Mechanical pre-stretch ratios in the 200–250% range are routinely achieved on cast film lines processing Chevron Phillips 6335B as the core layer of a three-layer A-B-C stretch wrap structure. In this configuration the butene copolymer LLDPE is metered at 60–70 wt% of the total melt stream, while the skin layers contain a metallocene-catalysed LLDPE with 2–4 wt% polyisobutylene cling additive. The cast line is typically a 75 mm single-screw extruder with L/D 30:1, a flat die gap of 0.50–0.80 mm, and a primary chill roll maintained at 18–24°C. Melt temperature at the exit of the adapter should be kept between 218°C and 232°C; sustained operation above that band accelerates oxidation of the cling additive and produces a visible deposit on the chrome-plated chill roll, which then transfers as a transfer mark to the film surface. Puncture resistance measured by ASTM D5748 on 20 µm symmetrical cast film normally falls between 0.8 J and 1.4 J, but published data for this exact resin-additive formulation is limited and plant-to-plant variation in cast roll temperature and vacuum box position can move the value outside that interval. Elmendorf tear by ASTM D1922 in machine direction typically exceeds 150 gf at 20 µm, while transverse direction tear is usually 100–130 gf because cast film is uniaxially oriented in the machine direction. Wound roll hardness is normally controlled at 80–85 Shore A on 76 mm paper cores; a harder roll increases core crush and film blocking, whereas a softer roll telescopes during transport. Peel cling values obtained by ASTM D5458 are adjusted by the skin-layer percentage and the polyisobutylene molecular weight, but the formulation must not exceed 1200 ppm erucamide if a food-contact wrapper is required, because migration of the slip additive into the cling layer lowers cling after 7 days of ambient storage.

The limiting production constraint in this application is gauge uniformity rather than maximum throughput. Automatic die bolt adjustment based on thickness feedback is required to hold a ±1.5% transverse gauge variation at line speeds of 300–400 m/min. Cold-roll friction and air knife position are used to prevent air entrapment between the cast web and the roll, because entrapment creates local quench delays that reduce optical uniformity. When 6335B is processed on an existing line originally designed for LDPE, the screw temperature profile is usually lowered by 10–15°C in the feed section to prevent premature melting and torque override. No predrying is required for this resin under normal storage; however, if bagged material is moved from a cold warehouse to a high-humidity conversion hall, surface condensation can introduce bubble defects in the cast sheet at start-up.

Why does blown food packaging film require a 2.2:1 blow-up ratio with butene copolymers?

Butene copolymer LLDPE responds to bubble geometry changes more strongly than higher-alpha-olefin copolymers because the short-chain branching distribution affects transverse direction tensile orientation. At 40 µm, a monolayer film extruded from a 90 mm grooved-feed blown film line with a 250 mm annular die and a 2.0 mm die gap typically shows a dart drop ASTM D1709 value of 180–220 g at a 2.2:1 blow-up ratio. Raising the blow-up ratio to 3.0:1 increases transverse direction tear but drops machine direction tear by 35–45%, which is detrimental on vertical form-fill-seal machines that pull the film against a forming collar. The frost line is therefore positioned at 5–7 die diameters above the air ring, and the melt temperature at the die is held at 190–210°C to maintain bubble stability without internal bubble cooling. Heat seal strength measured by ASTM F88 on a 40 µm monolayer film displays a sealing window from 105°C to 130°C at 0.5 s dwell and 0.3 MPa jaw pressure, with hot-tack values above 4 N/25 mm from 110°C to 125°C when tested by ASTM F1921. These values allow the same film to be used on both low-speed impulse sealers and high-speed continuous-band sealers, provided the jaw surfaces are maintained within a ±3°C band.

Food-contact status is referenced to FDA 21 CFR 177.1520 for olefin polymers, and the converter is responsible for extraction testing under the end-use conditions specified in that regulation. A slip-antiblock package of 500–1000 ppm erucamide and 300–600 ppm synthetic silica is usually required to maintain coefficient of friction below 0.25, but slip additive migration also widens the heat-seal temperature window by slightly depressing the seal initiation temperature. The film should not be blended with more than 15 wt% of a high-density polyethylene having a melt flow index below 0.5 g/10 min, because the viscosity mismatch at the die lip causes visible flow lines and a drop in dart impact below 120 g. When the film is used in fruit and vegetable bags, perforation is performed with needle rolls, and the polymer must not be formulated with processing aids that migrate to the hole edge and weaken tear propagation. High-temperature purging after 6335B should use an intermediate low-melt-index LLDPE rather than a direct HDPE purge, because the viscosity mismatch leaves carbonised residue on the barrel wall. During shutdowns longer than 30 min, the die head should be cooled to 160–170°C to limit gel formation; film haze by ASTM D1003 remains between 7% and 10% at 40 µm when the die exit temperature is within the recommended band but rises above 14% if the resin is overheated or the die lip is damaged.

The use of 6335B in 150 µm agricultural silage barrier film requires a three-layer coextrusion in which the core is loaded with 4–6 wt% carbon black masterbatch and the skin layers contain 8–12 wt% titanium dioxide masterbatch for reflectance. Production is carried out on a 75 mm single-screw blown film line with a 300 mm die, a 2.0 mm die gap, and a blow-up ratio of 2.4:1. UV stabilisation is achieved with 0.4–0.8 wt% hindered amine light stabiliser and 0.2–0.5 wt% benzophenone UV absorber, both expressed on total polymer weight. The carbon black concentrate increases melt viscosity at low shear rates, so the extruder screw speed is limited to keep the melt pressure below 35 MPa at the screen pack; higher pressures force black agglomerates through the mesh and produce visible streaks in the white skin. Dart impact by ASTM D1709 on the finished 150 µm film is strongly influenced by the regrind level and carbon black dispersion quality. A well-dispersed lot typically shows 400–600 g dart drop, but agglomerate-related impact loss can reduce that value by 20–30% if the masterbatch carrier resin is incompatible. After outdoor exposure, tensile elongation at break tested by ASTM D882 is expected to remain above 300% for at least 12 months under temperate climate conditions, while the same film without HALS falls below 200% elongation within 6–9 months. Fabricators should not assume that carbon black alone provides sufficient UV protection for silage film; the high moisture and organic acid environment inside the silage clamp accelerates oxidative degradation through acid-catalysed hydroperoxide decomposition.

Winding tension on the silage film line is set lower than for general-purpose film because the white skin layer contains TiO₂ particles that increase surface roughness and reduce interlayer friction. The typical roll length is 1500 m on 76 mm cores. If the roll is wound too tightly, blocking between the white and black sides produces a visible delamination mark every 1–2 m during unwinding in the field. The reverse side should not be corona treated above 38 dyn/cm, because excessive oxidation reduces surface wetting of the silage juice and promotes pinhole formation at film folds.

Low-temperature puncture resistance in frozen food packaging lines

At -25°C storage, butene copolymer LLDPE retains greater dart impact than LDPE of the same density because the short-chain branching disrupts crystallinity and prevents large spherulite growth. Frozen food bags made from 6335B are typically 50–75 µm, produced on a blown film line with a 1.8 mm die gap, a 2.5:1 blow-up ratio, and a frost line height of 4–6 die diameters. The short frost line promotes a finer crystal structure that improves low-temperature puncture resistance but also increases film haze above 10%, which is acceptable for most printed frozen food pouches. Dart drop tested after conditioning at -18°C for 24 h is generally 120–180 g for a 60 µm monolayer film, whereas the ambient dart drop may be 200–260 g. The difference is important because ambient values overstate the film's ability to withstand frozen bone-in meat punctures. The base resin class typically shows a brittleness temperature below -40°C by ASTM D746, but surface scratches from filling lines and sharp package corners act as stress concentrators and reduce that advantage. When the package contains whole poultry or bone-in red meat, 20–30 wt% of a metallocene-catalysed LLDPE with a density of 0.912 g/cm³ is blended with 6335B. This substitution increases low-temperature dart impact by 15–25% and lowers the seal initiation temperature by 3–5°C, but it also increases blocking tendency and requires higher anti-block loadings.

Insufficient regrind control is the most common cause of field failures in frozen food film. Regrind levels above 20 wt% are strongly discouraged because repeated extrusion histories reduce the low-temperature impact performance of the butene copolymer more than that of octene-based LLDPE. Film wrinkles and gauge bands generated by unstable frost lines create thin sections where puncture resistance drops below 100 g at -18°C. The converter should monitor gauge profile using a capacitance scanner and reject rolls with a ±5% local gauge deviation. When laminated to a polyester or oriented polyamide outer web, the 6335B layer is reverse printed or laminated with solventless adhesive; the corona-treated surface must be processed within 48 h or the surface energy decays below 38 dyn/cm, causing lamination voids.

When lamination sealant webs demand stable COF after corona treatment

The coefficient of friction for a 50 µm blown film made from 6335B is controlled by a migrating slip package containing 500–1000 ppm erucamide and 300–600 ppm silica anti-block. Corona treatment at 1.5 kW output and 80 m/min line speed raises the surface energy to 40–44 dyn/cm but also oxidises the surface, causing kinetic COF to increase from approximately 0.20 to 0.40 within 24 h if the slip additive concentration is too low. Laminators running solventless adhesive lines at 100–150 m/min require a stable kinetic COF below 0.25 for reliable roll unwinding and register control. Slip and anti-block levels are therefore adjusted on the basis of ASTM D1894 measurements made after 72 h of roll ageing, not immediately after winding. A film that meets the COF specification on the day of extrusion may fall out of specification after full migration of the erucamide and surface oxidation. The sealant web should not contain more than 1200 ppm erucamide because the bloom can transfer to the adhesive layer and reduce laminate bond strength by more than 20%.

Retort pouches containing meat or dairy products require the 6335B sealant layer to be blended with 15–20 wt% of an octene LLDPE having a density of 0.916 g/cm³. The octene copolymer lowers the sealing temperature and improves the hot-tack plateau during retort heating, while the butene copolymer contributes stiffness and tear resistance. If the 6335B layer is used neat in retort conditions at 121°C, seal delamination is observed on packs with heavy sauces because the seal interface cannot accommodate the thermal expansion of the contents. The laminate structure is usually 12 µm polyester / 9 µm aluminium foil / 50–70 µm modified sealant web. The sealant layer must pass ASTM F88 heat-seal strength testing after retort, with failure occurring by film tear rather than adhesive peel.

Extrusion parameters for heavy-duty industrial liner films

Blown films of 100–150 µm thickness for container liners are produced on 90 mm extruders with barrier screws of L/D 30:1. Melt temperature at the die is held at 190–215°C; a die gap of 2.0–2.5 mm and a blow-up ratio of 2.0:1 are selected to avoid excessive trapped air between the film sleeve and the container wall during insertion. The resin is frequently blended with 10–20 wt% recycled LLDPE from in-house edge trim. The regrind must have a melt flow index within ±0.5 g/10 min of the virgin resin when measured by ISO 1133-1:2022, otherwise the melt flow mismatch appears as gauge bands and poor bubble symmetry. Bubble stability is maintained by a dual-lip air ring supplied with chilled air at 10–18°C, and the frost line is kept below 4 die diameters to maximise bubble cooling. Dart impact by ASTM D1709 for a 100 µm film is expected in the range of 250–350 g, but the exact value depends on the recycled content and the screw temperature profile. Tensile elongation at break tested by ASTM D882 typically exceeds 500% in both machine and transverse directions for virgin film; the addition of 20 wt% regrind can reduce transverse direction elongation to 450% but still meets the requirements of most industrial liner specifications. EU REACH obligations for the finished liner fall on the importer or downstream user, not on the resin supplier, and the converter must maintain documentation for substances of very high concern if the recycled fraction contains unknown post-industrial material.

The liner is converted by hot-wedge or impulse welding, and hot-tack performance according to ASTM F1921 ensures that heat-sealed seams withstand fill stress during loading. The weld should be made at 115–125°C with a dwell time of 0.5–1.0 s; higher temperatures cause bead squeeze-out that crystallises and becomes a brittle seam failure point at low temperature. Storage of the finished liner rolls at temperatures above 35°C can cause blocking because the butene LLDPE surface softens and the anti-block package becomes less effective. The polymer should not be pre-dried unless condensation has occurred during outdoor storage, because hydrolytic degradation is not the primary concern for this resin family.