Copolímero de acetato de vinilo de etileno ELVAX 4355

On high-speed corrugated case sealing lines, ELVAX 4355 is melt-compounded at 30–40 wt% resin loading with rosin ester tackifiers and paraffin or microcrystalline waxes to produce hot-melt packaging adhesives. The grade is characterised by a vinyl acetate content of 25 wt% and a melt index of 43 g/10 min measured at 190 °C under 2.16 kg load in accordance with ASTM D1238 /ISO 1133-1:2022. The high melt index reduces shear stress in gear pumps and permits slot-die application at 150–170 °C, while the 25 wt% vinyl acetate content contributes to polar adhesion on clay-coated and uncoated corrugated board. In a jacketed sigma-blade mixer of 100–500 kg working capacity, the wax and hindered phenolic antioxidant are first melted at 130–140 °C; ELVAX 4355 pellets are then added in three equal charges under low-speed agitation of 30–50 rpm, with each charge allowed to reach visual clarity before the next. Tackifier is metered under nitrogen at 160–180 °C, and the finished melt is filtered through a 150–250 µm mesh before drumming or direct melt transfer to case sealers. Brookfield viscosity determined by ASTM D3236 at 180 °C typically falls between 800 mPa·s and 2,500 mPa·s, with the lower end associated with paraffin-wax-dominant formulas and the upper end with microcrystalline wax or high-softening-point rosin ester formulations. Open time in side-seam bonding is controlled between 2 s and 15 s by adjusting wax volume and tackifier softening point; compression dwell is set at 0.5–1.5 s and 30–60 N/cm². Fibre tear on corrugated board at 23 °C and 50% RH should exceed 90% when the adhesive film is 0.8–2.0 mm in thickness; low-temperature performance down to -10 °C is retained by replacing 10–15% of paraffin wax with microcrystalline wax, but this substitution also widens the melt transition and may reduce heat resistance by 5–8 °C as measured by ring-and-ball softening point.

Food-packaging grades are formulated so that the finished adhesive is evaluated under 21 CFR 175.105; the resin portion may be referenced under 21 CFR 177.1350 for ethylene-vinyl acetate copolymers. Final responsibility rests with the converter because migration of tackifier and wax components, not the EVA alone, determines overall compliance. Thermal stability boundaries are critical because the vinyl acetate moiety undergoes deacetylation above 220 °C, releasing acetic acid and shifting adhesion and colour. In production melters, the setpoint is therefore limited to 180 °C maximum for continuous operation, with upper dead-zone alarms at 190–200 °C; hold time at 180 °C should not exceed 4 h without viscosity checks. A shift of ±5 g/10 min in melt index, monitored by ASTM D1238, changes pump pressure in high-speed case sealers more than an equivalent change in tackifier loading.

What Limits Film Integrity in Wax-EVA Curtain Coating Under High Humidity?

Wax-coating lines producing moisture-resistant corrugated board use ELVAX 4355 at 2–10 wt% in refined paraffin wax to improve fold-crack resistance and adhesion to kraft liners. The addition raises Brookfield viscosity from approximately 10–20 mPa·s for neat paraffin at 120 °C to 30–80 mPa·s depending on concentration; viscosity is measured with a rotational viscometer under ISO 2555 or DIN 53019. The coating kettles are indirect-heated to prevent local overheating above 140 °C, because wax oxidation and EVA gel formation accelerate above 150 °C. At 2 wt% addition, the EVA modifies wax morphology by reducing crystal size and blocking crack propagation; at 8–10 wt%, the film takes on a more elastomeric character but the water vapour transmission rate measured by ASTM E96/E96M rises slightly compared with unmodified wax, so formulators must balance low-temperature flexibility against moisture barrier loss. High-humidity storage of coated board at 85% RH induces surface tack only when residual low-molecular-weight tackifier is present; ELVAX 4355 itself does not introduce hydrophilic functional groups, but its polar acetate groups can retain condensed water at film defects. Coating thickness is normally maintained at 25–50 µm on kraft liners; film integrity after 180° folding is evaluated by dye-penetration testing rather than tensile elongation alone.

Asphalt Softening-Point Gain After 5 wt% Addition

Addition of ELVAX 4355 to penetration-graded asphalt is performed in a high-shear mixer, typically a Silverson pilot-plant unit with a square-hole stator and rotor tip speed of 10–15 m/s at 170–180 °C. At 3–5 wt% addition, the copolymer swells in the maltene phase and forms a polymer-rich network on cooling; the ring-and-ball softening point measured by ASTM D36 rises from 48–52 °C for a 60/70 penetration-grade bitumen to 58–64 °C at 3 wt% and 62–70 °C at 5 wt%. Penetration at 25 °C under ASTM D5 decreases from 60–70 dmm to 35–45 dmm at 5 wt%, while Brookfield viscosity at 135 °C determined by ASTM D4402 increases into the 1,200–2,200 mPa·s range, still below the 3,000 mPa·s limit typically set for pumpable paving binders. The main processing constraint is storage stability: at addition levels above 6 wt%, gravitational phase separation can occur in unagitated tanks because the high melt index and high vinyl acetate content reduce the polymer-rich phase viscosity but do not eliminate density differences. Separation tendency is tested by the tube test according to EN 13399; the softening-point difference between top and bottom sections should remain below 5 °C for paving applications. To control oxidative hardening during blending, nitrogen sparging and a maximum hold time of 4 h at 180 °C are applied; the rolling thin film oven test ASTM D2872 is used to assess long-term ageing after commissioning. Rheological characterisation in a dynamic shear rheometer under ASTM D7175 shows that the 5 wt% blend retains a higher complex modulus at 60 °C than unmodified bitumen, but the phase angle decreases only moderately; this indicates improved rutting resistance without full elastomeric network formation. Published data for this specific grade in asphalt is limited, so field performance should be verified by trial sections.

Within polyolefin masterbatch production, ELVAX 4355 is employed as a high-melt-flow carrier resin for pigment and additive concentrates because the 25 wt% vinyl acetate content lowers crystallinity and permits filler loadings up to 60–70 wt% in colour concentrates. The carrier is melt-blended in a co-rotating twin-screw extruder with 40:1 L/D and segmented screws; barrel temperatures are set from 120 °C at the feed throat to 160 °C at the die, with vacuum devolatilisation at -0.08 MPa downstream of the mixing elements. At 43 g/10 min melt index, the melt viscosity is low enough to wet carbon black and organic pigments at high loading without exceeding torque limits on 75 kW drive systems; conversely, the same low viscosity creates strand-pelletising challenges if the melt temperature exceeds 170 °C, where strand breakage increases. The product pellets are pre-dried at 60–70 °C for 4 h when stored above 60% RH before extrusion to prevent surface splay. In downstream let-down into low-density polyethylene film at 2–5% concentrate addition, the acetate group promotes compatibility with polar pigments but can reduce thermal stability of the final film if the concentrate is exposed to repeated extrusion cycles; therefore, maximum regrind content is set at 10% for demanding film grades. Published data for this specific grade as a masterbatch carrier is limited, but the melt index and vinyl acetate content place it between conventional wax-based dispersants and low-MI EVA carriers.

When 25 wt% Vinyl Acetate Replaces 18 wt% VA in Toluene-Based Laminating Adhesives

Laminating adhesives based on toluene or toluene/methyl ethyl ketone solutions are formulated with ELVAX 4355 at 25–40 wt% solids, with the 25 wt% vinyl acetate content providing lower solution viscosity than lower-VA EVA grades at equal solids. Dissolution is performed in a closed coater-side stirred vessel at 40–60 °C; higher temperatures above 70 °C are avoided because solvent loss and viscosity drift complicate gravure feeding. The solution viscosity at 30 wt% solids in toluene at 23 °C is sufficiently low for direct gravure application at 2–5 g/m² dry coat weight; lamination nip temperature is maintained at 70–90 °C and pressure at 2–4 bar. The higher acetate content enhances adhesion to corona-treated polyester film and aluminium foil compared with 18 wt% VA grades, but plasticiser migration from flexible PVC can reduce bond strength over time. Residual solvent in the finished laminate is controlled below the converter's specification for indirect food contact; final compliance is assessed under EU Regulation 10/2011 or 21 CFR 175.105 depending on jurisdiction.

Under low-temperature self-adhesive label converting, ELVAX 4355 is compounded at 25–35 wt% with hydrocarbon or rosin ester tackifiers at 50–60 wt%, naphthenic oil at 5–10 wt%, and antioxidant at 1 wt% to produce pressure-sensitive hot-melt systems with reduced melt viscosity and lower adhesion build than styrenic block copolymer PSA. Mixing in a vertical twin-shaft mixer at 140–160 °C is completed within 45–60 min; coating through a slot die onto silicone release liner at 15–25 g/m² requires melt viscosity below 3,000 mPa·s at 150 °C by ASTM D3236. The 25 wt% VA content raises surface energy and peel adhesion on polar paper facestocks but limits heat resistance to 60–70 °C; cohesive failure may occur above 70 °C unless a high-softening-point tackifier is used. Loop tack measured by FINAT FTM 9 and 180° peel by FINAT FTM 1 are typically lower than SIS-based PSA at equivalent coat weight, which confines this EVA system to removable and semi-permanent logistics labels where low cost and high line speed dominate. Low-MI EVA alternatives would raise viscosity and reduce filler tolerance; ELVAX 4355 is selected when hot-melt tank pumping and die feed stability are the primary constraints.