Elvax 460 EVA resina de copolímero, espuma e calçado grau

Compression-moulded EVA midsole stock based on Elvax 460 is typically formulated with 100 phr resin, 2.2–3.5 phr azodicarbonamide, 0.7–1.1 phr dicumyl peroxide (40% active), 1.8–2.5 phr zinc oxide, 0.8–1.2 phr zinc stearate and 5–15 phr calcium carbonate. Elvax 460 contains 18% vinyl acetate and has a melt mass-flow rate of 2.5 g/10 min at 190°C/2.16 kg when tested to ISO 1133-1:2022; this reduces crystallinity and lowers viscous heating in the internal mixer while retaining sufficient green strength for two-roll mill sheeting. The compound is mixed in an internal mixer with a dump temperature of 105–115°C, homogenized on a two-roll mill at 95–105°C, and then cut into pre-weighed blanks. Expansion is carried out in a hydraulic compression press at 165–175°C under 120–160 kgf/cm² platen pressure for 6–8 min. The main process variable is the balance between dicumyl peroxide decomposition and azodicarbonamide gas evolution; premature press opening collapses cell walls, while excessive cure time drives compression set upward in the finished midsole and reduces the closed-cell recovery needed for repeated impact. Compliance of the finished foam is verified against ASTM D3575-20 for closed-cell foam physical properties and ASTM D395-18 compression set at 50% deflection. REACH Regulation (EC) No 1907/2006 Annex XVII screening applies to polycyclic aromatic hydrocarbon and heavy-metal content in finished consumer goods. Terminal articles include die-cut midsoles, platform wedge components, and footwear lift inserts. Amine-based antioxidants should be avoided because they interfere with peroxide cure kinetics.

Comparative formulation addition ratios for selected downstream foam processes are summarised in Table 1.

What Limits Short-Shot Foaming in EVA Footbed Injection Moulding?

When Elvax 460 is processed by injection moulding for closed-cell footbed components, the resin is pre-dried at 65°C for 4 h when storage relative humidity exceeds 60%, because absorbed water above 0.1 wt% creates surface pinholing and non-uniform cell nucleation. The compound is dosed with 0.6–1.2 phr active azodicarbonamide and 0.4–0.8 phr dicumyl peroxide, with barrel temperatures held between 180°C and 195°C. The injection screw is selected with 20:1 to 24:1 L/D and a shut-off nozzle to limit premature foaming in the barrel; check-ring non-return valves with restricted flow paths are avoided because shear heating can trigger gas separation before the cavity. Cavities are filled to 55–70% of volume, followed by decompression or precision mold opening. Shot weight is controlled to within ±0.4% to keep part density stable across a multi-impression tool, and clamp force is set between 250 t and 400 t depending on projected area and target expansion ratio. Compliance for finished footbeds is commonly governed by ZDHC MRSL v3.7 chemical screening and REACH Regulation (EC) No 1907/2006; mechanical properties are measured with ASTM D3575-20 for closed-cell foam tensile and ASTM D395-18 compression set at 50% deflection. Terminal finished types include foam footbeds, heel seats, rocker sole cores, and clog midsole blanks. The main processing boundary is the moderate melt index of Elvax 460: barrel temperatures above 200°C or residence time above 5 min can initiate pre-foaming, cause deposit build-up on the nozzle seat, and increase rejection rates from surface voids.

Electron-beam crosslinked foam sheet for protective sports padding and recreational matting is produced by feeding Elvax 460 with 7.0–10.0 phr azodicarbonamide, 0.8–1.5 phr triallyl isocyanurate co-agent, 1.0–2.0 phr zinc oxide, and 0.1–0.3 phr hindered phenolic antioxidant into a corotating twin-screw extruder with 40:1 L/D and barrel set points from 95°C to 135°C. The extruded sheet is calender-finished to uniform thickness, then passed through an electron-beam accelerator at a total dose of 40–80 kGy to partially crosslink the EVA matrix before entering a hot-air expansion tunnel at 200–220°C for 2–4 min. The radiation step replaces dicumyl peroxide and avoids residual peroxide decomposition products in the finished sheet, while also permitting continuous web processing. Gel content is generally bracketed between 35% and 65% because lower values permit cell coalescence in the expansion tunnel, whereas higher values reduce elongation below the level required for flexible protective padding. Compliance is screened against RoHS Directive 2011/65/EU and REACH Regulation (EC) No 1907/2006; protective sports padding may require impact attenuation testing under EN 1621-1:2012, while general closed-cell sheet is characterised to ASTM D3575-20. Terminal products are die-cut or thermoformed knee/elbow pads, helmet comfort liners, yoga mats, and gym mat top layers. Published plant-scale data for the exact electron-beam dose response of this specific grade is limited; the dose window should be bracketed during line qualification because under-dosing leaves partially coalesced cells and over-dosing raises gel content and reduces surface conformability.

Co-Vulcanization of EVA/EPDM Blends in Two-Hardness Sole Stocks

Elvax 460 is blended with EPDM for two-hardness sole units at 40–70 phr EVA and 30–60 phr EPDM to create a low-density foam layer co-vulcanized with a solid rubber outsole or midsole base. The compound contains 1.4–2.2 phr dicumyl peroxide, 0.5–1.0 phr triallyl cyanurate co-agent, 3.0–5.0 phr zinc oxide, 0.8–1.2 phr stearic acid, 10–30 phr N550 carbon black in the rubber-rich layer, and 1.8–3.0 phr azodicarbonamide in the foam-rich layer. Mixing is performed in an internal mixer; EPDM is first masticated at 60–70°C before addition of EVA to limit phase inversion and uncontrolled viscosity rise, then the batch is dropped at 115–125°C. The two layers are assembled as uncured sheets and press-cured at 160–170°C under 10–15 MPa for 7–10 min. The main process conflict arises from peroxide partitioning: dicumyl peroxide migrates preferentially into the amorphous EPDM phase, reducing crosslink density in the EVA foam phase and increasing compression set if co-agent addition is omitted. The triallyl cyanurate co-agent partially compensates by facilitating co-crosslinking at the EVA/EPDM interface, but exceeding 1.0 phr can produce a brittle foam layer. Compliance for the soling compound is anchored to ISO 4649:2017 abrasion, ISO 34-1:2015 tear strength, and ASTM D395-18 compression set. Terminal product types include dual-density sandal soles, outdoor shoe sole units, and foam-to-rubber transition strips. This configuration is unsuitable for amine-cured rubber additives, and mineral oil loading above 10 phr should be avoided because phase separation and surface bloom reduce interlayer adhesion.

Cork-filled EVA footbed shells are produced by mixing 55–70 phr Elvax 460 with 30–45 phr cork powder, 1.8–2.4 phr azodicarbonamide, 0.5–0.8 phr dicumyl peroxide, 1.2–2.0 phr zinc oxide, and 0.5–0.8 phr stearic acid. The mixer is run to a dump temperature of 105–115°C, then the stock is sheeted at 95–105°C and preheated in a compression press at 160–170°C for 6–8 min. Cork moisture content above 8% creates steam voids and splits at the foam core, so pre-drying of cork at 70–80°C to 2–4% moisture is mandatory in humid production sites. The cork particles act as nucleating agents and modify the recovery behavior of the EVA foam; below 30 phr the visual and mechanical effect is insufficient, while above 45 phr the sheet becomes brittle and die-cut edges chip. Compliance is screened under REACH Regulation (EC) No 1907/2006 and OEKO-TEX Standard 100 for footbed covers; mechanical properties follow ASTM D3575-20. Terminal products are contoured footbeds, sandal beds, and molded arch-support shells. This configuration is limited to compression moulding because cork-filled EVA cannot be safely processed through narrow-gap injection nozzles without hard particle bridging.

Textile-laminated EVA insock production begins with split crosslinked block foam produced from 100 phr Elvax 460, 3.2–4.6 phr azodicarbonamide, 0.8–1.0 phr dicumyl peroxide, 1.6–2.2 phr zinc oxide, 10–20 phr talc, and 0.5–1.0 phr polyethylene wax. The block is skived to 1.5–4.0 mm sheet, conditioned at 40–60°C, and corona-treated where adhesion must exceed 2.0 N/mm in subsequent peel. A solvent-free two-component polyurethane adhesive is applied by kiss-roll coating at 25–35 g/m², followed by nip lamination with polyester or cotton textile and 48 h aging before die cutting. The adhesive selection is critical because solvent-borne systems distort low-density EVA foam unless flash-off time and nip pressure are tightly controlled. Compliance for laminated insock articles is assessed using ISO 11339:2010 for T-peel adhesion, OEKO-TEX Standard 100 for textile components, and REACH Regulation (EC) No 1907/2006 for restricted substances in finished articles. Terminal products are die-cut padded insocks, footbed covers, heel grips, and tongue padding used in sport and casual footwear. Because the foam is skived from a block, local density variation is lower than in direct sheet foam, but thickness tolerance should be maintained within ±0.15 mm to avoid lamination voids.

When High-Filler EVA Foam Replaces Vulcanized Rubber in Anti-Fatigue Matting

In anti-fatigue matting, Elvax 460 is formulated with 100 phr resin, 30–60 phr calcium carbonate, 4.0–6.0 phr azodicarbonamide, 0.9–1.3 phr dicumyl peroxide, 2.0–3.0 phr zinc oxide, and 0.6–1.0 phr stearic acid. The compound is mixed in an internal mixer, sheeted on a two-roll mill at 95–105°C, and compression-moulded at 165–175°C for 8–10 min. The high filler level increases melt viscosity and gas nucleation pressure, producing smaller cells, but compression set rises rapidly when calcium carbonate exceeds 60 phr, and filler content below 30 phr seldom achieves the flex fatigue required for industrial standing mats. The production press should use daylight evacuation to limit trapped air and edge checks, and the compound must be cooled below 40°C before stacking to avoid blocking. Compliance for industrial mats is typically evaluated under ASTM D3575-20 closed-cell foam tensile, ASTM D395-18 compression set, and RoHS Directive 2011/65/EU; flame-resistance claims require separate additive validation because unfilled EVA is not inherently self-extinguishing. Terminal products are anti-fatigue standing mats, workshop floor top layers, and fitness mat underlays. The substitution of vulcanized rubber with high-filler EVA reduces part weight, but the material retains the characteristic EVA compression set and should not be specified where exposure to swarf oil or hot metal shavings is expected.