In multi-cavity injection moulding of transparent household appliance parts—blender jar bodies, food processor bowls, milk frother reservoirs, and vacuum cleaner dust cups—Kumho Petrochemical SAN 320N A is specified for the combination of amorphous light transmission, dimensional stability, and resistance to citric acid and detergent contact. Before moulding, the granulate is dried in a desiccant hopper dryer with air dew point below -30 °C and a hopper inlet temperature of 80 °C for 4 h, targeting residual moisture below 0.05 wt%; hydrolytic degradation at melt temperatures above 240 °C manifests as silver streaks and molecular weight loss that weakens weld lines at blade-support ribs. The plasticising unit uses a general-purpose screw with an L/D ratio of 20:1 to 25:1, a compression ratio of 2.5:1 to 3.0:1, and a non-return ring with radial clearance below 0.05 mm; this screw geometry prevents excessive shear heating in the high-viscosity SAN melt. Starting barrel setpoints are tabulated below based on a conventional hydraulic injection moulding machine with a shot size that uses 40% to 70% of the barrel capacity.

For transparent parts with wall thickness between 2.0 mm and 3.5 mm, the split line vents are cut to 0.02–0.03 mm land depth at the end of fill to prevent diesel burns. Linear mould shrinkage under ISO 294-4:2018 is typically 0.4% to 0.6%, requiring gate placement at the thickest section to reduce sink marks. Clamp force is calculated from projected area and cavity pressure; a projected area of 500 cm² with a peak cavity pressure of 35 MPa demands a clamp force above 1750 kN. Moulded parts for small appliances are evaluated for ignition resistance under IEC 60695-11-10:2013; SAN grades generally achieve a UL 94 HB classification at 1.5 mm thickness, but final certification is article-specific. Finished blender jar bodies withstand dishwasher detergents at 65 °C without stress cracking when the residual acrylonitrile monomer is controlled and gate areas are annealed by mould temperature rather than external reheat.

What Limits High-Gloss Cosmetic Packaging Moulds at Droppers and Closure Threads?

High-gloss closures, overlay caps, lipstick sleeves, and airless pump collars demand cavity surfaces polished to a roughness Ra below 0.05 µm according to ISO 4287:1997; the polymer must replicate that topography without sticking. SAN 320N A is pre-dried to 0.02 wt% moisture and run with a melt temperature of 235–245 °C and a mould temperature of 50–60 °C; if mould temperature falls below 45 °C, gloss measured at 20° under ISO 2813:2014 decreases because the frozen skin layer fails to replicate the polished tool. Caps with thread wall thickness of 0.8–1.2 mm are gated with a valve-gated hot runner; the valve-pin opening speed is set to 30–50 mm/s to avoid jetting. Hot-runner manifold and nozzle setpoints must not exceed 250 °C because acrylonitrile sequences degrade by intramolecular cyclisation and ammonia evolution; colour shift is measured by a spectrophotometer using ASTM E313-20 yellowness index, with a maximum ΔYI of 2.0 units across a 4 h run. Colour concentrate is a styrenic carrier at 2–3 wt%; UV absorber is used at 0.10–0.20 wt%; external lubricant, if required, is limited to 0.1 wt% of pentaerythritol tetrastearate because higher levels cause gate blush. Closure thread durability is validated on the customer's capping head; a typical requirement is 50 on/off cycles without stress whitening at 25 °C and 60% RH.

If a Converter Uses SAN 320N A in Dye-Based Ink Cartridges and Clear Stationery

For clear overlay windows in tape dispensers, document holders, and printer cartridge inspection strips, a single edge tunnel gate with a rectangular cross-section of 1.5 × 0.8 mm at the non-visible edge prevents visible gate scar; mould temperature is held at 40–50 °C and cooling time is set for a part wall thickness of 1.2–1.5 mm. This application does not require impact modification because the part is not load-bearing and the target flexural modulus under ISO 178:2019 is above 3000 MPa.

Where non-invasive diagnostic devices require a transparent rigid housing with limited contact time, SAN 320N A is used for analyser windows, cuvette trays, and instrument front bezels, but it is not suitable for steam sterilisation or prolonged contact with lipid-based reagents. Biological evaluation under ISO 10993-1:2018 is limited to surface-contacting devices with cumulative contact time below 24 h; the raw polymer and the finished device may give different biological responses because conversion additives, mould release agents, and frozen-in stress alter the surface. Moulding is carried out with a polished cavity and a mould temperature of 50–60 °C; gate location is moved away from the optical read area to avoid birefringence from residual flow orientation. Ethylene oxide sterilisation at 55 °C with 30% relative humidity and 600 mg/L EtO for 3 h is less damaging than gamma irradiation, but residual ethylene oxide must meet the limit assigned by ISO 10993-7:2008 for limited surface contact. Gamma irradiation at 25 kGy according to ISO 11137-1:2016 causes visible yellowing and a drop in impact strength above 10% of the unirradiated value in some SAN grades; published data for this specific configuration is limited, so dose mapping and post-irradiation tensile testing according to ISO 527-2:2012 are required before qualification. Steam autoclaving at 121 °C causes dimensional warpage and is not recommended.

Battery Container Stress-Crack Resistance and the Acrylonitrile Window

In visible battery enclosure windows and cell-retention frames for consumer battery chargers, the high acrylonitrile content that gives chemical resistance to alkaline electrolyte also raises the glass transition temperature and narrows the moulding window. If the melt temperature exceeds 250 °C, wall-adjacent layers near the gate develop a yellow-brown degradation layer; if the mould temperature is below 40 °C, frozen-in stress at the gate and snap-fit tabs leads to stress cracking when exposed to 5% potassium hydroxide solution at 45 °C for 7 days. Environmental stress cracking is assessed using a bent-strip fixture according to ISO 22088-3:2006 with 0.5% strain in the outer fibre and reagent contact on the tensile side. For a four-cavity hot-runner system with valve gates, cavity pressure transducers in each cavity should register peak cavity pressure of 45–55 MPa and a pressure integral within 5% across cavities; if pressure variation exceeds 10%, snap-fit tabs in the battery tray show differential shrinkage and ejection cracking. The gate is placed in a non-stress area; the tab is radiused to 0.8 mm minimum and ejection is delayed until part surface temperature is below 75 °C; forced ejection above this value causes tab shear striations. The finished window is specified for clarity after KOH splash exposure: the transmittance loss at 550 nm should be below 2% when measured by a spectrophotometer using ISO 13468-1:2019.

Direct-Gated Food-Contact Kitchenware and Melt Residence Limits

Transparent food-storage canisters, juice filter bowls, and ice-crusher chambers use direct sprue or hot-tip gating because the thick bottom centre needs packing; the gate vestige is then machined or flame-polished. Food-contact compliance for the polymer must be established under EU Regulation 10/2011 and its amendments; the final article is tested for overall migration in simulants assigned to the intended food categories, and the acrylonitrile specific migration limit is 0.01 mg/kg food or food simulant. For the U.S. market, styrene-acrylonitrile copolymers are referenced in 21 CFR 177.1040, but the moulded article must still be verified for end-use migration and residual acrylonitrile. The table below summarises the verification matrix.

Direct gating creates a hot core that requires controlled residence time. For SAN 320N A, the melt is kept at 230–240 °C and the shot is injected at 80–120 mm/s into a mould at 50–60 °C; because the gate freezes later than the wall, a holding pressure profile of 70 MPa for 6–8 s followed by 40 MPa for 10–15 s minimises sink marks without overpacking the centre. Overpacking beyond 90 MPa causes dimensional non-conformity in the lid thread and increases mould-opening force. Food-contact articles should not be hot-filled above 85 °C because SAN 320N A's Vicat softening temperature under ISO 306:2022 method B50 is near 101–107 °C for comparable grades, and steam sterilisation is not recommended. Contact with high-ethanol or high-limonene compounds above 10% concentration should be validated separately; citrus oil penetration can induce stress cracking in tight-thread lids.