Borealis HDPE HE2515 is a high-density polyethylene grade supplied by Borealis AG for extrusion coating and lamination. The grade is characterised by a nominal density of 0.951 g/cm³ when measured according to ISO 1183-1:2019 and a nominal melt flow rate of 15 g/10 min at 190 °C under a load of 2.16 kg per ISO 1133-1:2022. The product is manufactured using bimodal polymerisation technology, which produces a controlled broad molar-mass distribution and low catalyst-residue profile. Primary application areas include liquid packaging board, aluminium foil lamination for aseptic packages, paper cupstock, and flexible intermediate bulk containers. Converters use the grade where a combination of low neck-in, high line speed, and reduced moisture vapour transmission relative to low-density polyethylene coating resins is required. The technical data in this text are drawn from manufacturer-published product information, standardised test methods, and established extrusion-coating line practice. Each production lot is governed by the certificate of analysis issued with the shipment, not by average grade values.

Melt flow rate and density are the two most relevant incoming inspection parameters for extrusion coaters. A shift in melt flow rate from 15 g/10 min to 18 g/10 min changes drawdown behaviour, lowers melt strength, and can increase neck-in on a running line. A density shift of 0.002 g/cm³ changes the stiffness and barrier performance of the coated web. For coated paperboard destined to aseptic filling systems, incoming lots are therefore tested under ISO 1133-1:2022 and ISO 1183-1:2019, and the results are recorded in the converter’s raw-material verification plan. These measurements are also used to detect cross-contamination with LDPE or with lower-MFR HDPE grades during bulk handling.

The product is supplied as pelletised material in bulk or in 25 kg bags as agreed between the converter and the distributor. Storage in dry, closed silos or original packaging is recommended. Extended exposure to direct sunlight does not rapidly degrade HDPE but can increase surface contamination from dust. The shelf life is governed by the stabiliser package and by ambient storage temperature. No special ventilation is required for normal storage of unopened bags, but bins should be inspected for surface condensation before discharge into the feed hopper.

What Processing Conditions Are Required for Extrusion Coating Trials?

On single-screw extrusion coaters with screw L/D ratios of 25:1 to 30:1 and flat die gaps between 0.5 mm and 0.8 mm, the melt temperature at the die is normally maintained between 260 °C and 310 °C. The lower boundary is set by the crystalline melting range of HDPE and by the need to generate sufficient surface oxidation for adhesion to aluminium foil and corona-treated paper. The upper boundary is limited by thermomechanical degradation and gel formation. When line speed exceeds 150 m/min or when the target coat weight is below 20 g/m², the die temperature is shifted toward the upper part of this interval to reduce melt tension and improve substrate wetting. On heat-sensitive substrates, the lower end of the range may be tested first to protect the base web.

Neck-in is measured as the reduction in web width from the die width, expressed in millimetres per side. HE2515 is designed to show lower neck-in than low-density polyethylene grades of comparable melt flow rate, but the obtained value is line-dependent. The controlling variables are die-to-nip distance, die lip opening, haul-off tension, melt temperature, and the width of the melt veil. Published data for a fixed air gap of 200 mm and a die width of 500 mm for this specific grade are limited; converters normally establish neck-in acceptance limits through a structured line trial on the target substrate. Because neck-in changes with coat weight, trials are carried out at the minimum and maximum coat weights used in the qualification plan.

Pre-drying is not required for bulk moisture uptake because HDPE is non-hygroscopic. However, surface condensation can occur when cold pellets stored below 5 °C are moved directly into a coating hall at 25 °C and relative humidity above 60 %. Under these conditions, the condensed surface moisture is carried into the barrel and appears as pinholes or bubbles in thin coatings. A hopper dryer set at 60 °C for 2 h is used to remove surface moisture. The same practice is applied to regrind stored in unheated silos during winter months.

Extrusion coating screws for HDPE grades with MFR 15 g/10 min are generally built with compression ratios of 3:1 to 4:1 and a metering zone length between 6 D and 8 D. Feed-throat temperature is kept below 50 °C to prevent premature pellet melting and bridging; barrel zones are set from 180 °C near the feed to 300 °C before the adapter. Screens with breaker plates are used to filter gel particles larger than 100 µm when coating thin structures. These settings reduce pulsed flow and improve coat weight uniformity in the crossweb direction.

Rheologically, the high melt flow rate of HE2515 supports casting at coat weights below 20 µm on temperature-sensitive substrates. The melt viscosity at 190 °C is lower than that of HDPE coating grades with melt flow rates of 5 g/10 min to 8 g/10 min, which reduces screw torque and permits a lower barrel-temperature profile on small-diameter extruders. On production coaters with barrel diameters between 90 mm and 120 mm, the use of a barrier screw or a Maddock mixing section is standard because it disperses the stabiliser package and reduces unmelted-resin pulses at high throughput. Screw speed and back pressure are set to limit shear heating; if the measured melt temperature exceeds the set point by more than 10 °C, gel formation accelerates and die-lip deposits shorten operating campaigns.

In thin-gauge coating, draw resonance becomes more likely when the melt curtain is stretched beyond the critical draw ratio. The draw ratio is calculated from the die gap, coat weight, line speed, and polymer density. For HDPE, a lower melt strength than LDPE at equivalent MFR means that the air gap and the chill roll position are used as control variables. A short air gap below 150 mm is often necessary for coatings below 15 g/m²; longer air gaps can cause the curtain to oscillate and create transverse thickness bands. These bands are detected with a beta gauge traversing the web and are corrected by changing the haul-off speed profile.

For paperboard coating without foil, adhesion is developed primarily by melt pressure, substrate porosity, and surface pre-treatment. Corona treatment of the paperboard increases the polar surface energy and improves bond strength. The substrate is kept at a controlled moisture content, typically 6–8 %, because excessive moisture vaporises at the nip and causes blistering. These conditions are set on the basis of z-direction tensile or peel tests on the finished board.

Material Specifications and Standard Test Designations

Representative values for the grade are given in Table 1. These values are not lot-specific limits; the certificate of analysis issued per EN 10204 3.1 governs the released product. Mechanical testing is performed on compression-moulded plaques conditioned according to ISO 291 or ASTM D618.

The density of 0.951 g/cm³ places the product in the high-density class defined by ISO 472 and ASTM D883. The melt flow rate of 15 g/10 min is high enough for thin cast webs but low enough to retain measurable melt strength and neck-in control. The tensile modulus of 1100 MPa is higher than the 200–400 MPa typical of LDPE coating resins, which contributes to converted paperboard stiffness. The Vicat softening temperature of 122 °C and the DSC melting temperature of 133 °C define the thermal limits for hot-fill exposure of the finished laminate. These values are measured on standard specimens and do not directly translate to maximum service temperature in all package filling operations.

When HE2515 Replaces Low-Density Polyethylene in Flexible Packaging Lamination

Substituting HE2515 for a conventional LDPE extrusion coating grade changes the mechanical and barrier behaviour of the finished laminate. The density difference of approximately 0.04 g/cm³ increases the tensile modulus of the coating and reduces moisture vapour transmission at a given coat weight. The moisture vapour transmission rate is measured on the finished laminate by ISO 15106-1 or ASTM F1249. Published comparative data for HE2515 across all possible substrate combinations are limited, but HDPE coatings with higher crystallinity generally yield lower water vapour transmission than LDPE layers of the same thickness.

The thermal response is also altered. The melting temperature of approximately 133 °C is higher than the 105–112 °C typical of LDPE coating resins. The higher thermal resistance can be used in hot-fill and aseptic paperboard structures; however, the coating process demands higher melt temperature. Adhesion to aluminium foil is more dependent on melt-surface oxidation. On-line corona treatment of the melt and ozone generation at the die-to-nip gap are used to promote bonding. Without such oxidation, peel strength measured by ISO 11339 may fall below the target values set for aseptic structures. This places the practical processing window for foil lamination in a narrower band than that for paperboard coating.

Compared with LDPE grades of equivalent MFR, HE2515 has a narrower drawdown window in very thin coatings. Draw resonance becomes more likely when the melt curtain is stretched beyond the critical draw ratio, which is influenced by die gap, coat weight, line speed, melt temperature, and melt strength. The condition is managed by reducing the air gap, adjusting chill roll contact, and increasing line speed gradually during start-up. Converters moving from LDPE often observe higher die-lip deposit formation with HDPE; stable antioxidant packages and uniform die heaters reduce the cleaning frequency.

Assessing Food-Contact Compliance Under EU Regulation No 10/2011 and FDA 21 CFR 177.1520

The base polymer is formulated to support food-contact compliance under the European Commission Regulation (EU) No 10/2011 and the olefin polymer provisions of FDA 21 CFR 177.1520. The finished laminate must be tested by the converter with the intended food simulant, time, and temperature conditions because extrusion coating, corona treatment, and lamination can alter migration behaviour. For liquid packaging board, the relevant test methods include the EN 1186 series for overall migration and EN 13130 for specific migration testing. Compliance with these standards does not guarantee fitness for all food types; high-fat foods and high-temperature processing require additional validation.

The base polymer is not intentionally formulated with substances restricted under REACH Annex XIV. Users should confirm the current REACH registration and any national packaging requirements for printing inks, coatings, and recycled-content declarations. For direct food contact, the allowable use of regrind is governed by the converter’s hazard analysis and by the migration performance of the finished package rather than by a single resin property. A change in extrusion coater temperature or corona dose can modify the low-molecular-weight fraction and should re-trigger migration verification in critical structures.

A critical processing boundary appears during aluminium foil lamination. The practical melt temperature window is narrower than the general coating window because adhesion to foil depends on the concentration of oxidised species at the melt surface. At melt temperatures below 270 °C, adhesion to aluminium foil often becomes inconsistent on high-speed lines; above 310 °C, chain scission produces gel particles that accumulate as die-lip deposits and downweb contamination. The operating band for foil lamination on many coaters is therefore 280–300 °C. Temperature uniformity along the die is held within ±5 °C to prevent local cold edges and local oxidation-hot spots. Published data for this specific grade on all die geometries are limited; converters confirm the window by measuring peel strength on the laminate and by counting gel defects in the coated web.

In a converting operation running a 1 200 mm slot die with internal deckle rods, edge temperature drop can be a source of uneven neck-in. Zone-controlled die heaters and deckle positioning are adjusted to keep the melt curtain stable. When coating aluminium foil at 25 g/m², the die-to-nip distance is usually kept below 200 mm to limit melt cooling and neck-in. Long air gaps are avoided because the melt surface cools before contacting the foil, reducing the formation of the oxidised layer needed for adhesion. The chill roll surface finish and temperature also influence the surface roughness and coefficient of friction of the coated web; these parameters are checked against the packaging line’s frictional requirements.

Regrind management introduces a second operational boundary. Edge trim and start-up scrap can be reprocessed in the same coating line provided the material is ground, sieved, and dried to remove surface moisture. Repeated heat histories shift the melt flow rate upward and increase the concentration of oxidised species, which can affect gel count and adhesion. Regrind addition in direct food-contact layers is generally kept below 20 wt%, and melt flow rate is monitored before and after one heat history according to ISO 1133-1:2022. The exact permitted regrind level is determined by the packaging manufacturer’s quality system and by migration testing on the finished package rather than by a fixed rule for all structures.

In comparison with HDPE grades designed for blown film, the high MFR of HE2515 reduces bubble stability but improves flow through cast-extrusion dies. In comparison with injection moulding grades of similar density, the polymer has a more linear coating draw response and a lower tendency to neck-in under melt drawing, although the difference is material-specific and best evaluated by a line trial. Converters comparing resins should therefore specify density, melt flow rate, melt temperature, neck-in, drawdown, and adhesion to the intended substrate in the evaluation protocol, rather than selecting by density or melt flow rate alone.