Carbon Printers MPU 100 Multi-purpose Polyurethane is a light-processable polyurethane resin formulated for digital light synthesis platforms in the Carbon printer family. The product is supplied as a one-part photopolymerizable liquid that requires a forced-convection thermal post-cure to complete the secondary urethane network. Cured parts exhibit a nominal indentation hardness of 100 Shore A when measured to ASTM D2240-15 after the manufacturer’s recommended schedule. The material position in the portfolio is intermediate: it is not a high-elongation elastomer such as EPU 40 or FPU 50, nor a rigid structural polyurethane such as RPU 70 or RPU 130. Its primary usage includes gaskets, seals, cable strain relief, protective covers, vibration isolators, tooling fixtures, and low-pressure wear components in which cut resistance, elastic recovery, and impact absorption are required. Because open-source published data for the MPU 100-specific configuration is limited, numerical values in this document should be treated as product-family references and confirmed against the current supplier certificate of analysis before production release.

What Distinguishes MPU 100 from EPU 40, FPU 50, and RPU 70 in the Carbon Polyurethane Series?

MPU 100 occupies a modulus-hardness intersection that separates it from both elastomeric and rigid polyurethane grades. EPU 40 and FPU 50 are specified for high elongation and soft-surface gasketing, but they have lower cut-propagation resistance and lower surface hardness. RPU 70 and RPU 130 are specified for structural rigidity and higher heat deflection, but they have lower elongation at break and less damping. MPU 100 is therefore selected when a component must survive snap-fit insertion, retaining-ring seating, or particulate contact while remaining compliant enough to avoid cracking a mating polymer or lacquered surface. For objective comparison, the following test methods apply: ASTM D638-14 or ISO 527-2:2012 for tensile stress-strain, ASTM D624-20 Die C for tear strength, ASTM D395-18 Method B for compression set, ASTM D2240-15 for durometer hardness, and DIN 53512 for rebound resilience. Direct substitution from cast or millable polyurethane is not recommended without testing digital light synthesis coupons in the same build orientation because the dual-cure network contains acrylate-derived segments that alter elongation and tear relative to a cast polyurethane of the same Shore A hardness.

Uncured viscosity at 25 °C is shear-thinning. Low-shear viscosity controls puddle stability after the blade pass, while high-shear viscosity controls flux under the recoat blade. A lot-to-lot shift of ±10% in low-shear viscosity can alter green-state thickness by several micrometers if the machine’s closed-loop recoat force is not calibrated. Cartridges and bottles should be equilibrated at 23 ± 2 °C for 8 h before printing. The build chamber should be maintained at 30% to 50% RH. The recoat blade gap is machine-specific; typical digital light synthesis platforms for polyurethane resins operate with a gap between 100 µm and 250 µm. Exposure dose for a 100 µm slice is set by the working curve and should only be adjusted after measuring cure depth on a calibration staircase. At the 405 nm print wavelength, a dose deviation of ±5% changes cure depth sufficiently to affect channel features finer than 1 mm. Excessive dose produces over-cure in negative features, while insufficient dose produces green-state delamination. Printed parts should be rinsed in an approved solvent such as propylene glycol methyl ether acetate or the manufacturer’s specified rinse; solvent dwell above 5 min can soften thin walls. Residual solvent should be removed with low-velocity dry air before thermal post-cure. The oxygen-permeable build window maintains an inhibition layer; the printer’s oxygen setpoint should not be altered from the manufacturer’s resin-specific profile because a lower oxygen concentration increases through-cure and can bond the part to the window.

When Ambient Relative Humidity Exceeds 60% During Open-Bath Printing or Cartridge Storage

Moisture ingress is a process risk for MPU 100 because the polyurethane oligomer can react with atmospheric water before photopolymerization. The resulting hydrolysis and chain extension increase the gel point, raise resin viscosity, and can produce surface vesicles or interlayer delamination. In a production enclosure maintained at 20% to 40% RH, the interval between cartridge opening and printing should not exceed 4 h unless the system is purged with dry nitrogen. If the build basin remains idle for more than 8 h, the first build after restart should include an adhesion coupon at the outer corners of the platform. Vacuum drying of the uncured resin is not recommended; removal of low-molecular-weight volatiles changes viscosity and can invalidate the printer’s exposure parameters. For long-term storage, sealed cartridges should be kept at 15 °C to 30 °C, protected from light below 420 nm. Any lot that has been exposed to condensation or visibly increased haze should not be returned to the machine without rheological comparison to a retained reference.

Verification Matrix for Incoming Resin Lots

Before a new lot is released to production, the following minimum property envelope is checked against the supplier certificate of analysis. The matrix is not a full validation protocol; it is the incoming inspection gate for typical non-porous components with wall thickness below 3 mm.

Dynamic mechanical analysis of MPU 100 after full post-cure typically shows a glass transition temperature below 0 °C. At 23 °C, the material is in the rubbery plateau, and storage modulus should be measured using ISO 6721-1:2019 in tensile mode with a frequency sweep from 1 Hz to 10 Hz. Loss tangent at small strain is not a sufficient predictor of full-scale vibration isolation because polyurethane damping is amplitude-dependent. If the component is used for repeated compression, thickness recovery should be checked after 100,000 cycles at 10 Hz with a displacement limit of 20% of the original thickness. Published data for MPU 100 under these specific dynamic conditions is limited; endurance testing remains application-specific. Continuous service above 80 °C is not recommended because compression set becomes process-significant, and short excursions to 100 °C for 1 h should be validated on the actual part geometry.

Thermal Post-Cure Is a Two-Stage Isothermal Crosslinking Process

The green-state modulus of MPU 100 after printing and rinsing is below the final cured modulus because the secondary urethane network is incomplete. The thermal post-cure step in a forced-convection oven should be controlled by air temperature and part internal temperature, not only by the setpoint. A representative qualification profile for dual-cure polyurethane systems consists of ramp to 80 °C, hold for 2 h, ramp to 120 °C, hold for 6 h, and cool to 35 °C before support removal. The exact schedule for MPU 100 should be taken from the current supplier datasheet. For wall thickness above 10 mm, embedded thermocouples are required during process development because the exothermic urethane reaction can create a transient core temperature above the oven setpoint. Under-cured lots show increased compression set after 22 h at 70 °C; over-cure above 130 °C causes yellowing and reduces elongation at break without a corresponding rise in tensile strength. The reaction follows diffusion-limited isothermal kinetics at high conversion, and the final 20% conversion may require a hold at 120 °C because vitrification slows chain mobility. Post-cure ovens should be calibrated to ± 3 °C uniformity according to AMS 2750F or an equivalent internal procedure. Linear shrinkage during thermal post-cure is not uniform; typical dual-cure polyurethane systems can exhibit 0.3% to 1.5% linear shrinkage depending on wall thickness and build orientation. Scale-factor compensation should be derived from a three-dimensional fiducial artifact measured before and after cure.

Chemical resistance of MPU 100 should not be extrapolated from cast polyurethane specifications. The dual-cure network contains acrylate-derived segments from the photopolymerization step, which modify solvent diffusion relative to a cast polyurethane of the same Shore A hardness. For water and non-ionic detergent solutions, the material is suitable at temperatures below 50 °C. For hydrocarbon oils, esters, and ketones, immersion testing per ISO 1817:2015 is required before production use. Exposure to methyl ethyl ketone at 23 °C for 24 h can produce dimensional change exceeding 10% and surface tack. Alcohol rinses should not be used as the final cleaning stage because retained alcohol plasticizes the surface and lowers abrasion resistance. Amine-based additives, strong bases, and tin-based polyurethane catalysts must not be mixed into the uncured resin; premature crosslinking and measurable exothermic viscosity rise can occur within 30 min. If a lot shows color shift, surface tack, or viscosity spiking during handling, the resin should be quarantined and sampled for Fourier-transform infrared analysis against a retained reference. Migration of unreacted low-molecular-weight species can be detected by gas chromatography-mass spectrometry after solvent extraction; the cure index should be verified by measuring residual isocyanate via titration or FTIR. For food-contact or medical-skin-contact uses, migration testing and biocompatibility testing per ISO 10993-5 are required; no compliance should be inferred from general polyurethane chemistry.

With 100 Shore A Hardness, Support-Removal Geometry Becomes a Fatigue Initiation Variable

Support removal from MPU 100 printed parts requires lower peel force than rigid polyurethane grades, but over-cured supports can leave surface scars that become crack initiation sites under cyclic loading. For components subject to bending or compression, the build orientation should place the highest principal tensile stress parallel to the printed layers, not across them. Layer-to-layer adhesion in the green state should be confirmed using a knife-adhesion test on the first article. Support contact points should be located on non-functional surfaces and kept below 3 mm diameter. After support removal, light sanding or tumbling should be validated for dimensional change; abrasive finishing can reduce surface roughness from Ra 6 µm to Ra 1 µm but may alter the effective hardness of thin skins. If a part is exposed to cyclic bending, the orientation should avoid placing support contact marks in the tensile fillet radius. This is particularly relevant for snap-fit arms because the strain concentration at the root can exceed the nominal strain by a factor of 3 when the fillet radius is below 0.5 mm.

Production-scale digital light synthesis cells using MPU 100 should implement a first-part inspection plan that includes dimensional scan, durometer reading, and tear-coupon testing from each lot. Because dual-cure polyurethane lots can vary in oligomer molecular weight, the build parameter set should be re-qualified when the supplier changes lot manufacturing date or when the printer projection lamp output drifts more than 10% from the baseline radiometer reading. The product is not a food-contact grade; any FDA 21 CFR 177.1680 or EU 10/2011 compliance claim must be supported by migration testing on the cured part. Supplier documentation should include REACH SVHC statements and RoHS 2011/65/EU status for the cured polymer; liquid resin components are not identical to cured part composition.