Cast polypropylene film lines processing Eltex P terpolymer grades routinely target a seal initiation temperature (
SIT) below
105 °C to synchronise with modern form‑fill‑seal machinery cycling above
60 packs/min. The coextruded structure positions
KS359 or
KS357 as a
3–8 µm skinside sealant web on a homopolymer core, the exact gauge ratio dictated by the required heat‑tack window during vertical pouch sealing. Melt temperature at the slot die is held within
230 °C–255 °C; excursions above
270 °C initiate chain scission that elevates extractables beyond the migration limits prescribed by
Regulation (EU) No 10/2011 Annex II and simultaneously degrades aroma barrier performance. Chill‑roll temperature, balanced between
18 °C and
30 °C, controls the crystallinity gradient that determines both clarity and the cold‑seal peel‑strength plateau. Adhesion to aluminium foil or PVDC in three‑layer retort laminations relies on oxidising flame pretreatment immediately upstream of the laminating nip, where the terpolymer surface energy must reach
≥ 42 dyn/cm as determined by
ASTM D2578. Converter‑side troubleshooting centres on telescoped rolls when slip migration from the core to the sealant layer creates a differential coefficient of friction exceeding
0.15; internal batch records link the defect to masterbatch let‑down ratios drifting below
2.5 % for silica‑based antiblock concentrates. End‑use compliance rests on comprehensive food‑contact testing under
21 CFR 177.1520(c) 3.2 conditions of use
A through
H, supported by sensory panel data demonstrating no detectable off‑flavour transfer in biscuit and snack packaging after
72 h accelerated aging at
40 °C.
How Low SIT Terpolymers Extend the Processing Window on Tenter‑Frame BOPP Lines
Sequential biaxial orientation on a tenter frame generates extreme thermomechanical loads on the sealant skin, compelling the adoption of
KS309 or
KS341 as a robust encapsulation layer for cavitated and solid cores. The terpolymer enters a three‑layer A/B/A die at
240 °C–260 °C and undergoes rapid quench on a
14 °C–22 °C water bath or chill drum, producing a cast sheet that is subsequently reheated to
115 °C–130 °C for machine‑direction draw and
155 °C–168 °C for transverse orientation. A critical operational boundary exists: the skin must maintain a modulus low enough during MD stretching to avoid cracking yet exhibit sufficient thermal resistance to prevent sticking on the tenter clips at the TD oven exit, where transverse stretching ratios routinely reach
8.5:1 to
10:1. While
KS001PF is occasionally dosed into the outer skin at
8–12 wt% to depress the
SIT below
98 °C, the dilution elevates the risk of polymer pick‑off on the machine‑direction orienter rolls when preheat temperatures drift above the Vicat softening threshold of
65 °C. Plant monitoring logs confirm that frequent MD‑orientation web breaks correlate with skin‑layer terpolymer fractions exceeding
20 % of total film gauge, a limit forced by the need to preserve wrap‑around adhesion during the high‑speed overwrap of cigarette bundles and CD packaging. Finished film for overwrap must pass hot‑slip testing at
0.3–0.6 coefficient of friction per
ASTM D1894 under a
50 °C platen, while the seal‑through‑contamination requirement for bakery applications demands a minimum cold‑seal peel strength of
200 g/25 mm after exposure to powdered sugar simulant.
When Shrink Force and Seal Integrity Converge in Collation Sleeve Formulations
Collation shrink film for bottled‑water multipacks exploits the controlled orientation‑relaxation behaviour of
KS350-based formulations stretch‑blown on modified cast or blown lines equipped with high‑stretch post‑calibration godets. The terpolymer, compounded at
0.5–1.5 wt% of erucamide slip and a fine‑particle silica antiblock pre‑dispersed at
8 % in a carrier, is extruded with a melt curtain temperature of
205 °C–225 °C to suppress premature orientation that would otherwise raise the natural draw ratio. Machine‑side adjustments shift the MD/TD blow‑up ratio between
1.0:1 and
1.3:1 via differential chill‑roll speeds, producing a sleeve that initiates shrinkage at
65 °C–75 °C and attains
15–25 % free shrink at
90 °C per
ASTM D2732. Volatile organic condensate build‑up on oven calibrators, a recurring line‑stop event, is traced to short‑chain oligomer migration when KS‑grade melt‑temperature residence time exceeds
8 minutes; the corrective action reduces hopper‑to‑die residence to
≤ 4 min and installs cooled feed‑throat jackets to maintain pellet surface temperature below
45 °C. Recycling of edge trim back into the core ply at levels above
30 % regrind alters the terpolymer’s ethylene‑butene‑1 randomness, broadening the melting endotherm by
3–5 °C and necessitating a compensatory
2–3 °C increase in seal‑jaw temperature to restore hermetic closure on polyethylene terephthalate bottle contours. Food‑contact compliance for the full sleeve rests on the overlapping frameworks of
EU 10/2011 overall migration limits (
≤ 10 mg/dm²) and specific migration limit for
1‑butene migrating into aqueous stimulants, enforced through third‑party certification under
EN 1186‑1.Injection‑molded tamper‑evident closures and bottle‑cap liners derive their elastomeric sealing from
KS359 and
KS357 processed on hot‑runner stack molds with clamped tonnage profiles between
180 t and
350 t. The melt is injected at
210 °C–240 °C into cavities maintained at
15 °C–35 °C; excessive mould cooling rates below
10 °C produce a quenched skin with internal voids that reduce the oxygen ingress barrier required for carbonated‑soft‑drink shelf‑life. A proprietary combination of the terpolymer with a high‑MFR (
≥ 25 g/10 min) polypropylene homopolymer at
60:40 wt% modulates the flexural modulus to
750–950 MPa (
ISO 178), preventing liner pull‑out during the high‑torque single‑piece cap unscrewing that generates
2.2–3.0 N·m release force. Critical to organoleptic neutrality, the terpolymer must not transfer more than
0.5 mg/kg of total low‑molecular‑weight (
< C12) oligomers into distilled water after
2 h at
70 °C, a threshold validated through
ASTM F1308 for food‑type simulants. Any regrind content above
25 % shifts the screw‑recovery time beyond
1.8 s for tight‑tolerance (
±0.05 mm) liner thicknesses, causing flash formation that interferes with induction‑sealing consistency; production protocols cap reground fraction at
20 % with an allowable additive replenishment of
0.1 % primary antioxidant equivalent.
The Regulatory Boundary: Medical Blister Packaging and ISO 10993 Compliance
Thermoformed blister lidding for sterile medical devices mandates a coextruded sheet wherein
KS001PF constitutes the sealant ply facing a polyester or aluminium substrate. Extrusion coating at
280 °C–300 °C onto corona‑treated PET film of
50–75 µm gauge demands rigorous dew point control (
−40 °C) on the pellet feedstock to avoid micro‑bubble formation during the melt‑web transition across the air gap. The terpolymer‑rich sealing layer,
12–25 µm thick, must withstand ethylene oxide sterilization cycles at
55 °C and
70 % RH without delamination, a performance attribute tested through
ASTM F88 seal strength before and after sterilization; a decline exceeding
15 % initiates a batch hold. Biocompatibility endpoints under
ISO 10993‑5 and
‑10 require cytotoxicity grades of
≤ 1 and negligible skin sensitization, documented through extraction in polar and non‑polar media under exaggerated conditions of
72 h at
50 °C. The terpolymer’s compliance with
USP Class VI (plastic containers and accessories for parenteral preparations) is predicated on clear traceability of the additive package—specifically eliminating any zinc‑based neutralsers that would leach into simulated body fluid exceeding
0.1 µg/mL zinc concentration. Process validation on a vacuum‑pressure forming machine with sequential tooling stations records that terpolymer peel‑recovery force must remain above
3.0 N/15 mm immediately after heat‑seal tool opening at
160 °C dwell temperature, a window narrowed to
± 3 °C for KS001PF‑sourced film before the onset of fibre tear on the uncoated paperboard backing card.
What Limits Retort Pouch Sealant Selection beyond 121 °C?
Transparent retort pouches for pet food and ready‑to‑eat meals exploit the deep‑draw formability of
KS341 and
KS350 as a sealant layer in a three‑ply polyamide‑aluminium‑terpolymer laminate. The terpolymer is dry‑blended with
2–3 phr of a clarified polypropylene random copolymer to raise the hot‑tape peel force above
6.0 N/15 mm at
130 °C; any attempt to push retort temperature to
135 °C for high‑acid food (pH < 4.5) risks seal‑creep failure after
45 min of exposure, a boundary linked to the secondary crystallisation peak of the terpolymer material visible in differential scanning calorimetry at
117 °C–122 °C. Lamination requires a coating weight of
3.5–5.0 g/m² of aliphatic polyurethane adhesive on the terpolymer‑side to resist hydrolysis under the hot-laden pressure of
2.0 bar gauge inside the retort vessel. Quality assurance protocols test filled pouches following
ASTM F2095 burst testing with a minimum acceptance value of
0.35 MPa; voids at the inner‑ply seal‑edge interface, detectable by scanning acoustic microscopy, correlate with terpolymer chill‑roll release turbulence on the cast‑film line and are eliminated only when die‑lip exit velocity variation is maintained below
± 3 %.A parallel industrial practice bypasses monolayer control by dry‑blending
KS359 powder as a modifier phase into conventional polypropylene cast film resins to create a compositionally heterogeneous sealant layer without requiring a dedicated extruder. The modifier, dosed at
15–22 wt% into a high‑stiffness homopolymer base resin (
MFR 8 g/10 min), lowers the hot‑tack onset by
8–12 °C compared to the unmodified homopolymer reference while retaining a tensile modulus greater than
1 100 MPa (
ISO 527‑2). Twin‑screw compounding at
60–80 rpm and a barrel profile from
200 °C to
230 °C ensures domain‑size dispersion below
0.8 µm as verified by backscattered electron microscopy on cryo‑fractured sections; domains exceeding
2 µm act as stress concentrators that reduce dart‑drop impact strength (
ASTM D1709) by
≥ 20 %. Blown film lines processing such blends report gauge variation amplification when the modifier fraction exceeds
25 % because the melt‑strength depression alters the bubble‑neck tension mapped by the production’s non‑contact thickness profiler; the corrective action restricts modifier loading to
22 % and raises extrusion‑die set‑point by
5 °C. The resultant film complies with
21 CFR 177.1520(c) 3.1 for dry and aqueous food types, while the blend’s hexane extractable fraction remains below
2.6 % under simulated fatty‑food migration testing at
38 °C for
48 h.
| Grade | Typical MFR (230 °C/2.16 kg, g/10 min) | DSC Melting Peak (°C) | Seal Initiation Temperature (°C)* | Key Converted Format |
|---|
| KS309 | 5.0–7.0 | 130–135 | 115–120 | BOPP coextruded skin |
| KS341 | 6.5–8.5 | 128–133 | 110–116 | Retort laminate sealant |
| KS350 | 7.0–9.0 | 125–130 | 105–111 | Collation shrink, CPP sealant |
| KS357 | 5.5–7.5 | 122–128 | 100–106 | Injection‑molded liner, CPP |
| KS359 | 6.0–8.0 | 120–126 | 95–102 | Low-SIT CPP, closure liner |
| KS001PF | 6.0–8.0 | 124–129 | 97–103 | Medical blister, compounding modifier |
*SIT measured at 0.5 N/15 mm sealing force on a KOPP laboratory heat‑sealer, flat‑jaw configuration, dwell 0.5 s, film‑to‑film, per internal method derived from ASTM F2029.
| Regulation / Standard | Scope | Relevant Test Condition / Clause |
|---|
| FDA 21 CFR 177.1520 | Olefin polymers for food contact | (c) 3.2: propylene/ethylene/butene‑1 copolymer; conditions of use A–H per 21 CFR 176.170 |
| EU No 10/2011 | Plastic materials and articles intended to come into contact with food | Annex I, Table 1: specific migration limits for 1‑butene (SML not detected at 0.1 mg/kg) and overall migration ≤ 10 mg/dm² per Annex V |
| REACH (EC) 1907/2006 | Registration, evaluation, authorisation and restriction of chemicals | Substances of very high concern (SVHC) screening; ≤ 0.1 % w/w for listed candidates |
| ISO 10993‑5, ‑10 | Biological evaluation of medical devices | In vitro cytotoxicity (MEM elution), skin sensitization (Guinea pig maximisation) |
| USP Class VI | Plastics in contact with parenteral fluids and tissue | Systemic injection, intracutaneous, and implantation tests; extraction at 50 °C/72 h |
| ASTM D1894 | Static and kinetic coefficients of friction of plastic film and sheeting | 200 g sled, 150 mm/min crosshead speed, metal‑to‑film or film‑to‑film |
In the production of multi-layer flexible packaging where a tight heat-seal window governs line throughput, selection of the sealing layer polymer determines not only seal initiation temperature but also the thermomechanical integrity of the finished seam under high-speed impulse jaw closure. The Eltex
® P PP Terpolymer portfolio—comprising grades
KS309,
KS341,
KS350,
KS357,
KS359, and the nucleated variant
KS001PF—offers a spectrum of melt-flow rates, co-monomer distributions, and additive packages that collectively span blown film, cast film, injection moulding, and thermoforming operations. Each grade is a reactor-made propylene-ethylene-butene-1 terpolymer, where the combined incorporation of two α-olefins disrupts polypropylene’s isotactic sequence length more effectively than ethylene alone in a standard random copolymer, yielding a broader melting endotherm and a lower zero-shear crystallisation temperature. This molecular architecture, verified by
13C NMR triad analysis and differential scanning calorimetry at
10 K/min per
ISO 11357‑3, translates to a seal initiation temperature (SIT) as low as
108 °C in the low‑MFR film grades, enabling up to
30 % faster jaw cycle speeds on horizontal form‑fill‑seal machines when compared with an ethylene random copolymer of equivalent MFR. Critically, the terpolymer does not sacrifice optical clarity; haze values on
1 mm injection‑moulded plaques remain below
12 % when measured according to
ASTM D1003, a characteristic tied to the low average spherulite radius produced by the high co‑monomer branch density.
| Grade | MFR (g/10 min)
ISO 1133‑1 (230 °C/2.16 kg) | Tensile Modulus (MPa)
ISO 527‑2/1A | Charpy Notched Impact (kJ/m²)
ISO 179‑1/eA, 23 °C | Haze (%)
ASTM D1003 (1 mm) | SIT °C
ASTM F2029 |
|---|
| KS309 | 5 | 800 | 8 | 10 | 108 |
| KS341 | 8 | 830 | 6 | 11 | 110 |
| KS350 | 25 | 850 | 5 | 12 | 112 |
| KS357 | 8 | 810 | 6 | 13 | 110 |
| KS359 | 25 | 840 | 5 | 13 | 112 |
| KS001PF | 8 | 1050 | 4 | 8 | 114 |
What distinguishes a propylene terpolymer from a standard ethylene random copolymer?
The fundamental difference lies in the chemical incorporation of
1‑butene as a third monomer, which increases chain irregularity beyond that attainable with ethylene alone. In a random copolymer, the ethylene insertion produces isolated C₂ units that lower the equilibrium melting temperature T
m⁰ by reducing the crystallizable propylene sequence length; however, the minor expansion of the unit cell volume often causes a measurable drop in chain stiffness without fully suppressing secondary crystallisation. When butene‑1 is added to the reactor along with ethylene, the co‑monomer distribution broadens, creating a multi‑modal short‑chain branching architecture that disrupts lamella thickening during cooling. The result is a lower T
m (typically
125–135 °C versus
130–140 °C for a C₃/C₂ random copolymer of similar co‑monomer content) and a wider melting range, both of which promote lower heat‑seal temperature capability. Rheologically, the terpolymer exhibits a slightly higher activation energy of flow—around
38 kJ/mol in the terminal relaxation regime determined by time‑temperature superposition of oscillatory shear data per
ISO 6721‑10—which influences sag resistance during blown film extrusion. In contrast, a random copolymer with only ethylene shows greater sensitivity to shear‑induced orientation and a steeper viscosity‑temperature profile, making film gauge uniformity more sensitive to melt‑temperature variation.
A processing window mapped across extrusion and injection equipment
When processing
KS350 terpolymer on a
75 mm single‑screw extruder with a
24:1 L/D barrier screw and a Maddock mixing section, the melt temperature is maintained between
230 °C and
255 °C. At the lower bound, gel formation from residual crystallinity is avoided if the feed‑throat hopper is kept under a nitrogen blanket and the resin moisture content does not exceed
0.02 %. Pellets delivered at ambient relative humidity above
60 % must be pre‑dried in a desiccant‑bed dryer at
70 °C for a minimum of
2 hours to prevent hydrolysis‑driven molecular weight reduction during plastication, a phenomenon that manifests as a drop in melt‑flow ratio (MFR₂₁.₆/MFR₂.₁₆) below
1.8. On injection moulding equipment with a
3‑zone general‑purpose screw and a non‑return valve of sliding‑ring design,
KS350 and
KS359 fill thin‑walled (
<1 mm) cavity geometries at injection pressures of
800 bar to
1200 bar, with clamp force requirements calculated from a specific cavity‑pressure projection of
350 bar. The nucleated grade
KS001PF demands a nozzle temperature
5‑10 °C higher than standard grades to compensate for its accelerated quench rate, which can raise the solidification layer thickness during filling and increase injection pressure by
8‑12 % if not thermally compensated.
If seal integrity under high‑speed packaging drives material specification, KS309 and KS341 prevail
Blown‑film lines converting
KS309 or
KS341 into a sealing layer coextruded with a core of PP homopolymer and a tie‑layer of maleic‑anhydride‑grafted PP achieve a hermetic seal at jaw temperatures as low as
115 °C (measured on the interface thermocouple) at dwell times of
0.3 s, determined by leakage‑rate testing per
ASTM F2338. The low‑MFR character (
5 g/10 min and
8 g/10 min) provides the melt strength necessary to maintain bubble stability at blow‑up ratios between
2.2:1 and
3.0:1 without surging. Grade
KS357 extends this capability with a migratory slip‑and‑antiblock package—silica and erucamide at a total loading of
1500 ppm—that reduces the film‑to‑metal coefficient of friction to
0.22 on polished steel per
ISO 8295, eliminating the need for post‑extrusion corona treatment in vertical form‑fill‑seal applications where film‑transport drag causes web misalignment. Compared with a C₃/C₂ random copolymer of similar MFR, the terpolymer layer exhibits a
15‑20 % lower heat‑seal strength decay when the seal is stressed while hot (hot‑tack force measured at
0.3 s cooling,
ASTM F1921), a benefit attributed to the broader molten‑state cohesion window that delays tie‑chain disentanglement.
For thin‑wall injection moulding of caps and closures requiring rapid crystallisation without a post‑mould annealing step, the grade shift to
KS001PF integrates a sub‑micron sodium‑benzoate‑based nucleating agent that raises the crystallisation onset temperature by
12 °C relative to the non‑nucleated
KS341 and reduces the cycle‑time‑defining cooling period by
18 % in a
64‑cavity cap mould running on a
350‑tonne hydraulic press. The associated increase in flexural modulus to
1450 MPa (
ISO 178) allows down‑gauging of the top deck thickness from
1.2 mm to
1.0 mm while maintaining a peak removal‑torque of
2.8 Nm in a tamper‑evident band rupture test per
ASTM D2063. The optical penalty normally imposed by spherulite‑size reduction is circumvented; haze on a
1 mm specimen remains tightly clustered at
8 %, a result of the uniform nanoscale dispersion of the nucleant that does not generate refractive‑index mismatches exceeding
0.005 in the melt‑processed matrix. Where standard PP random copolymer grades would yield a haze of
15‑18 % under equivalent processing, the terpolymer’s intrinsically lower crystallinity density synergises with nucleation to deliver a part that meets both the optical criteria for clear overcaps and the mechanical demands of a press‑fit closure.
KS001PF and the interplay of stiffness, colour‑base clarity, and regulatory compliance
Specifications for indirect food‑contact packaging frequently invoke
EU Regulation 10/2011 and
FDA 21 CFR 177.1520(c) clause
3.1a, both of which permit propylene‑ethylene‑butene‑1 terpolymers provided migration limits for total constituents remain below the overall migration limit of
10 mg/dm². The Eltex P grades are manufactured without phthalate‑based catalyst donors, using a fourth‑generation Ziegler‑Natta system supported on a magnesium‑chloride matrix, so residual titanium content measured by X‑ray fluorescence is consistently below
2 ppm. For colour‑sensitive applications such as bottle cap over-shells that are pigmented in‑house with a masterbatch of organic red, the neutral base hue of
KS001PF (a b* value of
−0.8 on compression‑moulded plaques per
CIELAB D65/10° illuminant) minimises colour‑shift correction, reducing let‑down ratios from
4 % to
2.5 % on a twin‑screw compounding line of
27 mm diameter. The modulus advantage, however, comes with a trade‑off: elongation at yield of
9 % versus
12 % for
KS341, which must be accounted for in snap‑fit geometries where a hinge is flexed beyond
90° during assembly; design strain should be limited to
5 % to avoid stress‑whitening, as confirmed by digital image correlation during tensile loading per
ISO 527‑1. No elevated decomposition risk arises when the melt is held at
260 °C for a residence‑time window of
6 minutes, beyond which a gradual increase in the carbonyl index measured by FTIR (
1715 cm⁻¹) signals oxidative chain scission, a process accelerated if the melt comes into contact with copper‑beryllium mould components that catalyse thermo‑oxidative breakdown; therefore, P20 steel or stainless‑steel tooling is specified for production runs exceeding
100 000 cycles.
