Coextruded cast film used on horizontal form-fill-seal lines for washed-leaf and frozen vegetable packs positions a low-seal-initiation layer at the sealant interface. A production structure of 75 µm polyethylene print web with a 12 µm sealant web is run on a five-layer cast coextrusion line equipped with a 2,800 mm flat die, 0.8 mm die gap, and a mirror-polished chill roll held at 18°C. The sealant layer consists of 70 wt% ATTANE VLDPE 4201 (nominal density 0.912 g/cm³ per ASTM D792; nominal melt index 1.0 g/10 min per ASTM D1238 at 190°C/2.16 kg) and 30 wt% LDPE with nominal density 0.923 g/cm³ and melt index 1.5 g/10 min. Extruder barrel settings from feed to metering are 180°C, 195°C, 205°C, and 210°C; melt temperature measured at the die is 216°C. The 70/30 blend suppresses seal initiation enough that a 25 mm laboratory seal bar set at 0.4 MPa and 0.5 s dwell reaches the plateau at 94°C, whereas a 0.918 density octene LLDPE control reaches equivalent heat-seal force at 102°C under the same ASTM F2029 protocol. The benefit is not governed by density alone; elevated comonomer content broadens the heat-seal plateau and delays recrystallization at the seal boundary after jaw release. Seal failure in the field is seldom cohesive within the VLDPE-rich sealant; it occurs as delamination at the print web boundary when interlayer bond strength drops below 1.5 N/15 mm due to insufficient corona treatment.

Blocking resistance in high-speed VFFS is controlled by surface additives. Erucamide at 1,000–1,500 ppm lowers coefficient of friction to 0.15–0.25 per ASTM D1894 after 72 h at 40°C, but the migration equilibrium changes seal friction and can reduce hot-tack width measured by ASTM F1921. Converters that require a steeper hot-tack profile keep slip below 800 ppm and accept higher unwind friction on the converting deck. Pre-drying is not required at relative humidity below 60%; if pellet condensation occurs after cold shipment, nitrogen purge at 60°C for 4 h is sufficient. The resulting pillow packs for frozen spinach and mixed vegetables are sealed at 115°C and 0.5 s dwell on a VFFS machine with four pairs of serrated jaws; the filled packages must hold a minimum seal strength of 2.0 N/25 mm after 90 days at -18°C per ASTM F88. Food-contact status is covered by FDA 21 CFR 177.1520 and EU Regulation No 10/2011 with overall migration limit 10 mg/dm². The main process bottleneck is not sealing force but jaw contamination: low-density polyolefin fragments accumulate on polished sealing bars after 18–24 h of continuous operation and must be removed with a bronze scraper, not a steel blade, to avoid changing jaw surface roughness.

When Pallet Containment Demands Low-Temperature Prestretch and Puncture Resistance

Pallet wrap lines in cold storage often operate at 250–350% pre-stretch and ambient air temperatures below 10°C. Under these conditions a three-layer cast stretch film of 17 µm can be produced on a five-layer cast line with a 120 mm extruder fitted with 30:1 L/D screw and a 0.75 mm die gap. The core layer is 60 wt% ATTANE VLDPE 4201 and 40 wt% C4 LLDPE with nominal density 0.920 g/cm³; the skin layers use the same C4 LLDPE with 1.0–1.8 wt% polyisobutylene cling modifier of molecular weight 1,200–2,000 g/mol. Melt temperature measured at the feedblock is 218°C; the chill roll is maintained at 16–22°C. Too low a chill roll temperature increases film blocking because the VLDPE-rich core exudes low-molecular-weight oligomers to the skin interface. Peel cling is measured per ASTM D5458; target release is 0.8–2.0 N/25 mm after 7 days at 45°C. Dart impact after 48 h at -10°C is evaluated per ASTM D1709 Method B; converter trials on this gauge class generally set a minimum threshold of 150–185 g depending on pallet weight.

Machine-direction tensile response must survive contact with sharp bag corners; tensile elongation at break per ASTM D882 remains above 400% in the MD and 600% in the TD before pre-stretch, but orientation shifts these values downward by 100–150 percentage points at 300% pre-stretch. Pre-stretch above 350% can induce transverse-direction tear at edge nicks because the oriented VLDPE-rich core no longer blunts crack propagation as effectively as the unoriented web. Slit-edge quality therefore must be maintained with tungsten carbide knives and a gauge profile of ±3% across the jumbo roll, measured at 100 mm intervals with a capacitance gauge. The end product is used for pallet containment of bagged frozen vegetables, ice bags, and beverage multipacks stored at -18°C. Published data for the specific interaction of PIB cling modifiers with ATTANE VLDPE 4201 in high-core formulations is limited; when cling defects occur, the first corrective action is rebalancing the skin-to-core ratio rather than increasing PIB concentration.

For rigid substrate protection in metal service center processing, 40–60 µm three-layer cast films are coextruded with an embossed surface to reduce contact area and peel buildup. The pressure-sensitive layer contains 40–50 wt% ATTANE VLDPE 4201 and 50–60 wt% LDPE of density 0.918 g/cm³; the backing layer uses HDPE or LLDPE to provide stiffness. The low secant modulus of the VLDPE-rich layer improves conformation around coil edges and reduces stress whitening during application. Peel adhesion to AISI 304 stainless steel is measured according to ASTM D3330 Method A and typically remains between 0.5–1.5 N/25 mm after 6 months at 60°C and 95% RH. Higher VLDPE fractions reduce initial tack; loadings above 50 wt% produce edge lift on curved profiles because the layer flows under sustained stress. The converter target residual solvent is below 1 ppm; no tackifier is required.

Application to coil steel, aluminium extrusions, and PVC window profiles is performed on laminating stations with rubber nip rolls at 5–8 m/min; tension must be held below 0.6 N/mm width to prevent neck-in and thickness variation. The finished protection film is corona treated to 38–40 mN/m on the backing side but not on the adhesive side, because polar functional groups on the pressure-sensitive layer increase peel buildup and adhesive transfer after UV exposure. For outdoor storage beyond 12 months, the VLDPE-rich layer requires 2,000–3,000 ppm hindered amine light stabilizer and 1,500 ppm UV absorber; otherwise oxidation embrittlement causes film shatter during removal. Regulatory compliance for US and EU industrial use is verified under REACH SVHC absence and the 10-substance restriction list under RoHS 2011/65/EU as amended by Commission Delegated Directive (EU) 2015/863.

Heavy-Duty Sack Film with Enhanced Low-Temperature Puncture Resistance

Blown film used for 100 µm heavy-duty sacks in frozen fish and crushed-ice applications is run on a three-layer coextrusion line with die diameter 350 mm, die gap 2.2 mm, BUR 2.0:1, and frost line height 850 mm. The inner layer incorporates 25–35 wt% ATTANE VLDPE 4201 in a C6 LLDPE matrix of density 0.918 g/cm³ and melt index 1.0 g/10 min. The outer layers use HDPE/LDPE to maintain stiffness and surface gloss. The VLDPE-rich inner layer raises dart impact measured by ASTM D1709 Method B after 48 h conditioning at -18°C by 20–35% relative to a homogeneous C6 LLDPE control; the improvement shrinks if frost line height is raised above 1.0 m because orientation increases and the VLDPE crystals co-crystallize with LLDPE lamellae. Melt temperature at the die is 205–215°C; screw speed is adjusted to maintain backpressure below 25 MPa. Dart impact gains are accompanied by a drop in 1% secant modulus of 15–25%, which must be compensated with 5–8 µm higher total gauge if stack load at 40°C is the limiting specification.

The finished sacks are usually produced as side-gusseted tubes, corona treated to 38 mN/m, and flexo-printed at 120 m/min. Seal strength after gusset folding remains above 3.0 N/25 mm per ASTM F88. The main processing failure is bubble instability when the VLDPE-rich inner layer exceeds 35 wt% at high screw speed; the lower melt strength of the high-comonomer phase can cause draw resonance in the inner bubble near the air ring. Converters correct this by raising metering-zone barrel temperature by 5–8°C and reducing outer-layer HDPE melt flow differences. Puncture performance on frozen fish and crushed-ice sacks is further evaluated by holding filled bags at -18°C for 24 h and dropping them from 1.2 m onto a rough concrete floor; field performance correlates with cold dart impact but not with room-temperature tensile yield.

Extrusion Lamination Sealant Webs Enable Mono-Material PE Recyclable Pouches

Mono-material PE recyclable pouches for dry food and frozen fruit combine a 70 µm reverse-printed PE print web with a 25 µm sealant web containing 80–100 wt% ATTANE VLDPE 4201. Solventless lamination is run at 45–55°C core temperature with a two-component polyurethane adhesive coat weight of 1.8–2.2 g/m²; the sealant web is corona treated to 42 mN/m immediately before lamination. Lamination bond strength is checked per ASTM F904 and must exceed 1.5 N/15 mm with cohesive failure in the sealant web, not adhesive failure. The low heat-seal initiation of ATTANE VLDPE 4201 permits VFFS jaw settings at 105–115°C, avoiding thermal distortion of the reverse-printed web. Seal strength after 60 days at 35°C remains above 2.0 N/25 mm per ASTM F88. A 100% PE structure with density spread between 0.912 and 0.960 g/cm³ meets Association of Plastic Recyclers and RecyClass design-for-recycling guidance; EVOH barrier layers, if used for oxygen-sensitive dry products, are kept below 5 wt% to preserve recyclability.

The limiting factor is the sealant layer’s Vicat softening point near 85–90°C, which excludes retort operations above 121°C. Converters running hot fill at 90°C with dwell times over 3 s observe seal creep unless the sealant is constrained by a thicker outer layer of high-density PE. In coextruded structures, a thin tie layer of maleic anhydride grafted polyethylene at 3.0 µm may be required only when the sealant is directly combined with EVOH; in all-polyethylene structures no tie layer is needed. The main throughput bottleneck is tension control through the solventless laminator: low modulus 100% VLDPE webs elongate 1.5–2.5% under normal nip loads, and if unwind tensions exceed 12 N/m, web wander produces misregistered side seals. Published data for higher-barrier versions of this exact structure is limited; converters using EVOH should validate adhesive curing at 35–40°C for 7 days to prevent sealant-to-barrier delamination.

What Limits the Use of VLDPE in Healthcare Barrier Webs?

Healthcare barrier webs produced on rotary sealers require low seal temperatures to avoid damaging the nonwoven substrate. A 25 µm sealant film with 70 wt% ATTANE VLDPE 4201 and 30 wt% LLDPE is sealed to a pre-coated paper or nonwoven lidstock at 115°C and 0.6 s dwell under a 2.0 mm wide bar. Seals are tested per ASTM F88 and per ISO 11607-1 Clause 5 for sterile barrier system performance. Ethylene oxide sterilization at 55°C and 50% RH imposes stress on the seal interface; the VLDPE-rich layer may soften more than a standard LLDPE because the Vicat softening point of the resin is lower. If the device tray then goes through 60°C post-sterilization aeration, seal peel forces can shift toward fiber-tear failure. Published data for this specific configuration is limited; therefore target lines must run formal IQ/OQ/PQ and evaluate seal strength at 1 h, 24 h, and 7 days post-sterilization per ISO 11607-2.

Regulatory compliance starts with FDA 21 CFR 177.1520 for polyolefin food-contact equivalency, but medical device submissions require separate contact-substance evaluation under ISO 10993-5 and ISO 10993-10 for cytotoxicity and irritation. The resin is not typically supplied with a supplier-side USP Class VI certificate; if that certification is required, testing must be performed on the finished package, not on resin pellets. The main incompatibility in this application is not the sealant resin itself but the loss of seal peel predictability when the nonwoven contains fluorochemical treatments or silicone release coatings; converters must map seal force-temperature curves for every lot of lidstock because the surface energy window moves by 5–8 mN/m between vendor lots.

Chilled liquid bag-in-box liners fail at the shoulder crease by flex cracking because stress concentration aligns with the low-density tie region. A 50 µm three-layer liner film can be run on a cast line with a 0.9 mm die gap and 18–22°C chill roll, using a skin/core/skin structure in which the core contains 60–70 wt% ATTANE VLDPE 4201 and 30–40 wt% LLDPE of 0.918 g/cm³. The VLDPE core improves flex-crack resistance measured as pin-hole count after 1,000 cycles per ASTM F392 Method A; converters typically accept no more than 2 pin-holes per 300 mm² in the shoulder zone after 10,000 cycles. The high comonomer content broadens the interlamellar space and delays crack propagation, but the same molecular feature lowers oxygen barrier compared with HDPE-rich structures. Therefore liquid dairy and egg products with shelf life beyond 30 days require either a coextruded EVOH barrier layer or an outer LDPE/HDPE skin with higher crystallinity.

The film is filled at 4–8°C through a spout heat-seal at 130°C for 0.8 s; spout seal failure is minimized by raising the sealant layer VLDPE content to 80 wt% at the spout region, but this may reduce creep resistance under 20 L load. Creep testing is conducted by filling the liner with water at 40°C and observing deformation of the spout flange after 30 days; a flange displacement greater than 1.5 mm usually indicates insufficient backing-layer stiffness. Food-contact testing follows EU Regulation No 10/2011 and FDA 21 CFR 177.1520. Published data for pin-hole frequency versus VLDPE core loading in cast liners is limited; most converters establish acceptance curves on their own filling lines during seasonal humidity changes.