For heavy-duty industrial sack film produced from PetroChina Dushanzi KunLun mLLDPE EZP4002HH, the processing target is set by the nominal density of 0.940 g/cm³ measured under ISO 1183-1:2019 and the nominal melt mass-flow rate of 4.0 g/10 min measured under ISO 1133-1:2022. The grade is a metallocene linear low density polyethylene with a narrow molecular weight distribution. On a production-scale three-layer blown film line using a 65 mm grooved-feed extruder, an L/D 30:1 barrier screw, and a 300 mm spiral mandrel die, the melt temperature is held between 185°C and 205°C. The die gap is set at 1.8–2.2 mm. The blow-up ratio is kept between 2.0:1 and 2.3:1. Bubble oscillation appears when the frost-line height exceeds 1.1 m. The narrow molecular weight distribution reduces melt tension under high draw. Dry blending 15–20 wt% of high-pressure LDPE with a melt mass-flow rate of 0.25–0.30 g/10 min under ISO 1133-1:2022 stabilizes the bubble. The blend retains a dart impact of at least 700 g on 100 µm film under ASTM D1709-16ae1.

For sacks carrying polymer pellets, fertilizers, and fine chemical powders, the three-layer structure uses an inner sealant skin of 100 wt% EZP4002HH, a load-bearing core of 80 wt% EZP4002HH and 20 wt% LDPE, and an outer abuse skin containing 2 wt% slip/antiblock masterbatch. Total film gauge is 80–120 µm. Machine-direction elongation at break must exceed 500% under ISO 527-3:2018. The seal initiation temperature is 105–115°C under ASTM F1921-18. Filler addition is the main boundary. Calcium carbonate masterbatch at 3 wt% may be used for opacity. Loadings above 5 wt% lower machine-direction Elmendorf tear by more than 20% under ISO 6383-2:1983. The grade should not be processed above 220°C for more than 30 minutes, because consumed antioxidant can promote gel formation at the die lip. End products are open-mouth sacks and valve sacks with nominal fill weights of 25 kg or 50 kg.

What limits silage wrap puncture resistance when EZP4002HH is coextruded as the core layer?

Five-layer agricultural silage film designed for bales of 1.2–1.5 m diameter uses EZP4002HH as the structural core at 30–40 wt% of the total structure. The outer skin layers are based on a lower-density hexene LLDPE carrier containing polyisobutylene tackifier at 5–8 wt%. The film is produced on a cast film line with 75 mm extruders, an L/D 30:1 screw, a die gap of 0.5–0.8 mm, and an air gap of 120–150 mm. The chill roll temperature is kept at 18–22°C. The core layer is run at 210–230°C melt temperature to permit coextrusion with tackified skin layers. The skin layers cannot tolerate extended residence time above 230°C. Process conflict emerges when the core layer proportion exceeds 40 wt%. The film loses cross-direction elongation before break. The pre-stretch ratio on a bale wrapper set at 70% falls toward 55%. Published data for this exact configuration is limited. A mill trial with incremental 5 wt% changes is required to map the transition.

The film must meet EN 13207:2018 for thickness tolerance, tears, and mechanical properties after ageing. UV resistance is verified under ISO 4892-3:2016 at 3000 h exposure. Combined hindered amine light stabilizer and UV absorber loading is kept at 0.2–0.3 wt%. Higher loadings produce surface bloom. Cling force falls below 2.0 N/25 mm when tested as a tensile peel on a universal testing machine at 125 mm/min. Puncture resistance under ASTM F1306-21 with a 12.7 mm hemispherical probe at 100 mm/min should exceed 120 N at 25 µm film thickness. EZP4002HH as a core layer is not suitable for films thinner than 15 µm because the high-density fraction increases bending stiffness and prevents uniform pre-stretching. In contact with acidic silage condensate, the film must use acid-neutralizing stabilizers. Otherwise retained elongation at break after 12 months covered storage may fall below 300% under ISO 527-3:2018.

At pallet rates between 60 and 90 pallets/h, stretch hood lines expose the film to rapid draw and corner stress. A three-layer blown film structure with EZP4002HH in the core at 40–50 wt% and lower-density mLLDPE skins is used. The skins contain slip/antiblock masterbatch at 1.5–2.0 wt%. The die is 250 mm with a 2.0 mm die gap. The blow-up ratio is set at 2.4:1–2.6:1. The melt temperature is 195–210°C. Film gauge is 70–90 µm. A fluoropolymer processing aid is added at 200–400 ppm to suppress sharkskin melt fracture at the die lip. The film must achieve a machine-direction elongation at break above 600% under ISO 527-3:2018. The dart impact must exceed 800 g under ASTM D1709-16ae1.

The critical process conflict appears when final film thickness is reduced below 50 µm. The high-density core creates excessive bending resistance and uneven stretching across pallet corners. Stretch hood pre-stretch ratios are typically 60–70%. At 70% pre-stretch, the film retains sufficient recovery to clamp around the pallet base. Above 80% pre-stretch, elastic recovery falls and the film can tear at nail heads or protruding strapping clips. End products are hoods for palletized construction materials, bagged mineral products, and beverage crates. No drying is required if the resin is stored in sealed hoppers at relative humidity below 60%. Above 60% RH, surface condensation can produce feed throat surging. In such conditions, a hopper dryer at 60–70°C for 2 hours is acceptable but not mandatory.

Frozen food packaging seal integrity and hot tack limits at −25°C storage

Vertical form-fill-seal lines for frozen vegetables, seafood, and prepared meals use a three-layer coextruded film in which EZP4002HH forms the sealant layer at 100 wt%. The film is produced on a 55 mm extruder with an L/D 25:1 screw and a 200 mm die. Die gap is 1.8 mm. Blow-up ratio is 2.2:1. The sealant layer thickness is 20–30 µm within a total film of 60–80 µm. The hot tack initiation temperature of the sealant layer is 105–115°C under ASTM F1921-18. Seal strength at 180°C, 0.3 MPa, and 0.8 s should exceed 15 N/25 mm under ASTM F88/F88M-21. The film must resist puncture from frozen shrimp tails and fish bones. A probe penetration test under ASTM F1306-21 with a 6.4 mm hemispherical probe at 250 mm/min should exceed 60 N at −5°C and 45 N at −25°C.

The processing boundary is the melt temperature. Below 180°C, the sealant layer does not homogenize with the tie layer and produces melt interface distortion. Above 220°C, gels may form at gusset folds and break the seal. The frost line height is kept at 0.8–1.0 m to balance crystalline orientation. Excessive quench below 10°C air temperature produces high haze. Haze then exceeds 10% under ASTM D1003-13, which is unacceptable for clear frozen food windows. The film must comply with Regulation (EU) No 10/2011 overall migration limit of 10 mg/dm² and with FDA 21 CFR 177.1520 for olefin polymers. End products are pillow pouches for frozen corn, peas, mixed vegetables, and individually quick-frozen shrimp.

When EZP4002HH is used as the sealant web in solventless lamination of dry beverage mixes

Because dry beverage mixes require hermetic seals at high packaging speeds, the sealant web is often a 60 µm EZP4002HH film bonded to a 12 µm polyester or 18 µm biaxially oriented polypropylene print web. The film is produced on a blown line with a die gap of 1.8 mm. The surface is corona treated to a wetting tension of at least 38 mN/m under ISO 8296:2003 immediately before lamination. The adhesive is a two-component polyether-polyol/isocyanate solventless system. The metallocene sealant web must contain erucamide below 600 ppm and silicone oil below 200 ppm. Migratory slip additives above these limits reduce bond strength below 2.0 N/15 mm under ASTM F904-16. The film roll is stored at 25–30°C for 72 hours post-treatment. Wetting tension decays from 42 mN/m to 36 mN/m within 14 days at ambient warehouse conditions.

The sealant web must deliver a seal initiation temperature below 115°C under ASTM F1921-18. A hermetic seal is required at 150°C, 0.4 MPa, and 0.5 s on a rotary jaw packager. The package must survive an internal pressure test of 2.0 kPa for 30 s without seal creep under ASTM F1140/F1140M-21. The main process conflict is die-lip build-up. The grade’s narrow molecular weight distribution reduces melt fracture resistance. A processing aid at 300 ppm is required on lines above 120 kg/h throughput. Without the processing aid, die-lip deposits of oxidized oligomer may form after 8 hours and transfer to the film surface as white streaks. The grade is not suitable for direct contact with high-fat liquid products above 60°C, because environmental stress cracking may initiate at the seal area. End products are stick packs, pillow sachets, and block-bottom pouches for powdered drink concentrates and sweeteners.

Post-consumer recyclate dilution in carrier bags alters dart impact more than tear resistance

In thick-gauge carrier bags and mailing pouches, post-consumer recyclate is blended into the core layer while EZP4002HH forms the virgin skins. A three-layer blown structure with virgin skins of EZP4002HH and a core containing 20–30 wt% PCR LLDPE is produced at 80–100 µm. The die gap is 2.0 mm. The blow-up ratio is 2.3:1. The melt temperature is 190–210°C. The core layer must be melt filtered through a 100–150 mesh screen pack to remove gels and solid contaminants. The dart impact of 100% virgin EZP4002HH film at 80 µm is typically above 800 g under ASTM D1709-16ae1. At 30 wt% PCR, dart impact may fall to 550–650 g, still acceptable for non-hazardous goods. At 50 wt% PCR, dart impact drops below 400 g and tear resistance becomes highly variable because the PCR melt viscosity is outside the 0.5–1.0 g/10 min MFR window. The limiting boundary is therefore 30 wt% PCR for load-carrying bags and 50 wt% PCR only for lightweight inner liners.

The film is printed on high-speed flexographic lines running at 300 m/min. The surface must be treated to 40–42 mN/m under ISO 8296:2003. The coefficient of friction of the film must be controlled between 0.25 and 0.35 under ISO 8295:1995 to allow automated bag-magazine feeding. Slip additive addition is limited to 400–600 ppm erucamide. Higher levels bloom to the surface and reduce corona-treatable life. End products are reusable merchandise bags, courier envelopes, and thin mailing pouches. The film must not be used for direct contact with liquid fatty foods. The PCR-containing core is not food-contact cleared under Regulation (EU) No 10/2011 unless the PCR is produced from suitable food-contact-management feedstock. The virgin skins alone do not confer food-contact status to the entire structure.