VisiJet RBK-ENT-D75 is a multi-material composite supplied as two separate photopolymer build materials—VisiJet CR-BK (rigid black) and VisiJet CE-NT (elastomeric natural)—that are jetted together in a fixed ratio to produce a cured material with a nominal hardness of 75 Shore A. The product is intended for MultiJet Printing platforms that deposit both resins simultaneously at the same layer index, with the CE-NT phase contributing elastomeric recovery and the CR-BK phase contributing dimensional rigidity. It is not a pre-mixed single-cartridge resin; the two constituents remain discrete until droplet formation and UV polymerization on the build plane. Applications include rigid-to-soft integrated housings, sealing interfaces, cushioned mounting pads, bellows, grommets, and prototypes that replace two-shot injection molding with a single additive build. The cured material appears black-to-natural and exhibits a visibly mottled surface where the constituent droplets are not fully homogenized.

What distinguishes the RBK-ENT-D75 composite from its parent materials CR-BK and CE-NT?

Single-material VisiJet CR-BK is a rigid photopolymer with high modulus and limited elongation; single-material VisiJet CE-NT is a low-durometer elastomeric photopolymer. RBK-ENT-D75 sits between these two response envelopes. Hardness testing per ASTM D2240-15 or ISO 7619-1:2010 places the composite at approximately 75 Shore A, whereas CE-NT is supplied as a much softer material and CR-BK is evaluated on a Shore D scale. The composite therefore does not behave as a simple weighted average of the two parent resins. Because the two phases differ in crosslink density and modulus, the printed material contains a heterogeneous network of rigid and elastomeric domains. This structure can improve puncture resistance relative to CE-NT and can increase elongation relative to CR-BK, but it also introduces an internal interface that requires orientation-specific testing.

When the composite is compared with thermoplastic elastomers, the process boundary is significant: UV-jetted digital composites generally exhibit lower high-cycle fatigue life and higher compression set than injection-molded thermoplastic vulcanizates. Published data for this specific configuration under cyclic deformation is limited; designers should not transfer material allowables from unfilled TPU datasheets. Where cyclic flexure exceeds 10⁴ cycles, component-level fatigue testing should be performed on printed coupons with the intended build orientation and post-processing route. The product is also not a direct substitute for rigid stereolithography resins where dimensional tolerance below 0.1 mm must be held over a span exceeding 100 mm, because elastomeric recovery and residual support-wax removal can introduce local distortion.

A central process conflict in this multi-material system is the rheological contrast between the rigid and elastomeric phases. The rigid black resin typically has a higher viscosity at the jetting temperature, while the elastomeric natural resin is formulated for sustained droplet formation at lower viscosity. The printhead supplies both fluids through separate channels and joins them at the build plane; the resulting interphase is not homogeneous at the micrometer scale. This droplet-scale architecture creates a useful mechanical gradient but also produces an anisotropic tear path. Tear specimens notched along the build plane can propagate through the weaker elastomeric phase, while notches oriented across the build plane encounter alternating high- and low-modulus domains. Tear testing per ASTM D624-00(2020) should therefore include both trouser and 90° geometries, and the failure mode should be photographed to confirm whether crack deviation occurred.

Incoming material handling and batch verification follow the same practices as other UV-curable jetted resins. The cartridges are stored at controlled ambient temperature; condensation on the cartridge interfaces should be avoided because water can destabilize jetting. The two constituents are not manually mixed. Jetability is governed by the printer’s heated printhead and automated recirculation settings; the viscosity difference between the rigid and elastomeric phases is managed by the machine recipe, not by user adjustment. Offline cone-and-plate viscosity checks may be used as an incoming QC lot test, but the value alone does not predict droplet placement accuracy. Batch-to-batch variation is best detected by printing a standardized test block with a fixed layer thickness of 32 µm and measuring the resulting Shore A hardness, support-wax separation, and surface defect density.

Support wax removal and solvent conditioning limits

After the build is complete, the printed part contains support wax in overhanging and enclosed regions. Support removal is performed in a dedicated oven or solvent bath specified for the paired support material; mechanical scraping is used only for thick wax accumulations. Thermal removal must not exceed the continuous-use temperature of the composite or local gradients may permanently distort elastomeric walls. Solvent cleaning is typically performed with isopropyl alcohol or an approved equivalent. Prolonged immersion in aggressive solvents, especially ketones or chlorinated solvents, should be avoided because the CE-NT phase can swell and reduce surface hardness. A conservative cleaning sequence is a 5-minute solvent rinse followed by forced-air drying at ambient temperature. Conditioning before destructive testing is carried out at 23 ±2 °C and 50 ±5 % RH for a minimum of 40 h per ASTM D618-21.

Parts intended for dimensional inspection should be allowed to recover after support removal. The elastomeric phase has time-dependent recovery; measuring critical dimensions immediately after cleaning can give non-representative values. For thin sealing lips with cross sections below 2 mm, a stabilization period of 24 h under conditioned laboratory conditions is recommended before first-article inspection. Support residue left inside narrow channels is a known failure source for pneumatic and microfluidic prototypes; those geometries require internal flushing with warm solvent at low pressure and then verification by cross-sectioning one sample per build lot.

Support wax rheology interacts with the elastomeric surface. Because CE-NT-rich areas can deform under the heat of the support removal oven, parts with thin unsupported elastomeric overhangs should be oriented to minimize trapped wax volumes. The cleaning protocol for enclosed cavities should include multiple low-pressure flushes rather than a single high-pressure jet, because a high-velocity solvent stream can erode micro-thin elastomer walls. Where internal channels are smaller than 2 mm in diameter, the support-wax removal efficacy should be verified by CT or destructive sectioning of a witness sample from the same build. This is especially important for production-scale builds where a blocked channel may not be visible from the exterior.

When tight-tolerance seal features require compression set qualification

For gasket and sealing applications, the relevant failure mode is loss of sealing force over time. Compression set testing per ASTM D395-18 Method B using 25 % deflection for 22 h at 23 ±2 °C provides a short-term material comparison. Elevated-temperature testing should be added when the service environment exceeds 60 °C; the elastomeric phase may soften and accelerate stress relaxation. No universal continuous-use temperature should be assumed from the room-temperature hardness value. If the intended service includes sterilization, repeated compression, or exposure to oils, the finished printed part must be tested in the exact post-processed condition because residual support-wax removal chemicals can influence surface tribology and sealing. The heterogeneous interface between CR-BK-rich and CE-NT-rich regions can be a weakness when tensile peel loads act directly on the interface; seal roots should not be designed as a knife-edge transition between the two phases. Instead, the elastomeric region should overlap a rigid flange with a minimum contact length of 3 mm where the design permits.

For dynamic seals, the Mullins effect and hysteresis of the elastomeric phase should be accounted for in initial sealing force calculations. After the first compression cycle, the part may not return to its original free height; a conditioning pre-compression of 2–3 cycles before installation is a practical measure, but it must be validated on the production geometry. No single compression set figure can cover all post-cure or support-removal variations. Published data for this specific multi-material configuration under cyclic compression is limited; application-specific testing remains the controlling qualification path.

In application use, the composite is frequently selected for rigid mount faces with integrated flexible lips, such as robotic end-effector pads, instrument housings with damping edges, and fluid manifold covers with compressible sealing beads. The CR-BK phase provides thread-bearing or screw-boss capacity and dimensional location; the CE-NT phase provides conformability, vibration isolation, and low-pressure sealing. Multi-material jetting eliminates hand assembly of separately molded elastomer seals, but it does not create a true chemical weld at every droplet boundary. Peel loads normal to the interface must be qualified per ASTM D6862-11 or an equivalent method. For fatigue-relevant components, rotating-beam or flex-plate testing should be specified when the service load case involves repeated bending; a generic E-modulus from tensile testing is insufficient for life prediction because the composite is non-linear and strain-rate sensitive.

The composite should not be confused with casting resins such as dedicated investment-casting photopolymers or with high-temperature rigid MJP materials. It is not intended for burnout or for prolonged thermal exposure; the elastomeric phase does not volatilize cleanly and may leave residue in ceramic shells. For rigid tooling, high-modulus resins are more appropriate because RBK-ENT-D75 will deflect under clamping loads. For pure elastomeric parts with the lowest possible hardness, single-material CE-NT remains the relevant choice; adding CR-BK raises hardness and increases dimensional stability but reduces ultimate elongation. Selecting the composite is therefore appropriate only when the design requires a fixed intermediate hardness of around 75 Shore A and the printed part’s mechanical function is dominated by compression or low-pressure sealing rather than high-cycle flex fatigue.

Published technical data for this exact multi-material configuration under high-strain-rate loading, ultraviolet weathering, and long-term hydrolytic aging is limited. Designers should not extrapolate room-temperature Shore A hardness to low-temperature impact or high-humidity service. If the application requires outdoor weatherability, UV exposure testing per ASTM G154-16 or equivalent should be performed on printed plaques, because the elastomeric natural phase may yellow and embrittle faster than the black rigid phase. If the part will see continuous water immersion at temperatures above 40 °C, hydrolytic aging should be evaluated by measuring Shore A retention and volume change after immersion.

Regulatory status is application-dependent. The resin cartridges must be handled according to the current safety data sheet, and cured parts are not automatically food-contact, medical-grade, or sterilization-compatible. Compliance with Directive 2011/65/EU RoHS and REACH SVHC documentation should be confirmed from the production batch certificate for the specific cartridge lots. If the printed part is intended for skin contact or medical device use, testing per ISO 10993-1:2018 or applicable region-specific standards is required; the presence of residual support wax or cleaning solvent can alter the biological evaluation. No specific biocompatibility claim is extended by the product designation alone. The composite is not recommended for investment casting burnout or for direct food-contact seals without a food-contact grade confirmation.