On a high-stalk blown film line, Wanhua Chemical (Yantai) HDPE 7000F is introduced to the extruder feed throat after blending with slip and antiblock masterbatch. The extruder is a 90 mm single-screw unit with a grooved feed section and L/D ratio of 30:1. Melt temperature is maintained at 195–205 °C. The die is a 200 mm spiral mandrel die with a die gap of 1.4 mm. The blow-up ratio is set at 3.5:1 and the frost line height is held at 10 die diameters. These settings impose a high-stalk bubble geometry that produces balanced orientation in the machine and transverse directions. Film thickness is normally 20–25 µm. Tensile properties are evaluated by ISO 527-3:2018. Dart impact resistance is measured by ISO 7765-1:1988. Elmendorf tear resistance is measured by ISO 6383-2:1983. Slip additive concentration is 500–900 mg/kg erucamide. Antiblock is 2,000–4,000 mg/kg synthetic silica. Polymer processing aid is 300–500 mg/kg fluoroelastomer. The terminal structure is a vest carrier sack. Compliance is required with EU Directive 94/62/EC for packaging waste and REACH Annex XVII restrictions for phthalates and heavy metals. On production lines, bubble instability appears when the frost line is moved above 12 die diameters because melt strength drops and gauge variation exceeds ±2 µm. Batch-to-batch MFR variation is monitored because it shifts bubble stability at fixed screw speed, and producers issue certificates of analysis that include density by ISO 1183-1:2019 and melt mass-flow rate by ISO 1133-1:2022 at 190 °C/2.16 kg.

What Limits Gauge Uniformity in Heavy-Duty Refuse Sack Extrusion?

HDPE 7000F is also run in monolayer thick-gauge refuse sack and debris liner applications at 70–150 µm. On the same 90 mm grooved-feed extruder, the die gap is widened to 1.8–2.2 mm because thicker film requires lower internal pressure drop and reduced melt fracture. Blow-up ratio is reduced to 2.5:1–3.0:1 and the bubble is run as a low-stalk configuration. The frost line is kept at 5–7 die diameters. Melt temperature is raised to 200–210 °C to reduce viscosity without losing bubble stability. Carbon black masterbatch is added at 2.0–2.5 wt% for UV resistance and opacity. Hindered amine light stabilizer is incorporated at 0.1–0.3 wt% for long-term exterior exposure. Extrusion screws with intermediate mixing sections are used to disperse the masterbatch. Gauge variability is monitored by online capacitive or beta thickness gauges. Tensile strength is tested by ISO 527-3:2018. Puncture resistance is evaluated by ISO 7765-1:1988. Environmental stress-crack resistance is measured by ASTM D1693-21, method B. The terminal products are 120 L heavy-duty refuse sacks, construction waste bags, and industrial scrap liners. Concentration limits for lead, cadmium, mercury, and hexavalent chromium in packaging are controlled to 100 mg/kg per EU Directive 94/62/EC. Pre-drying is not required under normal ambient storage, but if regrind content exceeds 15 wt%, hopper drying at 65–70 °C for 2 h is recommended to avoid surface moisture defects.Three-layer coextrusion lines set the HDPE 7000F layer as the core or outer layer for moisture-stiffening in dry food packaging. The layer ratio is normally 25/50/25 or 30/40/30 by gravimetric output. The HDPE layer is processed at 190–205 °C. The sealant layer is a metallocene LLDPE run at 170–190 °C. The tie layer is an anhydride-modified polyethylene run at 185–200 °C. The die gap is 1.6–1.9 mm and the blow-up ratio is 2.8:1. Total film thickness is 40–70 µm. The HDPE layer contributes bending stiffness and water-vapour resistance. The LLDPE sealant layer contributes hot-tack and seal initiation. Seal strength is measured by ASTM F88/F88M-21. Hot tack is measured by ASTM F1921-18. Water vapour transmission rate is measured by ASTM E96-22 desiccant method. Food contact compliance is established under FDA 21 CFR 177.1520(c) for olefin polymers, EU Regulation 10/2011 with an overall migration limit of 10 mg/dm², and GB 4806.7-2016 for food-contact plastics. The terminal products are cereal box liners, dry soup pouches, and bakery film. On coextrusion lines, layer-thickness variation is checked by gravimetric hopper feedback. Deviations in the HDPE core beyond ±1.5% cause curling during bag-making and inconsistent web tension.

Comparative blown film process windows for three downstream structures using HDPE 7000F

Structure	Die gap (mm)	Blow-up ratio	Melt temperature (°C)	Film gauge (µm)	Primary test standard
Vest carrier sack	1.4	3.5:1	195–205	20–25	ISO 7765-1:1988
Heavy-duty refuse sack	1.8–2.2	2.5:1–3.0:1	200–210	70–150	ISO 527-3:2018
Coextruded dry food film	1.6–1.9	2.8:1	170–205	40–70	ASTM F88/F88M-21

When Frozen Food Packaging Requires Dart Impact Retention at −20°C

Plain HDPE 7000F film can become brittle at freezer temperatures, so processors dilute the HDPE phase with 10–30 wt% ULDPE or metallocene LLDPE to preserve low-temperature impact strength. The blend is compounded in the extruder with a mixing screw and processed on a three-layer blown film line. The die gap is set at 1.5–1.8 mm. The blow-up ratio is 2.5:1–3.0:1. The frost line is lowered to 4–6 die diameters to reduce frozen-in orientation. Melt temperature is kept at 190–200 °C to minimize thermal degradation during blending with higher-MFR ULDPE. The film is tested for dart impact at 23 °C and −20 °C by ASTM D1709-22, method A. Tensile properties at low temperature are evaluated by ASTM D882-18. The terminal products are frozen vegetable pouches, IQF seafood sacks, and ice bag liners. For food-contact use, the blend must meet FDA 21 CFR 177.1520(c) and EU Regulation 10/2011 overall migration limits. Use of slip and antiblock is restricted to 300–600 mg/kg erucamide and 1,000–2,000 mg/kg silica to avoid blocking at low ambient humidity. In low-temperature sealing operations, the LLDPE phase delivers seal initiation below 90 °C, while the HDPE phase maintains mechanical strength. Avoid direct combination with polypropylene above 5 wt% because phase incompatibility reduces film clarity and tear propagation resistance.

Vapour-Control Membrane Production from High-Molecular-Weight Film Resin

HDPE 7000F is used as the base polymer for building vapour-control membranes and radon barriers where low water vapour transmission is required. The resin is fed with a carbon black masterbatch at 2.0–2.5 wt% and a UV stabilizer masterbatch at 0.2–0.3 wt%. Film is produced on a blown film line with a die gap of 2.0–2.5 mm, blow-up ratio of 2.0:1–2.5:1, and melt temperature of 200–210 °C. The film gauge is 200–500 µm. Water vapour transmission rate is measured by ASTM E96-22 desiccant method. Tensile properties are measured by ASTM D882-18. Puncture resistance is measured by ASTM D4833-21. The terminal product is a damp-proof membrane or radon barrier installed under concrete slabs. Compliance is established under CE marking and EN 13984:2013 for plastic vapour-control sheets. The carbon black loading must be uniform. Pinholes caused by poor carbon black dispersion are detected by high-voltage spark testing on-line at 20–30 kV. Extruder zones above 220 °C are limited to residence times below 5 min to avoid oxidative gel formation. Published data for this specific configuration is limited, so processors validate membrane performance against project-specific water vapour resistance calculations rather than relying on generic film datasheets.