Sealant-layer curtain stability and hot tack on cast coextrusion lines for 90 °C hot-fill queues

Dow FLEXOMER VLDPE 1138, an ethylene/1-octene copolymer with nominal density 0.902 g/cm³ measured per ASTM D1505 and melt index 0.5 g/10 min measured per ISO 1133-1:2022 at 190 °C/2.16 kg, is specified in three-layer and five-layer cast coextrusion structures as the heat-sealable skin for flexible food packaging where reduced seal initiation temperature and high hot tack are required on vertical form-fill-seal and horizontal flow-wrap lines. The resin’s lower crystallinity compared with conventional LLDPE reduces the seal onset, but the 0.5 g/10 min melt index raises extruder backpressure and limits the minimum curtain thickness before draw resonance becomes unstable. In production, the sealant skin is metered at 8–20 µm of a total gauge of 40–90 µm, with core layers based on LLDPE or LDPE and tie layers where polyamide or EVOH barrier polymers are used. The formulation addition ratio: the sealant layer may be run at 90–100 wt% FLEXOMER VLDPE 1138 when the filling line demands seal initiation below 90 °C, or at 60–80 wt% with LDPE on lines running above 300 m/min; LDPE addition above 30 wt% raises seal initiation temperature and sacrifices hot tack, so the ratio is adjusted against packaging-machine dwell time and seal-bar geometry. Industry compliance for direct food contact is governed by FDA 21 CFR 177.1520(c) for olefin polymers, Regulation (EU) No 10/2011 Annex I and Annex II with overall migration limit 10 mg/dm² tested per EN 1186-1, and GB 4806.7-2016 for the finished multilayer structure. The downstream production process is cast film extrusion through a 0.3–0.8 mm die gap at melt temperatures of 210–240 °C, with a chill-roll temperature of 18–24 °C and an air knife or vacuum box to stabilize the melt curtain; the sealant skin is extruded at a lower temperature than the core to reduce gel formation from low-density fraction overheating. Terminal finished product types include pre-made pouches, lidding film for polypropylene or PET trays, frozen-food flow wrap, pillow packs for dry mixes, and hot-fill lidding for pasteurized products. The primary processing boundary is that the 0.5 g/10 min melt index demands a high-shear screw and narrow die-gap setting; at chill-roll temperatures above 28 °C, seal-layer blocking during windup becomes a measurable yield-loss mechanism.

What changes when a 0.902 g/cm³ VLDPE replaces LDPE in liquid carton extrusion coating?

In liquid-tight paperboard structures for gable-top cartons, portion packs, and cup stock, FLEXOMER VLDPE 1138 is introduced into the extrusion coating layer to reduce flex-crack failure at crease lines and to permit lower seal initiation on the filling line. The resin is commonly blended with autoclave LDPE at 15–35 wt% FLEXOMER VLDPE 1138; above 35 wt% the coating layer may exhibit excessive neck-in and reduced drawdown because the 0.5 g/10 min melt index is lower than typical coating-grade LDPE. Industry compliance standards for food-contact coated board include FDA 21 CFR 176.170(c) for components of paper and paperboard in contact with aqueous and fatty foods, Regulation (EU) No 10/2011 with overall migration tested per EN 1186-1, and GB 4806.8-2016 for food-contact paper and board in China. The production process is extrusion coating onto 12–24 g/m² aluminum foil or corona-treated paperboard at melt temperatures of 285–320 °C, line speeds of 150–300 m/min, and an air gap of 100–250 mm; adhesion to foil typically relies on 0.8–1.5 kW ozone treatment or a peroxide-containing LDPE layer, while the back-side heat-seal coating may use a VLDPE-rich skin layer. Terminal finished product types include gable-top liquid cartons, aseptic portion cups, ice-cream board, and laminated sachet reel stock. A noted limitation is that the low melt index of FLEXOMER VLDPE 1138 can raise melt pressure in a 90 mm single-screw extruder above 180 bar if the resin is run neat; converters therefore generally limit the neat fraction to coating layers above 25 g/m², and published data for neat VLDPE 1138 below 15 g/m² on high-speed lines remain limited.

Cast pallet stretch film operations specify FLEXOMER VLDPE 1138 in the cling or puncture-resistance layer of a three-layer A/B/C construction where the core contains linear LLDPE and the skin contains low-melt polyisobutylene tackifier. The addition ratio of FLEXOMER VLDPE 1138 is typically 20–35 wt% of the total polyolefin blend in the cast layer, with the balance a C6 or C8 metallocene LLDPE of melt index near 2.5–4.0 g/10 min; at ratios above 40 wt%, the 0.5 g/10 min melt index of 1138 reduces overall melt flow and increases motor load on the cast line extruder, while below 15 wt% the improvement in puncture and elongation becomes difficult to quantify in routine production QC. Industry compliance for industrial stretch film includes ASTM D5458-12 for cling, ASTM D5748-12 for protrusion puncture resistance, and ISO 527-3 for tensile elongation; where the stretch film is used for indirect food contact on palletized consumer goods, the formulation must also meet FDA 21 CFR 177.1520(c) if migration from the film is plausible. The downstream process is cast film extrusion on a 75–120 mm extruder with a 0.3–0.6 mm die gap, melt temperatures of 230–260 °C, and a chill-roll setpoint of 18–22 °C; the film is wound at 450–700 m/min and pre-stretched 200–300% on the packer or pre-stretch carriage. Terminal finished product types include machine film for high-speed rotary wrapping, hand film in 15–20 µm gauges, and agricultural bale wrap where puncture resistance is critical. A production bottleneck observed on cast lines running high VLDPE fractions is feedthroat bridging from soft low-density pellets; hopper agitation and a grooved feed section with water-cooled throat are recommended when the addition ratio exceeds 30 wt%.

When a low-smoke jacket compound must retain elongation at −25 °C under IEC 60502-1

Halogen-free flame-retardant cable jacket compounds based on LDPE/LLDPE and ethylene-vinyl acetate blended with magnesium dihydroxide or aluminum trihydroxide use FLEXOMER VLDPE 1138 as a low-temperature flexibility and elongation modifier without shifting the compound into elastomer-rubber classification. The addition ratio is 10–25 wt% of the total polymer fraction, replacing LDPE/LLDPE while maintaining the total polymer loading at 30–40 wt% against 60–70 wt% inorganic flame-retardant fillers; above 25 wt% the compound’s tensile strength may fall below the 9 MPa commonly required by cable jacket specifications, and below 10 wt% the improvement in low-temperature elongation is not measurable by routine QC. Compliance standards include IEC 60502-1:2021 for low-voltage power cable jackets, UL 1581 for cable insulation and jacket test methods, EN 50618 for photovoltaic cable, REACH regulation EC No 1907/2006, and RoHS Directive 2011/65/EU for restricted substances. The downstream production process is two-stage: a twin-screw compounding step on a 45–75 mm co-rotating machine with L/D 44–52 and melt temperature 150–170 °C to avoid decomposition of ATH/MDH, followed by cable jacket extrusion at 150–180 °C on a 90–120 mm single-screw line with a draw-down ratio between 1.5:1 and 2.5:1. Terminal finished product types include low-smoke zero-halogen industrial control cable jackets, solar PV cable sheathing, mining cable jackets, and mass-transit wire sheathing. A field-observed failure mode occurs when the compound is processed above 180 °C because ATH releases water and creates surface porosity; therefore the melt-temperature window is treated as a hard limit in production.

Silage bale wrap and agricultural blown-film structures in northern-crop regions require a combination of dart impact resistance, fold-crack resistance, and UV stabilization that is not met by standard LLDPE alone. FLEXOMER VLDPE 1138 is blended into the middle or inside layer of a three-layer blown film at 15–30 wt% of the total polyolefin fraction, with the outside layer containing UV-stabilized LLDPE and the inside layer containing tackified or slip-modified LLDPE; the addition ratio above 30 wt% is discouraged because the 0.5 g/10 min melt index reduces bubble stability and increases die residence time during gauge changes, while below 15 wt% the flex-crack resistance gain is difficult to quantify in short-run QC testing. Compliance reference points for agricultural films include EN 13207:2001 for silage thermoplastic films and EN 13206:2017 for agricultural greenhouse and low-tunnel covers, with mechanical tests such as ISO 527-3 for tensile properties, ISO 6383-2 for tear resistance, and ASTM D1709 for dart impact. The production process is multi-layer blown-film extrusion on a 65–90 mm grooved-feed extruder, die gap 1.0–1.6 mm, blow-up ratio 2.0:1–2.8:1, and frost-line height controlled at 600–900 mm above the die; the film is wound as 750 mm or 1500 mm bale-wrap reels with 25–50 µm gauge. Terminal finished product types include round bale silage film, greenhouse side sheets, and temporary silage clamp covers. Published data for FLEXOMER VLDPE 1138 specifically in UV-resistant agricultural outside layers is limited; the resin is therefore recommended for buried or shaded layers rather than prolonged direct-UV exposed surfaces unless the stabilizer masterbatch is validated at the converter’s own QUV protocol.