On high-speed blown-film lines designed for pallet stretch wrap, Sclair VLDPE 11C is run as a monolayer web or as the sealant/back skin in two-layer and three-layer stretch-film constructions. The resin’s very-low-density class, with a nominal density of 0.905 g/cm³ per ASTM D792 and a melt index of 1.0 g/10 min per ASTM D1238 at 190 °C/2.16 kg, places its extensional viscosity below that of conventional butene-LLDPE at equivalent melt temperature. Extrusion on a single-screw line with a 30:1 to 33:1 L/D barrier screw and a die gap of 1.2–2.0 mm is preferred; lower die gaps increase die-lip fouling from low-molecular-weight species, while higher gaps reduce melt homogenization and produce gauge bands. Melt temperature at the die is controlled between 210 °C and 240 °C, with the lower end favored for bubble stability and the upper end used only when line speed exceeds 300 m/min. Blow-up ratio is maintained at 2.2:1 to 3.0:1, and frost line height is set at 6–9 die diameters to balance machine-direction and transverse-direction orientation. Converter data from 250 mm and 350 mm die heads indicate that gauge variation is minimized when chilled air-ring air is delivered at 8–12 °C with a pressure differential of 3–5 kPa. Winding on turret winders with taper tension from 40–70 N/m prevents telescoping and hard-roll blocking.

Film produced at 20 µm nominal thickness typically meets converter specifications requiring dart drop impact of at least 150 g under ASTM D1709 method A and machine-direction tensile elongation above 300% under ASTM D882. Puncture resistance is assessed with ASTM D5748 using a 0.75 mm probe; values below 35 N on a 20 µm web generally indicate either excess process orientation or inadequate gauge control. Cling is not generated by the base resin alone; stretch-film converters introduce 0.5–2.0 wt% polyisobutylene or sorbitan-oleate additive masterbatch, which migrates to the film surface over 24–72 h under ambient storage. The low room-temperature modulus of VLDPE supports stretch force retention below 18 N/100 mm after 200% pre-stretch in machine-direction units. Above this stretch force boundary, high-noise necking and irregular load retention become observable on powered pre-stretch carriages.

What Limits Seal Initiation in Coextruded Polyolefin Sealant Webs?

VLDPE sealant layers based on Sclair VLDPE 11C are used in three-layer and five-layer barrier films for fresh meat, cheese, frozen food, and liquid-pouch packaging. Seal initiation is governed primarily by the short-chain branching distribution, melting onset, and heat-transfer uniformity at the seal bar; with density at 0.905 g/cm³, the sealant layer typically begins forming measurable seal strength at 82–92 °C in hot-tack testing. Published data for this specific configuration is limited, but comparative converter measurements against a 0.918 g/cm³ octene-LLDPE sealant show a seal-initiation shift of 5–12 °C to lower temperature on the same coextrusion line. The practical limit is not solely the resin melting point: seal-bar contamination from slip additives and anti-block particles can increase measured seal initiation by 3–7 °C because particulate surfaces disrupt interfacial wetting at the sealant web. Hot-tack force is measured according to ASTM F1921 with a 0.5 s dwell, 0.3 N/mm² seal pressure, and 200 mm/min peel speed; target values for stand-up pouch sealant layers are typically above 2.0 N/25 mm at 90 °C. Cooled seal strength is quantified under ASTM F88, with a threshold of 8 N/25 mm on 60 µm three-layer film. If the sealant layer drops below 15% of total film thickness, seal robustness becomes vulnerable to gauge variation and flex-crack propagation; high-speed pouch lines running at 80–120 cycles/min generally specify a sealant thickness band of 18–25% of total gauge. For food-contact compliance, the sealant layer is assessed under U.S. FDA 21 CFR 177.1520(c) 3.2a and EU Regulation (EU) No 10/2011 with overall migration below 10 mg/dm² under OM2 conditions. Downgauging the sealant layer below 12 µm requires revalidation because both migration testing and seal integrity are thickness-dependent.

Cast-film lines used for hand wrap and machine wrap operate at melt temperatures of 220–250 °C with Sclair VLDPE 11C, a 0.8–1.2 mm die gap, and an air gap of 15–25 mm before the chill roll. Because VLDPE has a relatively low melting point and limited melt elasticity, the draw ratio from die gap to final 12 µm film can be set from 25:1 to 45:1 without entering draw resonance when chill-roll temperature is maintained at 15–25 °C. The dominant process limitation in cast operation is chill-roll build-up from low-molecular-weight oligomers and surface additives; silicone-coated or ceramic chill rolls are used, and operators clean the roll every 6–8 h when line speeds exceed 400 m/min. Tensile properties for 12 µm cast web are commonly specified at MD stretch force below 20 N/50 mm at 200% elongation and TD elongation above 500% per ASTM D882. Coefficient of friction after 24 h annealing is 0.20–0.40 kinetic under ASTM D1894 when a slip additive is used; without slip, values above 0.60 lead to film-roll telescoping on high-speed automatic wrappers.

When liquid pouch integrity depends on flex-crack resistance and contaminated-seal tolerance

Vertical form-fill-seal pouches for liquid condiments, dairy products, and sauce portions use VLDPE sealant skins to provide flex-crack resistance and low seal initiation through splashed product. The flex-crack mechanism is dominated by crystalline lamellae thickness, amorphous-phase tie-chain density, and the ability of the sealant web to absorb strain without forming pinholes; the low density of Sclair VLDPE 11C increases the amorphous fraction relative to conventional LLDPE. In ASTM F392 Gelbo flex testing, converter specifications for 80 µm laminated pouch stock commonly require fewer than 10 pinholes per 10 cm² after 500 flex cycles, and VLDPE-rich structures are used to meet this threshold. The seal-through-contamination requirement is evaluated by applying 0.1 mL of water or oil-based test fluid to the seal area before jaw closure, then sealing at 95 °C for 0.5 s; residual seal strength must remain above 6 N/25 mm under ASTM F88. If the sealant layer contains more than 5 wt% anti-block concentrate, the contaminated-seal threshold drops sharply and the failure mode shifts from peel separation to cohesive substrate tearing, which is unacceptable on a filling line. The same VLDPE skin also functions as a flex-crack arrestor in laminated structures with oriented polyester or oriented polyamide outer layers, preventing early pinhole formation at the package corners.

Extrusion coating of Sclair VLDPE 11C onto biaxially oriented polypropylene and polyester substrates as a sealant web is performed on lines with a 300 mm or larger slot die, a 200–250 mm air gap, and line speeds from 80–250 m/min. The resin is usually blended with 10–30 wt% LDPE to reduce neck-in and improve melt-curtain stability; at 100% VLDPE, neck-in can exceed 5 cm at 200 m/min, whereas a 70/30 VLDPE/LDPE blend reduces neck-in to 2–3 cm on the same die. Melt temperature is kept between 250 °C and 280 °C to activate substrate surface adhesion because VLDPE requires a high melt enthalpy contact with the chilled roll and sufficient thermal exposure to the substrate face. Coating weight is typically 12–25 g/m²; below 10 g/m², pinhole defects increase, and above 30 g/m², blocking on the reel becomes a limiting factor. Seal strength through lamination is measured after 24 h at 23 °C and 50% RH according to ASTM F88; target values are 10 N/25 mm for polyester-based structures and 8 N/25 mm for oriented polypropylene.

Heavy-Duty Sack and Bag Sealing Grades in Form-Fill-Seal Lines

High-output form-fill-seal lines for heavy-duty sacks, pet food bags, and industrial liners use Sclair VLDPE 11C in the inner sealant layer because it permits sealing through dusty product at speeds of 60–90 bags/min. The screw design for this resin on a 75 mm extruder with 30:1 L/D is a single-flighted barrier profile with a compression ratio of 2.5:1; compression ratios below 2.0:1 cause melt-temperature fluctuations of ±5 °C, which directly affect seal consistency at the jaw. At the sealing jaw, dwell times of 0.3–0.5 s and jaw temperatures of 100–115 °C are typical for 70 µm laminated structures; continuous rotary sealers require the upper end of the temperature band because of shorter residence time. The seal layer also contributes puncture resistance during product drop; package drop tests from 1.5 m onto concrete require no seal breach when the sack carries 25 kg of granular product. Because VLDPE has lower modulus than LLDPE, converters compensate by increasing total film thickness by 5–10% when replacing a 0.918 g/cm³ sealant, but the lower seal initiation and improved impact toughness outweigh the stiffness penalty in dusty high-speed filling.