During blown film conversion of LLDPE-rich monolayer structures, LyondellBasell POLYBATCH™ Opaque Blue 40356 Concentrate Based In LLDPE is metered at the extruder throat through a gravimetric dosing unit into a host resin with melt flow index 0.8–2.0 g/10 min at 190 °C under 2.16 kg load per ISO 1133-1:2022. Letdown is held at 1.5–3.0 wt% for film gauges of 25–120 µm; below 40 µm, the 1.5–2.0 wt% range is preferred to limit pigment agglomerates and die-lip deposit on lines fitted with 80/100/120 mesh screen packs. Processing uses a single-screw extruder with 24:1–30:1 L/D, barrel profile 180–210 °C, and die 210–230 °C; blow-up ratio is set between 2.0:1 and 3.5:1. Light transmission of the pigmented film is measured per ASTM D1003-13; because the concentrate contains a high pigment loading in an LLDPE carrier, final optical density is a function of film thickness, letdown ratio, and frost-line cooling rate. The concentrate is not hygroscopic under sealed storage; bags opened at relative humidity above 60% should be pre-dried at 60–70 °C for 2 h in a desiccated-air hopper, while pre-drying above 80 °C should be avoided to prevent pellet surface melting and hopper bridging. Terminal non-food structures include opaque blue collation shrink film, freezer film, and heavy-duty shipping sacks; direct food-contact use requires lot-specific migration testing under EU 10/2011 Annex I and Annex V with an overall migration limit of 10 mg/dm², carrier resin assessment under 21 CFR 177.1520(c), and colorant compliance with 21 CFR 178.3297. A documented operational boundary is that the LLDPE carrier can reduce machine-direction tear propagation measured by ASTM D1922; comparative tear trials at 1.5 wt% and 3.0 wt% letdown are necessary before fixing the formulation.

Why Does Letdown Ratio Shift in Thin-Gauge Cast Film?

In cast film extrusion, the same concentrate is exposed to higher melt temperature and shorter residence time than in blown film, and letdown is typically reduced to 1.5–2.5 wt% for film thicknesses of 20–60 µm. The extruder is a single-screw machine with 30:1 L/D, barrel profile 200–240 °C, and a flat die with die gap 0.5–0.8 mm; the chill roll is maintained at 15–25 °C to freeze the LLDPE carrier before pigment particles can re-agglomerate. Die-lip deposit and streaking are the principal failure modes observed on production lines; increasing filtration to 100/120/150 mesh and reducing screw speed are more effective than increasing letdown when hue strength is insufficient. The terminal non-food articles are blue-tinted cast stretch film, hygiene packaging overwrap, and temporary surface-protection film. For food-contact converters, the final printed or laminated structure must comply with EU 10/2011 Annex II for plastic materials and 21 CFR 177.1520(c) for the PE carrier, but lot-specific documentation for the complete formulation is required. Because cast film can run at line speeds of 200–400 m/min, masterbatch particle size and carrier melt index must be matched to the host resin to avoid melt-pressure fluctuation at the feed throat; published lot-specific data for this product in ultra-thin film below 20 µm is limited, so a line trial at 1.5 wt% is required before commercial conversion.

For injection moulded blue caps and closures, the masterbatch is pre-blended by low-speed tumble mixing at 15–30 rpm for 10–15 min before gravimetric dosing into the machine feed throat. Letdown is generally 2.0–3.5 wt%; the host resin is HDPE or LLDPE with melt flow index of 4–20 g/10 min at 190 °C under 2.16 kg per ISO 1133-1:2022. Melt temperature is maintained at 200–230 °C and nozzle temperature at 210–240 °C; mould temperature is controlled between 15 °C and 30 °C for caps and closures with wall sections of 1.0–2.5 mm. Gate diameter is not reduced below 1.0 mm because small gates increase shear heating and can produce gate blush and flow lines around the hinge. The terminal articles are cosmetic tube closures, dispensing caps for household and industrial chemicals, and tamper-evident pail lids. Compliance for non-food closures falls under REACH and EU 94/62/EC heavy-metal limits; food-contact closures require migration testing under EU 10/2011 and 21 CFR 177.1520(c) plus colorant conditions under 21 CFR 178.3297. The dispersed pigment can act as a nucleating agent in polyolefins, and post-moulding shrinkage should be compared at 2.0 wt% and 3.5 wt% letdown on the production tool before dimensional capability is accepted.

Blow Moulded HDPE Container Sidewall Opacity and Drop Impact Retention

Extrusion blow moulding uses a letdown of 2.0–4.0 wt% in HDPE homopolymer or copolymer with melt flow index 0.3–0.8 g/10 min at 190 °C under 2.16 kg (ISO 1133-1:2022). Barrel melt temperatures are maintained at 180–210 °C, while the die head is set at 190–220 °C; parison swell is typically 20–35% above the die gap for monolayer containers. The terminal articles are opaque blue HDPE bottles for personal care, household cleaning, and agrochemical products; the blue concentrate supplies sidewall opacity to mask fill-level variation and reduce transmission of visible light. Sidewall opacity is measured as luminous transmittance per ASTM D1003-13 at the specified wall thickness. Drop impact retention is evaluated by ASTM D2463-15; because dispersed pigment can act as a nucleating agent and modify crystalline morphology in HDPE, impact retention should be compared between unpigmented and pigmented containers at the specified letdown rather than assumed from resin datasheets. Compliance for non-food containers falls under REACH and 94/62/EC heavy-metal limits; food-contact bottles additionally require migration testing under EU 10/2011 and 21 CFR 177.1520(c) plus colorant compliance under 21 CFR 178.3297. A limitation is that the LLDPE carrier can reduce melt strength of HDPE slightly; on deep-draw containers above 4.0 wt%, parison sag may increase, so drop impact per ASTM D2463-15 and column crush per ASTM D2659-16 should be included in the line trial.

When Extrusion Coating Lines Use Opaque Blue Concentrate in LDPE/LLDPE Blends

In extrusion coating and lamination onto paperboard, paper, or aluminium foil, the concentrate is added at 2.0–4.0 wt% to an LDPE/LLDPE blend with melt flow index of 4–15 g/10 min at 190 °C under 2.16 kg. The extruder is a 30:1–36:1 L/D single-screw machine with barrel temperatures from 280–320 °C; melt temperature at the adapter should not exceed 320 °C to avoid thermal hue shift and pigment degradation, and residence time should be kept below 10 min. Die-to-nip geometry is set to control draw-down and neck-in; chill-roll temperature is normally 15–25 °C, and corona pre-treatment of paperboard at 38–42 mN/m wetting tension is used before the molten web is applied. The terminal articles are opaque blue barrier wraps for non-food industrial packaging, paperboard cup outer layers, and coated paper for construction films. Because the LLDPE carrier contributes to draw-down and neck-in behaviour, the edge bead trim may increase with letdown; processors should measure neck-in at the specified line speed and adjust the deckle position accordingly. Food-contact laminates require the complete multilayer structure to meet EU 10/2011 overall migration limits and the PE layer to comply with 21 CFR 177.1520(c); heavy-metal content must remain within the 94/62/EC sum limit of 100 mg/kg for Pb, Cd, Hg, and Cr(VI).

Pipe Extrusion Requires Long-Term Hydrostatic Assessment Beyond Initial Pigment Dispersion

HDPE water and industrial pipe extrusion applies the concentrate at 2.0–5.0 wt% into PE100 or PE80 pipe grades; the LLDPE carrier is melt-compatible with pipe-grade HDPE but does not replace the stabilizer package. A single-screw extruder with 30:1–38:1 L/D and grooved feed section is operated at 190–230 °C, with melt temperature and head pressure monitored at the breaker plate; screen packs of 60/80/100 mesh are placed upstream of the die to remove undispersed solids. Vacuum calibration sleeves control outer diameter and wall thickness; blue pigmentation must remain uniform enough to avoid visible streaking at wall sections above 2.0 mm. The terminal product is blue HDPE cold-water service pipe, compressed-air line, and cable duct; potable-water contact requires extraction testing to NSF/ANSI/CAN 61 in North America or BS 6920 in the United Kingdom, while local drinking-water approvals must be obtained for the finished pipe. Thermal stability of the finished pipe is assessed by oxidation induction time per ISO 11357-6:2018 at 210 °C; dispersed pigment can reduce OIT if stabilizer demand is underestimated, so a comparative OIT test between unpigmented and pigmented pipe compound is necessary before long-term use. A limitation is that the LLDPE carrier has lower modulus than pipe-grade HDPE; at the upper letdown of 5.0 wt%, slow crack growth resistance measured by ISO 13479 may shift, and published data for this specific blue concentrate in pressure-pipe formulations is limited, so long-term hydrostatic testing at 20 °C / 50 yr per ISO 9080 is recommended for pressure-rated service.