In blown-film conversion of Sinopec Yanshan HDPE 7000F into thin-gauge vest carriers on grooved-feed extruders, the high molecular weight distribution of the grade imposes a high-stalk bubble configuration rather than the conventional low-stalk LDPE geometry. The published melt flow rate below 0.10 g/10 min under ISO 1133-1:2022 at 190 °C/2.16 kg and typical density of 0.949–0.953 g/cm³ require barrel zones from 180 °C at the feed throat to 200–210 °C in the metering section and 200–210 °C at the spiral mandrel die. Die gap falls between 1.5 mm and 2.0 mm, blow-up ratio is maintained at 3.5:1–4.5:1, and stalk height is held at 6–8 die diameters to stabilize the high-density melt. Film thickness for vest carriers is commonly 8–15 µm after down-gauging, and line output is constrained by bubble tension rather than extruder capacity.

To down-gauge further, converters dry blend 10–20 wt% LLDPE with 7000F to raise Dart impact and keep Elmendorf tear in the machine direction. When 100% HDPE substrate is required, the process window narrows; visual melt fracture may appear at outputs exceeding critical shear rates in the die land, so die land length and exit radius must be selected to keep shear stress below the melt fracture threshold. Slip and antiblock masterbatches are added at 0.5–1.5 wt%; coefficient of friction is monitored per ISO 8295:2021. Film tensile properties are tested per ASTM D882-18 or ISO 527-3:2018, dart impact per ASTM D1709-16a method A, and Elmendorf tear per ASTM D1922-15. Terminal products include grocery vest bags, fresh produce bags, retail carry-out bags, and light merchandise bags. On production lines, die-lip build-up and gel particles are the dominant failure modes when screen pack condition degrades; head-pressure rise of 10–15% above the clean condition is a common trigger for screen replacement.

How Does the 7000F Melt Structure Influence High-Stalk Bubble Stability in Bin Liner Extrusion?

Extrusion of refuse sacks from Sinopec Yanshan HDPE 7000F typically involves a let-down with up to 20 wt% LLDPE or LDPE to balance dart drop resistance, tear propagation, and seal initiation. The high molecular weight fraction of 7000F contributes to bubble stability at low thickness, but the melt requires sufficient back pressure and mixing; grooved-feed single-screw extruders with L/D 25:1–30:1 and spiral mandrel dies are generally used. Die gap is set between 1.5 mm and 1.8 mm, blow-up ratio at 3:1, and stalk height at 6–8 die diameters; melt temperatures are maintained at 190–210 °C to avoid excessive orientation in the machine direction.

Film for bin liners is commonly produced at 20–40 µm in black, grey, or green. Carbon black masterbatch is dosed at 1–3 wt% for UV resistance and opacity. The critical quality parameters include dart impact measured under ISO 7765-1:2004, Elmendorf tear under ISO 6383-2:2003, and tensile properties under ISO 527-3:2018. Refuse sacks are evaluated under EN 13592:2017 for industrial and household collection. Terminal products are municipal refuse sacks, clinical waste liners, recycling collection sacks, and garden waste sacks. Insufficient frost-line height or excessive stalk height produces bubble oscillation that shifts TD tear properties; converters typically maintain frost-line height within 2–3 die diameters of the bubble neck to limit gauge variation.

Industrial sack and FIBC liner webs produced from Sinopec Yanshan HDPE 7000F are typically extruded at 100–150 µm thickness for mineral concentrates, chemical powders, and food powders. The conversion uses an 80 mm grooved-feed extruder with L/D 30:1, a die diameter of 200–250 mm, die gap of 1.8–2.2 mm, blow-up ratio of 2.5:1–3.5:1, and melt temperature of 200–215 °C. The lower blow-up ratio increases film gauge uniformity across the web, which is critical for inner liners inserted into self-supporting FIBC bodies.

Antiblock is added at 0.3–0.6 wt% and slip at 0.5–1.0 wt% to prevent blocking during automated insertion. Heat-seal strength is measured under ASTM F88/F88M-15 after sealing at 0.5 s dwell and 1.0 N/mm² jaw pressure across a temperature ramp from 120 °C to 160 °C. For FIBC inner liners, conformance to ISO 21898:2019 and relevant REACH entry requirements is commonly evaluated. Terminal products include FIBC inner liners, 25 kg sack inserts, drum liners, and bulk chemical packaging liners. Operational limitation occurs when the line is used alternately for LDPE products without purging; residual LDPE lowers modulus and can reduce liner tear resistance.

Frozen Food Packaging Film Fracture Resistance at −25°C

In five-layer coextruded frozen food packaging, Sinopec Yanshan HDPE 7000F is used as the outer structural and moisture-barrier layer, typically at 10–20 µm of a 30–70 µm total structure. Tie layers at 2–4 µm and an EVOH core at 3–5 µm provide oxygen barrier; the HDPE layer reduces water vapour transmission at chilled and freezing temperatures. The HDPE layer is processed on a dedicated grooved-feed extruder at 190–215 °C with a die gap of 1.8–2.0 mm and blow-up ratio of 2.5:1–3.5:1. Excessive melt temperature above 215 °C increases gel formation and die-lip deposition in long runs.

Water vapour transmission is measured under ASTM F1249-20 at 37.8 °C and 90% RH; oxygen transmission under ASTM D3985-17 at 23 °C and 0% RH. Low-temperature tensile performance is checked under ASTM D882-18 at −25 °C, and Elmendorf tear under ASTM D1922-15. For direct food contact, the HDPE layer is assessed under FDA 21 CFR 177.1520, EU 10/2011, and GB 4806.7-2016; migration testing follows the applicable food simulant and time-temperature conditions defined in those regulations. Terminal products include frozen vegetable bags, IQF fruit packaging, ice block bags, and frozen poultry packaging. The operational boundary is blunt puncture at sub-zero handling; if distributors require lower brittle temperature, converters replace a portion of the HDPE layer with LLDPE or reduce layer thickness.

When 7000F Is Let Down with 10–20 wt% Metallocene LLDPE for Silage Covers

Agricultural silage covers require puncture resistance, UV stability, and oxygen barrier retention during outdoor exposure. Sinopec Yanshan HDPE 7000F is let down with 10–20 wt% metallocene LLDPE to maintain tear and impact after UV aging, while carbon black masterbatch is added at 2.0–2.5 wt% for opacity and ultraviolet shielding. A hindered amine light stabilizer is dosed at 0.3–0.6 wt%, and processing antioxidants are selected to avoid phenolic package interactions that accelerate yellowing in sulfur-containing cover environments.

Monolayer blown film is extruded at 150–200 µm with die gap 1.8–2.2 mm, blow-up ratio 3.0:1–4.0:1, stalk height 5–7 die diameters, and melt temperature 195–210 °C. The main process conflict is dispersing metallocene LLDPE without creating gel inhomogeneities; a Maddock mixing section or barrier screw is commonly required. Film tensile is tested under ISO 527-3:2018, dart impact under ISO 7765-1:2004, and accelerated weathering under ISO 4892-2:2013. Oxygen permeability is measured under ASTM D3985-17 at 23 °C and 0% RH. Terminal products are bunker silo covers, clamp silage films, and temporary agricultural enclosures. Published data for 7000F-specific weathering retention in agricultural service is limited; converter validation under actual UV dose remains required.

Breathable backsheet films for hygiene articles use Sinopec Yanshan HDPE 7000F as the polyolefin phase in highly filled calcium carbonate compounds. Calcium carbonate masterbatch is compounded at 35–50 wt% with a co-rotating twin-screw extruder to disperse filler and avoid agglomerates that create pinholes. The filled compound is then converted on a single-screw blown-film line with die gap 1.5–2.0 mm, blow-up ratio 2:1–3:1, and melt temperature 190–205 °C. After film formation, machine-direction orientation at 1.5:1–2.5:1 creates microvoids around calcium carbonate particles; basis weight is controlled at 18–35 g/m².

Tensile properties are measured under ASTM D882-18 and ISO 527-3:2018. Air permeability and water vapour transmission are the critical functional parameters; WVTR is determined under ASTM F1249-20 at 37.8 °C and 90% RH. Skin contact compliance for finished articles is assessed under applicable hygiene product standards and company protocols; polyolefin resin conformity follows FDA 21 CFR 177.1520 where US market use is intended. Terminal products include diaper backsheet film, adult incontinence backsheet film, and sanitary napkin barrier film. Equipment wear is the limiting operational factor: filler loadings above 50 wt% accelerate screw and die lip wear and raise head pressure above the efficient operating window.

Coextruded Geomembrane Core Layers Place Different Melt Strength Demands on 7000F

In flat-die coextruded geomembrane production, Sinopec Yanshan HDPE 7000F is used in the core layer of 0.75–2.0 mm sheet, with skin layers selected for stress-crack resistance and welding performance. Extrusion is carried out on single-screw machines with L/D 30:1, flat die width of 2–4 m, melt temperature 200–220 °C, and carbon black masterbatch at 2–3 wt%. The core layer must retain melt strength across the wide die without edge thinning or melt fracture; die lip adjustment and internal deckle bars are used to maintain gauge uniformity.

Geomembrane tensile behaviour is tested under ASTM D6693-22, oxidation induction time under ASTM D5885-13 at 200 °C, and low-temperature brittleness under ASTM D746-20. Density is determined under ASTM D1505-18. For HDPE geomembrane liners, GRI-GM13 is the commonly referenced specification for landfill and containment installations. Terminal products are landfill caps and base liners, pond liners, mining heap leach pads, and tunnel liners. The operational boundary is stress-crack resistance in contact with aggressive leachates; published data for this specific 7000F configuration is limited, and converter validation using ASTM D5397 notched constant tensile load testing is normally required.

Controlling Gel Count and Die-Lip Build-Up in Produce Bag Film

Thin produce bags made from Sinopec Yanshan HDPE 7000F at 5–10 µm place the highest demands on melt homogenization, die-lip cleanliness, and bubble tension control. Converters use grooved-feed extruders with L/D 25:1, die gap 1.5 mm, blow-up ratio 4:1, and stalk height 6–8 die diameters. Output is commonly held at 80–120 kg/h on 65 mm lines to maintain bubble stability; higher output reduces stalk stability and increases gauge variation beyond acceptable limits.

Gel particles and fisheyes are the main rejection criteria for produce bag film; on-line camera systems count defects above 0.5 mm while laboratory methods include ASTM D1003-21 for haze and ASTM D2457-13 for gloss. When 100% 7000F is used, the processing window is narrow; a 10 wt% LLDPE let-down reduces gel sensitivity and improves tear. At ambient humidity above 60% RH, hopper hot-air drying at 70–80 °C is used to prevent surface-moisture pinholes on the bubble, despite the non-hygroscopic nature of HDPE. Terminal products include produce roll bags, bakery bags, newspaper bags, and light produce pre-wrap.