RANPELEN PP Terpolymer SFC-750M is a propylene-ethylene-1-butene terpolymer supplied by Lotte Chemical Corporation for heat-seal layers in cast polypropylene, multilayer coextruded film, and blown film. The grade carries a nominal melt mass-flow rate of 7.0 g/10 min measured at 230 °C under 2.16 kg load in accordance with ISO 1133-1:2022, a density of 0.90 g/cm³ per ISO 1183-1:2019, and a DSC peak melting temperature in the range of 130–135 °C per ISO 11357-3. The terpolymer architecture reduces crystalline order relative to a propylene-ethylene random copolymer, which allows a lower seal initiation temperature while retaining adequate melt strength for cast film stability at 80–120 µm total thickness.

Compared with homopolymer PP film grades, SFC-750M has a flexural modulus that is approximately 45–55% lower, measured per ISO 178, and a tensile yield stress near 24–28 MPa per ISO 527-2. These reductions are intentional and correspond to a thinner lamellar crystal population and a broader crystal size distribution, which control seal initiation. The product is not intended for structural monolayer packaging; its function is as a sealant skin in coextruded laminates where the core layers supply stiffness and barrier.

Typical application configurations include 5–12 µm sealant skins on oriented polypropylene base films, 15–25 µm outer layers on cast polypropylene laminations for pouches, and 3–8 µm coating layers in extrusion-laminated barrier structures. In each configuration, the resin is mixed with the appropriate masterbatch for slip and antiblock; unmixed pellets can exhibit blocking in wound film at core diameters above 400 mm and winding tensions above 120 N/m.

How Does a Propylene-Ethylene-1-Butene Terpolymer Reduce Seal Initiation Temperature Relative to Propylene-Ethylene Random Copolymers?

The reduction in seal initiation temperature arises from the incorporation of 1-butene alongside ethylene in the polypropylene backbone. In a conventional propylene-ethylene random copolymer, ethylene units interrupt isotactic PP sequences and reduce the peak melting temperature to roughly 136–145 °C. The additional 1-butene comonomer in SFC-750M further decreases the critical crystallizable sequence length; the observed melting peak shifts to 130–135 °C, while the seal initiation temperature—defined as the temperature at which a 25 mm wide heat seal reaches 0.5 N/25 mm in a 180° peel test following ASTM F88/F88M-21—drops to approximately 112 °C. In contrast, a homopolymer PP film of equivalent melt flow rate typically requires a jaw temperature above 150 °C to reach the same threshold.

The butene comonomer broadens the crystal size distribution more than ethylene alone. Wide-angle X-ray scattering of analogous terpolymers shows a lower fraction of thick lamellae, which are responsible for high-temperature mechanical rigidity, and a corresponding increase in thinner lamellae that melt below 120 °C. This shift is measurable through a lower Vicat softening temperature of approximately 124–128 °C per ISO 306. The practical consequence is that SFC-750M can be sealed at jaw settings where a standard random copolymer would still behave as a stiff, non-fused web, reducing the heat load on temperature-sensitive packaged contents.

Against propylene-ethylene random copolymers with identical melt flow rate, the SFC-750M grade typically displays a 7–10 °C lower seal initiation temperature and comparable or slightly lower haze. The trade-off is a reduction in flexural modulus. Typical flexural modulus values are 850–950 MPa for SFC-750M per ISO 178, compared with 1,000–1,200 MPa for a standard PP random copolymer and 1,400–1,600 MPa for a homopolymer PP film grade.

In processing, the low crystallinity of SFC-750M requires careful chill-roll control to avoid blocking and gauge variation. On a cast film line with a 90 mm extruder and L/D 28:1 barrier screw, barrel zone temperatures between 190 °C and 230 °C are typical. A die temperature of 220–230 °C and a chill-roll set point of 18–24 °C are used to freeze surface gloss quickly. If the chill-roll temperature exceeds 28 °C, the film may exhibit blocking on the rewind at winding tensions above 150 N/m within 20–30 min.

Seal Initiation Thresholds and Hot Tack Force in High-Speed Vertical Form-Fill-Seal Packaging

Vertical form-fill-seal lines running at 60–100 packages/min require the sealant layer to develop useful seal strength within the short dwell time imposed by rotating sealing jaws. Dwell times below 120 ms are common. For SFC-750M, a seal-bar pressure of 0.3–0.5 MPa and a dwell time of 80 ms at 112 °C yields a seal strength near 1.5 N/25 mm, while at 120 °C the seal strength rises to 3.0–4.0 N/25 mm per ASTM F88/F88M-21. Hot tack force measured according to ASTM F1921 increases from 1.0 N/25 mm at 110 °C to 3.5 N/25 mm at 120 °C.

Compared with a standard random copolymer, this allows a packager to lower sealing jaw temperature by approximately 8–12 °C without sacrificing hot tack. Lower jaw temperatures reduce heat-induced shrinkage in oriented polypropylene base films and preserve barrier layer integrity. Below 105 °C, seal initiation is inconsistent; at temperatures above 140 °C, film distortion and edge weld formation may occur if dwell exceeds 1 s. The practical seal window is therefore bounded at approximately 110–135 °C.

On cast film lines, die-lip deposits are a known failure mode when the melt temperature exceeds 250 °C. The butene-rich phase can exude low-molecular-weight oligomers that condense on the die lip and cause die lines; the deposit is typically white and can be removed by purging with a homopolymer PP at 200 °C. The root cause is residence time rather than formulation. Converters should avoid long barrel hold-ups and should not run the resin at melt temperatures above 250 °C for longer than 30 min.

When SFC-750M Replaces Homopolymer PP in Coextruded Barrier Laminate Skins

Replacing a homopolymer PP skin with SFC-750M in a three-layer or five-layer barrier laminate reduces the minimum seal temperature by approximately 40 °C, allowing the converter to reduce seal jaw set points from 150 °C to 110–120 °C. That reduction is critical when the laminate contains EVOH or polyamide layers that are sensitive to thermal stress; EVOH layers exposed to sealing temperatures above 130 °C can develop microvoids at the tie-layer interface.

However, the downgauging limit of the sealant skin is different. A homopolymer PP skin can be downgauged to 3 µm because its higher modulus resists tearing during filling; SFC-750M at 3 µm may show pinholing in rough-handling distribution. Typical minimum sealant-layer thickness is 5–8 µm when the pouch will be used at 4 °C or below, and 8–12 µm for stand-up pouches with gusseted folds. Converters should validate puncture resistance via ASTM F1306.

On an extrusion laminating line with a 120 mm extruder and a T-slot die at 2,400 mm width, SFC-750M is applied at 15–20 µm onto aluminum foil or polyester film. The melt curtain is drawn at 30–50 m/min line speed and immediately nipped against the substrate at a chill roll temperature of 12–18 °C. If the melt curtain breaks, the cause is usually excessive melt temperature or moisture carryover from wet masterbatch; pre-drying of masterbatch at 70 °C for 2–3 h is specified when ambient relative humidity exceeds 60%.

Food-contact compliance for the grade is governed by FDA 21 CFR 177.1520(c) for olefin polymers in the United States and by EU No 10/2011 in Europe. Overall migration into food simulant D2 should be below 10 mg/dm² when measured by EN 1186-1; the exact value depends on the film structure and the additive package selected by the converter. For REACH, the resin is supplied with a declaration of compliance for substances of very high concern below 0.1 wt%. RoHS compliance for heavy metals is determined by IEC 62321 test methods. The resin does not contain intentionally added phthalates or bisphenol A.

Optical Haze, Gloss, and Overall Migration Limits Are Interrelated Through Crystallinity Control

The crystal population that governs seal initiation also controls optical haze. Because SFC-750M has a broader distribution of lamellar thicknesses, it avoids the large spherulitic superstructures that scatter light in homopolymer PP. On 50 µm cast film, haze is typically 1.2–1.8% per ISO 14782, and gloss at 60° is 120–140 GU per ISO 2813. The smaller crystallites reduce surface roughness, but they also create a more permeable amorphous fraction. For barrier-critical structures, the SFC-750M layer should be used as a sealant skin over a barrier core, not as a standalone barrier layer.

Migration and organoleptic performance are controlled by the same amorphous-phase mobility. Low-molecular-weight oligomers have higher diffusion coefficients in the butene-modified amorphous phase. Finished structures intended for fatty food contact above 40 °C should undergo sensory testing according to DIN 10955 or equivalent. Published data for specific migration of slip additives from SFC-750M into food simulant D2 is limited; converters should not extrapolate from propylene-ethylene random copolymer data.

Process limitations include autoclaving. The grade is not recommended for steam sterilization above 121 °C for periods longer than 30 min; at 135 °C, seal failure in a coextruded laminate may occur within 15–20 min due to partial melting of the sealant layer and edge creep.