Carbon Printers EPU 41 Elastomeric Polyurethane is a photopolymerizable urethane resin formulated for Carbon Digital Light Synthesis systems. The product is supplied as a liquid resin and produces a thermoset elastomer with a Shore hardness of 68A under ASTM D2240. Supplier-reported typical data list tensile stress at break at 8.6 MPa per ASTM D412, elongation at break at 225%, tear strength at 29 kN/m per ASTM D624 Die C, and compression set of 18% after 22 h at 70 °C per ASTM D395 Method B. The material is positioned as a production-grade elastomeric polyurethane for functional prototyping and short-run manufacturing, with a property envelope that differs from lower-tear silicone resins and from rigid polyurethane formulations. Published data for all print orientations and wall thicknesses remains limited; the values cited are representative of parts printed flat and post-cured according to the supplier’s recommended cycle.

On Carbon M2 and L1 platforms, EPU 41 is processed at a nominal layer thickness of 100 μm. Continuous liquid interface production maintains an oxygen-inhibited dead zone at the build window while a UV projection system crosslinks the acrylate-terminated urethane oligomer. The resin does not require heated reservoirs when the build chamber is maintained between 20 °C and 30 °C; chamber relative humidity above 60% RH can create surface tack and dimensional drift. After printing, residual uncured resin is removed in a two-stage bath of isopropyl alcohol or a fluorinated wash solvent. The post-cure cycle uses UV exposure followed by thermal stabilization. Batch-to-batch variation in resin age and water content can shift Shore hardness by ±2A and tensile strength by ±5%; the supplier recommends lot verification with ASTM D2240 and ASTM D412 before release of production parts.

What Mechanical Property Envelope Distinguishes EPU 41 from Lower-Durometer Elastomers?

Under quasistatic tensile loading, EPU 41 exhibits nonlinear hyperelastic behavior typical of segmented polyurethanes. The 225% elongation at break is lower than many injection-molded TPU grades that exceed 400% under ISO 37, but the combination with 29 kN/m tear resistance permits perforated and notched features. Dynamic mechanical analysis at 1 Hz shows a glass transition near -20 °C; below this threshold the elastomer stiffens significantly and loses elastomeric recovery. The 18% compression set after 22 h at 70 °C indicates moderate recovery after sustained compressive strain, which limits long-term static sealing performance unless the seal lip is designed with additional preload.

Continuous Digital Light Synthesis Processing Parameters

During printing, the build platform motion, oxygen concentration, and irradiation dose interact to control crosslink density. EPU 41 is less viscous than high-modulus rigid polyurethanes and can be printed with thinner walls and finer negative features, but unsupported overhangs below 30° from horizontal may require support structures to prevent delamination. Layer thickness is fixed at 100 μm on the standard process profile; deviations from this value require a validated process parameter set. The oxygen-inhibited dead zone must remain stable across the full build area. If oxygen concentration drifts, the first layers above the build window may show increased surface roughness and reduced tear strength. Post-print cleaning is a critical control point: residual uncured resin left in blind holes or lattice nodes will polymerize during post-cure and create brittle inclusions that reduce elongation at break. Drying after washing at 23 °C to 40 °C for a minimum of 2 h is recommended before post-cure, although published data for the effect of residual solvent on EPU 41 is limited.

The post-cure protocol modifies the final properties. Under-cured parts exhibit lower Shore hardness, higher compression set, and surface tack; over-cured parts can develop a hard skin layer that initiates crack propagation under cyclic strain. The supplier’s recommended post-cure for EPU 41 uses a UV chamber with emission in the 365–405 nm range and a thermal soak to complete urethane conversion. Parts should be allowed to cool to room temperature before mechanical testing because the glass transition is approached at higher cooling rates and residual stresses can distort thin sections.

Solvent Resistance, Thermal Loads, and Service Boundaries

EPU 41 is a urethane network whose chemical resistance is evaluated under ASTM D543; however, the supplier’s public datasheet does not provide complete immersion data for all production fluids. In aliphatic hydrocarbon oils, mass swell is generally low, but published data for specific EPU 41 configurations is limited. Continuous immersion in hot water above 60 °C accelerates hydrolysis. Exposure to concentrated acids, ketones, and chlorinated solvents should be avoided. The material is incompatible with amine-based additives and strong bases because these reagents attack the urethane linkages and can cause premature crosslinking or chain scission.

Thermal service is bounded by the -20 °C glass transition and the 70 °C compression-set test temperature. Intermittent excursions above 70 °C may cause softening and accelerated oxidative attack; prolonged exposure above 90 °C is not recommended. Flame resistance is not inherent; compliance with FMVSS 302 or ISO 3795 requires additional fire-retardant coatings or fillers that may alter mechanical properties. Outdoor use requires UV-stable coatings because the urethane network is susceptible to yellowing and surface chalking under sunlight.

When EPU 41 Is Specified for Dynamic Sealing Applications

In dynamic sealing applications, EPU 41 is used for dust boots, rod wipers, and gasket prototypes where fluid resistance is moderate and elastomeric recovery is required. The tear strength of 29 kN/m reduces lip tear during installation on shafts with a lead-in chamfer below 20°. However, compression set of 18% after 22 h at 70 °C means that a static seal compressed to 25% will not fully recover; flange preload must compensate for permanent set. The coefficient of friction is not provided in the supplier datasheet; sliding wear against steel or anodized aluminum must be measured under ASTM D5963 or customer-specific conditions. The material’s resistance to mineral oil is generally acceptable, but immersion in polar solvents, ketones, or brake fluid is not recommended without validation because these fluids can swell the urethane network and lower tensile strength. Published data for specific fluid aging of EPU 41 is limited.

For gaskets and seals, the printed surface roughness may require post-processing. As-built surfaces on the build platform side are smoother than the free surface; a gasket sealing on the free surface may leak until mechanical polishing or a conformal elastomeric coating is applied. Leak testing per ISO 22096 or customer-specific pressure decay is recommended before production release. The material’s permeability to gases is not provided in the standard datasheet.

Footwear midsole applications use EPU 41 primarily for lattice-based cushioning structures. Shore 68A base resin can be printed into cellular architectures whose compressive modulus is controlled by cell size and beam thickness; the same material bulk property remains unchanged. Cyclic compression testing under ASTM F1976-13 or ISO 14890 is required to establish fatigue life in the specific lattice geometry. Published data for fatigue behavior of EPU 41 latticed midsoles is limited. The absence of tooling permits regional stiffness gradients and multiple midsole sizes in a single build, which is difficult with injection-molded TPU.

Medical device housings and external components can use EPU 41 where supplier documentation for cytotoxicity per ISO 10993-5 and irritation/sensitization per ISO 10993-10 is accepted by the regulatory file. The material is not a long-term implant polyurethane; ISO 10993-6 implantation studies are required for tissue contact durations beyond the documented limits. Biocompatibility of the final printed part can be influenced by residual monomer, cleaning solvent retention, and post-cure by-products. Validation must be performed on the final geometry, not on cast test plaques.

Comparison with Injection-Molded TPU and Cast Polyurethane

EPU 41 differs from injection-molded thermoplastic polyurethane in that it becomes a thermoset network after post-cure. It cannot be re-melted or recycled as a thermoplastic. However, it can produce hollow lattices, blind internal channels, and undercuts without mold tooling. Injection-molded TPU grades often provide higher elongation at break, with many grades exceeding 400% under ISO 37, and better hydrolytic stability in hot water. Cast polyurethane can be formulated across a Shore range from 20A to 85A, while EPU 41 is fixed at 68A; cast formulations also allow hardness tuning through curative stoichiometry. The printed material eliminates mold cost for short-run production and reduces lead time from weeks to hours, but part-to-part consistency depends on resin lot, build chamber condition, and post-cure uniformity.

Compared with Carbon RPU 70 rigid polyurethane, EPU 41 is not a structural material. RPU 70 exhibits heat deflection temperature near 70 °C and flexural modulus above 1700 MPa under ASTM D790, while EPU 41 is an elastomer with Shore 68A. Compared with Carbon SIL 30 silicone, EPU 41 offers higher tear strength and tensile strength, but lower service temperature and lower resistance to polar solvents. SIL 30 is specified for high-elongation soft-touch and skin-contact applications; EPU 41 is specified when higher durometer and cut resistance are required.

Relative to the earlier EPU 40 grade, EPU 41 is positioned as a production-grade elastomeric polyurethane with updated documentation for biocompatibility and process robustness. Published side-by-side mechanical data for EPU 40 and EPU 41 are limited; therefore, material substitution requires re-validation of compression set and tear resistance on the target geometry.

Resin storage constraints for EPU 41 are established by the supplier. The resin should be kept in sealed containers between 15 °C and 30 °C, away from UV light. Moisture uptake can reduce crosslink density and lower Shore hardness by up to 3A in extreme humidity. Amine-based additives should be avoided because they can accelerate premature urethane crosslinking and raise resin viscosity. Palladium or platinum cure systems used in some silicone rubbers are not applicable to EPU 41 and can contaminate the oxygen-permeable build window if shared tooling is used.

For industrial vibration isolation mounts, EPU 41 can be printed as a single elastomeric component with integrated metal or rigid polymer inserts. The printed part must be washed, post-cured, and conditioned at 23 °C for 24 h before dynamic testing because residual solvent or moisture affects loss tangent and tear strength. Inserts should be pre-heated to 40 °C before printing to reduce interfacial delamination caused by thermal expansion differences. The supplier’s technical documentation does not provide a complete fatigue limit for bonded insert geometries; production-scale validation under ASTM D813 or ISO 6943 is required.