Elvax 760 EVA resina de copolímero, fio e cabo, adesivos e selantes grau

Elvax 760 ethylene-vinyl acetate copolymer resin is supplied as a pelletized semicrystalline thermoplastic grade positioned for wire-and-cable compounds, adhesives, and sealants. Unlike high-vinyl-acetate EVA types designed for high-polarity adhesion, this product carries a nominal vinyl acetate comonomer content of 9.3 wt% as determined by ASTM D5594 Fourier-transform infrared spectroscopy. Melt flow rate is 2.0 g/10 min when tested at 190 °C under a 2.16 kg load according to ASTM D1238 /ISO 1133-1. Solid-state density is 0.930 g/cm³ per ASTM D792. The DSC melt endotherm is reported near 96 °C per ASTM D3418, and the Vicat softening temperature is approximately 78 °C per ASTM D1525. At 9.3 wt% vinyl acetate, random acetate branches reduce crystallite thickness and lower the softening point relative to low-density polyethylene, but the resin remains strongly semicrystalline and less tacky than 18–28 wt% vinyl acetate products used in high-adhesion sealants.

In comparison with adjacent grades in the same ethylene-rich product family, Elvax 760 occupies a melt-flow midpoint that changes equipment loading and melt tension. Elvax 750, with a nominal 9.0 wt% vinyl acetate content and a melt flow rate of 7.0 g/10 min, is a low-viscosity grade that reduces torque and head pressure but produces lower melt strength. Elvax 770, with a nominal 9.3 wt% vinyl acetate content and 0.8 g/10 min melt flow rate, is a high-molecular-weight grade that favors blown-film and sheet melt stability but requires higher drive torque and barrel pressure. The 2.0 g/10 min value of Elvax 760 reduces pressure without sacrificing the melt strength needed for thick-wall profiles, cable jackets, and sealant tape substrates. On a 45 mm single-screw extruder with an L/D ratio of 30:1 and a compression ratio of 3.0:1, head pressure is typically lower than for a 0.8 g/10 min grade by more than 15–20% at equal output; exact values should be confirmed by capillary rheometry according to ASTM D3835 before die design.

What Limits Processing Latitude in Peroxide-Curable Wire and Cable Insulation?

In peroxide-curable wire-and-cable formulations, Elvax 760 is melt-compounded with crosslinking agents, antioxidants, and fillers before extrusion onto copper or aluminum conductor. Dicumyl peroxide half-life data place decomposition near 115 °C for 10 h and 135 °C for 1 h; therefore, rear-barrel and die temperatures are typically maintained below 120 °C to avoid scorch, while the 2.0 g/10 min melt flow rate provides sufficient fluidity. A production line using a 60 mm single-screw extruder with an L/D ratio of 24:1 and a 2.5:1 compression screw generally operates with barrel set points from 110 °C to 125 °C. After extrusion, the covered conductor enters a continuous vulcanization tube or dry-cure section at temperatures above 180 °C to decompose residual peroxide. Crosslink consistency is verified by hot-set testing under 0.2 MPa at 200 °C according to IEC 60811-507; common acceptance limits are hot-set elongation below 175% and permanent set below 15% after cooling, but final limits are set by the applicable cable specification such as EN 50363-1 or IEC 60502-1.

In this application, the low vinyl acetate content keeps dielectric constant and dissipation factor closer to polyethylene than do 18–28 wt% vinyl acetate grades, although the acetate groups increase polarity relative to low-density polyethylene. If stronger adhesion to metal shielding or a semiconductive layer is required, the formulator may blend Elvax 760 with a higher vinyl acetate grade or an acid-functionalized polyolefin. Amine-based stabilizers and amine-functional silanes are not recommended in peroxide-curable EVA compounds because they can consume free radicals and reduce gel content; phenolic antioxidants at 0.1–0.3 phr are normally preferred. Thermal excursions above 230 °C should be avoided because EVA begins to evolve acetic acid at elevated temperature, producing odor, surface defects, and reduced electrical performance.

For low-smoke flame-retardant cable jackets, Elvax 760 functions as a polyolefin matrix for aluminum trihydrate and magnesium dihydrate fillers. The polar vinyl acetate groups permit higher filler loadings than an LDPE of similar melt flow rate, but a processing threshold exists: at ATH loadings above 60 wt%, compound viscosity rises rapidly depending on filler particle size and surface treatment. A co-rotating twin-screw extruder with an L/D ratio of 40:1 and side-feeding is used in many industrial trials to introduce filler downstream of polymer melting; barrel temperatures in the melt section are limited to 130–150 °C because ATH releases hydration water near 180–200 °C, and premature dehydration creates voiding and pressure instability. Vacuum venting at −0.08 MPa in the last barrel sections removes water and low-molecular-weight volatiles before pelletizing.

In flame-retardant cable tests per IEC 60332-1-2 and IEC 60332-3-24, compound performance depends heavily on filler type and char-forming co-additives, not on the base resin alone. The selection of Elvax 760 instead of a high-melt-index EVA reduces melt dripping during vertical flame propagation because the higher molecular weight contributes to melt strength; however, published data for this specific configuration is limited, and full-scale cable testing must be run before specification.

Adhesion Onset and Wax Compatibility in Hot-Melt Adhesives and Sealants

In hot-melt adhesive and sealant compounding, low vinyl acetate EVA grades are selected when the bond line must resist shear and set rapidly after cooling. Elvax 760 is melt-blended with tackifiers, waxes, and antioxidants in a sigma-blade mixer or horizontal hot-melt kettle at 150–170 °C; the moderate melt flow rate requires sufficient torque, but the final melt can be pumped through hot-melt applicators with gear pumps rated to at least 1,000–2,000 mPa·s at 180 °C. Because the vinyl acetate concentration is 9.3 wt%, compatibility with highly polar rosin ester tackifiers is lower than for a 28 wt% vinyl acetate grade. Formulations often use aliphatic hydrocarbon tackifiers or rosin esters with acid numbers below 10 mg KOH/g and paraffin or microcrystalline waxes at 20–30 wt% to maintain a single-phase melt. If gross cloudiness or phase separation occurs, the formulation should be adjusted with a higher-VA EVA grade or a lower-polarity tackifier.

In sealant products, slump resistance is measured by ASTM D2202; the 2.0 g/10 min melt flow rate of Elvax 760 gives higher slump resistance than a 7.0 g/10 min grade at equal filler loading. Lap-shear adhesion on sanded aluminum per ASTM D1002 is generally lower than for 18–28 wt% VA grades, but the higher molecular weight of Elvax 760 relative to high-melt-index EVA supports higher cohesive strength. For low-energy substrates such as polyethylene and polypropylene, the lower polarity of Elvax 760 can reduce interfacial mismatch relative to high-VA EVA; however, surface treatment by corona or plasma remains the dominant variable in bonding performance.

Storage and handling boundaries are set by the resin’s thermal and moisture behavior. Pellets should be kept in sealed hopper loaders or original bags until needed. EVA is not highly hygroscopic, but surface condensation can occur if cold pellets are transferred into a warm production area at relative humidity above 80%. Incoming moisture content should be checked by Karl Fischer titration per ISO 15512; if moisture exceeds 0.05%, drying in a desiccant dryer at 60–65 °C for 2–4 h with a dew point of −40 °C is recommended. Drying temperatures above 80 °C must be avoided because pellet blocking can begin near the Vicat softening point of 78 °C. In extrusion, zone temperatures are typically set from 150 °C to 200 °C for non-peroxide compounds, with a flat-to-slightly-reverse profile to manage shear heating. A screen pack of 40/60/40 mesh or similar is usually installed at the breaker plate to trap gel particles; a pressure rise above 15–20% over the initial reading indicates the need for screen replacement.

For regulatory compliance, suppliers issue REACH and RoHS 2011/65/EU statements for the resin grade. Food-contact status for the final article must be evaluated under FDA 21 CFR 177.1350 or EU Regulation 10/2011, with migration testing performed on the finished article. The resin should not be combined with strong oxidizing agents or stored near open flame. Amine-based additives and certain metal stearates can alter long-term thermal stability; compatibility should be verified by oven aging at 150 °C followed by melt flow rate and color measurement. Incoming inspection plans for production use should include melt flow rate per ASTM D1238, vinyl acetate content per ASTM D5594, and moisture content per ISO 15512.