INEOS HDPE ELTEX CAP602 is a high-density polyethylene resin supplied in pelletised form for injection-moulded closure and cap applications. The grade is intended for thin-wall closures in contact with still water, carbonated soft drinks, dairy products, and pharmaceutical liquids where a combination of flow length, stress crack resistance, torque retention, and organoleptic neutrality is required. The resin has a controlled bimodal molecular weight distribution, which separates the high-molecular-weight fraction responsible for slow crack resistance from the lower-molecular-weight fraction that provides shear thinning and thin-wall fill capability. The product is manufactured by INEOS Olefins & Polymers and is ordinarily processed on high-cavitation injection moulding lines with hot runner systems, high-speed closure tooling, and automated vision inspection.

What Are the Nominal Melt-State and Solid-State Properties of ELTEX CAP602?

The table below lists typical property values published by the manufacturer for quality-control purposes. The values are not specification limits; lot-specific certificates of analysis should be used for release testing. Property comparisons should always be made at the same test method and conditioning history.

The melt flow rate of 2.0 g/10 min places the material in the low-flow closure moulding range. This MFR is deliberately selected to retain high molecular weight for environmental stress crack resistance while maintaining enough flow to fill tamper-evident bands and knurled sidewalls. The density of 0.956 g/cm³ balances stiffness for top-load strength with sufficient low-density amorphous fraction for impact and environmental stress crack resistance.

Stress Cracking, Closure Liner Interaction, and Organoleptic Boundaries

Environmental stress crack resistance is a primary failure mode in closure systems. In ASTM D1693-15, bent strip specimens are immersed in 10% Igepal CO-630 at 50 °C. The F50 failure time for ELTEX CAP602 is reported above 1000 h under standard laboratory conditions. This result does not guarantee field performance in a specific cap geometry because internal stress from gating, mould temperature gradients, and cooling-rate differences can shorten crack initiation time. For carbonated beverage closures, internal pressure from dissolved carbon dioxide acts as a sustained hoop stress on the closure shell. Stress concentrations at the root of the tamper-evident bridge and at the knurls are the most common crack initiation sites observed after top-load testing and torque-release testing. Closure top-load retention after carbonation aging is typically evaluated with a universal testing machine at a crosshead speed of 50 mm/min; published data for this specific configuration is limited.

Liners made from EVA, metallocene polyolefin elastomers, or PVC-free TPE are inserted or punched into closure shells. The insertion step generates radial stress at the liner seat; crack growth there is reduced by the high-molecular-weight tail of the bimodal distribution. When using PVC-free liners containing plasticisers, extraction testing should be performed under Regulation (EU) No 10/2011 or regional pharmacopoeia. Plasticisers can alter surface stress cracking behaviour. Taste and odour testing for mineral water closures is conducted according to EN 1622 or ASTM E1870; results are matrix-dependent and require validation on production-closed bottles.

Injection moulding converters running 48- to 96-cavity closure tools with hot runner systems observe that melt temperature uniformity across the manifold is a stronger predictor of cavity weight variation than barrel setpoint. The bimodal resin has a pronounced shear-thinning response; at injection shear rates above 1000 s⁻¹, apparent viscosity falls sharply, which permits fast filling of thin tamper-evident bands. Barrel temperature profiles are commonly set with rear zone 170–190 °C, middle zones 200–230 °C, and nozzle 210–240 °C, but actual melt temperature measured by needle pyrometer should remain below 240 °C. If hot runner tip temperatures fall below 190 °C, gate freeze-off occurs prematurely and produces short shots or weak gate areas. Mould coolant temperature is typically kept at 10–15 °C. Lower coolant temperature reduces cycle time but may increase residual stress at the gate, and this residual stress is measurable as an increase in crack density when closures are aged in ASTM D1693-15 solution. Cavity-to-cavity fill weight should be held within 0.5% of the mean; wider variation is associated with inconsistent top-load retention and cap torque failure. Screws with L/D ratio of at least 20:1 and compression ratio 2.0–2.5:1 are suitable for this density and MFR range.

When ELTEX CAP602 Is Introduced to Existing Unimodal HDPE Closure Lines

Unlike monomodal HDPE of similar density and MFR, the bimodal distribution displays a different relationship between shear rate and melt pressure. In a capillary rheometer at 190 °C, the apparent viscosity of ELTEX CAP602 at 100 s⁻¹ is higher than that of a unimodal grade with equivalent MFR, but at 1000 s⁻¹ the apparent viscosity becomes comparable or lower. This rheological signature means that process settings copied from a unimodal resin may need adjustment. Injection velocity should be increased to exploit shear thinning, but peak injection pressure should be monitored because the bimodal grade may show a steeper pressure rise if flow is restricted. When changing over from a unimodal grade, the barrel should be purged with a similar-MFR high-density polyethylene, not with general-purpose polystyrene or PVC, because thermal degradation products from purge resins can produce black specks in translucent closures. Regrind ratios above 20 wt% should be validated monthly by checking melt flow rate drift, notched Charpy impact at 23 °C, and closure top-load retention. The high-molecular-weight fraction is sensitive to repeated heat history; more than three injection cycles of the same regrind stream may shift the ESCR F50 value downward.

Thermal Stability Limits and Residence Time Tracking on Hot Runner Systems

The melt temperature window for ELTEX CAP602 is bounded on the lower side by flow freeze-off and on the upper side by oxidative degradation. At melt temperatures above 240 °C, thermal-oxidative chain scission and branching compete. Residence times longer than 8 min at 240 °C can generate gel particles and colour bodies. In practice, this means that hot runner systems with dead spots, long heated drops, or poorly purged colour change paths should be mapped by injecting a coloured purge and measuring residence time distribution. If any portion of the melt stream exceeds the 8 min boundary, the hot runner temperature should be lowered or the shot size increased to reduce residence time. If prolonged shutdown is necessary, the system should be purged with a lower-MFR HDPE and the hot runner setpoints reduced by 20–30 °C. On startup, discard the first five to ten shots from each cavity until melt temperature reaches the 190 °C lower boundary. Visual inspection for gels is performed on translucent or unpigmented closures; any gel above 0.5 mm diameter is cause for shutdown and purge. Gel content can be evaluated by counting specks on a standardized backlit fixture after moulding thin plaques.

Material Handling and Drying Requirements Are Controlled by Moisture Uptake Rate

HDPE is not hygroscopic in the same way as polyamide or PET, but condensation on cold pellet surfaces is a production-scale issue. If pellets are transferred from outdoor silos into a warm indoor hopper, the dew point difference can produce surface moisture above 0.05 wt%. At this level, injection moulding can produce splay, internal voids, and surface streaking in transparent or lightly pigmented closures. At relative humidity above 60%, pellets should be dried at 70–80 °C for 2–4 h in a desiccant dryer with a dew point below -30 °C. Hopper volumes should be sized to avoid bridging; bimodal HDPE pellet size distribution may segregate fines if the hopper is filled too quickly. Fines content should be kept below 0.5 wt% because fines melt earlier and can form degraded specks at the screw root. Closed-loop regrind should be free of caps containing silicone or EPDM liner fragments; such fragments reduce impact resistance and create delamination at the liner seat. Incompatibilities include PVC, PET, and certain ionomer residues; contamination above 1 wt% can be detected as delamination and a drop in notched Charpy impact.

Tracking Migration Limits Across Regional Food-Contact Frameworks

For closure applications, material conformance is lot-specific and should be verified against the supplier’s declaration. Under Regulation (EU) No 10/2011, overall migration from the finished closure must not exceed 10 mg/dm² under the test conditions appropriate to the food contact type and time–temperature exposure. For carbonated soft drink closures, the relevant test conditions may include aqueous and acidic simulants at low temperature and short duration, but actual conditions depend on the fill temperature and shelf life. Under FDA 21 CFR 177.1520, high-density polyethylene is a permitted olefin polymer for food contact subject to density and extraction constraints. For pharmaceutical closures, harmonised chapters such as USP <661.1> and <661.2>, or European Pharmacopoeia 3.1.3, may apply depending on the dosage form. ELTEX CAP602 may be used in colour-compounded form; the colour masterbatch and any slip or antioxidant additives must independently comply with the final food-contact or pharmaceutical requirement.

Published data for this specific configuration is limited when closures are exposed to high-pressure carbonation above 8 g/L CO₂, when liners contain migratory plasticisers, or when mould temperatures deviate outside 10–15 °C. The resin should not be used for hot-fill applications above 80 °C unless functional testing on production tooling demonstrates adequate dimensional stability. Chemical contact with strong oxidising agents, aromatic hydrocarbons, chlorinated solvents, and certain essential oils can reduce environmental stress crack resistance and should be evaluated by ASTM D543 or ISO 175. Contamination with polypropylene, PET, or acetal must be avoided; such incompatible polymer domains reduce notched impact and can delaminate. Processing at melt temperatures above 240 °C or residence times beyond 8 min invalidates organoleptic expectations and may generate gel defects. These boundaries should be treated as operational constraints rather than optional recommendations.