Extrusion Coating Grade EVOH

When Aseptic Carton Structures Require Oxygen Permeability Below 0.5 cm³/m²·day·atm at 65% RH

Extrusion coating grade EVOH with ethylene content between 32 mol% and 38 mol% is deposited as a discrete barrier ply in liquid paperboard carton stock. In a five-layer paperboard/tie/EVOH/tie/LDPE structure, the EVOH coating weight is normally held between 5 g/m² and 9 g/m², corresponding to a nominal dry thickness of 4–8 µm and 1.8–3.2 wt% of the total laminate including a 180–260 g/m² paperboard core. The tie layers are maleic anhydride grafted polyethylene applied at 4–8 g/m² per side; inner and outer LDPE sealing plies typically range from 18 g/m² to 30 g/m². Compliance for the EVOH ply in food contact is referenced to US FDA 21 CFR 177.1350 for ethylene-vinyl acetate-vinyl alcohol copolymers, EU Regulation (EU) 10/2011 as amended, and GB 4806.7-2016 for laminated food-contact plastic layers, with oxygen transmission measured according to ASTM D3985 at 23 °C and 65% RH. On a tandem extrusion coating line with a multi-manifold die, the EVOH melt temperature is maintained at 225–235 °C, the tie layer at 230–245 °C, and the LDPE at 280–315 °C; the cooling roll is held at 12–18 °C to set the barrier ply before slitting. Terminal formats converted from this stock include UHT milk cartons, plant-based beverage cartons, juice cartons, and cream-liqueur mini cartons where headspace oxygen ingress after a 90-day ambient shelf life must remain below 1.0 ppm.

On production-scale lines above 450 m/min, two failure modes are observed: edge neck-in of the EVOH layer reduces the effective barrier width by 8–15 mm per side, and the differential between LDPE melt temperature 280–315 °C and EVOH melt temperature 220–235 °C can induce micro-gels at the tie-layer interface if the EVOH residence time in the die exceeds 8 min. To prevent barrier layer rupture, screw configurations for the EVOH extruder are specified with a 30:1 L/D barrier screw and a compression ratio between 2.8:1 and 3.5:1. Pellet moisture must be below 0.1 wt%; predrying at 85–105 °C for 4–6 h in a desiccant dryer with a dew point below -30 °C is mandatory when plant relative humidity exceeds 60% RH. The EVOH layer cannot be exposed as the product-contact layer because at 85% RH and above, the material loses oxygen barrier performance by more than 50%; this is why the LDPE inner layer is maintained at not less than 18 g/m².

Downstream, the coated paperboard is roll-fed into die-cut blanks, creased, and side-seam sealed on aseptic converting lines. The sealing temperature at the longitudinal seam is controlled between 140 °C and 170 °C because peel adhesion of the EVOH-containing laminate falls below 2.5 N/15 mm if the sealing jaw temperature drops below 140 °C, while above 170 °C the inner PE layer degrades and creates pinhole defects.

In laminate tube converting for oral care and cosmetic pastes, an extrusion coating grade EVOH with ethylene content in the 38–44 mol% range is preferred over lower-ethylene barrier grades because the finished tube undergoes repeated flexural stress at the crimp and shoulder. The barrier ply is typically applied at 8–15 g/m² against an aluminium foil carrier 9–12 µm thick or a metallised PET carrier 12 µm thick, with maleic anhydride grafted polyethylene tie layers at 6–12 g/m² on each side of the EVOH. In a finished laminate of PE 80–120 µm/tie/EVOH/tie/PE/foil/PE, the EVOH layer accounts for approximately 5–8 wt% of the barrier film, excluding the foil. The relevant compliance framework for oral care packaging includes US FDA 21 CFR 177.1350 for the EVOH food-contact substance, EU Regulation (EC) No 1223/2009 for cosmetic product packaging compatibility, and EU 10/2011 when the tube is used for food-grade promotional or dual-use formulations. Downstream, foil-to-tube body lamination is run on an extrusion coating line at 200–300 m/min with the EVOH extruder barrel profile set from 180 °C at the feed throat to 235 °C at the adapter, while the LDPE extruder is run at 280–320 °C; a chill roll at 10–15 °C stabilises the quenched EVOH layer before winding. The converted tube stock is then slit into body blanks, side-seam sealed, and fitted with shoulder and cap on high-speed tube lines operating at 200–400 tubes/min. Finished tube applications include toothpaste tubes, cosmetic lotion tubes, barrier pharmaceutical ointment tubes, and condiment paste tubes where flavour oil retention after 12 weeks of ambient storage is part of the release specification.

During side-seam sealing of EVOH-containing tube laminate at 200–400 tubes/min, the EVOH barrier layer at the overlap seam is displaced by the polyethylene melt; if the EVOH layer is colder than 190 °C at the sealing station, it can form an unsealed channel with a width of 50–100 µm, causing visible flavour oil wicking within 6 weeks at 40 °C. This is controlled by preheating the laminate strip to 60–80 °C and by maintaining the seal bar dwell time between 0.4 s and 0.8 s.

What Limits Flavour Retention in Hot-Fill Barrier Cupstock?

For hot-fill paperboard cupstock, EVOH is inserted between two polyolefin layers because direct contact with liquid water at temperatures above 80 °C would plasticise the EVOH and collapse its oxygen barrier. The barrier layer is applied at 3–6 g/m² on a 180–250 g/m² paperboard core; tie layers at 4–6 g/m² and LDPE skins at 12–20 g/m² produce a cupstock laminate in which EVOH is 1.5–2.5 wt% of the total web. The critical processing boundary is the difference between the EVOH melt temperature and the LDPE melt temperature: on a single-pass tandem line, the EVOH is extruded at 220–235 °C while the adjacent LDPE at 280–315 °C can overheat the combined melt curtain through conductive contact in the die, so the feedblock must isolate the EVOH until the final 30–60 mm of flow path. Compliance testing for cupstock follows US FDA 21 CFR 177.1350, EU 10/2011, and BfR Recommendation XXXVI/1 where German market release is required; oxygen transmission is measured by ASTM D3985 at 23 °C and 50% RH. On cup converting lines, the coated stock is printed, blanked, and hot-air sealed; hot-fill cups are tested with water at 85–95 °C for 10–15 min and must retain seal integrity above 4 N/15 mm. Finished cupstock formats include hot beverage cups, soup containers, food trays, ice cream cups, and takeaway food boxes.

The dominant process conflict in barrier cupstock is the mismatch between LDPE and EVOH melt viscosities at the die. A coating-grade EVOH with MFR 7–15 g/10 min at 210 °C/2.16 kg has a typical shear viscosity at 100 s⁻¹ of 400–800 Pa·s, while LDPE at 300 °C is closer to 80–150 Pa·s. Without a combining adapter that maintains the EVOH as a discrete layer until the final 20–40 mm of flow, the low-viscosity LDPE displaces the EVOH and creates a discontinuous barrier with unstirred layer thickness variation above ±15%. Indicative gradient data for an EVOH layer of 38 mol% ethylene are provided below; values must be confirmed under converter-specific paperboard moisture conditions.

Pharmaceutical cold-form lidding foil conversion uses extrusion coating grade EVOH at 6–12 g/m² to create an oxygen-barrier ply between a heat-seal lacquer and an aluminium foil layer 45 µm thick. The structure is commonly lacquer/aluminium/EVOH/tie/PET or paper, where the EVOH layer is 3–6 wt% of the total lidding substrate. Primary packaging validation for this configuration references US FDA 21 CFR 177.1350 for the polymer food-contact layer, EU 10/2011 for migration compliance, ISO 15378:2017 for primary pharmaceutical packaging GMP, and USP 671 for moisture vapour transmission testing of the finished blister, with oxygen transmission determined by ASTM D3985. On the extrusion coating line, aluminium foil unwind tension is held between 0.5 N/mm and 1.5 N/mm to prevent flex cracks; the EVOH extruder barrel profile is set from 180 °C to 230 °C, and the line speed is limited to 200–350 m/min because higher speeds reduce tie-layer oxidation and lower peel adhesion below 3 N/15 mm in the final lidding. The converted rolls are slit to blister lidding widths and then sealed to cold-form cavities on blister lines operating at 40–80 cycles/min. Terminal formats include cold-form aluminium blister lidding for effervescent tablets, strip packs for antibiotics, transdermal delivery patch pouches, and desiccant-lined diagnostic kit lids.

In pharmaceutical lidding, the EVOH layer is not used as the sole moisture barrier; aluminium foil or PVDC provides the primary moisture barrier, while EVOH provides the oxygen barrier. At storage conditions above 30 °C/75% RH, the oxygen barrier of EVOH falls by 40–60%, so the EVOH layer must be buried between foil and a hydrophobic outer ply. If the EVOH is directly adjacent to the heat-seal lacquer without a tie layer, interlayer delamination occurs at seal temperatures above 160 °C and peel strength falls below 1.5 N/15 mm.

Assessing Barrier Recovery After 121 °C Retort

Retortable flexible packaging built around extrusion coating grade EVOH requires a high-ethylene copolymer grade, typically 38–44 mol% ethylene, because lower ethylene grades lose oxygen barrier irreversibly after saturated steam exposure. The EVOH ply is applied at 4–10 g/m² between two tie layers at 6–12 g/m², and the full laminate includes a 12–20 µm PET outer layer, a 9–12 µm aluminium foil or barrier oxide layer, and a 70–90 µm cast polypropylene sealant. In this stack, EVOH constitutes 3–6 wt% of the flexible film, excluding foil. Compliance for retort pouches is anchored to US FDA 21 CFR 177.1350, EU 10/2011, ASTM F88/F88M-15 for seal strength after retort, and ASTM D3985 for oxygen permeability before and after 121 °C, 30 min saturated steam retort. The production process on an extrusion coating/laminating line includes coextrusion of EVOH and tie-layer melt at 225–240 °C, lamination to foil at 250–300 m/min, and oven-assisted curing of the adhesive-tie interface at 35–45 °C for 24–48 h before slitting. A critical boundary is the moisture content of the converter environment: EVOH pellets predried to <0.1 wt% moisture in a desiccant dryer at 85–105 °C for 4–6 h prevent bubble defects. Terminal products include retort pouches for wet pet food, ready-to-eat rice, sauces, and baby food spouted pouches.

During saturated steam retort at 121 °C, water vapour penetrates the polyolefin skins and plasticises the EVOH, temporarily reducing oxygen barrier by 1–2 orders of magnitude. Barrier recovery after cooling to 23 °C and 50% RH is not immediate; converters typically allow 24–48 h conditioning before OTR release testing. Grades with ethylene content below 32 mol% cannot be used in retort structures because they exhibit irreversible haze and microvoid formation after exposure to >95% RH at 121 °C. Published data for specific EVOH extrusion coating weights in retort applications is limited; validation must be run on the actual pouch line with the intended fill product and headspace volume.

Side-seam gaps above 20 µm determine canister gas transmission

Composite paperboard canisters for infant formula, coffee, and powdered sports nutrition use extrusion coating grade EVOH on the inner wrap or on the paperboard core itself. The EVOH coating weight is set at 4–8 g/m², with tie layers at 4–8 g/m² and LDPE or LLDPE skins at 15–25 g/m²; in the final spiral-wound or convolute body, the EVOH layer is 1.5–3 wt% of the laminate excluding the metal end. Relevant product safety references are US FDA 21 CFR 177.1350, EU 10/2011, and GB 4806.7-2016, with oxygen ingress measured by ASTM D3985 at 23 °C and 50% RH. Converting lines for canister inner wrap run at 250–450 m/min using a monobloc or tandem extrusion coating station; the EVOH extruder is operated at 220–235 °C, and the coated web is either wound immediately or transported to a spiral-winder that applies the wrap to a paperboard body at 15–40 m/min. Because the fill environment for powdered infant formula demands oxygen control below 1% headspace O₂, the EVOH layer must be continuous across the side seam; microscopic side-seam gaps above 20 µm cause measurable oxygen ingress and are rejected by inline vision inspection. Finished canister types include infant formula cans, ground coffee canisters, tea leaf composite cans, and protein powder containers with reclosable injection-moulded rims.

On spiral-winding lines, the EVOH-coated inner wrap is cut and lap-sealed with a hot-melt side seam. The seam temperature is maintained at 130–150 °C; at temperatures below 130 °C, the polyethylene coating does not flow sufficiently to close side-seam capillaries, while above 150 °C the EVOH barrier layer can be displaced at the lap edge by more than 100 µm. Inline vision inspection with 20 µm resolution is applied to detect side-seam gaps, and gas-flush packed canisters are tested for oxygen ingress after 14 days at 40 °C and 75% RH with a rejection limit above 0.5% headspace O₂.