Copolímero de acetato de vinilo de etileno EVAtech EVA 120S/12N

EVAtech EVA 120S/12N Ethylene Vinyl Acetate Copolymer is a low-vinyl-acetate thermoplastic copolymer grade whose designation identifies a nominal vinyl acetate comonomer content of 12 wt% and a nominal melt flow index of 12 g/10 min determined at 190 °C/2.16 kg following ISO 1133-1:2022. The grade is supplied as pellets and is intended for cast film, extrusion coating, coextrusion sealant layers, injection molding, compounding, and masterbatch carrier operations where moderate polarity, low-temperature flexibility, and heat-seal response are required but high-VA softness and tack are not. Published property windows for 12 wt% VA EVA grades typically place density between 0.930 g/cm³ and 0.935 g/cm³ under ISO 1183-1:2019, Vicat softening temperature between 75 °C and 82 °C under ISO 306/A50, Shore A hardness between 90 and 96 under ISO 868, and tensile elongation at break above 600 % when tested on 2 mm plaques according to ISO 527-2:2012. The melting endotherm by differential scanning calorimetry commonly falls between 90 °C and 98 °C under ISO 11357-3:2018. These values are not lot-specific guarantees; final conversion settings should be based on the supplier certificate of analysis and first-article qualification.

Thermal Degradation Thresholds and Pre-Drying Boundaries

Processors using EVA 120S/12N in blown film, cast film, or extrusion coating must maintain melt temperature below the onset of vinyl acetate side-group elimination. Differential scanning calorimetry under ISO 11357-3:2018 places the melting endotherm near 90 °C to 98 °C, but thermogravimetric analysis under ISO 11358-1:2022 generally shows the onset of mass loss associated with acetic acid release above 230 °C in nitrogen and at lower temperatures in air. Production-scale experience with 12 wt% VA EVA grades on 30:1 L/D single-screw extruders indicates that barrel setpoints above 210 °C in the metering zone can generate localized melt temperatures exceeding 220 °C when high backpressure from fine screen packs is present, causing plate-out on die lips, yellowing, and corrosion of downstream equipment from acetic acid. Maximum metering-zone setpoints of 200 °C to 210 °C are typical, but actual melt temperature should be measured with a probe and not inferred from barrel setpoints alone. Pre-drying is not always required for sealed pellet shipments, but when warehouse relative humidity exceeds 60 % or when the grade is stored in outdoor silos, desiccant drying at 60 °C to 70 °C for 2 h to 4 h reduces surface moisture that otherwise produces bubble defects in cast film. Oven drying above 70 °C is not recommended because pellet surface tack and hopper bridging can occur. The material should not be stored in direct contact with copper, copper alloys, or oxidizing acids because copper ions accelerate thermo-oxidative degradation and acetic acid corrosion.

What Equipment Configuration Governs Extrusion Stability?

Melt processing behaviour of EVA 120S/12N is dominated by its comonomer content and nominal 12 g/10 min melt flow index. In single-screw extrusion, a screw with L/D between 24:1 and 30:1 and compression ratio near 3:1 is generally used; barrier screws with mixer sections are preferred over simple three-zone screws because the copolymer reaches stable melt viscosity at lower temperatures than LDPE but can form stagnant regions at shear rates above approximately 1,000 s⁻¹ when assessed by capillary rheometry under ISO 11443:2021. For cast film and extrusion coating, die gaps between 0.5 mm and 0.7 mm, air gap distances from 150 mm to 250 mm, and melt temperatures near 280 °C to 300 °C are frequently cited as starting points for low-VA EVA to balance adhesion and thermal stability, but published data for this exact configuration is limited and pilot-scale trials are required. In blown film, die gap settings of 1.0 mm to 1.5 mm, blow-up ratios from 2.0:1 to 2.8:1, and frost-line heights of 3D to 5D are applied to 12 wt% VA grades, with output derating when melt pressure exceeds 350 bar to avoid screw wear and localized overheating. Twin-screw compounding of EVA 120S/12N with fillers or masterbatches should use moderate specific energy input of 0.12 kWh/kg to 0.18 kWh/kg, temperature-controlled barrel zones, and side feeding for heat-sensitive or hygroscopic fillers to prevent hydrolytic degradation. Long residence times above 220 °C, particularly in stagnant adapters or melt pumps, are a greater risk than brief extrusion peaks because random chain scission at acetate groups follows time-temperature superposition kinetics.

When Injection Molding Replaces Extrusion in Low-Temperature Flexible Parts

Injection molding of EVA 120S/12N is applied to caps, gaskets, footwear components, vibration damping pads, and industrial cushioning where low-temperature impact resistance and chemical resistance are necessary. Starting-point barrel temperatures generally range from 160 °C to 200 °C, with the nozzle set 5 °C below the front zone to limit drool. Mold temperatures of 20 °C to 40 °C support crystallinity development and dimensional stability; wall thicknesses below 2 mm may require higher mold temperatures or higher injection speed to prevent short shots. Clamp force calculations should use cavity pressure values between 300 bar and 500 bar for parts with projected area above 500 cm², but final requirements depend on gate size, flow length, and wall thickness. Shrinkage is anisotropic: values from 1.2 % to 1.8 % in the flow direction and 1.0 % to 1.5 % transverse are observed on 60 mm plaques under ISO 294-4:2018. Mold release difficulties occur in deep-draw flexible parts because of the copolymer’s low surface hardness and high elongation; draft angles of 1° to 2° and PTFE-based release sprays reduce ejection defects. When replacing a high-flow LDPE in an existing mold, the converter should expect lower melt temperature capability, improved environmental stress crack resistance, lower seal initiation, higher part surface tack, and reduced modulus. Published data for this specific product in injection molding is limited; first-article trials are required to confirm gate freeze time and part release behaviour.

For masterbatch and pigment dispersion operations, EVA 120S/12N functions as a carrier resin at typical pigment or filler loadings of 20 wt% to 50 wt%. The polar vinyl acetate groups improve pigment wetting relative to LDPE carriers, which can reduce pressure build-up on screen packs and improve dispersion quality when assessed by filter pressure value testing according to the downstream converter’s internal method. At carbon black loadings above 45 wt%, melt viscosity increases sufficiently that barrel temperature adjustments may be required; operators using 40:1 L/D twin-screw extruders commonly limit specific energy input to 0.18 kWh/kg and add black through side feeders to keep melt temperature below 210 °C. The same carrier behaviour applies to flame-retardant concentrates, but brominated or chlorinated additives should not be processed with this EVA grade without verifying that additive decomposition products do not react with acetic acid released during thermal excursion.

In coextruded structures, EVA 120S/12N is placed as a sealant layer or tie layer where a balance between adhesion, sealing, and stiffness is required. Heat-seal initiation at 85 °C to 95 °C is typical for 50 µm cast film when tested under ASTM F2029-16 at 0.3 MPa sealing pressure and 1 s dwell. Hot-tack performance is lower than higher-VA grades because the plateau of seal strength at elevated temperatures is narrower; coextruded structures that require broad hot-tack windows generally use 18 wt% or 28 wt% VA sealants. Adhesion to aluminium foil and oriented polypropylene is improved relative to LDPE because the polar acetate function interacts with metal oxide and surface-treated polypropylene, but alkyd-based inks and certain low-molecular-weight amides can interfere with interlayer adhesion. For film converters, corona treatment above 38 dyn/cm is often used to improve lamination bonds; however, treatment levels above 44 dyn/cm can accelerate surface oxidation and reduce heat-seal strength. These operating limits should be confirmed by seal-strength testing under ASTM F88/F88M-21 and interlayer adhesion testing under ASTM F904-16.

Compared with EVA grades containing 18 wt% or 28 wt% vinyl acetate, EVA 120S/12N exhibits higher stiffness, lower tack, lower room-temperature clarity in thick sections, and higher seal initiation temperature. As vinyl acetate content increases from 12 wt% to 28 wt%, density rises from approximately 0.930 g/cm³ to 0.950 g/cm³, Shore A hardness decreases from roughly 94 to 75, and heat-seal initiation declines from about 85 °C to 55 °C under comparable processing histories. Compared with LDPE, the 12 wt% VA grade provides superior environmental stress crack resistance, lower heat-seal initiation, improved adhesion to polar substrates, and higher low-temperature impact toughness, but it has lower stiffness, lower upper-use temperature, and higher gas permeability. For optical transparency in cast film, 12 wt% VA EVA is not equivalent to 18 wt% or 28 wt% VA EVA; haze increases with lower VA content and with faster quench. These differences are summarized in Table 1.

Meeting Food-Contact and Substance Restriction Requirements

Food-contact evaluations for EVA 120S/12N must be performed on the final article, not the raw pellet. Ethylene vinyl acetate copolymers may be evaluated under 21 CFR 177.1350 when extractives limitations and intended use conditions are met. European Union compliance for plastic food-contact materials is assessed under Commission Regulation (EU) No 10/2011, including overall migration limits and specific migration limits for vinyl acetate monomer where applicable. REACH obligations under EC No 1907/2006 and RoHS restrictions under 2011/65/EU apply to finished articles in the European market, but RoHS compliance is not automatic for all additive packages or colorants. The raw EVA grade does not contain intentionally added phthalates, heavy metals, or ozone-depleting blowing agents; converters must verify the final compound against supplier declarations and test results. Table 2 defines the verification boundary.