DSM Somos Element is a low-viscosity liquid photopolymer specified for vat photopolymerization on 355 nm stereolithography systems. The material is supplied as an opaque white hybrid epoxy/acrylate resin and is currently distributed under the Covestro Additive Manufacturing portfolio following the 2021 transfer of DSM’s resin and functional materials business. The resin is used where the cured part is a sacrificial pattern for investment casting or where low liquid viscosity is required for high-speed recoating. It is processed on platforms such as the 3D Systems Viper si2 and ProX 800 at layer thicknesses from 50 µm to 150 µm. Liquid viscosity at 30°C is approximately 250 cP, and cured density is approximately 1.13 g/cm³. Table 1 lists representative cured mechanical ranges according to ASTM and ISO methods.

Values reflect conditioned post-cured coupons at 23 ± 2°C and 50 ± 5% relative humidity. Lot-specific values differ by laser system, build orientation, and post-cure protocol. The manufacturer’s controlled datasheet values should be used for design allowables rather than midpoint values from these ranges. Differences between vertical and horizontal build orientations can shift flexural modulus more than tensile modulus because interlayer crosslink density gradients are not isotropic; vertically built coupons tend to fail at lower elongation when loaded in the Z direction. A cured density of 1.12–1.14 g/cm³ is typical, but filler or pigment settling in long-idle vats can produce density gradients in large parts.

Material Condition and Cured-Property Benchmarking

On production stereolithography lines, viscosity at 30°C reduces recoat blade drag and permits shorter recoat intervals at 100 µm layer thickness. The 3D Systems Viper si2 with a 250 × 250 × 250 mm build envelope and a 355 nm solid-state laser is a common benchmark system; the ProX 800 with a 650 × 750 × 550 mm build envelope and dual 355 nm lasers is used for larger patterns. If the resin bath falls below 24°C, viscosity increases and may produce incomplete leveling, visible layer lines, and local delamination. The recommended build temperature is 25–30°C; resin temperature should be checked with an immersed thermocouple at build start and after idle periods longer than 60 min. A 100 µm build style with a laser power of 250–500 mW typically requires critical exposure of 10–14 mJ/cm² and hatch spacing of 0.10–0.15 mm. These parameters must be verified against the equipment manufacturer’s build style because beam diameter, scan speed, and resin age shift the working curve. Dimensional compensation for isotropic post-cure shrinkage is typically 0.2–0.8%, with higher values applied to thick sections and high post-cure doses.

Green parts are rinsed in two successive baths of isopropanol or tripropylene glycol monomethyl ether. First-bath agitation should not exceed 5 min to limit surface etch. Compressed air at 1 bar removes solvent from blind recesses. Post-cure in a UVA chamber with a dose of 30–40 J/cm² is typical. Uncontrolled thermal post-cure above 60°C can cause surface oxidation and reduce elongation at break.

The working curve for Somos Element follows the semi-log relationship between cure depth and exposure. At 355 nm, the penetration depth D_p is approximately 0.10–0.13 mm and the critical exposure E_c is approximately 6–10 mJ/cm². These values vary with resin age and photoinitiator concentration. Operators should regenerate the working curve after each 10% resin addition or after 30 days of vat residence time. Cure depth below 0.1 mm at nominal exposure indicates photoinitiator depletion or contamination; cure depth above 0.2 mm at the same exposure indicates overcure that will close small slots and holes.

How Does the Viscosity Profile of Somos Element Affect Recoat Efficiency?

The 200–300 cP viscosity at 30°C is lower than many high-modulus stereolithography resins, which often exceed 500 cP at the same temperature. This difference reduces the time required for the recoat blade to produce a level resin film, particularly over large cross-sections. Because recoating is frequently the rate-limiting step in vat photopolymerization, lower viscosity supports faster cycle times on platforms with gravity-fed recoaters. However, low viscosity also reduces hydrostatic resistance to part movement; large thin-walled sections may require anchor supports with a minimum contact diameter of 0.8 mm to prevent drift during build. Viscosity should be monitored with a rotational viscometer after resin additions; values above 350 cP at 30°C indicate aging, humidity uptake, or contamination with partially cured material.

Recoat efficiency can be benchmarked by measuring the time required to achieve a film thickness variation below 5 µm across a 200 mm span. On gravity-fed recoaters, blade gap is set between 0.10 mm and 0.20 mm; smaller gaps improve surface smoothness but increase shear and may overheat the resin. For high-speed builds, a blade speed of 100–200 mm/s is common with this viscosity class. Operators should log recoat time, blade speed, and resin temperature to detect drift before layer thickness errors occur.

Build orientation determines tensile and flexural property anisotropy. In vertical builds, interlayer planes are loaded in normal tension, and tensile strength may fall 5–10% below horizontally built coupons. Horizontal builds maximize tensile properties but increase surface stair-step on shallow slopes. Draft angles of 1° to 2° reduce visible layer lines on vertical walls. Shrinkage compensation is typically applied as 0.4% in X/Y and 0.6% in Z for 100 µm layers, but values should be derived from a calibration grid on the specific machine. A calibration plate with 50 mm, 100 mm, and 150 mm gauge blocks built in the same orientation as production parts provides the scaling factors. Dimensional deviation on a calibrated ProX 800 with 100 µm layers is generally within ±0.1 mm over a 100 mm span when the resin is maintained at 30°C and post-cure dose is held constant.

In investment casting pattern production, the cured polymer is used for disposable patterns that must be removed from a ceramic shell without cracking the shell or leaving conductive ash. Somos Element is specified in these workflows because the resin decomposes at a controlled rate during flash-fire and burnout cycles. A typical burnout profile for a 6 mm thick pattern includes a ramp of 1–2°C/min from ambient to 250°C, a hold at 250°C for 60 min, then a ramp to 700–900°C at 2–3°C/min. The shell is held at peak temperature for 120 min. Supplier literature reports residual ash after full burnout below 0.01% by mass of the original pattern, reducing the risk of inclusion defects in nickel-based and titanium casting alloys. If shell cracking occurs, the cause is usually trapped expansion from thermal gradients rather than incomplete polymer removal; reducing the ramp rate below 1.5°C/min or increasing shell permeability often resolves the failure on production lines.

When Ceramic Shell Burnout Becomes the Selection Criterion

The selection decision should prioritize residual ash and thermal expansion over tensile properties when the part is a sacrificial pattern. The coefficient of linear thermal expansion for cured Somos Element is approximately 90–110 × 10^-6 K^-1 below the glass transition, but thermal removal is dominated by chain scission and depolymerization rather than char formation. This behavior differs from filled stereolithography resins, which may contain silica or ceramic fillers that remain as solid residues and can damage ceramic shells. For high-volume foundry operations, the polymer should be validated against the specific shell chemistry and alloy pour temperature. Published data for specific shell chemistries is limited; a first-article burnout trial is required before production release. Residual ash should be measured by thermogravimetric analysis under air at 900°C after a 2°C/min ramp.

Comparative Position Within the Somos Portfolio

Somos Element occupies a narrow performance band: it is not an optical clarity resin, a high-impact thermoplastic analogue, or a ceramic-filled high-temperature resin. Compared with Somos WaterShed XC 11122, Element cures with lower optical transmittance and is typically selected for sacrificial patterns where clarity is irrelevant and ash content is controlling. Compared with Somos NeXt, Element has a lower notched Izod range and is less suited to snap-fit prototypes requiring impact resistance. Compared with Somos PerFORM, Element has significantly lower heat deflection temperature and flexural modulus, but it does not contain the high filler loading that complicates burnout and solvent rinsing. Somos Taurus offers higher impact toughness but may require higher laser exposure and longer recoat times. Element is therefore process-driven: it is selected for low viscosity, low-ash burnout, and dimensional stability in investment casting patterns rather than for end-use mechanical durability.

Batch-to-batch variance should be monitored by measuring viscosity at 30°C, density, and a cured tensile coupon from each lot. Viscosity outside the 200–300 cP band should arrest the lot for disposition. Cured tensile modulus below 2.0 GPa on vertically built coupons may indicate incomplete post-cure or moisture contamination. Fourier-transform infrared spectroscopy can monitor the disappearance of the acrylate double-bond peak at 810 cm^-1 and the epoxide band at 915 cm^-1 to verify conversion. Lot-to-lot glass transition temperature should remain within ±3°C of the reference lot.

Operational boundaries include sensitivity to moisture in the resin bath. At relative humidity above 60%, the uncured resin can absorb atmospheric water, shifting viscosity and producing microvoids during laser cure. The resin should be stored at 15–30°C in sealed opaque containers, and the vat should be covered during idle periods. The material is incompatible with strong acids, strong bases, and amine-based additives; contact with amine-bearing solvents can initiate premature crosslinking or generate exothermic conditions. Uncured material is classified as a skin and eye irritant under CLP Regulation (EC) No 1272/2008; handling requires nitrile gloves, safety glasses, and local exhaust ventilation. Compliance documentation should be requested for REACH Regulation (EC) No 1907/2006 and RoHS Directive 2011/65/EU if the finished part enters electrical or electronic equipment. Fully polymerized parts are typically considered non-hazardous solid waste, but uncured resin must not enter municipal waste streams.