At a melt index of 3.5 g/10 min measured per ASTM D1238 at 190 °C and 2.16 kg, and a density of 0.918 g/cm³ measured per ASTM D1505, ExxonMobil Exceed mLLDPE 3518CB is processed on a three-layer A/B/A cast stretch line with a die width of 2,200 mm and a maximum backing roll speed of 600 m/min. The core layer consists of 100 wt% 3518CB and occupies 60–70% of total web thickness. The cling layer is metered at 97.0–98.5 wt% 3518CB plus 1.5–3.0 wt% polyisobutylene tackifier masterbatch. The release layer is metered at 98.5–99.5 wt% 3518CB plus 0.5–1.5 wt% silica-based antiblock masterbatch. Barrel temperatures are set from 180 °C in the feed zone to 270 °C at the adapter; melt temperature at the die is held between 274 °C and 285 °C. The die gap is 0.45 mm to 0.65 mm. The air gap is 30 mm to 40 mm. Chill roll temperature is 18 °C to 24 °C. The finished film is slitted at 500 mm widths for machine wrap and 250 mm to 450 mm widths for hand wrap, with thickness from 12 µm to 35 µm. Compliance for the olefin polymer base in food contact is governed by 21 CFR 177.1520 and, for EU markets, Regulation (EU) No 10/2011; the tackifier and antiblock masterbatches require separate end-use migration evaluation. Pre-stretch on a powered carriage is set between 200% and 250%. Cling retention is measured with ASTM D5458; puncture propagation resistance is measured with ASTM D5748. At pre-stretch above 250% on 12 µm film, edge tear and transverse thickness variation increase unless the gauge control system maintains final film thickness tolerance within ±1.5% across the web.

Why Does Chill Roll Release Limit Line Speed Below 450 m/min?

High-speed cast film made with 3518CB fails at the chill roll interface before the extruder becomes pressure-limited when the release surface is not managed. At line speeds above 450 m/min, the polymer melt exits the die at 270–285 °C and quenches within 40–60 ms. Chill roll release is governed by the static coefficient of friction between the film and the matte or polished roll, measured per ASTM D1894. A static COF above 0.45 increases the risk of blocking on the roll and micro-tearing in the cast web. A static COF below 0.15 causes slip and air entrapment between the web and the chill roll, reducing heat transfer. The resulting quench rate variation changes crystalline orientation in the machine direction and produces bands of low elongation at the slitting edge. The formulation uses 0.5–2.0 wt% of a silica-based antiblock masterbatch with a median particle size of 2–4 µm in the release layer. Chill roll temperature is controlled between 18 °C and 24 °C with a water-side ΔT of 2 °C across the roll face. Release layer thickness is maintained at 1.0–2.0 µm. Terminal products in this configuration are 23 µm machine stretch wrap and 15 µm hand wrap. Regulatory compliance for the base resin falls under 21 CFR 177.1520 and Regulation (EU) No 10/2011; the antiblock masterbatch must comply with the relevant additive positive list. A limitation is the need for periodic roll cleaning after 8–12 h of continuous operation when low molecular weight species migrate to the film surface and transfer to the chill roll.

When 3518CB is coextruded as a heat-seal layer in form-fill-seal lamination, the sealant web is typically 10–15% of the total film thickness. The layer composition is 95–100 wt% 3518CB with 0–5 wt% slip and antiblock masterbatch, depending on slip requirements. The sealant layer is processed at a melt temperature of 255–270 °C without pre-drying at ambient humidity below 60% RH. The die gap is set at 0.60 mm and the line speed is maintained between 150 m/min and 250 m/min. Seal initiation temperature is measured per ASTM F88 on a 25 µm sealant layer after a 0.5 s dwell and 2.0 bar seal pressure; typical onset for standard mLLDPE cast films is between 85 °C and 95 °C, but converter-specific values must be confirmed because additive package and film thickness shift the curve. Hot tack force is measured per ASTM F1921 immediately after seal opening. The finished structure is used for dry food pouches, frozen vegetable bags, and milk powder sachets. Food contact compliance is established through 21 CFR 177.1520 for the polyolefin base and Regulation (EU) No 10/2011 with an overall migration limit of 10 mg/dm² for the final laminated structure. If the sealant layer is corona-treated before lamination, the surface energy should not exceed 38–42 dyn/cm measured per ASTM D2578, because higher treatment levels accelerate oxidation byproducts that reduce hot tack uniformity.

Screw Temperature Profiles and Gel Formation in 30:1 L/D Cast Lines

Cast sheet lines running 3518CB with barrier screws of 30:1 L/D and compression ratio 2.5:1 exhibit pressure instability when the feed throat temperature exceeds 60 °C. The recommended barrel set profile begins at 180 °C in zone one, 210 °C in zone two, 240 °C in zone three, and 260 °C in the adapter. Melt temperature measured by an immersion thermocouple before the die is maintained between 265 °C and 275 °C. At melt temperatures above 285 °C, oxidative gel formation in the die lip region increases over a 4–6 h run, with gel counts detected by a 50 µm resolution camera system. A startup purge ratio of 70 wt% fractional melt LDPE and 30 wt% 3518CB is used to reduce die-lip polyethylene oxidation during line stops longer than 15 min. The die gap is 0.5 mm. The air gap is 25 mm. Chill roll temperature is 20 °C. Finished film produced under these conditions is used for surface protection tape and neutral backing films. Mechanical properties are tested per ASTM D882; density is verified per ISO 1183-1. The base resin is not hygroscopic, but pre-drying is required at relative humidity above 60% for 2 h at 70 °C to avoid surface splay on film edges. The limitation is that metallocene-catalysed 3518CB has a narrower shear-thinning window than Ziegler-Natta LLDPE; extruder screw speeds above 120 rpm on 45 mm screws can generate melt pressure above 350 bar, which accelerates screw wear and adds shear heat beyond the set profile. Industrial surface protection films in this segment are assessed under REACH Article 33 SVHC disclosure and RoHS Directive 2011/65/EU for lead, cadmium, mercury, hexavalent chromium, PBBs, and PBDEs.

Substituting 3518CB into conventional LLDPE blown-film formulations at 70–85 wt% creates a bubble with lower melt strength than a Ziegler-Natta LLDPE. A typical blend is 80 wt% 3518CB and 20 wt% LDPE with melt index 0.25 g/10 min per ASTM D1238 to restore bubble stability. The blown-film line uses a 250 mm die, die gap 1.2 mm, blow-up ratio 2.5:1, and melt temperature 195–210 °C. Frost line height is maintained at 350–450 mm above the die face. Final film thickness is 40–70 µm. Blending is done by gravimetric feeders at the feed throat; no pre-compounding is required when the LDPE is added at 20 wt% or less. The film is printed and converted into frozen vegetable pouches and freezer bags. Cold-temperature impact is measured by ASTM D1709 Method A after conditioning at −20 °C for 24 h. Tear resistance is measured by ASTM D1922 in the machine direction after conditioning at 23 °C and 50% RH. Food contact compliance is governed by 21 CFR 177.1520 and Regulation (EU) No 10/2011; migration testing for the printed film is required for the finished package. The limitation is that lower blow-up ratios below 2.0:1 increase machine-direction tear strength but reduce transverse-direction impact resistance, so the optimum for frozen food is 2.5:1 to 3.0:1.

If 3518CB Replaces Conventional LLDPE in Heavy-Duty Industrial Liners

A three-layer blown-film structure for 100–150 µm industrial liners can replace 60–70 wt% of a conventional Ziegler-Natta LLDPE with 3518CB while retaining the remaining 30–40 wt% as fractional-melt LDPE. The blend is processed on a 1,200 mm die with die gap 1.5 mm, blow-up ratio 3.0:1, and melt temperature 200–215 °C. A carbon black masterbatch is added at 2–4 wt% only in the outer layers for UV resistance; the core remains unpigmented to preserve dart impact resistance. Dart impact is tested per ASTM D1709 Method B after conditioning at 23 °C and 50% RH. Elmendorf tear is tested per ASTM D1922. The finished liners are used for construction debris, mineral fillers, and bulk resin packaging. Compliance is limited to industrial packaging; the carbon black masterbatch must meet REACH and RoHS Directive 2011/65/EU restrictions. The operational boundary is that addition of recycled post-industrial LLDPE above 15 wt% increases gel defects and lowers puncture propagation resistance beyond acceptable limits unless a 100 µm continuous melt filter is installed before the die.

Surface Protection Films Demand a Tighter Melt Temperature Band Than Standard Cast Film

For extruded surface protection film, 3518CB is cast as a 30–60 µm backing web with an adhesive layer coextruded through a two- or three-layer feedblock. The backing layer is 90–95 wt% 3518CB; the remainder is a slip masterbatch. The adhesive layer is a hydrogenated styrenic block copolymer or acrylic formulation at 5–10 wt% of the total structure. Melt temperature in the backing layer is held between 265 °C and 275 °C, narrower than standard cast film because higher temperatures increase low molecular weight extractables that migrate into the adhesive and reduce peel adhesion. The die gap is 0.40 mm. The air gap is 20 mm. Chill roll is polished to Ra 0.02–0.05 µm and maintained at 15–20 °C. Thickness uniformity is monitored by a beta gauge and held within ±1.0% of nominal. The finished film is slit to 1,000–1,500 mm rolls and used for temporary protection of stainless steel, coated metal, and laminated panels. Peel adhesion is measured per ASTM D3330. The backing film tensile strength and elongation are measured per ASTM D882. Regulatory compliance is based on REACH, RoHS 3 Directive (EU) 2015/863 amending Annex II of Directive 2011/65/EU, and the absence of phthalates listed in Entry 51 of Annex XVII to REACH when the adhesive is formulated. The limitation is that reels stored above 35 °C show adhesive transfer to the backing due to micro-migration of oligomers from the mLLDPE surface.