DSM Somos Taurus is an unfilled stereolithography (SLA) photopolymer that reaches its specified mechanical and thermal stability only after a two-stage postcure comprising UV flood exposure and thermal aging. The liquid resin is imaged at 355 nm in vat photopolymerization platforms; the green-state part has only partial conversion, and the final crosslink density is established when UV-generated radicals and thermally activated secondary reactions proceed in the prescribed sequence. This dual-cure architecture places Taurus in a different process category from single-stage SLA resins whose properties are largely determined by laser energy alone. The material is specified for high-temperature tooling, wind-tunnel test articles, and short-run molding fixtures that require dimensional stability above ambient. Published property values are tied to ASTM and ISO test methods; production-scale processing data remain machine-dependent, particularly for beam power, recoater speed, and vat thermal uniformity.

What property envelope distinguishes Taurus from conventional SLA resins?

The cured material exhibits a balance of moderate heat deflection temperature and unfilled toughness. Property values in the table below are manufacturer-typical data for specimens that have undergone UV postcure followed by thermal postcure and were conditioned at 23 °C and 50 % relative humidity unless otherwise noted. Actual lot-to-lot variation in tensile properties can reach ±5 % of the nominal value depending on postcure chamber uniformity.

The heat deflection temperature at 1.82 MPa is the primary differentiator against general-purpose SLA resins, which typically fall below 65 °C under the same load. However, Taurus does not enter the extreme-temperature class of ceramic-reinforced SLA or sintered thermoplastics; components loaded above 76 °C under flexural stress begin accumulating irreversible deformation. The notched Izod value of 20 J/m is higher than that of many filled high-temperature photopolymers, but remains low compared with thermoplastic ABS or polycarbonate grades.

UV + Thermal Postcure Control and Vat Processing Boundaries

Green parts are removed from the build platform with residual liquid film that must be removed before postcure. Cleaning practice in production bureaus uses tripropylene glycol monomethyl ether followed by isopropanol; TPM removes uncured resin from recessed features, while IPA lowers the solvent load before drying. Solvent carryover into the thermal oven is a process hazard because residual alcohol can ignite during the thermal ramp. The cleaned green part should be air-dried until the surface is dry to the touch before UV flood exposure.

The UV postcure is typically performed in a flood chamber fitted with UVA lamps whose calibration is checked with a radiometer at 365 nm. Irradiance and dose are set to eliminate surface tack without over-exposing thin sections; the exact exposure time depends on part thickness, chamber reflectivity, and lamp age. Dose control is critical because an under-exposed surface continues to react during thermal postcure and can produce localized exothermic temperature excursions. After UV exposure, the part is transferred to a forced-air oven. A representative thermal postcure profile for high-temperature Somos grades uses a ramp rate of 1–2 °C/min to a hold temperature near 150 °C, a dwell of 2 h, and controlled cooling. Thick sections above 10 mm require longer dwell or staged holds because the low through-plane thermal diffusivity of the thermoset creates a lag between setpoint and core temperature. Core under-cure depresses the measured heat deflection temperature relative to the datasheet value; published data for the exact magnitude in Taurus is limited, so thermal mapping of thick-section builds is recommended.

The following operating ranges are representative of production service bureau practice for high-temperature SLA resins; Taurus-specific values must be confirmed against the current supplier datasheet.

In the vat, the resin is maintained near 30 °C. At 25 °C, the viscosity is approximately 2000 mPa·s; if the vat heater fails and the resin cools to 20 °C, viscosity rises and can exceed the recoat capacity of the build platform, producing layer starvation. The pigmented unfilled formulation has lower optical penetration depth than clear SLA resins; therefore, the scan speed, line spacing, and platform exposure must be calibrated for the target 355 nm system. Underexposed down-facing skins can transfer partially cured resin to subsequent layers, reducing dimensional accuracy and increasing the solvent load carried into postcure.

The UV-only state of Taurus is not representative of the final part. Thermal aging after UV exposure drives additional conversion of unreacted acrylate groups through a dark-cure pathway. If the thermal step is skipped, the crosslink density remains below the datasheet level, and the part may exhibit lower heat deflection temperature, higher water absorption, and reduced modulus. Conversely, over-thermal exposure above the recommended hold can cause oxidative discoloration and embrittlement. The window between under-cure and oxidative damage is narrow for pigmented high-temperature SLA polymers, and the exact boundary for Taurus should be established on the user’s oven because air exchange rate and load mass affect exotherm and heat transfer.

The liquid resin should be stored in sealed containers at 15–30 °C away from UV and daylight. If the container is left open in high-humidity environments above 60 % RH, water uptake can alter photoinitiator efficiency and produce an additional inhibition delay in the first layers. Re-coating after long build interruptions should include a manual stir cycle to redisperse any settled components, although Taurus is unfilled and less prone to settling than particle-filled resins.

When ceramic-filled high-temperature SLA materials are replaced by Taurus

Ceramic-filled photopolymers such as Somos PerFORM deliver heat deflection temperatures above 200 °C, but they impose high-viscosity handling and reduced elongation. Taurus occupies a lower-temperature niche in which the unfilled network provides easier recoating, lower particle settling risk, and less notch sensitivity in thin-wall features. The absence of hard-particle reinforcement eliminates the particle-size-dependent fracture path observed in some ceramic-loaded SLA materials, which can initiate at as-printed layer interfaces. However, the trade-off is explicit: the HDT at 1.82 MPa is approximately 100 °C lower than ceramic-filled high-temperature SLA resins, and Taurus is not a substitute for tooling that will see sustained mold temperatures above its HDT.

Compared with conventional unfilled SLA resins with HDT at 1.82 MPa below 65 °C, Taurus shifts the continuous-use boundary upward and permits short-run mold inserts for low-pressure processes. In injection molding trials on a 30-ton clamp force machine running polypropylene at 180 °C melt temperature, insert life is limited by surface wear and plasticization rather than by immediate fracture; however, production-scale data for semi-crystalline engineering resins are limited. The material should be evaluated with the actual molding pressure, clamp force, and thermal cycling profile before committing to production tooling. Sharp transitions in wall thickness can crack during thermal postcure; fillet radii at thick-to-thin junctions above 1.0 mm reduce the stress concentration.

In wind-tunnel test component fabrication, the UV + thermal postcure regime creates a more complete network than UV-only postcure, which reduces outgassing and dimensional drift during aerodynamic heating cycles. Service bureaus report that internal cavities must include drain and vent holes to allow uncured resin removal; trapped liquid resin expands during thermal postcure and can split thin walls. Orientation of large flat surfaces at an angle to the recoater blade prevents a meniscus defect that appears as periodic horizontal banding on vertical faces. This defect is not cosmetic only; the band spacing corresponds to the recoater pass interval and can reduce local flexural strength by introducing a resin-rich interlayer.

Linear shrinkage during the dual-cure sequence is not isotropic; thick sections shrink more in the Z direction because the layer-wise cure pattern and thermal postcure produce anisotropic stress. For mold inserts, compensating for Z shrinkage by scaling the CAD model is common, but the scale factor must be established experimentally on the target SLA platform. Unsupported faces below 45 ° from horizontal can curl during UV flood exposure because the front surface expands at a different rate than the cooler substrate; observed edge lift can reach 0.1–0.3 mm on parts longer than 100 mm if support pillars are too sparse. Published data on Taurus-specific curl magnitude is limited; iterative build trials with a dial indicator are recommended before committing to close-fit assemblies.

Compliance documentation should be verified against the current supplier safety data sheet. The liquid resin is registered under REACH 1907/2006 and contains acrylate and photoinitiator components requiring nitrile gloves, local exhaust ventilation, and eye protection. Cured parts are not certified for food-contact use under FDA 21 CFR 177 or for long-term implantation under ISO 10993. RoHS Directive 2011/65/EU applies to the final electrical or electronic assembly rather than to the raw photopolymer; downstream assemblers must confirm SVHC thresholds on the declaration of conformity. No UL 94 V-0 rating should be assumed unless verified by the manufacturer on a specific part thickness.