KOPELEN PP Terpolymer SB-550A, specified at 5.0 g/10 min melt flow rate under 230 °C/2.16 kg per ISO 1133-1:2022 and 0.90 g/cm³ density, is processed in three-layer coextruded cast polypropylene lines as the sealant web for retort and hot-fill flexible packaging. The ethylene–butene random distribution lowers the film-to-film seal initiation temperature to 105–115 °C, while maintaining a seal strength of 15–25 N/15 mm after 130–145 °C jaw sealing when measured under ASTM F88/F88M-21. In food-contact applications, the material is qualified under FDA 21 CFR 177.1520 for olefin polymers and EU No 10/2011 for plastic food-contact materials; overall migration is controlled below 10 mg/dm² using EN 1186-1:2002, and specific migration of PP comonomers is verified with fatty stimulants 95% ethanol and iso-octane per EN 1186-2 and EN 1186-14.

In the sealant layer, the formulation is set at 70–100 wt% SB-550A, with the balance as a higher-crystallinity random copolymer PP to widen the hot tack plateau between 120 °C and 150 °C on vertical form-fill-seal lines. Silica-based anti-blocking masterbatch, typically 5–10 wt% silica in a PP carrier, is added at 2–5 wt% of the sealant layer; erucamide or oleyamide slip masterbatch is added at 1–3 wt%, and total erucamide migration into food simulants is checked against the EU No 10/2011 specific migration limit. On lines with die widths above 2.8 m, edge encapsulation with 5–10 wt% homopolymer PP is used to reduce melt fracture at the deckle edges. Batch-to-batch seal initiation variability is reported below 2 K when extruder barrel temperatures are stable, but converters record a 4–6 K upward shift when corona-treated edge trim is reground into the core above 20 wt% of core throughput, which forces a compensating decrease in sealing speed.

Cast film production uses extruder L/D ratios of 28:1 to 32:1, barrier screws, and melt temperatures of 220–245 °C for the sealant layer. The flat die gap is 0.6–1.0 mm, the chill roll is held at 18–30 °C, and the vacuum box plus electrostatic pining is engaged above 100 m/min to suppress draw resonance. Corona treatment to 38–42 mN/m per ISO 8296:2003 is applied before lamination; treatment above 46 mN/m increases surface oxygen and can delay slip additive bloom past 72 h, causing high coefficient of friction during slitting. Terminal products include retortable stand-up pouches with outer polyester or nylon and aluminium foil barrier, hot-fill spout pouches, block-bottom coffee packs, and three-side-seal snack packs.

When SB-550A replaces random copolymer PP in oriented film sealant skins

On tenter-frame biaxially oriented polypropylene lines, SB-550A is coextruded as a 1–3 µm sealant skin on both faces of a homopolymer PP core. The lower crystallinity of the terpolymer skin reduces seal initiation temperature but also lowers the softening point; therefore, transverse direction pre-heat and stretching zones are held at 145–160 °C, and skin layer melt temperature is kept at 230–240 °C. If transverse direction temperatures fall below 145 °C, transverse bands and gauge variation appear; if they exceed 165 °C, the skin exhibits sticking to tenter clips and transfer marks on subsequent rolls.

Skin formulation is 70–100 wt% SB-550A, with 0–30 wt% random copolymer PP of melt flow rate 3–5 g/10 min to preserve stiffness during orientation. Anti-blocking masterbatch is added at 2–4 wt%; slip masterbatch containing 5–10 wt% erucamide is added at 0.5–1.5 wt%. Because additive bloom requires 24–72 h after winding, immediate slitting can produce kinetic coefficient of friction above 0.4; converters either age the master rolls at 35–40 °C for 24 h or reduce slip addition to 0.2 wt% to avoid downstream film blocking.

Cast pre-web is quenched at 20–30 °C, MD stretched at 120–135 °C with draw ratio 4.0–5.5:1, TD stretched at 150–165 °C with draw ratio 8.0–10.0:1, and annealed at 155–165 °C. Finished film thickness runs 18–25 µm at line speeds of 250–350 m/min; edge trim at 15–20% is pelletized and fed into the core at up to 25 wt% of core throughput. Food-contact compliance is assessed under FDA 21 CFR 177.1520 and EU No 10/2011; heat seal strength and hot tack are measured per ASTM F1921/F1921M-20 and ASTM F2029-21. Terminal products include snack food overwrap, graphics lamination film, confectionery twist-wrap, and label face stock requiring low-temperature sealing to oriented PP.

Blown film frost line stability and bubble optics

SB-550A is run in mono-layer and three-layer water-cooled or air-cooled PP blown film lines for low-haze overwrap and stationery films. The terpolymer gives haze of 2.0–4.0% at 25 µm in water-cooled processing, but bubble stability below 60 kg/h die throughput is dependent on frost line height and melt strength. In water-cooled systems with an internal mandrel, frost line height is kept between 5 cm and 15 cm; frost line heights above 20 cm produce bubble oscillation, uneven gauge bands, and increased blocking on the roll after 48 h storage.

The monolayer or skin formulation is 85–100 wt% SB-550A, 0–15 wt% metallocene LLDPE or propylene-based elastomer to improve machine-direction tear resistance, 1–3 wt% silica anti-blocking masterbatch, and 0.5–1.5 wt% slip masterbatch. Internal antistat masterbatch at 0.1–0.5 wt% is added when downstream sheet-fed printing generates static; the antistat reduces optical clarity by 1–2% haze after 30 days due to surface bloom. Extruder melt temperature is 210–230 °C, die gap 0.8–1.8 mm, blow-up ratio 1.8–2.5:1, and winding tension is held below 20 N/m.

Compliance testing includes FDA 21 CFR 177.1520, EU No 10/2011, and REACH Annex XVII; film for stationery may additionally be screened for heavy metals under EN 71-3:2019+A1:2021. Terminal forms are transparent magazine covers, floral sleeves, garment bags, and lamination base film for printed stationery. Published data for SB-550A in high-speed air-cooled PP bubble lines above 120 kg/h is limited; converters evaluating such lines should validate frost line control and roll blocking before serial production.

What governs extrusion coating adhesion to aluminium foil at 0.6–1.2 mm die gaps?

Because the non-porous foil surface provides no mechanical anchoring, extrusion coating of SB-550A onto aluminium foil is controlled by oxidative adhesion in the air gap. The coating blend is processed at melt temperatures of 275–295 °C, which is above the cast-film temperature range, to generate polar carbonyl species that bond to the metal surface. At melt temperatures below 270 °C, peel bond strength to foil typically falls below 150 g/15 mm; above 300 °C, visible gel formation and edge melt rupture increase over coating campaigns longer than 8 h.

The coating formulation uses 80–95 wt% SB-550A and 5–20 wt% maleic anhydride grafted PP with 0.5–1.5 wt% maleic anhydride graft content. Primer based on water-based polyurethane or polyethylenimine is applied at 0.3–1.0 g/m² dry coat weight, and the foil surface is pre-treated to 42–48 mN/m per ISO 8296:2003. Process stabilizer masterbatch at 1–2 wt% is included to suppress gel accumulation on the die lip. Aluminium foil thickness is 6–12 µm, and PP coating weight is 15–30 g/m².

The coating line uses a single-screw extruder with L/D 28:1 to 32:1, barrier screw, flat die gap 0.6–1.2 mm, air gap 150–250 mm, chill roll temperature 10–20 °C, and line speed 120–200 m/min. Bond strength is measured after lamination per ASTM F904-16, with typical acceptance 300–800 g/25 mm depending on foil gauge and primer chemistry. For food-contact lidding stock, compliance is reviewed under EU No 10/2011 and FDA 21 CFR 177.1520; aluminium foil substrate is assessed under EN 602:2004 where relevant. Terminal products include yogurt cup lidding foil, butter portion packs, pharmaceutical blister lidding, and heat-sealable foil for cosmetic sachets.

Ethylene oxide gassing exposes additive migration thresholds in sterile barrier webs

In terminal sterilized medical packaging, SB-550A is formed into clear or pigmented sealant webs where seal integrity after ethylene oxide gassing and low particulate release are critical. Erucamide slip is kept below 0.05 wt% in the contact layer because post-sterilization bloom to the seal interface reduces seal strength and can produce visible residues on device surfaces. Inorganic silica anti-blocking masterbatch is used instead, at 1–3 wt%, and the contact layer is formulated at 90–100 wt% SB-550A with 0–10 wt% polyolefin elastomer to raise puncture resistance.

Film production takes place in at least ISO 14644-1:2015 Class 8 cleanrooms on cast or blown lines with melt temperature 220–240 °C and film thickness 25–60 µm. Corona treatment is limited to 36 mN/m to reduce blocking and surface degradation. Regrind from sealant edge trim is excluded from the patient-contact layer; if used in a non-contact core, it is limited to 20 wt% and justified under ISO 11607-1:2019 clause 6.1.8. Sealing to lidding film or Tyvek is run at 125–145 °C, 0.3–0.6 MPa jaw pressure, and 0.5–1.5 s dwell. Seal strength is tested per ASTM F88/F88M-21 with typical acceptance 1.0–2.5 N/15 mm; dye penetration is checked per ASTM F1929-23, and bubble emission per ASTM F2096-11.

Biocompatibility is assessed by ISO 10993-5:2009 and ISO 10993-10:2010, and the polymer is typically evaluated against USP Class VI extraction at 121 °C. Sterilization validation follows ISO 11135:2014 for ethylene oxide and ISO 11137-1:2006/Amd 1:2013 for gamma or electron beam. Published data for SB-550A after 25 kGy gamma exposure in sealed pouches is limited; dose mapping, post-sterilization seal peel testing, and visual inspection are mandatory before release. Steam autoclave is not recommended as a primary sterilization route for SB-550A sealant webs because the softening range approaches typical autoclave temperatures and seal creep may occur. Terminal products include chevron pouches, header bags, film-to-film pouches for syringes and surgical kits, and vented blister lidding.

Liquid packaging for high-water-activity non-carbonated products such as condiments, wet wipes, and detergent sachets uses SB-550A as the sealant web in laminated pouches that do not enter retort or hot-fill service. The sealant film is compounded at 60–80 wt% SB-550A with 20–40 wt% higher-modulus random copolymer PP to prevent seal-through crease channels when sealing through product splash. Anti-blocking masterbatch is added at 3–6 wt%, and slip masterbatch is restricted to 0–1 wt% when the outer laminate is reverse-printed or when the pack is filled hot; excess slip bloom can reduce ink adhesion and increase seal contamination. Sealant layer thickness is 15–30 µm in a finished laminate of 60–120 µm.

The cast sealant film is laminated to printed polyester, biaxially oriented polypropylene, or aluminium foil with solventless polyurethane adhesive at 1.2–2.5 g/m² coat weight, nip temperature 55–65 °C, and web tension 15–30 N/m. Curing proceeds at 35–40 °C for 24–48 h before slitting. On vertical form-fill-seal conversion, jaw temperature is set 135–150 °C, dwell 0.3–0.8 s, and jaw pressure 0.3–0.6 MPa; seal-through creases and product splash contamination are mitigated by increasing sealant layer thickness to 25–30 µm or switching to flat serrated seal jaws.

Food-contact packaging requires FDA 21 CFR 177.1520 and EU No 10/2011; specific migration for aqueous and emulsion products is measured with 10% ethanol and 50% ethanol simulants per EN 1186-3 and EN 1186-9. Industrial detergent sachets may be evaluated for environmental stress-cracking resistance according to ASTM D1693-15. Terminal types include condiment sachets, wet wipe overwrap, liquid detergent pouches, and non-carbonated drink stick packs.