Liquid packaging board coaters running high-melt-strength LDPE grades often transfer the web from an unwind station through a corona treater before the molten curtain contacts the board in the nip. Borealis LDPE 122 MX is specified with a nominal density of 0.922 g/cm³ according to ISO 1183-1:2019 and a melt mass-flow rate of 12 g/10 min according to ISO 1133-1:2022 at 190 °C under 2.16 kg load. The grade is processed on tandem extrusion coaters equipped with 120 mm single-screw extruders having an L/D ratio of 30:1 and barrier screws optimised for polyethylene. Melt temperatures are maintained between 290 °C and 325 °C. The die gap is set at 0.4 mm to 0.8 mm. For aseptic brick-over-blade cartons, the outer LDPE coating weight is run at 12–20 g/m², while the inner food-contact layer is run at 20–35 g/m². Ozone treatment is applied at the die-to-nip air gap at concentrations of 0.3–0.8 kW/m of die width to raise surface polarity and improve adhesion to the paperboard surface. Without ozone, peel adhesion values measured by TAPPI T 540 can fall below converter specifications because fused polyethylene on cellulose forms a mechanical interlock only where the molten polymer penetrates the fibre network. Water vapour transmission rate is measured on finished board according to ASTM F1249 at 38 °C and 90% RH. The terminal products include gable-top milk packaging, juice bricks, aseptic cream cartons, and dry-food composite cans. Food-contact compliance is assessed under 21 CFR 177.1520(c) for olefin polymers and under Regulation (EU) 10/2011. Overall migration is tested according to EN 1186-1:2002 using simulant D2 for fatty foods and simulant A for aqueous products. In multi-layer structures, the LDPE layer is not in direct contact with the filled liquid in some formats, but the inner sealant layer still requires extraction testing because of the potential for pinholes. A production bottleneck on single-layer board is neck-in of the molten curtain at line speeds above 300 m/min. The melt flow reduces neck-in but also lowers melt strength, so die-lip opening and air-gap distance are adjusted to maintain a curtain width within ±5 mm of the target web edge. When the coating weight falls below 15 g/m², pinhole density in the finished carton can rise above 2 pinholes/m² unless the chill roll is polished and maintained at 10–18 °C with a mirror or matte finish specified by the converter. Edge trim is densified and fed back at 4–8 wt%; higher regrind levels can increase gel count and reduce drawdown.

How Does a 12 g/10 min Melt Mass-Flow Rate Affect Seal Initiation and Hot-Tack in Flexible Food Laminates?

In extrusion-laminated flexible packaging, LDPE 122 MX is coextruded or monolayer-coated onto oriented polyester, biaxially oriented polypropylene, aluminium foil, or metallised substrates. The sealant layer is applied at 15–25 µm thickness. The coated web is converted into pouches for dry soup mixes, condiment sachets, snack laminates, and frozen-food bags. Seal initiation temperature is influenced by the polymer's melting range and is measured according to ASTM F88 on fin-sealed specimens. For low-density polyethylene extrusion-coating grades, seal initiation can occur between 85 °C and 95 °C at a seal pressure of 0.35 N/mm² and 0.5 s dwell. Hot-tack strength is assessed on a spring-loaded hot-tack tester across a jaw temperature sweep from 80 °C to 130 °C. LDPE sealant layers typically display a hot-tack plateau from 90 °C to 115 °C. For retort or hot-fill pouches the sealant is often blended with 10–30% linear low-density polyethylene or metallocene polyethylene to improve toughness and seal-through-contamination performance. Coextrusion coating lines run the PE layer at 290–315 °C melt temperature with an air gap of 120–180 mm. The chill roll is set at 12–18 °C and nip pressure is held at 4–6 N/mm of roll face. LDPE 122 MX is selected because its melt flow allows wetting of foil without leaving uncoated streaks at line speeds above 200 m/min. However, if corona treatment of the substrate exceeds 46 dyn/cm, surface polarity can build up enough to cause backside treatment or blocking on the wound roll. The terminal laminated film is subjected to heat seal strength testing after 24 h conditioning at 23 °C and 50% RH. Minimum seal strengths of 2 N/15 mm are common for snack packaging, while heavy detergent pouches may require 4 N/15 mm. Food contact status for the sealant layer is evaluated under 21 CFR 177.1520 and EU Regulation 10/2011. The manufacturer's declaration covers overall migration limits of 10 mg/dm² for food simulants A, B, and D2 according to EN 1186.

In masterbatch production, LDPE 122 MX serves as a carrier resin for organic and inorganic pigments, optical brighteners, slip additives, and processing stabilisers. Twin-screw compounding is run on co-rotating extruders with L/D 44:1 and screw diameters from 50 mm to 92 mm. Distributive mixing elements are used rather than aggressive kneading blocks when the active ingredient is shear-sensitive. The carrier loading is typically 45–75 wt%. Pigment concentrations range from 20 wt% to 50 wt%, and wax dispersants are added at 5–12 wt%. The melt flow of LDPE 122 MX assists wetting of high-surface-area pigments, but it reduces melt viscosity. Screw speed is limited to 300–600 rpm to avoid overheating the melt beyond 220 °C. Filler masterbatches with calcium carbonate at 60–75 wt% loading generate high internal friction. Barrel cooling zones are set at 160–190 °C. Filter pressure value is measured according to EN 13900-5 with a 14 µm screen pack. Acceptable dispersion is normally indicated by a pressure increase below 0.4 bar/g after 5 min of extrusion. If the pressure rise exceeds 0.8 bar/g, the batch is reworked through a second pass or the screen pack is replaced. The carrier's melt flow rate is matched to the let-down resin to prevent gloss streaks and melt fracture in injection moulded or extrusion-coated parts. Converters running PP-based dilution systems often limit LDPE masterbatch addition to 3–5%. LDPE-based dilution systems can accept additions up to 8–10%. Terminal end products include carrier-bound masterbatches for polyolefin film, extrusion coating, and injection moulding. The masterbatch must comply with REACH registration obligations and with RoHS Directive 2011/65/EU if the final part enters electrical and electronic equipment. The main processing limitation is compatibility with incompatible polymer families. Adding an LDPE carrier into PP at levels above 5% can reduce stiffness and distort crystalline morphology.

Thin-Walled Closure Moulding Window and ESCR Constraints for High-Melt-Flow LDPE Blends

In injection moulding of flexible closures and dispensing plugs, LDPE 122 MX is used neat or blended with LLDPE, EVA, or polypropylene to balance flexibility, sealing, and dimensional stability. The high melt mass-flow rate allows multi-cavity tooling with cold runner systems to fill thin-walled sections down to 0.6 mm at injection pressures of 60–100 MPa. Melt temperature is set at 180–220 °C. Mould temperature is held at 15–35 °C for cycle times between 8 s and 15 s on 48-cavity to 96-cavity tools. Clamp force calculations for a closure with projected area of 4 cm² and 48 cavities require approximately 80–120 t of clamp force, depending on peak cavity pressure. The product is typically moulded with 2–4% colour masterbatch and 0.2–0.5% slip additive by let-down weight. The closure's low tensile modulus relative to PP makes it suitable for tamper-evident snap caps and overcap liners. Tensile properties after moulding are measured according to ISO 527-2:2012 using 1A specimens. Elongation at break for LDPE typically exceeds 300%, while tensile strength at yield remains below 12 MPa for high-melt-flow grades. Environmental stress cracking resistance is determined according to ASTM D1693 in 10% Igepal CO-630 at 50 °C. High-melt-flow LDPE can show substantial ESCR reduction when moulded with sharp radii or heavy knit lines. Moulders often specify a minimum notch-free ESCR of F50 > 24 h, although published data for this specific grade configuration is limited and part performance depends on residual stress. The main failure mode observed on production lines is gate blush or flow mark on the closure top surface when injection speed is below 40 mm/s. Processing adjustments include profiling injection speed and raising mould temperature at the gate. Materials regulations for closures in food and pharmaceutical packaging require compliance with 21 CFR 177.1520 and, in Europe, Regulation (EU) 10/2011. Specific migration testing under EN 1186 is required when the closure is in direct contact with fatty or acidic products.

Sterile barrier web converters run coextruded or laminated films in which the sealant layer is selected for low seal initiation and stable hot-tack over a narrow temperature window. LDPE 122 MX is applied as a peelable or weld-seal layer in medical device pouches, header bags, and lidding films, typically against uncoated or adhesive-laminated Tyvek, paper, or medical-grade polyester. The sealant layer thickness is controlled between 25 µm and 50 µm. The film is run on cast coextrusion lines with die temperatures of 200–240 °C. Seal strength is measured according to ASTM F88 at a jaw temperature of 120 °C, pressure of 0.28 MPa, and dwell time of 0.5 s. Target values depend on the pouch configuration. Peelable chevron pouches commonly target 1.0–2.5 N/15 mm. Sterile barrier performance is validated under ISO 11607-1:2019 and ISO 11607-2:2019 for terminally sterilised medical devices. For ethylene oxide sterilisation, the LDPE sealant layer maintains seal integrity after exposure to 55 °C and 70% RH during preconditioning. Gamma sterilisation at doses above 25 kGy can induce oxidative crosslinking and yellowing. When gamma compatibility is required, the film structure is reformulated with radiation-stable antioxidants and the dose is limited to 25–40 kGy under ISO 11137-1. In steam autoclave applications, plain LDPE is not suitable at 121 °C because the seal may creep under load. The layer is replaced by or blended with polypropylene or high-density polyethylene for steam-sterilised formats. Extractables testing is performed according to USP 661.1 for plastic packaging systems. The finished web is tested for particulate contamination and seal integrity by dye penetration according to ASTM F1929. The main processing limitation in production is blocking during roll storage. If the coefficient of friction exceeds 0.35 measured by ISO 8295, the wound film may telescope or block. Slip and antiblock masterbatches are added at 0.1–0.3 wt%.

When Coating Weight Falls Below 15 g/m² on High-Speed Cupstock and Plate Lines

When paper cup and plate converters reduce coating weight to cut cost, LDPE 122 MX is run at high line speeds on extrusion coaters with web widths up to 3.2 m. The polymer is applied at 10–18 g/m² on one or both sides of cupstock. The outer layer provides gloss, scuff resistance, and a printable surface. The inner layer provides water resistance and heat-seal integrity for cup side-seams and bottom discs. Melt temperature is held between 300 °C and 330 °C to lower melt viscosity and maintain curtain stability at low coating weights. Temperatures above 330 °C initiate thermal oxidation and can generate gel particles in recycled edge trim. The die air gap is set at 80–120 mm for low coating weights to reduce neck-in. The chill roll temperature is set at 10–16 °C with a matte finish to control gloss and release. For hot beverage cups, side-seam heat sealing is performed at 140–180 °C with 0.3–0.6 s dwell. The LDPE layer fuses to form a liquid-tight seam tested by filling with water at 90 °C for 30 min. A production failure observed on high-speed cup lines is the appearance of pinholes at coating weights below 12 g/m² when paper surface roughness exceeds 2 µm Ra. Converters compensate by increasing melt temperature or using a clay-coated board to smooth the surface. The finished cups and plates are tested for extractives under 21 CFR 177.1520 and EU Regulation 10/2011. For hot beverage applications, testing at 70 °C for 2 h in simulant A or simulant D2 is required depending on product category. Water resistance of the coated board is assessed by Cobb testing according to ISO 535:2014. Values below 2 g/m² are typical for properly sealed LDPE coatings. Edge trim and rejected cups are recycled back into the extrusion process at 5–10 wt%. Higher regrind levels can increase gel content and reduce adhesion. Converters limit trim rework based on gel inspection of the coated web.