Wet-Process Battery Separator Film: A Formulation and Extrusion Window

In wet-process lithium-ion battery separator production, Asahi Kasei SUNFINE UHMWPE SH810 is dry-blended with high-boiling paraffin oil and a minor high-density polyethylene fraction before entering a co-rotating twin-screw extruder with an L/D of 40:1 to 52:1. The polymer loading is typically maintained at 12–25 wt%, the HDPE fraction at 5–15 wt% of the polymer phase, and the balance is paraffin oil with a kinematic viscosity of 40–100 mm²/s at 40°C. Barrel zone temperatures are segmented from 160°C at the feed zone to 230–250°C at the die, and the thermal window is narrow because residence time beyond 8–12 min above 240°C increases gel-particle density and reduces the continuity of the extracted pore network. Process experience on industrial lines shows that a deviation of ±5°C in the final two zones changes Gurley air permeability by a measurable margin; therefore die-pressure monitoring and melt-pump filling stability are used as release criteria rather than barrel setpoints alone. The melt is cast through a T-die at a thickness of 0.6–1.2 mm, cooled, reheated to 90–125°C for biaxial stretching at area draw ratios of 6×6 to 9×9, passed through a solvent-extraction stage to remove paraffin oil, and heat-set at 120–135°C to stabilize the slit-like pore structure. Compliance for separator film intended for lithium-ion cells is anchored to ASTM D882 for tensile properties, JIS P8117 for Gurley air resistance, and ASTM D792 for density-based porosity; electrochemical cell-level validation falls under IEC 62660-1 and UN 38.3 transport testing, while REACH and the EU Battery Regulation 2023/1542 govern substance restrictions. Terminal products are single-layer or multilayer separators of 5–20 µm dry thickness with shutdown behavior at 130–140°C, supplied in roll widths of 350–1,000 mm for cylindrical, prismatic, and pouch cell formats.

Gel-spinning lines producing high-modulus polyethylene fiber meter SH810 into decalin or a high-purity paraffin oil at a polymer concentration of 5–10 wt%, with 0.1–0.3 wt% of a hindered phenolic antioxidant added to limit thermo-oxidative chain scission during dope preparation. The suspension is processed through a co-rotating twin-screw extruder with L/D of 32:1 to 48:1 and a spinneret plate heated to 180–250°C; solution homogeneity is critical because undissolved powder domains create filament breaks and reduce the maximum draw ratio. After extrusion through a multi-orifice spinneret, the gel filaments are quenched in a water bath at 5–15°C, calendered, and drawn in two stages at 120–150°C to total draw ratios exceeding 30:1. Residual solvent is extracted with n-hexane or methylene chloride and the yarn is dried under tension before winding. The applicable standards include EN 12562 for high-performance rope-grade filaments, ASTM D885 for tensile properties, and NIJ 0101.06 or VPAM APR 2006 for ballistic panel certification where the woven fabric is used in protective armor. Terminal products are continuous multifilament yarns of 100–1,600 dtex, unidirectional prepreg sheets, cut-resistant gloves tested under EN 388, mooring ropes under ISO 2307, and ballistic panels with face weights from 4.0–5.5 kg/m² depending on threat level. Production-scale experience shows that lot-to-lot variation in powder bulk density influences feed accuracy at low screw speeds; therefore loss-in-weight feeders with agitation and nitrogen-blanketed hoppers are deployed to prevent bridging and to maintain dope composition within ±0.5 wt% polymer solids.

What Limits Throughput When SH810 Is Ram-Extruded into Food-Grade Wear Guides?

In ram extrusion of wear guides and chain rails, SH810 is fed into a reciprocating hydraulic ram with a barrel temperature of 180–230°C and die back-pressure held between 3–10 MPa. The powder is metered at 100 wt% for natural food-contact profiles, or at 97–99 wt% with 1–3 wt% carbon black for UV-stabilized outdoor variants; when required, zinc stearate is added at 0.05–0.2 wt% as a lubricant but is excluded where EU 10/2011 food-contact migration limits are tighter. The production bottleneck is not the ram pressure but the sintering time required to eliminate fusion defects at the core of thick profiles; industrial records show that sections above 30 mm thickness require a dwell segment of 20–40 min in the heated die land, and a cooling rate below 2°C/min prevents sink marks and residual stress. Compliance is established through FDA 21 CFR 177.1520 for olefin polymers in food-contact articles, EC 1935/2004 and EU 10/2011 for overall migration, and 3-A Sanitary Standards where guide rails contact product in dairy or beverage filling lines. Terminal products are machined from extruded profiles into chain guides, star wheels, wear strips, and bottle-handling rails with thicknesses from 8 mm to 120 mm, widths up to 2,000 mm, and lengths limited only by downstream cutting equipment. The critical limitation of SH810 in this route is its high melt elasticity; die swell can reach 30–50% when the die land ratio is below 15:1, so dies are designed with a land length of 20–40 times the gap. Published data for this specific grade in high-speed automatic cutting lines is limited; therefore trial runs with lot-specific bulk density and flow properties are required before quoting output rates.

A TIPS-based flat-sheet membrane line using SH810 begins with a dry blend of the powder and a water-insoluble diluent at a polymer concentration of 10–18 wt%, plus 0.1–0.5 wt% of an antioxidant package. The blend is plasticated in a twin-screw extruder with a barrel profile from 150°C to 220°C, then cast through a coat-hanger die onto a chill roll held at 20–60°C to induce liquid-liquid or solid-liquid phase separation. The resulting nascent film is passed through an extraction bath containing methylene chloride or n-heptane at 30–45°C, dried in a multi-stage oven with residual solvent controlled below 0.1 wt%, and heat-set at 100–135°C to reduce pore collapse. Pore size is controlled by chill-roll temperature, polymer content, and extraction kinetics; measured mean flow pore diameters range from 0.05 µm to 1.0 µm using ASTM F316 bubble-point porometry, with pure water flux from 500 L/m²·h·bar to 5,000 L/m²·h·bar depending on pore size and thickness. Compliance for potable-water and process-filtration elements includes FDA 21 CFR 177.1520, NSF/ANSI 61, EC 1935/2004, and REACH; biomedical filtration components may require ISO 10993-5 cytotoxicity data and USP <88> biological reactivity testing. Terminal products are flat-sheet membranes of 0.5–2.0 m width, pleated filter cartridges, laboratory-grade microfiltration discs, and aeration diffuser sheets for wastewater treatment basins. In continuous production, the interaction between powder particle size distribution and diluent viscosity determines the maximum casting speed; if the melt is filtered through a 40 µm screen and the pressure differential exceeds 5 MPa, the feed system is adjusted to avoid gel accumulation and die-lip build-up.

Across the 220–245°C Sintering Plateau, Pore Integrity Becomes the Controlling Variable

For sintered porous parts, SH810 is dry-packed into a mold cavity at a fill density of 0.40–0.50 g/cm³ and compressed at 4–10 MPa before free sintering in a convection oven at 220–245°C for 20–40 min per 10 mm of section thickness. The addition ratio in this route is typically 100 wt% for a mono-polymer porous body; alternative formulations use 80–90 wt% SH810 with 10–20 wt% of a sacrificial pore former such as sodium chloride or a high-melting organic filler, removed after sintering by immersion in water or solvent. The terminal porosity spans 25–45 vol%, and the mean pore size is controlled between 5 µm and 80 µm by powder size fraction and compaction pressure. End products are silencers for pneumatic valves, battery vent membranes, laboratory filter tubes, and self-lubricating porous plugs used in low-speed bearings. Compliance verification uses ASTM D792 for density, ASTM D638 for tensile properties, and ASTM F316 for bubble-point and pore-size determination; food-contact grades are additionally tested under FDA 21 CFR 177.1520 and EU 10/2011. A process conflict arises because the powder’s high molecular weight resists particle coalescence at temperatures below 200°C, while oxidation begins to affect color and tensile elongation above 250°C in air; therefore the sintering window is maintained at ±5°C around the optimized plateau and oxygen content in the oven is kept below 5 vol% by nitrogen purge. Equipment behavior on production-scale sintering lines shows that temperature non-uniformity across large platens can create localized density gradients, so multi-zone radiant ovens with forced convection are used for parts above 600 mm in diameter or thickness above 50 mm.

Compression-molded stock shapes of SH810 intended for subsequent machining into medical device components are produced by filling a mold with powder, closing under 10–20 MPa, and sintering in a nitrogen-purged press at 200–230°C with a hold time of 30–60 min depending on thickness. The formulation is 100 wt% SH810, except where a small amount of medical-grade antioxidant at 0.05–0.2 wt% is permitted by the applicable material specification. The cooled slabs or rods are annealed below 120°C to relieve residual stress before machining into acetabular liners, tibial inserts, and surgical instrument wear components. Compliance for implantable applications is granted only after the final component is validated against ASTM F648, ISO 5834-2, and USP <88> Class VI; the raw powder alone does not confer implant-grade status. Processing records indicate that machined UHMWPE parts can exhibit dimensional recovery after machining if annealing is omitted, so fabricators stabilize semifinished stock at 90–110°C for 4–8 h prior to final turning or milling. Terminal products are highly crosslinked or non-crosslinked bearing surfaces finished to surface roughness below Ra 0.5 µm, and surgical instruments that require sterilization tolerance under ISO 17665-1 steam autoclave protocols. Published data for SH810 specifically in orthopedic bearing wear-testing is limited; therefore the grade must be qualified against a product-specific design file rather than relying on published processing guidelines alone.