In cast stretch film production, Versalis Clearflex CL508 with a density of 0.908 g/cm³ measured per ISO 1183-1:2019 and an MFR of 0.8 g/10 min measured per ISO 1133-1:2022 is fed to the core layer of a three-layer A/B/A coextrusion line at 10–20 wt% blended with a C8-mLLDPE having a melt flow rate of 1.0 g/10 min and a C4-LLDPE having a density of 0.918 g/cm³. The density of the VLDPE phase reduces the secant modulus of the core layer and permits gauge reduction without loss of puncture resistance. On a 75 mm single-screw extruder with 30 L/D barrier screw, feed zone set to 190°C, compression zones to 220–240°C, and melt temperature controlled at 238°C, the blend is extruded through an automatic die with a 1.5 mm die gap onto a matte chill roll maintained at 18–22°C. Air gap is held at 10–15 cm for edge stability. Film at 12 µm to 23 µm is subjected to ASTM D5748-19 puncture resistance; core inclusion of CL508 at 15 wt% shifts puncture propagation energy upward relative to a C4-LLDPE reference, but published data for this specific configuration is limited. Tensile elongation at break per ASTM D882-18 exceeds 500% at 23°C. Coefficient of friction per ASTM D1894-14 is controlled in the skin layers by a slip/antiblock masterbatch at 2–3 wt%; addition of slip to the core is avoided because migration of erucamide across the A/B interface retards cling performance. Field failures on cast stretch lines occur when the CL508 core fraction exceeds 30 wt%, producing edge tear at die lips due to insufficient melt strength, and when chill roll temperature rises above 25°C, producing blocking after winder roll build-up. The resin requires no pre-drying for standard cast film operations, but storage at relative humidity above 60% can introduce surface moisture that disrupts chill roll contact and should be avoided.

What Changes When 15–30 wt% VLDPE Replaces C4-LLDPE in Blown Sealant Layers?

When Clearflex CL508 is blended at 15–30 wt% into the sealant layer of a three-layer blown film, the seal initiation temperature falls by 6–10°C compared with a conventional C4-LLDPE sealant layer of equivalent density. This shift is measured as the temperature at which a 1 N/15 mm seal force is generated under 0.5 N/mm² dwell pressure and 0.5 s dwell time per ASTM F1921-18. The extruder configuration for the sealant skin is typically a 45 mm grooved-feed single-screw extruder with 28 L/D, barrel temperatures from 180°C to 210°C, and melt temperature at 205°C. Die gap is set at 2.0 mm, blow-up ratio at 2.2:1, and frost line height at 600–800 mm on a 250 mm three-layer die. Bubble stability is maintained because CL508 contributes no long-chain branching and the melt strength remains adequate up to a drawdown ratio of 3.0:1; beyond this, bubble oscillation and film thickness variation above ±5% are observed. The sealant layer is coextruded with a HDPE or MDPE core and a LLDPE outer skin to produce pillow pouches and frozen food bags. Heat seal strength per ASTM F88/F88M-21 on 50 µm blown film seals at 110°C remains above 8 N/15 mm after conditioning at -20°C. Compliance for food contact is documented under FDA 21 CFR 177.1520(c) and EU Regulation (EU) No 10/2011, with overall migration below 10 mg/dm² when tested with food simulants. Additive packages for slip and antiblock are limited to 0.5 wt% in the sealant layer because higher levels interfere with low-temperature seal initiation. Film producers report that die lip build-up is uncommon below 220°C, but at melt temperatures above 240°C the degradation of processing aids can generate specks that reduce the hot-tack window measured by ASTM F1921-18.

Because extrusion coating lines running at 300–500 m/min impose high draw-down forces and neck-in control requirements, Clearflex CL508 is blended with a low-density polyethylene having a melt flow rate of 4–7 g/10 min at CL508 fractions of 20–35 wt% for sealant webs on aluminium foil, paper, and oriented PET. The extrusion coating line uses a 90 mm single-screw extruder with 30 L/D, a T-slot die with internal deckle adjustment, and melt temperature controlled between 295°C and 310°C. Air gap is set at 150 mm to balance adhesion and neck-in; below 120 mm, adhesion to aluminium foil increases but edge bead formation becomes severe, and above 200 mm, neck-in reduces the effective coating width. Coating weights range from 15 g/m² to 25 g/m² for lidding applications. Adhesion to aluminium foil is tested by T-peel per ASTM D1876-08, with minimum values of 1.5 N/15 mm required for lidding. Heat seal strength after lamination is measured per ASTM F88/F88M-21 at seal temperatures of 120–140°C. The low crystallinity of CL508 contributes to a broad seal plateau, but the material must not be processed above 315°C because oxidative gel formation at the die lip generates deposits that transfer to the web. Chill roll temperature is maintained at 15–18°C with a matte finish to control coefficient of friction in the subsequent slitting operation. Pre-drying is not required for standard coating, but storage at relative humidity above 60% can produce pinholes in the coated web if surface moisture flashes at the air gap.

When Silage Bale Wrap Requires Sub-Zero Puncture Retention

When silage bale wrap is specified for winter storage and mechanical wrapping at temperatures below -10°C, Clearflex CL508 is incorporated at 20–35 wt% in a three-layer blown film with ethylene-vinyl acetate copolymer containing 5–9 wt% vinyl acetate and a C8-LLDPE. The skin layers carry a high-molecular-weight HALS stabilizer at 0.3–0.5 wt% and a UV absorber at 0.1–0.3 wt%; the core carries carbon black or titanium dioxide depending on field exposure requirements. Production on a 70 mm three-layer blown film line with 30 L/D extruders uses barrel temperatures of 170–200°C, a die gap of 1.8 mm, blow-up ratio 2.5:1, and frost line height 700–900 mm. Film thickness is held at 25–30 µm. Dart impact resistance per ASTM D1709-15a Method A on 25 µm film conditioned at -20°C is higher for the CL508-bearing structure than for a C4-LLDPE control of equal gauge, because the lower density phase absorbs impact energy without yielding at the puncture point. Elmendorf tear resistance per ASTM D1922-09 in the transverse direction is lower than machine direction, and field failures propagate from transverse tear at clamp marks when film contains more than 35 wt% CL508. Tensile elongation at break per ASTM D882-18 remains above 600% at -20°C. The low-temperature storage modulus of CL508 contributes to film conformability around bale shoulders without increasing cling force, so wrapping tension is set 10–15% lower than that of standard LLDPE wrap to avoid neck-in and roll telescoping. The film is not recommended for multi-season outdoor storage without full UV screening because the polyethylene backbone is susceptible to photo-oxidative chain scission.

FFS Heavy-Duty Sack Inner Webs and Cold-Drop Impact Resistance

In form-fill-seal heavy-duty sacks for polymer granules, fertilizers, and petrochemical resins, Clearflex CL508 is used in the inner layer of a three-layer coextruded blown film at 10–20 wt% with high-density polyethylene and linear low-density polyethylene to improve seal integrity and cold-drop impact resistance. Film thickness is typically 150–200 µm, and the inner sealant layer represents 20–25% of total gauge. Extrusion is performed on a three-layer blown film line with 80 mm main extruders and a 35 L/D barrier screw, die diameter 350 mm, die gap 2.5 mm, blow-up ratio 2.5:1, and melt temperature 200–220°C. The sealant layer is formulated with a slip/antiblock masterbatch at 0.5–1.0 wt% to sustain sack filling speeds without blocking after roll storage. Heat seal strength per ASTM F88/F88M-21 on 180 µm film sealed at 130°C with 0.5 s dwell time exceeds 10 N/15 mm. Cold-drop impact resistance is evaluated by filling sacks with 25 kg of resin and dropping from 1.5 m at -20°C; the CL508-containing inner layer reduces brittle failures in the seal area compared with unmodified HDPE inner layers. Production bottlenecks occur when the film bubble is quenched too rapidly at frost line heights below 500 mm, which increases the internal stress in the inner layer and reduces tear propagation resistance. Screw speed and output are set so that melt pressure remains below 350 bar to avoid excessive shear heating and degradation of processing aids. The outer HDPE layer provides puncture resistance, while the CL508-modified inner layer supplies the lower sealing temperature required on FFS lines running at 30–40 bags/min. No pre-drying is required, but resin stored in silos above 50°C may develop surface oxidation that raises gel counts in the film.

For medical device lidding and pouch webs, Clearflex CL508 is employed as the sealant layer in coextruded cast films at 15–25 wt% with polypropylene or polyethylene-based outer layers, selected for low extractables and a broad seal window under ISO 11607-1:2019. The cast coextrusion line operates in an ISO 14644-1 Class 8 cleanroom environment; extruder melt temperature is held at 220–240°C and the film is quenched on a 20°C chrome roll. Seal strength per ASTM F88/F88M-21 on 50 µm film sealed at 115–125°C with 0.5 s dwell time remains above 1.5 N/15 mm, the minimum commonly specified for pouch integrity. Cytotoxicity is assessed according to ISO 10993-5:2009, and physicochemical testing is aligned with USP <661.1> for plastic packaging components. The resin is suitable for ethylene oxide and gamma sterilization doses up to 50 kGy, but steam autoclave cycles exceeding 121°C are not recommended because the softening temperature of the VLDPE phase is close to the cycle temperature, leading to film distortion and seal creep. Moisture barrier requirements necessitate lamination or coextrusion with a barrier layer; CL508 alone does not provide a sufficient oxygen transmission rate for high-barrier medical pouches. Process experience on medical lidding lines shows that web tracking errors increase when the sealant layer thickness exceeds 20% of total gauge because the low modulus surface deforms under contact with forming collars. The film is wound at low tension, 50–70 N/m, to prevent blocking in storage.