Why Cast Pallet Stretch Film Lines Use Clearflex CH D0 as the Core Layer in Sub-12 µm Machine Wrap?

The nominal density of 0.900 g/cm³ and melt flow rate of 2.5 g/10 min at 190 °C/2.16 kg position this grade in the very low density polyethylene class, where reduced crystallinity relative to C4-LLDPE at 0.918 g/cm³ lowers tensile modulus and raises elongation at break under ISO 527-3. On a three-layer cast film line equipped with a 30:1 L/D barrier screw, a 200 mm slot die, an air gap of 120–180 mm, and a chill roll maintained at 18–25 °C, the grade is blended at 65–85 wt% in the core with a C6-LLDPE of 0.918 g/cm³ to recover machine-direction yield stress while retaining puncture resistance. The cling skin is compounded with 2–4 wt% polyisobutylene and 2000–5000 ppm silica antiblock, because the high amorphous fraction of CH D0 accelerates PIB migration to the film surface; cling force is measured at 25.4 mm/min crosshead speed according to ASTM D5458, and film is rejected for machine wrap if cling falls below 50 g/cm after 24 h ageing at 23 °C. Puncture resistance is measured with ASTM D5748 at 250 mm/min, and the down-gauging limit is set by the ability of the core to survive 250% prestretch on a rotary wrapping head without transverse tear propagation; the machine-direction Elmendorf tear should not fall below 300 g when tested under ASTM D1922. Draw resonance is observed when the melt draw ratio exceeds 30:1, and it is controlled by increasing the air gap to 180 mm, raising melt temperature to 230 °C, or reducing the die gap to 0.45 mm. Waste from core-layer melt fracture rises when the second barrel zone is below 190 °C because unmelted high-viscosity C6-LLDPE creates a rheological mismatch with the low melting point CH D0; gear-pump inlet pressure is therefore kept below 80 bar and screen-changer differential below 25 bar to avoid shear-induced gels.

In blown-film extrusion for frozen-food liners and flexible low-temperature pouches, the low crystalline fraction of Clearflex CH D0 reduces the modulus increase observed after conditioning at −18 °C for 24 h. The bubble is run on a grooved-feed extruder with a 30:1 L/D screw, a 200 mm spiral mandrel die, a die gap of 1.2–1.8 mm, and internal bubble cooling with a blow-up ratio of 2.2:1–2.8:1. Melt temperature is held between 180 °C and 205 °C because prolonged exposure above 220 °C generates gel particles and odour in the liner. The frost line height is set at 6–8 die diameters to balance machine-direction and transverse-direction Elmendorf tear measured by ASTM D1922, which prevents zipper tear during notched opening of the pouch. A process blend containing 10–20 wt% LDPE with a melt index of 0.3–0.8 g/10 min stabilizes the bubble, but additions above 25 wt% increase stiffness and reduce low-temperature dart impact below 400 g when tested under ASTM D1709 method A after conditioning at −18 °C. The seal layer is maintained at 8–12 µm within a total film thickness of 45–70 µm, and heat-seal strength is measured according to ASTM F2029 at 0.5 MPa bar pressure and 0.5 s dwell. The low seal-initiation temperature of CH D0, typically 5–10 °C below that of C4-LLDPE, allows sealing through product fines without distortion of the outer print web, but seal strength falls below 15 N/25 mm when the skin is diluted with more than 20 wt% reclaimed edge trim.

Sealant Skin Layer Chemistry in Five-Layer Barrier Coextrusions and the SIT Depression Mechanism

In a five-layer coextruded barrier film with PA6 or EVOH as the barrier core and maleated polyethylene tie resins, Clearflex CH D0 is used as the heat-sealable skin at a layer ratio of 15–25% of total film thickness. The depression in seal-initiation temperature relative to standard LLDPE is caused by the lower crystalline melting point and higher chain mobility of the butene-containing copolymer, allowing partial interfacial fusion at jaw temperatures of 85–95 °C in laboratory heat-seal tests conducted at 0.4 MPa for 0.5 s under ASTM F2029. Hot-tack strength, measured as peel force after a 50 ms seal dwell at 200 mm/min, remains above 3 N/25 mm at 110 °C, but it declines steeply when the skin contains more than 12 wt% high-density polyethylene from reclaimed barrier trim because the dispersed HDPE domains crystallize first and disrupt the fusion continuum. The viscosity ratio between the CH D0 skin and the maleated tie layer must not exceed 3:1 at the die lip, otherwise haze and interfacial waviness develop; converters narrow the gap by running the skin melt at 195–210 °C while holding the barrier layer at 230–245 °C. Food-contact status is supported by FDA 21 CFR 177.1520 and EU Regulation 10/2011, with overall migration below 10 mg/dm² according to EN 1186 and specific migration of comonomer and additives according to EN 13130. Direct fatty-food contact above 70 °C should not be assumed unless migration data for the exact layer structure are generated, because the low density and high comonomer content raise the extractable fraction relative to medium-density polyethylene.

Extrusion coating and lamination trials on aluminium foil and paperboard show that Clearflex CH D0 can replace an EVA copolymer only when the melt curtain is stabilised by a short air gap of 120–180 mm and a die temperature of 295–315 °C. The low density of the grade promotes surface oxidation at the substrate interface, improving adhesion to unprimed aluminium foil when the web is treated with a 2 kW corona discharge immediately before the laminating nip. Adhesion is quantified as the 180° peel force of a 15 mm strip separated at 100 mm/min according to ASTM F904; values below 3 N/15 mm indicate insufficient substrate wetting. Line speed is normally limited to 150–300 m/min because draw resonance becomes severe above this range when coating weight is below 15 g/m², appearing as transverse thickness bands and controlled by reducing the air gap, raising the chill roll temperature to 18–22 °C, or applying a high-pressure side constraint. Unlike EVA, the VLDPE grade generates less acetic acid and acetaldehyde at the die exit, but residence times longer than 20 min at 315 °C still create gel flecks in transparent coatings; the screw and adapter are flushed with LLDPE before shutdown. The resulting coating has lower heat-seal initiation than an LDPE coating of the same melt index, but its low modulus reduces the barrier contribution of a paperboard structure; converters compensate by increasing the paperboard caliper or replacing a 20 g/m² LDPE coating with a 25 g/m² CH D0 coating.

When Clearflex CH D0 Replaces an Ethylene-Octene Copolymer in TPO Impact Modification, Phase Morphology Controls the Low-Temperature Notched Impact

Polypropylene heterophasic compounds for injection-moulded automotive interior components are often modified with ethylene-octene copolymers at 10–25 wt%; substituting part of that impact modifier with Clearflex CH D0 requires verification that the dispersed rubber phase does not coalesce into a co-continuous network. Compounding is performed on a co-rotating twin-screw extruder with a 40:1 L/D barrel, screw speed of 250–400 rpm, barrel temperatures of 190–230 °C, atmospheric venting, and strand pelletising. The low density and narrow crystallinity distribution of the VLDPE grade produce a dispersed phase with number-average particle diameters of 0.5–2.0 µm when the screw configuration includes two kneading blocks downstream of the feed zone; this morphology is verified by scanning electron microscopy of cryofractured specimens etched with xylene at 90 °C. Notched Charpy impact strength at −30 °C, measured on ISO 179-1/1eA specimens cut from injection-moulded plaques, is most improved at 10–15 wt% CH D0 addition, but flexural modulus under ISO 178 falls by 10–20% at that loading and heat deflection temperature under ISO 75-2 decreases. Injection moulding trials on a 1200 kN clamp force machine with melt temperature of 220 °C and mould temperature of 35 °C show that additions above 20 wt% produce visible flow marks on textured surfaces, consistent with a viscosity mismatch between the PP matrix and the low-density dispersed phase. Published compound performance data for this specific grade in TPO formulations are limited; a five-point design of experiment in 5 wt% increments is required to establish the impact–stiffness balance for the target part geometry.

Rotomoulding the Grade Produces Low-Temperature Ductility but Requires Dense Particle Packing to Avoid Subsurface Voids

In rotational moulding of thin-walled tanks and buoyancy aids, Clearflex CH D0 is dry-blended with linear medium-density polyethylene at 25–50 wt% to improve low-temperature impact while retaining surface hardness. The mould is rotated at a speed ratio of 4:1 on a biaxial arm in an oven set to 260–285 °C, and the peak internal air temperature is held at 185–200 °C for 15–20 min to allow the low-density fraction to densify against the mould wall. Because the VLDPE powder fraction has a broad particle-size distribution with a mean particle diameter of 250 µm, fine particles below 150 µm fill interstices and reduce void formation; however, excessive fines above 25 wt% cause uneven flow and local hot spots. Low-temperature impact resistance is assessed on specimens cut from the moulded wall and conditioned at −20 °C for 6 h before an instrumented falling-weight test, with a ductility index above 70% required for service. Environmental stress-crack resistance is evaluated under ASTM D1693 condition B in 10 vol% Igepal CO-630 at 50 °C; the high comonomer content of CH D0 extends failure times relative to a medium-density rotomoulding grade of 0.935 g/cm³. The moulded part is not recommended for continuous exposure to hydrocarbon fuels or strong oxidizers unless post-moulding fluorination or crosslinking is applied, because the low crystalline network has higher permeation and lower creep resistance than a crosslinked high-density rotomoulding resin.