What Limits Wet-Process Separator Throughput When SUNFINE UH950 Is Used at the Casting Die?

In wet-process lithium-ion battery separator manufacturing, SUNFINE UH950 with a nominal viscosity-average molecular weight of 9.0×10⁶ g·mol⁻¹ imposes a significantly higher zero-shear viscosity in paraffin oil dispersions than UHMWPE grades below 3.0×10⁶ g·mol⁻¹. On cast-film lines fitted with slit dies having lip gaps of 0.8–1.2 mm, the practical polymer loading narrows to 12–20 wt% in mineral oil, whereas lower-molecular-weight grades typically operate at 22–30 wt% on the same equipment. This is not a formulation deficiency but a processing boundary: exceeding 20 wt% UH950 at 140–170 °C raises die head pressure above 10–14 MPa, producing edge melt fracture and increasing transverse gauge variation beyond ±1.5 µm. Production formulations therefore combine 12–20 parts UH950 with 80–88 parts medicinal-grade white oil, 0.05–0.20 parts hindered phenolic antioxidant, and 0.10–0.30 parts of a fluoropolymer processing aid where die lines persist. The gel film is cast onto a chill roll at 15–30 °C, extracted with n-hexane or methylene chloride in a countercurrent extractor, and biaxially stretched at ratios of 4:1 to 7:1 in the machine direction and 6:1 to 9:1 in the transverse direction, followed by heat setting at 120–130 °C. The high chain-entanglement density of UH950 supports the development of microfibrillar tie chains during stretching, which raises puncture strength and lowers Gurley air-permeability variability. Separator porosity is commonly 38–50% when tested by ASTM F316-03(2019), thickness ranges from 5–16 µm, and electrical resistance remains below 1.5 Ω·cm². Compliance is verified against IEC 62660-3:2022, the UN Manual of Tests and Criteria Part III subsection 38.3, and GB/T 36363-2018; separator-grade mineral oil must satisfy REACH and RoHS Directive 2011/65/EU restrictions. End products include prismatic EV cells, cylindrical 18650 and 21700 cells, and lithium iron phosphate energy-storage modules.

On production-scale cast-film lines equipped with co-rotating twin-screw extruders of L/D 48:1 to 60:1 and screw diameters of 65–120 mm, UH950 requires longer residence time for entanglement reduction than lower-molecular-weight powder. Screw speed is held between 100 rpm and 250 rpm, with barrel temperatures from 150 °C in the solids-conveying section to 180 °C at the die. If melt temperature exceeds 210 °C, paraffin oil begins to decompose and yellowing occurs; therefore upstream cooling zones are set at 120 °C in the feed section. Published data for this specific configuration is limited, but the upper processing limit of 230 °C for UHMWPE/paraffin systems is consistently reported in wet-process separator literature. Moisture in the UH950 powder must be kept below 0.05 wt% before compounding; at storage relative humidity above 60%, pre-drying at 80 °C for 4 h is required to prevent hydrolysis-like defects in the gel film.

Gel-spinning lines processing SUNFINE UH950 operate with a polymer concentration of 6–10 wt% in decalin or paraffin oil, because the entanglement density of 9.0×10⁶ g·mol⁻¹ resin raises solution shear viscosity beyond 300 Pa·s at 180 °C when concentration exceeds 10 wt%. Lower-molecular-weight grades are sometimes run at 12–18 wt%, but UH950 cannot maintain homogeneous spin-solution filtration at that loading without exceeding head pressures of 80–100 bar. Dissolution is performed in a jacketed stirred vessel at 150–170 °C for 60–120 minutes under nitrogen, with 0.1–0.5 wt% antioxidant based on polymer. The solution is passed through a 10–20 µm filter pack and a spinneret with 100–400 holes of 0.5–1.0 mm diameter, extruded into a water quench at 5–20 °C to form gel fiber, then drawn in two stages: first at 120–140 °C with a draw ratio of 3:1 to 5:1, later at 145–155 °C with a cumulative draw ratio of 30:1 to 60:1 depending on target tenacity. Residual solvent is extracted with n-hexane or dichloromethane, and the fiber is dried under controlled tension. Resulting tenacity is typically 3.0–4.0 GPa, tensile modulus 100–140 GPa, and elongation at break 2.5–4.0%, measured per ASTM D7269/D7269M-20. End products include ballistic panels qualified to NIJ 0101.06, cut-resistant gloves tested under EN 388:2016+A1:2018 with blade cut resistance per ISO 13997, maritime mooring ropes, and high-strength fishing lines. Amine-based antiozonants are avoided in this system because they migrate during extraction and can lower fiber surface adhesion in later coating operations.

Low-Shear Processing of UH950 Profiles by Reciprocating Ram Extruders

SUNFINE UH950 cannot be processed by single-screw melt extrusion without severe chain scission because the melt does not form a pumpable fluid at any practical temperature below decomposition. Ram extrusion is therefore used to compact and sinter UH950 powder directly into profiles. The process charges powder into a heated die at 180–220 °C under intermittent ram pressure of 20–40 MPa, with dwell times of 10–30 minutes for rods above 50 mm diameter. Weld lines between successive ram strokes are the principal defect source; pressure pulsation must be held below ±2 MPa to prevent weak transverse striations. Formulation is typically 100 parts virgin UH950, with 0.5–2.0 wt% UV-stabilizer masterbatch for outdoor components and 0.05–0.10 wt% calcium stearate where powder flow into the die throat must be improved. If static dissipation is required, 1.0–3.0 wt% conductive carbon black is added, but this raises abrasive wear rate against stainless steel counterfaces and is not used in food-contact grades. Compliance for food-contact profiles is governed by FDA 21 CFR 177.1520(c), EU 10/2011 Annex I, and material designation under ASTM D4020-18 and ISO 21304-1:2019. Mechanical acceptance testing follows ASTM D638-14 for tensile properties and ASTM D790 for flexural properties. End products include bottling-line guide rails, chain guides, star wheels, scraper blades, and wear strips for food-processing conveyors. If die temperature falls below 180 °C, incomplete sintering creates transverse cracking under load; if barrel temperature exceeds 230 °C, oxidative degradation discolors the profile and reduces notched impact strength.

Compression molding of UH950 into hopper and silo liners charges powder into a steel mold at 100 parts by mass, optionally modified with 0.5–2.0 wt% UV-stabilizer masterbatch and 0.2–0.5 wt% processing antioxidant. The press is preheated to 200–220 °C, and a specific pressure of 5–10 MPa is held for 20–40 minutes depending on sheet thickness. Cooling is controlled at 0.2–0.5 °C·min⁻¹ under maintained pressure to prevent warpage and residual stress. Sheets from 6–50 mm are standard; blocks up to 100 mm require extended soak times and nitrogen purge to limit oxidative gel formation at the surface. Because UH950 exhibits no melt flow, mold-filling defects cannot self-correct during heating, so powder distribution must be verified before the press closes. Published data for cooling-rate effects in sections above 80 mm is limited, but uncontrolled cooling is known to generate crystalline gradients that reduce notched Izod impact strength at the core. Compliance is evaluated under FDA 21 CFR 177.1520(c) and EU 10/2011 for food contact, with material designation per ASTM D4020-18 and ISO 21304-1:2019. End products include hopper liners, silo liners, chute liners, dock fenders, and chain wear strips.

When Sintered Porous Media Require Interconnected Porosity Below 40 µm

Sintering of UH950 powder for porous filtration media is conducted without a melt stage; controlled void formation depends on powder particle-size distribution and thermal history. UH950 powder classified to 100–300 µm fractions is dry-packed into molds and sintered at 180–210 °C for 30–120 minutes. The absence of melt flow preserves interstitial voids and creates interconnected porosity of 30–45%. Mean flow pore diameter measured by ASTM F316-03(2019) is typically 8–30 µm for 100–200 µm powder sintered at 190 °C for 45 minutes; published data for this specific configuration is limited, but the relationship between sieve fraction and pore size is well documented for UHMWPE sintered media. No binder is used: the formulation is 100 parts UH950 with 0.1–0.3 parts antioxidant dry-blended where extended service life at elevated temperature is required. The sintering oven must maintain temperature uniformity within ±3 °C; cold spots produce partial fusion and surface dusting, while hot spots above 220 °C collapse the pore structure. Medical and food-contact applications require raw material compliance with ISO 10993-1:2018 where relevant, FDA 21 CFR 177.1520(c), and EU 10/2011. End products include water-treatment aeration diffusers, pneumatic mufflers, laboratory filter plates, and venting membranes.

Lead-Acid Separator Rib Profile and Silica Loading Windows

Flooded and enhanced flooded lead-acid battery separators based on UHMWPE/silica compounds use UH950 at 15–25 parts per hundred compound, with precipitated silica at 55–65 parts, process oil at 15–20 parts, carbon black below 0.5 parts, and antioxidant at 0.2–1.0 parts. UH950 raises tensile strength and puncture resistance of the separator, but its high molecular weight increases compound viscosity; therefore the UHMWPE fraction is held at the lower end of the range when extrusion torque exceeds acceptable limits. Mixing is performed in an internal mixer at 130–170 °C, followed by extrusion through a flat die and calendering to 0.8–1.5 mm thickness. Rib profiles of 0.4–0.8 mm height are formed during calendering or embossing, depending on battery type. Process oil is extracted with n-hexane, and the separator is dried and wound under controlled tension. Compliance is assessed against IEC 60095-1:2021, EN 50342-1:2020, and JIS D 5301 for starter batteries; raw materials must meet REACH and RoHS Directive 2011/65/EU restrictions. End products include separators for automotive SLI batteries, enhanced flooded batteries, and deep-cycle flooded industrial cells. Extraction efficiency is critical because residual oil above 0.5 wt% increases separator electrical resistance and reduces cold-cranking performance.