In monolayer LLDPE blown-film lines equipped with a 30:1 L/D smooth-bore barrier screw and a 200–250 mm spiral mandrel die, LyondellBasell POLYBATCH™ Dark Grey 80431U Concentrate Based In LLDPE is pre-blended with the virgin film grade by tumble blending or gravimetric dosing before the feed throat. The LLDPE carrier is selected to approximate the melt viscosity of the dilution resin. When the host film resin has a melt flow rate of 1.0 g/10 min at 190 °C/2.16 kg, a concentrate based in LLDPE with a similar melt index reduces localized viscosity stratification in the melt channel and across the die lip. Typical let-down ratios for carbon black dark grey concentrates in monolayer blown film range from 2 wt% to 6 wt%, but the exact loading for 80431U must be established by bench-scale trials because LyondellBasell does not publish full pigment loading and complete rheological data in the public technical datasheet. Processing temperatures are normally set from 190 °C to 230 °C across the barrel and die. A die gap of 1.5 mm to 2.5 mm is commonly used, and blow-up ratio is held between 2.2:1 and 3.0:1. Frost line height is adjusted from 4 to 8 die diameters to balance machine-direction and transverse-direction tear. Dispersion is monitored at the screen changer by pressure rise. If the pressure increase exceeds 35% over a 4 h run, the operator should stop the line and inspect the screen pack for carbon black agglomerates or gel bodies. Film appearance is evaluated under 100× magnification, and mechanical properties are measured per ASTM D1709 and ASTM D1922. For food-contact film, migration of carbon black bound in LLDPE matrices is generally low because carbon black aggregates are not readily solubilized, but any surface-reactive species present in the masterbatch must be assessed by specific migration testing under the intended time and temperature conditions. Compliance must be confirmed on the finished packaging structure under EU No 10/2011 or FDA 21 CFR 178.3290; compliance cannot be inferred solely from the masterbatch composition. Pre-drying at 60 °C for 2 h is recommended when storage relative humidity has exceeded 60% and surface moisture is visible on pellets.

What Limits Carbon Black Dispersion in Thin-Gauge Cast Film?

In cast-film extrusion at final thickness below 20 μm, the primary dispersion risk is formation of pigment agglomerates when the concentrate is processed at an excessively low melt temperature or when the screw lacks sufficient distributive mixing. The concentrate should be dosed through a gravimetric hopper mounted above the feed throat to avoid pellet segregation. Melt pump inlet pressure stability is expected between 80 bar and 120 bar. Oscillation exceeding ±3 bar at the die entrance is commonly linked to inconsistent carbon black distribution or melt-temperature variation. A melt-temperature deviation of more than ±5 °C across the die can produce visible agglomerate streaks and optical haze variability. Chill roll temperature is maintained at 15 °C to 25 °C, while air knife position and vacuum box settings are trimmed to prevent frost line instabilities on the cast roll. A 75 mm single-screw extruder with 28:1 L/D and a dispersion mixer is typical for thin-gauge cast film. Optical haze is measured per ASTM D1003, and film defects are counted on a laser scanning inspection system. Published data for 80431U in this specific configuration is limited, so line trials are required to confirm minimum acceptable loading without sacrificing haze or tear performance.

When the Concentrate Is Introduced via Side-Feed on a Co-Rotating Twin-Screw Compounder

On a co-rotating twin-screw compounder with 40:1 L/D barrel and side-stuffer at barrel zone 6, a dark grey LLDPE-based concentrate can be fed into a tinted LLDPE compound at a let-down ratio that yields 0.1 wt% to 0.5 wt% final carbon black content for light grey tinting applications. In this configuration, the side-feed port bypasses the feed-throat screw flutes and reduces segregation of masterbatch pellets across the hopper. The screw design should use two or three kneading blocks at 45° to 90° staggering after the side-feed port, followed by vacuum devolatilization at −0.08 MPa to −0.09 MPa. Specific energy input is normally kept below 0.25 kWh/kg because carbon black particles in the concentrate already carry a wetted pigment surface. Excessive specific energy can re-agglomerate the pigment or degrade the LLDPE carrier. Melt temperature should remain below 240 °C for LLDPE carrier stability. A gear pump and 80/120/60 mesh screen pack provide constant die pressure and retain coarse particles. Dispersibility is checked by pressure filter test with a 14 μm filter. A pressure rise below 0.5 bar/g of pigment per minute is generally considered acceptable. Certain amine-based processing stabilizers can interact with carbon black surface chemistry during prolonged high-temperature residence; compatibility should be confirmed by thermal stability testing before production. Published data for 80431U under these exact conditions are not disclosed.

Accumulator-head blow molding lines running high-density polyethylene with a small addition of dark grey concentrate may use 80431U for dark grey refuse containers, industrial pails, or automotive fluid reservoirs. Because the carrier is LLDPE, dosing above 3 wt% into HDPE can reduce top-load strength and increase parison sag. The processor should verify the melt flow rate of the final blend does not shift by more than 10% from the base HDPE. Die head temperature is kept between 180 °C and 210 °C, and accumulator drop speed is adjusted to prevent draw-down. If colour streaks appear, inadequate distributive mixing in the extruder is the usual cause. Installing a static mixer downstream of the screen changer can improve colour uniformity. Physical performance is tested by stack loading per ISO 12048 or drop impact per ASTM D2463. Published data for 80431U in blow molding is limited.

Pipe Extrusion Back-Pressure and Carbon Black Agglomerate Filtration

Pipe extrusion of PE100 or PE4710 polyethylene pipe with a dark grey concentrate requires distinction between decorative colour tinting and long-term UV stabilization. Fully stabilized black or grey pipe formulations intended for outdoor exposure normally require 2.0 wt% to 2.5 wt% carbon black with a primary particle size below 25 nm and dispersion rating per ISO 18553. A dark grey LLDPE-based concentrate used at low let-down may not reach this carbon black loading. The resulting pipe may not satisfy the UV resistance requirements of ISO 4427 or ASTM D3350. For indoor colour coding, dosing is typically 1 wt% to 3 wt%. Extruder back pressure at the breaker plate should be monitored. An increase above 20% from virgin resin indicates screen blinding by agglomerates. A 60/80/100 mesh screen pack and an annular die with mandrel temperature 10 °C lower than the die body are common. Melt temperature for PE100 pipe is normally 200 °C to 220 °C. Dimensional stability is checked per ISO 3126, hydrostatic strength per ISO 1167, and carbon black dispersion per ISO 18553.

Injection molding of small grey components from LLDPE or LDPE can use the concentrate at 2 wt% to 4 wt%. Screw back pressure is set between 0.5 MPa and 1.0 MPa to improve homogenization without extending screw recovery time beyond the cooling time. Mold surface temperature between 15 °C and 40 °C affects colour depth and weld-line visibility. In dark grey parts, weld lines are readily detected when the concentrate is poorly distributed. The gate should be positioned to place knit lines outside cosmetic surfaces. Mechanical properties are measured per ISO 527-2 and ISO 179. No published data specific to 80431U in injection molding are available.