; it contains a percolated carbon-black network in an LDPE matrix. Electrical performance is process-dependent: dilution with virgin LDPE, gate shear, draw-down orientation, wall thickness, and cooling rate all shift measured resistance. Conditioning before electrical measurement follows ISO 291 at 23 ± 2 °C and 50 ± 5 % RH. Surface resistivity is determined according to ASTM D257-14 at 500 V and 60 s electrification; planar packaging films are tested under ANSI/ESD STM11.11; point-to-point resistance is recorded under IEC 61340-2-3. Pre-drying in a desiccant dryer at 70–80 °C for 2–4 h is imposed when pellet moisture exceeds 0.1 wt%, which commonly occurs after storage at relative humidity above 60% RH. Processing should avoid excessive external lubricants, release agents, and amine-based process aids because low-molecular-weight additives can migrate to the carbon-black surface and interfere with electron tunnelling between aggregates. Where grade-specific data is not published for a particular geometry, the stated ranges are class-typical for carbon-black-loaded LDPE rather than guaranteed specification limits.

Injection moulding of CA4676 into stackable ESD tote boxes requires controlled shear across the check ring, runners, gate, and weld lines because final point-to-point resistance is determined less by bulk resistivity than by local orientation of the carbon-black network. Moulding on a 120-tonne hydraulic injection-moulding machine with a 35 mm three-zone screw, 20:1–22:1 L/D, barrel profile 170/190/210/215 °C from feed to nozzle, and mould temperature 25–40 °C is used. Injection velocity is maintained at 30–60 mm/s; higher velocities create shear heating at the gate and can raise surface resistivity by fragmenting carbon-black structure. Gate land height is not less than 60% of the nominal wall thickness, and fan or edge gates are preferred; pin gates are avoided where wall thickness exceeds 2.0 mm. Hold pressure is set at 50–70% of peak injection pressure, with peak pressure ranging from 800 bar to 1200 bar, back pressure at 5–8 bar, and screw speed below 80 rpm. The addition ratio for conductive totes is 100 wt% CA4676, producing point-to-point resistance of 10^3–10^6 Ω measured by IEC 61340-2-3. When static-dissipative behaviour is specified for non-solder areas, a 70/30 w/w compound/virgin LDPE blend is let down to produce 10^7–10^9 Ω; further dilution is not used for this geometry because weld-line resistance can exceed the <10^11 Ω static-dissipative upper limit. Compliance is verified against ANSI/ESD S20.20-2021 and IEC 61340-5-1:2016 on production parts rather than laboratory plaques, since weld lines and gate shoulders can be 1–2 orders of magnitude higher than the bulk wall. Lot acceptance includes melt flow rate measurement at 190 °C/2.16 kg according to ISO 1133-1:2022; lot-to-lot MFR variation greater than ±15% triggers adjustment of the feed-zone setpoint to preserve injection cushion and resistance uniformity. Terminal products include matrix totes, stackable Euro containers, component bins, PCB transport boxes, rail-mounted part kits, and removable partition inserts for ESD-protected areas.

What Governs Thermoformability of Carbon-Black-Filled LDPE Sheet?

Sheet extrusion from CA4676 is carried out on a single-screw extruder with 25:1 L/D, a screen pack of 60/120/60 mesh, and a polished three-roll stack. Melt temperature is held at 210–225 °C; die lip gap is set at 1.2–1.5 times the target sheet thickness to compensate for die swell and carbon-black elasticity. Roll temperatures of 70–90 °C stabilize surface quality, and sheet thickness is controlled between 1.5 mm and 4.0 mm. Thermoforming is conducted on a plug-assist vacuum former with IR sheet surface temperature 120–140 °C, mould temperature 40–60 °C, and draw ratio kept below 3:1. Deep draw above 50 mm requires plug assist because carbon black reduces the effective forming window; if plug speed is too high, the side wall thins and the carbon-black network is oriented, shifting surface resistance from 10^4 Ω on flat surfaces to 10^8–10^10 Ω on the drawn side wall. Formulation addition uses undiluted compound or 85/15 w/w CA4676/virgin LDPE for conductive trays; up to 40 wt% virgin LDPE is used only when the article is specified as static dissipative at 10^6–10^9 Ω. Above 50 wt% virgin LDPE, thin-wall sections can lose percolation and exceed 10^11 Ω after forming. Conformance is anchored to ANSI/ESD STM11.11 for planar resistance, ASTM D638-14 for tensile properties, ISO 1133-1:2022 for incoming melt flow rate, and IEC 61340-5-1:2016 for packaging use. Terminal product types include thermoformed PCB trays, assembly nests, solder-bake carrier trays, component fixture trays, and conductive insert liners for corrugated packaging.

Blown-film conversion of CA4676 places two competing demands on the carbon-black network: sufficient filler concentration for low surface resistance and sufficient bubble stability for gauge control. A grooved-feed extruder with 25:1 L/D, melt filtration at 50/100/50 mesh, and die gap 1.2 mm is operated at melt temperature 180–200 °C, blow-up ratio 2.0–2.5:1, and frost line height 2–4 die diameters. Film gauge is controlled from 50 µm to 200 µm; carbon black raises infrared absorption, so the die and barrel settings are 10–20 °C lower than those used for unfilled LDPE at the same output. Undiluted CA4676 at 80 µm yields surface resistance 10^3–10^6 Ω according to ANSI/ESD STM11.11 and functions as a discharge-shielding barrier. For dissipative liners and pallet covers, 30–50 wt% CA4676 is let down into virgin LDPE to produce 10^8–10^10 Ω. Below 30 wt% compound, the percolation network becomes discontinuous in thin film, and measured surface resistance can exceed 10^11 Ω, failing the <10^11 Ω packaging requirement of ANSI/ESD S541-2019. Compliance verification includes ANSI/ESD S541-2019 for packaging classification, IEC 61340-2-3 for low-charging verification, and supplier declarations under RoHS 2011/65/EU and REACH 1907/2006. Terminal product types include black conductive ESD bags, flat bottom seal liners, protective sleeves, component cassette covers, and conductive pallet hoods.

Solvent-Contact Packaging and the Static Discharge Threshold

Extrusion blow moulding of conductive LDPE containers for solvent contact exposes the pinch-off seam to the highest resistance risk because carbon-black orientation in the weld region can interrupt the conduction path between interior and exterior surfaces. Containers are moulded on an accumulator-head blow moulder with melt temperature 190–210 °C, blow pressure 6–8 bar, mould temperature 10–30 °C, and wall thickness 0.8–2.5 mm. The addition ratio is 100 wt% CA4676 for conductive containers, producing point-to-point resistance below 10^6 Ω measured by IEC 61340-2-3. Dilution below 80 wt% compound is not used for solvent-contact items because the seam, handle bridge, and parting line can rise above 10^9 Ω even when the nominal wall remains conductive. The relevant compliance framework is IEC TS 60079-32-1, which addresses electrostatic charge control in potentially flammable atmospheres, combined with applicable transport packaging tests for the filled container. The material is not a substitute for equipment certification under ATEX 2014/34/EU; it dissipates static charge when the container is deliberately grounded during filling, pumping, and decanting. A production-scale failure mode is seam contamination by partial carbon-black degradation from excessive melt temperature; therefore melt residence time is kept below 4–6 min and start-up purge uses unfilled LDPE until melt temperature stabilizes. Terminal products include conductive jerrycans from 5 L to 60 L, laboratory waste bottles, solvent transfer pails, dose containers, and inner conductive liners for fibreboard drums.

In medium-voltage cable construction, semiconductive screens are not jackets; they are stress-control layers extruded directly over the conductor and over the insulation. Processing of CA4676 in this context is performed on a triple-head cable line with melt temperature 190–210 °C, extrusion pressure 100–200 bar, and draw-down ratio 1.02–1.10 to preserve layer thickness uniformity. The addition ratio is 20–50 wt% CA4676 let down in LDPE carrier resin, with final screen thickness between 0.5 mm and 1.5 mm. The controlling electrical property is volume resistivity below 10^2 Ω·cm at 90 °C, tested according to IEC 60811-501, because this determines the screen’s ability to confine the electric field and suppress partial discharge at the conductor-insulation interface. Cable design and thickness requirements are specified under IEC 60502-2 for extruded insulation systems. Published data for CA4676 in medium-voltage cable constructions is limited; the cited processing window is drawn from general carbon-black-loaded LDPE semiconductive screen practice rather than a specific supplied cable formulation. Batch-to-batch dispersion quality is monitored by screen pack pressure rise and optical film inspection, because large carbon-black agglomerates can produce surface protrusions that reduce breakdown strength. Terminal product types include conductor screens, insulation screens, and bonded semiconductive layers in underground medium-voltage distribution cables.

When Cleanroom Profile Extrusion Demands Wall Conductivity After Vacuum Calibration

Profile extrusion of conductive LDPE into cleanroom rails differs from injection moulding because the vacuum calibration process cools the wall skin before the core has fully relaxed, setting up a resistivity gradient across the cross-section. A single-screw extruder with 25:1 L/D and a vacuum sizing tank at −0.2 bar to −0.35 bar is used, with melt temperature 190–210 °C and line speed adjusted to keep drawdown below 10%. Profiles are extruded with wall thickness 1.0–2.5 mm; corner radii below 0.8 mm can show surface resistance 2–3 orders of magnitude higher than flat faces because the conductive network is disrupted by converging melt flow in the calibration die. Formulation addition is 80–100 wt% CA4676, since let-down below 70 wt% causes the vacuum-calibrated skin to exceed the <10^9 Ω point-to-point limit of ANSI/ESD S20.20-2021. Compliance testing is performed with IEC 61340-2-3 on the actual profile surface, not on compression-moulded plaques, and mechanical acceptance follows ASTM D638-14 on cut specimens. The line must avoid excessive use of water-based sizing lubricants that can deposit on the carbon-black surface; if used, the lubricant is removed by air blow-off before electrical testing. Terminal products include ESD guide rails, component feeders, clip-in PCB holders, bench protector edges, and antistatic cable ducts used in semiconductor and electronics assembly cleanrooms.