ELVAX 350 Ethylene Vinyl Acetate Copolymer

On corrugated case erecting and sealing lines running at 120–150 cartons per minute, the adhesive is applied from nozzle or roller melters at 160–175 °C onto clay-coated recycled linerboard. Elvax 350, with a nominal vinyl acetate content of 25 wt% and a melt index of 19 g/10 min at 190 °C/2.16 kg per ASTM D1238, is used in formulation ranges of 30–38 wt% polymer, 35–45 wt% hydrogenated rosin ester or C5/C9 hydrocarbon tackifier, 15–25 wt% paraffin/microcrystalline wax blend, and 0.3–0.8 phr hindered phenol antioxidant. The 25 wt% vinyl acetate units provide adhesion to polar fibre surfaces and broaden compatibility with rosin ester tackifiers, while the 19 g/10 min melt index limits stringing at high application speeds. Brookfield viscosity for this class falls between 700 mPa·s and 1,800 mPa·s at 175 °C per ASTM D3236, and ring-and-ball softening point is maintained at 85–105 °C per ASTM E28 to avoid case deformation on filling lines.

On the packaging line, the main process variable is viscosity drift in the melt reservoir. When a 20 L reservoir with nitrogen blanketing is operated at 165 °C for 8 h shifts, viscosity measured by ASTM D3236 typically stays within 700–1,000 mPa·s for a 35 wt% polymer formula. If the reservoir is left uncovered, surface skinning and oxidation raise viscosity by 15–30 % over the same period, causing pump cavitation and irregular bead width. Set time on kraft reboard is below 2 s at 20 °C ambient; open time measured on a heated steel plate at 160 °C is 3–6 s. Qualification of the final carton adhesive bond is performed by T-peel on clay-coated liner per ASTM D1876, with production acceptance at >3.0 N/cm; peel mode is predominantly cohesive within the adhesive, not interfacial.

End articles include corrugated shipping cases, coated paperboard trays, and multipack bottle wraps where the adhesive is not used as a direct food-contact layer. When the sealed article is intended for dry food transport, the adhesive layer is evaluated for incidental contact under 21 CFR 175.105; no separate food additive clearance is required for the polymer itself if the adhesive is separated by a functional barrier or meets the exclusion criteria.

What Limits String Drop-Off and Pop-Open Failures in High-Speed Bookbinding?

On perfect binding lines running at 8,000–18,000 cycles per hour, the adhesive is applied by a heated spine wheel or slot nozzle at 150–170 °C to roughened folded signatures, followed by side-glue application at 130–150 °C. Elvax 350 is used in spine formulas at 35–42 wt%, combined with 35–40 wt% rosin ester or hydrogenated rosin ester, 10–20 wt% microcrystalline wax, 5–10 wt% paraffin wax, and 0.4–0.8 phr phosphite antioxidant. The 19 g/10 min melt index permits penetration into the fold between uncoated offset papers without excessive press pressure, while the 25 wt% vinyl acetate content provides low-temperature hinge flexibility after the book is conditioned at −25 °C for 24 h.

Film thickness at the spine is retained between 0.35 mm and 0.50 mm. If thickness exceeds 0.55 mm, set time before cover nipping extends beyond 4–5 s, causing the cover to shift under the nipping station and producing spine crease lines. Side-glue application uses a separate nozzle at 130–150 °C with a vinyl acetate-rich formula of lower viscosity, but the same Elvax 350 may be used up to 30 wt% to prevent delamination of the hinge. Page-pull force is measured on a universal tester with a 500 N load cell at 50 mm/min; specimens are conditioned at 23 °C and 50 % RH per ISO 291. Cohesive failure in the paper substrate, rather than adhesive peeling from the spine, is the production target.

Production failures recorded on high-speed lines include stringing from the spine wheel when the adhesive contains excessive high-melt-index polymer without compensating wax, and char accumulation in Teflon-lined reservoirs when temperatures exceed 175 °C. To reduce these failures, a two-stage gear pump is operated at 10–15 bar backpressure and the return hose is kept below 1.5 m length to limit residence time. End products include perfect-bound softcover books, annual reports, and magazines where the spine adhesive must survive flatwise storage at 40 °C and 85 % RH without creep.

For curtain-coated corrugated produce boxes and linerboard used in ice-pack conditions, Elvax 350 is dispersed into molten food-grade paraffin at 5–12 wt% to increase fold-crack resistance and maintain a continuous moisture barrier at flute tips. The paraffin melting point is selected in the 54–60 °C range; the EVA-modified wax is applied at 110–125 °C through a slot die, roller coater, or curtain coater at line speeds of 200–350 m/min. The addition of Elvax 350 changes the melt rheology from a Newtonian paraffin of 3–8 mPa·s to a slightly shear-thinning blend of 20–80 mPa·s at 120 °C, depending on the microcrystalline wax co-loading.

Coating weight is controlled gravimetrically in the range of 18–35 g/m² for corrugated packaging; lower weights fail the water absorption criterion for ice-pack shipment. Water vapour transmission rate is tested per ASTM F1249 at 38 °C and 90 % RH; a 300 g/m² kraft liner with 25 g/m² EVA-modified paraffin shows a WVTR reduction of 40–60 % relative to uncoated liner. Cobb water absorption per TAPPI T441 remains below 5 g/m² after 2 min. Fold endurance of the coated board is checked by bending a 180° crease through the coated side; flaking or disbonding indicates insufficient EVA content or excessive wax crystallinity.

Compliance for food-contact packaging uses the finished coated board under 21 CFR 176.170 and 176.180; the paraffin and EVA components are typically covered when the coating is part of the paper component and no direct food separation is intended. In applications where the waxed board is used for frozen meat or poultry cartons, microcrystalline wax content is often raised to 20–30 % of the total wax phase to prevent cold-temperature cracking at −20 °C.

Calendering and Extrusion of High-Filler EVA Masterbatches.

Compounding Elvax 350 as a carrier resin for mineral and pigment masterbatches exploits the 25 wt% vinyl acetate content to wet filler surfaces and the 19 g/10 min melt index to maintain let-down in polyolefin processes at addition levels of 5–15 %. On a co-rotating twin-screw extruder of 34–44 L/D with segmented screw elements, the resin is starve-fed at 50–100 kg/h into the first barrel zone set at 90–110 °C. Filler is introduced through a side stuffer after the resin melting section; screw speed is maintained below 400 rpm to control specific energy below 0.15 kWh/kg. The melt temperature at the die is held at 130–140 °C to limit vinyl acetate degradation, which is detectable by acetic acid odour and a rise in melt pressure.

Filler loadings for calcium carbonate masterbatches range from 60–75 wt%, for titanium dioxide 50–70 wt%, and for conductive carbon black 40–60 wt%. The upper limit is determined by dispersion quality on a grindometer per ISO 1524, with a typical target of 25 µm for pigment concentrates and 50 µm for coarse mineral fillers. Filtration through a 100–150 mesh screen pack is standard before strand pelletizing; residual agglomerates above 0.3 mm create film-web breaks when the masterbatch is let down in LDPE film. Let-down ratios of 10:1 to 20:1 in blown film and 20:1 to 30:1 in injection moulding are used; the carrier resin contributes no separate functional phase in polyolefin formulations when properly dispersed.

Migration testing of the final article under EU 10/2011 or FDA 21 CFR 177.1520 is performed when the masterbatch is used in food-contact polyolefin packaging. The use of Elvax 350 as a carrier does not exempt the final package from overall migration limits; its vinyl acetate segments are in the overall migration matter and must be controlled by the converter.

Where cable sheath must satisfy the acid-gas conductivity limits of IEC 60754-2 and the vertical flame spread requirements of IEC 60332-1-2, Elvax 350 is used as a base resin or co-resin in a halogen-free filler-loaded compound. The formulation is built from 100 phr Elvax 350, 150–200 phr precipitated aluminium trihydroxide with a median particle size of 1.3–1.8 µm, 5–15 phr magnesium dihydroxide, 1–3 phr vinyl silane coupling agent, 0.5–1.5 phr hindered amine stabilizer, and 3–5 phr polyethylene wax process aid. Mixing is carried out in a 1.6–2.0 L intermeshing internal mixer at 40–50 rpm rotor speed and a chamber temperature of 120–140 °C. Discharge is controlled by melt temperature, not time; the compound is dropped at 135–145 °C to avoid premature peroxide decomposition in later crosslinking stages.

Extrusion of the sheath compound on a 45:1 L/D single-screw extruder with barrier screw and grooved feed section uses a barrel profile of 110–130 °C and a die temperature of 140–150 °C. If the ATH loading is below 160 phr, the compound may pass the flame test but fails the required oxygen index; if it is above 190 phr, tensile strength and elongation decline sharply. A production reference set is summarised below.

Cross-linking by peroxide or silane-grafting is used to maintain hot-set elongation below 175 % at 0.2 MPa load and 200 °C per IEC 60811-507. The final sheath is conditioned per ISO 291 and tested for tensile strength per ISO 527-2, elongation, and Shore A per ISO 868. Halogen content is verified below 0.1 % by ion chromatography after combustion per IEC 60754-1. End products include low-smoke zero-halogen sheathing for control and instrumentation cables in mass-transit and tunnel installations.

When Solvent-Borne EVA Sealants Must Meet Aromatic Solvent Restrictions Under REACH

Elvax 350 is dissolved in a non-aromatic solvent mixture of methylcyclohexane, acetone, and n-butyl acetate at 15–25 wt% solids for roll-coat and bead applications on aluminium induction-seal liners, metal crown closures, and flexible packaging laminates. The solvent system is selected to avoid toluene and xylene restrictions under REACH Annex XVII entry 48 and to control evaporation rate for film-forming. The solution exhibits Brookfield viscosity of 800–2,500 mPa·s at 25 °C and is filtered through a 50 µm cartridge before delivery to the coating head. Dry coat weights are held at 3–10 g/m² because lower weights produce pinholes in heat-seal layers and higher weights extend drying time.

The coated web passes through a forced-air tunnel with zonal temperatures of 60–80 °C and residence time of 10–30 s; residual solvent is measured by gas chromatography per ASTM D4526 or equivalent, with a production limit below 10 mg/m². Heat-seal activation of the dried film occurs at 90–110 °C under 2–4 bar jaw pressure for 0.5–2 s. T-peel adhesion on a 25 mm strip at 300 mm/min is used for lot release; values below 3 N/15 mm on aluminium foil are rejected. In retort-pouch liner structures, the seal is also held for 1 h at 121 °C and 0.1 MPa overpressure to confirm cohesive integrity.

Production failure modes include blocking of coated rolls at 35 °C/80 % RH when residual solvent exceeds the release limit, and phase separation when n-butyl acetate content drops below 10 wt% of the solvent blend during long runs. The solution is stored in stainless-steel pressure vessels under nitrogen at 20–25 °C; water ingress above 0.2 % causes gel particle formation and must be controlled by desiccant breather vents.