Borealis HDPE ME6052 is a high-density polyethylene injection moulding grade supplied in pellet form for thin-wall packaging, caps, closures, and technical components requiring a balance of flow length, stiffness, and environmental stress crack resistance. The resin is based on a bimodal cascade polymerisation route. Typical base-resin density is 0.964 g/cm³ when measured under ISO 1183-1, and the melt flow rate at 190 °C under 2.16 kg is 6.2 g/10 min according to ISO 1133-1:2022. These values place ME6052 in an intermediate-flow HDPE segment, below high-flow thin-wall grades with melt flow rates above 15 g/10 min and above blow moulding grades with melt flow rates below 2.0 g/10 min. The grade is specified where a processor requires high-density HDPE stiffness and stress crack resistance without moving to a lower-density hexene or butene copolymer or to polypropylene random copolymer. Compared with a conventional unimodal chromium-catalysed injection moulding HDPE, ME6052 differs mainly in the distribution of short-chain branches across the molar mass axis, which affects solid-state toughness, viscosity, and post-moulding shrinkage.

How Does the Bimodal Molecular Mass Distribution of ME6052 Modify the Stiffness–Toughness Balance Compared with Unimodal HDPE?

The bimodal molecular mass distribution creates a low-molar-mass fraction that reduces entanglement density during high-shear cavity filling and a high-molar-mass fraction that carries tie-chain load during solid-state deformation. In gel permeation chromatograms, the two populations are separated sufficiently to produce a distinct shoulder, although the precise peak positions are not defined by the specification. The low-molar-mass linear chains crystallise rapidly and increase density and tensile modulus, while the high-molar-mass chains contribute to toughness by forming tie molecules between lamellae. Under ISO 527-2/1A at 1 mm/min, the secant tensile modulus is approximately 1500 MPa, with a yield stress of 25 MPa and a yield strain of 8%. Under ISO 179-1/1eA, the Charpy notched impact strength at 23 °C is approximately 6.0 kJ/m²; at −30 °C, the value is approximately 4.0 kJ/m². An equivalent unimodal HDPE with the same ISO 1133-1 melt flow rate and similar density commonly falls below 4.5 kJ/m² at 23 °C. The practical distinction is that ME6052 retains stiffness near the upper HDPE range while providing a broader processing window for article designs with sharp radii, press-fit beads, or snap-fit features. These values are typical datasheet values, not specification limits, and lot-to-lot variation in molecular weight and additive package can shift individual results.

On a 2500 kN hydraulic injection moulding machine with a 40 mm three-zone barrier screw and 22:1 L/D ratio, the recommended barrel profile is 180 °C at the feed, 200 °C in the compression zone, 220 °C in the metering zone, and 230 °C at the nozzle. Mould temperature is controlled between 10 °C and 40 °C. For wall stock below 1.0 mm, the melt temperature should be maintained at 220 °C ± 5 °C; operation below 200 °C increases the filling-pressure requirement and can produce short shots near gate lands thinner than 0.6 mm. Residence time above 10 min at melt temperatures above 240 °C should be avoided because thermal-oxidative chain scission reduces the high-molar-mass fraction and lowers ISO 179-1/1eA Charpy notched impact strength. Although HDPE is not hygroscopic, condensation from cold-storage handling should be removed by drying at 60 °C for 2 h with dry air. A typical holding-pressure profile for a 1.2 mm closure is 400–600 bar for 8–12 s, followed by screw rotation at 80–120 rpm with back pressure 10–20 bar. Hot-runner temperatures should be set between 220 °C and 240 °C, with thermocouple placement at the gate and not only in the manifold. At screw speeds above 150 rpm on a 40 mm screw, shear heating can raise melt temperature by 5–10 °C, which partially offsets barrel set-point reductions but increases batch-to-batch variance in closure dimensions.

Thermomechanical Property Profiles and Standard Test Designations

The following representative values were generated on injection moulded specimens conditioned at 23 °C and 50% RH according to the relevant ISO method. They are provided for comparative selection and are not specification limits.

For converters moving from polypropylene random copolymer to HDPE ME6052, the density and stiffness are higher, but the processing window and long-term creep behaviour differ. In capillary rheometry under ISO 11443, the apparent viscosity at 1000 s⁻¹ and 220 °C is expected to be in the 180–220 Pa·s range, whereas a narrow-distribution high-flow thin-wall HDPE with a 2.16 kg melt flow rate above 15 g/10 min can show values below 120 Pa·s. The higher viscosity of ME6052 increases hot-runner pressure in a 48-cavity cap stack mould by approximately 10–15%, but the same high-molar-mass fraction reduces weld-line cracking in press-fit closures and improves top-load stability. Die swell is lower than that of a broad-distribution unimodal HDPE, which improves gate dimensional consistency at the expense of slightly faster gate freeze-off. Compared with a blow moulding HDPE with a melt flow rate near 1.0 g/10 min, ME6052 is not suitable for large-part extrusion blow moulding because its melt strength is too low and sag under parison weight is excessive. The resin is therefore selected for injection moulded articles where a blow moulding grade would not fill thin walls and a very high-flow HDPE would sacrifice environmental stress crack resistance.

When Wall Thickness Drops Below 0.8 mm, Melt Temperature Control Becomes the Critical Variable

In thin-wall injection moulding of ME6052, the process window has a measurable cliff edge rather than a linear response. For a 0.7 mm side wall and 140 mm flow length, increasing melt temperature from 200 °C to 220 °C reduces cavity filling pressure from an estimated 1200 bar to 800–900 bar, because the lower-molecular-mass fraction dominates high-shear flow and the frozen skin forms more slowly. At 200 °C, the solidification layer consumes the effective channel thickness quickly, and short shots occur when the gate land is below 0.6 mm. At 240 °C, the same tool may fill without pressure spikes, but the cooling time increases and oxidative chain scission can reduce ISO 179-1/1eA Charpy notched impact strength from approximately 6.0 kJ/m² to 4.2 kJ/m² after 10 min residence. Differential scanning calorimetry at 10 K/min shows the crystallisation exotherm near 115 °C; when the mould wall is at 20 °C, crystallisation begins during filling and reduces packing-pressure transmission. Raising the mould temperature to 40 °C improves holding-pressure transmission and reduces post-moulding warpage but increases cycle time by 5–8%. For tight-tolerance closures with a diameter of 75 mm, shrinkage stabilisation requires at least 24 h at 23 °C; parallel-to-flow shrinkage can reach 1.5–2.0% and perpendicular shrinkage 1.2–1.6%. Published multi-cavity hot-runner data for this exact grade and configuration is limited, so the above ranges should be confirmed by in-mould pressure sensors on the target tool.

In food-contact packaging, the grade is evaluated within the harmonised European framework for plastic materials and articles intended to come into contact with food. The base resin is supplied with a manufacturer statement that supports downstream migration testing under Regulation (EU) No 10/2011, and the applicable migration tests are selected according to Annex V conditions based on the intended use and contact ratio. In the United States, the olefin polymer falls under 21 CFR 177.1520, with the final article subject to extraction and end-test requirements under the applicable food type and use temperature. The product is formulated without heavy-metal pigments, phthalate plasticisers, or perfluoroalkyl substances. For electrical and electronic equipment, the base resin is not expected to contain cadmium, lead, mercury, or hexavalent chromium above the thresholds of RoHS Directive 2011/65/EU, and the analytical methods of IEC 62321 may be used for verification. Processing with copper-based pigments or halogenated flame-retardant masterbatches is not recommended because these additives can accelerate oxidative degradation and reduce ISO 179-1/1eA Charpy notched impact strength at −30 °C. Storage should be below 40 °C and out of direct sunlight; the resin has limited UV stability unless a UV stabiliser masterbatch is added.

Regulatory Status Is an Article-Level Determination, Not a Base-Resin Property

The following matrix summarises the applicable regulatory instruments, scopes, and verification conditions. A raw material statement does not replace the article-level declaration of compliance, which must be based on the exact processing history, additive package, and end-use conditions.