Kumho Petrochemical SAN 310CTR is a styrene-acrylonitrile copolymer supplied in pellet form for injection moulding of transparent, tinted, or opaque rigid components. The grade is placed within the manufacturer’s high-flow SAN range for thin-wall housewares, cosmetic packaging, appliance lenses, and light-transmitting covers. The aromatic styrene backbone provides stiffness and clarity, while the polar acrylonitrile comonomer raises resistance to household oils, aliphatic hydrocarbons, and stress-cracking agents relative to general-purpose polystyrene. Grade-specific values in the supplier lot certificate and technical data sheet are the controlling data for tooling validation; class-level values in this document are tied to standardized methods and are intended for preliminary engineering only.

Which Processing Window Avoids Splay and Gate Freeze in High-Flow SAN?

Pre-drying is applied when ambient relative humidity exceeds 60 %; a desiccant hopper dryer set to 80 °C for 2–4 h is typical. The target moisture level is below 0.1 % by loss-on-drying or Karl Fischer titration. Barrel zones from rear to nozzle are normally profiled from 180 °C to 230 °C; the rear zone remains cool enough for stable granule conveying, and the nozzle is held near the upper limit to prevent cold-slug formation. Melt temperatures above 250 °C accelerate yellowing and increase volatile generation; at full heat, residence time should be kept below 10 min.

Mould temperature between 40 °C and 80 °C controls surface gloss, residual stress, and gate-freeze behaviour. The lower half shortens cycle time but increases flow-front skinning and can freeze thin gates; the upper half is used for wall thickness below 1.0 mm. Injection velocity is established by short-shot study. For thin-wall parts, fill times of 0.3–0.6 s are a common starting window, followed by hold pressure until gate freeze. Backpressure equivalent to 0.5–1.5 MPa on the screw is adequate for melt-density control; higher backpressure can induce shear heating in this low-viscosity material and shift colour.

Shrinkage is anisotropic and is quantified under ISO 294-4:2018. Transparent SAN commonly exhibits in-flow moulding shrinkage of 0.3–0.7 %, and the cross-flow value can exceed the in-flow value by 10–20 %. The difference arises from flow orientation and packing pressure decay along the flow path. When dimensional stability of a lens, display cover, or mirror carrier is critical, the tool should be sampled with a statistically valid run of at least 30 shots at the intended melt temperature and mould temperature.

On a reciprocating screw machine with a general-purpose screw of 20:1 to 22:1 L/D, screw recovery is normally not the cycle-limiting stage for SAN 310CTR. Peripheral screw speeds above 0.5 m/s can generate local shear heating and discoloration. In hot-runner systems, the manifold is held 5–10 °C above the nozzle set point, while the gate tip is operated cooler to reduce stringing and gate blush. Production-scale faults with high-flow transparent SAN are most commonly linked to incomplete drying, excessive manifold temperature, or a worn non-return valve; a leaking screw check ring causes fill-weight drift and shot-to-shot viscosity variation. Dryer dew point is therefore monitored below −20 °C, and non-return ring clearance is checked against the machine maker’s specification.

Material Identity and Standardized Test Architecture

SAN 310CTR falls under CAS Registry Number 9003-54-7 as a styrene-acrylonitrile copolymer. The polymer is amorphous, non-rubber-modified, and transparent in its natural form. Commercial transparent SAN typically contains 24–31 wt% acrylonitrile; the nitrile group increases cohesion and solvent resistance, while excess acrylonitrile raises melt viscosity and yellowing tendency. The table below gives the test architecture for transparent SAN as a material class. Lot-specific values must be taken from the supplier certificate of analysis, because a grade’s exact melt flow and mechanical profile can vary with the production campaign.

Published data for this specific configuration is limited outside the manufacturer technical data sheet and certificate of analysis. The class-level ranges in the table are valid for preliminary feasibility studies but are not a substitute for lot-specific moulding trials.

Thermally Induced Yellowing Limits and Melt-Residence Boundaries

Yellowing in transparent SAN arises from thermal degradation of the nitrile-containing sequence. At melt temperature above 240 °C, discoloration becomes measurable within normal cycle times; at 260 °C, visible yellowing can occur within 10 min of static residence. For this reason, shot size should use 60–70 % of the barrel capacity so that hot material is renewed within one or two cycles. Purging before shutdown is performed with a lower-MFR SAN or SAN-rich regrind to remove overheated inventory.

Regrind addition is generally limited to 30 wt%; higher ratios reduce transparency by 1–3 % in ASTM D1003-13 tests and shift melt flow enough to require process adjustment. Avoid flame-treated regrind and ultraviolet-stabilized mixed lots because oxidized surfaces nucleate haze and can create visible flow lines in high-gloss cosmetic surfaces.

Compared with medium-flow SAN grades, 310CTR reduces fill pressure and permits thinner wall sections. The viscosity advantage is obtained through a shift in molecular weight distribution, so the high-flow product should be evaluated for a measurable reduction in notched impact or environmental stress-cracking resistance under constant strain. In aliphatic hydrocarbon contact, class-level data show that the lower molecular weight species depresses crack-initiation time; the final part must be validated with the intended load, crack-sensitive geometry, and chemical exposure using ISO 22088-3 or an internal constant-strain fixture.

Compared with ABS, SAN 310CTR has no rubber phase and therefore lower notched impact and lower density, but it avoids the opacity and melt-phase viscosity contributed by polybutadiene. Compared with GPPS, it retains higher heat resistance and better resistance to detergent and oil stress cracking, while requiring a higher melt temperature and a tighter drying protocol.

Stress-cracking resistance is controlled by acrylonitrile content, wall stress, and contact duration. The polymer is incompatible with strong acids, oxidizing acids, ketones, aromatic solvents, chlorinated solvents, and many ester plasticizers. Short-term contact with dilute household detergent, aliphatic hydrocarbons, and cosmetic paraffin oils is generally tolerated; however, a load-bearing clear housing exposed to aqueous detergent at 60 °C should not be released without constant-strain testing, because crack propagation can occur below the tensile yield. Water absorption remains below 0.3 % at equilibrium, but wet-heat exposure above 80 °C can reduce molar mass over time. These boundaries exclude 310CTR from continuous hot-water pressure components unless validated for the specific part.

Regulatory status for a given production lot must be verified from the supplier’s safety data sheet and product compliance statement because additive package and monomer residual levels vary. The base polymer is subject to registration obligations under REACH, and compliance with the RoHS recast 2011/65/EU must be confirmed for the finished article. Food-contact suitability is not inferred; any application requiring clearance must be supported by a supplier letter citing the applicable regulation and its conditions of use.

When a Clear Cosmetic Part Replaces a GPPS Moulding

When a clear cosmetic outer shell is converted from general-purpose polystyrene to SAN 310CTR, the tooling must be adjusted for a higher melt viscosity and a sharper viscosity rise near the solidification point. The gate land should be shortened or widened to reduce pressure loss; for direct sprue feed, a cold-slug well of 1.5 times the main runner diameter is recommended. The cavity should be purged of polystyrene residue before running SAN, because mixed melts can show haze at the flow front. The refractive index of SAN is close to that of GPPS, but stress birefringence around ribs and bosses becomes more visible; lower packing pressure and a mould temperature in the upper half of the 40–80 °C range reduce stress concentration. Cosmetic parts should be inspected under polarized light after 24 h to detect moulded-in stress.