Aseptic Carton Board Coating: Tension Transients, Adhesion Threshold, and Migration Limits

Borstar LLDPE LE6027 is specified for polyolefin plies in aseptic beverage cartons because the bimodal molar mass distribution produces a melt curtain that resists edge neck-in during high-speed extrusion coating. At 190 °C and 2.16 kg load the grade exhibits a melt flow rate of 7.5 g/10 min under ISO 1133-1:2022 and a density of 918 kg/m³ under ISO 1183-2:2019. In the product-contact sealing ply the addition ratio is typically 100 wt% LE6027. On manufacturing lines that require lower extruder screw torque during start-up, 10–20 wt% LDPE with a melt flow rate of 0.3–0.7 g/10 min is added. Blend fractions above 30 wt% are not recommended for low-temperature seal integrity because the seal initiation temperature rises beyond the range required for high-speed form-fill-seal carton sealing.

The downstream production process is extrusion coating onto liquid packaging board with a basis weight between 180 g/m² and 350 g/m². The polymer is fed into a single-screw extruder with an L/D 30:1 barrier screw and a Maddock mixing section. Barrel setpoints are 180–300 °C from feed to metering; adapter and T-die are held at 290–320 °C. A flexible-lip die with a die gap of 0.6–0.8 mm delivers the melt curtain across a deckle of 2,400–3,000 mm. The air gap is maintained between 160 mm and 220 mm. On commercial lines running 12–25 g/m² coating weight, line speeds range from 200 m/min to 400 m/min. The board enters with 5–8 wt% moisture. Melt curtain oxidation at the nip is tracked by infrared pyrometry because adhesion to paperboard and aluminium foil in the laminate requires a melt temperature above 285 °C and a board surface temperature of 35–50 °C. If melt temperature falls below 285 °C, the concentration of polar carbonyl groups generated by oxidation is insufficient for consistent peel adhesion to foil. If board moisture exceeds 8 wt%, steam blistering occurs at the nip and the coated board is rejected for pinholes.

During continuous coating campaigns longer than seven hours, low-molecular-weight species accumulate at the die lip and produce edge tear. Operators typically clean the die lip every 6–8 hours or install fluoropolymer edge shields. The exact interval depends on melt temperature and coating weight; published data specific to LE6027 under all deckle geometries are limited. Compliance for the food-contact sealing ply rests on Regulation (EC) No 1935/2004, Article 3, and Regulation (EU) No 10/2011, Annex I, Table 1. Water vapour transmission is checked by ASTM F1249-20 at 38 °C and 90% RH on the coated board. For the U.S. market, the polyolefin layer is covered by FDA 21 CFR 177.1520, while the coated paperboard falls under FDA 21 CFR 176.170. REACH Annex XVII restrictions on lead, cadmium, and polycyclic aromatic hydrocarbons apply to the formulated coating.

Terminal products include 200 mL to 1 L aseptic milk cartons, UHT juice cartons, gable-top beverage packages, and portion packs with foil or metallised barrier layers.

How Does the LE6027 Melt Film Perform Against Aluminium Foil at High Line Speeds?

The critical variable in foil-based lamination is not melt flow alone but the extensional viscosity during draw-down. Extrusion lamination of a 9 µm aluminium foil to a 12 µm PET film or 20 µm biaxially oriented polypropylene film with LE6027 as the bonding layer converts the polyolefin into a sealant and bonding medium in a single step. The addition ratio is 100 wt% LE6027. If high line-speed draw resonance appears, 5–15 wt% LDPE of 0.2–0.5 g/10 min melt flow rate is introduced to suppress web vibration, though published data for blend-specific adhesion on foil is limited. The melt layer is applied at 8–15 g/m²; at this coating weight the melt curtain must remain continuous across a die width of 1,600–2,600 mm without edge tapering.

On tandem extrusion laminating lines, the foil is corona-treated to 42–46 mN/m wetting tension and preheated to 80–110 °C before it reaches the nip. The LE6027 melt is extruded through a 0.5–0.7 mm die gap at 305–320 °C; the air gap between die exit and nip is shortened to 120–180 mm to minimise neck-in and carbonyl loss. Nip rolls of 300–400 mm diameter apply a linear pressure of 20–40 N/mm, while the chill roll is held at 15–25 °C. If the melt temperature drops below 300 °C, peel adhesion to the foil falls below 1.0 N/15 mm on draw-down coated substrates. If foil web tension falls below 80 N/m, wrinkle-induced coating voids appear. Line speed is limited to 150–300 m/min depending on coating weight and foil temper. At speeds above 300 m/min with 8 g/m² coating weight, published adhesion data for LE6027-specific configurations are limited.

Food-contact laminates are assessed according to Regulation (EU) No 10/2011, Annex I, Table 1, with overall migration using EN 1186-1:2002 in simulant B 3% acetic acid and simulant D2 vegetable oil when the foil laminate is used for acidic or fatty products. In the U.S., the polyolefin layer is regulated under FDA 21 CFR 177.1520, and the laminate structure is evaluated under FDA 21 CFR 177.1395 when the food-contact surface is the polyolefin layer. Terminal products are flat pouches for dry powders, stick packs for instant coffee powders, dry beverage sachets, and lidding films for dairy portion cups.

Paper cup stock coating uses LE6027 as the only polyolefin layer on both the food-contact surface and the backside, forming a liquid barrier on clay-coated board between 190 g/m² and 350 g/m². For pigmented white cupstock, the formulation is 90–95 wt% LE6027 plus 5–10 wt% PE-based white masterbatch; the masterbatch carrier must comply with the same food-contact requirements as the base resin. The coating weight is 10–20 g/m² per side, with melt temperature 280–300 °C and line speeds of 150–250 m/min on conventional coating lines. Regulation (EU) No 10/2011, Annex I, Table 1 and FDA 21 CFR 176.170 apply to the finished cupstock; EN 1186-1:2002 overall migration is the release criterion. The terminal products are hot beverage cups, cold drink cups, soup containers, and foodservice boxes.

Biaxially oriented polypropylene film extrusion coating with LE6027 from 8 g/m² to 12 g/m² creates a heat-sealable web for high-speed horizontal form-fill-seal packaging without laminating solvent. The addition ratio is 100 wt% LE6027; an antiblock masterbatch at 1–3 wt% is used only when the coated web is stored in roll form for more than 30 days at temperatures above 30 °C, because film-to-film blocking at the roll core increases with time. Process: the BOPP film is corona-treated to 38–42 mN/m and passed over a chill roll held at 15–20 °C; the melt is delivered through a 0.6 mm die gap at 290–315 °C with air gap 150–200 mm. Line speeds on 1,600–2,600 mm systems range from 180 m/min to 280 m/min; above 280 m/min, the film web tends to wrinkle at the tack point unless additional web stabilisation rollers are installed. Food-contact compliance is covered by Regulation (EU) No 10/2011 and FDA 21 CFR 177.1520, with heat-seal strength verified by ASTM F2029-16 at 140–160 °C jaw temperature and 0.5–1.0 second dwell. Terminal products are snack food laminates, bakery overwrap, confectionery wrappers, and flow-pack films.

When LE6027 Is Coextruded as the Sealing Layer on Board with an Oxygen Barrier Core

Coextruded barrier board for aseptic and extended-shelf-life liquid packaging positions LE6027 as the sealing layer rather than the entire coating. The downstream process uses a three-extruder feedblock system: one extruder delivers LE6027 for the 40–60 µm sealing ply, a second delivers a maleic anhydride-grafted tie resin at 5–10 µm, and the third delivers EVOH at 5–10 µm as the oxygen barrier core. Addition ratio for the LE6027 sealing layer is 100 wt%; the adjacent tie and EVOH layers are separate resin systems and are not diluted into the LE6027 extruder. If LE6027 is contaminated with more than 0.5 wt% tie resin, the heat-seal initiation temperature shifts and interlayer adhesion at the LE6027/tie interface decreases.

The coextrusion feedblock is mounted directly to a 0.7 mm die gap; melt temperatures for LE6027 are held at 290–315 °C while the EVOH stream is held at 230–250 °C to avoid gel formation. Line speeds of 200–350 m/min are reported on coated board. The critical operational boundary is shutdown: if the line stops for more than 5 minutes with EVOH in the die, the barrier layer begins to crosslink and must be purged with low-density polyethylene before restart. Purging with LE6027 alone is insufficient to remove retained EVOH gel from static areas of the feedblock.

The sealing layer meets Regulation (EU) No 10/2011, Annex I, Table 1; the entire structure is evaluated under EN 1186-1:2002 overall migration and EN 13130-1:2004 specific migration. FDA 21 CFR 177.1520 covers the olefin polymer sealing layer; FDA 21 CFR 177.1360 covers the EVOH barrier layer where applicable. Terminal products are rectangular aseptic cartons, high-barrier liquid packaging board for soup and sauce cartons, and portion packs requiring an oxygen barrier.

Moisture-barrier extrusion coating on kraft paper for pet food and dry-chemical sacks uses 15–30 g/m² of LE6027 to control moisture vapour transmission into hygroscopic fills. The addition ratio is 100 wt% virgin LE6027; post-industrial recycled LDPE is not introduced at percentages above 10 wt% without prior sensory testing because odour transfer into dry pet food fillings has been reported at higher recycled fractions, though published data for LE6027 blends with recycled LDPE is limited. Process: the kraft paper is 50–100 g/m² and enters the coating section at 3–5 wt% moisture; melt temperature is 280–300 °C, die gap 0.7 mm, and line speed 120–220 m/min. Cure is by chill-roll quenching at 15–20 °C; no post-curing step is required. REACH Annex XVII restrictions apply in the EU; food-contact requirements are generally not triggered for pet food sacks unless the fill is dual-purpose, but FDA 21 CFR 177.1520 and Regulation (EC) No 1935/2004 are often retained as operational quality references. Terminal products are multi-wall pet food bags, salt and mineral supplement sacks, and dry chemical packaging liners.