High-molecular HDPE film produced from PetroChina Sichuan HDPE FHM CRP 100N is processed as the sole thermoplastic in the 10 µm–18 µm carrier bag segment on high-stalk blown film lines. The grade is in the high-molecular HDPE film class; density on the certificate of analysis is usually specified in the 0.945 g/cm³–0.955 g/cm³ range under ISO 1183-1 and melt index under ISO 1133-1 condition T is generally below 0.10 g/10 min. Barrel set points from feed throat to adapter are 180 °C, 190 °C, 200 °C, 205 °C, 205 °C, and 210 °C, while the die zone is held at 205 °C. Melt pressure at the breaker plate is kept below 420 bar; pressure spikes above this threshold on 45 mm–65 mm grooved feed extruders create pinhole defects and visible die lines. A barrier screw with L/D 30:1 and a 1.0 mm–1.4 mm die gap supports a blow-up ratio of 3.5:1–4.5:1 and a stalk height of six to eight die diameters. The film resin is dry blended with 0.5 wt%–1.0 wt% of a processing-aid or slip/antiblock masterbatch; edge trim and start-up regrind are added back at up to 15 wt% through a 6 mm granulator screen. That regrind limit is set by the loss of dart impact resistance and the appearance of gel particles when regrind moisture exceeds 0.1%. Domestic carrier bag compliance follows GB/T 21661-2020 for plastic shopping bags, and export packaging is checked for the heavy metals sum limit of 100 ppm by weight under EU Directive 94/62/EC Article 11. The terminal product is a welded bottom-seam T-shirt bag with punched handle opening and a nominal wall thickness of 12 µm–18 µm. On a production scale, the principal failure mode is bubble instability caused by inadequate stalk cooling; it appears as gauge bands at the collapsed frame and later causes handle tearing at the punch press.

What Limits Downgauging Below 9 µm in Produce Roll Stock?

Downgauging of fresh produce roll stock below 9 µm on high-stalk HDPE bubble lines is constrained by dart impact retention, film blocking on the roll, and web tension control during perforation. A food-contact formulation for retail produce bags uses the same virgin FHM CRP 100N with a slip/antiblock masterbatch limited to 2.0 wt%; higher loadings reduce seal strength and can contribute to surface transfer during food contact. Processing on a 45 mm grooved feed extruder with a 200 mm die and a 1.0 mm die gap produces film in the 6 µm–12 µm range. The blow-up ratio is held at 3.0:1–3.5:1 and frost line height is controlled with chilled air to keep gauge variation below ±4% because perforation at 400 mm intervals amplifies any gauge band into a tear point. Food-contact compliance is verified against FDA 21 CFR 177.1520(c), EU Regulation (EU) No 10/2011 with an overall migration limit of 10 mg/dm², and GB 4806.7-2016. Additive compliance is checked under GB 9685-2016. The finished product is a center-fold produce bag roll, perforated at 350 mm–450 mm intervals, used on automatic dispensing frames in supermarkets. The operational boundary is below 7 µm; at that gauge, ASTM D1709 Method A dart impact values commonly fall below 90 g on automatic dispenser stock, blocking increases on the roll, and film breaks occur at the perforation line.

In refuse sack conversion, a three-layer A/B/A blown film line can use FHM CRP 100N as the two outer layers to encapsulate a post-consumer recycled polyethylene core. A starting weight distribution is 25 wt% virgin, 50 wt% PCR, and 25 wt% virgin, but the PCR melt index must be controlled between 0.2 g/10 min and 0.6 g/10 min when measured to ISO 1133-1. If the regranulate contains more than 20 wt% of multi-layer film scrap or EVOH-containing structures, gel accumulation on a 250-mesh screen changer reduces bubble stability and creates weak spots on the sack bottom. The extruder is a 65 mm grooved feed machine operating at 190 °C–210 °C, with a die gap of 1.4 mm–1.6 mm and a blow-up ratio of 2.5:1–3.0:1. The lower blow-up ratio preserves dart impact resistance in the recycled core. The terminal product is a drawstring or fold-top refuse sack in the 35 L–120 L range, tested to EN 13592:2017. Chemical compliance for municipal waste bags requires REACH SVHC screening when the PCR phase contains candidate-list substances above 0.1 wt%; the finished refuse sack is not automatically food-contact approved. The main production bottleneck is the batch-to-batch variance of PCR melt index; when the regranulate feed blend shifts by more than 0.15 g/10 min between batches, bubble diameter changes become visible within one minute and require automatic air ring adjustment.

Coextruded Cereal Liner Stock With HDPE Outer Skins and EVOH Oxygen Barrier

A five-layer symmetric structure can be run with FHM CRP 100N as the two outer skins, two tie-resin sub-skins, and an ethylene-vinyl alcohol copolymer core. The weight distribution is 30% HDPE, 10% tie, 20% EVOH, 10% tie, and 30% HDPE. This structure produces a 35 µm–50 µm liner that protects dry cereal from moisture vapour transmission and oxygen ingress. The HDPE outer skins are processed at 190 °C–210 °C, the tie resin at 195 °C–215 °C, and the EVOH core at 205 °C–220 °C. The die temperature is held at 215 °C to prevent interfacial instability at the tie/EVOH boundary. The die gap is 1.6 mm–1.8 mm and the blow-up ratio is 2.8:1–3.2:1. Food-contact compliance for the cereal liner requires the HDPE skin to comply with FDA 21 CFR 177.1520(c); the tie resin and EVOH must meet the respective monomer restrictions in EU Regulation (EU) No 10/2011. Migration testing is carried out on the finished multi-layer film with food simulant E for dry foods under test condition OM2. The terminal product is a bag-in-box liner or sealed cereal bag with end-seal integrity checked to ASTM F88. The main operational limitation is that the HDPE moisture barrier is not designed for retort or boil-in-bag cycles; exposure above 100 °C in the presence of heat-sealing jaws causes seal shrinkage and layer delamination. Production-scale failures are observed as curved seal geometry when the seal bar temperature exceeds 180 °C and as intermittent EVOH layer breaks when the die gap is below 1.4 mm.

When Heavy-Duty Industrial Liners Replace LLDPE on Wide-Die Blown Lines

On wide-die blown film lines with 65 mm grooved feed extruders, industrial liner film of 70 µm–100 µm thickness can be produced as a monolayer from FHM CRP 100N or as the outer ply of a coextruded liner for polymer granule and mineral filler packaging. The substitution from LLDPE is limited by melt pressure and bubble cooling capacity; the HDPE grade must be run at 200 °C–220 °C, with a die gap of 1.8 mm–2.2 mm, a blow-up ratio of 2.5:1–3.0:1, and a stalk height of four to six die diameters to reduce bubble instability. A 65 mm grooved feed extruder with a 300 mm die typically requires 0.30 kWh/kg–0.35 kWh/kg of specific energy input; the cooling ring must deliver sufficient air velocity to freeze the thicker melt without collapsing the bubble. The formulation includes 2.5 wt% carbon black masterbatch when UV resistance is required; carbon black dispersion is checked to ISO 18553 for agglomerate rating. Compliance for industrial packaging is driven by buyer technical agreements rather than direct food-contact regulation; REACH SVHC screening applies when recycled additives are used, and EU Directive 94/62/EC heavy metals limits remain applicable. The terminal product is a heat-sealed 25 kg–50 kg liner or a continuous tubular liner for FIBC inserts. The limitation is that HDPE liner heat seal strength is orientation-sensitive; seal bar temperature below 150 °C produces weak seals, while above 180 °C the film can shrink and distort. Production-scale failure modes include seal-burn pinholes when dwell time exceeds 1.2 s and film blocking on the roll when cooling air humidity exceeds 60% RH.