HANWHA EVA 1631

Compounding of HANWHA EVA 1631 for expanded footwear midsoles is carried out in an internal mixer with a fill factor between 0.70 and 0.85 and a drop temperature limited to 105–115 °C. The grade is a 16 wt% vinyl acetate ethylene-vinyl acetate copolymer; vinyl acetate content is determined by ASTM D5594, and melt mass-flow rate is reported under ISO 1133-1:2022 at 190 °C/2.16 kg on the lot certificate. Typical foam formulations for this resin contain 0.6–1.0 phr dicumyl peroxide, 0.8–1.5 phr azodicarbonamide, 0.5–1.2 phr zinc stearate, 2.0–4.0 phr zinc oxide, and 10–30 phr calcium carbonate. The processing window is narrow because dicumyl peroxide has a one-minute half-life near 171 °C, while azodicarbonamide activated by zinc oxide and zinc stearate evolves gas with an exothermic peak at 170–185 °C. In shuttle presses with 900–1,500 t clamp force, the mold is ramped from 150 °C to 175 °C over 8–15 min to build gel content before pressure release, which triggers expansion. If gas evolution precedes sufficient crosslinking, cell rupture and density increases above the target range are observed; if crosslinking overtakes gas evolution, blowing ratio remains below 1.5 and hardness rises. Foam density is measured by ISO 845; midsoles typically target 0.18–0.22 g/cm³ at 35–45% rebound resilience measured by DIN 53512. Because the 16 wt% vinyl acetate level is lower than 18–22 wt% vinyl acetate foam grades, the compound gives higher unfoamed Shore A hardness, typically 92–96 under ISO 868, and lower compression set but also reduced hot-tear resistance. Storage above 60% RH requires 4 h forced-air drying at 60 °C to bring surface moisture below 0.05%; trapped moisture causes pinholes and irregular cell collapse. Published data for EVA 1631-specific expansion ratios in injection-molded midsoles is limited; mold-shrinkage allowances should be established by pilot trials on the target press rather than taken from general EVA foam tables.

In halogen-free flame-retardant cable jacket production, EVA 1631 is introduced as the polar base resin in a co-rotating twin-screw extruder with L/D 44:1, barrel temperatures from 140 °C to 165 °C, and die temperature 160 °C. The compound typically contains 120–160 phr aluminum trihydroxide, 20–50 phr magnesium dihydroxide, 0.5–1.5 phr zinc stearate, 0.3–0.8 phr vinyltrimethoxysilane, and 1–2 phr silicone processing aid. The 16 wt% vinyl acetate comonomer content improves filler wetting and reduces agglomerate formation, which is monitored by screen pack pressure rise across a 40/60/80 mesh breaker plate; a pressure rise above 8 MPa during a 4 h run indicates filler dispersion instability and requires barrel cleaning or screw redesign. Barrel temperatures above 180 °C must be avoided because acetoxy elimination releases acetic acid, which corrodes unprotected nitrided barrels and causes melt index drift; therefore, the vacuum vent is operated at -0.08 MPa and the screw elements after the vent are corrosion-resistant. The finished jacket compound is tested according to IEC 60332-1-2 for vertical flame spread, UL 94 V-0 at 3.0 mm, ISO 4589-2 for oxygen index, IEC 61034-2 for smoke density, and IEC 60754-2 for acid gas release. Tensile strength and elongation at break are typically evaluated under IEC 60811-501 or ISO 527-2; values are specified in the end-use cable standard, not as fixed material properties. Published data for EVA 1631-specific halogen-free flame-retardant formulations is limited, so the formulation ranges are drawn from publicly available compound datasheets for 16 wt% vinyl acetate EVA grades. Continuous operating temperature of the jacketed cable should remain below 90 °C unless the compound is crosslinked or blended with LLDPE/POE, because hot set deformation under IEC 60811-507 increases rapidly above that threshold.

What Limits Hot-Melt Adhesive Compatibility at Low Temperatures for a 16 wt% VA Grade?

Hot-melt adhesive formulations based on EVA 1631 are typically run at 30–45 wt% base polymer with rosin ester tackifiers having softening points between 95 °C and 110 °C and paraffin wax concentrations of 15–25 wt%. Because the vinyl acetate content is 16 wt%, polyethylene crystallinity is higher than in 28 wt% vinyl acetate hot-melt grades, so tackifier solubility is lower and the cloud point rises. Mixtures above 35 wt% tackifier may phase separate during cooling and develop surface haze; this is detected by hot-stage microscopy at 10 °C/min cooling rate or by differential scanning calorimetry under ISO 11357-3. Melt viscosity is measured with a Brookfield thermosel according to ASTM D3236-88 at 180 °C; packaging grades typically fall between 1,200 mPa·s and 4,500 mPa·s, and the application head is maintained at 160–180 °C to avoid excessive thermal breakdown. Open time on corrugated board is adjusted between 2 s and 8 s by changing wax content; open time above 10 s generally requires a higher vinyl acetate grade or a lower-crystallinity metallocene blend. Low-temperature peels are evaluated with a conditioned mandrel bend at -10 °C using ASTM D3111 or equivalent internal methods; if the adhesive is formulated for deep-freeze packaging, EVA 1631 is blended with a lower-VA or POE component rather than used alone because brittle failure may occur below -15 °C. Published data for EVA 1631-specific hot-melt peel strength on difficult substrates is limited, so a 3 mm bead on 40 g/m² kraft liner is used as a screening test before full-scale packaging trials.

When Extrusion Coating Sealant Layers Require Reduced Neck-In Without Sacrificing Heat-Seal Initiation

Maintaining melt temperature below 240 °C at the die becomes the operating constraint when EVA 1631 is extrusion coated onto oriented polypropylene or polyethylene terephthalate. The line is configured with a 30:1 L/D single-screw extruder, barrel temperatures from 180 °C to 230 °C, and a flat die with an air gap below 120 mm. The lower vinyl acetate content provides higher melt strength than 28 wt% vinyl acetate grades, which reduces neck-in and improves draw-down stability at 80–150 m/min line speed. Heat-seal initiation is characterized by ASTM F88/F88M-21; for a 15 mm wide seal strip sealed at 120 °C with 0.5 s dwell and 0.3 MPa jaw pressure, a typical seal strength above 20 N/15 mm is expected, but the exact value must be confirmed because published data for EVA 1631-specific seal curves in coextruded sealant webs is limited. Corona treatment to 38–42 dyn/cm measured by ASTM D2578-23 is required for adhesion to PVDC-coated polyester or aluminum foil; untreated film drops below 34 dyn/cm and yields variable lamination bond strength under ASTM D1876. At die temperatures above 240 °C or residence time beyond 15 min, acetic acid is released from the vinyl acetate group, which can corrode the die lip and generate odor in the sealant layer; chrome-plated lip faces and frequent purging with low-density polyethylene are applied. This grade is not recommended for ultra-low-temperature seal applications that require seal initiation below 85 °C, because 16 wt% vinyl acetate cannot match the initiation temperature of 28 wt% vinyl acetate or metallocene plastomers.

For masterbatch carriers destined for polyolefin film lines, EVA 1631 is selected primarily for its ability to wet high-surface-area additives while retaining sufficient melt viscosity for pelletizing. Concentrates are produced on a co-rotating twin-screw extruder with L/D 40:1, barrel temperatures from 120 °C to 160 °C, and underwater pelletizing at 18–25 °C water temperature. A typical carrier loading is 70–85 wt% EVA 1631 with 10–20 wt% synthetic silica or talc and 1–3 wt% processing aid. Let-down into blown film LLDPE is performed at 3–5 wt%; dispersion quality is monitored by pressure rise across a 40/60/80 mesh screen pack and final film haze under ASTM D1003. Because the carrier has a lower melting point than the LLDPE matrix, pre-mixing in the hopper should avoid temperatures above 50 °C to prevent pellet sticking; storage above 60% RH requires drying to below 0.05% moisture before masterbatch extrusion. If the concentrate is intended for food-contact film, EVA 1631 may be used subject to 21 CFR 177.1350 specifications for ethylene-vinyl acetate copolymers and the overall migration limits of the finished film. No amine-based slip packages should be included at high loading because they can generate color bodies with vinyl acetate degradation products during retort or hot-fill testing.

Low-Density EVA Foam Sheet for Sports Mats and Cushioning

Flat die extrusion of chemically foamed EVA 1631 sheet requires a cooling and calibration stack that avoids premature skin solidification before gas nucleation. The extruder is typically a 45–75 mm single-screw machine with barrier screw and 30:1 L/D, barrel temperatures from 130 °C to 170 °C, and a flexible lip die set to 170 °C. Blowing agent masterbatch containing azodicarbonamide and bicarbonate-type activators is dosed at 1–4 wt%; the gas-laden melt enters a three-roll polishing stack with roll temperatures between 40 °C and 70 °C, drawing the sheet to 5–15 mm thickness. Density is controlled by ISO 845, typically between 0.10 g/cm³ and 0.25 g/cm³, with compression set measured under ASTM D3575 at 25% deflection after 24 h at 23 °C. Tear strength must be monitored because 16 wt% vinyl acetate sheets tend to tear at the cell walls when density falls below 0.12 g/cm³; production trials often raise vinyl acetate content or add SEBS at 5–15 phr when tear strength falls below 2.5 N/mm measured by ISO 34-1. The sheet surface is embossed at 90–120 °C to prevent sticking; storage of finished rolls at temperatures above 40 °C causes cell collapse and thickness loss. Published data for EVA 1631-specific foam sheet tear strength is limited, so the above boundary is a screening threshold based on 16 wt% vinyl acetate EVA foam compounds, and lot-specific validation is required.