BOEVOH — Biaxially Oriented EVOH Film Grade

In retort processing at 121 °C and 0.15 MPa overpressure, the biaxially oriented EVOH film grade is introduced as the oxygen-barrier core within a five-layer coextruded cast film, with polypropylene outer layers and maleated polypropylene tie resins. The barrier ply is specified at 8–12 µm in a total film thickness of 90–125 µm, corresponding to 6–10 vol% of the structure and roughly 5–8 wt% of the film mass; below 8 µm, oxygen transmission increases non-linearly after retort, while above 12 µm the film loses transparency and shows interlayer distortion during pouch forming. The downstream conversion line for transparent retort pouches runs a five-layer cast coextrusion die with a die gap of 1.8–2.0 mm, chilled roll temperatures between 18 °C and 25 °C, and line speeds of 120–180 m/min, followed by adhesive lamination to a retort-grade polypropylene sealant web using a solvent-free polyurethane system cured at 40–50 °C for 48–72 h. The EVOH melt temperature must remain between 210 °C and 230 °C, and residence time at the upper limit should not exceed 10 min; on twin-screw extruders with L/D 30:1 and screw speeds below 120 min⁻¹, this thermal window reduces gel counts below 0.5 per m², whereas longer residence at 230 °C initiates thermal degradation and produces black specks on the die lip. When ambient relative humidity exceeds 60%, the resin is pre-dried to moisture content below 0.1% before extrusion, because entrained moisture forms bubbles at the tie-layer interface and random optical defects known as fish eyes. Because biaxial orientation introduces frozen-in strain, the cast film web is annealed at 140–150 °C before pouch forming; without annealing, differential shrinkage during the retort cycle causes tie-layer delamination at the EVOH/PP interface when free-shrink exceeds 3% in both axes. Oxygen barrier after retort is verified in accordance with ISO 15105-2 at 23 °C and 85% RH, and seal integrity is tested per ASTM F88; the structure must retain package oxygen ingress below 0.5 cm³/m²·day after a 30 min retort cycle to meet typical ready-meal shelf-life targets. The EVOH layer is never used in direct contact with the food because moisture above 70% RH at the core raises oxygen permeability by more than one order of magnitude between 50% RH and 85% RH; the polypropylene outer layers therefore function as moisture shields, and transparent retort structures without aluminium foil demand careful PP crystallinity control. Terminal formats include retort pouches for ready-to-eat rice, sauces, tuna, pet food, and baby food. Compliance of the finished laminate is assessed under EU Regulation (EU) No 10/2011, EC 1935/2004, and FDA 21 CFR 177.1360 for the EVOH food-contact layer; converters additionally run migratable residual solvent checks against EU 10/2011 Annex II limits for the lamination adhesive.

What Limits Biaxially Oriented EVOH Retention in Vacuum Skin Packaging After Thermoforming?

When a non-forming web containing the oriented EVOH film is welded to a thermoformed APET or PE/PA rigid bottom web, the oxygen-barrier layer is subjected to 60–80% elongation in corner radii; this deformation geometry determines whether the vacuum skin package remains leak-tight under distribution vibration. The non-forming web typically places the EVOH ply at 3–5 µm within a 75–120 µm lidding or non-forming film, or 2–4 vol% of the total structure; thermoformable forming webs use 5–8 µm EVOH to compensate for thickness reduction in the drawn cavities. On rotary and flat-bed vacuum skin packaging lines, the bottom web is preheated to 120–130 °C, thermoformed over product-loaded cavities, and then the EVOH-bearing top web is sealed at 120–140 °C under 1–3 mbar residual chamber pressure; film tension is maintained at 0.3–0.5 N/mm to prevent orientation recovery wrinkles that appear as edge pleats near the seal area. Red meat formats use a modified atmosphere of 70% O₂ / 30% CO₂, while cheese and smoked fish use 70% N₂ / 30% CO₂; oxygen transmission through the EVOH-containing top web is measured by ASTM F1927 at 23 °C and 85% RH, and flex resistance is assessed by ASTM F392 with repeated flex cycles. Biaxial orientation improves the flex-crack resistance of the EVOH ply relative to cast EVOH of equivalent thickness because orientation distributes stress over two axes and inhibits microvoid propagation; published data for this specific configuration is limited, but converter trials indicate that pinhole-related oxygen leaks in VSP packs occur mainly where the top web is overstretched by more than 80% on sharp tray corners. The forming web is heated while the EVOH-bearing non-forming web is kept below 60 °C to avoid interlayer bubble formation and delamination; hot-plug contact with the EVOH side is not used. Finished terminal products include vacuum skin packs for beef steaks, lamb, poultry, cheese, smoked salmon, and marinated meat cuts. The laminate must satisfy EU Regulation (EU) No 10/2011, FDA 21 CFR 177.1360, and the tensile and seal requirements of ISO 527-3 and ASTM F88; the EVOH layer is never exposed as the food-contact surface, and material certification requires documentation of gel count and optical defects in the barrier ply.

Pharmaceutical Blister Lidding Foil Substitution and Child-Resistant Seal Activation

In replacement of full aluminium foil lidding for moisture-sensitive oral solid dosage products, a laminate of printed paper, biaxially oriented EVOH film, aluminium foil and heat-seal lacquer is slit to 310–330 mm reels for high-speed blister lines. The EVOH layer is maintained at 6–10 µm within a 60–90 µm lidding film, representing 7–12 wt% of the total laminate mass; at less than 6 µm, the oxygen barrier after creasing and opening feature formation becomes inconsistent, while at more than 10 µm the laminate loses deadfold and shows curl after ambient storage. Production begins with adhesive lamination of the printed paper to the EVOH-containing barrier web using a polyurethane adhesive at 2.5–3.5 g/m² on a gravure or flexo coater; web speed is held at 150–250 m/min, drying air temperature is 70–90 °C, and the finished roll is cured at 40–50 °C for 48 h. The heat-seal lacquer is then applied at 2–4 g/m² to the aluminium side and dried to a residual solvent level below 5 mg/m² total volatiles by headspace GC at 120 °C for 30 min; residual solvent above this threshold causes lacquer foaming and incomplete seal activation against PVC/PVDC or Aclar blister at 150–180 °C for 0.5–1.0 s. The lamination adhesive must not contain amine-functional curing agents above 0.5 wt% because residual amine migration to the EVOH interface reduces heat-seal adhesion after extended storage. Terminal finished types include child-resistant and senior-friendly lidding foils for tablets, capsules, diagnostic test strips, transdermal patches, and inhalation device blisters. Compliance is assessed against ISO 11607-1:2019, ISO 11607-2:2019, USP 661.1, and EU Regulation (EU) No 10/2011 where the lidding may be used for oral products with food-contact implications; pharmaceutical packaging additionally requires seal-peel strength per ASTM F88, oxygen ingress per ASTM F1927, and product-contact extractables under USP 1663. The EVOH ply is not sealed directly to the blister because the heat-seal lacquer and aluminium foil separate it from the PVC/PVDC; direct EVOH-to-PVC sealing produces low seal strengths and fibre tear after ageing.

High-gloss laminate tube bodies for fluoride toothpaste and oxygen-sensitive retinol creams incorporate the biaxially oriented EVOH film grade as the volatile-flavour barrier between polyethylene layers. The EVOH ply is set at 5–10 µm within a 250–400 µm tube laminate, equivalent to 1.5–3 vol% of the sidewall; the barrier layer does not contribute more than 2% of the laminate bending stiffness, so tube compression and rebound behaviour are governed by the HDPE carrier layers. The tube body is produced by extruding a five-layer coextruded sheet containing the oriented EVOH core, slitting the sheet into blanks, welding the side seam by high-frequency or hot-air welding at 350–450 kHz, and then attaching shoulder and cap in a continuous tube line; the EVOH layer must withstand 180° folding at the tube shoulder and crimping at the bottom seal without stress whitening. If the EVOH layer is mispositioned near the welding zone, dielectric heating can melt the barrier layer and create sidewall burn-through, so the converter maintains at least 25 µm of polyethylene between the EVOH ply and the weld edge. Terminal products include tubes for toothpaste, cosmetic creams, ointments, gels, and hair colorants. Compliance is governed by EU Regulation (EC) No 1223/2009 for cosmetic products, EU Regulation (EU) No 10/2011 where dual food-cosmetic use is declared, and FDA 21 CFR 177.1360 for the EVOH layer; finished tubes are tested for oxygen permeability by ISO 15105-2 at 23 °C and 60% RH, and for seal integrity by pressure decay at 0.5 bar over 10 s. In this well-established application, the primary process requirement is to keep the EVOH layer below 65% RH during tube storage before filling; otherwise the flavour barrier declines and the laminate may develop blisters when heated for shoulder attachment.

When Aseptic Bag-in-Box Liners Require Flex-Crack Resistance During Palletised Distribution

When aseptic bag-in-box liners for tomato paste, dairy concentrates or liquid whole egg are filled on high-acid lines at 70–85 °C, the EVOH layer must remain intact after repeated flexing against the corrugated outer carton during palletised transport and warehouse picking. The liner structure places the oriented EVOH film at 4–7 µm within a 60–110 µm three- or five-layer coextruded film, or 3–6 vol% of the total gauge; LLDPE outer layers of at least 30 µm on both sides keep the EVOH core below 65% RH during hot filling and ambient storage. Production is carried out on a multi-layer blown film line with a spiral mandrel die gap of 1.8–2.0 mm, blow-up ratio of 2.0–2.4, and EVOH melt temperature controlled at 205–220 °C; the tubular film is corona-treated, surface printed, and then converted into pouches with spouts by impulse or ultrasonic welding. Spiral mandrel dies can generate weld lines in the EVOH layer when melt flow path differences cause localised thinning; converters mitigate this by using melt equalising sections and by maintaining die temperatures within ±5 °C of the EVOH melt temperature. Aseptic filling systems subject the liner to steam sterilisation at 130 °C for 60 s or to peracetic acid at 0.5% and 25 °C; the EVOH layer requires complete encapsulation because direct contact with peracetic acid above 0.5% leads to surface saponification and loss of barrier. Flex-crack resistance is evaluated by ASTM F392 before and after repeated flexing, and oxygen permeability is measured by ASTM F1927 at 23 °C and 85% RH; accepted liners must not show an increase in oxygen transmission after flexing greater than 20% relative to the unflexed film, as specified by converter internal specifications. Terminal formats include bag-in-box liners from 3 L to 20 L for tomato paste, fruit purees, dairy concentrates, liquid whole egg, syrups, and edible oil. Compliance is anchored to EU Regulation (EU) No 10/2011, FDA 21 CFR 177.1360, and FDA 21 CFR 177.1520 for the polyethylene layers; converters additionally perform total migration testing under EU 10/2011 Annex III and sensory evaluation for taint-free products.

Barrier Shrink Bags for Sub-primal Meat Require Controlled Orientation Relaxation

The production of barrier shrink bags for sub-primal beef and bone-in pork uses a double-bubble process in which the BOEVOH-bearing tube is biaxially stretched at 80–90 °C and then allowed to relax by 5–10% in the transverse direction before winding. The EVOH layer is specified at 3–5 µm within a 50–70 µm shrink film, or 4–7 wt% of the total structure; this low thickness is sufficient because the biaxially oriented EVOH layer retains oxygen barrier after the bag is shrunk around the meat surface at 85 °C. The coextrusion step produces a five-layer tube with EVOH core, tie layers and PA or PE outer plies, followed by water quenching and reheating to 80–90 °C using infrared panels before simultaneous biaxial orientation at a blow-up ratio of 2.5–3.0 and a machine-direction draw ratio of 3.0–3.5. Annealing at 90–95 °C relaxes orientation in a controlled manner so that final free shrink at 85 °C is 15–25% in both directions per ASTM D2732, which avoids excessive shrinkage that would tear the EVOH layer during underwater shrink tunnel operation. Terminal formats include vacuum shrink bags for chilled and frozen primal cuts, sub-primals, whole poultry, and smoked meat. Compliance for the US market requires FDA 21 CFR 177.1360 for the EVOH layer and USDA FSIS acceptability for meat contact; EU uses EU Regulation (EU) No 10/2011 and EC 1935/2004. Seal strength after shrinkage is verified per ASTM F88 at 25 N/15 mm minimum, and puncture resistance is measured per ASTM F1306 to ensure the bag survives bone-in packing. The EVOH layer cannot be exposed to the 85 °C water bath without outer plies because direct hot-water contact at the cut edge causes edge whitening and local barrier loss within 2–3 mm of the seal.