PetroChina Lanzhou KunLun mLLDPE MPE3518, a metallocene-catalyzed ethylene/α-olefin copolymer with a nominal density of 0.918 g/cm³ and a melt flow rate of 3.5 g/10 min at 190 °C/2.16 kg, is introduced into frozen food packaging blown-film structures as a core or skin layer component at 20–40 wt% alongside conventional C4-LLDPE and an LDPE carrier. On a three-layer blown film line equipped with a 55 mm barrier screw at L/D 30:1, a die gap of 1.8–2.2 mm, and a blow-up ratio held between 2.2:1 and 2.8:1, the addition of MPE3518 raises bubble stability demands because the metallocene architecture generates a narrower shear-thinning profile than conventional Ziegler-Natta butene grades. Frost line height is typically maintained at 6–8 die diameters to balance transverse direction orientation and film optics, while melt temperatures are limited to 180–210 °C across barrel zones and 215 °C at the die to avoid surface degradation. For 50 µm webs, dart impact resistance is measured under ASTM D1709 Method A, Elmendorf tear under ASTM D1922, and tensile properties under ISO 527-3; converters routinely specify puncture failure as ductile elongation rather than brittle shattering at -20 °C storage temperatures. The low seal initiation temperature of MPE3518 permits fin-seal jaw settings between 105 °C and 125 °C in downstream form-fill-seal conversion, while oxygen transmission rate testing under ASTM D3985 and water vapour transmission rate testing under ASTM F1249 are used to verify barrier contribution in coextruded structures. Because the pure grade can produce sharkskin melt fracture at high extrusion shear rates, converters add 10–20 wt% of a high-pressure LDPE to reduce melt viscosity at the die lip; this also lowers extruder head pressure by improving wall slip in the final metering section. Food-contact compliance is documented through FDA 21 CFR 177.1520 for olefin polymers and EU No 10/2011 overall migration verification, with end-use migration testing dependent on the lamination adhesive and print system used in the final package.

What Limits Cast Film Throughput When MPE3518 Runs as a Stretch Wrap Base?

On tandem air-cooled cast film lines with chill roll diameters above 600 mm, die gaps between 0.6 mm and 0.8 mm, and an 80 mm extruder at L/D 30:1, MPE3518 is processed at melt temperatures of 240–265 °C and chill roll temperatures of 18–22 °C. The primary process constraint is draw resonance at high line speeds because the metallocene grades exhibit a relatively low melt strength; stable operation is typically achieved only after the addition of 10–15 wt% LDPE or by reducing haul-off acceleration to below 300 m/min during start-up, after which line speeds can be increased to 450–600 m/min. Neck-in at the chill roll is quantified by measuring edge bead width against the die width, and it is controlled through the die lip design and by maintaining a small air gap between 10 mm and 20 mm. Cast stretch film produced with MPE3518 is evaluated for puncture resistance under ASTM D5748, Elmendorf tear under ASTM D1922, and tensile elongation under ISO 527-3, with on-pallet retention tested by wrapping standard pallet geometries and measuring post-wrapping load shift after a 24-hour conditioning period at 23 °C and 50% RH. Cling is measured using a 180° peel test derived from ASTM D5458-95, and the unstretched film is required to retain peel force above 1.0 N/cm after storage at 40 °C for 7 days without excessive additive bloom. Because MPE3518 is not supplied with a cling additive, the cast film converter must add a low-molecular-weight polyisobutylene or migratory tackifier masterbatch at levels determined by peel testing; overdosing can create roll blocking, and underdosing causes pallet load failure during transit. Extruder backpressure is normally 15–25% higher than that of an equivalent melt flow rate C4-LLDPE under identical screw speeds, so the extruder motor load should be monitored against the manufacturer’s maximum continuous torque rating and the feed throat temperature kept below 50 °C to prevent premature pellet bridging.

Lamination sealant webs for stand-up pouches and pre-made side-gusset formats incorporate MPE3518 after corona treatment to a surface tension of 38–42 dyn/cm measured under ISO 8307 or ASTM D2578. Solventless polyurethane adhesive systems are applied at 1.5–2.5 g/m² and cured at 40–50 °C for 48–72 hours; the sealant film is subsequently tested for bond strength under ISO 11339 and seal strength under ASTM F88. The low seal initiation temperature of MPE3518 permits seal jaws to operate in the 105–125 °C window at dwell times between 30 ms and 80 ms, which is critical when sealing through contaminated powder fill lines on vertical form-fill-seal equipment. Hot-tack strength is characterised using ASTM F1921 at 0.5 mm sealing bar radius and peel speeds of 200 mm/min; converters require hot-tack force above 3 N/25 mm to prevent pouch opening before the seal has cooled. Coefficient of friction is measured under ISO 8295 and is typically controlled between 0.10 and 0.30 with slip masterbatch additions, otherwise pouch registration on high-speed fill lines becomes unstable. Because MPE3518 has a relatively narrow molecular weight distribution, it does not generate the same low-gel clarity as fractional-melt LDPE in thick films, but in thin sealant layers below 50 µm the optical haze is acceptable when measured under ASTM D1003. Conversion trials often expose a limitation when the sealant film is stretched over sharp gusset folds; the resin’s low shear-thinning behaviour in extruded film can produce local thickness thinning below 20 µm, so die uniformity and lip adjustment are monitored via online gauge scanning with 0.1 µm resolution. No chlorinated additives or heavy-metal-based stabilisers are used in this application, and the finished laminate is tested for primary aromatic amines from the adhesive system under EU 1935/2004 migration protocols where applicable.

When Agricultural Film Converters Require High Puncture Resistance and UV Stabilizer Loading Without Sacrificing Drawdown

Photodegradation and silage film puncture requirements impose a specific formulation strategy for MPE3518 in monolayer and three-layer greenhouse or silage films because the polymer is not stabilised for long-term outdoor exposure as supplied. On a 65 mm monolayer blown film line with a 2.2–2.4 mm die gap and blow-up ratio of 2.0:1–3.0:1, the base resin is compounded with 1.5–2.5 wt% of a HALS-based UV stabiliser masterbatch and, for silage cover applications, 2–4 wt% of a carbon black masterbatch whose dispersion quality is assessed under ISO 18553. Film thickness is typically 80–150 µm; at these gauges the dart impact resistance under ASTM D1709 and slow puncture resistance under ISO 6603-2 become the primary mechanical release criteria because the film must resist stubble, stone, and animal-hoof puncture without catastrophic splitting. Tensile elongation at break is measured under ISO 527-3 in both machine and transverse directions, with minimum elongation retained after 2000 hours of accelerated weathering under ASTM G154 cycle conditions. The narrow molecular weight distribution of MPE3518 can lower melt strength during high stalk-area bubble expansion; converters therefore operate at lower frost line heights and use internal bubble cooling to maintain gauge uniformity below ±5%. When carbon black is added, the blown bubble absorbs more infrared heat from the die, so air ring cooling must be increased by 15–20% relative to natural film to avoid bubble flapping and thickness bands. Extruder melt temperatures are held below 220 °C to avoid degradation of the HALS package, and screen packs with 100–250 µm mesh are employed to capture carbon black agglomerates above 100 µm that would otherwise form visible specks. In silage bag coextrusions, MPE3518 is placed in the outer layer with a white-opacified LDPE layer beneath it to reflect solar radiation and reduce oxygen ingress, while the inner layer uses an EVA or plastomer for high sealing integrity. Field performance data are collected as puncture events per square metre after installation, but published data for this specific configuration is limited; converters typically rely on the combination of ASTM D1709, ISO 6603-2, and on-farm tear initiation trials rather than a single laboratory test to qualify the film.

Heavy-duty sack coextrusions for polymer granulate and chemical powder filling use MPE3518 in the core or outer layer at 120–180 µm total gauge because the resin’s low extractable content and high dart impact strength reduce sack rupture during 1.5 m drop tests conducted under ISO 7965. A 90 mm blown-film extruder at L/D 30:1 runs a die gap of 2.0 mm and blow-up ratio of 1.8:1–2.2:1, with internal bubble cooling to stabilise the larger bubble diameter required for sack layflat widths above 600 mm. Because MPE3518 exhibits higher extensional viscosity than conventional hexene-LLDPE of similar melt index, the film reaches its tensile drawing limit at lower drawdown ratios; converters compensate by using a wider die and lower stalk height to avoid splitting of the bubble during gauge reduction. Elmendorf tear resistance under ASTM D1922 and trouser tear under ISO 6383-1 are evaluated because chemical powder sacks often fail from sharp-edged granulates or partially crystallised salts. The outer surface is corona treated to 40 dyn/cm for print adhesion, while the inner layer is formulated with slip and antiblock masterbatches at levels that maintain coefficient of friction below 0.25 under ISO 8295 to permit stable pallet stacking. Seal strength is measured on a hot-tack tester according to ASTM F88 at 120 °C sealing bar temperature and 300 N seal pressure; acceptable sacks require seal strength above 20 N/15 mm to resist payload settlement. The use of MPE3518 in this application is constrained by its lower melt strength relative to high-pressure LDPE, so purge procedures after shutdown must include a high-viscosity LDPE to remove carbonized material from the die lip before restarting with the metallocene grade.

Seal Initiation Temperature and Hot-Tack Window in Flowable Food Packaging

High-speed flowable food packaging lines running vertical or horizontal form-fill-seal equipment employ MPE3518 as the sealant layer because the low seal initiation temperature permits rapid sealing at jaw settings from 105 °C to 125 °C with dwell times as short as 30 ms. Hot-tack strength is measured under ASTM F1921 with a 0.25 mm radius sealing bar and peel speed of 200 mm/min; the minimum acceptable hot-tack force for product drop prevention in a 250 g pouch is 3 N/25 mm. Seal strength after cooling is evaluated under ASTM F88 and must exceed 15 N/25 mm to survive distribution vibration without peel failure. Because MPE3518 has a narrow melting distribution, the seal strength changes more rapidly with temperature than conventional ethylene-vinyl acetate sealants; converters therefore impose tighter seal bar temperature control of ±5 °C across the jaw width to avoid cold-seal leaks or over-seal thinning at the pouch edges. Contamination resistance is checked by sealing through a controlled level of dry seasoning powder or liquid oil mist and then repeating ASTM F88; the sealant layer must retain at least 60% of its clean-film seal strength to pass. The film is also evaluated for blocking resistance under ASTM D3354 at 50 °C and 0.5 kPa for 24 hours, with unsealed film surfaces required to separate without visible surface transfer. Additive selection is restricted because migratory slip agents can reduce hot-tack performance at high seal jaw temperatures; converters therefore use non-migratory slip packages or keep erucamide levels below 500 ppm in the sealant layer. Oxygen permeation after filling is measured under ASTM D3985 at 23 °C/0% RH for dry powder products, while moisture barrier requirements are determined under ASTM F1249 at 38 °C/90% RH. The sealant web is typically coextruded with a barrier core of EVOH or metallised polyester, and the adhesion between the sealant layer and tie layer is verified under ASTM D1876 peel testing; failure must occur in the film, not at the interface, to prevent delamination during microwave reheating or immersion in hot water.

Machine direction orientation lines processing MPE3518 at draw ratios of 3:1–5:1 are used to produce thin gauge films for flow-wrap and shrink-sleeve label substrates where gauge uniformity below 30 µm is required. On an MDO line with preheat roll temperature of 90–105 °C, annealing roll temperature of 110–120 °C, and a draw gap of 2–4 mm, the resin’s narrow molecular weight distribution allows rapid orientation with relatively low memory shrinkage after the annealing section. The oriented film is tested for shrinkage under ASTM D2732 or ISO 11501, with label applications requiring less than 5% residual shrinkage in the machine direction at 90 °C for 10 min. Tensile modulus after orientation is measured under ISO 527-3; the machine direction modulus typically increases by more than 200% relative to the cast web, and the transverse direction modulus drops below 150 MPa, so downstream slitting equipment must use low-tension unwind to prevent web stretching. The unoriented cast web is produced at line speeds below 200 m/min to prevent edge draw resonance before the MDO unit, and edge trim is recycled into the core layer of a coextruded structure to maintain stable orientation. Optical haze is measured under ASTM D1003 and is influenced by the draw ratio; at 4:1 orientation, the haze of 25 µm film from MPE3518 is normally below 5%, which is acceptable for transparent label facestock but may require a coextruded gloss layer when used as a laminating film. Because MPE3518 contains no slip or antiblock as supplied, silica masterbatch is added at 500–1000 ppm to prevent roll blocking during orientation; overdosing can create surface scratches visible under ASTM D2457 gloss testing. The final oriented film is often slit to narrow widths for high-speed packaging machines, and edge quality is assessed by measuring burr height under optical magnification at 50×; burrs above 5 µm are rejected because they generate dust and interfere with downstream sealing.