Chimei KIBISAN SAN PN-139H is a styrene-acrylonitrile copolymer pellet supplied for injection moulding of transparent rigid articles. Within the KIBISAN SAN family, PN-139H is positioned as a high-flow variant intended for thin-wall parts, multicavity tooling, and geometries where the pressure requirement for filling governs the process. A typical melt flow rate of 25 g/10 min is reported when measured at 200 °C under 5 kg load in accordance with ISO 1133-1. The corresponding density is 1.06 g/cm³ under ISO 1183-1. These figures are typical published values and do not replace lot-specific certificate-of-analysis data. The material is not an impact-modified grade; it is selected for clarity, stiffness, and chemical resistance rather than for ductile failure behaviour.

Optical performance depends on mould surface quality, melt temperature, and contamination. Transparent injection-moulded plaques typically show light transmission of 88–90 % through 3 mm thickness when measured under ISO 13468-1. Haze values below 1.0 % are achievable on polished cavity inserts with surface roughness Ra below 0.05 µm. These optical values are not inherent to the pellet alone; splay, cold slugs, black specks, and jetting defects degrade clarity far more than the base polymer.

Shrinkage behaviour should be characterised on the actual tool geometry because wall thickness, gate location, and packing pressure shift shrinkage from the low end to the high end of the stated range. For ribs and bosses with local thickness above 3 mm, sink-mark risk increases. Processors typically reduce sink by applying packing pressure near 80–100 MPa and maintaining gate seal for 0.5–1.5 s per millimetre of wall thickness.

Does PN-139H sacrifice thermal capability when replacing lower-flow KIBISAN SAN grades?

Substitution of PN-139H for a lower-flow grade such as PN-127H should be evaluated with the understanding that flow improvement is obtained at the cost of heat deflection. Published typical data place PN-139H at 88 °C HDT under 1.82 MPa by ISO 75-2/A, while the heat-resistant SAN grade is typically reported in the range of 96–98 °C under the same load. Vicat softening temperature follows the same direction: approximately 106 °C for PN-139H under ISO 306/B50. The difference arises from the molecular design required to increase melt flow. Consequently, PN-139H is not recommended for continuous mechanical load at ambient service temperatures above 85 °C unless creep and softening behaviour are validated on the finished part. Glass transition temperature determined by differential scanning calorimetry under ISO 11357-2 is approximately 105–110 °C; this value explains the onset of dimensional relaxation in hot-fill or dishwashing environments.

When replacing heat-resistant SAN in transparent appliance parts, process engineers should compare not only heat deflection temperature but also the temperature at which the part softens under moulded-in stress. Residual stress from ejection or unbalanced cooling can reduce the practical service temperature by 5–10 °C. Annealing at 85 °C for 2 h after moulding reduces orientation-induced shrinkage and improves dimensional stability, but it adds a secondary operation and may reduce impact strength if cooling rates are not uniform across the cross-section.

Before melt processing, the granules should be dried at 80 °C for 2–4 h in a desiccant dryer or hot-air hopper dryer when ambient relative humidity exceeds 60 %. Target residual moisture is below 0.05 % because higher moisture produces splay, silver streaks, and surface haze in transparent mouldings. Barrel temperature profiles for injection moulding are commonly set from 210 °C near the feed throat to 240–260 °C at the nozzle. Mould temperature is maintained between 40 °C and 80 °C; the upper half of this range aids gloss reproduction and flow-length development in thin walls. A general-purpose screw with L/D ratio of 20:1–24:1 and compression ratio between 2.2:1 and 2.6:1 is adequate for homogeneous melt delivery. High-shear mixing sections are unnecessary because the pellets are already fully compounded resin.

Hot-runner systems present a processing risk for SAN because hold-up at elevated temperature causes thermal yellowing. Nozzle and manifold temperatures above 280 °C should be avoided. Residence time at melt temperature should remain below 5 min; after that interval, degradation shifts the yellowness index and generates black specks in transparent parts. In production experience with multicavity tools, inter-cavity fill imbalance greater than 2 % of total fill time creates visible flow lines and density variation in clear parts. Valve-gated hot runners require independent tip temperature control to prevent cold slugs or drool at gate edges. Regrind addition is possible at levels up to 20 wt% without loss of transparency if the regrind is dried and free of dust; higher levels may shift the melt viscosity and increase the risk of gels in the melt stream.

Venting is critical for this grade. Vent depths of 0.02–0.04 mm at the end of fill reduce diesel-effect burns in thin-wall transparent mouldings. Insufficient venting also raises cavity pressure and creates short shots at gates opposite the vents. Spiral flow length for a 1.5 mm wall at 240 °C and 80 °C mould temperature is typically in the range of 350–450 mm under injection pressure of 80–120 MPa; however, published data for this specific configuration is limited because spiral-flow results depend on gate geometry and cavity surface finish.

Published capillary rheometry for this specific grade is limited; SAN melts of comparable melt flow rate exhibit shear-thinning behaviour with apparent viscosity in the range of 300–600 Pa·s at 100 s⁻¹ and 100–200 Pa·s at 1000 s⁻¹ at 220 °C. These values are illustrative for mould-filling simulation and should not be used as specification limits. Injection velocity and gate size must be selected together to avoid jetting in transparent parts. Gates smaller than 0.8 mm or injection velocities above 500 mm/s can produce snake-like surface defects; a small cold slug well before the cavity or a larger gate reduces this failure mode.

When High-Flow SAN Replaces General-Purpose Polystyrene in Transparent Oil-Exposed Parts

Compared with general-purpose polystyrene, PN-139H shows reduced swelling and stress cracking in aliphatic hydrocarbons, vegetable oils, and household detergents. The acrylonitrile comonomer increases the solubility parameter of the polymer matrix and provides resistance to nonpolar solvents. In contrast, aromatic hydrocarbons, ketones, esters, and chlorinated solvents attack SAN and must be excluded from cleaning and secondary assembly operations. Methyl ethyl ketone and toluene, for example, produce crazing and softening at low stress levels; mould-release agents and adhesive systems based on these solvents are unsuitable. For bonded assemblies, ultrasonic welding and hot-plate welding are preferred over solvent bonding because solvent cements formulated for acrylic or polystyrene often cause microcracking in SAN parts.

Solvent compatibility, craze initiation, and secondary assembly boundaries

The notched Charpy impact strength of PN-139H is approximately 1.5 kJ/m² under ISO 179-1/1eA at 23 °C. This value is below that of ABS and high-impact polystyrene, so snap-fit hooks, thin screw bosses, and snap arms require radiused transitions and generous melt-flow paths to prevent brittle failure. The flexural modulus of 3400 MPa indicates that the material is stiff; stiffness contributes to dimensional stability but also concentrates stress at sharp corners. Under repeated load, the tensile stress at yield of 70 MPa should be derated if the part operates in contact with oils that plasticise the surface over time.

Typical moulded articles include transparent kitchen appliance housings, blender jars, cosmetic packaging, pen barrels, battery housings, and control knobs. Wall thickness in these applications commonly ranges from 1.0 mm to 2.5 mm. The high-flow characteristic of PN-139H supports filling of long flow paths, but the material is not suitable for continuous outdoor exposure without UV stabilization because styrene-acrylonitrile copolymers undergo photo-oxidative yellowing. Silicone-based mould-release agents with high molecular weight can deposit on cavity surfaces and transfer to parts, increasing haze. If external release is necessary, a water-based release with volatile carrier is preferred. Color masterbatches should use a SAN carrier; polystyrene-based colorants above 3 wt% can depress Vicat temperature by 2–5 °C and increase haze. Pre-colored grades are preferred for optical parts because pellet-level dispersion of pigments is controlled.

If the grade is used in repeated-use food-contact articles, the finished moulding must be tested for overall migration and specific migration under EU 10/2011 or the applicable FDA 21 CFR sections. The resin supplier may provide regulatory statements for the raw material, but conversion, colourants, and processing aids can change the compliance status of the final article. REACH SVHC declarations and RoHS compliance under 2011/65/EU are typically available from the supplier for the base polymer. Electrical applications that require a defined flame class are usually limited to UL 94 HB at 1.6 mm; PN-139H is not an inherently flame-retardant grade. Lot-to-lot melt flow rate variation should be expected within the manufacturer’s specification window. When a moulding process operates at the thin-wall short-shot limit, even a change of 2 g/10 min in melt flow rate can require adjustment of injection velocity or melt temperature to maintain part mass within tolerance.