Mitsui Chemicals Evolue mLLDPE SP2020 is a metallocene-catalysed linear low-density polyethylene with a nominal melt mass-flow rate of 2.0 g/10 min at 190°C/2.16 kg per ISO 1133-1:2022 and a density of 0.918 g/cm³ per ISO 1183-1. The narrow composition distribution of the metallocene backbone lowers seal initiation and increases hot-tack response compared with conventional Ziegler-Natta LLDPE of equal density. The same molecular structure also reduces extensional strain-hardening relative to autoclave LDPE. That behaviour must be accounted for in blown film bubble stability, cast film draw resonance, and melt curtain neck-in during extrusion coating. The following application blocks are limited to downstream converting configurations in which the grade is specified, and each block separates processing limits, compliance obligations, and failure modes.

In a three-layer coextruded blown film for dry food and frozen food packaging, SP2020 is run as the sealant skin at 12–20 µm of a total gauge of 50–70 µm. The skin extruder is typically a 65 mm or 75 mm grooved-feed barrier-screw unit with 28:1 to 30:1 L/D and a Maddock mixing section. Barrel temperatures from the feed throat to the adapter are set at 170°C, 185°C, 195°C, and 205°C. Melt temperature at the die entry is held between 190°C and 205°C. A die diameter of 250 mm, a die gap of 1.8 mm, and a blow-up ratio of 2.0:1 to 2.6:1 are used. Frost line height is maintained at 8–10 die diameters to stabilise the bubble before crystal orientation freezes the film. Addition of 10–15 wt% LDPE improves bubble stability on monotower internal bubble cooling lines but raises the seal initiation temperature by several degrees because the branched LDPE component solidifies later and shifts the seal plateau upward. The exact shift is converter-specific and must be measured per ASTM F88/F88M-21 at the target sealant thickness. Heat-seal settings on horizontal flow-wrappers typically fall in the 110–125°C range at 0.3 MPa bar pressure and 0.5 s dwell. Hot-tack performance after jaw opening is assessed per ASTM F1921-20. Direct food-contact status is supported by FDA 21 CFR 177.1520(c) for olefin polymers. European Union use requires overall migration below 10 mg/dm² under EU Regulation 10/2011 and test method EN 1186-1. Gauge uniformity below ±5% across the web is critical. Higher variation produces local seal-strength collapse at package corners, especially when the sealant skin drops below 10 µm in the layflat edge zones. Melt pressure at the screen changer is normally recorded between 18 MPa and 22 MPa. A pressure rise above 28 MPa at constant screw speed indicates gel accumulation on the screen pack and requires screen replacement.

What Governs Melt Curtain Neck-In in Extrusion Lamination with Evolue SP2020?

Extrusion lamination of SP2020 onto aluminium foil, PET, or oriented polypropylene converts the resin into a sealant web at coat weights from 15 g/m² to 25 g/m². The laminator configuration is typically a 90 mm single-screw extruder with 30:1 L/D, a 1000 mm slot die, and a 0.8 mm die gap. Melt temperature at the die is maintained between 295°C and 315°C. Air gap is set between 120 mm and 180 mm. Line speed for a 20 g/m² coating on PET ranges from 100 m/min to 150 m/min. The controlling variable is neck-in, the transverse contraction of the melt curtain between the die lips and the nip. Because mLLDPE has weaker extensional strain-hardening than autoclave LDPE, neck-in is greater and edge-bead thickening increases. At an air gap of 150 mm, edge trim width is normally increased; the exact trim width depends on die width and draw ratio. Draw ratio for a 0.8 mm die gap to 20 g/m² coating is approximately 35:1 to 40:1. Curtain sagging or edge weave below 290°C is corrected by raising the adapter and die temperatures, not by reducing line speed alone. Internal die lip carbonisation is controlled by a streamlined adapter with no stagnation pockets and by an LDPE purge sequence before shutdown. Substrate adhesion on PET requires corona pre-treatment to 42–46 mN/m, while aluminium foil adhesion is dominated by mechanical interlocking and the oxide state of the foil surface. Seal strength after lamination is tested per ASTM F88/F88M-21. Backpressure at the screen changer is monitored; excursions above 28 MPa indicate gel accumulation or melt filtration blockage. Edge trim regrind up to 15 wt% can be returned if it is dry and free of ink and adhesive splice tape contamination. No pre-drying is required unless surface condensation from storage above 60% relative humidity is present. In that case surface moisture causes bubble defects in the melt curtain and a 70°C hopper dryer for 2 h is used before processing.

A cast-film process for medical device packaging sealant webs uses SP2020 at thicknesses from 25 µm to 50 µm. The line consists of a 45 mm single-screw extruder with 28:1 L/D, an 800 mm slot die, a 0.6 mm die gap, a 60–80 mm air gap, and a chill roll set at 20–25°C. Melt temperature is held at 220–240°C. Higher temperatures degrade the resin into oxidized gel particles that appear as optical defects at 50 µm under laser gel inspection. Anti-block and slip masterbatch letdown is controlled at 2–4 wt%. Haze is measured per ASTM D1003-13. The grade is suitable for clear lidding and flow-wrap components where optical clarity after lamination is specified. Tensile properties are tested per ASTM D882-18 at a crosshead speed of 500 mm/min. The sealant web is subsequently laminated to medical paper or PET. Sterile barrier system validation requires peel strength per ASTM F88/F88M-21 and compliance with ISO 11607-1:2019. If the device is sterilised by gamma radiation, the irradiation dose range must be validated for the complete laminate. The polyethylene sealant layer may undergo limited crosslinking or chain scission depending on dose rate and oxygen exposure. Published data for this specific configuration is limited, and the converter must establish the dose-response curve. Draw resonance becomes a limiting factor below 20 µm when the air gap exceeds 80 mm or when chill roll friction changes due to surface wear. The line operator logs chill roll torque and gauge profile. Gauge variation above ±4% causes inconsistent sealing on tray lidding lines. Nip pressure is maintained between 3 N/mm and 5 N/mm to avoid air entrapment without creating surface blocking.

Dart Drop, Tear Anisotropy, and Film Toughness in Heavy-Duty Sack Lines

Heavy-duty sacks for polymer granules, fertilizers, and industrial powders are extruded from SP2020 at final gauges of 100 µm to 180 µm. Monolayer blown film is produced on high-stalk bubble equipment with a die diameter of 300 mm, a die gap of 1.6–2.0 mm, a blow-up ratio of 2.5:1 to 3.0:1, and a melt temperature of 185–200°C. A high blow-up ratio increases transverse orientation and reduces the MD/TD tear imbalance. Dart impact resistance is determined per ASTM D1709-16a method B or method A depending on total gauge. Elmendorf tear is measured per ASTM D1922-15. Because mLLDPE delivers higher dart impact at equivalent gauge than butene LLDPE, downgauging from 140 µm to 120 µm is sometimes possible, but only after field stacking tests confirm creep and tear resistance. Addition of 15–25 wt% HDPE increases modulus and reduces elongation. The blend is processed on the same line but requires a higher barrel temperature profile of 195–210°C to prevent unmelted HDPE domains. Slip and anti-block levels are adjusted to produce a coefficient of friction between 0.35 and 0.50 per ISO 8295:1995. Filling machines with screw auger systems demand consistent COF. Sacks that block in storage cause misfeed and line stoppage. The elastic recovery of mLLDPE after film winding creates tight rolls if corona treatment exceeds 44 mN/m. Converters reduce winding tension and use oscillating haul-off. Edge trim and start-up scrap are recycled at 10–15% without loss of dart impact if gel count is controlled below the line camera threshold. Melt pressure is maintained below 25 MPa at the die. Higher pressure indicates severe gel build-up or incorrect screen pack selection.

Vertical form-fill-seal lines for liquid detergent refill pouches and dry powder food packages use a laminate of 12 µm PET, print, adhesive, and an SP2020 sealant web of 40–60 µm. The sealant web is often produced in the converter’s blown or cast film line and then laminated. On the VFFS machine, jaw temperature is set between 120°C and 135°C, seal dwell is 0.35–0.60 s, and bar pressure is 0.3–0.5 MPa. The low seal initiation of the metallocene resin permits jaw temperature reduction of 5–10°C compared with conventional LLDPE sealants on the same line. This reduction is confirmed by peel testing per ASTM F88/F88M-21 rather than by machine display values. Hot-tack force is measured per ASTM F1921-20 and is the governing property when the filled product mass pulls the seal immediately after jaw release. Seal-through-contamination performance with dusty powders is limited by the contaminant layer at the seal interface. A serrated jaw profile and local dwell increase are used rather than excessive temperature. Burst strength of the finished pouch is tested per ASTM F1140/F1140M-22. Leak testing is performed per ASTM D3078-21 for vacuum bubble leak detection. Organoleptic tests are relevant for food packaging. The converter must document no off-taste transfer under EN 1186-1 and the applicable EU Regulation 10/2011 migration limits. In continuous operation, the screw barrel temperature profile on the laminating extruder is set at 300–310°C for the SP2020 layer to reduce melt viscosity and promote wetting of the print primer. At these temperatures, residence time before the die is kept below 15 min and screw speed is limited to below 80% of the extruder maximum to avoid gel formation.

When a Polyethylene Sealant Web Is Coextruded Against EVOH in Chilled-Food Barrier Film

Five-layer barrier film for chilled food packages positions SP2020 as the food-contact sealant, with EVOH as the oxygen barrier layer and maleic anhydride-grafted polyolefin as the tie layer. The die is a 300 mm multi-layer spiral mandrel or pancake die with layer distribution controlled by independent melt pumps. EVOH is processed at 205–225°C. SP2020 is processed at 190–205°C. A common die setpoint of 205°C is maintained to avoid EVOH thermal degradation and to keep SP2020 viscosity low enough for uniform layer distribution. Interfacial instability appears as wavy shrink and barrier delamination when the viscosity ratio between SP2020 and EVOH exceeds approximately 3:1 at the die shear rate of 10–100 s⁻¹. Blending 5–10 wt% LDPE into SP2020 lowers the sealant viscosity and improves layer uniformity but increases seal initiation temperature. The change in seal initiation must be revalidated per ASTM F88/F88M-21. Oxygen transmission rate of the finished film is measured per ASTM D3985-17. SP2020 contributes no measurable oxygen barrier and is not relied upon for barrier performance. Film stiffness and package deadfold are controlled by an external HDPE or PP layer, not by SP2020. In thermoforming applications, the sealant layer is below 20 µm and must survive sealing against a rigid tray without splitting. Layer thickness uniformity below ±5% per layer is required. Layer ratio errors above 5% produce sealant consumption deviation and destabilise the EVOH layer. The line operator logs melt pressure per layer at the die. A pressure variation above ±0.5 MPa at constant output indicates feedblock or spiral mandrel fouling.