On a five-layer cast stretch line with a 2,800-mm die and a haul-off target of 350 m/min, Marlex 7120B is introduced into the core layers at 70–80 wt% blended with a 0.918 g/cm³ metallocene octene LLDPE at 20–30 wt%. The skin cling layers receive 1.5–3.0 wt% polyisobutylene in a low-density carrier resin, while the outer abrasion layer is formulated with 20 wt% LDPE to reduce roll blocking. Extrusion melt temperature is held between 240°C and 265°C, the die gap is set to 0.8 mm, and the chill roll temperature is maintained at 18–22°C with a dual air knife pressure of 6–10 kPa. At haul-off speeds above 400 m/min, neck-in increases and edge thickness variation exceeds ±8% unless the die lip heaters are trimmed; acceptable neck-in is kept below 30 mm per side. Compliance for pallet stretch wrap used as an indirect food transport aid is assessed under FDA 21 CFR 177.1520 for olefin polymers and under EU Regulation 10/2011 when the film is placed in direct contact with unpackaged food, with overall migration not exceeding 10 mg/dm² under the applicable food simulant migration test. Puncture propagation resistance is measured by ASTM D5748, stretch force by ASTM D5458, and coefficient of friction by ASTM D1894. The terminal product is a 20–23 µm machine-grade stretch film roll, typically 500 mm wide and 1,500 m long, for rotary pallet wrappers. Transverse chatter on the chill roll below 15°C is a production-scale failure linked to insufficient internal chill water flow; the corrective action is to raise roll temperature to 20°C and verify air knife volume before restarting.

How Does 7120B Behave at 2.5 Blow-Up Ratio on High-Stalk Lines?

Because 7120B is a 1-butene LLDPE with a 0.918 g/cm³ density and a 1.0 dg/min melt index, a 2.5:1 blow-up ratio on a high-stalk line collapses unless the compound is modified with 15–20 wt% LDPE. The LDPE fraction raises melt strength and stabilizes the bubble on an 80-mm extruder with a 30:1 L/D grooved-feed section, a 200-mm spiral mandrel die, and a 1.6-mm die gap. Frost line height is maintained at six to eight die diameters, and die melt temperature is held at 199–210°C. The formulation for a frozen-food packaging web uses 85 wt% 7120B, 15 wt% LDPE with a 2.0 dg/min melt index, erucamide slip at 600–1,000 ppm, and silica antiblock at 2,500–5,000 ppm. The blown film is converted into 40–50 µm pillow pouches for frozen vegetable and bakery overwrap. Direct food contact compliance is established under FDA 21 CFR 177.1520(c) for olefin polymers, subject to end-use extractive limitations for the finished film; under EU Regulation 10/2011 the overall migration limit is 10 mg/dm² in food simulant A, B, and D2 under the stated time and temperature conditions. Tensile properties are tested according to ASTM D882, Elmendorf tear according to ASTM D1922, and dart impact according to ASTM D1709. Organoleptic failure occurs when erucamide slip is overdosed above 1,500 ppm and migrates into the packaged food matrix; sensory transfer is evaluated by ASTM F1308 in end-use qualification. No amine-based antistat is added because the migration of low-molecular-weight amines can destabilize heat seal strength and produce off-taste.

Heavy-Duty Sack Extrusion and Seal Integrity Under FFS Conditions

Form-fill-seal conversion of heavy-duty sacks places a simultaneous demand on heat seal initiation temperature and hot-tack window; both parameters are measured per ASTM F88 and ASTM F1921. 7120B is employed in a three-layer blown film structure at 80 wt% in the core and sealant layers, with 20 wt% LDPE for melt strength and a 5 wt% HDPE fraction in the outer layer to increase stiffness and blocking resistance; the combined film caliper is 90 µm with a gusseted tube width of 360 mm. On a 90-mm extruder with a barrier screw and a 350-mm die gap of 2.2 mm, the blow-up ratio is 2.2:1 and the melt temperature is 215–230°C. The finished sack is used for chemical resin export, construction aggregate, and polymer powder packaging; it must pass a 1.2-m dart impact test according to ASTM D1709 and an Elmendorf tear test according to ASTM D1922, with minimum values specified by the end user, not by resin lot. Batch-to-batch variance in reground edge trim above 20 wt% produces gel accumulations in the 90-mm screw channels and causes seal interruption at 1.5 seals per minute on a commercial FFS line; this is controlled by keeping regrind below 20 wt% and by using a 100-mesh breaker plate. Heavy metal compliance for the ink-free sack structure follows EU Packaging Directive 94/62/EC, with the sum of lead, cadmium, mercury, and hexavalent chromium below 100 mg/kg when tested by EN 14582:2016.

Agricultural silage covers produced from 7120B-based blown film use either a 150-µm black monolayer or a 75-µm black/white coextrusion, the white layer containing 8–10 wt% titanium dioxide masterbatch for solar reflectance and the black layer 6–8 wt% carbon black masterbatch. A large-blown film conversion on a 90-mm extruder with a 500-mm die, 2.4-mm die gap, and 2.0:1 blow-up ratio is typical; melt temperature is 210–225°C to avoid degradation of the light stabilizer package. The compound is prepared with 0.3–0.5 wt% HALS and 0.2 wt% phenolic antioxidant; no low-molecular-weight amine antistat is used because it may bloom to the surface and accelerate carbon black rub-out. The terminal product is a 4-m-wide silage cover, 150 µm thick, used for bunker silo or bale wrap. UV resistance is evaluated by ASTM G154, with a criterion of less than 50% retained tensile elongation after 1,500 hours for seasonal covers. Long-term storage in contact with silage leachate below pH 4 requires verification of additive migration under REACH and national fertilizer-contact regulations; no direct food contact status is claimed.

When Cast Film Haul-Off Speeds Exceed 300 m/min

Below haul-off speeds of roughly 180 m/min, the cast film edge bead is ordinarily manageable in 7120B sealant webs, but above 300 m/min the edge pinning force and draw resonance must be controlled by an air knife and by die-lip temperature profiling. Cast lamination structures for non-retort flexible packaging use 7120B as a 20–30 µm sealant layer on aluminium foil or PET, blended with 15–20 wt% LDPE to reduce neck-in. The web is coextruded with an ethylene acrylic acid copolymer tie layer when foil adhesion is critical; the tie layer comprises approximately 10% of total web thickness. Extrusion melt temperature is 280–300°C, die gap is 0.7 mm, and the substrate is primed with an ozone dose of 10–20 mg/m² or corona treatment to 42 dyne/cm. The composite is tested for seal strength per ASTM F88 and oxygen permeability per ASTM F1927. End products include dry beverage premix pouches and wet-wipe lidding, where the sealant must withstand a 25-second dwell at 150°C but is not intended for retort exposure above 121°C because the butene backbone lacks sufficient high-temperature creep resistance. When line speed is pushed to 350 m/min, the die exit film temperature measured by infrared pyrometer should not exceed 310°C; prolonged excursions above that value accelerate antioxidant consumption and create oxidation islands visible as yellow streaks. Published data for film performance above 400 m/min with this specific butene grade is limited; converter trials with a 0.55-mm die gap and a dual-zone chill roll are required before release.

Treated 18-µm Overwrap Film on 80-mm Extruders with 2.0-mm Die Gaps

A treated 18-µm overwrap web produced from 7120B on an 80-mm extruder benefits from the 1.0-dg/min melt index because the film can be drawn to a 2.0-mm die gap without excessive melt fracture. The application targets outer-wrap packaging for paper towel bundles and tissue multipacks, where the film is printed in flexo and surface-treated to 38–42 dyne/cm before printing. Formulation consists of 90 wt% 7120B and 10 wt% LDPE, with slip at 800–1,200 ppm and antiblock at 2,000–3,000 ppm. On a 220-mm die, the blow-up ratio is 2.0:1, frost line height is set at 500–700 mm, and die melt temperature is 200–215°C. The finished web is tested for dart impact by ASTM D1709, Elmendorf tear by ASTM D1922, and haze by ASTM D1003. Potential blocking in the roll is controlled by storage below 35°C and by avoiding winding tension above 12 N/cm. No direct food contact claim is made for the overwrap unless the converter validates the printed film under 21 CFR 177.1520 and the applicable food additive clearances for the printing ink and varnish.