A Sealant Web for High-Speed Flow-Wrap Without Solvent Reforming

On a three-layer BOPP tenter line, the heat-sealable skin layer is extruded from a propylene-ethylene-1-butene terpolymer through a coextrusion die with a chilled roll at 25–30 °C and a die gap of 1.5–2.0 mm. TF400 is metered at 100 wt% of the sealant skin layer; for a finished web of 20–25 µm, a 1.0–1.5 µm sealant skin contributes approximately 8–12 wt% of the total film mass. The core is a homopolymer polypropylene with a melting point above 160 °C, and the opposite skin is formulated with slip and antiblock masterbatch to maintain kinetic coefficient of friction at 0.25–0.45 under ASTM D1894-14. Melt temperature at the die is held at 235–245 °C using a 33:1 L/D barrier screw, with shear heating limited to keep melt temperature below 280 °C. Machine-direction stretching is set at 4.5:1–5.5:1 and transverse-direction stretching at 8:1–10:1, followed by heat-setting at 160–165 °C. The butene comonomer suppresses crystallinity selectively in the seal skin, so seal initiation temperature remains in the 100–115 °C range when measured under ASTM F1921-18. Because comonomer distribution controls seal onset, the converter verifies lot-specific MFR under ISO 1133-1:2022 condition M before line-speed qualification; variation in melt flow rate shifts melt pressure and seal-bar setpoint on high-speed horizontal flow-wrappers.

Compliance for food-contact flow-wrap records begins with FDA 21 CFR 177.1520(c) for olefin polymers and EU Regulation (EC) No 10/2011, including an overall migration limit of 10 mg/dm² in finished-film simulant testing according to Annex V. Packaging waste obligations reference Directive 94/62/EC, and non-food overwrap exported to the EU carries RoHS Directive 2011/65/EU Annex II limits for lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE. Corona treatment of the print side is controlled to 38–42 mN/m; overtreatment above 42 mN/m oxidizes the seal side and can narrow the hot-tack plateau.

Terminal converted articles include biscuit bunch wrap, bakery and confectionery flow-pack, produce bunch wrap, CD/DVD overwrap, flower sleeves, and carton overwrap for cosmetics. On horizontal form-fill-seal machines running 250–400 packs/min, seal jaw temperature is set 15–25 °C above measured seal initiation temperature, jaw pressure is held at 40–80 N/cm², and dwell time is 0.2–0.5 s. A production-scale failure mode observed on lines with worn rotary jaws is seal edge thinning caused by oscillating jaw pressure, which increases seal strength variation beyond 0.5 N/15 mm across the web. The material is not specified for retort sterilization above 121 °C or for hot-filled goods above 95 °C, because seal-area softening under headspace pressure produces seal creep and leaker reject rates unless a second mechanical seal is applied.

Cast polypropylene coextrusion that places 100 wt% TF400 as the sealant layer against a PETG tray is used in sterile barrier systems under ISO 11607-1:2019. The three-layer cast web is produced on a chill roll line with 180 mm barrier screw extruders having L/D 30:1, a feedback coextrusion block, a 2,500 mm die width, and a polished chromium chill roll held at 22–26 °C. The sealant layer thickness is 10–15 µm within a total web thickness of 45–55 µm; a PP homopolymer core provides bending stiffness, and the print skin is a corona-treated random copolymer. Melt temperature at the die is 225–240 °C, and line speed is 120–200 m/min. Vacuum venting and die-exit scavenging are required to minimize thermo-oxidative degradation and to prevent volatile oligomer deposition on the chill roll surface. Antiblock masterbatch dosage of 0.2–0.5 wt% synthetic silica with a median particle size of 4–5 µm is adjusted to hold kinetic coefficient of friction at 0.25–0.45 under ASTM D1894-14 without raising haze above 2.0% under ASTM D1003-13.

Regulatory documentation for medical device packaging includes ISO 10993-5:2009 for cytotoxicity and ISO 10993-10:2010 for skin sensitization, evaluated under a ISO 10993-1:2018 biological evaluation plan. Sterilization compatibility is verified with ethylene oxide under ISO 11135:2014 and e-beam under ISO 11137-1:2006. For food-contact secondary applications, material compliance references FDA 21 CFR 177.1520(c) and EU Regulation (EC) No 10/2011. Because the terpolymer contains no plasticizer, label-free medical packaging is feasible, but process oils from extrusion gearboxes and silicone-based roll treatments must be excluded from the sealant side. Terminal articles include lidstock for preformed PETG trays housing syringes, surgical sutures, introducer catheters, and IVF cannulas; header bags for trauma plates and screws; and double pouches for single-use instruments. Seal qualification uses ASTM F88/F88M-15 with a target of 2.5–4.0 N/15 mm depending on tray flange width. Dimensional stability during ethylene oxide sterilization is evaluated by ASTM D1204-14 shrinkage after 30 min at 121 °C; shrinkage above 2.0% machine direction causes lidstock curl and tray flange lift. The grade is not intended for steam sterilization at 134 °C or for reusable autoclavable packaging.

When Extrusion Coating Replaces Solvent-Based Sealants on Paperboard

Extrusion coating with polypropylene terpolymer onto paperboard is performed on a tandem line in which the paper surface is first flame- or corona-treated to a wetting tension of 40–44 mN/m before the molten web contacts the substrate through an air gap of 150–250 mm. TF400 is applied at 100 wt% as the coating layer; typical coating weight is 12–25 g/m², corresponding to a gauge of 13–27 µm. The extruder is a 120 mm single-screw unit with L/D 30:1, a barrier screw, and a T-slot die fitted with internal deckles. Melt temperature at the die is 240–260 °C, and the chill roll is held at 15–20 °C to quench the coating rapidly. Direct lamination to unprimed aluminum foil is not specified; peel strength under ASTM F88/F88M-15 remains below 1.0 N/15 mm unless a maleic anhydride-grafted PP tie layer is coextruded between the terpolymer and the foil. Published data for primerless direct PP terpolymer coating onto aluminum foil is limited; converter trials are required for any unsupported foil replacement.

Regulatory requirements for paperboard food cartons include FDA 21 CFR 176.170(c) for paper and paperboard components in contact with aqueous and fatty foods, EU Regulation (EC) No 10/2011, and Directive 94/62/EC for packaging and packaging waste. Mineral hydrocarbon migration from the paperboard itself is controlled separately by the paper mill and is not addressed by the PP coating layer. Finished-article compliance is documented by extraction testing according to EN 1186-1:2002 for overall migration and EN 13130-1:2004 for specific migration. End uses include frozen food cartons, ice cream cupstock, fast-food beverage cups, paperboard trays for chilled prepared meals, and bakery boxes. The coating removes the need for solvent-based nitrocellulose or vinyl lacquers on the sealing surface, but does not provide a gas barrier suitable for extended shelf-life meat or cheese without an additional metallized or EVOH layer.

On cup-forming machines running 180–300 cups/min, the seal is made at 115–125 °C with a dwell of 0.3–0.8 s and pressure of 60–120 N/cm². Pinhole testing by EN 13676:2001 is used to detect coating defects; a pinhole rate above 5 holes/m² is rejected for liquid packaging. Melt curtain neck-in of 20–30 mm per side at 200 m/min must be compensated by deckle width settings 120–130 mm beyond substrate width, and die lip buildup is controlled by cleaning every 24–48 h. At melt temperatures below 235 °C, edge tear and uneven coating weight increase; above 260 °C, oxidative degradation produces gel particles that catch on the die lip and drop into the coating, a known source of sporadic pinhole defects.

Low-Temperature Hot Tack in Vertical Form-Fill-Seal Line Startups

Vertical form-fill-seal packaging with polypropylene terpolymer film requires a hot-tack window that permits jaw release after 0.05–0.15 s while the filled product still exerts downward force on the seal. TF400 in blown film is processed either as the inner seal layer of a coextruded tubular structure or as a monolayer after blending 70–90 wt% TF400 with 10–30 wt% metallocene LLDPE of density 0.918–0.922 g/cm³; the LLDPE improves bubble stability and dart impact resistance but raises seal initiation temperature by 3–8 °C. Blown film equipment includes a 200 mm air-cooled die with gap 0.8–1.2 mm, blow-up ratio 2.2:1–2.8:1, frost line height 6–8 die diameters, and melt temperature 210–230 °C. Barrel zone settings for a 90 mm barrier screw are 190/210/220/220/220 °C; melt pressure above 350 bar indicates insufficient melt temperature or screen blockage. The film is quenched rapidly at the frost line to minimize blocking inside the collapsing frame.

Hot tack is measured under ASTM F1921-18 at 0.1 s delay and 0.2 N/mm² seal pressure; a minimum hot tack of 1.5 N/15 mm across a 15–25 °C window is required for 30–60 cycles/min VFFS lines. The butene comonomer lowers the temperature at which chain segments interdiffuse across the seal interface compared with propylene-ethylene random copolymer, but the plateau is narrow. Seal bars longer than 300 mm require independent temperature zones because edge cooling after shutdown produces 3–6 °C lower edge seal temperatures and intermittent seam failures. Film blocking in the filling tube can occur at ambient temperatures above 35 °C; slip masterbatch dosage is adjusted to maintain kinetic coefficient of friction at 0.20–0.40 under ASTM D1894-14.

Compliance for food contact uses FDA 21 CFR 177.1520(c) for the PP phase and the same olefin polymer condition for the LLDPE blend counterpart, with EU Regulation (EC) No 10/2011 overall migration applied to the finished film. Terminal products include frozen vegetable pillow packs, frozen seafood pouches, textile compression bags, electronic accessory dust covers, and consumer goods mailers. The film is not specified for heavy liquid detergent packaging above 1 L unless the outer layer is pigmented and the seal is reinforced with a second gusseted seam; lower stiffness of the terpolymer seal layer can permit creep failure at the bottom seal when headspace CO₂ is released by dry ice or oxygen absorbers.

In-mold labeling converts a cast film backside seal layer to a bond surface against molten polypropylene during container injection molding. The backside seal layer is run at 100 wt% TF400 with a thickness of 5–8 µm on a printable facestock of 50–75 µm; the facestock is a biaxially oriented PP white cavitated core or a matte cast PP sheet. During injection molding, PP melt at 220–240 °C contacts the label held in the mold by static pinning; the terpolymer seal layer softens at 105–115 °C, and melt pressure of 0.1–0.3 MPa drives the label into the mold texture without melting through the facestock. Clamp force on multi-cavity yogurt cup molds typically ranges from 1,500–2,500 kN; filling and holding pressures must be balanced to avoid label wash-off at the gate. The cast film process uses a 150 mm extruder with L/D 30:1, a polished matte chill roll at 22–26 °C, and line speed of 80–150 m/min. Printability is controlled by surface tension of 38–42 mN/m after corona treatment under ASTM D2578-17.

Label compliance for food containers demands EU Regulation (EC) No 10/2011 when the label is counted as part of the outer non-food-contact side but may migrate through the container wall under certain test conditions; FDA 21 CFR 177.1520(c) applies to the PP resin. For non-food containers, RoHS Directive 2011/65/EU Annex II restricts lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE to 0.1 wt% in homogeneous materials. Terminal products include injection-molded polypropylene yogurt cups, margarine tubs, ice cream containers, paint pails, and storage boxes. Dimensional stability of the label film is verified by heating at 120 °C for 5 min; shrinkage above 2.0% machine direction and 1.0% transverse direction causes pre-distortion and gate-area blisters. Stored rolls must not exceed 40 °C or 70% RH; blocking of the seal side occurs at elevated temperatures because the terpolymer surface softens and interdiffuses under roll wrap pressure.

What Limits Lamination Speed on Solventless Lines?

Flexible pouches that require high-speed solventless lamination use a cast polypropylene seal web made from 100 wt% TF400 as the inner food-contact ply, laminated to metallized BOPP or reverse-printed PET. The cast web is 30–50 µm thick and is produced on a five-layer cast line at 220–240 °C melt temperature with a chill roll at 22–26 °C. Solventless polyurethane adhesive is applied at 1.2–2.0 g/m²; nip temperature is 50–60 °C, and ageing is conducted at 40 °C for 24–72 h to complete primary and secondary amine reaction. Lamination speed is limited by the terpolymer web’s thermal shrinkage when exposed to the laminating nip and adhesive curing exotherm; above 250 m/min, machine-direction wrinkles develop if tension exceeds 0.3 N/mm. A converter observed intermittent wrinkles when the unwind splice tension varied by more than 0.05 N/mm, indicating that closed-loop tension control is required before line-speed increases.

Compliance for laminated food packaging includes FDA 21 CFR 177.1520(c) for the PP sealant web, EU Regulation (EC) No 10/2011 for the finished laminate, and Directive 94/62/EC for packaging waste. Adhesive-specific migration must be evaluated under EN 1186-1:2002; isocyanate-based solventless adhesives require complete curing before food contact, and residual monomer is tested according to EN 13130-1:2004. For dry powder and fatty snack applications, the sealant web cannot be replaced by a random copolymer with a higher seal initiation temperature without reducing pouch line speed. Terminal pouch formats include stand-up pouches for dry foods, powdered beverage mixes, pet food, and laundry detergent refills. Seal strength after lamination is qualified by ASTM F88/F88M-15 with a target of 3.0–5.0 N/15 mm for 15 mm wide seals; delamination at the adhesive interface is separately checked by ASTM D1876-08 T-peel. The material is not suitable for retort pouches or boil-in-bag applications above 100 °C, because the sealant layer softens and can flow under pressure, producing channel leaks during vertical retort baskets.