On a 250–350 g/m² solid bleached sulfate paperboard line, SCHULARENE™ N3102 is applied as a single-layer extrusion coating at 18–25 g/m². Desiccant drying to a residual moisture below 250 ppm by Karl Fischer titration per ISO 15512:2019 is necessary because ester linkages in polylactic acid undergo hydrolysis at melt temperatures above 200 °C. Extrusion is run through a 90 mm single-screw extruder with a 30:1 L/D ratio and a coat-hanger die with a 0.5 mm lip gap. Melt temperature at the die is held between 210 °C and 225 °C; a rise above 230 °C triggers chain scission, visible as increased die drool, lower melt strength, and acrid lactide odour. Adhesion to paperboard is promoted by in-line corona pre-treatment at 2.0 kW to raise wetting tension above 48 mN/m before the melt curtain contacts the substrate at a 120–180 mm air gap. The coated board is quenched on a polished chill roll held at 18–28 °C to limit crystallinity and retain heat-seal response. T-peel adhesion is evaluated per ISO 11339; values below 1.5 N/15 mm generally correspond to clean film-stock separation rather than fibre tear after creasing. Finished cups, trays, and sandwich wedges made from this stock are intended for cold or ambient food contact; hot-fill exposure above 80 °C shortens structural integrity because PLA softens near its glass transition and crystalline phases are intentionally minimised during quench. Industrial compostability of the coated paperboard is assessed under EN 13432, with disintegration testing in wet organic waste streams per ISO 20200. Migration compliance for food contact is typically verified under Regulation (EU) No 10/2011 using total migration tests per EN 1186-1. Line trials show that moisture in the paper can create pinholes if the substrate is not preheated to 40–50 °C before the coating nip; steam release from fibre pores is a more common defect source than polymer degradation.

What Limits Extrusion Lamination Speed on Metallised Cellulose Film Substrates?

Melt curtain stability at air gaps above 180 mm becomes the dominant limiter because PLA exhibits lower elongational viscosity than LDPE at comparable coating speeds. On a tandem extrusion lamination line, SCHULARENE™ N3102 is extruded at 8–15 g/m² between a metallised cellulose film and a transparent cellulose or paper outer web. The barrier substrate is corona-treated to 50 mN/m before the nip. A 65 mm single-screw extruder with a 25:1 L/D barrier screw feeds a coat-hanger die fitted with a 0.4 mm restrictor bar. Melt temperature is reduced to 195–210 °C to protect the vacuum-deposited aluminium layer from thermal distortion. This lower melt temperature raises effective viscosity and reduces draw resonance only if the air gap is shortened to 80–120 mm. Industrial laminators report that web speeds above 150 m/min produce edge-neck-in above 25 mm unless edge encapsulation or electrostatic pinning is applied. Bond strength after 24 h conditioning is tested per ISO 11339; a target of 2.0–4.0 N/15 mm is common for flexible packaging. Optical density of the metallised layer is monitored with a densitometer before and after lamination; localised thermal damage appears as pinholes visible under transmitted light at 10× magnification. The final laminate is used for compostable coffee pouches and dry-food flow-wrap, where barrier arises primarily from the metallised layer, not from the PLA tie layer. Compliance for industrial compostability is assessed under EN 13432; the metallised coating must disintegrate with the cellulosic substrate, and the aluminium thickness is normally below 0.1 µm to avoid inhibition in anaerobic digester feedstocks. Published data for this specific configuration is limited; differential shrinkage between cellulose and PLA can exceed 1.5% when the laminate is exposed to 40 °C at 50% RH for 48 h, producing observable curl in roll-fed pouch stock.

Heat-Seal Initiation Temperature and Jaw-Pressure Windows

Before heat-seal performance is evaluated on a jaw-type laboratory sealer, the SCHULARENE™ N3102 sealant layer is conditioned at 23 °C and 50% RH for 48 h per ISO 291. N3102 is used as the sealant layer on compostable pouches at 10–15 µm thickness in a coextruded structure, often adjacent to a PBAT or PBS tie layer to prevent cracking at fold lines. Differential scanning calorimetry per ISO 11357-3:2018 shows a glass transition near 55–60 °C and a cold-crystallisation exotherm between 95 °C and 125 °C; sealing is therefore performed below the cold-crystallisation onset to avoid embrittlement. On a rotary heat sealer, acceptable seals are formed with jaw temperatures of 105–115 °C, dwell times of 0.3–0.5 s, and pressure between 0.3 N/mm² and 0.5 N/mm². Seal strength is measured per ASTM F88/F88M; values of 6–10 N/15 mm are typical for snack-bar wrappers, while values below 4 N/15 mm correspond to seal initiation failure in high-speed vertical form-fill-seal lines. The operational boundary is narrow: increasing jaw temperature to 125 °C raises seal strength but leads to blocking when the outer layer is also PLA-based. Differential scanning calorimetry of the sealed interface shows a melting endotherm at 145–155 °C only when the seal cycle exceeds 0.8 s; this recrystallised fraction reduces tear resistance. The finished pouch is suited for dry snacks, powdered beverages, and frozen dairy overwrap, with industrial compostability certified under ASTM D6400 or EN 13432 depending on the destination market. Food-contact migration is assessed under Regulation (EU) No 10/2011, with total migration below 10 mg/dm² in tests per EN 1186. Because PLA sealant layers can stick to steel jaws, release liners or PTFE-coated jaw covers are specified; without these, line stops above 15 min produce polymer build-up on the sealing surface.

Typically, moulded bagasse and bamboo fibre trays exhibit surface roughness values between 8 µm Ra and 25 µm Ra, which requires a heavier SCHULARENE™ N3102 coating of 25–40 g/m² to form a continuous film without pinholes. The substrate is first dried to 5–8% moisture content because residual water flashes into steam at the laminating nip and perforates the molten PLA. A flat-bed laminator with a heated roll at 160–190 °C and nip pressure of 0.6–1.0 N/mm² is used when the tray geometry cannot be coated by extrusion. Alternatively, a sheet extruder feeds a curtain coating die directly onto the moulded fibre web before a textured silicone rubber roll presses the melt into fibre pores. Adhesion is tested by cutting a 25 mm strip and peeling at 90° after conditioning at 23 °C/50% RH; cohesive fibre failure indicates adequate anchorage, while clean delamination below 1.0 N/25 mm signals insufficient surface wetting. The PLA layer acts as a water and grease barrier for cold salads, chilled deli meals, and airline meal trays. Cobb water absorption of the coated article is measured per ISO 535; a 30 min Cobb value below 5 g/m² is attainable on high-density moulded fibre, whereas uncoated fibre exceeds 30 g/m². However, the PLA coating is not a substitute for PE or PP in prolonged hot-fill applications; continuous contact with liquids above 90 °C accelerates hydrolysis and leads to surface blisters. The finished articles are tested for disintegration under ISO 20200 and for ecotoxicity in compost per EN 13432; the coating layer loses integrity within 12 weeks in industrial composting, while the fibre matrix disintegrates more quickly. Published data for this specific configuration is limited; pilot-scale measurement on a 300 mm wide benchtop laminator shows that pinhole density falls below 5 pinholes/m² only when coating weight is maintained above 30 g/m².

When Coating Weight Drops Below 12 g/m², Pinhole Density and Barrier Failure Become Non-Linear

A reduction from 18 g/m² to 8 g/m² on a smooth PLA base film produces a more than proportional increase in pinhole density because melt curtain thickness fluctuations become comparable to the draw resonance wavelength. SCHULARENE™ N3102 is applied on a cast coating line with a 0.5 mm slot die, 6–10 m/min linear speed, and a chill roll at 20–25 °C. Surface defects are quantified using a laser scanning system at 100 µm resolution. At 12 g/m², pinhole density on a smooth substrate is measured at 0–5 holes/m²; at 8 g/m², pinhole density increases to 30–60 holes/m² across the web due to draw resonance and edge-tear propagation. Water vapour transmission through the coated film is measured per ISO 15106-3 at 38 °C/90% RH; the transition from 12 g/m² to 8 g/m² raises the mean WVTR from approximately 140 g/(m²·day) to 260 g/(m²·day) because pinholes bypass the PLA layer. Oxygen transmission per ISO 15105-2 at 23 °C/0% RH rises similarly, although PLA is not a high-oxygen barrier and should not be specified where an oxygen transmission rate below 100 cm³/(m²·day·bar) is required. The defect mode shifts from discrete pinholes to continuous edge-thinning when the die lip opening is narrowed to 0.3 mm without adjusting the air gap; web breaks become frequent above 60 m/min. Thin-gauge coating on high-speed lines therefore requires a smaller die gap and a shorter air gap of 80–100 mm, combined with edge pinning via electrostatic discharge. This scenario is relevant for compostable produce bags and bread bags, where moisture barrier is secondary to compostability. A lower coating weight also reduces blocking during rewind; blocking force remains below 0.5 N/15 mm when chill roll temperature is kept below 25 °C. Industrial compostability is certified under EN 13432.

Optimising Chill-Roll Temperature Profiles Without Sacrificing Seal Initiation

Chill-roll quench temperature shifts the amorphous-to-crystalline ratio in SCHULARENE™ N3102 because PLA crystallises slowly from the melt and the roll contact time is short. On a cast-coated paperboard line, the first chill roll is set between 15 °C and 20 °C for rapid quench to maximise sealability; a second roll at 40–50 °C then reheats the film surface to reduce condensation and static. If the first roll is raised to 35 °C, crystallinity measured by differential scanning calorimetry per ISO 11357-3:2018 increases by 3–5% absolute, but the heat-seal initiation temperature shifts upward by 4–6 °C. This shift is critical in vertical form-fill-seal operations where jaw settings are fixed. High crystallinity also reduces film-to-fibre adhesion on laminated trays; peel adhesion per ISO 11339 can fall below 1.2 N/15 mm when the quench roll exceeds 30 °C. Conversely, chilled rolls below 10 °C cause condensation and frost on the surface, creating visible haze when processed in plants above 60% RH. The line should specify a dual-shell spiral-baffled roll with 0.5 mm nickel-chromium plating and a surface roughness below 0.05 µm Ra to allow defect-free release after the nip. Roll temperature is monitored with embedded resistance temperature detectors and closed-loop water tempering. This process window is relevant for heat-sealable lidding films and flow-wrap overwraps where low-temperature sealing is required for high-fat contents such as nuts and chocolate. The final film is tested for seal strength per ASTM F88/F88M and for dimensional stability at 70 °C for 2 h; shrinkage above 3% indicates excessive frozen-in orientation from a cold roll. Pilot-scale measurements on a 500 mm cast film line show that a two-roll profile with 18 °C first roll and 45 °C second roll retains seal initiation below 100 °C while preventing condensation defects.

In solvent-free lamination lines, SCHULARENE™ N3102 is applied as a 5–10 g/m² tie layer between a translucent cellulose label facestock and a compostable release liner. The coating head is a 400 mm slot-die hot-melt station with a barrel temperature of 190–210 °C and a gear pump delivering 0.6–1.2 kg/h. Viscosity at 200 °C is measured with a capillary rheometer per ISO 11443; apparent shear viscosity in the 500–1500 s⁻¹ range determines coat-weight uniformity, and values outside the supplier’s specified curve lead to chatter marks at line speeds above 40 m/min. The laminate is passed through a rubber-covered nip roll at 0.4–0.6 N/mm² to force the PLA into paper microfibrils. Adhesion is tested by tape snap-off at 90° and by peel per ISO 11339; fibre tear from the label face indicates cohesive substrate failure, while adhesive failure at the PLA-cellulose interface below 0.8 N/15 mm requires corona pre-treatment above 52 mN/m. The resulting label stock is used for produce stickers, wine-label facestock, and tamper-evident banding on compostable coffee cups. Dimensional stability is evaluated at 50 °C and 80% RH for 24 h; labels can curl more than 5 mm if the release liner absorbs moisture unevenly. This application uses N3102 as a thin functional adhesive rather than a structural film; therefore, mechanical performance of the final label depends on the cellulose facestock, and the PLA layer contributes mainly to the compostable end-of-life pathway. Certification under EN 13432 requires the adhesive layer to disintegrate during biological waste treatment; ecotoxicity testing is performed according to EN 13432 Annex E. Pilot trials on a 300 mm label laminator report stable coat weights at 8 g/m² when the die-to-nip distance is held below 50 mm.