On a 75 mm single-screw blown film line fitted with a 30:1 L/D barrier screw and a 250 mm spiral mandrel die, Dushanzi Petrochemical LLDPE LL0410KJ is processed at a melt temperature of 195–210°C for heavy-duty industrial sack film. The nominal melt flow rate of 1.0 g/10 min at 190°C/2.16 kg under ASTM D1238-23 and nominal density of 0.918 g/cm³ under ASTM D792-20 place this grade in the low-melt-index blown film segment. The die gap is held at 2.0–2.4 mm and the blow-up ratio is limited to 2.5:1–3.5:1. Below 2.0:1 BUR, transverse direction tensile properties fall sharply because the bubble is not sufficiently expanded. Above 3.5:1, bubble hunting appears on conventional single-lip air rings unless an IBC cage with segmented airflow is used.

Frost line height is set between 350 mm and 500 mm above the die face for 50–70 µm sack film. An ultrasonic thickness gauge keeps gauge variation within ±5%. When LL0410KJ is run without LDPE, pressure before the screen changer commonly remains between 240 bar and 280 bar. If pressure exceeds 300 bar, melt fracture appears on the inner bubble surface as herringbone defects. A fluoropolymer processing aid at 0.03–0.05 wt% is added only when micron-scale surface roughness limits flexographic print quality. The addition must follow the supplier’s dispersion protocol because localized fluoropolymer droplets create visible gel-like particles in clear sack windows.

Commercial formulations for 25 kg fertilizer sacks blend 80 wt% LL0410KJ with 20 wt% of an LDPE homopolymer having a melt flow rate near 2.0 g/10 min. The LDPE phase increases melt extensibility and permits a shorter frost line, but it reduces dart impact. Batch-to-batch shifts in the butene-1 comonomer distribution of LL0410KJ can alter dart impact on 50 µm film by up to 15% on the same line. Tensile properties are measured on 25 mm wide strips at 500 mm/min crosshead speed according to ASTM D882-22. Machine-direction elongation at break should remain above 600%; values below 500% indicate excessive thermal degradation or gel build-up on the screw root. Dart drop impact testing follows ASTM D1709-22 Method A on 50 µm film. A failure height below 100 g for a 38.1 mm dart generally disqualifies the film for heavy export bags. For low-temperature container transport, the same film is conditioned at -20°C for 24 h and must not show brittle splitting during a crumpling test. Terminal products include chemical fertilizer sacks, resin export bags, and mineral filler packaging. Published data for the specific sack-film configuration on this grade is limited; converters must qualify each gauge and blend ratio on the target line.

Evaluate UV Stabilizer Partitioning Before Selecting a Greenhouse Film Masterbatch

LL0410KJ does not contain a hindered amine light stabilizer package sufficient for multi-season greenhouse exposure. A three-layer greenhouse film with a total thickness of 150 µm places the core layer at 40% of total thickness and uses LL0410KJ in the inner and outer layers at 30% each. The outer layer is dusted with 0.4 wt% of a HALS having a molecular weight above 1000 g/mol, combined with 0.2 wt% of a benzophenone UV absorber. The core layer carries 0.1 wt% of a phosphite stabilizer to reduce gel formation during recycled edge-trim incorporation. A workable starting formulation for the inner layer is 99.3 wt% LL0410KJ, 0.4 wt% HALS, 0.2 wt% UV absorber, 0.05 wt% calcium stearate acid scavenger, and 0.05 wt% phenolic antioxidant.

Sulfur vapor from greenhouse fumigation converts to acidic condensate on the film surface. Under 50°C daytime inner-surface temperatures, this acid attacks unprotected phenolic antioxidants and can cause film embrittlement within 8–12 months. The calcium stearate dose in the inner layer functions as an acid buffer and must not exceed 0.1 wt%; higher levels migrate and reduce interlayer adhesion in three-layer film. Films containing 0.2 wt% or higher amine-based antistatic agents should not be placed in the same layer as LL0410KJ because surface migration interferes with heat-seal performance in subsequent silage bag conversion.

Greenhouse film extrusion uses a die gap of 2.5 mm and a blow-up ratio of 3.0:1. The line speed is normally 40–55 m/min for 150 µm film. Chill air at 18°C or lower reduces stress concentration at the frost line. Raising the frost line above 600 mm reduces transverse direction impact strength because the butene side branches of LL0410KJ are not fully oriented in that geometry. Weathering performance is tested according to ASTM G154-23 cycle 1 using UVA-340 lamps. A retention of tensile elongation at break above 50% after 3000 h exposure is a minimum acceptance criterion for multi-season greenhouse covers. Terminal products include greenhouse film, low-tunnel crop covers, and silage cover sheets. For silage covers, LL0410KJ is blended with 5–10 wt% metallocene LLDPE to improve dart impact without excessively reducing tear propagation resistance.

What Limits Low-Temperature Dart Impact in Frozen Food Bag Film?

Frozen food bags produced from LL0410KJ are judged by seal reliability on vertical form-fill-seal lines and by puncture resistance after filling at -25°C. The comonomer type creates a lower melting peak at 122–124°C under ASTM D3418-21. This permits a seal initiation temperature of 105–115°C at a seal pressure of 0.3 N/mm² and a dwell time of 80–120 ms on VFFS jaws. Seal strength reaches 12–15 N/25 mm on 50 µm film at a jaw temperature of 130°C when tested according to ASTM F88-21. Hot tack strength below 2.0 N/25 mm at 110°C under ASTM F1921-18 causes opening of the bottom seal before the filled bag reaches a conveyor belt on high-speed packaging lines.

The limiting property is not room-temperature dart impact but low-temperature fracture behavior. LL0410KJ is a butene-copolymer LLDPE; when cooled below -20°C, dart impact decreases more than a hexene-copolymer film of the same density. For frozen vegetable bags exposed to sharp-frozen product, the film is therefore downgauged no lower than 70 µm. On a 90 mm extruder with a 28:1 L/D screw, a melt temperature of 190°C is preferred. Processing above 220°C creates carbonyl species that shift the seal initiation curve upward by 3–5°C, which narrows the operating window on VFFS machines. Extrusion back pressure should remain below 260 bar; higher resistance indicates inadequate screw recovery time and can produce inconsistent seal layer thickness.

Direct food contact compliance is established only for the base polymer under 21 CFR 177.1520 and EU Regulation 10/2011 with overall migration below 10 mg/dm². Additives in the finished film must be selected from confirmed lists because the base resin clearance does not automatically cover the compounded film. For export to China, GB 4806.7-2016 also applies to food-contact plastic articles and requires additional migration testing on the final film.

Terminal products include frozen vegetable bags, pastry bags, and ice-plant packaging. Converters must validate seal performance on the intended VFFS line because jaw temperature distribution and cooling air flow influence hot tack more than resin melt flow rate alone.

Palletization lines producing stretch hood film from LL0410KJ normally run the resin as a minor phase in a cast film blend, not as a neat polymer. A five-layer cast line producing 90 µm film uses an outer skin with 30 wt% LL0410KJ and 70 wt% octene-copolymer LLDPE of density 0.912 g/cm³. The blending is necessary because LL0410KJ alone does not retain elastic recovery above 70% after 300% elongation under ASTM D5459-22; with the octene grade, recovery exceeds 85%. The cast film is quenched on a chill roll at 15–18°C and corona treated to 42–46 mN/m before winding.

Stretch hood equipment applies film around pallets at up to 250% stretch. A butene-rich LLDPE film can experience localized necking at pallet corners if film thickness variation exceeds ±4%. LL0410KJ flows through the melt pump at 200–215°C and the die lip gap is set at 0.6–0.8 mm in the cast line. Back pressure above 270 bar on the extruder feeding LL0410KJ is reduced by blending 20–30% of an LDPE homopolymer with a melt flow rate of 1.9 g/10 min. The terminal products are stretch hood films for palletized beverage, PET preform, and bagged cement loads. LL0410KJ is not recommended for hand stretch wrap below 25 µm because the butene side branch structure cannot deliver sufficient machine-direction extensibility on high-speed wrappers.

A Sealant Layer Resin Is Judged by Hot Tack, Not Just Melt Flow

Flexible packaging converters select LL0410KJ for a coextruded sealant layer because it provides a broader seal temperature window than an LDPE-only sealant. In a three-layer barrier film with EVOH, the sealant skin is 20–25% of the total thickness and is extruded through a 50 mm satellite extruder. The layer temperature at the feedblock is kept at 205–215°C. Below 200°C, the sealant layer can exhibit interfacial instability with the tie layer. The film structure is processed on a blown line with a die gap of 2.0 mm and a BUR of 2.0:1 to reduce EVOH orientation and prevent sealant-layer chatter.

Hot tack is measured according to ASTM F1921-18 at a seal pressure of 0.5 N/mm² and seal time of 0.2 s. A sealant web with LL0410KJ at 20 µm layer thickness typically reaches 1.0–1.5 N/25 mm at 95°C and 3.0–4.0 N/25 mm at 115°C. Below 90°C the hot tack collapses because the amount of molten polymer at the seal interface is insufficient to form an entangled joint before the VFFS jaws open. Seal strength is tested after 24 h aging according to ASTM F88-21. Values below 10 N/25 mm on a 20 µm sealant layer indicate additive bloom or excessive processing temperature.

Processors should avoid placing LL0410KJ directly adjacent to EVOH without an adhesive tie layer; the difference in melt elasticity can produce wavy edge defects during high-speed slitting. The sealant layer must not incorporate erucamide slip at more than 500 ppm. Higher levels bloom to the surface and reduce seal strength by 20–30% after 72 h of roll storage. Terminal structures are stand-up pouches for dry food, detergent refill bags, and medical device pouches where retort conditions are not required. For hot-fill or retort applications, a higher-density heat-seal resin is substituted because LL0410KJ softens too early under sustained thermal load.