Blown film extrusion of low-density polyethylene (LDPE) in Saudi Arabia operates within a processing window defined by melt-flow index, die land length, bubble cooling, and additive migration. Tasnee LDPE 4025AS and 1925AS are specified for monolayer and coextruded film lines where converters balance extrusion pressure, drawdown, and slip/antiblock properties. Melt-flow rate is determined under ISO 1133-1:2022 with a 2.16 kg load at 190 °C; density is measured under ISO 1183-1:2019 or ASTM D1505. Commercial film LDPE typically spans a density of 0.918–0.930 g/cm³ and a melt-flow index from 0.2 g/10 min to 4.0 g/10 min. Lower melt-flow indices are retained for high-melt-strength film and higher indices are used for thin-gauge or high-output lines.

Tasnee LDPE 4025AS and 1925AS: Saudi Film Grades Explained

The two grades differ by melt-flow index and additive package rather than density alone. The suffix “AS” conventionally designates an antiblock/slip formulation in polyolefin grade nomenclature. Numeric fields can encode melt-flow and density targets, but certified values must be taken from the Tasnee certificate of analysis because lot-to-lot variation in additive dose and molecular weight distribution influences neck height, frost line position, and film blocking.

Published data for the exact melt-flow and mechanical values of these two Saudi film grades is limited outside supplier documentation. In high-pressure LDPE production, reactor pressure and chain transfer agent control short-chain branching and molecular weight distribution. The branched architecture increases shear thinning and extensional viscosity, which stabilizes the blown film bubble at blow-up ratios in the range of 2:1–3:1.

Film converters in the Middle East, South Asia, and North Africa typically evaluate these grades on high-output monolayer lines extruding shrink film, heavy-duty packaging, agricultural film, and lamination film. Selection between a lower-MFR grade such as 1925AS and a higher-MFR grade such as 4025AS, if the designation follows standard melt-flow encoding, is driven by motor load, die pressure, bubble stability, and final dart impact requirement.

Why Does Melt-Flow Index Control Film Bubble Stability?

Melt-flow index corresponds to low-shear viscosity; blown film dies expose the melt to high shear and extensional flow. Lower-MFR resin produces higher head pressure, higher melt strength, and greater stability at large blow-up ratios, while higher-MFR resin reduces motor load and allows thin-gauge down-gauging but narrows the stable bubble envelope when frost line height is fixed. The MFR of the resin should be confirmed against ISO 1133-1:2022 or ASTM D1238-20 because small differences in molecular weight distribution can shift neck height and frost line position.

On conventional single-screw extruders with L/D ratios of 24:1–30:1 and barrier screws, die gaps are commonly set between 0.6 mm and 1.5 mm. The bubble is cooled by a dual-lip air ring or internal bubble cooling. Frost line height is maintained between 2 and 5 die diameters for optical clarity and gauge uniformity. Lower-MFR grades may require a 5–10 °C higher adapter temperature to control die pressure, although this narrows the oxidative safety margin.

Melt fracture and sharkskin occur when die wall shear stress exceeds a critical threshold. The onset is more likely with high-viscosity, low-MFR LDPE at low melt temperature. Corrective actions include raising die temperature, reducing screw speed, increasing die gap, or blending with a small portion of high-MFR LDPE. These interventions alter gauge and mechanical properties, so process adjustments must be recorded against thickness maps generated by online capacitance or near-infrared gauges.

Extruder barrel zone temperatures for LDPE film are set in a rising profile from feed throat 150 °C to adapter 200–220 °C, with melt temperature not exceeding 240 °C to limit oxidative chain scission and gel formation. Oxidation induction time measured under ISO 11357-6 should be monitored if regrind levels exceed 20% or if residence time exceeds 5 min at process temperature. Pre-drying of LDPE pellets is not normally required; only moisture-sensitive masterbatch carriers or regrind stored at relative humidity above 60% require drying before extrusion. Crosslinked gel particles appear as lens-shaped optical defects, die lip deposition, and random thickness bands.

The “AS” additive package addresses friction and blocking through controlled migration of slip agents and dispersed antiblock particles. Erucamide-based slip systems require 24–72 h post-extrusion to bloom fully to the surface. Static and kinetic coefficient of friction are measured under ASTM D1894-11; blocking load is classified under ASTM D3354-11. High antiblock particle load reduces blocking but can increase haze and reduce gloss, measured under ASTM D1003-13 and ASTM D2457-13.

Film toughness of LDPE is evaluated using dart impact ASTM D1709, Elmendorf tear ASTM D1922, and tensile properties ISO 527-3. LDPE branched architecture produces lower tensile modulus, lower dart impact, and lower tear than linear-low-density polyethylene at equivalent gauge, so LDPE is selected for clarity, softness, and processability rather than puncture resistance. In blown film, MD/TD tear imbalance is controlled by blow-up ratio and frost line height; increasing blow-up ratio reduces orientation imbalance but destabilizes the bubble if die gap is excessive.

Seal initiation temperature of LDPE film is typically between 105 °C and 125 °C for a 0.5 s dwell at 2 bar. Hot-tack performance is evaluated under ASTM F1921; ultimate seal strength under ASTM F88. Surface-active additives that migrate excessively can reduce seal strength, so seal-layer formulations are selected with controlled slip additive addition and minimal processing aids.

Post-extrusion surface treatment by corona discharge raises film surface energy for printing and lamination. Untreated LDPE surface energy is typically 31–32 mN/m; corona treatment commonly brings it to 38–42 mN/m. Dyne level is measured using wetting solutions under ASTM D2578-17. Migration of slip agents after corona treatment can reduce surface energy; converters therefore specify triboelectric and print performance after the slip bloom period, not immediately after extrusion.

Where 4025AS is used as a seal layer and 1925AS as a core or skin layer in multi-layer structures, the viscosity ratio at feedblock shear rates should remain close to 1 to prevent interfacial instability. Layer thickness tolerance is maintained by gear pump discharge consistency; variation below 1% prevents encapsulation defects in five-layer blown film dies. The melt temperature difference between coextruded layers should not exceed 10 °C at the die adapter.

Regrind from edge trim and start-up scrap is introduced at 10–25% by mass depending on film optical requirements. Multiple heat histories increase the concentration of oxidized species and crosslinked particles; gel counts should be monitored using in-line melt filtration or screen packs with mesh openings between 250 µm and 400 µm. When gel concentrations rise, dust and polymer fines in regrind must be removed by densification or air classification.

When extruder pressure fluctuations exceed ±10% of setpoint

Pressure fluctuations greater than ±10% of setpoint on a single-screw extruder indicate feed-throat instability, partially blocked screen packs, or temperature stratification across the die. The corrective hierarchy is to inspect the breaker plate and screen pack for gel contamination, verify the barrel zone profile, measure melt temperature with an insertion thermocouple at the adapter, and purge the die if oxidized gel specks appear. Internal bubble cooling and dual-lip air rings improve heat transfer but cannot compensate for inadequate melt homogeneity.

At a fixed die gap, unstable melt delivery creates thickness bands and frost line movement. A gauge variation above ±5% of nominal for technical film usually correlates with pressure fluctuations, air-ring asymmetry, or inadequate downstream nip alignment. The die should be cleaned when die lip deposits span more than 20% of circumference, because localized contamination disrupts both film gauge and surface optics.

Blow-up ratio, neck height, and frost line height determine molecular orientation. For LDPE film, a blow-up ratio of 2:1–3:1 is common; higher BUR improves transverse direction tear but reduces machine direction tear. Film thickness is measured under ASTM D374 or ISO 4593. Process records should separate thickness average, eccentricity, and random gauge band defects, because gauge variance contributes to film blocking and winding defects.

Optical defects are classified by gel size and frequency. A common converting specification rejects film with gel particles larger than 100 µm when visible under transmitted light. Haze values for LDPE blown film are typically 4–8% for thin-gauge film, and gloss at 60° may range from 60 to 80. These values are influenced by melt temperature, frost line height, and antiblock particle size.

Film grades intended for direct food contact are assessed under FDA 21 CFR 177.1520(c) for olefin polymers and under EU Regulation (EC) No 10/2011 for overall migration into food simulants. Annex II of EU Regulation (EC) No 10/2011 specifies an overall migration limit of 10 mg/dm² for general food contact. Converters document conformance through certificates of analysis, batch traceability, and migration testing linked to the final food contact application. REACH Regulation 1907/2006 and RoHS Directive 2011/65/EU apply to articles containing organic additives or color concentrates that may include restricted substances.

LDPE film grades from Saudi Arabia are not a direct substitute for linear-low-density polyethylene in high-puncture applications. The operational boundaries of 4025AS and 1925AS are determined by the supplier melt-flow range, the additive dose, and the converter’s ability to control bubble cooling and film gauge. Excessive regrind levels, high processing temperatures, or multilayer viscosity mismatch can produce gel defects, surface slip variability, and inconsistent seal performance.