EVOH for Paper & Board Coating

Hot Cupstock Coating Lines Operate Against a Narrow Thermal Window

On polyethylene-free single-wall cupstock lines, the aqueous ethylene-vinyl alcohol copolymer dispersion must be film-formed at a web temperature low enough to avoid skinning and high enough to remove residual water before the sheet enters the stack. A dry EVOH deposit of 8–14 g/m² is commonly specified for hot beverage paperboard because lower deposits leave pinholes at the cup side-seam compression zone, while higher deposits increase sidewall stiffness and axial crack propagation during cup forming. The dispersion is typically let down from supplier solids of 38–42 wt% to application solids of 25–35 wt% with deionized water, producing a wet film coverage of 24–40 g/m² depending on the anilox cell volume. In production, a central-impression flexographic station with a chambered doctor blade and anilox volume of 18–28 cm³/m² is operated at 120–220 m/min, with the air dryer set to 85–115 °C and the web surface held at 70–95 °C. If the web exceeds 95 °C, the EVOH dispersion skins over and forms comet-shaped pinholes; if the rewind core temperature is above 45 °C, blocking between the barrier layer and the printed reverse side is a documented converter failure. The compliance position for this cupstock construction is anchored to FDA 21 CFR 176.170 for aqueous and fatty food contact, EU Regulation (EC) No 1935/2004, and Commission Regulation (EU) No 10/2011, with overall migration testing carried out according to EN 1186-1:2002 and the accepted limit set at <10 mg/dm². The terminal formats include single-wall hot beverage cups, soup cups, and double-wall cup stock where the reverse-side EVOH layer is positioned behind additional insulating paper plies. In hot-fill operations, the barrier layer is not used as a direct water barrier; a hydrophobic polyolefin or wax topcoat of 1–3 g/m² is applied over the EVOH because oxygen barrier loss accelerates above 70% RH and condensate from steam or hot liquid penetration will otherwise plasticize the copolymer.

What Limits EVOH Dispersion at Crease Lines on Fatty Food Cartons?

Grease resistance of folding carton stock cannot be inferred from flat-sheet barrier values because the functional failure occurs at die-cutting creases and folded seams, where crack opening in the dry polymer film determines oil penetration more than the diffusion coefficient of the copolymer itself. Folding cartons for biscuits, crackers, chocolate, and cream-filled bakery goods therefore use a lower EVOH dry coat weight of 5–10 g/m² combined with 10–20 wt% of an acrylic or ethylene-acrylic acid dispersion in the dry resin fraction. The acrylic let-down reduces transverse crease crack length from over 2 mm to below 1 mm after die-cutting, while the grease kit rating under TAPPI T 559 remains at or above 7 on the coated side when the flat coating is intact. The EVOH dispersion is prepared at 25–32 wt% solids and applied by an offline rod coater or gravure coater at 80–180 m/min; the board is first primed with 0.8–1.5 g/m² dry of a cationic starch or synthetic primer to prevent absorption into the clay-coated surface. Drying is performed at 90–110 °C air temperature with a web temperature below 85 °C. Oxygen transmission rate measured by ASTM D3985-17 at 23 °C and 50% RH typically falls from >100 cm³/m²·day·atm for uncoated recycled board to 3–8 cm³/m²·day·atm at a 10 g/m² dry deposit; water vapour transmission rate measured by ISO 15106-2:2003 at 38 °C and 90% RH remains in the range of 20–60 g/m²·day, confirming that the EVOH layer is not a moisture barrier. Regulatory documentation for this application cites FDA 21 CFR 176.180 for dry foods and FDA 21 CFR 176.170 for fatty foods, with European declarations under EU Regulation (EU) No 10/2011 and the BfR Recommendation XXXVI paper and board food-contact framework. Terminal products are flat-folded cartons and crash-lock boxes requiring grease resistance at folded hinges rather than long-distance liquid barrier.

Frozen bakery and ice cream carton stock requires an oxygen barrier that remains functional after moisture condensation from repeated freeze-thaw cycling. EVOH dispersion applied at 6–12 g/m² on the inner face of wet-strength litho-laminated board is not used as a direct water barrier; in this application it is always layered with a hydrophobic topcoat of 1–3 g/m² low-melt-point polyolefin or wax-based dispersion. The EVOH coat weight is deliberately kept below 10 g/m² on crease-prone dimensions because the frozen board is die-cut after coating, and transverse creases are opened under -18 °C service conditions. Published converter data for this specific configuration is limited, but the working range is derived from frozen food packaging trials and inline optical coat-weight measurement records.

Application is performed on a reverse-side gravure station after the sheet is printed; the substrate temperature entering the coating nip is held at 25–35 °C to control condensate. Dryer sequence uses three zones of 60 °C, 80 °C, and 95 °C with total dwell of 4–8 s, because high first-zone heat causes steam bubbling in the fibre mat. A post-coat infrared densification step at 900–1,200 kW/m² is used to fuse the EVOH skin before the topcoat is applied, reducing pinholes at the fibre ends. Under FDA 21 CFR 176.170 and EU Regulation (EU) No 10/2011, migration testing is conducted with EN 1186-13:2002 for fatty food simulants, and sensory panel thresholds for off-taste are checked according to EN 1230-1:2009; overall migration is maintained below 10 mg/dm². Terminal products include frozen pie cartons, ice cream cake boxes, and frozen pastry cartons, where the EVOH layer suppresses oxidative rancidity of high-fat fillings during 12–24 months of frozen distribution under fluctuating cold-chain relative humidity.

When Aqueous EVOH Is Substitute-Coated on Gable Top Liquid Board Lines

On gable top liquid board converting lines, aqueous EVOH dispersion is being evaluated as an internal oxygen-barrier primer beneath extrusion-laminated polyethylene. This configuration is distinct from cupstock and carton applications because the EVOH layer must survive a downstream PE melt curtain at 280–320 °C and must not carry more than 1.5–2 wt% residual moisture into the lamination nip. The working dry coat weight on clay-coated gable top board is 3–8 g/m², which corresponds to a continuous EVOH layer thickness after calendering of 2–7 µm. Surface roughness above 6 µm PPS measured according to ISO 8791-4:2007 has been associated with void pathways and barrier loss in this low-coat-weight regime. The aqueous formulation is maintained at 30–38 wt% solids with 150–350 mPa·s viscosity at 25 °C, using 90–98 wt% EVOH dispersion solids, 0.1–0.3 wt% wetting agent, and 0.2–0.5 wt% thickener. A curtain coater is operated at 250–450 m/min, followed by air-cushion or infrared drying to <2% residual moisture before the first PE layer is extruded. Failure at the PE interface is observed when the EVOH skin retains more than 2% moisture, because the expanding water vapour creates microvoids under the molten polyethylene. Published data for this specific configuration is limited; converter laboratory trials and equipment supplier coating-window recommendations provide the cited ranges. Compliance documentation requires the full multilayer structure to meet FDA 21 CFR 176.170 and EU Regulation (EU) No 10/2011, with migration testing according to EN 1186-2:2002 and overall migration below 10 mg/dm². Terminal products are gable-top cartons for UHT milk, juice, and plant-based beverages, but the aqueous EVOH layer is not in direct liquid contact; it must remain fully encapsulated between polyethylene skins to prevent water plasticization and barrier collapse during chilled or ambient liquid storage.

Spray-Coating Moulded Pulp Without Uniform Coat Weight

Because moulded pulp substrates have an open porous surface and three-dimensional draft angles, transfer of EVOH dispersion requires a non-contact coating process such as airless spray or curtain misting. Dry coat weight on moulded fibre trays is specified at 10–30 g/m², but the measured standard deviation across a tray is often ±30–50% with a single-pass airless spray; a two-layer programme is therefore used in production. A seal coat of starch or polyvinyl alcohol at 5–10 g/m² dry is applied first to close the fibre pores, followed by EVOH dispersion at 10–20 g/m² dry, diluted to 18–28 wt% solids. Airless spray nozzles operate at 0.5–2.5 bar fluid pressure with a tip producing 60–80 µm droplets, and overspray recovery of 30–40% is common on deep-draw trays. Drying uses a three-stage infrared programme of 120 °C for 20–30 s, 150 °C for 10–20 s, and ambient air impingement for 5–10 s, because higher surface temperatures can delaminate the starch seal coat. Compliance references are FDA 21 CFR 176.170 for aqueous and fatty food contact, EU Regulation (EC) No 1935/2004, Commission Regulation (EU) No 10/2011, and EN 15593:2008 for hygiene management in food packaging manufacture. The EVOH layer in moulded pulp meat trays is not intended for direct liquid exudate contact; an absorbent pad must be placed between the product and the coated surface because continuous moisture contact at >70% RH will plasticize the EVOH and reduce oxygen barrier. Terminal products include moulded pulp trays, plates, and cup lids for fresh meat, poultry, seafood, and prepared ready-meal formats where the oxygen barrier limits oxidative off-flavour development during 5–14 days of chilled retail display.

Indicative barrier performance data reported by dispersion suppliers for clay-coated solid bleached sulphate board are presented below. Actual values depend on substrate porosity, primer type, topcoat film integrity, and the presence of recycled fibre.

In foodservice clamshell and snack-box converting, the coating survives hot food contact temperatures up to 80 °C and simultaneous oil and water vapour extraction from fried foods. The EVOH dispersion is applied on the interior side of litho-laminated SBS or CRB board at a dry deposit of 4–8 g/m², with a subsequent heat-sealable polyethylene dispersion topcoat of 1–2 g/m² to prevent blocking during stacked storage in high-humidity kitchens. The formulation is prepared at 30–35 wt% solids from a 38–40 wt% supplier dispersion, with 0.05–0.15 wt% anti-foam and 0.1–0.3 wt% surface tension modifier. A press viscosity of 80–180 mPa·s at 25 °C is maintained for the anilox roller, specified at 14–20 cm³/m² with hexagonal cell geometry, and the narrow-web flexographic line runs at 60–150 m/min through a dryer set to 70–90 °C. Higher impingement temperatures warp the low-caliper board and have been observed to create flute shadowing on CRB substrates. Compliance references are FDA 21 CFR 176.170 for both aqueous and fatty foods, EU Regulation (EU) No 10/2011, and EN 15593:2008; migration testing under hot-fill conditions uses food simulant D2 or vegetable oil according to EN 1186-2:2002, with sensory odour testing per EN 1230-1:2009. Terminal products include coated-paperboard clamshells for fried chicken, French fries, nachos, and takeaway snack boxes; the EVOH layer limits oil staining and oxygen-related off-flavour development during short hot-hold and delivery windows rather than providing long-shelf-life barrier.