The liquid resin designated DSM Somos 7110 Epoxy Photopolymer, UV & Thermal Postcure is an epoxy-based photopolymer formulated for vat photopolymerization platforms operating at a laser wavelength of 355 nm. The product is supplied as an unfilled liquid with a density of approximately 1.12 g/cm³ at 25 °C and a reported viscosity near 250–330 cps at 30 °C. The standard processing path involves layered photopolymerization followed by a two-stage postcure: ultraviolet flood exposure for green-state hardening and controlled thermal aging to raise heat deflection temperature and stabilize the epoxy network. Because the resin cures by cationic ring-opening polymerization rather than free-radical acrylate propagation, the as-built part retains latent reactive species that respond to thermal postcure. This dual-cure behavior differentiates Somos 7110 from single-stage acrylate resins that require only UV exposure and from fully thermal epoxy systems that cannot be shaped by stereolithography.

What does thermal postcure alter in the cured epoxy network?

Mechanical property data generated under ASTM D638 and ASTM D790 show that UV-only postcure produces a partly cured network with measurable stiffness and strength, but the heat deflection temperature remains below the values required for many secondary tooling processes. Manufacturer-published values for UV-only postcure list tensile strength in the 40–45 MPa range and elongation at break between 8% and 12%. After the combined UV and thermal postcure, tensile strength typically increases to 45–50 MPa, and elongation at break moves to approximately 11–15%. The most pronounced shift occurs in heat deflection temperature under 0.46 MPa, which rises from roughly 46 °C after UV-only exposure to approximately 65 °C after thermal aging. Flexural modulus, measured with ASTM D790, remains in the 2000–2500 MPa band, indicating that thermal postcure does not fundamentally reorder the polymer backbone but increases crosslink density and relaxes local stress concentrations.

On production stereolithography platforms equipped with 355 nm solid-state lasers and tuned for 100–150 µm layer thickness, the resin is typically held at a vat temperature near 30 °C to maintain consistent recoating behavior. High-humidity environments above 60% RH can alter the cure response of the epoxy formulation; production lines therefore use desiccant dryers or conditioned build chambers when ambient moisture exceeds this threshold. Recoat blade speed and wait time are set to avoid bubbles in the high-viscosity regions surrounding vertical walls, and the laser exposure is adjusted by measuring the cured line width on a standardized test grid. Because the cationic cure continues after the laser pass, dark cure contributes to part stiffness within minutes after the build, but it is not sufficient to replace the separate UV and thermal steps. Builds with trapped resin pockets or closed hollow sections require drain holes of at least 3–5 mm diameter to prevent hydrostatic pressure or residual uncured resin release during postcure. Postcure chambers should maintain uniform UV irradiance of at least 5–10 mW/cm² across all surfaces, and thermal ovens should be ramped at 0.5–1.0 °C/min to avoid thermal shock in thick cross-sections.

Dimensional tolerance, shrinkage, and patternmaking envelope

Dimensional stability after full postcure is characterized by linear shrinkage measurements on standardized test bars and by coordinate scanning of benchmark parts. Manufacturer documentation reports volumetric shrinkage low enough for master pattern work, but the practical tolerance envelope depends on part geometry, layer thickness, and postcure fixture support. On an unfilled epoxy system of this class, linear shrinkage of fully postcured bars is typically below 0.3%; however, printed thin walls and unsupported overhangs can distort before postcure if the as-built green strength is insufficient for handling. The resin is therefore used where the required pattern tolerance is ±0.1 mm to ±0.2 mm for parts under 150 mm, with wider tolerances expected for larger tools or asymmetric mass distribution. The unfilled formulation produces a translucent amber part with visible layer lines after sanding; secondary finishing by abrasive blasting or primer filling is standard before mold rubber or ceramic shell work.

In investment casting foundries, the material is used selectively as a master pattern for silicone tooling rather than as a first-choice direct burnout resin, because the epoxy composition requires staged burnout schedules and the published ash content for direct burnout is limited. When direct burnout is attempted, the schedule requires staged heating to 600–700 °C with air flow to oxidize carbon residues before metal pour. Foundries using this resin report that a slow ramp through 300–500 °C is critical because rapid volatilization generates internal pressure that can crack the ceramic shell. The resin is more commonly used as a master pattern material for room-temperature vulcanizing silicone molds; in this application the highest service temperature is determined by the HDT and the exotherm of the curing silicone. If the silicone cure temperature exceeds 65 °C, postcured Somos 7110 can soften sufficiently to distort under clamping pressure, so mold boxes are maintained below the HDT or the tools are postcured at higher temperature for longer time to maximize crosslink density.

When thermal postcure is omitted, the upper service temperature falls below moldmaking thresholds

The distinction between UV-only and UV-plus-thermal processing is not merely a laboratory curiosity. A production part that receives only UV flood exposure retains a heat deflection temperature under 0.46 MPa near 46 °C. Moldmaking operations that involve heated release agents, silicone vulcanization at 70–80 °C, or low-pressure thermoplastic molding at 80–100 °C can therefore induce surface deformation, edge rounding, and loss of critical dimensional features. For elevated-temperature service, the thermal postcure step is mandatory. Manufacturer guidance describes thermal aging in the 60–80 °C range, with dwell time extended to 2–4 h for sections thicker than 10 mm. While this raises HDT, it does not convert the material into a high-temperature polymer. Continuous exposure above 80 °C remains outside the recommended operating envelope for load-bearing tools, and published data for long-term creep performance above this temperature is limited.

Comparative selection against other photopolymer grades focuses on the trade-off between rigidity and impact resistance. Water-resistant epoxy resins such as DSM Somos WaterShed XC 11122 provide lower moisture absorption and are used where clarity and low water uptake are required, but they can exhibit lower heat deflection temperature after standard postcure. General-purpose acrylate photopolymers typically build faster and are more easily post-processed by UV alone, but they show higher linear shrinkage and are more sensitive to oxygen inhibition at the build surface. The cationic epoxy mechanism in Somos 7110 reduces oxygen inhibition during laser exposure, which supports more consistent cure near the vat surface but also requires careful control of residual dark cure.

Solvent exposure is not a minor post-processing variable

The cured epoxy network resists water and many aqueous cleaning solutions but is negatively affected by chlorinated solvents, strong ketones, and high-pH strippers. Immersion in methylene chloride or acetone causes swelling, surface crazing, and loss of dimensional stability within minutes to hours. Cleaning of green parts should therefore use isopropyl alcohol or proprietary resin wash formulations, and solvent contact time should be limited to 5–10 min with agitation. After postcure, the material retains moisture uptake near 0.5% under ASTM D570, which is acceptable for temporary tooling but not for continuous water immersion. For applications requiring repeated steam autoclave exposure, the resin is not recommended unless a sealed surface coat is applied. The resin is also incompatible with amine-based epoxy hardeners applied as coatings before full postcure because the amine accelerates crosslinking at the surface and produces brittle skin layers.

In production environments, lot-to-lot monitoring has identified viscosity drift as the most common batch-level variable. When incoming lots are not rechecked against the machine calibration curve, the laser penetration depth and recoating thickness can shift enough to change part dimensions by 0.05–0.10 mm on long builds. Manufacturers and service bureaus therefore maintain incoming viscosity acceptance windows of 250–350 cps at 30 °C and adjust build parameters after each lot change. Shake-based remixing before pouring is required because the epoxy components can stratify after prolonged storage. Shelf life is specified by the supplier as 12–24 months in unopened containers under dry, dark storage conditions; containers that have exceeded the recommended storage temperature or absorbed moisture may show longer dark cure and higher residual tack. These batch-control measures are more critical for Somos 7110 than for free-radical acrylate resins because the cationic cure is more sensitive to nucleophilic contaminants and water.

Material handling documentation classifies the uncured resin as a skin and eye irritant requiring chemically resistant gloves, safety glasses, and local exhaust ventilation around the vat. The cured polymer is not marketed as a food-contact or medical-grade material, and no FDA 21 CFR 177 clearance is implied by standard supplier documentation. EU operations should verify REACH registration and RoHS compliance for the specific lot because pigment-free formulations of this class do not generally contain the heavy metals restricted under RoHS Directive 2011/65/EU, but importers must confirm. The product is intended for industrial use, not for consumer handling, and uncured resin should be disposed through licensed hazardous-waste channels after the working life of the vat is exceeded.