3D Systems VisiJet M2R-GRY is an opaque gray acrylate-based photopolymer formulated for MultiJet Printing equipment, specifically the ProJet MJP 2500 and 2500 Plus material bays. The product is jetted as a low-viscosity liquid at a nominal layer thickness of 32 µm and cured by an integrated UV lamp. VisiJet M2R-GRY is used for rigid form-fit-function prototypes, assembly fixtures, inspection gauges, and parts requiring a neutral gray surface for optical scanning or photographic documentation. Because the material is UV-curable, it remains a liquid until exposed to the UV source; this permits high feature resolution and smooth sidewalls without the melt-derived striations associated with fused filament fabrication. Support structures are produced from a separate thermally removable wax and are removed after the build through a heated oven cycle.

How Does Jetting and UV Cure Influence the Final Polymer Network?

MultiJet Printing shears the liquid resin inside piezoelectric printheads; the formulation is maintained within the manufacturer’s specified viscosity window to avoid nozzle dropout and satellite droplet formation. UV irradiation triggers radical photopolymerization through the photoinitiator package, producing a crosslinked acrylate network. Crosslink density controls hardness, modulus, and solvent resistance. On production ProJet MJP 2500 Plus systems, UV lamp irradiance decay is a documented cause of surface tack and lower Shore D values; routine irradiance checks and lamp replacement according to the service interval are required before high-tolerance builds. Layer-to-layer adhesion depends on adequate overcure because the incoming layer must bond to the previously polymerized surface before oxygen inhibition quenches radical sites. Operators inspecting partially cured parts report that insufficient UV dose appears first as edge delamination at thin ribs and as a greasy surface film on downward-facing features. These failure modes are not unique to VisiJet M2R-GRY but are a direct consequence of acrylate photopolymerization kinetics.

Typical cured-state values reported for VisiJet M2R-GRY, based on parts built at 32 µm layer thickness and handled under the manufacturer’s standard support-removal protocol, are consolidated below. These values are not batch-specific guarantees and should be verified for critical applications using the cited test methods.

Because heat deflection temperature is 50 °C at 0.45 MPa, M2R-GRY is not intended for continuous load-bearing service above that temperature. Creep, stress relaxation, and dimensional recovery should be evaluated under ASTM D2990 when fixtures apply sustained clamping loads. In snap-fit and interference-fit prototypes, the tensile elongation of 20% provides moderate ductility, but repeated bending at strains approaching break can create surface microcracks from the crosslinked network’s limited capacity for plastic flow. The Shore D value of 65 places the material in the rigid engineering plastic range but below many glass-filled polycarbonate grades. Designers should therefore maintain thicker bosses and generous radii at stress concentrations.

Support Wax Removal and Dimensional Stabilisation

Support structures are printed from a thermally removable wax formulation; after the build, the entire part block is heated in a dedicated oven so support wax drains from internal channels and undercuts. The cycle temperature remains below the heat deflection temperature of the cured polymer to minimise distortion. Because VisiJet M2R-GRY is a crosslinked thermoset, it does not flow during wax removal, but residual stress from layer-by-layer cure can relax when the part is held at elevated temperature. Critical dimensions should be inspected after cooling and after a 24 h dwell on a flat ceramic or granite surface to account for short-term creep recovery. Ultrasonic cleaning in mild detergent followed by compressed-air drying removes residual wax from fine features. Solvent wiping with acetone or methyl ethyl ketone is not recommended because these ketones can induce surface crazing in crosslinked acrylate networks. Alkaline baths should also be avoided unless abbreviated immersion testing is performed, as ester-containing acrylate linkages may hydrolyse under strongly basic conditions.

When M2R-GRY Is Selected Over M2R-WT, M2R-BK, or M2R-CL in Functional Prototype Programs

M2R-GRY’s neutral gray tone is selected when visual inspection, structured-light scanning, or photogrammetry requires low specular reflectance. Compared with M2R-WT, the gray surface reduces glare under collimated lighting and shows less visible dust accumulation during handling. Compared with M2R-BK, M2R-GRY provides more visible surface texture under low-angle illumination, which aids in detecting sink marks, knit lines, or step artefacts from the 32 µm build layers. M2R-CL can be polished to near-optical clarity, but M2R-GRY is fully opaque and does not require sequential polishing to achieve a homogeneous appearance. Mechanical property differences across the M2R family are relatively small; selection is typically driven by optical behaviour, part documentation requirements, and downstream finishing operations. For applications that will be painted or epoxy-coated, M2R-GRY offers a neutral base that does not alter final colour rendition as strongly as black substrates. The material is compatible with standard structural adhesives, but bond strength should be verified under ASTM D3163 because the crosslinked surface has lower solvent penetration than amorphous thermoplastics.

M2R-GRY is not a castable photopolymer and is not a substitute for VisiJet M2 CAST in lost-wax investment casting; the crosslinked acrylate network does not melt cleanly from ceramic shells and can leave carbonaceous residue. For direct investment casting patterns, a dedicated castable resin with low ash content should be selected. Customers requiring burnout patterns should therefore verify the material’s ash specification before use.

Cartridge storage between 18 °C and 28 °C is specified to maintain consistent jetting behaviour; prolonged storage outside this window can alter viscosity and pigment dispersion. Before loading into the ProJet MJP 2500 Plus material bay, cartridges should be brought to room temperature and mixed according to the supplier’s instruction. Production records indicate that inadequate cartridge agitation after standing can produce temporary color streaking in early build layers until the pigment re-suspends. This effect is cosmetic and does not alter bulk mechanical properties, but it can interfere with inspection objectives. Moisture uptake in cured parts is generally low, but dimensional stability in environments above 60% relative humidity should be assessed for critical metrology fixtures. Water absorption testing under ASTM D570 should be performed if parts are exposed to humid environments for extended periods.

Dimensional Compensation Is Governed by Build Orientation and Lamp Stability

Layer-by-layer photopolymerization produces small volumetric shrinkage that must be managed through machine calibration and build orientation. In production, the MJP software applies scale factors to the sliced model to compensate for predictable x-y and z-axis deviations; the exact compensation factors are proprietary but are stabilised by maintaining the UV lamp and printhead within service limits. Wall thickness below 0.5 mm increases the risk of distortion during support removal because the heat from the wax-removal oven can soften thin sections. Ribs with height-to-thickness ratios above 6:1 should be supported or thickened to prevent lateral buckling during cooling. Dimensional audits on MJP-built fixtures typically reference ISO 2768-1 or company-specific internal standards. Parts built at 32 µm layer height show step artefacts on low-angle surfaces; these artefacts are not eliminated by M2R-GRY and require vapour smoothing or hand finishing if cosmetic surfaces are mandatory. Vapour smoothing compatibility must be confirmed with the material supplier before use, as aggressive solvent vapour can attack the crosslinked acrylate surface.

When M2R-GRY parts are to be adhesive-bonded or painted, surface preparation includes light sanding with 320–400 grit abrasive and solvent degreasing with isopropyl alcohol. Because the crosslinked photopolymer surface is less permeable than solvent-cast acrylic or ABS, solvent-borne adhesives may require longer open times; bond strength should be checked by lap-shear testing under ASTM D3163. Water-based adhesives generally perform poorly unless the surface is mechanically abraded to increase roughness. Electrically, M2R-GRY is not conductive; static charge accumulation can be managed with topical antistatic coatings, but the coatings may alter surface appearance and are not permanent. Dielectric strength and surface resistivity are not typically specified by the manufacturer; parts destined for electrical enclosures must be evaluated under IEC 60243-1 and ASTM D257.

Uncured VisiJet M2R-GRY is classified as a skin and eye irritant according to the Safety Data Sheet; handling requires nitrile gloves, protective eyewear, and local exhaust ventilation. Liquid waste must be treated as hazardous and disposed of under national regulations, with EU users referencing Directive 2008/98/EC. Cured parts may be handled without special ventilation, but grinding or sanding operations that generate fine dust should use dust extraction to limit particulate exposure. Regional chemical inventory compliance under REACH and analogous frameworks must be verified by the user because cured and uncured articles are treated differently. The material is not claimed for food-contact service under FDA 21 CFR 177 or for implantable medical use under ISO 10993 unless a separate validation program is completed. Flammability ratings under UL 94 are geometry-dependent and must be tested on the final printed component. Published data for long-term outdoor UV weathering of M2R-GRY is limited; if outdoor exposure is anticipated, an accelerated weathering program under ASTM G154 or ISO 4892-3 is required before field deployment.