Kumho Petrochemical SAN 315TR is a transparent styrene-acrylonitrile copolymer resin supplied for injection moulding and extrusion applications where elevated melt flow must coexist with optical clarity and resistance to aliphatic hydrocarbons, fats, and dilute aqueous media. The product belongs to the high-flow segment of the producer’s SAN range and is typically specified for thin-wall parts, transparent housings, cosmetic packaging, and appliance components. The grade designation TR denotes a transparency-optimised variant, while the numerical series identifies a styrene-acrylonitrile ratio balanced to maintain heat deflection, stiffness, and processability. Because SAN is an amorphous random copolymer, the material exhibits dimensional stability, high surface hardness, and a transmitted-light profile approaching that of general-purpose polystyrene but with measurably better environmental stress-crack resistance and oil resistance attributable to the nitrile repeat unit.

What separates SAN 315TR from lower-flow transparent styrene-acrylonitrile copolymers?

Compared with high-heat SAN grades in the same product family, SAN 315TR achieves higher melt volume-flow rate by controlled adjustment of molar mass distribution and, where applicable, comonomer ratio. The practical consequence is a broader flow-length-to-wall-thickness capability for injection moulding, but this is purchased at a modest reduction in heat deflection temperature and notched impact. Published data for this specific configuration is limited outside the producer’s certificate of analysis; however, the grade is commonly positioned in the melt flow index band of 25–35 g/10 min when measured according to ISO 1133-1:2022 at 220 °C under a 10 kg load. In contrast, a general-purpose transparent SAN may exhibit a melt flow index closer to 10–15 g/10 min under the same conditions, and a high-heat SAN may show values of 4–8 g/10 min. The higher flow allows filling of nominal wall sections below 1.5 mm without raising melt temperature beyond the thermal stability limit.

The acrylonitrile content in SAN 315TR is typically maintained within the range of 24–28 wt%, a window that raises the glass transition temperature relative to polystyrene while providing solvent resistance to household oils and dilute acids. The styrene-rich continuous matrix preserves transparency because the comonomer does not create a separate light-scattering phase. Residual monomer levels in a modern mass-polymerised SAN process are generally below 500 mg/kg for styrene and below 50 mg/kg for acrylonitrile, which is significant for food-contact evaluations and low-odour applications. In production-scale desorption trials, purging with nitrogen after polymerisation reduces residual acrylonitrile further; the actual specification must be obtained from the manufacturer’s batch certificate.

Mechanical and thermal response limits under standardised loading

For incoming quality control and part design, the following representative benchmark ranges are compiled from public and producer-published data for high-flow transparent SAN grades. They should not be used as a raw material acceptance specification where a producer certificate of analysis is available.

The ranges in Table 1 are compiled from public and producer-published data for high-flow transparent SAN grades and should not be used as a raw material acceptance specification. The producer’s certificate of analysis for the specific lot, including sample preparation and conditioning under ISO 291 or ASTM D618, supersedes these representative values. Changes in colour, ultraviolet stabilisation, or external lubricant packages can shift the mechanical values without changing the base resin designation.

For incoming quality control, melt flow index should be measured according to ISO 1133-1:2022 or ASTM D1238-13 after drying. Because SAN 315TR is hygroscopic, moisture changes melt flow; laboratories must dry pellets before measurement. The standard method requires conditioning at 23 °C and 50 % relative humidity unless otherwise specified; however, for moisture-sensitive SAN, the producer’s certificate often reports values on dry pellets. Interlaboratory scatter for melt flow index of SAN can be ±3–5 % due to barrel temperature calibration and piston travel error, so a single point outside the specification does not justify rejection without replicate testing.

When thin-wall optical parts require stable flow-front advancement

Tooling trials on transparent high-flow SAN conducted on a 120 t toggle-clamp machine with a 30 mm general-purpose screw having an L/D of 22:1 indicate that consistent filling of 1.0–1.5 mm wall sections is achieved with barrel temperatures of 210 °C to 230 °C and a nozzle temperature of 220 °C to 235 °C. Insufficient melt temperature produces visible flow marks and irregular fill fronts; excessive melt temperature increases the b* yellowness index and reduces transmitted light. For a 1.2 mm plaque mould, field data show that raising the injection velocity from 30 mm/s to 70 mm/s reduces flow-front hesitation but can increase surface shear marks; the processing window for a given tool is typically established by short-shot study rather than by single-point parameter transfer.

Closed-loop hot-runner systems with independently controlled tips are preferred for transparent SAN; valve gates should be operated with delayed opening to reduce gate blush. A mould temperature of 40–70 °C is typical; water channels should be spaced to maintain a temperature difference of ≤5 °C across the cavity to prevent differential shrinkage and birefringence. For optical parts, diamond-polished cavity surfaces and a draft angle of at least 0.5° are used to avoid ejection marks.

SAN 315TR is resistant to aliphatic mineral oils, vegetable fats, lubricating greases, dilute acids, and dilute alkalis at room temperature. It is not recommended for continuous contact with ketones, esters, aromatic hydrocarbons, chlorinated solvents, or concentrated oxidising acids because these fluids can induce crazing or surface etching. In thick moulded sections, residual moulded-in stress from high packing pressure or non-uniform cooling can shorten the time to environmental stress-crack failure in the presence of essential oils and aggressive cosmetic formulations. For parts destined for fragrance packaging, an annealing cycle at 70 °C for 2 h and a maximum pack pressure below 80 MPa are commonly used to reduce surface tensile stress. Published data for this specific configuration is limited; actual chemical resistance should be confirmed by immersion tests under ASTM D543 or ISO 22088-3 for the actual formulation.

Barrel temperature and residence time determine the upper processing boundary

The upper melt processing boundary of SAN 315TR is governed by thermo-oxidative yellowing and chain scission rather than by a sharp melt transition. In continuous injection moulding, the resin should not remain at barrel temperatures above 240 °C for more than 5–8 minutes. Longer residence times, particularly with a large barrel and a small shot weight, result in progressive yellowness and loss of impact strength; colour shift can be tracked by ΔYI or Δb* measurements. The recommended shot-to-barrel ratio is 50–70 % of the injection capacity. If the moulded part mass is below 30 % of the maximum shot weight, lowering the rear zone temperature to 190 °C and using a shorter cycle is preferred to reduce thermal history.

Processing on a twin-screw extruder for compounding or masterbatch preparation should avoid melt temperatures above 220 °C when a high residual acrylonitrile comonomer is present; for injection moulding, general-purpose screws with a compression ratio of 2.0–2.5:1 are preferred. Abrupt temperature drops in the hot runner manifold can create freeze-off at gate diameters below 1.0 mm; gate lands should be polished and sized to produce shear heating without exceeding the degradation threshold.

Before processing, the resin must be dried to a residual moisture level below 0.05 wt%. SAN absorbs atmospheric moisture; at melt temperatures above 230 °C, excessive moisture hydrolyses nitrile groups and produces splay, silver streaks, and reduced surface gloss. A desiccant dryer with a dew point of −30 °C to −40 °C and a drying temperature of 75 °C to 80 °C for 3–4 h is an appropriate starting point. In transfer lines exposed to relative humidity above 60 %, hopper dryers without closed-loop desiccant beds are insufficient, and the moisture content of the feedstock should be verified by Karl Fischer titration according to ISO 15512 or an equivalent moisture balance method.

Because SAN 315TR is polar due to acrylonitrile, it is incompatible with many olefinic purging compounds; purging with general-purpose polystyrene or the same SAN family is recommended. Residual PVC in the barrel or hot runner can accelerate degradation and yellowing at melt temperatures above 220 °C. The resin should not be mixed with acetal resins, as formaldehyde generation can occur. Batch-to-batch variance in colour is minimised by closed-loop bulk polymerisation; however, regrind ratios above 30 % may increase haze and reduce impact, so the maximum regrind fraction should be validated on the specific part.

Regulatory documentation and food-contact assessment

SAN 315TR can be evaluated under EU Commission Regulation (EU) No 10/2011 for plastic food-contact materials, subject to migration testing of total volatile substances and acrylonitrile-specific migration limit. In the European Union, acrylonitrile monomer is controlled by a specific migration limit of 0.01 mg/kg. In the United States, styrene-acrylonitrile copolymers may be cleared for food-contact use under 21 CFR 177.1040 if residual acrylonitrile monomer levels are below the prescribed analytical limit. The producer’s food-contact statement should be obtained for the specific grade; industrial grades may not be food-contact compliant because of additive packages.

Unfilled natural SAN 315TR generally meets the RoHS Directive 2011/65/EU restrictions for lead 0.1 wt%, cadmium 0.01 wt%, mercury 0.1 wt%, hexavalent chromium 0.1 wt%, and polybrominated biphenyls and diphenyl ethers 0.1 wt% in homogeneous material, provided no contaminated feedstock or additive is used. Compliance under REACH Regulation (EC) No 1907/2006 must be confirmed for the specific grade and any masterbatch or processing aid present in the finished article.

Application data from moulding shops indicate typical uses for SAN 315TR include transparent kitchen appliance bowls, blender jars, food processor lids, water filter housings, cosmetic containers, lipstick cases, components for small household appliances, and transparent covers where moderate impact resistance is sufficient. The grade is not intended to replace impact-modified polymers such as ABS or polycarbonate in applications requiring ductile failure under high strain rate; notched impact of SAN 315TR is lower than ABS because SAN does not contain a rubbery dispersed phase. Compared with general-purpose polystyrene, the grade provides higher heat resistance, better oil resistance, and lower tendency to craze around metal inserts; compared with acrylic, SAN 315TR offers easier injection moulding but lower surface hardness and weatherability. Outdoor exposure without UV stabilisation leads to yellowing and embrittlement, so transparent load-bearing parts should specify an appropriate UV-stabilised variant.