Borealis HE1105, catalogued under the BorPure HE1105 trade designation, is a high-density polyethylene resin produced through the Borstar PE dual-reactor cascade. The grade is assigned to injection-molded closure and small-part applications in which the melt flow rate must remain high enough for high-cavitation tooling without sacrificing environmental stress crack resistance. The nominal melt flow rate is 5.0 g/10 min at 190 °C/2.16 kg measured to ISO 1133-1, and the nominal density is 0.950 g/cm³ measured to ISO 1183-1. These are typical release values, not minimum specification limits, and lot-to-lot control should be tied to the converter’s incoming resin inspection plan.

The bimodal molecular weight distribution is produced by sequential polymerization in a loop reactor followed by a gas-phase reactor. The low-molecular-weight fraction contributes shear-thinning behavior in narrow gates, hot-runner drops, and thin closure skirt sections. The high-molecular-weight fraction raises the concentration of interlamellar tie chains, which is the structural basis for improved slow-crack-growth resistance under environmental stress. This separation of flow and toughness is less pronounced in conventional unimodal HDPE grades produced in a single-reactor slurry process. The material therefore belongs to a broader class of bimodal closure resins that reduce the usual inverse relationship between mold-filling ease and stress-crack resistance.

Mechanical property data for HE1105 are generated on injection-molded specimens under ISO 294-4 conditioning and test protocols. The primary datasheet values are summarized below. They are single-point typical values and should not be used for design calculations without safety factors derived from actual process conditions.

These properties place HE1105 in the medium-stiffness HDPE range. Higher-density closure grades in the 0.954–0.960 g/cm³ range may provide higher top-load capability, but they typically exhibit reduced environmental stress crack resistance at equivalent melt flow. Lower-density grades may improve flexibility and cap-seal conformity at the cost of ring stiffness and dimensional stability under elevated warehouse temperatures. The selection therefore depends on the closure’s sealing-rib geometry, neck finish tolerances, and the carbonation level of the filled beverage.

What separates HE1105 from lower-flow unimodal HDPE and higher-flow closure grades?

The comparison between HE1105 and a conventional unimodal HDPE of similar 0.950 g/cm³ density and 5.0 g/10 min melt flow is not limited to molecular weight distribution shape. In the bimodal Borstar PE architecture, the high-molecular-weight fraction is present at a concentration sufficient to increase tie-chain density without raising the zero-shear viscosity to unprocessable levels. This structural characteristic is expressed in long-term slow-crack-growth tests such as ISO 16770 full-notch creep and in bottle closure stress-cracking evaluations under ASTM D1693 condition A. The practical consequence is a lower incidence of annular stress cracking in closures exposed to carbonated water, citrus flavor compounds, or dilute surfactant residues from filling-line lubrication.

Relative to higher-flow Borealis closure grades with nominal melt flow rates around 9.0 g/10 min, HE1105 trades some fill ease for improved slow-crack resistance. The higher-flow grades are typically selected for large-diameter still-water closures, thin-walled overcaps, or closures produced in very high cavitation where screw recovery and injection pressure are the cycle-time constraints. HE1105 is typically selected for carbonated soft drink closures in which internal pressure acts on a tamper-evident band and sealing annulus, generating sustained hoop stress. In such parts, a reduction in melt flow rate from 9.0 g/10 min to 5.0 g/10 min may increase injection pressure by a measurable amount, but the resulting tie-chain density reduces field failure risk more than the processing penalty increases manufacturing cost. Published data for this specific configuration is limited because stress-crack performance is strongly influenced by tool gate geometry, cooling rate, and colorant addition.

The grade is not directly comparable to polypropylene closure resins. Polypropylene offers higher temperature resistance and can be used for hot-fill or retort applications, but it requires different closure design due to lower notch sensitivity and different sealing-creep behavior. HE1105 should not be substituted into a tool balanced for polypropylene without a new mold-filling study and a reassessment of shrinkage, because the two polymer families differ in compressibility, holding-pressure response, and thermal expansion.

Melt and Mold Conditions for High-Cavitation Hot-Runner Closure Tools

High-cavitation production of 30/25 mm carbonated soft drink closures with HE1105 normally employs a general-purpose polyolefin screw with an L/D ratio between 20:1 and 25:1 and a compression ratio between 2.5:1 and 3.0:1. Barrel profiles are typically set from 180 °C in the feed zone to 220–240 °C at the front zone, with hot-runner manifolds held between 225 °C and 245 °C. These are starting conditions rather than fixed specifications, because melt homogeneity and residence time vary with screw diameter, back pressure, and shot size as a fraction of screw recovery stroke. Back pressure is maintained between 5 bar and 15 bar to achieve melt uniformity without excessive screw-forward time. Nozzle and hot-runner temperature must be verified independently because radiative heat loss at the drop tips can create localized cold slugs that shear at the gate and cause visible flow marks.

Mold temperature is one of the critical boundary conditions. For thin-wall closures, cavity surface temperatures between 10 °C and 25 °C are used to reduce cooling time and maintain dimensional stability. Below 10 °C, condensation risk increases in humid plants, and water droplets on mold steel can produce splay and irregular sealing-rib formation. Above 25 °C, cycle time increases and part shrinkage becomes more variable across high-cavitation tools, especially when cooling water is not balanced across cavity rows. A mold-temperature variation greater than 5 °C across the cavity array can create cap weight and sealing-rib dimension variation that is detectable in pressure-retention testing.

Injection velocity should be profiled to avoid jetting and gate blush. Valve-gated hot-runner systems with positive needle shutoff are preferred because HE1105 has a low enough melt viscosity to drool from open hot-runner tips during mold-open or screw-recovery phases. The valve gate also reduces gate-stringing on tamper-evident bands. Fill speed is set so that the melt front advances rapidly through the skirt and top plate but decelerates at the end of fill to avoid overshooting into flash at the parting line. Holding pressure is normally set between 250 bar and 450 bar at the cavity, depending on part projected area and gate freeze time. A 32-cavity tool may require clamp force from 150 t to 250 t, while a 96-cavity tool may require 350 t to 500 t or more depending on projected area per cavity and cavity pressure at switchover. These values are estimates for tooling feasibility; the final clamp requirement must be calculated from the actual projected area and the measured cavity pressure trace.

Drying is not normally required for HDPE because the polymer is not hygroscopic. However, surface moisture from condensation during silo storage or transfer in high-humidity air with relative humidity above 60 % can cause surface defects. If splay or irregular gloss is observed, hopper drying at 80 °C for 2 h may remove surface water. The converter should avoid adding flame-retardant or amine-based antistatic masterbatches unless organoleptic validation has been completed on the finished closure.

When Carbonation Pressure Retention and Organoleptic Neutrality Constrain Cycle Time

Carbonated soft drink closures made from HE1105 must retain internal pressure while resisting top-load, drop impact, and unscrewing torque. The resin itself is not a gas-barrier polymer; the package seal is primarily mechanical. Closure performance is therefore evaluated on the assembled bottle under internal pressures of 3.0–4.5 bar at 23 °C, with pressure loss monitored over the intended shelf life. Published data for this specific configuration is limited because bottle neck finish, liner geometry, tamper-evident band design, and capping torque dominate the result. The resin contributes by maintaining sealing-rib geometry under stress relaxation and by resisting slow crack growth at the annular hinge points where molded-in stress is highest.

Organoleptic neutrality is conversion-dependent. HE1105 is supplied with a stabilizer package intended for taste- and odor-sensitive applications, but the converter must control melt residence time and temperature to prevent the formation of volatile aldehydes and ketones. Prolonged hold-up in dead spots of the hot-runner manifold, or repeated processing of regrind that has been exposed to line lubricants, can generate organoleptic defects at parts-per-billion thresholds in mineral water and other still beverages. Sensory evaluation is often conducted under EN 1622 or an equivalent internal panel, but the numerical threshold for a particular volatile compound is product-specific. A reduction in screw forward time at excessive back pressure can degrade organoleptics even when MFR and tensile properties remain within specification.

The processing window becomes narrower when closure wall thickness drops below 0.6 mm. At this thickness, the interaction between gate diameter, fill speed, and holding pressure becomes the dominant source of sealing-rib variation. Very high melt temperatures improve fill at thin sections but increase odor risk and reduce melt strength at the valve gate. Very low melt temperatures reduce organoleptic risk but may create gate blush and short shots in the tamper-evident band. Published data for this specific configuration is limited across different hot-runner suppliers, so molders typically establish a production envelope using design-of-experiments on the actual tool and beverage filling line.

Compliance standards applicable to BorPure HE1105 in food-contact closures

Under United States food-contact regulations, olefin polymers are addressed in 21 CFR 177.1520. Because HE1105 has a density of 0.950 g/cm³, it falls within the polyethylene category for which use in contact with food is permissible, subject to end-use condition limitations established in 21 CFR 176.170(c) table 2. The finished closure must be tested for total extractives if it is used with alcoholic, fatty, or high-temperature food simulants. The resin supplier’s food-contact declaration should be matched to the specific colorant and processing aid formulation used in production.

In the European Union, plastic food contact materials are controlled under Regulation (EU) 10/2011. A closure produced from HE1105 must meet the overall migration limit of 10 mg/dm² under EN 1186-1 migration testing using the appropriate food simulant for the intended beverage. Specific migration limits for antioxidants, neutralizers, and any intentionally added substances are set by the final formulation and must be confirmed against the resin supplier’s food-contact declaration. The resin is not a substitute for finished-article compliance testing, because the surface-to-volume ratio of a closure differs from the standard test specimen and process residues can alter migration behavior.

Under REACH, the polymer itself is excepted from registration under Article 2(9), but monomers and any intentionally added substances above registration thresholds must be registered by the supplier. Under the RoHS Directive, the resin is not within scope unless the closure is incorporated into electrical or electronic equipment; if it is, the converter must verify lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE concentrations against the 0.1 % threshold for homogeneous materials.

Converters should not rely on resin certificates alone because the final closure requires finished-article validation under national drinking-water requirements if the application includes prolonged contact with potable water. Cold-water drinking-water closures may require additional testing under local standards such as UK BS 6920 or German KTW guidelines when specified by the end customer. Published data for this specific configuration is limited because the approval status depends on the complete formulation and conversion history of the finished part.