HANWHA EVA 1157 Copolímero de acetato de vinilo de etileno

HANWHA EVA 1157 is a semicrystalline ethylene-vinyl acetate copolymer produced by Hanwha Chemical and positioned as a general-purpose injection-molding and compounding grade. The resin is specified around a nominal vinyl acetate content of 15 wt% and a melt flow index of 7.0 g/10 min measured under ASTM D1238 conditions of 190 °C and 2.16 kg. A density of 0.938 g/cm³ is reported under ASTM D1505. These three descriptors place EVA 1157 in the intermediate segment of the product family: it is lower in melt viscosity than extrusion grades with melt indices below 2.0 g/10 min and higher in melt strength than high-flow grades in the 20 g/10 min to 30 g/10 min range. The 15 wt% vinyl acetate content lowers polyethylene crystallinity enough to improve low-temperature flexibility and environmental stress-crack resistance, while maintaining sufficient stiffness and dimensional stability for molded applications. In contrast to higher-VA grades used in hot-melt and sealant systems, EVA 1157 exhibits lower surface tack, reduced polar substrate adhesion, and a higher crystalline melting peak.

The tabulated values are representative lot averages and are not specification limits unless separately fixed in a certificate of analysis. Dimensional design should be based on the producer’s lot-specific data, particularly because ethylene-vinyl acetate lot viscosity can shift within the control window without altering the nominal grade designation.

In injection molding trials on a 350 t toggle-clamp machine with a 25 mm low-compression screw, EVA 1157 exhibits adequate homogenization when barrel set points are maintained at 150 °C to 190 °C from feed to metering zones and the nozzle is kept below 200 °C. Melt temperature measured at the nozzle should remain between 180 °C and 210 °C. At the lower boundary, short shots, gate-stringing, and higher injection-pressure demand become more frequent; at the upper boundary, surface gloss deteriorates and volatiles from vinyl acetate decomposition begin to appear as subsurface bubbles. Mold temperature is typically held at 20 °C to 40 °C. Regulated rather than chilled-water cooling is preferred because excessively rapid quenching increases frozen-in stress in sections thicker than 3 mm. Injection velocity is set to produce a flow-front velocity of 30 mm/s to 80 mm/s for wall thicknesses of 1.0 mm to 3.0 mm. Hold pressure is maintained at 50 % to 70 % of peak cavity pressure to compensate for a linear mold shrinkage typically in the range of 0.8 % to 1.2 %. These conditions are starting points and require adjustment against gate geometry, runner balance, and hot-runner temperature drop.

At melt temperature 190 °C, the material shows shear-thinning behavior; injection-pressure demand is reduced more effectively by increasing melt temperature within the qualified window than by raising screw speed. Gate land length should not exceed 0.75 mm for wall thicknesses of 1.5 mm to 2.0 mm. In multi-cavity tools, sequential valve gating is preferred because unbalanced filling produces differential orientation and post-mold warpage. Weld-line strength is lower than in high-VA grades because of reduced chain-end interdiffusion at the flow front. When a weld line cannot be moved, vent the knit point and use a melt temperature at the upper end of the permitted range to improve flow-front healing. Dimensional stability in closure liners and cable-filling applications benefits from post-mold annealing at 60 °C for 30 min to 60 min. Continuous-use temperature under load is generally below 60 °C because the material approaches its Vicat softening point; above that boundary creep accelerates unless the applied stress is below 0.5 MPa.

Rheological and thermal boundaries during single-screw plasticization

For single-screw plasticization, a screw compression ratio of 2.5:1 to 3.0:1 with a gradual transition zone is preferred because the melt is shear-sensitive at elevated temperature. Screw speed is normally limited to 60 rpm to 120 rpm on a 50 mm diameter extruder; higher speeds reduce melt homogeneity and extend screw recovery time without proportional throughput gains. Residence time at melt temperature should not exceed 10 min. Thermal degradation of the vinyl acetate comonomer becomes measurable near 230 °C, releasing acetic acid that etches unplated steel surfaces and produces dark specks in unpigmented or translucent parts. Barrel zones should therefore be interlocked to shut down if any zone exceeds 220 °C. When processing is interrupted, the barrel is purged with a low-melt-index polyethylene before shutdown to displace acidic residue. Purging with polycarbonate or polyvinyl chloride is avoided because the degradation products from those resins are incompatible with residual acetic acid and can form carbonized deposits on screw flights.

Moisture control before processing is handled by desiccant drying at 60 °C for 2 h to 4 h when the resin has been exposed to ambient relative humidity above 50 %. A dryer dew point below -30 °C is maintained. Residual moisture below 0.03 wt% prevents splay and weld-line porosity. Sealed bags are stored below 40 °C and away from direct ultraviolet exposure. If cold pellets are moved into a warm production hall, condensation forms on pellet surfaces; unopened bags are tempered for 12 h to 24 h before opening in humid plants. The resin is supplied as pellets, and batch-to-batch melt-index variation is controlled within a typical specification window of ±0.7 g/10 min. Hardness is less sensitive to lot variation, generally remaining within ±2 points when measured by ASTM D2240.

What distinguishes a 15 wt% VA, 7 g/10 min EVA from film-grade and high-VA copolymers?

A direct comparison is made against three reference families. Against a low-VA ethylene copolymer with 5 wt% to 9 wt% vinyl acetate, EVA 1157 has a lower Vicat softening point of approximately 58 °C, greater low-temperature flexibility, and improved environmental stress-crack resistance in polar detergent environments. The trade-off is lower tensile modulus and lower upper service temperature. Against a high-VA resin containing 25 wt% to 28 wt% vinyl acetate, EVA 1157 exhibits higher stiffness, lower surface tack, lower polar substrate adhesion, and higher crystalline melting point. That makes the grade less suitable for high-cling film or hot-melt sealant systems and more suitable for injection molded articles, cable sheathing compounds, and crosslinked foam formulations where excessive softness and blocking are undesirable. Against a low-melt-index extrusion grade near 1.5 g/10 min, EVA 1157 fills thin-wall cavities at lower injection pressure and shorter cycle time, but it has lower melt strength for monolayer blown film and may produce higher neck-in in profile extrusion. Published data for direct comparison of these grades under identical tooling is limited; the differences are inferred from measured melt-flow and vinyl acetate content rather than from single-cavity comparative molding trials.

In masterbatch and mineral-filled compounding on a co-rotating twin-screw extruder with L/D 40:1, EVA 1157 is melt-fed in the main feed and fillers such as talc or calcium carbonate are side-fed after the melting zone. Barrel temperatures follow 130 °C to 190 °C, with the die held at 180 °C. Screw speed of 250 rpm to 400 rpm disperses the filler, but the kneading-block zone is restricted to 10 % to 15 % of total screw length to avoid shear heating above 200 °C. Vacuum devolatilization at -0.06 MPa to -0.08 MPa is applied before the die. In formulations with calcium carbonate above 40 wt%, strand brittleness increases; pelletizing may require a strand die with 6 mm holes and reduced line speed to prevent fracture. For chemical blowing agent masterbatches, azodicarbonamide is added in a side-feed zone held below its decomposition onset of 195 °C. The resin also permits pigment loadings up to 60 wt% in black masterbatches when melt temperature is kept below 200 °C and die pressure is limited to 12 MPa; carbon black introduces adsorbed moisture and volatiles, making vacuum venting necessary for strand quality.

When chemical foaming places melt strength and gas-nucleation efficiency in direct conflict

When EVA 1157 is used in crosslinked closed-cell foam, the formulation is typically compounded with azodicarbonamide at 1.5 phr to 2.5 phr and dicumyl peroxide at 0.5 phr to 1.0 phr. The peroxide-containing compound is mixed at 90 °C to 105 °C on a two-roll mill or internal mixer to avoid premature scorch. Curing and blowing are run at 165 °C to 175 °C for 3 min to 8 min. The objective is to match peroxide half-life with the gas evolution profile of the blowing agent. If crosslinking occurs too early, gas expansion is restrained and foam density remains high. If gas evolution occurs before sufficient network formation, the medium melt strength of EVA 1157 is insufficient to prevent cell coalescence, producing irregular large voids and poor compression set. The 7.0 g/10 min melt flow index is therefore an operational compromise: it aids dispersion of peroxide and blowing agent but demands tighter cure-time control than a low-flow foam grade. Published data for this specific formulation configuration is limited; acceptable foam density and hardness are generally achievable only when melt temperature during subsequent expansion is controlled within a narrow window and the compound is not stored beyond 24 h after peroxide addition.

Environmental stress-crack resistance is improved relative to high-density polyethylene and low-VA copolymers when the resin is exposed to polar surfactants and alcohols. However, EVA 1157 remains susceptible to swelling in ketones, esters, and chlorinated solvents. Immersion testing under ASTM D543 is required before specifying the resin for chemical tank fittings, dispenser components, or pump housings. The base copolymer is generally not classified as hazardous under EU CLP Regulation (EC) No 1272/2008. Food-contact suitability for ethylene-vinyl acetate copolymers is evaluated under 21 CFR 177.1350 and EU Regulation (EU) No 10/2011 when migratory extractables meet the prescribed limits. Heavy metal restrictions under RoHS Directive 2011/65/EU are generally met by the base resin. Combustion of the material in oxygen-limited conditions may produce carbon monoxide and acetic acid; incineration should be conducted with adequate ventilation and emission control. When color or filler masterbatches are added, melt-flow shift is measured by ASTM D1238 on the final compounded pellet, not on the neat resin, because additives change the viscosity response and can move the practical processing window outside the neat-grade limits.