SINOPEC EVA 4F2

SINOPEC EVA 4F2 is a low-vinyl acetate ethylene-vinyl acetate copolymer pellet grade positioned for film, lamination, and moderate-seal packaging structures where the processing behaviour of LDPE is retained while introducing measurable comonomer-derived toughness. Published technical data associated with the grade list a vinyl acetate comonomer content of 4.0 wt% determined by Fourier transform infrared spectroscopy and a melt mass-flow rate of 2.0 g/10 min when tested at 190 °C under a 2.16 kg load in accordance with ISO 1133-1:2022. Density is reported at 0.925 g/cm³ using ISO 1183-1:2019. These values place the grade below typical high-VA adhesive and foam grades and above standard LDPE film homopolymers in terms of chain irregularity and low-temperature crack resistance.

Because the vinyl acetate content is low, the copolymer retains a relatively sharp crystalline melt peak rather than the broad endotherm seen in high-VA EVA. Differential scanning calorimetry following ISO 11357-3:2018 typically gives a peak melting temperature near 106 °C, with a Vicat softening temperature of approximately 88 °C under Method A50 per ISO 306:2022. The tensile response, measured on compression-moulded plaques according to ISO 527-2:2021, is close to LDPE-like stiffness but with improved elongation; a representative yield stress of 9.0 MPa and elongation at break of 600 % are stated as typical values, not contractual minimums.

Table 1 consolidates representative data extracted from supplier technical documentation. Lot-specific certificates of analysis should govern final acceptance because specification limits may be broader than the listed values.

These property anchors do not describe processability on a specific line. Film converters should verify melt temperature, back pressure, and melt curtain stability on the intended equipment because the processing window is sensitive to residence time rather than to MFR alone.

How Does Melt-Temperature Control Affect Film-Grade Extrusion of SINOPEC EVA 4F2?

In blown film, the recommended melt path is constrained by the onset of acetate-elimination degradation. On single-screw extruders with L/D ≥ 25 and a screened barrier or Maddock mixing section, barrel temperatures from 160 °C to 190 °C and die-head temperatures from 180 °C to 210 °C are used. The melt temperature measured at the die lip should remain below 220 °C; excursions above this threshold accelerate liberation of acetic acid, promote gel formation, and corrode unprotected die surfaces. Hard chrome or electroless nickel plating on die lips and downstream idlers is specified on production lines where temperatures tend to drift.

Die gap settings between 0.8 mm and 1.2 mm are typical for LDPE-compatible film grades. Blow-up ratios are held at 2.0:1 to 3.0:1, and the frost line is maintained at 4 to 8 die diameters above the air ring. Higher blow-up ratios increase transverse direction orientation but may reduce bubble stability if the film enters the frost line with insufficient melt strength. Chilled-air air rings with single-lip or dual-lip control are used; internal bubble cooling is generally not required for film below 100 µm.

Residence time is a critical variable. On 90 mm single-screw lines with L/D 30, residence times above 6 min are avoided by reducing screw speed only within the gearbox’s allowed range. Purge using a low-MFR LDPE after shutdown and before long idle periods prevents stagnation in the adapter and screen changer. Continuous screen packs with 60/100/60 mesh configurations are used to keep back pressure in the range 10 MPa to 25 MPa without causing excessive shear heating.

For melt fracture control, the apparent shear viscosity of a 2.0 g/10 min low-VA EVA at 190 °C is typically reported in the range 300 Pa·s to 500 Pa·s at 10 s⁻¹; published data for 4F2 specifically under capillary rheometry are limited. Die-land shear rates should be kept below 1,000 s⁻¹ to avoid sharkskin surface defects in thin-gauge film.

Cast film and extrusion-lamination lines expose the material to a different heat history. In these processes, melt curtain stability is governed by the ratio of melt strength to gravitational draw; the 2.0 g/10 min MFR provides a wider draw window than a 0.5 g/10 min LDPE and a narrower window than a 7 g/10 min extrusion-coating grade. Typical melt temperatures for lamination are held between 250 °C and 290 °C; above 300 °C fuming increases rapidly, and the extraction duct must be designed for acetic acid. The substrate is pre-treated to a wetting tension of at least 38 mN/m before lamination; otherwise peel strength falls below the target. For paper and board lamination, in-line ozone treatment of the melt curtain is used to raise surface energy for peel-strength retention; generator output is scaled to web width and line speed rather than fixed.

Published data for specific multi-layer coextrusion structures containing 4F2 as a skin layer are limited. In the absence of line-specific validation, the material is introduced in blends with LDPE to modify adhesion without sacrificing bubble stability. Coextrusion feedblock and die design should avoid long interfacial residence time because degradation products at the EVA/LDPE interface can create optical defects.

Slip and Antiblock Formulation Boundaries in Low-VA EVA Film

Surface modification is required to control blocking because the polar ester functionality raises film-to-film friction compared with pure LDPE. Erucamide slip masterbatch is added at 500 ppm to 1500 ppm active slip, and synthetic silica antiblock is incorporated at 1000 ppm to 3000 ppm. Below these ranges, machinability on vertical form-fill-seal equipment degrades; above them, coefficient-of-friction values decline but haze increases and heat-seal strength decreases. The equilibrium coefficient of friction is measured after 48 h of aging at 23 °C per ISO 8295:2004 because erucamide migration is time-dependent.

High levels of slip should not be combined with corona treatment placed before the sealing operation, because surface oxidation retards slip bloom and creates non-uniform seal performance. The preferred sequence is to treat the film for print adhesion after sealing, or to use a segmented treatment lane. Excess silica above 3000 ppm can produce die-pressure fluctuations and accelerate screen-pack plugging on lines without gear pumps.

Compared with LDPE film resins, SINOPEC EVA 4F2 lowers the crystalline ordering and shifts the DSC melting peak downward by approximately 5 °C to 10 °C. The actual heat-seal initiation shift must be measured on the target packaging line because seal-bar pressure, dwell time, and film thickness dominate the result; hot-tack evaluations are conducted per ASTM F1921-20 where sealing reliability is critical.

Compared with a 14 wt% VA copolymer, the lower comonomer level retains more stiffness and dimensional stability but loses softness, tack, and low-temperature flexibility. At equivalent melt flow rate, the storage modulus at 23 °C for a 4 wt% VA EVA is reported in the range 100 MPa to 150 MPa when measured by dynamic mechanical analysis per ISO 6721-1:2019, while a 14 wt% VA grade falls below 80 MPa. These class-level comparisons explain the difference in handling stiffness; lot-specific dynamic mechanical analysis is necessary for design calculations. This distinction is critical in stretch film and frozen-food packaging; selecting 4F2 in place of a higher-VA grade reduces cling but improves score-line flex-crack resistance when combined with an appropriate LDPE fraction.

If Higher-VA Copolymer Is Specified for Sealant or Foam End-Uses

In applications where a specification demands vinyl acetate contents above 14 wt%, crosslinkable foam density below 40 kg/m³, or low-temperature seal initiation below 80 °C, SINOPEC EVA 4F2 is not an equivalent substitute. Its comonomer content is insufficient to deliver the necessary polarity for hot-melt adhesion to polar substrates or the softness required in EVA foam formulations. Replacement without requalification can produce seal leakage, lower peel values, and higher-density foam. Converters with existing screw and drying infrastructure for LDPE can trial the grade more efficiently than users coming from high-EVA processing, where lower process temperatures and vented barrels may not be present.

Before food-contact use, verification of compliance with EU 10/2011, FDA 21 CFR 177.1350, and any applicable national standards is required from the supplier certificate of conformance for the exact lot. The base resin is typically not formulated with intentionally added heavy metals, but additives and colour concentrates may alter the compliance status. REACH and RoHS compliance is compound-specific; no statement for the neat pellet can be extended to finished film, laminates, or coated papers without testing migration and total extractables.

Pellets should be stored in sealed containers below 40 °C and protected from direct sun. If bags are opened for more than 4 h under relative humidity above 60 %, surface moisture can produce voids in cast film and blown film bubble instability. Predrying at 60 °C to 70 °C for 2 h to 4 h using a desiccant dryer with a -30 °C dew point is specified before extrusion in humid environments.

On production-scale lines, the most commonly reported failure modes are melt curtains that tear at high draw ratios, bubble instability when the frost line is placed above 8 die diameters, and die-lip deposit formation after prolonged operation above 220 °C. These are managed by lowering die pressure, adjusting air-ring velocity, and increasing purge frequency rather than by altering the polymer specification. In lamination, inadequate substrate pretreatment is more often responsible for low peel strength than variation in the resin lot.