When a seal bar temperature of 115°C defines line speed
In vertical form-fill-seal (VFFS) and horizontal flow-wrap installations running at machine speeds exceeding
40 m/min, the dwell time available for the fin-seal jaw cycle collapses to
0.2–0.4 seconds. A polypropylene terpolymer sealant web that consistently initiates fusion at
112–115°C—as measured by flat-jaw hot-tack tests under
ASTM F1921-12 (Method B)—permits the packaging engineer to drop the set temperature by
8–12°C versus a standard random copolymer grade, thereby reducing the thermal load on the product and expanding the processing window before the onset of seal-through-wrinkle failures. On cast-film lines equipped with a
90 mm single-screw extruder (L/D
33:1, compression ratio
2.8:1), COSMOPLENE FL7013E2 is typically processed neat as the sealant ply without carrier resin dilution; the recommended melt temperature at the die lip is held within
240–260°C, while the chill-roll set-point is maintained at
18–22°C to lock in an amorphous surface morphology that depresses seal initiation temperature. Addition levels of anti-block masterbatch (synthetic silica in PP carrier) are kept between
2.5 wt% and
4.0 wt%, as higher loadings raise the static COF above
0.25 and compromise optical haze—a parameter routinely monitored per
ASTM D1003-21 (Procedure A, haze <
2.5% for
30 µm film). Regulatory compliance for direct food contact rests on the finished film passing overall migration limits prescribed in
EU Regulation (EC) No 10/2011 (Annex II, OML
10 mg/dm²) and the substance-specific restrictions of
FDA 21 CFR 177.1520 (c)
3.2a, as well as the applicable national implementations such as the BfR Recommendation VI for polypropylene. The end products span leaf-salad pillow pouches, frozen-vegetable polybags, and bakery-window carton overwraps where fusion at the seal-contamination interface—flour dust, oil mist—must hold a minimum hermetic seal strength of
8 N/15 mm according to
ASTM F88/F88M-21 at a jaw force of
0.3 MPa. One repeat failure mode observed on high-output cast lines stems from melt-temperature stratification in the adapter block; a thermal gradient exceeding
±3°C across the die width causes micro-crystalline domains in the web that elevate the lowest sealable temperature by
4–6°C, effectively erasing the economic speed advantage. To counteract this, static mixers with a minimum
6-element configuration are inserted between the extruder gate and the feed-block, restoring the narrow seal plateau required for ultra-fast machinery.
Seal initiation temperature depression in BOPP sequential stretching
Coextruded biaxially oriented polypropylene films destined for high-speed cigarette overwrap and confectionery twist-wrap rely on a skin layer that must survive a
5.0 × 9.2 simultaneous or sequential draw ratio without causing inter-layer delamination. After the cast sheet leaves the quench drum at
20°C, the machine-direction orienter applies pre-heat at
125–132°C over a series of differential-speed rolls before the transverse stretching in a tenter oven peaking at
165–170°C. FL7013E2, slot-cast as the terpolymer skin at
1.2–2.0 µm thickness within a
20 µm overall gauge (constituting
6–10 wt% of the total structure), experiences a true strain sufficient to align the amorphous tie chains while still resisting flow-induced crystallisation that would raise the post-orientation seal initiation temperature beyond the target of
< 95°C for high-slip films. The formulation requires the addition of a migratory slip agent—erucamide at
800–1200 ppm—that blooms to the surface after winding to achieve a dynamic COF of
0.20–0.25 per
ISO 8295:2004; however, equilibrium migration takes
72–96 hours at
35°C and any residual monomer trapped in the skin risks elevating the total extractives above the
5 mg/kg specific migration limit for primary aromatic amines where dual-use food types are concerned. The plant practice of inline corona treatment immediately ahead of the pull-rolls sets the surface energy above
38 dyn/cm (measured with a dyne-pen kit conforming to
ASTM D2578-23), which improves metallization anchorage when the film is converted as the outer ply of a laminate. Compliance with
FDA 21 CFR 177.1520 and
EU 10/2011 is validated by extraction in
3% acetic acid,
10% ethanol, and isooctane simulants at
40°C for
10 days. Even so, an operational boundary emerges around the tenter’s exhaust humidity: at a relative humidity below
30%, static discharge triggers dust attraction on the terpolymer surface, rendering the final reel unsuitable for high-clarity over-wrap, forcing the operator to hold the hall within
45–55% RH. Finished reel goods become tobacco over-wrap, chocolate-bar flow-pack, and CD jewel-case windows where the combination of low-temperature sealing and optical brilliance provides the primary functional value.A melt curtain exiting the coat-hanger die at
285°C accelerates across the air gap into a laminating nip formed by a polished chill roll operating at
22°C and a pressure roller applying
40 N/mm linear force, fusing a
18 g/m² layer of FL7013E2 directly onto the clay-coated side of a
250 g/m² solid bleached sulphate board. This extrusion-coated substrate is the precursor to hot-fill smoothie cups and microwaveable soup containers where the seal integrity of the lid flange must withstand a burst pressure exceeding
120 kPa after a double-seam closure. Because FL7013E2 contains no polar functionality, an oxidative pre-treatment of the board surface is executed through an inline corona discharge at
3.5 kW immediately before the melt curtain impinges, elevating the substrate surface energy to a minimum of
42 dyn/cm; alternatively, an aqueous priming of polyethylenimine (diluted to
0.5% solids) is roller-applied to generate chemical anchoring sites. The 100%-terpolymer coat weight can be reduced to
12 g/m² when an adhesion-promoting tie resin is blended at
8 wt%, though the dilution shifts the Vicat softening point upward by
4–6°C and must be re-validated for cup-forming on high-cavity thermoforming tools. Food-contact status for coated paper and paperboard falls under
FDA 21 CFR 176.170(c) (Components of paper and paperboard in contact with aqueous and fatty foods) and the relevant BfR Recommendation XXXVI; migration testing simulates hot-fill at
88°C for
2 hours using a
50% ethanol simulant for fatty foods. The single largest cause of field reject is a phenomenon called “fibre-tear delamination” at the skirt seam, verified by peeling the flange at
90° angle under
500 mm/min crosshead speed (
ASTM D903-98): when the chill-roll temperature drops below
16°C, the rapid quench yields a high fraction of mesomorphic phase that embrittles the coating and favours adhesive failure over cohesive fibre pull-out. Finished articles include coffee take-away lids, grease-resistant folding cartons for pizza, and ice-cream tubs.
How does bubble stability influence sealant layer gauge uniformity?
On a three-layer blown-film line configured for heavy-duty industrial sacks and pet-food bags, the inner sealant ply (Layer A) employs FL7013E2 as a
25 wt% fraction of the total structure, sandwiched between a high-density polyethylene stiffening core (Layer B) and a printable LLDPE/LDPE outer skin (Layer C). The rheological challenge arises because the terpolymer, at its recommended processing temperature of
210–235°C inside the
250 mm spiral-mandrel die, exhibits a shear viscosity that is
40–50% lower than that of the adjacent HDPE melt under the same shear rate, resulting in an interfacial instability that manifests as a long-wavelength variation in layer thickness—often called “chevron chatter” on the frost line. To suppress this, the die-gap is constrained to
1.2 mm and the blow-up ratio is maintained at a conservative
2.0:1, with the frost-line height manually kept at
280–320 mm from the die face because a higher frost line allows the laminate viscosity to equilibrate before crystallisation pins the interface. The addition level of FL7013E2 is deliberately kept below
30 wt%; exceeding this threshold at a die-head pressure below
28 MPa causes the sealant layer to encroach into the core in a waveform pattern, giving a local heat-seal strength oscillation of
±15% around the mean
12 N/15 mm value when tested per
ASTM F88/F88M-21. From a regulatory standpoint, the complete film is assessed under
FDA 21 CFR 177.1520 or
EU 10/2011 with specific migration simulations using dry-food simulant Tenax® for
10 days at
40°C, as the target end-use precludes prolonged moist contact. The finished sacks are collated on wicketed bundles for automated opening-filling-closing lines handling urea, grain, and landscaping mulch; a critical seal criterion post-filling is the resistance to a drop-impact of
1.8 m per
ISO 7965-1:2015, which requires the bag’s bottom gusset seal to withstand the shock without the terpolymer layer extruding out of the seam—a phenomenon traced to a low zero-shear viscosity of the neat grade and mitigated by compounding with
3 phr of a high-melt-strength PP modifier that elevates the elongational viscosity at Hencky strain rates above
0.5 s⁻¹. This formulation adjustment, however, adds a pre-compounding step performed on a co-rotating twin-screw extruder (D
25 mm, L/D
40) before pelletising, which alters the economic equation and is only justified for sack uses above
50 kg net fill weight.
Under anhydrous conditions: extrusion coating aluminium foil with PP terpolymer
Push-through blister lidding for pharmaceutical tablets—paracetamol, acetylsalicylic acid, ibuprofen—demands a sealant layer that hot-seals through a lacquer primer onto the PVC/PVDC blister cavity at a jaw temperature below
160°C while presenting an extraction profile compliant with both the European Pharmacopoeia monograph
3.1.5 (Polypropylene for containers and closures) and
USP <661.1> plastic materials of construction. FL7013E2 is melt-extruded at
28 µm thickness directly onto a
20 µm soft-annealed aluminium foil substrate pre-heated to
125°C; the foil has received a coating of
0.8 g/m² solvent-based polyurethane primer (dry solids) applied by a gravure station and cured for
36 hours at
45°C to ensure the isocyanate functionality fully cross-links before the polymer curtain impinges. The terpolymer is fed using a
65 mm extruder with a grooved-barrier feed section and dried to a residual moisture of
< 150 ppm via a desiccant dryer operating at
75°C for
3 hours, because any moisture in the feed splits into steam at the die lip, creating micro-pinholes that later show up as gas-chromatography-detectable helium leaks under
ASTM F2096-14 burst testing (pass criterion: no visible bubbles at
20 kPa differential pressure). The application is performed at a line speed of
120 m/min with the chill roll held at
30°C, producing a film stack that is slit into
164 mm wide reels for conversion on a pressure-sensitive adhesive lamination line adding the print-receptive polyester outer layer. In this niche, FL7013E2 operates at
100% concentration without dilution, because even
2 wt% of a processing aid can leach a non-volatile residue exceeding the
5 mg per dosage unit limit stipulated in the
ICH Q3D guideline for elemental impurities, compromising batch release. The composite lid foil also satisfies the peel-force opening specification of
5–10 N/15 mm when measured at
300 mm/min crosshead speed per
EN 868-9:2018 (closure systems for medical packaging), a range that keeps the lidding intuitive for geriatric patients yet secure against child-curiosity. Processors frequently report a rolling-bank build-up on the back-up roll if the melt temperature strays above
310°C, at which point the stabiliser package begins to volatilise and coats the polishing drum, forcing a line stop every
6–8 hours for cleaning—a production constraint that makes the film particularly suitable for dedicated long-run EU GMP-certified cleanrooms rather than short trial campaigns.
Testing the limits of seal-through-contamination in retort pouches
When a laminate pouch containing curry sauce or ready-to-eat rice undergoes retort sterilisation at
121°C for
30 minutes under an overpressure of
0.18 MPa, the innermost polypropylene sealant layer is subjected to conditions that push the material into its rubbery plateau, reducing the room-temperature seal strength from
38 N/15 mm to a hot-seal value of merely
4–6 N/15 mm at the point of maximum thermal stress within the retort basket. In these three-ply laminates (PET
12 µm / aluminium
9 µm / cast polypropylene
70 µm), FL7013E2 is incorporated at
35–45 wt% in the cast PP layer together with a polypropylene impact copolymer having an ethylene content of
8–10% and a melt flow rate of
1.5 g/10 min (
ISO 1133-1:2022, Condition M) to raise the flexural modulus at
130°C above the threshold that resists pouch-panel buckling inside the rack. The cast monolayer sealant film is produced on a
1,200 mm wide line with an L/D of
30:1 and a chlorinated-polyolefin-optimised barrier screw; the melt is filtered through a
25 µm screen pack to remove any gel particles that would nucleate pinholes under fluctuating autoclave pressure. Adherence to
FDA 21 CFR 177.1390 (Laminate structures for use at temperatures up to
135°C) is confirmed by extraction testing with
n-heptane at
66°C for
2 hours, representing fatty-food conditions, and by overall migration into olive oil for
30 minutes at
121°C. One operational limit emerges when the pouch filler splashes a proteinaceous drip onto the seal area; FL7013E2 tolerates a finite contaminant layer of less than
0.3 mg/cm² vegetable oil equivalent before the seal bar requires a temperature-compensation ramp of
+3.5°C per 0.1 mg/cm² beyond the clean-film setpoint of
140°C, a sensitivity that necessitates electrostatic drip removal systems upstream of the jaw. Finished retort pouches are sold into military field rations, airline meals, and ambient-stable pet-food trays, where a post-retort burst strength of
55 kPa minimum (
ASTM F1140/F1140M-13) and a lid-seal visual clarity sufficient to read a newspaper through the pouch wall remain the non-negotiable quality gates.
| Process Condition | Cast Film Sealant | BOPP Skin | Extrusion Coating | Blown Film Sealant | Blister Lidding | Retort Laminate |
|---|
| Typical FL7013E2 fraction in layer (wt%) | 96–100 | 100 | 92–100 | 25–30 | 100 | 35–45 |
| Melt temperature at die (°C) | 240–260 | 250–265 | 280–300 | 210–235 | 305–315 | 235–250 |
| Seal initiation temperature window (°C, ASTM F2029) | 112–118 | 93–98 (post-orientation) | 115–122 | 110–117 | 130–142 (to primed blister) | 118–125 (before retort) |
| Critical humidity / moisture boundary | chill-roll dew point 8°C | tenter hall RH 45–55% | substrate moisture < 5% | pellet moisture < 200 ppm | pellet moisture < 150 ppm | pellet moisture < 100 ppm |
A secondary comparative table that would exceed the document’s permitted number has been omitted; the single table above aggregates the cardinal processing constraints that deviate across the six application segments and serves as a cross-reference for production engineers conducting first-article trials on converting equipment.
COSMOPLENE PP Terpolymer FL7013E2 is a propylene-ethylene-butene-1 terpolymer designed specifically for coextruded sealing layers in flexible packaging structures. The resin carries a nominal melt mass‑flow rate (MFR) of
7 g/10 min when tested at
230 °C under
2.16 kg load in accordance with
ISO 1133‑1:2022. Its density, measured by
ISO 1183‑1 on compression‑moulded specimens, typically falls at
0.90 g/cm³. Incorporation of butene‑1 as a third comonomer depresses the crystallinity below that of conventional propylene‑ethylene random copolymers, yielding a peak melting temperature of approximately
125–130 °C by differential scanning calorimetry (
ISO 11357‑3) and a seal initiation temperature (SIT) as low as
105 °C when evaluated on cast film of
30 µm thickness per
ASTM F2029. The grade complies with
FDA 21 CFR 177.1520(c) 3.1a,
EU Regulation 10/2011, and the applicable provisions of
REACH and
RoHS 2011/65/EU, making it suitable for direct food contact in multilayer laminates. Its additive package includes a controlled level of slip and antiblock agents to maintain a kinetic coefficient of friction below
0.30 (
ASTM D1894) on untreated film surfaces.
How Does the Terpolymer Composition Alter Seal Initiation Temperature Relative to Standard Random Copolymers?
The stepwise reduction in seal initiation temperature derives directly from the disruption of isotactic polypropylene sequences. In a propylene-ethylene random copolymer, ethylene units interrupt the regularity of the polypropylene backbone, but the residual crystallinity remains sufficient to sustain a melting onset near
135 °C and an SIT around
125 °C for a
7 MFR grade. When butene‑1 is incorporated as a third monomer, the ethyl branch in the comonomer side chain creates additional steric hindrance that further reduces the average lamellar thickness. Calorimetric data on FL7013E2 show a broad melting endotherm with a low‑temperature shoulder extending to
95 °C, and hot‑tack measurements on a cast‑film line with a seal bar pressure of
0.4 MPa demonstrate a usable hot‑tack window starting at
108 °C, whereas a comparable random copolymer requires at least
128 °C to achieve a hot‑tack force exceeding
2.0 N/25 mm (
ASTM F1921). The consequence for packaging speeds on vertical form‑fill‑seal (VFFS) equipment is a proportional decrease in required seal bar dwell time: field data from lines running at
120 packs/min indicate that FL7013E2 sustains hermetic seals at dwells of
30–40 ms, compared with
50–60 ms for ethylene‑propylene random grades. This advantage is particularly pronounced when sealing through product contamination, where the terpolymer’s lower melt viscosity at the seal interface promotes polymer flow into surface irregularities.
Film Extrusion Equipment Requirements and Processing Window Limitations
FL7013E2 is processable on standard single‑screw extruders equipped with barrier‑type screws having an L/D ratio of at least
24:1 and a compression ratio between
3.0:1 and
3.5:1. A screen pack of
250/150/100/60 mesh is typical for cast film to remove incidental gels. The recommended melt temperature profile ranges from
210 °C in the feed zone to
240 °C at the die, with the flat‑die temperature maintained within
±2 °C across the width to avoid transverse thickness variation. Although polypropylene is not hygroscopic, prolonged exposure to relative humidity above
70 % can introduce surface moisture that generates splay marks on rapid quenching. Therefore, when ambient dew point exceeds
−20 °C, a desiccant drying step at
80 °C for
3 h is recommended for resin stored in open silos. The low crystallinity inherent to the terpolymer narrows the processing window for chill‑roll temperature compared to homopolymer or random copolymer films. At chill‑roll temperatures above
30 °C, insufficient cooling rate leads to blocking on the roll surface, whereas descending below
15 °C can induce excessive quench‑related haze without a commensurate gain in seal performance. The optimal chill‑roll set‑point is therefore
20–25 °C, with a water inlet temperature of
18 °C. On a three‑layer cast line producing
50 µm sealant film with FL7013E2 as the skin layer, a line speed of
150 m/min is routinely achieved using a die gap of
0.7 mm. For biaxially oriented polypropylene (BOPP) applications, the terpolymer is coextruded as a sealant skin on the outside of a homopolymer core, and the machine‑direction stretching ratio is reduced by
0.2–0.3 units relative to standard formulations to prevent premature crystal break‑up that would diminish seal strength. Pre‑heating roll temperatures are lowered by
5 °C to compensate for the faster melting onset of the terpolymer.
Without a section heading, the following outcome emerges from continuous manufacturing audits. On a high‑speed VFFS line handling salted snack bags, substitution of a standard propylene‑ethylene random copolymer with FL7013E2 at the
20 µm sealant layer thickness permitted an increase of line speed from
85 packs/min to
105 packs/min while maintaining a seal strength above
8 N/25 mm (
ASTM F88). The seal bar temperature was lowered from
135 °C to
115 °C, which reduced energy consumption for the sealing jaw by approximately
12 % and eliminated film burn‑through failures that previously occurred at package corners when the line stopped momentarily with the jaws in contact. Optical properties of the finished laminate, measured on the inner sealant side, showed a haze value of
1.8 % (
ASTM D1003,
50 µm film) and a
60° gloss of
105 GU (
ASTM D2457), outperforming the random copolymer benchmark which exhibited haze
3.5 % and gloss
92 GU at identical thickness. The improvement in clarity is attributed to the reduced spherulite size in the terpolymer, as the butene‑1 comonomer suppresses nucleation of large crystalline domains.
Comparative Properties: FL7013E2 Terpolymer vs. Propylene-Ethylene Random Copolymer (7 MFR, Cast Film)
| Property | Test Method | FL7013E2 | Random Copolymer |
|---|
| Melt mass‑flow rate (230 °C/2.16 kg) | ISO 1133‑1 | 7.0 g/10 min | 7.0 g/10 min |
| Density | ISO 1183‑1 | 0.90 g/cm³ | 0.90 g/cm³ |
| Melting peak (DSC, 10 °C/min) | ISO 11357‑3 | 128 °C (broad) | 142 °C |
| Seal initiation temperature (SIT, 30 µm film) | ASTM F2029 | 105 °C | 125 °C |
| Hot‑tack force at 115 °C, 0.4 MPa, 30 ms | ASTM F1921 | 2.8 N/25 mm | <0.5 N/25 mm |
| Haze (50 µm film) | ASTM D1003 | 2.0 % | 3.8 % |
| Gloss (60°, 50 µm film) | ASTM D2457 | 103 GU | 90 GU |
| Tensile modulus at yield (MD/TD) | ISO 527‑3 | 550 / 520 MPa | 780 / 750 MPa |
| Flexural modulus | ASTM D790 | 650 MPa | 950 MPa |
| Coefficient of friction (dynamic) | ASTM D1894 | 0.25 | 0.28 |
The data in the table underscore that the principle trade‑off for lower seal initiation and superior optics is a reduction in stiffness. The tensile modulus of FL7013E2 is approximately
30 % lower than that of a typical ethylene‑propylene random copolymer, which must be considered when designing the overall laminate stiffness. In vertical form‑fill‑seal constructions, the lower modulus enhances conformance to irregular product shapes but may require a thicker core layer if the laminate must resist puncturing from sharp snack food edges. Field data from pouch converters indicate that a
5 µm increase in the HDPE or homopolymer PP core thickness is sufficient to restore puncture resistance, without negating the cycle‑time advantages gained from the terpolymer sealant.
When Substituting into Existing Random Copolymer Formulations, What Adjustments to Barrel Temperature Profiles Are Needed?
Migration from a propylene‑ethylene random copolymer to FL7013E2 typically necessitates a reduction of the overall melt temperature by
5–10 °C to compensate for the lower melting point and to forestall degradation of the butene‑1 segments under prolonged shear. Screw speed is often increased by
5–10 % to achieve equivalent throughput because the terpolymer exhibits slightly higher melt viscosity at the reduced processing temperature; however, the shear‑thinning index (power‑law index
n) remains within
0.35–0.40 over a shear rate range of
100–1000 s⁻¹, as determined by capillary rheometry at
230 °C. The first barrel zone should be set to
180–190 °C, compared with
190–200 °C for random grades, to avoid premature melting that would interfere with solids conveying. The screen‑changer and adapter temperatures are maintained at
220–230 °C, ensuring adequate filtration without promoting crosslinking in the melt. Die‑land temperature is lowered by
5 °C to raise the melt viscosity at the lips, thereby improving gauge uniformity; a draw‑resonance throat visible at high line speeds is suppressed by this adjustment. In cast‑film operations, the air‑gap between die exit and chill roll is shortened by
2–3 mm to minimize neck‑in, which was found to increase by approximately
15 % when the terpolymer is run under the same conditions as a random copolymer. This neck‑in behavior is attributable to the lower crystallization temperature (onset
95 °C vs.
110 °C for random copolymer), which delays strain‑hardening in the melt web. By reducing the air gap and accelerating the quench rate via chill‑roll water circulation at
0.7 m³/h, edge‑trim waste is kept below
4 % of the total web width.
Limitations inherent to the terpolymer chemistry must be observed. FL7013E2 is not recommended for retort or steam‑sterilization applications because the low melting point leads to seal‑area deformation above
121 °C, and prolonged exposure to high‑energy radiation for sterilization crosslinks the butene‑1 sequences, resulting in embrittlement. The resin should not be compounded with amine‑based antistatic additives that can catalyze premature degradation of the terpolymer backbone at extrusion temperatures. Furthermore, in direct‑food‑contact structures intended for fatty foods, compliance with the specific migration limit for butene‑1 oligomers must be verified under the intended time‑temperature conditions according to
EU Regulation 10/2011 Annex III, although published data for this specific grade indicate that extraction into
95 % ethanol at
60 °C for
10 days yields total migration below
5 mg/dm². The seal‑strength retention after a
24‑h immersion in
3 % acetic acid at
40 °C remains above
90 % of the original value, as measured per
ASTM F88, demonstrating sufficient chemical resistance for acidic food packaging. Nevertheless, converters performing high‑temperature pasteurization at
95 °C for
30 min should conduct product‑specific seal‑integrity tests because the seal‑zone temperature may transiently exceed the melting onset, causing partial loss of interfacial entanglement.
