| HS Code | 354974 |
| Material Type | High-density polyethylene (HDPE) |
| Density | 0.957 g/cm³ |
| Melt Flow Rate 190c 2 16kg | 0.25 g/10 min |
| Tensile Modulus | 1300 MPa |
| Tensile Stress At Yield | 29 MPa |
| Tensile Strain At Break | >600% |
| Charpy Notched Impact Strength 23c | 20 kJ/m² |
| Charpy Notched Impact Strength Minus 30c | 6 kJ/m² |
| Vicat Softening Temperature | 127 °C |
| Melting Temperature | 134 °C |
| Crystallization Temperature | 115 °C |
| Water Absorption | <0.01% |
| Environmental Stress Cracking Resistance | >1000 h |
| Shore D Hardness | 62 |
| Thermal Conductivity | 0.4 W/m·K |
| Coefficient Of Linear Thermal Expansion | 1.2E-4 /°C |
As an accredited Borealis HDPE BL2571 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Borealis HDPE BL2571 is supplied in 25 kg polyethylene bags, stacked on pallets and shrink-wrapped for transport. |
| Container Loading (20′ FCL) | 20′ FCL container loading of Borealis HDPE BL2571: 25 kg bags, palletized, securely stowed, typically 25 metric tons per container. |
| Shipping | Borealis HDPE BL2571 is typically shipped in 25 kg PE bags, palletized and stretch-wrapped, or in bulk containers. It is not classified as dangerous goods for transport. Store dry, ventilated, away from ignition sources and sunlight, keeping packaging closed to prevent moisture and contamination. |
| Storage | Store Borealis HDPE BL2571 indoors in a cool, dry, well-ventilated warehouse, away from direct sunlight, heat, sparks, flames, and strong oxidizers. Keep original bags or packaging closed to prevent moisture, dust, and contamination. Stack pallets securely, avoid excessive height, and protect from mechanical damage and prolonged UV exposure. Maintain temperatures below 50°C and use first-in, first-out stock rotation. |
| Shelf Life | Borealis HDPE BL2571 shelf life is 24 months when stored in original packaging, cool, dry, away from direct sunlight. |
Borealis HDPE BL2571 is a high-molecular-weight high-density polyethylene grade for extrusion blow moulding. Incoming melt-flow-rate verification should be performed at 190 °C under 2.16 kg load according to ISO 1133-1; density should be checked by ISO 1183-1 method A or D. The supplier certificate of analysis is the authoritative source for lot-specific melt-flow-rate, density, ash and ESCR values. The scenarios below cover established industrial packaging and technical-container applications. They do not constitute a food-contact, pharmaceutical, medical-device or potable-water compliance statement unless the finished article is validated against a current regulatory certificate.
A 20 L or 25 L tight-head jerrycan for emulsifiable concentrates, suspension concentrates, soluble liquids and water-dispersible granules requires the monolayer wall to survive closure integrity tests after drop conditioning and to resist stress cracking caused by ester solvents, aromatic co-formulants and surfactant systems. The container is qualified as a UN 3H1 or UN 1H1 plastics packaging under 49 CFR 178.509. The performance test sequence is drop test 49 CFR 178.603, leakproofness test 49 CFR 178.604, hydrostatic pressure test 49 CFR 178.605 and stacking test 49 CFR 178.606. Chemical compatibility screening should follow ISO 16104 where the packaged liquid is a dangerous goods formulation. In monolayer construction, virgin high-density polyethylene typically accounts for 95–98 wt%, ultraviolet or colour masterbatch for 2–4 wt%, and processing aid for 0.5–1.0 wt% only when die-lip build-up or melt fracture raises rejected container counts. Clean in-house regrind from trimmed flash may be introduced at 10–15 wt% provided the same UN drop, leakproofness and hydrostatic pressure sequence is repeated on the regrind-containing container; post-consumer regrind is excluded from the structural wall for dangerous goods certification.
Typical monolayer blow moulding uses a shuttle or accumulator machine with a barrier screw having L/D 24:1–30:1, a melt temperature of 185–205 °C, a die head temperature of 190–210 °C, a die gap of 1.4–2.0 mm and blow pressure of 0.6–0.8 MPa. Mould temperature is held at 10–30 °C. Parison programming with 10–100 point wall-thickness control is necessary when shot weight exceeds 1 kg because top-wall thinning and pinch-off flash variation become the dominant rejection causes. Cooling time for a minimum wall of 1.0–1.5 mm is conventionally 18–35 s, but cycle time must be revalidated on the production line because hydraulic clamp response, mould venting and chiller capacity affect sidewall solidification. Finished products are 1 L, 5 L, 10 L, 20 L and 25 L narrow-mouth and wide-mouth jerrycans for crop-protection, veterinary and industrial biocide concentrates. Closures, vented caps and induction-seal liners are secondary components but are tested with the container under the same UN sequence.
| Performance test | U.S. reference | Recorded variable |
|---|---|---|
| Drop test | 49 CFR 178.603 | Closure integrity and wall fracture after drop conditioning |
| Leakproofness | 49 CFR 178.604 | Internal air pressure retention |
| Hydrostatic pressure | 49 CFR 178.605 | Internal water pressure at specified test pressure |
| Stacking | 49 CFR 178.606 | Deformation at specified temperature and duration |
On a high-cavity wheel blow moulder, the selection criterion shifts from ESCR alone to melt-strength retention under fast cycles and consistent die swell across multiple cavities. Concentrated laundry liquids, fabric softeners and hard-surface cleaners are linked to anionic and nonionic surfactant packages that can initiate slow crack growth in low-molecular-weight HDPE grades lacking sufficient tie-molecule content. Regulatory obligations for the finished package include the EU Packaging and Packaging Waste Directive 94/62/EC, the EU Detergents Regulation 648/2004 for the filled article and REACH Annex XVII restrictions where applicable. In this segment, titanium dioxide-based white masterbatch addition is commonly 3–5 wt%, colour concentrate is 1–2 wt%, and processing aid masterbatch is 0.5–1.0 wt% only if melt fracture or die-lip deposit increases line rejection above 2%. The process is a vertical rotary wheel blow moulder with 6–12 stations, a single-screw extruder of L/D 24:1 or greater, melt temperature 185–205 °C, mould chiller supply at 8–15 °C, blow pressure 0.55–0.75 MPa and a typical cycle of 8–14 s for a 1 L bottle. The terminal product range is 500 mL, 750 mL, 1 L, 2 L and 5 L bottles for detergent, fabric softener, surface cleaner and disinfectant concentrates.
Where monolayer high-density polyethylene fails through excessive solvent permeation or environmental stress cracking, a co-extruded wall is assembled with a structural HDPE layer and a barrier layer. The minimum role of high-density polyethylene in this structure is to carry top-load strength, drop impact resistance and pinch-off weld integrity while the polar barrier layer limits permeation of aromatic hydrocarbons, ketones, esters and oxygenated fuel additives. The finished article is qualified as a UN 3H1 or UN 1H1 plastics packaging under 49 CFR 178.509 when intended for dangerous goods; layer adhesion is screened by peel testing under ASTM F904-16 rather than by visual evaluation. Barrier performance may be measured as oxygen transmission rate under ASTM D3985-17 for formulations where oxidation is the primary failure mode. In terms of wall mass distribution, the outer structural HDPE layer commonly represents 40–60 wt%, the inner HDPE contact layer 15–25 wt%, a closed-loop regrind HDPE layer 20–30 wt%, tie layers 2–5 wt% and an EVOH or polyamide barrier layer 3–7 wt%. Colour masterbatch within the HDPE layers remains at 2–4 wt%.
The downstream process is a multi-layer extrusion blow moulder with separate extruders for HDPE, tie resin and barrier resin feeding a spiral mandrel or stack-type co-extrusion die. HDPE melt temperature is maintained at 190–205 °C; EVOH melt temperature is held at 170–190 °C to avoid crosslinking or gel formation; tie resin is an anhydride-modified LLDPE processed in the same temperature range. Blow pressure is 0.6–0.8 MPa, mould temperature 8–20 °C and total wall thickness 0.8–1.6 mm. Near-infrared thickness gauges are used to monitor layer distribution because a missing tie layer produces delamination that may escape routine leak testing. The terminal products are 1 L, 5 L and 10 L containers for solvent-based paint thinners, methylated spirits, ketone-containing cleaning formulations, fuel additives and agricultural adjuvants. This structure is not the same as a fluorinated monolayer wall; fluorination changes the surface chemistry of the article rather than introducing a discrete polar barrier layer.
Accumulator-head blow moulding of 30 L to 120 L open-head drums and 1000 L intermediate bulk container inner bottles moves the critical process window from cycle-time reduction to parison sag control and clamp force stability. Shot weights above 4 kg create a long exposed parison that tears or becomes eccentric if melt strength is insufficient; the observed failure is not a leak but a wall-thickness distribution below the minimum at the bottom-radius transition. The applicable packaging standard for a removable-head HDPE drum is UN 1H2 under 49 CFR 178.509, with maritime shipments following the IMDG Code 6.1.3 test provisions where invoked. For ultraviolet exposure during outdoor storage, weather-resistant compound design is controlled by xenon-arc exposure according to ISO 4892-2 or ASTM D2565; the failure criterion is retained tensile elongation at break rather than colour change alone. In formulation, the HDPE compound for large parts typically consists of 93–96 wt% virgin high-density polyethylene, 2–4 wt% UV-stabilizer masterbatch and 2–3 wt% carbon black masterbatch where outdoor service is specified. Clean closed-loop regrind at 10–15 wt% is accepted only when generated from the same part family and after melt-flow-rate shift is verified.
The accumulator machine uses a screw diameter of 90–120 mm, L/D 24:1–30:1, shot capacity 5–15 kg, melt temperature 185–200 °C, die gap 1.8–2.8 mm and blow pressure 0.6–0.9 MPa. Mould cooling water is held at 5–15 °C because the centre-thick section loses heat more slowly than the pinch-off regions. Sequential parison programming with 64–128 point control is mandatory for asymmetric parts and deep-draw geometries; a single-thickness parison produces excessive flash at the bottom and thin walls at the shoulder. Cooling time for a 2–4 mm wall is typically 180–480 s, but the limiting factor is often clamp stability and flash trimming rather than polymer solidification. Terminal products include 30 L, 60 L and 120 L open-head drums for inks, coatings, adhesives and water-treatment chemicals, as well as closed-head industrial containers where the top weld must survive drop testing and internal pressure cycling.
A processing boundary exists around 20 wt% closed-loop regrind because repeated heat history reduces high-molecular-weight fractions and reduces environmental stress crack resistance. The relevant test is ASTM D1693 condition B, supplemented by ISO 22088-3 constant tensile load testing where a faster ranking is required for formula compatibility screening. Tensile yield strength is monitored by ASTM D638 to detect gross degradation, but tensile yield alone is insufficient because ESCR failure develops at stress levels below yield. The compound ratio is therefore controlled as 80–85 wt% virgin high-density polyethylene, 15–20 wt% clean closed-loop regrind and 2–3 wt% masterbatch. Exceeding 20 wt% regrind does not automatically disqualify the material, but it triggers revalidation because melt-flow-rate may rise and parison sag may increase on large shot weights; published data for this specific grade at extended regrind fractions in ESCR-critical industrial packaging is limited and must be generated on the actual machine. The downgauged wall may pass burst pressure and still fail long-term ESCR, so burst testing alone is not a substitute for standard ESCR testing.
Regrind handling starts with grinding trimmed flash and rejected preforms to 3–5 mm flake, dedusting to remove fines below 0.5 mm, and gravimetric feeding into the main extruder hopper. A vacuum-vented single-screw extruder operated at -0.08 MPa vent pressure is used to remove moisture and low-molecular-weight volatiles; melt temperature is kept at 190–205 °C and excursions above 210 °C are treated as a process deviation because thermomechanical degradation accelerates and surface gel counts increase. ESCR specimens are pulled at least once per 24 h of continuous production for safety-relevant container types, and the production record includes regrind fraction, melt-flow-rate shift, die head pressure and extrusion current. The terminal products in this segment are non-food industrial containers, including detergent bottles, oil bottles, water-treatment chemical containers and non-UN general-purpose packaging. If regrind-containing containers are intended for UN 3H1 or UN 1H1 dangerous goods service, the complete package test sequence must be repeated with the regrind-containing wall.
Agricultural water-storage tanks, horticultural sprayer tanks and outdoor chemical dosing vessels require a stabilization package that resists ultraviolet embrittlement and thermal oxidation during intermittent liquid service. The failure mode after several seasons is not tensile yield loss but microcrack formation at moulded-in stress concentrations such as threaded inserts, weld lines and demoulding ejection pads. Weathering qualification is performed by ISO 4892-2 xenon-arc exposure or ASTM D2565 with retained elongation at break measured by ISO 527-2 or ASTM D638. The compound for outdoor service typically includes 93–97 wt% high-density polyethylene, 3–5 wt% UV-stabilizer masterbatch and 2–3 wt% carbon black masterbatch where carbon black is compatible with the chemical contents. Light-coloured tanks use hindered amine light stabilizer systems instead of carbon black, but the service life is strongly dependent on wall thickness and stabilizer dispersion quality. A dispersion assessment under ISO 18553 is used to reject masterbatch streaks that create local degradation sites.
Processing uses an accumulator blow moulder with shot capacity appropriate for 100–500 L tanks, melt temperature 185–200 °C, mould temperature 5–15 °C and blow pressure 0.6–0.9 MPa. Wall thickness ranges from 3–6 mm. The cycle is dominated by cooling time of 240–600 s because the lower corners and insert bosses retain heat long after the sidewall has separated from the mould. Threaded inserts are either post-mould welded or moulded-in and must be tested for pull-out after thermal cycling because the differential shrinkage of metal inserts in HDPE creates residual stress. The terminal products are 100 L, 200 L and 500 L vertical water storage tanks, horticultural spray tanks and outdoor chemical mixing vessels. These articles are not automatically suitable for potable-water contact unless a separate regulatory assessment is completed for the final stabilized compound.
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Borealis HDPE BL2571 is a high-density polyethylene grade identified by the model designation BL2571 and supplied in pellet form for extrusion blow moulding. The material is produced with a bimodal molar-mass distribution, which alters the balance between shear flow and melt strength relative to conventional unimodal HDPE. The grade is positioned for rigid containers in the small-to-medium capacity segment, typically below 5 L, where controlled wall thickness, top-load resistance, and chemical compatibility are simultaneous requirements.
Melt mass-flow rate is measured in accordance with ISO 1133-1:2022 procedure A at 190 °C under 2.16 kg. Density is determined by ISO 1183-1:2019 using an immersion or gas pycnometry method. Tensile yield and modulus are tested by ISO 527-2:2012 on type 1BA specimens. Notched impact resistance is assessed by ISO 179-1:2010 using Charpy edgewise specimens. Environmental stress crack resistance is ranked under ASTM D1693-21, condition A or B, in a nonylphenol ethoxylate solution at 50 °C. Lot-specific certificates of analysis state the controlled release values; the current manufacturer’s technical data sheet should be consulted for exact typical values, because production campaign variation is expected.
The product is not formulated as a pressure pipe resin, a rotational moulding powder, or a blown film grade. Those differences are important when line engineering changes are evaluated.
Processing is carried out on continuous-extrusion or accumulator blow moulding machines, including shuttle and rotary platform configurations. A grooved-feed extruder with screw diameter of 60–120 mm and length-to-diameter ratio between 24:1 and 30:1 is typical for this viscosity class. Melt temperature measured at the die head should be maintained between 180 °C and 210 °C. Temperatures below 180 °C increase parison surface roughness and may reduce weld-line integrity at the pinch-off; temperatures above 210 °C accelerate thermo-oxidative degradation and reduce melt strength, resulting in parison sag and uneven wall thickness.
Die gap settings from 1.5 mm to 2.5 mm and blow ratios from 2:1 to 4:1 are typical starting points for containers between 0.2 L and 5 L. Parison programming should be adjusted for the higher melt strength of a bimodal high-molecular-weight grade; stroke-dependent wall-thickness control with 10–100 set points is used on modern accumulator machines. The die swell is larger than that of a low-molecular-weight injection moulding grade, so tooling with an expansion ratio below the blow ratio is required.
Regrind from trimmed flash can be added at 10–30% by weight if the material is dried and fines content is controlled below 0.5%. Pellet drying is not required for sealed packaging stored below 60% relative humidity; if condensation is observed or storage exceeds 6 months, a desiccant dryer at 70–80 °C for 2–4 h is recommended. Residual moisture should be below 200 ppm by ISO 15512:2019 Karl Fischer titration. Batch-to-batch melt pressure fluctuation greater than ±10 bar at constant screw speed should trigger checks for regrind particle-size segregation or feed throat bridging.
For colouring, natural pellet feed can be blended with a polyethylene-based colour masterbatch at 2–5% by weight. Metering at the throat is preferred to avoid screw speed changes. Let-down ratio should be verified by ash testing or by loss-on-ignition according to an internal method; colourant carriers with melt flow rate above 20 g/10 min may reduce melt strength if overdosed.
Rheological control on the line should include continuous recording of extruder head pressure, melt temperature, and screw speed. The shear viscosity of high-density polyethylene blow moulding grades at 190 °C and shear rates between 10 s−1 and 1000 s−1 follows shear-thinning behaviour; power-law index values commonly fall between 0.3 and 0.5. Published data for this specific configuration is limited, so process capability studies should be based on the lot certificate and validated tooling.
Common blow moulding defects observed on production lines include uneven wall thickness at the upper shoulder, pinch-off flash stringing, and surface pitting. Uneven wall thickness is corrected by modifying parison programming points rather than increasing melt temperature. Pinch-off flash stringing is controlled by die gap adjustment and by maintaining clamp force within the range given below. Surface pitting often originates from moisture in regrind or from degraded pellets; drying regrind below 200 ppm moisture and screening out fines below 0.5 mm reduces the defect.
The bimodal architecture of BL2571 is the principal point of difference from conventional unimodal HDPE. In a unimodal resin, an increase in molar mass simultaneously increases tensile strength, impact resistance, and environmental stress crack resistance but reduces melt flow and raises head pressure. The bimodal distribution allows a controlled concentration of high-molar-mass chains to improve stress crack resistance while a lower-molar-mass component maintains processability. The practical consequence is that BL2571 can be run at similar melt temperatures to a unimodal grade but with lower parison sag and higher melt tension.
Stiffness is measured by tensile modulus under ISO 527-2:2012 or flexural modulus under ISO 178:2019. Density within the high-density polyethylene class, typically 0.945–0.965 g/cm³, controls the modulus. For barrier-sensitive formulations, the actual density of BL2571 controls water-vapour transmission rate and oxygen permeability; published data for this specific configuration is limited for wall thickness below 0.6 mm.
Environmental stress crack resistance under ASTM D1693-21 is the key ranking method for containers holding surfactants, bleach solutions, or oil-based cosmetics. The failure mode is brittle cracking initiated at surface imperfections; bimodal high-molecular-weight grades generally exhibit longer F50 times than unimodal grades of equivalent density. Because ESCR is strongly influenced by comonomer type and distribution, the manufacturer’s published data should be used for comparative evaluation.
Compared with a high-flow HDPE injection moulding grade with melt flow rate above 20 g/10 min under ISO 1133-1:2022, BL2571 has lower melt flow and therefore higher melt strength and better ESCR. Compared with a pipe-grade HDPE classified under ISO 4427-1:2019, BL2571 is not assigned a minimum required strength value and is not formulated for hydrostatic pressure service. Compared with polypropylene random copolymer used in blow moulding, BL2571 has a higher density and a lower melt flow, which increases stiffness but limits processing on lines designed for low-viscosity polypropylene.
Thermal stabilisation of the resin is designed for multiple extrusion passes within the recommended regrind fraction. Oxidation induction time measured at 200 °C under ISO 11357-6:2018 is used to monitor retained stabiliser activity; values below 20 min may indicate excessive reprocessing or inadequate regrind drying. The additive package is not intended for prolonged outdoor exposure; long-term ultraviolet stabilisation of the finished article requires a separate UV masterbatch.
| Property | Standard | Process relevance |
|---|---|---|
| Melt mass-flow rate | ISO 1133-1:2022 | Extrusion output, parison sag control |
| Density | ISO 1183-1:2019 | Stiffness, permeability, top-load classification |
| Tensile yield and modulus | ISO 527-2:2012 | Container hoop strength, burst resistance |
| Charpy notched impact | ISO 179-1:2010 | Drop impact at 23 °C and subzero |
| Environmental stress crack resistance | ASTM D1693-21 | Compatibility with surfactants and oxidising agents |
In a production line currently running a conventional unimodal HDPE blow moulding grade with density near 0.955 g/cm³, substitution with BL2571 should begin with parison programming trials. The higher melt strength of the bimodal material reduces sag; operators may lower the melt temperature by 5–15 °C or reduce accumulator drop speed. Die swell is usually higher, so parison diameter must be checked at the start and end of the shot. Sectional wall thickness measurement at the shoulder, sidewall, and pinch-off is required; a minimum wall thickness of 0.8–1.2 mm is common for household chemical bottles up to 2 L.
Container drop impact should be tested at 23 °C and 4 °C according to ASTM D2463-15 or ISTA 1A procedures. The pinch-off weld is the critical failure zone; insufficient clamp force below 1.5 kN/cm of pinch-off length produces incomplete fusion and low-temperature fracture. A clamp force of 1.5–3.0 kN/cm is typical for this segment.
Chemical compatibility trials use immersion of filled containers at 40–60 °C for 14–30 days, followed by ESCR ranking and burst testing. Published data for this specific configuration is limited when the test medium is a fully formulated detergent rather than the Igepal solution specified in ASTM D1693-21; pilot-scale storage trials are therefore used for validation.
If the line was originally designed for a grade with melt flow rate above 1.0 g/10 min, the lower melt flow of BL2571 may require an increase in extruder head pressure or a reduction in screw speed. Melt temperatures should not be raised above 210 °C to compensate for high pressure, because this degrades the high-molar-mass fraction and reduces ESCR. Instead, screw speed, temperature profile, and accumulator fill time should be rebalanced.
Compliance documentation for BL2571 should be obtained from the supplier’s product stewardship group. For food contact applications in the European Union, the moulded article must comply with Regulation (EU) 10/2011, including an overall migration limit of 10 mg/dm² and any specific migration limits for additives listed in Annex I. In the United States, the resin may be used in food contact applications covered by 21 CFR 177.1520 when end-use extraction conditions match the intended food type and temperature. The current regulatory certificate states any limitations for fatty foods, hot-fill, or repeated use.
REACH compliance is verified through the supplier’s Article 33 declaration for substances of very high concern; the RoHS Directive 2011/65/EU Annex II restricted substances apply only if the finished article falls within the electrical and electronic equipment scope. The resin does not contain a flame-retardant package and is not classified as a pressure pipe material under ISO 4427-1:2019. Continuous service above 80 °C, outdoor exposure without ultraviolet stabilisation, or contact with strong oxidising acids should be avoided unless validated by end-use testing.
Migration kinetics of HDPE additives follow Fickian diffusion models; the diffusion coefficient increases with temperature and decreases with molar mass. The practical consequence is that hot-fill applications require specific migration testing under the intended filling temperature and contact time. Published data for BL2571 under fatty-food simulants is limited; the supplier’s compliance certificate must state whether the grade is cleared for simulant D2 (vegetable oil) or only for aqueous and acidic simulants.
| Requirement | Designation | Documentation |
|---|---|---|
| EU food contact | (EU) 10/2011 | Declaration of compliance; specific migration data |
| US food contact | 21 CFR 177.1520 | FDA food contact letter |
| REACH SVHC | Regulation (EC) No 1907/2006 | Article 33 declaration |
| RoHS restricted substances | Directive 2011/65/EU | Supplier statement; XRF or ICP-MS screening |
On a continuous-extrusion shuttle line producing 1 L high-density polyethylene bottles at a cycle time of 8–12 s, mould temperature is normally held at 10–20 °C with closed-loop chiller control. Cooling air or chilled water is applied to the mould cavity; inadequate cooling below 10 °C can cause condensation-related surface defects, while temperatures above 20 °C can extend cycle time and increase shrinkage variation. Shrinkage of high-density polyethylene in blow moulding typically ranges from 1.5–3.0% in the longitudinal direction and 0.5–1.5% in the transverse direction, depending on mould temperature and blow ratio; tooling dimensions are adjusted accordingly.
Process records should include melt temperature, extruder head pressure, parison length, container weight, and drop impact at 23 °C and 4 °C. Melt temperature deviation greater than ±5 °C from the validated set point or head pressure deviation greater than ±10 bar is a trigger for process investigation. Batch-to-batch variance in bimodal HDPE can occur if the high-molar-mass fraction is not adequately dispersed; this can appear as intermittent melt fracture or variable die swell. In such cases, a screen pack change, screw speed increase of 5–15%, or a melt temperature increase of 5–10 °C may restore stable parison formation, provided the upper temperature limit is not exceeded.
For an accumulator machine producing 5 L containers with a shot weight of 180–220 g, accumulator fill time and drop time are the primary process variables. Drop time beyond 2–4 s at melt temperature 190 °C can cause visible parison sag; a drop time below 1 s may produce surface flow marks. Published data for this specific configuration is limited, so initial mould trials should use a design of experiments with three levels of melt temperature, blow air pressure, and blow time to define the process window.
On high-cavity rotary blow moulding lines producing 250 mL containers, cycle time is often limited by cooling time rather than extrusion rate. Cooling time for HDPE at 10 °C mould temperature can range from 5 s to 12 s depending on wall thickness and mould thermal conductivity. Increasing cooling-air flow beyond 15 m/s provides diminishing returns and may cause surface haze. Published data for this specific configuration is limited, so cooling time should be confirmed by thermocouple measurements in the mould wall.
