Borealis HDPE FS1470 is supplied as a high-density polyethylene resin intended for high-stalk blown film extrusion. The grade is produced in a Borstar twin-reactor polymerisation configuration, which creates a controlled high-molecular-weight fraction for melt strength and a lower-molecular-weight fraction for processability. The nominal melt flow rate under ISO 1133-1:2022 is 0.7 g/10 min at 190 °C under 2.16 kg, and the nominal density under ISO 1183-1:2019 is 0.947 g/cm³. These values place FS1470 in the high-density stiffness range while avoiding the extreme die-head pressure observed in narrow-MWD metallocene HDPE grades. Converted articles include heavy-duty shipping sacks, agricultural liners, hygiene packaging films, and laminating substrates in which tensile modulus and dart impact resistance are jointly specified.

On single-screw blown film lines with grooved feed sections and L/D 30:1 barrier screws, the recommended barrel temperature profile starts with a feed section at 170–185 °C and rises to a metering section at 200–220 °C. Melt temperature measured at the adapter should be held between 190 °C and 215 °C; melt temperatures above 230 °C increase the probability of gel formation and reduce dart drop measured by ASTM D1709-22. Die gap settings from 1.2 mm to 1.8 mm are typical, with a die set point of 200–225 °C. Internal bubble cooling is recommended above 100 kg/h net output on dies larger than 200 mm diameter because the air flow required to hold the frost line rises non-linearly with line speed and can shift bubble instability into the 4:1 blow-up ratio threshold. Hopper-holding time beyond 8 h at ambient humidity above 60% RH has been associated with surface streaking on production lines; desiccant predrying at 80 °C for 4 h is therefore specified for storage conditions exceeding these limits.

What melt rheology distinguishes FS1470 from conventional unimodal HDPE film grades?

The primary difference appears in the shear-thinning profile measured by capillary rheometry according to ISO 11443:2021. FS1470 exhibits a higher zero-shear viscosity than a unimodal HDPE of equal melt flow rate, but its Carreau-Yasuda slope moves the apparent shear viscosity at 1000 s⁻¹ into the same processing corridor as a conventional 0.7 g/10 min unimodal material. The effect on a 70 mm extruder is predictable motor load and melt pressure while extensional viscosity at Hencky strain rates between 0.1 s⁻¹ and 1.0 s⁻¹ remains higher than that of conventional HDPE film grades. This combination improves bubble stability at high neck heights and reduces melt fracture in low die-gap configurations. A conventional unimodal HDPE with identical density and MFR typically exhibits higher die swell and a lower melt strength plateau in Rheotens testing; the bimodal architecture therefore permits a smaller die gap without sacrificing bubble integrity. Published data for the exact extensional viscosity master curve for this specific grade is limited; full capillary rheometry on the production lot is recommended before modifying die gap or blow-up ratio.

Downgauging performance is evaluated primarily through dart drop, Elmendorf tear, and tensile modulus measurements on 25 µm blown film. The supplier technical datasheet lists a typical film tensile modulus in machine direction of 1100 MPa under ISO 527-3:2018, with tensile stress at yield near 25 MPa and elongation at break above 600%. Dart drop impact at 25 µm is typically 170 g using ISO 7765-1:1988 or ASTM D1709-22 Method A. Elmendorf tear values are approximately 0.4 N in machine direction and 1.2 N in transverse direction under ISO 6383-2:1983. The balance between stiffness and impact permits a reduction from 30 µm to 20 µm in simple unsupported film structures without losing minimum dart drop specifications, provided the bubble is operated with constant frost line height and the die lip is free of oxidised polymer deposits. Field data from 90 mm high-stalk lines indicates that capacitance gauge variation remains below ±4% at 80 m/min when neck height is maintained at 8–10 times the die diameter.

Comparative film data are generated at 25 µm thickness on a high-stalk blown film line with a 3:1 blow-up ratio and are intended only for material selection. The values below contrast FS1470 with a conventional unimodal HDPE of comparable flow and density.

Corona treatment and film-surface adhesion thresholds

Untreated blown HDPE film from FS1470 typically presents a surface energy of 31–33 mN/m when tested with formamide and ethylene glycol mixtures under ISO 8296:2003. For solvent-free lamination to reverse-printed BOPP or polyester, corona treatment must raise surface energy to at least 38 mN/m; for UV flexographic inks, the accepted production range is 42–48 mN/m. Treatment decay is a function of slip and antistatic additive migration. Films stored in rewind form at 35 °C for more than 4 weeks can lose 6–10 mN/m at the outer lap due to additive bloom, so inline treatment immediately before coating or printing is preferred. Because the grade has no inherently polar comonomer, oxidative treatment by corona or plasma must generate oxygen-containing groups on the surface. On a 2.0 m wide central-impression flexo line at 150 m/min, a ceramic electrode corona unit with an output of 1.8 kW is generally required to hold 40 mN/m after treatment; configurations with bare steel electrodes may require 15–20% higher power. Dyne solutions specified by ASTM D2578-23 should be applied within 15 min of treatment to avoid wetting hysteresis from surface reorientation.

Compliance documents for FS1470 should be obtained from the supplier for each lot. Typical food-contact statements reference EU Regulation (EU) No 10/2011 and 21 CFR 177.1520, but final article migration testing under the intended food simulant and time-temperature condition is required. A total migration certificate for the neat resin does not cover printed or laminated structures, and the absence of a specific certification for the final structure must be addressed by the converter. The grade is not supplied under a USP Class VI or ISO 10993 biocompatibility certification and must not be used as a primary component of implantable medical devices. It is not recommended for continuous service in concentrated oxidising acids, chlorinated solvents above 40 °C, or environments with high levels of free chlorine. Environmental stress cracking resistance should be evaluated under ASTM D1693-21 Condition A if the converted article contacts surfactants or hydrocarbons. In processing, avoid combination with amine-based antifog concentrates that generate water-soluble amine by-products, because these can reduce adhesion of water-based laminating adhesives and shift coefficient of friction above 0.4 measured by ISO 8295:2008. The material is not designed for rotomoulding; attempts to process FS1470 in a rotomoulding oven lead to incomplete sintering at cycle times below 30 min because of the high-molecular-weight fraction.

When line speeds exceed 80 m/min and internal bubble cooling becomes pressure-limited

At net outputs above 100 kg/h on a 250 mm die, the pressure in the internal bubble cooling plenum must be controlled separately from the main cooling air ring. The recommended lower nip closing height for high-stalk operation is 8 times the die diameter; below this, collapse-frame rubbing can reorient the film and create transverse gauge bands at ±6% variation. Frost line height measured from the die face is typically held at 600–900 mm for 25 µm film at 3:1 blow-up ratio. If line speed exceeds 80 m/min, the IBC air exchange rate should be raised in steps of 10% until the frost line returns to set point. This is not an indefinite remedy because open-loop IBC systems reach a maximum stable plenum pressure near 2.5 kPa. Closed-loop control of upper nip speed should use a feedback loop with a deadband of ±1 m/min to prevent oscillation. Operators commonly observe that die-head melt pressure rises from 350 bar to 420 bar when the screen pack is loaded after 6–8 h of processing at high regrind content. A screen pack sequence of 20/40/20 mesh is required if post-industrial regrind above 15 wt% is introduced. Failure to remove oxidised gel particles from the lip assembly leads to visible die lines with a linear density greater than 1 per 100 m of film wound at 25 µm.

In refuse bag and retail carrier film conversion, the grade permits reduction from 30 µm to 20 µm while maintaining dart drop above 150 g under ASTM D1709-22; however, the transverse-direction tear of the lower-thickness film remains close to 0.8 N and must be accounted for in handle-cut stress concentration zones. In agricultural liner applications, field exposure to UV requires a stabiliser masterbatch from the compounder; unstabilised neat resin shows rapid embrittlement after 600 h of QUV exposure using ASTM G154-23 cycle. For heavy-duty shipping sacks, side gusset adhesion on flexo-printed areas should be verified with seal strength testing according to ASTM F88/F88M-23, with a minimum seal strength of 12 N/25 mm at 160 °C seal temperature and 0.5 s dwell time. If the converter requires a gloss or low-haze film, FS1470 is not optimum; haze measured by ASTM D1003-21 on 25 µm film is approximately 63%, whereas cast film LLDPE typically falls below 5%. This difference is an inherent property of the high-density blown film morphology and is not correctable by processing changes alone.