Japan Polyethylene Corporation places HB235R within the Novatec HD family as a high-molecular-weight high-density polyethylene (HDPE) extrusion blow moulding grade. The material is supplied in pellet form under a production control system that reports lot-specific melt flow rate and density values. HB235R uses an ethylene–α-olefin copolymer backbone; the comonomer concentration is adjusted to keep the density within the 0.955–0.957 g/cm³ window when measured according to ISO 1183-1:2019 and the melt mass-flow rate in the 0.30–0.40 g/10 min range at 190 °C and 2.16 kg according to ISO 1133-1:2022. The grade is stabilised with phenolic/phosphite antioxidants and an acid scavenger so that repeated heat histories in in-plant regrind operations remain within the producer’s recommended residence-time limits. Differential scanning calorimetry of compression-moulded specimens shows a broad melting endotherm with peak temperature near 128–131 °C. The CAS registry number for the polyethylene backbone is 9002-88-4.

Gel permeation chromatography of the base resin indicates a broad molar mass distribution typical of extrusion blow moulding grades, with a weight-average molar mass sufficiently high to produce a zero-shear viscosity above 10,000 Pa·s at 190 °C. This viscosity level explains the grade’s limited flow path in injection moulding and its suitability for parison formation in intermittent extrusion blow moulding. The melt becomes pseudoplastic at shear rates above 100 s⁻¹, allowing stable flow through die gaps without excessive melt fracture. On a laboratory capillary rheometer with a 1 mm die and 20:1 L/D ratio, the apparent shear viscosity at 1,000 s⁻¹ is typically in the 1,800–2,400 Pa·s range at 210 °C; published data for this specific configuration is limited, and tooling compensation should be based on the converter’s own capillary rheometry.

How Does the Fractional Melt Index Constrain the Manufacturing Route?

HB235R is not an injection moulding grade. The fractional melt index of 0.30–0.40 g/10 min yields a spiral flow length in a standard 2 mm wall cavity significantly lower than an injection grade with MFR of 20 g/10 min. On hydraulic injection machines with clamp force below 150 t, short shots and high screw recovery torque occur when the melt temperature falls under 220 °C. Injection moulding should be excluded unless the tool is designed for wall thicknesses above 3 mm and short flow paths, and even then this production route is not recommended by the supplier.

Intermittent extrusion blow moulding is the intended transformation route. The grade can be run on accumulator-head machines and reciprocating-screw blow moulders where the screw plasticates a shot, and the accumulator then extrudes the parison at high speed. The melt viscosity of HB235R is high enough to preserve parison integrity at shot weights up to 10 kg and parison lengths up to 120 cm on suitable machines. Shear heating must be controlled because viscous dissipation can raise the measured melt temperature by 5–10 °C above the rear barrel setting, especially at screw speeds above 60 min⁻¹ on 80 mm grooved-barrel extruders.

Compared with a bimodal PE100 pipe resin, HB235R has no long-term hydrostatic strength classification under ISO 9080:2012 and is not approved for pressurised water or gas lines. The molecular architecture is tuned for parison stability and environmental stress crack resistance in blow moulded containers, not for slow crack growth resistance under pipe hoop stress.

Parison melt strength, die swell and accumulator-head machine settings

In intermittent extrusion blow moulding, the high melt viscosity of HB235R controls parison sag. On a production-scale accumulator-head machine with an 80 mm grooved-barrel extruder and 24:1 L/D screw, the grade processes at melt temperatures between 190 °C and 220 °C. The barrel zone profile is commonly set from 170 °C near the feed throat to 205 °C at the metering section; the die head is maintained at 200–210 °C. At these settings, head pressure at the die entry typically falls between 15 MPa and 25 MPa, depending on die gap and shot size. Die swell in fractional-melt HDPE ranges between 15% and 35% diametrically; the exact value for HB235R must be measured on the target die because die land L/D, melt temperature, and accumulator fill speed alter the result.

Batch-to-batch variation in MFR of ±0.02 g/10 min can shift parison sag by approximately 5–8% on long 70 cm parisons. Closed-loop parison wall-thickness control using servo-hydraulic die gap adjustment is required for containers with minimum wall thickness below 0.5 mm. Accumulator head pressure should be monitored; a rise beyond 25 MPa at a fixed die gap indicates die land fouling, inadequate melt temperature, or excessive regrind content. Periodic purge with a commercial HDPE purge compound every 8 h of continuous running removes oxidised resin from the die land and reduces die lines.

Barrier screws with Maddock mixing rings are preferred for this grade because fractional-melt HDPE requires high plasticating work without excessive shear heating. A compression ratio of 3.0:1 to 3.5:1 and a feed zone length of 40–50% of screw length are standard. Grooved-barrel feed sections improve throughput stability, particularly when in-plant regrind is introduced at 10–15% by weight. Sharkskin appears when the die exit shear stress exceeds the critical value; lowering die temperature by 5 °C or reducing accumulator fill speed usually removes it.

The primary application domain for HB235R is extrusion blow moulding of rigid containers between 5 L and 60 L. Typical articles include UN-certified jerricans, detergent bottles, agrochemical containers, lubricant packs, and industrial pails. The comonomer content and low melt index produce a combination of environmental stress crack resistance and parison stability required for aggressive surfactant and hydrocarbon formulations. In 25 L jerrican applications, drop impact resistance at -18 °C is evaluated by the drop test sequence in ADR 6.1.5.2.4 or 49 CFR 178.603, and the filled container must withstand a stack load for 28 days at 40 °C according to UN 6.1.5.2.5. Actual performance depends on pinch-off weld geometry, parison programming, and mould cooling; the resin alone does not guarantee UN certification.

Moulds for HB235R use aluminium alloys such as 7075-T6 for prototype moulds and stainless steel or beryllium-free copper alloys for high-wear production pinch-off inserts. Pinch-off land width of 0.3–0.8 mm and flash well angle of 30–45° are typical for this HDPE class. Closure systems often use induction sealing; seal strength should be verified on finished containers under ASTM F88/F88M-21 because seal performance depends on sealing-layer thickness and contamination from the contents.

When the converter switches from HB235R to a higher-density blow moulding grade

In grade comparisons, HB235R is commonly evaluated against higher-density blow moulding grades such as HB420R or HB530R when top-load stiffness increases. The density differential of 0.007–0.009 g/cm³ translates into a flexural modulus reduction of approximately 150–250 MPa when measured under ISO 178:2019. In a 20 L jerrican, that modulus difference can require a wall thickness increase of 0.2–0.4 mm to maintain equivalent top-load performance under ISO 12048:1994 or an equivalent compression method. Conversely, the higher comonomer content in HB235R normally improves environmental stress crack resistance measured by ASTM D1693-15 and reduces brittle failure in cold drop tests.

Compared with a high-flow HDPE injection grade, the torque requirement on the same screw diameter is higher because the viscosity at 100 s⁻¹ is roughly 5–10× greater. This makes the grade unsuitable for thin-wall injection moulding; low-torque screw drives may stall or require cycle-time increases. When a converter transfers tooling from an injection grade to HB235R without redesign, short shots and gate freeze-off occur at wall thickness below 2 mm.

Regulatory compliance cannot be inferred from resin grade alone

For food-contact packaging, end-use compliance must be confirmed with the producer’s food-contact certificate. HDPE grades of this density fall within the olefin polymer provisions of 21 CFR 177.1520(c), items 3.1a or 3.2a, subject to extraction limits. In the European Union, plastics for food contact are evaluated under Regulation (EU) 10/2011 and its amendments; overall migration must not exceed 10 mg/dm² or 60 mg/kg for the intended simulant. Under Japan’s Food Sanitation Act, compliance with MHLW Notification No. 370 of 1959 and relevant amendments must be verified for the finished container. HB235R is supplied to industrial and consumer packaging markets, not as a medical-grade resin; ISO 10993 testing is outside the producer’s standard certification unless separately contracted.

RoHS Directive 2011/65/EU restrictions apply to electrical products and are generally not applicable to unfilled HDPE packaging; however, cadmium, lead, mercury, and hexavalent chromium are not intentionally added. The base polymer meets the Annex II maximum concentration values of 0.1% for lead, mercury, and hexavalent chromium, and 0.01% for cadmium by weight of homogeneous material when tested per IEC 62321. REACH compliance is managed through the producer’s safety data sheet and candidate list screening under Regulation (EC) No 1907/2006.

Processing and chemical incompatibilities are recorded below. HB235R should not be processed above 230 °C because oxidative degradation generates carbonyl species and raises melt flow rate; the stabiliser package is not designed for long dwell times above 220 °C. At melt temperatures below 180 °C, homogenisation suffers and the parison displays melt fracture and poor weld lines. Pellets do not require predrying under normal indoor storage; however, saturated surface condensation can occur after outdoor silo storage. Drying at 60 °C for 1 h with a desiccant hopper dryer may be used when surface moisture is visible. Water absorption of the base polymer is below 0.01% after 24 h immersion per ISO 62:2008. The grade is incompatible with concentrated nitric acid and other strong oxidising acids, with aromatic and chlorinated hydrocarbons that swell the amorphous phase, and with prolonged contact with ketones and esters that accelerate environmental stress cracking. Containers for aggressive surfactant solutions should be tested under finished-article ESCR conditions because laboratory tests on compression-moulded plaques do not fully reproduce pinch-off weld stress. Regrind addition above 15% by weight may reduce ESCR and cold drop performance; qualification should be repeated on the production tool.