DSM Somos WaterClear 10120 is an epoxy-based photopolymer formulated for 355 nm stereolithography platforms. The resin cures by cationic ring-opening polymerization of cycloaliphatic epoxide groups when exposed to scanned UV laser energy; the green-state conversion is deliberately incomplete, and subsequent UV post-cure drives additional crosslinking that determines final thermomechanical behavior. Published datasheet values list density at 1.13 g/cm³ at 25°C under ISO 1183 and viscosity at 260 cP at 30°C under rotational viscometry. The liquid is supplied as a low-viscosity material that can be processed in standard recoater systems without heated vats, although the vat should be held near 30°C to keep rheological conditions within the specification envelope. Parts are produced in a near-colorless condition that can be further clarified by surface polishing and clear coating. The product is not a high-elongation, impact-modified clear SLA resin, nor is it a water-washable formulation; solvent cleaning and post-cure are required to achieve the published mechanical properties.

The grade number 10120 identifies a rigid, glassy epoxy network within the Somos clear-resin family. The cured material is specified for applications requiring optical transparency, low bulk color, and high dimensional fidelity. Published tensile strength is 45 MPa under ASTM D638, tensile elongation at break is 2.5% under ASTM D638, and flexural strength is 69 MPa under ASTM D790. The heat deflection temperature is listed at 46°C at 0.46 MPa and 45°C at 1.82 MPa under ASTM D648. Hardness is 80 Shore D under ASTM D2240. Water absorption is reported as 0.35% after 24 h at 23°C under ASTM D570. These values place the product in the rigid, low-elongation segment of transparent SLA materials, in contrast to clear impact-modified or ABS-like resins that may exhibit higher elongation but lower optical clarity and surface hardness.

What Separates WaterClear 10120 from Impact-Modified Clear SLA Resins?

In comparison with Somos WaterShed XC 11122, the most significant distinction is mechanical response. WaterClear 10120 is specified with tensile elongation at break of 2.5% under ASTM D638, whereas WaterShed XC 11122 is published as a higher-elongation, moisture-tolerant clear SLA material; direct comparative data under identical build and post-cure conditions is limited. The flexural modulus of WaterClear 10120 is listed at 1900 MPa under ASTM D790, which supports stiff, dimensionally stable parts but limits snap-fit and clip deflection. Impact-modified clear grades commonly report higher elongation and greater energy absorption before fracture, while WaterClear 10120 exhibits notched Izod impact of 20 J/m under ASTM D256, indicating brittle crack propagation at room temperature. The material is therefore selected where stiffness, clarity, and dimensional fidelity are more important than flexural durability or snap-fit behavior.

WaterClear 10120 also differs from water-washable SLA resins and general-purpose clear photopolymers in its post-processing requirements. It is not designed for water-based resin removal; freshly built parts must be cleaned with solvent, typically isopropyl alcohol or a supplier-approved wash solvent, followed by drying and UV post-cure. Compared with general-purpose clear SLA materials, WaterClear 10120 is formulated to reduce bulk color after post-cure, although residual yellowness index is influenced by post-cure dose, atmosphere, part thickness, and thermal history. Reactive diluents should not be added to lower viscosity, because they alter the cationic curing profile and can depress the heat deflection temperature. The resin should also not be blended with amine-based additives or hardeners, which can initiate uncontrolled epoxy crosslinking in the vat and render the batch unusable.

The following table summarizes the published typical property envelope for cured specimens after recommended UV post-cure. Values are predictive for unfilled, fully dense parts built at 100 µm layer thickness; thin walls and down-facing surfaces may show lower property retention.

The combination of 45 MPa tensile strength and 2.5% elongation at break under ASTM D638 places the cured network in the glassy, brittle category at 23°C. Notched Izod impact of 20 J/m under ASTM D256 confirms low energy absorption before crack propagation, a limit that must be accounted for in thin-walled optical housings and unsupported flanges. The reported heat deflection temperature of 46°C at 0.46 MPa and 45°C at 1.82 MPa under ASTM D648 defines a relatively low upper service temperature under mechanical load. Water absorption of 0.35% after 24 h under ASTM D570 is moderate for an epoxy SLA resin; in humid environments, dimensional stability and optical quality require preconditioning or clear coating.

Recoating Dynamics, Laser Parameters and Post-Cure Thermal Cycle on 355 nm Platforms

At the specified viscosity of 260 cP at 30°C, the resin wets and levels after recoater passes more rapidly than high-viscosity filled SLA materials. This permits thin layer settings, typically 100 µm to 50 µm depending on equipment, but requires recoater blade speed reduction when building large flat optical surfaces to avoid bubble entrapment. The low viscosity also creates less resistance to overhang sag; support structures for lenses and light-transmitting laminates should use a contact patch sufficient for the green modulus of the material. In production-scale stereolithography systems equipped with 355 nm solid-state lasers, the working curve is machine-specific. Published penetration depth and critical energy values for WaterClear 10120 across all 355 nm platforms are limited; process owners must determine the working curve using the platform-specific beam profile, vat temperature control, and recoat geometry.

Green-state handling requires removal of uncured resin from internal cavities and recesses before post-cure. Solvent cleaning should be conducted as a short rinse rather than prolonged immersion, because the epoxy network can absorb solvent and temporarily lose surface hardness. After solvent removal, UV post-cure is generally conducted in a chamber operating at 365 nm to 405 nm, with duration set by the equipment manufacturer. Incomplete post-cure leaves a tacky green surface and depresses the heat deflection temperature, while excessive post-cure heat above the HDT can cause distortion of unsupported optical walls. In production-scale batches, viscosity should be checked with a cone-and-plate rheometer at 30°C before starting large builds; abnormal viscosity increase indicates partial polymerization or water contamination.

Transparent flow-visualization manifolds, lighting housings, and optical prototypes place the material under combined internal pressure, thermal load, and solvent contact. The 45°C HDT at 1.82 MPa restricts continuous service under mechanical load; test loops operating above this temperature require external support or a different resin. Surface polishing from 600 grit through 2000 grit, followed by mineral oil or a clear urethane coating, removes layer lines and restores transparency. The material is not formulated for long-term outdoor UV stability; a UV-blocking clear coat is required because the epoxy matrix yellows under prolonged UV exposure. For lighting applications, thermal rise from the lamp source must be measured at the part surface, because local temperatures above 45°C can cause creep or optical distortion.

Investment casting patterns represent a separate application condition. The resin has been evaluated for patterns where low residual ash after burn-out is required, but published quantitative ash residue data for this specific grade is limited. Foundries should validate pattern inflation, shell cracking, and residual ash under their specific burn-out schedule rather than relying on generic epoxy SLA values. The low viscosity also supports fine internal channel geometry, but support removal from thin-walled ceramic core passages must be verified before shelling.

When Moisture Uptake, Solvent Contact and Regulatory Documentation Govern Material Selection

Moisture absorption of 0.35% after 24 h under ASTM D570 indicates that parts can take up water when exposed to high humidity. At ambient relative humidity above 60% RH, preconditioning before optical coating is recommended; the drying temperature should remain below the heat deflection temperature to prevent deformation. Chemical compatibility tests on the cured epoxy network show resistance to mild aqueous acids and bases, but aggressive organic solvents such as ketones, esters, and chlorinated solvents cause swelling, cracking, and loss of dimensional fidelity. Alcohol-based cleaning solvents should be used as short rinse steps rather than immersion baths; prolonged contact can plasticize the surface and reduce scratch resistance. Amine-based additives or hardeners must not be introduced into the liquid resin because they can initiate uncontrolled crosslinking in the vat.

The product is supplied with a safety data sheet that classifies handling and disposal requirements. Users requiring food-contact, medical-device, or implantable declarations must request current regulatory status from the supplier because published ISO 10993 or FDA 21 CFR data for this specific grade is limited. The operational boundary table below consolidates the critical process and service limits for shop-floor reference.