Borealis HDPE FL5580 is processed as a high-density, high-molecular-weight blown-film grade on conventional mono-layer lines equipped with grooved-feed extruders. Nominal density is 958 kg/m³ determined by ISO 1183-1:2019 Method A, and melt flow rate at 190 °C/2.16 kg is reported at 0.55 g/10 min by ISO 1133-1:2022 Procedure A. For T-shirt carrier bag film, practical thickness spans 12–20 µm. Die gaps of 1.4–1.8 mm, blow-up ratios from 3.5:1 to 4.5:1, and frost-line heights of 5–8 die diameters maintain bubble symmetry. The melt exhibits the expected high viscosity of a fractional-melt HDPE; stable extrusion therefore requires feed-zone temperatures beginning at 180 °C, metering-zone temperatures of 200–210 °C, and die temperatures held between 195 °C and 205 °C. On a 90 mm groove-fed extruder with 30:1 L/D, die-head pressure typically remains below 420 bar when melt temperature exceeds 200 °C. Screw speeds above 35 rpm without a fluoroelastomer processing aid can initiate sharkskin at the die exit; addition of 400–800 mg/kg polymer processing aid suppresses melt fracture and permits line speeds of 45–60 m/min at 15 µm. Tensile properties measured to ISO 527-3 on 20 µm film fall near 29 MPa yield stress in both machine and transverse directions. Elmendorf tear according to ISO 6383-2 is strongly anisotropic for this resin, with machine-direction values typically below 0.3 N and transverse-direction values near 1.5–2.5 N, which must be accounted for in perforation design and handle strength. Density above 0.950 g/cm³ also reduces water vapour transmission; published values for 25 µm HDPE film at 23 °C and 85% relative humidity by ISO 15106-3 typically range from 4.0 g/m²·day to 5.5 g/m²·day. Post-industrial regrind addition should not exceed 12 wt% without re-evaluating dart drop and tear strength, because the high-molecular-weight fraction degrades under repeated extrusion heat histories. Corona treatment to a surface energy of 38–42 mN/m after treatment at approximately 2 kW is normally adequate for flexographic water-based inks, but ink adhesion should be revalidated according to ASTM F2252-13 after any change in film age or corona power.

What Extruder and Die Parameters Prevent Melt Fracture in Sub-15 µm Film?

Melt fracture in blow-extruded FL5580 originates mainly in the die land when wall shear stress exceeds a critical threshold at insufficient melt temperature. Published extrusion studies on similar high-molecular-weight HDPE film grades report sharkskin onset when apparent wall shear rate in a spiral mandrel die with 1.2 mm gap exceeds roughly 450 s⁻¹; the exact threshold for FL5580 is not published, but plant trials on a 70 mm single-screw extruder with 28:1 L/D and a 300 mm die show that melt temperature below 195 °C at screw speeds above 28 rpm produces visible surface roughness. Raising the die set temperature from 180 °C to 205 °C increases melt temperature only 6–8 °C, because viscous dissipation in the metering zone remains moderate. A more effective intervention is widening the die gap from 1.2 mm to 1.6 mm, which reduces wall shear stress by approximately 35–45% at constant output. Alternately, addition of 500 mg/kg of a free-flowing fluoroelastomer-based processing aid masterbatch coats the die lip and postpones sharkskin to output rates 25–35% higher. The processing aid must be metered at the feed throat and pre-blended for 15 min in a low-shear tumble mixer; pellet segregation in the hopper causes intermittent surface defects. Die-lip purge cycles should be scheduled every 8 h, because oxidised low-molecular-weight species accumulating at the lip increase the onset of melt fracture. Screw geometry with a Maddock mixing section in the final third of a 25:1 barrier screw improves thermal homogeneity, but excessive shear heating can raise melt temperature above 220 °C, at which point gel particles and odour may develop. Stable sub-15 µm film production is achieved when the frost line is set 4–6 die diameters above the die exit and the collapsing frame maintains bubble symmetry; downstream web tension should not exceed 12 N per 100 mm width to avoid blocking of the soft HDPE surface. Melt pressure after PPA addition commonly drops 20–40 bar, which reduces motor load and permits a line-speed increase of 10–15%. Surface quality is verified by optical haze measurement according to ASTM D1003-21 and by tactile comparison against retained production standards from the previous run.

Blown film for frozen-food packaging uses FL5580 when the converter requires low-temperature puncture resistance and stiffness at −18 °C without shifting to an LLDPE-dominant structure. Compounding begins with 88–94 wt% FL5580, 5–10 wt% C₆-LLDPE with melt index 0.9 g/10 min, and 1–2 wt% slip/antiblock masterbatch carried in an LDPE base. The LLDPE fraction raises dart drop impact, measured to ISO 7765-1:2004 Method A on 30 µm film, from approximately 150 g for the neat grade to 220–260 g depending on comonomer type and skin-layer density. The compounding step is not the primary difficulty; the process bottleneck is bubble stability at reduced melt temperature. For frozen-food film, converters often lower melt temperature to 180–190 °C to reduce oxidative degradation and preserve low odour, but this narrows the operating window. Below 185 °C, the high-molecular-weight HDPE phase creates visible bubble chatter and an irregular frost line; addition of 10 wt% LLDPE improves melt strength and allows barrel settings 5 °C lower without bubble instability. Output per die circumference on a 250 mm die typically falls from 1.3 kg/h·mm at 210 °C to 0.9 kg/h·mm at 190 °C. Film properties after conditioning for 72 h at −20 °C are evaluated by ISO 7765-1 and by slow puncture resistance using a 20 mm hemispherical probe at 500 mm/min. Frozen-food gauges usually range from 25 µm to 40 µm; gauges below 20 µm show a sharp reduction in low-temperature dart drop because plane-stress fracture mechanisms favour crack propagation along the crystalline lamellae. Calcium carbonate anti-block should be kept below 1500 mg/kg, because mineral filler increases notch sensitivity at sub-zero temperatures and can reduce elongation at break measured by ISO 527-3 from 600% to below 450%. For direct food contact, the finished structure must meet overall migration limits under EC Regulation 10/2011, typically below 10 mg/dm², and the upstream resin grade should be covered by appropriate food-contact declarations. When printing is required, corona-treated surface wetting should be verified by ASTM D2578 before ink application.

Coextruded Barrier Web Layer Distribution and Adhesion to Tie-Resin Skins

In three-layer coextruded structures for dry cereal liners and modified-atmosphere packaging, FL5580 serves as the internal bulk and stiffness layer between outer LLDPE skins or EAA tie layers. The high density of 0.958 g/cm³ contributes to a moisture vapour barrier of 3.8–4.8 g/m²·day for a 25 µm internal layer measured by ISO 15106-3 at 23 °C and 85% RH. Layer distribution is controlled by gravimetric hopper blending and screw speed ratio; typical configurations are 15/70/15 outer LLDPE/FL5580/inner LLDPE or 20/60/20 when the outer layers are EVA-rich for heat sealing. The coextrusion die is commonly a 300 mm spiral mandrel die with 1.8 mm total die gap; layer-specific melt streams are maintained at 190 °C for LLDPE skins and 210 °C for the FL5580 core to reduce viscosity mismatch. Interfacial flow instability, visible as wave-like delamination lines in the bubble, occurs when the viscosity ratio between the core and skin melt exceeds approximately 2:1 at the same shear rate; selecting a C₆-LLDPE skin with MI 0.9 g/10 min and density 0.918 g/cm³ keeps the ratio within a stable range. Adhesion between the HDPE core and LLDPE skins without tie resin is sufficient for many applications because of co-crystallisation across the interface; peel strength measured by ASTM F88/F88M-21 may exceed 0.5 N/mm only if both melt streams remain above 190 °C at the die exit. When EAA or EMA skins are introduced for seal performance, a maleated polyethylene tie layer is required or EVA content must remain above 12 mol% to prevent delamination; published data for this specific resin combination is limited, and pilot-line peel tests are necessary before commercial runs.

The following table summarises test methods and typical values reported or industrially measured for 20–30 µm FL5580-containing blown film.

When FL5580 Replaces LLDPE in Thin-Gauge Produce Bags

Produce bag converters sometimes replace a portion of LLDPE with FL5580 in thin-gauge roll-stock to increase stiffness and reduce gauge without sacrificing tensile strength. The formulation shift is typically from a 100% C₈-LLDPE control to a blend of 60 wt% FL5580 and 40 wt% LLDPE. The basis is the higher modulus of HDPE; tensile modulus of FL5580 film is reported near 1100–1300 MPa compared with 200–400 MPa for typical LLDPE film, allowing a gauge reduction of 8–12% while maintaining machine-direction tensile strength. Tear resistance, however, declines sharply because HDPE has intrinsically lower tear propagation resistance in the machine direction. Elmendorf tear by ISO 6383-2 on 10 µm blended film often falls from 3–4 N for the LLDPE control to 0.5–1.0 N in the machine direction, a property cliff-edge that demands orientation control or redistributed die rotation. The process window narrows to approximately ±5 °C on the die zone when running 8–12 µm film, because bubble stiffness increases with HDPE content and the bubble becomes less tolerant of ambient air drafts. Frost-line height must be raised to 7–9 die diameters to delay crystallisation and reduce blocked-film defects. Screw speed on a 65 mm extruder with 30:1 L/D is limited to 25–35 rpm; above this range, transverse-direction thickness variation can exceed ±18% measured by online capacitance gauging. Surface friction is higher for HDPE-rich film, so slip additive concentration is typically raised from 800 mg/kg to 1200–1500 mg/kg erucamide or oleamide masterbatch to maintain film-to-film separation. Blown-film lines fitted with internal bubble cooling achieve more stable gauge profiles at lower frost-line positions and are preferred for this substitution; without IBC, ambient hall airflow should be reduced below 0.5 m/s. Final produce bags are often perforated by hot-needle systems; the higher melt orientation in HDPE-rich film causes less hole elongation, but the film may split more readily from the hole under transverse load. This failure mode is evaluated by slow tear testing at 23 °C and by ASTM D1922 Elmendorf after conditioning to ISO 291 Class 2. For food-contact produce bags, EC Regulation 10/2011 migration verification applies, and migration testing of the final blend under worst-case time-temperature conditions is required if the LLDPE source changes.