UBE POLIETYLENE V315 Copolímero de acetato de vinilo de etileno (UBE)

UBE Polyethylene V315 is a high-pressure ethylene-vinyl acetate copolymer supplied by UBE Corporation as pelletised resin for extrusion coating, blown film, injection molding, and masterbatch carrier applications. The grade is typically specified at a nominal vinyl acetate content of 15 wt% and a melt mass-flow rate of approximately 3.0 g/10 min when measured at 190 °C under 2.16 kg load according to ISO 1133-1:2022. The random incorporation of the polar acetate side group into the polyethylene backbone reduces lamellar thickness and overall crystallinity relative to branched low-density polyethylene. Published property ranges for this comonomer class include a density of 0.930–0.940 g/cm³ under ISO 1183-1, a Vicat softening point of 63–70 °C under ISO 306 A50, and tensile elongation at break above 700% under ISO 527-2. The main differentiation from homopolymer low-density polyethylene is the acetate side group, which raises surface polarity, improves adhesion to aluminium foil and paper, increases low-temperature toughness, and lowers heat resistance. Compared with higher-vinyl-acetate EVA copolymers containing 25–33 wt% vinyl acetate, V315 retains higher melt strength, lower moisture uptake, and reduced acetic acid generation during processing, but offers a narrower low-temperature flexibility window and lower adhesion to highly polar substrates such as polyamide and polyvinyl alcohol.

What Limits Adhesion and Low-Temperature Flexibility When V315 Replaces Homopolymer LDPE?

The adhesion improvement of V315 over low-density polyethylene is governed by the concentration and surface migration of acetate groups. The 15 wt% vinyl acetate content increases the polar component of surface energy, but oxidation or corona discharge is still required on polymer film substrates to produce durable bond strength. On extrusion coating lines, corona pretreatment of film substrates to a wetting tension of 38–42 mN/m under ASTM D2578 improves peel performance; aluminium foil requires removal of rolling oils and may be ozone-treated or flame-treated. Peel strength is configuration-dependent because film thickness, air gap, melt temperature, and substrate gauge alter the result more than the resin alone, so no single peel value should be treated as a specification limit. Low-temperature flexibility results from the reduction in crystallinity to approximately 25–35% by heat of fusion, compared with 45–55% for branched low-density polyethylene. This reduces stiffening at sub-ambient temperatures, but V315 remains less flexible than EVA grades containing 25–33 wt% vinyl acetate. The thermal cliff is most visible at the Vicat softening point: the value falls from approximately 93–100 °C for LDPE to 63–70 °C for V315, which excludes the material from hot-fill and retort packages unless it is protected by a higher-temperature structural layer.

Extrusion lamination lines using a 90 mm single-screw extruder with a 24:1–30:1 L/D barrier screw and a coat-hanger die typically process V315 at melt temperatures of 210–230 °C. Cylinder zones are set between 150 °C and 220 °C; the feed throat is kept below 40 °C to prevent pellet bridging. Screen packs of 60/80/120 mesh generate back pressure and improve melt homogeneity. The material should not be held above 250 °C for more than a few minutes because thermal deacetylation releases acetic acid, which attacks unplated die lips and produces an acrid odour. A die-lip gap of 0.7–1.0 mm and an air gap of 80–150 mm provide a balance between bond strength and neck-in. For aluminium foil lamination, the foil web is often preheated to 50–70 °C immediately before the nip to reduce thermal shock and improve adhesion.

Vicat Softening Point, Melt Mass-Flow Rate, and Film Draw Stability

The two most important incoming quality-control values for processing are the melt mass-flow rate and Vicat softening point. Melt mass-flow rate at 2.16 kg is a low-shear measurement of molecular weight, but extrusion coating draw stability correlates more strongly with melt strength and high-shear viscosity. A grade with 3.0 g/10 min melt flow has lower draw resonance resistance than a fractional-melt flow LDPE, especially when the air gap is long. The following table provides typical ranges for a V315-class 15 wt% vinyl acetate EVA copolymer. These are not specification limits and should be confirmed against the certificate of analysis for each lot.

Tensile properties are reported from ISO 527-2 with Type 5A or Type 1B specimens; parallel ASTM D638-14 data may differ because of specimen geometry and strain rate. The melt mass-flow rate is expressed in g/10 min and is an inverse measure of melt viscosity at low shear; it does not predict high-shear extrusion pressure or die swell.

In tubular blown film, V315 is processed at a blow-up ratio of 2.0:1–2.8:1 and a die gap of 0.8–1.5 mm. Melt temperatures are kept at 160–190 °C to preserve bubble stability; above 190 °C the lower melt tension can induce bubble wander and variability in thickness. Frost line height is adjusted to 3–6 die diameters to balance quench and film optics. The heat-seal initiation temperature is typically 95–110 °C under ASTM F88, lower than low-density polyethylene and therefore useful for sealant layers in coextruded films. Hot tack performance is dependent on seal bar temperature, dwell time, and gauge; processors should map seal windows on the actual line because laboratory data under ASTM F1921 may not transfer directly to packaging machines.

For injection molding of flexible closures and technical parts, barrel temperatures from 160 °C to 200 °C and a nozzle setting not exceeding 200 °C are typical. Mold temperatures are held at 20–40 °C, and back pressure is limited to 3–6 MPa to reduce shear heating. Clamp force requirements usually fall between 1.0 t/cm² and 1.5 t/cm² of projected area for thin-wall parts. Because V315 is a low-vinyl-acetate grade, purging from a polyolefin screw can be performed with standard low-density polyethylene or fractional-MFI LDPE. Purging should continue until no acetic acid odour is detected at the die exit. Hot-runner channels should be streamlined and free of dead spots; dwell times longer than 120 s at temperatures above 220 °C promote yellowing and localised deacetylation.

When Extrusion Lamination Exceeds 80 m/min, Does Neck-In Increase?

Neck-in increases with line speed because the molten curtain spends less time in the air gap and the viscoelastic melt tension is progressively exceeded. For a low-viscosity V315 melt, a change in line speed from 40 m/min to 80 m/min can raise neck-in by 10–20 mm on a standard die, although the exact value depends on die width, die-lip gap, melt temperature, and coating thickness. To reduce draw resonance, the die-lip gap can be increased to 0.8–1.0 mm, the air gap shortened to 100 mm or less, or a coextruded LDPE skin layer can be added to raise melt curtain strength. Melt temperature should remain at 210–230 °C; reducing it to 190 °C may increase melt tension, but it also raises the risk of gauge bands and reduces foil wetting.

Preventing Acetic Acid Evolution During High-Shear Compounding

High-shear twin-screw compounding with modular 40:1 L/D corotating screws requires tight thermal control. EVA decomposition above 230 °C follows pseudo-first-order chain scission; the acetate side group releases acetic acid. The acid can attack calcium carbonate fillers, generating carbon dioxide and microvoids, and can corrode iron-based barrel liners and die plates. Barrel zones in compounding are therefore set from 140 °C to 180 °C, with die temperature at 180 °C and specific energy input below 0.25 kWh/kg. Residence time is kept under 120 s. Screws should use neutral kneading blocks rather than aggressive reverse elements. The resin is pre-dried at 55–60 °C for 2–4 h when stored at relative humidity above 70%; although V315 absorbs less moisture than higher-VA EVA grades, surface condensation can generate splay in thin films.

Regulatory status for V315 is application-specific. For food-contact use, the base ethylene-vinyl acetate copolymer may fall under FDA 21 CFR 177.1350, which covers ethylene-vinyl acetate copolymers with specified extractable limits and use conditions. In the European Union, plastic food-contact articles must comply with Regulation (EU) No 10/2011; vinyl acetate monomer has a specific migration limit of 12 mg/kg food simulant. REACH registration and RoHS heavy-metal restrictions should be verified against the supplier's current certificate. The following matrix lists the principal standards used in incoming quality control and compliance review.

Within the low-vinyl-acetate EVA product family, V315 is positioned between lower-flow grades and higher-flow grades. A lower-flow grade increases melt strength for tubular blown film and deep-draw thermoforming; a higher-flow grade fills thin-wall injection molds more readily but may increase gate blush and sink marks. The chemical resistance and service temperature are governed primarily by the 15 wt% vinyl acetate content, not by melt flow. Continuous load-bearing service above 60 °C is not recommended. The product is also unsuitable for direct contact with strong oxidising acids and with some amine-based processing aids because residual acidic species may promote salt formation and plate-out. These boundaries should be confirmed by end-use testing.