A melt mass-flow rate of 20 g/10 min (ISO 1133-1:2022, 190 °C/2.16 kg) and a density of 0.957 g/cm³ (ISO 1183-1:2019) place Sinopec Hainan HDPE M5720-S (HN8920) in the thin-wall injection moulding window for 0.45–0.80 mm dairy tubs, deli containers, and snap-on lids. The grade is processed on high-speed toggle-clamp machines of 3,500–4,500 kN using a general-purpose polyolefin screw with L/D 20:1–24:1 and compression ratio 2.5:1. Melt temperatures between 200 °C and 225 °C and mould temperatures between 12 °C and 22 °C are used, with injection velocities of 120–200 mm/s through direct edge gates or valve gates. Packing pressure is set at 35–50 MPa for 0.8–1.5 s before gate freeze; total cycle time on a 32-cavity cold-runner or 48-cavity hot-runner tool is typically 5.5–8.0 s. For direct food contact under EU Regulation 10/2011 as amended and FDA 21 CFR §177.1520, the converter must verify overall migration in the finished article below 10 mg/dm² after exposure to 40 °C for 10 days with 50 % ethanol as simulant; compliance cannot be transferred from the resin certificate alone. The standard formulation is dry-blended with 2.0–3.0 wt% titanium dioxide concentrate and 0.05–0.10 wt% erucamide slip additive. Pre-drying at 80 °C for 2 h is required only if resin has been stored below 10 °C at relative humidity above 60 %. Batch-to-batch changes in molecular weight distribution are small but can shift pack-to-fill transition by ±0.3 s, which is relevant for in-mould labelling systems where label displacement occurs if holding pressure is released too early. Terminal articles are 500 ml yogurt cups, 250 ml cream-cheese tubs, and 750 ml delicatessen trays with sidewall thickness not exceeding 0.65 mm.

What Occurs When 38-mm HDPE Closures Are Demoulded at 8 °C and Torque-Tested on a Capper Head?

In closure production, the balance between demoulding at low mould temperature and capper torque retention is governed by the crystalline morphology frozen into the part during the first 2.0–3.0 s after hold pressure release. M5720-S is processed at melt temperatures of 210–235 °C with mould circuits held at 8–15 °C; mould temperatures above 20 °C extend cycle time and reduce the hoop stiffness of the tamper band under high-speed capping. Multi-cavity valve-gated tools of 48–72 cavities require a two-stage injection profile: initial velocity of 60–80 mm/s through a 0.6–0.8 mm pinpoint gate followed by 40–60 mm/s during packing to avoid gate blush on the underside of the shell. Hold pressure is set at 45–60 MPa for 0.5–1.0 s; total cycle time for a 2.5 g polyolefin closure is 5.0–7.5 s on a 2,500 kN machine. Torque retention is tested after 24 h at 23 °C and 50 % relative humidity using ASTM D2063-12; the specification is commonly a removal torque not less than 0.6 N·m and not more than 2.0 N·m on the capper head. Additives are limited to 1.5–2.5 wt% colour masterbatch and 0.05–0.10 wt% of a compliant slip/antiblock combination. The grade is not recommended for carbonated soft-drink closures where internal pressure retention above 6 bar and repeated CO₂ exposure are required, because the high MFR and narrow molecular weight distribution reduce environmental stress crack resistance relative to lower-flow HDPE grades. Terminal parts are 38 mm tamper-evident closures for aseptic dairy and condiment packaging.

Five-Litre Open-Head Pail Moulding: Gate Type, UN Marking, and Stack Compression

Five-litre open-head pail bodies are gated through a direct central sprue or a tab gate at the bottom centre to avoid visible flow lines on the cylindrical sidewall. At a shot weight of 120–180 g, the mould is run at 15–25 °C with melt temperature 200–230 °C; injection speed is kept below 100 mm/s for the first 50 % of fill and raised to 150 mm/s for the remaining volume to prevent jetting and air entrapment in the handle bosses. Hold pressure of 50–65 MPa for 3.0–5.0 s compensates average linear shrinkage of 1.5–2.0 % in the sidewall. The formulation for black paint and construction-chemical pails consists of 1.5–2.5 wt% carbon black masterbatch with 40 % pigment loading and 0.1–0.3 wt% processing stabiliser; for light-coloured food pails the black masterbatch is replaced by 2.0–3.0 wt% titanium dioxide concentrate. When the pail is used for hazardous goods, it must pass UN Model Regulations Chapter 6.1 performance testing: 6.1.5.3 drop test from 1.2 m at −18 °C for packing group II, 6.1.5.6 stack compression for 28 days at 40 °C, and leakproofness under 20 kPa. M5720-S pails pass these tests when sidewall thickness is not less than 1.4 mm and the rim carries a continuous sealing lip of 2.0 mm thickness. Terminal parts include 5 L and 10 L open-head pails with metal bale handles and lids of a separate lower-MFR high-density polyethylene grade.

Where injection-moulded crates, vegetable trays, and logistics boxes of 40 × 60 cm footprint are stored outdoors and handled by forklift, the critical properties are low-temperature impact, creep resistance, and ultraviolet stabilisation rather than food-contact migration. The grade is dry-blended with 2.0–4.0 wt% UV-stabilised masterbatch containing hindered amine light stabiliser and a carbon black or titanium dioxide base; carbon black loadings of 0.8–1.2 wt% in the final part are typical for agricultural crates stored beyond 12 months. Moulding is performed on 8,000–12,000 kN hydromechanical machines with a melt temperature of 220–250 °C and mould temperature of 10–20 °C, using a cold-runner sprinkler gate system of 6–8 gates to reduce effective flow length below 280 mm. Injection velocity is set to 80–120 mm/s; hold pressure of 55–70 MPa is maintained for 5.0–8.0 s. Cycle time for a 1.8 kg crate is 35–45 s. Low-temperature drop resistance is tested per ASTM D5276-19; a common specification is no functional failure after a 1.2 m flat drop at −20 °C after UV ageing. The main processing bottleneck is warpage at the base grid due to differential cooling between the 4.0 mm ribs and 2.5 mm deck; mould-temperature control within ±2 °C across the cavity is required. For crates above 3 kg shot weight, a lower-MFR HDPE grade is generally specified because M5720-S has limited melt cushion stability in very thick sections. Terminal articles include stackable vegetable crates with interlocking lugs, industrial tote boxes, and returnable transit packaging for automotive components.

When a Toy Component Requires EN 71-3 Migration Compliance and 1.6 mm Wall Uniformity

Moulded toy assemblies made from M5720-S are tested under the Toy Safety Directive 2009/48/EC and the harmonised standard EN 71-3:2019+A1:2021 for migration of heavy metals into 0.07 mol/L hydrochloric acid. Because pigments and processing aids are the main source of extractable elements, the converter must use masterbatches supported by EN 71-3 certificates and keep total additive loading below 3.0 wt% unless migration is revalidated on the finished toy. The grade itself is typically formulated without intentionally added heavy-metal colourants. Processing windows for small toy components with wall thickness 1.6–3.2 mm use melt temperatures of 210–235 °C, mould temperatures of 15–25 °C, and injection velocities of 100–150 mm/s. Multiple textures and snap-fit undercuts demand a minimum demoulding draft angle of 1.0° and controlled shrinkage of 1.2–1.8 % after 24 h at 23 °C. Batch-to-batch colour variation is controlled by dosing 1.0–2.0 wt% masterbatch through a gravimetric blender; short-shot variance above 1.5 % in multi-cavity family tools is often caused by unbalanced runner pressure rather than by the resin melt index. The terminal part is a push-together construction toy component or bath-toy shell, where the final assembly must also comply with REACH Annex XVII restrictions on phthalates and RoHS 2011/65/EU if electronic parts are included.

In diagnostic and laboratory consumable moulding, USP 661.1 extractables testing and USP 661.2 packaging-system testing replace food-contact migration limits for products such as sample racks, cuvette washing cassettes, and disposable pipette tip racks. M5720-S is used where the moulded part is a housing or rack, not a primary blood-contact device; the grade is not certified under ISO 10993-1:2018 for long-term implantation, and published data for this specific configuration is limited. Moulding is run at melt temperatures of 195–215 °C, lower than for food and toy applications, to limit oxidative degradation that raises total organic carbon in USP 661.1 water extract. Mould temperature is held at 10–18 °C to produce a low-gloss, dimensionally stable rack. Total cycle time for a 0.4 kg, 96-tip rack is 22–30 s; hold pressure is 50–60 MPa for 2.0–4.0 s. Additive ratios are the most restrictive among all downstream segments: only 0.5–1.5 wt% certified masterbatch is added, and external lubricants are excluded unless results from USP 661.1 extractable metals and residue on ignition are available. The main processing risk is burn marks at the live-hinge end of hinged racks when melt residence time exceeds 15 min; therefore, shot size is set above 30 % of barrel capacity and back pressure is limited to 0.5–1.0 MPa. Terminal products include autoclave-resistant racks rated for 121 °C for 20 min.